[PROJECT FOCUS] Meet South Africa’s largest bio filtration plant | Infrastructure news

The Coegakop Biofiltration Plant is nearing completion and is designed to treat groundwater rich in dissolved iron and manganese. The plant is designed with a capacity to treat up to 20 Mℓ/day of potable water for Nelson Mandela Bay Municipality (NMBM).

By Kirsten Kelly

This is the fourth and final phase of the Coegakop Wellfield project – part of the NMBM Water Master Plan to augment municipal water supply.

“Groundwater is being used in the fight against the worst drought in Nelson Mandela Bay’s recorded history. NMBM conducted groundwater investigations during the 2010/11 Eastern Cape drought, and it was found that some properties owned by NMBM had a high groundwater potential. One of the most favourable areas for developing a wellfield was located at the foot of Coegakop. The wellfield site was therefore named the Coegakop Wellfield,” says Matthew Hills, civil engineer: Water & Sanitation Subdirectorate, NMBM.

PhasesDescription of workTimeframeEstimated cost  Drought fundingStatus
OneGroundwater source identification2010 – 2013R11 500 000R0Complete
TwoDrilling of exploration and probe boreholes2013 – 2015R23 000 000R0Complete
ThreeDrilling of production boreholes and pipelines2015 – 2018R55 500 000MDG R19 998 483.85Complete
FourConstruction of treatment works2017 – 2023R309 700 000MDRG R23 444 064.63Construction
TOTALR399 700 000R43 432 548
Co-funding received in the form of the Municipal Disaster Grant and Municipal Disaster Recovery Grant was essential to getting this project off the ground.

Following an exploration phase in 2014, a decision was taken during 2015 to develop the groundwater resources by drilling five production boreholes in the Coegakop Wellfield.   

“The production boreholes themselves are unique for a municipal drinking water supply scheme as they are large-diameter boreholes (300 mm), quite deep (250-300 m) and are artesian – meaning the water can flow from the boreholes on their own pressure,” explains Kosie Smit, principal engineer, Zutari.

The borehole water from the wellfield is of good quality but contains elevated concentrations of dissolved iron and manganese. The Coegakop Water Treatment Works (WTW) was therefore designed and built to produce water that complies with the water quality requirements of SANS 241:2015 ‘Drinking water’.


Biofiltration refers to the process whereby organic bacteria grown in the filter beds aid in the removal of dissolved minerals.

“The Coegakop WTW uses biofiltration technology because it is an affordable, efficient, sustainable and reliable treatment solution with low maintenance costs. The normal filtration process requires the use of more chemicals, so this approach reduces our operational cost and is also better for the environment,” explains Hills.

Preekstoel Plant in Hermanus is the only other filtration plant of this kind in the country, but it treats 10 Mℓ/day, as opposed to the 20 Mℓ/day treatment capacity of the Coegekop WTW. Once complete, the Coegakop WTW will be the largest biofiltration plant of its kind in South Africa, and possibly the most ambitious biological manganese removal plant in the world (treating high concentrations up to 2.5 mg/ℓ).

Hills adds that the cost per kilolitre of water is less than other treated water within NMBM because it is being sourced straight out of the ground.

“The numbers still need to be verified. However, once the plant is fully operational, NMBM is confident that Coegakop will supply the lowest cost per kilolitre of water within the NMBM water supply system. Aside from the iron and manganese elements, the water is pristine and characterised by low levels of salinity.”

Besides the water purification, there are no additional bulk transfer costs, since the treated water goes straight to the existing Coegakop reservoir approximately 650 m away. From there, distribution pipelines supply Motherwell, the Coega SEZ and an expanding consumer zone.

“Having a second source of water supplying the Coega SEZ is essential for investor confidence and will unlock the potential for further development and job creation,” says Matthews.

The proposed treatment process primarily involves biological oxidation and filtration of iron and manganese, as well as the stabilisation and disinfection of groundwater from the Coegakop Wellfield.

Groundwater initially enters the works at the raw water inlet chamber where pH and oxygen levels are adjusted before the water is distributed to the sand filters.

There is a two-stage biofiltration treatment process removing iron and then manganese. The iron and manganese in the groundwater is initially in a dissolved state and cannot be removed by conventional filtration alone. Inside the filters are dedicated strains of bacteria that are cultivated to facilitate the oxidation of iron and manganese. Solid precipitate particles are formed and then filtered out.

The filtrate then flows by gravity through a packed limestone bed, stabilising the pH levels. From there, it moves into a treated water storage tank. A residual dose of chlorine (as calcium hypochlorite) is added into the treated water storage tank, controlled by a chip-feeder dosing system. This is done to protect water against downstream contamination. The treated water is then pumped to the Coegakop reservoir for distribution to NMBM communities.

The filters are backwashed with a combined water/air-scour system, drawing water from the manganese filtrate tank, and supplying air from dedicated backwash blowers. The spent backwash water is fed to backwash water recovery ponds where the solid residue settles, and the supernatant is pumped back to the head of the works. Settled solids are allowed to dry over time and are periodically removed for disposal off-site.

This treatment process relies on interstage filter feed pumps, backwash pumps, backwash blowers and treated water high-lift pumps.


Automated control and instrumentation systems will ensure that the treatment process operates effectively and that the process controllers can monitor all activities centrally. Automated reporting will be generated, assisting with compliance reporting. This is primarily done through a SCADA system.

“NMBM is refining its ability to operate plants remotely as well as record, view and manage data. With the drought, the balance between water demand versus available supply is precarious and we need to react rapidly to any changes within this system. Adopting a modern SCADA system is a huge step in the right direction towards achieving an optimised, efficient and reliable water supply system,” explains Hills.

He adds that digitising an entire water supply system (let alone a WTW) is a lengthy process.

“Local support is a key factor. We selected a supplier that has a large local footprint and has resources available in Gqeberha. It was also important that open-source protocol communication be employed, as NMBM did not want to be locked into a single service provider through proprietary software. The use of a gateway manager as opposed to an APN fixed IP solution gave further control of the SCADA network to NMBM. Because of this open-source focus, NMBM is able to modify the SCADA system as necessary and is not fully reliant on a third party.

It is essential to have very clear idea of what one needs and to consider aspects like the type of hardware, security, graphic user interface, alarms, signal tag naming and licensing, but more importantly to have this well documented in a functional design specification for including within future tender documents.

From there, third-party system integrators can be appointed to add to the SCADA system within a given scope. Taking ownership of the SCADA system is central to digitising your network. Additionally, there must be a designated person to drive the process as well as interact and coordinate between network engineers, hardware and software suppliers, the IT department, and system integrators.

Currently, NMBM is focused on creating interconnectivity between all components of its water and sanitation system, such as boreholes, reservoirs, surface water sources, treatment works, flow meters and pump stations. It is not efficient to constantly send people out to inspect parts of our system when it can be done remotely.

NMBM is using technology to protect its groundwater. “This is a precious resource and we must ensure that our abstraction rate is sustainable. The Coegakop Wellfield is not a short-term emergency drought intervention; it is part of our long-term water augmentation plans,” states Hills.

The boreholes at Coegakop are equipped with level and flow sensors linked to the SCADA system. Overall, this determines how abstraction rates affect the overall aquifer. Effects of abstraction are monitored on boreholes further upstream of the Coegakop Wellfield near Kariega. This information is transferred to the Coegakop WTW and shown on the plant SCADA. This will ensure that timely interventions can be made to the abstraction rates that would prevent any detrimental groundwater draw-down effects.

The data will also prove invaluable for the Department of Water and Sanitation in monitoring water use in terms of the licensed aquifer abstraction.

The backwash water recovery process and the five production borehole pump stations (spread across the Coegakop Wellfield, extending about 1.5 km away from the WTW) can be controlled remotely.

Operator-centric design

Architecturally, the design of the Coegakop WTW revolves around ease of circulation, putting the people who operate the works at the centre of the design concept. The WTW building was also designed to prioritise the security, safety, comfort, ergonomics, accessibility and work experience of the operators. 

“First, most of the treatment processes and equipment, as well as the control room, laboratory, offices and operators’ facilities were in a single building. The operators could view all major equipment from a single, easily accessible position, right outside the control room,” says Smit.

He goes on the state that this created a challenge, as it is easier for designers and the construction team to be able to work on components individually.

“The operator-centric approach resulted in a complex, integrated and dense design that combined interrelated treatment processes and equipment, sophisticated control systems, multiple foundation platforms, multistorey/water-retaining structures, all in a single building under one roof.”

It drove the development of a special layout with the aim to assist process controllers by configuring equipment in a logical way, enabling effective control of each system.

This was achieved by locating related equipment close together and ensuring clear visibility for processes that require monitoring. For instance, the upper filter gallery is visible from the control room, while the machine room is visible from both levels of the filter gallery. The design also facilitated simple circulation for normal routes taken by process controllers by minimising level changes, providing multiple routes within the building and limiting the need for exposure to wind or rain.

This plant is a good example of human-centric design, valuing personnel.

Virtual reality

3D modelling was used as a design collaboration tool for the various engineering and architectural disciplines, which was later built into the virtual reality (VR) and augmented reality (AR) software.

“We used VR to serve three main functions on this project:

  1. It instils confidence in the client regarding the design of the WTW. They get a personal sense of the plant, which is difficult to achieve from looking at 2D drawings, or a scaled model.
  2. It helps a lot to detect design clashes (civil, mechanical, electrical, services) and to optimise the spatial layout. The spatial design becomes tangible and instinctive, allowing the designers to grasp the relative size and positioning of equipment at a human scale. This helps us simulate the operator’s everyday working experience (Will pipes be in the way? Will they be able to reach certain valves? Does a room really need to be so big?).
  3. It develops a virtual operation and maintenance/training simulator for future plant operators who can practice various operating scenarios or protocols in a safe, offline environment,” states Smit.
VR and AR was also used to:

  • ensure adequate allowance for maintenance, dismantling, access, overhead lifting
  • allow for improvements in constructability considerations
  • aid the construction team in their planning and envisaging of the required product
  • present the project to those providing funding.
Since the operators at Coegakop will be stationed there on a 24/7 basis, the WTW was designed to ensure maximum security for them. To achieve this, the process and administration components are housed in one secure, self-contained building. This includes the treatment equipment and laboratory, boardroom, offices, canteen and workshops.

“The project involved rigorous and highly collaborative interaction between the client, engineers, architects, geohydrologists, environmental practitioners, 3D software modellers and VR programmers. Through exploration, innovative use of technology and collaborative use of design, the Coegakop WTW can successfully supply safe water to a water scarce NMBM,” says Hills.

Smit concludes that the engineering team (including the client) for this project comprised an unusually young and talented team (several of whom gained their professional registration during this project) that worked in a highly collaborative way.

“The Coegakop WTW is an incredible achievement for us to be able to deliver infrastructure of this quality to the people of NMBM, and a strong reminder that we as South Africans can and should take a leading role in solving our own water challenges,” he concludes.

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