Complete water resource and wastewater management
of moving forward with PVC pipe technology
WASTEWATER SLUDGE – a growing liability or existing resource?
Sanitation systems where the sewer does not go
HOW MUCH IS A WETLAND ACTUALLY WORTH?
stand-alone or wireless
Pressure Ranges
0…5 to 0…100 mH2O
Total Error Band
±0,1 %FS @ 0…50 °C
Recording Capacity
57‘000 measuring points
Dimensions ø 22 mm
Special Characteristics Also available in ECO design
2G 3G 4G
Pressure Ranges
0…1 to 0…30 bar
Total Error Band
±0,2 %FS @ 0…50 °C
Accuracy
±0,05 %FS
Interfaces
RS485, 4…20 mA
Special Characteristics
ø 16 mm
Communication
Mode
2G / 3G / 4G / LoRa NB-IoT LTE 2M
Sensor Interfaces
RS485, SDI-12, analog, digital
Battery Life Up to 10 years
Celebrating its 20th birthday this year, Sizabantu Piping Systems has grown from a trading company to one providing the
and
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WISA Contacts:
HEAD OFFICE
Tel: 086 111 9472(WISA)
Fax: +27 (0)11 315 1258
WISA’s Vision Inspiring passion for water
Physical address: 1st Floor, Building 5, Constantia Park, 546 16th Road, Randjiespark Ext 7, Midrand Website: www.wisa.org.za
BRANCHES
Central Branch (Free State, Northern Cape, North West)
Chairperson: Dr Leana Esterhuizen
Company: Central University of Technology
Tel: +27 (0)51 507 3850
Email: lesterhu@cut.ac.za
Eastern Cape:
Branch Contact: Dan Abrahams
Company: Aurecon
Tel: +27 (0)41 503 3929
Cell: +27 (0) 81 289 1624
Email: Dan.Abraham@aurecongroup.com
Gauteng
Branch Lead: Zoe Gebhardt
Cell: +27 (0)82 3580876
Email: zoe.gebhardt@gmail.com
KwaZulu-Natal
Chairperson: Lindelani Sibiya
Company: Umgeni Water
Cell: +27 (0)82 928 1081
Email: lindelani.sibiya@umgeni.co.za
Limpopo
Chairperson: Mpho Chokolo
Company: Lepelle Northern Water
Cell: +27 (0)72 310 7576
Email: mphoc@lepelle.co.za
Mpumalanga
Chairperson: Lihle Mbatha (Acting)
Company: Inkomati-Usuthu Catchment Management Agency
Tel: +27 (0)13 753 9000
Email: mbathat@iucma.co.za
Western Cape
Chairperson: Natasia van Binsbergen
Company: AL Abbott & Associates
Tel: +27 (0)21 448 6340
Cell: +27 (0)83 326 3887
Email: natasia@alabbott.co.za
Namibia
Please contact the WISA Head Office at admin@wisa.org.za for more information
I stumbled upon Adam McKay’s recent film – Don’t Look Up – in December, and kept drawing parallels to our reaction to the water crisis.
The film revolves around the discovery made by an astronomy grad student and her professor of a comet orbiting within the solar system. The problem: it’s on a direct collision course with Earth. The other problem: no one really seems to care. They attempt to warn people. They appeal to the White House. They go to the media. Lastly, they appeal to the business leaders hoping to profit from the big ball of minerals headed our way. But people aren’t eager to hear the message, and the planetkilling comet becomes a social media debate between those who believe in science and those who believe it to be a hoax. It is a comedy about how even the most obvious of threats fails to stir collective action. It makes the point that there is nothing that can sway the public to save the world in any meaningful sense. We’re just too concerned with our own lives.
Demand for water in South Africa is expected to rise by 17.7 billion m³ in 2030, while water supply is projected to amount to 15 billion m³ – representing a 17% gap between water supply and demand...
I have read and heard these statistics so many times that when people include them in a submission or mention them in an interview, I cut them out of my articles because everyone in the water industry
knows this already. These statistics have been mentioned in numerous articles published within mainstream media. And yet ... Twitter is filled with the latest gossip around the Real Housewives of Durban.
Collective action
There will never be any collective action without leadership. This point is driven home in the movie where the American president initially dismisses claims by science, then decides to take action when it’s politically expedient to do so, and then changes course when there is a possibility of making money out of the impending disaster.
The good news is that the South African water and sanitation sector has good leadership. I have heard only praise about our new Minister of Water and Sanitation, Senzo Mchunu. And the industry is excited about the appointment of a permanent Director General in Dr Sean Douglas Phillips.
There are solutions to this crisis. They are included in every issue of WASA now have to roll up our sleeves and get moving.
I hope you enjoy the first issue of the year and, please, don’t hesitate to contact me with any industry news.
When I first came across a computer, I always knew that it would play a significant role in people’s lives, but I never imagined that it could be your only connection to the outside world. Like many people in our industry, my meetings have been mostly online during the past two years. WISA has operated online too. We have presented a number of online webinars and training courses, as well as hosted our biennial 2020 conference virtually. While we will continue to embrace the positives of online meetings, webinars, training and conferences (affordability, time and accessibility), we are extremely excited about the prospect of being able to physically gather as an industry. Our 2022 WISA Conference
will be a hybrid event and will be hosted at the Sandton Convention Centre in September 2022.
South Africa’s fourth wave of the pandemic is waning, and restrictions on public movement have mostly been lifted. Worldwide, billions of people have been vaccinated against Covid-19 and we are somewhat closer to normal than 2020. The world is also better prepared to tackle potentially bad variants than at any other point in the pandemic so far.
Hibernation is ending
After directing our energy at surviving and adjusting to the pandemic, we now need to re-energise ourselves for an exciting year. Municipal elections are concluded, and coalition governments have mostly been formed. Our new
Minister has found his feet and a permanent Director General has been appointed. The water sector is poised to attack the water crisis and implement policies, projects and new technologies that can solve many of our problems. It’s time to interact with our colleagues and friends in person, and celebrate the successes and new scientific solutions in our industry. We want to welcome in the new leadership in the Department of Water and Sanitation, pledge our support in person and formalise relationships. We are looking forward to bringing an end to any sort of stagnation caused by Covid-19. Let’s appreciate just how resilient we have been by taking a look back at how we have endured the past two years, and look forward to a productive and exciting year ahead.
If
there is one new
year’s resolution that every government body, business and South African needs to make, it’s to use water efficiently. By Dan Naidoo, chairman, WISA
The 2018 National Water and Sanitation Master Plan identified a water supply deficit of 17% by 2030. Despite this, South Africans use more water than the global average – 234 litres per person daily – which means the country’s per capita water consumption is higher than the global average of 173 litres.
With a lack of funding to boost supply, minimal to zero water tariff increases and a growing need for water subsidies for the indigent, the efficient use of water must be a priority. It is nonsensical to invest in increasing water supply when we are not using water efficiently. We need to make the average South African understand that we cannot provide more water without everyone using water they already have access to sparingly.
Managing demand, reducing water losses and decreasing non-revenue water is a mantra that water professionals have been singing to politicians for many years. Due to the inefficient use of water, South Africa has to constantly direct funds (that we don’t have) to the upgrading of pipelines, water and wastewater plants, and dams.
Based on rising populations, economic growth projections and current efficiency levels, demand for water in South Africa is expected to rise by 17.7 billion m³ in 2030, while water supply is projected to amount to 15 billion m³.
The word ‘demand’ needs to be unpacked. Is that demand realistic? Should we be chasing that demand as a target? Or should we be debating it? Can we do more with less?
We need to consider water’s circular economy and its entire value chain. We need to look around wastewater as a resource; we need to go back to the basics.
A circular economy offers an opportunity to recognise and capture the full value of water – as a service, an input to processes, a source of energy, and a carrier of nutrients and other materials.
Collaboration is needed
There must be a joint effort in managing water losses and fixing infrastructure. What quick gains can we achieve when focusing on the efficient use of water? Agriculture uses more than 60% of our water resources. Looking at places like Australia and much of the US, the agricultural use of water is extremely efficient, and there are many new technologies that help farmers to manage irrigation better. Are we assisting our farmers? Is the water industry having discussions and sharing knowledge with our farmers? Farmers played a pivotal role in saving Cape Town from ‘Day Zero’. Many institutes and organisations have launched and are running water efficiency programmes. Here is a non-exhaustive list:
• The National Business Initiative has launched a water programme to address South Africa’s risk.
• The UN has launched the CEO Water Mandate – an industry-driven initiative to reduce water stress.
• AQUAffection has the #SurplusWater2025 programme to work towards achieving a water surplus.
• The CSIR has created a Smart Water Use Division to provide knowledge, innovation, skills and services to improve water supply and demand management through effective water resource planning.
• Rand Water’s Water Wise campaign is aimed at increasing awareness of the need to value water and to use it wisely. We need to take these messages and amplify them to the South African public.
“Thousands have lived without love, not one without water”. The relevance of this old quote, by poet WH Auden, is reinforced by the recent role WASH initiatives play in preventing the transmission of Covid-19. Baloyi Mogau, disaster risk management graduate, outlines the crucial elements and benefits of water quality.
Water pollution, urbanisation, population growth and the transmission of diseases – coupled with the prominence of the impacts of climate change and food security issues in vulnerable communities –place increasing pressure on water quality. As the world’s population is expected to reach nine billion by 2037, the increasing demand for potable water exacerbates the risks for water planners and authorities in addressing the shortages of adequate quality of water supply.
However, such risks can be mitigated and prevented, provided adequate and risk-informed preparatory measures are implemented promptly. Conversely, the procedures for averting the crises embedded in those risks do not come cheap or without effort.
Water quality is essential for lifesupporting processes for both marine and terrestrial lives. By taking the nutrient contents of water from a health and chemical perspective into account, water quality has a great effect
on how life cycles are maintained and sustained.
Moreover, water quality defines the required standards and conditions for safe water. The management of water quality promotes the consideration of principles relating to the microbial, chemical and radiological aspects of water, as well as their acceptability standards. In other words, for water to be acceptable, it should adhere to the prescribed microbial, chemical, and radiological standards for water potability. Water quality practitioners also consider consumer satisfaction,
specifically with regard to the appearance, taste and odour of water. Thus, the acceptability of water is influenced by the utilisation purpose of the water (agricultural, industrial, domestic and recreational use).
Natural water quality is measured to assess and prioritise the establishment of either ‘residual’ or ‘chemical’ water disinfection plants for a sustainable quality water supply that also reduces the susceptibility to the transmission of waterborne diseases. Water quality standards describe, monitor and control the conditions of water by ensuring that it withstands the rigorously derived testing standards for acceptability and qualification to serve specific purposes, including cooking and drinking. In simple terms, it measures the content of impurities using physical, biological and chemical methods.
Poor water quality can pose health risks to both people and the ecosystem, leading to degradation of the available water resources, which has an adverse impact on
the health of plants and animals. The pollution of water resources – through the improper disposal of polymers and wastewater (unauthorised effluent discharges) as well as chemical spillages – can result in odorous water streams and increase the concentration of harmful chemicals in water resources. These can subsequently compromise air quality, the atmosphere, as well as the quality of precipitation by contributing towards acid rain. Additionally, poor water quality can increase the prevalence of diseases, including cholera, diarrhoea, polio and others associated with acute and chronic lung diseases.
To combat some of the above-mentioned water-related problems, governmental policies are ratified and enacted to regulate and impose punitive judgments or penalties on transgressors.
Issues relating to water quality are mitigable, requiring collaborative efforts and a willingness to act by all parties. Despite a plethora of probable water quality management solutions, the scant presence of residual disinfection plants in rural communities in South Africa warrants the evaluation of legislative compliance, capacity-building efforts, the competencies of water practitioners, and proper policy implementations relating to the provision of safe drinking water in South Africa.
Currently, water quality is mediocre in South Africa. Mining industries and
power-generating plants have a significant impact on water quality and agricultural production in South Africa. The failure to adopt the technology used in the eMalahleni Water Reclamation Plant to recover drinkable water from acid mine drainage elucidates the lack of responsibility and commitment towards preserving and maintaining the country’s water quality. Furthermore, coal also poses a threat to water resources, while rehabilitation costs the government over R1 billion on an annual basis. Mine dumps established on dolomitic areas have a negative impact on the underground water quality in Gauteng.
Water is essential for a just transition in green economic development and the strengthening of sustainable development, yet low levels of collaborative effort are seen in the development of sustainable and resilient water systems.
The implementation of water-related policies centred around collaborative
efforts has proven to be efficient in addressing problems such as water pollution, water financing, water administrative issues, and inadequate water supply within an international context. However, the nonbinding aspects and the dominance of Eurocentric policy designs, as well as inequalities in water resource management capacity between countries have resulted in a lag in policy implementation in South Africa, necessitating a reassessment and evaluation of best-fit limitations in international policies to better suit the South African water quality context.
Water quality policies provide guidelines and frameworks for water quality and supply by specifying the legal functions for quality control and quality assurance in water supplies. These frameworks specify the criteria for using various disinfection methods and how to ensure a sustainable drinking water supply.
The effectiveness of water quality policies, frameworks and other supportive instruments relies heavily on the level of implementation, legislative enforcement, and the willingness to play a role by the parties responsible for the practice. There is a strong need for a collaborative engagement in dealing with the current water realities. It is not only the government that should be responsible for the production and distribution of clean water, but also private companies, especially large water consumers and polluters such as those in the mining sector.
Celebrating its 20th birthday this year, Sizabantu Piping Systems has grown from a trading company to one providing the marketing and sales function for a major South African thermoplastic pipe manufacturer – Molecor.
Sizabantu is a Southern African agent for a world leader in thermoplastic (PVC-O) pipe technology, Molecor, and is a joint venture partner in a production facility with Molecor in the Richards Bay Industrial Development Zone.
Significantly, all the Sizabantu management throughout Southern Africa are qualified and highly experienced people who have been in the thermoplastic piping system industry for many years. They know quality products, customer service, product availability and commercial competitiveness are paramount in this highly competitive market.
The company currently supplies highquality, locally manufactured, thermoplastic piping system products into the Southern African market. The maximum diameter and pressure rating of the PVC-O pipes available are substantially greater than previously available and this has enabled Sizabantu to compete in markets that were hitherto beyond the scope of previously available thermoplastic piping systems.
PVC pressure pipes
PVC pressure pipes were first used in Germany about 85 years ago. About 60 years ago, PVC pipes were introduced into South Africa but were not enthusiastically received. Today, for
example, more than 95% of domestic sewerage reticulation pipes are PVC. Things have changed.
Scientists, polymer technologists and processing engineers have enabled the Allowable Design Stress (σ) for HDPE to improve from 5 MPa to 8 MPa – a substantial 60% increase. However, the increase in PVC’s strength, enabled by improved technology, is even more substantial, going from 10 MPa to 36 MPa – a incredible 260% increase.
In the 1970s, the PVC industry entered the mining services market following a successful project, led by Dr Ken Hart. A high-impact pipe PVC-HI (SANS 1283) was developed that satisfied the mining industry's requirements and enabled PVC pipes to be used for underground services. Following on from this work, another
development project, led by Mike Osry, developed PVC-M (SANS 966-2) in the mid-1990s by adding impact modifiers, commonly CPE (chlorinated polyethylene), or rubber toughened acrylics, or a combination thereof, to the PVC material to increase its impact strength. This enabled the material to exhibit ‘tough’ characteristics that facilitated the reduction of the Design Coefficient (C) from 2 to 1.4, thereby increasing the Allowable Design Stress (σ) from 12.5 MPa to 18 MPa. About 40 years ago, PVC-O (oriented unplasticised polyvinyl chloride – SANS 16422) was developed. The molecular orientation process results in the improvement of physical and mechanical properties of the material. In the intervening 40 years, there have been improvements in PVC-O material: from Classification 315 material initially to Classification 500 material currently – the nomenclature represents 10 times the MRS (Minimum Required Strength) of the material.
The latest PVC-O material, Classification 500, must have an MRS of not less than 50 MPa at 50 years, that with a Design Coefficient (C) of 1.4 gives a σ-value of 36 MPa – where σ = MRS/C. It is a substantial improvement, which is twice the Allowable Design Stress (σ) of PVC-M. This is made possible by improved in-line
production technology, which Sizabantu Piping Systems’ Spanish technology partner Molecor excels at developing, and the company’s TOM® 500 PVC-O pipes are produced locally in Richards Bay.
Innovation – TOM® 500 PVC-O Innovation is one of Molecor’s core values. With TOM® 500 PVC-O branded pipes, the company increased the range of PVC-O pipes from the previous limit of 315 mm OD PN16 (PN is the working pressure in bar) to 630 PN25, with the M-OR-P3136 system in 2010. Then, in 2013, to 800 PN20, with the M-OR-P3180 system. Further to 1 000 PN16 in 2020 and 1 200 PN16 with the M-OR-P5012 system in 2021. Currently, the complete range of pipe diameters is available up to PN25. These are exciting developments for the thermoplastic pipe industry that have enabled it to compete in the large-diameter, high-pressure pipe market, which was previously beyond its capability.
These innovations and the latest high-technology polymers have enabled the service life of TOM® 500 PVC-O thermoplastic pipes to be greater than 100 years – which is now the duration demanded by owners and consultants. This is more than twice the ISO protocol requirement that thermoplastic pipes’ design service life shall not be less
than 50 years, which is 438 000 hours on the polymer’s Creep Rupture Regression Curve.
This property of TOM® 500 PVC-O thermoplastic pipes is one of the cornerstones of Sizabantu’s success, together with its industry expertise, customer service culture and local manufacturing facility. These attributes
standing still, you are probably going backwards.
PVC pipe technology has improved substantially, and is continuing to improve, thereby giving the pipeline industry proven materials to use for large-diameter, high-pressure, bulk supply pipelines – a market that steel and ductile iron have dominated historically. PVC-O pipes are lightweight, have a negligible friction increase over time, do not corrode, do not require expensive cathodic protection, give labour-intensive emerging contractors equal opportunity to compete, have extremely high impact strength, low creep, low celerity and extremely low embedded energy – maybe it is the material to help save the Earth?
As government, metros, municipalities and local authorities strive to provide
have also enabled Sizabantu to grow its export business into Africa, with one of its largest irrigation schemes, in Angola, an example of the success in this market. They illustrate that despite the competitive nature of the market, they are succeeding and prove an axiom of today’s world – if you are
services to more people – with an ever-increasing demand, and limited funding – the advantages of using TOM® 500 PVC-O thermoplastic pipes and fittings become self-evident.
The future prospects appear to be promising for the product. More than 4 km of 1 000 mm OD PN16 pipe have already been supplied and installed in Europe in 2021 and the first 1 000 mm OD pipes are expected to be supplied in South Africa in 2022. This will be another significant milestone for the South African thermoplastic pipe industry.
Industrial water reuse in South Africa is lagging. Currently, very little to no data exists regarding wastewater reuse options, treatment options and capabilities, or costs – which can be used for decision-making. In response to this, a national Atlas and Decision-based Support System has been developed.
By Maronel Steyn & Dr Chavon Walters
Further research and information is needed to identify wastewater and industrial effluent volume availability, quality and fitness for use in South Africa. A country-level assessment of the industrial effluent reuse potential can assist in identifying opportunities to unlock ‘new water’.
National Atlas
The national Atlas has been developed for the potential bulk-scale reuse of industrial effluent in South Africa. The Atlas is essentially a compilation of geographic information system (GIS) maps that have been created by digitising large-volume (bulk) water users/consumers of water in South Africa, as well as the respective industry sectors producing and discharging bulk volumes of wastewater in South Africa.
In that context, the Atlas:
• defines water reuse and discusses the drivers of industrial reuse in South Africa
• summarises the legislation underpinning industrial water reuse in the country
• provides examples of a few existing industrial reuse projects/activities currently taking place in South Africa
• describes ‘fitness for use’ and the typical wastewater effluent quality for different industries
• identifies some of the current barriers to industrial effluent reuse
• geographically maps the largest consumers of water and effluent producers in South Africa, both at a national and provincial level.
Information in the Atlas was developed using open-source data obtained from:
• Department of Water and Sanitation (DWS).
• Water Use Authorisation and Registration Management System (WARMS) – the official national register of water use in South Africa. The DWS WARMS database contains detailed information and reports on South African water users who use this resource (surface water and groundwater) for irrigation and industrial use, including mining, power generation, recreational purposes and watering livestock in the country.
• QA Data Reports for water consumption and effluents produced.
The Atlas presents maps at both national and provincial context, and provides a visual account of both the volumes of water used and effluent produced per industry sector.
• From a national perspective, wateruse-intensive industries were largely represented by the agriculture sector, mostly through irrigation. Second to agriculture was water supply services, urban industry, mining and non-urban industry.
• Water use for mining was the highest in Mpumalanga, followed by Gauteng, the North West, Northern Cape and Limpopo.
• Mpumalanga had the highest water withdrawals, followed by the Free State, Eastern Cape and Gauteng provinces.
• In all provinces, the largest water use was for agricultural irrigation, except in Gauteng, where industrial water use was the highest.
• The second highest industrial water use was the Western Cape. In the Western Cape, the highest water withdrawals per sector were for agricultural irrigation, followed by urban industry and water supply services.
• A large portion of non-urban industrial water use was identified in KwaZulu-Natal and Mpumalanga.
• The Northern Cape province had the lowest registered water withdrawal of all provinces.
• From a national perspective, the highest effluent produced was registered by urban/domestic (sewage treatment works), followed by mining. Mining effluent was recorded in all provinces except the Western Cape.
• Gauteng was the highest ranked province in terms of wastewater discharge, followed by Mpumalanga and the Eastern Cape provinces, respectively.
• Discharging wastewater effluent was associated with urban areas and industry. Large-scale irrigation
with wastewater is largely limited to the Breede-Gouritz catchment in the Western Cape.
• The provinces that registered the lowest effluent volumes were Limpopo and the Northern Cape.
Wastewater generation per industrial sector
The water consumption rates of industrial users are significantly higher than those of individual households.
Provincial average values for individual water consumption range from:
• 182 litres per capita per day (ℓ/c/d) for Limpopo
• to 305 ℓ/c/d for Gauteng. This suggests that the average consumption rates for a household of four persons is in the order of one kilolitre per day, or 0.001 megalitres per day (Mℓ/d).
By contrast, manufacturing plant/ factory water consumption rates are three orders of magnitude higher in some industries:
• Paper and pulp uses between 0.1 Mℓ/d to 150 Mℓ/d.
• Wet-cooled power stations (Matla and Lethabo) require in the order of up to 100 Mℓ/d.
• Dry-cooled power stations (Kendal and Matimba) use in the order of 10 Mℓ/d.
• Sugar mills consume between 0.6 Mℓ/d to 6.8 Mℓ/d.
• Oil refineries consume between 5 Mℓ/d and 10.5 Mℓ/d of water.
Industrial water users return significant fractions of their water consumption to the municipal wastewater system or the environment as effluent, except for wet-cooled power stations where water use is nearly entirely consumptive.
Decision-based Support System (DSS)
The authors realised that this Atlas provided only a one-dimensional and geographical overview of industrial reuse effluent volumes (based on water-use licence registrations). As a
Reuse: The beneficial use of reclaimed or treated wastewater
Reclamation: The treatment of wastewater for reuse, either directly or indirectly as potable or nonpotable water
Recycling: The reuse of wastewater, with or without treatment
result, an Excel-based DSS for the bulk-scale reuse of industrial effluent was developed (a web-based and mobile application is in the process of being developed).
This assists municipal and industry partners, and water quality managers to make informed decisions for possible reuse options. The tool aims to directly assist by linking industrial effluent volumes and quality to fitness for use, and linking it with specific industries in the geographical vicinity based on industryspecific water quality and quantity requirements.
The DSS can be particularly useful in wastewater reuse, as it can aid in the evaluation and selection of alternatives for a given reuse application. In addition, the tool will enable engineers and industry partners to collaborate to identify and employ treatment technologies and capabilities to link industrial effluent quality and volumes available to those of potential user requirements in a geographical area.
Effluent reuse (treating the final effluent to potable standards for on-site reuse, typically for non-product contact purposes), with or without energy recovery (biogas), represents the largest opportunity for water savings in the sector.
For more information regarding the Atlas and DSS, please contact msteyn@csir.co.za or cwalters@csir.co.za.
Every industry needs water – from cooling, heating, fabricating, processing and washing to steam production and even transportation. Endress+Hauser has a wide portfolio of measurement instrumentation and automation solutions, as well as decades of experience in optimising industrial wastewater treatment processes.
Industrial production accounts for 20% of global water consumption. Depending on the application and industry, the water needs to have different properties to ensure the quality of the finished product and the overall safety of production. Furthermore, water must be safely discharged. No matter if the water ends up in a natural body of
in most cases some form of wastewater treatment is necessary.
“Generally, water treatment in an industrial plant has the same goals as in a municipal treatment plant. Most of the established applications that are used in municipal plants can be found in industrial water treatment plants. The main challenge is to balance out the water quality and the treatment costs,” explains Heidrun Tippe, global industry manager: Water and Wastewater, Endress+Hauser.
Membrane filtration
One example is with membrane filtration. Depending on the pore size, membrane filtration can be applied to achieve different treatment targets: from mechanical separation of bacteria or viruses up to single ions for desalination during the preparation of process water. It can also be used for water reuse by filtering already used water. The main parameters for optimising the membrane filtration are inlet quality and pressure. Measuring these can help to prevent damage to the membranes.
Endress+Hauser has a range of pressure and quality sensors that are perfectly fit for this task.
Another challenge faced by both municipal and industrial wastewater operators is sludge handling. Disposing of sludge is expensive, so it is common practice to reduce the amount of sludge – either by dewatering it through the addition of conditioners like polymers or lime milk, or by anaerobic digestion. The pulp and paper and food industries produce wastewater with a high biological load and anaerobic digestion is a very efficient pre-treatment process. Plus, it generates biogas, which can be used as an energy source for other treatment processes. Basic process control like the measurement of the inlet load, level, temperature, pH/ORP and biogas production is needed to monitor the process accurately and optimise it. One of the toughest measurement challenges is the biogas flow because of the high water saturation of the gas and very low pressures. Endress+Hauser’s unique ultrasonic flow devices offer a solution to this challenge.
WEC Projects has secured a R3 million contract for the expansion of the mine’s sewage treatment facility. The company installed the original treatment plant in 2012 and will integrate the new system into the existing facility, increasing throughput from 100 m3 to 150 m3 per day to meet the requirements of an increase in the number of staff at the mine.
The main sewage treatment facility will consist of a WEC Projects Model A treatment plant – an extended aeration system using conventional activated sludge to process the sewage. The wastewater passes through a mechanical screen, which removes solids and is then treated by a biological reactor that integrates anoxic, aerobic and clarification zones.
Reed bed wetland system
While the treatment plant itself is a standard installation, the mine requested a variation to the original project scope – a man-made natural reed bed wetland system that will provide a ‘polishing’ phase to the treatment process, using natural organisms and filtration processes to further clean the wastewater.
“This is a particularly unique feature for a mine, as such reed bed wetlands are usually built for much larger installations such as municipal sewage treatment. The government’s mandate for water
conservation has forced companies in Botswana to apply creative thinking to overcome the challenge of operating in an arid country,” says Wayne Taljaard, MD of WEC Projects.
After treatment, the water will enter the reed bed wetland area where it will percolate through the reed bed, allowing microorganisms to break down contaminants such as sulfur, heavy metals and chlorine. The water produced by this process, while not for human consumption, will be reused by the mine for applications such as irrigation and dust suppression.
To create the wetland, a shallow dam will be built, its bottom filled with gravel
Located in the eastern Kalahari Basin – where water is scarce and temperatures average 35°C – Lucara Botswana’s Karowe diamond mine is due for an improved sewage treatment facility.
and reeds planted. The water from the treatment plant will feed into the wetland area where nature will be left to take its course.
“The reed bed solution offers a number of advantages for the mine, as the effluent will be relatively odourless and is flexible enough to cope with fluctuations in input. It also requires little maintenance once it is up and running, and will ensure that the mine remains within the confines of the law,” adds Taljaard.
Until 2021, the water sector was a limited part of the Dekra Industrial portfolio.
“We are certain that the expansion of our service offering in the water sector will become an integral part of our ‘one stop’ NDT and inspection basket of services, generating valuable new business for the company going forward – as well as adding significant value to the water sector itself,” says Johan Gerber, managing director, Dekra Industrial.
In light of the fact that a shortage of water is becoming a concerning threat to South Africa’s sustained economic development, Dekra Industrial acknowledges that – with its vast experience in the field of corrosion control and NDT solutions – expanding its expertise in the water sector makes complete sense.
Dekra Industrial will reposition itself strategically – not only as an NDT
A specialist in non-destructive testing (NDT) and inspection services, Dekra International is offering its existing services to the water industry.
inspection services provider but also a holistic, ‘one-stop-shop’ service provider of NDT inspection, corrosion control, welding, water leakage detection, and certification services.
“It makes absolute sense to additionally offer corrosion control, painting and blasting to the water sector,” agrees Eddie van Hansen, GM, Dekra Industrial SA. “Above-ground pipelines, water purification plants, reservoirs, tanks and dam walls are all areas where corrosion takes place. By offering a multifaceted approach, we will be able to supply our clients with a complete solution,” he says.
Another technology offered by Dekra is inspection technology through drones. “Drone technology is enabling companies like Dekra Industrial to really push the boundaries of non-destructive testing and inspection,” Van Hansen comments, adding that the company aims to use this platform for advanced inspection and testing in a wide range of industrial applications.
“For example, when we do concrete inspections using drone technology, we are able to pick up problems that were previously hard to detect,” says Van Hansen.
“In terms of the water sector, drone inspections can be done on dam walls and other concrete structures that are affected by water and corrosion. Furthermore, by offering cement inspections on water tanks, we can detect leakages and ultimately save money and large maintenance costs further down the line for both private and municipal water entities,” he adds.
Dekra Industrial also believes that loss of water due to ageing or poorly maintained infrastructure can be solved using automated drone inspections, by using a drone programmed to follow a specific route and digitally map cracks and leakages: “The camera essentially controls the drone and is able to detect hazards – for example – in water reservoirs or tanks. The visual data obtained from the drone is recorded and – thanks to the use of dimension data analytics and thermal imaging – water infrastructure such as tanks, dam walls or reservoirs can then be repaired, section by section,” explains MC Liebenberg, advanced technology manager, Dekra Industrial.
“Important water resources such as the Vaal Dam would benefit hugely from regular drone inspection. It has been estimated that up to 30% of its water volume is lost before it reaches storage, due to rust and corrosion
Infrared technology, when applied within the context of drone inspections, can also effectively inspect areas at risk of cracks and leakage
leakages in underground pipes. Using drone inspection, we would be able to locate the leakages, clean and inspect the area, and finish with the powder coating and a final leak check – applying our ‘one-stop’ ethos in a practical water application,” Liebenberg points out.
Other innovative technologies for the water industry
Other NDT methods used to measure and analyse cracks running through concrete water storage tanks, dam walls and similar water infrastructure include the ultrasonic method, which takes place inside the concrete and is not invasive or
destructive in any way. In addition to this, alternate current field measurements, acoustic emissions and the use of a Hovermap (where an additional thermographic camera with in-built software is attached to a drone) are other innovative testing and inspection options used by Dekra Industrial.
“Infrared technology, when applied within the context of drone inspections, can also effectively inspect areas at risk of cracks and leakage. For example, groundpenetrating radar is particularly effective when the detection of water leaks under substrate such as tarmac is required,” Liebenberg adds.
• 96 years of experience, through global parent company Dekra International
• Dekra Institute of Learning specialises in the field of safety, health and environmental management, accredited with various SETAs under the umbrella of SAQA. Dekra provides a range of custom-made training solutions aimed at individuals and companies alike
• Has a presence in over 60 countries and on six continents
• Dekra Industrial SA provides safety solutions across a multitude of industries, including power generation, oil and gas, construction, petrochemical, manufacturing, fabrication, pulp and paper, rail, mining, steel industry and foundries
• Level 3 BBBEE compliant, with 51% black woman ownership
• RD 0034 compliant, a nuclear safety compliance standard, and one of the few NDT companies locally to hold the ISO 45001 certification
Armed with the vision to create a world of universal access to clean water and safe sanitation, the WASH R&D Centre – previously called the Pollution Research Group – focuses on building knowledge and delivering insight that provides solutions for global water and sanitation challenges through an integrative, transdisciplinary approach.
The late Professor Chris Buckley, former director of the University of KwaZuluNatal (UKZN) WASH R&D Centre, strongly encouraged collaboration with researchers in agriculture, development studies, chemical and civil engineering, economics, statistics, modelling, and social sciences when solving water and sanitation challenges,” says Dr Colleen Archer, parasitologist and head of laboratory, UKZN WASH R&D Centre. She adds that this approach has
filtered into the structure of the WASH R&D Centre, where its key activities include:
• research support to eThekwini Municipality on aspects of water and sanitation service delivery and management
• provision of technical, engineering and laboratory support to developers of new sanitation technologies being tested in the field
• research into the circular economy and the link between sanitation and agriculture
• engaging with communities and households participating in water and sanitation research projects
• supervision of postgraduate students in projects related to water, sanitation, agriculture and health
• strengthening existing collaborations with funders, government bodies, research organisations and industry, and forging new relationships.
Community engagement
The Social Sciences Division plays a huge role within the UKZN WASH R&D Centre. “Social acceptance of sanitation technology is pivotal to the success of new toilets. Sanitation pilot projects must be placed within a community that accepts them. The community needs to understand the value the toilets can bring, and often need to accept that they are not a permanent feature. Furthermore, new sanitation technology relies on feedback from
the community for modifications and improvement,” explains Thabiso Zikalala, acting lab manager, WASH R&D Centre.
Collaborative partnership with eThekwini Municipality
Since 2003, the UKZN WASH R&D Centre has provided eThekwini Municipality’s Water and Sanitation Unit (EWS) with scientific support to develop and implement innovative water and sanitation services to the underserved, along with efforts to maintain cost-competitive waste treatment services to industry, and ensure the health and environmental status of rivers and beaches is maintained. Over the years, memoranda of agreement have been signed between the two organisations to formalise the collaboration.
Most projects conducted by the WASH R&D Centre have an impact on water and sanitation service delivery in eThekwini, and EWS is a key partner in the Centre’s research.
“We believe in conducting research that can be applied in our own ‘backyard’. This collaboration ensures the success of new sanitation technologies because they are thoroughly tested by us both in the field and in our laboratory. EWS is dedicated to improving sanitation,” states Archer.
Bioprocessing laboratory
The WASH R&D Centre maintains a modernised bioprocess engineering
laboratory with specialised equipment for analysing wastewater, compost and faecal sludge samples, and conducting research on innovative wastewater and sanitation technologies.
In addition to standard equipment, the laboratory is also fitted with:
• MPAES for testing heavy metals and nutrients
• CNS analyser that provides a ratio of carbon, nitrogen and sulfur content
• freeze dryer for safer shipment of samples around the world
• particle-size analyser that can detect the smallest particle within a sample. “We work with human excreta and sewage samples from non-sewered sanitation systems, decentralised wastewater treatment plants (including Dewats), and centralised wastewater treatment plants to obtain design and
“We provide a quick turnaround time when delivering results of analyses and are therefore often used by clients in the water and wastewater industry. We also have a small pilot laboratory in Newlands Mashu,” adds Zikalala.
The WASH R&D Centre has one of the few laboratories in the world that conducts environmental helminth testing.
Helminth eggs (and larva) are the infective stages of parasitic worms and pose a risk to human health. They are excreted in the faeces of infected individuals and are thus concentrated in sewage sludge. They provide health and environmental risks to householders, communities and those involved in the toilet-emptying process.
diversion (UD) toilets. As opposed to wastewater, UD toilet waste is solid and a more suitable method needed to be developed to process samples, as the USEPA method was unsuitable,” explains Archer.
Together, the student and Archer developed the first version of the helminth testing protocol that has subsequently been modified by Archer and her current PhD student. “We have now created a test method that can be applied to any sample type – from liquid to soil,” she adds.
Due to their hardiness and longevity of Ascaris (a genus of helminths) eggs are used as a marker for the safe reuse of sanitation products. There is a worldwide shortage of these eggs (for use in research) and importing them is difficult, as government is strict about bringing in pathogens.
The Centre has therefore set up a pig farm, where two pigs are moderately infected with Ascaris suum and eggs are excreted in their faeces. These eggs are harvested and used for experimental purposes. “We spike them into test toilets that claim to destroy pathogens on-site so that the faeces can safely be used as soil conditioner. Once eggs pass through the toilet, we retrieve, count and evaluate their viability status, and incubate them to see if larvae develop,” explains Archer. Alarmingly, she adds, “Many laboratories that conduct helminth tests do so incorrectly. When looking at their lab results, this becomes apparent when they merely report ‘viable helminth eggs present’ without identifying the types of helminth eggs. There are many different organisms that live in the soil and produce eggs that look like pathogens, and when there is no specification, it is safe to assume that eggs (and possibly other artefacts) were simply counted under a microscope.” On-site toilet systems must demonstrate pathogen inactivation to be ISO 30500 accredited, hence the need for an accredited helminth test.
ISO 30500 and ISO 7025
New sanitation technologies are tested against metrics set down by the ISO 30500 standard for both mechanical functions (e.g. flushing, quantity of water used, amount of waste left in bowl) and chemical testing by the laboratory (e.g. COD, pH, TSS, ammonia reduction, nitrogen reduction and phosphorus reduction). “It is very expensive to do all the tests recommended by ISO 30500. Currently, the Water Research Commission is working on ‘setting a standard within a standard’ – a ‘Mark System’ where it is compiling a list of essential tests that must be passed for the toilet to be given the stamp of approval, indicating that the system is accepted for use,” explains Zikalala.
According to Archer, the laboratories that conduct ISO 30500 testing need to be ISO 17025 accredited. “This is an incredibly costly venture; it’s an intensive procedure and laboratories need to employ more staff due to the huge amount of paperwork that must be produced and maintained.”
Currently, the WASH R&D Centre is working towards ISO 17025 accreditation for its helminth and the total solids tests. There is no other laboratory in Africa accredited for an environmental helminth method. “Our forms have been submitted and we are hoping to be accredited within the first half of 2022,” states Archer.
The laboratory conducts both standardised tests and well as specific tests developed by the laboratory, which have been published in a book –Methods for Faecal Sludge Analysis.
The testing of faecal sludge is an intricate process. Since standard methods for sampling and analysing faecal sludge do not currently exist, results are not comparable, the actual variability is not yet fully known,
and the transfer of knowledge and data between different regions and institutions is challenging and often arbitrary. Due to this lack of standard analytical methods for faecal sludge, methods from other fields – such as wastewater management, and soil and food sciences – are frequently applied. However, these methods are not necessarily the most suitable for faecal sludge analysis and have not been specifically adapted for this purpose. The UKZN WASH R&D Centre has therefore developed test methods best suited to faecal sludge.
“The aim of this book is to provide a basis for the standardisation of faecal sludge methods from on-site sanitation technologies, for improved communication between sanitation practitioners, and for greater confidence in the data generated. The book presents background information on types of faecal sludge, methods for sample collection, health and safety procedures, case studies of experimental design, an approach for estimating faecal sludge at communityto city-wide scales, modelling containment and treatment processes, recipes for simulants, and laboratory methods for faecal sludge analysis currently in use by faecal sludge laboratories,” adds Zikalala.
“We are passionate about developing and teaching people in the water and sanitation field, where they can eventually work in key positions within the sector and use their background, knowledge and passion to improve sanitation,” says Archer.
The laboratory trains local and foreign MSc and PhD students on how to use the laboratory equipment and perform tests, and has assisted in training laboratory staff from many countries, including India, Tanzania, Malawi and Cambodia.
Largely driven by legislation, wastewater sludge is increasingly viewed as a resource. Rudi Botha, senior water sector analyst at GreenCape*, talks to WASA about wastewater sludge beneficiation and its circular economy solutions.
The Department of Forestry, Fisheries and the Environment, and the waste management divisions of municipalities largely consider waste as a resource. This perception has filtered into the water industry, where the energy and resource recovery from wastewater sludge is regarded as an attractive business model. However, our sector has not yet made the requisite shift where wastewater sludge transitions from a growing liability to a resource. Wastewater sludge is still a nuisance in terms of water management and is seldom a focus of the treatment process,” explains Botha.
“If sludge were viewed as a valuable resource and there were an emphasis on how to harness that resource, the treatment process would change.
This would make it easier to recover the treated water from wastewater, as well as nutrients, energy and soil conditioners,” adds Botha.
The City of Tshwane has an agreement with a fertiliser manufacturer to process their sludge into compost for blending into fertiliser products. However, the other metros are facing transport and disposal costs of about R330 million per year. The disposal of wastewater sludges is an enormous cost to the operations of wastewater treatment works (WWTWs).
The City of Cape Town (CCT), for example, currently spends around R60 million per year to
dispose of (or apply to land) about 200 dry tonnes per day of dewatered primary and waste activated sludge (WAS) it generates, with an average moisture content of 83% (ranging between 58% and 92%).
This amounts to 74% of provincial sludge production. Half of the CCT’s sludge (the WAS) is in dry mass and applied to agricultural land, while the other half (primary and blended sludge) is treated and sent to the Vissershoek private landfill.
Legislation – a driver to a more circular economy
Waste and wastewater discharge regulations, such as the ban on landfilling of liquid waste, and the Western Cape plan to divert organic waste from landfill (50% diversion targeted this year and 100% by 2027) are key drivers for resource recovery projects at WWTWs.
Furthermore, the 2017 amendment to Schedule 2 of the Electricity Regulation Act (No. 4 of 2006) provides the policy and regulatory framework for municipalities to develop their own electricity generation, such as biogas and combined heat and power (CHP) projects.
“A circular economy minimises waste; regenerates ecosystems; and keeps products, components, and materials, including biological materials, at their highest use and/or value for as long
as possible. Municipalities, notably metropolitan areas, are large consumers of goods and services. As such, they are well placed to drive circularity at scale. Nowhere is this more relevant than the CCT with its planned shift to wastewater sludge and digestate beneficiation,” highlights Botha.
Many WWTWs currently dispose of wastewater sludge at landfills. They will now have to find alternative, sustainable ways of sludge disposal.
“In response to these two regulatory restrictions, the CCT is starting the transition towards anaerobically digesting its total wastewater treatment work sludges. Over the next 15 years, the CCT will be investing in the establishment of two regional biosolids beneficiation facilities with a third facility planned to serve future demand,” explains Botha.
Biosolids beneficiation facilities (BBFs)
As a result of the legislation, the CCT is transitioning towards anaerobically digesting its wastewater sludges in BBFs to:
• produce A1a class treated digestate cake that is safe for unrestricted use, nutrient rich, odour free and low in contaminants
• work towards sustainable sludge treatment, including electricity generation from biogas, reusable heat generation and recovery of nutrients
• reduce its climate change liability. A service contract (SCMB 82/11/20) is currently in place to dispose of (or apply to land) the CCT’s sludge. This contract will expire at the end of June 2023. However, it is expected that the CCT will re-tender for disposal, land application and/or beneficiation services for primary, WAS and blended sludge.
Once the first BBF has been commissioned, WAS and digestate cake will be available as part of the service contract, as well as emergency beneficiation/disposal of primary and blended sludge in case diverting is required.
All the primary and blended sludge will be digested at the first BBF, but there will be insufficient capacity to digest all the CCT’s WAS until the second BBF is commissioned (within 15 years). In the long term, an increased sludge production associated with population growth will require a third BBF facility or another circular solution for the WAS.
“What is challenging in the municipal space is sourcing funding needed to provide resource recovery facilities –BBFs have a large capital cost and there is minimal grant funding available for them. Due to the cost of the technology, large quantities of sludge need to be treated to allow for the efficiency of scale to be viable, for example, in metros,” explains Botha.
The public perception and safety concerns regarding the use of wastewater sludge for energy production, agricultural application and saleable products to the public represent some of the major barriers to sludge beneficiation projects.
“As an example, it is acceptable to grow grass from beneficiated wastewater sludge, but there is still uncertainty around growing vegetables – especially regarding pharmaceuticals found in wastewater sludge,” says Botha. She adds that there is also an issue around legislation. “While legislation has been a driver, it is also a barrier. There are a lot of private sector players that are ready to beneficiate organic waste, but legislation requires these companies to go through an environmental impact assessment process to get a waste licence. This is a huge cost and can take two to three years to obtain.”
However, the good news is that this process may be simplified for qualifying companies. Norms and standards for composting have been published and are being developed for organic waste treatment. Once promulgated, these norms and standards will streamline the whole process and will allow for qualifying facilities to operate without a waste licence, provided they comply with standard procedures and capacity limitations set forth.
According to Botha, the composting of wastewater sludge is easier with smaller quantities, while stabilising the sludge and using it as part of fertilisers is being successfully done on a larger scale. “These fertilisers are registered and externally monitored. On the nutrient side of sludge beneficiation, one can utilise the carbon, nitrogen and phosphorus and put it back into soil to help plants grow. Various processes can be used to harness energy from sludges too.”
The increasing costs of electricity (27% over the next three years) will enhance the financial benefits of investing in sludge
beneficiation to produce energy. This can be done via anaerobic digestion (biogas), pyrolysis, gasification, hydrothermal carbonisation, etc.
Some WWTWs have anaerobic digesters but they are often not heated nor run optimally, and the gas is not captured.
“While significant work has been done by the CCT to start shifting wastewater sludge from a liability to a resource, there has been exciting work in other provinces. Johannesburg has the Northern WWTW with anaerobic digesters and a biogas-toenergy facility (that was privately run) – the first in the country. However, the facility did not receive enough gas to produce
Some WWTWs have anaerobic digesters but they are often not heated nor run optimally, and the gas is not captured
a sustainable source of energy for the WWTW. Tshwane is investigating hydrothermal carbonisation. Both Johannesburg and Tshwane have successfully targeted the agriculture sector with their sludge. EThekwini has a number of anaerobic digesters, and some are fitted with biogas-to-heat facilities where the heat energy is reused within the digestion process. I am excited to see these developments and look forward to wastewater sludge being a bigger part of the circular economy,” concludes Botha.
*All GreenCape’s research into wastewater sludge beneficiation has been funded by the City of Cape Town.
Demand for facilities that offer an alternative to landfilling, through the beneficiation of sludge beyond its waste classification or into saleable products, is rising
general, energy recovery and agricultural/ commercial beneficiation solutions are complementary, because by-products from the energy recovery options are well suited to agricultural and commercial
QFS designs, manufactures, installs, commissions and maintains membrane plants and general water treatment equipment. The company recently experienced differential pressure increases due to fouling of the membranes in one of its desalination plants.
A2 Mℓ/day seawater ultrafiltration unit (SWUF) that abstracts water from a river estuary near the mouth entering the Indian Ocean experienced differential pressure due to fouling of the membranes. This reduced the plant production by increasing the daily downtime required for chemical cleaning of the membranes.
To identify the root cause of the fouling, QFS took samples from the raw water feed (upstream river) and fibre from the fouled membrane. The raw water samples were sent for analysis to two independent laboratories while the fouled membrane fibre samples were sent to the Central Analytical Facilities of Stellenbosch University for analysis with a scanning electron microscope (SEM).
FIGURE 3 The analysts noted that the clay-like samples show a presence of diatoms, which are algae with silica cell walls. The observed diatoms have a size of 5 µm to 30 µm based on the SEM images. The presence of diatoms would suggest the presence of diatomaceous earth, which is the diatoms’ fossilised remains, with the characteristics of a fine, highly porous and siliceous powder used in the ceramics industry. Diatomaceous earth generally has a size of 10 µm to 200 µm
Conclusion
A combination of aluminium silicates and diatomaceous earth is contributing to the formation of clay layering in between precipitated salt layers. A large presence of diatoms generally coincides with nutrient-rich water. It is known that the river from which the plant abstracts is subject to sewer run-off and sewage dumping. Although the feedwater turbidity, total suspended solids and total dissolved solids (TDS) are all within design specifications, it is evident that the combination of the abovementioned solids creates a clay-like surface coating. This coating proved difficult to remove from the membrane fibres that standard backwashing and chemical cleaning could not successfully remove. A combination of various detergents was tested and resulted in the successful cleaning of the membrane samples. This combination was recreated using industrial chemicals with the active ingredients of the abovementioned detergents, and used to successfully clean the UF membranes, bringing it back to a baseline state.
Pressure is a vital factor in desalination. WASA speaks to Martijn Smit, Managing Director for Netherlands, Belgium and Southern Africa of Keller, a global expert and manufacturer of pressure management systems.
In the reverse osmosis desalination process, a pressure greater than the osmotic pressure applied to the saline water will cause fresh water to flow through the membrane while holding back the solutes (salts). The pressure needed is typically between 50 kPa and 60 kPa, which is the perfect range for the Keller range of sensors,” adds Smit.
Furthermore, pressure sensors should be fitted to filters. “Salt water goes through a filtration process before reverse osmosis. Differential pressure sensors should be fitted to the filters to determine the contamination levels of the filters and the best time to replace them, as they are costly.” He adds that one also needs to measure the inlet pressure of the pumps, as well as the levels of the desalinated water collected in the tank.
Deploying desalination as a key strategy in Africa’s water security mix has been boosted in recent years as renewable energy becomes more efficient
Salt in the water eventually corrodes standard stainless-steel sensors; therefore, Keller’s sensors can be manufactured in titanium or Hastelloy that gives resistance to chlorides and sulfates.
The Keller pressure transmitters that can be used in the desalination process are the 23SY series, 23SX series and 33X series. The 36XiW-CTD sensor can be used to measure water levels, temperature and conductivity (amount of salt in the water), in addition to pressure.
“Due to Africa’s water crisis, governments and foreign investors are
In the reverse osmosis desalination process, a pressure greater than the osmotic pressure applied to the saline water will cause fresh water to flow through the membrane while holding back the solutes (salts)
pouring billions into schemes to turn seawater into safe drinking water. The long-term prospects for desalination as a key strategy in Africa’s water security mix have been boosted in recent years as renewable energy becomes more efficient, and the method of converting brine and other desalination waste products into useful commodities, like hydrochloric acid, through standard chemical processes makes facilities more cost-effective,” concludes Smit.
Keller has its headquarters in Winterthur, Switzerland, and is Europe’s leading manufacturer of media-isolated pressure transducers and transmitters. The entire production process – from the manufacturing of the individual components and the calibration of the sensors through to the final quality control of the finished products – takes place at the company’s headquarters. Instrotech distributes Keller products to the South African and African markets.
Decentralised wastewater treatment systems (DEWATS) are the sweet spot between waterless on-site sanitation and conventional sewers with centralised wastewater treatment. Bremen Overseas Research and Development Association (BORDA) has been partnering with eThekwini Municipality to pilot and implement DEWATS wherever a wastewater processing solution is needed. By Kirsten Kelly
DEWATS is an approach rather than a technical hardware package. With DEWATS, the system must be adapted to suit a specific context,” explains Lloyd Govender, project engineer, BORDA SA.
The standard system is independent of electricity and chemicals (but can be modified to use both) and is easy to install. DEWATS is also tolerant towards inflow fluctuations. It can treat between 1 m 3/day and 1 500 m 3/day of wastewater.
“The aim is to keep the construction of DEWATS simple. When disseminating information, there should be basic diagrams and all construction materials should be as generic as possible –
easily found at any hardware store. This helps in ensuring all DEWATS parts are readily available for construction and maintenance,” adds Govender. BORDA has worked out that DEWATS needs 1.5 m 2 in space per person. They have successfully reduced the size of the system every year through continuously assessing their current system.
The global NGO has worked with eThekwini Municipality for many years to exchange knowledge and build capacity in the water and sanitation sector. They advise on innovative technologies and the local implementation of
DEWATS, while funding student research and projects.
While South Africa has strict wastewater discharge limits, DEWATS can be modelled to achieve different discharge criteria. Additional mechanisms can be added like ultraviolet disinfection or chemical treatment with chlorine.
Settler
The first stage is the settler, or septic tank. This consists of a minimum of two, sometimes three, compartments. The settling chamber allows for the wastewater to settle first, where scum is formed at the top and heavy particles
sink to the bottom. A grease trap can also be used in the settler.
Wastewater will flow through the first chamber and solids will settle, with the rest of the wastewater flowing up and down from one chamber to the next. This extends the retention of solids, achieving better treatments.
The second chamber is usually half the width of the first compartment. It contains only a little sludge, which allows for the water to flow without disturbance from rising gas bubbles. Two treatment principles –namely the mechanical treatment by sedimentation and the biological treatment (sludge digestion) by contact between fresh wastewater and active sludge – are taking place. Optimal sedimentation occurs when the flow is smooth and undisturbed. Biological treatment is optimised by quick and intensive contact between new inflow and old sludge.
As the settled sludge passes through the system, it sinks lower. The wastewater particles that are not heavy enough to sink move to the anaerobic baffled reactor. The inlet and outlet have a t-pipe, preventing blockages. The outlet should be about 20 cm lower than the inlet.
DEWATS usually achieves a 20% to 30% biological oxygen demand (BOD) removal efficiency.
Desludging is necessary every one to three years and can be achieved with a vacuum truck or something similar. Dissolved and suspended matter passes untreated to the next stage.
Anaerobic baffled reactor
This is a usually a precast concrete block chamber
because it is difficult to steal and cannot be sold for scrap. The baffled reactor consists of a series of chambers designed to increase the path taken by particles from the time they enter the inlet and leave at the outlet.
“Initially, we designed an ABR with seven chambers, but it was found that three or four chambers are all that is needed,” adds Govender.
Suspended and dissolved solids in the pre-settled wastewater undergo anaerobic degradation. The activated sludge settles down at the bottom of each chamber and the influent wastewater is forced to flow through this sludge blanket where anaerobic bacteria make use of the pollutants for their metabolism.
Progressive decomposition occurs in the successive chambers.
A part of the last chambers can optionally be filled up with coarse filter material like stones, cinder or plastic rings. The filter material acts carrier material for an attached biofilm, consuming the organic water pollutants. That kind of reactor is called combined ABR. In ABR plants, the pathogen reduction ranges from 40% to 75%. The baffled reactor is resistant to shock load and variable inflow. It operates by gravity and maintenance is reduced to desludging of the chambers at intervals of one to two years. Subsoil construction of the module saves space.
time, number of chambers, temperature and the outflow velocity. The ABR can achieve up to 95% of BOD removal,” states Govender.
Biogas digester (BGD) DEWATS allows for the utilisation of biogas,
with BOD of not less than 1 000 mg/ ℓ is required to serve one kitchen. In order to get strong substrate from domestic wastewater, flow stream separation from toilets and less concentrated greywater are recommended.
“Key design parameters in the ABR are the retention
By using BGDs, approximately 200 litres of biogas can be recovered from 1 kg of COD (chemical oxygen demand) removed. On household level, this requires 2 m³ to 3 m³ of biogas per day for cooking, meaning 20 m³ wastewater
Biogas plants are designed as half-ball shape, made by bricks and integrated into the ground. Incoming wastewater is separated into liquid and solid phases, and organic solids are biologically digested.
Processes take place without oxygen input under anaerobic conditions, generating biogas useful for cooking, light and heating. However, Govender notes that there are instances where BGD components are stolen and sold for
how would one decide which family can use it? In these circumstances, biogas must be used for communal lighting and heating.”
The anaerobic filter, also known as a fixed-bed
their scrap value. “Also, one has to consider the infrastructure required (and its maintenance) for biogas storage and usage. For example, if the biogas generated by 10 families can only be used by one family,
the dispersed or dissolved organic matter within a short retention time. It is designed based on the amount of wastewater received per day. Most of the microorganisms are immobile; they attach
themselves to solid particles or the reactor walls, for example. Filter material –such as gravel, rocks, cinder or specially formed plastic shapes – provides additional surface area for them to settle. The material needs to be non-porous and between 3 cm and cm in diameter. By forcing the fresh wastewater to flow through this material, intensive contact with active microorganisms is established – the larger the surface for microbial growth, the quicker the digestion. Comprising two chambers, the anaerobic filter forces the wastewater to flow upwards.
Mechanical siphon
In order to achieve a system that is independent of electricity, a mechanical siphon is used for the distribution of wastewater from the collection chambers on to the constructed wetlands. This is achieved by using the principles of buoyancy. While this type of pump is available in Europe and the US, it was decided that it should be designed in Africa, to ensure readily parts.
BORDA, together with Partners in Development, began the design and testing of a mechanical siphon in South Africa for use on the Banana City DEWATS in KwaZulu-Natal. Designed with easily accessible materials (steel and plastic) that are found in any hardware store, the
mechanical siphon can achieve a flow rate of over 60 ℓ/s. The design of the pump is available to the public and does not have any intellectual property rights attached to it.
“DEWATS can have two types of wetlands – vertical flow, where wastewater will flow vertically from the top, and horizontal flow, where the wastewater flows across the wetland,” explains Govender.
The wastewater is pumped into two constructed wetlands, with each wetland designed to treat to the necessary COD limit. Both aerobic and anaerobic conditions are used to treat the nitrogen compounds, pathogens and organic pollutants. The wastewater is then discharged to an outfall structure that prevents soil erosion.
Planted gravel filters are suitable for wastewater with a low percentage of suspended solids that have already been removed by pre-treatment. The main removal or treatment mechanisms are biological conversion, physical filtration and chemical adsorption. In the case of planted gravel filters, the bottom slope is 1% and the flow direction is mainly horizontal in agricultural systems and vertical in environmental discharge systems.
The gravel filter is permanently soaked with partially treated wastewater and operates as partly aerobic, partly anoxic and partly anaerobic. It combines physical filtration processes and the influence of plantation (on the biological treatment process and oxygen intake). The BOD reduction rate is 75% to 90% and
• An expert NGO specialising in full-cycle decentralised sanitation
• Together with governments, local enterprises and partner organisations, BORDA works on-site to improve communal planning processes, sanitation supply structures and basic needs services. They tackle unsolved sanitation challenges and bring tried and tested solutions to challenging places
• Headquarters in Bremen, Germany, and regional offices in Tanzania, India, Jordan, Thailand and Mexico
• With a network of local partner organisations, BORDA is active in more than 20 countries
• BORDA has been working in South Africa since 2006 to extend the wastewater infrastructure for inhabitants of peri-urban areas
• Focused on projects in new and existing low-income housing developments, informal settlements and schools
• Has partnered with eThekwini Municipality to exchange knowledge and build capacity in the water and sanitation sector, and to advise on innovative technologies and local implementation of DEWATS
pathogen removal rates are high, but dependent on the composition of the incoming wastewater. The operation and maintenance requirements are considered simple.
“Constructing a fence around the wetland adds to the cost of DEWATS, but there is always a possibility that children will play within the wetland or people will use the wetland as a toilet. One can also prevent this from happening through the design of the wetland. Tall or spiky plants can be added to the perimeter. Plants can be used to attract birds and insects and create a habitat,” adds Govender.
Constructed wetlands take up a lot of space but you can design them innovatively, which makes a world of difference to the acceptability of decentralised systems.
“DEWATS is doomed to fail if there is no education on why the system is in place and what it does. A good portion of one’s annual operations and maintenance budget should be allocated towards continuous community education. This prevents vandalism and theft, while improving community acceptance,” says Govender.
“Sometimes, communities perceive DEWATS as inferior to conventional wastewater treatments. They do not want to see the treatment, but we use education and transform these initial negatives into strengths and positives. Before we lay the first brick
on-site, we must have acceptance by the community. Education campaigns teach the community the value of a good sanitation system. We distribute pamphlets, conduct training courses, and transfer knowledge to the community on the importance of not just having a system but practising good personal hygiene. You would be surprised how happy the communities are to receive this form of knowledge,” he adds.
These systems are also designed so that local community members can be
employed to build and operate them, thus creating a feeling of ownership.
Construction
Different combinations of treatment modules can be used, depending on factors like the required treatment efficiency, costs and land availability. Making the best use of gravity, DEWATS is placed at the lowest point of the site being serviced. The entire system (except for the constructed wetlands) is underground, and this reduces any smell due the anaerobic treatment. The plants can also block off the smell and the vent pipes are strategically positioned above nose level at the DEWATS site.
“To be sustainable, DEWATS must be low-cost, require little to no water and electricity to run, use locally available materials and bio-based processes and, most importantly, be simple to operate and maintain. Sustainability also requires buy-in and ownership from the local community, as well as policy support from local government. BORDA and its partners design, implement and evaluate decentralised sanitation systems around the world. Our partnerships are leading the way in piloting innovative solutions in the face of increasing water scarcity,” concludes Govender.
TABLE 1 Centralised vs Decentralised Systems Centralised systems Decentralised systems
Flexibility
Cost
• Difficult to adjust size
• Prone to complete system failure
• Dimensions have to cater for high fluctuations
• High investment costs
• Pumping costs for both treated and untreated wastewater
• Size adjusted when and where needed
• Does need maintenance, but significantly less
• Can adapt to flow changes
• Built where needed
• Reuse options where needed
In a joint venture with a local construction, concessions and manufacturing group, WEC Projects has designed and built a water treatment plant that will supply potable water to a large community in Gauteng.
The R270 million plant is designed to provide 60 Mℓ/day and was commissioned as part of a R1 billion upgrade project for the community, which has experienced a considerable increase in demand for potable water over the last few years. The scope of work for WEC Projects included mechanical, electrical and instrumentation work.
WEC Projects, with a joint venture partner, was awarded the contract to expand the existing facility in 2016. However, due to the complexity of the project and the need for buy-in from the local communities benefiting from the treatment plant, final commissioning only took place in 2021.
undergoes dissolved air flotation to remove any remaining solids and oils.
The clarified water then enters a rapid gravity sand filtration system to remove particles. This type of filtration system was specified due to the higher filtration rate it provides compared to conventional sand filters – which is
time through a filter system containing granular activated carbon. This process removes organic chemicals and other similar impurities.
The final process is the chlorification of the water to ensure that any harmful impurities such as bacteria are removed.
Raw water is drawn from a nearby dam and pumped to the facility – where it undergoes clarification to remove suspended solids. After the primary clarification process, the water
necessary for a plant required to supply more than 500 000 people.
After exiting the sand filter, the water is pumped to the ozonation facility for rapid oxidation and disinfection. It is then put through a second filtration process – this
“This was a challenging project. The design of the plant required the water to undergo a complex processing solution to achieve the quality level required by the local municipality. We were also required to integrate the new plant module into the existing treatment plant.
As a result, the plant uses a sophisticated and advanced control and instrumentation system to ensure consistent quality and plant uptime. While the requirements were for a water treatment plant capable of delivering 60 Mℓ/day, the new plant has been tested successfully to 120 Mℓ/day, ensuring that it will be able to handle increased demands well into the future,” concludes Wayne Taljaard, MD of WEC Projects.
Understanding the economic value of a wetland can positively influence decisions around wetland management. SRK Consulting was appointed to calculate the value of the ecosystem services provided by the Papenkuils Wetland, as well as the potential change in value of these services, if an existing diversion weir were to be raised. By Kirsten Kelly
Located within the Western Cape, the vast Papenkuils Wetland is fed primarily by the Breede River, but also the Holsloot River, a smaller tributary of the Breede. A diversion weir redirects a portion of that water into Brandvlei Dam and away from the wetland; raising the weir by 30 cm to improve the supply of irrigation water would further increase the volume of water diverted away from the wetland into Brandvlei Dam.
The Western Cape Department of Environmental Affairs and Development Planning tasked SRK Consulting with establishing the value of ecosystem services provided by the Papenkuils Wetland, in order to inform its policy and management. The first step was to identify the services of the ecosystem.
Services of the Papenkuils Wetland Wetlands in general sustain unique environments in terms of fauna and flora, and are among the most productive ecosystems in the world. “They provide ecosystem services that have direct use value (these are easier to quantify because they are typically valued in traditional markets) and more discreet indirect and non-use values that are harder to calculate,” explains Matthew Law, principal environmental economist and management consultant, SRK Consulting.
An example of a direct use value is grazing on the wetland itself. The combination of shallow water and high nutrient levels in wetlands creates highly productive agricultural areas; the direct use value of grazing was calculated by establishing the carrying capacity of the wetland and comparing this to
the capacity of surrounding dry-land grazing areas. Another example of a direct use value is the waterblommetjies harvested from the wetland and sold by the local community. “We were able to calculate the direct use value of this wetland service per hectare, based on the number of harvesters and waterblommetjies sold,” he continues.
Water quality amelioration is an ecosystem service with indirect use value (as opposed to direct economic benefits), as wetlands remove contaminants and improve water quality. Wetland vegetation can help to trap suspended material, remove nutrients and conduct chemical detoxification. In the absence of these wetland services, farmers downstream will receive poor water quality, adversely affecting agricultural production and causing siltation of irrigation systems, with associated direct costs to farmers.
“As markets for the water quality amelioration function of wetlands do not exist, in order to value this service, we calculated the replacement costs of the construction and operation of a water treatment plant that provides a similar amelioration function of the Papenkuils Wetland,” adds Law.
Other examples of indirect use values provided by the ecosystem services of this wetland include carbon sequestration (calculated from the amount of carbon sequestered by the wetland and the internationally recognised social cost of carbon avoided through the provision of this service), floodwater abatement, and groundwater recharge (both calculated by establishing the replacement cost of a water impoundment or dam of similar capacity).
Another category of ecosystem service value is non-use value – the intrinsic value that people derive from the mere knowledge that an environmental resource exists. For example, people value the Kruger National Park, even though they may never actually visit the reserve. Intrinsic value is not traded in markets and is unpriced. It is therefore necessary to assess the relative economic worth of these unpriced goods and services using non-market valuation techniques, such as the contingent valuation method.
Like most wetlands, the Papenkuils Wetland allows for a concentrated streamflow to spread out over a large area and consequently provides significant temporary storage. Particularly in the Papenkuils, braided channels and large ponded areas (indeed, the word kuil can mean pool, pit or bunker) provide large storage areas. The net effect of this storage is to dampen the peak flow entering the wetland, allowing for longer and lower outflows. In addition, thick grassed, reeded and palmiet areas contribute to slowing the velocity of water and further attenuating the peak inflows – and also providing for longer, lower outflows.
In order to calculate the value of each service provided by the Papenkuils Wetland, SRK Consulting modelled the potential changes in use and non-use value. This calculation was based on the changes in ecosystem service levels – i.e. flood abatement, groundwater recharge, sediment retention, agricultural resource provisioning, harvesting of natural resources, nutrient reduction/ water quality amelioration, carbon sequestration, tourism and recreation, and intrinsic value – that would result from an increase in water abstraction upstream of the wetland. It estimated direct use values, calculated the replacement cost for services providing indirect use values, and conservatively estimated intrinsic values based on the intrinsic value of fynbos in South Africa.
SRK Consulting developed a hydrological model to ascertain the current level of ecosystem services. This was formulated from a number of studies. Initially, a 30-year time series of daily inflows into the wetland
was derived using the characteristics of contributing catchments and daily climate time series in an agrohydrological model. These inflows were assigned to the relevant inflow streams and diversion criteria applied to estimate current and future flows
into the wetland. Satellite images were then used to determine the areas of inundation of water in the wetland over a few years of record. These inundation states were correlated with the associated time interval cumulative discharge and then extrapolated to the full long-term time series.
An extensive topographical survey was conducted, mapping out the water levels and flows, and the agricultural drains of the wetland. Soil profiling and soil-water status monitoring was done to show how water naturally seeps down and accumulates in and around the wetland, and to evaluate the extent and time it took for soils to dry out. Further water quality and isotope samples were extracted at strategic locations over a five-month period. These short-term observations were used, together with the long-term predictions, to estimate the average and range of water inundation, vegetation health, sediment and nutrient uptake.
Dr Simon Lorentz, principal hydrologist, SRK Consulting, states that parts of the Papenkuils Wetland were already in poor condition – especially in the upper part, where trenches had been dug and water diverted away from the wetland for agricultural use.
“SRK Consulting evaluated the volume of nutrients taken up by the Papenkuils Wetland under various water use conditions,” says Lorentz. “Water samples were taken from water running in streams, the near-surface water and
groundwater. We found some fairly high nutrient loads in the streams coming out of the vineyard. This was due to the stockpiling of fertilisers.”
The southern part of the Holsloot River was mostly impacted by agricultural diversion, while the river’s northern part was bunded up to prevent further spillage into the wetland.
Automatic sensors were added to the Holsloot River to measure electrical conductivity (or salinity) as well as depths of flow. Changes in salinity and depths were monitored over time. “We had to conduct our studies over a small portion of the dry period and would have liked to have surveyed changes in the wetland over a dry and wet season, but we had time constraints. We therefore used six years of historic satellite imagery and worked out the relationship between water coming into wetland and water diverted from the wetland, as well as wetland inundation,” says Lorentz.
Wetland inundation (when the wetland is mostly covered in water) is a feature of the benefit of the wetland to sustain vegetation, attenuate peak flows, and take up nutrient loads. This is important because water running through preferential pathways in a wetland can cause soil erosion. Furthermore, if soils, fauna and flora do not have sufficient contact with water, water will merely channel straight through the wetland – and chemicals and nutrients will not be absorbed.
Through the hydrological model, SRK Consulting could anticipate the changes in the Papenkuils Wetland service level provision over a 25-year period, should the weir be raised by 30 cm.
“We were able to establish the cost of treating water diverted from the wetland to the same quality achieved through natural filtration in the wetland, the reduction of grazing areas, and the reduction in the extent of the wetland itself. From there, we modelled the costs over the 25-year period based on the change in flow,” adds Law.
Another interesting component of the economic model was the tourism benefit of freshwater resources. SRK Consulting used the spatial density of photos uploaded on the Flickr website – an online photo management and sharing application – to estimate what percentage of tourism spend in the local municipality was on attractions near freshwater resources, including wetlands. “With Flickr, we georeferenced all photographs to that local municipality and calculated the density of the photographs that were within the range of wetlands and watercourses. By doing this, we were able to demonstrate that tourists are attracted to wetlands and watercourses, and then coarsely estimate the tourism value of wetlands in the region. The theoretical drop in tourism could then be calculated
based on the decreasing size of the wetland from increased abstraction,” explains Law.
Conclusion
“One of SRK’s recommendations was to remediate some of the diversions made by farmers. These diversions have an adverse effect on the wetland – possibly more than the weir diversion. When a farmer uses a wetland for grazing livestock, they typically cut a trench down the middle of the wetland to form an agricultural drain, drawing the water down and causing meadowlands to grow. This makes the wetland drier than it ought to be,” says Lorentz.
It was found that raising the weir would significantly reduce the area of the wetland (particularly the southern part). This would potentially have a knock-on effect across all of the wetland habitats identified in the system.
In the end, it was found that the Papenkuils Wetland generates services to the value of R50.3 million per annum. The envisaged weir diversion would reduce the service value of the wetland by an average of about R6 million per annum (i.e. an economic cost of abstraction of R6 million), leading to a total loss in net present value of approximately R140 million (i.e. after time preference discounting of the annual cost stream has been applied) over the 25-year period.
“Most of the studies and work done on wetlands focus on assessing the potential impacts of human demands. This was a study that SRK Consulting was particularly excited to take part in, as it quantified the value
of a wetland in economic terms to inform policy. Instead of identifying threats and recommending mitigation measures, this study established the value of the wetland to society, which drives home the message as opposed to simply characterising potential threats and recommending mitigation efforts,” concludes Roanne Sutcliffe, environmental and bioresources engineer at SRK Consulting. Read the paper here:
Soil profiling was done to show how water naturally seeps down and accumulates in and around the wetland
The safety and healthy development of South Africa’s children are crucial and should be prioritised. Access to proper water and sanitation is a basic right that children in underdeveloped areas struggle to have.
By Ziyanda Majodina
SThe provision of better sanitation directly impacts children’s learning abilities, as it mainly affects learners’ enjoyment of the environment – which enables the enjoyment of other rights such as the right to education
Regardless of far-reaching praise for the country’s progressive Constitution –which entrenches the unqualified right to basic education – as well as consistent lip service advocating the importance of basic education for alleviating poverty and inequality, the South African democratic state has failed to make toilets in schools safe for schoolchildren.
outh Africa’s school infrastructure still poses a great threat to the safety and development of its children. In developed areas, the provision of classrooms, electricity, water and sanitation facilities has been extensive but nearly the opposite has happened for underprivileged areas. Taking into account the huge school infrastructure backlogs in the majority of schools built by the apartheid government, as well as limited public funds during the postapartheid years, improving the provision and quality of school infrastructure has proved to be a daunting task.
According to Section27, a publicinterest law centre that uses and
develops the law to promote and advance human rights, students and teachers suffer the most atrocious conditions with the sanitation facilities provided and the rights of children are infringed upon on a daily basis. This is reinforced by the July 2021 report on water and sanitation by the South African Human Rights Commission, which revealed that over a million learners and teachers either have no access to sanitation or still use pit toilets.
TABLE 1
Number of schools with no water and affected teachers and learners
Number of schools using pit latrines and affected teachers and learners
assessment conducted on the most suitable sanitation technology for each particular school.
(3) Sanitation facilities could include one or more of the following: (a) Water borne sanitation; (b) small bore sewer reticulation... Since as far back as 2013, the Department of Basic Education (DBE) banned pit toilets for use in schools. Thus, according to the DBE’s own standards, pit toilets are unlawful. Acknowledging the urgent need for safe and hygienic sanitation during the Covid-19 pandemic, the DBE spent R600 million on the provision of emergency water and sanitation infrastructure. While these temporary solutions are necessary and certainly
A pit latrine is a type of toilet that collects human faeces in a hole in the ground. Urine and faeces enter the pit through a drop hole in the floor, which might be connected to a toilet seat or squatting pan for user comfort. Pit toilets can be built to function without water or can have a water seal, being a pour-flush pit latrine.
In January 2014, it was reported that five-year-old preschool learner Michael Komape from Limpopo had fallen and drowned in a school pit latrine. Two years later, five-year-old Oratilwe Dilwane suffered severe injuries after falling into a pit latrine in his school in the North West province. In 2018, another five-year-oldlearner, Lumka Mketwa, drowned in a pit latrine at a school in the Eastern Cape.
The conditions of school toilets prove that the right to education in a safe and decent place to learn has been infringed upon. Below is an excerpt from the South African Schools Act (No. 84 of 1996): ‘Regulations relating to minimum uniform norms and standards for public school infrastructure’, which was gazetted in November 2013: 12. Sanitation
(1) All schools must have a sufficient number of sanitation facilities that is easily accessible to all learners and educators, provide privacy and security, promote health and hygiene standards, comply with all relevant laws and are maintained in good working order.
(2) The choice of appropriate sanitation technology must be based on the
welcome, they are a short-term solution to a historical problem, which needs to be addressed systematically and sustainably. Furthermore, the DBE did not receive additional money to fund these interventions: instead, the money for these costly emergency Covid-19 sanitation facilities was drawn from already stretched budgets for school infrastructure, at the expense of planned infrastructure projects.
Water seen as a privilege, not a right
In the ‘For water for life’ podcast’s 17th episode, entitled Water and security (www.jojo.co.za/for-water-for-lifepodcast), Elizabeth Biney, researcher at Equal Education, says: “So, in some areas, water is not an issue, access to water is not an issue; in other areas, it is a privilege. Where access to water is deemed a privilege and not so much a human right, we see that sanitation infrastructure is very poor and that having a flushing toilet is unimaginable.”
In 2020, the UN estimated that a fifth of South Africans live in extreme poverty. Education is a powerful tool for changing that. South Africa’s Constitution is applauded for its expansion on human rights, dignity, equality and freedom, which was a necessary framework following apartheid rule, which was a crime against humanity.
The provision of better sanitation directly impacts children’s learning abilities, as it mainly affects learners’ enjoyment of the environment. “The way we use water, the way we think about water and the way we interact with water needs to improve and needs to change. And we need to think about it holistically and not just [as] a thing that we pay for and just drink for our body. It has social implications,” Biney adds.
Government’s efforts to intervene in issues around pit toilets, poor infrastructure and backlogs include the introduction of the Sanitation Appropriate for Education (SAFE) initiative, whose aim is to attempt to eradicate basic pit toilets in schools. This initiative is hampered by generally slow delivery.
Not having a reliable, clean water supply – provided by tanks, taps and other forms of easily accessible
– leads to unfortunate events such as the loss of lives of young children. Another pressing issue is the backlog of fixing the infrastructure of classrooms, classroom desks and the maintenance of the infrastructure that already exists.
“We are looking at the related services or facilities that enable teaching and learning to happen smoothly and properly: the access to electricity, the water issue, the toilets issue and the classroom space,” says Biney. The Eastern Cape in particular faces the issue of poor infrastructure where most schools are still made of mud, zinc and asbestos; in Limpopo, the issue of water and sanitation is extreme.
Also on the podcast, Afua Wilcox, architect and doctoral student, says, “Now we still have all this infrastructure –water systems and water drainage – that was built over 50 years ago. It is old and was not necessarily well maintained.
“Infrastructure is suffering because it falls through the cracks – a lot of our budgets are going towards Sandton instead of the CBD. Sandton is in the north of Johannesburg as opposed to the centre of the city and all the money that could be used to overlap and create a bigger and more well-maintained Johannesburg CBD has developed two divided CBDs; thus the maintenance budget has been spread sparsely,” Wilcox adds.
In the time Section27 has been monitoring school sanitation, there have been a few ostensible attempts by either the Limpopo Department of
The condition of school toilets proves that the right to education in a safe and decent place to learn has been infringed upon
Education or the Department of Basic Education to improve the situation. However, these attempts have been incomplete, poorly coordinated, and based on inaccurate data.
Irrespective of the commendable South African Constitution and Bill of Rights, the issue of clean water and proper sanitation in less privileged provinces and schools is dire.
The protection of young lives and striving to ensure equal developmental opportunities are granted should be prioritised. There needs to be both commitment and action to maintaining schools and providing clean water.
The entry was awarded second place for the ‘Supply and Delivery of Waterborne Structures’ project within Rustplaas Village in Mkhondo Municipality, Mpumulanga.
The Rocla Sanitation/Izandla Ziyagezana collaboration emerged as a result of Izandla Ziyagezana’s support for Rocla Sanitation’s Thuthukisa Initiative of “taking the factory to the people by empowering communities to be manufacturers in their own right”. Izandla Ziyagezana has specialised in the community manufacturing and erection of low-flush sanitation since it was formed in 2006.
“The Rustplaas Project has created 23 new jobs, and we thank Mkhondo Local Municipality for supporting this initiative. Projects such as Rustplaas show how job creation can be achieved in its simplest form through a transfer of skills on how to manufacture sanitation units of a good quality. The Rocla Sanitation Thuthukisa Initiative benefits both the local community and small businesses like my own,” says Dumisani Simelane, MD of Izandla Ziyagezana.
Rocla Sanitation partnered with Izandla Ziyagezana Trading to enter their Mkhondo-based Community Cast Factory in the IMESA/ CESA Excellence Awards 2021, in the Community Upliftment and Job Creation category.
With the Rustplaas Project, there has been on-site casting and stripping of 238 twin eco toilet top structures and pit structures in the 2020/21 financial year, and a further 204 top structures in the 2021/22 financial year. The Rustplaas community has also been trained in the receiving and dispatching of casting kits and the associated materials from stores. SMMEs and community members were trained in:
• mixing and batching
• casting and levelling of concrete
• curing and aftercare of concrete
• stripping and cleaning of products cast
• packing of stock and yard housekeeping
• loading and delivery of products
• on-site training in erecting
• administration and bookkeeping.
A concept called ‘pancake casting’ enabled Rocla Sanitation to offer on-site manufacturing capability that requires only a small piece of land and almost no infrastructure. This process involves casting one item on top of another in frameless, single-use moulds of a similar size in a planar form.
The panels are continuously cast one on top of another until typically full stacks of four toilets or four twin eco pits are reached. The product is usually left to cure for two weeks. New castings can continue to be made during this curing process at other locations, using the same tools.
“Communities that urgently require toilet units are often found in rural areas of the country. Many of these areas have no infrastructure. Meaning ‘to share’, the Thuthukisa Initiative’s philosophy led to the development of the ‘Community Cast’ toilet unit that can be simply manufactured by local community entrepreneurs or SMMEs and be ready for use within two weeks,” adds Andre Labuschagne, product development manager for Rocla Sanitation. “We look forward to continuing our relationship with Izandla Ziyagezana and will be collaborating with them on an 800-unit waterborne toilet project in Driefontein, Mkhondo, shortly,” concludes Labuschagne.
The IMESA/CESA Community Upliftment and Job Category focuses on projects demonstrating labour-intensive construction, skills development, and community awareness and participation
Water-efficiency management company MIYA Water believes that a holistic, integrated approach to water management yields the best results
People try to confront water losses through different methods – leak detection, pressure management, asset management and metering – and seldom tackle everything together.
Water utilities typically use one company for engineering and planning, another company for pressure management, and another for leak detection. This removes accountability from all companies. MIYA has a holistic approach to non-revenue water (NRW),” explains Noam Komy, chief growth officer at MIYA.
NRW is a global phenomenon; an average of 34% of treated water never reaches its destination worldwide.
South Africa’s NRW is close to 40%.
“There is little point in building dams and increasing water supply when one is losing 40% of one’s existing supply,” states Komy. Commercial elements, legalities, pressure, leaks, repairs and maintenance are tackled as a complete water
efficiency project by MIYA. By using a turnkey approach, the company is held accountable for achieving a specific result.
“Everything must work together and must be coordinated to get a maximum impact,” adds Komy. “For example, leak detection and pressure management must be combined. High pressure intensifies existing leaks. If pressure in the system is reduced, leak detection will be affected.”
MIYA also uses a degree of flexibility when tackling a water-efficiency project. “South African cities are changing at a rapid rate and while it is important to develop a plan, it is
equally important to be flexible in the plan’s implementation. For example, the original plan may focus on water pressure but, once work starts, it may become apparent that there should be a greater focus on service connections,” says Komy.
Tenders should always include quality and should not be solely price-driven. MIYA focuses on material specifications and the quality of work, as water infrastructure should be durable and have longevity.
Output-based approach
MIYA typically enters into performancebased contracts with clients, where a certain portion of its fee is fixed and another portion is related to savings achieved. “Our contracts are output-driven. NRW projects have a high degree of complexity. Our deliverables are never based on building or replacing assets –MIYA is tasked with achieving (and maintaining) an agreed-upon result within a stipulated amount of time,” explains Komy.
MIYA can take care of the commercial management of the project, as well as billing and collections, as these considerations make a project viable. “It is easier for water projects to secure funding when a professional, private company controls billings and collections. MIYA often works on a concession model where we are responsible for the full management of the water system, usually including necessary improvements,” says Komy.
“South Africa is blessed with some brilliant engineers and water scientists and, when working there, MIYA was particularly impressed with South Africa’s emphasis on stakeholder engagement. We have adopted this in the other countries in which we operate,” adds Komy.
Wherever the company operates, MIYA focuses on building local capacity and employing local people. “We create jobs; we do not destroy jobs. All of our projects entail education, training and improvement of the workforce and community. It is incredibly rewarding to be a part of a person’s professional development.”
In the Bahamas, MIYA ran a programme to educate children on water wastage. It then ran a competition where the household that could decrease water usage the most won a prize. Household consumption was measured before and after the programme, and it
was found that water wastage was reduced.
Komy believes that South Africa has all of the necessary elements to transform into a top-performing water industry. “There is a greater need for more public-private partnerships, as well as the privatisation of some water utilities. Governance issues and a lack of experience in project preparation are the main problems. Government has to play a role in holding companies accountable for achieving agreed-upon results.”
• Established: 2007
• Since 2020, MIYA Water is fully owned by Antin Infrastructure Partners
• Present on five continents
• Total employees: 600
• Provides water services to 9 million people around the world
Water is used across all types of industrial applications, including energy. In most energy scenarios, water is important for cooling; without it, a power generation site (of any kind) will stop operating.
According to Chetan Mistry, strategy and marketing manager for Xylem Africa, there are many examples of the water and power relationship. “In 2013, India had to shut down a thermal plant due to severe water shortages. On several occasions in the past 20 years, Australia has reduced coal power operations to safeguard municipal water supplies. And in South Africa, new power plants built in the past decade have started using more expensive dry cooling systems due to insufficient water supplies.”
A report from the World Bank states that between 2010 and 2014, more than 50% of the world’s power utility and energy companies have experienced water-related business impacts. At least two-thirds of power utilities indicate that water is a
substantive risk to business operations. The relationship is set to become more strained: by 2035, the world’s energy consumption will grow by 35%, increasing water consumption by 85%.
A total of 2.5 billion people do not have access to reliable electricity, and 2.8 billion live in water-stressed areas. Much of that pressure exists in sub-Saharan Africa. The African Development Bank notes that Africa has the lowest electrification rate of all regions. It is estimated that only 43% of the population has access to electricity, compared with 77% in the developing world. In sub-Saharan Africa, the ratio is much lower, at 32% – and only 18% in rural areas.
Undoing the vicious cycle
“It is a vicious cycle: no water means no power, and no power means no
water. Fortunately, a lot can be done to reverse the situation. In the past, water has not been treated with the same level of scrutiny and management that is applied to energy. But presently, companies are scrutinising their water usage, looking for leaks and other forms of waste, and taking action to create their own water stockpiles, such as capturing rainwater or recycling greywater,” explains Mistry.
“Every time someone learns to use water more efficiently and values the resource, it is a change. Whether they use drip irrigation for their veggie garden, recycle water for other uses, or diligently report leaks they see, it all counts. Once we understand that water and energy come together to make our world possible, we start taking water more seriously,” he concludes.
A study* was conducted to determine the presence and concentrations of per- and polyfluorinated alkyl substances (PFASs) in the Roodeplaat and Hartbeespoort dams – dams that provide water for domestic consumption, irrigation, fishing and recreational activities.
By Bulelwa Batayi & Professor Okechukwu Jonathan Okonkwo
PFASs are man-made organic chemicals that are used in the production of industrial and consumer products such as firefighting foams, paints, non-stick cookware and food packaging. PFASs have hydrophilic and hydrophobic properties, are non-degradable in the environment, bio-accumulative and toxic. They are ubiquitous and, therefore, have been found in air, surface water, sediment, fish, wildlife and human blood.
High PFAS levels have been linked to increased liver and kidney dysfunction, reduced postnatal survival with impaired growth, cardiac abnormalities, maternal weight loss, mortality, and induced immunological alterations in laboratory animal studies. They also have carcinogenic properties. Consequently, PFASs, particularly perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) and their salts have been listed in the Stockholm Convention as persistent organic pollutants (POPs). Countries have set restrictions and regulations on the use of PFOS and other PFASs to minimise human exposure to these compounds.
Three water treatment plants abstract raw water from Roodeplaat Dam, which is located approximately 24 km north-east of Pretoria, north of the Magaliesberg range. While the dam supplies potable water to three provinces – namely Gauteng, the North West and Limpopo – the quality of the water is a cause for concern.
Hartbeespoort Dam is located in the North West province, in the Crocodile River catchment, within the Limpopo River system. It is a storage reservoir primarily providing water for irrigation and domestic consumption, recreation, and compensation flows to downstream portions of the Crocodile River. About 90% of the inflow of the Hartbeespoort Dam is derived from the Crocodile River, which is balanced by inflow generated from the Magalies River watershed. Since the Crocodile River drains a large, highly industrialised and urbanised area, the dam is subject to high levels of pollution.
A total of 30 water samples were collected from different points at each dam, using a hosepipe sampler from downstream to upstream during winter and summer months.
Roodeplaat Dam
Nine different PFAS compounds were detected in both dams.
• Hartbeespoort Dam – PFAS concentrations were in the range of 1.38 to 346.32 nanograms per litre (ng/ℓ), with Point C having the highest recording. This could be due to the dumping of waste at the banks of the Jukskei River, which drains into the Crocodile River.
• Roodeplaat Dam – PFAS concentrations were in the range of 2.31 to 262.29 ng/ℓ, with Point B having the highest recording. This could be due to the Hartebeesspruit and Pienaar rivers, as the catchments are located in highly populated and industrialised areas.
PFAS concentrations were higher in the summer months. High rainfall in these months may enhance the leaching of waste dumped near the riverbanks into the rivers that drain into the dams.
The concentrations of the PFOA and PFOS compounds found in the dams were higher than the recommended lifetime health advisory issued by the US Environmental Protection Agency for drinking water (70 ng/ℓ). However, the level of human exposure to these compounds from drinking water is unknown.
This study reported higher concentrations of PFASs than those reported in developing countries such as Uganda, Singapore and Vietnam but lower than levels reported in developed countries like Germany, Japan and China.
*The study was conducted by Professor Okonkwo and his EnvironmentalAnalytical Research in Chemistry group at the Department of Environmental, Water & Earth Science, Tshwane University of Technology.
Consulting engineering and infrastructure advisory firm Zutari has designed a spillway to boost dam safety by preventing overtopping at the Garden Route Dam, the main supply for George in the Western Cape.
The design was put to the test towards the end of November when it began spilling following torrential rains in the area. “I am happy to report that the spillway is behaving as expected,” reports Dr Frank Denys, associate and expertise leader: Dams, Zutari.
“The duckbill-shaped spillway significantly increased both the storage capacity of the dam and the discharge capacity of the spillway so as to boost the dam’s water supplies without compromising its safety by preventing overtopping,” comments Denys. The
Dams, Zutari
project won an award for technical excellence in the SAICE Southern Cape Branch Regional Awards 2020.
George Municipality states on its website that while the heavy rainfall and flash floods on 22 November had “understandably overshadowed” the dam’s overflowing on the same day, it remained a celebration of innovative engineering and a significant milestone in the city’s long-term water security.
Prior to the flood event, the water level in the dam was roughly 1 m below the crest of the spillway. This volume was rapidly filled up in the course of the early morning and the spillway started overflowing at roughly 08:30. The peak of the flood occurred at 13:00, according to the Department of Water and Sanitation’s water level data record. The water level recorder logged a maximum overflow depth of 0.509 m over the crest, which equates to about 50 m³/s in discharge. This thus appears to have been a relatively minor event, with the dam designed to cater for much higher flows. That said, the incoming flood was partially attenuated or absorbed by the storage volume in the dam basin.
Duckbill
Due to the new spillway, the increased storage capacity of the Garden Route Dam was achieved by raising its full
supply level by 2.5 m – thus enlarging the storage volume by 2.5 million m³.
The solution centred on a sophisticated hydraulic design in the form of a novel, non-linear spillway in the shape of a duckbill. Although duckbill or bathtub spillways are not unique, they are rare worldwide.
“The design is relatively new in the engineering world, and as far as we know is not being used in this way in South Africa,” says Lionel Daniels, acting director: Civil Engineering Services, George Municipality. It was extensively researched by Zutari and tested by the Department of Water and Sanitation’s Hydraulic Laboratory in Pretoria, with its shape designed to slow down water flow using basic physics principles.
“The project showcased how relatively small, well-engineered and optimised adjustments can provide a more resilient water supply system without compromising on dam safety. Furthermore, the expansion of existing water supply resources is preferable to the development of new sites, as it limits the environmental impact to an already impacted site. Despite the novel nature of the engineered solution, this unique and innovative project had a low capital cost and a small, estimated maintenance cost,” explains Denys.
Zutari used its industry expertise to amend the hydraulic design to ensure that the weir would behave in a safe and predictable manner. The shape of the duckbill causes flow on opposite ends of the overflow flow to collide within the duckbill, causing an upwelling, also known as flow bulking, which breaks the flow’s momentum and causes it to lose its energy. The flow from the rounded upstream end of the spillway is not so opposed and causes this upwelling of flow to move toward the exit of the spillway at rapid velocity. This increase in velocity reduces the water level to a lower elevation such that it can safely pass under the bridge over the spillway. The final duckbill spillway design resulted in a total spillway length of 80 m, with a maximum discharge capacity of 570 m³/s at a freeboard of 4.1 m.
Multidisciplinary engineering consulting company GIBB was awarded the contract to design and oversee the construction of Nalubaale Dam in Uganda. Despite disruptions related to the pandemic, construction deadlines were met, high technical standards were achieved, and the project budget was not exceeded.
Tocated three kilometres downstream from the source of the Nile River in Jinja, Uganda, the Nalubaale hydropower station’s first turbine unit was commissioned in 1954. Cracks were first noticed in the powerhouse structure in 1964. These were caused by an alkaliaggregate reaction (AAR). Cracks had also developed in the main dam wall and leakages from the reservoir were observed against the downstream face.
All repair attempts before 2020 had a limited service life as long as the concrete kept on swelling due to AAR.
Louiza van Vuuren, civil engineer, GIBB, says Eskom Uganda decided to implement a new grouting programme to improve the structural and functional integrity of the dam structure. The grouting approach used by GIBB was based on the GIN (grouting intensity number) method. The acceptable pressures and volumes of grout injected were derived from stability calculations to avoid hydro-jacking of the dam’s concrete during grouting.
“The specifications stipulated that the pressures used for grout injection should be controlled with a pressure transducer, which is fitted to a grout pump equipped with an automatic data acquisition system capable of measuring, displaying, and recording data in real time,” explains Van Vuuren.
The contractor mobilised to site in December 2020, initially commencing with the drilling and grouting works on a trial section of the dam. This was to confirm or modify the grouting method (boundary curve, boreholes spacing, stop criteria); the grout mix design and grouting materials; as well as the equipment such as pumps, mixers, sensors and automated control devices, among others.
Primary holes were inspected with a borehole imaging device to establish typical crack elevations, directions and widths, and to inspect the mass concrete condition. This led to the detection of large cracks of up to 17 mm wide. Crest levelling surveys of the concrete blocks were also conducted to detect any evidence of hydro-jacking.
Due to the grout trial section taking longer than originally anticipated, the project experienced a slow start, compelling the contractor to increase the number of employees on-site – as well as drilling equipment – to catch up with the planned schedule.
Van Vuuren says the practical completion of the drilling and grouting works was achieved before the original completion date of the contract and within the original budget.
Flow in an open channel is measured by inserting a hydraulic structure into the channel, which changes the level of liquid in, or near, the structure.
By Peter van der Merwe, consultant for flumes and weirs
By selecting the shape and dimensions of the hydraulic structure, the rate of flow through or over the restriction will be related to the liquid level in a known manner. Thus, the flow rate through the open channel can be derived from a single measurement of the liquid level. The hydraulic structures used in measuring flow in open channels are known as primary measuring devices, with the level being measured using a secondary device that converts the level to a flow measurement. The relationship between level and flow has been investigated both theoretically and experimentally and the results well documented in the ISO standards.
The hydraulic theory for predicting discharge through long-throated
flumes is a result from over a century of development. The initial laboratory and theoretical studies on critical depth flumes were made in 1849 and later in 1896. These studies were extended into the early part of the 20th century and the theory and dimensional requirements for these flumes were well known by the 1950s.
However, calibration still required an empirical discharge coefficient. Theoretical predictions of flow were investigated in 1963 and further refined in 1975 by the stage-discharge theory, or calibration model. In 1978 and 1981, a procedure for determining the required head loss across these flumes was developed.
One of the first standards for the longthroated flume was the BS 3680-4A:1981 standard. This was superseded by BS ISO 4359:1983 and subsequently ISO 4359:2013. The flume is now known as
the rectangular long-throated (RLT) flume, a type of standing-wave or critical-depth flume, and the ISO 4359:2013 standard clearly states that the expression ‘Venturi’ is not applicable to open channel flumes. A Venturi meter is a closed-conduit system with the head measurement at two locations and flow calculated with Bernoulli’s energy equation.
The design of this flume does not require in situ calibration, as, after years of research and testing in the field, the procedure for its design has been accepted and standardised. As the flume design is based on critical flow, the calculation is based on fundamental hydraulic theory, without the need for hydraulic laboratory testing to derive the formulae, as for other forms of empirical flow measurement structures such as the Parshall flume.
Long-throated flumes are generally composed of five primary str uctural components:
• An approach channel for the development of uniform and symmetric flow conditions and the establishment of a stable water surface whose elevation can be determined accurately
• A converging transition section in which the subcritical approach flow accelerates smoothly towards the throat with no discontinuities or flow separation
• A throat, or control section, in which the flow passes through critical depth
• A diverging transition in which the velocity of the supercritical flow exiting the throat section is reduced and energy is dissipated or partially recovered. If energy recovery is not required, a truncated transition can be used
• A tail water channel where the water level is a function of the flow rate and the hydraulic properties of the downstream channel and structures
Design of long-throated flume
In producing these flumes, designers are often discouraged by the complex mathematics of hydraulics.
The flow conditions are uniquely dependent on the upstream head (subcritical flow must exist upstream of the flume), after which the flow accelerates through the contraction and passes through its critical depth. The water level downstream of the structure should be low enough to have no influence upon its performance.
The calculations needed to compute head-discharge relationships and evaluate design alternatives are iterative, and computer programs greatly facilitate analysis of these structures. Early programs written in Fortran used a batch mode of operation to analyse the performance of single designs. In the 1990s, the International Institute for Land Reclamation and Improvement in the Netherlands and the Agricultural Research Service in the USA developed interactive computer programs for long-throated flume design. With the advent of modern spreadsheets, the ISO standard, the flume geometry and a design optimisation routine, the rating tables, staff gauge data, and stage discharge-head curves can be generated. A primary advantage of these long-throated flumes for open channel flow measurement is the theoretical predictability of their hydraulic performance. Provided that critical flow occurs in the throat, a rating table can be calculated with an error of less
than 2% of the measured discharge. The throat, perpendicular to the direction of flow, can be designed in such a way that the complete range of discharges can be measured accurately. The required head loss over the flume is minimal, ensured by modular flow, which occurs when a unique relationship exists between the upstream referenced head and the discharge. With their gradual converging transition, these structures have little problem with floating debris. Field observations and laboratory tests have shown that these structures can be designed to pass sediment transported by open channels with subcritical flow.
In order to obtain critical flow within the throat of the flume, the following conditions are applied:
• To obtain the required hydrostatic pressure conditions occurring at the control section, the throat of the flume should be long enough for the flow to be parallel with the flume invert.
• The flume throat must be shaped so that there is no energy loss between where the head is gauged and the point where critical flow occurs.
• To obtain the ‘modular’ condition, the flume throat shall constrict the channel enough to raise the energy level in the throat sufficiently higher than the downstream energy level. Modular flow is not dependent on the tail water levels.
The following geometric constraints must be taken into consideration with the iterative design process:
• Channel/flume width: B > b / 0.7 (145 mm min)
• Throat width: b ≥ 100 mm
• Throat width: b < 0.7 * B
• Flume inlet radius: 2 * (B - b)
• Flume inlet length: (1.750.5) * (B - b)
• Throat length: hmax / L ≤ 0.5 (maximum 0.67 with +2% uncertainty)
• Discharge length (1:6): 3 * (B - b)
• Total flume length: K + L + D
• Maximum head: hmax / b ≤ 3
• Discharge truncation (1:33): 0.5 * D
The RLT (rectangular long-throat) flume – also known as a critical depth flume – is covered by ISO 4359:2013 and relies on the occurrence of critical flow in the flume throat. When this occurs, independent of the conditions downstream, there is a unique relationship between the upstream head and the discharge for a given flume geometry.
Under similar hydraulic and other boundary conditions, these are usually the most economical of all structures for accurately measuring open channel flows, provided that conditions confirm the feasibility of a flume.
The Xhora Off-Channel Storage Dam is 230 m long, has a 29.4 m crest and is classified as a category 2 dam. It is a zoned earth fill embankment dam on an unnamed tributary of the Xhora River and has a gross storage capacity of 2.7 million m3
Earth filled embankment dam
Materials are very important to the design and construction of an earth embankment dam. Hard rock and crushed rock products are required for the rip rap, as well as filters and drains within the dam. Therefore, a hard rock quarry was developed within the basin primarily utilising the igneous granophyre rock with the overburden indurated siltstone.
The embankment was constructed with different zones, where the central core acted as the low-permeability zone of the dam – available in the reservoir basin. However, materials available in the basin had a fairly low plasticity so, for backfilling of the cut-off trench, a more flexible clay
Located in the Elliotdale District of Mbhashe Local Municipality in the Eastern Cape, the Xhora Off-channel Storage Dam was built to give greater security of supply to the Xhora Water Supply Scheme (Xhora WSS), which provides potable water to 70 000 people.
material was imported from a decomposed dolerite borrow pit about 8 km away.
Construction
Dams can cause loss of life and extensive damage should they fail, and a spillway is a key component of a dam for the safe discharge of flood waters. A 25 m long ogee side-channel spillway on the right flank with a 5 m wide channel was constructed. It has been designed for a 1:100 return period flood of 87 m3/s and safety evaluation flood of 165 m3/s.
The spillway discharge curve was obtained using computational fluid dynamics software. Due to the proximity of the water treatment works downstream of the spillway, the design of the stilling basin needed to be accurate. The novel design was developed and model tested by Stellenbosch University.
The dam was fitted with outlet pipework, the stilling basin, twin box culvert as part of
the river diversion works, water abstraction facilities and associated pipework, as well as a pedestrian bridge across the spillway for the local community.
A double-barreled diversion culvert was constructed to allow for floodwater during construction. The diversion culvert provides passage for the two outlet pipes, a domestic supply to the water treatment works, and for emergency emptying of the dam, as well as making provision for environmental releases. On completion of the dam, the culvert was closed through the installation of two sets of precast reinforced concrete planks, with the void between the planks filled with mass concrete post-grouted through a tube manchette system.
In the initial design process, the team debated how to abstract water for domestic consumption. The preferred water for domestic consumption should be drawn from the surface waters of the dam, which are oxygenated. Typically, an intake tower is constructed with inlets at various levels to be operated so that water can be abstracted close to the surface as the reservoir level moves up and down. As the water demand on the scheme is relatively small, the
cheapest solution was considered to be a floating intake.
The floating intake structure consists of a stainless-steel float filled with foam and anchored in place with chains that are connected to concrete blocks on the floor of the reservoir. The intake screen is attached to the float with a flexible steel-reinforced mining hose conveying water to the outlet pipework through the river diversion culvert. This resulted in a substantially cheaper intake structure when compared with an intake tower. Due to the relatively shallow depths in the dam, it is a fairly simple process to replace the intake system, after approximately 25 years, utilising divers.
A substantial portion of water in the dam is pumped from the Xhora River via a diversion weir. This makes the water rather expensive; it was therefore necessary to ensure a relatively low permeability of the foundation. Geotechnical investigations revealed that while the foundation rock was generally of low permeability, there were areas with moderately weathered rock and zones of high permeability. The grouting design required the primary holes to extend to a depth of up to 30 m.
This is deeper than what would normally be implemented, but zones of leakage were detected to this depth. The grouting consists of drilling holes into the rock foundation, pressure testing with water to determine if there are leakage paths within that section or stage (measured in lugeons), and then pumping in a cement grout to fill leakage paths and ultimately to backfill the hole. The grouting was carried out in 4-5 m stages, depending on the depth, into the rock.
To avoid the need to construct and grout through a wide and anchored reinforced concrete pad, a less-used approach to the grouting was adopted. To allow for a higher first-stage grouting pressure and produce greater penetration into the fine fissures that existed in the bedrock, the cut-off trench was first excavated and backfilled, then the temporary grouting standpipes were installed through the imported clay cut-off. This allowed for a significant increase in the overburden pressure, and therefore the pressure that could be specified for the grouting, particularly in the upper 5 m of the grout holes.
To minimise the environmental impact of the dam and the effect of siltation, the Xhora Dam was designed as an offchannel storage dam in a small section of the catchment.
Environmental water releases are scheduled to maintain the aquatic environment within the river channel downstream of the dam.
The section of the river channel on the downstream left bank was an area of significant environmental value. This was demarcated a no-go area and required preservation. To ensure that the water table was preserved to support the local ecosystem, the raw water pipeline to the water treatment works was constructed as a weir so that the water level could be maintained in the channel between the dam and the pipe crossing of the water course. Some protected trees were removed to construct the dam and a number of compensatory trees were planted to replace this loss.
Extensive community consultations took place during the feasibility, design and construction stages over the many years of the project and eventually the dam construction. The ongoing community engagement was an important aspect to managing expectations for the delivery of water, and work opportunities.
The construction of a dam has impacts on the surrounding community – both in terms of access constraints as well as occupying land that may have been used for agricultural purposes or housing. In the years preceding the construction of the dam, three households who would be near either the dam construction or the full supply level of the dam were identified. To ensure their safety, a process of cooperative relocation was undertaken. The three families were relocated to new houses that were constructed for them, and they were very happy with the outcome.
During the community consultations, a key concern to the community was maintaining access, as the dam would
Spillway channel and stilling basin under construction
create a divide in the community. The outcome of the consultations was the construction of a pedestrian bridge across the spillway and the provision for safe access across the dam wall. Various community members owned lands within the inundated area of the basin. Processes were undertaken to compensate these community members for the loss of the lands used for agricultural processes – a complex task where there are no title deeds. The overall contract, which included pipelines and pump stations, employed 109 local people for 17 900 person days.
Diversion culvert complete with coffer dam under way, hard rock quarry in basin, core trench being excavated, and downstream drainage blanket placed
Design, construction, monitoring and commissioning: Hatch
Contractor: Stefanutti Stocks Mfuraa Consortium
Geological and material investigations: Terreco Geotechnical
Environmental: Pollution Control Technologies
Institutional and social development: Thetha
Health and safety: Sange Institute of Health and Safety
Stilling basin design and model testing: University of Stellenbosch
Blasting and quarry: Baydrive Mining and Civils
Grouting and rock anchors: Wepex
Concrete batch plant: Lafarge
Joint laboratory: Road Lab
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