Journal of Water Reuse and Desalination Sample Issue

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© IWA Publishing 2014 Journal of Water Reuse and Desalination

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Comparative assessment of managed aquifer recharge versus constructed wetlands in managing chemical and microbial risks during wastewater reuse: a review A. F. Hamadeh, S. K. Sharma and G. Amy

ABSTRACT Constructed wetlands (CWs) and managed aquifer recharge (MAR) represent commonly used natural treatment systems for reclamation and reuse of wastewater. However, each of these technologies have some limitations with respect to removal of different contaminants. Combining these two technologies into a hybrid CW-MAR system will lead to synergy in terms of both water quality and costs. This promising technology will help in the reduction of bacteria and viruses, trace and heavy metals, organic micropollutants, and nutrients. Use of subsurface flow CWs as pre-treatment for MAR has multiple benefits: (i) it creates a barrier for different microbial and chemical pollutants, (ii) it reduces the residence time for water recovery, and (iii) it avoids clogging during MAR as CWs can

A. F. Hamadeh (corresponding author) G. Amy Water Desalination and Reuse Center/King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia E-mail: ahmed.alhamadat@kaust.edu.sa S. K. Sharma UNESCO-IHE Institute for Water Education, Westvest 7, 2611 AX, Delft, The Netherlands

remove suspended solids and enhance the reclaimed water quality. This paper analyzes the removal of different contaminants by CW and MAR systems based on a literature review. It is expected that a combination of these natural treatment systems (CWs and MAR) could become an attractive, efficient and cost-effective technology for water reclamation and reuse.

Key words

| aquifer recharge, bank filtration, constructed wetlands, pathogen removal, pharmaceutically active compounds, soil aquifer treatment, water reuse

INTRODUCTION There is a growing pressure on water resources worldwide,

conventional wastewater treatment methods (Sharma &

resulting from high population growth and thus increasing

Amy ).

water demands. Nowadays, treated wastewater effluent is

Bank filtration (BF) can be considered to be a robust

well accepted as one of the important water resources in

treatment system able to maintain its active processes

many parts of the world. Treated wastewater has the poten-

through extreme scenarios such as temperature changes,

tial to become an important water source for different

high contaminant concentration peaks, and shorter resi-

purposes, but the quality of the treated wastewater is often

dence times due to flood events (Schmidt et al. ).

a potential constraint, depending on the specific (re)use.

CWs are engineered systems that have been designed

Natural wastewater treatment systems, namely, con-

and constructed to utilize the natural processes involving

structed wetlands (CWs) and managed aquifer recharge

wetland vegetation, soils, and associated microbial assem-

(MAR) which comprises aquifer recharge and recovery

blages to assist in treating wastewaters. They are designed

(ARR), soil aquifer treatment (SAT), and river bank filtration

to take advantage of many treatment mechanisms that

(RBF), are simple, cost-effective, robust, chemical-free, and

occur in natural wetlands, but do so within a more con-

efficient methods to further polish wastewater effluents.

trolled environment. CWs for wastewater treatment may

Their extreme simplicity in construction, operation and

be classified according to the wetland hydrology (free

maintenance makes these natural systems competitive with

water surface (FWS) and subsurface flow (SSF) systems).

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CWs and MAR review paper

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SSF CWs can be further classified according to the flow

active compounds (PhACs) and personal care products

direction (horizontal (HF) and vertical (VF)) (Vymazal

(PCPs)), nutrients (nitrogen and phosphorus), organic

).

matter and pathogenic microorganisms from MAR and

The treatment mechanisms that occur in CWs

CWs. Moreover, the potential integration of applying

and MAR systems include settling, microbial oxidation,

CWs and MAR either in hybrid or integrated processes

anaerobic decomposition, nitrification, denitrification,

under different environmental conditions, different water

adsorption, desorption, and precipitation. CWs systems

qualities and different types of CWs has also been

use many plants such as cattails and bulrushes, and their

investigated.

associated bacterial populations, to break down contami-

Synergies between CWs and MAR are expected to

nants into relatively innocuous byproducts. Thus, CWs

enhance the removal capabilities of micropollutants, nutri-

can effectively treat domestic wastewater, industrial waste-

ents,

water, animal wastewater, contaminated groundwater,

wastewater in a sustainable way, which cannot be achieved

mine waste, urban runoff, and other contaminated waters

by MAR or CWs alone. The following sections summarize

(Kadlec & Wallace ).

the performance of MAR, CWs and the potential combi-

Natural wastewater treatment systems are used through-

bacteria,

and

viruses

from different

types

of

nations thereof for removal of different contaminants.

out the world for wastewater treatment to enhance reclaimed water quality to be reused for different purposes such as groundwater recharge. CWs and SAT can be applied to primary or secondary effluents, allowing the removal of

ORGANIC MATTER AND SUSPENDED SOLIDS REMOVALS

most bacteria and other microorganisms and the degradation of bulk organic matter. SAT can also remove part

CWs and MAR are very effective in total suspended solids

of the nutrients and a wide range of organic micropollutants

(TSS) removal (Table 1). In both systems, most of the

(OMPs), while CWs are efficient in removing bulk organics

removal occurs within the first few meters of travel dis-

and suspended solids, but are less effective than SAT in

tance from the inlet zone. Adsorption and biodegradation

removing nitrogen and phosphorus compounds. Hybrids

are considered to be the dominant removal processes in

that integrate different natural treatment systems are

these systems (Maeng et al. ). TSS in wastewater efflu-

expected to be more effective for water reclamation and pro-

ent is usually relatively fine and in organic form (sewage

vide multiple barriers for different contaminants.

sludge, bacteria, floes, algal cells, etc.). The main constituent that must be removed from the effluent before it is applied to a SAT system is TSS due to infiltration basin

RESEARCH METHODOLOGY

clogging. However, a higher biochemical oxygen demand (BOD) content would also result in somewhat lower

Several research studies have been conducted throughout

hydraulic loading rates (HLR) for the SAT system and

the world to study the efficiency and capability of MAR

would require more frequent basin cleaning. Thus, using

and CWs to remove wastewater-derived contaminants

CWs as a pre-treatment for ARR and SAT systems will

(bulk organic matter, OMPs, nitrogen, phosphorus and pathogenic microorganisms) from primary and secondary effluents through the natural, chemical and biological processes associated with soils and plants.

This study is based on an extensive literature review, the performance data of more than 30 CWs and 20 MAR systems all over the world; pilot and field scale systems were included. The collected data were used for the analysis of the removal efficiencies of OMPs (such as pharmaceutically

Table 1

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BOD5 and TSS removals through MAR and different types of CWs

System

BOD5 % removal

TSS % removal

Reference

FWS CWs

73

73

Vymazal ()

HF CWs

75

75

Vymazal ()

VF CWs

90

89

Vymazal ()

MAR

90

90

Oron ()

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not only reduce TSS from the influents but also avoid

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NITROGEN AND PHOSPHORUS REMOVAL

potential clogging and maintain the HLR. Dissolved organic carbon (DOC) removal through BF,

Nitrogen species present in wastewater usually include var-

for Lake Tegel in Berlin (Germany), was 44% over 135

ious forms of organic and inorganic nitrogen (ammonium,

days of residence time as shown in Figure 1. This removal

nitrite and nitrate). Significant nitrification and subsequent

could be enhanced up to 80% for a longer distance as

denitrification normally occur and remove nitrogen through

shown in Table 2. Chung et al. () found that a 72%

the treatment systems.

removal of DOC could be achieved within 5 days of hydrau-

Nitrogen removal has been observed through CWs and

lic residence time (HRT) through a subsurface flow

MAR systems. Table 3 shows the removal efficiencies for

horizontal CW.

different nitrogen species in a BF system.

Hybridization between these two systems will enhance

It was found that 40–70% removal could be achieved

the DOC removal and also reduce the residence time, as

for different nitrogen species in different types of CWs,

shown in Figure 2.

as shown in Table 3. VF CWs are more efficient in

Figure 1

Table 2

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DOC removal through bank filtration for Lake Tegel in Berlin (Source: Grunheid et al. 2005).

DOC removal efficiency by bank filtration technology

RBF site location

Distance well from river (m)

Residence time (day)

Influent conc. (mg/l)

Effluent conc. (mg/l)

Removal efficiency (%)

Reference

Lake Tegel Berlin (Germany)

30 25 55 77 90

84 90 90 117 135

7.5

5.5 5.6 5 4.7 4.2

27 25 33 37 44

Grunheid et al. ()

Lake Tegel Berlin (Germany)

100

135

7.5

1.5

80

Jekel & Gruenheid ()

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Figure 2

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Table 3

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CWs and MAR review paper

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DOC accumulative removal through CW-MAR hybrid system.

TN, NH4þ-N and NO3 -N removals through MAR and different types of CWs (Sources: Idelovitch et al. 2003; Vymazal 2005, 2010)

Treatment

NO 3 -N % removal

NHþ 4 -N % removal

TN % removal

technique

efficiency

efficiency

efficiency

FWS CWs

61

47

51

HF CWs

39

35

38

VF CWs

(–97)

73

43

MAR

62

60

70

ammonia removal because they normally operate under oxic conditions which promote nitrification. The phosphorus is removed during SAT by adsorption to soil during reclaimed wastewater percolation through the soils and sediments and/or a chemical precipitation reac-

Figure 3

TN, NHþ 4 -N, NO3 -N, P, and TP removals through CWs and MAR systems.

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tion with the calcium and magnesium ions present in the soil (Idelovitch et al. ). Plant uptake, in the case of

High ammonia removal can be achieved if VF CWs

CWs, tends to have a relatively small effect on removal

are used before MAR and generate nitrate. However,

(Vymazal ).

using

The synergy between these two systems will be useful to enhance nitrogen removal, as shown in Figure 3.

HF

CWs

before

MAR

and

after

VF

CWs

will enhance the removal of all nitrogen and phosphorus species.

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OMP REMOVAL

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Several metals show very high removals through BF, such as iron and chromium, while others show high removals

Municipal wastewater represents the main disposal pathway

through both systems, such as zinc. However, metals

for PhACs and PCPs consumed in households, hospitals and

removals can be clearly enhanced through the combined

industry. After passing through a wastewater treatment

system (e.g. Cd, Pb, Cr and Fe), as shown in Figure 5, although

plant, the treated wastewater is often discharged into

some metals show some persistence for the CW-MAR hybrid

rivers and streams, which may percolate or infiltrate into

system such as selenium, tin and silver.

groundwater or pass through river banks. Several OMPs, such as bezafibrate, ketoprofen, iopromide, gemfibrozil, erythromycin, trimethoprim and fluextine, appear to be

PATHOGEN REMOVAL

removed effectively during MAR and/or CWs. However, OMP removal will be enhanced through the CW-MAR com-

Pathogenic bacteria, viruses and Cryptosporidium can be

bined system, especially for some OMPs which show

effectively reduced or eliminated during soil passage but

resistance such as diclofenac, clofibric acid, carbamazepine

for reasons that are not entirely understood (Hiscock &

and dilantin, as shown in Figure 4.

Grischek ). During soil passage, microorganisms may be removed from the aqueous phase primarily by straining, inactivation, and attachment to the aquifer grains (in combi-

METALS REMOVAL

nation with inactivation). CWs have been found to reduce microbial pathogens with varying but significant degrees of

During water percolation through soil, trace elements such as

effectiveness. As water passes through a CW system, patho-

iron, manganese, and various heavy metals are eliminated by

gens are removed through a combination of physical

filtration and sorption processes. In an aerobic environment,

mechanisms (filtration and sedimentation) and chemical

ion exchange processes at negatively charged surfaces can

mechanisms such as oxidation and adsorption to organic

achieve removal, while in an anoxic environment, the

matter. CWs are highly efficient and remove 2logs of Giar-

removal of metal ions is dominated by precipitation reactions

dia and around 1log of Cryptosporidium. At the same

with sulfide. Plant uptake was also found to be an influential

time, MAR shows lesser removal for both organisms, as

removal process in CWs (Cheng et al. ).

shown in Table 4. However, the hybrid system is expected

Figure 4

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OMP removal through CWs and MAR systems (Sources: Conkle et al. 2008; Matamoros & Bayona 2008; Snyder et al. 2008; Onesios et al. 2009; Valsero et al. 2010; Sharma et al. 2011; Hamadeh et al. 2012).

Figure 5

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Metals removal through CWs and MAR systems (Sources: Laszlo & Literathy 2002; Kropfelova et al. 2009).

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Table 4

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Removal of Giardia and Cryptosporidium through CWs and MAR (Sources: Bosu-

Table 6

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ben 2007; Kadlec & Wallace 2008)

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Reduction of viruses through gravel HF CWs and MAR (Sources: Bosuben 2007; Harun 2008; Kadlec & Wallace 2008)

Bacteria

CWs removal (log)

MAR removal (log)

Organism

HF CWs (log)

MAR (log)

Giardia

2

1.6

FRNA cacteriophage

3.07

6.2

Giardia

2

1.9

Fecal streptococci

2.1

3.3

Cryptosporidium

1

0.5

Enteroviruses

0.69

2.3

Cryptosporidium

1

1

Somatic coliphages

1.3

5.3

Clostridium

2.8

4.7

Poliovirus

4.1

4.6

to guarantee high reduction of both Giardia and Cryptosporidium as shown in Figure 6.

MAR and CW systems are very efďŹ cient in microorganism removal, as shown in Table 5. The combination will substan-

Synergetic effect between the two processes will enhance virus removal and reduce risks.

tially reduce their risk. Generally, MAR shows better removal

CWs and MAR are contrasted, as shown in Figure 7,

for all types of viruses than CWs as shown in Table 6.

indicating high removal for FRNA bacteriophages; however this virus can be used as an indicator of the fate of human enteroviruses as they are very similar in physical size and structure and capable of surviving in many sewage treatment processes.

FUTURE RESEARCH AND PRACTICAL APPLICATION FOR THE CW-MAR HYBRID SYSTEM This review indicates that the hybrid CW-MAR system could be an effective multi-barrier technology and the removal efďŹ ciencies for different contaminants can be maximized in such hybrid systems. Such a hybrid can enhance the

Figure 6

Table 5

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Giardia and Cryptosporidium removal through CWs and MAR systems.

Bacteria removal through CWs and MAR (Sources: Gilbert et al. 1976; Laszlo & Literathy 2002; Akber et al. 2003; Cameron et al. 2003; Garcia et al. 2008; Kadlec & Wallace 2008; Abidi et al. 2009)

Bacteria

FWS CWs removal (log)

SSF CWs removal (log)

MAR removal (%)

Fecal coliform

2.5

2.6

100

Total coliform

2.74

2.48

100

Fecal streptococci

3.17

2.45

99.93

E. coli

0.20

1.45

100

Salmonellae

NA

3.84

100

Figure 7

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Virus log removals through CWs and MAR systems.

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removal efficiencies for DOC, different nutrients and guarantee high removals for bacteria and viruses. A number of metals and OMPs can be virtually completely removed while removal of some others can be improved, especially for those that are persistent.

Practical studies are required to prove the benefits of this promising technology, involving laboratory scale studies followed by field studies to analyze the mechanism of removal of different contaminants in the hybrid system under different water quality and process conditions. Specifically, the ability of such a system to remove suspended solids, bulk organic carbon, trace organic compounds, as well as bacteria and viruses, should be investigated. Besides that, economic feasibility studies should be conducted in parallel to analyze capital, operation and maintenance costs of this technology in comparison with other mechanized wastewater reclamation reuse technologies.

CONCLUSIONS A CW-MAR hybrid system provides an effective treatment technology of reclaimed water for replenishing aquifers and subsequent reuse. This hybrid system embodies the performance advantages of both processes and exhibits very good potential for the removal of bulk organics, suspended solids, OMPs, nutrients (nitrogen and phosphorus) as well as pathogens, bacteria and viruses. Furthermore, a CWMAR hybrid system is a cost-effective, sustainable and efficient treatment technology which can promote water reuse for different applications. It is expected that this technology can produce water of high quality, meeting the direct potable reuse requirements, help to store and increase water in the aquifer and create a reliable water resource from wastewater effluent, overcoming the psychological barrier of water reuse.

ACKNOWLEDGEMENTS This study was carried out under the framework of UPaRF NATSYS project of UNESCO-IHE, Delft, The Netherlands of which KAUST, Saudi Arabia is a partner.

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REFERENCES Abidi, S., Kallali, H., Jedidi, N., Bouzaiane, O. & Hassen, A.  Comparative pilot study of the performances of two constructed wetland wastewater treatment hybrid systems.

Desalination 246, 370–377.

Akber, A., Al-Awadi, E. & Rashid, T.  Assessment of the use of soil aquifer treatment (SAT) technology in improving the quality of tertiary treated wastewater in Kuwait. Emirates J. Eng. Res. 8 (2), 25–31.

Bosuben, N.  Framework for feasibility of bank filtration technology for water treatment in developing countries. MSc thesis, UNESCO-IHE, Delft, The Netherlands.

Cameron, K., Madramootoo, C., Crolla, A. & Kinsley, C.  Pollutant removal from municipal sewage lagoon effluents with a free-surface wetland. Water Res. 37, 238–243.

Cheng, S., Vidakovic-Cifrek, Z., Grosse, W. & Karrenbrock, F.  Xenobiotics removal from polluted water by a multifunctional constructed wetland. Chemosphere 48, 415.

Chung, A. K., Wu, Y., Tam, N. F. Y. & Wong, M. H.  Nitrogen and phosphate mass balance in a sub surface flow constructed wetland for treating municipal wastewater. Ecol. Eng. 32, 81–89.

Conkle, J., White, J. & Metcalfe, C. D.  Reduction of pharmaceutical active compounds by a lagoon wetland wastewater treatment system in southeast Louisiana.

Chemosphere 73 (11), 1741–1748.

Garcia, M., Soto, F., Gonzales, J. & Becares, E.  A comparison of bacterial removal efficiencies in constructed wetlands and algae-based systems. Ecol. Eng. 32, 238–243.

Gilbert, R., Gerba, C., Rice, R., Bouwer, H., Wallis, C. & Melnick, J.  Virus and bacteria removal from wastewater by land treatment. Appl. Environ. Microbiol. 32 (3), 333–338.

Grunheid, S., Amy, G. & Jekel, M.  Removal of bulk dissolved organic carbon (doc) and trace organic compounds by bank filtration and artificial recharge. Water Res. 39 (14), 3219–3228.

Hamadeh, A., Lens, P. & Amy, G.  Pharmaceutical compounds removal by constructed wetlands under different redox conditions. 9th INTECOL International Wetlands Conference, June 3–8 2012, FL, USA. Harun, C. M.  Analysis of removal of multiple contaminants during soil aquifer treatment. MSc thesis, UNESCO-IHE, Delft, The Netherlands.

Hiscock, K. M. & Grischek, T.  Attenuation of groundwater pollution by bank filtration. J. Hydrol. 266 (3–4), 139–144.

Idelovitch, E., Icekson-Tal, N., Avraham, O. & Michail, M.  The long-term performance of Soil Aquifer Treatment (SAT) for effluent reuse. Water Sci. Technol. 3, 239–246.

Jekel, M. & Gruenheid, S.  Bank filtration and groundwater recharge for treatment of polluted surface waters. Water Sci. Technol. 5 (5), 57–66.

Kadlec, R. & Wallace, S.  Treatment Wetlands, 2nd edn. CRC Press, NY, USA.

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Kropfelova, L., Vymazal, J., Svehla, J. & Stichova, J.  Removal of trace elements in three horizontal sub-surface flow constructed wetlands in Czech Republic. Environ. Pollut.

157, 1186–1194.

Laszlo, F. & Literathy, P.  Laboratory and Field Studies of Pollutant Removal: Understanding Contaminant Biogeochemistry and Pathogen Removal. Kluwer Academic Publishers, Dordrecht, The Netherlands.

Matamoros, V. & Bayona, J.  Behavior of emerging pollutants in constructed wetlands. Env. Chem. 5, 199–217.

Maeng, S. K., Sharma, S. K., Abel, C. D. T., Song, K. G., Magic Knezev, A. & Amy, G.  Effects of effluent organic matter characteristics on the removal of bulk organic matter and selected pharmaceutically active compounds during managed aquifer recharge: column study. J. Contam. Hydrol. 140–141, 139–149.

Onesios, K. M., Yu, J. T. & Bouwer, E. J.  Biodegradation and removal of pharmaceuticals and personal care products in treatment systems: a review. Biodegradation 20, 441–460.

Oron, G.  Management of effluent reclamation via soilaquifer-treatment procedures. WHO Expert Consultation on Health Risks in Aquifer Recharge by Recycled Water, 8–9 November 2001, Budapest.

Schmidt, C. K., Lange, F. T. & Brauch, H. J.  Characteristics and evaluation of natural attenuation processes for organic

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micropollutant removal during riverbank filtration. Regional IWA conference on groundwater management in the Danube River Basin and other large River Basins, 7–9 June 2007, Belgrade, pp. 231–236.

Sharma, S. K. & Amy, G.  Natural treatment systems. In: Water Quality and Treatment: A Handbook on Drinking Water (J. K. Edzwald, ed.), 6th edn. American Water Works Association & McGraw-Hill Inc., USA. Sharma, S. K., Caballero, M., Maeng, S. K. & Amy, G.  Removal of organic micropollutants in SAT and hybrid SAT systems. IWA Water Reuse Conference, 15–20 September 2011, Barcelona, Spain.

Snyder, S. A., Wert, E. C. & Lei, H.  Removal of EDCs and Pharmaceuticals in Drinking and Reuse Treatment Processes.

AWWARF, Denver, CO, USA. Valsero, M., Matamoros, V., Sidrach-Cardona, R., MartinVillacorta, J., Becares, E. & Bayona, J.  Comprehensive assessment of the design configuration of constructed wetlands for the removal of pharmaceuticals and personal care products from urban wastewaters. Water Res. 44, 3669–3678.

Vymazal, J.  Horizontal subsurface flow and hybrid constructed wetlands systems for wastewater treatment. Ecol.

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Vymazal, J.  Review: constructed wetlands for wastewater treatment. Water Res. 2, 530–549.

First received 10 March 2013; accepted in revised form 13 June 2013. Available online 24 July 2013

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The transport of three emerging pollutants through an agricultural soil irrigated with untreated wastewater Juan C. Durán-Álvarez, Yamani Sánchez, Blanca Prado and Blanca Jiménez

ABSTRACT The aim of this work was to determine the mobility of naproxen, carbamazepine, and triclosan through a wastewater-irrigated agricultural soil. Transport experiments were carried out using undisturbed soil columns taken at 10 and 40 cm depths. The mobilization of the pollutants was evaluated using two hydrological regimes transient flow for superficial columns and steady-state conditions for the sub-superficial columns. Results demonstrated that preferential flows are present in the superficial soil, and transient flow conditions facilitate the movement of the pollutants through the soil. Conversely, displacement of the contaminants in the sub-superficial soil columns was slower than that observed in the superficial soil. Triclosan was not found in the leachates of the soil columns at the two depths, indicating the strong retention of the compound by the soils. Conversely, naproxen and carbamazepine were determined in leachates of the soil columns at both depths.

Retardation in the transport of carbamazepine was higher than that observed for naproxen in the two tested soils. Naproxen and triclosan showed some degree of dissipation, while carbamazepine was recalcitrant. It was concluded that the natural depuration system studied is capable of retaining and

Juan C. Durán-Álvarez Yamani Sánchez Engineering Institute, National Autonomous University of Mexico, 3000 University Ave., Coyoacan, 04510, Mexico, D.F., Mexico Blanca Prado Geology Institute, National Autonomous University of Mexico, 3000 University Ave., Coyoacan, 04510, Mexico, D.F., Mexico Blanca Jiménez (corresponding author) International Hydrological Programme, UNESCO, 1 Miollis St., 75732 Paris, France E-mail: b.jimenez-cisneros@unesco.org

removing the studied pollutants and thus the risk of groundwater pollution is minimized.

Key words

| pharmaceuticals, solute transport, sorption, undisturbed soil columns, wastewater reuse

INTRODUCTION Wastewater reuse for agricultural irrigation is a practice

emerging pollutants to enter into the environment. These

gaining popularity worldwide, notably in developing

pollutants are residues of substances used in everyday con-

countries where, due to the scarcity of treatment facilities,

sumer products, such as pharmaceuticals, personal care

untreated wastewater is frequently used (Jiménez & Asano

products, flame retardants, plasticizers, additives, etc.

). In the near future, an increment is expected in the

(Petrovic et al. ). Conventional wastewater treatment

volume of wastewater reused for agricultural irrigation

systems have demonstrated the partial removal most emer-

because: (1) it represents an easy and cheap way to dispose

ging pollutants, and thus a fraction of the original

of wastewater; (2) it is an option to relieve water stress in

compound along with a group of its by-products are released

arid and semiarid zones; and (3) wastewater is a source of

into the environment (Ratola et al. ). Despite emerging

nutrients for the receiving soils, increasing crop yields and

pollutants being present in water bodies at trace levels (con-

thus the profits of farmers (Jiménez ). However, waste-

centrations are reported in the range of ng/L to μg/L), their

water reuse can spoil the quality of surface and subterranean

occurrence is related to endocrine disruption effects as well

water sources in and nearby the irrigated area. It is well

as to systemic damage in vulnerable organisms (Naidoo

known that wastewater is the main route of so-called

et al. ; Brausch & Rand ; Vandenberg et al. ).

doi: 10.2166/wrd.2013.003

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In zones where treated wastewater is used for agricultural

agent triclosan, through a long-term wastewater-irrigated

purposes, emerging pollutants have been found in waste-

agricultural soil; the method being by undisturbed soil

water-irrigated soil and in the water bodies nearby

column experiments performed using two hydrological

(Gottschall et al. ). One example of a long-term irriga-

regimes.

tion system reusing untreated wastewater can be found in Tula Valley, central Mexico. In this zone, a flow of up to 5.2 million m3/s of untreated wastewater, produced by the

METHODS

22 million people living in Mexico City’s metropolitan zone, is used to irrigate 85,000 ha of agricultural fields

In this section, the methodology followed to obtain the soil

( Jiménez & Chávez ). Even though wastewater used

columns, perform the transport experiments, and determine

for irrigation does not receive any kind of treatment, a sig-

the target pollutants in the liquid and soil samples is

nificant decay in the concentration of some contaminants,

described.

e.g., heavy metals, microbiological agents, and organic compounds (e.g., some emerging pollutants) has been observed

Chemicals

during the transportation, storage, and application of wastewater on the soil, as reported by Jiménez & Chávez ()

All of the target compounds as well as the surrogate stan-

and Chávez et al. (). Wastewater depuration has demon-

dards ketoprofen and [2H16] bisfenol-A and the internal

strated to be so efficient that the aquifer of the irrigated area,

standards [2H4] 4-n-nonylphenol and clofibric acid were

which has been recharged with the infiltrated wastewater for

purchased from Sigma-Aldrich (St Louis, MO). The solvents

several decades, is used as the only drinking water source

used for the analysis were high-performance liquid chrom-

for the 500,000 people living in the Tula region, only chlori-

atography (HPLC) grade and purchased from Burdick and

nation being applied as disinfection prior to distribution.

Jackson (Morristown, NJ). The derivatizing agents N-tert-

The removal and dissipation of emerging pollutants in the

butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA)

Tula Valley region may be attributed to natural attenuation

with 1% of t-butyldimethylsilylchlorane (TBDMSCI) and

processes, such as photodegradation, biodegradation, and

N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) with 1%

sorption onto the soil. In this sense, it is necessary to eluci-

of trimethylsilylchlorane (TMSCI) were also obtained from

date how these pollutants mobilize or degrade in the soil in

Sigma-Aldrich. Oasis HLB extraction cartridges (200 mg,

order to understand how depuration works, as well as its

60 cc) were bought from Waters (Milford, MA). For exper-

potential limitations. Soil column experiments are useful

iments, standard solutions containing the mixture of the

to describe the mobility of contaminants through the soil

target pollutants were prepared at concentrations of 10, 1,

porous media, assessing separately the factors that influence

and 0.1 ng/μL using methanol as solvent. For the analytical

this process. The vertical movement of the emerging pollu-

procedure, internal and surrogate standards solutions were

tants toward the aquifer may depend on: (1) the chemical

prepared, in methanol, at 10 ng/μL. Table 1 displays the rel-

properties of the solutes; (2) the hydrological regime at

evant chemical properties of the target compounds.

which water infiltrates through the soil; and (3) the physical and chemical properties of the soil. The polarity of the mol-

Soil columns’ collection and soil characterization

ecules as well as the structure and texture of the soil also have a decisive role in delaying the transport of pollutants.

Undisturbed soil columns were taken from a cropland

On the other hand, preferential flows within the soil struc-

where irrigation using untreated wastewater has occurred

ture can accelerate the migration of pollutants into the

for the last 85 years.

aquifer (Wehrer & Totsche ). The aim of this work

Soil columns were collected in triplicate at two soil

was to determine the transport of three emerging pollutants,

depths: 5–30 and 40–55 cm depth. The superficial soil col-

namely the non-steroidal anti-inflammatory drug naproxen,

umns were 25 cm high and 15 cm wide, while the sub-

the antiepileptic carbamazepine, and the antimicrobial

superficial columns were 15 cm high and 9 cm wide. To

11

J. C. Durán-Álvarez et al.

Table 1

|

|

Transport of emerging pollutants through untreated wastewater irrigated soils

Relevant chemical properties and structure of the studied compounds

Table 2

|

Journal of Water Reuse and Desalination

Chemical structure

Naproxen

pKa

b

4.1

3.2

a

13.9

Carbamazepine

2.3

8.4

Triclosan

logKow

4.8

Parameter

10 cm

60

pH

8.01

Electrical conductivity (μS/cm)

1,546

9.6

Acidic ionization constant.

Log of the octanol–water partition coefficient.

b c

W

Determined at 25 C.

2014

40 cm

8.14 1,601

Total organic carbon (mg/g)

25

18

Sand (%)

12

13

Silt (%)

43

38

Clay (%)

45

49

3

a

|

Soil sample depth

(mg L–1)

17.7

04.1

Physical and chemical properties of the studied soils

c Water solubility

Compound

|

Bulk density (g/cm )

1.1

Texture

Clay loam

Specific surface area (m2/g)

66.4

Naproxen (ng/g)

2.7

1.0

Carbamazepine (ng/g)

6.2

1.4

Triclosan (ng/g)

9.4

6.3

1.3 115

obtain the soil columns, a pit of 90 cm deep was dug and the soil monoliths were carved directly in the wall of the pit. Once shaped, the monoliths were put into stainless

Transport experiments

W

steel cases, and liquid paraffin (at 60 C) was poured in the free space between the soil and the stainless steel

The transport assays were carried out separately for super-

case, in order to both fix the monolith to the column

ficial and sub-superficial soil columns by simulating

and avoid the border effect. The soil columns were

irrigation events using a 0.01 M CaCl2 solution as irrigation

W

stored in plastic bags at 4 C until the transport assays.

water. Water was applied at the top of the soil columns

Before experiments, 50 g soil samples were taken at the

using two hydrological regimes: (1) transient flow for the

top of the three columns corresponding to each soil

superficial soil columns, in order to emulate the infiltration

depth and were combined to obtain one composite

of water through the soil during irrigation; and (2) steady-

sample. Parameters shown in Table 2 were determined

state flow conditions for the sub-superficial columns,

for the soil samples using standard methodologies

aimed to simulate the slow infiltration of the irrigation

(Carter & Gregorich ).

water through the sub-soil. All the soil columns were

The pH and the electrical conductivity were measured in a 1:1 soil:0.01 M CaCl2 suspension using a sensION156

weighed prior to the experiment in order to determine the initial water content.

HACH pH/conductivity meter. Concentration of soil

The experimental setup used for the superficial soil col-

organic carbon was determined using the Walkley–Black

umns is shown in Figure 1(a). In the first step, 950 mL of the

chromic acid wet oxidation method. Soil bulk density

0.01 M CaCl2 solution, containing the conservative tracer

was obtained by weighing soil cores, which were taken

bromide (0.1 M) – as KBr salt – and a mixture of the emer-

directly in the field. The determination of the soil particle

ging pollutants (10 μg/L, each), were applied to each

size distribution and texture was done using the Bouyou-

column. Water was poured in the 10 cm head space of the

cos hydrometer method. Additionally, the specific surface

columns, and water was allowed to infiltrate through soil

area of the soil particles was measured using the

by gravity. After infiltration, the soil in the columns was

Brunauer–Emmett–Teller

adsorption

allowed to dry for the next 4 days. Subsequently, eight irriga-

method. Lastly, the background concentration of the

(BET)

nitrogen

tion events consisting only of the application of the 0.01 M

target compounds in the tested soils was quantified prior

CaCl2 solution were carried out in order to displace both

to the experiments.

the tracer and the target pollutants. The time lapse between

12

J. C. Durán-Álvarez et al.

Figure 1

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|

Transport of emerging pollutants through untreated wastewater irrigated soils

Journal of Water Reuse and Desalination

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04.1

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2014

Setup of the transport experiments for the superficial (a) and sub-superficial (b) soil columns.

each irrigation event was 4 days at a controlled temperature W

carried out for 27 h, corresponding to 0.5 pore volume. In

of 25 C. Throughout the irrigation events, leachates were

the third stage, the displacement of the compounds and

recovered at the bottom of the soil columns and discretized

the tracer was carried out by applying the 0.01 M CaCl2 sol-

into 100 mL sub-samples.

ution sole for 780 h, equivalent to 13 pore volumes.

For the sub-superficial columns, transport experiments

Once transport experiments were concluded, the soil

under steady-state flow conditions were set up as shown in

columns were weighed in order to determine the mass of

Figure 1(b). The irrigation solution (0.01 M CaCl2) was sup-

water retained by the soil. Then, the soil monoliths were

plied to the soil columns using a Gilson Miniplus 3

cut into three equal sections, soil was air-dried for 24 h

peristaltic pump at a constant flow rate of 0.125 mL/min.

and homogenized by sieving through a 2 mm pore sized met-

Water was sucked from the bottom of the columns using

allic mesh. Concentration of the target pollutants was

the same peristaltic pump (the outflow rate was therefore

determined in both leachate samples and the soil collected

equal to the inflow rate). The pH and electrical conductivity

at the end of the experiment. Both the distribution of the

of the leachate was measured online throughout the exper-

target pollutants throughout the soil column at the end of

iment and recorded in a data-logger. Leachate was

the experiment and the mass balance was obtained from

discretized into 7.5 mL sub-samples, using a GE Frac-912

the analysis of the soil samples.

fraction collector, and stored in glass tubes. The transport experiment in the sub-superficial columns was divided into

Emerging pollutants’ analysis

three stages. In the first stage, which took 48 h, irrigation was performed using the 0.01 M CaCl2 solution alone until

Concentrations of the target pollutants were determined in

the equilibrium conditions were achieved (i.e., pH and elec-

the leachates following the procedure developed and vali-

trical conductivity values in leachate were constant,

dated by Gibson et al. (). The pH of the liquid

stabilization of the flow rate at the entry and at the exit of

samples was adjusted to 2 using sulfuric acid (98%); then,

the column). In the second stage, the mixture of the emer-

the surrogate standards ketoprofen and [2H16] bisphenol-A

ging pollutants (10 μg/L, each) and the conservative tracer

were added. Samples were passed through the Oasis HLB

bromide (0.1 M) were applied as a pulse. The pulse was

cartridges, which were previously conditioned twice with

13

J. C. Durán-Álvarez et al.

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Transport of emerging pollutants through untreated wastewater irrigated soils

Journal of Water Reuse and Desalination

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2014

5 mL of acetone and once with 5 mL of 5% acetic acid sol-

of sample was injected in the splitless mode. The oven temp-

ution, using a vacuum flow equivalent to 5 mL/min. After

erature program was as follows: 100 C for 1 min, ramp of

passing the liquid samples, naproxen and carbamazepine

20 C/min to 280 C, and 280 C for 10 min. The detector

were eluted from cartridges with 5.5 mL of a mixture

was used in the selected ion monitoring (SIM) mode. The

40:60 of acetone:sodium bicarbonate 0.1 M, adjusted to

temperature of the electron impact source was 230 C,

pH 10; then, the cartridges were dried for 1 h with

with electron energy of 70 eV. Calculation of the analytes’

W

W

W

W

W

vacuum at a flow rate of 10 mL/min. Following the drying

concentration was done through the internal standard

step, triclosan was eluted with 5 mL of acetone. Both

method. Quality assurance was guaranteed by the use of sur-

phases were concentrated using a gentle atmosphere of

rogate standards. The recoveries obtained were 90–96% for

ultra high purity nitrogen and the water remaining in the

ketoprofen and 88–91% for [2H16] bisfenol-A.

sample was removed by adding anhydrous sodium sulfate.

Lastly, the internal standards clofibric acid and [2H4] 4-n-

Data analysis

nonylphenol were added to samples and derivatization was performed, through the production of methyl-silyl deri-

The transport parameters for target emerging pollutants and

vates, using the agents MTBSTFA for naproxen and

tracer (i.e., retardation factor, solute dispersion, and deter-

carbamazepine, and BSTFA for triclosan.

mination coefficient) were determined by the analysis of

Analysis of soil was performed using the method pro-

the breakthrough curves. For the sub-superficial soil col-

posed and validated by Durán-Álvarez et al. ().

umns, the solution of the classic convection–dispersion

Extraction of the analytes was done through the pressurized

equation for the solutes was achieved using the CXTFIT

liquid extraction technique, using a Dionex ASE® 200

2.1 code (Toride et al. ). The code was used in the

device. For this, 5 g of soil and 2 g of diatomaceous earth,

inverse mode for either equilibrium or non-equilibrium con-

the latter used as dispersing agent, were accurately weighed

ditions. The solution of equation was fitted to the

in 22 mL ASE stainless steel cells and extracted using the

experimental

hexane:acetone:acetic acid (49:49:2 v/v/v) mixture. Surro-

method. Due to the non-symmetry of the breakthrough

gate standards were added to samples prior to extraction.

curves obtained for the superficial columns, the CXTFIT

The extraction conditions were as follows: two cycles,

code could not be executed using these results. Therefore,

W

data

by

the

least-squares

optimization

100 C, 10.34 MPa, 0 min of pre-heat, 5 min of heating

determination of the retardation factor in the superficial

time, 5 min of static time, and flush at 60%. The extracts

soil columns was done by the visual analysis of the break-

were evaporated to reach a volume of ∼3 mL. After evapor-

through curves.

ation, 20 mL of HPLC-grade water was added to the concentrates. The resulting solutions were passed through the Oasis HLB cartridges, previously conditioned as stated

RESULTS AND DISCUSSION

above. Naproxen and carbamazepine were eluted from cartridges using the 40:60 acetone:sodium bicarbonate 0.1 M

In this section, the discussion of the most relevant results of

solution, while triclosan was eluted using 5 mL of a 50:50

the transport experiments is shown. The results obtained for

acetone:dichloromethane solvent mixture. After elution,

the superficial and sub-superficial soil columns are displayed

the sample preparation procedure was the same as

separately.

described for liquid samples.

Separation and quantification of the analytes were carried out using a HP 6890 gas chromatograph in tandem

Transport of emerging pollutants in superficial soil columns

with a HP 5397 mass selective detector. The chromatographic column was a fused silica capillary column

Figure 2 shows the breakthrough curves of both the conser-

(30 m × 0.25 mm, 0.25 μm of film thickness). The carrier

vative tracer bromide and the pharmaceutical compounds

gas was helium at a constant flow of 1 mL/min, and 1 μL

naproxen and carbamazepine. In this figure, the relative

14

J. C. Durán-Álvarez et al.

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Transport of emerging pollutants through untreated wastewater irrigated soils

Journal of Water Reuse and Desalination

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2014

Regarding the target emerging pollutants, naproxen and carbamazepine were found in the leachate samples at different times throughout the experiment, while triclosan was not observed in leachate samples. This behavior may be caused by two phenomena, which may occur simultaneously: (1) the irreversible sorption of the antimicrobial agent onto the soil particles; and (2) its rapid biodegradation by the native microorganisms of the soil.

Retardation factors of the compounds detected in the leachates could be determined by the analysis of the breakthrough curves, establishing the value of this factor as the center or gravity of the curve. Retardation factor Figure 2

|

Breakthrough curves of the bromide tracer and the target emerging pollutants corresponding to the superficial soil columns.

was 3.8 for carbamazepine and 1.5 for naproxen. Higher retardation of carbamazepine compared to naproxen has been reported by others (Chefetz et al. ), and may

concentration of the target emerging pollutants in leachates

be explained by the higher affinity of the antiepileptic

is plotted with the total volume of leachate normalized to

drug to the soil organic matter. Conversely, naproxen

the pore volume of the soil column (Vaccumulated/Vpore;

molecules, occurring in their negative dissociated form

pore volume ¼ 1,035 mL). The asymmetry observed in the

at the pH values of soils (Table 1), may be repelled to

bromide breakthrough curve indicates the rapid movement

an important extent by the soil organic matter and clay

of water and solutes through the soil columns (Melamed

particles.

et al. ). This behavior may be attributed to: (1) the occur-

In spite of the molecules of naproxen undergoing anion

rence of preferential paths within the soil monolith; and (2)

exclusion by the soil particles, the mobilization of this

the repulsion forces between the bromide anion molecule

pharmaceutical through the soil was not as rapid as that

and the negatively charged soil components (i.e., soil

observed for the bromide. This is explained by the organic

organic matter and clay), which is known as anionic exclu-

nature of the molecule, which maintains an organic

sion (Gvirtzman & Gorelick ). Within the soil porous

domain consisting of a double ring structure. Through the

network, preferential paths occur as the result of both the

organic moiety, naproxen molecules may be sorbed by

presence of roots and stones, the activity of macrobiota

both the soil organic matter and clay (Chefetz et al. ).

(e.g., worms, ants, or beetles) and the tillage activities. The

According to the mass balance, 14.5% of the amount of

preferential paths may consist of either a single channel

naproxen entering into the soil columns was degraded,

through the soil profile or the complex connectivity of the

while for carbamazepine this value was zero. In the case

pores within the soil matrix. In any case, preferential paths

of triclosan, the compound was not found either in the lea-

result in the fast movement of the solutes (the tracer and pol-

chate samples or the soil at the end of the experiments,

lutants) through the soil monolith (Kung et al. ).

indicating that the compound was degraded at some point

Regarding anion exclusion, this phenomenon has been pre-

of the experiment. Ready biodegradation of triclosan in

viously reported in similar soils (García-Gutiérrez et al.

aerobic soils has been reported by Cha & Cupples ().

; Prado et al. ). Anion exclusion may be patent not

In general, little is known about the microorganisms leading

only for bromide but also for the negatively charged con-

to the biodegradation of emerging pollutants in soil. Recent

taminants such as naproxen and the dissociated fraction of

evidence points to bacteria Pseudomonas putida and Sphin-

triclosan at the pH value of the soil (see pKa values of triclo-

gomonas sp. and fungus Trametes versicolor as the

san in Table 1). Mass balance for bromide showed that

microorganisms responsible for the biodegradation of phar-

neither degradation nor accumulation nor production

maceutically active substances in the soil (Kagle et al. ;

occurred throughout the soil column experiment.

Girardi et al. ).

15

J. C. Durán-Álvarez et al.

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Transport of emerging pollutants through untreated wastewater irrigated soils

Journal of Water Reuse and Desalination

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2014

Transport in sub-superficial columns For the sub-superficial soil columns, bromide breakthrough curves were shown to be symmetrical (Figure 3). This indicates that transport of water and solutes was carried out without the occurrence of preferential flows. This may be due to the high content of expansive clays in the soil. Bromide retardation factor was below 1 (0.85), indicating the occurrence of an anion exclusion phenomenon, caused by the negative charge that dominates in the soil. The slight tailing observed in the bromide breakthrough curve may be

Figure 4

|

caused by an intra-particle diffusion phenomenon, which

Breakthrough curves of the emerging pollutants corresponding to the subsuperficial soil columns.

may occur in soils where micro pores are abundant, e.g., clayey soils (Brusseau & Rao ).

The presence of naproxen and carbamazepine in leachates was observed prior to the application of the pulse containing the target compounds. This indicates the occurrence of a readily translocable initial mass of these compounds in the studied soils, which can move into the aquifer during rain events. Triclosan was not observed in the leachate samples, indicating that this compound can be irreversibly retained by soil or degraded within the soil matrix. In accordance with this behavior, it is recommended that the metabolites generated by the biodegradation of triclosan as well as their potential to reach the groundwater should be studied.

According to the breakthrough curves (Figure 4), naproxen was more displaceable than carbamazepine in the sub-superficial soil columns. The same behavior was observed by Chefetz et al. () in transport experiments

using disturbed soil columns. Table 3 shows the transport parameters of the target compounds and the tracer, obtained using the CXTFIT mode.

Similar to that observed in the superficial soil columns, the retardation factor of naproxen was lower than obtained for carbamazepine. The rapid transport of naproxen through the sub-superficial soil may be caused by the same anion exclusion observed for the bromide tracer. On the other hand, the low mobility of carbamazepine and triclosan through the soil can be explained by their sorption onto the soil organic material, as has been demonstrated by Williams et al. () and Lozano et al. (). The notorious dispersion observed in the carbamazepine breakthrough curves is indicative that there are strong interactions between the soil components and the pharmaceutical compound, such as sorption and probably intra-particle diffusion, as was suggested by the tracer tests.

Mass balance showed losses of naproxen and triclosan (13 and 98%, respectively) during the experiment, proving the degradation of the target compounds, notably for

Table 3

|

Transport parameters of the tracer and the target pollutants for the subsuperficial soil a

Retardation

Figure 3

|

Bromide breakthrough curve corresponding to the sub-superficial soil columns

Determination

Solute

factor

Dispersion

coefficient

Bromide

0.85

2.7 × 10 3

0.93

3

Naproxen

1.8

3.6 × 10

Carmabazepine

8.2

4.3 × 10 4

0.9 0.97

(circles represent the measured data and crosses represent data obtained using the CXTFIT model); the panel on the left represents the concentration in

a

the pulse.

experimental data.

Determined by the least-squares optimization method by comparing the modeled and the

16

J. C. Durán-Álvarez et al.

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Transport of emerging pollutants through untreated wastewater irrigated soils

triclosan. Degradation of naproxen and triclosan was similar for both soil depths. On the other hand, high recovery of carbamazepine in leachate and the soil (>97%) was indicative of its recalcitrance, which is consistent with those reported in the literature (Clara et al. ). In the case of carbamazepine, degradation was higher in the subsuperficial soil than in the superficial soil.

CONCLUSION Infiltration of wastewater through soil proved to be efficient in retaining the emerging pollutants tested. Natural attenuation mechanisms, such as sorption onto the soil organic matter and biodegradation, occurred in the soil porous media, delaying the arrival of these contaminants to the aquifer and thus minimizing the risk of groundwater pollution. The mobilization of the target emerging pollutants was higher in the superficial soil due to both preferential paths through the soil column and the anion exclusion of the negatively dissociated compounds. Conversely, delay in the transport of the pollutants in the sub-superficial soil was higher than that observed in the superficial soil, indicating that the closure of preferential paths upon the humidification of soil in the steady-state hydrological regime contributes to the higher retention of these compounds in the soil matrix as well as to their degradation.

ACKNOWLEDGEMENT We would like to acknowledge the Dirección General de Asuntos del Personal Académico de la UNAM (DGAPAUNAM) for funding this research through the project IN101610.

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Kagle, J., Porter, A. W., Murdoch, R. W., Rivera-Cancel, G. & Hay, A. G.  Biodegradation of pharmaceutical and personal care products. Adv. Appl. Microbiol. 67, 65–108.

Kung, K. J. S., Steenhuis, T. S., Kladivko, E. J., Gish, T. J., Bubenzer, G. & Helling, S.  Impact of preferential flow on the transport of adsorbing and non-adsorbing tracers. Soil Sci. Soc. Am. J. 64, 1290–1296.

Lozano, N., Rice, C. P., Ramirez, M. & Torrents, A.  Fate of triclosan in agricultural soils after biosolids application.

Chemosphere 78, 760–766.

Melamed, R., Jurinak, J. J. & Dudley, L. M.  Anion exclusion– pore water velocity interaction affecting transport of bromine through an Oxisol. Soil Sci. Soc. Am. J. 58, 1405–1410.

Naidoo, V., Wolter, K., Cuthbert, R. & Duncan, N.  Veterinary diclofenac threaten Africa’s endangered vulture species. Regul. Toxicol. Pharm. 53, 205–208.

Petrovic, M., Radjenovic, J., Postigo, C., Kuster, M., Farre, M., López de Alda, M. & Barceló, D.  Emerging contaminants in waste waters: sources and occurrence. In: The Handbook of Environmental Chemistry: Emerging Contaminants from Industrial and Municipal Waste (D. Barcelo & M. Petrovic, eds). Springer-Verlag, Berlin, pp. 1–35.

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Prado, B., Duwig, C., Etchevers, J., Gaudet, J. P. & Vauclin, M.  Nitrate fate in a Mexican andosol: is it affected by preferential flow? Agr. Water Manage. 98, 1441–1450.

Ratola, N., Cincinelli, A., Alves, A. & Katsoyiannis, A.  Occurrence of organic microcontaminants in the wastewater treatment process – a mini review. J. Hazard.

Mater. 239–240, 1–18.

Toride, N., Leij, F. J. & van Genuchten, M. T.  The CXTFIT Code for Estimating Transport Parameters from Laboratory or Field Tracer Experiments, Version 2.0. Report of the U.S. Salinity Laboratory, Riverside, California.

Vandenberg, L. N., Colborn, T., Hayes, T. B., Heindel, J. J., Jacobs Jr, D. R., Lee, D. H., Shioda, T., Soto, A. M., vom Saal, F. S., Welshons, W. V., Zoeller, R. T. & Myers, J. P.  Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses. Endocr. Rev. 33, 1–78.

Wehrer, M. & Totsche, K. U.  PAH release from tar-oil contaminated soil material in response to forced environmental gradients: implications for contaminant transport. Eur. J. Soil Sci. 59, 50–60.

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Qual. 35, 1779–1783.

First received 8 February 2013; accepted in revised form 15 May 2013. Available online 7 June 2013

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Sustainable water management with multi-quality recycled water production: the example of San Luis Potosi in Mexico Valentina Lazarova, Lucina Equihua and Alberto Rojas

ABSTRACT This paper presents and discusses the performance, reliability of operation, socio-economic and environmental aspects and benefits of the Tenorio Project in San Luis Potosi. This is the first project in Mexico making possible the production of multi-quality recycled water for planned water reuse for different purposes, including industrial cooling in a power plant, agricultural irrigation, groundwater restoration and environmental enhancement. Long-term water quality monitoring demonstrated the reliability of operation of the selected treatment trains, which were well adapted to local conditions and the given reuse application. The major challenge was the control of the conductivity and silica content in recycled water for industrial reuse, which needed complementary investigations and the implementation of an additional treatment by ion exchange. The reliable operation of the power plant with recycled water encouraged other industries to explore water reuse

Valentina Lazarova (corresponding author) Suez Environnement, 38 rue du president Wilson, Le Pecq, France E-mail: valentina.lazarova@suez-env.com Lucina Equihua DegremontMexico, Reforma 350, Torre del Angel, 06600 Mexico D.F., Mexico Alberto Rojas Comisión Estatal del Agua, Mariano Otero No. 905, Barrio de Tequisquiapam, San Luis Potosi, Mexico

as an option, as well as the possibility of improved treatment. Once the main technical and social challenges of the original project were overcome, the project acquired a new dimension with the request of the industrial client to improve water quality by means of reverse osmosis. In return, the power plant proposed giving their right for water withdrawal from the aquifer to the City of San Luis Potosi, allowing thus the availability of freshwater for augmentation of the potable water supply.

Key words

| agricultural irrigation, environmental enhancement, industrial reuse, water reuse

INTRODUCTION San Luis Potosi is the eleventh most populated metropolitan

recharge of artificial lakes, fountains) and industrial reuse

area in Mexico with more than 1.3 million inhabitants, and is

mainly for cooling (Olivo & Martínez ). In consequence,

situated in a semi-arid region with less than 400 mm of

seven wastewater treatment plants (WWTPs) were built for

annual rainfall. The intensive industrial and economic devel-

this purpose with an additional one under construction. At

opment of this city has always been related to water

present, 70% of the wastewater of San Luis Potosi is treated

availability and water conservation efforts. Since 1961, the

and 100% of treated wastewater is recycled (Equihua ;

water withdrawal from the two main aquifers has been

Rojas ).

strongly restricted and poor quality wastewater has been

In this context, the main objective of this paper is to present

used for irrigation purposes (Diario Oficial de la Federación

and discuss the performance, reliability of operation, socio-

). In the late 1990s, the State Water Commission (CEA),

economic aspects and benefits of Tenorio – Villa de Reyes,

the Government of San Luis Potosi, decided to implement an

the largest WWTP, which has operated since 2006 and treats

Integral Plan for Sanitation and Water Reuse aiming to sub-

45% of the total wastewater of the city of San Luis Potosi.

stitute groundwater resources by recycled water for a

This project, known as the Tenorio Project, is the first one in

number of non-potable uses, including agricultural irrigation,

Mexico making possible the production of multi-quality

urban reuse (recreational parks, sport and golf courses,

recycled water for planned water reuse for different purposes,

doi: 10.2166/wrd.2013.006

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including industrial use, agricultural irrigation, groundwater

development in the cooling towers of the power plant

restoration and environmental enhancement.

of Villa de Reyes.

Water quality has been monitored daily over 6 consecutive years by means of composite 24 h sampling of the

MATERIAL AND METHODS

activated sludge and the advanced treatment for industrial reuse and monthly sampling of the treatment line for agricul-

The Tenorio WWTP was designed for a total capacity of 3

tural reuse and environmental enhancement. Results from

1,050 L/s (90,720 m /d) and it uses the following treatment

the first year of operation (2006) were not considered for

steps (Figure 1):

this paper as several adjustments were made to the process

•

Screening, grit and grease removal and advanced primary

in that year. Physical-chemical parameters were measured

treatment in lamellar clarifiers enhanced with chemicals

according to the Standard Methods (). Microbiological

for the total capacity. The main objective of this treatment

parameters were measured in grab samples. On-line moni-

is the removal of suspended matter before discharge into

toring of recycled water was implemented at the inlet to

the Tenorio Reservoir, a wetland.

the industrial end-user, the power plant.

•

•

Natural engineered treatment and polishing for at least

Observation of birds at 10 set-points around the

51,840 m3/d in a constructed wetland, with a semi-

Tenorio Reservoir was used to evaluate the positive

rectangular shape, a total surface of 179 ha and a stor-

impact of the improved recycled water quality on this con-

age capacity of 2.65 Mm3, named Tenorio Reservoir,

fined ecosystem. At each observation point, five counts

for agricultural reuse. The main objective of this treat-

were performed at two different periods in 2011 and at

ment is the removal of organic matter and faecal

the beginning of 2012. In total, 100 counts were carried

coliforms before the water is pumped for irrigation of

out to determine the total number of birds and to identify

fodder crops.

different species.

3

Secondary treatment for up to 38,880 m /d by activated sludge with nitrogen removal, followed by tertiary treatment with lime, sand filtration, ion exchange softening

RESULTS AND DISCUSSION

and chlorine disinfection for industrial reuse. The main objective of this treatment is the reduction of nutrients,

Recycled water quality and quantity

organic and suspended matter, silica, calcium hardness and phosphate content, as well as the removal of bacteria

The results of water quality monitoring during the whole

in

operating period 2007–2012 are summarised in Table 1.

Figure 1

order

|

to

avoid

scaling,

Flow diagram of the treatment process.

biofouling

and

algal

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V. Lazarova et al.

Table 1

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Characteristics of raw sewage and recycled water with different quality for agricultural irrigation and industrial uses by the power plant (January 2007–April 2012)

Parameter

Raw wastewatera

Primary effluenta

Tenorio Reservoir effluent to reuse in agricultureb

Reclaimed water to power planta

TSS (mg/L)

188.96 (±72.78)

33.18 (±20.82)

25.83 (±10.73)

3.30 (±2.71)

BOD5 (mg/L)

286.49 (±93.73)

36.8 (±21.85)

31.4 (±13.96)

2.96 (±2.1.83)

COD (mg/L)

524.1 (±226.46)

99.7 (±51.81)

81.2 (±28.9)

16.2 (±13.07)

PTOTAL (mg/L)

8.5 (±3.38)

6.2 (±1.91)

6.2 (±1.20)

1.2 (±0.8)

Total Kjeldahl nitrogen (mg/L)

34 (±8.91)

26.8 (±8.94)

22.3 (±5.1)

1.6 (±3.59)

Faecal coliforms /100 mL

4.57 × 109 (±1.33 × 102)

8.72 × 102 (±2.21 × 102)

240 (±189)

18.56 (±16.6)

Total hardness (mg/L)

115 (±29.86)

Not measured

Not measured

109.3 (±23.42)

Silica (mg/L)

104.3 (±20.69)

Not measured

Not measured

64.5 (±7.82)

TSS: total suspended solids; BOD5: biological oxygen demand; COD: chemical oxygen demand. a

Average (standard deviation) from 1945 daily composite samples.

Average from 54 monthly composite samples.

b

The annual consumption of each type of recycled water

suspended solids to an average value of 82.2 mg/L (Figure 3(a))

is shown in Figure 2. The major reuse applications and the

preserving the fertilising capacity of treated effluents

associated volumes of recycled water are as follows:

by

•

polishing in the wetland (Tenorio Reservoir) ensured good

• •

Industrial reuse of up to 9.9 Mm3/yr in the 700 MW Power Plant Villa de Reyes for cooling purposes, saving

maintaining

its

nutrient

content.

The

additional

additional removal of suspended solids to an average value of

currently 7.9 Mm3/yr of potable water (average daily

28.2 mg/L. The observed high values above 35–40 mg/L are

flow of 21,600 m3/d).

due to microalgae development. The average concentration

Agricultural irrigation with up to 23.9 Mm3/yr (average

of organic matter in the recycled water for irrigation is BOD5

daily flow of 52,785 m3/d) for fodder crops, such as

(biological oxygen demand) 31.4 mg/L, total phosphorus

fodder, corn, barley and alfalfa.

6.2 mgPtot/L and nitrogen 22.3 mgN/L as total Kjeldahl

Environmental enhancement with the restoration of the

nitrogen.

wetland for wildlife habitat.

The high residence time of the primary effluent in the Tenorio Reservoir with an average value of 40 days

Water quality for agricultural reuse

ensures good disinfection of the effluent with about 7.3 log removal of faecal coliforms. The mean concentration

Despite the strong variations in raw wastewater quality,

of faecal coliforms in the outlet was 240 MPN/100 mL

advanced primary treatment ensured good removal of

(MPN: most probable number) for the 2-year period of 2010–2011 (Figure 3(b)), which is largely below the WHO guidelines () of 1,000 Escherichia coli/ 100 mL despite the very high inlet values of up to 9 to 11 log.

Salinity is one of the most important agronomic parameters as high salinity can damage salt-sensitive plants and decrease crop yields. As shown in Figure 4, average salinity remains below 900–1,000 μS/cm, with periodic increases to 1,300–1,400 μS/cm, which is within the range of tolerance of irrigated crops. More stringent requirements

Figure 2

|

Evolution of the annual production of the two qualities of recycled water of the Tenorio WWTP.

apply to the recycled water for industry with a permitted value of 1,200 μS/cm.

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Figure 3

|

Evolution suspended solids (a) and faecal coliforms (b) in the outlet of the Tenorio Reservoir before the use for agricultural irrigation.

Figure 4

|

Evolution of the conductivity in secondary effluent for a 6-year period (2007– 2012).

Figure 5

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Evolution of the silica in secondary effluent for a 6-year period (2007–2012).

Water quality for industrial reuse The Villa de Reyes power plant is, at present, the The major challenge for operation of the Tenorio WWTP

main consumer of high quality recycled water for cooling

was the compliance and the reliability of the recycling plant

purposes. After 6 years of operation and demonstrated

for the supply of recycled water to the industrial user, the

reliability of operation, the power plant has evaluated

power plant. In this respect, the major problem was the aver-

the overall benefits of the use of treated water and has

age value of the conductivity, which was 5 to 10% above the

requested that the treatment level be increased in order

800 μS/cm contract guarantee. After several months of inves-

to reduce silica and dissolved solids content. The main

tigation, a higher conductivity limit of 1,200 μS/cm was

objective is to produce demineralised water, which will

accepted in exchange for a lower silica content of 65 ppm

allow complete elimination of their groundwater con-

instead of the initial guarantee of 85 ppm (Figure 5).

sumption. In order to avoid increasing the unitary cost

In order to meet this new guarantee level, over a 6-month

of recycled water, the power plant management has

test period, several combinations of chemicals were used to

proposed

increase the removal of silica (sodium hydroxide and lime,

rights to the State Water Commission, and thus, augment

sodium aluminate and lime, etc.) and ion exchange softening

the drinking water resources of the Metropolitan Area

was implemented in order to treat the hardness increase as a

by up to 13.8 Mm3/yr at a reasonable cost for the

consequence of the silica removal process.

population.

transferring

their

groundwater

extraction

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Sustainable water management with multi-quality recycled water production

Water quality in distribution network

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area, in accordance with state or national environmental policy.

Another significant challenge was bacterial control in the conveyance system to the industrial end-user (40 km of 3

As shown in Figure 6, the reservoir was surveyed from 10

of intermediate storage). Due to the

observation points. During each of the three surveys, a total

large flow variations associated with daily and seasonal

of 100 counts were performed. The results enabled the identi-

energy production, total residence time varied from 16 to

fication of 56 species of birds: 23 aquatic, 28 terrestrial and

60 h. This increased significantly the chlorine demand and

five predators. The 56 species belong to 23 families, the

made the residual chlorine control very challenging. As a

families with larger number of species were Anatidae (9),

result, the problem of bacterial regrowth in the pipe and

Ardeide (6) and Tyrannidae (5) (Figure 7). Four species

intermediate tank became an issue for the power plant oper-

have been classified as protected birds by the Mexican Gov-

ation. The solution came after several weeks of tests with a

ernment. The polishing wetland is located in the route of

non-oxidant biocide and dispersant agents that were applied

several migratory species that have colonised the site for regu-

in combination with chlorine. Finally, the bio-monitoring

lar nesting. Consequently, 48 of the observed species are

allowed establishment of the basis for biofilm control and

migratory birds. The average total number of birds counted

fine tuning came as a second priority to optimise doses,

in the area surveyed (2,703 m2) was 1514 birds.

pipe and 4,000 m

while maintaining the guaranteed bacterial count and residual chlorine at the end of the pipe.

This study demonstrated the role of the Tenorio Reservoir in the enhancement of biodiversity, in terms not only of the increase of the bird population, but also for the floral diversity and small mammals. The birds are essential for maintaining

Environmental enhancement and preservation of

the health of the surrounding ecosystem. Some species also

biodiversity

contribute to controlling pests and vectors of several diseases by eating insects and rodents. As a result of this study, the cre-

An ecosystem monitoring programme has been launched for

ation of a protected area with a mitigation zone in the

the Tenorio Reservoir that had deteriorated in the past due to

surroundings is under consideration by local authorities.

the discharge of untreated wastewater. In 2006, the reservoir was modified to perform as a wetland. As a consequence of the improved water quality, a large diversity of migratory birds has been encountered in recent years.

During the period from December 2011 to April 2012, three surveys to monitor the bird population, flora and fauna on the Tenorio Reservoir. The major objectives of this study were to:

• • • •

produce a baseline of information on the diversity of resident and migratory birds; identify indicator species of environmental quality; determine values of ecological importance with distribution patterns and temporal dynamics; propose guidelines for management and conservation of the environment to regulate land use in the catchment area (control of the urban and industrial growth in the

•

area); determine the importance of wetlands as a basis for protection of biodiversity and the ecological status of the

Figure 6

|

Location of the ten birds observation points in the Tenorio Reservoir.

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V. Lazarova et al.

Figure 7

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Views of the bird populations of American black-winged stilt Himantopus mexicanus and white-faced ibis Plegadis chihi (left) and Anatidae family (right).

Costs and benefits of the Tenorio recycling scheme The Tenorio WWTP was built under a BOT (Build, Operate and Transfer) contract with 18 years of operation and maintenance. BOT contracts in Mexico have become a very important tool to finance projects with long-term contracts that guarantee reliable operation and maintenance of the facilities during the life of the contract. The cost of

• • •

The population established near the plant improved their living standard as the ecological environment of the zone was enhanced.

In addition, the existing two aquifers were preserved from pollution with untreated wastewater and the water balance has been re-established for one of them.

Indirect augmentation of drinking water resources has been possible due to the saving of 48 Mm3 that were

Tenorio-Villa de Reyes project was $585,277,351 (May

not extracted from the aquifer for industrial uses by the

2000); 40% was subordinated support or non-refundable

power plant in the past 6 years, as well as due to a new

from the trusteeship for infrastructure in charge of Banco

project that is in progress which will allow provision of

Nacional de Obras y Servicios and the 60% left risk capital

an additional volume of 13.8 Mm3/yr of potable water

comes from private funds.

to the City of San Luis Potosi if the power plant transfers

The most important benefits of this first large water

its rights for extraction of groundwater.

reuse project in Mexico, widely recognised by all stakeholders, can be summarised as follows:

•

Strong social benefits, as the production of recycled water with fit-for-purpose water quality enabled resolution of

CONCLUSIONS

the existing conflicts for water supply between the agri-

• • • •

cultural and industrial sectors.

The long-term water quality monitoring and performance

Health benefits have also been significant because the

analysis demonstrated the feasibility and economic viability

mortality rate caused by gastrointestinal diseases that

of integrated water management with multi-quality recycled

existed in the zone irrigated with raw wastewater was

water by means of the implementation of appropriate treat-

reduced.

ment technologies well adapted to local conditions. The two

Economic benefits for industry and farmers have been

treatment trains of the Tenorio WWTP in San Luis Potosi

acknowledged due to the reliable supply of a drought-

consistently produced recycled water of the quality required

proof alternative water resource.

for agricultural irrigation, environmental enhancement and

Environmental benefits consisted in the rehabilitation of

industrial uses.

the stabilisation pond into a natural wetland, preserving

The major challenge was the investigation and the

biodiversity and providing habitat for wild birds and

improvement of recycled water quality for industrial

other animals.

reuse. Conductivity, silica and hardness were the mean par-

A programme to implement a protected area with a miti-

ameters to be improved and a good balance was achieved

gation zone is in progress to assure the long-term

by lowering silica level, which allowed increase of the

preservation of the restored micro-ecosystem.

number of concentration cycles in the cooling towers, in

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Sustainable water management with multi-quality recycled water production

order to compensate the slightly higher salinity observed during certain periods.

At the present, after 6 years of operation, the power plant management consider that the operation with recycled water is reliable, and have also expressed their desire to prepare a feasibility study to evaluate the installation of reverse osmosis units to reduce silica levels to 10 ppm which will allow them to stop using groundwater and replace it 100% by recycled water.

The irrigation of 500 ha with good quality recycled water reduced water-related diseases and increased the public acceptance of the crops. The aquifer balance of one of the aquifers has been recovered by the substitution of the groundwater with recycled water for industrial and agricultural uses.

The satisfactory operation of the power plant with recycled water encouraged the industry to explore new possibilities of improved treatment. Finally, other industries are interested in substituting their groundwater consumption with recycled water given the economic benefits and the demonstrated reliability of this water reuse system.

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REFERENCES Diario Oficial de la Federación  Actualización de la disponibilidad media anual de agua subterránea acuífero (2411) San Luis Potosi, Estado de San Luis Potosi.

Equihua, L. O.  Reuso de agua en la agricultura y en la industria en México: Caso del Proyecto San Luis Potosi, Foro del Agua 2006.

Olivo, S. & Martínez, J. B.  Saneamiento integral de las aguas residuales de la zona conurbada de San Luis Potosi-Soledad de Graciano Sánchez, S.L.P, Comisión Nacional del Agua, Gerencia Estatal en San Luis Potosi, San Luis Potosi, CONAGUA Congress.

Rojas, A.  Experiencia de reuso del agua tratada en la Zona Metropolitana de San Luis Potosi. Jornadas técnicas sobre la recarga artificial de acuíferos y reuso del Agua, Instituo de Ingeniería UNAM, 9–10 June 2011, Mexico DF, Mexico.

Standard Methods  Standard Methods for the Examination of Water and Wastewater, 21st edn. American Public Health Association, American Water Works Association and Water Environment Federation.

WHO  Guidelines for the Safe Use of Wastewater, Excreta and Greywater. Volume 2: Wastewater Use in Agriculture.

3rd edn. World Health Organization, Geneva, Switzerland.

First received 10 February 2013; accepted in revised form 29 April 2013. Available online 8 July 2013

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Improving biological phosphorus removal in membrane bioreactors – a pilot study S. Smith, G. Kim, L. Doan and H. Roh

ABSTRACT With increasing water reuse applications and possible stringent regulations of phosphorus content in secondary and tertiary effluent discharge in Florida, USA, alternative technologies beyond conventional treatment processes require implementation to achieve low phosphorus (P) and nitrogen (N) concentrations. A pilot scale membrane bioreactor (MBR) system, operated in Florida, adopted the University of Cape Town (UCT) biological process for the treatment of domestic wastewater. The system operated for 280 days at a wastewater treatment facility with total hydraulic

S. Smith (corresponding author) G. Kim L. Doan H. Roh Doosan Hydro Technology, LLC, 912 Chad Lane, Tampa, FL 33619, USA E-mail: ssmith@doosanhydro.com

retention time (HRT) of 7 h and sludge retention time (SRT) of 20 days. Operating conditions were controlled to maintain specific dissolved oxygen (DO) concentrations in the reactors, operate at suitable return activated sludge (RAS) rates and to waste from the appropriate reactor. This process favored biological phosphorus removal and achieved 94.1% removal efficiency. Additionally, chemical oxygen demand (COD) and N removal were achieved at 93.9% and 86.6%, respectively.

Membrane operation and maintenance did not affect the biological P removal performance but enhanced the process given the different operating requirements compared to that required with the conventional UCT process alone. Conclusively, the result of the pilot study demonstrated improvement in biological phosphorus removal. The UCT-MBR process tested achieved average effluent nitrogen and phosphorus concentrations of 5 mg/L as N and 0.3 mg/L as P. Key words

| enhanced biological phosphorus removal (EBPR), membrane bioreactor, phosphorus removal, water reuse

INTRODUCTION Membrane bioreactors (MBRs) are becoming the advanced

treated for the additional removal of nutrient and contami-

solution for water reuse as fresh water demands continue

nants using advanced technologies such as reverse osmosis

to increase and environmental contamination of drinking

technology (Comerton et al. ). The lack of US federal

water sources becomes of greater concern. As stated by

regulations governing water reuse treatment criteria then

the National Research Council (NRC), wastewater reuse

places responsibility on local and state agencies to develop

is intended to be utilized as a means to recover resources

such regulations (USEPA ). Water quality discharge

such as nutrients, energy and water (NRC ). In the

limits, specifically nitrogen and phosphorus, established

case that water is being recovered for reuse or solely dis-

are dependent on the specific application and receiving

charged as treated wastewater, water quality is important.

water body for which effluent is discharged. These regu-

Depending on the application, stringent effluent limits are

lations are important for the protection of aquatic

specified for the protection of public health and the

systems harmed by the effects of nutrient loading which

environment. For such reasons, MBRs are most practical

can increase algae growth, develop algal blooms, deplete

to achieve suitable effluent quality that can be further

oxygen

doi: 10.2166/wrd.2013.119

concentrations

and

decrease

water

clarity

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(USEPA b). Several guidelines can apply and have

treatment, such as with the UCT (University of Cape

been summarized by the United States Environmental Pro-

Town) process, in conjunction with coagulant for the

tection Agency (USEPA) in their 2012 Guidelines for

additional removal of phosphorus (Wentzel et al. ;

Water Reuse Report.

Comeau et al. ; Rittmann & McCarty ; Tchobano-

Several US states, including California, Nevada, Ari-

glous et al. ; USEPA a). This is feasible due to

zona, and Texas, practice water reuse as a means for

the nitrogen removal process being well known and

water conservation and groundwater recharge (USEPA

easily optimized based on the design and operating par-

). The list extends to worldwide countries, including

ameters of the biological system. Phosphorus, on the

Singapore, Saudi Arabia, Australia and Israel (Bahri &

other hand, can be chemically or biologically removed.

Asano ). This further emphasizes the importance for

Chemical treatment involves direct precipitation (as

appropriate water quality regulation, especially with

implied earlier with the use of coagulant) for the physical

regard to discharge of high nutrient concentrations and

removal of P compounds whilst biological removal

harmful contaminants. The California Department of

involves bacteria removing phosphorus via their meta-

Public Health (CDPH), for example, regulates wastewater

bolic pathways (USEPA a). Although enhanced

reuse under the water recycling criteria, commonly

biological phosphorus removal (EBPR) can be optimized

known as the Title 22 reuse criteria (CDPH a, b).

for the general Florida P requirements, there are treat-

However, these regulations do not address nutrient cri-

ment limitations and performance instability, especially

teria on a statewide basis and are controlled depending

with fluctuating wastewater and sludge characteristics

on the geographical region and receiving water body

( Jenkins & Tandoi ; Liu et al. ; Mino et al.

type (King ). However, in other countries, as previous

). If biological phosphorus removal can be enhanced

literature has referenced, such as Germany and the Neth-

alongside MBRs, it potentially reduces the coagulation

erlands,

requirement with the UCT or other nutrient removal pro-

stringent

regulations

have

already

been

implemented with discharge criteria of 0.5 and 0.15 mg/

cess (Galil et al. ; Lee et al. ; Monclús et al.

L as phosphorus (P) for the respective countries (Lesjean

). With the new regulations to be implemented,

et al. ).

increasing the potential for P removal prior to coagulant

Current Florida general wastewater regulations permit

use will directly aid in reducing coagulant dose require-

discharge concentrations for phosphorus and nitrogen are

ments to achieve the low P limit. Even more so, it can

1 mg/L as P and 3 mg/L as nitrogen (N). Future regu-

reduce the effluent P sufficiently for further reduction by

lations from the Florida Department of Environmental

additional membrane or ion exchange technologies

Protection (FDEP) may impose even more stringent nutri-

(USEPA b). This study evaluates the feasibility of a

ent discharge requirements on wastewater treatment and/

UCT biological process combined with membrane tech-

or water reclamation plants if approved by USEPA (Mat-

nology (MBR) for the efficient removal of both N and P

thews et al. ). More recently, the nutrient criteria for

concentrations, more specifically P, without additional

streams, lakes and estuaries has been approved by the

chemical requirements.

USEPA in late 2012. The regulation is being implemented to protect high quality waters and to prevent further impairment of waters including estuarine, coastal and

MATERIALS AND METHODS

inland waters using a measurable criteria (King ).

Phosphorus and nitrogen concentrations as low as

MBR pilot system

0.05 mg/L as P and 1.27 mg/L as N are to be implemented for secondary or tertiary effluent discharge to estuaries and

The pilot system was designed for the operation of the

rivers or lakes (USEPA ).

UCT process and consisted of an intake system, fine

In general, the current water quality requirements for

screen, biological reactors, and a membrane tank along

N and P can be achieved successfully using biological

with ancillary equipment as shown in the process flow

27

S. Smith et al.

Figure 1

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Improving biological phosphorus removal in UCT-MBR

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Process flow schematic for the UCT-MBR pilot.

diagram in Figure 1. The total volume of the biological 3

reactors was 6.3 m including the anaerobic, anoxic and

LMH (L/m2 h). General MBR operational set points and values were in accordance with the manufacturer’s specifi-

aerobic reactors while the MBR membrane tank volume

cations for filtration, backwash, maintenance cleaning and

was 1.5 m3. The system was designed to isolate membrane

clean-in-place (CIP) cleaning.

filtration from the biological process and allow sludge wasting from the membrane tank as opposed to wasting

Process operation

from the aerobic reactor. The intake was screened through a 1.0 mm perforated drum screen (Cleantek Water Sol-

The MBR pilot system was operated over 280 days at the

utions, Sweden). Each reactor was designed as a

Howard F. Curren advanced wastewater treatment plant

completed mixed reactor using industrial mixers (Light-

(AWTP) in Florida, USA, with domestic wastewater over

nin, USA). Rotary lobe pumps (Boerger LLC, Germany)

seasonal periods – summer and winter. The pilot system

recirculated sludge from the aerobic to the anoxic and

was installed near the influent end of the primary clarifier

from the anoxic to the anaerobic reactor and sludge

and was seeded with mixed liquor gathered from the

pump (Mudsucker, USA) controlled the sludge retention

AWTP aerobic and denitrification (anoxic) return acti-

time (SRT) by wasting from the MBR tank. Return acti-

vated sludge (RAS) lines. The concentration of the

vated sludge (RAS) from the MBR tank occurred by

seeded sludge was 3 g/L. Wastewater was withdrawn at

gravity overflow. Additional equipment required for mem-

the influent of the clarifier and pumped to the pilot

brane operation, air scouring, and aeration include self-

system through a coarse screen prior to the system drum

priming centrifugal pumps for the feed (Pacer Pumps,

screen.

USA) and filtrate (Iwaki America, USA) and rotary

The UCT process hydraulic retention time (HRT) was

lobe blowers (Dresser Roots, USA) for aeration and air

fixed at 7 h and the SRT was controlled at 20 days. Wast-

scouring.

ing also controlled the mixed liquor suspended solids

The MBR system utilized a submerged, polyvinylidene

(MLSS) below 10 g/L in the biological reactors and

fluoride (PVDF) hollow fiber microfiltration membrane of

below 12 g/L in the MBR tank. Fixed blower operation

nominal pore size 0.1 μm. Two membrane elements were

maintained the dissolved oxygen (DO) concentration in

installed into the MBR tank, each with 25 m2 surface area.

the aerobic reactor at 2 mg/L. Membrane operation

3

Pilot design capacity varied between 19–26 m /d and was

included four operational steps including filtration, back-

dependent on membrane flux operation between 18–24

wash, chemical enhanced backwash (CEB) and CIP.

28

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Improving biological phosphorus removal in UCT-MBR

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Maintenance cleaning was completed with sodium hypo-

performance. Standard methods and Hach Test’N Tube

chlorite (NaOCl) and citric acid (if necessary). CEB

Plus™ kits (HachTNTplus™) with the UV-visible spectro-

cleaning was performed once a week using a filtration/

photometer (Hach, USA) were used for analyses (APHA/

backwash cycle counter or based on a trans-membrane

AWWA/WEF ). These utilized USEPA methods

pressure (TMP) trigger set point. MBR filtrate flow was

including Methods 365.1 and 365.3 for P and Method

controlled according to the variable frequency drive.

410.4 for chemical oxygen demand (COD) and soluble

This, in turn, fixed the HRT of the biological process.

COD (sCOD). Ammonia utilized Method 350.1, 351.1

CIP cleaning was triggered based on elapsed time of oper-

and 351.2. Nitrate, nitrite, and phosphate concentrations

ation (every 6 months) and based on the TMP observed.

were confirmed using ion chromatography (Dionex,

Table 1 describes the operating parameters of the UCT

USA) based on the Standard Method SM4110B. Turbid-

process and the MBR membrane during this study.

ity of the filtrate was also verified using the Standard Method SM2130B using the portable and online sensor

Analytical methods

(Hach,

USA).

Lastly,

biochemical

oxygen

demand

(BOD) was measured based on the AWWA Standard The pilot system was monitored utilizing online sensors

Method (SM 5210B). MLSS and mixed liquor volatile

and through laboratory analyses conducted on weekly

suspended solids (MLVSS) were also measured using

samples collected. Online sensors installed included pH,

AWWA Standard Methods (SM2540D and SM2540E

ORP (oxidation reduction potential), DO and turbidity

respectively).

(Hach, USA). The pH, ORP and DO sensors were installed at the beginning and end of each reactor to monitor the water quality. The DO sensor in the aerobic

RESULTS AND DISCUSSION

reactor was utilized to control the DO concentration in the aerobic tank by means of controlling the operational

Biological performance

speed of the aeration blower. A portable multi-probe sensor (WTW, Germany) was used for system monitoring

Evaluation of the pilot results indicated that the modified

and for online sensor verifications especially for DO, pH

UCT-MBR process efficiently removed phosphorus beyond

and ORP.

previous technological limitations. Complete nitrification

Weekly sampling and analyses were conducted for evaluation

of

nutrient

removal

and

membrane

was achieved in the system as indicated by the low concentration of ammonia in the effluent. Denitrification, however, was incomplete contributing to N effluent con-

Table 1

|

centrations averaging above 4 mg/L as N. The minimum MBR membrane operating parameters for UCT

Parameter

Value/Set point

Filtrate flow rate

15–23 L/min (Q)

Filtrate flux

18–24 LMH

Air scouring flow rate

54–170 L/min

MBR tank feed flow rate

5Q (75–115 L/min)

RAS recirculation to aerobic and anaerobic tank

3Q-4Q (45–92 L/min)

effluent N and P achieved was 1.23 and 0.001 mg/L, respectively. However, these were not achieved in conjunction with each other. Evaluation of the overall UCT process indicated efficient removal of COD, BOD, nitrogen, phosphorus and ammonia from the wastewater throughout the study and each are shown in Table 2 below.

The MLSS concentration was monitored during the

Filtration:Backwash

9 min:1 min

study by means of sampling. Wasting was not conducted

CEB

Every 1,000 filtration cycles

initially until the MLSS concentrations increased above

CIP

Every 6 months or TMP > 28 kPa

30 days after start-up operation. Figure 2 shows the

6 g/L in the aerobic reactor. This occurred approximately MLSS trend throughout the study. Solids concentration

29

S. Smith et al.

Table 2

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Biological performance of UCT-MBR

Influent Unit

Total

Effluent Soluble

Total

Soluble

Removal efficiency

COD

mg/L

513 ± 102

214 ±35

31 ± 14

–

93.9 ± 2.7

BOD

mg/L

173 ± 58

–

2 ±4

–

98.8 ± 2.4

Total nitrogen

mg/L as N

37 ± 7

30 ± 4

5±3

5±2

86.6 ± 5.7

Total phosphorus

mg/l as P

5.39 ± 1.12

2.53 ± 0.10

0.28 ± 0.32

0.29 ± 0.40

94.1 ± 8.3

Ammonia

mg/L as N

–

27 ± 4

–

0.17 ± 0.55

99.4 ± 2.0

Nitrate

mg/L as N

–

0.04 ± 0.05

–

3.5 ± 2.7

–

nitrification and organic oxidation. The COD and BOD trend are shown in Figure 3.

As previously mentioned, high phosphorus removal was achieved during this study. Figure 4 demonstrates the phosphorus and nitrogen removal trend throughout the study and the effects of process operation on P removal including variations in wastewater characteristics.

More so, the changes in internal sludge recirculation (RAS) did have some effect with some decrease in removal efficiency observed for both P and N removal especially after the second CIP clean. Towards the end Figure 2

|

MLSS Concentration for the UCT-MBR pilot.

of the pilot study, nitrogen removal was beginning to decline and become more unstable as further demonstrated by the effluent N and P concentrations in

continued to increase even after commencing wasting indicating rapid growth in the reactors. The variations observed were as a direct result of sludge loss during CIP cleaning.

Additionally, operation of the UCT process with 4Q

Figure 5. This interference was directly caused by the changing wastewater characteristics and lower internal recirculation rates (3Q). Furthermore, this demonstrated competition of phosphorus removing organisms (phosphorus

showed even distribution of sludge within the biological system. However, energy consumption lowered feasibility for future application. For this reason, just prior to the first CIP, the internal recirculation rates were lowered to 3Q. The wastewater characteristics indicated stable COD and BOD concentrations incoming to the plant during summer and winter periods with a minor dilution in the summer. Importantly, COD concentrations were sufficient to support biological P release and uptake along with denitrification. The optimized DO control of the aeration in the aerobic reactor maintained oxygen transfer despite increase in MLSS concentrations allowing for complete

Figure 3

|

COD and BOD removal efficiency in UCT process.

30

S. Smith et al.

Figure 4

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Improving biological phosphorus removal in UCT-MBR

Journal of Water Reuse and Desalination

Figure 6

Nutrient removal efficiency with UCT process.

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Effluent phosphorus and influent sCOD concentrations in pilot system.

observation and recording of membrane TMP given flux operation was fixed. Fouling was not rapid in this study and TMP values were stable for flux values 18–20 LMH. In addition to this, membrane air scouring was fixed at 170 L/min which contributed to the high DO concentrations observed in the MBR tank. Concentrations varied between 4 and 6 mg/L and were dependent on the MLSS concentration. Overall, membrane performance indicated a robust membrane which can recover after maintenance or CIP cleaning and can be seen in Figure 7.

Figure 5

|

Comparative evaluation of effluent phosphorus and nitrogen concentration.

Biological phosphorus removal Given the results of the study, a general mass balance of

accumulating organisms) with denitrification bacteria for

phosphorus must be conducted in order to determine

available COD and is trended in Figure 6.

the mechanism of phosphorus removal and to confirm

The average N removal did not satisfy the Florida regulation of 3 mg/L as N. Future improvements through increased RAS rates or by increasing the HRT in the anoxic reactor can improve N removal.

Membrane performance Throughout pilot operation, membrane performance was stable and demonstrated effluent water quality with turbidity 0.01 NTU. Throughout the study, flux operation varied between 18 and 24 LMH in order to evaluate membrane

performance

permeability

was

and closely

fouling

trends.

monitored

Membrane

through

the

Figure 7

|

Membrane performance trend with UCT process.

31

S. Smith et al.

biological

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Improving biological phosphorus removal in UCT-MBR

phosphorus

removal

by

‘luxury

uptake’

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4 mg/L were maintained in the membrane tank. More so,

( Jeyanayagam ). The phosphorus mass balance can

this

be directly determined based on the complete analysis

removal as evident by the ammonium concentrations

of the soluble P content within the biological process,

observed within the system and shown in Table 3. Hence,

as well as the P content within the biomass from the

wasting to control SRT occurs from the reactor with the

RAS and waste activated sludge (WAS) lines. The bound-

highest uptake of phosphorus. This aided in the efficient

ary layer for phosphorus mass balance was determined

removal

and is shown in Figure 8.

observed also suggest some colloidal rejection of phos-

Samples analyzed during the study provide the phos-

condition

phorus

of

enhanced

nitrification

phosphorus.

further

The

reducing

effluent

the

and

ammonia

concentrations

effluent

phosphorus

phorus profile of the biological process and are listed in

concentration or by additional phosphorus uptake at the

Table 3. Initial evaluation of the phosphorus profile

surface of the membrane by the biofilm attached at the sur-

within the biological reactors demonstrates suitable phos-

face. This requires additional study and evaluation for

phorus release in the anaerobic reactor and significant

confirmation.

uptake in the anoxic, aerobic and MBR reactors. Further

Additionally shown in Table 3 are the nitrogen and

evaluation of the profile demonstrates additional P uptake

sCOD profiles within each biological reactor. This also

in the MBR tank from which sludge is wasted. P uptake

demonstrates the effect of nitrogen, particularly nitrate, on

in the aerobic reactor was suitable due to the fixed DO

the phosphorus removal mechanism by biological uptake.

concentration at 2 mg/L. Membrane air scouring contribu-

The results demonstrate consistent low nitrate concen-

ted to the additional P uptake as DO concentrations above

tration in the anaerobic reactor. This directly contributed

Figure 8

Table 3

|

|

Mass balance boundary layer for phosphorus.

Phosphorus and nitrogen concentrations in reactors

Soluble COD

Soluble phosphorus

Soluble total nitrogen

Soluble nitrate

Ammonium

Sample

(mg/L)

(mg/L as P)

(mg/L as N)

(mg/L as N)

(mg/L as N)

Influent

214 ± 35

2.53 ± 0.10

30 ± 4

–

Anaerobic

49 ± 13

9.42 ± 5.21

8±3

0.74 ± 3

Anoxic

47 ± 21

1.75 ± 0.94

4±2

2±3

27 ± 4 5±3 0.57 ± 0.80

Aerobic

45 ± 13

1.02 ± 1.43

4±2

3±3

0.48 ± 0.89

MBR

46 ± 14

0.48 ± 1.07

4±2

3±3

0.13 ± 0.51

Effluent

31 ± 14

0.28 ± 0.32

5±2

4±3

0.17 ± 0.55

32

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Improving biological phosphorus removal in UCT-MBR

to the efficient phosphorus release observed in the anaerobic reactor and reduced competition.

CONCLUSIONS The UCT-MBR pilot system was evaluated for improvement of the EBPR process as a solution to the upcoming stringent regulations for P content in secondary and tertiary discharge in Florida, USA. The EBPR was enhanced by sustaining optimal conditions favorable for the release and uptake of phosphorus. Important design factors and operating parameters were controlled and were observed to enhance biological performance whilst eliminating biological competition. Phosphorus concentrations in the effluent averaged at 0.3 mg/L as P under appropriate operating conditions. Nitrification was also further enhanced within the MBR system where nitrogen removal achieved average effluent concentrations of 5 mg/L as N. The results of this study provided information relevant for parallel assessment of both the UCT process and MBR membrane performance. The process configuration maintained optimal DO and recirculation rate conditions supporting phosphorus luxury uptake and biological nitrogen removal. These key operating parameters enhanced EBPR without the use of coagulants or precipitation mechanisms. Therefore, enhanced biological phosphorus removal with MBR process application is feasible and is dependent on the appropriate biological process utilized and importantly, the operating conditions of the biological process.

REFERENCES APHA/AWWA/WEF  Standard Methods for Examination of Water and Wastewater, 22nd edn.

American Public Health Association/American Water Works Association/Water Environment Federation, Washington, DC. Bahri, A. & Asano, T.  Global Challenges to Wastewater Reclamation and Reuse. In: On the Water Front - Selections from the 2010 World Water Week in Stockholm (J. Lundqvist,

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ed.). Stockholm International Water Institute (SIWI), Stockholm, Vol. 2, pp. 64–72.

CDPH a California Department of Public Health – Regulations Related to Recycled Water January 2009. In: Titles 22 and 17 California Code of Regulations – California Department of Public Health’s Recycled Water Regulations.

California, pp. 10–33.

CDPH b Treatment Technology Report for Recycled Water.

State of California – Health and Human Services Agency.

Carpinteria, California, pp. 60.

Comeau, Y., Rabionwitz, B., Hall, K. J. & Oldham, W. K.  Phosphate release and uptake in enhanced biological phosphorus removal from wastewater. J. (Wat. Pollut.

Control Fed.) 59 (7), 707–715.

Comerton, A. M., Andrews, R. C. & Bagley, D. M.  Evaluation of an MBR–RO system to produce high quality reuse water: Microbial control, DBP formation and nitrate. Wat. Res. 39 (16), 3982–3990.

Galil, N., Malachi, K. B.-D. & Sheindorf, C.  Biological nutrient removal in membrane biological reactors. Environ.

Eng. Sci. 26 (4), 817–824.

Jenkins, D. & Tandoi, V.  The applied microbiology of enhanced biological phosphate removal – accomplishments and needs. Wat. Res. 25 (12), 1471–1478.

Jeyanayagam, S.  True confessions of the biological nutrient removal process. Florida Wat. Res. J. (January), 37–46.

King, E.  Introduction to Development of Numeric Nutrient Criteria in the State of Florida (ed.) E.S.A. Board, EPA Office of Water, Washington, DC. Lee, H., Han, J. & Yun, Z.  Biological nitrogen and phosphorus removal in UCT-type MBR process. Wat. Sci. Technol. 59 (11), 2093–2099.

Lesjean, B., Gnirss, R., Adam, C., Kraume, M. & Luck, F.  Enhanced biological phosphorus removal process implemented in membrane bioreactors to improve phosphorous recovery and recycling. Wat. Sci. Technol. 48 (1), 87–94.

Liu, W.-T., Nakamura, K., Matsuo, T. & Mino, T.  Internal energy-based competition between polyphosphate- and glycogen-accumulating bacteria in biological phosphorus removal reactors – Effect of P/C feeding ratio. Wat. Res. 31 (6), 1430–1438.

Matthews, R., Cisterna, R. & Sharp, R.  Impacts of Florida’s new and proposed numeric criteria on water reuse opportunities. 26th Annual Water Reuse Symposium, September 11–14, 2011, Phoenix, AZ. Mino, T., van Loosdrecht, M. C. M. & Heijnen, J. J.  Microbiology and biochemistry of the enhanced biological phosphate removal process. Wat. Res. 32 (11), 3193–3207.

Monclús, H., Sipma, J., Ferrero, G., Comas, J. & Rodriguez-Roda, I.  Optimization of biological nutrient removal in a pilot plant UCT-MBR treating municipal wastewater during startup. Desalination 250 (2), 592–597.

NRC  Water Reuse: Potential for Expanding the Nation’s Water Supply Through Reuse of Municipal Wastewater.

National Academies Press, Washington, DC.

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Rittmann, B. E. & McCarty, P. L.  Environmental Biotechnology: Principles and Applications. McGraw-Hill, New York.

Tchobanoglous, G., Burton, F. L., Eddy, M. & Stensel, H. D.  Wastewater Engineering: Treatment and Reuse, 4th edn.

McGraw-Hill, New York.

USEPA  State Adoption of Numeric Nutrient Standards (1998–2008).

USEPA a Nutrient Control Design Manual – State of Technology Review Report. EPA, EPA/600/R09/012.

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USEPA b Nutrient control design manual state of technology review report. US Environmental Protection Agency, National Risk Management Research Laboratory, Water Supply and Water Resources Division.

USEPA  Water Quality Standards for the State of Florida’s Lakes and Flowing Waters (ed.) EPA, Vol. 40 CFR Part 131, pp. 197.

USEPA  Guidelines for Water Reuse. In: EPA/600/R-12/618.

Wentzel, M., Lötter, L., Loewenthal, R. & Marais, G.  Metabolic behaviour of Acinetobacter spp. in enhanced biological phosphorus removal – a biochemical model. Wat. SA 12 (4), 209–224.

First received 1 March 2013; accepted in revised form 19 May 2013. Available online 1 July 2013

34

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Seawater desalination using forward osmosis process Parida Venketeswari, Ong Say Leong and Ng How Yong

ABSTRACT This study aims to evaluate the feasibility of the forward osmosis (FO) process for seawater desalination. The leakage of boron from the seawater into the draw solution was also studied.

According to the WHO guideline, the maximum permissible limit of boron in drinking water is 2.4 ppm. Preliminary results of boron rejection by forward osmosis membrane were found to be 60–70%. Minimal fouling of the FO membrane was observed in the experimental run spanning over 70 days. Under the given set of test conditions, flux of 1.4 L m

2

h

1

was found throughout the

run and there was no significant decline in the flux. With a flux recovery of 40% which is the same

Parida Venketeswari Ong Say Leong Ng How Yong (corresponding author) Centre for Water Research, Department of Civil and Environmental Engineering, Faculty of Engineering, National University of Singapore, Block E1A #07-03, 1 Engineering Drive 2, Singapore 117576 E-mail: howyongng@nus.edu.sg

as that of the reverse osmosis (RO) process, FO could be potentially utilized for seawater desalination applications.

Key words

| boron rejection, forward osmosis, membrane fouling, scaling, seawater desalination

INTRODUCTION The current scenario of global water crisis demands innova-

(CTA) could draw about 5 L of potable water from seawater

tive and novel technologies that not only provide elevated

using 1 kg of glucose–fructose draw solution. It was

throughput and productivity, but also ensure optimum

intended to commercialize seawater desalination to produce

energy efficiency at the same time. Today, the most consist-

a stand-alone emergency water supply on lifeboats.

ent and reliable technology to extract fresh water from

Recently, other draw solutions such as ammonium bicarbon-

seawater is the reverse osmosis (RO) process (Elimelech &

ate (McCutcheon et al. ) have been experimented with

Phillip ). However, the energy consumed by this process,

for their potential use in solute extraction and reusability.

including the pressure exchangers at the brine stream is

In these tests, 0.5 M NaCl representing seawater was used

3

of water produced (Mezher et al.

as the feed while 6 M ammonium bicarbonate was employed

). Furthermore, it also faces the issue of membrane

as draw solution. Preliminary results substantiated that FO

fouling.

membrane helped produce higher flux compared to RO

roughly 3–4 kWh m

At the turn of the new century, scientists have shown

membrane. A recent research article (Phuntsho et al. )

keen interest in electro-deionization technologies, forward

reported using fertilizer solutions as draw solutions for sea-

osmosis (FO) process and nanofiltration using carbon nano-

water desalination using the FO process.

tubes, in order to address the challenges faced by the RO

Earlier research on seawater desalination using the FO

process (Shea ). The FO process is a viable prospect

process was generally concerned with the choice of draw

for seawater desalination by extracting water molecules

solution and flux recovery (Kravath & Davis ; McGin-

from the seawater into a draw solution. In addition to the

nis et al. ) However, fouling propensity of seawater on

applications of FO available in the literature (Cath et al.

the FO membrane, the necessity for any seawater pretreat-

), it could be prudently employed for seawater desalina-

ment prior to passage through the FO membrane, and

tion due to its low energy consumption and lower fouling

boron rejection by the FO membrane have not been

propensity. Reports (Kessler & Moody ) suggest that a

studied in detail. Recently, Jin et al. () investigated

flat sheet FO membrane made from cellulose triacetate

boron

doi: 10.2166/wrd.2013.009

passage

through the

FO membrane

in two

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Seawater desalination using forward osmosis process

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membrane orientation modes, namely the dense layer

solution due to its high osmotic pressure obtained at low

facing the feed solution and the dense layer facing the

solute concentrations, comparatively lower cost, low toxicity

draw solution. Under simulated test conditions, artificial

and ease of reconcentration through low pressure systems,

seawater (i.e., 0.5 M NaCl) was tested at batch scale with

such as nanofiltration. Nanofiltration technology is used

the addition of boron solution. Boron rejection was better

for the separation of water molecules from the concentrated

for the dense layer facing the feed solution mode due to

draw solute.

effective and efficient rejection of boron. Furthermore, it

The FO flat sheet membrane used was purchased from

was reported that the boron rejection increased with

HTI Inc., USA. A 0.45-μm polyethersulphone (PES) MF

increasing membrane water flux.

membrane was used to treat seawater prior to filtration

Nevertheless, there is a necessity to use actual seawater

with FO membrane.

and run it in continuous mode to investigate the boron flux

The experimental set-up (Figure 1) consisted of sub-

and hence its rejection by the FO membrane. Fouling due to

merged FO membrane modules in seawater, with the draw

seawater exacerbates the plant throughput, thus affecting

solution circulating inside it. The draw solution tanks were

the water production efficiency. As far as the RO process

placed on a weighing scale to measure the change in the

is concerned, fouling in seawater desalination is basically

weight of the draw tank, from which the membrane water

due to particulate matter, organic compounds and biological

flux was calculated. Two types of seawater feed were

growth (Magara et al. ). Furthermore, Huertas et al.

tested simultaneously, one pretreated with MF and the

() have investigated the impact of biofouling on RO

other with no pretreatment. This helped study the effects

membrane boron rejection. It was observed that the boron

of pretreating the seawater before the actual FO filtration

rejection dropped by 45% for RO membrane fouled by P.

process. A seawater retention time of 3 days was maintained

aeruginosa PAO1. The decrease in boron rejection was

in the FO reactor tanks.

attributed to biofilm growth that enhanced concentration

Boron determination in seawater feed and subsequent

polarization of salts, including boron, near the membrane

seepage into the draw solution were measured using ICP-

surface. Generally, a decrease in boron rejection is observed

OES (inductively coupled plasma optical emission spec-

when biofouling occurs. Therefore, research is necessary

trometry) method at 249.772 nm as per ASTM-3120 B

into membrane fouling, boron rejection by the FO mem-

protocol. An ion chromatogram was used to monitor the

brane, impact of pretreatment of seawater using the

ions present in the seawater and draw solution. Turbidity,

microfilter (MF) membrane and overall recovery of the

SDI and pH of the feed seawater solutions were measured

system for seawater desalination. Tapping the osmotic gradi-

intermittently. A nephelometer (Hach 2100 N Turbiditi-

ent energy of the highly concentrated sodium sulphate as a

meter, USA) was used to measure solution turbidity. GE

draw solution in the FO process, seawater was desalinated

Osmonics’ (USA) SDI kit was used for measuring the SDI

at laboratory scale in this study. Studies on flux perform-

of feed seawater solution. The SDI is a measure of the

ance, fouling and boron rejection of the FO membrane

capacity of any feedwater to foul RO membranes. The SDI

were carried out.

is determined from the fouling rate of a 0.45-μm filter at a pressure of 30 psi and is described in the ASTM standard method D4189 (Eaton et al. ). At the end of the exper-

MATERIALS AND METHODS

iments, the FO membrane was subjected to destructive testing to investigate the degree of fouling on its surface

Surface seawater with pH of about 8.1 and total dissolved

using scanning electron microscopy (SEM-XL-30-FEG, Phi-

solids of 32,500 ppm was used. It had a nominal silt density

lips, Germany). Prior to taking the SEM images, membrane

index (SDI) of 4, turbidity of 1–2 NTU and total organic

samples were prepared by freezing the membrane at

50 C

carbon of about 4–5 ppm. Sodium sulphate solution with a

in a chiller for 2 hours followed by freeze drying at

70 C

W

W

concentration of 1.15 M was employed as the concentrated

and 0.01 mbar (vacuum conditions) for 7–8 hours. This

draw solution. Sodium sulphate is used as a suitable draw

was done in order to keep intact the foulant layer of the

36

Figure 1

P. Venketeswari et al.

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Seawater desalination using forward osmosis process

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Submerged membrane reactor set-up.

membrane, without the formation of cracks upon direct

0.2 NTU are mostly beneficial as RO influent. It is to be

drying.

noted that these parameters are mere indicators of a typical feedwater’s fouling potential and may not be singled out as the only cause of fouling. In this study, results on turbidity

RESULTS AND DISCUSSION

and SDI showed reduction in each parameter to a consider-

Over 70 days of the experiment run, no cleaning of the mem-

seawater were 4.2 and 3, respectively. The raw seawater tur-

able extent. The SDI15 of raw seawater and MF-pretreated brane was required, since the FO water flux decline was

bidity was about 1–2 NTU, while that after MF treatment

negligible over the entire period of the experiment. The

was about 0.5 NTU. Figure 2 shows the photographic

water flux was maintained at around 1.4 L m

2

h 1.

images of SDI filter strips tested for raw seawater and MFpretreated seawater. Thus, MF pretreatment did help in

Effects of MF pretreatment

reducing the turbidity and SDI of the feed seawater significantly.

In theory, MF pretreatment should impact the membrane fouling tendency since it can remove fine particles larger

Seawater fouling of FO membrane

than 0.1 μm, thereby reducing the fouling tendency of the feed water. The MF pretreatment thus aids in the removal

As reported in the literature, RO membranes are highly vul-

of suspended particulate matter to alleviate fouling and

nerable to biofouling. In addition, the compact cake layer so

ageing, and reducing the frequency of intermittent cleaning

formed is difficult to remove unless chemical cleaning is

for the downstream membrane process – FO process in this

initiated. However, in the case of FO membrane, the

study. SDI and turbidity are indicators for the quality and

degree of cake formation would be less compact since no

efficiency of pretreatment of a feed water sample. Generally,

hydraulic energy is used to force the feed seawater across

SDI less than 3 is preferable for RO influent (Greenlee et al.

the membrane (Mi & Elimelech ). The draw solution

), while feedwaters with SDI greater than 4 need a suit-

on the other side of the membrane ‘sucks’ water from the

able pretreatment. Similarly, turbidity values less than

feed side across the FO membrane, thus imparting less

37

Figure 2

P. Venketeswari et al.

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Seawater desalination using forward osmosis process

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SDI15 filter strips after testing for (a) feed seawater, (b) MF-pretreated seawater.

pressure on the foulants on the feed side and making the

Furthermore, the experimental flux obtained was lower

foulant layer less compact and easily removable. The water

than the critical flux above which fouling occurred. How-

flux decline and normalized flux profile of the membrane

ever, a slightly higher flux was observed for the FO

was also monitored in this study (Figure 3). It is observed

membrane subjected to MF-pretreated seawater. Hence,

that the flux decline was not significant for both with and

the seawater with MF pretreatment helped to improve the

without MF pretreatment. This could be due to the hydro-

FO water flux, but the effects were not very significant in

philic CTA make of the membrane that prevented

this study due to very low experimental water fluxes

excessive fouling on the membrane surface, thereby causing

obtained.

significant flux decline. In addition, due to operation of the

After the completion of 70 days of continuous operation,

membrane in the FO mode, the dense layer facing the feed

the FO membrane surface was analysed using SEM with

seawater

energy dispersive X-ray spectroscopy (EDX) to identify the

Figure 3

|

solution

side

avoided

fouling

Effect of MF pretreatment on flux and normalized flux.

effectively.

38

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Seawater desalination using forward osmosis process

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elemental group composition. The FO membrane subjected

on its surface. It is to be noted that although there were signs

to direct raw seawater showed signs of scaling deposits on

of scaling on the FO membrane surface for the FO mem-

its surface. Figures 4(a)–4(c) show the SEM images of the

brane subjected to non-pretreated seawater, it was not

FO membranes treating MF-pretreated seawater and raw

significant enough to reduce the membrane water flux.

seawater, respectively. At 200× magnification, scaling over

Figure 4(d) shows the photographic image of the FO mem-

the FO membrane surface was much greater for the FO

brane subjected to non-pretreated seawater. The extent of

membrane subjected to non-pretreated seawater. This scal-

fouling on the membrane was not severe.

ing on the FO membrane surface subjected to nonpretreated seawater could be due to the precipitation of cal-

Boron rejection

cium sulphate or calcium carbonate crystals. EDX analysis of the scaled membrane surface (Table 1) confirmed the

Seawater contains boron with a concentration as high as

presence of calcium. The reason for the excessive scaling

5 ppm. When seawater is desalinated by the membrane pro-

observed on the FO membrane surface that was subjected

cess, leakage of boron can be significant. For natural

to non-pretreated seawater could be due to the excessive

seawater of pH 8, boron rejection by the FO membrane is

organic fouling during the initial stages that further led to

low, around 60–70%. Since boron in potable water (i.e.,

inorganic fouling (i.e., scaling) similar to the ‘cake enhanced

drinking water) is fatal to the human body, it is a serious

concentration polarization’ effect (Hoek & Elimelech ).

challenge to prevent boron leakage into the permeate side.

However, for the FO membrane pretreated with MF, the

In the RO process, raising pH in the second pass is one of

extent of organic fouling was low, preventing further scaling

the viable options to reduce boron leakage. Boron specific

Figure 4

|

SEM images of (a) FO membrane treating MF-pretreated seawater – less fouling; FO membrane treating seawater with no pretreatment – excessive scaling 200× (b) and 3,500× (c); and (d) photographic image of FO membrane treating seawater with no pretreatment.

39

Table 1

P. Venketeswari et al.

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Seawater desalination using forward osmosis process

EDX analysis for scaling on FO membrane surface subjected to non-pretreated seawater

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rejection was obtained (Figure 5(b)). This could be attributed to the fact that fouling could reduce boron rejection by hindering back-diffusion of boron into the bulk feedwater,

Elements

wt%

C

7.40

resulting in rising boron concentration near the FO mem-

N

Negligible

brane surface, thus enhancing the boron passage into the

O

76.51

draw solution (Huertas et al. ). As a result, boron con-

Na

0.22

centration in the draw solutions for the FO system with

Mg

0.10

non-pretreated seawater was slightly higher. It is also to be

Al

0.30

noted that a decreasing trend in the FO membrane boron

P

0.24

rejection is due to the accumulation of boron in the draw

S

0.23

tank. Nevertheless, it is concluded that MF pretreatment

K

0.07

of seawater could enhance boron rejection of the FO

Ca

14.46

Fe

0.61

membrane.

Salt rejection

ion exchange resins have also been used. The FO membrane

The overall FO membrane rejection for chloride was con-

could not reject all the boron effectively, with an overall

stant at about 97% at the end of the experimental run

boron rejection of 60%. Figure 5 shows the concentration

(Figure 6).

of boron in the FO reactors and draw solution tanks. It was observed that the concentration of boron kept increasing over the experimental run, owing to its accumulation

CONCLUSION

in the draw tank. Comparing the boron concentrations in draw solutions, it was observed that the boron leakage was

The FO process, in conjunction with a post-treatment pro-

slightly greater when non-pretreated seawater was used,

cess,

unlike the case when MF-pretreated seawater was used in

desalination, provided that the issue of boron rejection

the FO reactor. Thus with MF pretreatment, a better boron

could be tackled effectively. As far as fouling is concerned,

Figure 5

|

could

be

potentially

utilized

for

seawater

Boron (a) concentration profile and (b) rejection percentage by FO membrane subject to MF-pretreated seawater and seawater with no pretreatment over the experimental run of 70 days.

40

Figure 6

P. Venketeswari et al.

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Seawater desalination using forward osmosis process

FO membrane chloride (Cl ) rejection profile.

the FO process has an added advantage since minimal deposition of foulants occurred. MF pretreatment of seawater reduced the FO membrane water flux decline slightly compared to non-pretreated seawater. The normalized flux decline profile affirmed that the FO membrane was able to withstand fouling to a significant extent. The low flux conditions and the CTA FO membrane’s inherent hydrophilic nature had led to minimal fouling or scaling on the membrane surface. The overall boron rejection by the FO membrane was about 60–70%. In order to produce potable water within boron regulation, post-treatment of the diluted draw solution is necessary.

REFERENCES Cath, T. Y., Childress, A. E. & Elimelech, M.  Forward osmosis: principles, applications, and recent developments.

J. Membrane Sci. 281 (1–2), 70–87.

Eaton, L. S., Clesceri, A. E. & Greenberg, A. D. (eds)  Standard Methods Handbook for the Examination of Water and Wastewater. AWWA, APHA, WEF, Washington, DC.

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Elimelech, M. & Phillip, W. A.  The future of seawater desalination: energy, technology, and the environment.

Science 333, 712–717.

Greenlee, L. F., Lawler, D. F., Freeman, B. D., Marrot, B. & Moulin, P.  Reverse osmosis desalination: water sources, technology, and today’s challenges. Water Res. 43 (9), 2317– 2348.

Hoek, E. & Elimelech, M.  Cake-enhanced concentration polarization: a new fouling mechanism for salt-rejecting membranes. Environ. Sci. Technol. 37 (24), 5581–5588.

Huertas, E., Herzberg, M., Oron, G. & Elimelech, M.  Influence of biofouling on boron removal by nanofiltration and reverse osmosis membranes. J. Membrane Sci. 318 (1–2), 264–270.

Jin, X., Tang, C. Y., Gu, Y., She, Q. & Qi, S.  Boric acid permeation in forward osmosis membrane processes: modeling, experiments, and implications. Environ. Sci. Technol. 45 (6), 2323–2330.

Kessler, J. O. & Moody, C. D.  Drinking water from sea water by forward osmosis. Desalination 18 (3), 297–306.

Kravath, R. E. & Davis, J. A.  Desalination of sea water by direct osmosis. Desalination 16 (2), 151–155.

Magara, Y., Kawasaki, M., Sekino, M. & Yamamura, H.  Development of reverse osmosis seawater desalination in Japan. Water Sci. Technol. 41 (10–11), 1–8.

McCutcheon, J. R., McGinnis, R. L. & Elimelech, M.  A novel ammonia–carbon dioxide forward (direct) osmosis desalination process. Desalination 174 (1), 1–11.

McGinnis, R. L., McCutcheon, J. R. & Elimelech, M.  A novel ammonia-carbon dioxide osmotic heat engine for power generation. J. Membrane Sci. 305 (1–2), 13–19.

Mezher, T., Fath, H., Abbas, Z. & Khaled, A.  Technoeconomic assessment and environmental impacts of desalination technologies. Desalination 266, 263–273.

Mi, B. & Elimelech, M.  Organic fouling of forward osmosis membranes: fouling reversibility and cleaning without chemical reagents. J. Membrane Sci. 348 (1–2), 337–345.

Phuntsho, S., Shon, H. K., Hong, S., Lee, S. & Vigneswaran, S.  A novel low energy fertilizer driven forward osmosis desalination for direct fertigation: evaluating the performance of fertilizer draw solutions. J. Membrane Sci. 375 (1–2), 172–181.

Shea, A. L.  Status and Challenges for Desalination in the United States. Japan–USA Joint Conference On Drinking Water Quality Management and Wastewater Control. March 4. Available at: www.niph.go.jp/soshiki/suido/pdf/h21JPUS/ abstract/r9-1.pdf.

First received 9 February 2013; accepted in revised form 7 June 2013. Available online 17 July 2013

41

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Effects on macronutrient contents in soil-plant irrigated with different quality waters and wastewaters M. T. Orta de Velásquez, K. Velázquez Pedroza, I. Yáñez-Noguez, I. Monje-Ramírez and A. E. Campos-Reales-Pineda

ABSTRACT The goals of this research were focused on investigating the effects of irrigation with untreated wastewater, ozone-enhanced primary treated wastewaters (O3EPTW), tap water and tap water þ fertilizer on the macronutrient content in soil and plant tissues. The effect on plant development was evaluated by growing Lactuca sativa in soils irrigated with these different quality waters and wastewaters, and by determining the macronutrients content in water, soil and plants. In this study, the soils irrigated with O3EPTW showed increased organic matter concentrations, which is advantageous for crop cultivation. The electric conductivity for the O3EPTW irrigated soils remained

M. T. Orta de Velásquez (corresponding author) K. Velázquez Pedroza I. Yáñez-Noguez I. Monje-Ramírez A. E. Campos-Reales-Pineda Universidad Nacional Autónoma de México, Instituto de Ingeniería, Edificio 5, 1er Nivel, Cub 213, Circuito Escolar, Ciudad Universitaria, 04510 México DF, México E-mail: mortal@ii.unam.mx

below those of the tap water þ fertilizer and untreated wastewater. The soil irrigated with tap water þ fertilizer showed a marked decrease in pH, and its long-term use could lead to soil acidification. Macronutrient levels in plant tissues (N, K and Mg contents) were similar for all irrigation waters, except for tap water which always remained lower than the others. It was concluded that the use of O3EPTW may become a good irrigation alternative that can be employed without the health risks associated with the use of untreated wastewaters, also reducing the adverse effects on soil’s salinity or acidification.

Key words

| macronutrients, ozone-enhanced primary treated wastewaters (O3EPTW), wastewater reuse

INTRODUCTION Sometimes wastewater is the only available alternative for

available for plant growth; as well as diminishing the soil’s

agricultural irrigation, but its use represents a potential

pH (Kiziloglu et al. ; Adrover et al. ). Kiziloglu

health hazard due to its elevated content of pathogenic

et al. () also reported on the changes in chemical soil

microorganisms, including Helminth eggs. Pathogenic

characteristics (N, P, K, Ca, Mg and Na contents) evaluated

microorganism concentrations can be lowered by the use

after irrigation with untreated, preliminary and primary trea-

of an advanced primary treatment (APT), which provides

ted wastewater. They concluded that the soils irrigated with

an effluent beneficial to agriculture because of its nutrients

wastewater showed an increase on the yield of the plants and

content (Orta de Velásquez et al. ). The nutrients con-

in their macro and microelement content. Hence, waste-

tained in reclaimed wastewater can contribute to crop

water has a high nutritive value that can improve plant

growth, but periodic monitoring of nutrient levels is

growth, reduce fertilizer application and increase crop pro-

needed to avoid an imbalance in nutrient supply for the

ductivities of poor fertility soils. However, while untreated

irrigated plants (Pedrero et al. ). Previous research has

wastewaters can be used on agricultural land for a short

shown that the use of wastewater for crop irrigation may

period of time, primary-treated wastewaters can be used in

increase soil salinity, organic matter content, levels of

sustainable agriculture over a long term (Kiziloglu et al.

exchangeable cations, phosphorus, and other microelements

).

doi: 10.2166/wrd.2013.016

42

M. T. Orta de Velásquez et al.

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Effects on macronutrient contents in soil-plant irrigated with different waters

Conversely, a study in Brazil (Herpin et al. ) found

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METHODS

that the use of a secondary effluent to irrigate coffee crops had three major disadvantages: (1) an increase in soil sodi-

In order to evaluate the effects on macronutrients content (N,

city; (2) a reduction of the soil’s organic matter level with

P, K) and ion concentrations (Naþ, Ca2þ, Mg2þ, and SO2 4 ) in

a decrease in cationic exchange capacity; and (3) a discre-

the soil-plant system, irrigation experiments were carried out

pancy in the nutrient balance for the soil-plant system.

in a greenhouse during 120 days using Italian lettuce (Lactuca

That research also found that the soil’s N, P and S concen-

sativa). For this purpose, five types of water were employed

trations were insufficient for coffee cultivation. It was

for irrigation: tap water, tap water þ fertilizer, untreated

concluded that the macroelements (N, P, K, Mg and Na)

wastewater and ozone-enhanced primary treated wastewaters

content in coffee plant tissues were within the normal

(O3EPTW). The number of analysed samples is specified in

ranges for the plant (with the exception of Ca, for which

each subsection. During the experimentation period, each

higher values were measured). On the other hand, Kiziloglu

type of irrigation water was prepared every time just before

et al. () established that the macronutrients content in

irrigation, according to the procedures described below.

plant tissue depends on the type and quality of water used for irrigation; the P, K, Ca, Mg and Na content in two crops (cauliflower and squash) decreased in the following order: untreated wastewater > pre-treatment > primary treatment > tap water.

Up to this date, there are few investigations regarding macronutrients content in soil-plant systems irrigated with

Types of water used for irrigation

•

Tap water: used as a control to evaluate the evolution of

•

Tap water þ fertilizer: used to simulate ideal nutrient con-

primary treated wastewater (Kiziloglu et al. ), and

sol Multipurpose, manufactured by SQM (Sociedad

lished research in this field focuses only on irrigation with et al. ; Kalavrouziotis et al. ; García-Delgado

•

et al. ), but not on the effects that can be observed on

•

application of ozone at the coagulation step (ozone-

•

productivities for irrigated plants. Nevertheless, the relation-

followed by chlorination (O3 þ NaOCl): carried out in a O3/L H2O, followed by 2 mg/L of NaOCl contacted for

plants was not investigated. Therefore, the aim of the pre-

subjected to an ozone-enhanced primary treatment) on the

of these methods.

O3 disinfection (O3EPTW-A); the combination of ozone semi-batch reactor applying a total ozone dose of 20 mg

ship between the nutrient content of the water, soil and

different quality waters and wastewaters (including those

A and B): these were obtained by treating in the labora-

sand filtration (10 μm sieve) and disinfection by either

during a preliminary evaluation of the influence of the trea-

sent research is to evaluate the effect of the irrigation with

discharges.

Ozone-enhanced primary treated wastewaters (O3EPTW,

Campos-Reales-Pineda et al. (), followed by silica

water’s phytotoxicity and improved germination rates

findings could result in beneficial effects such as improved

the Cerro de la Estrella Wastewater Treatment Plant

tory the influent from the CEWWTP, according to

enhanced primary treatment, O3EAPT), reduced the waste-

ted effluents on plant seedlings. It was mentioned that those

Untreated wastewater: collected from the influent of

influent of this treatment plant mostly receives municipal

ments such as an APT. demonstrated that the use of an APT that combined the

Quimica y Minera de Chile S.A.).

(CEWWTP), located in the southeast of Mexico City. The

macronutrient changes by using physical-chemical treatA previous study (Campos-Reales-Pineda et al. )

ditions for growing L. sativa. It was prepared using the recommended mixture of the commercial fertilizer Ultra-

none with ozonated primary treatment. Most of the pubbiological treatment effluents (Isea et al. ; Heidarpour

the original nutrients content of the soil.

•

60 min.

NaOCl disinfection (O3EPTW-B): dosing only 20 mg/L NaOCl and contacted for 60 min.

macronutrients content in soil and plant tissues of Italian

The chemical oxygen demand (COD), biochemical oxygen

lettuce.

demand (BOD5), total suspended solids (TSS), turbidity

43

M. T. Orta de Velásquez et al.

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Effects on macronutrient contents in soil-plant irrigated with different waters

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and pH were determined according to Standard Methods for the Examination of Water and Wastewater (APHA ).

Faecal coliforms (FC) were quantified by the Membrane Filtration method (NMX-AA-102-SCFI-), using Difco MFC W

selective agar media and incubation in a water bath at 44.5

±2 C for 24 h. Helminth eggs (HE) were determined in W

accordance to the NOM-001-SEMARNAT- procedures.

These physicochemical and microbiological parameters were measured weekly.

Throughout the irrigation experiments, a total of 40 subsamples were collected to produce a composite sample for each type of irrigation water. Cations (Kþ, Naþ, NHþ 4,

2 3 Ca2þ, Mg2þ) and anions (NO 2 , NO3 , SO4 , PO4 ) were

analysed using an ion chromatography system (Model ICS1500, Dionex, Sunnyvale, CA, USA).

Growing L. sativa Figure 1

|

Randomised irrigation arrangement employed in the greenhouse.

A greenhouse with 10 drawers (0.169 m3 each) was used to conduct the irrigation experiments. Each drawer was filled with 75 kg of sandy loam virgin soil suitable for agriculture.

exchangeable cations (Kþ, Naþ, Ca2þ, and Mg2þ) were

Two drawers were used for each type of water and 10 plants

analysed following the NOM-021-SEMARNAT- pro-

of L. sativa were grown in every drawer. Lettuce seedlings

cedures. Kþ and Naþ were measured by flame atomic

were planted in January 2011 and the plants were harvested

emission spectrometry (FAES) using a Single-Channel Digi-

in May 2011. The randomised irrigation arrangement

tal Flame Analyzer (Model EW-02655-00, Cole-Parmer

employed in the greenhouse is shown in Figure 1. The green-

Instrument Company, Chicago, IL, USA). Ca2þ and Mg2þ

W

house temperature was maintained between 10 and 25 C.

were determined by inductively coupled plasma atomic

Irrigation was carried out every other day: initially, a

absorption

water volume of 100 mL per plant was used, until a final

UNICAM 989 Solaar AA Spectrometer (Thermo Elemental

volume of 400 mL per plant was reached at the end of the

Corp., Franklin, MA, USA). Soil physicochemical analyses

experiments. When the plants were harvested (day 120)

(pH, electrical conductivity (EC), available P and organic

the crop productivities were evaluated by measuring the

matter content) were determined according to the NOM-

length and the weight of the irrigated plants.

021-SEMARNAT-. After soil digestion in microwave

spectrometry

(ICP-AAS)

with

a

Model

3 and filtration, NHþ 4 and PO4 were also analysed using an

Macronutrients content (soil and plant tissues)

ion chromatography system (Model ICS-1500, Dionex, Sunnyvale, CA, USA).

Macronutrients in soils were determined at the beginning of

For plant tissues, the N, P, K, Ca and Mg content were

the experiment (virgin soil, before any irrigation) and at 40,

measured after harvesting all L. sativa plants (20 plants for

80 and 120 days of crop cultivation. One hundred grams

each type of irrigation water). The lettuces were washed

of soil were taken from each plant (20 plants for each water

with distilled water and placed in paper bags to reduce

type). In every case, the subsamples were mixed and a total

excess moisture until analysis. In order to obtain enough

of 2 kg of soil was collected to form a composite sample.

biomass to perform the plant tissue analyses, composite

Soil samples were dried, sieved (No. 10 sieve opening,

samples were also prepared in this case. After diacid mixture

W

2.0 mm), and preserved at 4 C until analysis. The

digestion, N concentrations were determined by the Total

44

M. T. Orta de Velásquez et al.

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Effects on macronutrient contents in soil-plant irrigated with different waters

Kjeldahl Nitrogen method; P was analysed by using a

Table 1

|

Journal of Water Reuse and Desalination

account to perform the composite sampling procedures for ionic content in water; and macronutrients content in soil and plant tissues (US EPA ).

Temporal composite sampling was used for each of the

2014

Untreated Wastewater

O3EPTW-A

O3EPTW-B

Parameter

(Mean ± S.D.)

(Mean ± S.D.)

(Mean ± S.D.)

COD (mg/L)

322.4 ± 44.6

82.6 ± 28.1

82.5 ± 38.0

BOD5 (mg/L)

172.0 ± 12.2

31.3 ± 11.3

34.2 ± 11.1

TSS (mg/L)

56.3 ± 8.7

16.2 ± 14.3

41.6 ± 12.1

Turbidity (NTU)

234.0 ± 40.3

84.5 ± 0.7

87.3 ± 3.1

pH

7.5 ± 0.03

7.6 ± 0.06

7.6 ± 0.01

FC (CFU/ 100 mL)

1.14 × 10

0

1 × 102

Helminth eggs/L

20

0

0

ICP-AAS as was done for soils analyses.

Appropriate considerations on compositing were taken into

|

O3EPTW

(Thermo Fischer Scientific Inc., Waltham, MA, USA); and

Composite sampling

04.1

Physicochemical and microbiological characterization of wastewaters

Thermo Spectronic Genesys 10 UV spectrophotometer the K, Ca and Mg content were determined by FAES and

|

7

five different quality waters and wastewaters to analyse their corresponding ionic concentrations. In every case, 40 subsamples were collected periodically throughout the 120

physicochemical and microbiological parameters for unrest-

days of plant irrigation. During the experiment, a volume

ricted irrigation (cultivation and harvesting of forage, grains,

of water equivalent to 10% of that used to irrigate the

fruits and vegetables that are eaten raw, such as lettuce) as

W

crops was collected, mixed and stored at 4 C until analysis.

Spatial composite sampling was applied in soils for each

established in the local regulation (NOM-001-SEMARNAT-).

pair of irrigation drawers (Figure 1) to study the evolution of

Table 2 shows the cationic and anionic content for the

macronutrients and its characteristics during crop irrigation.

composite sample analysis of the different types of water

Consequently, five different composite samples were taken

used for irrigation as an average of the 120-day trial.

at 40, 80 and 120 days. Each composite sample was well

Between the treated and untreated wastewaters, the cat-

homogenised and formed by taking 20 evenly distributed

þ 2þ 2þ ionic concentrations (NHþ and Naþ) are in 4 , K , Ca , Mg

representative subsamples.

the same order of magnitude. This result suggests that the soils irrigated with O3EPTW (A, B) can maintain the nutritional content (except PO3 4 ) for its reuse in agricultural

Statistical tests

irrigation. This is in accordance with previous results for The crop productivities for each type of irrigation water were assessed at cultivation (day 120). The plant length and weight data (n ¼ 20 in every case) were subjected to a

Table 2

one-way analysis of variance (ANOVA) to establish the similitudes

between

samples.

The

statistical

tests

were

conducted with the XLSTAT package under EXCEL.

Ion

The quality of the untreated and treated wastewaters used in the irrigation experiments is presented in Table 1. It was corroborated that both O3EPTW (A and B) complied with the

Tap water

Tap water þ

O3EPTW

mg/L

fertilizer

O3EPTW-A

O3EPTW-B

wastewater

Untreated

0.20

79.73

24.41

27.81

27.62

Kþ

5.19

147.90

14.58

12.05

13.39

Ca

21.72

24.31

27.85

27.11

29.43

Mg2þ

20.09

25.40

18.95

18.19

19.42

þ

Untreated and treated wastewater quality

Ionic concentrations in waters and wastewaters used for irrigation

NHþ 4 2þ

RESULTS AND DISCUSSION

|

Na

31.01

31.22

63.58

60.09

63.60

PO3 4

0.68

11.49

4.87

4.38

9.50

SO2 4

34.48

71.73

76.14

78.13

60.61

NO 3

2.06

18.10

14.23

11.08

12.70

NO 2

0.04

0.03

0.58

0.32

0.42

45

M. T. Orta de Velásquez et al.

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Effects on macronutrient contents in soil-plant irrigated with different waters

Journal of Water Reuse and Desalination

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conventional APT effluents (Orta de Velásquez et al. ).

accumulated in all soils (except O3EPTW-A); the largest

With regard to the tap water þ fertilizer, it can be seen that

increase in Kþ content occurred for the tap water þ fertilizer

the NHþ 4 concentration is around three times that of the

irrigation (Figure 2(c)). Parameters such as Naþ, Ca2þ,

wastewaters, while the Kþ content is almost 10-fold. As

SO2þ 4 , EC and organic matter, had a similar behaviour and

expected, tap water does not show a considerable nutritional

their contents in all soils tended to increase during the

þ 3

value in N, P, K ions (NHþ 4 , K , PO4 , NO3 , NO2 ). The con-

crop cultivation (Figure 2(d), (e), (g), (h), (j)).

centrations of these ions are low for the tap water, which is

In spite of the increasing exchangeable ionic concen-

consistent with previously reported values ( Jiménez-Cis-

trations in soils, it was found that the irrigation with

neros ); and its concentrations comply with the

O3EPTW did not change the soil’s salinity classification

regulations for drinking water (NOM-127-SSA1-).

(NOM-021-SEMARNAT-) as determined by its electrical

However, with regard to the untreated wastewater, the

conductivity, EC (Figure 2(h)). During the 120 days of crop

O3EPTW (A and B) exhibited a decrease in the phosphate

irrigation, the EC of the soils irrigated with O3EPTW (A and

content and an increase of sulphates. Tap water þ fertilizer

B), remained consistently lower than the values measured in

(PO3 4 :

the soils irrigated with tap water þ fertilizer (between 33

11.49 mg/L) and nitrate (NO 3 : 18.10 mg/L) anions. This

and 58% lower) and untreated wastewater (around 65%

indicates that for the tap water þ fertilizer, there are more

lower). These results are consistent with the findings of

ions available for plant growth and development.

Kiziloglu et al. (), where the salinity of the soil irrigated

contained the highest concentrations of phosphate

with primary treated wastewater was about half of that Macronutrients content in soil

contained by the soils irrigated with untreated wastewater.

For the current research, this can be explained by a

According to the properties for soil fertility (NOM-021-

buffer effect that may be promoted by the ozone-oxidised

SEMARNAT-), the virgin soil displayed ‘very low’ con-

organic matter. The organic matter of the two irrigation

NHþ 4

þ

(110.0 mg/kg);

waters that were subjected to ozonation (O3EPTW) will con-

while its P (13.1 mg/kg) and Mg2þ (473.0 mg/kg) contents

tain higher levels of COOH groups. The formation of these

were classified as ‘low’, and the levels of Ca2þ (1448.0 mg/

groups can increase the soil’s cation exchange capacity (Bot

kg) as ‘medium’. Additionally, the soil contained a high per-

& Benites ) and, consequently, the soils irrigated with

centage of organic matter (6.59%, important for moisture-

O3EPTW will exhibit a lower EC than that for untreated

centrations of

(21.7 mg/kg) and K

retention). Its pH of 6.60 was considered neutral. Figure 2

wastewater and tap water þ fertilizer throughout all cul-

shows the evolution of macronutrients and soil character-

tivation. According to the NOM-021-SEMARNAT-

istics for the five types of irrigation water during crop

classification, at 120 days of crop cultivation the soil irri-

cultivation.

gated with untreated wastewater was the only case that

A large percentage of nitrogen was accumulated in the

started to show signs of salinisation.

soil irrigated with tap water þ fertilizer (Figure 2(a)). The

On the other hand, the soil irrigated with tap water þ

irrigation with tap water did not provide a significant

fertilizer showed a marked decrease in its pH (pH: 5.52;

supply of NHþ 4 , so its availability in the soil was almost com-

Figure 2(i)), so its long-term use can lead to soil acidification.

pletely consumed. The untreated wastewater showed a slight

In contrast, the soil samples irrigated with untreated waste-

increase in nitrogen concentration at 80 and 120 days. The

water and O3EPTW (A and B) maintained a pH between 6.1

NHþ 4

and 6.2, which is similar to that of the untreated wastewater.

at 40 days, but then it showed a decrease in its concen-

The acidification of the soil irrigated with tap water þ fertili-

tration, being more pronounced for the O3EPTW at the

zer can be explained by a variety of factors, including the

end of the cultivation period.

nitrification of ammonium (Vázquez-Montiel et al. ),

O3EPTW irrigation showed a slight increase in soil

In all cases, soil concentrations of P decreased at 120

oxidation of sulphites and the production of organic acids,

days (Figure 2(b)). This suggests that there is an important

which are a consequence of the mineralization of organic

demand for this element by the crops (CPHA ). Kþ

matter (Oliveira et al. ).

46

Figure 2

M. T. Orta de Velรกsquez et al.

|

|

Effects on macronutrient contents in soil-plant irrigated with different waters

Evolution of macronutrients and soil characteristics during crop irrigation.

Journal of Water Reuse and Desalination

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47

M. T. Orta de Velásquez et al.

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Effects on macronutrient contents in soil-plant irrigated with different waters

Lastly, it was observed that the content in organic

Journal of Water Reuse and Desalination

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L. sativa crop productivity

matter increased in all soil samples (Figure 2(j)). For the untreated wastewater and treated wastewaters soils, the

Figure 4 shows the length and weight for the lettuce plants at

increase is due to the organic content of these waters, in

harvest (day 120). The statistical analysis (ANOVA) of the

addition to the presence of crop residues. In the case of

plant productivities allowed confirmation that there are stat-

tap water, this was attributed to the presence and degra-

istical differences between the growths of lettuce plants

dation of plant debris and humus.

irrigated by the five types of water.

As expected, the plants irrigated by the tap water þ fertilizer displayed the largest productivities (p ¼ 0.000 for

Macronutrients content in plant tissues

lengths and weights) due to the highest macronutrients conWith regard to the macronutrients content in plant tissues

tent in the corresponding irrigation water and soil (Table 2

(Figure 3), it was noted that for all irrigation waters the N,

and Figure 2).

K and Mg content in plant tissues were similar. However,

The lengths of the plants irrigated by untreated waste-

the plants irrigated with tap water þ fertilizer exhibited the

water showed a smaller length than those that were

highest P and Ca content.

irrigated with O3EPTW (A and B), and the tap water (p ¼

In plant tissues, the nutrient content for the treated and

0.003). With regard to the lettuce weights, no statistical

the untreated wastewaters appeared to be within the

difference was found between the plants irrigated with

reported ranges for L. sativa (Alzate & Loaiza ). Let-

O3EPTW (A and B), tap water and the untreated wastewater

tuces, like many other crops, can easily assimilate

(p ¼ 0.0712).

nutrients that are provided by reclaimed municipal waste-

Therefore, the O3EPTW irrigation can be employed as

waters; because most of them exist as free ionic species,

an option to the use of tap water wherever water resources

which are readily available for plant uptake (Pereira et al.

are limited, or as an alternative to the untreated wastewater

).

irrigation without the microbiological risks that its use

Another interesting result is that the content of nutrients

represents.

and ions (N, P, K, Ca and Mg) in plant tissues irrigated with

A factor to be considered is that the original soil already

treated and untreated wastewater was broadly similar to that

contained sufficient nutritional components necessary for

of the plants that were irrigated with tap water sup-

the single-season crop cultivation like the one carried out

plemented

differing

in this research. However, the benefits of irrigating soils

concentrations found in soils and irrigation waters. This

with O3EPTW treated waters (such as the increase in

shows that the nutrient assimilation by the crops is not

organic matter content) could become more evident if

affected by the O3EPTW irrigation.

depleted soils are used.

with

fertilizer,

despite

the

Figure 4 Figure 3

|

N, P, K, Ca and Mg content in lettuce plant tissues.

|

L. sativa productivities (lengths and weights at cultivation, n ¼ 20) for the different quality waters and wastewaters.

48

M. T. Orta de Velásquez et al.

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Effects on macronutrient contents in soil-plant irrigated with different waters

For this purpose, in future studies it is recommended to use a depleted or an infertile soil (without any nutrients,

Journal of Water Reuse and Desalination

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2014

agricultural irrigation because it maintains adequate levels of nutrients content in the water, soil and plant tissues.

like for example, sand; or tezontle, a type of volcanic-rock), in order to minimize interferences from nutrients that are already present in the original (starting) soil. Additionally, it

REFERENCES

is necessary to consider that there are other factors (such as biological ones) that may also affect the plant growths.

CONCLUSIONS O3EPTW irrigation can provide an alternative to untreated wastewater (without the microbiological risks that its use represents) or replace the need of fresh water for irrigation (wherever water resources are limited).

According to Mexican legislation (NOM-001-SEMARNAT-), the quality of the O3EPTW waters allows their use for unrestricted irrigation (for watering vegetables and agricultural products that are eaten raw).

The increase in organic matter content with lower electrical conductivity values for O3EPTW soils can provide positive effects in the long term that could lead to enhanced crop productivities, and a better management of wastewater and agricultural resources.

The soil irrigated with untreated wastewater started to show signs of salinisation, while soil acidification occurred with the tap water þ fertilizer. These issues did not occur with O3EPTW water irrigation due to a buffer effect on the electrical conductivity of the ozone-oxidised organic matter.

The irrigation of L. sativa with treated wastewaters maintained the macronutrient content in the cultivated plant’s tissues. For plant tissues, the N, K and Mg contents were similar, except for tap water, which always remained lower.

For the crop productivities, between the treated and the untreated wastewaters the plant lengths showed statistically significant differences; no differences were found with regard to plant weights. Due to an abundance of macronutrients in ionic form, plant growth was the highest for tap water þ fertilizer for this single-season crop cultivation experiment.

The results of this study confirm that the use of O3EPTW (A and B) represents a good alternative for

Adrover, M., Farrús, E., Moya, G. & Vadell, J.  Chemical properties and biological activity in soils of Mallorca following twenty years of treated wastewater irrigation. J. Environ. Manage. 95, 188–192.

Alzate, J. F. & Loaiza, L. F.  Monografía del cultivo de la Lechuga. Colinagro. Bogotá, Colombia.

APHA, AWWA, WEF  Standard Methods for the Examination of Water and Wastewater, 21st edn. American Public Health Association/American Water Works Association/Water Environment Federation, Washington, DC, USA. Bot, A. & Benites, J.  The Importance of Soil Organic Matter – Key to Drought-resistant Soil and Sustained Food Production. Food and Agriculture Organization of The United Nations, FAO Soils Bulletin 80, Rome, Italy.

Campos-Reales-Pineda, A. E., Orta de Velásquez, M. T. & RojasValencia, M. N.  The use of ozone during advanced primary treatment of wastewater for its reuse in agriculture: an approach to enhance coagulation, disinfection and crop productivities. Water Sci. Technol. 57 (6), 955–962.

CPHA  Manual de fertilizantes para cultivos de alto rendimiento. Manual of Fertilizers for High Yield Crops (Spanish Edition). California Plant Health Association, LIMUSA, México D. F. García-Delgado, C., Eymar, E., Contreras, J. I. & Segura, M. L.  Effects of fertigation with purified urban wastewater on soil and pepper plant (Capsicum annuum L.) production, fruit quality and pollutant contents. Span. J. Agric. Res. 10 (19), 209–221.

Heidarpour, M., Mostafazadeh-Fard, B., Abedi Koupai, J. & Malekian, R.  The effects of treated wastewater on soil chemical properties using subsurface and surface irrigation methods. Agric. Water Manage. 90 (1–2), 87–94.

Herpin, U., Gloaguen, T. V., da Fonseca, A. F., Montes, C. R., Campos Mendonca, F., Pasos Piveli, R., Breulmann, G., Forti, M. C. & Melfi, A. J.  Chemical effects on the soil-plant system in a secondary treated wastewater irrigated coffee plantation field study in Brazil. Agric. Water Manage. 89 (1–2), 105–115.

Isea, D., Bello, N., Vargas, L., Durán, J., Yabroudi, S. & Delgado, J.  Acumulación y lixiviación de metales macronutrientes en suelos irrigados con aguas residuales tratadas. Interciencia 29 (12), 660–666.

Jiménez-Cisneros, B.  La Contaminación Ambiental en México: Causas, Efectos y Tecnología Apropiada. Limusa, Colegio de Ingenieros Ambientales de México A. C., México.

Kalavrouziotis, I. K., Robolas, P., Koukoulakis, P. H. & Papadopoulos, A. H.  Effects of municipal reclaimed wastewater on the macro- and micro-elements status of soil

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and of Brassica oleracea var. Italica, and B. oleracea var.

Gemmifera. Agric. Water Manage. 95 (4), 419–426.

Kiziloglu, F., Turan, M., Sahin, U., Kuslu, Y. & Dursun, A.  Effects of untreated and treated wastewater irrigation on some chemical properties of cauliflower (Brassica olerecea L. var. botrytis) and red cabbage (Brassica olerecea L. var. rubra) grown on calcareous soil in Turkey. Agric. Water Manage. 95 (6), 716–724.

NMX-AA-102-SCFI- Que describe un método para la detección y enumeración de organismos coliformes, organismos coliformes termotolerantes y Escherichia coli presuntiva, método de filtración de membrana (Official Mexican Standard NMX- AA-102-SCFI-2006. Describes a detection and count method for coliform organisms, thermo-tolerant coliform organisms and presuntive Escherichia coli by the membrane filtration method).

August 21st, 2006. Diario Oficial de la Federación, DOF, México.

NOM-001-SEMARNAT- Que establece los límites máximos permisibles de contaminantes en las descargas residuales en aguas y bienes nacionales (Official Mexican Standard NOM001-SEMARNAT-1996. Establishes the maximum limits permissible for contaminants in wastewater discharges to water and national resources). January 6th, 1997. Diario Oficial de la Federacion, DOF, México.

NOM-021-SEMARNAT- Que establece las especificaciones de fertilidad, salinidad y clasificación de suelos, estudio, muestreo y análisis (Official Mexican Standard NOM-021SEMARNAT-2000. Establishes the specifications for fertility, salinity and soil classification, study, sampling and analyses).

December 31st, 2002. Diario Oficial de la Federación, DOF, México.

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NOM-127-SSA1- Salud ambiental, agua para uso y consumo humano-límites permisibles de calidad y tratamientos a que debe someterse el agua para su potabilización (Official Mexican Standard NOM-127-SSA1-1994. Environmental Health, Water for human use and consumption. Permissible Limits for Quality and treatments that must be applied for water purification). January 18th, 1996. Diario Oficial de la Federación, DOF, México.

Oliveira, F., Matiazzo, M., Marciano, C. & Rosseto, R.  Efeitos de aplicaçoes sucessivas de lodo de esgoto em Latossolo Amarelo distrófico com cana-de-açucar: carbono orgânico, conductividade eléctrica, pH e CTC. Revis. Bras. Ciênc. Solo 26 (2), 505–519.

Orta de Velásquez, M. T., Yáñez-Noguez, I., Jiménez-Cisneros, B. & Luna-Pabello, V. M.  Adding silver and copper to hydrogen peroxide and peracetic acid in the disinfection of an Advanced Primary Treatment effluent. Environ. Technol.

29 (11), 1209–1217.

Pedrero, F., Kalavrouziotis, I., Alarcón, J. J., Koukoulakis, P. & Asano, T.  Use of treated municipal wastewater in irrigated agriculture – Review of some practices in Spain and Greece. Agric. Water Manage. 97 (9), 1233–1241.

Pereira, B. F., He, Z., Stoffella, P. J., Montes, C. R., Melfi, A. J. & Baligar, V. C.  Nutrients and nonessential elements in soil after 11 years of wastewater irrigation. J. Environ. Qual. 41 (3), 920–927.

US EPA  EPA Observational Economy Series, Composite Sampling. Vol. 1, United States Environment Protection Agency, Washington, DC, EPA-230-R-95-005.

Vázquez-Montiel, O., Horan, N. J. & Mara, D. D.  Management of domestic waste-water for reuse in irrigation.

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First received 22 February 2013; accepted in revised form 17 June 2013. Available online 13 August 2013

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The River Segura: reclaimed water, recovered river M. A. Ródenas and M. Albacete

ABSTRACT The Region of Murcia is located in southeast Spain, an area known for structural water stress. The most important water source that runs through the Region is the Segura River, which is the main irrigation water resource. Late last century there was a significant environmental problem in the Segura River caused by an increase of inadequately treated wastewater discharges, in a period of low flow rates and intensive use of water resources. The situation reached such a critical point, that the Regional Government presented a General Plan for Wastewater Reclamation, to be developed in 10 years. This paper details the content and guidelines in the Plan, as well as aspects related to policy development and objective achievement: water availability has increased and the Segura River

M. A. Ródenas (corresponding author) Dirección General del Agua, Consejería de Agricultura y Agua, Región de Murcia, Plaza Juan XXIII, 30008 Murcia, Spain E-mail: miguela.rodenas@chsegura.es M. Albacete ESAMUR Entidad de Saneamiento y Depuración de la Región de Murcia, C/ Madre Paula Gil Cano s/n, Torre Jemeca, 30009 Murcia, Spain

conditions have improved. In short, it can be concluded that wastewater reclamation marks a good starting point for bettering water management in arid areas. Furthermore, the case of the Region of Murcia reveals that comprehensive action lines and optimized engineering and knowledge of wastewater management is highly beneficial.

Key words

| agriculture water reuse, environmental water reuse, river recovery, wastewater management system, wastewater treatment plants, water reclamation planning

INTRODUCTION Background

Murcia. River water resources are depleted in the middle and low stretches, meaning no water reaches the river mouth.

The Region of Murcia, located in the extreme western Med-

In the 1980s, irrigation increased significantly and so did

iterranean area (southeast Spain), has a dry climate (average

business activity of the canning industry, both coinciding with

rainfall 300 mm) and a population of 1.5 million people.

a long, severe drought (especially in the 1992–1995 period).

Weather conditions and hundreds of years of expertise in

There was a double negative impact: on the one hand, river

irrigation techniques have made this Region a prime fruit

flow decreased, and on the other, industrial and urban waste-

and vegetable producer. The strategic location of Murcia

water discharges increased, with not enough treatment

in the EU has contributed to making fruit and vegetable

systems in operation. As a result, the self-purification capacity

exports one of the main economic pillars of this Region

of the river collapsed, leading to a condition of permanent

(Ródenas ).

pollution that was lethal for river life in the middle and low

The Segura River, the main irrigation resource in the

stretches. The river banks degraded significantly and there

Region, runs through all of Murcia. Water flow in the river

were foul smells in the towns near the river banks, especially

is fully managed by head reservoirs. The highly monitored

in the city of Murcia (400,000 people), causing profound

Segura basin, with an average runoff (natural scheme) of

public rejection and social alarm (Ródenas ).

803 Hm3 year-1 (MMA ), allows for an average water 3

The evolution of these situations is presented in Figure 1,

availability factor of 500 m person year-1 (Ródenas ).

which includes monthly water quality and flow data gathered

In spite of significant efforts aimed at saving water and opti-

at the Contraparada control station between the years 1975

mizing its use, there is still a structural water shortage and

and 2011. The Contraparada control station, located about

insufficient guarantees of water supply in the Region of

10 km upstream from the city of Murcia, is considered

doi: 10.2166/wrd.2013.044

51

M. A. Ródenas & M. Albacete

Figure 1

|

|

The environmental recovery and an increase of water availability

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Water quality and flow of the Segura River in Contraparada. Moving average 12 periods. Sources: Nicolás (1987); García Balibrea (2000); CHS (2011).

representative of the middle stretch. Biochemical oxygen

STRATEGY AND IMPLEMENTATION

demand (BOD5) peaks of 250 mg L 1 equivalent to raw wastewater with no dilution, were observed. In other words, the

Development and design of the treatment plant

river had turned into a sewer.

This 10-year Plan, originally created in 2001, included an Objectives

environmental assessment and public consultation process before it was signed by the Region of Murcia Government.

The severe water pollution affecting the middle stretch of

One of the aims of the Plan was to coordinate the

the Segura River moved the Region of Murcia Parliament

actions lines established by different public administration

to adopt a policy (Law /), which included the develop-

bodies (National, Regional and Municipal). The basic legal

ment of a ‘General Plan for Wastewater Reclamation’

framework of the Plan was determined by Community

between 2001 and 2010 (hereafter referred to as the ‘Plan’)

Directives: 91/271/EEC and 2000/60 (Water Framework

(Master Plan –), in addition to other measures.

Directive) as well as a number of applicable water norms

The Plan included two main objectives: the environ-

in Spain: Water Laws and Coastal Laws. Plan implemen-

mental recovery of the Segura River and an increase of

tation was also coordinated with other plans: Royal

water availability by means of wastewater treatment and

Decree-Law 11/95 of National Sewerage and Water Treat-

reuse. Another general objective, in line with Directive /

ment Plan (Ministerio de Obras Públicas, Transportes y

/EEC (), was aimed at ensuring wastewater treatment.

Medio Ambiente ), elaborated within the context of

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the implementation of the European Directive 91/271/CEE, Royal Decree-Law / of Hydrologic National Plan (Law 10/2001 ), Water Plan for the Segura River Basin () and Spain’s National Plan for Sewage Sludge ().

Four basic policies were established to achieve Plan objectives: (1) build the necessary collection systems and wastewater treatment infrastructures; (2) implement a management system to ensure proper infrastructure maintenance and operation; (3) monitor wastewater discharge to the sewerage system; (4) facilitate industrial waste treatment at the source.

Figure 2

|

Alhama: tertiary treatment plant.

Design criteria for wastewater treatment plants installations specialized in organic pollution removal. In this The Plan established that treatment plants should supply

Secondary Treatment phase, the reference effluent limits are

reusable water suitable for two main purposes: discharge

25 mg L 1 BOD5 and 35 mg L 1 SS (suspended solids) (Direc-

in the river for ‘indirect reuse’ downstream (the most

tive //EEC). Depending on specific circumstances, the

common scenario), or ‘direct reuse’ as irrigation water in

conventional activated sludge system (including pre-decanting

the case of water shortage. In the case of ‘indirect reuse’,

or ‘Primary’) could be used, as well as other process possibili-

it is necessary to minimize water environment impact

ties such as extended aeration (reactor þ clarifier system) and

because dilution is simply not possible. As for ‘direct

double stage (double system – reactor þ clarifier system in

reuse’, it is necessary to ensure that water quality is suitable

series) (Tchobanoglous et al. ). Extended aeration is the

for irrigation purposes (Ródenas ).

most commonly applied option because of its robustness,

The criteria selected for the process engineering in

easy operation and long life.

water treatment were based on information published in international guidelines and studies (Mujeriego ; Tcho-

More stringent treatments

banoglous et al. ; Asano et al. ). Thus, in order to design new treatment plants, Plan guidelines determine

Biological treatment processes include More Stringent

that in addition to conventional ‘Secondary Treatment’, it

Treatments to ensure nutrient removal. This treatment is

is also necessary to implement advanced treatment pro-

much more intense and even mandatory in case of dis-

cesses in all treatment plants: ‘More Stringent Treatments’

charges in sensitive areas so as to prevent eutrophication

to eliminate nutrients and specific ‘Tertiary Treatments’ to

(Directive //EEC).

favour reuse (Figure 2). These higher treatment standards

In order to remove nitrogen compounds in wastewater, a

and their application to all treatment plants, is a differentiat-

nitrification-denitrification process is followed. In addition to

ing feature of the Region of Murcia Plan.

improving biological sludge and effluent treatment, this process favours energy recovery. Generally speaking, the

Secondary treatments

reference value for Nt content in the effluent is 15 mg L 1, or 10 mg L 1 in the case of larger agglomerations

The good condition of urban wastewater in the Region of

(>100,000 h e 1). Treatment plants in the Plan must also be

Murcia usually facilitates its biological treatment. Hence, the

capable of removing phosphorus compounds, the other

general approach for Secondary Treatment is based on the

main nutrient in wastewater; some installations partially

process of biological purification of activated sludge. One of

reduce their content by biological means and in all cases it

its advantages is the creation of high-performance, compact

is necessary to use chemicals to ensure total phosphorus

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content reduction. The reference value for total phosphorus in the effluent is 2 or 1 mg L 1, depending on conurbation size (Master Plan –).

Tertiary treatments The Plan establishes gradual implementation of Tertiary Treatments aimed at minimizing suspended matter and disinfecting thoroughly so as to improve water reuse health guarantees. The design criteria included in Title 22 of the California Water Code (), which has been scientifically recognized, universally accepted and widely borne out by experience, were used as a reference. The reference effluent values in Tertiary Treatments are turbidity <2 NTU and

Figure 3

|

Detail of San Pedro treatment plant.

total coliforms <2.2 cfu 100 mL 1. The Royal Decree-Law 1620/2007 of Purified Water Reuse () established the

general scheme for installation of treatment plants and col-

legal regime of treated wastewater reuse after the Plan was

lecting

launched. Treatment usually includes additional processes

frameworks and is implemented based on technical criteria

such as floculation, coagulation and complementary clarifi-

for environmental, economic and energy efficiency.

systems

because

it

goes

beyond

municipal

cation (generally lamellar), followed by filtration. There is

The Plan includes total wastewater collecting, building

a large variety of filtering devices installed. An open sand

massive intake areas and collecting systems so as to connect

bed filter is the most commonly used, although other types

as many agglomerations as possible, even those of a smaller

have also been built such as closed sand bed filter, ring fil-

size. Plan guidelines also recommend that water collection

ters, mesh filter or cloth filter. There are also dynamic

be prioritized at collecting systems, reducing the number

filters for continuous backwash filtration. The most used dis-

of treatment plants and making these as large as possible.

infection process is ultraviolet radiation, although an

Although the cost of collecting systems is initially higher,

additional chlorination labyrinth is always used and even a

they are more beneficial in the long term: better treatment

maturation pond for natural disinfection in some cases

performance and lower treatment, management and control

(Master Plan –).

costs. Collecting systems also contribute to minimizing the

Due to the specificities of certain locations, some treat-

inevitable environmental and social impacts resulting from

ments include the use of membrane biological reactors

the construction of a treatment plant. All these aspects

(MBR). The MBR process requires much less space than a

have been properly assessed.

conventional treatment plant and provides water of exceptional quality. Important installations in the Region of

Design of the wastewater management system

Murcia use the MBR technology, including the application of ultrafiltration membranes. The San Pedro del Pinatar

One of the basic policies included in the Plan was aimed at

treatment plant (built in 2007) should certainly be referred

determining how to manage the infrastructures built. Law

to in that regard, for its large capacity (20,000 m³ day 1) in

/ established a ‘Wastewater Reclamation Levy’ as an

the European Union (Figure 3).

economic tool funding their maintenance, operation and control. In addition, the regional agency ESAMUR was cre-

Collecting systems

ated in 2002 to specifically work on these areas.

The Wastewater Reclamation Levy is a targeted regional

The Plan of the Region of Murcia overarches other munici-

tax that levies wastewater discharge to the public sewerage

pal urban plans. This is of relevance when establishing the

system. The tax, proportional to the level of contamination,

54

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M. A. Ródenas & M. Albacete

The environmental recovery and an increase of water availability

is based on the ‘you contaminate, you pay’ principle. This

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Infrastructure installation

tax was first levied in 2003.

A total of 47 large wastewater treatment plants (500– 100,000 m3 day 1) have been built within the framework

Control of industrial discharges and treatment at source

of the Plan, with a maximum daily treatment capacity of 540,000 m3 (70% Tertiary) (Figure 4).

Industrial discharges can damage infrastructures, inhibit

Most of these infrastructures were built by the Conse-

biological treatment processes and introduce undesirable

jería de Agricultura y Agua – Dirección General del Agua

elements hampering future reuse. Thus, one of the main pol-

(Region of Murcia), with 70–80% funded by the European

icies in the Plan focuses on facilitating purification at the

Union (ERDF and Cohesion Fund). These subsidies were

source and monitoring industrial discharges to the sewerage

vital for the implementation and economic feasibility of

system.

the Plan.

The larger volumes of industrial discharges in the

Other treatment plants built within the scope of this

Region of Murcia come from the food industry and canning

Plan were funded by the central Spanish Government and

sectors, with significant amounts of biodegradable organic matter. All industrial discharges require municipal authoriz-

some city councils. ESAMUR has played a key role in the

ation; ESAMUR assists and collaborates with city councils

rehabilitation of 50 additional treatment plants in small

on this matter. The actual Wastewater Reclamation Levy

agglomerations.

The collecting systems built serve 99.4% of the urban

is an economic deterrent that somewhat drives firms to

population, and 97.7% of them are connected to treatment

reduce pollution at the source.

plants. The total investment in infrastructures made or committed by the different administration bodies amounts to about € 635 million.

RESULTS AND DISCUSSION Management results for the treatment and reuse system After implementation of Plan policies, current indicators and their evolution are presented (Table 1) (ESAMUR Figure 4

Table 1

|

|

). Figure 5 includes ESAMUR data related to the

Treatment plant implementation.

Operation results 2003–2010 (ESAMUR)

Operation

Treated wastewater

Ud. 3

Hm

2003

2004

2005

2006

2007

2008

2009

2010

96.1

106.1

105.7

100.7

102.5

99.6

102.1

110.9

Evacuated sludge

Tm × 1,000

75.1

96.1

99.0

103.8

117.9

128,3

134.9

128.8

Received BOD5

Tm × 1,000

49.5

54.4

56.0

52.7

50.9

48.3

43.7

40.1

Removed BOD5

Tm × 1,000

41.6

47.8

50.0

48.6

48.1

47,1

42.8

39.3

Removal BOD5

%

84%

87.8%

89.0%

92.0%

94.4%

97.6%

97.9%

97.9%

Consumed energy

GWh

48.7

53.6

56.9

56.5

59.7

65.6

66.1

63.4

0.51

0.51

0.54

0.56

0.58

0.66

0.65

0.57

Electric ratio

3

kWh m

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In 2010, the 97 treatment plants in the system treated 111 Hm³ of wastewater. The overall contamination load elimination performance reached 97.9% for BOD5; this remarkable performance was achieved by applying the most rigorous treatments in the Plan (ESAMUR ).

It is estimated that in 2010, around 100 Hm3 has been reused ‘directly’ or ‘indirectly’ in the Segura River or its tributaries, for a value of 90% of all the water treated. The Figure 5

|

Influent quality.

remainder of treated waters, found mostly in coastal installations, have not been used in farming due to their high

industrial contamination load found in water treatment plant influents, which shows a declining trend partly as a result of industrial treatment at the source. This trend is largely due to better discharge control and to the deterrent effect of the tax.

salinity content.

Approximately 50% of all wastewater treated has undergone additional tertiary treatment, as specified in Title 22 of the California Water Code. This percentage will increase in 2011 once operational tests of tertiary systems recently built have been completed. Thanks to the implementation of the Plan, the treated water supplied contributed to a 13% increase in natural river basin resources. Thus, the objective has been achieved (Figure 6).

Recovery of the Segura River Figure 7 includes graphs produced by the Public Water Authority for the Segura River (CHS), showing the history of organic contamination in the Segura River (left) and at three specific control points (right) in the high, medium and low stretches (Abarán, Contraparada and Orihuela – downstream from the city of Murcia) (CHS ). Plan implementation has contributed to neutralize the negative

Figure 6

|

Reclaimed water.

Figure 7

|

Water quality in the Segura River.

effects of wastewaters, resulting in better water quality.

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management in dry areas that contributes to increasing water availability and reducing contamination.

This work also shows the advantages of comprehensive pre-planning as a rational, effective method that helps to solve complex problems associated with water management.

An example of this is the Region of Murcia General Plan for Wastewater Reclamation (2001–2010); the objectives in the Plan have been satisfactorily achieved in a reasonable period of time.

The contribution of hundreds of professionals and companies engaged during the Plan creation and implementation has strengthened wastewater management knowledge and engineering in the Region of Murcia.

Figure 8

|

Fishing in the Segura River, Murcia.

REFERENCES

Figure 9

|

Recovered birdlife fauna.

The city of Murcia has clearly realized the recovery of the Segura River, including its flora and fauna. Citizens come near the Segura and fishing, canoeing and water sports enthusiasts are now found enjoying the river (Figures 8 and 9). This Plan objective has also been achieved (Figure 6).

CONCLUSIONS The work carried out in the Region of Murcia concludes that wastewater reclamation is a good, basic principle of water

Asano, T., Burton, F. L., Leverenz, H. L., Tsuchihashi, R. & Tchobanoglous, G.  Water Reuse: Issues, Technologies, and Applications. Metcalf & Eddy/AECOM, McGraw-Hill, New York, USA. California Water Code  In: Irrigation with reclaimed municipal wastewater, a guidance manual, 1984. California State Water Resources Control Board. Report number 84-1 Wr. University of California, Sacramento, California, USA. CHS  Continental water quality evolution in the Segura basin.

Hydrologic Year Report 2009–2010. Public Water Authority for the Segura River, Murcia, Spain.

Council Directive 91/271/EEC  Concerning urban wastewater treatment. Official Journal of the European Communities No. L 135 30/05/1991, 1991, 0040–0052.

ESAMUR  Regional Entity for Sanitation and Treatment.

Available at: http://www.esamur.com/ (30 December 2010).

García Balibrea, J.  Current situation report of Segura River as it passes through the provinces of Murcia and Alicante.

Public Water Authority for the Segura River, Murcia, Spain.

Law 3/2000 on Wastewater Reclamation and Wastewater Treatment Levy. Official Bulletin of the Region of Murcia, BORM. Law 10/2001  National Hydrologic Plan. Official Bulletin of the State, Spain.

Ministerio del Medio Ambiente  Spain’s National Plan for Sewage Sludge 2001–2006. Official Bulletin of State, BOE. Ministerio de Obras Públicas, Transportes y Medio Ambiente  Official Bulletin of the State, BOE, Spain. National Sewerage and Water Treatment Plan.

MMA (Ministerio de Medio Ambiente)  Secretaría de Estado de Aguas y Costas. Water in Spain. White Book.

Mujeriego, R.  Manual of Irrigation with Reclaimed Municipal Wastewater. Politechnic University of Catalonia, Barcelona, Spain.

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Nicolás, E.  Segura River water quality evolution during the last 13 years, 1975–1987. Public Water Authority for the Segura River, Murcia, Spain.

Master Plan for Urban Wastewater Sanitation and Treatment in the Murcia Region – Official Bulletin of the Region of Murcia, BORM. Segura River Basin Hydrological Plan  Official Bulletin of the Region of Murcia, BORM. Ródenas, M. A.  Treatment and Reuse of Wastewater. In: The Culture of Water in the Segura Basin (Cajamurcia Fundation, ed.). Murcia, Spain.

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Ródenas, M. A.  Water Reuse. In: River Basin Authority 75th Anniversary, Spain.

Ródenas, M. A.  Water reuse policies of the Murcia Region.

In: Reclaimed Water Reuse (Euro-Mediterranean Water Institute, ed.). Jiménez Godoy Press, Murcia, Spain, pp. 69–89.

Royal Decree-Law 1620/2007 Purified Wastewater Reuse  Official Bulletin of the State, Spain.

Tchobanoglous, G., Burton, F. L. & Stensel, H. D.  Wastewater Engineering: Treatment, Disposal and Reuse.

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First received 22 February 2012; accepted in revised form 21 May 2013. Available online 5 July 2013