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© IWA Publishing 2014 Water Science & Technology: Water Supply
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Perspectives on drinking water monitoring for small scale water systems Benoit Roig, Estelle Baures and Olivier Thomas
ABSTRACT Drinking water (DW) is increasingly subject to environmental and human threats that alter the quality of the resource and potentially of the distributed water. These threats can be both biological and chemical in nature, and are often cumulated. The increase of technical frame of water quality monitoring following the evolution of water quality standards guarantee the regulation compliance in general but is not sufficient for the survey of small scale water system efficiency. The existing monitoring is not well suited to insure a good quality of distributed water, especially in the event of a sudden modification of quality. This article aims to propose alternative solutions, from the examination of monitoring practices, in a bid to limit the risk of deterioration of DW quality. Key words
| drinking water quality, management, monitoring, threat
Benoit Roig (corresponding author) University of Nimes, Rue du docteur Georges Salan, 30021 Nimes, France E-mail: benoit.roig@unimes.fr Benoit Roig Estelle Baures Olivier Thomas EHESP Rennes, Sorbonne Paris Cité, Avenue du Professeur Léon Bernard – CS 74312, 35043 Rennes Cedex, France and INSERM, UMR IRSET Institut de recherche sur la santé l’environnement et le travail - 1085, LERES, Rennes, France Benoit Roig Environment and Health Research Laboratory (LERES), Advanced School of Public Health (EHESP), Avenue du Professeur Léon Bernard – CS 74312, 35043 Rennes Cedex, France
CONTEXT A relevant regulatory frame
comply with increasingly exacting legislation on water quality. They also need to face emerging issues related to the
Water supply is becoming a matter of concern with regard to
constant appearance of new chemicals in water (pharma-
a growing population and concomitant usages for industries
ceutical, endocrine disruptors, etc.) whose effects on the
or agriculture. Even where water quantity does match water
environment and health are still not very well known.
demand, the quality of resources may be degraded by natural
Even if earlier laws did exist (US Clean Water Act in
(climate) or anthropogenic (discharges, runoff, etc.) press-
1972, French first water law in 1964), water quality regu-
ures. The provision of improved-quality water for the
lations have been strengthened since the end of the 1990s.
entire worldwide population is now an objective mentioned
For example, under the amendment of the Safe Drinking
on the agendas of major international organizations and
Water Act in 1996, the US Environmental Protection
national governments (Unicef & WHO ).
Agency (USEPA) sets health-based quality standards of
The United Nations General Assembly has recently
several contaminants in drinking water. The European Com-
recognized that ‘safe and clean drinking-water and sanitation
mission approved the Drinking-water Directive (DWD) in
is a human right essential to the full enjoyment of life and all
1998 and the Water Framework Directive (WFD) in 2000.
other human rights’ (United Nations ). The recognition of
The latter establishes an objective of good status for all
this right implies the protection of water resources used for
waters by 2015, a framework to ensure public health security
drinking water supply. Water producers are required to
for water intended for human consumption and an obligation
doi: 10.2166/ws.2013.211
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to promote a policy for the management and protection of
(Richardson et al. ), wildlife, topography, geology, vege-
water resources. In 2011, the EU concluded that no legisla-
tation and the impact of climate change, particularly with
tive revision of the DWD under the ordinary procedure was
respect to the frequency and severity of droughts or rainfalls.
required and challenged for a coordinated implementation
Anthropogenic driving forces come from each of the key sec-
of both (Falkenberg & Bloech ). However, even if knowl-
tors that use water (industry, energy production, public water
edge of the status of water has considerably improved (three
supply and agriculture) and include point sources (e.g. waste-
implementation reports were published), according to the
water discharges) and non-point sources (e.g. surface runoff).
commission, more efforts are needed to ensure the achieve-
For example, municipal wastewater discharge can be a major
ment of the directive objectives in the 2015, 2021 and 2027
source of pathogens; urban runoff and livestock can contribute
planning cycles (Falkenberg & Bloech )
substantial microbial load; body contact recreation can be a
Australian Drinking Water Guidelines (ADWG) were also
source of faecal contamination; and agricultural runoff, includ-
published in 2004 providing a comprehensive list of potential
ing agrochemicals and manure (the main sources of nitrate and
hazardous agents in drinking water. These guidelines consider
pesticides) can lead to increased treatment challenges. Water
continuous, intermittent or seasonal pollution patterns, as well
contamination by pathogens is of particular interest both
as extreme and infrequent events such as droughts and floods.
because of its consequences (waterborne infectious disease)
At the same time, the World Health Organization (WHO)
and because of the difficulty of predicting it (due to failure of
proposed in the revised Water Quality Guidelines the develop-
the use of indicator organisms (Harwood et al. ). Emerging
ment and implementation of water safety plans (WSP) by
pollutants are also increasingly under consideration (Deblonde
water suppliers for a new preventive risk management
et al. ; Boxall ; Tiehm et al. ), due to poor knowledge
approach (Bartram et al. ). This approach aims to
of their impact on the population at ultratrace concentrations
ensure the safety of a drinking water supply through the use
(Touraud et al. ; Stuart et al. ). For the first time, three
of a comprehensive risk assessment and risk management
substances (diclofenac, 17β-estradiol, 17α-ethynylestradiol),
approach (Hulsmann ). These plans should address all
was just included in the priority list of the WFD. Even though
aspects of the drinking water supply, focusing on control of
there are no agreed environmental quality standards at the
abstraction, treatment and delivery of drinking water. They
moment, such molecules have been monitored in a number
consist in particular of the identification of control measures
of installations as well as in many resources since several
in the drinking water system that will collectively control
years (Deblonde et al. ; Rodil et al. ).
identified risks and ensure that health-based targets are met. For each control measure identified, an appropriate means
Climate change issues
of operational monitoring should be defined so as to ensure that any deviation from required performance is detected both rapidly, and in good time.
Climate changes act as an indirect aggravating factor for the anthropogenic pressures on the environment (Cromwell et al. ; Delpla et al. ; Roig et al. ). In particular, the
Some efforts to be pursued
main determinants of climate change having a direct or indirect impact on water quality are air temperature and extreme water
Despite this regulatory framework, water quality compli-
events (flood, drought) (Van Vliet & Zwolsman ; Brodie &
ance is not fulfilled in small scale water systems (SSWS) in
Egodawatta ; Hrdinka et al. ). Resource availability is
particular for microbiological quality (Pitkänen et al. ;
linked to these periods (Ranjan et al. ; García-ruiz et al.
Risebro et al. ). It is stated that in Europe, 30 to 50%
; Nan et al. ), and it becomes important to consider
of water distributed by SSWS would often be of impaired
these extreme events in assessing both evolution of water
quality (Richardson et al. ; Falkenberg & Bloech ). More generally, water resource quality is influenced by
stress and efficiency of the treatment processes (Wilby et al. ; Johnson et al. ; Emelko et al. ).
both ‘natural’ and anthropogenic driving forces. The former
Changes in water temperature may modify the ecology
include spatial and temporal variation in water availability
of freshwater ecosystems and degrade water quality
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(Delpla et al. ). Most physico-chemical (solubilization,
strong oxidants (chlorine, ozone, chlorine dioxide, chlora-
complexation, degradation, evaporation, photolysis, etc.)
mines) that oxidize the organic matter and bromide
and biological (microorganisms catabolism, etc.) reactions
naturally present in most source waters, forming so-called
are promoted by an increase in temperature and/or in
disinfection by-products (DBP), the trihalomethane (THM)
solar irradiation (Malmaeus et al. ; Monteith et al.
of which such as haloacetic acids, oxyhalides, haloacetoni-
; Soh et al. ). Droughts, for example, increase the
triles,
concentration of dissolved substances in water while at the
haloamines, nitrosamines, iodo-THM (Mouly et al. ),
same time decreasing the concentration of dissolved
have been more investigated due to their potential cancero-
oxygen (Prathumratana et al. ; Van Vliet & Zwolsman
gen suspected effect (Singer ). In addition, many factors
halonitromethanes,
haloamines,
iodo-acids,
). But droughts can also promote the assimilation
significantly influence the formation of DBP: temperature,
of nutrients by plants or the adsorption/complexation of
pH and dissolved organic carbon (DOC), ammonia and
heavy metals on total suspended solids (TSS) or sediment.
ions bromides concentrations, as well as the types of treat-
Phototransformation
processes
occurring
in
the
environment should also be considered because they gener-
ment applied, the doses of chlorine and time of contact (Nikolaou et al. ; Teksoy et al. ).
ate transformation products (Buerge et al. ; Petrovic &
Water supply size can also be involved in water quality
Barceló ; Canonica et al. ), the toxicity of which
degradation. Small scale water supply is of particular inter-
remains questionable in some cases.
est, and remains a significant challenge for many countries
Heavy rainfall events produce an increase in river flow
– partly because human, technical and financial resources
rates, the higher risk of which is an increased transport of
are limited (Hulsmann ; United Nations & WHO
pollutants by runoff. In temperate countries, predictions
). Sadiq et al. () have shown, with the small utility
forecast an increase in mean volume of each rainfall event
performance indicators, that a link could be established
(Brunetti et al. ; Bates et al. ). In addition, rainfall
between the various technical (source and treated water
is admitted to be one of the more climatic factors affecting
quality, infrastructure) and non-technical (human and oper-
the microbial quality of very small (private) water supplies
ational factors) characteristics of water supply systems and
(Richardson et al. ).
the distributed water quality of small utilities. WHO esti-
Climate change is not the sole factor responsible for
mates that 10% of European citizens receive drinking
alteration of water quality. Global changes, including soil
water from these small or very small systems, including pri-
use, urbanization and its consequences on moisture, etc.,
vate wells. But only 60% of the small water supply zones
also contribute to water quality degradation (DiDonato
deliver water which is fully compliant with the requirements
et al. ; Carlson et al. ; Astaraie-Imani et al. ).
of the Drinking Water Directive 98/83/EC. Lastly, socioeconomic factors like demographic devel-
Specificity of SSWS
opments, urbanization, economic progress, and social changes, as well as lack of investment in rural and municipal
In addition to natural and anthropogenic pressure, drinking
water supplies, can also influence water quality.
water quality degradation can be affected by treatment plant inefficiency through the process itself and the water supply size. Concerning treatment processes, some outbreaks in
MONITORING SYSTEMS
the recent past (Curriero et al. ; Schuster et al. ; Tickner & Gouveia-Vigeant ; Aryal et al. ),
Parameters and proxies
showed a need for regular reevaluation of techniques to ensure effective drinking water disinfection. This is particu-
With the implementation of WSP, water quality control is a
larly important to protect small (vulnerable) water supplies
key point both in ensuring the safety of a drinking water
(Pitkänen et al. ). Indeed, such processes, in addition
supply and in assessing hazards linked to the deterioration
to effectively eliminating harmful microorganisms, are
of water body quality, for example surface and karstic
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resources (Bates et al. ; Bartram et al. ). Drinking
these parameters is, on the whole, satisfactory. Quality limits
water guidelines are proposed from country to another
have been established to allow quantified quality control.
country based on the WHO Guidelines for drinking-water
Conventional parameters are generally recognized as rel-
quality (WHO ). They may be different among countries.
evant for health risk assessment for drinking water and easy
For example, the management framework of drinking water
to measure in a qualified laboratory (accredited and agreed).
quality in Australia (with ADWG), the UK (with BS6700)
However, the list of parameters even completed by specific
and the USA are considered stronger compared than the
hazardous substances is actually not complete as some emer-
Canadian one, while as developing countries, India needs
ging substances showing toxic or ecotoxic effects, will likely
to improve its BIS 10500-1991 and China is still working on
be soon considered (e.g. estrogens). Another limitation of
its premature water standards (Kusumawardaningsih ).
such parameters becomes clear when water is subjected to
In Europe, the regulations organize water quality con-
unexpected quality variations, in particular in case of global
trol from catchment to treatment plant, using a number of
changes (namely climatic events with change in heavy rain
parameters (Table 1). In regular situations, characterized
pattern) or accidental or intentional contamination. These
by a limited seasonal variation and a homogeneous compo-
parameters can also fail to provide the right answer with
sition in time and space, water quality monitoring based on
regard to public health concerns. For example, the use of
Table 1
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Parameters and proxies used for quality control of surface (SW), ground (GW) and treated waters (adapted from Mons (2008))
Resource Parameter
SW
GW
Treated water
Proxy
Turbidity, NHþ 4 , UV
Microbiological parameters E. coli Enterococci, Clostridium perfringens Total coliforms Colony count, total cell counts, cultivation-free viability analysis Giardia/Cryptosporidium, Enteric viruses, Campylobacter Chemical parameters Arsenic, fluoride, selenium, nitrate Benzene, benzo(a)pyrene, boron, bromate, 1,2-dichloroethane, nitrite, antimony, cadmium, copper, chromium, lead, mercury, nickel, PAHs, organic micropollutantsa, tetra- & trichloroethene, disinfection by-products, sodium, calcium, magnesium, sulphate
Organoleptic, UV absorption, global toxicity, genotoxicity, endocrine disruption
Cyanides Pesticides Ammonium Iron, manganese Physico-chemical parameters
UV visible absorption
DOC/TOC, turbidity W
Taste, odour, colour, pH, chloride, alkalinity, conductivity, T , O2 Other parameters Genotoxicity, acute toxicity, algae toxins, AOC/BDOC Radioactivity W
PAHs: polycyclic aromatic hydrocarbon, DOC: dissolved organic carbon, TOC: total organic carbon, UV: ultraviolet, T : temperature, O2: dissolved oxygen, AOC: assimilable organic carbon, BDOC: biodegradable dissolved organic carbon. a
General group, consisting of e.g. pharmaceuticals, industrial pollutants, endocrine disrupting chemicals (EDCs), etc.
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indicator organisms (total and faecal coliforms, enterococci,
transient water degradation. For example, in sanitary con-
Clostridium perfringens) has often proved to be powerless
trol, the frequency of monitoring a SSWS, serving less
to predict the presence or absence of pathogens (Harwood
than 5,000 people is performed between once a year and
et al. ; Field & Samadpour ). Simple monitoring
once every 5 years (depending on the flow rate) for the
schemes based on detection of a single indicator are not ade-
resource and between once a month and once every 5
quate for public health protection.
years for the corresponding treated water (distribution and
In this context some proxies giving a global assessment
consumption points) (Table 2).
of one or several parameters may be used (as for example:
Water sampling frequencies vary from a country to
turbidity for bacterial contamination, UV spectrometry for
another sometimes depending on the type of quality par-
organic contamination). Generally more rapid and simple
ameters. For example the sampling frequency varies form
to measure than conventional parameters (proxies can be
once a month (<100 inhab.) to once a day (>100,000
implemented on line), they are meanwhile less specific.
inhab.)
But they can be used after comparative validation with the
For chemical monitoring the frequency varies from twice
for
microbiological
monitoring
in
Australia.
related parameter(s), including all analytical criteria, in par-
per year (<5,000 inhab.) to once a month (>5,000 inhab.).
ticular, reproducibility and repeatability in order to estimate
Appropriate techniques for water quality monitoring
the measurement error. This is of high importance especially
imply consideration of the entire analytical chain, from
when decision making is based on these proxies.
sampling strategy to transmission of results. Numerous analytical techniques are available, as reported in the
About sampling programs relevance
WHO Guidelines for drinking water quality (WHO ). However, it is not unusual to find different results for an
Because monitoring is carried out under a discontinuous
identical sample because of variability in one, or several,
way (based on sampling and laboratory analysis) the
steps of the analytical procedure (including sampling, trans-
choice of sampling frequency may be not adapted to
port, storage, and sample preparation and analysis).
Table 2
|
Example of sampling schedule and water sanitary control analysis programme for small and medium water supplies (adapted from the French Decree of 11 January 2007 (Journal Officiel 2007; Bessonneau et al. 2011)
Annual frequency Water resource Flow (m3/day)
GRa
SRa
<10 10 to 99 100 to 1,999 2,000 to 5,999
0.2b 0.2 0.5 1
0.5 1 2 3
Distribution and consumption points
Annual frequency
Population supplied (inhabitant)
Flow (m3/day)
P1c
P2
D1
D2
0 to 49
0 to 9
1
0.1/0.2
2/4
0.1/0.2
50 to 499
10 to 99
2
0.2/0.5
3/4
0.2/0.5
500 to 1,999
100 to 399
2
1
6
1
2,000 to 4,999
400 to 999
3
1
9
1
5,000 to 14,999
1,000 to 2,999
5
2
12
2
a
Source of raw water: groundwater resource (GR) and surface resource (SR).
b c
0.1, 0.2 and 0.5: analysis frequency every 10 years, 5 years and 2 years respectively.
The P (production) and D (distribution) analyses provide information about the parameters specified in the regulations and are carried out (P2 and D2 are complementary to P1 and D1
respectively, giving only microbiological and organoleptic quality data treatment effectiveness).
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Commonly-used methods are based on spot sampling.
perturbation of the water body considered. These early warn-
But this approach is not always representative of the overall
ing systems, able to analyze and interpret results in real time
quality of the water body. In particular it is limited where it
(Storey et al. ) are, in general, not specific (some are like
consists of producing data that are both geographically and
immunoassays), but inform of the overall water quality (pres-
temporally representative of the chemical and biological
ence/absence or toxic/not toxic, etc.) as for example daphnia
quality of a water body.
and algal toximeter that detect the whole toxicity in environ-
Monitoring evolution
permit frequent and rapid analysis and are adapted to manage
mental samples ( Jeon et al. ; Mons ). These methods sensitive locations such as SSWS. However, one of the main The cost of monitoring is also an influencing criterion for
drawbacks of these biological based methods for drinking
the implementation of water control, due to the demand
water monitoring could be in some cases their cross-reactivity
that more and more substances/parameters be examined
with chlorine.
in order to ensure water quality. Alternatives to standardized
Performance assessment is a requirement for a large use of
methods are now on offer, such as onsite measurement (in
these techniques. Currently, it is based on linearity domain,
situ, on line) and sampling (passive samplers). The methods
repeatability, limit of detection, limit of quantification, speci-
are complementary to laboratory analysis, and can be used
ficity,
to track the dynamic of the contaminant, map the distri-
performances in the laboratory using reference material and
bution of pollutants in time and space, measure evolution
calibrated solutions, followed by (ii) a verification of the analyti-
robustness
and
includes
(i)
validation
of the
rather than concentration, and for water quality screening.
cal characteristic directly on the field by insisting on the
These methods started to be developed 20 years ago,
robustness (Gonzalez et al. ; Roig et al. ). However,
out of the miniaturization, automation and adaptation of
this methodology, well adapted for laboratory transposed
laboratory techniques to make direct use in the field a
chemical methods becomes limited when qualitative, semi-
possibility. There is a set of current methods (on site, in
quantitative as well as biological methods are considered.
situ, on line) (Greenwood et al. ; Roig et al. )
The next evolution in such techniques is currently
which are able to provide quantitative, semi-quantitative
underway, with the association of telecommunication and/
and qualitative information by expressing conventional
or data transfer procedures (Figure 1). Such progress favours
parameters and/or proxies in a faster way. New on line and/or in situ monitoring tools, based on integrated sensor technology (measurement þ results interpretation) (Hassan ) have emerged in recent years. These consist more of evaluation of quality difference between a normal situation and a contamination event due to biochemical and physical interaction (Kroll ; Storey et al. ) than a quantitative assessment of a contaminant. They are mainly used to detect intentional as well as accidental contamination events in a more reliable and less expensive way (Skadsen et al. ). Initially based on physico-chemical principle, other monitoring tools have emerged by exploiting the sensitivity of biological systems. Bioindicators, bio or immunoassay and biomarkers, based on living organisms or part of them respectively, were proposed as on-line or field methods. Their sensitivity is not only used for the detection of ultratrace level of contaminant but to detect more early any
Figure 1
|
Evolution of monitoring techniques.
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transport of the signal (obtained by on site devices) instead
of treatment by-products and minimize operational costs.
of transport of the sample itself.
Understanding the reasons for variations in raw water qual-
However the ability to collect, store and use large
ity is important, because this will influence treatment
amounts of data from in situ sensor networks require new
requirements, efficiency and the resulting health risk associ-
techniques and approaches for quality assurance/quality
ated with the finished drinking water.
control (QAQC). Indeed, sensors can occasionally malfunc-
The end-of-pipe approach can also be of benefit, particu-
tion in particular in extreme environments, or are prone to
larly in adapting the treatment process to the water quality
fouling and drift, and communication systems can corrupt
and the dynamic of its evolution. This is of particular inter-
data (Wagner et al. ). QAQC need to include sensor
est when rapid environmental modifications occur.
calibration methods, and data-correction approaches, in par-
In practice, remediation actions of stakeholders (people,
ticular correction of out of range/anomalous values,
organisms water authorities, etc.) implemented with respect
correction for instrument fouling and drift, correction of
to regulation compliance or local initiatives must be con-
values, and correction of any known bias in the sensor
sidered for the reduction of point source discharge and
data (Pellerin et al. ). In practice, quality assurance
non-point source (diffuse) pollution. As an example, the
algorithms can be employed for each measured quantity
impact of intensive agriculture on surface water quality
within a subset of neighbouring sensors, or for averages of
coupled to climate change effects with modification of rain
multiple sensors (Collins et al. ).
patterns can be limited both by animal farming and fertilization control and redesign of protection area of catchment
Finally, modelling can also be envisaged.
including wetlands and long residence time reservoirs acting as passive pretreatment steps. In this context, reme-
HOW CAN THESE NEW THREATS BE MANAGED?
diation actions must be coherently implemented at local or regional scale depending on the size of the catchment.
It is possible to propose different mitigation options for
Regardless of whether the approach is from the source or
ensuring the quality of distributed water. The first approach
end-of-pipe, flexible monitoring tools (devices, practices, and
could be to consider the use of long-term and short-term
methodologies) are assets in orientating adaptation toward
health effect monitoring. Several information systems (com-
new threats, particularly in the event of sudden disruption
pulsory
toxic
to normal functioning. In such situations, reactivity and
surveillance) are available to alert the general public to
decision making in management of local and global changes
health-related issues, but specific field investigation are how-
need to be improved in order to anticipate the impact down-
ever to be carried out to establish a link with water whatever
stream of the source of contamination. This is even more
the system (Beaudeau et al. ). New data sources can also
challenging for shared water bodies at national or inter-
be used. For example, data relating to the reimbursement of
national level. It is estimated that two out of three of the
medication collected by the Health Service (in France) may
great rivers and aquifers in the world are shared between sev-
or
voluntary
reporting,
syndromic
or
facilitate the daily monitoring of health-related events at
eral countries, and that two out of five people depend on
local level (Tuppin et al. ); or multi-source system
these shared waters. Although this partition is often the
which will join together various databases of medical and
source of significant regional tensions, few international
medical-administrative activity (hospital admissions, medi-
agreements on water management exist.
cal insurance and anatomical pathology) (Tuppin et al.
Environmental sensor networks (ESN) is a trend which
; Beaudeau et al. ). However, this approach remains
is currently developing as a result of technological advances
limited for a study of the dynamic of the water quality
in the miniaturization of electronics and wireless communi-
evolution.
cation technology. Several systems have been already
Effective catchment management has many benefits.
developed, but they include only specific generic environ-
Decreasing water source contamination means that less
mental
treatment is required. This may, in turn, reduce production
positioning system (GPS), water, air and soil temperature,
parameters
such
as
meteorological,
global
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consequences
shares the threat of drought with Mediterranean
monitoring ocean conditions, volcanic processes, and so
countries, whereas Northern France could experience
on (Hart & Martinez ). They are well suited to large-
wetter winters like North European countries.
tection
of
water
bodies
and
sensitive
areas.
•
Southern
|
solved oxygen and chlorophyll, and are dedicated to
suit specific actions such as water production, and the pro-
worldwide.
14.1
conductivity, pressure, humidity, and soil moisture, pH, dis-
scale environmental processes, but need to be adapted to
spread
|
France
Risk surveillance, based on the collection of both environmental and health data (medical treatment, drug
ESN
prescription, epidemiological studies, etc.) and the devel-
perspectives need to include sensor modules producing
opment of tools for modelling the link function between
data on chemical and biological parameters. The possibility
water factors and health outcomes (Quenel ).
of being constantly connected to the data source allows water managers to be in close contact with the environment they depend upon (in terms of water resource, natural and anthropogenic pressure). Until we have an intelligent system capable of autonomous decision making, ESN, combined with a network of laboratory-based experts, offer the possibility of collection and analysis of data at all levels (as appropriate), from local to global. In addition occurrence data are not enough to assess the population’s exposure and make links between water quality failure and environmental or public health outcomes. Water quality management can therefore be improved through
From the above considerations, an enlargement of the DW quality monitoring purpose could be proposed with the integration of water system breakdowns and accidental or intentional contamination, leading both to water of impaired quality with likely health consequences. In this frame, Figure 2 displays the necessary adaptation of monitoring schemes between classical monitoring for the survey of water quality and the operational monitoring for a rapid diagnosis in case of accidental or intentional contamination of water. On one hand the implementation of classical monitoring based on sampling and laboratory analysis is well fitted for long-term survey and regulation compliance. On the other hand the use of rapid measurement devices
consideration of issues such as the following:
giving suited information (on time, easily understandable,
•
Structural changes in water systems, annual flows transferred between interconnected water systems, and hydraulic residence time distribution parameters (e.g. percentiles 50, 90, 100 and corresponding areas). In France, the SISE-eaux database (Health and Environment information system – water supply) introduces these new items and functionalities to improve knowl-
•
and available) constitutes an adapted monitoring for early warning. In between, the monitoring must be designed if needed for measuring transient water quality variations following hydroclimatic conditions (heavy rain for example) or more simply to detect water treatment breakdowns. Finally, Table 3 summarizes the main information used, and required, for a better water quality management.
edge of exposure throughout the country. Water operators’ safety rules: anti-intrusion alarms, pump breakdowns, excess turbidity, lack of chlorine, and frequency of follow-up visits. The reporting and recording of such signals would also help identify adverse acute water contamination factors and spot any water systems
•
subject to a sudden threat. Worldwide consequences of water contamination, in particular for transboundary water bodies or catchment. International and regional exchanges about both risk and mitigation measures are crucial in anticipating, and efficiently allocating, national resources (Pascal ). For
example,
concerns
about
climate
change
Figure 2
|
Evolution of water quality monitoring form.
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Table 3
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Data for water quality management and prediction
Type of information
Water quality
Laboratory measurement On line/on site measurement Sensors network
Complementary
Treatment plant and networks supervision Public health data
Hydro meteorological data Historical quality data
Relevance
Availability
Linked to monitoring design Regulation Transient variations Remote assistance Process control Decision making
Sampling delay Analysis delay Parameters limitation EWSa Very partial EWS
Material breakdown
EWS
Waterborne Epidemics Selectivity Climate event Anticipation
Delay in data collection Authorization needed
Characterization of normal conditions
Data collection
External data validation and storage
a
Early warning systems.
CONCLUSION
this evolution still needs years of development before it will, on the one hand, be available for numerous pollutants, and
Drinking water quality (from resource to tap) must be mon-
on the other, be accepted by the authorities and operators.
itored thoroughly in order to preserve the population from
The integration of secondary data in addition to real-
the consequences of contamination (natural, anthropogenic,
time interpretation and analysis of quality data now seems
accidental or intentional). In the face of increased threats
essential to ensuring reliable drinking water management.
due to environmental or human pressure, monitoring
These type of data should be considered as a preliminary
should be flexible and able to be adapted to any variation,
alert to potential causes of water quality failure (which
in order to drive water managers in their decision making.
may be more or less long term), and consequently, could
In particular, during exceptional events leading to a high
be useful in mitigating the effect of such crises.
variation in water quality (raw or treated water), they
Such evolutions in drinking water monitoring are
should be very responsive and able to adapt the general pro-
required in particular for small water supplies, serving 50
cedure to comply with quality standards and ensure the
to 5,000 citizens, which appear to be the most vulnerable
safety of the population.
drinking water systems regarding sanitary outbreaks.
In recent years, many emerging technologies have been developed to complement the existing laboratory-based methods (based on the expression of a parameter or proxy)
ACKNOWLEDGEMENTS
which are too slow to develop operational response and do not provide an adequate level of public health protection in
The authors would like to acknowledge the invaluable
real time. While these techniques are promising, particularly
help of Fleur Chaumet, Hardiesse Bessonneau and Ianis
in terms of reactivity and response time, they remain insuffi-
Delpla.
cient when prediction or anticipation are required – in the event, for example, of global-scale water management. With a view to further improvement in operational drinking water monitoring, a network of sensors with remote piloting will allow a sample signal (rather than an actual sample) to be sent to the laboratory (expert network). Yet
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Pitkänen, T., Karinen, P., Miettinen, I. T., Lettojärvi, H., Heikkilä, A., Maunula, R., Aula, V., Kuronen, H., Vepsäläinen, A., Nousiainen, L.-L., Pelkonen, S. & Heinonen-Tanski, H. Microbial contamination of groundwater at small community water supplies in Finland. Ambio 40 (4), 377–390. Prathumratana, L., Sthiannopkao, S. & Kim, K. W. The relationship of climatic and hydrological parameters to surface water quality in the lower Mekong River. Environment International 34 (6), 860–866. Quenel, P. Public health surveillance and the environment. Rev Epidemiol Sante Publique 43 (5), 412–422. Ranjan, P., Kazama, S. & Sawamoto, M. Effects of climate change on coastal fresh groundwater resources. Global Environmental Change 16 (4), 388–399. Richardson, H. Y., Nichols, G., Lane, C., Lake, I. R. & Hunter, P. R. Microbiological surveillance of private water supplies in England: the impact of environmental and climate factors on water quality. Water Research 43 (8), 2159–2168. Risebro, H. L., Breton, L., Aird, H., Hooper, A. & Hunter, P. R. Contaminated small drinking water supplies and risk of infectious intestinal disease: a prospective cohort study. PloS One 7 (8), e42762. Rodil, R., Quintana, J. B., Concha-Graña, E., López-Mahía, P., Muniategui-Lorenzo, S. & Prada-Rodríguez, D. Emerging pollutants in sewage, surface and drinking water in Galicia (NW Spain). Chemosphere 86 (10), 1040–1049. Roig, B., Valat, C., Berho, C., Allan, I. J., Guigues, N., Mills, G. A., Ulitzur, N. & Greenwood, R. The use of field studies to establish the performance of a range of tools for monitoring water quality. Trends in Analytical Chemistry 26 (4), 274–282. Roig, B., Allan, I., Mills, G. A., Guigues, N., Greenwood, R. & Gonzalez, C. Existing and new methods for chemical and ecological status monitoring under the WFD. In: Rapid Chemical and Biological Techniques for Water Monitoring (C. Gonzalez, R. Greenwood & P. Quevauviller, eds). John Wiley & Son, Chichester, pp. 39–50. Roig, B., Baures, B., Jung, A., Delpla, I. & Thomas, O. Rainfall and Water Quality. In: Rainfall: Behavior, Forecasting and Distribution (O. E. Martín & T. M. Roberts, eds). Nova Publisher, 91–104. Sadiq, R., Rodríguez, M. J. & Tesfamariam, S. Integrating indicators for performance assessment of small water utilities using ordered weighted averaging (OWA) operators. Expert Systems with Applications 37 (7), 4881–4891. Schuster, C., Ellis, A., Robertson, W., Charron, D., Aramini, J., Marshall, B. & Medeiros, D. Infectious disease outbreaks related to drinking water in Canada, 1974-2001. Canadian Journal of Public Health. 96 (4), 254–258. Singer, J. Formation and characterization of disinfection byproducts. In: Safety of Water Disinfection: Balancing Chemical and Microbial Risks (G. F. Craun, ed.). ILSI Press, Washington, 201–221. Skadsen, J., Janke, R., Grayman, W., Samuels, W., Tenbroek, M., Steglitz, B. & Bahl, S. Distribution system on-line
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Towards sustainable sanitation – the HAMBURG WATER Cycle in the settlement Jenfelder Au Kim Augustin, Anne-Katrin Skambraks, Zhiqiang Li, Thomas Giese, Ulf Rakelmann, Franziska Meinzinger, Henning Schonlau and Christian Günner
ABSTRACT One of the largest urban development projects at present in Hamburg is the conversion of former military barracks into a new residential area for about 630 households, called Jenfelder Au. The urban design concept for this 35 ha area follows a high quality approach to develop a carbon-neutral, attractive neighbourhood for approx. 2,000 inhabitants abundant with green space and urban water. HAMBURG WASSER, Hamburg’s water supply and wastewater utility, is rethinking the way of wastewater management by implementing an integrated concept for decentralised wastewater treatment and energy production – the so-called HAMBURG WATER Cycle® (HWC) – in this new residential area, based on source control of wastewater. Stormwater, greywater and blackwater are
Kim Augustin Anne-Katrin Skambraks (corresponding author) Zhiqiang Li Thomas Giese Ulf Rakelmann Franziska Meinzinger Henning Schonlau Christian Günner HAMBURG WASSER, Billhorner Deich 2, 20539 Hamburg, Germany E-mail: anne-katrin.skambraks@hamburgwasser.de
collected separately and then treated separately on site in Jenfelder Au. The realisation of the HWC will be the hitherto largest demonstration of a resource oriented sanitation concept working with vacuum technology for the collection of concentrated blackwater. This concept intends to establish synergy between wastewater management, waste management and energy production, and contributes to an improved local natural water cycle. Key words
| blackwater digestion, energy generation, HAMBURG WATER Cycle®, source separation
INTRODUCTION The need for higher energy and resource efficiency in the deliv-
rainfalls, challenge and overburden existing drainage infra-
ery of basic infrastructure services – drinking water supply,
structure (Funke ; Schramm ). In most cases, the
wastewater management, energy supply and solid waste man-
enlargement of sewers as an adaptation to climate change
agement – becomes more and more urgent, as factors such as
is limited by both the available space in inner city grounds
urbanisation, climate change and aging infrastructure facilities
and economic factors.
represent challenges for future service provision.
The typical economics of existing centralised infrastruc-
By 2020 about 56% of the world’s population will live in
ture turns out to be a serious dilemma since ageing
urban areas (United Nations ) and the growth of these
infrastructure is a key challenge for most constructed infra-
urban areas is expected to take place mainly in low- and
structure facilities (Jacobi & Sympher ; Ugarelli et al.
middle-income countries (Satterthwaite ). Solutions
). Yet the traditional replacement of assets with again
for the provision of the above mentioned infrastructure ser-
long lifetimes may not be an appropriate way to achieve
vices often have to cope with rapid development and scarce
future infrastructure service provision, which may need to
natural resources.
be more resilient and adaptable to the impacts of urbanis-
The effects of climate change, such as changes in pre-
ation and climate change. (Hillenbrand & Hiessl ).
cipitation patterns and the tendency towards heavier
The development of decentralised infrastructure systems
doi: 10.2166/ws.2013.158
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seems to be a promising solution to this dilemma. However,
area. The surrounding neighbourhood of Jenfeld has a high
the potential of decentralised ‘island’ solutions still needs to
proportion of subsidised housing and a diverse socio-
be demonstrated, evaluated and verified, especially when
economic mix. The built environment is dominated by an
these systems do co-exist within centralised infrastructure.
anonymous, uniform appearance with monotonous residen-
In Hamburg, the second largest city in Germany, the
tial high-rise buildings. The FHH conducted an urban
water supply and wastewater utility company HAMBURG
development plan competition for the conversion of the
WASSER has achieved for the first time, a decentralised and
former barracks in 2005/2006, which was intended to also
integrated infrastructure concept, namely the HAMBURG
improve the image of the neighbourhood Jenfeld. The win-
WATER Cycle® (HWC), within its conventional centralised
ning concept was offered by West 8 Urban Design &
wastewater management infrastructure. This innovative infra-
Landscape Architecture and focussed on a high-quality
structure concept links wastewater management with energy
approach to developing a sustainable and attractive neigh-
production and aims at providing a carbon-neutral wastewater
bourhood with abundant green spaces and water bodies.
concept for cities of the future.
The urban development plan features a range of diverse
The HWC is part of the large urban development project
building types and a variety of public spaces. Three major
‘Jenfelder Au’ of the Free and Hanseatic City of Hamburg
design principles, which are ‘Partial Collectivity’, ‘Clear
(FHH) in the district Hamburg-Wandsbek. The city stipu-
Individuality’ and ‘Sustainability’ are dominating West 8’s
lated ambitious development goals for the urban planning
design for Jenfelder Au. This refers to a strong emphasis
of this new settlement when conducting the urban develop-
on social sustainability, which is of particular importance
ment plan competition.
in areas such as the Jenfeld neighbourhood that have been
The integrated infrastructure concept, HWC, as well as
neglected by urban planning processes in the past. The
the winning concept for the urban development plan, is
urban design with different housing types therefore aims to
widely considered as a promising, innovative and sustain-
attract a wide variety of different residents ranging from
able example of water sensitive city planning. The urban
lower to upper middle class and an urban mix of younger
development plan for Jenfelder Au was awarded the ‘Gold
and older people. Plot sizes are compact and provide for
Award’ in the 2009 International Urban Landscape Award
attractive and affordable townhouses with gardens.
(IULA) because of its outstanding architectural, social, econ-
The housing area is improved by incorporating an inter-
omic and ecological elements. The quality of urban living is
esting mix of space for living and working, as well as various
enhanced by energy-efficient and resource-optimised con-
other functions such as small businesses, services, municipal
struction and the integrated approach regarding the
facilities, restaurants and cafes, retail and day-care centres.
multiple urban functions (e-architect ).
These functions, integrated into the urban development plan, turn Jenfeld into a ‘city of social sustainability’. The area is planned to be urban, yet green, which is reinforced
SUSTAINABILITY ASPECTS OF THE URBAN PLANNING IN JENFELDER AU
by the incorporation of water and green areas into the public space. Water bodies (i.e. the Cascade Park and the Kuehnbachteich, which is a water body located in the
In the following sections the urban development project Jen-
centre of the area), greened places, avenues and garden
felder Au is presented, focussing on the urban planning and
plots are incorporated into the entire area. Figure 1 shows
the infrastructure planning.
the new plan for Jenfelder Au and highlights the mix of living and working as well as the green elements in the
Jenfelder Au – the urban development plan for integrating social and ecological sustainability
urban layout. A main square at the centre of the area, where small businesses, services and cafes are located next to public
The FHH decided to develop a former military barracks
green spaces and dwellings, provides for a good mix of cul-
area in the district Hamburg–Wandsbek into a new housing
tural, social and public functions. The green spaces are
15
Figure 1
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Bird’s eye view of the attractive town houses with gardens and PV panels on the roofs (FHH, West 8 & BRW 2006).
closely connected to the semi-natural use of rainwater
Some existing buildings of the former barracks are going
within the urban landscape. The rainwater will be collected
to be refurbished and integrated into the housing concept. A
in small ditches and will feed the water cascade in the main
parade ground is going to be maintained as an historic monu-
green area (‘Cascade Park’). The cascade then discharges
ment and upgraded by the integration of private gardens.
into the central pond called Kuehnbachteich, which is in
However, military ornaments are going to be covered to
fact a rainwater retention basin (see Figure 2). This basin
reflect the future peaceful use. North of the new development
3
has a retention volume of 5,000 m , and is designed for rain-
area is designated as a commercial area for various low emis-
fall events with a return period of 30 years. In Jenfelder Au,
sion uses such as stores, small trade and offices.
urban design functions, such as providing public recreational space, are merged with rainwater infrastructure
Townhouse architecture
provision. Not only the urban development plan, but also the suggested architectural housing types, reflect the modernity and high quality of living space that is planned in Jenfelder Au. The design principles ‘Partial Collectivity’ and ‘Clear Individuality’ are mainly transported in the development of townhouses. According to West 8’s design concept, townhouses are a combination of row houses and freestanding family homes. Gardens are also important elements, and they provide attractive alternatives to the often monotonous suburban developments. The townhouse type covers a variety of housing types that help residents to express their personal lifestyle and individuality. Yet, a certain unity (a ‘common canon of design’) contributes to the feeling of identity and security across the diverse social and cultural Figure 2
|
Rainwater management in Jenfelder Au (FHH, West 8 & BRW 2006).
mix (e-architect ).
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According to West 8 the housing architecture of Jenfelder Au is characterised as follows (e-architect ):
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the neighbourhood. The following sections highlight the key characteristics of the HWC and its implementation in Jenfelder Au. A more detailed description of the planning
‘One of the most important aspects of the design is the indi-
process and the technical design can be found in Augustin
vidual unity of each building. This means that the buildings
et al. ().
can stand alone, but also can be attached to each other, which will intensify the lively urban atmosphere of the neighborhood. The buildings are close together, their proportions are relatively narrow and high, and the corresponding plots are very compact. The combination of these characteristics enables the realization of affordable housing units with a strong expression. Due to the relatively
high
density,
a
quarter
of
small-scale,
yet
urbanized, can arise. Although each building will have its individual character, it is possible to develop a large number of houses at once: the developer offers potential buyers an architectural variety of housing types, and each individual house can then have its own façade design. This makes a natural architectural mix possible.’ The design principle ‘Sustainability’ means that a neighbourhood will be built which is future-oriented, ecological and carbon neutral. This is accomplished by incorporating renewable energy generation and achieving self-sufficiency in terms of energy use. The roofs of the residential buildings offer the potential to generate renewable energy by being equipped with photovoltaic and solar thermal systems. The design of the townhouses supports the technical systems by using the technical conditions for photovoltaic systems as a design element for the roof slope and orientation (see Figure 1). In addition to the consideration of generation of
Source separation of household wastewater flows Wastewater systems with source control offer a higher potential to combine infrastructure services (water, energy, waste) in a more efficient way than the conventional sewerage system working with flushing toilets, mixed sewers and end-of-pipe treatment (Otterpohl et al. ). Based on the different characteristics of wastewater flows, different treatment processes can be applied. The main differentiation of household wastewater flows concerns the toilet wastewater (blackwater, i.e. urine and faeces with or without toilet paper), which is rich in organic matter and nutrients, and the water from kitchens and bathrooms (greywater), which produces larger volumes with lower concentrations of pollutants. Based on this understanding, HAMBURG WASSER developed an innovative and integrated concept for wastewater treatment and energy production – the so-called HWC and adapted it for the new settlement Jenfelder Au (Schonlau et al. ). The HWC concept is based on following characteristics:
•
Separation of different household wastewater flows at
•
Collection of concentrated blackwater by means of
their source: blackwater, greywater and rainwater.
renewable energy, Jenfelder Au will also see a new approach
vacuum technology, i.e. with vacuum toilets and vacuum
to urban wastewater management. For the first time on a
pipe network.
large scale the HWC developed by HAMBURG WASSER
•
Utilisation of blackwater and additional biomass (e.g.
will be implemented and adapted to the local conditions
organic waste or grease) in a district anaerobic digester
in Jenfeld.
for the generation of heat and electricity in a combined
• THE HAMBURG WATER CYCLE – AN INTEGRATED INFRASTRUCTURE CONCEPT (NOT ONLY) FOR THE NEW SETTLEMENT JENFELDER AU
•
heat and power plant (CHP). Decentralised treatment of separated greywater from showers, sinks, etc. On-site management of rainwater to close local natural water cycles. Figure 3 illustrates the basic flows of the HWC concept
The HWC combines sustainable sanitation with on-site
as it will be implemented in Jenfelder Au. The primary
energy generation and delivers heating energy directly to
objectives of this first implementation of its kind on a
17
Figure 3
K. Augustin et al.
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HAMBURG WATER Cycle® – wastewater concept.
larger scale are to gain more experience in terms of the
such as organic household waste or contents of grease
general aspects of the economic feasibility and the oper-
traps, e.g. from restaurants.
ation and maintenance as well as measuring actual data
In a feasibility study regarding renewable energy supply
to compare to the predicted benefits. The main focus for
HAMBURG WASSER showed that the whole heat demand
the time being is on energy generation from the digested
of Jenfelder Au could be covered by locally generated
blackwater. Other benefits such as nutrient recovery or
biogas from blackwater and organic waste together with
water recycling are going to be investigated for their basic
geothermal energy and solar heat. The heat supply of the
feasibility but are not currently implemented in Jenfelder
630 households (ca. 4.5 MWh per household and year)
Au, since their economic rate of return under present con-
could be covered by three local, regenerative energy
ditions (e.g. current mineral fertiliser prices and water
sources:
prices) is too low. 1. Biogas generated from the digestion of blackwater and Energy from wastewater
organic waste. The treatment plant is designed to feed a CHP with a capacity of 100 kWel and 135 kWth. The gen-
When completed the HWC concept will demonstrate a
erated heat is fed into a heat network serving the
minimisation of the need of non-renewable energy sources
residents of Jenfelder Au and partially used to heat up
and will highlight the potential energy generation based on
the fermentation unit. The generated electricity is used
the separation of blackwater. In contrast to conventional
to run heat pumps at affiliated decentralised geothermal
wastewater treatment of mixed wastewater, aerobic and
plants. Energy from blackwater and organic waste is cov-
thus energy-intensive treatment of the blackwater is not
ering about 30% of the settlement’s heat energy demand –
required. Instead, anaerobic processes are used to treat the
this share can be further increased by an increased
blackwater and to generate biogas. There will be one facility
amount of digested high caloric waste, such as grease
for the entire neighbourhood, which will be located in the
trap residues.
Northern part of the area designated for commercial land
2. Solar heat can be generated on lean-to roofs of the settle-
use. In addition to the blackwater from the households of
ment. About 10% of the settlement’s heat energy demand
Jenfelder Au the plant will be fed with other organic waste
can be covered by solar heat.
18
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3. Geothermal energy can generate up to 40% of the settle-
Although the main focus is on renewable energy gener-
ment’s heat energy demand. This share is limited by the
ation, the HWC also provides for wise management of other
available space for the drillings in the public greens and
resources. In particular, sustainable water use is an impor-
the geological conditions on site.
tant aspect of the concept. Since the vacuum toilets only
The peak load heat energy, which constitutes about 20% of the total heat demand, can be covered in various ways, e.g. using a gas boiler, a wood pellet boiler or a connection to a nearby district heating network. In addition a high share of the electricity demand of Jenfelder Au could be generated locally by solar panels on rooftops and surplus electricity from the CHP. This energy concept based on local regenerative energy sources and the HWC is a great step towards energy self-sufficient cities of the future. In 2012 the FHH started a tender procedure for the heat supply procurement contract in the settlement based on the above presented integrated wastewater and energy concept of the HWC. The outcome of the tender will define the energy concept which is in any case based on the ‘HWC biogas’ from separated blackwater.
need about a quarter of the usual flush water volume (about 1–1.5 l per flush), this saves large amounts of valuable drinking water. In Jenfelder Au more than 12,500 m3 drinking water will be saved annually that would be otherwise flushed down the toilets. Since the greywater is separately collected and treated, appropriate technologies can be used ranging from hightech treatment to allow water reuse for various purposes to low-tech natural treatment technologies such as planted soil filters and ponds resulting in water fit for irrigation purposes. Due to the relatively low pollution of the greywater these extensive treatment processes can be designed in such a way that land use is minimised and costs are saved. Since in Hamburg water reuse is not required due to the good availability of water resources, these aspects of the HWC are not incorporated in Jenfelder Au, but the aim is to implement greywater treatment processes with high flexibility and robustness. According to current planning status, a
BENEFITS OF THE HWC CONCEPT
trickling filter will be used for greywater treatment. Rainwater in Germany is often mixed with domestic and
The realisation of the HWC in Jenfelder Au will be the lar-
industrial wastewater, which can result in combined sewer
gest working demonstration of a resource oriented
overflows leading to the pollution of receiving water
sanitation concept within an urban environment in
bodies. The HWC concept integrates separate and on-site
Europe. It will also be the largest installation of vacuum
management of rainwater and uses the rainwater runoff as
technology for separate collection of blackwater in a resi-
landscape shaping elements, for example in rainwater cas-
dential area, although this technology has been widely
cades or in the semi-natural retention pond.
applied in cruise ships, aircrafts and trains. The approach
Other resources that the HWC aims to address are nutri-
makes it feasible to combine the infrastructure services of
ents that can be found in domestic wastewater and that can
wastewater management and energy generation and to con-
be used as plant fertilisers. The macronutrients nitrogen and
tribute to increased resource efficiency. However, even if
phosphorus are of particular interest due to their energy-
the HWC concept offers synergy effects between different
intensive production (nitrogen) and their limited availability
infrastructure services, several utilities will provide these
in terms of finiteness, natural pollution and skewed global
services in Jenfelder Au: HAMBURG WASSER is in
distribution (phosphorus). Both nutrients can be found in
charge of the wastewater management, an energy contrac-
wastewater and are particularly present in urine or black-
tor is in charge of providing the heat supply and
water (Meinzinger & Oldenburg ). The separate
Hamburger Stadtreinigung is in charge of the waste dispo-
collection and low dilution of these flows is therefore very
sal. The technical linkages of the HWC concept must find
beneficial for the recovery of nutrients. Beside the direct
their way to transcend traditional organisational bound-
use of these separated wastewater flows in agriculture after
aries to make use of the full potential of the integrated
sufficient treatment to reduce pathogen contents, there are
concept.
currently several processes under consideration to extract
19
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the nutrients and make them available in a more concen-
costs during the construction. The community in the neigh-
trated form (Balmer ; Maurer et al. ; Alp ).
bourhood
However, these are pilot investigations and still uneconomi-
functional and spatial mix set in West 8’s urban planning
cal. Yet, several authors suggest that future prices for
concept and the people show interest in the new technol-
mineral fertiliser may rise significantly and therefore options
ogies used in the HWC such as the vacuum toilets.
for nutrient recovery such as provided by the HWC will
particularly
appreciates
the
well-balanced
HAMBURG WASSER is the first German water and wastewater company that is integrating a decentralised,
become increasingly important. Overall, the HWC will contribute significantly to
source separating concept into its operational structures.
making the area Jenfelder Au a low carbon neighbourhood.
The projection of investment costs for this new infrastruc-
In contrast to conventional wastewater collection with
ture concept indicates higher costs than for a conventional
maximum concentrations of about 900 mgCOD/l the collec-
wastewater disposal concept. These additional costs are cov-
tion of blackwater in vacuum toilets yields about 10 times
ered by HAMBURG WASSER and by external funds such
higher concentrations of organic matter of approximately
as the EU LIFEþ programme. LIFE is the EU’s financial
10,000 mgCOD/l. This is a prerequisite for the efficient
instrument supporting environmental and nature conserva-
anaerobic treatment of the wastewater.
tion pilot or demonstration projects with European added value (European Commission ). Operating a decentralised system such as HWC will require new operating
CONCLUSION
structures
to
be
implemented
within
HAMBURG
WASSER. However, the biggest challenge is the implemenThe HWC is an innovative wastewater concept based on
tation of a new technology for wastewater transport and its
source separation of domestic wastewater flows and their
technical and legal implications; so far HAMBURG
efficient treatment and use. The concept contributes signifi-
WASSER operates gravity flow sewers as well as pressure
cantly to the sustainable profile of Jenfelder Au by
sewers. The vacuum technology for Jenfelder Au is an inno-
combining urban water and waste infrastructures with
vation
local energy production. Concentrated blackwater is anaero-
department as well as for the planning department and the
bically
whereas
legal department. Lacking experience with the vacuum tech-
greywater and rainwater are separately collected, treated
nology so far, HAMBURG WASSER was dependent on
digested,
thereby
generating
energy,
with
relevance
for
the
networks
operation
according to their specific characteristics, and returned to
external facilities as reference for the planning and the
the local natural water cycle. The use of vacuum toilets
future operation. Several technical details of the vacuum
instead of conventional gravity-driven toilets will save
network in Jenfelder Au are tailor-made in-house develop-
annually more than 12,500 m3 of water. Recovery of nutri-
ments, which were subject to extensive planning and
ents and water recycling are further options for improved
testing (Skambraks et al. ). Furthermore, the legal
resource management.
department introduced the new technology for wastewater
The concept will be implemented for the first time in
transport to the current legal framework of HAMBURG
Jenfelder Au in Hamburg, Germany. Jenfelder Au is an out-
WASSER by an amendment to the wastewater law of Ham-
standing example of sustainable urban planning and will
burg (HmbAbwG). This amendment process started early in
provide affordable housing for more than 600 households.
2010 and is still ongoing (Skambraks et al. ).
After the first construction phases finishes in 2013, the
Despite the additional costs and the special challenges
first inhabitants are expected to populate the new quarter
of the vacuum technology, the implementation of the
in 2014. So far the new concept gets positive feedback
HWC in the settlement will also generate benefits. Residents
from current property developers, who are in charge to con-
will save on their water bills due to reduced water consump-
struct the separate blackwater and greywater drainage
tion. The provision of energy from decentralised sources
systems within the houses. The future benefits of the HWC
allows a decreased dependency on external energy suppliers
concept are expected to make up for the higher investment
and their pricing policies. Other benefits such as water
K. Augustin et al.
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Sustainable sanitation in Jenfelder Au
Water Science & Technology: Water Supply
recycling or nutrient recovery will not yet be financially exploited in this first implementation in Jenfelder Au, but present promising options particularly from a global perspective as a response to diminishing and deteriorating natural resources such as phosphate rock (Cordell et al. ). The implementation of the HWC in Jenfelder Au will present a valuable opportunity for more detailed research in the field of source separation of wastewater and improved resource efficiency. HAMBURG WASSER intends to carry out more research to improve robustness and efficiency of blackwater and greywater treatment. Furthermore, challenges such as the elimination of pharmaceutical residues from wastewater or the further use of the digester effluent as fertiliser or soil conditioner can also be addressed by the HWC and will be further investigated in an extensive research project funded by the German Federal Ministry of Education and Research (BMBF). First results of these supporting research activities are expected for the year 2013.
ACKNOWLEDGEMENTS The authors wish to thank Freie und Hansestadt Hamburg (the municipality of Hamburg) and Bezirksamt Wandsbek (the
district
of
Wandsbek)
for
supporting
the
implementation of the HAMBURG WATER Cycle® in Jenfelder Au. Planning and construction is partly funded by the LIFEþ programme of the European Commission, Directorate General Environment (LIFE10 ENV/DE/158). Research on the HAMBURG WATER Cycle® in Jenfelder Au is carried out in the project ‘KREIS’ and is co-financed by the German Federal Ministry of Education and Research under the programme Research for Sustainable Development financial
(FONA)
support
of
(Reference: both
033L047B).
programmes
is
The
gratefully
acknowledged.
REFERENCES Alp, Ö. Further Treatment of Digested Blackwater for Extraction of Valuable Components. PhD Thesis, Hamburg University of Technology, Germany.
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Augustin, K., Skambraks, A.-K., Li, Z., Giese, T., Rakelmann, U., Schonlau, H. & Günner, C. HAMBURG WATER Cycle in the Settlement Jenfelder Au – Integrating the Infrastructure Services of Water and Energy. IWA Conference Cities of the Future, Stockholm, 22–25 May 2011. Balmer, P. Phosphorus recovery – an overview of potentials and possibilities. Water Science and Technology 49 (10), 185–190. Cordell, D., Drangert, J.-O. & White, S. The story of phosphorus: global food security and food for thought. Global Environmental Change, Elsevier 19 (2), 292–305. e-architect Neues Wohnen Hamburg-Jenfeld. West 8 wins International Urban Landscape Gold Award. 28 Jan 2010. http://www.e-architect.co.uk/hamburg/ neues_wohnen_hamburg_jenfeld.htm (accessed 14 June 2011). European Commission Environment LIFE Programme. http://ec.europa.eu/environment/life/ (accessed 2 April 2013). FHH, West 8 & BRW Neues Wohnen in Jenfeld – Funktionsplanung (Function scheme of the area Neues Wohnen Jenfeld) (in German). Funke, R. Berücksichtigung von Starkregen infolge Klimaveränderung? Auswirkung auf die Bemessung am Beispiel Hamburgs (Consideration of intense rain due to climate change? Effects on design for the example Hamburg). DWA Landesverbandstagung Nord 2007, 117–128. Hillenbrand, T. & Hiessl, H. Sich ändernde Planungsgrundlagen für Wasserinfrastruktursysteme. Teil 1: Klimawandel, demographischer Wandel, neue ökologische Anforderungen (Changing requirements for water infrastructure. Part 1: Climate change, demographic change, new ecological requirements). KA – Abwasser, Abfall 12 (53), 1265–1271 (in German). Jacobi, D. & Sympher, K.-J. Sewer rehabilitation in Berlin. Water Science and Technology 46 (6–7), 379–387. Maurer, M., Pronk, W. & Larsen, T. A. Treatment processes for source-separated urine. Water Research, Elsevier 40, 3151–3166. Meinzinger, F. & Oldenburg, M. Characteristics of source-separated household wastewater flows: a statistical assessment. Water Science and Technology 59 (9), 1785–1791. Otterpohl, R., Albold, A. & Oldenburg, M. Source control in urban sanitation and waste management: systems with reuse of resources. Water Science and Technology 39 (5), 153–160. Satterthwaite, D. The Transition to a Predominantly Urban World and its Underpinnings. International Institute for Environment and Development. Human Settlements Discussion Paper Series, http://pubs.iied.org/10550IIED. html (accessed 2 August 2012). Schonlau, H., Rakelmann, U., Li, Z., Giese, T., Werner, T., Augustin, K. & Günner, C. Pilotprojekt für ein ganzheitliches
21
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Entwässerungskonzept in Städten (Pilot project for a holistic urban drainage concept). KA Korrespondenz Abwasser, Abfall 55 (10), 1095–1099 (in German). Schramm, E. Klimatische Herausforderungen für städtische Wasserinfrastrukturen in Deutschland (Climatic Challenges for Urban Water Infrastructures in Germany). IBA-Labor Ressource Wasser, Hamburg, Germany, 5 & 6 November 2009, pp. 18–22 (in German). Skambraks, A.-K., Augustin, K. & Meinzinger, F. Hamburgs dezentrales Entwässerungssystem HAMBURG WATER Cycle in der Jenfelder Au (The decentralised drainage system HAMBURG WATER Cycle in the settlement Jenfelder Au, Hamburg). 13. Kölner Kanal und
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Kläranlagen Kolloquium 2012, Aachener Schriften zur Stadtentwässerung Band 16, 18/1–18/12 (in German). Ugarelli, R., Venkatesh, G., Brattebo, H. & Saegrov, S. Importance of investment decisions and rehabilitation approaches in an ageing wastewater pipeline network. A case study of Oslo (Norway). Water Science and Technology 58 (12), 2279–2293. United Nations Department of Economic and Social Affairs, Population Division. World Urbanization Prospects: The 2011 Revision, CD-ROM Edition, http://esa.un.org/unup/ CD-ROM/Urban-Rural-Population.htm (accessed 8 May 2013).
First received 24 August 2012; accepted in revised form 19 April 2013. Available online 13 September 2013
22
© IWA Publishing 2014 Water Science & Technology: Water Supply
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Fluorescence characteristics of natural organic matter in water under sequential exposure to UV irradiation/ chlor(am)ination Qianjun Guo, Zaili Zhang, Zhengbo Ma, Yongmei Liang and Wei Liu
ABSTRACT The organic matter in International Humic Substances Society Natural Organic Matter (IHSS NOM) water exposed to ultraviolet (UV) irradiation and chlor(am)ine sequentially under practically relevant conditions was characterized based on fluorescence spectra. IHSS NOM water exposed to UV irradiation or chlor(am)ine alone was also evaluated. Both chlor(am)ine alone and UV/chlor(am)ine exposure showed similar chlor(am)ine demand and fluorescence spectra. UV irradiation and UV/ chlorine exposure diminished the fluorescence intensity of IHSS NOM water, while UV/chloramine exposure resulted in increased fluorescence intensity. When compared with the results obtained following chlor(am)ination alone, IHSS NOM water showed decreased chlorine decay and increased chloramine decay after UV irradiation/chlor(am)ination. Additionally, IHSS NOM water exposed to UV/
Qianjun Guo Zaili Zhang Zhengbo Ma Yongmei Liang Wei Liu (corresponding author) School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China and Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Guangzhou 510275, China E-mail: esslw@mail.sysu.edu.cn
chloramine and chloramine showed less disinfection by-product (DBP) formation than water subjected to UV/chlorine and chlorine. Overall, these findings indicate that UV irradiation degrades NOM molecules to low-molecular-weight fractions, facilitating the subsequent reaction with chlor(am)ine. However, chlorine and chloramine play different roles in the reaction. Chlorine degradation and substitution dominates the process of UV/chlorine exposure, while chloramine substitution is the major reaction during UV/chloramine exposure. Key words
| chlor(am)ination, natural organic matter, sequential disinfection, UV
INTRODUCTION Chlorine is the chemical oxidant most commonly used
cannot be used as a stand-alone disinfectant (Hassen et al.
worldwide for drinking water disinfection (Deborde &
). Accordingly, combined use of UV and chlor(am)ine
von Gunten ); however, its use has been decreasing,
to maintain lasting residual activity and disinfection effects
mainly because of the formation of toxic, mutagenic and car-
has been studied. The combination of UV irradiation as a
cinogenic disinfection by-products (DBPs) and residual
primary disinfectant and free chlorine or monochloramine
chlorine during the disinfection process (Ates et al. ).
as a secondary disinfectant (sequential disinfection) has
Moreover, chlorination has low efficiency against viruses,
been shown to prevent subsequent microbial regrowth and
bacterial spores and protozoan cysts (Korich et al. ).
produce a synergetic disinfection effect (Shang et al. ).
Ultraviolet (UV) irradiation is a promising alternative to
DBPs are formed when natural organic matter (NOM) in
free chlorine as a primary disinfectant because of its ability
water reacts with a disinfectant (White et al. ). The most
to inactivate Cryptosporidium parvum without producing
common DBPs include trihalomethanes (THM) and halo-
DBPs at common disinfection doses (Liu et al. ). How-
acetic acids (HAA). Humic substances (HS) are commonly
ever, owing to a lack of residual activity and the possible
found in natural waters, including humic acids (HA), fulvic
repair of UV-damaged microorganisms, UV irradiation
acids (FA) and humins, which have different characteristics.
doi: 10.2166/ws.2013.166
23
Q. Guo et al.
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NOM under UV irradiation/chlor(am)ination
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The effects on NOM water and the dominate reaction
Ultra Pure water to prepare NOM water samples. The
during the sequential exposure of UV/chlor(am)ine have
NOM solutions were then passed through 0.45 μm
rarely been reported. Wang et al. () reported that the
cellulose acetate membrane filters and the filtrates were
sequential disinfection of UV and chlorine effectively con-
collected to make stock NOM solutions. The concen-
trolled photoreactivation and minimized the concentration
trations of NOM in the stock solutions were quantified
of chlorine, decreasing the genotoxicity of treated waste-
by dissolved organic carbon (DOC) analysis using a
water. Liu et al. () reported that monochloramine
total organic carbon (TOC) analyzer (Shimadzu TOC-
could be a better secondary disinfectant owing to its much
5000A, Japan), after which they were freshly diluted to
smaller DBP formation and lower decay rate. Therefore,
3 mg/L as DOC using ultra pure water containing phos-
the present study was conducted to investigate how
phate buffer (pH ¼ 7.5, 0.05 M) to prepare the testing
NOM transforms during the sequential exposure to
solutions.
UV/chlor(am)ine and elucidate the mechanism of the reac-
A free chlorine stock solution (about 1 g/L as Cl2) was
tion. International Humic Substances Society (IHSS) NOM
freshly prepared before each test by diluting a 4.5%
waters were used in this study, and chlor(am)ine was used as
sodium hypochlorite (NaOCl) solution (Allied Signal,
the disinfectant. Changes in NOM during the disinfection
USA) with a chlorine-demand-free pH 7 phosphate buffer
process were identified by three-dimensional excitation–
solution (0.05 M) to a concentration of approximately
emission matrix fluorescence spectroscopy (3D-EEM). The
1,200 mg/L. The stock solution was periodically standar-
residual chlor(am)ine concentration, which was character-
dized by the DPD/FAS method. The monochloramine
ized by decay chlor(am)ine kinetics curves, was also
solution was freshly prepared by combining an ammonia
investigated.
chloride (Riedel-de Haën, Germany) solution and a free chlorine stock solution at a chlorine-to-nitrogen mass ratio of 4:1. The solution was rapidly mixed for over 30 min
MATERIALS AND METHODS
prior to usage to ensure that free chlorine was completely converted to monochloramine.
UV irradiation systems Analytical methods Collimated-beam UV apparatuses consisting of two lowpressure UV (LPUV) lamps (254 nm, UVP, Upland, CA,
The concentrations of residual chlor(am)ine in the aqueous
USA) were used to apply UV exposure (Liu et al. ).
solutions were measured by the 4,500-Cl F DPD/FAS
The UV lamps were turned on 30 min prior to the exper-
method (Standard Methods ).
iments to ensure constant radiation output. At the range in
Fluorescence 3D-EEM measurements were conducted
which the water samples were irradiated, the average UV
using a Hitachi F-4500 fluorescence spectrometer that
intensity of collimated irradiation from the LPUV apparatus
employed a xenon excitation source (150W), with excitation
was 0.25 mW/cm2, as determined by a radiometer (DRC-
and emission slits set to a 10 nm band-pass and a scan speed
100X, Spectronics, USA). The UV dosage (mJ/cm2) was cal-
of 1,200 nm/min. To obtain fluorescent 3D-EEMs, exci-
culated as the product of the measured intensity and
tation wavelengths were incrementally increased from 250
exposure time. A small glass dish (internal diameter
to 400 nm in 5 nm steps and emission wavelengths were
50 mm) containing the test solution (20 mL in volume and
incrementally increased from 270 to 550 nm in 5 nm steps.
8 mm in depth) was used to expose the water samples.
To limit second-order Raleigh scattering, a 290 nm cut off was used for all samples. All samples were diluted to a
Reagents and water
final DOC and pH of 1.5 mg/L and 7.5, respectively, with 0.01 M KCl.
Suwannee River NOM (RO isolation, Cat. 1R101N, from
According to Liu et al. (), concentrations of
the IHSS, MN, USA) were dissolved into Maxima
chloroform and HAA (only dichloroacetic acid (DCAA)
Q. Guo et al.
24
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NOM under UV irradiation/chlor(am)ination
Water Science & Technology: Water Supply
and trichloroacetic acid (TCAA) in this experiment) in
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Data analysis
aqueous samples were measured using a gas chromatograph
(Trace
GC
2000,
Thermo
Finnigan,
USA)
Chlor(am)ine decay kinetics
equipped with an electronic capture detector (ECD) and a DB-5 ms fused silica capillary column (30 m × 0.25 mm
The chlorine decay curves fit the parallel first-order model,
ID, 0.25 μm film thickness, J&W Scientific) according to
while the cubic polynomial model was most suitable for
USEPA methods 551 and 552 (USEPA ), respect-
the chloramine decay curves in reused water, both of
ively. The temperature program for THM detection was
which have no significant relationship with conditions of
W
35 C for 5 min, followed by an increase to 70 W
W
at
W
10 C/min, which was held for 8 min, then to 100 C at
water (Huang et al. ). The parallel first-order model was as follows:
W
10 C/min, which was held for 3 min. The temperature W
program for HAA detection was 35 C for 10 min, followed W
W
h i C ðtÞ ¼ C0 xe k1t þ ð1 xÞ e k2t
(1)
by an increase to 70 at 5 C/min, which was held for W
W
10 min, then to 100 C at 5 C/min, which was maintained for 5 min, after which the temperature was increased
Koechling () observed that initial chlorine decay is
to 135 C at 5 C/min, where it was held for 10 min. The
composed of a rapid initial decay and a second component
concentrations of cyanogen chloride (CNCl) in the
that decays more slowly. In this model, C(t) is the residual
W
W
aqueous samples were determined by membrane introduc-
chlorine concentration at time t, C0 is the initial chlorine
tion mass spectrometry (MIMS) method (Yang & Shang
concentration, x is the chlorine decay attributed to rapid
).
reaction, k1 is the first-order rate constant for rapid chlor-
Experimental procedures
ine decay, and k2 is the first-order rate constant for slow chlorine decay (Chiang et al. ). This model assumes that there are two kinds of constituents in water that
Sequential exposure to UV radiation and chlor(am)ine was
react with chlorine: fast reacting components, which
used in the study. The UV doses in the trials were 0, 20,
exert initial chlorine decay; and slow reacting components,
and 60 mJ/cm2, with exposure times of 0, 80, and 240 s,
which are responsible for long-term chlorine demand
respectively.
(Clark & Sivaganesan ).
A total of 100 mL (in 20 mL aliquots) of IHSS NOM
The cubic polynomial model is as follows:
solution diluted to a final pH of 7.5 was exposed to UV irradiation at the dosages listed above. Each water
C ðtÞ ¼ at3 þ bt2 þ ct þ C0
(2)
sample was mixed with chlorine or chloramine solutions at an initial concentration of 4.5 mg/L, and the reactions
where C(t) is the chloramine concentration at time t, C0 is
in the solutions were immediately quenched by the
the initial chlorine concentration, and a, b, and c are
addition of excess sodium thiosulfate (1 mL, 10 g/L).
constants.
Each mixed solution was then measured by the 4500-Cl F DPD/FAS method or 3D-EEM. To measure fluorescence during the sequential application of UV irradiation and
Fluorescence spectra analysis
chloramine, water samples exposed to UV radiation alone were also analyzed using the same procedures described
EEM peaks of NOM have been associated with humic-like,
above, without the addition of chlor(am)ine. All tests and
tyrosine-like, tryptophan-like, or phenol-like organic com-
measurements were duplicated and the figures presented
pounds (Chen et al. ). As previously reported
below show the average values of each duplication. The
(Leenheer & Croue ), peaks at different excitation/emis-
error bars of each value indicate the range of the two
sion wavelengths (Ex/Em) are related to different organic
measurements.
components (Table 1).
Q. Guo et al.
25
Table 1
|
|
NOM under UV irradiation/chlor(am)ination
Major fluorescent components in excitation/emission matrix
Range of excitation (nm)
Range of emission (nm)
Component type
220–250
280–300
Tyrosine-like
220–250
320–350
Tryptophan-like
280
350
Phenol-like
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RESULTS AND DISCUSSION Water samples exposed to UV irradiation alone 3D-EEM showed the excitation/emission wavelengths (Ex/ Em) and fluorescence intensity of analyte. In the Ex/Em spectrum of IHSS NOM water (Figure 1), lower contour
270–290
300–330
Soluble microbial byproduct-like
230–270
380–460
Fulvic acid-like
tour lines. Two main peaks with higher fluorescence
300–360
410–480
Humic acid-like
intensity appeared. The lower one surrounded by denser
Figure 1
|
lines showed a higher fluorescence intensity than other con-
Ex/Em spectrum of peak A and peak B in IHSS NOM water after exposure to UV irradiation alone (pH ¼ 7.5, DOC ¼ 3 mg/L). (a) 0 mJ/cm2, (b) 20 mJ/cm2, (c) 60 mJ/cm2.
26
Q. Guo et al.
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NOM under UV irradiation/chlor(am)ination
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contour lines was defined as peak A, and the upper one was defined as peak B (Figure 1). Evaluation of the Ex/Em spectrum of IHSS NOM water exposed to UV irradiation alone (Figure 1) revealed that peak A was located at the excitation/emission wavelengths (Ex/Em) of 275/450 nm for all UV dosages, while peak B was observed at the Ex/Em wavelengths of 325/450 nm for 0 mJ/cm2 and 320/440 nm for both 20 and 60 mJ/cm2. Peak A was related to FA-like organics and peak B corresponded to HA-like organics (Table 1). The shift in emission maximum is caused by a reduction in the degree of the π-electron system, such as a decrease in the number of aromatic rings, reduction in conjugated bonds in a chain structure, or conversion of a linear ring system to a non-linear system (Coble ; S´wietlik & Sikorska ). Additionally, Senesi () reported that the shift could also be caused by elimination of carbonyl, hydroxyl and amine
Figure 2
|
Fluorescence intensity of peak A and peak B in IHSS NOM water after exposure to UV irradiation alone (pH ¼ 7.5, DOC ¼ 3 mg/L).
functional groups. According to Ex/Em spectrum of IHSS NOM water exposed to UV irradiation alone (Figure 1),
adsorbed photons and were primarily degraded into low-
UV irradiation shifted the fluorescence maxima toward
molecular-weight organic acids under UV irradiation.
shorter wavelengths for peak B, but induced no changes in peak A. Thus, UV irradiation may lead to the degradation
IHSS NOM water exposed to UV/chlorine sequentially
of aromatic rings and removal of some functional groups in HA (peak B).
Peak A was located at Ex/Em wavelengths of 270–285/430–
Figure 2 showed the fluorescence intensity of IHSS
455 nm, while peak B was observed at Ex/Em wavelengths
NOM water after exposure to various types of UV
of 315–325/430–450 nm. Peak A was related to FA-like
irradiation. UV irradiation alone led to a reduction in the
organics and peak B corresponded to HA-like organics
fluorescence intensity of both peak A and peak B. High-
(Table 1). Since the shifts in Ex/Em wavelengths were
molecular-weight chromophores in HA may be decomposed
uncertain and were all within the range of the certain
to low-molecular-weight ones following UV irradiation
organic compounds, the characteristics of the fluorescence
(Uyguner & Bekbolet ). Preferential degradation of
spectra were neglected here.
higher-molecular-weight chromophores by UV irradiation
The fluorescence intensity of peaks A and B followed a
and increases in low-molecular-weight chromophores have
similar pattern (Figure 3). The fluorescence intensity showed
previously been demonstrated using size-exclusion chrom-
a substantial decrease during the rapid chlorine decay
atography (SEC) (Thomson et al. ; Liu et al. ).
stage. Electron-withdrawing substituents (–NO2, –COOH,
The effects of NOM exposed to UV irradiation alone for
–CHO, –N ¼ N–) and halogen substituents of benzene
normal disinfection have been reported in many studies.
rings usually have weaker fluorescence intensity (Li ).
After UV irradiation, humus macromolecules adsorb pho-
Moreover, depletion of aromatic rings can lead to decreased
tons, resulting in photochemical transformations (Corin
fluorescence intensity (Uyguner & Bekbolet ). Conse-
et al. ; Uyguner & Bekbolet ). A few low-molecular-
quently, it is reasonable to assume that free chlorine reacts
-weight organic carboxylic acids such as oxalic, succinic,
with activated aromatics via electrophilic substitution reac-
formic and acetic acids have been identified and quantified
tions, leading to subsequent ring opening followed by
as photodegradation products (Corin et al. ). Therefore,
further fragmentation, which can be attributed to decreased
it is assumed that HS in NOM water, especially HA,
fluorescence intensity during the rapid chlorine decay stage.
Q. Guo et al.
27
|
NOM under UV irradiation/chlor(am)ination
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sharp slope was identified to be the rapid decay stage, and the second section was the slow decay stage. The rapid chlorine decay rate k1 was reduced after UV irradiation, indicating that UV irradiation could slow down the chlorine decay in the rapid decay stage. The hydroxyl substituent groups (OH, O ) on the aromatic rings influence the rate of chlorine substitution by changing the charge density of the aromatic rings, leading to a faster reaction rate of hypochlorous acid with phenolate (O ) species than neutral phenol species (Duirk et al. ). The residual chlorine concentrations C(t) after UV irradiation were larger than those of samples not subjected to UV irradiation, suggesting that UV irradiation could lessen the chlorine decay. According to Thomson et al. (), both UV irradiation and chlorination cause degradation of aromatic rings. Some chlorine demand is exerted Figure 3
|
Relationship between fluorescence intensity of peak A and peak B under sequential exposure to UV irradiation/chlor(am)ination (pH ¼ 7.5, DOC ¼ 3 mg/L).
via oxidative reactions that do not covalently bind chlorine into reaction products (Christman et al. ). Therefore, chlorine demand for substitution and oxidation decreases
These assumptions are consistent with previous findings
as the concentration of HS decreases after UV irradiation.
(Thomson et al. ). The hydroxyl and phenols groups
That is to say, chlorine decay is reduced after UV irradiation.
on the aromatic rings are in the ortho/para-direction, resulting in chlorination of the aromatic ring by stepwise 2, 4, 6-
IHSS NOM water exposed to UV/chloramine
substitution followed by ring cleavage leading to chloroform
sequentially
formation (Duirk et al. ). The correlation coefficients (R 2) of the chlorine decay
Ex/Em characteristics were similar to that mentioned
curves of IHSS NOM water indicated a good fit with the
above. Peak A was located at 275–285/430–455 nm while
parallel first-order model (Figure 4). The rapid drop with
peak B was observed at 315–325/430–450 nm. Fluorescence intensity generally tends to be enhanced with time (Figure 5). Additionally, electron-donating groups (–OH, –NH2, –OR, –NR2) substituted for aromatic rings can generally increase fluorescence intensity (Li ), and the decay of chloramine released ammonia for subsequent nitrification (Sung et al. ). Thus, chloramine exposure may generate more –NH2 substituent groups, resulting in enhanced fluorescence intensity. The correlation coefficients (R 2) of the chloramine decay curves of IHSS NOM water were greater than 0.96, which fit the cubic polynomial model well (Figure 6). There are no obvious rapid and slow decay stages for chloramine. When compared with a, b and c of 0 mJ/cm2 UV dosage, chloramine decay with UV dosage of 60 mJ/cm2 was accelerated, and the
Figure 4
|
Chlorine decay curves in UV-irradiated IHSS NOM waters (pH ¼ 7.5, DOC ¼ 3 mg/L).
extent of chloramine decay was enhanced after UV irradiation. As discussed above, UV irradiation decomposes
Q. Guo et al.
28
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NOM under UV irradiation/chlor(am)ination
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disinfection reduces the generation of THM and HAA significantly (82.8 and 68.7%, respectively) from organic matter with a Ku molecular weight of less than 10 (Gao et al. ). The effect of chloramination is weakened somewhat as the organic molecular weight increases (Gao et al. ). Therefore, it is assumed that chloramine exposure primarily leads to substitution of reactive sites other than ring-opening oxidation. DBP formation The formation of DBPs, including chloroform, DCAA, TCAA, and CNCl, after sequential exposure of IHSS NOM water samples to solely chlor(am)ine and UV/chlor(am)ine were tested (Figure 7; Liu et al. ). On the whole, DBP formation was increased to a certain degree comparing the Figure 5
|
Relationship between fluorescence intensity of peak A and peak B under
results of UV/chlor(am)ine (shaded bars) with solely chlor
sequential exposure to UV irradiation/chlor(am)ination (pH ¼ 7.5, DOC ¼
(am)ine (black bars). UV irradiation does not appear to gen-
3 mg/L).
erate DBPs, and only small quantities of aldehydes have been detected in UV-irradiated wastewater samples at
high-molecular-weight HS, and more ammonia was released
doses up to 200 mJ/cm2 (Linden et al. ). Therefore,
for subsequent reaction (Sung et al. ). Thus, more chlora-
the increments of DBPs after UV/chlor(am)ine may due to
mine is consumed for substitution, which accounts for the
the oxidation of UV irradiation which led to degradation
extension of chloramine decay after UV irradiation.
of NOM molecules and then facilitated subsequent reaction
HOCl is the main effective constituent of chloramine dis-
of chlor(am)ine with NOM molecules.
infection. However, as a disinfectant, chloramine releases
Moreover, IHSS NOM waters exposed to UV/chloramine
lower quantities of HOCl than chlorine, and chloramine
and chloramine showed less DBP formation than those exposed to UV/chlorine and chlorine, and the formation of
Figure 7 Figure 6
|
|
Chloroform, DCAA, TCAA and CNCl formation in IHSS NOM water exposed to
Chloramine decay curves in UV-irradiated IHSS NOM water (pH ¼ 7.5, DOC ¼
solely chlor(am)ine and UV/chlor(am)ine (pH ¼ 7, DOC ¼ 5 mg/L, UV dosage ¼
3 mg/L).
60 mJ/cm2).
29
Q. Guo et al.
|
NOM under UV irradiation/chlor(am)ination
TCAA and chloroform was drastically diminished in the UV/ chloramine and chloramine trials. These findings indicate that chlorine substitution and degradation of NOM molecules was much greater than that of chloramine, and generated more completely oxidized products such as chloroform.
CONCLUSIONS UV irradiation led to a decrease in the fluorescence intensity of IHSS NOM water samples. The subsequent chlorination and chloramination resulted in weakened and strengthened fluorescence intensity, respectively. Investigation of the residual chlor(am)ine concentration revealed that UV irradiation decreased chlorine decay and increased chloramine decay. UV irradiation also resulted in increased DBP formation. Degradation of NOM molecules after UV irradiation facilitated the reaction of chlo(ra)mine with NOM molecules, resulting in the formation of DBPs. UV irradiation facilitates degradation of HS, leading to less chlorine demand for degradation. Conversely, UV irradiation exposes more active sites to chloramine substitution, enriching chloramine demand for substitution. Both UV irradiation and chlorination could degrade high-molecular-weight aromatic HS, but chloramination mainly played a substitution role. In summary, UV treatments play the same role in UV/chlorine and UV/chloramine processes, both of which degraded high-molecular-weight NOM. Moreover, it is also proposed that chlorine degradation and substitution dominates the process of UV/chlorine disinfection, while chloramine substitution is the major reaction occurring during the UV/chloramine disinfection process.
ACKNOWLEDGEMENT This study was supported by the National Nature Science Fund of China (Project 50978259).
REFERENCES Ates, N., Kitis, M. & Yetis, U. Formation of chlorination byproducts in waters with low SUVA–correlations with SUVA
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and differential UV spectroscopy. Water Research 41 (18), 4139–4148. Chen, W., Westerhoff, P., Leenheer, J. A. & Booksh, K. Fluorescence excitation emission matrix regional integration to quantify spectra for dissolved organic matter. Environmental Science and Technology 37 (24), 5701–5710. Chiang, P. C., Chang, E. E., Chuang, C. C., Liang, C. H. & Huang, C. P. Evaluating and elucidating the formation of nitrogen-contained disinfection by-products during pre-ozonation and chlorination. Chemosphere 80 (3), 327–333. Christman, R. F., Norwood, D. L., Millington, D. S., Johnson, J. D. & Stevens, A. A. Identity and yields of major halogenated products of aquatic fulvic acid chlorination. Environmental Science and Technology 17, 625–628. Clark, R. M. & Sivaganesan, M. Predicting chlorine residuals in drinking water Second order model. Journal of Water Resources Planning and Management 128 (2), 152–161. Coble, P. G. Characterization of marine and terrestrial DOM in seawater using excitation–emission matrix spectroscopy. Marine Chemistry 51, 325–346. Corin, N., Backlund, P. & Kulovaara, M. Degradation products formed during UV-irradiation of humic waters. Chemosphere 33 (2), 245–255. Deborde, M. & von Gunten, U. Reactions of chlorine with inorganic and organic compounds during water treatmentkinetics and mechanisms: a critical review. Water Research 42 (1–2), 13–51. Duirk, S. E., Bridenstine, D. R. & Leslie, D. C. Reaction of benzophenone UV filters in the presence of aqueous chlorine: kinetics and chloroform formation. Water Research 47 (2), 579–587. http://dx.doi.org/10.1016/j.watres.2012.10.021. Gao, N., Wang, X., Zhou, C. & Chu, W. Influence of chloramine disinfection on DBPs from different organics. Journal of Tongji University (Natural Science) 37 (12), 1633–1637. Hassen, A., Mahrouk, M., Ouzari, H., Cherif, M., Boudabous, A. & Damelincourt, J. J. UV disinfection of treated wastewater in a large-scale pilot plant and inactivation of selected bacteria in a laboratory UV device. Bioresource Technology 74 (2), 141–150. Huang, G. X., Qian, Y. J., Ge, J. J., Ne, Y. H., Liu, W. & Liang, Y. M. Influencing factors of residual chlorine decay curve and its mathematical model. Acta Scientiarum Naturalium Universitatis Sun Yat Seni 48 (4), 113–117. Koechling, M. T. Assessment and Modeling of Chlorine Reactions with Natural Organic Matter: Impact of Source Water Quality and Reaction Conditions. PhD Thesis, Univ. of Cincinnati, Cincinnati. Korich, D. G., Mead, J. R., Madore, M. S., Sinclair, N. A. & Sterling, C. R. Effects of ozone, chlorine dioxide, chlorine, and monochloramine on Cryptosporidium parvum oocyst viability. Applied Environmental Microbiology 56 (5), 1423–1428.
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Leenheer, J. A. & Croue, J. P. Characterizing aquatic dissolved organic matter. Environmental Science and Technology 37 (1), 18A–26A. Li, Jianping Advanced Analytical Chemistry. Metallurgical Industry Press, Beijing, China, 1, p. 17. Linden, K. G., Soriano, G. S., Dodson, G. S. & Darby, J. L. Investigation of disinfection by-product formation following low and medium pressure UV irradiation of wastewater. In: Proceedings of the WEF Disinfection Specialty Conference, Baltimore, MD, pp. 137–147. Liu, W., Andrews, S. A., Bolton, J. R., Linden, K. G., Sharpless, C. M. & Stefan, M. Comparison of DBP formation from different UV technologies at bench scale. Water Science and Technology: Water Supply 2 (5–6), 515–521. Liu, W., Cheung, L. M., Yang, X. & Shang, C. THM, HAA and CNCl formation from UV irradiation and chloramination of selected organic waters at practical conditions. Water Research 40 (10), 2033–2043. Liu, W., Zhang, Z. L., Yang, X. & Liang, Y. M. Effects of UV irradiation and UV/chlorine co-exposure on natural organic matter in water. Science of the Total Environment 414, 576–584. Senesi, N. Molecular and quantitative aspects of the chemistry of fulvic acid and its interactions with metal ions and organic chemicals. Part 2. The fluorescence spectroscopy approach. Analytica Chimica Acta 232, 77–106. Shang, C., Cheung, L. M. & Liu, W. MS2 coliphage inactivation with UV irradiation and free chlorine/ monochloramine. Environmental Engineering Science 24 (9), 1321–1332.
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Standard Methods for the Examination of Water and Wastewater 20th edn, American Public Health Association/ American Water Works Association/Water Environment Federation, Washington, DC, USA. Sung, W., Huang, X. & Wei, I. W. Treatment and distribution system effects on chloramine decay, pH, nitrification, and disinfection by-products: case study. Journal of Water Resources Planning and Management 131, 201–207. S´wietlik, J. & Sikorska, E. Application of fluorescence spectroscopy in the studies of natural organic matter fractions reactivity with chlorine dioxide and ozone. Water Research 38 (17), 3791–3799. Thomson, J., Parkinson, A. & Roddick, F. Depolymerization of chromophoric natural organic matter. Environmental Science and Technology 38 (12), 3360–3369. US Environmental Protection Agency Methods for the determination of organic compounds in drinking water: Supplement I, EPA-600/4–90/020, Cincinnati. Uyguner, C. S. & Bekbolet, M. Evaluation of humic acid photocatalytic degradation by UV-vis and fluorescence spectroscopy. Catalysis Today 101, 267–274. Wang, X., Hu, X., Hu, C. & Wei, D. Sequential use of ultraviolet light and chlorine for reclaimed water disinfection. Journal of Environmental Sciences 23 (10), 1605–1610. White, D. M., Garland, S., Narr, J. & Woolard, C. R. Natural organic matter and DBP formation potential in Alaskan water supplies. Water Research 37 (4), 939–947. Yang, X. & Shang, C. Quantification of aqueous cyanogen chloride and cyanogen bromide in environmental samples by MIMS. Water Research 39 (9), 1709–1718.
First received 31 January 2013; accepted in revised form 21 May 2013. Available online 12 September 2013
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Rapid inactivation of Salmonella by a quaternized biopolymeric flocculant Gurpreet Kaur Khaira, Abhijit Ganguli and Moushumi Ghosh
ABSTRACT We report the characteristics and biocidal properties of a biopolymeric flocculant produced by Klebsiella terrigena capable of flocculating Salmonella efficiently from water. In order to impart an antimicrobial function, the native biopolymer was quaternized and the trimethyl biopolymeric derivative (TMB) was analysed physically, chemically and for flocculating properties. The quaternized biopolymer was evaluated for antimicrobial effects against four strains of Salmonella namely,
Gurpreet Kaur Khaira Abhijit Ganguli Moushumi Ghosh (corresponding author) Department of Biotechnology, Thapar University, Patiala-147004, Punjab, India E-mail: mghosh@thapar.edu
S. typhimurium ATCC 23564, MTCC 1251, MTCC 98 and S. typhi MTCC 733. TMB did not differ significantly (p < 0.05) in either chemical and physical properties or flocculating ability when compared to its native counterpart. TMB completely inactivated Salmonella (60 μg/mL, at ambient temperature) within 60 min of exposure. Cell injury and death were evidenced by rapid increase in electrical conductivity in the media and release of intracellular alkaline phosphatase and glucose-6phosphate dehydrogenases indicating permeation of cells. Electron micrographs revealed grossly altered morphology suggesting damage to the cell membranes as a possible reason for inactivation. The results of this study suggest a potential application of the developed biocidal bioflocculant for water treatment. Key words
| biocidal, bioflocculant, cell membrane, Salmonella, quaternization
INTRODUCTION Waterborne diseases pose a great burden on global public
In recent years, cationic polymers with modified quatern-
health (WHO ). Salmonella spp. (Salmonella paratyphi
ary ammonium groups with antimicrobial properties have
A, B and C) are among the prevalent water-borne patho-
been developed. Some of these polymers, for example chito-
genic bacteria in developing nations (Sharan et al. ).
san, have shown promising results as antimicrobials
They are of considerable significance as they result in
(Siedenbiedel & Tiller ). The biocidal activity of these poly-
approximately 5.5 million cases (both waterborne and food-
mers is attributed to their ability to interact with the bacterial
borne diseases) of enteric fever each year (Sharan et al. ).
cell wall, which results in disruption of the underlying cyto-
Transmission through water becomes evident considering
plasmic membrane (Choi et al. ; Mcbain et al. ). No
that individuals infected with Salmonella shed the organ-
studies to date have attempted (to the best of our knowledge)
isms in their faeces, which can enter domestic sewage
to chemically modify microbial biopolymeric flocculants, to
which, if insufficiently treated or inadequately disinfected,
endow biocidal properties against waterborne pathogens.
can consequently contaminate drinking water sources (Maskey
et
al.
).
Environmental
considerations
An extracellular biopolymeric flocculant from an environmental isolate of Klebsiella terrigena has been
demand the development of effective, economically viable
thoroughly investigated in our earlier studies (Ghosh et al.
and ecofriendly replacements of conventional synthetic floc-
a, b); the bioflocculant possesses unique attributes in
culants and disinfectants for water treatment, based upon
terms of robustness and high flocculating ability for water-
renewable organic materials which degrade naturally.
borne
doi: 10.2166/ws.2013.169
pathogens.
We
envisaged
that
imparting
an
32
G. K. Khaira et al.
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Quaternized biopolymer flocculant for Salmonella inactivation
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antimicrobial function to this flocculant may enable inacti-
Synthesis and characterization of N, N, N trimethyl
vation and simultaneous removal of these pathogens
biopolymeric derivative (TMB)
during water treatment. Therefore, in this study we chemically
modified
the
bioflocculant
by
quaternization,
Purified biopolymer (150 mg) was dissolved in dimethylsul-
compared its intrinsic characteristics with its native struc-
phate (2.4 mL) and deionized water (0.6 mL). The solution
ture and investigated its biocidal properties with a possible
was then filtered to eliminate the impurities. Sodium hydrox-
mechanism of inactivation against Salmonella.
ide (0.18 mg) and sodium chloride (0.132 mg) were added to the resulting suspension, followed by stirring the solution at ambient temperature for 6 hr. The product was precipitated
MATERIALS AND METHODS
using acetone, filtered and vacuum dried. White precipitates obtained were redissolved in deionized water (20 mL), sub-
All the chemicals were purchased from the Sigma chemical
jected to dialysis using a dialysis tubing (Cellulose, MWCO
company (Sigma, MO, USA).
12000,) for one day; and lyophilized to obtain powder (4.5 mg) (Belalia et al. ). NMR analysis was also carried out: 1H NMR spectra of
Bacterial strains and culture conditions
biopolymer and N, N, N-trimethyl derivative (TMB) were An industrial wastewater isolate, previously isolated and
recorded using a Bruker Avance II (400 MHz) spectrometer.
identified in our laboratory as Klebsiella terrigena (Accession
For this analysis, samples were dissolved in D2O (sup-
number MTCC 7805), was used in this study. The strain was
plementary
preserved in glycerol stock solutions at 80 C. For pro-
iwaponline.com/ws/014/169.pdf).
W
data;
available
online
at
http://www.
duction of biopolymer, the strain was grown in 1 L of medium (polypeptone 5 g/L, diammonium sulphate 2 g/L,
Physico-chemical analysis of TMB
yeast extract 1 g/L, CaCl2 0.7 g/L, NaCl 0.1 g/L, MgSO4 2 g/L, K2HPO4 1 g/L, glucose 1 g/L, agar 3 g/L) on a rotary W
The total sugars, neutral sugar, uronic acids, amino sugar con-
shaker (120 rpm/min) at 30 C for 48 hr. Cultures of S. typhi-
tent and pyruvic acid of the biopolymer and TMB were
murium (ATCC 23564, MTCC 1251, MTCC 98) and S. typhi
performed as described by Yokoi et al. (). Elemental analy-
MTCC 733 were grown in brain heart infusion (BHI) broth
sis was carried out with a 2400 II elemental analyser (Perkin
W
by incubating at 37 C, for 6–8 hr with agitation (120 rpm).
Elmer Company, USA). Fractionation and purification were achieved using gel chromatography on a Sepharose 4B
Biopolymer production
column followed by elution with a 0.4 M NaCl buffer. The ultrastructure of purified TMB was observed by scanning elec-
Cells were removed from the culture medium by centrifu-
tron microscopy (SEM) (JSM 541-V, JEOL, Japan).
gation (12,000 g) and the biopolymer was separated by the addition of two volumes of ethanol (99.5%) to 500 mL of
Measurement of flocculating activity
concentrated supernatant, and allowed to precipitate at 40 C for 24 hr. The precipitated polymer was collected by
TMB and biopolymer were evaluated for their ability to floc-
filtration (Whatman GF Filter) and dialysed extensively,
culate suspended solids of varied size. A standard solution of
W
against deionized water. Crude biopolymer was purified by
suspended solids of 100, 1,000 and 2,000 NTU was made by
addition of a 10% solution of cetylpyridinium chloride.
suspending active carbon, silica, magnesium hydroxide, cel-
The precipitated polymer complex was collected by centrifu-
lulose and yeast in 100 mL water. A bacterial suspension
W
gation at 10,000 rpm for 20 min at 4 C and redissolved in
(gram-negative bacteria including Salmonella) was also
10% NaCl solution. Three volumes of ethanol were added
used for this study. A suspension was prepared by diluting
to recover the purified biopolymer, which was further dia-
the suspension from stock (0.4–0.7%) to desired turbidity
lysed and lyophilized (Ghosh et al. a, b).
with a turbidimeter (Cyber Scan TBDIR1000 Meter, The
33
G. K. Khaira et al.
|
Quaternized biopolymer flocculant for Salmonella inactivation
Netherlands). An assay was performed by adding 10 mL
|
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2014
Electrical conductivity measurement
CaCl2 (5 mM), 0.5 mL biopolymer (2 mg/L) and 9.5 mL of distilled water to 80 mL of these solutions. The pH was
The mid-log phase cells of Salmonella were harvested by
adjusted to 7 ± 0.2 and the solutions were allowed to stand
centrifugation at 11,000 × g for 10 min. The pellets were
at room temperature for 5 min. Twenty millilitre aliquots
washed and resuspended in 0.1 M phosphate buffer (pH 7.4).
were withdrawn from the upper phase and the turbidity
The final cell suspensions were adjusted to 107 CFU/mL and
was measured. Flocculating activity was calculated by
mixed with TMB and biopolymer (40 and 60 μg/mL, 100
recording optical density with a spectrophotometer at
and 150 μg/mL, pH 7.0, respectively), and then the mixtures
550 nm. Flocculating activity of purified biopolymer and
were incubated at room temperature. Measurements of their
TMB in water was measured against distilled water as a con-
electrical conductivity were taken every 10 min for 2 hr.
trol according to the method of Kurane et al. (). Activity (%) was defined and calculated as:
Permeation of the cytoplasmic membrane
ðB AÞ=B × 100
The biopolymer and TMB (100 μg/mL) were added to a
where A is optical density of sample at 550 nm and B is opti-
0.85% (w/w) NaCl solution containing Salmonella strains
cal density of reference at 550 nm.
each at 107 CFU/mL. Following incubation at 37 C for W
The activity was expressed as the mean value from tripli-
8 hr, a 0.2 mL aliquot of the cell suspension was withdrawn and added to the reaction mixture. Alkaline
cate determinations.
phosphatase (ALP) and glucose-6-phosphate dehydrogenDetermination of antibacterial activity
ases
(G6PDH)
activity
was
determined
using
the
method of Malamy & Horecker () (supplementary The antibacterial spectrum of the biopolymeric derivative
data; available online at http://www.iwaponline.com/ws/
was determined against S. typhimurium ATCC 23564,
014/169.pdf).
MTCC 1251, 98 and S. typhi MTCC 733. The cultures W
were revived in BHI broth by incubating at 37 C for 6 hr.
Electron microscopy
For a preliminary screening, an agar disc diffusion assay (supplementary data; available online at http://www.
Salmonella cells treated with TMB as described above
iwaponline.com/ws/014/169.pdf) was performed and diam-
were used to visualize structural damage, following 20,
eters of inhibition zones were observed (data not shown).
40 and 60 min of incubation (supplementary data;
The experiments were performed in triplicates.
available online at http://www.iwaponline.com/ws/014/
To investigate the killing kinetics, the antibacterial
169.pdf) by SEM.
activity of TMB was assayed by the microdilution method, using a sterile 96-well microtiter plate reader (Bioscreen C, Thermo labsystems, Helsinki, Finland). Briefly, serial two-
RESULTS AND DISCUSSION
fold dilutions of TMB solutions were prepared in the appropriate culture medium in sterile 96-well round
Synthesis and characterization of N, N, N trimethyl
bottom polystyrene microtiter plates (Raafat et al. ).
biopolymeric derivative
Final TMB concentrations used were 1–100 μg/mL. The four strains of Salmonella were grown in the respective W
Figure 1 depicts the
1
H-NMR spectra of the native
broth at 37 C to an optical density of 1 at 600 nm and
biopolymer
subsequently diluted in the same medium to about
respectively. The spectra revealed an intense signal at
107 CFU/mL. The solutions of biopolymer and TMB were
3.66 ppm corresponding to the trimethylammonium
added, and the minimal inhibitory concentration (MIC)
group. Sieval et al. () indicated that the peak at
was determined (Andrews ) for 3 hr.
3.6 ppm is assigned to the trimethyl amino group, the
and
quaternized
biopolymer
(TMB),
G. K. Khaira et al.
34
|
Figure 1
1
|
Quaternized biopolymer flocculant for Salmonella inactivation
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2014
H NMR spectra of biopolymer (a) and TMB (b) dissolved in D2O.
peak at 3.1 ppm is assigned to dimethyl amino groups
The SEM observations indicated a similar porous
and the peaks between 4.7 and 5.7 ppm are assigned to
surface morphology of TMB to that of the native struc-
1
ture. The small pores were non-uniform in size and
H protons. Methylation of the amino groups in the C-2 position of
distribution, and appeared as interconnected channels
the biopolymer to form quaternary amino groups with fixed
(supplementary data; available online at http://www.
positive charges on the repeating units of the TMB polymer
iwaponline.com/ws/014/169.pdf).
chain may be inferred from the obtained results. Physico-chemical characteristics of TMB
Flocculating efficiency of the quaternized biopolymer
Both physical and chemical characteristics of TMB were
TMB and the biopolymer, at the optimum doses of 0.2 and
compared with its native counterpart (Table 1).
2 ppm, respectively, showed similar flocculating activity at low, medium and high levels of turbidity.
Table 1
|
The biopolymer and TMB aggregated a wide range of
Compositional analysis of biopolymer and TMB
S.no.
Components
Biopolymer composition (%)
TMB composition (%)
1.
Total sugar
69.8
66.8
2.
Amino sugar
6.87
5.8
3.
Protein
6.73
2.45
4.
Pyruvic acid
0.6
7.4
5.
Uronic acid
1.12
2.83
6.
Carbon
14.73
12.73
7.
Hydrogen
1.23
1.01
8.
Nitrogen
0.64
0.44
colloidal particles, over concentrations of 0.1–10 ppm. As illustrated in Figure 2, the most effective flocculation was achieved in suspensions comprising very small and small sized particles even at low concentrations of the polymer. The flocculation efficiency in the suspension of medium sized particles ranged from 30 to 40% (that too at relatively higher concentrations of polymer). The suspensions of large sized particles showed 50–65% flocculant activity at the same concentration range that flocculated in the range of 70–90% in the case of small and very small sized particle suspensions.
35
G. K. Khaira et al.
|
Figure 2
|
Quaternized biopolymer flocculant for Salmonella inactivation
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Efficiency of removal of varied size colloidal particles in solution (at 100 NTU) dosed with TMB (0.2 ppm). The corresponding sizes of the particles are the following: ∼0.5–0.8 μm
(bacterial cell suspension), ∼4–7 μm (kaolin, yeast cell suspension, cellulose), ∼15–20 μm (silica), ∼100 μm (active carbon).
This might be due to non uniform distribution of pore size on
inhibition by TMB, the native biopolymer failed to inhibit
the biopolymer surface; also the number of sites available for
Salmonella (data not shown). Moreover, TMB significantly
binding small and very small sized particles might be more
inhibited the growth of Salmonella in 60–90 min at concen-
than that for binding medium and large sized particles.
trations ranging from 50 to 100 μg/mL. The analysis of bacterial growth in the presence of var-
Biocidal activity of quaternized biopolymeric flocculant
ious concentrations of quaternized biopolymer over time indicated no significant change (P > 0.05) in growth behav-
against Salmonella
iour at a concentration of 10 μg/mL, with respect to the The antibacterial activity of the biopolymer and TMB was
control (cells without TMB). For concentrations of 10 and
assessed thereafter against Salmonella by observing the
35 μg/mL, the growth profile was different from the control
zones of inhibition and determining MICs (Table 2). Results
(P < 0.05) whereas at concentrations of 50 μg/mL, the qua-
obtained by the agar disc diffusion assay indicated a strong
ternized biopolymer inhibited cell growth. The killing efficacy of 60 μg/mL of TMB when challenged upon
Table 2
|
Minimum inhibitory concentration (MIC) of quaternized biopolymer (TMB)
S.no.
Cultures
MIC (μg/mL) of TMB
1.
S. typhimurium ATCC 23564
63
2.
S. typhimurium MTCC1251
62
3.
S. typhimurium MTCC 98
62
4.
S. typhi MTCC 733
60
approximately 107 cells/mL of pathogen is illustrated in Figure 3, 3.5 log reduction was achieved by 60 min at ambient temperature. The higher antibacterial activity of TMB could be due to the interaction between the positively charged amino groups of the biopolymer and negatively charged cell surface of gram negative bacteria.
36
G. K. Khaira et al.
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Quaternized biopolymer flocculant for Salmonella inactivation
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released (data not shown). In the supernatant of Salmonella strain treated with native biopolymer, a complete absence of ALP and G6PDH was observed as expected, in contrast to the TMB. In the supernatant of TMB treated Salmonella, the release of enzymes reached a plateau in 3 hr for ALP and in 6 hr for G6PDH. These results agreed with those of Malamy & Horecker () who reported that ALP was an extracellular enzyme, while G6PDH was found in the cell membrane, suggesting the cell membrane to be a likely target of TMB.
Figure 3
|
Time-dependent killing efficacy of TMB (60 μg/mL) and biopolymer (146 μg/mL)
Scanning electron microscopy
against Salmonella.
To observe the ultra structural change caused by TMB treatElectrical conductivity of cell suspensions of TMB
ment, SEM data were collected for treated bacterial cells at
treated bacteria
various time intervals. The intracellular changes were observed in TMB treated Salmonella when compared to
The electrical conductivity of the cell suspensions for Sal-
the non-treated cells. Remarkable modifications of cell
monella treated with biopolymer (100 and 150 μg/mL) and
membrane and disruption of cell membranes occurred
TMB (40 and 60 μg/mL) showed a time-dependent increase
after only a short period of exposure (Figure 4).
(Figure S-2, supplementary data; available online at http://
Overall, the observations of the present study indicated
www.iwaponline.com/ws/014/169.pdf). Differences in the
the efficacy of TMB in inactivating Salmonella by directly
changes of the electrical conductivity between the treat-
damaging cell membranes; whether flocculation of Salmo-
ments also suggested that the effect of TMB on the
nella is followed by inactivation remains to be examined.
membrane permeability of Salmonella was greater than
Based on the results of this study, a potential application
the biopolymer.
of the TMB for inactivating Salmonella in water may be envisaged, given the efficacy, flocculating ability and safety
Effect of TMB on leakage of enzymes
demonstrated by oral toxicity studies in mice (unpublished observations). Thus the newly developed bioflocculant may
The effects of biopolymer and TMB on the leakage of ALP
have important applications in removing and inactivating
and G6PDH have been expressed as units of enzyme
Salmonella in water.
Figure 4
|
SEM of S. typhimurium treated with TMB. S. typhimurium, in mid-logarithmic growth at 107 CFU/mL, was incubated with TMB (60 μg/mL): (a) 0 min; (b) 30 min; (c) 60 min; (d) view of a single cell.
37
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Quaternized biopolymer flocculant for Salmonella inactivation
CONCLUSIONS This study effectively demonstrated the biocidal effects of a polymeric flocculant produced by K. terrigena. Quaternization was effective in imparting biocidal properties to the native biopolymer, the quaternized biopolymeric flocculant led to rapid inactivation of Salmonella strains. Cell death occurred presumably by a rapid release of cytoplasmic enzymes and changes in electrical conductivity. Gross morphological changes in cell membranes of bacteria were observed from electron micrographs of exposed cells. The newly developed biocidal biopolymeric flocculant may have important applications in removing and inactivating Salmonella in water.
ACKNOWLEDGEMENTS The authors would like to gratefully acknowledge the Department of Science and Technology (Water Technology Initiative, Govt of India), New Delhi, for funding the present study.
REFERENCES Andrews, J. M. Determination of minimum inhibitory concentrations. Journal of Antimicrobial Chemotherapy 48 (1), 5–16. Belalia, R., Grelier, S., Benaissa, M. & Coma, V. New bioactive biomaterials based on quaternized chitosan. Journal of Agricultural and Food Chemistry 56 (5), 1582–1588. Choi, B. K., Kim, K. Y. & Yoo, Y. Z. In vitro antimicrobial activity of a chitooligosaccharide mixture against Actinobacillus actinomycetemcomitans and Streptococcus mutans. International Journal of Antimicrobial Agents 18 (6), 553–557.
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Ghosh, M., Pathak, S. & Ganguli, A. a Effective removal of cryptosporidium by a novel bioflocculant. Water Environment Research 81 (2), 160–164. Ghosh, M., Pathak, S. & Ganguli, A. b Application of a novel biopolymer for removal of Salmonella from poultry wastewater. Environmental Technology 30 (4), 337–344. Kurane, R., Takeda, K. & Suzuki, T. Screening and characteristics of microbial flocculants. Agricultural and Biological Chemistry 50 (9), 2301–2307. Malamy, M. H. & Horecker, B. L. Release of alkaline phosphatase from cells of Escherichia coli upon lysozyme spheroplast formation. Biochemistry 3 (12), 1889–1893. Maskey, A. P., Day, J. N., Phung, Q. T., Thwaites, G. E., Campbell, J. I., Zimmerman, M., Farrar, J. J. & Basnyat, B. Salmonella enterica serovar Paratyphi A and S. enterica serovar Typhi cause indistinguishable clinical syndromes in Kathmandu, Nepal. Clinical Infectious Diseases 42 (9), 1247–1253. Mcbain, A. J., Ledder, R. G., Moore, L. E., Catrenich, C. E. & Gilbert, P. Effects of quaternary-ammonium-based formulations on bacterial community dynamics and antimicrobial susceptibility. Applied and Environmental Microbiology 70 (6), 3449–3456. Raafat, D., Bargen, K., Haas, A. & Sahl, H. Insights into the mode of action of chitosan as an antibacterial compound. Applied and Environmental Microbiology 74 (12), 3764–3773. Sharan, R., Chhibber, S. & Reed, R. H. Inactivation and sublethal injury of Salmonella typhi, Salmonella typhimurium and Vibrio cholera in copper water storage vessels. BMC Infectious Diseases 11, 204. Siedenbiedel, F. & Tiller, J. C. Antimicrobial polymers in solution and on surfaces: overview and functional principles. Polymers 4 (1), 46–71. Sieval, A. B., Thanou, M., Kotze, A. F., Vehoef, J. C., Brusse, J. & Junginger, H. E. Preparation and NMR characterization of highly substituted N-trimethyl chitosan chloride. Carbohydrate Polymers 36 (2), 157–165. WHO Guidelines for drinking-water quality. http://www. who.int/water_sanitation_health/dwq/fulltext.pdf (accessed 9 April 2013). Yokoi, H., Yoshida, T., Mori, S., Hirose, J., Hayashi, S. & Takasaki, Y. Biopolymer flocculant produced by an Enterobacter sp. Biotechnology Letters 19 (6), 569–573.
First received 2 March 2013; accepted in revised form 28 May 2013. Available online 12 September 2013
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Use of cisterns during antiquity in the Mediterranean region for water resources sustainability Larry W. Mays
ABSTRACT From the early civilizations people in arid and semi-arid regions have relied on collecting or ‘harvesting’ surface water from rainfall and storing the water in human-made reservoirs or ‘cisterns.’ The storage of rainwater runoff has been constructed in the entire region around the Mediterranean and the Near East since the 3rd millennium
BC.
Not only were cisterns used to store rainfall runoff
they were also used to store aqueduct water to allow for seasonal variations in the supply. Cisterns
Larry W. Mays Civil and Environmental Engineering Group School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, Arizona 85287-5306, USA E-mail: mays@asu.edu
during ancient times ranged from the construction of irregular shaped holes (tanks) dug out of sand and loose rock, and then lined with plaster (stucco) water proofing, to the construction of rather sophisticated structures such as those built by the Romans and Byzantines. The primary objective herein is to provide a review of the use of cisterns by ancient civilizations in the Mediterranean region, and to relate the use of these cisterns to water resources sustainability of the past and the present, outlining the lessons learned. Key words
| Byzantines, cisterns, Greeks, Minoans, Romans, water resources sustainability
INTRODUCTION ‘The centrality of freshwater in our lives cannot be overesti-
have been directed at discussing cisterns during antiquity
mated. Water has been a major factor in the rise and fall of
and their importance for human survival. A brief review of
civilizations’ (UN Secretary General Kofi Annan; United
the use of cisterns by ancient civilizations is presented
Nations ). Mays () defined water resources sustain-
herein. This is not a complete and thorough review by any
ability as ‘the ability to use water in sufficient quantities and
account but does include cisterns used as part of water har-
quality from the local to the global scale to meet the needs of
vesting systems and as storage of aqueduct water for
humans and ecosystems for the present and the future to sus-
seasonal variation of available water.
tain life, and to protect humans from the damages brought
Cisterns have ranged from clay pots to very large under-
about by natural and human-caused disasters that affect sus-
ground structures. The Mycenaeans (in Mycenae in
taining life.’
continental Greece by the end of the 13th century
BC)
built
Cisterns were used by ancient civilizations for water
an underground cistern. This cistern was supplied by water
resources sustainability, and have continued to be used
from the Persia spring through a 200 m long buried conduit
since; however, their importance for modern day water
dug into the rock. A terracotta pipe is still visible at the roof
supply purposes has somewhat vanished in developed
of the cistern (Taylor ).
parts of the world, but has continued in many developing
Even the grand aqueducts constructed by the Romans
parts of the world. The importance of cisterns, however, is
were not built to provide drinking water or to promote
becoming more and more recognized throughout the
hygiene. Roman cities instead depended mainly upon cis-
world as a traditional knowledge (Laureano ), another
terns or wells in individual houses for drinking water
factor in water resources sustainability. Few publications
(Hodge ; Mays ; Angelakis et al. ).
doi: 10.2166/ws.2013.171
39
L. W. Mays
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Cisterns during antiquity in the Mediterranean region
FIRST EFFORTS TO CONTROL WATER WITH CISTERNS AND REFERENCES IN THE BIBLE TO CISTERNS
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et-Tell), there was discovered a large cistern dating to around 2500
BC
which could hold nearly 7,500 m3 of
water. It was carved out of solid rock, lined with large stones and sealed with clay to prevent leaking. Some sites
Probably the first successful efforts to control water by
contained over 50 cisterns (Tell en-Nasbeh). The Umm al-
humans were made in Mesopotamia and Egypt. The con-
biyara (the mother of all cisterns) is at the ancient site of
struction and use of cisterns has been traced back to the
Edom, which became the Nabataean city of Petra.
Neolithic Age when waterproof cisterns (lime plastered) were built in the floors of houses in villages in the Levant (Miller ) by the late 4th millennium
BC.
In Mari, in
MINOANS (CA. 3200–1200
BC)
ancient Mesopotamia, a canal connected to the city from both ends and passed through the city. Servant women
The Minoan culture flourished during the Bronze Age in
filled the 25 m3 cistern of the palace with water supplied by
Crete. A systematic evolution of water management in
the canal. Later on other cisterns were built in Mari and con-
ancient Greece began in Crete during the early Bronze
nected to an extended rainfall collection system. The ancients
Age, i.e. the Early Minoan period (ca. 3000–2150
used a lime plaster to cover bedrock to prevent seepage and
Myers et al. ). Wells, cisterns, water distribution, foun-
loss of water from the cisterns. The use of cisterns in ancient
tains,
times ranged from storing rainwater in harvesting systems to
prehistoric Crete rivers and springs provided people with
storing water delivered by aqueducts originating in distant
water. Starting in the Early Minoan period II (ca. 2900–
springs and streams. Rainwater harvesting systems include
2300
a catchment area for rainfall interception; a cistern for
and aqueducts were used. Also, the Minoan architecture
storage; a conveyance system to deliver the water from the
included flat rooftops, light wells, and open courts which
catchment to the cistern; and a method to draw upon the sto-
played an important role in the water management. The
rage for consumption. The catchment ranged from rooftop
rooftops and open courts acted as catch basins to collect
areas to courtyards and plazas.
rainwater from which it flowed to storage areas or cisterns.
and
BC),
even
recreational
functions
existed.
BC,
In
a variety of technologies such as wells, cisterns,
The Bible refers to cisterns many times. One example is
The Minoan settlements used cisterns about 1,000 years
when Jeremiah, the prophet, proclaimed a scathing indict-
before the classical and Helenistic-Greek cities. Cisterns
ment against Israel and their idolatrous ways. He accused
were used to supply (stored runoff from roof tops and
them of worshiping false gods which he compared to cis-
court yards) water for the households through the dry sum-
terns that could not hold water (broken cisterns). In
mers of the Mediterranean. The two earliest large cisterns of
Jeremiah 2:13, ‘For my people have committed two evils;
Minoan Crete were built in the first half of the 2nd millenwhich was the time of the first Minoan palaces at
they have forsaken me the fountain of living waters, [and]
nium
hewed them out cisterns, broken cisterns, that can hold no
Myrtos-Pyrgos (see Cadogan ). Figure 1(a) shows one
water.’ During Biblical times cisterns were also used as
of two cisterns at Myrtos-Pyrgos. These cisterns remain an
underground chambers, such as hiding places for fugitives,
unusual feature of the Minoan settlement, as the Myrtos
burial places, and even as prison cells. Jeremiah was held
River supplied water to the base of Pyrgos Hill. Both cisterns
as a prisoner in a muddy cistern which belonged to Mal-
are circular with vertical walls and rounded bottoms. The
chaiah, the son of King Zedekiah (Jeremiah 38:6), from
walls and bottom are coated with white lime plaster 1–
where he was eventually hauled up with ropes. Jeremiah
2 cm thick (Cadogan ). Similar round structures exist
14 also gives us a description or definition of droughts.
at Knossos, Mallia, and Phaistos, which have been called
BC,
Many ancient cisterns have been discovered throughout
granaries, but according to Cadogan this is improbable
Jerusalem and the entire land of Israel. At the site believed
because of their locations at the bottom of hills. It would
by some to be that of ancient Ai of the Bible (Khirbet
have been difficult to prevent water from running into the
40
L. W. Mays
Figure 1
|
|
Cisterns during antiquity in the Mediterranean region
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Cisterns at (a) Myrtos-Pyrgos and (b) Kato Zakros (photo copyright by L.W. Mays).
round structures during a storm. Figure 1(b) shows a cistern
then flowed from the settling tank to the main cistern for
at Kato Zakros.
water storage. Steps, shown in Figure 2(b) were used to des-
Tylissos was one of the important cities in ancient Crete during the Minoan era, flourishing (ca. 2000–1100
BC)
as a
cend down to the various water levels. The hill of Phaistos was settled for the first time at the
peripheral center dependent on Knossos. The water supply
end of the Neolithic period (4th millennium
system to Tylissos included an aqueduct developed in the
the early Bronze Age (during the Early Minoan period)
Minoan period that was constructed of closed pipes and
the Minoans built above the ruins of the Neolithic houses.
curved stone channels. Secondary conduits were used to
At the end of the prepalatial period Phaistos became
convey water to a settling tank constructed of stone (see
very prosperous with the construction of the first palace
Figure 2(a)), used to remove sediment and/or suspended
(ca. 2000–1900
sediments. Also note the hole in the lower part of the tank
of Phaistos, as well as in other cities and villages in
which enabled the tank to be drained for cleaning. Water
Minoan Crete depended directly on rainfall, collected from
Figure 2
|
BC).
BC).
Later in
The water supply system in the Palace
Cistern in Tylissos, Crete. (a) Sedimentation tank in foreground with stone channel connecting to cistern. (b) Steps leading down to cistern (photo copyright by L.W. Mays).
41
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Cisterns during antiquity in the Mediterranean region
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roofs and courtyards and then directed to cisterns. The drainage systems were in some cases conveyed into terracotta vessels near light wells, which acted as water collectors.
GREEKS (CA. 750–146
BC)
During the archaic (ca. 750–480 480–323
BC)
BC)
and the classical (ca.
periods of the Greek civilization, cisterns
were similar to those built by the Minoans. Most Greek houses had a cistern supplied by rainwater for purposes of bathing, cleaning, houseplants, domestic animals, and even for drinking during shortages of water. Most likely the water was of a quality of what we would today consider as sub-potable. Aristotle in his Politics (vii, 1330b) written in the 320s
BC
asserts that ‘cities need cisterns for safety in
Figure 3
|
Cistern in the classical Greek city of Dreros on Crete. Shown are the steps leading down to the bottom of the cistern located in the Agora. There is also another set of stairs leading down into the cistern (photo copyright by L.W. Mays).
war.’ During this time a severe 25-year drought required the collection and saving of rainwater (Camp ). Also about this time cisterns were built in the Athenian Agora for the first time in centuries (Parsons ; Crouch ).
The lack of adequate surface and groundwater from sources on the Greek islands, which are arid and semi-
Most of the ancient Athenian Agora cisterns have been
arid, resulted in the use of rainfall-runoff harvesting by
dated between the 4th and 1st century BC. These cisterns are
the inhabitants. One of many examples is in Aegina
believed to have had a secondary use when the natural
where the uncovered cisterns were called Mpourdechtes.
supply of water was insufficient. Water from the wells
The construction of these cisterns consisted of a combi-
would have been used for drinking, while the water stored
nation of masonry walls and curved parts of the natural
in the cisterns would have been used for washing. Rainwater
rock beneath resulting in an irregular shaped cistern (Anto-
was stored in the cisterns after being collected from the sur-
niou ). There are still surviving Mpourdechtes, made
rounding roofs and drained into the eaves’ gutter that
mostly of stone masonry, which are more regular in shape
drained into a canal at ground level that connected to a cis-
that have been dated to the Hellenistic period. Also there
tern. These cisterns had a diameter of approximately 3 m,
are many Mpourdechtes with irregular stone masonry
and a flask-like shape, probably in order to avoid collapses
constructed mostly of large stones, such as the small Mpour-
of the rock formations. Frequently, two successive cisterns
dechtis at Hellanio’s Zeus sanctuary that is similar in
were connected through a channel, while the walls of the
construction to the Hellenistic impromptu fortification
cistern and the channels were plastered with a mortar.
walls (Antoniou ).
The city-state of Dreros during the Classical Greek period
During the Hellenistic period (ca. 323–146
BC)
further
is located near Neapolis in eastern Crete in the district of
developments were made by the Greeks in the construction
Lassithi. Dreros was constructed on a saddle between two
and operation of cisterns, which most likely peaked during
peaks on the slope of Mount Kadistos. A large rectangular cis-
this period. Because of the lack of adequate water supplies
3
tern (13 × 5.5 × 6 m ) was constructed in the Agora for the
on most Greek islands, cisterns were used. The water
purposes of water supply (Antoniou et al. ). According
supply in several Greek cities was dependent entirely on
to Myers et al. () this was the first and largest cistern
rainfall which was collected from the roofs, yards and
ever known at that time. Figure 3 shows the cistern in the
other open spaces. During this time the technology of cis-
ancient Greek city of Dreros on Crete.
terns progressed (Mays ).
42
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Cisterns during antiquity in the Mediterranean region
ROMANS (CA. 3RD CENTURY In 265
BC
BC–4TH
CENTURY
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AD)
Rome’s power extended only to northern Italy,
and 120 years later it extended from Spain to eastern Asia and the Aegean Sea. During the Roman period larger scale hydraulic works (mainly water supply systems) characterized the advances in water technology. Roman engineers used the technologies of previous periods to their advantage and constructed advanced cisterns for their larger projects such as the Piscina Mirabilis (discussed below) for the Serino Aqueduct system (De Feo & Napoli ). The Romans made extensive use of cisterns, so that herein only a very few of the many that were built will be explored. In
Figure 5
|
Cistern at top of hill in Iasos, Turkey (photo copyright by L.W. Mays).
Figure 6
|
Roman cistern in Ilici, Spain (photo by L.W. Mays).
Figure 7
|
Roman Cistern at Thera on Santorini (photo copyright by L.W. Mays).
the Roman town of Pompeii, with the extensive water distribution system including both aqueduct water and well water, the roofs of houses collected rainwater that flowed through terracotta pipes down to cisterns where water was stored for domestic use. In Pompeii, the aqueduct and well water were contaminated as a result of the volcano, requiring cisterns to be used for drinking water (Crouch ). Figures 4–8 show various Roman cisterns. Figure 4 shows the remains of a cistern built below the Acropolis in Athens. Figure 5 is a Roman cistern built in Iasos, Turkey. Figure 6 shows a rather unusual Roman cistern at Illici near modern day Elche, Spain, with a bottle shaped structure below the opening. Figure 7 shows the remains of a Roman cistern at Thera on Santorini.
Figure 4
|
Roman cistern below Athens Acropolis (photo copyright by L.W. Mays).
|
2014
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Cisterns during antiquity in the Mediterranean region
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The Romans also built very large cisterns. The Piscina
a settling tank before water entered the storage chambers
Mirabilis (Figure 8) is one of the largest Roman cisterns
(Wilson ). At Tugga, Thuburnica, Thapsus and Uthina
3
(capacity of 12,600 m of water) (De Feo et al. ). The cis-
the transverse chamber was placed between the parallel
tern was supplied by water from the Augustan aqueduct, the
chambers and the outlet, with no settling (Wilson ). At
Serino aqueduct that was built from Serino to Miseno. The
Thuburnica and the Ain el-Hammam cisterns at Thugga
Serino aqueduct, 96 km long with seven branches, supplied
the entrance of the aqueduct channel runs along an internal
many towns including Pompeii, Herculaneum, Acerra,
wall of the cistern so that it distributes water to the cistern
Atella, Nola, and others. The total drop in elevation from
chambers. Cisterns at Dar Saniat in Carthage were con-
the source, the Acquaro-Pelosi spring in Serino, to the Piscina
structed with three settling basins and two storage
Mirabilis is 366 m (0.38%). This large cistern is 72 m by 27 m
reservoirs, each having two compartments with a total
in plan and is 15 m deep (according to Hodge ()).
storage capacity of 2,780 m3.
Other large Roman cisterns have been found in Spain,
Cisterns may have also been used as a means to store
southern Italy, Crete, Asia Minor, with the largest number
water for fighting fires. Fahlbusch () argues that the big
in North Africa. Wilson () points out that in Roman
cistern at the acropolis of Pergamum may have been used
North Africa vast cistern complexes were used in conjunc-
for this purpose. This cistern, 4.55 m in diameter and
tion with the aqueducts. These cisterns had capacities that
6.20 m in depth, with a different type of construction, differs
were often several thousand m3, that were much larger
in comparison to the normal rainwater cistern of the time.
than the domestic cisterns. These cisterns in North Africa
This large cistern at Pergamum was built of mortared ashlars
were typically located where the aqueducts reached the
and did not have a stone ceiling which may indicate a differ-
edge of towns. Wilson () describes two types of
ent use. One question has been whether the cistern was built
common cistern complexes in North Africa, both of which
in the Hellenistic or the Roman era, with Fahlbusch ()
were used at Uthina in Oudna, Tunisia. Large cross-vaulted
stating that it was surely built in Roman times.
chambers, with a roof supported by piers, is one type of cistern. A second common type of cistern complex includes several barrel-vaulted chambers with a transverse (connecting) chamber set across them.
TERMESSOS (CA. 4TH CENTURY AD)
BC–5TH
CENTURY
In the cisterns at Tuccabor and Djebel M’rabba in Tunisia, the transverse chamber was placed between the
Termessos (originally an ancient Pisidian city possibly
inlet and the parallel chambers and the chamber served as
dating back before the 14th century
BC)
is located about
53 km northwest of Antalya, Turkey, in a valley on the steep slopes of the Gulluk in the Taurus Mountains at an elevation of over 1,000 m. What is known of the history of Termessos begins when Alexander the Great surrounded the city in 333
BC,
but failed to conquer. The people of Ter-
messos were the Solyms, not Greeks, and spoke a language referred to as Solymish. The area has no rainfall from the beginning of April to the end of October. Because of the lack of rainfall and the inability to transport water as a result of the steep topography, the people of Termessos made extensive use of collecting rainfall runoff for storage in cisterns and even constructed a dam (Kurkcu ). During the Hellenistic period the city adopted the Greek culture and language and other advances occurred during Figure 8
|
Piscina Mirabilis (copyright by L.W. Mays).
the Roman times. Termessos went through a gradual decline
44
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Cisterns during antiquity in the Mediterranean region
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and was finally abandoned in the 5th century AD. Two of sev-
carved out of the highland and evolved into bell-shaped cis-
eral cistern locations at Termessos are illustrated in Figure 9.
terns. These large cisterns are similar to large rooms carved
These cisterns certainly show influences of both Greek and
out of vertical walls into which complex canals and pipe net-
Roman construction.
works flow (Laureano ). What is so unique is that the Nabataeans used every slope and surface as a means to harvest rainfall and stored every water source from a few drops
NABATAEANS (CA. 300
BC–300 AD)
Rainwater harvesting was used extensively in Petra by the Nabataeans (ca. 300
BC–300 AD).
to large floods. This is why Strabo, the 1st century geographer, described Petra as ornamented with fountains and basins (Laureano ). Khottara make use of traces of moisture and night con-
In Petra this meant using
densation of fog and dew by harvesting the condensation
the technology in elevated places and on bare sandstone
(humidity) by causing it to drip into tanks, cisterns, or chan-
walls with many innovations. The Nabataeans used various
nels that catch the water on the walls and convey it to pools.
types of cisterns that they carved out of the rock and water-
These structures provide water all year round. At the other
proofed using chalk. These cisterns ranged from small pools
extreme, one cistern called Bir Huweimel at the bottom of
in the highlands to catch runoff, to rectangular shaped cis-
Ras as-Slimane, actually traps flood water using a large
terns at the bottom of the natural dips. Small pools were
room (depth of 9 m) excavated in the riverbed. Flood water is diverted to water intakes and decanting basins to fill the large cistern where the water is stored. A staircase is used to enter the cistern and water is drawn from the cistern through a well shaft.
BYZANTINES (CA. 330–1204
AD)
The Byzantine Empire and Eastern Roman Empire are names used to describe the Roman Empire during the Middle Ages, with the capital in Constantinople (Istanbul). During the thousand-year existence of the empire its influence spread widely into North Africa and the near East during the Middle Ages. Figure 10 shows a Byzantine cistern at the base of the acropolis in Athens, which is a covered cistern. Both open-air (uncovered) and covered cisterns were built during this time period. One of the earliest cisterns was built in the 4th century
AD
in Modestus (Mango ).
The cistern was built from 363 to 369
AD
and measured
approximately 154 m × 90 m in ground plan and was most likely uncovered. Covered cisterns were more numerous than open-air cisterns. At least around seventy of them existed in Constantinople, though not all of them have been verified by archeological evidence. During the Byzantine times in Constantinople at least 36 Figure 9
|
(a) Remains of cistern in Termessos (photo copyright by L.W. Mays). (b) Shows five inlets for cisterns at Termessos for which there are actually three different cistern chambers (photo copyright by L.W. Mays).
cisterns were constructed (Lerner ). The Basilica Cistern, or in Turkish the Yerebatan Sarayi’, was the largest
45
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Cisterns during antiquity in the Mediterranean region
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drained from the cistern two of the 336 columns were discovered to rest on ancient carved heads of Medusa. Other Byzantine cisterns located in Sultanahmet include the Binbirdirek Cistern, or Cistern of Philoxenos, and the Theodosius Cistern. The most important open cisterns received water predominantly from the Belgrade forest west of the city. Aqueducts were used to convey water to the city and the cisterns were also located on the hills of Constantinople. The architecture of cisterns during the 4th to the 6th centuries provides an understanding of the standardization of architecture during that time period. The building materials were different as compared to the Roman construction of Figure 10
|
cisterns. Constantinopolitan cisterns were built with brick Byzantine cistern at the base of the acropolis in Athens (photo copyright by L.W. Mays).
instead of the Roman concrete vaults, and marble columns instead of Roman brick and cement piers (Yavuzturk & Ozyalavac ).
3
(140 m × 70 m and capable of holding 80,000 m ) known covered cistern, probably completed in the early 6th century. This cistern, shown in Figure 11, is an underground
OTTOMANS (CA. 1299–1922
AD)
cistern located in Sultanahmet, having 336 marble columns each 9 m high. The columns are arranged in 12 rows each
During the 16th century AD of the Ottoman period in Turkey
with 28 columns, spaced 4.9 m apart. The cistern was built
a different type of cistern (see Figure 12) emerged in rural
underneath the Stoa Basilica which is a large public
areas, particularly in southwest Anatolia. These cisterns
square on the First Hill of Constantinople during the reign
were built for military logistic purposes for the Ottoman
of Emperor Justinian I in the 6th century. Water was sup-
Army. These circular shaped cisterns are about 7 m in diam-
plied to the cistern by an aqueduct from springs in
eter, with a domed roof of a height about one third of the
Marmara, which is west of the city. When the water was
diameter. The cistern was built on a superstructure 1–2 m
Figure 11
|
Basilica cistern of Constantinople in Istanbul, Turkey (photo copyright by Susi. K. Mays).
Figure 12
|
Ottoman cistern built for military purposes of the Ottoman Army, located near Bodrum, Turkey (photo copyright by L.W. Mays).
46
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Cisterns during antiquity in the Mediterranean region
high and a substructure a few meters in depth, with stairs that descended to the bottom of the cistern. Most of these
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Ancient water technologies such as cisterns were characterized by simplicity, easy operation, and requiring no
cisterns are still used for livestock water supply (Ozis ).
complex controls, making them more sustainable. How-
Koyuncu et al. () focused on nomad cisterns in Anta-
ever the successful design and operation of some of
lya stating that around 110 cisterns have been located with
these systems were massive achievements, even by
the following construction: cisterns with wells, cistern
modern day standards. Keeping in mind that the funda-
wells with staircases, cisterns with gable roofs and
mental concepts of the conservation of mass, energy
vaulted/cupola cisterns. These cisterns were the products
and momentum did not exist, these systems were built
of nomad migration in the Antalya area. The cisterns were
and provided for water resources sustainability.
plastered on the outside with a plaster khorasan mortar.
•
The ancients considered water security as one of the critical aspects of the design and construction of their water supply systems. Water security is a modern day concern around the world, particularly from the viewpoint of ade-
LESSONS LEARNED AND WATER RESOURCES SUSTAINABILITY
quate water supply, and now from the viewpoint of possible terrorist activity targeting water supply systems which can debilitate such systems. Water supply security
A brief review of some of the types of cisterns used during
has been important throughout history and must con-
antiquity has been presented in order to illustrate the progression of advances and to relate how humans have used this technology to advance water resources sustainability.
•
tinue to be in the future. The looming present day water crisis in many parts of the world must be faced using traditional knowledge and tech-
These unique structures have allowed humans to live in
niques inherited from the past, in addition to our present
arid and semi-arid regions of the world for well over 5,000
day technological capabilities, for more sustainable ways
years. These hydraulic structures are certainly evidence of
of dealing with water scarcity, particularly in developing
the social, political, and economic conditions, and most
parts of the world. The use of cisterns as a part of rainwater
likely the military conditions, of the various periods of
harvesting systems can be implemented today, particularly
human history. The overall goal of water resources manage-
in many developing parts of the world where this technol-
ment must be water resources sustainability, as evidenced by
ogy is lacking to strive for water resources sustainability.
the ancients. Because water impacts so many aspects of our existence, there are many facets that must be considered in water resources sustainability (see Mays ). Some lessons learned include the following:
•
•
Many ancient water infrastructure projects were built in a piecemeal fashion over many years such as Rome (over 500 years, funded with the spoils of war and heavy taxes on conquered countries), but were not maintained
A combination and balance of smaller scale measures
after the wars ended. The government did not account
(such as cisterns for water harvesting systems) and
for the expense to the future generations, a lesson being
large-scale water supply projects (such as cisterns for sto-
learned by many modern day nations.
rage of aqueduct flows) were used by many ancient civilizations such as the Minoans, Greeks, Romans,
•
As a concluding remark, the ancients lived more in har-
Byzantines, and Ottomans.
mony with nature and the environment as opposed to our
The ancient water technologies of cisterns should be con-
modern day society. As water systems are very dynamic,
sidered, not as historical artifacts, but as potential models
especially in arid and semi-arid lands, traditional method-
for sustainable water technologies for the present and the
ologies such as cisterns have proven to be very effective in
future. A key factor in sustaining traditional water man-
both the past and the present, and should be part of our
agement systems depends on placing a premium on
future. Our generation is not sustainable in that we are
such methods which have proven to be successful,
ignoring future generations, creating problems for them
especially in arid and semi-arid lands.
such as our contributions to climate change and our
47
L. W. Mays
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Cisterns during antiquity in the Mediterranean region
continual greed for more. We need to learn from the ancients, they have spoken. Will we listen?
REFERENCES Angelakis, A. N., Mays, L. W., Koutsoyiannis, D. & Masmassis, N. Evolution of Water Supply Through the Millennia. IWA Publishing, UK. Antoniou, G. Mpourdechtis: ancient roofless cistern type in Aegina. In: Proc. 1st IWA International Symposium Water and Wastewater Technologies in Ancient Civilizations (A. D. Angelakis & D. Koutsoyiannis, eds). National Agricultural Research Foundation, Iraklio, Greece, held 28–30 October 2006, pp. 463–467. Antoniou, G., Xarchakou, R. & Angelakis, A. N. Water cistern systems in Greece from Minoan to Hellenistic period. In: Proc. 1st IWA International Symposium Water and Wastewater Technologies in Ancient Civilizations (A. D. Angelakis & D. Koutsoyiannis, eds). National Agricultural Research Foundation, Iraklio, Greece, held 28–30 October, pp. 457–462. Cadogan, G. Water management in Minoan Crete, Greece: The two cisterns of one Middle Bronze Age Settlement. In: Proc. 1st IWA International Symposium Water and Wastewater Technologies in Ancient Civilizations (A. D. Angelakis & D. Koutsoyiannis, eds). National Agricultural Research Foundation, Iraklio, Greece, held 28–30 October, pp. 447–456. Camp, J. M. Drought and Famine in the 4th Century, In: Studies in Athenian Architecture, Sculpture, and Topography presented to Homer A. Thompson, Hesperia, Supplement 20, pp. 9–17. Crouch, D. P. Water Management in Ancient Greek Cities. Oxford University Press, New York. De Feo, G. & Napoli, R. M. A. Historical development of the Augustan Aqueduct in Southern Italy: twenty centuries of works from Serino to Naples. Water Science and Technology: Water Supply 7 (1), 131–138. De Feo, G., De Gisi, S., Malvano, C. & De Biase, O. The greatest water reservoirs in the ancient Roman world and the ‘Piscina Mirabilis’ in Misenum. Water Science and Technology: Water Supply 10 (3), 350–358. Fahlbusch, H. The big cistern on the acropolis of Pergamum – a reservoir for the storage of water to fight against fire. In: Proceedings of the 3rd IWA Specialized Conference on Water and Wastewater Technologies in Ancient Civilizations, Istanbul, Turkey, March 22–24.
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Hodge, A. T. Roman Aqueducts and Water Supply, 2nd edn. Gerald Duckworth & Co. Ltd, London, UK. Koyuncu, I., Altinbas, M., Aydin, A. F., Guclu, S., Turken, T., Ecis, R., Yildiz, A. & Tutuncu, H. Nomad cisterns in Antalya. In: Proceedings of the 3rd IWA Specialized Conference on Water and Wastewater Technologies in Ancient Civilizations, Istanbul, Turkey, March 22–24. Kurkcu, M. Termessos water construction searches: dams. In: Proceedings of the 3rd IWA Specialized Conference on Water and Wastewater Technologies in Ancient Civilizations, Istanbul, Turkey, March 22–24. Laureano, P. The Water Atlas: Traditional Knowledge to Combat Desertification. Laia Libros, Barcelona, Spain. Lerner, D. Large Byzantine water storage cisterns. Quarterly Journal of Engineering Geology 22, 173–174. Mango, C. The water supply of Constantinople. In: Constantinople and Its Hinterland (C. Mango, G. Dagron & G. Greatrex, eds). Society for the Promotion of Byzantine Studies Publications 3, Aldershot. Mays, L. W. Water Resources Sustainability. McGraw-Hill, New York, USA. Mays, L. W. Ancient Water Technologies. Springer Science and Business Media. B.V., Dordrecht, The Netherlands. Miller, R. Water use in Syria and Palestine from the Neolithic to the Bronze Age. World Archaeology 2.3 (February), 331–341. Myers, W. J., Myers, E. E. & Cadogan, G. The Aerial Atlas of Ancient Crete. University of California Press, Berkeley and Los Angeles, California, USA. Ozis, U. Outlook on ancient cisterns in Anatolia. In: Proceedings of the International Conference on Rain Water Cistern Systems (F. N. Fujimura, ed.). University of Hawaii at Manoa, Turkey, June. Parsons, A. W. Klepsydra and the paved court of Pythion. Hesperia 12, 191–267. Taylor, W. The Mycenaeans. Thomas & Hudson, London. United Nations Water for People, Water for Life. United Nations World Water Development Report, World Water Assessment Programme. UNESCO Publishing and Berghahn Books, Barcelona, Spain. Wilson, A. Urban water storage, distribution, and usage. In: Water Use and Hydraulics in the Roman City (O. KoloskiOstrow, ed.). Kendall/Hunt Publishing Company, Dubuque, Iowa. Yavuzturk, S. P. & Ozyalavac, A. N. The hidden water structures of Istanbul: cisterns. In: Proceedings of the 3rd IWA Specialized Conference on Water and Wastewater Technologies in Ancient Civilizations, Istanbul, Turkey, March 22–24.
First received 31 March 2013; accepted in revised form 29 May 2013. Available online 12 September 2013
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Life cycle analysis of two Hungarian drinking water arsenic removal technologies C. J. Jones, D. Laky, I. Galambos, C. Avendano and V. L. Colvin
ABSTRACT Determining a technology’s merit as a solution to Hungarian drinking water arsenic contamination goes beyond technical concerns: environmental and economic aspects also play very important roles. In an effort to address the current arsenic drinking water requirements in Hungary, life cycle analysis (LCA) methodology was applied on two example arsenic removal technologies, coagulationfiltration and adsorption, from cradle to grave. A distribution of 500 m3/day was assumed, along with a range of possible operation boundary conditions modelled solely for As treatment. Nine out of 10 considered impact categories tended to favour coagulation-filtration, however realistic variations in water chemistry and product characteristics led to some overlap of their environmental impact. Unlike other studies on water systems, electricity did not have a large direct impact; this was due to the focussed nature of this study on individual treatment technologies rather than an entire water supply system. Regeneration of the adsorption technology filter material was also observed to require nearly the same mass of materials for one regeneration as what was needed to support the coagulation-filtration technology for an entire year. Hazardous waste was surprisingly not reduced
C. J. Jones (corresponding author) C. Avendano V. L. Colvin Department of Chemistry, Rice University, P.O. Box 1892, MS 60 Houston, TX USA 77251-1892 E-mail: cj2@rice.edu D. Laky Department of Sanitary and Environmental Engineering, Budapest University of Technology and Economics, H-1111 Budapest, Műegyetem rakpart 3., Hungary I. Galambos Faculty of Food Science, Department of Food Engineering, Corvinus University of Budapest, H-1118 Budapest, Ménesi út 44, Hungary
for adsorption compared to coagulation-filtration due to prefiltration requirements and an extra regeneration, even though adsorption shifts some of the environmental burden to the production phase. Additionally, cost analysis observes that coagulation-filtration is the cheaper of the two technologies; its highest cost is that of waste disposal, while the highest single expense modelled is that of the adsorption media cost. Key words
| adsorption, arsenic technologies, coagulation, drinking water, life cycle analysis
INTRODUCTION Long-term human exposure drinking water studies have
such as mining (WHO ), drinking water arsenic con-
shown that arsenic is associated with liver, lung, kidney,
tamination can also be caused naturally by arsenic-rich
skin, and bladder cancers, as well as other non-cancerous
rocks through which the water has filtered.
problems such as micronuclei or chromosomal aberrations,
In Hungary, a country noted for having one of the most
DNA damage, sister chromatid exchange, peripheral vascu-
alarming arsenic concerns in Europe (Petrusevski et al.
lar disease, diabetes mellitus, hypertension or ischaemic
), arsenic is found in deep confined aquifers of an exclu-
heart disease (Rahman ; Marchiset-Ferlay et al. ).
sively natural origin. As a consequence of the reductive
A worldwide concern, high groundwater concentrations of
conditions in these layers, arsenic is mostly found as arsenite
arsenic can be found in places including Argentina, Bangla-
(As(III)). In 2001, new drinking water standards were intro-
desh, Canada, Chile, China, Hungary, India, Japan, Mexico,
duced in Hungary lowering the earlier existing 50 μg/L
Poland, Taiwan, Thailand, USA, and Vietnam (Smedley &
arsenic standard (MSZ 445 ) to the corresponding 98/83
Kinniburgh ; Mohan & Pittman ). Although some-
EU Directive () level of 10 μg/L. Currently at many
times anthropogenic in nature due to industrial activity
settlements, temporary solutions are installed to alleviate
doi: 10.2166/ws.2013.165
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the arsenic problem, therefore new drinking water treatment
However, LCA methodology has yet to be utilized broadly
technology must be put into operation or existing systems
or on various types of arsenic technologies in drinking
have to be upgraded in the near future to provide a final sol-
water. Here we report a holistic analysis of two Hungarian
ution for arsenic removal.
arsenic removal technologies by employing such an LCA
Several feasible technologies exist to remove arsenic, the
study. This research addresses important questions between
most ubiquitous being the conventional coagulation-
technologies regarding cost, waste disposal, electricity con-
filtration method (Gregor ; Wickramasinghe et al.
sumption, global warming effect, and others. Utilizing PE
). The technology consists of three steps: the oxidation
International’s GaBi 5 software for database and organiz-
of arsenite (As(III)) to arsenate (As(V)), the conversion of
ational support, detailed, quantitative data were used to
soluble arsenate to an insoluble form by addition of metal
answer questions regarding product production, use, and
salts (usually Fe(III) or Al(III)), and the subsequent removal
end-of-life phases. By providing a good comparison between
of the solid particles from the water by sedimentation, rapid
products, with Hungarian wells and water parameters as a
sand filtration, or microfiltration (Han et al. ; Floch &
model, we demonstrate the benefits and drawbacks for
Hideg ; Wickramasinghe et al. ). Another common
each potential solution to the arsenic issue.
technology is one of adsorption. The system is relatively simple: as water passes through the media, arsenic is adsorbed to the surface. There are several such arsenic
METHODS
adsorbents available on the market or under investigation; according to the review of Mohan & Pittman (), iron
The purpose of this LCA was to model and compare annual
based materials are usually capable of removing arsenic with-
removal of arsenic with a given water quality and quantity,
out pre-oxidation, while As(III) → As(V) conversion is needed
while providing the necessary amount of water to an example
for the aluminium-based adsorbents.
municipality. Two arsenic removal technologies were mod-
Arsenic removal in Hungary currently proceeds via
elled: coagulation-filtration and a cerium based example of
coagulation combined with rapid sand filtration; this is
adsorption technology. The exact design of a drinking water
achieved through artificial, dosed Fe additions or natural,
treatment plant depends on a region’s water chemistry, water
in-situ Fe coagulant in areas with high enough iron content
demand and other conditions or circumstances at that specific
(Driehaus ). However, recent attention has been paid to
settlement. Therefore, in this study, a reasonable flow rate,
other methods such as adsorption due to ease of operation,
arsenic concentration, and initial raw water chemistry were
diminished chemical demand, and potential production of
assumed. Calculations were executed for three different but
less hazardous waste. Variations between potential removal
realistic scenarios: a best, average, and worst-case with varying
systems are numerous, including different production
design parameters of favourable and less-favourable con-
requirements, other operation-phase inputs, and waste dis-
ditions for the technology at hand. In short, the best case
posal. Any insight into how these differences compare
scenario assumed optimum conditions for the removal of
with regard to technical efficiency, financial burden, and
arsenic, e.g. few contaminants such as silicate or phosphate
environmental impact would aid decision makers in deter-
that interfere with removal, ideal pH, maximum lifespan per-
mining
a
formance of products used, etc.; the worst case assumed the
methodology to compare and contrast such technological
maximum functional opposite values, while the average case
solutions for the Hungarian arsenic problem is of great use.
sought a middle-ground between the two extremes.
the
most
suitable
technology.
Therefore,
Life cycle analysis, or LCA, methodology satisfies these needs: inputs and outputs within a chosen system boundary
Coagulation-filtration and cerium adsorption
are compared. Similar studies have been undertaken for
technology
comparing other water systems, including work on technologies for arsenic in wastewater (Dodbiba et al. ) and
A schematic diagram of coagulation-filtration and adsorp-
domestic water use in the USA (Arpke & Hutzler ).
tion methods is illustrated in Figure 1. Coagulation
50
Figure 1
C. J. Jones et al.
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Life cycle analysis of Hungarian drinking water arsenic removal technologies
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Coagulation-filtration (a) and adsorption (b) model scheme (light grey boxes are included in model, dashed light grey boxes have partial data, and dark grey boxes are excluded).
technology consists of the following steps: water intake,
together with manganese and other contaminants. The last
aeration, oxidation by KMnO4, coagulation by FeCl3 salt,
step of the technology is final disinfection (usually chlorine
rapid sand filtration, and final disinfection. Aeration is
or sodium-hypochlorite is used) in order to prevent
often applied in deep confined aquifers where reductive con-
microbial growth in the water supply network.
ditions are dominant, and dissolved gases (methane or
Adsorption technology makes use of these steps in a simi-
aggressive carbon-dioxide) might also be present in the
lar manner. Following aeration, oxidation, and a small
water. Moreover, iron and some manganese can also be oxi-
capacity rapid sand filter to remove excess iron and manga-
dized by dissolved oxygen. For arsenic removal a strong
nese, adsorption is applied for arsenic removal. NaOH,
oxidant (e.g. KMnO4) is needed, because arsenic cannot
NaClO and HCl are used for regeneration after saturation of
be oxidized by dissolved oxygen. KMnO4 is also able to oxi-
the adsorbent; the regenerate must be treated as hazardous
dize iron and manganese if these compounds were not
waste while backwash water can be treated as normal sewage.
efficiently oxidized by oxygen. FeCl3 is used as a coagulant, and after mixing the chemical, the water is directed to the
Water system scenarios
rapid sand filters, where iron, manganese and arsenic are filtered out. Backwash of the rapid sand filter is often required
Uniformly two important quantities were initially set for
every 1–2 days to remove arsenic-containing iron flocs,
each scenario: a 500 m3/day treated water volume to
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distribution, as this water quantity was near the average
phosphate content found at many water sources (Laky &
needed for affected Hungarian settlements (Government
István ). Finally, the filter depth was increased due to
Decree No. 201/2001 ), and a 50 μg/L arsenic level
the high floc density in this scenario and the logistical
that agreed with the maximum allowable concentration
need to achieve a minimum backwash frequency of 24 h.
according to the previous Hungarian arsenic standard
Dual-density sand was used, having a high 1,700 g/m2 load-
(MSZ 445 ). Some values, such as water loss, iteratively
ing capacity capable of mimicking a two-tank solution using
vary between technology and scenario as a percentage of the
a double-layered rapid sand filter.
water produced. All design parameters and calculations
Scenario design for the adsorption technology pro-
were made according to typical Hungarian values and
ceeded similarly. For the best case scenario, cost and
based on experiences of full and pilot-scale treatment
shipping was calculated based on the assumption that the
plants; see Tables 1 and 2 for coagulation and adsorption
adsorbent is produced in Hungary, while in the other scen-
technology details, respectively.
arios production abroad was assumed. All water conditions
Best case scenario calculations for coagulation, for
were identical: aeration, rapid sand filtration, chemical oxi-
example, were based on raw water containing negligible
dation, and all required parameters for these processes must
iron and manganese; low-level potassium permanganate oxi-
be applied for iron and manganese removal to make the
dant and FeCl3 levels (0.5 mg/L) were therefore sufficient to
technology ‘functional and feasible’ in the average and
convert the soluble arsenic to particulate form. To accu-
worst case scenario, while the best case scenario did not
rately determine backwash frequency and total flow, these
require such presteps. Adsorbent regeneration would also
values were then used to calculate a hypothetical tank
vary depending on the arsenic content of the well and
design and filtration area based on the Hungarian Technical
presence of other competing ions, e.g. phosphate ion con-
Guidelines (MI-10-135-4 ) and Mészáros (). Low
centration. More frequent regenerations may be required,
amounts of particulate iron and manganese generate a rela-
therefore the industry suggested the best and average case
tively low 1.25 mg/L floc density, so an 8 m/h filtration
scenarios include three regenerations a year, while the
velocity was assumed, resulting in 2.5 m2 filtration area.
worst case assumed four regenerations. Backwash for the
The loading capacity of the filter was assumed to be
adsorbent filter was also recommended weekly.
1,000 g/m2. These values resulted in a backwash frequency
Waste was handled almost identically for each scenario,
of 100 h; however, it is recommended (MI-10-135-4 )
aside from the resulting quantity. In the case of coagulation-
that the filters are backwashed at least every second day,
filtration, backwash water was directed to a sedimentation
so a 48 h backwash frequency was applied. Backwash was
tank and allowed to reach a 1% total mass, arsenic-
carried out with around 15 m/h intensity and lasted about
containing hazardous sludge. The supernatant from the sedi-
half an hour. Besides water, the rapid sand filters were
mentation tank was directed to a nearby river or urban
backwashed with air at an intensity of 60 m/h for 10 min.
drainage system (collecting rainwater), while the hazardous
Subsequently, the average and worst case scenarios
waste (1% sludge) was stored at a hazardous waste disposal
increased their modelled interferences. In the average scen-
site. In the case of adsorption, no concentration process has
ario, 1 mg/L natural iron and 1 mg/L natural manganese
yet been applied from the industry data source. Additionally,
content were assumed with 2 mg/L added iron coagulant;
any rapid sand filtration in the adsorption model also used
the worst case scenario contained 3 mg/L natural iron and
the 1% concentration method applied in coagulation-
2.5 mg/L manganese. In the latter case we assumed that
filtration to remove hazardous flocs.
an additional 3 mg/L iron was needed due to the level of arsenic and unfavourable quality of the water, in spite of
LCA methodology
the fact that 3 mg/L of in-situ coagulant was already present in the water as coagulant. A relatively high oxidant demand
Boundary conditions for the model included only steps
(10 mg/L KMnO4) was also assumed, which is not rare to
necessary for arsenic treatment. Plant infrastructure, which
use in Hungarian waters due to the high humic and
is currently not an issue, municipalities in Hungary are
52
Table 1
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Design parameters used in GaBi and scenario descriptions of the coagulation-filtration technology
Good scenario
Average scenario
Worst scenario
Unit
Parameter comments
Initial arsenic concentration
50
50
50
μg/L
Uniform initial value
Initial (natural) iron concentration
Negligible
1.0
3.0
mg/L
Uniform initial value
Initial (natural) manganese concentration
Negligible
1.0
2.5
mg/L
Uniform initial value
Input flow rate
509
539
553
m3/day
Calculated by iteration; based on treated water flow rate & backwash demand
Treated water flow rate
500
500
500
m3/day
Uniform initial value
Air oxidant used
40.8
43.1
44.2
Nm3/day
8% total flow
KMnO4 dose
0.5
3.0
10.0
mg KMnO4/L
Assumed; based on typical values; partial data in model
FeCl3 coagulant dose
0.5
2.0
3.0
mg Fe/L
Assumed; based on typical values; partial data in model
Filtration velocity
8.5
4.3
3.3
m/h
Assumed; based on typical values
2
Design parameters
Initial water quality
Water quantity
Design parameters
Filtration area
2.5
5.2
7.0
m
Calculated; input flow rate divided by filtration speed
Filter layer depth
1.5
1.5
2
m
Assumed; based on typical values; worst case assumes two layer, dual-density sand
Sand filter volume
3.75
8.1
14.0
m3
Calculated; filtration area multiplied by depth of filter layer
Floc concentration
1.25
9.5
23
mg/L
Calculated; 1 mg/L dissolved iron or manganese forms 2 mg/L Mn and Fe flocs; 1 mg/L added KMnO4 forms 0.5 mg/L Mn-flocs
Filter sand loading capacity
1,000
1,000
1,700
g/m2
Assumed; based on typical values; worst case assumes two layer, dual-density sand
Calculated RSF BW frequency
96
24
26
hours
Calculated; loading capacity of the filter divided by the filtration velocity and total concentration of flocs
Req’d backwash frequency
48
24
24
hours
Backwash is needed at least after 48 h of operation
Req’d backwash volume per day
9.4
39.0
52.0
m3/day
Calculated; filtration area × 15 m/h backwash intensity and 0.5 h of backwash; BW req’d every 2nd day in best case
Backwash air used per day
25
52
70
Nm3/day
Calculated; filtration area × 60 m/h backwash air intensity for 10 min; BW req’d every 2nd day in best case
Percent backwash of total purified water
1.8
7.5
9.4
%
Calculated; amount of backwash water divided by input flow rate
Hazardous waste annually
34.1
142.0
191.1
m3
Calculated; 1% of the amount of BW water per day multiplied by 365 days
Non-hazardous waste annually
3,378
14,054
18,919
m3
Calculated; 99% of BW per day
412.02
824.04
824.04
MJ/year
Calculateda
Energy demand Pumping of backwash water
(continued)
C. J. Jones et al.
53
Table 1
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continued
Design parameters
Good scenario
Average scenario
Worst scenario
Unit
Parameter comments
Req’d mixing
226.59
353.15
396.4
MJ/year
Assumed TETRAMIX static mixer
FeCl3 coagulant
Negligible
210
2,180
km
Assumed; shipping is 1, 2, and 4 times a year for the good, average, and worst, respectively
KMnO4 oxidant
Negligible
210
2,180
km
Assumed; shipping is 1, 2, and 4 times a year for the good, average, and worst, respectively
Quartz sand
Negligible
210
545
km
Assumed; 1 shipment; replacement in every 8 years
Shipping distances
a
For the calculation of energy demand the following equations were used: P(watts) ¼ flow capacity (Q) × fluid density (p) × gravity (g) × height differential (ΔH )/time conversion;
E(joules) ¼ P × t.
required to support, and spare parts were not considered
emitted in the model from cradle-to-grave (Guinée et al.
in the model. Additionally, steps that are necessary but
; EN ISO ).
unassociated with arsenic removal, or identical in both technologies such as chlorination disinfection, were neglected. In Figure 1, light grey boxes indicate steps which were
RESULTS AND DISCUSSION
included, and dark grey boxes indicate the excluded steps. Some steps also relied on calculations from partially avail-
Each impact category is broken down into its greatest contri-
able or assumed data due to high financial cost for data or
butors in Figures 2 and 3.
lack of information; these are shown in dashed light grey
A key observation would be the lack of effect caused by
boxes and detailed in Tables 1 and 2. Results produced by
electricity use, both independently and relatively between
these models are only valid within the context of these con-
the technologies. Electricity has in the past been claimed
ditions and the described water quality scenarios.
to be one of the greatest contributors to environmental
Technologies were studied using GaBi 5, software which
impacts in water systems (Raluy et al. ; Godskesen
was made commercially available from PE International; its
et al. ), however as seen in Figures 2 and 3, it does not
professional database was used as a source for datasets on
appear once as a top contributor for environmental
production of chemicals, energy, and transportation as
impact. This does not say electricity is without impact over-
well as European environmental impact information.
all; for example, the pumping demand of water over a year is
Inputs for the individual technologies, and details regarding
a huge electricity consumer. In our present case, initial
their operation, are from industrial sources and pilot/full-
attempts were made at modelling plant-wide electricity
scale systems. Variations in these scenarios listed in Tables 1
pumping requirements, and this plant electricity predictably
and 2 can be seen as error bars, illustrating the effects of
demonstrated a majority impact contribution to categories
dynamic water chemistries and technology differences.
such as global warming potential (GWP). It quickly
Impact analysis was conducted on categories of global
became apparent that inclusion of plant electricity would
warming, eutrophication, ozone layer depletion, acidifica-
lead to more uncertainty and distract from our purpose in
tion, human toxicity, terrestrial toxicity, freshwater aquatic
examining the technologies at hand; pumping is a universal
toxicity, and marine aquatic toxicity potentials, as well as
requirement for plant functionality regardless of the technol-
abiotic depletion of elements and fossil fuels. Each of the
ogy installed. As such, plant electricity was treated as
categories use an equivalence method calculated to evaluate
external to our LCA focus and neglected in the rest of the
potential environmental impact; this technique is then used
study. Electricity still has an effect from within production
to compare each chemical or material that is consumed or
of materials involved in this study, but the point is that it
54
Table 2
C. J. Jones et al.
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Design parameters used in GaBi and scenario descriptions of the adsorption technology
Design parameters
Good scenario
Average scenario
Worst scenario
Unit
Parameter comments
50
50
50
μg/L
Uniform initial value
Initial water quality Initial arsenic concentration Natural iron concentration
Negligible
1.0
3.0
mg/L
Uniform initial value
Natural manganese concentration
Negligible
1.0
2.5
mg/L
Uniform initial value
Input flow rate
502
524
532
m3/day
Calculated by iteration; based on treated water flow rate & both backwash demands
Treated water flow rate
500
500
500
m3/day
Uniform initial value; based on typical values
Oxidant air used
0
43.3
44.4
Nm3/day
8% total flow
KMnO4 dose
0
2.5
8
mg KMnO4/L
Assumed; based on typical values; partial data in model
Filtration velocity
0
7.52
5.52
m/h
Assumed; based on typical values
2
Water quantity
Design parameters
Filtration area
0
2.90
4.02
m
Calculated; input flow rate divided by filtration speed
Filter layer depth
0
1.5
2.0
m
Assumed; based on typical values; worst case assumes two layer, dual-density sand
Sand filter volume
0
4.35
8.04
m3
Calculated; filtration area multiplied by depth of filter layer
Floc concentration
0
5.25
15
mg/L
Calculated; 1 mg/L dissolved iron or manganese forms 2 mg/L Mn and Fe flocs; 1 mg/L added KMnO4 forms 0.5 mg/L Mn-flocs
BW air used
0
52
70
Nm3/day
Calculated; filtration area × 60 m/h backwash air intensity for 10 min; BW req’d every 2nd day in best case
Calculated RSF BW frequency
0
25.4
24.2
hours
Calculated; loading capacity of the filter divided by the filtration velocity and total concentration of flocs
Chosen RSF BW frequency
0
7
24
hours
Adsorbent BW frequency
7
5
7
day 3
Provided by industry
Req’d adsorbent BW volume
5
5
5
m
Provided by industry
Percent BW of total purified water annually
<1
4.5
6.0
%
Provided by industry and calculated
Regenerations annually
3
3
4
–
Provided by industry 3
Regeneration water demand
162
162
216
m /year
Provided by industry
NaOH (25%) for regeneration
14,440
14,400
19,200
L/year
Provided by industry
NaClO (12%) for regeneration
171
171
228
L/year
Provided by industry; partial data in model
HCl (35%) for regeneration
267
267
356
L/year
Provided by industry
3
Regeneration wastewater
99.6
99.6
132.8
m /year
Provided by industry
Hazardous waste annually
55.0
144.0
196.1
m3/year
Provided by industry and calculated; 1% of RSF BW and all regen waste
Non-hazardous waste annually
698
8535
11,596
m3
Calculated; all adsorbent BW (continued)
C. J. Jones et al.
55
Table 2
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continued
Good scenario
Average scenario
Worst scenario
Unit
Parameter comments
Pumping of backwash water
39.24
863.28
863.28
MJ/year
Calculated
Regeneration
151.35
151.35
201.4
MJ/year
Provided by industry
Req’d mixing
0
353.15
396.4
MJ/year
Assumed TETRAMIX static mixer
Adsorbent
210
9,000
9,000
km
Assumed; 1 shipment; replacement every 10 years (good and average scenario), 7 years (worst scenario)
Quartz Sand
Negligible
210
545
km
Assumed; 1 shipment; replacement in every 8 years
NaOH solution (25%)
Negligible
210
2,180
km
Assumed; shipping is 1, 2, and 4 times a year for the good, average, and worst, respectively
NaClO solution (12%)
Negligible
210
2,180
km
Assumed; shipping is 1, 2, and 4 times a year for the good, average, and worst, respectively
HCl solution (12%)
Negligible
210
2,180
km
Assumed; shipping is 1, 2, and 4 times a year for the good, average, and worst, respectively
Design parameters
Energy demand
Shipping distances
was not a direct consequence of arsenic removal technology
benchmark, comparing the environmental effect of arsenic
use.
removal against such shipping and handling impacts. Shipping and handling for products and the associated
A subject of much debate is hazardous waste manage-
fuel production were major contributors in several impact
ment (Figure 3). Under ‘ideal’ best case water conditions,
categories (Figures 2 and 3), leading to two observations.
coagulation-filtration was capable of producing nearly half
Firstly, coagulation-filtration had roughly half the impact of
the waste of the adsorption. However, both technologies
adsorption in several impact categories; this was due to the
produced relatively the same amount of hazardous waste
number of products and larger quantities required by the
in average and non-ideal worst case scenarios. Additionally,
adsorption technology. These impacts can be greatly reduced
this particular adsorption technology did not have a standar-
by procuring materials near to a plant and within Hungary,
dized waste concentration technique for the adsorbent
shipping in bulk, and combining goods in one shipment. Sec-
media, an important tool in further mitigating waste and sig-
ondly, it is worth noting that the total mass required for one
nificantly lowering its environmental impact and cost;
regeneration was nearly the quantity required to support
prefilters,
coagulation-filtration for an entire year. As such, reducing
technique seen in coagulation.
the chemical demand for regeneration would greatly minimize this shipping burden and overall impact.
however,
did
use
the
1%
concentration
Finally, in modelling these technologies, one major drawback was the lack of solid production information.
It is important to note that a more generalized model
Assumptions had to be made to fill this information gap,
without a connection to a real-world scenario, comparing
with remarkable consequences as seen in GWP in Figure 2.
only technical aspects, might exclude this shipping and
The assumed production for the adsorbent is for common,
handling impact. In this study, one technology required
easily produced oxide; note this is now one of the highest
both a large chemical supply and costly international ship-
contributors to GWP. This value could be lower for the
ping; the other required neither. Including this information
actual material, but it is possible that more uncommon or
is crucial in accounting for the impact due to the operation
difficult-to-make products would generate several times to
of these technologies. One could also use this example as a
orders of magnitude higher an impact. Gaining an honest
56
Figure 2
C. J. Jones et al.
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Environmental impact assessment from the top four contributors in each category. Note that electricity is not a major direct contributor. An equivalence method for each category is applied to chemicals and materials in accordance with International Organization for Standardization (ISO) and Institute of Environmental Sciences (CML) methods. An example of the equivalence method is given (top right); carbon dioxide is set as a standard value for GWP, and other compounds are given relative values through the cited ISO method. Note: scale bars for all figures represent extremes resulting from calculated best, average, and worst case scenarios and do not have relation to standard deviation.
representation of the technology landscape will require
Costs could also be significantly reduced through a
modelling more solutions to the arsenic problem, as well
number of other changes. Regenerations for the media
as further compliance from industries to fully participate
were costly due to high chemical demand; sodium
in such studies.
hydroxide itself made up nearly 96% of the regeneration expense. Reduction of all shipping distances and other
Cost analysis
quantities of the various chemicals required would also decrease costs. Many prices, however, are difficult to
The two technologies modelled differ greatly in the location
reduce if water standards are to be met for particularly
of their greatest financial burden, as illustrated in Table 3.
difficult water systems, so several parameters cannot
Coagulation-filtration was the cheaper of the two technol-
easily be reduced, e.g. potassium permanganate for
ogies; its largest expense lies in proper hazardous waste
arsenic oxidation, or the reduction of sand volume used
disposal, and excessively so in the worst case scenario. For
in the filter tank. Future technologies may be required,
adsorption, foreign-purchased adsorbent media in the
such as means to further reduce, extract, or make use of
worst case scenario was the single most expensive line
hazardous chemicals from waste, before these costs can
item in the study.
be diminished.
57
Figure 3
C. J. Jones et al.
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Adsorption technology shifts impacts to pre-operational phases in comparison to coagulation-flocculation. Fuel production or shipping is the first contributor for five of the potentials due to transportation requirements. Abiotic depletion is the only category with greater impact than adsorption in the average case; however, overlap and variability are high. Hazardous waste production for coagulation-filtration is half that of adsorption in the ideal scenario, while nearly equivalent in non-ideal scenarios. All toxicity potentials indicate less risk in the majority of coagulation-filtration scenarios.
58 C. J. Jones et al.
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Annual cost analysis comparing modelled operation-phase coagulation-filtration and adsorption technologies, in Hungarian forints and euros. System was built off expenditures for a plant with a daily water distribution of 500 m3/day
Coagulation-filtration
Adsorption
Good scenario
Average scenario
Worst scenario
Good scenario
Design parameter
Forint
Euro
Forint
Euro
Forint
Euro
Forint
Quartz sand
20,000
66
40,000
131
75,000
246
–
Average scenario
Worst scenario
Euro
Forint
Euro
Forint
Euro
–
40,000
131
75,000
246
597,455
490
149,364
1,959
896,182
2,938
–
–
–
–
–
–
Adsorbent media
–
–
–
–
–
–
5,775,000
18,934
7,150,000
23,443
10,214,286
33,489
KMnO4 oxidant
88,288
289
529,729
1,737
1,765,764
5,789
–
–
438,883
1,406
1,394,679
4,573
All regeneration chemicals
–
–
–
–
–
–
1,730,721
5,674
1,730,721
5,674
2,307,628
7,566
NaOH
–
–
–
–
–
–
1,656,000
5,430
1,656,000
5,430
2,208,000
7,239
NaHClO
–
–
–
–
–
–
20,520
67
20,520
67
27,360
90
HCl
–
–
–
–
–
–
54,201
178
54,201
178
72,268
237
Energy for mixing
1,669
5
2,715
9
2,715
9
–
–
2,715
9
2,715
9
Energy for sand filter backwash
3,090
10
6,180
20
6,180
20
–
–
6,180
20
6,180
20
Energy for sorbent filter backwash
–
–
–
–
–
–
294
1.0
294
1.0
294
1.0
Energy for regeneration
–
–
–
–
–
–
111
0.4
111
0.4
149
0.5
Hazardous Waste Disposal
1,706,250
5,594
7,153,090
23,453
9,555,000
31,328
2,750,000
9,016
7,198,500
23,602
9,807,300
32,155
Total operational costs per year
1,970,329
8,290
8,331,752
34,715
12,303,556
51,264
10,256,127
33,626
16,554,690
54,278
23,805,516
78,051
Technology contribution to cost of 1 m3 water to users
10.63
0.03
42.47
0.14
61.18
0.20
56.35
0.18
86.85
0.30
130.80
0.43
Water Science & Technology: Water Supply
FeCl3 coagulant
Life cycle analysis of Hungarian drinking water arsenic removal technologies
Table 3
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CONCLUSIONS
REFERENCES
Coagulation-filtration and cerium adsorption technologies
Arpke, A. & Hutzler, N. Domestic water use in the United States. Journal of Industrial Ecology 10 (1–2), 169–184. Arsenic in drinking water. Fact sheets WHO (World Health Organization) http://www.who.int/mediacentre/factsheets/ fs210/en/index.html (accessed 19 February 2009). Directive 98/83/EC on the quality of water intended for human consumption Accessible at http://eur-lex.europa.eu/ LexUriServ/LexUriServ.do?uri=CELEX:31998L0083:EN: NOT (accessed 15 May 2012). Dodbiba, G., Nukaya, T., Kamioka, Y., Tanimura, Y. & Fujita, T. Removal of arsenic from wastewater using iron compound: comparing two different types of adsorbents in the context of LCA. Resources, Conservation and Recycling 53 (12), 688–697. Driehaus, W. Technologies for arsenic removal from potable water. In: Natural Arsenic in Groundwater: Occurence, Remediation and Management (J. Bundschuh, P. Bhattacharya & D. Chandrasekharam, eds). A.A. Balkema Publishers, Leiden, The Netherlands, pp. 189–203. EN ISO 14044 Environmental Management – Life Cycle Assessment – Requirements and Guidelines. Floch, J. & Hideg, M. Application of ZW-1000 membranes for arsenic removal from water sources. Desalination 162 (1–3), 75–83. Godskesen, B., Zambrano, K. C., Trautner, A., Johansen, N. B., Thiesson, L., Andersen, L., Clauson-Kaas, J., Neidel, T. L., Rygaard, M., Kloverpris, N. H. & Albrechtsen, H. J. Life cycle assessment of three water systems in Copenhagen – a management tool of the future. Water Science and Technology 63 (3), 565–572. Government Decree No. 201/2001. (X.25.) On the quality standards and monitoring of drinking waters 2001 Accessible at http:// net.jogtar.hu/jr/gen/hjegy_doc.cgi?docid=A0100201.KOR (accessed 28 March 2012). Gregor, J. Arsenic removal during conventional aluminiumbased drinking water treatment. Water Research 35 (7), 1659–1664. Guinée, J. B., Gorrée, M., Heijungs, R., Huppes, G., Kleijn, R., de Koning, A., van Oers, L., Wegener Sleeswijk, A., Suh, S., Udo de Haes, H. A., de Bruijn, H., van Duin, R. & Huijbregts, M. A. J. Handbook on Life Cycle Assessment. Operational Guide to the ISO Standards. Kluwer Academic Publishers, Dordrecht. Han, B., Runnells, T., Zimborn, J. & Wickramasinghe, R. Arsenic removal from drinking water by flocculation and microfiltration. Desalination 145 (1–3), 293–298. Hungarian Technical Guidelines MI-10-135-4 Water treatment equipment. Elimination of iron and manganese. Laky, D. & István, L. Arsenic removal by ferric-chloride coagulation – effect of phosphate, bicarbonate and silicate. Water Science and Technology 64 (5), 1046–1055.
were modelled competitively on an example Hungarian municipality affected by arsenic. Nine out of 10 considered LCA environmental impact categories favour coagulation, however realistic variations in water chemistry and technical aspects lead to some environmental impact overlap. A more moderate waste impact during the adsorption operation was found to be countered by impacts generated in production and delivery, however this shift of waste and other environmental impacts to pre-operational phases may in part make disposal and treatment easier to handle. Regeneration was observed to be the single most costly, chemically demanding, and environmentally taxing portion in operation of the adsorbent, requiring nearly the same mass of materials for one regeneration as what is needed to support the coagulation-filtration technology for an entire year. Efforts by producers of adsorption media to reduce the number and cost of required regenerations, as well as efforts to produce locally, would drastically increase their appeal to municipalities. This study used LCA methodology to enumerate and evaluate the numerous technical, economical, and environmental concerns in choosing an appropriate arsenic removal technology. Given their local water conditions, municipalities might use this study to examine and compare which operational setup will work best for them. However, no ‘magic bullet’ for arsenic contamination has yet been found for all water conditions, and individual choices made for hazardous waste mitigation are fundamental for whatever technology is chosen.
ACKNOWLEDGEMENTS This work was supported by a Fulbright student grant and the Wagoner Foreign Study Fellowship. We kindly thank Dr István Licskó (associate professor, Budapest University of Technology and Economics) and Dr István Zádor (research engineer, S- Metalltech 98 Ltd) for their advice and guidance.
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Marchiset-Ferlay, N., Savanovitch, C. & Sauvant-Rochat, M. P. What is the best biomarker to access arsenic exposure via drinking water? Review. Environment International 39 (1), 150–171. Mészáros, G. Subsurface Water Treatment. Eötvös József College – Technical Faculty, Baja. Mohan, D. & Pittman, C. U. Arsenic removal from water/ wastewater using adsorbents – a critical review. Journal of Hazardous Materials 142 (1–2), 1–53. MSZ 445, 1989 Hungarian Standard on the quality of drinking water. Petrusevski, B., Sharma, S. K., Schippers, J. C. & Shordt, K. Arsenic in drinking water. Thematic Overview Paper No. 17. IRC, Delft, The Netherlands.
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Raluy, G., Serra, L. & Uche, J. Life cycle assessment of MSF, MED and RO desalination technologies. Energy 31, 2361–2372. Rahman, M. Arsenic and contamination of drinking-water in Bangladesh: a public-health perspective. Journal of Health, Population and Nutrition 20 (3), 193–197. Smedley, P. L. & Kinniburgh, D. G. A review of the source, behavior and distribution of arsenic in natural waters. Applied Geochemistry 17 (5), 517–568. Wickramasinghe, S. R., Han, B., Zimbron, J., Shen, Z. & Karim, M. N. Arsenic removal by coagulation and filtration: comparison of groundwaters from the United States and Bangladesh. Desalination 169 (1–3), 231–244.
First received 23 January 2013; accepted in revised form 21 May 2013. Available online 12 September 2013
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Technical inefficiency effects in a stochastic production function for managerial incentives in public water utilities Silver Mugisha
ABSTRACT Performance of state-owned water utilities in developing countries is often weak. This study estimates the impact of managerial incentives upon efficiency using a stochastic frontier production function with revenue water as the output. The empirical analysis utilises unbalanced panelled data consisting of revenue water, connections, operating expenditure, water delivered and staff, from Uganda’s 19 National Water and Sewerage Corporation (NWSC) sub-utilities for a 9-year period, 2002–2010. The inefficiency effects are modelled as a function of utility-specific variables: service coverage, level of financial incentives, target difficulty, and year of observation. While financial
Silver Mugisha University of Florida, USA; Water Services Management, UNESCO-IHE, Delft, The Netherlands; and Institutional Development & External Services, National Water & Sewerage Corp., Uganda E-mail: silver.mugisha@nwsc.co.ug
incentives and increased service coverage improve efficiency, targets (such as the reduction of nonrevenue water) that are perceived as excessive by employees may reduce it. The findings suggest some policy implications: utility managers in the public water sector need to incorporate monetary incentives and increase service coverage to reduce non-revenue water. However, targets need to be set with great care and with transparency. Key words
| incentives, stochastic frontier production function, Uganda, water utilities
INTRODUCTION Non-revenue water (NRW) is defined as the difference
of water distribution pipes. There may be a much greater
between the system input volume of water and billed author-
financial and environmental return on investment (ROI)
ised consumption (Lambert ). According to Kingdom
from long-term inspection programmes focusing on large
et al. (), NRW is one of the major issues affecting
diameter distribution mains. Identifying and solving NRW
water utilities in the developing world. High levels of
issues early can lead to big savings over the lifetime of a
NRW reflect huge volumes of water being lost through
water pipeline. Many utilities look towards increasing bill-
leaks, not being invoiced to customers (generally reflecting
able water by increasing treatment capacity at the plant;
theft), or both. It seriously damages the financial viability
however by addressing and eliminating causes of non-
of water utilities through lost revenues, increased oper-
revenue water, the overall efficiency of the network of
ational costs, and reduced water quality. According to
distribution pipes can also be increased.
Asian Development Bank (), before cities consider
Clearly, from the definitions above, one of the surrogate
expanding their distribution networks, they should first
ways of reducing NRW in a water utility is to maximise
look to reduce NRW. This will lead to greater overall effi-
volumes of revenue water (sales), given a vector of oper-
ciency and financial sustainability. A key issue is whether
ational inputs. This paper investigates factors that influence
state-owned water utilities are capable of providing manage-
inefficiency using a stochastic frontier production function
rial incentives and setting reasonable targets that promote
for revenue water operations of utilities in Uganda’s National
performance improvements.
Water and Sewerage Corporation (NWSC). The model incor-
Increased levels of NRW can reflect large volumes of
porates specific incentives facing water utility managers
water being lost through leaks distributed across a network
(proxied by the ratio of maximum incentive payment to
doi: 10.2166/ws.2013.168
62
S. Mugisha
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Managerial incentives in public water utilities
Water Science & Technology: Water Supply
employee expenses) as well as the difficulty of meeting reduction of NRW targets (captured by required percentage
Table 1
|
|
14.1
1998
2010
research question: does service coverage, NRW target diffi-
1. Service coverage
48%
74%
culty, level of financial incentives and year of observation
2. Total connections
50,826
261,000
3. New connections per year
3,317
25,000
influence the level of utility inefficiencies in a production environment involving revenue water output?
4. Staff per 1,000 connections 36
6
5. Collection efficiency
65%
98%
6. NRW
60% (Kampala ∼ 33.2% (Kampala 65%; others ∼ ∼ 36%; other 57%) towns ∼ 15%)
7. Proportion metered accounts
65%
99.6%
8. Annual turnover (million USD)
10
65
NWSC PERFORMANCE AND CHALLENGES NWSC is a public corporation, currently operating in the 23 largest towns in Uganda. The operational structure is organised in such a way that there is a Head Office that plays the oversight role (performance regulation). Operations management
is
carried
out
through
19
sub-utilities
whose
2014
NWSC performance, 1998–2010
Performance indicator
improvement). Specifically, the paper investigates the
|
9. Profit (before depreciation) 4.0 (loss) (million USD)
12.5 (surplus)
relationship with the Head Office is regulated by sets of internally delegated performance contracts, which specify obligations, targets and incentive arrangements, among
expansion and enabled maintenance programmes to be
others. Some of the sub-utilities are comprised of clusters of
scheduled and implemented.
two or three towns. The sub-utilities have sufficient manage-
Despite the accomplishments, NWSC still faces chal-
rial autonomy, mainstreamed through the contracts, to
lenges of high NRW, among others. Specifically, the level
conduct operations and maintenance, and carry out delegated
of NRW in Kampala still remains high and reflects sub-
investments and staff recruitments. All the sub-utilities are
optimal operational performance. Over the past decade,
responsible for both water and sewerage operations.
NWSC has designed incentive plans to improve perform-
Mugisha et al. () outline a number of reform initiat-
ance. The most recent plans involve a Base Incentive,
ives in NWSC since 1998. Table 1 documents the positive
which is adjusted by meeting minimum service standards
impacts of these initiatives. Notably, service coverage in
and rewards for improving operating margins, improving
urban areas has increased from 48 to 74% (about 3.5 M
the working ratio, reducing NRW, and improving connec-
people are served as at 2010). In addition, new connections
tion efficiency. The latter three terms are given specific
increased from 3,300 to 25,000 per year. This trend is attrib-
weights – reflecting organisational priorities and local cir-
uted to the new connection policy that was introduced in
cumstances. In addition, reductions in total billing arrears
2004. The NWSC New Connection Policy involves pro-
are rewarded. An example of such an incentive plan for
vision of free new connection materials for both water and
Kampala Water Supply Area is shown in Box 1 below.
sewerage for the first 50 m of a customer’s connection. It
Of course, partial performance measures need to be aug-
was introduced through a tariff adjustment of about 9%
mented by advanced statistical techniques to obtain more
reflecting extra funding requirements. Non-revenue water
comprehensive indicators of performance. Such techniques
(NRW) has fallen dramatically: from about 60 to 33% (Kam-
help decision-makers understand the factors that influence
pala is at 36%, while other areas are now at 15%). On the
inefficiency in a production process where the output is
financial side, annual turnover (revenue) has improved
water sales (affected by NRW). Establishing such a pro-
from about US$10 million to US$65 million. Because of
duction function can go a long way in informing policy
this performance, operating profit after depreciation has
formulation processes to address inefficiencies in key
improved from losses of US$4.0 million to a surplus of
aspects of water utility operations in developing countries,
US$12.5 million. Positive cash flows have financed network
specifically focusing on NRW management strategies. This
63
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Managerial incentives in public water utilities
Water Science & Technology: Water Supply
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14.1
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Box 1 | Incentive Formula for Kampala Water Supply Area (2008–2010) The Incentive Fee (IF) is paid to the Operator on a prorated and weighted basis once the Operator exceeds the Minimum Performance Standards (MPS) for the parent indicators. The IF computation is prorated between the MPS and the desired target Performance Standards for parent indicators at the end of the Contract duration or the end of the respective months as the case may be. The improvements in a parent indicator that contribute to the IF are capped and are limited to the achievement of the desired target performance standard. If the Area improves performance beyond the desired target performance standards, that improvement beyond the desired performance standard, except for the cash operating margin, does not contribute to the IF: thus, the IF is capped. In this regard, the incentive fee for Kampala Water is computed as follows: General Formula IF ¼ BIF* (P/N) þ {X%*(OME–OMO)*[aWRpa þ bNRWpa þ cCEpa]} þ YTApa Specific Formula IF ¼ 139,037,000*(P/N) þ {15%*(OME–OMO)*[0.4WRpa þ 0.3NRWpa þ 0.3CEpa]} þ 10,000,000TApa where: BIF ¼ Ushs.139,037,000 is the Base Incentive (Ushs. – Ugandan Shillings) P ¼ the weighted number of minimum service standards that have been achieved for the given month N ¼ 100, is the total weighted number of minimum service standards to be achieved X% ¼ 15% is the agreed proportion (%) of the improvement in operating margin (OM) to be retained by the Operator as bonus OMO ¼ Minimum cash operating margin based on the agreed operating expenditure (Base Fee þ Performance Fee) and the set Minimum Standard for revenue collections OME ¼ the achieved cash operating margin during the month being evaluated WRpa ¼ Percentage incremental achievement in the improvement of the Working Ratio NRWpa ¼ Percentage incremental achievement in the reduction of Non-Revenue Water CEpa ¼ Percentage incremental achievement in the increase in Connection Efficiency TApa ¼ Percentage incremental achievement in the reduction of Total Arrears Z ¼ Ushs.10,000,000 is the agreed incentive attached to reduction of arrears (debts) a, b, & c ¼ Area specific weights for Parent Targets for computing Incentive Fees where a þ b þ c ¼ 1. The percentage incremental achievement (PIA) is computed as follows: PIA ¼ [(Ia – Im)/(It – Im)]*100 where: Im ¼ the minimum performance standard for a given indicator It ¼ the desired target performance standard for a given indicator for the month or quarter in question Ia ¼ the actual achieved performance level for a given indicator for the month. Source: NWSC ().
study aims at taking the analysis beyond partial efficiency
utility managers and regulators involved in design of incen-
measures to a more comprehensive technical efficiency
tive schemes and policies for NRW management in
analysis. The study results have strong implications for
developing countries.
64
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Managerial incentives in public water utilities
Water Science & Technology: Water Supply
PAST STUDIES
|
14.1
|
2014
public companies. Mugisha () investigates the effects of incentive applications on technical inefficiencies for NWSC
The measurement of the technical efficiency of a firm rela-
water sub-utilities. This study expands this analysis, using a
tive to other firms or to the ‘best practice’ in an industry
bigger sample in a pooled framework (covering more
has been of interest to water utility regulators, performance
years), to include more efficiency variables, and to determine
monitors and researchers. Berg & Marques () identify
the impact on technical efficiency by level of financial incen-
120 quantitative journal articles on water utilities, but only
tives, service coverage and target difficulty. In other words,
three on Africa—which is somewhat surprising given the sig-
the study is, partly, an extension of goal setting theory,
nificant amount of international donor funding that has
which Mugisha () does not cover.
gone into the region. So this paper fills some gaps in literature by determining factors that influence inefficiency of water utilities. Therefore, this study increases the number of technical efficiency studies on Africa. Moreover, it is one of the few studies that investigate environmental factors that affect efficiency in a production function that incorporates NRW.
EFFICIENCY FRONTIER MODEL FOR PANEL DATA Consider a translog stochastic production frontier for panel data,
The study draws upon work by Battese & Coelli () who proposed a model for technical inefficiency effects in
ynt ¼ β 0 þ
K X
a stochastic frontier production function for panel data. The model estimates the parameters of the stochastic frontier
and
inefficiency
model
simultaneously,
given
distributional assumptions associated with panel data on
i¼1
þ
K X
β i ln xint þ
K X K 1X β ln xint ln x jnt 2 i 1 j¼1 ij
λi ln xint t þ ϕ1 t þ ϕ2 t2 þ vnt unt
i¼1
n ¼ 1, 2, . . . , N; t ¼ 1, 2, . . . , T
(1)
the sample firms. According to Coelli & Battese (), provided the effects are stochastic, the model permits the
where ynt is the log of output (quantity of delivered water); ln
estimation of both technical change in the stochastic fron-
xint is the log of i-th input quantity; t is a time trend; vnt is an
tier and time varying technical inefficiencies. The current
error term (noise) that picks up what the model cannot
study applies this model to unbalanced panelled data of
explain; unt is the inefficiency term, preceded with a negative
NWSC’s utilities for the period 2002–2010.
sign because inefficiency means less output; and the Greek
There have been many applications of frontier pro-
letters depict unknown parameters to be estimated. Accord-
duction functions to water utilities over the years. These are
ing to Coelli et al. (), the vnt is assumed to be
summarised by Abbott & Cohen () and illustrated further
independent and identically distributed (iid) N(0, σv 2)
by Berg (). Mugisha et al. () outline the use of internal
random errors, distributed independently of unt. The unt
incentive contracts to improve water utility performance for
term is a non-negative random variable, associated with tech-
the case of Uganda’s NWSC. They conclude that no simple
nical inefficiency of production, which is assumed to be
recipe for promoting efficiency exists. However, they point
independently distributed, such that unt is obtained by trunca-
out useful ingredients, including proper contract framework
tion (at zero) of the normal distribution with mean, znt δ and
design, competition for managerial responsibility, effective
variance, σ 2; znt is a (1 × m) vector of explanatory variables
business planning, performance monitoring and the use of
associated with the technical inefficiency of production for
managerial incentives. Correia & Marques () apply a mul-
firms over time; δ is an (m × 1) vector of unknown coefficients
tiproduct translog cost function, using unbalanced panelled
to be estimated. The explanatory variables are discussed in
data to investigate the effects of ownership, size and diversifi-
greater detail in the next section.
cation on efficiency in Portuguese water utilities. They find
Battese & Coelli () state that the model of ineffi-
that private companies are slightly more efficient than
ciency effects can only be estimated if the inefficiency
65
S. Mugisha
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Managerial incentives in public water utilities
Water Science & Technology: Water Supply
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14.1
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2014
effects are stochastic; and the error distribution is specified.
considered for empirical application of our model specified
Hence, the analysis needs to include statistical hypothesis
above. We chose this period because it represents the time
tests about the inefficiency effects. These and other null
when internal incentive contracts have taken root in
hypotheses of interest are tested using the generalised
NWSC operations. The efficiency variables considered in
likelihood-ratio, LR, defined by Equation (2),
this study include; promised financial incentive, revenue water target difficulty, service coverage, and time trend,
LR ¼ 2 ln½L(H0 )=L(H1 )
(2)
which are used to explain the differences in inefficiency effects among NWSC utilities. The use of these variables
where L(H0) and L(H1) are the values of the likelihood func-
illustrates policy variables that are viewed as critical for
tion under the specifications of the null hypotheses, H0 and
NRW management in developing countries. A summary of
H1, respectively. Asymptotically, the LR statistic has a chi-
the sample data on the different variables in the stochastic
square distribution with degrees of freedom equal to the
frontier and inefficiency model, used in this study, is pre-
number of restrictions involved. It should be noted that
sented in Table 2.
where the null hypothesis includes the restriction γ ¼ 0 (a
We take the model of the production function at a single
point on the boundary of the parameter space), the likeli-
connection level because this is the primary unit of focus in
hood ratio statistics will have asymptotic distribution equal
the management of NRW in developing countries. In
to a mixture of chi-square distribution (1=2)χ20 þ (1=2)χ 21 .
addition, the production variables of water supplied, staff,
The maximum likelihood technique is proposed for simul-
operating expenditure and connections are all highly corre-
taneous estimation of the parameters of the stochastic
lated and considering them as separate production input
frontier and the model for the technical inefficiency effects.
variables in that form would result in statistical bias. More-
The likelihood function is expressed in terms of the variance
over, dividing by connections, all through the variables, is
parameters as shown in Equations (3) and (4),
aimed at estimating a production function at the level of individual connected unit in a variable returns to scale
σ 2s
¼
σ 2v
þσ
2
(3) Table 2
γ ¼ σ 2 =σ 2s
The technical efficiency of production for the n-th firm at the t-th observation, which is between zero and one and is inversely related to technical inefficiency, is defined by Equation (5). The efficiencies are estimated using a predictor that is based on the conditional expectation exp ( unt), presented in Coelli et al. (), and is incorporated in FRONTIER Version 4.1. TEnt ¼ expð unt Þ
|
(5)
Summary statistics for variables in the stochastic frontier production function for NWSC sub-utilities (per annum)
(4)
Sample
Standard
Min.
Variable
mean
deviation
value
1. Revenue water (m3)
2,376,345
5,911,924
130,890 30,293,700
2. Water 3,649,026 production (m3)
10,044,216
166,951 50,444,455
3. Connections (No.)
9,528
23,259
597
146,243
4. Staff (No.)
62
121
8
715
5. Op.Ex. (×1000,Ushs)
2,519,540
6,215,943
198,316 39,692,746
6. Service coverage (%)
64
15
31
90
30.65
8.50
218.22
7.15
92.09
142.86
DATA AND EMPIRICAL APPLICATION
7. Max. earnable 53.92 incentive (%)
Unbalanced panelled data on all NWSC sub-utilities (12–19
8. Revenue water target difficulty (%)
sub-utilities making 146 observations in a pooled framework) from Uganda for the period 2002–2010 are
106.24
Source: Analysis from NWSC Audited Reports, 2002–2010.
Max. value
66
S. Mugisha
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Managerial incentives in public water utilities
Water Science & Technology: Water Supply
(VRS) framework. According to Coelli et al. (), once a model involves efficiency variables which relate to scale,
|
14.1
|
2014
Year/t is the year of observation (expressed in terms of 1, 2, ………..,9)
the elasticity is given by the proportionate effect on pro-
βs are unknown coefficients to be estimated
duction
δs are unknown scalar quantities to be estimated. A negative
of
changes
in
input
variables
and
the
environmental variable. Since all efficiency variables in
value of δj would mean that the corresponding environ-
this study are not related to scale, we do not express any
mental variable has a positive impact on the reduction
of them per connection, except for input and output
of firm technical inefficiencies (see Equation (5)).
variables. The stochastic frontier production function, at connec-
We use the time trend in both the production frontier
tion unit level, to be estimated, is obtained from
estimation and the mean efficiency sub-equation because
Equation (1),
we want to observe the behaviour of revenue water output and inefficiency effects, over time. The expected signs of the βs and δs in Equations (6) and (7) are not
lnðRWit Þ ¼ β 0 þ β 1 lnðSit Þ þ β 2 lnðPit Þ þ β 3 lnðXit Þ
clear in all cases. However, in the NWSC case, the sum
þ β 4 t þ 0:5β 5 ðlnðSit ÞÞ2 þβ 6 lnðPit ÞlnðSit Þ
of the first-order input coefficients would be expected to
þβ 7 lnðSit ÞlnðXit Þ þ β 8 lnðSit Þt þ 0:5β 9 ðlnðPit ÞÞ2
be greater than unity, suggesting increasing returns to
þβ 10 lnðPit ÞlnðXit Þ þ β 11 lnðPit Þt þ 0:5β 12 ðlnðXit ÞÞ2
scale at a single connection level – in other words, a
2
þβ 13 lnðXit Þt þ β 14 t þ vit uit i ¼ 1, 2, . . . , N ðnumber of utilitiesÞ; t ¼ 1, 2, . . . , 9: (6)
change in inputs results in a bigger change in outputs. This is because sub-utilities tend to favour increased single connections as a way of increasing service coverage and maximising water sales (output). Kingdom et al.
where the subscripts i and t refer to the i-th utility and the
() suggest the need for strong incentives, autonomy
t-th observed data, respectively. The technical inefficiency
and commitment for staff involved in NRW activities. In
effects are assumed to be defined by
this case, the elasticity related to staff should have a positive sign, suggesting that increasing staff increases the
uit ¼ δ 0 þ δ I ðServ Coverageit Þ þ δ 2 ðIncentiveit Þ þ δ 3 ðTarget Diff it Þ þ δ 4 ðYearit Þ
production output of revenue water. However, extra staff (7)
may be involved in perpetuating illegal connections due to poor remuneration, greed and/or recruitment
ln represents the natural logarithm (i.e., to base e)
history, leading into negative elasticity. This observation
RW represents revenue water (water sales) per connection
is in line with a recent study by Delavallade (),
(cubic m per connection)
which associates more corruption with firms that
S represents staff per connection (number per connection)
are less competitive. Moreover, additional staff may lack
P is the water production per connection (cubic m
competencies in respect to NRW reduction and, by
per connection) X is the operating expenditure per connection (Ushs per connection) vit is the error term (where noise is defined in the previous section) Serv-Coverage is the proportion of target population that is served with water services (%) Incentive is the percentage of maximum promised incentives to total employee costs (%) Target-Diff is the proportion of negotiated RW target to average RW value for the previous 12 months (%)
default, may not be helpful in water loss control activities. Another variable we analyse in this study is water produced (P). An increase in water produced per connection is expected to result in increased revenue water if utility employees have strong incentives to maximise revenue water. In NWSC sub-utilities where revenue water is a priority for maximising cash operating margins (revenue collections minus expenditure), the elasticity with respect to this input is expected to be positive. However, more water per connection may mean that the network is more pressurised, leading to more leaks and bursts,
67
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Managerial incentives in public water utilities
Water Science & Technology: Water Supply
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14.1
|
2014
resulting in a negative coefficient (interpreted as elas-
who win contracts through their competing for ‘lead-part-
ticity). Part of the additional water supply may also be
ner’ responsibilities, where the main evaluation criteria
consumed by inactive (suppressed) accounts whose con-
incorporate competitive targets. After selecting a lead part-
sumption is not being monitored. The associated theft
ner, he/she then selects a team and obtains agreement for
may not be deterred by utility managers and staff or it
specified ‘winning’ targets. Therefore, target difficulty is
could be facilitated by bribes. All these factors can con-
self-imposed through a competitive managerial process.
tribute to an increase in NRW.
However, target difficulty can be a strong perverse incen-
The other input parameter in Equation (6) is operating
tive leading to internal squabbling and complaints.
expenditure (X). An increase in operating expenditure per
Consequently the sign of the coefficient is unclear in the
connection is expected to improve capabilities and motiv-
case of NWSC utilities: it could be positive or negative,
ation of operating teams to increase revenue water; we
depending on the feasibility of meeting targets and
would expect a positive elasticity for this input. In NWSC
employee perceptions of fairness.
distribution utilities, there is a strong orientation towards
The sign of the Year variable in the model for the ineffi-
cost optimisation: all performance priorities relate to
ciency effects (Equation (7)) is expected to be negative. This
increasing cash operating margins, which depends on
implies that the levels of inefficiency effects of utilities
increased revenue water. Therefore we expect a positive
should tend to decrease over time. That is, utility managers
elasticity with respect to this input. However, if increased
are expected to make their utilities more efficient as they
expenditures only end up financing unrelated activities like
gain experience and expertise. In addition, this time-trend
travel allowances, cleaning services, and meeting expenses,
is expected to pick up the influence of factors that vary sys-
this scenario could result into a negative elasticity.
tematically through time which are not included in the
Turning to the inefficiency drivers, we consider cover-
inefficiency model.
age, incentives, and the stretch required to meet targets. In
In line with Estache et al. () and Coelli et al. (),
developing countries, low water service coverage is expected
this study sets all period numbers to 1 and the utility num-
to be associated with high NRW due to illegal water uptake
bers vary from 1 to 146 (even though the data are from 12
by small scale independent providers to meet unsatisfied
to 19 firms over a period of 9 years). This is done to
demand. If this is the case, service coverage in the ineffi-
ensure that the Frontier program treats each observation
ciency equation (Equation (7)) is expected to have a
individually. According to Coelli et al. (), if this is not
negative sign. That is, we expect that greater levels of service
done, we would be imposing a restriction on the model
coverage will be associated with smaller values of ineffi-
that the technical efficiency of the i-th firm must be constant
ciency effects. On the other hand, the sign of the
across all the 9 years (which is imposed by the Frontier pro-
coefficient for the incentive index is expected to be negative
gram when panel data are used). Using this methodology,
if increased level of promised incentives reduces production
also in line with Berg & Lin (), we utilise pooled data.
inefficiency. This expectation stems from research by
In addition, Coelli et al. () point out that in order to
Mugisha () who finds that both financial and emotional
interpret the estimated first order parameters in the stochas-
incentives have positive effects on the level of technical
tic frontier analysis (SFA) function as production elasticities
efficiency in utility operations.
easily, evaluated at the sample means, we can express all
The sign of the coefficient of target difficulty in the inef-
data in deviations from the sample means. Consequently,
ficiency model is expected to have a positive sign to the
in this analysis, all data have been computed as deviations
extent that high targets put pressure on managers to inno-
from the column sample means. The time trend variable is
vate and increase performance. However, high targets
also in deviation from the mean, that is, as the mean of
which are set without a full acceptance by all ‘shop’ floor
the time trend variable is 4.658 (un-panelled data) in this
employees may yield resentment, especially after compar-
instance, the mean corrected trend variable is converted
ing their targets with those of perceived peer utilities.
from (1, 2, 3, 4, 5, 6, 7, 8, 9) to ( 3.658, 2.658, 1.658,
High targets are in the interest of NWSC utility managers
0.658, 0.342, 1.342, 2.342, 3.342, 4.342). Furthermore,
68
S. Mugisha
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Managerial incentives in public water utilities
Water Science & Technology: Water Supply
according to Berg & Lin (), multi-collinearity influences the statistical significance of the model. The robustness of a model can be checked through a multi-collinearity test, to
Table 3
|
|
|
14.1
2014
Maximum likelihood estimates
Type (logged variable)
Coefficient
t-ratio
determine whether two or more independent variables are
beta 0
very highly correlated: if two independent variables are
beta 1 (ln S)
0.026
0.030
0.862
beta 2 (ln P)
0.911
0.028
31.966
highly correlated, there is no way to tell how much effect each has separately. In our case, after running a multiple correlation test with all regressors, we do not find high correlations between them (the range is 0.007–0.65).
0.211
Standard error
0.216
0.045
4.778
beta 4 (t)
0.008
0.005
1.597
0.103
0.049
2.105
0.311
0.130
2.387
beta 5 (ln S)2 beta 7 (ln S*ln X)
The maximum likelihood estimates from the Frontier 4.1
25.274
beta 3 (ln X)
beta 6 (ln S*ln P)
RESULTS AND DISCUSSION
0.008
0.124
0.129
0.960
beta 8 (ln S*t)
0.015
0.021
0.735
beta 9 (ln P)2
0.222
0.124
1.801
0.095
0.138
0.691
beta10 (ln (P)*ln(X)) beta11 (ln(P)*t)
0.002
0.026
0.085
beta12 ((lnX)2)
0.097
0.240
0.403
beta13 (lnX*t)
0.023
0.026
0.900
beta14 (t*t)
0.009
0.005
1.879
delta 0
0.210
0.246
0.851
delta 1 (Serv-Coverage)
0.006
0.001
5.189
large number of connections is preferred. The estimated
delta 2 (Incentive)
0.276
0.082
3.364
coefficients of water production and operating expenditure
delta 3 (Target-Diff)
0.242
0.223
1.083
variables, 0.911 and 0.216, respectively, are significant, sig-
delta 4 (Year)
0.015
0.012
1.281
sigma-squared
0.019
0.003
6.582
Gamma
0.962
0.003
program for the translog specification in Equation (6) and inefficiency model in Equation (7) are shown in Table 3. The signs of the estimated β-coefficients of the first order parameters of stochastic frontier are as expected. Also, as expected, the sum of the first-order input parameters is greater than one, implying that a
nifying a strong relationship between these two inputs and output. Specifically, production input refers to the amount of water that the utility takes from the environment and makes available for distribution. It has the highest elasticity and consequently would imply that utilities would
301.331 2
All variables shown in Table 3 are logged. Log likelihood function ¼ 1.714 × 10 ; LR test of the one-sided error ¼ 9.508 × 101 with number of restrictions ¼ 6 [note that this statistic has a mixed chi-square distribution]; number of iterations ¼ 29; mean efficiency ¼ 0.86954030.
be able to better consolidate their results in terms of monetisation of delivered volumes by acting on the stage of
depends on the level of water production input per con-
water purification. In addition, the variable of water pro-
nection.
duced
interactive effect (at p ¼ 0.05) of staff increment on rev-
becomes
crucial
in
determining
a
positive
From
water
at
our
evidence,
average
values
the of
only
significant
elasticity of staff factor. The small and insignificant value
enue
of the staff coefficient could be due to a relatively high
connection is given by 0.311*P–0.103*S. The effect is
expenditure
per
number of employees that are not directly involved in rev-
obtained by taking first order derivatives of dependent
enue water enhancement activities. The coefficient for the
variable with respect to natural logarithm of staff per con-
Year indicates that the value of output has tended to
nection, for only significant coefficients. That means the
increase by a small but significant rate over the 9-year
effect of staff on revenue water depends, partly, on the
period. The squared and multiplicative terms for the Trans-
level of water production input per connection. The evi-
log model indicate that revenue water falls off with the
dence also shows that expenditure has a significant effect
square of staff size, but the coefficient on the multiplicative
(p ¼ 0.01) on revenue water. This means utilities with
term (S*P) is positive and significant. This interaction
higher levels of production and higher levels of expendi-
between staff and production variables shows that the
ture are likely to sell more water (at the connection unit
net effect of staff per connection on revenue water
level) than those with correspondingly low inputs.
69
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14.1
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We analyse the marginal productivities at different input
proportion of total employee costs tend to be less inefficient.
domain thresholds (quartiles) as shown in Table 4 to assess
In other words the effect of incentives on inefficiency (elas-
the consistency of the elasticities obtained in Table 3.
ticity of 0.28) is significant (p ¼ 0.01) at average values of
Clearly, Table 4 shows consistency in the signs and magni-
service coverage, target hurdle and time trend. This evi-
tudes of marginal productivities. The magnitudes of the
dence suggests that a 10% increase in promised level of
elasticities are also consistent.
incentives results in a 2.8% reduction in inefficiency of pro-
The estimated coefficients in the inefficiency model for
ducing a revenue water output. This result in turn shows that
all data points, at the mean, are of particular interest in
without the incentive plan, the average efficiency for the 146
this study. The Service Coverage coefficient is negative and
observations would have been about 0.83 instead of 0.87.
significant, which suggests that utilities with higher service
Similarly, target difficulty has a large but insignificant nega-
penetration are more efficient than those where service cov-
tive effect of 24.2% on inefficiency at average values of
erage is low. Of course, lower service coverage may also be
service coverage, promised incentive level and time trend.
due to the higher costs of reaching potential customers in
If significant, the findings would suggest that 1% increase
low density areas. Future work should incorporate network
in target difficulty results in 0.24% increase in inefficiency
density into the model, since this should contribute to effi-
of producing the output, indicating that without effects of
ciency. The negative and significant estimate for Incentive
target difficulty, the average efficiency of 146 observations
implies that utilities with higher target incentives as a
would have been 0.9 instead of 0.87. In other words, the positive coefficient for Target-Difficulty signifies that utilities
Table 4
|
with more hard-to-achieve revenue water targets could be Analysis of marginal productivities at different input domain levels
% Quartile
25
beta 0
50/median
0.110** 0.030
beta 1 (ln S)
0.165** 0.006
75
more inefficient. This issue warrants more attention in
Mean
0.231** 0.008
0.211**
future studies. The positive but small coefficient of Year suggests that the
0.029
inefficiencies of production of the utilities have tended to
beta 2 (ln P)
0.857**
0.902**
0.954**
0.911**
increase in the 9-year period. Judging from the trend of per-
beta 3 (ln X)
0.228**
0.174**
0.184**
0.216**
formance programmes in NWSC, this is not surprising given
beta 4 (t)
0.040*
0.016*
0.017*
0.008*
that a significant number of re-engineering policies were
0.126*
0.109*
0.116*
0.103*
beta 5 (ln S)2 beta 6 (ln S*ln P)
0.373**
0.318**
0.366**
implemented between 2002 and 2005, while the period
0.311*
2006–2010 has been devoted to consolidation and learning
0.124
from change management challenges encountered. Specifi-
beta 7 (ln S*ln X)
0.020
0.082
0.076
beta 8 (ln S*t)
0.026*
0.021*
0.029*
0.015
cally, some re-engineering programmes introduced include:
0.146*
0.243*
0.178*
0.222*
internal contracts in 2000–2004, stretch-out and one-minute
0.139*
0.144*
0.131*
2
beta 9 (ln P)
beta10 (ln (P)*ln (X))
0.095
management programme in 2003–2004, and a new connection policy in 2004. After 2005, only internally delegated area man-
beta11 (ln(P)*t)
0.022*
0.000
0.013
0.002
agement contracts (IDAMCs) have been used as a
beta12 ((lnX)2)
0.367*
0.231*
0.225*
0.097
management tool; and the impact of this technique seems to
beta13 (lnX*t)
0.012
0.022
0.015
0.023
have hit a plateau. In 2011, the corporation embarked on
beta14 (t*t)
0.006*
0.007*
0.005*
0.009*
major innovative programmes like e-payments, and Perform-
delta 0
0.040
0.003
0.034
0.210
ance, Autonomy, Creativity and Empowerment (PACE)
delta 1 (ServCoverage)
0.008** 0.005** 0.006** 0.006**
delta 2 (Incentive)
0.414** 0.253** 0.277** 0.276**
delta 3 (Target-Diff) delta 4 (Year)
contracts to return to earlier (more rapid) efficiency trends. Therefore, since the Year variable in the model may represent
1.619* 0.004
the scale of performance improvement programmes (PIPs)
0.971*
1.035*
0.242*
over the study period, the positive sign is not surprising. This
0.009
0.006
0.015*
result is in line with research by Colon () who concludes
(*) represents statistical significance at 5% level while (**) represents 1%.
that although internal contractual tools with their incentives
70
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mechanisms have brought positive changes in NWSC (decen-
The discussions above do reinforce the findings of past
tralisation, better corporate culture, capacity building and
studies. For example, the evidence obtained in this study
knowledge management), there is need for a new set of re-
shows consistent results with those obtained by Mugisha
engineering programmes to turn around recent performance
(). In the latter study, a log-linear input distance func-
trends. On the other hand, the estimate of the variance par-
tion is used with financial incentives being the only
ameter, γ, is close to one, which indicates that the
explanatory variable in the inefficiency sub-equation. In
inefficiency effects are likely to be highly significant in the
addition, the connections are modelled as output. Clearly,
analysis of value of output of the utilities.
this study shows that with the inclusion of more explana-
Generalised likelihood-ratio tests of null hypotheses,
tory variables in the inefficiency sub-equation, the
that the inefficiency effects are absent or have simpler speci-
significance of the incentive variable is enhanced. The
fications are presented in Table 5. The first null hypothesis
study also finds consistency with the assertion that monet-
specifies that a Cobb-Douglas function is a suitable specifica-
ary incentives promote efficiency in public water utilities.
tion: it is strongly rejected. The second null hypothesis,
Moreover, this study enhances our understanding of
which specifies that inefficiency effects are not stochastic,
target setting in water utilities, given that the attributes of
is also strongly rejected. The third null hypothesis, which
a good target are largely inconclusive in goal setting
suggests that the inefficiency effects are absent in the
theory. According to Li and Butler () the results of a
model is strongly rejected. Lastly, the fourth null hypothesis,
laboratory study demonstrated that goal rationales were
which suggests that inefficiency effects are not a linear func-
especially important for increasing goal commitment
tion of service coverage, incentive, target difficulty and year
when goals were assigned rather than participatively set.
of observation, is also strongly rejected at 1% level of signifi-
Similarly, Zetik & Stuhlmacher (), through a meta-
cance. These tests imply that the joint effects of these four
analysis, find that more difficult goals lead to higher out-
explanatory variables on the inefficiencies of production
comes than less difficult goals. In our study, the results
are significant although the individual influences may
seem to be the reverse: perceived difficult goals result in
differ in levels of statistical significance.
poor operating efficiencies. In the present analysis, it
Clearly, the inefficiency effects in the stochastic frontier
appears that inadequate participation of most NWSC uti-
production function are stochastic and are related to service
lity employees in target setting may be damaging
coverage, level of incentives, target difficulty and time of
employee motivation, leading to a potential impact of
observation.
Target-Difficulty on performance. The result suggests that the current target-setting process, which is mainly set through a competitive bidding process associated with
Table 5
|
Tests of hypotheses for parameters of the inefficiency frontier model
top managers, needs to be improved.
Log
χ20:99
Test
Null hypothesis
likelihood
value
statistica
Given model (from Equation (6))
171.42
CONCLUSIONS
H0: Cobb-Douglas; β5 ¼ β6……. ¼ β14 ¼ 0
136.03
21.67
70.78
H0: γ b ¼ 0
123.88
11.34
95.08a
is documented in Mugisha (). Managerial incentives
H0: γ ¼ δ0 ¼ δ1 ¼ δ2 ¼ δ3 ¼ δ4 ¼ 0
139.89
18.48
63.06a
have been adopted in Tanzania, Zambia, Kenya, some
H0: δ1 ¼ δ2 ¼ δ3 ¼ δ4 ¼ 0
139.81
13.28
63.22a
Nigerian states, and in other nations. The performance
a
a
The diffusion of water utility incentive programmes in Africa
On the value of test statistic indicates that it exceeds the 99th percentile for the corre-
sponding χ2-distribution: so the null hypothesis is rejected. b
If the parameter γ is zero, then the variance of the inefficiency effects is zero and the
model reduces to a traditional mean response function in which the variables, servicecoverage, incentive and target difficulty are included in the production function. In this case, the parameters δ0 and δ4 are not identified. Hence the value of the test statistic for this null hypothesis is obtained from χ23 -distribution.
improvements stimulated by managerial incentives bring hope to those who have doubted the ability of developing nations to overcome the many hurdles faced by decisionmakers (including political patronage, corruption, lack of transparency, weak governance, and poor information
71
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systems). The results of this model for technical inefficiency
efficient in reducing NRW. The evidence suggests that
effects using a stochastic frontier production function
investing in NRW reduction without contingent service cov-
suggest that these programmes can be expected to improve
erage enhancement plans (expansion plans) may not yield
performance. However, experience suggests that developing
optimal results. Third, target difficulty was found to be pro-
and implementing appropriate incentives is an evolutionary
moting inefficiency, clearly showing that performance
process. Furthermore, excessively stringent targets (such as
targets need to be set with care and transparency. In con-
for reductions in NRW) can actually reduce efficiency,
clusion, the results support the trend towards greater
although the channels leading to the negative effects are
public sector accountability, through benchmarking activi-
still unclear. In addition, resources might have been devoted
ties by regulators and managers and a more commercial
to improving other dimensions of performance, such as an
(less political) orientation for state-owned enterprises. How-
increased number of hours of service per day.
ever, this is easier said than done in practice. This is because
The study uses a model of technical inefficiency effects,
most water utilities in developing countries are faced with
involving a constant term, service coverage, incentives,
challenges of political interference, corruption and nepo-
target difficulty and year of observation; these factors are
tism tendencies. All these are practical constraints to
shown to be significant components in the inefficiency
moving towards better performance and governance. The
sub-equation of the stochastic frontier production function.
results contribute to the growing literature on the impact
Specifically, we find that utilities with higher levels of ser-
of explicit managerial incentives on state owned enterprises
vice coverage and incentives are more technically efficient.
(SOE) performance. The study also suggests several lines of
Our evidence suggests that incorporating incentive plans
further research related to the development and implemen-
can result in approximately 4% (0.83 to 0.87 efficiency
tation of managerial incentives. More comparative studies
score) increase in revenue output. Using the NWSC’s
need to be conducted to overcome the weaknesses of this
annual revenue output of 48,260,661 m3, at a current aver-
study resulting from small values of elasticities and poor stat-
3
age tariff of US$0.7 per m , a 4% change in output
istical significance of the parameters in the translog
translates directly to about US$1.4 million in a US$60
specification. The possibility of use of a Cobb-Douglas func-
million turnover utility.
tional form could be explored, using a different data set,
On the other hand, utilities with easier to achieve targets
although the LR test rejects it in this study.
are more efficient than their counterparts with more difficult targets. This result suggests that an examination of the target-setting process is warranted. Our evidence suggests that effects of target difficulty can cause inefficiencies to
REFERENCES
the tune of about US$1.0 million revenue losses per annum in a US$60 million annual turnover utility. More applied work is called for: a multi-output and multi-input production technology, using a distance function specification, would enable an expansion of output variables to include service quality (such as hours of operation per day) as well as other inputs. Of course, as usual, data availability is the major constraint for analysts. The empirical evidence points towards a number of policy implications. First, utility managers need to incorporate financial incentives in their performance improvement plans if they want operating teams to have sufficient momentum to improve production. Second, the evidence suggests that utilities with higher service coverage levels are more
Abbott, M. & Cohen, B. Productivity and efficiency in the water industry. Utilities Policy 17, 233–244. ADB The Issues and Challenges of Reducing Non-Revenue Water. Asian Development Bank, Publication Stock No. RPT102319. Battese, G. E. & Coelli, T. J. A model for technical inefficiency effects in a stochastic frontier production function for panel data. Empirical Econ. 20, 325–332. Berg, S. V. Water Utility Benchmarking: Measurement, Methodologies and Performance Incentives. IWA Publishing, London. Berg, S. V. & Lin, C. Consistency in performance rankings: The Peru water sector. J. Appl. Econ 40 (6), 793–805. Berg, S. & Marques, R. Quantitative studies of water and sanitation utilities: a benchmarking literature survey. Wat. Policy 13, 591–606.
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Managerial incentives in public water utilities
Coelli, T. J. & Battese, G. E. Identification of factors which influence the technical inefficiency of Indian farmers. Aust. J. Agric. Econ. 40 (2), 103–128. Coelli, T., Prasada Rao, D. S. & Battese, G. E. An Introduction to Efficiency and Productivity Analysis. Kluwer Academic Publishers, Dordrecht, The Netherlands. Coelli, T., Estache, A., Perelman, S. & Trujillo, L. A Primer on Efficiency Measurement for Utilities and Transport Regulators. WBI Development Studies, World Bank, Washington, DC. Colon, M. Re-balancing commercial and engineering activities: A way forward for NWSC. The Water Herald, NWSC-Uganda 3 (1), 8–13. Correia, T. & Marques, R. C. Performance of Portuguese water utilities: How do ownership, size, diversification and vertical integration relate to efficiency? Wat. Policy 13 (3), 343–361. Delavallade, C. What drives corruption? Evidence from North African firms. J. Afr. Economies 21 (4), 499–547. Estache, A., Rossi, M. A. & Ruzzier, C. A. The case for international coordination: Evidence from the measurement of efficiency in South America. J. Regul. Econ. 25 (3), 271–295. Kingdom, B., Liemberger, R. & Marin, P. The Challenge of reducing Non-Revenue Water (NRW) in Developing Countries – How the Private Sector Can Help: A Look at Performance-Based Service Contracting. Water Supply and Sanitation Sector Board Discussion Paper Series, Paper No. 8, 2006, World Bank, Washington, DC.
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Lambert, A. Assessing Non-Revenue Water and its Components. Water 21, August 2003. Li, A. & Butler, A. B. The effects of participation in goal setting and goal rationales on goal commitment: An exploration of justice mediators. J. Bus. Psychol. 19 (1), 37–51. Mugisha, S. Effects of Managerial Incentives Intensity and Performance Monitoring Modes on Water Utility Efficiency and Productivity Growth: Findings National Water and Sewerage Corporation, Uganda. Unpublished PhD Thesis, Makerere University. Mugisha, S. Effects of incentive applications on technical efficiencies: Empirical evidence from Ugandan water utilities. Utilities Policy 15 (4), 225–233. Mugisha, S. Utility Benchmarking and Regulation in Developing Countries: Practical Application of Performance Monitoring and Incentives. International Water Association, London. Mugisha, S., Berg, S. V. & Muhairwe, W. T. Using internal incentive contracts to improve water utility performance: The case of Uganda’s NWSC. Wat. Policy 9 (3), 271–284. NWSC Kampala Water Internally Delegated Area Management Contract (2006–2010). NWSC Unpublished document, P.O. Box 7053, Plot 39, Jinja Road, Kampala, Uganda. Zetik, D. C. & Stuhlmacher, A. F. Goal setting and negotiation performance: A meta-analysis. Group Processes Intergroup Relations 5 (1), 35–52.
First received 11 October 2012; accepted in revised form 24 May 2013. Available online 13 September 2013
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Use of PCA-RBF model for prediction of chlorophyll-a in Yuqiao Reservoir in the Haihe River Basin, China Liu Xiaobo, Dong Fei, He Guojian and Liu Jingling
ABSTRACT Chlorophyll-a is a well-accepted index for phytoplankton abundance and population of primary producers in an aquatic environment. The relationships between chlorophyll-a and 18 chemical, physical and biological water quality variables in YuQiao Reservoir (YQR) in the Haihe River Basin in P.R. China were studied by using principal component analysis (PCA) coupled with a radial basis function network (RBF) model to predict chlorophyll-a levels. Principal component analysis was used to simplify the complexity of relations between water quality variables. Score values obtained by PC scores were used as independent variables in the RBF models. In the forecast, only five selected score values obtained by PC analysis were used for the prediction of chlorophyll-a levels. Correlative analysis between the modeled results and observed data indicates that the correlative coefficient is 0.61, and analysis of the forecast error rate shows that the average forecast error is 32.9%, proving the viability of the forecast model. Key words
| chlorophyll-a, principal component analysis, radial basis function network, reservoirs, water quality
Liu Xiaobo (corresponding author) Dong Fei Department of Water Environment, China Institute of Water Resources and Hydropower Research, Beijing 100038, China E-mail: xbliu@iwhr.com Liu Xiaobo Liu Jingling School of Environment, Beijing Normal University, Beijing 100875, China He Guojian Department of Hydraulic Engineering, Tsinghua University, State Key Laboratory of Hydroscience and Engineering, Beijing 100084, China
INTRODUCTION Haihe River Basin is one of the areas lacking water
the case of reservoirs built for drinking water supply. Intense
resources in China, and the water environment has deterio-
blooms of primary producers increase the cost of water treat-
rated seriously in the past 50 years. YuQiao Reservoir
ment and consequently the cost of water use. Photosynthesis
(YQR), one of the 23 drinking water source reservoirs in
and phytoplankton are the main interrelated components of
the Haihe River Basin and the main drinking water source
primary production in aquatic environments, and chloro-
of Tianjin city, China, has been polluted and its eutrophic
phyll-a
state is more serious. There has been significant concern
abundance (Vollenweider et al. ; Egna & Boyd ). Pri-
about the water quality in the reservoir, with a focus on
mary production supports higher trophic level organisms,
nutrient loadings from tributary inflow and surrounding
including fish, through the food web in aquatic environments.
land uses, because eutrophication in drinking water source
The concentration of phytoplankton in the aquatic system
reservoirs has become a threat to human health. In 1997,
depends on a number of variables, including availability of
an algal bloom was found in the reservoir. Many studies
nutrients, quantity of light, temperature and other physico-
have been conducted on YQR, both in situ and experimen-
chemical properties of the water body, as well as grazing
tally (Wang et al. ; Chen et al. ).
pressure and interactions between these physical, chemical
is
the
fundamental
index
of
phytoplankton
Reservoirs are engineered structures built for a number of
and biological properties of the system. An important chal-
socio-economic benefits, e.g. hydropower production, recrea-
lenge for scientists is to develop analytical tools that can be
tion and sport activities, commercial fisheries, flood control,
used to understand the interaction and behavior of factors
irrigation and water supply. Uncontrolled increase in primary
involved in a multidimensional process such as primary pro-
productivity of freshwater bodies is not always desired as in
duction, and to provide the necessary tools for monitoring
doi: 10.2166/ws.2013.175
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and management of resources. Modeling is regarded as an
scores of 18 physical, chemical, and biological water quality
important analytical tool for biological and ecological studies
parameters from YuQiao Reservoir in the Haihe River Basin
(Cacho ; Tufford & McKeller ). According to Elliott
(P.R. China) were used as independent variables in a radial
et al. (), the demand for workable models of lake and
basis function neural network (RBFNN) model for prediction
reservoir ecosystems has grown consistently, mainly due to
of chlorophyll-a levels.
economic interests of water industry management and the scientific curiosity of limnologists. Models are considered to be essential tools in studies of large reservoirs due to reservoir
METHODS
complexity in terms of morphometry, hydrology, ecology and internal and external forcing functions. One of the
Study areas
approaches which receives growing interest and is becoming popular in ecological and environmental modeling is the com-
One of the 23 drinking water source reservoirs in Haihe River
ponent analysis, e.g. principal component analysis (PCA)
Basin, YQR (40 020 N, 117 250 E) is located northeast of
(Flink et al. ; Chen & Mynett ). The main concern
Tianjin as shown in Figure 1. This reservoir is a key regulating
of component analysis is to understand modes of action or be-
reservoir of the Project of Water Transfer from Luanhe River
havior of components of a system and its subsystems.
to Tianjin (PWTLT), and is the main drinking water source
Principal components analysis, which is widely used in
for more than four million Tianjin residents.
W
W
aquatic environmental and ecological modeling studies,
YQR covers a flow area of 2,060 km2 with a total storage
offers an objective method for handling large sets of biotic
capacity of 15.6 × 108 m3. The average depth of the reservoir is
and abiotic data and aids in reducing the complexity of multi-
about 4.6 m and the largest depth at the dam is about 14 m.
dimensional systems by maximization of component loadings
Major tributaries in the YQR basin include Shahe River,
variance and elimination of invalid components (Bengraine
Lihe River and Linhe River, among which, Shahe River and
& Marhaba ; Loska & Wiechula ). PCA further
Lihe River merge into Guohe River and flow into YQR. The
enables one to extract interpretable information to explain physicochemical parameters of a system by explaining the variance–covariance structure of the original variables. In recent years, PCA has been employed either alone or in combination with other methods to model biological and ecological processes. However, as water quality can be affected by so many factors, traditional data processing methods are no longer good enough for solving the problem as such factors show a complicated nonlinear relation to the variables of water quality forecast. On the other hand, the neural network (ANN), which is built by Fortran 90, can imitate such basic characteristics of the human brain as self-adaptability, self-organization and error tolerance and has been widely adopted for mode identification, analysis and forecast, system recognition and design optimization (Niu et al. ; Kunwar et al. ). The main purpose of the present study was to use a multivariate statistical approach to classify predictor variables according to their interrelation and to predict chlorophyll-a levels in a reservoir. For this purpose, principal component
Figure 1
|
Map of Yuqiao Reservoir in Haihe River Basin.
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outflow of YQR is Zhouhe River, supplying water to Tianjin.
2005, and the reservoir was sampled twice per month within
From 1983 to 2000, there was 42.174 × 108 m3/a water from
this period. Water temperature (T C), pH, electrical conduc-
the basin flowing into YQR, of which the contribution of
tivity (EC), Secchi disk depth (SD) and dissolved oxygen
Shahe River was 57.9%, Lihe River was 30.2%, and Linhe
(DO) were measured in situ. Chemical oxygen demand
8
3
W
River was 11.9%. Added to this, water supply of 10 × 10 m /
(CODMn), biochemical oxygen demand (BOD), suspended
a was also transfered from Luanhe River to YQR through a
solids (SS), total hardness (TH), total solids, total bacteria
tunnel of length 12.5 km, along the Lihe and the Guohe
count, total nitrogen (TN), nitrite-nitrogen (NO2-N), nitrate-
Rivers from the start of PWTLT, downstream of Daheiting
nitrogen (NO3-N), ammonia-nitrogen (NHþ 4 -N), non-ionic
Reservoir.
ammonia (NH3-N), total phosphorus (TP) and chlorophyll-a
However, in recent years, along with the development of
were also determined in the laboratory.
farmland fertilization and fisheries in the area, tons of animal
Based on existing measured values and correlative analysis,
waste were being spread on fields each year in the low lying
the 18 factors mentioned above are to be used in PCA. In
areas, and at least once each year water was diverted into
addition, the present chlorophyll-a value (Chl-at) will have
the reservoir to store drinking water for Tianjin and to relieve
some impact on the value 15 days later (Chl-atþΔt), so 18 factors
pressure from upstream reservoirs in other provinces during
are determined to be affecting factors for the forecast, i.e., the
the rainy season through the PWTLT. The net effect of the
input variables of the model, and chlorophyll-a, being the
diversion was to flood the reservoir and stir up the nutrients
study objects, are output variables. The model intends to
into the water supply. This problem was exacerbated by the dis-
achieve a forecast of what the chlorophyll-a value (Chl-atþΔt)
charge of nutrient rich water from fishponds that continue to
will be in 15 days’ time from the current values of the 18
operate around the reservoir. In the midst of this critical area
water quality variables, or affecting factors.
where water enters the reservoir, a massive dredging operation is removing mountains of sand from the lake and river bottom
Model description
for use by the construction industry. As a result, the content of nitrogen and phosphorus in the water keeps rising, resulting in
Statistical methods
massive production of undesirable water plants such as fungus and waterweeds and their over-nutrition. To ensure the safety of drinking water, it is important to
Using SPSS 10.0, principal component analysis was performed on these 18 water quality parameters to rank their
initiate a comprehensive treatment of the reservoir’s water
relative significance and to describe their interrelation patterns
quality, in addition to the restriction and standardization
as well as their effect on the chlorophyll-a levels. PC scores of
of development in farming and fisheries in the proximity
all 18 water quality parameters were used as independent vari-
of the reservoir. As a result, this paper studies water quality
ables ((Xi), i ¼ 1, 2,…, 14) in multiple linear regression analysis
forecast in Yuqiao Reservoir to gain a better understanding
to predict the chlorophyll-a (Y) abundance.
of possible water quality changes in the future. The study will provide scientific evidence for water quality manage-
Principal component analysis
ment and propose necessary action to foresee and prevent any future problems, thus playing a positive role in securing
Bartlett’s sphericity test (χ 2 with degrees of freedom ¼
the safety of water supply in Tianjin.
1/2[p(p 1)]) was used to verify the applicability of principal component analysis to row data (Stevens ).
Data collection
Eigenvalues of PCs were obtained by using the following equation given by Johnson & Wichern ():
Chlorophyll-a is a major parameter for evaluating water quality of lakes and reservoirs. This paper studies the forecast of chlor-
jR λIj ¼ 0
(1)
ophyll-a in Yuqiao Reservoir. Data used in the development of the prediction model were collected fortnightly from 2003 to
where I is the identity matrix and λ the eigenvalue vector.
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The standardized weights of the variables (tij) in the PCs
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and mixture models. The RBFNN is a forward network model with good performance, global approximation, and
were then calculated by using the equation below:
is free from the local minima problems. It is a multi-input, (R λI)T ¼ 0
(2)
single-output system consisting of an input layer, a hidden layer, and an output layer. During the data processing, the
where T is a p × p dimension matrix, which contains standar-
hidden layer performs nonlinear transforms for the feature
dized weight values (tij) of each variable in the PCs.
extraction and the output layer gives a linear combination
Due to differences in the units of variables used in PCA, a correlation matrix of variables (Rp×p) was used to obtain
of output weights. The structure is shown in Figure 2. The input is n-dimensions, learning samples are,
eigenvalues and weights of variables. Eigenvector λ was
(X, Y ), where X ¼ (X1, X2, …, XN) is the input variable,
used to obtain unrotated factor loadings. Vik indicates the
Xi ¼ ðxi1 , xi2 , , xin ÞT ð1 i N Þ, and the expected output
values of rotated factor loadings, which were obtained by
is Y ¼ (y1, y2, …, yN), and N is the training number. When
variamax rotation. Rotated loadings in PCs indicate the per-
the input is Xi, the output of the jth node in the hidden
cent contribution of the corresponding variable to the PC
layer can be expressed as:
and are called the loading of ith variable in kth PC (correlation between variable i and kth PC). These loading values were used to group variables in PCs. Coefficients in the PCs show the percent contribution of
Xi Cj G Xi , Cj , σ j ¼ exp 2σ 2
(4)
corresponding variables and are called the loading of ith
T where Cj ¼ c j1 , c j2 , , c jn and σj are the center and
variable in kth PC (correlation between i variable and k PC).
width of the Gaussian function of the jth node in the
Score value (skj) for jth observation in kth PC was obtained from the weight of variables in PCs and standar-
hidden layer. For an input Xi, the expected output of the network is:
dized variables by using the following equation: skj ¼ t1k z1j þ t2k z2j þ . . . . . . þ t pk z pj
(3)
yi ¼
M X G Xi , Cj , σ j wj þ ei
(5)
j¼1
where j ¼ 1, 2,…, n are the indices of observations; k ¼ 1,
In equation (5), wj is the weight between the jth neuron
2,…, q, are the indices of principal components; p the
of the hidden layer and output neuron. M stands for neuron
number of independent variables; skj the standardized score
number in the hidden layer, and yi and ei are the expected
value of jth observation in kth PC; zpj the standardized
output of Xi and the error of fitting, respectively. ei can be
value of pth variable of jth observation, calculated from z ¼ xp x=sx , where xp is the original value of pth variable;
obtained by transposition of equation (5), that is:
and tpk the standardized weight of the pth variable in kth PC. The approach was employed in using PC scores in RBF
ei ¼ yi
M X G Xi , Cj , σ j wj j¼1
analysis, utilizing only five PCs with eigenvalues greater than 1 out of 18 principal components. Radial basis function network Radial basis functions emerged as a variant of artificial neural networks in the late 1980s (Yee & Haykin ). However, their roots are entrenched in much older pattern recognition techniques as for example potential functions, clustering, functional approximation, spline interpolation
Figure 2
|
Structure of RBF neural network.
(6)
L. Xiaobo et al.
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Use of PCA-RBF model for prediction of chl-a in Yuqiao Reservoir
As for the selection of the center parameter of the Gaussian function, this paper uses the orthogonal least square
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be used for sample assessment and center selection. When ρi satisfies:
algorithm. The least square algorithm is also applied to train the output weight in order to minimize total error, that is:
min E ¼
ρi ¼
i X
ej ,
ρi > ρ
(14)
j N 1X e2 2 i¼1 i
(7)
Equation (5), above, can be written in a matrix form as
the calculation terminates. The ith sample with maximal ρi is chosen as the network center. 0 < ρ < 1 is the preset tolerant variance limit. Weight can be determined by ^ ¼ A 1 S. W As mentioned before, score values of only five selected
follows:
PCs were included as independent variables in the RBF Y ¼ PW þ E
(8)
where Y ¼ ½y1 , y2 , yN T , P ¼ [P1, P2, …, PN] is the output matrix
of
the
hidden
layer,
and
neural network model. During the forecasting process, 72 RBFNN are established to predict the Chl-atþΔt.
Pi ¼ ½ pi1 , pi2 ,
, piN ði ¼ 1, 2, , N Þ. W and E are output weights and
RESULTS
error vectors. To carry out orthogonal decomposition on P:
The data for PCA come from the 3 years from 2003 to 2005, in total 72 groups of measured values (72 × 18) at
P ¼ HA
(9)
Yuqiao Reservoir, in which 48 groups of data from 2003 to 2004 are used for RBF neural network training. The
where A is an upper triangular matrix with diagonal value 1,
measured values of 2005 are used for forecasting to test
and matrix H contains the orthogonal vectors Hi. Equation
the model.
(8) can be changed into: Y ¼ PA 1 (AW) þ E
The value of χ 2, calculated as 348.3 by Bartlett’s sphericity test (d.f. ¼ 91, P < 0.01), implies that the principal (10)
component analysis is applicable to our data set. According to principal component analysis, out of 18 principal com-
Suppose S ¼ AW, then, Y is transformed as: Y ¼ PA 1 S þ E ¼ HS þ E
ponents only five PCs with eigenvalues higher than 1 were selected for multiple linear regression analysis. Selected (11)
PCs explained 78.041% of the total variation of variables in the PCA (Table 1).
Therefore, by using the least squares methods S is obtained from equation (11) as:
S ¼ HT H
ei ¼
1
si wTi wi YT Y
For the first five PCs, component loadings from the PCA are presented in Table 2. The bold marked loads indicate the highest existing correlation between variables and corre-
HT Y
(12)
sponding component. For instance, T, Chl-at, CODMn, TP,
Table 1
|
Descriptive statistics of selected PCs
(13)
Because the number of hidden layers, M, that satisfy the training accuracy and generalization ability are far less than the training number, N, the accumulating variance, ρi, can
PC1
Eigenvalue Cumulative variance proportion (%)
PC2
PC3
PC4
PC5
5.962
3.578
1.734
1.544
1.229
33.124
53.000
62.653
71.214
78.041
L. Xiaobo et al.
78
Table 2
|
|
Use of PCA-RBF model for prediction of chl-a in Yuqiao Reservoir
PC2
14.1
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2014
ables were then multiplied to obtain the score values of PCs.
Loading of variables (Vik) PC1
|
The weight of variables and values of standardized vari-
Results of principal component analysis
Variables
Water Science & Technology: Water Supply
PC3
The score values obtained from PCA were used as indepenPC4
PC5
dent variables in RBF analysis to determine the most significant PCs for chlorophyll-a level (Chl-atþΔt).
T
0.797
0.047
0.228
0.291
0.253
pH
0.505
0.054
0.584
0.262
0.129
Predicted (modeled) values of chlorophyll-a using the
EC
0.157
0.815
0.168
0.432
0.160
RBF model and the observed values are given in Figures 3
NH3-N
0.243
0.226
0.374
0.207
0.645
and 4 for comparison. It can be seen that the observed
NO3-N
0.563
0.610
0.324
0.292
0.099
and modeled Chl-a values are in good agreement, Correla-
NO2-N
0.091
0.611
0.478
0.390
0.342
tive analysis between the two groups of data indicates that
TN
0.267
0.638
0.423
0.373
0.134
the correlative coefficient is 0.61, and analysis of the forecast
DO
0.542
0.237
0.575
0.363
0.241
error rate shows that the average forecast error is 32.9%.
BOD5
0.429
0.268
0.165
0.276
0.314
From Figure 3, it can be seen that the forecast results are
TP
0.795
0.264
0.168
0.053
0.069
bigger than observed values from July to October. Since
SS
0.702
0.227
0.035
0.042
0.100
the sample data were collected from 2003 to 2005, it indi-
Non-ionic ammonia
0.813
0.040
0.029
0.110
0.245
cates that the forecast model is relatively data-bound.
CODMn
0.874
0.210
0.009
0.112
0.219
time to time with new measured values. Several forecast
Total solids
0.180
0.783
0.152
0.483
0.030
0.622
0.167
0.066
0.131
0.475
values in the figures deviate more from actual measured
Total bacteria count Chl-at
0.906
0.156
0.055
0.093
0.064
TH
0.343
0.835
0.262
0.159
0.117
SD
0.458
0.216
0.417
0.513
0.196
Therefore it is quite necessary to update the model from
values due to the fact that forecast values can be affected by many factors during the study. In addition to the identified affecting factors, many other factors, such as weather conditions or environmental pollution, can affect the forecast values every moment. They can be very unpredictable and thus make the study work more difficult. Nevertheless, the average forecast error rate indicates that the overall fore-
SS, Chla, NH3-N, non-ionic ammonia, total bacteria count
cast results are fairly good with the error rate controlled
and BOD5, which showed the highest correlation with
within an acceptable range, proving the viability of the
PC1 were evaluated as a group.
forecast model.
Figure 3
|
Chl-a observed value and modeled value using RBF.
L. Xiaobo et al.
79
Figure 4
|
|
Use of PCA-RBF model for prediction of chl-a in Yuqiao Reservoir
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Correlation analysis between observed value and modeled value.
DISCUSSION
results in general and can be used for water quality forecasts of the reservoir.
Various models and approaches have been employed by
Moreover, this model can be extended to further appli-
different researchers to model primary production in
cations. Provided that other water quality variables of this
aquatic environments. Some have defined chlorophyll-a
reservoir are to be forecasted, or a number of variables are
relations with biotic and/or abiotic factors as univariate
to be forecasted simultaneously, it is only necessary to ident-
and some have adapted a multivariate linear or nonlinear
ify the affecting factors first, then create the forecast model
approach. Regardless of the scope of the model, generally
in the way mentioned above, decide the input and output
2
the R -value is accepted as a standard criterion for the pre-
variables for the model, use existing measured values as
dictive success of the models (Hakanson et al. ). A
sample data for training, obtain the best working model by
2
univariate simple regression model can yield a high R -
changing the network’s internal structure and variables,
value but may fail to define the complex nature of the eco-
and complete the model with simulation testing. If the cor-
system. Multivariate models capable of assessing large
relation between the forecast and actual measured values
number of variables and interrelations are therefore, more
is fairly good, the forecast model is viable and can be applied
successful in defining and predicting biological processes
to real practice.
such as primary production. In the present study the
In this sense the forecast model is characterized by its
relationships between several biotic and abiotic parameters
extendability and practicability. Nevertheless, due to the
with chlorophyll-a have been investigated using a multi-
fact that water quality forecasts can be easily affected by
variate approach and the model has been able to predict
the external environment (Vandenberghe et al. ), the
chlorophyll-a levels in a reservoir.
obtained model sometimes produces results which are
This paper adopts the PCA and RBF neural network
very different from the actual values, therefore further
technology to achieve easier and faster water quality fore-
study needs to be done in future work to identify the suitable
casts at Yuqiao Reservoir. The study has the 2003–2005
forecast model, understand its laws of changes and solve the
actual measured values of the reservoir as sample data to
problem of forecast deviation.
train the model. Simulation results showed that the forecast model is data-bound and therefore it is necessary to update the model from time to time with more actual measured
ACKNOWLEDGMENTS
values. Selection of affecting factors also plays a key role since they can have a great impact on the forecast results.
This work was supported by the National Natural Science
It is concluded that the model can produce good forecast
Foundation of China (51209230); the Key Project of
80
L. Xiaobo et al.
|
Use of PCA-RBF model for prediction of chl-a in Yuqiao Reservoir
Chinese National Programs for Fundamental Research and Development (973 Program: 2006CB403400).
REFERENCES Bengraine, K. & Marhaba, T. F. Using principal component analysis to monitor spatial and temporal changes in water quality. J. Hazard. Mater. B 100 (1–3), 179–195. Cacho, O. J. Systems modelling and bioeconomic modeling in aquaculture. Aquacult. Econ. Manage. 1 (2), 45–64. Chen, L. D., Peng, H. J. & Fu, B. J. Seasonal variation of nitrogen-concentration in the surface water and its relationship with land use in a catchment of northern China. J. Environ. Sci. 17 (2), 224–231. Chen, Q. & Mynett, A. E. Integration of data mining techniques and heuristic knowledge in fuzzy logic modeling of eutrophication in Taihu Lake. Ecological Modeling. 162 (1–2), 55–67. Egna, H. S. & Boyd, C. E. Dynamics of Pond Aquaculture. CRC Press, USA. Elliott, J. A., Irish, A. E., Reynolds, C. S. & Tett, P. Modelling fresh water phytoplankton communities: an exercise in validation. Ecological Modeling 128 (1), 19–26. Flink, P., Lindell, T. & Ostlund, C. Statistical analysis of hyperspectral data from two Swedish lakes. Sci. Total Environ. 268 (1–3), 155–169. Hakanson, L., Malmaeus, J. M., Bodemer, U. & Gerhardt, V. Coefficients of variation for chlorophyll, green algae, diatoms, cryptophytes and blue-greens in rivers as a basis for predictive modelling and aquatic management. Ecological Modeling 169 (1), 179–196.
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Johnson, R. A. & Wichern, D. W. Applied Multivariate Statistical Analysis. Prentice-Hall Inc., Englewood Cliffs, USA. Kunwar, P. Singh, Ankita, Basant, Amrita, Malika & Gunja, Jain Artificial neural network modeling of the river water quality—A case study. Ecological Modelling 220 (6), 888–895. Loska, K. & Wiechula, D. Application of principal component analysis for the estimation of source of heavy metal contamination in surface sediments from the Rybnik Reservoir. Chemosphere 51 (8), 723–733. Niu, Z. G., Zhang, H. W. & Liu, H. B. Application of neural network to prediction of coastal water quality. Journal of Tianjin Polytechnic University 25 (2), 89–92. Stevens, J. Applied Multivariate Statistics for the Social Science. Hillsdale, New Jersey, USA. Tufford, D. L. & McKeller, H. N. Spatial and temporal hydrodynamic and water quality modeling analysis of a large reservoir on the south Carolina (USA) coastal plain. Ecological Modeling 114 (2–3), 137–173. Vandenberghe, V., Bauwens, W. & Vanrolleghem, P. A. Evaluation of uncertainty propagation into river water quality predictions to guide future monitoring campaigns. Environmental Modelling & Software 22 (5), 725–732. Vollenweider, R. A., Talling, J. F. & Westlake, D. F. A Manual on Methods for Measuring Primary Production in Aquatic Environments, 2nd edn, Blackwell Scientific Publications, Oxford IBP Handbook, No. 12, p. 225. Wang, X. H., Yin, C. Q. & Shan, B. Q. Control of diffuse P-pollutants by multiple buffer/detention structures by Yuqiao Reservoir, North China. J. Environ. Sci. 16 (4), 616–620. Yee, P. V. & Haykin, S. Regularized Radial Basis Function Networks: Theory and Applications. John Wiley, Hoboken, NJ, USA.
First received 11 February 2013; accepted in revised form 12 June 2013. Available online 12 September 2013
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Modelling both the continual erosion and regeneration of discolouration material in drinking water distribution systems W. R. Furnass, R. P. Collins, P. S. Husband, R. L. Sharpe, S. R. Mounce and J. B. Boxall
ABSTRACT The erosion of the cohesive layers of particulate matter that causes discolouration in water distribution system mains has previously been modelled using the Prediction of Discolouration in Distribution Systems (PODDS) model. When first proposed, PODDS featured an unvalidated means by which material regeneration on pipe walls could be simulated. Field and laboratory studies of material regeneration have yielded data that suggest that the PODDS formulations incorrectly model these processes. A new model is proposed to overcome this shortcoming. It tracks the relative amount of discolouration material that is bound to the pipe wall over time at each of a number of
W. R. Furnass (corresponding author) R. P. Collins P. S. Husband R. L. Sharpe S. R. Mounce J. B. Boxall Civil and Structural Engineering, Pennine Water Group, University of Sheffield, Sir Frederick Mappin Building, Mappin St, Sheffield, S1 3JD E-mail: wrfurnass1@sheffield.ac.uk
shear strengths. The model formulations and a mass transport model have been encoded as software, which has been used to verify the model’s constructs and undertake sensitivity analyses. The new formulations for regeneration are conceptually consistent with field and laboratory observed data and have potential value in the proactive management of water distribution systems, such as evaluating change in discolouration risk and planning timely interventions. Key words
| discolouration, distribution networks, water quality modelling
INTRODUCTION The occurrence of discoloured water in drinking water dis-
could be mobilised (e.g. from a burst or controlled flow
tribution
increase such as from flushing);
systems
(DWDS)
is
often
attributable
to
particulate matter, detected as turbidity, that had been attached to pipe walls but, following the onset of anomalous hydraulic
conditions
(e.g.
flow
increases),
becomes
entrained in the bulk flow. Discolouration can be associated with aesthetic, chemical and/or microbiological water quality failures (Vreeburg & Boxall ). In recent years an interest has developed in modelling the relationship between water main condition and the turbidity generated as a result of material erosion from the pipe wall (Boxall et al. ; Vreeburg ; Ryan et al. ). Such discolouration modelling can potentially offer:
•
• •
predictions of the turbidity or suspended solids concentration that would result from increasing flows in a main (given a calibrated discolouration model); a means for designing the hydrant flushing operations that are often used for cleaning distribution mains so as to decrease discolouration risk to a satisfactory level. It was originally thought that discolouration was due to
the re-suspension of sediments but Boxall et al. () calculated that the size and density distributions of discolouration material do not usually allow for gravitational settling. They proposed the Prediction of Discolouration in Distribution
an estimation of the quantity of discolouration material
Systems (PODDS) model under which material (organic
within a length of main and the ease with which it
and inorganic matter) instead ubiquitously and continually
doi: 10.2166/ws.2013.176
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Modelling the erosion and regeneration of discolouration material in distribution systems
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binds to the pipe wall around its circumference as cohesive
(98% in Husband et al. ()). Ideally, conditioning oper-
layers with a single ‘shear strength’ τc [Pa]. PODDS was pri-
ations would be designed and assessed using discolouration
marily developed to model the material erosion process and
models that can track the amount of material at the wall of
increases in bulk water turbidity. Its erosion mechanism is
a main (discolouration potential) over multi-month or
as follows:
multi-year periods and can be used to calculate the optimal
1. An increase in pipe flow causes an increase in the shear stress τa [Pa] at the wall. 2. Material then erodes from the wall and becomes entrained in the bulk flow at a rate that is a function of τa–τc if τa > τc. 3. As a result, the amount of material at the wall decreases but its strength τc increases. It is therefore possible to ‘flow condition’ a main by
frequency and magnitude of controlled flow increases. Discolouration material regeneration processes have been investigated during several field studies. This is typically achieved by first flushing a main once whilst measuring flow Q(t) and turbidity T(t) at the downstream end. The relationship between turbidity and total suspended solids (TSS) at the levels seen in DWDS is approximately linear (Boxall et al. ), allowing turbidity to be treated
increasing τa above prevailing conditions to remove all
as a concentration. The amount of material that is mobilised Ð flush end during the flush is therefore flush start T (t) Q(t) dt (assuming
material weaker than a ‘target’ τa.
the water entering the main has negligible turbidity). The
An inverse linear relationship between the amount of
main is then flushed again several months later and the
material at the wall and τc simulates layers being eroded
same calculation performed. A coarse relative regeneration
from weakest to strongest upon an increase in τa; this
rate can be calculated from the ratio of the two material
approach to modelling erosion events has been validated
quantities and the duration of the ‘regeneration period’.
using field data (Boxall & Saul ; Boxall & Prince
In the Netherlands, Blokker et al. (, Table 2) flushed
). When PODDS was originally developed, functional-
12.3 km of mains of different diameters and materials (ø ¼
ity was included to allow for the regeneration of cohesive
63 300 mm; asbestos cement and PVC) within distribution
layers (following layer erosion then a decrease in τa) as the
area ‘site A’ on three occasions. Decreasing material quan-
reverse of mobilisation, i.e. from strongest to weakest. This
tities were mobilised with each flush but the material
was not based on any observations or data, rather that it
regeneration rate across flushes 1–2 and 2–3 was constant,
was readily implemented at the time of encapsulating the
indicating that regeneration is a continuous, potentially
model within a modified version of the EPANET DWDS
linear process. In England, Husband & Boxall () under-
modelling software (Boxall & Saul ; USEPA ).
took repeated distribution main flushing. They found
An understanding of discolouration risk and material
evidence of regeneration being a linear process that con-
regeneration processes is particularly important in trunk
tinues until the material at the pipe wall reaches a steady
mains due to the large populations supplied. Flow condition-
state, with that state being dictated by prevailing hydraulic
ing is now being used as a management strategy for (a) the
forces.
non-disruptive cleaning of trunks that have been linked to
Discolouration potential and material regeneration rates
discolouration complaints and (b) improving the condition
have been detected and quantified for a variety of pipe diam-
of trunks to allow them to be operated at higher flows
eters, pipe materials and source water types (Blokker et al.
(Husband et al. ). Precise flow adjustments are made
; Husband & Boxall ). Husband & Boxall () cal-
to mobilise discolouration material in a controlled, predict-
culated the relative annual material regeneration and the
able way; this material then typically passes through the
average regenerated turbidity between flushes for 67 pipes
DWDS to consumers at acceptably low concentrations.
in England. Results highlight the effect that material
Flow conditioning can be difficult due to the range and gran-
supply from the pipe wall (iron corrosion) and bulk water
ularity of flow control needed and the infeasibility of
(organic-rich surface water sources) can have on relative
flushing to waste in the majority of cases. However, it can
regeneration rates. The background water quality does not
be much cheaper than asset replacement or refurbishment
however appear to correlate with discolouration potential
W. R. Furnass et al.
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Modelling the erosion and regeneration of discolouration material in distribution systems
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(see Figure 9 in that article). Overall, Husband & Boxall
model that as discolouration material erodes from weakest
() observed that regeneration rates in networks that do
to strongest-bound layers that the inverse may be true for
not contain iron mains are largely driven by the bulk
regeneration.
water quality. Further, Vreeburg et al. () showed that
The findings of these field studies concur with those of
the installation of 0.1 μm filtering in distribution systems sig-
laboratory experiments. Sharpe et al. () connected
nificantly reduces regeneration rates but regeneration still
three parallel pipe loops (high-density polyethylene; 203 m
occurs.
long; internal diameter of 79.3 mm) to a tank with a 24 h
During their field studies, Husband & Boxall ()
system residence time. The tank was fed with treated moor-
increased the flow (and therefore shear stress) during each
land runoff via a cast iron trunk main. After being cleaned
flush in steps to assess the relationships between discolour-
using high flushing flows and super-chlorination, the pipes
ation potential and shear strength. As can be seen from
were subjected to a 28-day material accumulation phase
Figure 1 the initial flush of each main generated more turbid-
during which a different steady boundary shear stress was
ity than the subsequent flushes, implying that the cohesive
imposed per pipe. During a subsequent material mobilis-
material layers had not fully regenerated (reached a steady
ation phase, the flow (and τa) was maintained for a
state) over the intervening period(s). However, a turbidity
duration of three pipe turnovers at each of several discrete
response can be seen during later flushes for each increase
levels. Turbidity was monitored at the downstream ends of
in shear stress, indicating that all strengths of cohesive
each pipe loop and was normalised by the background tur-
layers are regenerating simultaneously. This contradicts the
bidity
assumption made during the development of the PODDS
Figure 1
|
prior
to
the
mobilisation
phase.
The
entire
W
experiment was undertaken at 8 then 16 C. Figure 2
Turbidity data from the repeated flushing of distribution mains. Flush 1 data shown in Figure 1(a) previously published in Husband & Boxall (2010). Figure 1(b) previously published in Husband et al. (2010). (a) Groundwater, internal diameter (ID) ¼ 100 mm, unlined cast iron. (b) Surface water, ID ¼ 73 mm, unlined cast iron. (c) Surface water/ groundwater blend, ID ¼ 72 mm, polyethylene. (d) Surface water blend, ID ¼ 150 mm, asbestos cement.
W. R. Furnass et al.
84
Figure 2
|
|
Modelling the erosion and regeneration of discolouration material in distribution systems
Water Science & Technology: Water Supply
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Results of laboratory studies into discolouration material regeneration (previously unpublished). Material layers were developed over 28 days under a steady boundary shear stress of 0.1 Pa (0.2 L s 1) at 8 C and 16 C. These layers were then eroded through imposing a series of discrete increases in shear stress. W
W
shows that the discolouration material accumulates a variety
that the wall of pipe p is anticipated to experience. The
of shear strengths simultaneously, rather than stronger-
applied hydraulic shear stress at the wall at time t is τ a Pa.
bound material binding to the wall before weaker-bound
Under eroding conditions (τ a τ), the rate of change of condition is driven by the ‘excess shear stress’ τ a τ (as per
material. At present PODDS can only model material erosion and
the PODDS model) to ensure that weaker layers erode quicker
not regeneration as its formulations cannot permit all layer
than stronger ones (Equation (1)). The lack of an equivalent
strengths to regenerate simultaneously: the scalar τc can
term in Equation (1) for regenerating conditions (τ a < τ)
only decrease during erosion and increase during regener-
reflects the fact that regeneration is not necessarily primarily
ation. A new model that is not subject to this limitation is
driven by hydraulic forces. This distinction can be seen in
presented in the following section.
the units of the erosion rate coefficient β e ¼ [Pa 1 s 1 ] and regeneration rate coefficient β r ¼ [s 1 ]. These units ensure that φ(τ, t) is unitless and so can be ‘clipped’ to [0, 1].
METHODS The simultaneous regeneration of discolouration material
8 β ðτ a τ Þ @φðτ, tÞ < e ¼ βr : @t 0
τa τ ∧ 0 < φ < 1 τa < τ ∧ 0 < φ < 1 φ 0∨φ 1
(1)
over a range of shear strengths could be modelled if the amount of material at the wall is tracked over time for an
The clipping mandates that the model be evaluated
array of discrete shear strengths. In contrast, the PODDS
numerically over a mesh bounded by τ ∈ ½0, τ max and
model assumes that there is a simple, linear relationship
t ∈ [0, tmax ]. The change in condition of material with dis-
between the scalar shear strength and the discolouration
crete strength τi is calculated iteratively over discrete time
potential.
steps as per Equation (2).
Let the material condition function φ (τ, t) be the relative amount of discolouration material bound to the wall of a pipe p with shear strength τPa at time t. Here τ is a vector
φðτ i , tÞ ¼ φðτ i , t ΔtÞ þ
dφðτ, tÞ Δt dt
(2)
and should not be confused with the scalar τc in the PODDS model. Let φ(τ, t) ∈ [0, 1] where 0 corresponds to
In a similar manner to PODDS, the material flux rate
complete depletion (no material) and 1 to maximum
from a unit area of pipe wall to the bulk water (Equation
accumulation/regeneration
Let
(3)) is a function of the change of material condition discre-
τ ∈ [0, τ max ], where τmax equals the maximum shear stress
tely integrated over the range of eroding material strengths.
(maximal
material).
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Modelling the erosion and regeneration of discolouration material in distribution systems
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It is hypothesised that the material flux of material from the
complete and instantaneous mixing. The reference implemen-
bulk water to the wall is negligible relative to the flux of
tation can presently model only a single pipe.
material to the bulk so the former is not modelled directly in Equation (3), only via the regeneration rate parameter βr.
RESULTS AND DISCUSSION dN(t) ¼ α dt
X i
ðφðτ i , tÞ φðτ i , t ΔtÞÞ dτ for τ a τ i
(3)
The model constructs were initially verified through supplying the reference implementation with artificial data.
If turbidity is proportional to TSS and is therefore a con-
Figure 3 demonstrates the functionality of the model using
centration of discolouration material then it is proposed that
a simple shear stress profile. Although the condition of
material quantity be measured in Turbidity Pseudo-Mass
250 layers was tracked during the execution of the simu-
Units (TPMU) where 1 TMPU ¼ 1 NTU m (Nephelometric
lation the changing condition of just three layers has been
Turbidity Unit). So in Equation (3) the material release
plotted to illustrate the presented concepts (Figure 3 (a–ii)).
3
rate from a unit area of pipe wall, dN(t)=dt, and the material
All layers are eroded by the first step increase in shear
release coefficient α have units of [TPMU Pa 1 m 2 ] and
with the weakest material being eroded more quickly, as
[TPMU m 2 s 1 ] respectively.
can be seen in the plot of φ. Material with strengths of 0.2
A reference implementation of this model has been
and 0.3 Pa then regenerates to a maximal level when the
coded using Python’s scientific computing functionality
shear drops to below 0.2 Pa. Upon a second step increase
(Oliphant ). A Lagrangian, time-driven mass transport
in shear stress only the strongest of the three explicitly
model (Rossman & Boulos ) has been included to model
depicted shear strengths withstands the eroding forces.
the advection and mixing of turbid water and for calculating
All three identified strengths then subsequently regenerate
the turbidity at DWDS points of supply. The mass transport
when the applied shear stress drops down to 0.1 Pa.
model tracks the concentration and volume of a number of dis-
Figures 3 (a–iii) and (a–iv) show two spikes in the mass
crete water plugs as they move through each pipe. It assumes
release rate dN(t)/dt and the downstream turbidity T(t)
Figure 3
|
A demonstration of how the proposed model generates a turbidity response at the downstream end of a single pipe. Pipe internal diameter ¼ 75 mm; roughness ¼ 0.1 mm; length ¼ 20 m; Δt ¼ 0:5 s; 250 τ bands (Δτ ¼ 0:0026 Pa); if τ i < τ a (t ¼ 0) then φ(t ¼ 0, τ i ) ¼ 0 else φ(t ¼ 0, τ i ) ¼ 1; β e ¼ 0:1 Pa 1 s 1 ; β r ¼ 0:005 s 1 ; α ¼ 4:0 TPMU Pa 1 m 2 ; flow Q ∈ ½0:68, 1:75 L s 1 . (a) From top to bottom: (i) a temporal shear stress profile (model input); (ii) the changing condition φ(τ, t) for τ ∈ { 0:2, 0:3, 0:4} due to erosion and regeneration; (iii) the rate of material release dN(t)/dt due to the erosion of all layers weaker than the shear stress; (iv) the turbidity response (model output). (b) Variation in relative material condition φ with respect to time and shear strength. White indicates shear strengths that are completely depleted; black indicates maximal material at a shear strength.
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that correspond to the erosion driven by the two step
The trunk main was modelled as a single length as it
increases in shear stress. Note that the model permits differ-
does not feature any branches and there is little evidence
ent layer strengths to erode from strongest to weakest but
for longitudinal variation in material accumulation quan-
regenerate independently.
tities or rates. A shear stress time-series profile was
The functionality of the proposed model was further ver-
calculated from the flow profile using a Darcy Weisbach
ified through calibrating the model using the flow and
roughness of 0.1 mm (from a calibrated hydraulic model of
turbidity data associated with three consecutive flow trials.
the main). Relative material quantities were tracked for
The flow in a trunk main that links a treatment works to a
100 discrete shear strength bands; these bands correspond
service reservoir was temporarily increased for operational
to the range of shear stresses experienced over the simu-
reasons on three separate occasions over a 72.2 day-period
lation period (1.55 × 10 11 to 7.73 Pa).
to atypical levels. The concrete-lined ductile iron main is
Estimating the amount of material φ at each strength τi
3.7 km long and has an internal diameter of 440 mm. The
at t ¼ 0 is non-trivial as the initial system state depends on
system configuration and the first of the flow trials are
the material erosion and regeneration over the months or
detailed in Seth et al. (). Discolouration issues associ-
possibly years prior to the first flow trial. Stepped flow
ated with the main persisted following the upgrade of the
increases during the first trial showed that significant
treatment works’ filters, suggesting that turbidity events
material erosion only occurred when the shear stress
were due to material mobilisation within the main.
was increased from approximately 3.0 to 3.3 Pa. It
The following data were collated for calibrating a model
was therefore assumed for this first verification that
of the trunk main:
φ(τ i , t ¼ 0) ¼ 0 if τ i < 3:15 Pa otherwise φ(τ i , t ¼ 0) ¼ 1 for
•
each strength τi.
• •
Pipe flow (Δt ¼ 1 min for trials 1 and 3; Δt ¼ 15 min for trials 2 and between trials). Turbidity at the downstream end of the main (Δt ¼ 10 s for trials 1 and 3; Δt ¼ 5–25 min for trial 2; no monitoring between trials). Turbidity at the upstream end of the main (i.e. treatment outflow; Δt ¼ 15 min).
The upstream turbidity profile was used as an input to the Lagrangian transport mechanism to model the influx of suspended material from upstream. Once the model had been configured, it was calibrated by manually adjusting the model parameters to minimise the integral of squared errors (ISE) between non-zero turbidity observations and the corresponding turbidity pre-
The aim was to minimise the dissimilarity between the
dictions. The best achieved fit is shown in Figure 4 (ISE ¼
turbidity observations during the trials and the turbidity pre-
1136 NTU2 and R 2 ¼ 0.73 with β e ¼ 1:66 × 10 4 Pa 1 s 1 ,
diction generated by the model.
β r ¼ 5:84 × 10 8 s 1 and α ¼ 1:13 TPMU Pa 1 m 2 ). The
Figure 4
|
Details of model validation for 3.7 km-long trunk main. (a) Boundary shear stress profile over and between three flow trials covering a 72.2 day period. (b) The variation in relative material quantity φ for three selected shear strength bands shows erosion and regeneration occurring at different strengths.
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model fit over each of the three trial periods is shown in
the accuracy and precision of the model inputs and the
more detail in Figure 5.
instrumentation used to capture that data and also by the
Figures 4 and 5 demonstrate that the proposed model is
accuracy desired by the end user.
capable of emulating material erosion and regeneration over
Currently the same values of α, βe and βr are assumed for
a period that features three successive flow trials using a con-
all shear bands i.e. the model is simpler than the four-par-
tinuous stream of data and a constant parameter set. The
ameter PODDS model; however the implementation of
strength-dependent nature of the erosion process and
the proposed model allows the inclusion of varying values
strength-independent regeneration process can be seen in the
of α, βe and βr, allowing for more complex behaviour to be
time-series plots of relative material for selected strength bands.
reproduced if required. It is also felt that parameters α, βe
A manual exploration of the parameter space for the
and βr are more physically realistic than their PODDS
model instance used for validation suggested that for a
counterparts and relative values can be intuited for different
given dataset there are multiple fitting optima and there is
systems. In accordance with the observations in Husband &
covariance between the parameters. To further complicate
Boxall () and Husband & Boxall () an uncondi-
(and potentially increase the dimensionality) of the model
tioned, corrodible, unlined iron pipe is expected to release
fitting process, there is uncertainty in the initial system
much material during erosion (high α) but this process is
state. It may therefore be desirable if not mandatory to use
unlikely to result in material exhaustion (low βe). The sub-
a metaheuristic such as evolutionary or swarm optimisation
sequent regeneration should be relatively quick (high βr).
(e.g. Kennedy et al. ) to efficiently explore the problem
In polyethylene (PE) pipes βe should be relatively high as
space when fitting the proposed model to a dataset. In
material exhaustion can easily be achieved although the
addition, it may be possible to achieve more accurate cali-
amount of material mobilised, and therefore α, will be low.
flow-trial-specific
Regeneration and βr will be slower and lower than for
brations
if
continuous
rather
than
turbidity data are used.
unlined iron pipes. βr represents different processes in
The model is largely mesh independent i.e. the material
unlined iron and PE pipes; it is a proxy for a variety of com-
mobilised over a simulation Ntotal is relatively independent
plex processes including iron corrosion, scale formation,
of both Δτ and Δt as is necessary for a numerical model.
slime development and biofilm growth.
However, the accuracy of Ntotal asymptotically converges
The shear strength range over which material erosion
as the values of Δτ and Δt decrease (Figure 6), thus sensitivity
and regeneration are to be discretely tracked must be
analysis can be conducted to give maximum sensible values
decided at the start of a model run. It is computationally
for both and limit the computational effort required for
inefficient to simply pick a large number for τmax, the
simulations. When calibrating the model for real-world sys-
upper bound of that range. For a particular simulation τmax
tems the maximum values of Δτ and Δt may be limited by
could be set to the shear stress above which material erosion
Figure 5
|
Model validation for 3.7 km-long trunk main. (a) Boundary shear stress profile, (b) predicted variation in relative material quantity φ for selected shear strength bands, (c) predicted material flux rate dN(t)=dt from each m2 of pipe wall and (d) predicted and observed turbidity response at the downstream (‘d/s’) end of the main for each of three successive flow trials.
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Figure 6
|
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Modelling the erosion and regeneration of discolouration material in distribution systems
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Sensitivity of the proposed model to Δτ. (a) dN(t)=dt and T(t) for a constant τ range but different values of Δτ (given a pulse increase in τa). (b) The accuracy of the model
predictions asymptotically improves when Δτ decreases.
has not been detectable in similar mains to the one being
this may not be practical given the cost in terms of water
modelled. However, there is contradictory evidence for the
wastage, energy, time and money and the risk to customers.
conditions required for ‘clean’ pipes:
It is suggested that a risk-based approach be taken and τmax
•
In the Netherlands pipes are considered clean if flushed
•
Attempts to calibrate the PODDS model for plastic mains
by the modeller by estimating the maximum flow over the
in the UK indicated that no more material was being
simulation period. The method for calculating that flow will
eroded from the wall when the shear stress exceeded ∼
depend on whether the motivation for the modelling work
1.2 Pa (Husband & Boxall ) yet Sharpe et al. ()
is to study the discolouration risk that may result from a
•
1
at 1.5 m s
(Vreeburg & Boxall ).
be based on the maximum shear stress that a main is anticipated to experience. A value can therefore be determined
saw material erosion at much higher shear stresses in
burst (in which case the orifice equation could be used to esti-
PVC pipes under laboratory conditions.
mate flows) or from deliberately increasing the mean flow up
During hydrant flushing fieldwork Husband & Boxall
to a target level for operational reasons.
() did not find any evidence of there being a cleaning shear stress in unlined iron pipes.
The proposed model still requires thorough validation, primarily to explore the error in predictions made using calibrated models and continuous flow data. This should be
Instead, one could attempt to measure rather than esti-
done through testing its applicability to different systems.
mate the cleaning shear stress for the main(s) of interest but
It is also necessary to investigate whether temporal variance
89
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Modelling the erosion and regeneration of discolouration material in distribution systems
in parameters such as βr is significant and therefore needs to be modelled. It is the intention to integrate the model within an existing hydraulic modelling package, as was done for PODDS. This will allow for the modelling of dendritic and looped multiple-pipe systems and could allow simulations to be set up and executed from a graphical environment that is familiar to the water industry and academia.
CONCLUSIONS In this paper a new model has been proposed for tracking over time both the erosion and accumulation/regeneration of cohesive layers of discolouration material from the walls of water distribution systems. The existing PODDS model may be suitable for modelling material erosion but its formulations do not represent material regeneration processes. The proposed model is not subject to that limitation. A software implementation and a material transport model have been coded as software so as to verify the empirical, numerical model and test for mesh independence. The model’s material-strength-dependent erosion and strengthindependent regeneration processes have been demonstrated through manually fitting the model to continuous flow and partly continuous turbidity data from a series of trunk main flow trials. If the model can successfully be validated then it could be used to design and schedule flow conditioning operations for managing discolouration risk.
ACKNOWLEDGEMENTS This research was undertaken as part of the Pipe Dreams project (Engineering and Physical Sciences Research Council grant EP/G029946/1). Fieldwork was conducted in conjunction with Anglian Water, Northumbrian Water, United Utilities and Yorkshire Water.
REFERENCES Blokker, E. M., Schaap, P. G. & Vreeburg, J. H. Comparing the fouling rate of a drinking water distribution system in two
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different configurations. In: Urban Water Management: Challenges and Opportunities. Centre for Water Systems, Exeter, UK. Boxall, J. & Prince, R. Modelling discolouration in a Melbourne (Australia) potable water distribution system. Journal of Water SRT – Aqua 55 (3), 207–219. Boxall, J. B. & Saul, A. J. Modeling discoloration in potable water distribution systems. Journal of Environmental Engineering 131, 716. Boxall, J. B., Saul, A. J., Gunstead, J. D. & Dewis, N. Regeneration of discolouration in distribution systems. In: ASCE EWRI Conference Proceedings. Philadelphia, USA. Boxall, J. B., Skipworth, P. & Saul, A. J. A novel approach to modelling sediment movement in distribution mains based on particle characteristics. In: Water Software Systems: v. 1: Theory and Applications, B. Ulanicki, B. Coulbeck and J. P. Rance (eds). Research Studies Press, Hertfordshire, UK, pp. 263–273. Husband, P. S. & Boxall, J. B. Water Distribution System Asset Deterioration and Impact on Water Quality: A Case Study. ASCE, Hawaii, pp. 516–516. Husband, P. S. & Boxall, J. B. Field studies of discoloration in water distribution systems: Model verification and practical implications. Journal of Environmental Engineering 136 (1), 86–94. Husband, P. S. & Boxall, J. B. Asset deterioration and discolouration in water distribution systems. Water Research 45 (1), 113–124. Husband, P. S., Jackson, M. & Boxall, J. B. Trunk main discolouration trials and strategic planning. In: Urban Water Management: Challenges and Opportunities. Centre for Water Systems, Exeter, UK. Husband, P. S., Whitehead, J. & Boxall, J. B. The role of trunk mains in discolouration. Proceedings of the ICE – Water Management 163, pp. 397–406. Kennedy, J. F., Eberhart, R. C. & Shi, Y. Swarm Intelligence. Morgan Kaufmann Publishers, San Francisco. Oliphant, T. E. Python for scientific computing. Computing in Science & Engineering 9 (3), 10–20. Rossman, L. & Boulos, P. Numerical methods for modeling water quality in distribution systems: A comparison. Journal of Water Resources Planning and Management 122 (2), 137–146. Ryan, G., Mathes, M., Haylock, G., Jayaratne, A., Wu, J., NouiMehidi, N., Grainger, C. & Nguyen, B. V. Particles in water distribution systems. Tech. Rep. 33, Cooperative Research Centre for Water Quality and Treatment, Salisbury, Australia. Seth, A. D., Husband, P. S. & Boxall, J. B. Rivelin trunk main flow test. In: Proc. of the 10th International Conference on Computing and Control for the Water Industry, CCWI, 1–3 September, Sheffield, UK. Sharpe, R., Smith, C., Biggs, C. A. & Boxall, J. B. Pilot scale laboratory investigations into the impact of steady state conditioning flow on potable water discolouration. In: Proc. 12th Annual Conference on Water Distribution Systems
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Modelling the erosion and regeneration of discolouration material in distribution systems
Analysis (WDSA), K. E. Lansey, C. Y. Choi, A. Ostfeld & I. L. Pepper (eds). ASCE, Tucson, AZ, USA. USEPA EPANET. http://www.epa.gov/nrmrl/wswrd/dw/ epanet.html. Vreeburg, J. Discolouration in drinking water systems: A particular approach. PhD thesis, Delft University of Technology, The Netherlands.
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Vreeburg, J. H. G. & Boxall, J. B. Discolouration in potable water distribution systems: A review. Water Research 41, 519–529. Vreeburg, J., Schippers, D., Verberk, J. & van Dijk, J. Impact of particles on sediment accumulation in a drinking water distribution system. Water Research 42 (16), 4233–4242.
First received 29 November 2012; accepted in revised form 14 June 2013. Available online 13 September 2013
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Microbiological performance of novel household water treatment devices in India Z. P. Bhathena, S. Shrivastava, Poonam Londhe and Joe Brown
ABSTRACT Commercial innovation of household-scale water treatment (HWT) devices is rapid in India, where unsafe drinking water contributes to the high burden of disease and death associated with diarrhoeal diseases. Performance testing data for novel devices are not publicly available and there has been no systematic attempt to independently verify manufacturer effectiveness claims. We purchased three gravity-driven HWT devices available on the Indian market to evaluate their performance in reducing bacteria, viruses, and protozoan surrogates in the laboratory according to World Health Organization testing protocols. Results indicated that technologies were moderately effective in reducing Escherichia coli (1.6–2.9 log10) and MS2 (1.4–2.8 log10), and less effective against Bacillus subtilis spores (0.73–2.2 log10) and 3 μm microspheres (0.33–0.56 log10), as means over the testing period
Z. P. Bhathena (corresponding author) S. Shrivastava Poonam Londhe Dept of Microbiology, Bhavans Research Centre, Bhavans College, Andheri, Mumbai 58, India E-mail: zarine_bhathena@rediffmail.com Joe Brown Georgia Institute of Technology, School of Civil and Environmental Engineering, 790 Atlantic Drive, Atlanta, GA 30332-0355, USA
(750–4,000 l). Effectiveness declined sharply over the duration of testing for each device, suggesting that the manufacturer-specified effective lifespans were overestimated for all devices. Moderate variability was observed across challenge conditions intended to represent actual use conditions, but performance was not significantly different between challenge waters or ambient testing temperature. Our results suggest that these novel devices do not meet international minimum performance recommendations and that manufacturer effectiveness claims are misleading. Further technological innovation and regulation in this sector may serve to protect public health. Key words
| drinking water, hygiene, performance testing, water purifiers
INTRODUCTION An estimated 97 million people in India lack access to an
transport, storage, and handling (Wright et al. ).
‘improved’ water source (WHO/UNICEF ), and many
Because the quality of drinking water may not be trusted,
more may rely on microbiologically or chemically unsafe
household
water
treatment
(especially
boiling)
is
water since ‘improved’ does not always equal ‘safe’
common in India (Clasen et al. ), even in households
(WHO a; Onda et al. ). Only 23% of the total
that are connected to a piped water supply. Poor access
population is served by a household-level piped water
to safe water is in part responsible for high childhood
connection. Connected households in India may experi-
mortality due to diarrhoea in India, which has been esti-
ence frequently intermittent service, which is a risk
mated by various methods to be as few as 212,000 (Liu
factor for microbial contamination. The remaining 77%
et al. ) or up to 535,000 (Boschi-Pinto et al. )
rely on surface water, private or public wells, rainwater
deaths per year. India has more deaths due to diarrhoea
harvesting, or other sources. While water supplies may
in children than any other country (ibid.; WHO Global
often be low-risk at the point of treatment or distribution,
Health Observatory ).
any drinking water collected outside the home is at high
Because universal, safe, reliable, on-plot water supply
risk of microbial contamination by the time it is ulti-
may be years away for most Indians, household-level water
mately consumed, due to possible re-contamination in
treatment (HWT) may help increase access to safer drinking
doi: 10.2166/ws.2013.177
Z. P. Bhathena et al.
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Microbiological performance of water treatment devices in India
water (Mintz et al. ; Sobsey ; WHO ). A wide
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MATERIALS AND METHODS
variety of household-level water treatment devices are now available in the Indian market, mostly aimed at middle to
Devices
upper-income consumers in urban areas (Brown et al. ). Despite increasing sales and growth in the Indian
We purchased three filtration devices (Table 1) for testing.
water
technologies
From an informal survey of Mumbai retail outlets stocking
have been subjected to laboratory testing to verify manufac-
HWT products, these models were most common apart
turers’ claims of microbiological effectiveness, so their role
from the Hindustan Unilever Pureit device, which has pre-
in increasing access to safe water in India remains
viously been tested in a similar manner (Clasen et al. ).
unknown.
Each device varied by treatment mechanism, design life,
treatment
device
market,
few
In this paper, we describe systematic testing of three
flow rate, and effectiveness claims. Devices required no elec-
widely available, gravity-driven, household-scale drinking
tricity or pressurized water input (operating by gravity only),
water filtration devices on the Indian market. Our objec-
no chemical dosing by the user, and included integrated safe
tive in undertaking this research was to evaluate the
storage of treated water up to 18–20 L. Units were designed to
performance of the devices for their ability to remove
operate as ‘table top’ filters, rather than plumbed-in devices
microbes from water over long-term daily use, under rea-
such as point-of-entry (POE) or under-sink technologies.
listic use conditions, and in accordance with recently published guidance and recommendations for microbial
Testing procedure
performance testing by the World Health Organization (WHO b). A secondary aim of our study was to
We used current WHO (b) performance testing rec-
assess whether chemical leachate from filtration devices
ommendations in developing laboratory methods. The 12
could result in any health risks, which has been suggested
devices (four of each) were assembled according to manufac-
previously (Brown et al. ). The microbiological per-
turers’ instructions. The devices were monitored for their
formance and chemical leachate data that we have
performance
produced is a necessary first step in a broader assessment
(Table 1), with 24 L of microbe-spiked challenge water
of the potential current and future roles these previously
(Table 2) dosed per day manually. Challenge water was pre-
uncharacterized devices may play in providing safer
pared daily from a stock solution of microbial cultures at
drinking water in India.
each spike point, with simultaneous bacteria and virus spikes
Table 1
|
throughout
their
recommended
lifespan
Devices tested, reported mechanisms, and recommended lifespan
Device name and
Manufacturer
Flow
Treated water
retail cost in
recommended
rate (ml/
storage volume
Mumbai (2011)
Reported active mechanism
design life
min)
(litres)
Claims
Tata Swatch (Rs 1195)
Granular media filtration and inactivation via contact with silver nanoparticles
3,000 l
20–100
18 L
99.99% reduction of bacteria and viruses from water
Kent Gold (Rs 2495)
Hydrophilic ultrafiltration membrane encased within a hollow fibre tube, sediment filter for removal of suspended impurities, activated carbon filter augmented with silver nanoparticles
4,000 l
20–130
20 L
‘Healthier water’. NSF certified cyst reduction
Aquasure PCTi (Rs 2290)
‘Positively charged attractors’ that trap microbes. Proprietary ‘microfibre mesh’ employing nanotechnology.
750 l
20–45
20 L
Removes ‘all’ disease causing bacteria, viruses, and cysts
Z. P. Bhathena et al.
93
Table 2
|
|
Microbiological performance of water treatment devices in India
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dissolved matter; and (2) packaged mineral water seeded
Characteristics of challenge water
with 1% (v/v) sterilized untreated wastewater to represent
Parameters
Challenge water 1
Challenge water 2
Source
Packaged mineral water
Packaged mineral water seeded with autoclaved 1% untreated sewage
Test waters were seeded with known concentrations of bac-
Chlorine, mg/l
<0.01
<0.01
The test microbes and surrogates were chosen based on
pH, range (mean)
7.0–8.0 (7.5)
7.0–8.5 (7.5)
WHO (b) recommendations and were used as surrogates
Turbidity, NTU, range
<1–5
31–40
for pathogenic bacteria, viruses, and protozoa potentially
Temperature, range (mean)
28–33 C (30.5 C)
18–23 C (20 C)
Total suspended solids (TSS), mean
2
3.6
Total organic carbon (TOC), mg/l
< 0.01
poor quality of water with high organic load (Table 2). teriophage, bacteria, and surrogates for protozoan parasites.
found in untreated drinking water. The bacterial group W
W
W
was represented by Escherichia coli ATCC 10536 and
W
was spiked into the input water at a concentration of 106 cfu/ml. The viral group was represented by male-specific coliphage MS2 ATCC 15997, spiked at a concentration of 105 pfu/ml in input water. The protozoan group was rep-
0.01–0.02
resented by 3 μm microspheres (Fluroesbrite Plain YG 3.0 μm microspheres, Polysciences Inc., PA, USA), this would conservatively estimate removal by size-exclusion
on the first day and spores and microspheres the second. New W
for protozoa (e.g., Cryptosporidium oocysts are 4–6 μm).
stock cultures were prepared once per week and stored at 4 C.
Bacillus spp. spores have been suggested as experimental
Filters were cleaned when needed to restore flow rate, accord-
surrogates for Cryptosporidium oocysts in treatment process
ing to manufacturers’ instructions. Samples of untreated and
and transport modelling (Dey ; Nieminski et al. ;
treated water were assayed for test microbes and a comparison
Chauret ; Verhille et al. ; WHO b). We spiked
of concentrations in pre- and post-treatment water was used to
Bacillus subtilis ATCC 6633 spores into the input water at
determine the log10 reduction of test microbes.
a concentration of 104 cfu/ml, as we did not know whether
To obtain representative microbial performance data from devices, log reduction values were determined at 0,
the technologies would remove oocyst-sized particles by size exclusion only.
25, 50, 60, 75 and 100% of the manufacturer-recommended life spans of the devices, consistent with WHO (b) rec-
Microbiological analysis
ommendations. At these sample points, we collected the first 500 ml of throughput for analysis. Because the Tata
E. coli ATCC 10536 was grown overnight, washed with
Swatch device employed silver-augmented granular media
phosphate-buffered saline (PBS), and adjusted to a culture
requiring extended contact time to achieve optimal perform-
density of 0.1 OD at 620 nm corresponding to approxi-
ance, we tested samples from this device as the first 500 ml
mately 108 cfu/ml. 1 ml of this culture suspension was
throughput and additionally after 3 hours of contact time
added per litre of test water to attain a final concentration
attained by blocking the outlet such that the input water col-
of 107 cfu/100 ml. E. coli were enumerated in pre- and
lected in the chamber and was effectively in contact with the
post-filtration samples by filtering 100 ml of sample
germicidal agent for 3 hours, after which the outlet was
through 47-mm diameter, 0.45 μm pore size cellulose
released and water collected for analysis.
ester filters using a membrane filtration apparatus (USEPA ), followed by incubation on Endo agar.
Challenge waters
W
Plates were incubated at 37 C for 18–24 h and E. coli concentrations expressed as colony forming units (cfu) per
Two types of test waters were used in challenge tests, con-
100 ml of water.
sistent with WHO (b) recommendations: (1) packaged
MS2 bacteriophage suspensions were cultivated to
mineral water to model high quality water with low
obtain high-titre stocks (1014 pfu/ml). Phages were harvested
94
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Microbiological performance of water treatment devices in India
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and spiked into challenge waters to concentrations of
Kruskal–Wallis one-way analysis of variance (Kruskal &
105 pfu/ml. MS2 bacteriophages in pre- and post-treatment
Wallis ) to compare means across testing parameters
water were enumerated following the double agar layer
(challenge water type, temperature) and for comparing
(DAL) procedure (USEPA ). Plaques were counted
device performance. Differences between groups were con-
and expressed as plaque forming units (pfu) per 100 ml.
sidered to be statistically significant at a significance level
B. subtilis spores were obtained by culturing B. subtilis W
ATCC 6633 on sporulating agar (AK#2) for 5 days at 35 C
of α ¼ 0.05. All statistical testing was performed in Stata version 12.1 (StataCorp, College Station, TX, USA).
± 2, with the culture aseptically scraped into 5 ml PBS and heated at 80 C for 30 min (Dey ; Chauret ). Spore W
stock thus prepared and confirmed microscopically was
RESULTS
spiked into challenge test water to achieve the concentration of 104 cfu/ml. Both pre- and post-treatment samples were W
pre-treated by heat exposure at 80 C for 30 min before culturing on nutrient agar with 0.05% bromothymol blue by the W
Results from microbial challenge testing are summarized in Table 3. Over the cumulative testing period per filter, all filters reduced E. coli, MS2, B. subtilis spores, and
pour plate method. The plates were incubated at 37 C for 24
microspheres, although reductions declined over the rec-
hours.
ommended
Microspheres were spiked into test waters to a concen-
lifespans
of
the
devices
and
moderate
variability of challenge water type stored at varied tempera-
tration of 104 cfu/ml. 5 ml of pre- and post-treatment
tures. Figure 1 presents a summary of mean reductions
samples were filtered using 25 mm filters and individual
collapsed across challenge conditions.
microspheres were counted via epifluorescent microscopy and counts expressed as microspheres per 100 ml.
For the Tata Swatch device, mean reductions of E. coli across testing conditions were 1.6 log10 (range 0.10–7.1) and 2.6 log10 (range 0.10–7.4) after 3 hours of contact time
Physico-chemical parameters
before analysis. The devices were more effective against MS2, with mean reductions of 2.3 log10 (range 0.50–7.1)
Challenge test water samples used were analysed at every
and 2.8 log10 (range 0.50–7.1) after 3 hours’ contact time.
spike point for physico-chemical parameters like turbidity,
B. subtilis spores were reduced by a mean of 0.83 log10
total organic carbon, pH, and chlorine according to Stan-
(range 0–3.1) and 0.73 log10 (range 0–3.5) after 3 hours.
dard Methods (Eaton et al. ). Post-treatment samples
Microspheres were reduced minimally over the rec-
collected after every spike point challenge were analysed
ommended device lifespan, by a mean 0.33 log10 (range
for turbidity and samples were collected and preserved
0.10–1.1) or 0.43 log10 (range 0.20–1.8) after contact time.
for metals analysis (Al and Ag). Aluminium (Al) was
Our hypothesis that greater contact time with silver-
assayed in pre- and post-treatment Aquasure PCTi
amended media would result in greater microbiological
device-treated water while silver (Ag) residue detection
reductions was not supported by these data, however, as per-
was performed on samples before and after passage
formances against E. coli, MS2, and spores were not
through Tata Swatch and Kent Gold devices by ICP-
significantly different between the two types of samples
OES (inductively coupled plasma–optical emission spec-
(p ¼ 0.25, p ¼ 0.53, p ¼ 0.66, respectively).
trophotometry (ThermoFisher Scientific Model: I-CAP
The Kent Gold device reduced E. coli by a mean of
6300)).
1.8 log10 (range 0.1–7.2), MS2 by a mean of 1.4 log10
Statistical methods
and microspheres by 0.49 log10 (range 0.20–1.8). The Aqua-
(range 0–7.1), B. subtilis spores by 1.4 log10 (range 0–1.4), sure PCTi device reduced E. coli by a mean of 2.9 log10 Log10 reduction values calculated from pre- and post-treat-
(range 0.80–7.4), MS2 by a mean of 2.1 log10 (range 0.50–
ment assays were not normally distributed. We used the
7.1), B. subtilis spores by 2.2 log10 (range 0.10–6.8), and
Mann–Whitney U test (Mann & Whitney ) and the
microspheres by 0.56 log10 (range 0.060–2.2). Reductions
Z. P. Bhathena et al.
95
Table 3
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Microbiological performance of water treatment devices in India
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Challenge effectiveness against test microbes (log reduction values) over defined lifespan E. coli
B. subtilis spores
MS2
3 μm Microspheres
Spike point W
W
30 C Mean temperature Challenge water
W
15–20 C
W
30 C
W
15–20 C
W
30 C
W
15–20 C
W
30 C
15–20 C
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
0%
2.0
2.7
2.0
0.8
7.1
7.0
7.1
7.0
2.0
2.4
2.4
3.1
1.0
1.1
0.9
0.9
25%
1.0
0.7
2.4
3.0
1.7
1.5
1.8
2.8
0.8
0.3
1.7
1.9
0.2
0.3
0.2
0.3
50%
2.9
2.8
2.8
1.8
1.7
2.1
2.1
1.8
1.2
0.2
0.6
0.4
0.2
0.2
0.2
0.3
60%
1.8
1.5
0.5
1.8
0.8
0.8
0.5
0.5
0.0
0.4
0.0
0.5
0.2
0.2
0.2
0.3
75%
1.9
1.3
0.8
1.3
0.9
0.8
2.6
2.6
0.0
0.1
0.2
0.0
0.2
0.2
0.1
0.2
100%
0.9
1.1
0.1
1.0
0.6
0.6
0.8
0.6
0.0
0.5
1.1
0.1
0.1
0.2
0.1
0.2
Tata Swatch
Tata Swatch, allowing for 3 h of contact time before sampling 0%
7.4
7.2
7.4
7.2
7.1
7.0
7.1
7.0
1.9
2.0
2.1
3.5
1.4
1.8
1.1
1.4
25%
2.8
0.9
2.2
1.9
5.2
5.2
1.7
5.2
0.4
0.8
0.5
0.3
0.2
0.3
0.2
0.3
50%
2.8
2.8
2.1
1.8
2.8
2.2
1.8
2.2
0.3
0.2
0.3
0.2
0.2
0.3
0.2
0.3
60%
2.7
1.5
2.8
1.8
1.1
0.5
0.5
0.5
1.0
0.4
1.5
1.1
0.2
0.3
0.2
0.3
75%
1.9
1.3
0.8
1.5
0.9
2.6
2.6
2.6
0.0
0.1
0.1
0.1
0.2
0.2
0.2
0.2
100%
0.1
0.1
0.6
0.8
0.6
0.6
0.6
0.6
0.3
0.0
0.1
0.2
0.2
0.2
0.2
0.2
0%
1.4
7.2
2.9
3.3
2.7
2.0
7.1
7.0
2.1
6.8
2.0
6.8
1.6
1.8
1.3
1.4
25%
1.5
3.8
1.5
3.1
0.1
0.0
0.1
0.1
0.9
1.9
0.8
1.8
0.4
0.4
0.5
0.6
50%
1.5
2.9
3.0
2.7
1.7
1.8
1.7
1.7
1.1
1.0
2.1
0.9
0.3
0.4
0.4
0.4
60%
1.1
0.1
0.9
3.0
0.9
1.7
2.1
1.3
0.1
0.6
1.7
0.7
0.3
0.3
0.3
0.3
75%
0.6
0.8
0.9
1.9
0.6
0.6
0.6
0.6
0.0
1.4
0.0
0.0
0.2
0.3
0.2
0.3
100%
0.5
0.7
0.9
1.9
0.6
0.6
0.5
0.4
00
1.3
0.0
0.0
0.1
0.2
0.2
0.3
0%
3.5
7.2
7.4
1.5
7.1
7.0
2.5
7.0
6.1
6.8
6.8
4.8
1.6
2.2
0.9
1.3
25%
2.5
3.5
1.2
5.0
1.0
0.8
1.1
0.5
2.0
1.4
0.7
1.1
0.1
0.2
0.2
0.2
50%
3.0
2.2
1.8
2.6
1.5
0.8
1.6
1.8
1.3
0.7
1.6
1.3
0.6
0.4
0.6
0.2
60%
0.8
2.7
1.3
2.5
1.5
0.8
1.5
0.7
0.8
0.1
1.8
2.1
0.7
0.5
0.6
0.3
75%
2.6
3.3
1.7
3.7
1.5
2.1
1.8
1.9
2.3
2.0
1.2
0.8
0.3
0.3
0.6
0.3
100%
2.7
2.9
3.0
0.9
2.2
2.0
1.3
1.3
1.6
1.6
1.9
1.6
0.2
0.3
0.4
0.4
Kent Gold
Aquasure PCTi
of E. coli (p ¼ 0.033), B. subtilis spores (p ¼ 0.0011), and
each analyte, reductions did decrease significantly over the
microspheres (p ¼ 0.010) were significantly greater in the
testing period (p < 0.001), suggesting greater performance
Aquasure PCTi device, and increased against MS2 although
initially followed by sharp declines (Table 3; Figure 1).
not meeting the significance criterion (p ¼ 0.081).
Chemical conditions in challenge waters were main-
Mean reductions did not vary significantly by challenge
tained and analysed at sampling points. We did not assess
water for E. coli (p ¼ 0.26), MS2 (p ¼ 0.84), B. subtilis
turbidity reduction, since pre- and post-treatment turbidity
spores (p ¼ 0.96), or microspheres (p ¼ 0.19). Also, we did
was low (<1 NTU). We noted that the Tata Swatch leached
not observe any differences in mean log10 reductions by ambi-
a mean 0.042 mg/l Ag into product water over the course
ent temperature (p ¼ 0.98, 0.89, 0.70, 0.93, respectively). For
of testing (range: <0.01–0.05 mg/l). Aluminium leaching
96
Figure 1
Z. P. Bhathena et al.
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Microbiological performance of water treatment devices in India
Water Science & Technology: Water Supply
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Summary of mean log10 reduction of E. coli, MS2, B. subtilis spores, and microspheres by device and lifespan testing point. Each bar represents the mean value of the four conditions (two temperatures and two challenge waters).
from devices was below detectable limits (<0.01 mg/l). All
peer-reviewed literature, however. None of the devices
units exhibited clogging and markedly reduced flow rates
tested would have met more stringent applicable inter-
after 75% of life span was achieved, particularly with the
national standards such as those published by NSF-
higher turbidity challenge water 2.
International (NSF ) or the US Environmental Protection Agency (USEPA ). The NSF and EPA standards recommend a 6 log10 reduction of bacteria,
DISCUSSION
4 log10
reductions of viruses, and a 3 log10 reduction of protozoa. These results may be contrasted with similar testing of
All devices tested provided measurably improved water over
other common, commercially available devices for treating
the course of testing, although reductions of microbes and
household drinking water, including technologies from
microspheres declined over the course of testing (p <
East Asia (Brown et al. ) and India (Clasenet al. ).
0.001; Table 3; Figure 1). Results therefore suggest that the
We examined the results in light of the claims made by
useful life of all devices has been overestimated by manufac-
manufacturers. The Tata device performed well under the
turers, as effectiveness claims are only likely to be met early
claim of 99.99% reduction of bacteria and viruses, even
in testing if at all. Based on mean performance only, technol-
allowing for increased contact time with media. The Kent
ogies would fail to meet WHO minimum recommended
device did produce water that could be claimed as
performance for microbiological water purifiers at the ‘pro-
‘healthier’,
tective’ level, which specifies a minimum of 2 log10 (99%)
performance levels were not met (WHO b). Aquasure’s
reduction of bacteria and protozoa, and a 3 log10 (99.9%)
claim that ‘all’ microbes are eliminated is not tenable
reduction in viruses. ‘Interim’ status is based on meeting
given these results, although its performance exceeded that
two of these three conditions and providing evidence of
of the other devices tested.
although
minimum
WHO-recommended
the impact on health. The Aquasure PCTi device would
No significant Ag or Al leaching was observed from
meet this interim target if supported by health impact data,
these devices over a range of use conditions. The measured
as mean performance exceeded 2 log10 for E. coli and B.
mean Ag leaching from the Tata device was well under the
subtilis spores. No such evidence has been reported in the
WHO-recommended limit of 0.1 mg/l (WHO a).
97
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Microbiological performance of water treatment devices in India
CONCLUSIONS The microbiological performance data that we have produced is a necessary first step in assessing the potential current and future roles these devices may play in providing safer drinking water in India. Although devices did measurably improve water quality, especially early in testing, reductions in key microbes and microspheres did not indicate that technologies could meet international minimum standards for drinking water treatment. We recommend improvements in treatment technology and limiting unsubstantiated claims about microbiological effectiveness that accompany these products. Given the widespread and growing need for potable drinking water in India (Mudur ; Neeri ) and the serious risk of sickness and death associated with consuming unsafe water, consumers should not be misled by dubious claims of effectiveness. The importance of truth in advertising for water treatment technologies is of great importance because, in most cases, users cannot verify that devices do what manufacturers claim.
REFERENCES Boschi-Pinto, C., Velebit, L. & Shibuya, K. Estimating child mortality due to diarrhea in developing countries. Bulletin of the World Health Organization 86, 710–717. Brown, J., Outlaw, T., Clasen, T., Wu, J. & Sobsey, M. Safe Water for All: Harnessing the Private Sector to Reach the Underserved. Report, World Bank/International Finance Corporation, Washington, DC. Brown, J., Ratana, C., Wang, A. & Sobsey, M. Microbiological effectiveness of mineral pot filters in Cambodia. Environmental Science and Technology (Accepted and published online, 3 October 2012). Chauret, C. Chlorine dioxide inactivation of Cryptosporidium parvum oocysts and bacterial spore indicators. Applied and Environmental Microbiology 67 (7), 2993–3001. Clasen, T., McLaughlin, C., Nayaar, N., Boisson, S., Gupta, R., Desai, D. & Shah, N. Microbiological effectiveness and cost of disinfecting water by boiling in semi-urban India. American Journal of Tropical Medicine and Hygiene 79 (3), 407–413. Clasen, T., Nadakkati, S. & Menon, S. Microbiological performance of a water treatment unit designed for household use in developing countries. Tropical Medicine and International Health 11 (9), 1399–1405. Dey, B. P. USDA/FSIS microbiology laboratory guidebook, 3rd edn, United States Department of Agriculture, Food
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Safety and Inspection Service, Washington, DC (http://www. fsis.usda.gov/science/microbiological_Lab_Guidebook/). Eaton, A. D., Clesceri, L. S., Rice, E. W., Greenberg, A. E. & Franson, M. A. H. (eds) Standard Methods for the Examination of Water & Wastewater, 21st edn. American Public Health Association, American Water Works Association, Water Environment Federation, Washington, DC. Kruskal, W. H. & Wallis, W. A. Use of ranks in one-criterion variance analysis. Journal of the American Statistical Association 47 (260), 583–621. Liu, L., Johnson, H. L., Cousens, S., Perin, J., Scott, S., Lawn, J. E., Rudan, I., Campbell, H., Cibulskis, R., Li, M., Mathers, C. & Black, R. E. Child health epidemiology reference group of WHO and UNICEF. Lancet 9;379 (9832), 2151–61. Epub 2012 May 11. Mann, H. B. & Whitney, D. R. On a test of whether one of two random variables is stochastically larger than the other. Annals of Mathematical Statistics 18 (1), 50–60. Mintz, E. D., Reiff, F. M. & Tauxe, R. V. Safe water treatment and storage in the home: a practical new strategy to prevent waterborne disease. Journal of the American Medical Association 273 (12), 948–953. Mudur, G. India’s burden of waterborne diseases is underestimated. British Medical Journal 326, 1284. NEERI Potable water quality assessment in some major cities in India. Journal of Institute of Public Health Engineers 4, 65. Nieminski, E. C., Bellamy, W. D. & Moss, L. R. Using surrogates to improve plant performance. Journal of the American Water Works Association 92 (3),67–78. NSF American National Standard/NSF International, Microbial Water Purifiers (ANSI/NSF P231). NSF International, Ann Arbor, MI. Onda, K., LoBuglio, J. & Bartram, J. Global access to safe water: accounting for water quality and the resulting impact on MDG progress. International Journal Environment Research Public Health 9 (3), 880–894. Sobsey, M. Managing Water in the Home: Accelerated Health Gains from Improved Water Supply. World Health Organization, Geneva. WHO/SDE/WSH/02.07. USEPA Guide Standard and Protocol for Testing Microbiological.Water Purifiers. United States Environmental Protection Agency, Washington, DC. USEPA (United States Environmental Protection Agency) Method 1602: Male-specific (Fþ) and somatic coliphages in water by single agar layer (SAL) procedure. USEPA Office of Water, Publication EPA 821-R-01-029, Washington, DC. USEPA (United States Environmental Protection Agency) Method 1604: Total coliforms and Escherichia coli in water by membrane filtration using a simultaneous detection technique (MI Medium). Publication EPA-821-R-02-024. USEPA Office of Water (4303T), Washington, DC. Verhille, S., Hofmann, R., Chauret, C. & Andrews, R. Indigenous bacterial spores as indicators of Cryptosporidium
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inactivation using chlorine dioxide. Journal of Water and Health 1 (2), 91–100. WHO (World Health Organization) Combating Waterborne Disease at the Household Level. World Health Organization, Geneva. WHO (World Health Organization) a WHO Guidelines for Drinking Water Quality, 4th edn. World Health Organization, Geneva. WHO (World Health Organization) b Evaluating Household Water Treatment Options: Health-Based Targets and Performance Specifications. World Health Organization, Geneva.
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WHO (World Health Organization) Global Health Observatory Global Burden of Disease, 2004 Update. WHO, Geneva. www.who.int/evidence/bod (accessed 1 October 2012). WHO/UNICEF Progress on drinking-water and sanitation: 2012 Update. Joint Monitoring Programme for Water Supply and Sanitation report available online at wssinfo.org. (accessed 12 October 2012). Wright, J., Gundry, S. & Conroy, R. Household drinking water in developing countries: a systematic review of microbiological contamination between source and point-of-use. Tropical Medicine and International Health 9 (1), 106–117.
First received 29 November 2012; accepted in revised form 17 June 2013. Available online 13 September 2013
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Antagonism between clinical and environmental isolates of Pseudomonas aeruginosa against coliforms Vinicius Vicente Martins, Ana Carolina Macarenco, Débora Galves Gradella and Eliana Guedes Stehling
ABSTRACT Water is essential to life, yet many people worldwide do not have access to clean drinking water and suffer or die from preventable diseases caused by unsafe water. Microbiological water analysis is based on coliform bacteria, but these microorganisms can have their growth affected by others, such as Pseudomonas aeruginosa. A total of 60 isolates of P. aeruginosa was investigated in this study to obtain better knowledge about the relationship between P. aeruginosa pigments and the effect of antagonism against coliforms. Of these, 40 isolates were isolated from
Vinicius Vicente Martins Ana Carolina Macarenco Débora Galves Gradella Eliana Guedes Stehling (corresponding author) Departamento de Análises Clínicas, Toxicológicas e Bromatológicas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto – USP – Ribeirão Preto, Brazil E-mail: eliana.stehling@gmail.com
environmental samples (drinking water and soil) and 20 from clinical patients. Three environmental coliform isolates from water samples, two Escherichia coli and one Klebsiella pneumoniae, and an Enterobacter aerogenes were used in antagonism tests. The results have demonstrated that these bacteria were inhibited by P. aeruginosa by an effect known as antagonism. The inhibitory action of P. aeruginosa against coliforms was more effective when P. aeruginosa produced pyocyanin and/or pyoverdin. Key words
| antagonism, coliforms, environmental strains, Pseudomonas aeruginosa, pyoverdin
INTRODUCTION The improvement of global access to clean drinking water is
P. aeruginosa is a bacterium distributed in nature and
a cheap and effective way to improve global health. More
has received the definition of ubiquitous bacteria (Shao
than 1.1 billion people lack access to improved drinking
et al. ). It possesses the capacity to metabolize indepen-
water, and as a consequence, millions suffer from preventa-
dently of the supplement of nutrients and has a great armory
ble illnesses and die every year (Montgomery & Elimelech
of survival strategies, ranging from pigments to the pro-
). Testing for the presence of coliforms is an analysis
duction of biofilm (Klausen et al. ; Kipnis et al. ).
that guarantees the quality of the water. Escherichia coli
This bacterium can secrete a variety of pigments, including
and thermotolerant coliforms (Klebsiella, Enterobacter,
pyocyanin (blue-green) and pyoverdin (yellow-green and
Citrobacter) are the most important indicators of contami-
fluorescent) (Kipnis et al. ; Ganter et al. ).
nation in water (Foppen & Schijven ), but several
Pyocyanin (PCN) is a zwitterion that can easily penetrate
factors can be responsible for failure in drinking water
biological membranes. It can be recovered from the sputum
analysis, including interaction with other organisms, such
of cystic fibrosis (CF) patients and ear secretions infected
as Pseudomonas aeruginosa (Rompré et al. ;Vaconcelos
by P. aeruginosa (Lau et al. ; Liu & Nizet ).
et al. ). When this type of error happens, the water might
However, besides its role in the infections caused by
be considered as safe and potable, when in fact, it can be
P. aeruginosa strains, pyocyanin has been related to an antag-
contaminated by fecal coliforms and other pathogens,
onistic
which can cause human diseases.
especially against coliform bacteria, through the generation
doi: 10.2166/ws.2013.178
phenomenon
against
other
microorganisms,
100
V. V. Martins et al.
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Antagonism between Pseudomonas aeruginosa and coliforms
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of reactive oxygen species, which could be the major factor of
The soil samples were collected from plantation areas of
P. aeruginosa antimicrobial activity (Vaconcelos et al. ).
different crops and also from sand (Table 1). The samples
Pyoverdin (PVD), which is considered a virulence factor
were collected 5 cm below the land surface in sterile con-
(Musthafa et al. ), is a siderophore excreted in large
tainers. One gram of each soil sample was dispersed in
amounts by P. aeruginosa, which has a strong iron require-
9 mL of 0.85% NaCl into sterile test tubes and a series of
ment (ÓMay et al. ). It is a powerful iron chelating
dilutions from 10 2 to 10 10 were prepared in 0.85%
agent that helps in the transport of iron from the extracellu-
NaCl. A 0.2 ml aliquot of the appropriate dilution was
lar environment via outer membrane proteins with a specific
spread aseptically onto cetrimide agar and incubated at
receptor (Hannauer et al. ).
37 C for 48–72 h.
W
The aim of this study was to obtain further knowledge
Typical P. aeruginosa colonies were confirmed by oxidase
about how the pigment production by P. aeruginosa can
test, pigmentation, growth at 42 C, and biochemical tests, e.g.
affect coliform growth. For this, two experiments were car-
citrate assimilation (þ), carbohydrate fermentation ( ), indol
ried out. In the first experiment, with a total of 60 isolates
( ), and lysine decarboxylase ( ) (Casanovas-Massana et al.
W
of P. aeruginosa isolated from drinking water, soil and clini-
; Murray et al. ), and also confirmed by PCR using
cal sources, the action of the pigments was tested using the
specific primers to amplify the open reading frame of the
agar disk experiment, in which the pigment(s) is diffused
oprL gene (De Vos et al. ; Zanetti et al. ). The primers
into the solid medium, without bacteria interaction. In the
(Invitrogen, Brazil) had the following sequences: PAL1, 50 -
second experiment, the interaction between P. aeruginosa
ATGGAAATGCTGAAATTCGGC-30 (a 21-mer correspond-
and coliform bacteria in a liquid medium containing a low
ing to the beginning of the open reading frame of oprL);
amount of nutritional resources was tested to discover
and PAL2, 50 -CTTCTTCAGCTCGACGCGACG-30 (a 21-mer
whether the pigment-producing bacteria have an advantage
corresponding to the end of the open reading frame of
over those which do not produce pigment.
oprL). PCR products separated by 1.8% agarose gel electrophoresis were visualized by staining with ethidium bromide. P. aeruginosa ATCC 27853 served as a positive control.
MATERIALS AND METHODS
Coliform isolates were isolated from water samples as described above and were identified by using MacConkey
Isolation and Identification
agar (Difco) and eosin-methylene-blue agar (Difco) at W
37 C for 24–48 h of incubation. Biochemical tests were perIn total 20 P. aeruginosa clinical isolates were obtained from
formed by Enterobacterial Panel (Probac do Brasil).
patients with CF (Table 1) who attended the School Hospital of Campinas State University (UNICAMP), Brazil, between
Antagonism tests in a solid medium
April 1996 and January 1998 (Ethical Commission Process number no. 045/98 CEP/FCM from 05/27/98).
The antagonism tests in a solid medium were conducted as
For isolation of 20 P. aeruginosa isolates from water,
described by Ichikawa et al. (). The Muller-Hinton (MH)
samples were collected from aquatic habitats (Table 1),
agar (Difco) disks were prepared with a sterilized barren
from three different Brazilian states, into sterile flasks. For
cylinder of 8 mm, after which 30 μL of a 0.5 McFarland
the isolation of bacterial colonies of P. aeruginosa, 100 mL
P. aeruginosa solution were inoculated onto the surface of
aliquots were filtered through sterile 0.45 mm pore mem-
the disks. After incubation at 37 C for 48 h, these disks, con-
W
brane filters (Millipore), 47 mm in diameter, with the aid
taining growths of P. aeruginosa, were transferred onto the
of a vacuum pump. Membranes aseptically removed from
agar surface, where coliforms were spread on and incubated
the filtration equipment were placed on the surface of cetri-
at 37 C overnight. The inhibition zones formed were
W
mide agar (Difco) plates and incubated at 37 C for 48–72 h.
W
measured. A greater inhibition zone diameter indicated
Isolation of 20 P. aeruginosa isolates from soil was per-
more coliform susceptibility to P. aeruginosa. The antagon-
formed as described previously by Mukherjee et al. ().
ism test was performed with all 60 isolates of P. aeruginosa.
V. V. Martins et al.
101
Table 1
|
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Antagonism between Pseudomonas aeruginosa and coliforms
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Results of the presence of antagonism between P. aeruginosa and coliform bacteria related to pigment production and sources of strains
Strain
Source
Sample
Pigment
Ec1
Ec2
Kp1
Ea1
Pa01
Clinical
Patient with CF
PVD
þ
þ
Pa02
Clinical
Patient with CF
PVD
þ
þ
Pa03
Clinical
Patient with CF
PCN
þ
þ
þ
þ
Pa04
Clinical
Patient with CF
PCN and PVD
þ
þ
þ
þ
Pa05
Clinical
Patient with CF
PCN and PVD
þ
þ
þ
þ
Pa06
Clinical
Patient with CF
PCN
þ
þ
þ
þ
Pa07
Clinical
Patient with CF
PCN
þ
þ
þ
þ
Pa08
Clinical
Patient with CF
PCN and PVD
þ
þ
þ
þ
Pa09
Clinical
Patient without CF
PCN
þ
þ
þ
þ
Pa10
Clinical
Patient without CF
PVD
þ
Pa11
Clinical
Patient without CF
PVD
þ
Pa12
Clinical
Patient with CF
PVD
þ
Pa13
Clinical
Patient with CF
PVD
þ
Pa14
Clinical
Patient with CF
PCN
þ
þ
Pa15
Clinical
Patient with CF
None
Pa16
Clinical
Patient without CF
PVD
þ
Pa17
Clinical
Patient with CF
PCN
þ
þ
þ
þ
Pa18
Clinical
Patient with CF
PCN
þ
þ
þ
þ
Pa19
Clinical
Patient with CF
PCN
þ
þ
þ
þ
Pa20
Clinical
Patient with CF
PVD
þ
þ
þ
þ
Pa21
Water
Residence
PCN
þ
þ
þ
Pa22
Water
Residence
PCN
þ
þ
þ
Pa23
Water
Residence
None
Pa24
Water
Residence
None
Pa25
Water
Residence
None
Pa26
Water
Residence
None
Pa27
Water
Residence
PVD
þ
Pa28
Water
School
PVD
þ
Pa29
Water
School
PVD
Pa30
Water
Well
PVD
þ
Pa31
Water
Well
PCN and PVD
þ
þ
þ
þ
Pa32
Water
Well
PVD
Pa33
Water
Well
PVD
Pa34
Water
Well
PVD
Pa35
Water
Well
PVD
Pa36
Water
Well
PVD
Pa37
Water
Well
PVD
Pa38
Water
Well
PVD
Pa39
Water
Well
PVD
Pa40
Water
Well
PVD
(continued)
V. V. Martins et al.
102
Table 1
|
|
Antagonism between Pseudomonas aeruginosa and coliforms
Water Science & Technology: Water Supply
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14.1
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2014
continued
Strain
Source
Sample
Pigment
Ec1
Ec2
Kp1
Ea1
Pa41
Soil
Lettuce
None
Pa42
Soil
Sand
None
Pa43
Soil
Chilli
None
Pa44
Soil
Sugar Cane
None
Pa45
Soil
Sugar Cane
None
Pa46
Soil
Orange
None
Pa47
Soil
Orange
None
Pa48
Soil
Orange
None
Pa49
Soil
Chrysanthemums
None
Pa50
Soil
Chrysanthemums
None
Pa51
Soil
Chrysanthemums
PVD
Pa52
Soil
Chrysanthemums
None
Pa53
Soil
Garden
PCN and PVD
þ
þ
Pa54
Soil
Garden
None
Pa55
Soil
Garden
None
Pa56
Soil
Garden
PVD
Pa57
Soil
Garden
None
Pa58
Soil
Garden
None
Pa59
Soil
Soya
None
Pa60
Soil
Soya
PVD
Antagonism tests in a liquid medium
variance (ANOVA) tests were performed to determine whether there exists a difference between the E. coli (Ec2)
The antagonism tests in a liquid medium were performed as
growth when in contact with different isolates of P. aerugi-
described by Vaconcelos et al. () using an E. coli isolate
nosa after 24, 48 and 72 h, in the antagonism test in the
(Ec2) and 10 P. aeruginosa isolates. McFarland solutions
liquid medium.
(0.5) were prepared from a 24 h growth after which the CFU mL 1 was determined by the Most Probable Number (MPN) method. After this, the necessary volumes from both
RESULTS AND DISCUSSION
bacteria to achieve a final concentration of 100 CFU mL 1 in a 100 mL solution of diluted MH (0.5% m.m 1) were calcuW
The antagonism test in the solid medium was performed with
lated. After 24, 48 and 72 h of incubation in a shaker (37 C
two E. coli isolates (Ec1 and Ec2), a K. pneumoniae (Kp1) and
and 80 rpm), the E. coli CFU mL 1 was determined by the
an Enterobacteraerogenes (Ea1), all of them being isolated
MPN method (US Food and Drug Administration ).
from well water. Ec1 and Kp1 were isolated from a sample
Statistical analysis
and Ea1 from a sample without P. aeruginosa isolation. At
in which P. aeruginosa was isolated concomitantly and Ec2 the end of the experiment the P. aeruginosa isolates were anaFisher’s exact test was done to verify and confirm if the pro-
lyzed to determine if they showed antagonism or not by
duction
measuring the inhibition halo. The results are given in Table 1.
of
pigment
is
related
to
antagonism.
The
determination of the MPN was done using the MPN calcu-
From the clinical isolates (n ¼ 20), 40% (8 isolates) pro-
lation program distributed by Jarvis et al. (). Analysis of
duced only pyocyanin, 40% (8 isolates) produced only
|
V. V. Martins et al.
103
Antagonism between Pseudomonas aeruginosa and coliforms
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2014
pyoverdin and 15% (3 isolates) produced both pigments.
showed a more inhibitory power against coliform bacteria,
The bacteria that produced both pigments presented antag-
when compared with pyoverdin.
onism against all coliforms tested. From the pyocyanin
In the antagonism experiment on solid medium per-
producers, all showed antagonism against Ec2 and Ea1,
formed by Vasconcelos et al. (), E. aerogenes and E.
whereas just one did not show antagonism against Ec1
coli suffered antagonism against P. aeruginosa, with E. aero-
and Kp1. From the pyoverdin producers, 12.5% (1 isolate)
genes being more sensitive. Our results show the same
presented antagonism against Ec1 and Kp1, 50% (4 isolates)
pattern where Ea1 (n ¼ 22) was the most sensitive followed
against Ec2 and 87.5% (7 isolates) against Ea1. The isolate
by Ec2 (n ¼ 21). Ec1 (n ¼ 12) and Kp1 (n ¼ 15) were less sus-
without pigment did not present antagonism.
ceptible against P. aeruginosa. These results show that
From the water isolates (n ¼ 20), 10% (2 isolates) pro-
coliform isolates from a sample without P. aeruginosa pres-
produced
ence were more sensitive than isolates from a sample with P.
pyoverdin and 5% (1 isolate) produced both pigments. The
aeruginosa, suggesting a resistance acquisition by these
isolate which produced both pigments showed antagonism
bacteria.
duced
only
pyocyanin,
75%
(15
isolates)
against all coliforms. The pyocyanin producers presented
All bacteria that produced both pigments and only pyo-
antagonism against Ec2, Kp1 and Ea1. From the pyoverdin
cyanin (n ¼ 15) showed antagonism against Ec2 but not
producers, 13.3% (2 isolates) presented antagonism against
with Ec1, which was isolated from a sample in which
Ec2, 6.67% (1 isolate) against Kp1 and none against Ec1
P. aeruginosa was present. This suggests that E. coli can
and Ea1. The bacteria with no pigment production did not
become resistant to pyocyanin when it comes in contact
present antagonism.
with P. aeruginosa in the environment. Hassett et al.
From the soil isolates (n ¼ 20), 15% (3 isolates) pro-
() investigated how P. aeruginosa protects itself against
duced pyoverdin, 5% (1 isolate) produced both pigments
pyocyanin, comparing how P. aeruginosa and E. coli act
and 80% (16 isolates) did not produce any pigment. The iso-
when pyocyanin is present. This resistance was attributed
late that produced both pigments showed antagonism only
to several factors, including enzymes (catalase and super-
against Ec2 and Ea1. The other P. aeruginosa isolates
oxide dismutase (SOD)) production and the penetration of
which produced pyoverdin or no pigment did not present
the pyocyanin through the cell membrane. Battistoni et al.
antagonism.
() demonstrated that the over expression of SOD in
Using Fisher’s exact test (H0 ¼ pigment production and
E. coli enhanced its resistance to macrophages, a phagocyte
antagonism are independent), it was confirmed that the pig-
that reduces oxygen to hydrogen peroxide, superoxide and a
ment production and antagonism are dependent for all
hydroxyl radical as an antimicrobial defense. An unex-
tested coliforms (P < 0.05) (Table 2). The frequencies of inhi-
pected mutation that allows E. coli to produce more
biting the growth of coliform bacteria tested are shown in
catalase and/or SOD is a possible explanation for this resist-
Table 2. The data indicate that the production of pyocyanin
ance to pyocyanin, a molecule that can generate radical species. It was possible to observe that 4.2% of only pyoverdin
Table 2
|
producers (n ¼ 24) showed antagonism against Ec1, 25%
P-value for Fisher’s exact test and frequency (%) of occurrence of antagonism between isolates of producing and non-producing pigment P. aeruginosa and
against Ec2, 8.3% against Kp1 and 29% against Ea1
coliforms
(Table 2). One reason why it was not possible to observe
Pigment
Ec1 (%)
Ec2 (%)
Kp1 (%)
Ea1 (%)
Pyocyanin (n ¼ 10)
70
100
90
100
Pyoverdin (n ¼ 24) Both (n ¼ 5)
4.2
25
8.3
29
80
100
80
100
None (n ¼ 21)
0
0
0
0
P-value
0.0049
< 0.0001
0.0005
< 0.0001
antagonism in all pyoverdin producers relates to the quantity of the pigment produced, as it was possible to visualize that those which produced a lot of pigment showed antagonism, and the others which produced less pigment, did not present antagonism (results not shown). West & Buckling () correlated that the amount of siderophore produced is directly proportional to the virulence of the microorganism.
104
V. V. Martins et al.
|
Antagonism between Pseudomonas aeruginosa and coliforms
The antagonism test in the liquid medium was performed with 10 isolates, among them, one pyocyanin producer, three
Water Science & Technology: Water Supply
|
14.1
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2014
we also found cases in which strains of P. aeruginosa were lacking pigments, but still behaved antagonistically.
pyoverdin producers, one that produced both pigments and
In a scenario proposed by Nicholson (), competition
five bacteria without pigment production. The diluted
for a limited resource can be categorized into two groups:
medium, containing only the necessary amount of nutrients,
contest and scramble. Contest competition happens when
was used to stimulate the competition for nutrients. This test
direct and antagonistic interactions between competitors
was performed against Ec2, which was the most sensitive
occur, with the ‘champion’ appropriating the resources.
E. coli in the antagonism test in the solid medium.
Scramble competition happens when competitors without
According to Figure 1, after the interaction between the
direct interaction utilize the limited resources rapidly. Apply-
bacteria for a period of 72 h, the results confirmed the exper-
ing this simple scenario, P. aeruginosa with pigment(s)
iment carried out on the solid medium where the bacteria
production is using contest competition to survive, whereas
which
effective
P. aeruginosa without pigment production is using scramble
(PANOVA,24h ¼ 0.0010; PANOVA,48h < 0.0001; PANOVA,72h <
competition. In the first 24 h, apart from clinical isolates
0.0001), especially after 48 h from the initiation of the exper-
Pa23 and Pa01, it was not possible to detect a big difference
iment, when some results showed a difference of about four
in the growth between P. aeruginosa with and without pig-
orders of magnitude, when compared with the strains that
ment production. But after 48 h, bacteria growth with
showed no pigment production, which achieved a maximum
pigment production was larger, showing that the contest
difference of two orders of magnitude.
competition is more successful when compared to scramble
produced
pigment
were
the
most
Thus, while we revealed a significant positive corre-
competition. In other words, the production of pyocyanin
lation between the presence of pigments and antagonism,
(antibiotic) and pyoverdin (siderophore) made P. aeruginosa
Figure 1
|
Results of the antagonism test in liquid medium against Ec2 (PCN ¼ Pa18; PCN and PVD ¼ Pa 31; PVD ¼ Pa01, Pa27 and Pa51; No pigment ¼ Pa23, Pa26, Pa41, Pa49 and Pa57).
105
V. V. Martins et al.
|
Antagonism between Pseudomonas aeruginosa and coliforms
Water Science & Technology: Water Supply
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14.1
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2014
‘stronger’. But if we look deep into the ‘microbial jungle’, the
and it can present antagonism against E. coli and coliforms,
way a microorganism interacts and fights for nutrients is
causing an error in the microbial analysis.
more complex. Hibbing et al. () wrote a review about these ways of survival, discussing that they can range from antibiotics and siderophore production to stock of nutrients
CONCLUSIONS
and quorum sensing. The comparison between the antagonistic effect of pyo-
This study shows that production of pyocyanin and pyover-
verdin and pyocyanin in the solid medium showed that there
din by P. aeruginosa enhanced its antagonistic effect against
is a tendency for pyocyanin to be more important than pyo-
coliform bacteria when compared with P. aeruginosa with-
verdine for antagonism, as observed in Table 2. In this test,
out pigment production. This ability can cause a mistake
although the production of pigment was not quantified, it
in water sample analysis, making it possible to consider
was observed visually that different quantities of pigment
water clear and safe when, actually, it is not.
were produced. In the liquid medium, however, the correlation between antagonism and the type of pigment produced is not possible. These results show that when P. aeruginosa is present in water samples, it can influence the growth of coliform bacteria, and during water analysis it can cause a misreading of the result, allowing in some cases for a water sample to be considered as safe to drink when actually it is unsafe and dangerous. Vaconcelos et al. () emphasized that the presence of P. aeruginosa in a water sample is a problem and suggested that its presence should be investigated, together with the presence of fecal coliforms, improving the quality of water analysis. Our results support the Vaconcelos et al. () statement. The Australian Government published the ‘Review of Coliforms as Microbial Indicators of Drinking Water Quality’ (National Health and Medical Research Council ), in which it recommends to change the use of coliforms as microbial indicators of drinking water quality. In this review, some issues are discussed that the current analysis presents, such as the demonstration of whether the water treatment process is working effectively. To verify the success of the treatment after chlorination, the absence of total coliforms and E. coli are verified, but the problem is that coliforms are more sensitive to chlorination when compared with protozoan pathogens. Shrivastava et al. () showed that in river samples containing P. aeruginosa, E. coli, Klebsiella spp., Enterobacter spp. and other bacterial species, after suboptimal chlorine treatment, all bacteria were killed except the multidrug-resistant P. aeruginosa. This illustrates a great problem because P. aeruginosa is an important nosocomial pathogen, so it can cause diseases,
REFERENCES Battistoni, A., Donnarumma, G., Greco, R., Valenti, P. & Rotilio, G. Overexpression of a hydrogen peroxide-resistant periplasmic Cu, Zn superoxide dismutase protects Escherichia coli from macrophage killing. Biochem. Biophys. Res. Commun. 243, 804–807. Casanovas-Massana, A., Lucena, F. & Blanch, A. R. Identification of Pseudomonas aeruginosa in water-bottling plants on the basis of procedures included in ISSO 16266:2006. J. Microbiol. Methods. 81, 1–5. De Vos, D., Lim Jr, A., Pirnay, J. P., Struelens, M., Vandenvelde, C., Duinslaeger, L., Vanderkelen, A. & Cornelis, P. Direct detection and identification of Pseudomonas aeruginosa in clinical samples such as skin biopsy specimens and expectorations by multiplex PCR based on two outer membrane lipoprotein genes, oprI and oprL. J. Clin. Microbiol. 35, 1295–1299. Foppen, J. W. A. & Schijven, J. F. Evaluation of data from the literature on the transport and survival of Escherichia coli and thermotolerant coliforms in aquifers under saturated conditions. Water Res. 40, 401–426. Ganter, M. T., Roux, J., Su, G., Lynch, S. V., Deutschman, C. S., Weiss, Y. G., Christiaans, S. C., Myazawa, B., Kipnis, E., Wiener-Kronish, J. P., Howard, M. & Pittet, J. Role of small GTPases and αvβ5 Integrin in Pseudomonas aeruginosa-induced increase in lung endothelial permeability. Am. J. Respir. Cell Mol. Biol. 40, 108–118. Hannauer, M., Barda, Y., Mislin, G. L. A., Shanzer, A. & Schalk, I. J. The ferrichrome uptake pathway in Pseudomonas aeruginosa involves an iron release mechanism with acylation of the siderophore and recycling of the modified desferrichrome. J. Bacteriol. 5, 1212–1220. Hassett, D. J., Charniga, L., Bean, K., Ohman, D. E. & Cohen, M. S. Response of Pseudomonas aeruginosa to pyocyanin: mechanisms of resistance, antioxidant defenses, and demonstration of a manganese-cofactored superoxide dismutase. Infect. Immun. 60, 328–336.
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Hibbing, M. E., Fuqua, C., Parsek, M. R. & Peterson, S. B. Bacterial competition: surviving and thriving in the microbial jungle. Nature Rev. Microbiol. 8, 15–25. Ichikawa, T., Date, M., Ishikura, T. & Ozaki, A. Improvement of kasugamycin-producing strain by the agar piece method and the prototroph method. Folia Microbiol. 16, 218–224. Jarvis, B., Wilrich, C. & Wilrich, P. T. Reconsideration of the derivation of most probable numbers, their standard deviations, confidence bounds and rarity values. J. Appl. Microbiol. 109, 1660–1667. Kipnis, E., Sawa, T. & Wiener-Kronish, J. Targeting mechanisms of Pseudomonas aeruginosa pathogenesis. Med. Maladies Infect. 36, 78–91. Klausen, M., Heydorn, A., Ragas, P., Lambertsen, L., AaesJorgensen, A., Molin, S. & Tolker-Nielsen, T. Biofilm formation by Pseudomonas aeruginosa wild type, flagella and type IV pilimutans. Mol. Microbiol. 48, 1511–1524. Lau, G. W., Hassett, D. J., Ran, H. & Kong, F. The role of pyocyanin in Pseudomonas aeruginosa infection. Trends Mol. Med. 10, 599–606. Liu, G. Y. & Nizet, V. Color me bad: microbial pigments as virulence factors. Trends Microbial. 17, 406–413. Montgomery, M. A. & Elimelech, M. Water and sanitation in developing countries: including health in the equation. Environ. Sci. Technol. 1, 17–24. Mukherjee, K., Tribedi, P., Chowdhury, A., Ray, T., Joardar, A., Giri, S. & Sil, A. K. Isolation of a Pseudomonas aeruginosa strain from soil that can degrade polyurethane diol. Biodegradation 22, 377–388. Murray, P. R., Baron, E. J., Pfaller, M. A., Tenover, F. C. & Yoklen, R. H. Manual of Clinical Microbiology Vol. 1, 10 ed. ASM Press, Washington, D. C. Musthafa, K. S., Saroja, V., Pandian, S. K. & Ravi, A. V. Antipathogenic potential of marine Bacillus sp. SS4 on N-acyl-homoserine-lactonemediated virulence factors production in Pseudomonas aeruginosa (PAO1). J. Biosci. 36, 55–67. National Health and Medical Research Council Review of Coliforms as Microbial Indicators of Drinking Water Quality Commonwealth of Australia. National Health and Medical
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Research Council (Australian Government), Biotext Pty Ltd, Canberra. Nicholson, A. J. An outline of the dynamics of animal populations. Aust. J. Zool. 2, 9–65. O’May, C. Y., Sanderson, K., Roddam, L. F., Kirov, S. M. & Reid, D. W. Iron-binding compounds impair Pseudomonas aeruginosa biofilm formation, especially under anaerobic conditions. J. Med. Microbial. 58, 765–773. Rompré, A., Servais, P., Baudart, J., de-Roubin, M. & Laurent, P. Detection and enumeration of coliforms in drinking water: current methods and emerging approaches. J. Microbial. Methods. 49, 31–54. Shao, Z., Zhang, Y., Ye, Q., Saldanha, J. N. & Powell-Coffman, J. A. C. elegans SWAN-1 binds to EGL-9 and regulates HIF-1-mediated resistance to the bacterial pathogen Pseudomonas aeruginosa PAO1. PLoS Pathog. 6, 1–11. Shrivastava, R., Upreti, R. K., Jain, S. R., Prasad, K. N., Seth, P. K. & Chaturvedi, U. C. Suboptimal chlorine treatment of drinking water leads to selection of multidrug-resistant Pseudomonas aeruginosa. Ecotox. Environ. Safe. 58, 277–283. US Food and Drug Administration Bacteriological Analytical Manual - Most Probable Number from Serial Dilutions. US Food and Drug Administration, Silver Spring, MD. Vaconcelos, U., Lima, M. A. G. A. & Calazans, G. M. T. Pseudomonas aeruginosa associated with negative interactions on coliform bacteria growth. Can. J. Pure Appl. Sci. 4, 1133–1139. Vasconcelos, U., Calazans, G. M. T., Andrade, M. A. G. & Medeiros, L. V. Evidência do Antagonismo Entre Pseudomonas aeruginosa e BactériasIndicadoras de Contaminação Fecal emÁgua. Hig.Aliment. 21, 127–130. West, S. A. & Buckling, A. Cooperation, virulence and siderophore production in bacterial parasites. Proc. R. Soc. B. 270, 37–44. Zanetti, M. O., Martins, V. V., Pitondo-Silva, A. & Stehling, E. G. Antimicrobial resistance, plasmids and class 1 and 2 integrons occurring in Pseudomonas aeruginosa isolated from Brazilian aquatic environments. Water Sci. Technol. 67, 1144–1149.
First received 22 February 2013; accepted in revised form 17 June 2013. Available online 12 September 2013
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A novel acoustic imaging tool for monitoring the state of rapid sand filters Nihed Allouche, Dick G. Simons, Paul Keijzer, Luuk C. Rietveld and Joost Kappelhof
ABSTRACT A new technology based on acoustic waves is developed to monitor the state of sand filters used in drinking water treatment. Changes in the sand filter, due to the removal of suspended particles from the water and their accumulation in the pores, result in an increase of the bulk density and acoustic speed of the granular material. Consequently, the reflected acoustic response changes as the filter is in use. To monitor these changes, an instrument composed of an omnidirectional transmitter and an array of hydrophones was built. With frequencies ranging between 10 and 110 kHz, high resolution is achieved in the vertical direction enabling the detectability of clogged layers with a minimum thickness of 1 cm. The novel instrument is tested by conducting a monitoring experiment in a filter used in practice. A 2D scan over a part of the filter was performed and repeated every 2 hours over a period of 10 days. An analysis of the data revealed a local increase of the reflected acoustic response with increasing filter run time. The changes in acoustic signal are mainly observed at the upper 5 cm of the sand bed. It is also
Nihed Allouche (corresponding author) Dick G. Simons Acoustic remote sensing group, Delft University of Technology, The Netherlands E-mail: nelallouche@hotmail.com Paul Keijzer Electronic and mechanical support division, Delft University of Technology, The Netherlands Luuk C. Rietveld Department of Water Technology, Delft University of Technology, The Netherlands Joost Kappelhof Waternet, The Netherlands
clear that the filter bed is slowly compacting as a function of time. The total compaction after a period of 10 days reached 3.5 cm. The filter bed is expanded again during the cleaning procedure. Once the procedure is completed, the upper 30 cm of the filter becomes more transparent, showing small accumulations of material at greater depth. The observed changes in the filter bed demonstrate the potential of this acoustic-based tool to monitor the state of rapid sand filters and optimise their performance. The new tool can be used to evaluate the cleaning procedure and is valuable in detecting lateral variations in the filter bed. These variations may indicate local clogging that needs to be removed effectively to avoid deterioration of the overall performance in the long term. This type of information is difficult to obtain from the monitoring techniques currently used in drinking water treatment. Key words
| imaging, rapid sand filters, ultrasound
INTRODUCTION Drinking water companies usually use sand filters for water
anthracite. Deep-bed filtration occurs where particles
treatment. Sand filtration is a rather simple process: the
accumulate over the entire depth of the filter bed. The
water is passed through a sand bed and suspended particles
filter grains are considered as collectors, whereas the accu-
and microorganisms including bacteria are retained by the
mulated particles will act as additional collectors, making
sand grains (Huisman ). These particles affect the prop-
the filtration step more efficient during the start-up phase
erties of the filter and can cause its performance to
(ripening period). The fluid velocity within the pores will
deteriorate by blocking the water flow through the sand
increase as the particles accumulate and finally detachment
bed. Graded sand with an effective grain size of 0.35 to
will occur. Thus, in a filter layer that has reached a saturated
2.6 mm is normally used for this purpose, sometimes with
but metastable configuration of deposits, attachment and
an additional coarser layer of material on top such as
detachment
doi: 10.2166/ws.2013.174
of
particles
will
occur
simultaneously
108
N. Allouche et al.
|
A novel acoustic imaging tool for monitoring
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(Amirtharajah ). Finally filters are cleaned by reversing
sediment-water interaction through ion exchange on acous-
the flow direction, a procedure known as backwashing.
tic wave propagation (Li & Pyrak-Nolte ). Here, a
Employed often in drinking water production, rapid
reduction in the acoustic wave amplitude was correlated
sand filtration is part of a wider water treatment process
with a decrease in the total number of ions in the pore water.
that needs to be monitored continuously. Typically, this is
In this paper, we explore the potential of acoustic waves
done by controlling the quality of the effluent by monitoring
to monitor sand filtration by measuring the effect of clog-
turbidity (Kim & Tobiason ). An increase in turbidity is
ging. An instrument, composed of an omnidirectional
associated with deterioration in the filter performance.
broadband transmitter and an array of hydrophones, was
Pressure measurements are conducted as well in order to
developed in order to test the method in practice. A monitor-
monitor the state of the filter. Generally, this type of
ing experiment, using this novel instrument, was conducted
measurement serves as an indication of the amount of clog-
on a full-scale sand filter during a complete filter run.
ging in the filter bed. When a critical value is reached, the cleaning procedure is started. However, the pressure values are averaged over the whole filter bed and hence
ACOUSTIC IMAGING OF SAND FILTERS
information on the local distribution of particle accumulations is not provided.
Acoustic imaging is a widely used technique based on the
Some attempts were also made to record events in fil-
propagation of sound waves. These waves are mechanical
tration and backwashing by applying video endoscopy (Ives
disturbances that are carried through the inspected object
). However, these endoscopies have limitations in the
and reflected at boundaries separating layers with contrast
optical resolution (Ives ). Samples from the sand bed
in density ρ and sound speed c. For a sand filter, these
are frequently taken to the laboratory for a more detailed
boundaries can either represent a sand layer with a different
analysis. This can take a few days whereas real time charac-
grain size and porosity or an accumulation of impurities that
terization is essential to reduce the risks and costs involved
resulted locally in the clogging of the pores. The amplitude
with water treatment. Long-term effects such as mixing of
of the reflected signal depends on the contrast in acoustic
sand layers and the formation of mud balls are also not
impedance, i.e. the product of the sound speed and density,
detected with the controlling and monitoring techniques
whereas its arrival time is affected only by the sound speed.
used in practice. Therefore, Ives () suggested using
Attenuation through homogeneous layers affects signifi-
other techniques, such as tomography, to study filtration.
cantly the amplitude and the frequency content of the
Acoustic imaging is a more suitable method to reveal the
signal. Sound waves are attenuated by intrinsic absorption
spatial distribution of clogging over the filter in time. Acous-
inherently present in the homogeneous medium and also
tic waves carry information about the media they travel
by small-scale scattering (Lurton ). An increase of
through. They are reflected at boundaries representing a
local accumulations in the sand layer is expected to result
change in medium parameters. For a sand filter, this can
in stronger attenuation of the waves, thereby reducing
either be a layer with a different grain size, grain material
their penetration depth.
or a local accumulation of suspended particles in the
In the water treatment process, suspended particles and
pores. Despite their great potential, acoustic-based tech-
colloidal solids are removed from the water and accumu-
niques are not yet fully explored as a monitoring tool nor
lated in the pores, which reduces the pore volume in the
widely applied for water treatment. Nevertheless, a few applications can be found in the literature. Acoustic waves
sand filter and hence the porosity. Consequently, the saturated bulk density of the sand, ρsat is expected to change
were used by researchers to detect the distribution of immis-
with increasing run time of the filter. The saturated bulk den-
cible liquids such as NAPL in a tank filled with sand (Geller
sity as a function of porosity can be computed using the
et al. ). They showed that small NAPL saturations are
equation
easily detected from the amplitude of the acoustic waves. Another example involves a study of the effect of
ρsat ¼ nρw þ ð1 nÞρg
ð1Þ
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where n is the fractional porosity, ρw is the density of the
the state of a filter while in use. Figure 1 shows a schematic of
pore water and ρg is the bulk density of the mineral grains.
the instrument, which is composed of an omnidirectional
The porosity affects also the sound speed as indicated by
transmitter and a receiving hydrophone array. Both the
the Wood equation
signal emitted by the transmitter and the signal measured by
csat
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Kg Kw =ð½nKg þ ð1 nÞKw Þ ¼ ρsat
each hydrophone are recorded. A dedicated software package ð2Þ
has been developed to gain control of the parameters of the transmitted signal and visualize the recorded response. The transmitter sends out a chirp with linearly increasing fre-
where Kw and Kg denote the bulk moduli of the water and
quency. This type of signal is chosen over a single frequency
the sand grains in N/m , respectively (Stoll ). Both the
pulse in order to improve the vertical resolution of the
saturated bulk density and the sound speed are expected
images. In the case of a linear chirp, the vertical resolution
2
to increase as porosity decreases (Hamilton ). This implies that the amplitude of the acoustic wave Ar, reflected
Δz ¼ c=2B
ð4Þ
at the top of the sand bed, also increases as shown by the folis inversely proportional to the bandwidth B, whereas the ver-
lowing equation:
tical resolution of a single frequency sinusoid depends linearly Ar ¼
ρsat csat ρw cw ρsat csat þ ρw cw
ð3Þ
on the pulse duration. We typically sweep the frequency from 10 to 110 kHz. Assuming an average sound speed c of 1,500 m/s, this range of frequencies allows us to achieve a ver-
where cw denotes the sound speed of the water (Lurton
tical resolution of approximately 1 cm. This implies that
). In theory, this relation can be used to quantify the
clogging in the filter bed of similar size can potentially be
changes in density due to the filtration process from the
detected by the instrument.
measured acoustic response.
The reflected signals are recorded by five hydrophones arranged along two perpendicular lines. The single hydrophones are omnidirectional. Using an array instead of a
EXPERIMENTAL SET-UP
single hydrophone improves the sensitivity in the vertical
Instrument description
in this case, from the sides of a filter. The response function
direction and helps suppress undesired reflections arriving, of this array depends on the distance between the hydroBased on the acoustic imaging principles described in the pre-
phones, the frequency of the transmitted waves and the
vious section, we developed an instrument that is able to image
direction of the incoming wave.
Figure 1
|
W
A sketch of the developed instrument: an omnidirectional transducer sends a signal out which is then recorded by a hydrophone array with a beam opening angle of 34 . Reflections arriving outside the beam opening angle are strongly suppressed. The recorded acoustic signal is subsequently processed to a final image.
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The distance between the hydrophones is 1.25 cm, cor-
and is variable during the filtration process. The instrument
responding to l/2 at a frequency of 60 kHz, with l being
was placed on top of the filter as shown in Figure 2. The
the wavelength. The 3 dB points of the response function
monitoring experiment was conducted over a period of 10
defines the beam opening angle θ, which equals 34 at
days where the state of the filter was imaged before the
60 kHz. The beam opening angle directly relates to the hori-
cleaning procedure and continued until a full cycle (period
zontal resolution of the instrument via
between two clean states of a filter) elapsed. A scan along
W
the x-direction, indicated by the line in Figure 2, was Δx ¼ 2d tanðθ=2Þ
ð5Þ
repeated every 2 hours. The sensors were positioned 45 cm below the water surface and moved in 1 mm incre-
where d is the distance between the target and the hydro-
ments. A 90 cm long scan took about 15 min to complete.
phone array. Extending the size of the array by adding more hydrophones will improve the horizontal resolution.
Processing of the data
The transmitter and the hydrophone array are attached to a robot which can move in three directions along an alu-
The signal emitted by the transducer is a 2 ms long chirp
minium frame. The robot is controlled via the computer and
with a frequency range of 10 to 110 kHz. The chirp is com-
can be programmed to perform a scan in two directions and
pressed by applying a specific processing flow aimed at
repeat it over a given period in time.
enhancing the vertical resolution of the recorded data. To this end, we use deconvolution to recover the impulse response and then apply a lowpass filter to reduce the arte-
Monitoring experiment
facts introduced at the high frequencies. This is described by
To assess whether the developed instrument is able to detect
the following equation:
changes in a filter used for water treatment, we performed a monitoring experiment in a rapid sand filter put at our disposal by a Dutch water company. The filter is used at the early
RðfÞ ¼ FðfÞ
DðfÞ SðfÞ
ð6Þ
stages of the water treatment process and is typically 156
where S( f ) is the spectrum of the chirp, D( f ) is the spectrum
hours in use before the cleaning procedure is started. The
of the recorded signal, F( f ) is a low pass filter and R( f ) is
filter is about 10 m long and 5 m wide and is divided into
the result. The processing steps are summarized in Figure 3:
two compartments separated by a channel built to drain
the chirp and the recorded signal are combined to obtain the
water used in the backwashing procedure. The filter bed is
final reflected response. The peaks obtained at the end of the
1.3 m thick and is composed of sand with a grain size
processing flow are related to various arrivals reflected at
between 0.8 and 1.25 mm. A stack of sand layers with
boundaries with contrasts in acoustic properties. The
increasing grain size is placed below the filter bed for support. Table 1 shows the composition of the filter bed material. The water height above the filter bed is 1.25 m
described processing flow is applied to the sum of the five hydrophones and is repeated at recordings acquired at a horizontal increment of 1 mm. Figure 4 shows a typical image obtained for a 90 cm long profile (i.e. a stack of 901
Table 1
|
Composition of the filter used in the experiment
transmissions). In this image, the depth axis is computed
Thickness [cm]
Grain size [mm]
130
0.8–1.25
15
1.25–2.0
15
2.0–3.0
15
3.0–5.0
15
5.0–8.0
from the arrival time assuming a constant sound speed of 1,500 m/s. The reflection from the top of the sand bed is identified at a depth of 80 cm. Reflections from the water surface and the filter walls are also detected in the scan. They have a strong presence because of the large impedance contrast encountered at the water/air interface and the water/filter wall interface.
111
Figure 2
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A picture showing the instrument placed on a sand filter. The line indicates the location of the scan.
However, they are not interfering with the reflection
We start first by evaluating the effect of backwashing on
from the sand bed and can thus be removed from the
the filter. This is done by comparing the images before and
scan. The monitoring experiment started by acquiring a
after the cleaning procedure. These images are displayed in
scan of the filter which was already 4 days in use. After
Figure 5. It is clear that the amplitude of the signal, reflected
cleaning the filter by backwashing, the scans were repeated
at the top of the sand, decreased after backwashing. This was
every 2 hours until it was cleaned again after 10 days.
more the case in Figure 5(d) than in 5(b). This can be explained by the fact that the latter was scanned directly after the backwashing whereas the first scan was performed
RESULTS AND DISCUSSION
a few hours later. Another explanation could be that the cleaning procedure was shorter at the start of the experiment
The results of the monitoring experiment are discussed in
and therefore not all the impurities were removed.
detail in this section. The changes in the measured acoustic
Lateral variations in the amplitude of the reflected
signal, as a function of time and position in the filter bed, are
response were observed at the top of the sand bed. Some
presented. The observed acoustic changes are compared to
spots, indicated by the white circles, appeared to be more
pressure measurement and interpreted to obtain infor-
clogged than others. However, the locations of these spots
mation on the filtration process and the state of the filter
were variable. They are impurities probably originating
bed. The interpretation is supported by an acoustic model-
from deeper parts of the filter which were not entirely
ling study which provides insights on the effect of clogging
removed due to the limited duration of the cleaning pro-
on the acoustic signal. The results are finally summarised
cedure. When the flow direction was reversed, they ended
in a sketch illustrating different stages of the filter bed
up at a different location in the filter bed. From the data, we
during the experiment.
observed that these spots get clogged faster than other parts
112
Figure 3
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Processing ďŹ&#x201A;ow applied to obtain a scan. The chirp (top left) and the recorded signal (top right) are transformed to the frequency domain where we apply deconvolution. The obtained spectrum is subsequently ďŹ ltered and transformed back to the time domain.
113
Figure 4
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An acoustic image of the filter obtained after processing and converting the arrival time to depth. The colour denotes the amplitude of the reflected signal. Four reflections are labelled: the direct wave, reflections from the water surface, top of the sand bed and the filter wall.
of the filter. This is because they acted as additional collec-
direct wave and the wave reflected at the water surface are
tors, making it easier for suspended particles to be retained
included in the figure to evaluate whether changes in the
from the water (Amirtharajah ). As the filter was in use,
emitted signal or the water level have taken place. A clear
the rest of the sand bed got clogged as well, increasing the
trend, showing a slow compaction of the sand bed, can be
amplitude of the reflected response as shown in Figure 5(c).
observed, i.e. reflection from the top of the sand bed is
Small-scale variations in acoustic response corresponding to accumulations of impurities were distributed over the top 20 cm of the sand bed as it can be seen in Figure 5(b).
placed at greater depths. This effect is reversed when the cleaning procedure is started. The sand bed is then expanded.
These accumulations, with sizes in the order of a few centi-
A few hours after backwashing was completed, the
metres, were only detectable shortly after backwashing. In
depth of the filter bed stabilized. The variation in the
the remaining scans of the filter they were masked by the
depth of the sand bed as a function of time is plotted in
strongly reflecting clogged top of the sand. The relative
Figure 7(a). Over a period of about 200 hours, the total com-
‘transparency’ of the filter occurs only at the early stage of
paction was 3.5 cm. The changes in the filter bed depth
the filter run when the pores in the upper 5 cm of the
correlate well with changes in the pressure difference
filter were not clogged, allowing more acoustic energy to
measured between two levels in the sand (Figure 7(b)).
penetrate the deeper parts of the filter.
The water level, estimated from the acoustic wave reflected
Scans of the filter were repeated every 2 hours. Figure 6
at the water surface, is plotted also in Figure 7(c). The water
shows the changes in acoustic response with respect to time,
level is generally constant except for some jumps. The first
averaged over the length of the profile for all scans. The
jump, also visible in the pressure measurement, is associated
114
Figure 5
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Acoustic images of the filter: (a) at the start of the monitoring experiment, (b) after backwashing, (c) after 10 days of filter use and (d) after backwashing again.
with the backwashing of an adjacent filter. When one filter is not in use, more water is distributed over the remaining filters, thereby increasing the overall water level. There was a slight drop in the water level before it increased again at the end of the filter run time resulting in a large peak. This peak, which preceded the backwashing, can also be identified in the pressure measurement. Due to lateral variations in the sand bed, the amplitude trend in Figure 6 is less obvious than that of the depth. Figure 8 shows an average image of the 90 cm long profile repeated for all days of the experiment. As the filter was in use, the clogged layer at the top of the sand bed became thicker as small-scale accumulations stuck together (compare Day 2 and Day 3). In the last 2 days of the filter run time, deeper clogging became more aligned forming another
Figure 6
|
The average acoustic response over the 90 cm long profile plotted for all scans performed every 2 hours.
115
Figure 7
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(a) The average depth of the filter bed plotted for each scan. (b) The difference in pressure measured during the monitoring experiment. (c) The water level height above the sensors determined at each scan.
Figure 8
|
Scans of the filter bed averaged from all measurements taken during 1 day.
clogged layer. As more pores were clogged in the upper part
clogging of the rapid sand filtration system mainly occurred
of the sand, the pore flow velocity increased and fewer solids
in the top layer of the filter bed and the clogging zone gradu-
accumulated there. Deeper parts took over until the filter
ally expanded when saturation occurred (equilibrium
resistance reaches a maximum. We observed that the
between attachment and detachment) (Amirtharajah ).
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This is also indicated by the, more or less, linear increase of
sands. The latter is not visible due to the intrinsic absorption
the pressure drop, since cake filtration on top of the filter
in the sand layer. This explains as well why the reflection
bed will result in an exponential increase (Ives ) and
from the supporting layer in the full-scale sand filter was
strictly deep bed filtration in a quadratic increase.
not visible in the data. Lower frequencies are required to
Using acoustic modelling techniques, we can support the
detect it.
observations described above. The wavenumber integration
During filtration, most of the particles were retained first
method, also known as the reflectivity method, is selected
at the top of the sand bed as shown in Figure 8. This resulted
for this purpose (Kennett ; Ursin ). Theoretically,
in a thin layer with acoustic properties different from those of
the filter bed can be modelled as a stack of homogeneous
the clean sand bed. Corresponding changes in porosity affect
layers with different acoustic properties. Attenuation is
the acoustic response. Figures 10(a) and 10(b) show the result
accounted for by making the sound speed complex valued.
of decreasing the fractional porosity from 0.37 to 0.3, 0.2, 0.1
For simplicity, we model only the case of a plane wave inci-
and 0.05 for two layer thicknesses, 1 and 5 cm, respectively.
dent vertically on the layered sand filter. A schematic of the
When the clogged layer is as thin as 1 cm, the amplitude of
sand bed used for the modelling is shown in Figure 9. Similar
the wave reflected at the top of the sand bed increased as
to the real filter, a 1.30 m thick sand layer with a grain size of
the pore volume was reduced. This is consistent with the
0.8 mm and a porosity of 0.37 is placed on top of a sand layer
acoustic images shown in Figure 5 where the amplitude of
with coarser grains. The acoustic properties of the sand layers
the filter bed reflection increases with time as a result of clog-
are taken from the literature ( Jackson & Richardson ).
ging. The same effect occurs when the layer thickness is 5 cm.
The density of the sand grains is 2,670 kg/m3 and the bulk
However, a second arrival with smaller amplitude also
moduli of the water and the grains are 2.2 × 109 and 4 ×
became visible. This corresponds to the reflection originating
10
2
N/m , respectively. The source and receiver are located
from the bottom of the clogged layer. The difference between
in the water at 80 cm distance from the top of the sand bed, as
the two figures is caused by the interference pattern.
10
in the real experiment. The reflected response computed for
Obviously, the thicker the layer the better the top and
the chirp with a frequency bandwidth of 10 to 110 kHz is
the bottom are separated acoustically. In the experiment,
also displayed in Figure 9. Three arrivals are visible: the
this thickening of the clogged layer at the top of the sand
direct wave, travelling directly between source and receiver,
bed occurred quite quickly (after a few hours). From
the reflection from the top of the sand bed and the reflection
Figure 10(b), it can also be noticed that the reflection from
from the interface separating the fine and coarse-grained
the bottom of the clogging was arriving earlier in time as the porosity decreased. The difference in travel time is caused by an increase in acoustic speed as predicted by the Wood equation (see Equation (2)). Based on the above observations, provided by the acoustic measurement and supported by the modelling study, we can make a qualitative construction of the state of the filter during one run. First of all it must be noted that a small mass increase caused by the deposits, about 1–2% of the filter mass and resulting in a large hydraulic resistance (Mays & Hunt ), can be detected by the acoustic measurements. Further, Figure 11 illustrates different stages in the filter, starting after backwashing when small particles were left behind. As the filter is in use, more particles were accumulated in the sand but mainly at spots where the pore
Figure 9
|
The three-layered model used for the computation (left). The positions of the source and receiver are denoted by a circle and a triangle, respectively. The modelled acoustic response (right).
volume was reduced and the particles acted as additional collectors (Amirtharajah ). More particles were removed
117
Figure 10
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The effect of porosity on the acoustic response reflected at the top of the sand layer for a clogged layer with a thickness of 1 cm (a) and 5 cm (b).
filter, described in detail in this section, demonstrates the great potential of the acoustic-based instrument as a monitoring tool. Images of the filter bed can be obtained anywhere in the filter bed. This can help in detecting local clogging that can cause the overall performance of the filter in the long term to deteriorate, e.g. through the formation of mud balls that are formed at the top and, in time, grow and sink to the bottom, clogging the water collection infrastructure (Brouckaert et al. ). The new tool can also be deployed to evaluate and optimise the cleaning procedure. In contrast to the pressure measurements, the information obtained is not averaged over the whole filter bed. In the future, further improvements can be made to extract information from the deeper part of the filter and more effort can be put into the quantification of porosity changes and the detection of mud balls.
CONCLUSIONS Figure 11
|
A schematic illustration of the different states of a rapid sand filter starting shortly after backwashing (a) and ending when the upper layer is clogged (c).
An acoustic-based instrument was developed as a monitoring tool for a water treatment process. This instrument,
from water and accumulated in the upper part of the sand.
composed of a broadband transmitter and an array of hydro-
Slowly this part became clogged and particles were deposited
phones, was tested in an experiment conducted in a rapid
in deeper parts. The filter bed was slowly compacting. In the
sand filter used in practice. The state of the filter was mon-
final stage, various clogged layers with decreasing thick-
itored for a period of 10 days. As supported by the
nesses were formed. The information on the state of the
modelling study, an overall increase of the reflected acoustic
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response was observed in the data. Acoustic waves are sen-
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REFERENCES
sitive to changes in porosity. The density and acoustic speed increase when the water in the pores is replaced by suspended particles, thereby increasing the amplitude of the reflected acoustic response. The increase was mainly observed in the upper 5 cm of the sand bed. The performed scans showed also a slight compaction of the filter bed, when put in use, and expansion after backwashing was completed. Once cleaned, the upper 30 cm of the filter becomes ‘transparent’ and small accumulations of particles appear. These are not easily detectable because they are masked by the strongly reflecting clogged shallower part. It is clear that suspended materials are first retained at the top 5 cm of the sand bed before deeper parts take over. Furthermore, it can be stated that the backwashing procedure is very important because, if not performed properly (e.g. short duration), it may result in local variation in the filtering ability of the sand bed. This will affect the overall performance of the sand filter in the long term. The tool can then be used to optimise the cleaning procedure and detect variations in the quality of the sand bed. This information cannot be provided by the currently used monitoring techniques such as pressure and turbidity measurements.
ACKNOWLEDGEMENTS The authors thank the Dutch government for subsidizing this project within the Innowater program, and Waternet for allowing us to use their sand filter and providing the necessary technical support.
Amirtharajah, A. Some theoretical and conceptual views of filtration. Journal of AWWA 80 (12), 36–46. Brouckaert, B. M., Amirtharajah, A., Brouckaert, C. J. & Amburgey, J. E. Predicting the efficiency of deposit removal during filter backwash. Water SA 23 (5), 633–640. Hamilton, E. L. Geoacoustic modelling of the sea floor. Journal of Acoustical Society of America 68, 1313–1340. Huisman, L. Rapid filtration. Delft University of Technology Lecture Notes. Geller, J. T., Kowalsky, M. B., Seifert, P. K. & Nihei, K. T. Acoustic detection of immiscible liquids in sand. Geophysical Research Letters 27, 417–420. Ives, K. J. Filtration studied with endoscopes. Water Research 23 (7), 861–866. Ives, K. J. Filtration progress- more questions arising with fewer answers. Water Science and Technology WS 2 (1), 213–222. Jackson, D. R. & Richardson, M. D. High Frequency Seafloor Acoustics. Springer-Verlag, New York. Kennett, B. Seismic Wave Propagation in Stratified Media. Cambridge Univ. Press, UK. Kim, J. & Tobiason, J. E. Particles in filter effluent: the roles of deposition and detachment. Enviromental Science and Technology 38, 6132–6138. Li, X. & Pyrak-Nolte, L. J. Acoustic monitoring of sedimentpore fluid interaction. Geophysical Research Letters 25, 3899–3902. Lurton, X. An Introduction to Underwater Acoustics: Principles and Applications. Springer-Praxis, UK. Mays, D. C. & Hunt, J. R. Hydrodynamic aspects of particle clogging in porous media. Environmental Science and Technology 39, 577–584. Stoll, R. D. Velocity dispersion in water-saturated granular sediment. Journal of Acoustical Society of America 111, 785–792. Ursin, B. Review of elastic and electromagnetic wave propagation in layered media. Geophysics 48, 1063–1081.
First received 8 October 2012; accepted in revised form 10 June 2013. Available online 13 September 2013
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Hand-pump subsurface arsenic removal: the effect of groundwater conditions and intermittent operation S. C. Borges Freitas, D. van Halem, M. M. Rahman, J. Q. J. C. Verberk, A. B. M. Badruzzaman and W. G. J. van der Meer
ABSTRACT Hand-pump subsurface arsenic removal (SAR) has been investigated in rural Bangladesh with different groundwater conditions and intermittent operation modes. Multiple injection-abstraction cycles were performed after injection of 1 m3 of aerated water. From these experiments it can be concluded that hand-pump SAR, in the traditional injection-abstraction design, does not provide drinking water below the WHO arsenic guideline of 10 μg/L. Results show that arsenic removal was not enhanced by: (i) injection of O2-rich water, (ii) higher Fe:As ratios in the groundwater, or by (iii) multiple injection-abstraction cycles, i.e. at location 1, the breakthrough occurred at abstractioninjection ratios of Va/Vi ¼ 2, for cycle 23. It is proposed that dissolved organic carbon (DOC), bicarbonate and phosphate have a significant effect on the arsenic adsorption process. However, iron removal was very efficient and abstraction-injection ratios increased within successive cycles, with Va/Vi > 8 for cycle 23. Furthermore, intermittent operation reduced arsenic concentrations after stop and restart, suggesting insufficient contact time between soluble arsenic and oxidized iron surfaces around the tube well. Key words
| Bangladesh, groundwater conditions, hand-pump, intermittent operation, iron, subsurface arsenic removal
S. C. Borges Freitas (corresponding author) D. van Halem M. M. Rahman J. Q. J. C. Verberk W. G. J. van der Meer Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevinweg 1, Delft, The Netherlands E-mail: S.C.BorgesFreitas@TUDelft.nl M. M. Rahman Department of Geology, Faculty of Earth and Environmental Sciences, University of Dhaka, Curzon. Hall Campus, Dhaka-1000, Bangladesh A. B. M. Badruzzaman Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh W. G. J. van der Meer Oasen Drinking Water Company, P. O. Box 122, 2800 AC Gouda, The Netherlands
INTRODUCTION Arsenic contamination of groundwater occurs naturally in
of injection-abstraction has been proposed as a low-cost
Bangladesh and has become a serious problem due to the
technology to remove arsenic from groundwater, namely
extensive use of tube wells for drinking water abstraction
subsurface arsenic removal (SAR) (van Halem et al.
during the last decade. Analyses of groundwater have
). During SAR, aerated water is periodically injected
revealed that at many locations arsenic exceeds the WHO
into an aquifer through a tube well, forming an oxidation
guideline and the Bangladesh drinking water standard, 10
zone in the subsurface. Thus adsorbed Fe2þ is oxidized,
and 50 μg/L, respectively (BGS/DPHE ; WHO ).
creating new adsorptive iron hydroxide surface areas.
This metalloid threatens the long-term sustainability of the
When abstraction starts, groundwater with soluble Fe2þ
local ecosystem and, when it enters the food chain, is a
and trace elements passes through this oxidation zone.
serious hazard to human health (Smith et al. ; WHO
Consequently, the formed iron hydroxides adsorb soluble
; Dittmar et al. ).
constituents, such as iron, arsenic and other dissolved
For many decades, subsurface iron removal (SIR) or in
anions and cations (Figure 1). This process is explained
situ iron removal, has been used in Europe (von Oesten
by adsorptive-catalytic oxidation theory (Van Beek ).
; Van Beek ; Mettler ). The same principle
When SAR treatment is applied, higher volumes of
doi: 10.2166/ws.2013.180
120
Figure 1
S. C. Borges Freitas et al.
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Schematic of SAR principle and hand-pump SAR experimental setup.
groundwater with lower iron and arsenic concentrations
removal depends on the iron removal processes, as precipi-
can be abstracted (Va) than the volume of oxygen-rich
tated iron hydroxides form the adsorptive surfaces for the
water that was injected (Vi). The SAR technology makes
arsenic adsorption. In theory, the more oxygen is injected,
use of consecutive sequences of injection (Vi) – abstraction
the more iron is oxidized and the more sorption sites are
(Va), referred to as a cycle. The normalized concentration,
available (Sharma et al. ; Dixit & Hering ). There-
C/C0, as a function of the volumetric ratio Va/Vi defines
fore, for arsenic removal during SAR, the Fe:As molar
the effectiveness of the method.
ratio and contact time are proposed to be important factors
Previous research has shown that the groundwater com-
(van Halem et al. ). The presence of anions such as sul-
position has a large influence on the efficiency of the SAR
phate, bicarbonate and phosphate play an important role in
process (Kent & Fox ; Moed et al. ). Arsenic
inhibiting arsenic removal by iron hydroxides (Appelo et al.
121
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Hand-pump subsurface arsenic removal
). The competition for adsorptive sites between arsenic
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Table 1
2 species and other ions in groundwater (PO3 4 , SO4 ,
HCO 3 and dissolved organic carbon (DOC), amongst
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Water quality conditions of the investigated wells
units
Location 1
Location 2
Location A
Location B
20.5
21.4
*n.m.
*n.m.
others) has been investigated in laboratory settings (Meng
Depth
m
et al. ; Stachowicz et al. ; van Halem et al. ).
pH
6.98
6.95
6.85
6.85
EC
μS/cm
630
580
*n.m.
*n.m.
Eh
mV
T
W
Due to the specific binding at the ferric hydroxide surface, phosphate competes directly with arsenic for sorption sites on soil iron hydroxides (Davenport & Peryea ). DOC has also been found to affect arsenic adsorption (Xu et al. ; Grafe et al. ). Organic matter forms complexes with surfaces of the iron hydroxides, hindering the arsenic adsorption. Thus, the presence of high DOC (>5 mg/L) enhances arsenic leaching from soil grains increasing its mobility (Lin et al. ). The effectiveness of SAR is expected to depend largely on local groundwater conditions. Previous SAR studies have been performed at high phosphate and low DOC levels (van Halem et al. ) or with limited field measurements (Sarkar & Rahman ; Sen Gupta et al. ). The objective of this study was to gain insight into the application and performance of hand-pump SAR in rural Bangladesh: (a) in diverse groundwater conditions; and (b) studying the influence of intermittent operation on the subsurface arsenic
C
μmol/L
As
130
137
*n.m.
170
26.5
26.5
*n.m.
*n.m.
3.59
2.71
1.94
1.94
As(III)
2.94
2.20
1.6
1.66
Fe
0.14
0.23
0.018
0.27
Fe:As
38
83
9
139
Mn
0.00
0.00
0.045
0.006
Naþ
1.29
1.09
0.39
1.04
Ca
1.46
0.61
2.1
2.8
Mg2þ
1.65
1.65
*n.m.
*n.m.
2þ
K
þ
0.18
0.19
*n.m.
*n.m.
HCO 3
mmol/L
4.87
3.20
*n.m.
*n.m.
PO3 4
0.001
0.001
0.035
0.053
SO2 4
0.01
<DL
*n.m.
*n.m.
NO 3
0.12
0.04
*n.m.
*n.m.
Cl
1.13
1.13
*n.m.
*n.m.
5.05
4.82
1.47
*n.m.
DOC
mg/L
adsorption process, i.e., the role of kinetics during SAR.
*n.m. – not measured.
MATERIAL AND METHODS
a previous SAR study in Manikganj district (locations A and
The present study – locations 1 and 2 – is compared with B), with different groundwater conditions, specifically high The Muradnagar upazila, located about 100 km southeast of
phosphate and low levels of DOC (van Halem et al. ).
Dhaka, was selected for the field application of hand-pump
The groundwater composition of the locations 1, 2, A and
SAR. The local groundwater is known to have high iron and
B is given in Table 1.
arsenic concentrations, low phosphate and pH 6.9–7.0. New wells were drilled using the ‘sludger’ method, a manual dril-
Injection-abstraction cycles
ling technique (BGS/DPHE ). Each 38 mm (1.5 inch) tube well has a depth of 20.5 to 21.5 meters with a well
The combination of showerheads and disk aerators provided
screen of 3 meters length placed at the bottom of the tube
high oxygen concentrations (0.28 mmol/L) in the storage
well. The SAR installations were connected to the hand
tank. The injection volumes were limited to 1 m3 of aerated
pumps fixed in the new wells. Pipes, valves and flow
groundwater, performed every evening 15 to 18 h before
meters were installed to monitor injection and abstraction
abstraction started. The subsurface treated water was
processes. At each SAR unit a storage tank combined with
abstracted using two different electrical suction pumps with
showerheads and disk aerators was placed in an elevated
different pumping rates: 19 L/min at location 1, 22 L/min
area to be used for injection. The experimental setup of
at locations A and B, and 28 L/min at location 2.
both SAR units, referred to as location 1 and 2, is illustrated in Figure 1.
To monitor the injection-abstraction processes, samples were
collected
and
analysed
with
field
test
kits,
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EconoArsenic Quick™. Arsenic speciation was done using
Different intermittent experiments were performed: (A)
the field Clifford method (Clifford et al. ). All analyses
cycle 18, run abstraction until Va/Vi ∼ 1 and stop; and (B)
were confirmed in the laboratory (Perkin-Elmer Flame
cycle 20, run abstraction until Va/Vi ∼ 2.5 and stop. In
AAS 3110, Perkin-Elmer Flame GF-AAS 5100PC and
both experiments (A) and (B), the abstraction process re-
Perkin-Elmer 4300 ICP-OES). Sampling points were
started again 4 hours after the stop without any injection
installed and multimeters were fixed inline to monitor pH
process. Another final regular cycle (23) was performed as
(WTW SenTix41), oxidation-redox potential (WTW Sentix
a reference. During the intermittent operation experiments
ORP), dissolved oxygen (WTW Cellox 325) and electrical
the abstraction rate was decreased to 13 L/min.
conductivity (EC) (TetraCon 325). The EC of injected water is lower than that of the groundwater, indicating when groundwater arrives at the well, and is thus used as a tracer.
RESULTS AND DISCUSSION
Intermittent operation
Iron and arsenic removal
In rural Bangladesh, shallow tube wells with suction hand
The purpose of this study was to gain insight into the appli-
pumps are a very popular technology at the household
cation and performance of hand-pump SAR in diverse
level because they are easy to operate and cost-effective
groundwater conditions in rural Bangladesh. The break-
(BGS/DPHE ). In order to simulate the ‘typical’ hand-
through curves of iron and arsenic during injection-
pump operation, the SAR unit at location 1 was operated
abstraction cycles 1 and 6, at locations 1, 2, A and B are
intermittently, characterized by starts, stops and re-starts.
illustrated in Figure 2 ((a) cycle 1-Fe, (b) cycle 6-Fe, (c)
This simulation is referred to as intermittent operation.
cycle 1-As, (d) cycle 6-As).
Figure 2
|
Iron and arsenic breakthrough curves at locations 1, 2, A and B during: (a) cycle 1-Fe, (b) cycle 6-Fe, (c) cycle 1-As, and (d) cycle 6-As.
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Figure 2(a) shows that during cycle 1 an iron break-
at both locations A and B. Figure 2(d) shows that arsenic
through of C/C0 ¼ 0.5 occurred around Va/Vi ∼ 2 for
adsorption slightly improves with higher contact time. How-
location 1, 2 and B. At location A the breakthrough curve
ever, an incomplete breakthrough curve for arsenic was
was somewhat peculiar, due to the presence of low concen-
observed at all locations. The contact time in the oxidation
trations of iron (<0.018 mmol/L). Figures 2(a) and 2(b)
zone was still insufficient, while adsorption sites for arsenic
clearly show that the removal efficiency of iron improved
were still available.
after successive cycles, Figure 2(b) shows that iron break-
An additional finding was that at locations 1 and 2 the
through (C/C0 ¼ 0.5) occurred around Va/Vi ∼ 5, Va/Vi ∼
dissolved oxygen levels in the injection water were higher
3.5 and Va/Vi ∼ 4.5 for location 1, 2 and B. With break-
than at locations A and B; thus highly aerated injection
through curves like this, mass balances were calculated.
water does not increase arsenic removal. Furthermore,
For cycle 6, an estimated iron removal was found to be
higher Fe:As molar ratios, of 38, 83, 9 and 139, at locations
0.58, 0.90 and 0.94 mmol in total at locations 1, 2 and B,
1, 2, A and B, respectively, do not increase arsenic removal.
respectively. At location A, small amounts of iron were
Complex groundwater matrices have a large influence
removed (∼0.18 mmol), given the small levels of iron pre-
on the arsenic adsorption process. At locations 1 and 2,
sent in the groundwater. It is noteworthy that, during both
the DOC and bicarbonate concentrations were high
cycles 1 and 6, the iron breakthrough was delayed compared
(Table 1). Therefore, interference with the arsenic adsorp-
to the arrival of the groundwater front (¼tracer) at the well,
tion process could have occurred. Organic matter and
when Va/Vi ¼ 1.
bicarbonate ions do not directly occupy the available sorp-
Figure 2(c) shows that arsenic levels increased rapidly,
tion sites, but can cover and ‘mask’ their surfaces, as a
simultaneously with the groundwater front, Va/Vi ¼ 1, for
shield, not allowing other ions to pass through and be
cycle 1. At location A and cycle 1, a peculiar arsenic break-
adsorbed (Harvey et al. ; Appelo & de Vet ;
through curve, similar to that of iron, is illustrated. For
Peyton et al. ). Contrary to locations 1 and 2, the
cycle 6, Figure 2(d), arsenic breakthrough occurred after
levels of phosphate were high at locations A and B, in con-
Va/Vi ¼ 1.5. At location B, arsenic breakthrough (C/C0 ¼
centrations high enough to interfere with arsenic adsorption
0.5) occurred after Va/Vi ¼ 1 and Va/Vi ¼ 1.5, respectively,
(Appelo & de Vet ; van Halem et al. ). At locations
for cycles 1 and 6. It can be observed that at location 1
A and B, phosphate is identified as the major competing
arsenic breakthrough occurred after Va/Vi ¼ 0.5 and
anion, while at locations 1 and 2, DOC and bicarbonate
Va/Vi ¼ 1.8, in cycles 1 and 6, respectively. Two locations,
are proposed to
1 and B, show a slight enhancement in arsenic removal
adsorption.
interfere, inhibiting higher arsenic
after successive cycles. Therefore, results show that arsenic breakthrough has a noteworthy delay compared to the
Intermittent operation
tracer, i.e., the arrival of the groundwater front at the well. At location 2, arsenic breakthrough occurred
Figure 2(d) shows incomplete arsenic breakthrough curves,
around Va/Vi ¼ 1 for both cycles 1 and 6, not showing
suggesting an insufficient contact time. In order to under-
any improvement of removal efficiency. Given the different
stand the kinetics of arsenic adsorption in the subsurface,
settings, the tailings displayed by the arsenic breakthrough
the hand-pump behaviour was simulated. Figures 3(a1)
curves were very similar at all locations. Compared to iron
and 3(b1) illustrate the curves for arsenic and Figures 3
removal efficiencies, arsenic was removed only in small
(a2) and 3(b2) show the curves for iron during intermittent
amounts.
operation and a regular cycle.
Based on the operational conditions mentioned in the
The intermittent operation experiments (A) and (B) show
‘Material and methods’ section, calculations show that the
that at the start of the process the arsenic curve follows the
contact time in the oxidation zone between fresh ground-
same pattern as a regular cycle during SAR. The process
water and formed iron hydroxides was approximately 25
was stopped after Va/Vi ∼ 1 and C/C0 ¼ 0.35 in experiment
and 17 min, at locations 1 and 2, respectively, and 20 min
A, and stopped after Va/Vi ∼ 2.5 and C/C0 ¼ 0.70 in
124
Figure 3
S. C. Borges Freitas et al.
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Arsenic and iron breakthrough curves during different intermittent operation experiments and a regular cycle.
experiment B. After the shutdown of the process, the
formed iron hydroxides was increased to approximately
arsenic concentration was reduced, with a decrease in
37 min. SAR was slightly more effective at a longer contact
arsenic levels of 0.49 and 1.25 μmol/L, respectively. After
time, but still insufficient. Based on these results, calcu-
restarting the process, the breakthrough of arsenic was
lations show that if the contact time is longer than 90 min,
resumed, reaching C/C0 ∼ 1 at Va/Vi ¼ 8, for all experiments.
with a pumping rate lower than 5 L/min, the more efficient
The results show that if a repeated intermittent operation
the arsenic adsorption will be. Longer contact time with the
were used, partial arsenic would be continuously adsorbed
iron hydroxides enhances the equilibrium and kinetics of
after every stop mode and the arsenic breakthrough would
arsenic adsorption.
be delayed.
The intermittent operation also had an effect on iron
The regular cycle 23, shows C/C0 ¼ 0.5 was reached for
removal. When abstraction was resumed following a stop,
iron and arsenic at Va/Vi ¼ 7 and Va/Vi ¼ 2, respectively.
the concentration of iron increased compared to the
From these results, it is concluded that arsenic removal
decreased concentration of arsenic. A peak in iron levels
slightly improved when compared to cycle 6 in Figure 2(d),
of 0.004 and 0.002 μmol/L was observed in Figures 3(a2)
but clearer is the improved iron removal after successive
and 3(b2), followed by a small drop, before iron levels
cycles. The total arsenic removal was higher during inter-
increased again. During the stop, mobilization of adsorbed
mittent operation, compared to reference cycle 23. In the
Fe2þ occurs. Although, as expected, SIR improved consider-
subsurface the contact time between the arsenic and
ably after successive cycles.
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Under different groundwater compositions and intermit-
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REFERENCES
tent operation, the results show that drinking water can be provided below the Bangladesh arsenic guideline of 50 μg/L. Although the WHO guideline of 10 μg/L was not achieved. Therefore, under these conditions, the conventional operation as a ‘single’ injection-abstraction mode with injection volumes limited to 1 m3 does not seem to be a feasible option for arsenic removal. Iron removal, however, was very efficient and abstraction-injection ratios (Va/Vi) increased every successive cycle. SIR showed great potential for decentralized application at community-scale in Bangladesh.
CONCLUSIONS Hand-pump SAR has been investigated at different locations in Bangladesh with the traditional single injection-abstraction mode. From these experiments is concluded that, for common groundwater conditions in Bangladesh, SAR at the handpump level does not provide drinking water that meets the WHO arsenic guideline of 10 μg/L. The removal of arsenic was not enhanced by: (i) higher oxygen concentration in the injection water; (ii) higher Fe:As ratios in the groundwater; or (iii) multiple injection-abstraction cycles. It is proposed that DOC, bicarbonate and phosphate have a significant effect on the arsenic adsorption process. The removal of iron, however, was very efficient and injection-abstraction ratios (Va/Vi) increased with successive cycles. Furthermore, intermittent operation reduced arsenic concentrations, indicating the importance of adsorption kinetics during handpump operation.
ACKNOWLEDGEMENTS The authors would like to thank the key partners in Bangladesh, Department of Public Health Engineering, Dhaka University and Bangladesh University of Engineering and Technology, for a fruitful collaboration. The authors are grateful for the financial assistance provided by the Netherlands Organization for Scientific Research (NWO) in the integrated programme of WOTRO Science for Global Development.
Appelo, C. A. J. & de Vet, W. W. J. M. Modelling in situ iron removal from groundwater with trace elements such as As. In: Arsenic in Groundwater (A. H. Welch & K. G. Stollenwerk, eds), Kluwer Academic, Boston, USA. Appelo, C. A. J., Van Der Weiden, M. J. J., Tournassat, C. & Charlet, L. Surface complexation of ferrous iron and carbonate on ferrihydrite and the mobilization of arsenic. Environmental Science and Technology 36 (14), 3096–3103. BGS/DPHE Arsenic Contamination of Groundwater in Bangladesh. Volume 2, Final Report, BGS Technical Report WC/00/19. British Geological Survey / Department of Public Health and Engineering. Clifford, D. A., Karori, S., Ghurye, G. & Samanta, G. Field Speciation Method for Arsenic Inorganic Species. AWWA Research Foundation, Denver, Colorado, USA. Davenport, J. R. & Peryea, F. J. Phosphate fertilizers influence leaching of lead and arsenic in a soil contaminated with lead arsenate. Water, Air, and Soil Pollution 57–58, 101–110. Dittmar, J., Voegelin, A., Roberts, L. C., Hug, S. J., Saha, G. C., Ali, M. A., Badruzzaman, A. B. M. & Kretzschmar, R. Spatial distribution and temporal variability of arsenic in irrigated rice fields in Bangladesh. 2. Paddy soil. Environmental Science and Technology 41 (17), 5967–5972. Dixit, S. & Hering, J. G. Comparison of arsenic(V) and arsenic(III) sorption onto iron oxide minerals: Implications for arsenic mobility. Environmental Science and Technology 37 (18), 4182–4189. Grafe, M., Eick, M. J., Grossl, P. R. & Saunders, A. M. Adsorption of arsenate and arsenite on ferrihydrite in the presence and absence of dissolved organic carbon. Journal of Environmental Quality 31 (4), 1115–1123. Harvey, C. F., Swartz, C. H., Badruzzaman, A. B. M., Keon-Blute, N., Yu, W., Ali, M. A., Jay, J., Beckie, R., Niedan, V., Brabander, D., Oates, P. M., Ashfaque, K. N., Islam, S., Hemond, H. F. & Ahmed, M. F. Arsenic mobility and groundwater extraction in Bangladesh. Science 298 (5598), 1602–1606. Kent, D. B. & Fox, P. M. The influence of groundwater chemistry on arsenic concentrations and speciation in a quartz sand and gravel aquifer. Geochemical Transactions 5 (1), 1–12. Lin, H. T., Wang, M. C. & Li, G. C. Effect of water extract of compost on the adsorption of arsenate by two calcareous soils. Water, Air, and Soil Pollution 138 (1–4), 359–374. Meng, X., Bang, S. & Korfiatis, G. P. Effects of silicate, sulfate, and carbonate on arsenic removal by ferric chloride. Water Research 34 (4), 1255–1261. Mettler, S. In-situ removal of iron from groundwater: Fe(II) oxygenation, and precipitation products in a calcareous aquifer. PhD Dissertation, Swiss Federal Institute of Technology, Zurich. Moed, D. H., Van Halem, D., Verberk, J. Q. J. C., Amy, G. L. & Van Dijk, J. C. Influence of groundwater composition on
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subsurface iron and arsenic removal. Water Science and Technology 66 (1), 173–178. Peyton, G. R., Holm, T. R. & Shim, J. Development of Low cost Treatment Options for Arsenic Removal in Water Treatment facilities. Report ISWS Contract Report 2006–09. Sarkar, A. R. & Rahman, O. T. In-situ Removal of Arsenic Experiences of DPHE-Danida Pilot Project. Arsenic Mitigation Component, Danida SPS for Water Supply and Sanitation, Dhaka, Bangladesh. Sen Gupta, B., Chatterjee, S., Rott, U., Kauffman, H., Bandopadhyay, A., DeGroot, W., Nag, N. K., CarbonellBarrachina, A. A. & Mukherjee, S. A simple chemical free arsenic removal method for community water supply - A case study from West Bengal, India. Environmental Pollution 157 (12), 3351–3353. Sharma, S. K., Kappelhof, J., Groenendijk, M. & Schippers, J. C. Comparison of physicochemical iron removal mechanisms in filters. Journal of Water Supply: Research and Technology - AQUA 50 (4), 187–198. Smith, A. H., Lopipero, P. A., Bates, M. N. & Steinmaus, C. M. Arsenic epidemiology and drinking water standards. Science 296 (5576), 2145–2146.
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Stachowicz, M., Hiemstra, T. & van Riemsdijk, W. H. Multicompetitive interaction of As(III) and As(V) oxyanions with 2 Ca2þ, Mg2þ, PO3 4 , and CO3 ions on goethite. Journal of Colloid and Interface Science 320 (2), 400–414. Van Beek, C. G. E. M. Experiences with underground water treatment in the Netherlands. Water Supply 3 (1), 1–11. van Halem, D., Moed, D. H., Verberk, J. Q. J. C., Amy, G. L. & van Dijk, J. C. Cation exchange during subsurface iron removal. Water Research 46 (2), 307–315. van Halem, D., Olivero, S., de Vet, W. W. J. M., Verberk, J. Q. J. C., Amy, G. L. & van Dijk, J. C. Subsurface iron and arsenic removal for shallow tube well drinking water supply in rural Bangladesh. Water Research 44 (19), 5761–5769. von Oesten, G. Verfahren zur Enteisenung von Grundwasser im Untergrund selbst (Patentschrift Nr. 114709. Kaiserliches Patentamt Berlin). WHO Guidelines for drinking-water quality, First Addendum to Third Edition, Volume 1 Recommendations, World Health Organization, Geneva. Xu, H., Allard, B. & Grimvall, A. Effects of acidification and natural organic materials on the mobility of arsenic in the environment. Water, Air, and Soil Pollution 57–58, 269–278.
First received 12 March 2013; accepted in revised form 1 July 2013. Available online 12 September 2013
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Evaluating groundwater sustainability for fractured crystalline bedrock Meredith J. Metcalf and Gary A. Robbins
ABSTRACT Water sustainability is an important concern for communities that rely on groundwater in fractured rock; yet the complexity of the fracture system and the unknown rate of recharge make quantifying groundwater availability difficult, if not impossible, using conventional water balance calculations. This study provides a new approach for estimating groundwater sustainability in fractured rock that entails synthesis of pre-existing well data into a comprehensive database that permits defining bedrock groundwater drainage basins and flow for use in estimating recharge and usage. The method was tested in the Coventry Quadrangle, Connecticut and entailed the use of more than 2,500 wells. Groundwater recharge and usage were estimated for each drainage basin and the sustainability of each basin was determined by taking the difference between these estimates.
Meredith J. Metcalf (corresponding author) Environmental Earth Science Department, Eastern Connecticut State University, 83 Windham Street, Willimantic, Connecticut 06226, USA E-mail: metcalfm@easternct.edu Gary A. Robbins Department of Natural Resources and the Environment, University of Connecticut, 1376 Storrs Road, Storrs, Connecticut 06269, USA
Additionally, temporal analysis of well parameters indicated a decrease in well yield by approximately 20% and the depth to water declined. The method demonstrated here provides a means to allow the consideration of groundwater sustainability in land use planning and decisionmaking. Key words
| drainage basins, fractured bedrock, groundwater, recharge, sustainability
INTRODUCTION Rural communities in New England, as well as other regions
The sustainability of the groundwater resource is and
across the world, principally rely on groundwater extracted
will become more of a concern with population growth
from fractured crystalline and sedimentary bedrock. Despite
and perhaps changes in climate. The usual method for eval-
the importance of and reliance on groundwater in the frac-
uating aquifer sustainability by conducting water balance
tured rock, little is known about the water supply making
calculations is generally not achievable when describing
it difficult to manage on a regional or town wide basis. Fun-
fractured bedrock conditions. A major constraint in con-
damental
stewardship
ducting water balance analyses is the lack of information
practices as they relate to usage of water remain unan-
on bedrock recharge rates. Such data are not readily avail-
swered. These questions include: what is the potential
able owing to the high cost for data collection, the
limit of a local water supply, and has the water supply
complexity of the fracture network, and a lack of studies
been impacted by human development, and if so, how?
directed at sustainability. Advances in technology have
The lack of knowledge on the supply of and demands on
allowed scientists to use geographic information systems
groundwater can result in poor decision-making in land
(GIS) and remote sensing as tools to conduct spatial ana-
use planning related to new development. For example,
lyses to better understand the effects of landscape change
questions
concerning
current
without proper knowledge of the sustainability of the
on groundwater and surface water (Prasad et al. ;
supply, a new development can overtax the water supply
Biswas ; Bhalla et al. ). Most recently, GIS has
in an area, which would impact nearby domestic wells, sur-
been used to determine groundwater zones influenced by
face water bodies, wetlands, etc.
development (Jaiswal et al. ), to delineate groundwater
doi: 10.2166/ws.2013.179
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potential zones (Krishnamurthy et al. ; Murthy ; Obi Reddy et al. ; Pratap et al. ), and to conduct groundwater modeling (El-kadi et al. ; Shahid et al. ; Saraf et al. ). This research is directed at using GIS and a database developed using well completion reports (boring logs) to evaluate the sustainability of groundwater within fractured rock.
DESCRIPTION OF THE STUDY AREA The Coventry Quadrangle exemplifies typical groundwater conditions for the State of Connecticut, as well as other New England states and mountainous regions, where the fractured crystalline bedrock is the main source of water supply. Additionally, this study area has undergone highdensity development between 2002 and 2006 (CLEAR ) that is expected to continue in the foreseeable future (CtSDC ), which offers the opportunity to determine
the
impact
of
development
on
groundwater
sustainability. The Coventry Quadrangle is located in northeastern Connecticut and is intersected by the towns of Andover, Coventry, Mansfield, Tolland, and Willington (Figure 1). Although Connecticut has a highly variable lithology, the Coventry Quadrangle is dominantly composed of Paleozoic and Proterozoic gneiss and schist with small intrusions of dolerite and diorite scattered throughout. The surficial materials found within the Quadrangle are dominantly till and thick till, with areas of alluvium, sand, gravel, fines, or a combination thereof dispersed over the extent of the Quadrangle. The thickness of the overburden material ranges from 0 meters (outcrops are
Figure 1
|
Location of the Coventry Quadrangle in the state of Connecticut.
present) to approximately 49 meters (Meyer et al. c). A medium-sized valley follows the meandering stream
completion reports for the Coventry Quadrangle in Con-
and cuts through the center of the Quadrangle in a north-
necticut (Meyer et al. ; Metcalf & Robbins ).
south direction.
This pilot study included the development of a well completion report database, the digitization of records, the incorporation of quality assurance elements in digi-
DATA SOURCES
tizing records, and the use of the databases for performing geologic and water resource related assess-
As part of a US Geological Survey funded STATEMAP
ments (Meyer et al. a, b, c). The locations of more
project, in collaboration with the Connecticut Geological
than 2,500 wells that were used in this study are shown
Survey, a pilot study was initiated to digitize well
in Figure 2.
129
Figure 2
M. J. Metcalf & G. A. Robbins
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Evaluating groundwater sustainability for fractured bedrock
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Location of wells with well drilling information within the Coventry Quadrangle.
METHODOLOGY FOR DETERMINING SUSTAINABILITY OF BEDROCK DRAINAGE BASINS As described by Metcalf et al. () in detail, a hydraulic head map of the groundwater flow in the fractured rock of the Coventry Quadrangle was developed by using ArcGIS® to map water level data from well completion reports. The groundwater flow direction was used to delineate groundwater drainage basins for the fractured rock, as shown in Figure 3. Divergent flow lines defined
Figure 3
Bedrock groundwater drainage basins defined by Metcalf et al. (2013).
() using the specific capacity of the wells, the average hydraulic gradient (dh/dL) of the drainage basin, the area of each basin (A), and the length of the discharge boundary (L) for each basin. The following equation was used to determine an average rate of recharge (i) for each basin:
recharge areas within the Quadrangle and convergent flow lines defined areas of discharge. The bedrock
|
i¼
TL(dh=dL) A
(1)
groundwater drainage basins and the physical characteristics of the wells associated with each basin were used
The rate of groundwater usage for each basin was cal-
to estimate the rate of groundwater recharge. Parameters
culated by multiplying the number of homes within each
necessary for estimating the rate of recharge per basin
basin (extracted using ArcGIS®) by the average domestic
per
the
residence water use of 414.722 cubic meters (109,558 gal-
average transmissivity (T) defined by Huntley et al.
lons) per year (Rockaway et al. ) and dividing by the
year
using
Equation
(1)
were
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area of each basin. The sustainability of the groundwater
of the observed well yields was calculated for each time
in the fractured rock was determined by taking the differ-
period, as well as the average depth to water.
ence between estimates of the water availability (i.e., recharge estimates) and estimates of water usage within a 1 year period for each fractured rock groundwater
RESULTS AND DISCUSSION
basin delineated in Figure 3. Groundwater drainage basins that have a greater quantity of water recharging the
bedrock
than
consumed
are,
thus,
Sustainability of bedrock drainage basins
considered
sustainable.
Figure 3 shows the 136 bedrock groundwater drainage basins that were delineated using the hydraulic head map. Ninety-four of these basins have been delineated completely within the Quadrangle and provide the basis
METHODOLOGY FOR DETERMINING GROUNDWATER SUSTAINABILITY AS IT RELATES TO URBAN GROWTH
for this study. Table 1 shows the summary statistics for Table 1
|
Summary statistics for recharge and usage in the 94 basins delineated within the Quadrangle
Well productivity (defined by well yield), depth to water, and
Standard
the number of wells installed were analyzed as a function of time to determine whether the demands on the groundwater resource have been altered due to increased housing and/or population growth in the Coventry Quadrangle. The well completion report database devised for the STATEMAP project resulted in the use of 2,538 wells (Figure 2) to observe these temporal trends. The wells were sorted by completion date and grouped into the following time periods: 1965–1970, 1970–1975, 1975–1980, 1980–1985, 1985–1990, 1990–1995, 1995–2000, 2000–2005, and 2005–2010. Given the log normal distribution of observed well yields for the study area, demonstrated in Figure 4, the geometric mean
Figure 4
|
Average
7.3 × 10 3 Recharge (cubic meters/year)
Minimum
Maximum
Deviation
7.0 × 10 4
9.8 × 10 2 2.0 × 10 3
Basin area (meters2)
9.8 × 105
2.1 × 105
4.9 × 106
7.7 × 105
Number of homes
19.2
0
71
15.7
0
4.8 × 10 2 1.0 × 10 2
Usage (cubic 1.1 × 10 2 meters/year) Recharge usage (cubic meters/year)
0.4 × 10 3
Frequency distribution of well yield (left) and the log of well yield (right) demonstrating the log normal nature of well yield.
4.2 × 10 2 1.4 × 10 1 2.1 × 10 2
131
M. J. Metcalf & G. A. Robbins
|
Evaluating groundwater sustainability for fractured bedrock
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recharge and usage in the delineated drainage basins.
these estimates are based on the assumption that the aver-
Although on average it would appear that the usage and
age recharge and usage are the same every year (no net
recharge were almost the same for the Quadrangle, it
gain or loss). Thus, the groundwater bedrock supplies for
was found that 51 of the basins proved to be using ground-
the majority of the basins in this study area appear to be
water at a rate greater than recharge, 37 of the basins had
unsustainable.
recharge values that exceeded the rate of usage, and recharge and usage were equal within a 10% difference in six of the basins. Figure 5 shows the distribution of
Groundwater sustainability as it relates to urban growth
these basins along with the percent difference (100% × ((recharge-usage)/recharge)) between recharge and usage
Well completion reports for this study dated from Decem-
across the study area. It should be kept in mind that
ber 1965 to December 2007. The total number of wells, the geometric mean of the well yields, and the average depth to water are shown in Table 2 for each time period. Due to the inadequate number of wells available for the time periods 1965–1970 and 2005–2010, the cumulative number of wells and geometric mean of well yields were analyzed from 1970 to 2005. Figure 6 demonstrates that as more wells were installed between the years 1980 and 2005, the cumulative geometric mean of the well yields had decreased by 20%. The average depth to water had remained relatively constant during this period, until more recently as shown in Figure 7. The more recent decline in water level does not appear to be due to an increase in the number of homes, but rather an increase in well yields on a per home basis. This may reflect wells being drilled to greater depths in order to increase yields for larger homes or perhaps as a result of more homes being constructed at higher elevations as shown in Figure 8.
Table 2
|
Summary statistics for well completion reports for each time period
Time Period
|
Geometric Mean of Yield
Average Depth
Number of Wells
(cubic meters per second)
to Water (meters)
5
2.19 × 10 4
9.51
1970–1975
143
4.67 × 10
4
7.99
1975–1980
354
5.21 × 10 4
8.15
1980–1985
318
4.20 × 10
4
8.49
1985–1990
546
4.38 × 10 4
8.55
1990–1995
401
4.01 × 10
4
8.13
1995–2000
348
3.89 × 10 4
8.33
4
10.41
4.73 × 10 4
8.94
1965–1970
Figure 5
Total
Distribution of drainage basins and the percent difference (100% × ((recharge-
2000–2005
349
usage)/recharge)) between recharge and usage for each completely deli-
2005–2010
77
neated basin within the Coventry Quadrangle.
5.20 × 10
132
M. J. Metcalf & G. A. Robbins
|
Evaluating groundwater sustainability for fractured bedrock
Water Science & Technology: Water Supply
Figure 6
|
Cumulative number of domestic wells installed and the cumulative geometric mean of observed well yields for the years 1970â&#x20AC;&#x201C;2005.
Figure 7
|
Cumulative number of domestic wells installed and the average depth to water for wells within the Coventry Quadrangle for the years 1970â&#x20AC;&#x201C; 2005.
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133
Figure 8
M. J. Metcalf & G. A. Robbins
|
|
Evaluating groundwater sustainability for fractured bedrock
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Average surface elevation and average depth of completed well for wells within the Coventry Quadrangle for the years 1970–2005.
CONCLUSIONS A method has been presented that is useful for estimating the sustainability of the fractured bedrock groundwater. The calculations represent conditions on average and do not address the impact of season variations on groundwater sustainability. However, it is expected that where groundwater usage far exceeds recharge for specific bedrock drainage basins, wells in these areas may be most susceptible to seasonal drought conditions. The method demonstrated here would be useful to assess the viability of a development that relies on the bedrock groundwater and in planning and zoning decision making.
REFERENCES Bhalla, R. S., Pelkey, N. W. & Prasad, K. V. Application of GIS for evaluation and design of watershed guidelines. Water Resource Management 25, 113–140.
Biswas, B. Changing water resources study using GIS and spatial model – a case study of Bhatar Block, District Burdwan, West Bengal, India. Journal of the Indian Society of Remote Sensing 37, 705–717. Center for Land Use Education and Research (CLEAR) Connecticut’s Changing Landscape. University of Connecticut, Middlesex County Extension Center, Haddam, CT, March 2013, available online at http://clear.uconn.edu/ projects/landscape/your/town.asp. Connecticut State Data Center (CtSDC) Connecticut County Projections. University of Connecticut, Storrs, CT, March 2013, available online at http://ctsdc.uconn.edu/projections/ ct_counties.html. El-kadi, A. I., Oloufa, A. A., Eltahan, A. A. & Malic, H. U. Use of a geographic information system in site-specific groundwater modeling. Ground Water 32, 617–625. Huntley, D., Nommensen, R. & Steffey, D. The use of specific capacity to assess transmissivity in fractured-rock aquifers. Ground Water 30 (3), 396–402. Jaiswal, R. K., Mukherjee, S., Krishnamurthy, J. & Saxena, R. Role of remote sensing and GIS techniques for generation of groundwater prospect zones towards rural development-an approach. International Journal of Remote Sensing 24, 993–1008. Krishnamurthy, J. N., Venkatesa, K., Jayaraman, V. & Manivel, M. An approach to demarcate ground water potential
134
M. J. Metcalf & G. A. Robbins
|
Evaluating groundwater sustainability for fractured bedrock
zones through remote sensing and geographic information system. International Journal of Remote Sensing 17, 1867–1884. Metcalf, M. J. & Robbins, G. A. Deciphering trends in ground water quality and quantity in the fractured bedrock in the Coventry Quadrangle, Connecticut using GIS. Geological Society of America, Northeastern/Southeastern Section Meeting, abstracts with program, March 15, oral presentation, Baltimore, MD, p. 32. Metcalf, M. J., Robbins, G. A., Meyer, T. & Thomas, M. Defining ground water drainage basin boundaries and recharge for fractured crystalline bedrock using domestic well databases. Geological Society of America, Northeast Section Meeting, March 15–18, oral presentation, Bretton Woods, NH. Meyer, T., Metcalf, M., Robbins, G. & Thomas, M. a Bedrock Elevation Contours, Coventry Quadrangle, Connecticut [map]. 1:24,000. 7.5 Minute Series. Connecticut Geological and Natural History Survey and Connecticut Department of Environmental Protection, Hartford, Connecticut. Meyer, T., Metcalf, M., Robbins, G. & Thomas, M. b Bedrock Elevation Confidence Isopleths, Coventry Quadrangle, Connecticut [map]. 1:24,000. 7.5 Minute Series. Connecticut Geological and Natural History Survey and Connecticut Department of Environmental Protection, Hartford, Connecticut. Meyer, T., Metcalf, M., Robbins, G. & Thomas, M. c Surficial Materials Thickness Contours, Coventry Quadrangle, Connecticut [map]. 1:24,000. 7.5 Minute Series. Connecticut Geological and Natural History Survey and Connecticut Department of Environmental Protection, Hartford, Connecticut. Meyer, T. H., Metcalf, M. J., Robbins, G. A. & Thomas, M. A. Development of bedrock surface elevation and depth to bedrock maps for the Coventry Quadrangle,
Water Science & Technology: Water Supply
|
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2014
Connecticut, using water wells and Lidar data. Geological Society of America, Northeastern Section Meeting, abstracts with programs, March 22, poster, Portland, Maine, p. 42. Murthy, K. S. R. Groundwater potential in a semi-arid region of Andhra Pradesh: a geographical information system approach. International Journal of Remote Sensing 21 (9), 1867–1884. Obi Reddy, G. P., Chandra Mouli, K., Srivastav, S. K., Srinivas, C. V. & Maji, A. K. Evaluation of groundwater potential zones using remote sensing data – a case study of Gaimukh watershed, Bhandara district, Maharashtra. Journal of the Indian Society of Remote Sensing 28 (1), 19–32. Prasad, R. K., Mondal, N. C., Banerjee, P., Nandakumar, M. V. & Singh, V. S. Deciphering potential groundwater zone in hard rock through the application of GIS. Environmental Geology 55, 467–475. Pratap, K., Ravindran, K. V. & Prabakaran, B. Groundwater prospect zoning using remote sensing and geographical information system: a case study in Dala-Renukoot Area, Sonbhadra District Uttar Pradesh. Journal of the Indian Society of Remote Sensing 28 (4), 249–263. Rockaway, T. D., Goomes, P. A., Rivard, J. & Kornstein, B. Residential water use trends in North America. Journal American Water Works Association 103 (2), 76–89. Saraf, A. K., Choudbury, P. R., Roy, B., Sarma, B., Vijay, S. & Choudbury, S. GIS based surface hydrological modeling in identification of groundwater recharge zones. International Journal of Remote Sensing 25 (24), 5759–5770. Shahid, S., Nath, S. K. & Roy, J. Ground water potential modeling in soft rock area using GIS. Journal of Remote Sensing 21 (9), 1919–1924.
First received 15 January 2013; accepted in revised form 1 July 2013. Available online 12 September 2013
135
© IWA Publishing 2014 Water Science & Technology: Water Supply
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A comparative study of greywater from domestic and public buildings C. Santos, C. Matos and F. Taveira-Pinto
ABSTRACT Greywater (GW) can be an important resource for urban water consumption, replacing potable water for purposes that do not require drinking water quality. If applied on a large scale, this practice will reduce the potable water demand and the wastewater produced in urban areas, minimizing the negative impacts and costs of water extraction and wastewater treatment. A correct characterization of GW is important to assess its potential for a direct reuse or, if not possible, to make a correct definition of a feasible and cost-effective treatment system. This article aims to contribute to the characterization of GW produced in washbasins and showers in domestic and public buildings. A compilation of several works on GW collection and sampling produced by the authors is presented. Samples were taken from GW produced in showers and washbasins in households, changing rooms and in a restaurant. Results are compared with values presented in similar studies and compared
C. Santos (corresponding author) F. Taveira-Pinto Department of Civil Engineering, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto, Portugal E-mail: csantos@fe.up.pt C. Matos Engineering Department, Science and Technology School, University of Trás-os-Montes e Alto Douro, Quinta de Prados, apartado 1013, 5001-801 Vila Real, Portugal
with standards and guidelines published in different countries. Key words
| greywater, sustainability, water reuse
INTRODUCTION Greywater (GW) is defined as wastewater from showers,
By reducing potable water consumption in urban
baths, hand basins, laundry, washing machines and kitchen
areas, important economic savings can be achieved, not
sinks. Many authors and guidelines around the world con-
only for the population but also for governments. The
sider GW as wastewater only from showers, baths and
inefficient use of water has not only negative consequences
hand basins, excluding the more contaminated water from
for the environment but it also represents higher energy
washing machines and kitchen sinks. Compared to domestic
use in treatment plants and supply systems, with extra
wastewater, GW generally contains lower concentrations of
financial and environmental costs (Santos & Taveira-
organic pollutants and nutrients but a higher amount of sur-
Pinto ).
factants (Paris & Schlapp ). GW has the potential to be
As an example of potential economic and environ-
an important resource for urban water consumption since it
mental benefits of GW reuse, three houses with GW
can replace potable water in uses that do not require drink-
systems were studied in England. The system collected
ing water quality (such as irrigation and toilet flushing),
GW from the bath and bathroom washbasins and then fil-
reducing the demand on potable water supply. However,
tered and disinfected it. Treated water was then used to
as Mandal et al. () point out, this is not the only benefit
flush toilets. The potable water saved ranges from 24% in
of this practice. GW reuse also conserves water resources
a family of seven persons, up to 65% in a family of three
for potable uses and decreases the amount of wastewater
(EA ). On the other hand, in a small building with 30
sent to the downstream wastewater infrastructure (including
inhabitants, almost 300 m3 of potable water per year can
collection, treatment and disposal) and the negative impacts
be saved by reusing GW (about 30% of the total water con-
on the receiving environment.
sumption (Santos )).
doi: 10.2166/ws.2013.181
136
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Greywater from domestic and public buildings
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This practice gains major importance in countries suffer-
practices followed at household levels (Pinto et al. ).
ing from severe water stress and droughts and, for this
When analyzing different types of buildings, other than
reason, governments in countries such as Australia are
residential dwellings, this variation can be more significant.
developing policies and on-ground actions for conserving
Summarizing, it can be said that the volume and concen-
and recycling water (Pinto et al. ). While practical guide-
tration of this separately collected wastewater flow
lines for the reuse of GW for irrigation are being made
depend on consumer behavior and vary according to its
available by government agencies involved in water manage-
source (Paris & Schlapp ).
ment and regulation, there are a number of issues related to
This article aims to contribute to the characterization
human, soil and plant health risks and environmental pol-
of GW produced in washbasins and showers in domestic
lution that need further investigation to promote safe
and public buildings. As it is believed that human behavior
reuse. There is an urgent need to examine these issues and
or activities influence GW quality and quantity, it is
concerns and seek answers to specific questions and
expected that GW collected in domestic buildings should
develop guidelines with local data to ensure the sustainabil-
be different from that collected in public ones. A compi-
ity of GW reuse (Pinto et al. ).
lation of several works on GW collection and sampling
However, any strategy of water reuse that involves
produced by the authors is presented. Samples were taken
changes in people’s habits will have to achieve social accep-
from GW produced in showers and washbasins in house-
tance to be successful (Friedler et al. ; Matos et al. ).
holds, changing rooms and a restaurant. Results are
Water reuse needs to include community and stakeholder
compared with values presented in similar studies and
participation from the beginning and so its public accep-
with standards and guidelines published in different
tance has to be assessed. Muthukumaran et al. ()
countries in order to conclude whether it is possible to
concluded that community receptivity for reusing GW is
reuse it directly or after treatment.
highest for uses such as irrigation and flushing toilets but decreases if personal contact with GW is needed. This reveals that people are aware that GW may contain harmful substances. In fact, due to the presence of microbial agents
MATERIALS AND METHODS
and since in on-site systems GW is reused in close proximity to the general population, safe reuse is only possible after
GW from domestic buildings
appropriate treatment that increases its sanitary, environmental and aesthetic quality (Friedler & Gilboa ).
To determine GW quality in domestic buildings, indepen-
Nowadays, there are many types of GW reuse systems
dent samples were collected from eight single family
with significant differences in terms of their complexity.
houses, varying in the number of inhabitants from 2 to 6
They vary from small simple systems that drain water
people per house. GW was separated by its origin and
directly to the garden without storage, to large complex sys-
samples were then collected in bathtubs and washbasins.
tems with storage tanks also integrated with rainwater harvesting systems (EA ).
In each sample the following physical and chemical parameters
were
analyzed:
pH,
electrical
conductivity,
The importance of a correct characterization of GW
temperature and chemical oxygen demand (COD). All
lies in the assessment of its potential for direct reuse or,
parameters, except COD, were analyzed with sensors. COD
if not possible, the correct definition of the treatment
was analyzed in accordance with Standard Methods for the
system in order to achieve a feasible, cost-effective one.
Examination of Water and Wastewater (AWWA-APHE-
The main aspects for a correct design of the treatment
WPCF ). Total dissolved solids (TDS) concentration
unit are the site conditions and GW characteristics which
was calculated indirectly from the electrical conductivity
are quite variable among households (Mandal et al. ).
value measured, using the following expression:
This variability is mainly due to the type of detergents used, washed goods, lifestyle of occupants and other
EC[dS=m] × 640 ¼ TDS[mg=L]
C. Santos et al.
137
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Greywater from domestic and public buildings
Water Science & Technology: Water Supply
Microbiological parameters were also analyzed, namely
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RESULTS AND DISCUSSION
total and fecal coliforms which were determined following standard procedures (APHA ).
GW quality is expected to vary widely due to different uses of sanitary installations (in this case, showers and washba-
GW from public buildings
sins). In the public buildings this variation should be more
In the public buildings, GW was collected from washbasins
people and, consequently, the amount of dirtiness, soaps,
of a changing room exclusively used by the employees and
bathing products and other pollutants varies accordingly
also in a public toilet of a restaurant, both located in the Fac-
with every usage.
significant since those installations are used by diverse
ulty of Engineering of Porto University, Portugal. Other
Results obtained from the physical, chemical and micro-
samples of GW were collected from showers located in a
biological analysis of GW collected in residential and public
changing room for the employees of a wastewater treatment
buildings are presented in Tables 1 and 2.
plant in Vila Nova de Gaia, Portugal. The collection and
Results presented in Table 1 show high concentrations of solids (TSS, TDS and TS). In public buildings GW pre-
sampling of GW was made on a weekly frequency. Samples were taken, preserved and analyzed in accord-
sents a much higher concentration of dissolved solids,
ance with Standard Methods for the Examination of Water
which can be explained by a greater use of soaps when
and Wastewater (AWWA-APHE-WPCF ). Determined
washing hands and the fact that source water may be
parameters included pH, Total and Volatile Suspended
more saline. By comparing the concentrations of solids in
Solids (TSS and VSS), Total Solids (TS), Ammonia (NH3),
washbasins and showers, it can be seen that values are
Total Phosphorus (TP), Organic Matter (COD and BOD
very similar in these two places, both in public and dom-
(biochemical oxygen demand)) and Turbidity.
estic buildings.
Samples of GW were also analyzed for microbiological
In washbasins the organic matter was found to be simi-
parameters, namely total and fecal coliforms, in the Micro-
lar in domestic and public buildings; however GW from
biological Laboratory of the Faculty of Engineering of
showers presents higher COD values in domestic showers
Porto University.
than in public ones. This can be due to the quantity of
Table 1
|
Physical and chemical parameters (mean and standard deviation – SD) Washbasins
Baths/showers
Type of building
Public
Domestic
Public
Domestic
Number of samples
16
8
4
8
SD
Mean
pH
0.2
7.3
Conductivity (μs/cm)
–
–
SD
Mean
0.5
7.1
21.1
100.9
SD
Mean
0.3
6.9
–
–
SD
Mean
1.1
6.7
42.3
94.6
TSS [mg/L]
36
74
–
–
13
58
–
–
TDS [mg/L]
100
282
–
65
194
269
–
61
VSS [mg/L] TS [mg/L]
27
64
–
–
3
43
–
–
106
356
–
–
198
326
–
–
NH3 [mg/L]
0.5
0.9
–
–
0.8
8.6
–
–
TP [mg/L]
0.3
0.7
–
–
0.2
1.3
–
–
COD [mg/L]
67
179
–
197
85
197
–
540
BOD [mg/L]
18
59
–
–
116
129
–
–
25.1
–
–
–
–
–
–
Turbidity (NTU)
0.3
C. Santos et al.
138
Table 2
|
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Greywater from domestic and public buildings
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Microbiological parameters
Washbasins
Baths/showers
Type of building
Public
Domestic
Public
Domestic
Number of samples
6
8
1
8
SD
Mean
SD
Mean
SD
Mean
SD
Mean
Fecal coliforms (cfu/100 mL)
0
0
5.2E þ 02
3.3E þ 02
0
0
6.0E þ 04
4.5E þ 04
Total coliforms (cfu/100 mL)
2.3E þ 07
3.5E þ 07
3.5E þ 04
5.4E þ 04
0
0
1.1E þ 05
2.2E þ 05
Fecal streptococci (cfu/100 mL)
1.9E þ 03
2.6E þ 03
–
–
–
–
–
–
Pseudomonas aeruginosa (cfu/100 mL)
0
0
–
–
–
–
–
–
soaps used in domestic showers. On the other hand, the ten-
mainly used for showering, or were in a restaurant, so it is
dency of taking longer showers in public buildings, once
expected that people who use these facilities do not use
there is no worry about the cost of water, leads to a more
the toilets nearby very much. Results were compared with data from similar studies
diluted GW, and thus to lower concentrations. The variation of pH and total phosphorus is not signifi-
undertaken in different countries and presented in Table 3. Comparing data from Tables 1 and 2 with values from
cant in the different uses and buildings studied. However, higher concentrations of ammonia and BOD were registered in samples from showers, probably due to the existence of urine. Microbiological contamination, in terms of fecal coliforms
is
very
elevated
in
domestic
buildings
but
surprisingly it was not found in washbasins and showers in the public buildings. This may be explained by the possible presence of young children, using diapers, in domestic
the literature (Table 3), it can be seen that:
•
pH values, in general, do not vary significantly and the
•
electrical conductivity measured in domestic buildings is
•
ones obtained in this study are similar to the references; very low when compared to the references; values of total solids are higher than the ones presented by other authors but in this study, and also in the litera-
buildings. The diaper change is a process that can imply
ture, the dissolved fraction is higher than the suspended
some contamination with fecal coliforms. On the other
one;
hand, total coliforms were found in GW from washbasins in both types of buildings, and were higher in the public buildings. The washing temperature in washbasins is generally not very high and so total coliforms may be resistant to the environment and even reproduce (Gilboa & Friedler ). Public buildings may generally have a higher contamination in total coliform rates than domestic buildings due to the fact that the temperature used in washbasins in public buildings is generally lower than in domestic ones.
• • •
values of ammonia are included in the range presented by Christova-Boal et al. () and total phosphorus is lower than the values from literature; COD and BOD also present values that are higher than the literature but are in the range of Christova-Boal et al. (). microbiological parameters (fecal and total coliforms and fecal streptococci) are in the range presented by other authors.
Another interesting result is that even though there were many total coliforms in the public buildings, none of them
To assess the reuse potential of the collected GW, results
were fecal coliforms. This is probably due to the fact that
were also compared with the normative references and
these washbasins were either located in a dressing room
guidelines published in different countries (Table 4).
C. Santos et al.
139
Table 3
|
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Greywater from domestic and public buildings
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2014
References of GW characteristics Mandal et al. (2011)
Merz et al. (2007)
washbasins and kitchen sink
Bath, laundry and wash basins
Showers
Mean
Min
Max
Mean
Mean
pH
7.1
7.3
8.1
7.7
7.6
EC (μs/cm)
–
489.0
550.0
519.5
645.0
67.0
TSS [mg/L]
63
12
18
14.8
–
–
TDS [mg/L]
–
342
487
414.5
–
–
TS [mg/L]
5
–
–
–
2
0.5
NH3 [mg/L]
–
–
–
–
–
TP [mg/L]
–
1.5
3.4
2.5
–
COD [mg/L]
208
244
284
264.0
109
33.0
BOD [mg/L]
151
56
100
78.0
59
13.0
Turbidity (NTU)
–
20.6
38.7
29.7
29
11.0
33
24.0
60
240
Fecal coliforms (cfu/100 mL)
6.6E þ 05
3.7E þ 04
3.8E þ 04
3.8E þ 04
1.4E þ 05
1.1E þ 05
3.8E þ 04
9.3E þ 04
1.7E þ 02
3.3E þ 03
Total coliforms (cfu/100 mL)
4.7E þ 07
3.5E þ 04
3.6E þ 04
3.5E þ 04
–
–
–
–
5.0E þ 02
2.4E þ 07
Fecal streptococci (cfu/100 mL)
–
–
–
–
–
–
–
–
79
2.4E þ 03
Pseudomonas aeruginosa (cfu/100 mL)
–
–
–
–
–
–
3.3E þ 03
3.1E þ 03
–
–
References
Paris & Schlapp (2010)
Collecting place
Showers, laundry,
Table 4
|
Gilboa & Friedler (2008)
Christova-Boal et al. (1996)
Baths, showers and washbasins
Bathroom water
SD
Mean
SD
Min
Max
0.4
–
–
–
–
–
–
–
–
–
–
48
120
–
–
–
–
–
–
–
–
–
–
–
< 0.1
15.0
–
–
–
0.11
1.8
148
49.0
–
–
95
29.0
76
200
Water quality parameters for urban reuse
References
Portugal (ANQIP 2011)
Application
A, B
pH
–
Germany (FBR 2005)
UK (BSI 2010)
USA (US EPA 2004)
C, D
A, B
C
A
D
B
A to D
–
–
5 – 9.5
5 – 9.5
5 – 9.5
5 – 9.5
6–9
TSS [mg/L]
10
10
–
–
–
–
–
–
TDS [mg/L]
–
–
–
–
–
–
–
500–2,000*
BOD [mg/L]
–
–
–
–
–
–
–
10
Turbidity (NTU)
2
2
–
< 10
< 10
–
< 10
2
Fecal coliforms (cfu/100 mL)
1,000
200
< 10/mL
–
–
–
–
None detectable
Total coliforms (cfu/100 mL)
10,000
10,000
< 100/mL
10
1,000
1,000
10
–
Fecal streptococci (cfu/100 mL)
–
100
–
–
–
–
–
–
Pseudomonas aeruginosa
1 cfu/mL
–
–
–
–
–
–
< 1 cfu/mL
A – Toilet flushing, B – Laundry, C – Spray application (pressure washing, garden sprinkler and car washing), D – Garden watering (non spray). * Only for irrigation.
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Comparing the obtained results (Tables 1 and 2) with
care to avoid cross connections and the contamination of
the limit values presented in Table 4 it is possible to con-
the potable water supply network, for example by clearly
clude that GW has to be treated prior to its reuse.
identifying non-potable supply systems. In public buildings,
Although parameters such as pH and TDS are in accord-
these systems must be frequently inspected, especially in
ance with the presented limits, TSS and organic matter
places where the risk of potable contamination is higher,
(measured by BOD) are too high.
such as the non-potable reservoir and its potable back-up
Microbiological parameters are also out of the rec-
supply.
ommended range both in domestic and public buildings, indicating that there has to be a disinfection of GW prior
CONCLUSIONS
to reuse. A GW treatment unit is important not only to guarantee a safe reuse, in terms of public health, but also to assure the
This study shows that GW quality varies significantly in
proper functioning of the piping system and all the supplied
public and domestic buildings. Different uses made of sani-
equipment that can be damaged by the accumulation of
tary installations, the existence of young children, the
solids, for example, and formation of biofilm. Both in dom-
amount of dirtiness, soaps and bathing products, the temp-
estic and public buildings, GW must not be stored for too
erature in washbasins, and the time spent in the shower
long since the existing nutrients, organic matter and high
are the main factors that explain the different values
temperatures are ideal conditions for bacterial growth.
obtained in domestic and public buildings, especially in
Because of this, it is recommended that reuse should
terms of dissolved solids, COD and microbiological
occur only a few hours after GW is collected.
contamination.
More standards or legislation must be published in this
Results of GW quality obtained in this study are compar-
area, for example in the European Union, to define the
able with similar studies, but do not comply with limit values
limits for quality parameters of non-potable water use.
defined in standards and guidelines from Portugal,
Public buildings showed high microbiological contami-
Germany, UK and USA. Although parameters such as pH
nation (Table 2) so, even after treatment, reuse should
and TDS are in accordance with the presented limits, TSS
only be possible for purposes with no human contact
and organic matter are too high. Microbiological parameters
(sprinkler irrigation with treated GW should not be
are also out of the recommended range both in domestic
allowed). Management teams must be responsible for moni-
and public buildings, indicating that GW must be disinfected
toring treated GW frequently, and this type of monitoring,
prior to its reuse.
including sampling frequency and controlling parameters, must also be presented in standards or legislation.
GW characteristics presented in this study confirm that it is important to develop and optimize GW treatment sys-
In domestic buildings, inhabitants should be responsible
tems and make them safe and effective for specific non-
for the treatment system and the type of uses where non-
potable uses, in order to promote further development and
potable water is consumed. When human contact may
a large scale integration of GW reuse in urban areas. Both
occur, inhabitants must be encouraged to frequently moni-
in public and domestic buildings it can be seen that GW
tor their treated GW quality. To support this practice,
needs treatment which must be defined considering the
governments
reuse purposes, and the risk exposure of the population.
must
provide
user-friendly
information
packages and educational programs to inform the population about the advantages of this practice, its risks and to encourage the installation of safe GW reuse systems.
ACKNOWLEDGEMENTS
On the other hand, GW reuse systems must be carefully studied and designed in order to maximize the benefits to
The authors are grateful to SOPSEC S.A. and the Portuguese
users and guarantee their safety. When designing and
Foundation for Science and Technology (FCT) for all the
installing these systems, it is very important to take some
support in many aspects of this research, namely for the
141
C. Santos et al.
|
Greywater from domestic and public buildings
PhD grant SFRH/BDE/15620/2006. We would also like to thank Eng. Vítor Figueira for his support.
REFERENCES ANQIP ETA 0905 – Sistemas prediais de reutilização e reciclagem de águas cinzentas (SPRAC), versão 1. Associação Nacional para a Qualidade das Instalações Prediais (in Portuguese). APHA Standard Methods for the Examination of Water and Wastewater, 18th edn. American Public Health Association, Washington, DC, USA. AWWA-APHA-WPCF Standard Methods for the Examination of Water and Wastewater. 17th edn. American Public Health Association, Washington, DC. BSI BS 8525-1:2010 Greywater Systems - Part 1: Code of Practice. British Standards Institution, UK. Christova-Boal, D., Eden, R. E. & McFarlane, S. An investigation into greywater reuse for urban residential properties. Desalination 106 (1–3), 391–397. EA Greywater for Domestic Users: An Information Guide. Environment Agency. Bristol, UK. FBR Information Sheet H 201: Greywater Recycling Planning Fundamentals and Operation Information, 1st edn. Fachvereinigung Betriebs – und Regenwassernutzung e.V., Darmstadt, Germany. Friedler, E. & Gilboa, Y. Performance of UV disinfection and the microbial quality of greywater effluent along a reuse system for toilet flushing. Science of the Total Environment 408 (9), 2109–2117. Friedler, E., Lahav, O., Jizhaki, H. & Lahav, T. Study of urban population attitudes towards various wastewater reuse options: Israel as a case study. Journal of Environmental Management 81 (4), 360–370.
Water Science & Technology: Water Supply
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14.1
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2014
Gilboa, Y. & Friedler, E. UV disinfection of RBC-treated light greywater effluent: Kinetics, survival and regrowth of selected microorganisms. Water Research 42 (4–5), 1043– 1050. Mandal, D., Labhasetwar, P., Dhone, S., Dubey, A. S., Shinde, G. & Wate, S. Water conservation due to greywater treatment and reuse in urban setting with specific context to developing countries. Resources Conservation and Recycling 55 (3), 356–361. Matos, C., Friedler, E., Monteiro, A., Rodrigues, A., Teixeira, R., Bentes, I. & Varajão, J. Academics perception towards various water reuse options: University of Trás-os-Montes e Alto-Douro – UTAD Campus (Portugal) as a case study. Urban Water. Merz, C., Scheumann, R., El-Hamouri, B. & Kraume, M. Membrane bioreactor technology for the treatment of greywater from a sports and leisure club. Desalination 215 (1–3), 37–43. Muthukumaran, S., Baskaran, K. & Sexton, N. Quantification of potable water savings by residential water conservation and reuse – A case study. Resources, Conservation and Recycling 55 (11), 945–952. Pinto, U., Maheshwari, B. L. & Grewal, H. S. Effects of greywater irrigation on plant growth, water use and soil properties. Resources Conservation and Recycling 54 (7), 429–435. Paris, S. & Schlapp, C. Greywater recycling in Vietnam – Application of the HUBER MBR process. Desalination 250 (3), 1027–1030. Santos, C. Otimização ambiental do uso de água em edifícios (in Portuguese). PhD Thesis, Faculdade de Engenharia, Universidade do Porto. Santos, C. & Taveira-Pinto, F. Analysis of different criteria to size rainwater storage tanks using detailed methods. Resources, Conservation and Recycling 71, 1–6. US EPA EPA/625/R-04/108 Guidelines for Water Reuse. US Environmental Protection Agency, Washington, DC, USA.
First received 15 April 2013; accepted in revised form 8 July 2013. Available online 12 September 2013
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Formation characteristics of haloacetic acids from phenols in drinking water chlorination Fei Ge, Fei Tang, Yin Xu and Yao Xiao
ABSTRACT Haloacetic acids (HAAs) are typical chlorination disinfection by-products in drinking water. Apart from natural organic matter, synthetic organic compounds in raw water contribute to HAAs due to their high frequency of detection in raw water and high reactive activities with chlorine. Formation characteristics of HAAs from synthetic organic compounds were investigated using seven phenols as models in the chlorination process. Two HAAs, trihaloacetic acid (TCAA) and dihaloacetic acid (DCAA), were generated and TCAA was the main product. The molar yields of HAAs varied between 0.087 mol/(mol phenol) from resorcinol to 0.251 mol/(mol phenol) from 2,4,6-trichlorophenol at pH
Fei Ge (corresponding author) Fei Tang Yin Xu Yao Xiao Department of Environmental Science and Engineering, Xiangtan University, Xiangtan, Hunan 411105, China E-mail: gefeixtu@sina.com.cn
7.0. Phenols having para- or ortho-substituent groups were found to have higher reactive activities than those having meta-substituent groups in forming HAAs. HAA formation potential (HAAFP) of raw water was significantly enhanced with spiked phenols. These results indicate that synthetic organic compounds in raw water have high activities in yielding HAAs, and more research should be focused on their behaviors in drinking water disinfection. Key words
| chlorination, drinking water, HAAs, phenols
INTRODUCTION It has been well documented that chlorination disinfection
organic compound in clear raw water (Reckhow et al.
by-products (DBPs) are produced through the reaction of
). With serious water pollution in many regions, large
chlorine with natural organic matter (NOM) (Boyce &
quantities of synthetic organic compounds, e.g., phenols,
Hornig ; Reckhow et al. ; Bond et al. ).
nitrobenzenes, anilines, and chlorobenzenes have been
Among these DBPs, haloacetic acids (HAAs), which are
detected in raw water (Chen et al. ; Li et al. ).
potentially carcinogenic after trihalomethanes, are typically
Although their levels are generally in the range of ng/L to
the second most abundant class on a mass basis in drinking
μg/L, these organic compounds usually have higher reactive
water (Krasner et al. ; Yan et al. ). The most
activities with chlorine than NOM does (Hu et al. ;
common of the nine chlorinated and/or brominated HAAs
Dodd & Huang ); therefore, the contribution of these
are dichloroacetic acid (DCAA) and trichloroacetic acid
organic compounds to HAA formation requires further
(TCAA) (Qi et al. ). As HAAs are known or suspected
investigation.
carcinogens, their concentrations in drinking water have
Phenols are widely used in the production of pesticides,
been regulated in the water standards of the WHO, EC,
dyes, drugs, plastics, antioxidants, and in leather preser-
and US EPA among others. As an example, the US EPA
vation (Vermeulen et al. ). Due to their high levels
has limited a total of five HAAs with the maximum contami-
and frequencies of detection in raw water, 11 phenols
nant level of 60 μg/L under the Stage 1 Disinfectants/
were classified by the US EPA as priority pollutants in
Disinfection By-products Rule (Hozalski et al. ).
the environment, and these include phenol, 3-methyphe-
Previous studies have generally regarded NOM as the main precursor of HAAs, for NOM is the predominant doi: 10.2166/ws.2013.154
nol,
4-nitrophenol,
2,4-dichlorophenol,
and
2,4,6-
trichlorophenol (Mattinez et al. ). Thus, phenols
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Formation of haloacetic acids from phenols in water chlorination
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could be selected as a model in researching the formation
compounds and investigated their behavior in forming
characteristics
HAAs in chlorination. The objectives are: (1) to show
of
HAAs
from
synthetic
organic
compounds.
the chlorination kinetic process of phenols in forming
In previous studies, it was found that chlorination of
HAAs; (2) to compare the formation characteristics of
phenols progressed in a number of steps. The first step is
HAAs from phenols with different substituent groups;
the chlorination of the aromatic ring, which leads to the
(3) to present the variation of HAA formation potential
formation of mono-, di-, and trichlorophenols (Patnaik
(HAAFP) from raw water spiked with phenols; and (4)
et al. ; Ge et al. , ). With the following steps
to discuss a possible rate-determining step of phenols in
of ring cleavage and hydrolysis, phenols may generate
forming HAAs.
HAAs, THMs, and other DBPs (Boyce & Hornig ; Rebenne et al. ; Blatchley et al. ). Some dihydroxybenzenes and monohydroxybenzenes are chosen as
MATERIALS AND METHODS
model compounds in researching the chlorination kinetics of the THM formation mechanism from humic acid. As we
Materials
know, resorcinol was determined to have a much higher THM formation potential than other phenolic compounds,
Trichloroacetic
and hence is regarded as the main component of humic
(DCAA), and chloroacetic acid (CAA) with purities
acid in forming THMs (Rebenne et al. ; Yang &
greater than 99% were obtained from Acros Organics.
Shang ). Rebenne et al. () investigated the chlori-
1,000 mg/L TCAA, DCAA, and CAA stock solutions
nation of phenols and the formation of chloroform,
were prepared in tert-butyl methyl ether (MtBE). Seven
demonstrating that the yields of chloroform are dependent
model phenols: phenol, 4-monochorophenol (4-MCP),
on the type and position of the substituents of phenols.
2,4-dichlorophenol
Further investigations were conducted by Gallard & von
(TCP), resorcinol, 3-methylphenol (m-cresol), and 4-nitro-
Gunten (), who found that resorcinol had the highest
phenol (4-NP) were also purchased from Acros Organics
molar yield while p-nitrophenol had the lowest of 13
with purities greater than 98%. Their physicochemical
phenols in chloroform formation at pH 8.0. However, the
properties are listed in Table 1. 1,000 mg/L of phenol
formation of HAAs may be quite different from that of
and resorcinol stock solutions were prepared which was
THMs in the chlorination process. For example, THMs
based on the mass of raw material and diluted to target
have been enhanced in alkaline media while HAAs are
concentration with Milli-Q pure water (Mill-Q SP VOC,
enhanced in acid media in the chlorination of phenol
Millipore, Bedford, MA). Meanwhile, 1,000 mg/L of
(Guo & Chen ). Bond et al. (a) have studied the
4-MCP, 2,4-DCP, m-cresol and 4-NP, and 250 mg/L
disinfection by-products formation and fraction behavior
2,4,6-TCP standard solution were also prepared with
of natural organic matter surrogates and proved that ferulic
raw material and then diluted to target concentration
acid
(TCAA),
(2,4-DCP),
dichloroacetic
acid
2,4,6-trichlorophenol
acid has higher activity than resorcinol in yielding HAA9.
with Milli-Q pure water, and 5–10 mL methanol in
Guo & Chen () investigated the halogenating reaction
100 mL aqueous solution (reagent for high-performance
activity of five aromatic organic compounds (AOCs) and
liquid chromatography, HPLC) were added due to their
demonstrated that the chlorination or bromination reac-
low aqueous solubility, respectively (spiked methanol
tion activities for the AOCs with electron donating
does not yield HAAs in the chlorination process proved
functional groups were higher than for those with electron
by our experiment). A stock of free chlorine solution
withdrawing functional groups. To our knowledge, the for-
was prepared from commercial sodium hypochlorite
mation characteristics of HAAs from phenols have never
(NaOCl, 5% active chlorine) and then diluted with
been investigated in detail and remain uncertain.
Milli-Q pure water. The acute concentration of sodium
Based on the above background, in this investigation we selected seven phenols as model synthetic organic
hypochlorite solution was standardized by sodium thiosulfate titration.
F. Ge et al.
144
Table 1
|
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Formation of haloacetic acids from phenols in water chlorination
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Selected physicochemical properties of phenols
lgKow
Sw (g/100 mL, H2O, 25 C)
pKa
94.1
1.51
8.02
9.95
2-Monochlorophenol
128.5
2.15
2.10
8.44
2,4-Dichlorophenol
163.0
3.25
0.50
7.77
2,4,6-Trichlorophenol
197.5
3.75
0.042
6.19
4-Nitrophenol
139.1
1.79
1.63
7.08
m-Cresol
108.1
1.96
0.51
10.0
Resorcinol
110.1
0.88
147.3
9.91
Compound
Molecular formula
MW (g/mol)
Phenol
W
Data from Gnaim & Sheldon (1995) and Wagner & Schulz (2001).
Chlorination procedure
2.29 mg/L humic acid, with pH adjusted to 7.0, then 1 μmol/L phenol and resorcinol were added and the
Kinetic experiment
same chlorination procedure as before was followed. Samples of 25 mL were taken out at 0.5, 2, 10, 24, 48,
Sodium hypochlorite was added with a concentration of
and 72 h.
423 μmol/L in 500 mL aqueous solution, and then pH was adjusted to 7.0 by 50 mL phosphoric acid buffer solution
Impact of pH
and measured with a pH-meter (Mettler-Toledo, Switzerland). Then, 10 μmol/L phenol, 4-MCP, 2,4-DCP, 2,4,6-
Sodium hypochlorite was added with a concentration
TCP, resorcinol, m-cresol, and 4-NP were added to the
of 423 μmol/L in 500 mL aqueous solution, pH was
amber glass reactors, respectively, and placed in an air
adjusted to 6.0, 7.0, 8.0, and 9.0, and 106 μmol/L
bath with temperature maintained at 25 ± 1 C and recipro-
phenol was spiked in amber glass reactors. Samples of
cating rate at 120 rpm. Samples of 25 mL were taken out at
25 mL were taken out at 5, 10, 20, 30, 60, 120, 180,
0.08, 0.16, 0.5, 1, 2, 4, 6, 10, 14, 24, 36, and 48 h.
and 240 min.
W
The residual sodium hypochlorite in all samples was Spiked raw water experiment
decomposed by adding excess sodium thiosulfate, and then samples at different reaction times were analyzed by gas
Sodium hypochlorite was added with a concentration of
chromatography-electron capture detector (GC-ECD) (Shi-
423 μmol/L in 500 mL natural water, which contained
madzu GC-14C).
F. Ge et al.
145
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Formation of haloacetic acids from phenols in water chlorination
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Analysis conditions HAA concentrations for all samples were analyzed using a modified version of US EPA method 552.2. A 25 mL sample was acidified with 1.5 mL concentrated sulfuric acid and extracted with 3 mL of MtBE spiked with 300 μg/ L 1,2-dibromopropane as internal standard. Approximately 12 g of sodium sulfate was added to enhance the extraction. Then, 1 mL MtBE extraction was removed and mixed with 2 mL 10% sulfuric acidified ethanol and incubated for 2 h W
at 50 C for HAA derivatization. After the derivatization, the solution was back-extracted with 5 mL 10% sodium sulfate solution to remove the excess methane. 1 μL MtBE extraction was injected under splitless injection mode for GC-ECD analysis with a SPB-5 fused silica capillary (25 m length × 0.32 mm
i.d. × 0.25 μm
film
thickness).
The
W
column temperature was kept at 40 C for 3 min and W
W
W
increased from 100 C to 240 C at a rate of 10 C/min, held for 2 min. The concentrations of HAAs were determined by comparing the peak height of the samples and the calibration curves of the standards. The correlation coefficient of calibration curves of HAAs was greater than 0.99. The detection limits of DCAA and TCAA were 0.020 and 0.019 μg/L, respectively.
RESULTS AND DISCUSSION
Figure 1
|
Comparison of HAA formation in chlorination of different phenols (phenols ¼ 10 μmol/L, [HOCl] ¼ 423 μmol/L, pH 7.0).
Formation of HAAs from phenols in chlorination Moreover, molar yields and formation rates of TCAA Seven phenols: phenol, 4-MCP, 2,4-DCP, 2,4,6-TCP, resorci-
and DCAA were compared in the chlorination of the seven
nol, m-cresol, and 4-NP were selected to investigate the
phenols. In Figure 1(a) and Table 2, it is noted that the high-
formation characteristics of HAAs from phenols in water
est molar yield and formation rate of TCAA was obtained
chlorination.
from
2,4,6-TCP
(0.224 mol/mol
phenol).
Meanwhile,
TCAA and DCAA were detected in the chlorination
2,4-DCP (0.212 mol/mol phenol), 4-MCP (0.195 mol/mol
process and TCAA was the main product. Figure 1 shows
phenol), and phenol (0.157 mol/mol phenol) also had high
the variation of TCAA and DCAA in reaction time from
molar yields and formation rates of TCAA. For 4-NP
the seven phenols. TCAA and DCAA quickly yielded a
(0.220 mol/mol phenol), although the formation rate of
response in 5 min when the phenols were in contact
TCAA was far lower than that of 2,4,6-TCP, the molar yield
with chlorine, and then increased rapidly with time,
of TCAA was almost as high as that of 2,4,6-TCP. However,
especially in the initial 30 min. The plateau of HAA yield
dramatically lower molar yields and formation rates of
was observed to be 14 h from phenol, 4-MCP, 2,4-DCP,
TCAA
2,4,6-TCP, m-cresol, and resorcinol, whereas it was delayed
phenol) and resorcinol (0.067 mol/mol phenol). The com-
until 36 h from 4-NP.
parison of molar yield and formation rate of DCAA from
were
obtained
from
m-cresol
(0.070 mol/mol
F. Ge et al.
146
Table 2
|
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Formation of haloacetic acids from phenols in water chlorination
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addition, the electron withdrawing substituent group of
Molar yields of HAA formation from chlorination of phenols at pH 7.0
Molar yields of HAAs, mol/mol phenol Compound
TCAA
DCAA
Phenol
0.157
0.022
4-Monochlorophenol
0.195
0.025
2,4-Dichlorophenol
0.212
0.025
phenols was found to decrease the formation rate of HAAs, e.g., –NO2, for the electron withdrawing substituent group would block the electrophilic substitution in the first step of chlorination.
Chlorination of raw water with spiked model phenols
2,4,6-Trichlorophenol
0.224
0.027
4-Nitrophenol
0.220
0.025
To better understand the formation process of HAAs from
m-Cresol
0.070
0.020
phenols in an actual aquatic environment, phenol and
Resorcinol
0.067
0.020
resorcinol were selected and then added to raw water in chlorination (the physicochemical properties of the raw
seven phenols is presented in Figure 1(b) and Table 2. Although minor differences occurred under the same chlorination conditions, the highest molar yield of DCAA from the seven phenols was still obtained from 2,4,6-TCP (0.027 mol/mol phenol), while the lowest yield of DCAA was achieved from m-cresol (0.020 mol/mol phenol) and resorcinol (0.020 mol/mol phenol). These results indicate that phenols have high reaction activities with chlorine and generate HAAs in water disinfection. The formation potential of TCAA and DCAA is strongly related to the type and position of the substituent group of phenols. Summarizing the results, it is noted that phenols having para- and ortho-substituent groups have higher molar yields of HAAs, e.g., 4-MCP, 2,4-DCP, 2,4,6-TCP, and 4-NP; whereas phenols having a meta-substituent group have lower molar yields of HAAs, e.g.,
water are listed in Table 3). DCAA and TCAA were detected in the chlorination process and the results are shown in Figure 2. It was observed that concentrations of TCAA were enhanced with spiked phenol or resorcinol in raw water, while DCAA was affected little in this process. TCAA increased by 0.12 μmol/L in the initial 30 min with spiked phenol in raw water, and thereafter, approximately increased by 0.20 μmol/L at 72 h. This indicated that the HAAFP of the raw water was significantly enhanced. However, TCAA only increased by 0.05 μmol/L in the initial 30 min, with a final increase of 0.08 μmol/L at 72 h with spiked 1 μM resorcinol in the raw water. These results were consistent with the above formation potentials of HAAs from seven model phenols in chlorination, which further demonstrated that phenol had higher molar yields of HAAs than resorcinol.
resorcinol and m-cresol. These results were similar to the report of Bond et al. (a, b, ), who found in
Effect of pH on formation of HAAs from phenol
studying the disinfection by-products formation and frac-
in chlorination
tion behaviour of natural organic matter surrogates that ferulic acid has high HAA formation while resorcinol
Due to its high frequency of detection and concentration in
has low HAA formation. However, our data were dra-
raw water, phenol was selected from the seven model
matically different from the investigations of THMs
phenols to further investigate the effect of pH on the
formation in the chlorination of phenols. Gallard & von Gunten () studied the formation of chloroform from 13 phenols at pH 8.0 and reported that the highest molar yield was from resorcinol (0.95 mol/mol phenol) and the molar yields of CHCl3 from phenol, 4-MCP, 2,4-DCP,
and
2,4,6-DCP
was
between
0.10
and
0.11 mol/mol phenol, while the lowest molar yield of CHCl3
was
from
4-NP
(0.05 mol/mol
phenol).
In
Table 3
|
Physicochemical properties of raw water
No.
Item
1
pH
3
Carbonate, mg/L
5
Chloride, mg/L
7
Nitrate, mg/L
Value
No.
Item
Value
6.61
2
Humic acid, mg/L
116.04
4
Sulfate, mg/L
17.18
6
Phosphate, mg/L
0.01
9.32
8
Phenol, mg/L
0.016
2.53 31.03
147
F. Ge et al.
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Formation of haloacetic acids from phenols in water chlorination
Water Science & Technology: Water Supply
Figure 3 Figure 2
|
Chlorination of raw water with addition of phenol and resorcinol (phenols ¼
|
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2014
Effects of pH on formation of HAAs from chlorination of phenol (phenol ¼ 106 μmol/L, [HOCl] ¼ 423 μmol/L).
1 μmol/L, [HOCl] ¼ 423 μmol/L, pH 7.0).
formation of HAAs. From Figure 3 it can be seen that the
of DCAA varied little over the same pH range. The differ-
formation of TCAA was observed to be significantly influ-
ence in pH effect on yields of DCAA and TCAA may be
enced by pH while a minor influence was obtained on the
due to the different hydrolysis intermediates. DCAA precur-
formation of DCAA. With the increase of pH, the yield of
sors have been found to be less hydrophobic than TCAA
TCAA declined gradually. For example, in the initial
(Liang & Singer ). Similar phenomena were reported
5 min, the concentration of TCAA achieved 0.30 μmol/L at
by Guo & Chen (), who had tested the effect of pH
pH 6.0 while it was only 0.53 × 10–3 μmol/L at pH 9.0. At
on HAA formation for the reaction of aqueous chlorine
240 min, TCAA decreased from 1.64 to 0.36 μmol/L when
with phenol and found that HAA production decreased
pH increased from 6.0 to 9.0. However, the concentration
with increase of the pH.
F. Ge et al.
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Formation of haloacetic acids from phenols in water chlorination
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Rate determining step in the formation of HAAs from
concentration of HAAs was not in proportion to the concen-
phenols
tration of TCP in solution. For HAAs it was 1.86 μmol/L at pH 6.0 while it was only 0.57 μmol/L at pH 9.0. This indi-
Chlorination of phenols is a successive progress. The first
cates TCP is not a rate-determining intermediate in
step is the chlorination of the aromatic ring, leading to the
generating HAAs.
formation of mono-, di-, and trichlorophenols (Patnaik
Mechanistic studies by Reckhow & Singer () have
et al. ; Ge et al. , ). With the next steps of
linked a rise in levels of DCAA to diketone and then alde-
ring cleavage and hydrolysis, phenols gradually produce
hyde formation after oxidation. Conversely, and in
HAAs (Boyce & Hornig ; Rebenne et al. ; Blatchley
agreement with the resorcinol data, TCAA formation has
et al. ). Thus, the yield of trichlorophenol was a necess-
been likened to THM formation and may proceed through
ary step in the formation of HAAs. In our previous
common intermediates (Reckhow et al. ; Bond et al.
experiments, five chlorophenols were detected quantitat-
a, b). These results suggest hydrolysis is a key rate-limit-
ively by HPLC in the chlorination process, including
ing step in yielding HAAs, and further investigation may
2-monochlorophenol (2-MCP), 4-monochlorophenol (4-
need to be conducted in determination of the hydrolysis pro-
MCP), 2,6-dichlorophenol (2,6-DCP), 2,4-dichlorophenol
ducts and the other DBPs being formed in chlorination of
(2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) (Ge et al.
phenols.
, ). Figure 4 shows the distribution of chlorophenols including MCP (2-MCP and 4-MCP), DCP (2,4-DCP and 2,6-DCP), TCP (2,4,6-TCP) and HAAs in chlorination of phenol at various pH values at 240 min (the ratio of each component remained steady at 240 min). It was observed that the concentration of TCP was only 3.83 μmol/L at pH 6.0 while at pH
9.0,
74.62 μmol/L
was
achieved;
however,
the
CONCLUSION In drinking water treatment, synthetic organic compounds could react with chlorine and contribute to HAAs. Using phenols as models of synthetic organic compounds, it was observed that TCAA and DCAA were generated and TCAA was the main HAA in chlorination. HAA yields from phenols depended on the type and position of the substituents linked to the benzene ring. The sequence of molar yield of HAAs is 2,4,6-TCP > 4-NP > 2,4-DCP > 4-MCP > phenol > m-cresol, resorcinol. Phenols that have para- and ortho-substituent groups have higher activities than those having a meta- substituent group in forming HAAs. Moreover, the HAAFP of raw water was significantly enhanced with spiked phenols. These results indicated that some synthetic organic compounds in raw water have high activities in forming HAAs and more research should be conducted on their behaviors in water chlorination.
ACKNOWLEDGEMENTS We gratefully acknowledge the financial support from the Figure 4
|
Chlorination products of phenol at various pH values (phenol ¼ 106 μmol/L, [HOCl] ¼ 423 μmol/L, T ¼ 240 min).
Program for New Century Excellent Talents in University of
China
(NCET-10-0148),
Research
Foundation
of
149
F. Ge et al.
|
Formation of haloacetic acids from phenols in water chlorination
National Natural Science Foundation of China (No. 21277114).
REFERENCES Blatchley III, E. R., Margetasb, D. & Duggirala, R. Copper catalysis in chloroform formation during water chlorination. Water Res. 37, 4385–4394. Bond, T., Henriet, O., Goslan, E. H., Parsons, S. A. & Jefferson, B. a Disinfection by-product formation and fractionation behaviour of natural organic matter surrogates. Environ. Sci. Technol. 43, 5982–5989. Bond, T., Goslana, E. H., Jefferson, B., Roddick, F., Fan, L. & Parsons, S. A. b Chemical and biological oxidation of NOM surrogates and effect on HAA formation. Water Res. 43, 2615–1622. Bond, T., Goslan, E. H., Parsons, S. A. & Jefferson, B. A critical review of trihalomethane and haloacetic acid formation from natural organic matter surrogates. Environ. Technol. Rev. 1, 93–113. Boyce, S. D. & Hornig, J. F. Reaction pathway of trihalomethane formation from the halogenation of dihydroxyaromatic model compounds for humic acids. Environ. Sci. Technol. 17, 202–211. Chen, H. R., Zhu, L. Z., Yang, K., Ge, F. & Chen, Y. Y. Concentration and pollution characteristics of phenols in Qiangtang river. Chinese Environ. Sci. 25, 729–732. Dodd, M. C. & Huang, C. Transformation of the antibacterial agent sulfamethoxazole in reactions with chlorine: kinetics, mechanisms, and pathways. Environ. Sci. Technol. 38, 5607–5615. Gallard, H. & von Gunten, V. Chlorination of phenols: kinetics and formation of chloroform. Environ. Sci. Technol. 36, 884–890. Ge, F., Zhu, L. Z. & Chen, H. Effects of pH on chlorination process of phenols in drinking water. J. Hazard. Mater. 133, 99–105. Ge, F., Zhu, L. Z. & Wang, J. Distribution of chlorination products of phenols under various pH in water disinfection. Desalination 225, 156–166. Gnaim, J. M. & Sheldon, R. A. Highly regioselective orthochlorination of phenol with sulfuryl chloride in the presence of amines. Tetrahedron Lett. 36, 3893–3896. Guo, G. M. & Chen, X. D. Halogenating reaction activity of aromatic organic compounds during disinfection of drinking water. J. Hazard. Mater. 163, 1207–1212.
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Hozalski, R. M., Zhang, L. & Arnold, W. A. Reduction of haloacetic acids by Fe0: implications for treatment and fate. Environ. Sci. Technol. 35, 2258–2263. Hu, J. Y., Aizawa, T. & Ookubo, S. P. Products of aqueous chlorination of bisphenol A and their estrogenic activities. Environ. Sci. Technol. 36, 1980–1987. Krasner, S. W., Weinberg, H. S., Richardson, S. D., Pastor, S. J., Chinn, R., Sclimenti, M. J., Onstad, G. D. & Thruston, A. D. Occurrence of a new generation of disinfection byproducts. Environ. Sci. Technol. 40, 7175–7185. Li, X., He, M., Sun, Y. & Xia, X. Distribution of nitrobenzenes in the Yellow River from Xiaolangdi to Gaocun reach. Chinese J. Environ. Sci. 27, 513–518. Liang, L. & Singer, P. C. Factors influencing the formation and relative distribution of haloacetic acids and trihalomethanes in drinking water. Environ. Sci. Technol. 37, 2920–2928. Mattinez, D., Pocurull, E., Marce, R. M., Borrull, F. & Calull, M. Separation of eleven priority phenols by capillary zone electrophoresis with ultraviolet detection. J. Chromatogr. A 734, 367–373. Patnaik, P., Yang, M. & Powers, E. Phenol-chlorine reaction in environmental water: formation of toxic chlorophenol derivatives. American Lab. New 32, 16. Qi, Y., Shang, C. & Lo, I. M. C. Formation of haloacetic acids during mono- chloramination. Water Res. 38, 2375–2383. Rebenne, L. M., Gonzalez, A. C. & Olson, T. M. Aqueous chlorination kinetics and mechanism of substituted dihydroxybenzenes. Environ. Sci. Technol. 30, 2235–2242. Reckhow, D. A. & Singer, P. C. Mechanisms of organic halide formation during fulvic acid chlorination and implications with respect to preozonation. In: Water Chlorination: Environmental Impact and Health Effects (R. L. Jolley, ed.). Lewis Publishers, Chelsea, MI. Reckhow, D. A., Singer, P. C. & Malcolm, R. L. Chlorination of humic materials: by-product formation and chemical interpretations. Environ. Sci. Technol. 24, 1655–1664. Vermeulen, A., Welvaert, K. & Vercammen, J. Evaluation of a dedicated gas chromatography mass spectrometry method for the analysis of phenols in water. J. Chromatogr. A 1071, 41–46. Wagner, K. & Schulz, S. Adsorption of phenol, chlorophenols, and dihydroxy- benzenes onto unfunctionalized polymeric resin at temperatures from 294. 15 to 318.15 K. J. Chem. Eng. Data 46, 322–330. Yan, X. J., Bao, R. L., Yu, S. L., Li, Q. F. & Chen, W. Photocatalytic oxidation of humic acid and its effect on haloacetic acid formation potential: a fluorescence spectrometry study. Water Sci. Technol. 65 (9), 1548–1556. Yang, X. & Shang, C. Chlorination byproduct formation in the presence of humic acid, model nitrogenous organic compounds, ammonia, and bromide. Environ. Sci. Technol. 38, 4995–5001.
First received 30 January 2013; accepted in revised form 10 April 2013. Available online 12 September 2013
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Disinfection performance of nanosilver and impacts of environmental conditions on viral inactivation by nanosilver Yang Xu, Xiaona Chu, Jiangyong Hu and Say Leong Ong
ABSTRACT Three types of nanosilver materials, which were commercial, chemically-synthesized and biologicallysynthesized, respectively, were compared in terms of the disinfection efficiencies against Escherichia coli and MS2 coliphage in order to pinpoint promising material with the best performance. Disinfection results showed biologically-synthesized silver nanoparticles (referred to hereafter as ‘bio-AgNPs’) had the best disinfection performance, 10 mg/L of which was able to inactivate all the E. coli in 1 min (>6 log removals) and achieved 4 log removals of MS2 coliphage. Bio-AgNPs were therefore selected
Yang Xu Xiaona Chu Jiangyong Hu (corresponding author) Say Leong Ong Water Science & Technology Laboratory, Department of Civil and Environmental Engineering, National University of Singapore, Singapore 117576 E-mail: ceehujy@nus.edu.sg
for further study in terms of effects of the concentration and contact time as well as the impacts of environmental conditions on the viral inactivation. Given the viral inactivation profile of bio-AgNPs shown in this study, it could be concluded that viral inactivation by bio-AgNPs could be inhibited by total organic carbon (TOC) (10 mg/L as humic acid) and chloride ion (5 mg/L) to a large extent while Ca2þ/Mg2þ/ionic strength only had minor effects on the viral inactivation at high concentrations (188 mg/L as CaCO3 of hardness or 5.6 mM of ionic strength, respectively). This part of the study may help enlighten further mechanism studies on viral inactivation by nanosilver. Key words
| disinfection, environmental conditions, Escherichia coli, MS2 coliphage, nanosilver
INTRODUCTION Drinking water treatment is always of great concern world-
attracted attention from many researchers for its unique
wide and there are many problems associated with lack of
properties and potential application in many areas (Rai
clean and safe water: 1.2 billion people lack safe drinking
et al. ); and it has been developed as a novel disinfec-
water, 2 billion have poor sanitation, millions of people
tant that could be applied in water treatment due to its
die annually from waterborne diseases directly (Mont-
high intrinsic toxicity to microbes and insignificant harmful
gomery & Elimelech ) and many more are still
effects on humans (Fabrega et al. ; Dankovich & Gray
suffering from water-related issues. However, conventional
; De Gusseme et al. ). Previous studies convincingly
disinfection methods have many inherent drawbacks that
demonstrated the potential use of nanosilver and the feasi-
can no longer be tolerated: chlorination and ozonation
bility of nanosilver disinfection in water treatment against
have disinfection by-products formation issues and ultra-
both bacteria and viruses.
violet irradiation leaves no disinfection residues along the
Apart from chemical synthesis, which has been inten-
distribution system. Therefore, there is an urgent need to
sively studied in the past decade, Sintubin and his co-
develop a novel and robust disinfection strategy while avoid-
workers recently explored an innovative way to produce
ing those adverse effects.
nanosilver using Lactobacillus fermentum (Sintubin et al.
Silver and silver-related materials have been used and
). Nanosilver obtained with this method was reduced
recognized for centuries as a sustainable strategy against
and immobilized in the bacterial cell wall, which served as
microbial growth (Silver et al. ). Now nanosilver has
a carrier matrix for nanosilver, preventing nanoparticles
doi: 10.2166/ws.2013.183
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from aggregating. Researchers from the same group further
this study was 18 mΩ pure water produced by MilliQ water
evaluated the disinfection capacity of this biogenic nanosilver
purification system (Millipore, USA). Commercial silver
against UZ1 bacteriophage and Murine Norovirus 1 (De Gus-
nanoparticles (99.5% pure, referred to hereafter as ‘com-
seme et al. ) and investigated the potential application in
AgNPs’) were purchased directly from Sigma-Aldrich, USA
membrane technology (De Gusseme et al. ).
and used without further purification. Chemically synthesized
Although there are considerable studies on the synthesis
silver nanoparticles (referred to hereafter as ‘chem-AgNPs’)
and antimicrobial effects of nanosilver materials (Sondi et al.
were synthesized based on a previous publication (Pal et al.
; Wiley et al. ; Sintubin et al. ), few studies have
) with minor changes. Typically, 0.5 ml of 0.01 M
compared different kinds of nanosilver in terms of antimicro-
NaBH4 was rapidly injected into a solution containing
bial ability (El Badawy et al. ; Zhang et al. ).
0.5 ml of 0.01 M AgNO3 and 20 ml of 1 mM sodium citrate.
Particularly, little direct comparison of nanosilver from var-
The solution obtained was vigorously stirred for 5 min and
ious sources has been performed against Escherichia coli
aged for 1.5 hours to serve as Ag seed solution. Subsequently,
and MS2 coliphage, which are surrogates commonly used in
after 100 ml of 1 mM AgNO3 was boiled, 3 ml of Ag seed sol-
the field of drinking water quality control. To fill this research
ution and 1.04 ml of 0.1 M sodium citrate were added and the
gap, our study first compared nanosilver from three sources in
solution was kept at boiling point until it turned greenish
terms of disinfection efficiencies. Subsequently we adopted the
yellow. After being cooled down to room temperature, the
nanosilver material giving the best performance, which was
obtained nanosilver colloids were washed with DI water
bio-AgNPs, for further experiments in order to obtain the pro-
three times using a centrifuge (13,000 × g, 15 min).
file of inactivation against MS2 coliphage by bio-AgNPs. In
Biologically synthesized silver nanoparticles (referred to
order to do so, effects of contact time and concentration of
hereafter as ‘bio-AgNPs’) were synthesized according to
bio-AgNPs were studied while typical environmental con-
Sintubin et al. (). Typically, some biomass of L. fermen-
ditions were also assessed, including ionic strength,
tum ATCC 11976 was harvested and washed three times by
electrolytes (hardness and chloride ion) and total organic
centrifuge (5,000 × g, 10 min) after 48-hour incubation in
carbon (TOC) concentrations. To the best of our knowledge,
Man–Rogosa–Sharpe broth (Oxoid, UK) at 30 C. After
although impacts of these conditions have been widely studied
being diluted to 4.6 g (as cell dry weight (CDW)) per litre,
on bacterial growth (Fabrega et al. ; Jin et al. ), no sys-
the biomass was alkalified by adding 2.56 v% of 1 M
tematic study on viral inactivation has been reported yet. Thus
NaOH solution. 16.5 mg/ml (as Ag) of Ag(NH3)2NO3 sol-
this study aims at filling this gap. Despite the fact that mechan-
ution was then added into the alkalified biomass to
isms remain not fully understood, nanosilver was believed to
achieve a ratio of 1:4.6 for Ag:CDW. The mixture was care-
þ
W
inactivate microorganisms in three ways: (1) Ag ions released
fully covered with aluminium foil and shaken at room
from nanosilver, which may interfere with DNA replication
temperature (28 C) for 24 hours. Bio-AgNPs were then pur-
and protein function (Morones et al. ); (2) the adhesion
ified using a centrifuge (10,000 × g, 15 min).
W
of nanosilver to the microbes (Elechiguerra et al. ); and
A transmission electron microscope (TEM, JEM 3010,
(3) ROS formation (Sintubin et al. ). Behaviours of nanosil-
300 kV, JEOL Ltd, Japan) was used to characterize AgNPs
ver under different conditions in our study may enlighten
in this study, samples of which were prepared by depositing
further the study of mechanisms in this field.
a drop of freshly prepared AgNPs suspension (aqueous) on a carbon coated copper grid and air-drying at room temperature overnight. The TEM test was associated with energy-
MATERIAL AND METHODS
dispersive X-ray spectroscopy (EDX, INCAx-Sight, Oxford Instruments) in order to further verify AgNPs. Inductively
Production of nanosilver
coupled plasma optical emission spectrometry (ICP-OES, PerkinElmer, USA) was used to quantify the concentration
Chemicals used were purchased from Sigma-Aldrich, USA,
of AgNPs synthesized after being digested with HNO3 and
unless specified. Deionized water (DI water) used throughout
H2O2 according to US EPA 3050B.
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Growth and detection of E. coli and MS2 coliphage
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to previous studies (Fabrega et al. ; El Badawy et al. ; Jin et al. ). The concentration of bio-AgNPs and
E. coli ATCC 15597 and MS2 coliphage ATCC 15597-B1
contact time were fixed at 10 mg/L and 10 min, respectively,
were chosen as models of bacteria and viruses in water
in this part of the study.
and purchased directly from ATCC. All incubations were W
conducted at 37 C and 120 rpm. A culture of E. coli ATCC 15597 was incubated in tryptic soy broth (TSB,
RESULTS AND DISCUSSION
Oxoid, UK) overnight. One millilitre of such E. coli overnight culture was transferred and incubated in 30 ml of
TEM characterization of three selected nanosilver
TSB for 4 hours to obtain E. coli at exponential phase,
materials
which was washed three times using a centrifuge (2,500 × g, 10 min) before inactivation experiments. MS2 coliphage ATCC 15597-B1 was mixed with E. coli
TEM images of the nanosilver are shown in Figure 1. It should be noted the com-AgNPs had severe aggregation,
of exponential phase and incubated for 20 hours. As-
with sizes ranging from 70 nm (inset of Figure 1(a)) to several
prepared MS2 suspension was centrifuged at 3,600 × g for
hundred nanometres (Figure 1(a)) while chem-AgNPs were
10 min and the obtained supernatant was passed through
smaller in size, ranging from 20 to 100 nm (Figure 1(b)).
a 0.22 μm sterile filter. The filtrate was used as the MS2
Compared with the study of Pal et al. (), chem-AgNPs
stock. Detection of E. coli and MS2 coliphage relied on
in this study were successfully synthesized as they had the
the plate culture method and the standard double agar over-
same size and shape. Bio-AgNPs (Figures 1(c) and 1(d))
lay technique, respectively, this latter method is explicitly
might have the best dispersion as the biomass served as a scaf-
described elsewhere (Butkus et al. ).
fold, thereby avoiding aggregation from occurring (Sintubin
Bacterial and virus inactivation by AgNPs
nanoparticles proven by EDX (data not shown). The dark
et al. ). Black dots in Figures 1(c) and 1(d) are silver area in Figure 1(c) was simply the TEM copper grid AgNPs suspension was mixed with washed E. coli (or MS2 coliphage stock) to render a 10 ml reaction system that included 10 mg/L of AgNPs and ca. 105 CFU/ml of E. coli (or ca. 106 PFU/ml of MS2 coliphage). Such reactions were continuously stirred at room temperature and covered with aluminium foil to minimize the impact of ambient light. Samples were taken after 5-, 10-, 30- and 60-min contact time. Inactivation was expressed as log values (base 10), which equals log10 (C0/Ct). Each experiment was conducted in triplicate and error bars denote one standard deviation. Study on effects of electrolyte and TOC Sodium nitrate was selected to simulate ionic strength while calcium nitrate and magnesium nitrate were selected to simulate the hardness present in natural water. Sodium chloride was introduced as the source of Cl while humic acid was used as the source of TOC. These conditions were chosen because antimicrobial effects of nanosilver were reported to be affected by these conditions according
Figure 1
|
TEM images of (a) com-AgNPs, (b) chem-AgNPs, and (c) and (d) bio-AgNPs. Insets are respective single particles with the same scale bar of 20 nm.
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determined by EDX (data not shown). From Figure 1(c), it is
times were carried out with the same outcome gained. Con-
clearly seen that most of the silver nanoparticles were located
sidering this 6.3-log removal is the detection limit of this
in the cytoplasm with some of them on the cell wall (Figure 1
detection method, no error bar is given and data points
(d)). Apart from better dispersion, the size of the bio-AgNPs
only for 1 and 5-min contact time are shown.
was smaller (around 10 nm in Figure 1(d)) than that of
The conclusion that bio-AgNPs have a better perform-
either com-AgNPs or chem-AgNPs. These TEM images
ance against E. coli is in good agreement with Sintubin
were consistent with those provided in the study of Sintubin
et al. (). It was reported that bio-AgNPs had much
et al. ().
lower values of minimal inhibition concentration (MIC) and minimal bactericidal concentration (MBC) against E.
Bacterial and viral inactivation
coli than chem-AgNPs had (Sintubin et al. ). In spite of the different quantification methods (MIC/MBC versus
Comparison of com-AgNPs, chem-AgNPs and bio-AgNPs
plate culture method), their findings could be supportive
against E. coli is summarized in Figure 2. Performances of
that bio-AgNPs are more likely to be the better disinfectant
com-AgNPs and chem-AgNPs were gradually enhanced by
compared to com-AgNPs and chem-AgNPs.
increase of contact time from 5 to 60 min; however, no sig-
Comparison of three types of nanosilver against MS2
nificant difference between these performances were
coliphage is shown in Figure 3. Similar to the results for
detected (P ¼ 0.81). One possible reason that chem-AgNPs
E. coli, bio-AgNPs achieved the best performance of all
were no better than com-AgNPs could be the severe aggrega-
three, inactivating 3.0 and 4.3 log MS2 with contact times
tion of nanoparticles as denoted in the TEM images, which
of 5 and 10 min, respectively. Extending the contact time to
was in good agreement with a previous study regarding the
30 min or even 60 min didn’t increase the log removal much.
size effect of nanosilver (Morones et al. ). On the other
Inactivation of MS2 coliphage by bio-AgNPs with vary-
hand, astounding disinfection performances were achieved
ing contact time and concentration of bio-AgNPs was
by bio-AgNPs. There were no colonies seen on the plates
profiled in order to optimize the conditions so as to fulfil
after overnight incubation of bio-AgNPs treated samples,
the 4-log viral removal recommended in drinking water
even for those samples of 5-min contact time, which
guidelines by USEPA (Figure 4). Five mg/L of bio-AgNPs
denoted greater than 6.3 log removals. In fact, experiments
was not capable of achieving 4 log removals even if the con-
with shorter (1-min) and longer (10, 30 and 60-min) contact
tact time was up to 120 min, while 10 mg/L of bio-AgNPs
Figure 2
|
Comparison of log removals of E. coli by three types of nanosilver. Concen-
Figure 3
|
tration of AgNPs was 10 mg/L. Some error bars may be smaller than the
Comparison of log removal of MS2 coliphage by three types of nanosilver. Concentration of AgNPs was 10 mg/L. Some error bars may be smaller than
depicted symbols.
the depicted symbols.
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et al. () that Ca2þ and Mg2þ ions may serve as ionbridges and enhance the contact between cell surface and silver nanoparticles, which were both negatively charged in their case. Such enhanced contact would apparently enhance the antibacterial effect of silver nanoparticles as observed by Jin and her co-workers. This is the initiative to examine the effect of divalent ions on nanosilver disinfection performance. Effects of Ca2þ and Mg2þ concentrations on viral inactivation are summarized in Figure 5, which shows that log removal of MS2 coliphage decreased as concentration of hardness
increased.
Log
inactivation
by
bio-AgNPs
decreased incrementally from 4.0 log and 4.5 log to 1.5 log Figure 4
|
Log removal of MS2 coliphage by bio-AgNPs.
and 1.6 log for Ca2þ and Mg2þ, respectively, when the hardness (either Ca2þ or Mg2þ) increased from 0.94 to 188 mg/L as CaCO3. Such findings were contradictory to Jin’s study.
was capable of fulfilling 4-log removal in only 10 min. On
Therefore, one thing that is certain is that the ‘ion-bridge
the other hand, increasing the dosage from 10 to 25 mg/L
theory’ proposed by Jin et al. () may not be applicable
had no significant benefits (P ¼ 0.84); and increasing the
to the case of the MS2, even if the MS2 coliphage and bio-
contact time did not result in an increase in log inactivation
AgNPs were both negatively charged.
of MS2 after 10 min for 10 mg/L dosage. Such a phenom-
To further examine this result, sodium nitrate was intro-
enon was also observed in De Gusseme et al. (), in
duced to simulate the ionic strength in previous studies, with
which no increase of log inactivation was gained after 3 h.
an attempt to understand whether the decreased log
These two findings helped to determine that 10 mg/L of
removals could be attributed to increased ionic strength.
bio-AgNPs for 10 min was the recommended condition
Concentrations of NaNO3 were delicately tuned so as to
afterwards. De Gusseme et al. () reported viral removal of bioAgNPs on UZ1 bacteriophage. That disinfection performance was slightly better than this study and the main reason might be the resistance difference between UZ1 and MS2. UZ1, a DNA phage, is rarely used as an indicator in drinking water quality control whilst a previous study has already suggested that only F-specific RNA phages (e.g. MS2 coliphage) would have a resistance high enough to be considered as an acceptable indicator (Havelaar et al. ). Therefore a study on removal of MS2 would be of greater significance in drinking water quality control. Effects of ionic strength, calcium and magnesium ion concentrations Ca2þ and Mg2þ were reported to be able to affect silver nanoparticles stability and, as a consequence, the bacterial inactivation as well (Jin et al. ). It was proposed by Jin
Figure 5
|
Effects of ionic strength and hardness on log removal of MS2 coliphage by bioAgNPs. Dashed line denotes log removal by bio-AgNPs in DI water.
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be equivalent to the corresponding ionic strength of each
et al. (), in which the effect of organic matter was
hardness sample (either Ca2þ or Mg2þ). Results showed a
studied on bacterial growth in the presence of silver nano-
similar trend was observed and these three arrays of results,
particles. Fabrega and co-workers proposed that humic
furthermore, were not significantly different (P > 0.5).
acid may present a physical barrier between AgNPs and bac-
2þ
2þ
might be
teria, thereby impeding interaction between them. Thus our
believed to simply result from the impacts of ionic strength
results (Figure 6(a)) were in good agreement with the pro-
and it is further suggested that divalent cations may not
posed mechanism and may suggest viral inactivation of
serve as an ion-bridge in the case of viral inactivation by
bio-AgNPs might be attributed to physical contact between
bio-AgNPs, which was suggested in Jin et al. (). One
AgNPs and viruses.
Therefore, the adverse impacts of Ca
and Mg
possible reason for this decreased log removal is the
Results regarding effects of Cl could be well explained
enhanced aggregation of nanoparticles promoted by higher
by the fact that the toxicity of silver largely depends on the
ionic strength (El Badawy et al. ), and subsequently
presence of ligands (Ratte ). It is proposed that when
such aggregation would inhibit the disinfection performance
Agþ is released from nanoparticles, Cl may precipitate
(Morones et al. ). However, this proposed ‘aggregation’
Agþ in situ on the surface of nanoparticles. Such a precipi-
might be flawed since bio-AgNPs were believed to be fixed
tate may likely form an inert layer on the surface of
in and protected by biomass (dead cells) from aggregation.
nanosilver, thereby ‘quenching’ the disinfection perform-
Future study is needed to further elaborate this result.
ance of nanosilver. This proposed model was in good agreement with studies of Ho et al. () and Levard
Effects of TOC and chloride ion concentrations
et al. ().
TOC and Cl revealed detrimental impacts on bio-AgNPs in terms of viral inactivation (Figure 6). Ten mg/L of TOC ren-
CONCLUSION
dered a decrease of log removal from 3.3 to 0.4 logs while further increasing the concentration of TOC to 30 mg/L
Nanosilver from three sources, namely com-AgNPs, chem-
would totally inhibit the viral inactivation of bio-AgNPs
AgNPs and bio-AgNPs, were compared in terms of log inac-
(Figure 6(a)). Catastrophic results also occurred in the case
tivation against E. coli and MS2 coliphage. Bio-AgNPs,
of Cl , in which even 1 mg/L of Cl could decrease log
which had a smaller particle size and less aggregation
removal from 4.3 to 2.5 and 5 mg/L or more of Cl would
than the other two, achieved the best and formidable
totally inhibit the bio-AgNPs’ performance.
performance against both E. coli and MS2 coliphage,
Although viral and bacterial inactivation are two differ-
10 mg/L of which was capable of inactivating 6-log E. coli
ent scenarios, hints might be found in the study of Fabrega
and 4-log MS2 in 5 min. Bio-AgNPs disinfection against
Figure 6
|
(a) Effects of TOC and (b) effect of chloride ion on log removal of MS2 coliphage by bio-AgNPs. Dashed line denotes log removal by bio-AgNPs at the same conditions in DI water.
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MS2 was optimized and 10 mg/L for 10-min contact time was the recommended condition if 4-log viral removal is required. Effects of ionic strength, selective electrolyte and TOC were subsequently evaluated with bio-AgNPs at a concentration of 10 mg/L for a contact time of 10 min. Ionic strength and hardness would only affect the disinfection performance at a high concentration (5.6 mM, 188 mg/L as CaCO3 for ionic strength and hardness, respectively). TOC and chloride were found to dramatically affect the viral inactivation of bio-AgNPs, in which 30 mg/L of TOC (as humic acid) and 5 mg/L of Cl totally quenched the antiviral effects of bio-AgNPs. Such findings may suggest viral inactivation be attributed to physical contact between nanosilver and viruses. Results showed that there should be a strict requirement for the source water if we intend to apply nanosilver in the drinking water disinfection process.
ACKNOWLEDGEMENT The authors would like to acknowledge the financial support from the National Research Foundation and the Economic Development Board (SPORE, COY-15-EWIRCFSA/N197-1) and JSPS/NUS research project (R-302000-050-133/112).
REFERENCES Butkus, M. A., Labare, M. P., Starke, J. A., Moon, K. & Talbot, M. Use of aqueous silver to enhance inactivation of coliphage MS-2 by UV disinfection. Applied and Environmental Microbiology 70, 2848–2853. Dankovich, T. A. & Gray, D. G. Bactericidal paper impregnated with silver nanoparticles for point-of-use water treatment. Environmental Science & Technology 45, 1992–1998. De Gusseme, B., Hennebel, T., Christiaens, E., Saveyn, H., Verbeken, K., Fitts, J. P., Boon, N. & Verstraete, W. Virus disinfection in water by biogenic silver immobilized in polyvinylidene fluoride membranes. Water Research 45, 1856–1864. De Gusseme, B., Sintubin, L., Baert, L., Thibo, E., Hennebel, T., Vermeulen, G., Uyttendaele, M., Verstraete, W. & Boon, N. Biogenic silver for disinfection of water contaminated
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with viruses. Applied and Environmental Microbiology 76, 1082–1087. El Badawy, A. M., Luxton, T. P., Silva, R. G., Scheckel, K. G., Suidan, M. T. & Tolaymat, T. M. Impact of environmental conditions (pH, ionic strength, and electrolyte type) on the surface charge and aggregation of silver nanoparticles suspensions. Environmental Science & Technology 44, 1260–1266. El Badawy, A. M., Silva, R. G., Morris, B., Scheckel, K. G., Suidan, M. T. & Tolaymat, T. M. Surface charge-dependent toxicity of silver nanoparticles. Environmental Science & Technology 45, 283–287. Elechiguerra, J. L., Burt, J. L., Morones, J. R., Camacho-Bragado, A., Gao, X., Lara, H. H. & Yacaman, M. J. Interaction of silver nanoparticles with HIV-1. Journal of Nanobiotechnology 3, 6. Fabrega, J., Fawcett, S. R., Renshaw, J. C. & Lead, J. R. Silver nanoparticle impact on bacterial growth: effect of pH, concentration, and organic matter. Environmental Science & Technology 43, 7285–7290. Havelaar, A. H., Butler, M., Farrah, S. R., Jofre, J., Marques, E., Ketratanakul, A., Martins, M. T., Ohgaki, S., Sobsey, M. D. & Zaiss, U. Bacteriophages as model viruses in waterquality control. Water Research 25, 529–545. Ho, C. M., Yau, S. K. W., Lok, C. N., So, M. H. & Che, C. M. Oxidative dissolution of silver nanoparticles by biologically relevant oxidants: a kinetic and mechanistic study. Chemistry - An Asian Journal 5, 285–293. Jin, X., Li, M. H., Wang, J. W., Marambio-Jones, C., Peng, F. B., Huang, X. F., Damoiseaux, R. & Hoek, E. M. V. Highthroughput screening of silver nanoparticle stability and bacterial inactivation in aquatic media: influence of specific ions. Environmental Science & Technology 44, 7321–7328. Levard, C., Michel, F. M., Wang, Y., Choi, Y., Eng, P. & Brown Jr, G. E. Probing Ag nanoparticle surface oxidation in contact with (in)organics: an X-ray scattering and fluorescence yield approach. Journal of Synchrotron Radiation 18, 871–878. Montgomery, M. A. & Elimelech, M. Water and sanitation in developing countries: including health in the equation. Environmental Science & Technology 41, 17–24. Morones, J. R., Elechiguerra, J. L., Camacho, A., Holt, K., Kouri, J. B., Ramírez, J. T. & Yacaman, M. J. The bactericidal effect of silver nanoparticles. Nanotechnology 16, 2346–2353. Pal, S., Tak, Y. K. & Song, J. M. Does the antibacterial activity of silver nanoparticles depend on the shape of the nanoparticle? a study of the gram-negative bacterium Escherichia coli. Applied and Environmental Microbiology 73, 1712–1720. Rai, M., Yadav, A. & Gade, A. Silver nanoparticles as a new generation of antimicrobials. Biotechnology Advances 27, 76–83. Ratte, H. T. Bioaccumulation and toxicity of silver compounds: a review. Environmental Toxicology and Chemistry 18, 89–108. Silver, S., Phung, L. T. & Silver, G. Silver as biocides in burn and wound dressings and bacterial resistance to silver
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compounds. Journal of Industrial Microbiology & Biotechnology 33, 627–634. Sintubin, L., De Gusseme, B., Van der Meeren, P., Pycke, B. F. G., Verstraete, W. & Boon, N. The antibacterial activity of biogenic silver and its mode of action. Applied Microbiology and Biotechnology 91, 153–162. Sintubin, L., De Windt, W., Dick, J., Mast, J., van der Ha, D., Verstraete, W. & Boon, N. Lactic acid bacteria as reducing and capping agent for the fast and efficient production of silver nanoparticles. Applied Microbiology and Biotechnology 84, 741–749.
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Sondi, I., Goia, D. V. & Matijevic´, E. Preparation of highly concentrated stable dispersions of uniform silver nanoparticles. Journal of Colloid and Interface Science 260, 75–81. Wiley, B., Sun, Y. G. & Xia, Y. Synthesis of silver nanostructures with controlled shapes and properties. Accounts Chemical Research 40, 1067–1076. Zhang, H. Y., Smith, J. A. & Oyanedel-Craver, V. The effect of natural water conditions on the anti-bacterial performance and stability of silver nanoparticles capped with different polymers. Water Research 46, 691–699.
First received 7 March 2013; accepted in revised form 15 July 2013. Available online 12 September 2013
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Comparing electrochemical disinfection with chlorination for inactivation of bacterial spores in drinking water L. Mezule, M. Reimanis, V. Krumplevska, J. Ozolins and T. Juhna
ABSTRACT Drinking water disinfection techniques without the dosage of chemicals are regarded as more advantageous in terms of costs and practical use. Here we investigated the efficacy of electrochemical disinfection for inactivation of Bacillus subtilis spores – a model microorganism of highly resistant pathogens. The effect of electrochemical disinfection with TinO2n 1 ceramic electrodes which generate active chlorine from chloride in situ, was compared to the traditional chlorination in which active chlorine was produced from addition of sodium hypochlorite. Research was performed on a batch scale with a synthetic buffered drinking water containing 35.5 mg/l of chloride ions. Spore viability was analysed with both cultivation and cell potential for dividing (direct viable count method). The results showed that at similar residual disinfectant concentrations x
L. Mezule (corresponding author) V. Krumplevska T. Juhna Department of Water Engineering and Technology, Riga Technical University, Azenes 16/20 – 263, LV-1048 Riga, Latvia E-mail: Linda.Mezule@rtu.lv M. Reimanis J. Ozolins Faculty of Materials Science and Applied Chemistry, Riga Technical University, Azenes 14/24, Riga, Latvia
contact time (CT value), electrochemical disinfection was over three times more effective in neutralizing both cultivable B. subtilis spores and those with cell potential for dividing than traditional chlorination. As in chlorination, electrochemical disinfection was shown to be water-pH dependent and the lowest CT value of 112 mg/l min 1 (2-log removal) was obtained at pH 6. The lowest efficiency for both techniques was observed at pH 8. In conclusion, electrochemical disinfection is a viable in situ method even at low levels of chlorides in drinking water and appears to be more effective than simple chlorination with the addition of the active chlorine species when highly resistant microbial forms are analysed, however, to apply the technology on a large scale additional studies on potential formation of disinfection by-products must be performed. Key words
| chlorination, drinking water, electrochemical disinfection, spores
INTRODUCTION Over the last decade, electrochemical disinfection has
shown that the combination of mixed oxidants with chlorine
gained great interest as one of the alternatives to chemical-
increases the disinfection efficiency (Son et al. ). How-
based methods (e.g. chlorination, ozonation) due to its
ever, the exact mechanisms of disinfectants produced in
high effectiveness and environmental compatibility (Ker-
the process of electrolysis on the bacteria are not yet fully
wick et al. ; Martínez-Huitle & Brillas ). During
understood, which limits the implementation of this
the electrochemical treatment, active disinfectant (hypo-
method in general practice.
chlorous acid, hypochlorites) with a residual disinfectant
Usually one of the factors affecting the process of elec-
effect is generated at the anode from chloride ions
trolysis is the type of electrodes used, which have to
that are naturally found in the water (Kraft et al. a; Berg-
possess good mechanical properties, low porosity, low elec-
mann & Koparal ). Simultaneous generation of other
trical resistivity and good electrochemical properties for
oxidative species, such as •OH, O3, H2O2 and •O2 (Serrano
chlorine production. Previous studies have shown that
et al. ; Jeong et al. ), may provide an additional dis-
higher efficiency is achieved from Pt and Ti anodes covered
infecting effect (Cong et al. ). Previous reports have
with different metal oxides (RuO2, IrO2) (Martínez-Huitle &
doi: 10.2166/ws.2013.182
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Brillas ; Jeong et al. ) or boron doped diamond
of inactive and germinated spores can be performed. In
(Kraft ). However, extensive application of precious
this study the spores of Bacillus subtilis were chosen to rep-
metals in drinking water treatment is limited because of
resent a microorganism that is one of the most resistant
their cost and potential formation of harmful by-products
against disinfection. Thus, the effect of electrochemical disin-
when applied to drinking water (Bergmann ). Pro-
fection with non-stoichiometric titanium oxide based
duction of non-stoichiometric TinO2n 1 (n – from 4 to 10)
ceramic electrodes was investigated on the viability of
at high temperatures increases the amount of oxygen
B. subtilis spores in the system with low chloride ion concen-
vacancies in the crystal, thus increasing its electroconductiv-
tration, and comparing it with the traditional chlorination
ity. The application of extrusion technology and two-stage
method. The kinetics of spore inactivation were determined
W
thermal treatment (1,350–1,450 C) has enabled electrical
by using the concept of residual disinfectant concentration
resistivity below 1 Ω/m to be obtained (Rubenis et al.
multiplied by the contact time (CT) (White ).
). Furthermore TinO2n 1, in comparison to pure titanium or titanium dioxide, has a high resistance to corrosion, which is more preferable for long term application in drink-
MATERIALS AND METHODS
ing water, and it has been shown to be effective in generating active disinfectant from very low chloride con-
Bacterial strains and culture conditions
centrations (Kraft et al. b). Previous studies (Delaedt et al. ; Gusmão et al. )
B. subtilis ATCC®6051TM spore suspensions were prepared
have shown that apparent disinfection efficacy is dependent
from stock cultures grown on R2A medium (Oxoid Ltd, UK)
on the analytical methods used to measure the metabolic
at 30 C. Cultures were scraped off the plate, re-suspended in
activity of bacteria. Thus, measurement of cultivability with-
sterile phosphate buffered saline (PBS) and incubated for 6
out assessing other markers of the bacterial viability can
days at 30 C. After the incubation the samples were twice
lead to under-dosing of disinfectants and consequently to
washed (centrifugation for 2 min at 13,000 g) with sterile dis-
human exposure to the pathogens that are surviving drink-
tilled water. To assess the formation of spores, they were
ing water disinfection. It has been shown that bacteria
stained with 5% malachite green for 5 min. Then the slide
exposed to stress have the ability to divide only a certain
was rinsed with tap water and counterstained for 30 s with
number of times (Button et al. ) and it is not sufficient
2.5% Safranin O, then washed with water and air-dried.
to produce visible colonies, but enough to persist in the
The samples were visualized with light microscopy (Leica
environment. Up to date various cell metabolism markers,
DM LB, Germany), by counting the percentage of spores
like enzymatic (Hoefel et al. ) or respiratory activity
and vegetative cells. Only samples with a minimum of
(Reimanis et al. ), have been applied, however, most of
98% spores were used for further analyses.
W
W
these assays are not suitable for the analyses of highly resist-
The exact concentration of the spores was determined
ant microbial forms, e.g. spores, which are generally
according to a modified method described by Schichnes
dormant and unresponsive to traditional viability assays.
et al. (). In brief, a small amount of sample was filtered
However, their inactivation is of high importance due to
through a 25 mm diameter, 0.2 μm pore size filter (Anodisc,
the potential health hazards.
Whatmann), and without removing it from the filtration
In situ analyses of the cell ability to divide (direct viable
device, covered with ice cold MAA solution (three volumes
count, DVC) can be used to detect all cells and spores with
of methanol and one volume of acetic acid) for 5 min.
the potential to multiply (Kogure et al. ) and not only
After the incubation the MAA was removed and the filter
those able to form colonies. The method is based on the incu-
covered with ice cold ethanol (96%) for 1 min. Then the
bation of samples with antimicrobial agents and nutrients,
filter was air-dried and stained with 10 μg/ml DAPI (40 ,6-dia-
where the antibiotic at a certain concentration inhibits
midino-2-phenylindole, Applichem, Germany) for 30 min,
DNA synthesis and prevents cell division without affecting
washed with sterile distilled water and air-dried. Spore con-
other cellular processes. As a result simultaneous detection
centration
in
the
suspension
was
determined
with
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epifluorescence microscopy by counting 20 random fields of
performed where spores (∼106/ml final concentration)
view (excitation: 340/380 nm; emission: >425 nm, dichro-
were added to 0.5 l of sterile synthetic water (0.039 M NaH2-
matic mirror 565 nm, Leica DM LB, Germany).
PO4, 0.061 M Na2HPO4, pH 6 or 7) containing 8.21 mg/l sodium hypochlorite solution.
Sample preparation and treatment To 0.5 l of sterile synthetic spore/cell free water (0.039 M NaH2PO4, 0.061 M Na2HPO4, with or without 1 mmol KCl, pH 6, 7 or 8) B. subtilis spores with a final concentration of ∼1 × 106/ml were added. Water treatment with electrolysis was performed in a specially made electrolytic cell (Figure 1) consisting of a pure TinO2n 1 ceramic anode (Rubenis et al. ) with an area of 12.1 cm2 and a cathode made of stainless steel (AISI 304), with a total surface area of 18 cm2. The cathode consisted of two identical plates placed in parallel on either side of the anode, 5 mm away from it (Reimanis et al. ). Power to the electrochemical reactor was supplied by HQ Power, PS5005 (0–50 V DC, 0–5 A direct current rectifier). A standard electrolysis process was carried out at current intensity 0.1 A, temperature 23 ± 2 C with intensive stirring. W
Samples were collected before the electrolysis (0 h) and after 2, 4, 6, 24 and 30 h of treatment. To account for the residual effect and radicals formed, pH buffered water samples with 1 mmol KCl (35.5 mg/l Cl ) were electrochemically treated for 2 h, stopped and then inoculated with spores (∼106/ml) and placed on an orbital shaker (150 rpm min). Samples were collected before inoculation and after 2, 4, 6, 24 and 30 h. Additionally, control analyses with traditional chlorination were
Immediately after sampling, quenching with an equal concentration of 0.02 M sodium thiosulphate solution was performed. To activate spores and inactivate vegetative W
cells, prior to further analyses, heat treatment at 70 C for 30 min was performed. Simultaneously 10 ml of sample solution was analysed by the DPD colorimetric method (ISO ) to determine total chlorine levels formed. All experiments were performed in triplicate. Cultivation Cultivable spores were determined by the plate count technique. Decimal dilutions of the samples were inoculated onto R2A medium (Oxoid Ltd, UK) and incubated for 24 h W
at 30 C. Typical colonies were counted and results expressed as CFU per millilitre. All samples were analysed in triplicate. Direct viable count Cell potential for dividing was determined by the modified DVC method of Kogure et al. () and combined with DAPI staining. In brief, samples were incubated in double diluted tryptone soya broth (Oxoid Ltd, UK) and 30 μg/ml pipemidic acid (Sigma Aldrich, Germany), mixed for 19 h at 30 C with constant shaking. They were then filtered W
through a 25 mm diameter, 0.2 μm pore size, filter (TrackEtched, Sartorious), washed with sterile water, then fixed and stained with DAPI for 10 min. Spore, short ( 1.5 μm) and elongated ( 1.5 μm) cell counts were determined by epifluorescence microscopy by counting 20 random fields of view (excitation: 340/380 nm; emission: >425 nm). Statistical analyses and calculation of disinfection efficacy
Figure 1
|
Experimental setup for electrochemical disinfection studies (a) including the electrode design (b): 1–adjustable DC power supply; 2–electrolytic cell; 3–high precision voltmeter, Peaktech 3360 DMM; 4–high precision ammeter, Meterman DM9B; 5–magnetic stirrer, MMS-300, Biosan; 6–thermostat; 7–glass beaker, 1 L; 8–stainless steel cathode; 9–TinO2n 1 ceramic anode; 10–wires; 11–magnet.
Levels of inactivation were determined by plotting (MS Excel 2007) the average percentage of organisms or CFU against exposure time (hours). For determination of the residual disinfectant concentration × contact time (CT
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values) in mg/l min 1, the Chick-Watson model was used
decreased over a longer period, which could be explained
(Hoff ).
by complete conversion of chloride ions to chlorine with simultaneous evaporation or other mechanisms which were not investigated in this study. A higher potential for
RESULTS AND DISCUSSION
chlorine formation was observed at lower water-related pH values, however, the overall trend in the decrease of
Chloride ion concentration in drinking water usually ranges
chlorine concentration after 6 h was observed irrespective
from a few (spring water) to several hundred mg/l (high sal-
of the system pH.
inity waters), however, concentrations below 50 mg/l could
Studies on the inactivation of Bacillus spp. spores with
be regarded as typical for drinking water from surface and
traditional chlorination have shown that CT values vary
groundwater sources (WHO ). In this study sterile, pH
not only for different species but also for the same species
buffered water containing 35.5 mg/l chloride ions was
and often exceed 500 mg/l min 1 (Brazis et al. ; Rice
subjected to electrochemical treatment with a TinO2n 1
et al. ; Morrow et al. ). In the present study, 2 log
anode, and showed a potential for formation of more than
reduction in culturable counts was obtained after 48 and
3 mg/l of total chlorine during the first 4 h of electrolysis
89 min at the system pH of 6 and 7 respectively (Table 1)
using low current intensity (Figure 2). This concentration
giving CT values of 394 and 731 mg/l min 1 in a system of high spore concentration (106 spores/ml). The observed reduction in culturable counts decreased exponentially with very strong correlation between the data (R 2 ¼ 1) irrespective of the pH. Differences with the previously reported results can be linked to a strong dependency of system pH and temperature, cultivation methodology or Bacillus spore variability. Nevertheless, most of the studies are based on the estimation of disinfection efficiency from culturable counts, which detects only those spores with unlimited potential for dividing (Son et al. ). However, it has been shown before that counts of bacteria which are able to elongate, i.e. DVC counts, are usually higher than
Figure 2
|
Formation of chlorine from 35.5 mg/l chloride ions during electrochemical treatment (TinO2n 1 electrode, 0.1 A, RT, variable water pH values). Error bars represent the standard deviation from three separate experiments.
Table 1
|
the plate counts (Joux & Lebaron ; Hoefel et al. ), which was also observed in this study where more than two
CT values for 99 and 99.99% inactivation of cultivable B. subtilis spores and those with cell potential for dividing at variable treatment regimes (0.1 A, RT, 106 spores/ml) CT, mg/l min 1 99% inactivation
Treatment regime
pH
NaOCl
6 7
Electrolysis
Pre-electrolysis (35 mg/l KCl, 2 h) n/d – not determined by statistical analyses.
Cultivable counts
99.99% inactivation Elongated cells
Cultivable counts
Elongated cells
394 731
1,100 1,051
846 1,502
2,874 2,570
6 7 8
112 120 2,260
203 256 2,586
253 233 5,023
950 809 5,656
6 7
1,983 n/d
1,052 9,044
4,285 n/d
2,308 22,859
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times higher CT values were required to inactivate elongated
showed a clear decrease in elongated cell counts already
cells at pH 6. A similar trend was observed for pH 7.
after 2 h – the samples contained mostly un-germinated
Electrochemical treatment with low chloride ion con-
spores at pH 6 and 7 (Figures 3(a)–3(c)). To evaluate the
centration showed that within 2 h of treatment cultivable
single effect of electrochemical treatment, studies without
spore counts decreased by 2 log, following an exponential
any chloride ions were performed and showed that the
decrease (R 2 ¼ 0.943 for pH 6 and R 2 ¼ 0.958 for pH 7) to
effect is minor – during 30 h of electrolysis less than 1 log of
more than 5 log after 6 h of treatment. For all three types
both cultivable spores and those able to divide were neutral-
of pH values tested, pH 8 was shown to be the least efficient
ized (Figure 4). However, a minor increase in cultivable
since a decrease of less than 99% was still observed with
counts and decrease in dead spore counts during the first
both culturable and DVC counts (Figures 3(a) and 3(d))
2–4 h could be attributed to activation of spores at an initial
after 30 h. This could be linked to more active dissociation
stage, thus increasing disinfection efficiency with simul-
of hypochlorous acid at higher pH values (White ).
taneously generated chlorine – indicating a two parameter
Additionally, to increase the efficiency, longer treatment
effect – electrolysis as such and generated chlorine.
was not used, since the chlorine concentration in the system after 30 h decreased below 0.2 mg/l (Figure 2).
The analyses on residual disinfectant effect generated during electrolysis (spores subjected to electrochemically trea-
Comparison of chlorination and electrochemical treat-
ted water) showed that it cannot be regarded as strong,
ment on counts of both cultivable B. subtilis spores and
especially for pH 7 where the CT value for cells able to
those with cell potential for dividing, showed higher removal
divide increased to 20,000 mg/l min 1. For culturable counts
rates for electrochemical treatment where CT values were
at pH 7 no CT value was calculated because of low correlation
more than three times lower than when applying hypochlorite
between the data points (R 2 < 0.5). At the same time for pH 6
(Table 1) for both pH 6 and 7, suggesting simultaneous for-
some residual disinfecting effect was observed (Table 1), and
mation of other oxidants (Jeong et al. ) and their
the effect was more stable with respect to data correlation
disinfecting properties. Similar observations have been made
between three separate assays performed (R 2 ¼ 0.998).
in mechanically mixed oxidant systems which showed
In general, one of the features of TinO2n 1 electrodes when
higher disinfectant properties than chlorine alone. However,
compared to other electrodes, e.g., Pt, TiO2, IrO2, is that they
these studies were limited to cultivation analyses and system
produce dominantly active chlorine species, whereas other
pH >8 (Son et al. ). In our study microscopy analyses
oxidative species, such as .OH, O3, H2O2 and .O2, are not produced. However, the finding that at similar CT values a higher efficacy of spore removal with electrochemical disinfection was obtained, implies that there are some secondary mechanisms generated, which should be studied in future.
Figure 3
|
Changes in concentration of B. subtilis spores which are able to divide (elongated) after subjection to electrochemical treatment for 2 h (TinO2n 1 electrode, 30 mg/l chloride ions, 0.1 A, RT) in water with pH 6 (b), pH 7 (c) and pH 8 (d) when compared to non-treated control (a). Bar 5 μm.
Figure 4
|
Single effect of electrochemical treatment (TinO2n 1 electrode, no chloride ions, 0.1 A, RT) on cultivable (Δ) and dead (□) spores at pH 6 (dark) and pH 7 (light). Error bars represent the standard deviation from three separate experiments.
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It can be summarized that electrochemical disinfection of drinking water with TinO2n 1 electrodes and low chloride
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10/APIA/VIAA/012 ‘Development of innovative water procession technology using nanostructured ceramic’.
ion concentration is the most effective at pH 6 which correlates with the efficiency of traditional chlorination. This study showed that electrochemical disinfection is more effective in neutralization of bacterial spores – the most
REFERENCES
resistant microorganism form, However, to apply electrochemical
treatment
to
large
scale
drinking
water
disinfection, future studies must be performed to analyse potential formation of harmful by-products and evaluate the disinfection efficiency of biofilm-harboured bacteria which are regarded as a threat to drinking water quality.
CONCLUSIONS This study showed that when using mechanically resistant, low-cost TinO2n 1 electrodes for drinking water treatment with low chloride ion concentration, more than three times lower CT values can be obtained for inactivation of B. subtilis spores. A similar trend was observed for both cultivable spores and those able to divide, with the latter still being recorded when no culturable counts occurred which is attributed to higher CT values needed for full spore inactivation. Studies on the influence of water pH on electrochemical disinfection showed that the process is more efficient at lower pH values (6 and 7). Electrochemical disinfection of water at pH 8 was shown to be ineffective, giving more than 5 times higher CT values than at pH 6 and 7. The highest disinfection efficiency was obtained when chloride ion containing water was electrochemically treated, electrolysis as such showed no disinfecting properties. However, studies showed that pre-electrolysed water has a residual disinfectant effect and, thus, electrochemical treatment, after detailed assessment of potentially harmful byproduct formation, could be applied as an effective disinfection technology.
ACKNOWLEDGEMENT This work has been supported by European Regional Development Fund Project No. 2010/0257/2DP/2.1.1.1.0/
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Kerwick, M. I., Reddy, S. M., Chamberlain, A. H. L. & Holt, D. M. Electrochemical disinfection, an environmentally acceptable method of drinking water disinfection? Electrochemica Acta 50 (25–26), 5270–5277. Kogure, K., Simidu, U. & Taga, N. A tentative direct microscopic method for counting living marine bacteria. Canadian Journal of Microbiology 25 (3), 415–420. Kraft, A. Doped diamond: a compact review on a new, versatile electrode material. International Journal of Electrochemical Science 2, 355–385. Kraft, A., Blaschke, M., Kreysig, D., Sandt, B., Schroder, F. & Rennau, J. a Electrochemical water disinfection. Part ii: hypochlorite production from potable water, chlorine consumption and the problem of calcareous deposits. Journal of Applied Electrochemistry 29 (8), 895–902. Kraft, A., Stadelmann, M., Blaschke, M., Kreysig, D., Sandt, B., Schroder, F. & Rennau, J. b Electrochemical water disinfection part i: hypochlorite production from very dilute chloride solutions. Journal of Applied Electrochemistry 29 (7), 861–868. Martínez-Huitle, C. A. & Brillas, E. Electrochemical alternatives for drinking water disinfection. Angewandte Chemie International Edition 47 (11), 1998–2005. Morrow, J. B., Almeida, J. L., Fitzgerald, L. A. & Cole, K. D. Association and decontamination of bacillus spores in a simulated drinking water system. Water Research 42 (20), 5011–5021. Reimanis, M., Mezule, L., Malers, J., Ozolins, J. & Juhna, T. Model water disinfection with electrolysis using TinO2n 1
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containing ceramic electrodes. Environmental Biotechnology 7 (1), 34–40. Rice, E. W., Adcock, N. J., Sivaganesan, M. & Rose, L. J. Inactivation of spores of Bacillus anthracis sterne, Bacillus cereus, and Bacillus thuringiensis subsp. Israelensis by chlorination. Applied and Environmental Microbiology 71 (9), 5587–5589. Rubenis, K., Ozolins, J., Pura, A., Locs, J., Reimanis, M., Narkevica, I. & Berzina-Cimdina, L. The influence of thermal treatment on the properties of TiO2 ceramics obtained by extrusion. Scientific Journal of RTU. Material Science and Applied Chemistry 25 (1), 71–75. Schichnes, D., Nemson, J. A. & Ruzin, S. E. Fluorescent staining method for bacterial endospores. Microscope 54 (2), 91–93. Serrano, K., Michaud, P. A., Comninellis, C. & Savall, A. Electrochemical preparation of peroxodisulfuric acid using boron doped diamond thin film electrodes. Electrochimica Acta 48 (4), 431–436. Son, H., Cho, M., Kim, J., Oh, B., Chung, H. & Yoon, J. Enhanced disinfection efficiency of mechanically mixed oxidants with free chlorine. Water Research 39, 721–727. White, G. C. Handbook of Chlorination and Alternative Disinfectants, 4th edn, John Wiley & Sons, Inc., New York, USA. WHO Chloride in Drinking Water. Originally published in: Guidelines for Drinking-water Quality, 2nd edn. Vol. 2, WHO Press, World Health Organization, Geneva, Switzerland.
First received 20 March 2013; accepted in revised form 15 July 2013. Available online 12 September 2013
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Removal of DOM and AOC in a full-scale advanced water treatment plant: effects of operational periods of BAC filters J. Lohwacharin, Y. Yang, N. Watanabe, A. Phetrak and S. Takizawa
ABSTRACT Water utilities in Japan want to reduce residual chlorine levels so as to reduce disinfection byproducts and the chlorine smell, but bacterial regrowth is a concern. In advanced water treatment plants using ozonation and biological activated carbon (BAC), BAC plays the most important role in reducing assimilable organic carbon (AOC). Therefore, we analyzed the removal of dissolved organic matter (DOM) and AOC by full-scale BAC filters with different operational periods. Seasonal variation in AOC in raw water was wide, with a maximum of 306 μg acetate-C/L in November, and ozonation increased AOC. Nonetheless, BAC filters that had operated for 6 years produced water with lower AOC than ones with shorter operational periods, although they released a small amount of aromatic DOM. A diagram was constructed to derive the required levels of residual chlorine for no bacterial regrowth at various AOC levels of BAC effluents, which were linked with the operational periods of BAC filters and AOC in the ozonation effluents. Although BAC filters operated for longer than 100 weeks can effectively reduce AOC, lowering AOC levels in the ozonation effluent was indispensable for preventing bacterial regrowth in the water supply network at lower levels of residual chlorine than at present. Key words
| assimilable organic carbon (AOC), biological activated carbon (BAC), dissolved organic
J. Lohwacharin (corresponding author) A. Phetrak S. Takizawa Department of Urban Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan E-mail: jenyuk@env.t.u-tokyo.ac.jp Y. Yang School of Environmental Engineering, Beijing Normal University, No. 19 Xinjiekouwai Street, Beijing 100875, China N. Watanabe Division of Energy and Environmental Systems, Faculty of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
matter (DOM), drinking water treatment, ozonation
INTRODUCTION Dissolved organic matter (DOM), measured as dissolved
Over a long period of operation, the microorganisms on
organic carbon (DOC), in drinking water sources is usually
BAC become acclimatized to the AOC produced by ozona-
not easily biodegradable, since bacteria have already
tion, but DOC removal by BAC is reduced because of the
consumed the easily biodegradable fraction (Coble ).
loss of adsorption sites. In addition, the efficacy of DOC
Pre-oxidation (e.g., ozonation) of water increases the concen-
and AOC removal by full-scale water treatment systems
trations of biodegradable dissolved organic carbon (BDOC)
may differ with differences in raw water quality (which
and easily assimilable organic carbon (AOC) (van der Kooij
depends on sources of DOM) and in design and operation
et al. ; Xu et al. ). The formation of biodegradable
conditions. In Japan, the AOC levels are high (100 μg acet-
products stimulates biological activity in the subsequent
ate-C/L)
biological activated carbon (BAC) filters, resulting in higher
(Soonglerdsongpha et al. ). This relatively high fraction
in
comparison
with
DOC
(<0.80 mg/L)
removal rates of DOM in BAC filters and extension of BAC
of BDOC is of great concern to the Japanese water utilities,
service lifetime. Biological activities on BAC play a key role
which want to lower the residual chlorine levels in their
in controlling the biological stability of drinking water in dis-
water supply network. Nonetheless, the removal of different
tribution systems (Janssens et al. ).
components of DOM and AOC, as well as the possible
doi: 10.2166/ws.2013.185
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release of DOM from BAC, has not yet been related to the
(5–16 weeks), 3rd (17–31 weeks), 4th (32–54 weeks), 5th
operational periods of BAC filters in full-scale water treat-
(55–99), and 6th (6 years) periods.
ment plants (WTPs). Therefore, we investigated the effects
Water samples were prefiltered onsite through a 0.45 μm
of operational period on the removal of DOC and AOC by
PTFE filter (Dismic-45HP, Advantec, Japan) and stored in
BAC filters that had operational periods of between 1
glass vials at 4 C in the dark until DOM analysis. Unfiltered
week and 6 years. Typical operational periods for BAC fil-
samples were stored in glass bottles prepared following the
W
ters in Japan were 4‒6 years whereas BAC filters in The
method of van der Kooij et al. () and APHA () for
Netherlands were operated for longer than 18 months
AOC determination. Table 1 presents the ozone dose and
(van der Helm et al. ). We carried out experiments to
water quality parameters of the ozonation effluent.
quantify and characterize DOM components in the effluent and backwash water of BAC filters, to determine AOC levels
Analytical methods
after treatment by BAC filters, and to illustrate the relationship between operational period and no-regrowth AOC
AOC measurement relied on the simultaneous incubation of Pseudomonas fluorescens strain P17 (ATCC 49642) and Aqua-
levels at different residual chlorine levels.
spirillum sp. strain NOX (ATCC 49643) in pasteurized samples. AOC is expressed as μg/L of acetate C equivalents (μg of acetate-C/L) (van der Kooij et al. ; APHA ).
MATERIALS AND METHODS
High-performance size-exclusion chromatography (HP-SEC) Water samples
analysis was performed on a Protein Pak 60 (Waters Corp., Milford, MA, USA) column and a LC-10ADvp liquid chrom-
Samples were collected once or twice a month from
atography pump connected to a SPD-M10Avp diode array
December 2010 to December 2011 at an advanced WTP
detector (Shimadzu Corp., Kyoto, Japan) at 254 nm. Poly-
in the Tone River Basin, Japan. The plant, which can pro-
styrene sulfonate salt standards with various molecular
duce 1.7 million m /day, uses coagulation – primary rapid
weights (MWs) were used to calibrate the SEC column. DOC
sand filtration (1 SF), ozonation, BAC filtration, chlori-
was measured by the non-purgeable organic carbon method
nation, and secondary rapid sand filtration (2 SF). The
on a TOC-5000A analyzer (Shimadzu) in triplicate. UV absor-
dosage of polyaluminium chloride coagulant was 20–
bance at 254 nm (UVA254) was measured with a UV/Vis
W
W
70 mg/L. The contact time for ozonation was 12 min, and
spectrophotometer (U-2010, Hitachi, Ltd, Tokyo, Japan). A flu-
the retention time on BAC filters was 15 min at a filtration
orescence spectrophotometer (F-4500, Hitachi) equipped with
rate of 250 m/day, which was equivalent to 100 bed
a xenon lamp as the excitation source was used to measure
volumes/day. The BAC filters were backwashed with air
major fluorophores of DOM. Three-dimensional (3D) fluor-
and water every 5 days. The plant operates 40 BAC filters
escence excitation–emission matrix (3D F-EEM) spectra were
that began operation in 2005. The filters were grouped
collected at excitation spectra of 220–450 nm at 5 nm intervals
into six operational periods: the 1st (1–4 weeks), 2nd
and at emission spectra of 230–600 nm at 2 nm intervals. The
Table 1
|
Ozone dose and water quality parameters of ozonation effluent
Parameter
Unit
Arithmetic mean
Standard deviation
Minimum
Maximum
DOC
mg/L
0.940
0.222
0.602
UVA254
cm 1
0.012
0.005
0.006
1.374 0.020
pH
–
7.45
0.29
7.01
8.01
Ozone dose
mg-O3/L (mg-O3/mg-DOC)
0.45 (0.47)
0.26 (0.20)
0.18 (0.21)
0.96 (0.93)
Residual ozone
mg-O3/L
0.09
0.03
0.07
0.16
Temperature
W
6.8
4.5
C
13.4
25.4
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EEM data were corrected for instrument bias and inner filter-
which was unexpectedly higher than the 0.13 for DOC. Aro-
ing effects following Lawaetz & Stedmon ().
matic DOM is considered to be more easily adsorbable on BAC than hydrophilic DOM, which can be more easily biodegradable than aromatic DOM. Degradation of large-MW
RESULTS AND DISCUSSION
aromatic DOM by ozonation decreases the removal rate of
DOM removal by BAC filters
low-MW hydrophilic acids (Xu et al. ), which are readily
\The DOC removal by individual filters depended on their
BAC. This estimation was also supported in this study as
UVA254 by new BAC filters, whereas ozonation produces biodegradable, and thus increases the DOC removal rate by
operational periods (Figure 1). The effluent concentrations
shown by HP-SEC and 3D F-EEM in the following section.
(C) of BAC filters were normalized to the influent concen-
The effluent UVA254 increased noticeably, to a C/C0 of 0.67–
trations (C0) to show the removal of DOC and UVA254, which represents the aromatic chromophores present in DOM molecules. The BAC filters in the 1st period of operation (1–4 weeks) gave an average C/C0 of 0.13 (n ¼ 9), suggesting
0.70 in the 4th and 5th periods (32–99 weeks) of operation. Eventually, the 6-year filters produced effluents with UVA254 values that were up to 2.75 times those of the influents. This indicates that the 6-year BAC released aromatic DOM.
that 13% of the influent DOC was non-adsorbable on BAC. The C/C0 increased markedly with operational period, follow-
DOM characterization
ing a typical sigmoidal adsorption breakthrough curve. Nonetheless, breakthrough was not complete, probably because of biodegradation (Janssens et al. ; van der Aa et al. ). After 6 years of operation (the 6th period), C/C0
We used HP-SEC and 3D F-EEM analyses to characterize DOM present in the influents and effluents of the BAC filters. HP-SEC chromatograms show the size fractions of
averaged 0.78, indicating a quasi-steady removal rate of 22%,
UV254-absorbing DOM (hereafter referred to as ‘aromatic
which was higher than the rates of 8 to 14% reported in pilot
DOM’) in the solution. The chromatogram of the BAC-
studies that employed a shorter retention time of 10‒14 min (Servais et al. ; Babi et al. ). The highest levels of DOC recorded in the BAC filter effluents were 1.00 mg/L. The BAC filters removed less UVA254 than DOC (Figure 1). In the 1st period (1–4 weeks), the C/C0 of UVA254 was 0.32,
filter influent (Figure 2(a)) had peaks at 1,750 and 1,320 Da, corresponding to humic substances (Jarusutthirak & Amy ), and at 820 and 660 Da, corresponding to lowMW aromatic DOM (Xu et al. ). BAC filters of different operational periods had different abilities to treat DOM in the ozone effluent (BAC influent). BAC filters in the 1st operational period effectively removed aromatic DOM fractions with MW >1,000 Da, eliminating the peaks at 1,320, 1,750, and 2,140 Da, and removing half of the low-MW aromatic DOM (Figure 2(a)). Removal of aromatic DOM >1,000 Da declined markedly in the 3rd period, suggesting partial pore blockage that interfered with the adsorption of other molecules. The BAC filters in the 5th period (55–99 weeks) were not very effective in removing aromatic DOM. The BAC filters in the 6th period (6 years) removed no aromatic DOM of 660, 820, 1,320, or 1,750 Da, and released large-MW aromatic DOM at 2,140–2,390 Da. We further investigated the release of aromatic DOM from the 6th period BAC filters by analyzing spent back-
Figure 1
|
Effluent concentration (C ) normalized to the influent concentration (C0) of DOC and UVA254. Inset shows correlation of C/C0 of UVA254 against C/C0 of DOC of the effluent of 6-year BAC filters on a 1:1 scale.
wash water of the 4th (45-week) and 6th period (6-year) BAC filters. Figure 2(b) shows an example of the MW
168
Figure 2
J. Lohwacharin et al.
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Removal of DOM and AOC in a full-scale water treatment plant
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Representative MW distribution of aromatic DOM: (a) in the effluents of BAC filters, (b) in backwash water: (i) 6th period BAC effluent, (ii) 6th period BAC spent backwash water, (iii) 4th period (45-week) BAC effluent, (iv) 45-week BAC spent backwash water, and (v) backwash water. The BAC effluent was collected just before backwashing.
distribution of aromatic DOM in each BAC-filter effluent
Ex/Em ¼ 275/310). Mayer et al. () reported that these pro-
collected before backwashing, in backwash water, and in
teinaceous
spent backwash water. The high-MW aromatic DOM was
intensities at shorter wavelengths, i.e. peak T2 (Ex/Em ¼
released during the backwashing of the 6th period BAC
215–220/340) and peak B2 (Ex/Em ¼ 220–225/310).
filter but not the 4th period filter.
fluorophores
showed
stronger
fluorescence
The reduction of 3D F-EEM fluorophores by BAC filters
Backwashing may detach the superficial biofilm layers
is presented in Figure 3 as the ratios between the effluent
(i.e., shear losses) (Rittman ; Liu et al. ). During
and influent fluorescence intensities (F/F0). The BAC filters
washing, lysis of cells close to the biofilm-supporter interface
in the 1st period gave F/F0 ratios of 0.06–0.18 for peaks A, C,
causes detachment of fixed biomass, since nutrients are lim-
and T1, and 0.38 for peak T2, which corresponded to the
ited in the deep parts of the biofilm, where some microbes
non-adsorbable DOM, comprising 13% of the total DOC
cannot survive. The biofilm mass can increase or decline
in the influent (Figure 1). The ratios increased noticeably
with time until a steady state results, wherein the growth
in the 3rd period, in particular from 0.39 to 0.69 for peak
rate is balanced by the decay and shear losses (Liu et al.
T2 and from 0.18 to 0.49 for peak A. In the 4th period, the
). Cell lysis can release DOM, both biodegradable and refractory, into water. The refractory compounds can be cell wall (peptidoglycan) and cell membrane (lipopolysaccharide)
components
( Jarusutthirak
&
Amy
).
Therefore, a greater release of DOM would be expected from the 6th period BAC filters, wherein the microbial community has developed extensively. Fluorescence spectroscopy is useful to identify DOM transformations in water treatment processes, since the wavelengths at which absorption (excitation, Ex) and emission (Em) occur are specific to the molecules (Coble ). Coble () defined two groups of humic-like compounds and two groups of aromatic amino acids: (1) those stimulated by UV excitation (peak A; Ex/Em ¼ 240–250/380–480); (2) those stimulated by visible excitation (peak C; Ex/Em ¼ 330–350/
Figure 3
|
(a) Ratios of effluent (F) to influent (F0) fluorescence intensities of 3D fluor-
420–480); (3) tryptophan-like compounds (peak T1; Ex/Em ¼
escence excitation (Ex) – emission (Em) matrix components by operational period. Error bars show SD. A ¼ fulvic-like; C ¼ humic-like; T ¼ tryptophan-like
275/340); and (4) tyrosine-like compounds (peak B1;
compounds.
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F/F0 of peak C increased markedly from 0.26 to 0.40, but the
some aromatic compounds (van der Kooij et al. ). Aqua-
ratios of peaks A, T1, and T2 increased only slightly, by ca.
spirillum sp. strain NOX utilizes mainly carboxylic acids,
10%. From the 4th to the 5th periods, however, the ratios
including formic, glyoxylic, oxalic, pyruvic, and acetic
of humic substances (peaks A and C) and tryptophan-like
acids (van der Kooij & Hijnen ).
compounds (peaks T1 and T2) increased by about 20–32%
AOC levels were monitored in February (winter),
and 10–14%, respectively. The results show that BAC
August (summer), and November (autumn) 2011. The
removed humic substances more efficiently than aromatic
AOC in raw water was dominated by AOC-P17 (∼80–96%;
proteins, but the removal rates declined as adsorptive sites
Figure 4), consistent with previous results (Soonglerd-
became exhausted. The 3D F-EEM showed an increase in
songpha et al. ), and increased from 100 μg acetate-C/L
humic- (peak C), fulvic- (peak A), and tryptophan-like
in February to 306 μg acetate-C/L in November. The coagu-
(peak T2) signatures after treatment by BAC filters in the
lation–1 SF reduced the total AOC by 6–21%. Ozonation
W
6th period (Figure 3), consistent with the results of Figures 1
significantly increased AOC, particularly AOC-NOX. This
and 2. It was reported that microbes on BAC generated
suggests an abundance of oxalate, which strain P17 cannot
tryptophan-like proteins (Mayer et al. ; Liu et al. ).
utilize (van der Kooij & Hijnen ), in the ozonation byproducts. Ozonation increased the total AOC in coagu-
AOC removal
lation–1
W
SF water to 184–356 μg acetate-C/L at an
average ozone dose of 0.47 mg-O3/mg-DOC. This obserPseudomonas fluorescens strain P17 can utilize a variety of
vation is consistent with other reports that ozonation
easily biodegradable organic substrates, including amino
increased AOC levels ( Janssens et al. ; van der Kooij
acids, some carboxylic acids, carbohydrates, alcohols, and
et al. ; Soonglerdsongpha et al. ).
Figure 4
|
AOC concentrations and composition along the treatment process: (a) February 2011, (b) August 2011, (c) November 2011, and (d) total AOC and DOC concentrations. Error bars show standard deviation.
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The BAC filters reduced AOC by 66–71% of BAC-filter influent AOC in the 6th period, by 45–50% in the 5th period, by 55–68% in the 4th period, and by 28% in the 2nd period (Figure 4(d)). Other researchers reported comparable total AOC reduction by full-scale BAC filters (73– 86%) (Chien et al. ; Soonglerdsongpha et al. ). In spite of the seasonal variation in AOC in the raw water, the 6th period BAC produced biologically stable water with AOC levels of 62–116 μg acetate-C/L at a residual chlorine concentration of 0.67–0.96 mg/L, which is within the range of biologically stable finished water given by LeChevallier et al. (). This result demonstrates that although DOM is thought to comprise decomposed microbial cells released into treated water, the 6th period BAC filters can steadily remove AOC and, thus, can achieve biostability of finished water.
Figure 5
|
Relationship between residual chlorine concentration and no-regrowth AOC levels of finished water, and predicted AOC levels in BAC effluents as a function of BAC-filter operational period. No-regrowth AOC levels from the literature. The no-regrowth regression line was performed using SigmaPlot 12 software based on the Marquardt–Levenberg algorithm.
It is interesting to note that the reduction of AOC-NOX by BAC filters did not change with increasing operational
(Figure 4(d)). To meet the no-regrowth requirement when
period (Figures 4(a)–4(c)). This result suggests that car-
the AOC in the ozone effluent is 200 μg acetate-C/L (the
boxylic acids are primary substrates utilizable by bacteria
nearest value plotted in Figure 5) requires BAC filters with
growing on BAC since the 2nd period. In contrast, the
an operational period of >180 weeks at a residual chlorine
BAC microbes in the 6th period were acclimatized to a var-
of 0.8 mg/L. However, to avoid the chlorine smell and to
iety of organic substrates and removed a significant portion
reduce the formation of disinfection byproducts, many
of AOC-P17, whereas those in the 2nd period, which were
Japanese water utilities lower the residual chlorine level to
still acclimating, were not able to remove AOC-P17.
0.4 mg/L. Therefore, a lower ozone dosage that generates AOC levels of 80–100 μg acetate-C/L in combination with
Application of AOC data to operation of BAC filters
BAC filters with operational periods of 40–90 weeks is required to achieve a no-regrowth AOC level of 40 μg acet-
Using data drawn from the literature (van der Kooij et al.
ate-C/L. This comparison indicates that reducing AOC in
; LeChevallier et al. ; Chen et al. ; Chien
the ozone effluent is more important than maintaining a
et al. ; van der Helm et al. ; Soonglerdsongpha
longer operational period of BAC filter if we want to
et al. ), we plotted residual chlorine concentrations
reduce the residual chlorine level below 0.4 mg/L. However,
against no-regrowth AOC levels (Figure 5). Using the Leven-
the seasonal fluctuations in AOC in the raw water,
berg–Marquardt algorithm in SigmaPlot 12 software, we
especially the very high levels in November (Figures 4(c)
fitted a curve to the AOC removal data obtained in this
and 4(d)), make it difficult to control AOC levels only by
study, along with two values from the literature (Soonglerd-
reduced ozone dose. Further study is needed to reveal the
songpha et al. ), and the operational periods of BAC
factors, and control measures if possible, affecting the fluctu-
filters (Supplementary data, Fig. a, available online at
ations in AOC of raw water.
http://www.iwaponline.com/ws/014/185.pdf). Using this regression curve, we then plotted the effluent AOC level by operational periods of BAC filter for BAC influents of
CONCLUSIONS
80, 100, 150, 200, 300, and 400 μg acetate-C/L (Figure 5). The AOC in the ozone effluent (i.e., BAC influent)
1. The 1- to 16-week BAC preferentially removed aromatic
was lowest in February (winter), at 184 μg acetate-C/L
DOM with MW >1,000 Da (i.e., humic substances).
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Removal of DOM and AOC in a full-scale water treatment plant
The removal of this fraction declined with the increase of operational period, indicating the loss of adsorptive sites in the BAC. In contrast, the 6-year BAC-released aromatic DOM with MW >2,000 Da, characterized by 3D F-EEM signatures of humic- and fulvic-like compounds. The released aromatic DOM was associated with decomposed microbial cells that had been attached to the 6-year BAC. 2. AOC in raw water varied widely, peaking at 306 μg acetate-C/L in November (autumn). Levels this high require operational adjustments such as lowering the ozone dose, not replacing BAC in autumn, and increasing residual chlorine to lower bacterial regrowth in water supply systems. AOC in ozonation effluent also varied, but the 6-year BAC was able to maintain low AOC levels in the BAC effluents even in the high AOC period. 3. A diagram constructed to relate the operational period of BAC filters with AOC in the BAC effluent can be used to estimate the minimum residual chlorine concentration for no bacterial regrowth. For the AOC level of BAC influents in this study (ca. 200‒300 μg-C/L), we suggest maintaining the BAC filters with an operation period of 180‒270 weeks at a residual chlorine of 0.8‒1.2 mg/L to achieve no-regrowth requirement.
ACKNOWLEDGEMENTS This study was supported by the Environment Research and Technology Development Fund (S-8) of the Ministry of the Environment, Japan; by a Grant-in-Aid for Scientific Research (#22404012) from the Japan Society for the Promotion of Science (JSPS); by a JSPS Postdoctoral Fellowship (#21-09290); and by the CREST Project Fund of the Japan Science and Technology Agency. The authors thank the managers of the WTP for their help.
REFERENCES APHA Standard Methods for the Examination of Water and Wastewater, 21st edn, American Public Health Association, Washington DC, USA.
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Babi, K. G., Koumenides, K. M., Nikolaou, A. D., Makri, C. A., Tzoumerkas, F. K. & Lekkas, T. D. Pilot study of the removal of THMs, HAAs and DOC from drinking water by GAC adsorption. Desalination 210 (1–3), 215–224. Chen, C., Zhang, X., He, W., Lu, W. & Han, H. Comparison of seven kinds of drinking water treatment processes to enhance organic material removal: a pilot test. Science of the Total Environment 382 (1), 93–102. Chien, C. C., Kao, C. M., Dong, C. D., Chen, T. Y. & Chen, J. Y. Effectiveness of AOC removal by advanced water treatment systems: a case study. Desalination 202 (1–3), 318–325. Coble, P. G. Characterization of marine and terrestrial DOM in seawater using excitation-emission matrix spectroscopy. Marine Chemistry 51 (4), 325–346. Janssens, J. G., Meheus, J. & Dirickx, J. Ozone enhanced biological activated carbon filtration and its effect on organic matter removal and particular on AOC reduction. Water Science and Technology 17 (6–7), 1055–1068. Jarusutthirak, C. & Amy, G. Understanding soluble microbial products (SMP) as a component of effluent organic matter (EfOM). Water Research 41 (12), 2787–2793. Lawaetz, A. J. & Stedmon, C. A. Fluorescence intensity calibration using the Raman scatter peak of water. Applied Spectroscopy 63 (8), 936–940. LeChevallier, M. W., Welch, N. J. & Smith, D. B. Full-scale studies of factors related to coliform regrowth in drinking water. Applied and Environmental Microbiology 62 (7), 2201–2211. Liu, B., Gu, L., Yu, X., Yu, G., Zhang, H. & Xu, J. Dissolved organic nitrogen (DON) profile during backwashing cycle of drinking water biofiltration. Science of the Total Environment 414 (0), 508–514. Mayer, L. M., Schick, L. L. & Loder, T. C. Dissolved protein fluorescence in two Maine estuaries. Marine Chemistry 64 (3), 171–179. Rittman, B. E. The effect of shear stress on biofilm loss rate. Biotechnology and Bioengineering 24 (2), 501–506. Servais, P., Billen, G. & Bouillot, P. Biological colonization of granular activated carbon filters in drinking-water treatment. Journal of Environmental Engineering 120 (4), 888–899. Soonglerdsongpha, S., Kasuga, I., Kurisu, F. & Furumai, H. Comparison of assimilable organic carbon removal and bacterial community structures in biological activated carbon process for advanced drinking water treatment plants. Sustainable Environment Research 21 (1), 59–64. van der Aa, L. T. J., Rietveld, L. C. & Van Dijk, J. C. Effects of ozonation and temperature on the biodegradation of natural organic matter in biological granular activated carbon filters. Drinking Water Engineering and Science 4, 25–35. van der Helm, A. W. C., Rietveld, L. C., Bosklopper, T. G. J., Kappelhof, J. W. N. M. & van Dijk, J. C. Objectives for optimization and consequences for operation, design and concept of drinking water treatment plants. Water Science and Technology: Water Supply 8 (3), 297–304.
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van der Kooij, D., Visser, A. & Hijnen, W.A.M. Determining the concentration of easily assimilable organic carbon in drinking water. Journal of American Water Works Association 74 (10), 540–545. Xu, B., Gao, N.-Y., Sun, X.-F., Xia, S.-J., Simonnot, M.-O., Causserand, C., Rui, M. & Wu, H.-H. Characteristics of organic material in Huangpu River and treatability with the O3-BAC process. Separation and Purification Technology 57 (2), 348–355.
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Integrated Water Resources Management for meso-scale ungauged river basins in Russia T. Terekhanova, O. Berezina, J. Tränckner, S. Dvinskih and P. Krebs
ABSTRACT In the last 5 years Russia developed Schemes of Integrated Use and Protection of Water Objects (SKIOVO) aiming at remediating and maintaining water resources quality. The main limitation of the schemes is seen in their large spatial scale, which is determined by the available environmental monitoring data. The meso-scale catchments are usually ungauged, which does not allow monitoring and management of water quality on the respective scale and thus they are not included in the schemes. This can have severe consequences, if the catchment is used for drinking water supply (DWS) from surface waters. This is shown in the example of the Nytva river basin, where raw water is extracted from the eutrophic Nytva reservoir for DWS. The solution of the problem is seen in the application of structured water quality mitigation measures, included in the basin management plan.
T. Terekhanova (corresponding author) J. Tränckner P. Krebs Institut für Siedlungs- und Industriewasserwirtschaft, TU Dresden, D-01062 Dresden, Germany E-mail: tatyana.terekhanova@mailbox.tu-dresden.de O. Berezina S. Dvinskih Institute of Hydrology and Water Resources Management, Perm State University, Russia
A method to develop such a plan is presented here. The preliminary results of system screening (identification of problems and drivers) and material flow analysis (MFA) have shown that the reservoir is hypertrophic and the probable drivers are emissions from cattle breading, point sources and erosion from arable land. Apart from first measurements, soft factors and the problem of eutrophication identification are discussed, pointing out the need for further studies with regard to eutrophication in the reservoir and the analysis of stakeholders and material flow. Key words
| eutrophication, Integrated Water Resources Management, MFA, phosphorus, ungauged river basins
INTRODUCTION Water resources management in Russia has strong long-
Disorientation in the planning procedure can lead to the
lasting tradition in elaboration of water resources manage-
deterioration of the current water quality status. Surface
ment plans (Pryazhinskaya et al. ). In the last 5 years
water quality conservation is highly relevant in Russia,
19 Schemes of Integrated Use and Protection of Water
since approximately 70% of water supply works used treated
Objects (SKIOVO), i.e. river basin management plans, for
surface water (WaterWiki ).
the whole of Russia were developed. On the one hand the
Considering that in the major regions of Russia continu-
integration of the SKIOVO is modern resources manage-
ous water supply is possible only by seasonal runoff
ment practice, but on the other hand, there are several
regulation, the reservoirs are the primary sources of (drink-
limitations of the schemes which are described in the
ing) water throughout the year. Due to long retention and
reviewed literature, outlining key issues like the poor data
accumulation time water quality in reservoirs is very sensi-
background for planning especially on meso-scale where
tive to both diffuse and point pollution. Consequently, it is
planning takes place (Pryazhinskaya et al. ).
inevitable to supplement large scaled SKIOVO, with inte-
These limitations have led to the situation that any econ-
grated water resources management plans for meso-scale
omic planning in ungauged small and medium scale basins
catchments. The question arises how should the manage-
cannot be implemented based on the available schemes.
ment plans be developed taking into account existing
doi: 10.2166/ws.2013.186
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monitoring data scarcity regarding water quality and quan-
weeks during the spring. The Nytva reservoir is the only
tity in Russia?
source of drinking and process water supply of the regional
Therefore, the main objective of this work is to develop a
centre Nytva (20,000 inhabitants). Operators severely
general method for basin management planning for ungauged
struggle with an ineligible water quality (algae, ammonia,
meso-scale catchments. For that several steps have to be per-
dissolved organic carbon (DOC), pathogens) for this pur-
formed: (i) identification of a representative study case in
pose. The situation is similar for the entire Kama river
Russia; (ii) system screening (data, stake-holders, controlling
basin, in which 77% of the drinking water is extracted
organizations, limitations); (iii) development of a theoretical
from surface reservoirs.
approach for basin management under environmental data
The fact of reservoir eutrophication is verified through
scarcity conditions; (iv) application of the approach in a
the primary analysis of data on water quality from the
case study towards implementation of the basin management
Nytva Water Works Operator (sample near intake mouth),
plan; (v) adjusting the theoretical approach and presentation
which shows significant increase of chemical oxygen
of the management plan to the stakeholders in the region.
demand (COD), NH4 and Fe concentrations during the veg-
The present paper reports upon an initial phase ((i), (ii)) of
etation period (Appendix, Figure A1, available online at
the project work including investigation of water quality pro-
http://www.iwaponline.com/ws/014/186.pdf). At the same
blem in the case study Nytva reservoir (Kama river basin), the
time, oxygen deficit and basic medium (pH ∼8) indicate
application of the system screening method consisting of
intense ongoing biological processes in the water body.
water user analysis in the studied basin and material flow
The actual Federal Program on Nytva reservoir recovery
analysis (MFA) with regard to the problem of drinking
proposes only classical curative in-stream measures for
water source eutrophication.
remediation of landing and eutrophication (sediment dredging) and fails in providing any basin-oriented remediation measures (NRM ). This lack in planning originates
MATERIALS AND METHOD
from data scarcity, because in the Nytva basin, as well as on the majority of other similar catchments environmental
Case study and problem description
monitoring is not carried out. Developing management plans is therefore becoming a scientific objective, before
As case study the Nytva river basin (Permsky Krai) is chosen
defining engineering or operational tasks.
due to the following criteria. Firstly, the catchment is representative for sub-catchments of the Kama river basin, which
Approach
includes more than 500 similar watersheds. Secondly, as for many other tributaries in the Kama river basin, the main
The applied method for step (i) and (ii) is elaborated based
stream in the catchment is ponded into a reservoir for
on the classical systems analysis and Integrated Water
water supply purposes. With regard to water resources man-
Resources Management (IWRM) decision support approach
agement, the Kama SKIOVO acts on a global basis or
proposed by Blumensaat et al. (). For the ungauged river
proposes only in-stream measures, but does not contain
basins the application of the method for plan elaboration
2
3
2
any details to meso-scaled catchments (10 –10 km ), like
may be limited to four main work packages excluding the
Nytva basin (Prokhorova & Belyaev ).
design of basin development scenarios for initial phase. 2
The total area of the Nytva basin is 832 km . The total length of the river is 67 km. Total number of inhabitants is
(i) Definition of current system state deficits and pressures
78,000. The river was ponded in year 1756 on the 55th km
through water quality and water user analysis. The
for the needs of metal work in the town of Nytva. The sur-
water quality deficits have been defined through avail-
face area of reservoir is 9.1 km2 and water volume is 32.2
able literature, official data sources or mass-media. The
3
million m . Total annual runoff is 160 million m³/a, from
analysis of water users was based on the identification
which 80% are snow-melting water passing within four
of water cycle elements (natural and socio-economical)
T. Terekhanova et al.
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involved in the processes of water and associated matter
basin water usage inventory is a subject of preliminary
transport and transformation processes. The structure of
system modelling by means of MFA (Brunner &
water user analysis prioritizes the investigation of press-
Recherberger ). In this study (with insufficient
ures as well as requirements of each water user in the
data background) both the ‘export coefficient’ (EC)
basin. The information about users was collected
and
according to the key characteristics: type of use
approaches (Terekhanova et al. ) have been applied
(intake, discharge, aquatorium), location (coordinates,
in order to estimate main phosphorus flows in the
direct, diffuse), dynamics of use (daily, seasonally,
Nytva basin. The C × D approach has been used for
etc.), user requirements to water quality, and possible
the primary evaluation of the annual total phosphorus
consequences of use. Based on the analysis of infor-
(TP) load in the river network. The calculations were
mation on deficits, water user loads and requirements
conducted under the assumption of constant annual
the spatial matrix was constructed.
discharge rate for all sub-basins (6.3 l/s*km2) and
‘concentration × discharge’
(C × D)
MFA
(ii) Application of short-term monitoring in the form of field
runoff-independent concentration values (based on
excursions and daily observation of indicative par-
single grab sampling). The TP emission pattern in the
ameters. The measurement campaigns have been
basin has been estimated based on the concept of nutri-
undertaken over the vegetation period in Nytva basin
ents balancing model MONERIS (MONERIS ).
and Nytva reservoir (Figure 1). The sampling points were distributed so as to cover the nutrients inflow
The emissions pathways considered in the model were
with tributaries and to observe the state of the reservoir
selectively calculated using EC-approach, similarly to the
(Figure 1). The measurement campaign has included: (i)
method proposed by LAWA for estimation of the lake (reser-
monthly water sampling from the tributaries (May–
voirs) states under data scarce conditions (LAWA ).
August); (ii) daily observation of pH, dissolved O2 and
Therefore, for six sub-catchments the TP emissions from
temperature by the local volunteer; (iii) field excursion
atmospheric deposition on the water surface (assuming 30
on Nytva reservoir including sampling (mixed, over
kg*km²/a; LAWA ), erosion from forested (assuming 5
depth), pH, temperature and O2 measurements (over
kg*km²/a; LAWA ) and arable land (assuming 20
depth).
kg*km²/a;
LAWA
),
input
from
point
sources
(iii) Modelling of the processes relevant for most significant
(WWTP), rural inhabitants not connected to WWTP (assum-
water users explicitly considering different scales
ing 2.5 g/Ca*d; MONERIS ) and cattle breading wastes
(spatial, temporal, level of detail). The set-up of a
(8.11 kg/Ca*a; Rekomendazii ) were estimated based
Figure 1
|
Monitoring points in Nytva basin and in Nytva reservoir.
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on available statistical information (population and live-
the higher algae (photosynthesis) activity in the reservoir
stock number) and basic GIS data (areas, location).
(Figure 2).
Process-oriented modelling were not required, as it is more
More spatially distributed measurements of tempera-
suitable for the most relevant parameters to allow studying
ture, O2 and pH, performed in the field excursion (middle
possible effects of management measures.
of vegetation period) on the reservoir, have shown the formation of stratification in gulfs (despite the relatively small average depth of ca. 3 m) as well as in the main channel
RESULTS
(although location along main wind direction enhances the mixing) (Figure 2). Oxygen concentrations are high at
Deficits analysis
the surface and significantly lower at the bottom, which supports the hypothesis of highly intensive algae activity,
The daily dynamics of dissolved O2, temperature and pH
consuming easily available CO2, producing oxygen and
are strongly correlated (Figure 2), which justifies the
increasing the pH through the entire reservoir (pH 8–9 in
hypothesis of intensive biological processes. Moreover,
the top 1 m).
the positive correlation between O2 saturation and water
The analysis of the water quality in Nytva reservoir has
temperature and O2 concentration and pH-value point to
finally confirmed the hypothesis on the high trophy level. As
Figure 2
|
Daily pH, t and O2 concentration in Nytva reservoir in point B (June–August) (top); oxygen saturation and pH (middle); and nutrient concentrations (bottom) in Nytva reservoir observed during field excursion (July).
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eutrophication indicator only TP has been measured, whose
reservoir (D, E, F) (Figure 3, bottom left). As currently the
concentration (average ca. 500 μg/l, Figure 2) in the reservoir
data on hydrological mode of the basin and inner reservoir
is equivalent to the trophy level of hypertrophic lake (Höll
TP balance are not available, it was not possible to conduct
). Moreover, the total nitrogen:total phosphorus (TN:TP)
closed annual balancing for entire studied system. The sim-
ratio used as indicator of algae species dominance (Smith
plified daily balance results into 109 kg TP/d input, some
) is not higher than 10 (Figure 2), that refers to the domi-
15,800 kg TP stored in the reservoir (only in water, at vege-
nance of blue-green algae in the reservoir (Smith ).
tation period) and 48 kg TP/d outflow (for mean discharge of summer low water period).
User analysis in the basin
The total TP emission in the basin approximates 68 tonnes/a, with the highest intensity in sub-basins C
Based on generally available and archive information about
(179 kg/a km2 with main input cattle breading) and A
the region the database of economic activities has been col-
(88.9 kg/a km2 with major input from point sources). The
lected. The activities in the basin have been evaluated
total basin emission from cattle breading equals to the sum
whether they could intensify the eutrophication processes,
input from all other sources (Figure 3, top left). Other impor-
especially phosphorus delivery to the water body. As
tant emission pathways are point sources and erosion of
known, these are usually cattle breading, waste water treat-
arable land. The emission patterns in the sub-basins vary
ment plants (WWTP) and aquaculture, which are found in
according to the economic activities and the land use
the basin. The analysis of the water use declarations has
(Figure 3, top right).
shown that most of the industries are indirect dischargers,
The comparison of estimated cumulative emissions and
while three main direct waste water dischargers in the basin
measured (runoff independent) loads in corresponding river
are WWTP in Vereschagino, in Sheriya and in Nytva (down-
stretches shows significant overestimation of the cumulative
stream of the Nytva reservoir). The information about
emission or underestimation of loads in the river network
pollution loads from cattle breading and aquaculture is not
(Figure 3, bottom right). Namely, pronounced difference is
available, as farmers and operators are not obliged to declare
found for the sub-basin C, where cattle breading emission
it. Any information about fertilizer application and the areas
is dominant. This exhibits that the method of emission esti-
of crop cultivation (erosion rates) is currently not available,
mation from cattle breading has to be adjusted. Additionally,
either. Even without respective database it is probable, that
the discrepancy in the estimation is caused by emissions
the discharges of WWTP, aquacultures and cattle breading
loads retention (delivery rates), which was not considered
are the main sources for water quality deterioration in
in the calculations.
Nytva reservoir. The highest requirement on water quality in the basin is set by the drinking water supply (DWS) for the city of Nytva, extracting its raw water from the Nytva
DISCUSSION
reservoir (Appendix, Figure A2, available online at http:// www.iwaponline.com/ws/014/186.pdf).
the
Regarding eutrophication problem during the investigation
hydrography and main economic activities the basin has
Considering
it was found out that the data from the communal Nytva
been divided into six sub-catchments (pools) with outlets
Water Works do not directly allow to identification of any
according to the location of sampling points (Appendix,
eutrophication problem in contrast to data of measurements
Figure A2).
conducted in the context of this work. According to the official data on polyphosphate concentrations stay constant
Material flow analysis
over a year and equals analytical detection threshold (according to FSETNC ()). The estimation of possible
The total load, discharged with tributaries into the reservoir
TP concentrations from the samples through COD and con-
is estimated to be around 40 t/a. The most intense TP loads
tent of algae protoplasm has shown that the TP
are assigned to sub-basin A and in the close vicinity to the
concentrations should be one order of magnitude higher
178
Figure 3
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Total phosphorus emissions in the Nytva basin (top, left) and sub-basins (top, right); estimated TP loads in river network (bottom, left); estimated cumulative TP emissions vs. measured riverine load in Nytva basin.
than the analytical limit. It was assumed, that by the appli-
of the eutrophication degree, the sediment dredging should
cation of dissolved sulfuric acid the algae membrane
be complemented by phosphorus
cannot be destroyed. Application of concentrated sulfuric
measures, which should be investigated model-based and
acid (instead of dissolved) for the analytic procedure has
constructively included in the basin management plan. For
resulted in concentrations close to the estimated ones.
that the source of the pollutants, its transport and the
This raises the question about the reliability of rare available
dynamics in the reservoir should be identified.
source controlling
data on water quality in the Nytva reservoir basin, especially
Another issue is the soft factors of the basin
with regard to effluents quality of communal WWTP (recon-
management in Nytva. Firstly, the problem lays in the
struction needy state). On the other hand, the study on the
responsibility areas and interests of stakeholders. There is
comparison of both chemical analytical methods (Russian
no unique state authority, which is responsible for the
and German) should be performed, before any conclusions
water quality as a whole. One is responsible for the water
are drawn.
only and another is responsible for the banks only. The
Nytva river basin management: what’s next? The pre-
drinking water works operator is responsible and interested
liminary research results do not contradict the decision on
only in its products quality at the outlet. Moreover, the gov-
currently undertaken measures for remediation of water
ernance disorientation in the eutrophication problem is seen
quality in Nytva reservoir. Certainly sediment dredging is
in the absence of any legal regulation mechanisms for phos-
necessary, but is however very expensive, has to be repeated
phate containing detergents, livestock slurry disposal,
on a regular basis, and the influence of stirring up sediments
nutrients elimination in WWTP, fertilizer application, etc.
on the water quality in drinking water source is hardly
Therefore, the elaboration of management plan for Nytva
known. Obviously, in order to achieve sustainable reduction
basin will not only have a scientific character, but will also
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require some administrative and legislative support, at least
the results further studies on water balance and rainfall-
on the regional level.
runoff modelling in the basin, hydro-biological investi-
Although the water quality in the Nytva reservoir meets
gations on the ecosystem processes in the reservoir
the Russian requirements for raw water for DWS
(especially phosphorus dynamics in the system biomass –
(SanPiN2.1.5.980–00.2.1.5. ), the measured higher pH
sediment – water) and phosphorus transport processes in
values and higher concentrations of NH4 in the source
groundwater (relevant for identification of retention rates
may cause risks in DWS through their influence on the
for emissions of cattle breading and rural waste water) are
effectiveness of the chlorine disinfection (applied in Nytva
essential to conduct. The gathering of this information will
Water Works) and carcinogenic chloramine formation
allow modelling of phosphorus flows in the basin with
(Höll ; Acero et al. ; Deborde & von Gunten
help of a modelling tool with higher spatial and temporal
). Therefore, the drinking water supply from eutrophic
resolution.
reservoir does not only induce technological problems, but may also cause severe health risks for consumers.
Therefore, the implementation of an IWRM approach within a basin management plan for ungauged meso-scale river catchments in Russia requires several conditions to be fulfilled: (i) the responsibility of the water resources qual-
CONCLUSIONS AND OUTLOOK
ity should be addressed to a limited number of authorities; (ii) the water resources policy should be reorganized in
The analysis of the Nytva reservoir field survey and
order to involve the stakeholders (water users) into the man-
sampling results has shown that the studied water body is
agement process; (iii) a centralized monitoring and data
hypertroph with the dominance of the blue algae. The
management system at least for the basin, where the surface
described state is relevant for the middle of the vegetation
waters are used for DWS, should be set up in order to per-
period 2012. In order to evaluate the suitability of the reser-
form operative water quality and pollution hazards
voir for future DWS, the investigation of water quality
assessment and develop pro-active risk management
should be carried out in other seasons, especially in winter
concepts.
low water and snow melting period, when the reservoir is filled for the use in the subsequent summer period. Moreover, the study on legal and technological boundary
REFERENCES
conditions for DWS from eutrophic reservoirs in Russia should be conducted in order to implement short-term measures for human health risks reduction. Regarding the drivers of the eutrophication it can be concluded, that main economic activities in the basin to a certain degree determine the current state of the reservoir. Although results of user analysis in the Nytva basin have been presented here for basin regionalization, it is considered not complete yet. The acquired database should be transferred into GIS environment and supplemented with updated land use, livestock and population inventory as well as with data on technological water cycles of industries (quantity and quality). The preliminary MFA with a distinct uncertainty has shown that phosphorus input load in the Nytva reservoir originates from cattle breading wastes, effluent of communal WWTP and erosion from arable land. For the refinement of
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First received 9 February 2013; accepted in revised form 19 July 2013. Available online 12 September 2013