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Inside Joburg’s wastewater treatment works — the complex process of keeping drinking water safe

Inside Joburg’s wastewater treatment works — the complex process of keeping drinking water safe
The dewatered sludge, a byproduct of treating sewerage, in the sludge drying bed, which solar-dried and composted and taken to local farmers. (Photo: Julia Evans)
Julia Evans
By Julia Evans
26 Jun 2023
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Against the backdrop of the cholera outbreak that has now left more than 30 people dead, Johannesburg Water invited the media to one of the entity’s best-functioning sewerage works. But one working sewerage works is a drop in the river when 40% of SA’s wastewater treatment works are woefully inadequate.

Driefontein Wastewater Treatment Works (WWTW), in Krugersdorp, is one of six wastewater treatment works owned and operated by Johannesburg Water, which is mandated to provide water and sanitation services to the residents of the City of Johannesburg. 

As the second smallest Johannesburg Water sewerage works, Driefontein WWTW services the suburbs of Roodepoort, Muldersdrift, Mogale and Rietfontein, and has a nominal treatment capacity of 55 megalitres per day — although the average flow coming through is 42 megalitres a day, which is about 75% of its design capacity.

The treated sewage water (effluent, or green drop — not what we get out the taps) gets discharged into the Crocodile River — the upper part of which drains into Hartbeespoort Dam.

Jacqueline Ngwenya, the Driefontein works manager, explained during a tour of the plant last week that “our compliance over the years has been really good” with the works’ average effluent compliance at 97%, compared to the Department of Water and Sanitation (DWS) Water Use Licence standards that require 90% compliance.

She attributes the success to good management and that Johannesburg Water has invested capital in new technology and infrastructure to ensure their processes are optimised and efficient. 

Driefontein was first commissioned in the early 1970s as a 15-megalitre treatment capacity plant, but over the years it has been upgraded to be able to treat a capacity of 30 megalitres (finished in 2008) and then 55 megalitres (finished in 2016). 

Ngwenya said that Johannesburg Water has a master plan which predicts and plans for future developments, and they will be adding another 25 megalitres, taking them to 80 megalitres treatment capacity in the future.

This, along with plans to expand other plants and build a new one (currently a plan for a WWTW in Lanseria) should be able to service population expansion, which was one of the issues Rooiwal WWTW in Hammanskraal — the root of the cholera issue — faced.

A drop in the river


While Driefontein has a 97% compliance according to their own strict standards (and a 100% effluent quality compliance according to the DWS’ 2022 Green Drop report), the five other WWTW that Johannesburg Water manages are not faring as well. 

Ennerdale and Olifantsfontein comply with two out of three effluent categories, Bushkoppies and Northern Works complies with one out of three effluent categories, and Goudkoppies fails all three categories. 

“The lack of microbiological compliance at all plants except for Driefontein presents serious health risks to downstream users,” the report warned.

Ngwenya said that Bushkoppies treatment plant — which services the southern suburbs of Johannesburg, Soweto East and industries to the south of Johannesburg — was issued with an incorrect water use licence (told to treat water to drinking water standards), so they are waiting for their licence to be rectified. 

Goudkoppie, which services the city centre and south-eastern areas of Johannesburg has an alarming 59% compliance. Ngwenya said this plant battles vandalism and theft of infrastructure.

“In the south [of Johannesburg] there’s a lot of cable theft and vandalism of equipment and infrastructure that needs to be replaced,” said Ngwenya.

And there are many other WWTW from other municipalities that run into the Crocodile River.

Professor Anthony Turton, a water resource management specialist at the Centre for Environmental Management at the University of the Free State explained to Daily Maverick that, “almost 40% of all our wastewater treatment plants today are as dysfunctional as one can get.”

Read more in Daily Maverick: The simplest solution to SA’s cholera crisis is fixing our broken sewerage systems

And as Turton explained, while 97% for Driefontein is good, “there is no single number that’s acceptable, because if you’ve got one sewerage works discharging into a very big river, then 90% is okay, because of a thing called the dilution capacity.”

But while a bug in a million litres of water is insignificant, “if you’ve got 850 wastewater works, 40% of which are non-compliant, and you are collectively releasing five million litres of water per day, only 15% of which has been treated to a decent standard, then you start overloading the system.”

Turton was referring to the reinstated 2022 Green Drop Report from April which indicated that 334 out of 850 WWTWs were in critical condition

“That was a total of 39% of all WWTW in 90 municipalities. And since then the situation has significantly deteriorated,” said Turton.

Out of the five billion litres of sewage discharged into SA’s rivers daily, only 15% of it is treated to a satisfactory standard, the rest of which comes from the 334 dysfunctional WWTW.

Turton, who was also the former vice-chair of the research advisory panel for the National Water Resource Strategy at the CSIR, explained that we need to have a functional sewerage system that has 100% compliance across the board because South Africa practises an indirect reuse strategy. 

“All of our sewage water is indirectly reprocessed back as drinking water. And it’s done this way because people don’t like the idea of drinking sewage water,” said Turton. 

“If we discharge the wastewater into a river, then there’s no distinction between sewage water and river water,” said Turton explaining that if we then abstract water from a river we treat it to potable (drinking) water levels. 

“And then people don’t make the link between sewage and drinking water — which is why the Green Drop report is so important because it gives us the standard of discharge at the end of the pipe at wastewater works into the river.”

The root of the problem: investment and State Capture


Like many people who work for Johannesburg Water, Ngwenya has the expertise, knowledge, and capabilities to get her job done.

When asked if she felt frustrated that her work was discredited during a water shortage crisis or cholera outbreaks, she said, “unfortunately for us in this industry, I don’t think government and municipalities realise how much investment they need to do in terms of capital.” 

Ngwenya previously worked as a microbiologist in Johannesburg Water’s Cydna laboratory before coming to Driefontein.

“I think we’re very reactive instead of being proactive. Because all of this could be prevented if we took our work seriously in terms of making resources available.

“I don’t think all the other colleagues in the other wastewater treatment works are just sitting there. They are frustrated because there’s no money that’s been invested, and without equipment and infrastructure, there’s literally nothing anyone can do.”

Turton agreed about a proactive approach, saying that, “every wastewater works I’ve ever been to has been a reactive management style.”

But he added that it’s not just investment that’s needed, but sorting out corrupt tenders in the procurement of expensive equipment needed for these treatment works. 

“I think part of it is that the procurement systems are generally woefully overburdened,” said Turton, explaining that wastewater treatment works have been a critical part of State Capture because there are many high-cost items needed for sewerage works. 

“In many cases, the procurement systems have been captured or have been manipulated. So it’s difficult to procure stuff through the normal tendering process.

“We’ve got evidence from the Rooiwal Wastewater Treatment Works where corrupt tenders were given to people without any skills or knowledge, with hundreds of millions of rands worth of tenders involved.”

Turton said that in some cases he’s been involved in, a legitimate order would take months because the process has been so corrupted.

How our Wastewater Treatment Works (should) work


Ngwenya took the media through the treatment processes at Driefontein WWTW.

Preliminary treatment: 


Once the incoming sewerage (influent) arrives in the works, it goes through a static manual screen — which has rakes that filter out materials (like rags, tyres, big stones) that could damage the downstream equipment.

Jacqueline Ngwenya, Driefontein Wastewater Treatment Works manager, explains how the online monitoring systems work. (Photo: Julia Evans)



After that, it goes through a mechanical screening building, where plastics and tissues are removed.

After going through a washer (which removes the organics from the materials), the effluent goes through de-gritting tanks that remove grit and sand.

water treatment works Grit and sand are removed from the effluent. (Photo: Julia Evans)


Primary treatment:


Now that the sewage has been prepared, it can begin the main process of cleaning. The pre-treated flow is split between two parallel primary clarifiers, which separate the readily settleable solids from wastewater.

The raw sludge is circled in the primary sedimentation tanks before making its way into fermentation tanks. The sludge is fermented so it can later be used as a food substrate (contributes to either growth or burning of the nutrients that need to be removed from the dirty water).

water treatment works The primary sedimentation tanks, where the raw sludge is circled before going into fermentation tanks. (Photo: Julia Evans)



“You want to produce volatile fatty acids that you’re going to use for the biological nutrient removal process,” explained Ngwenya. The acids are eaten up by microorganisms in the system, which aids in phosphorus removal.

NOTE: While Driefontein only releases 0.2 milligrammes per litre of phosphate into the Crocodile River after the effluent is treated (way below the 1 milligram per litre of phosphate the DWS allows), most WWTW release a high content of phosphate, due to the lack of efficiency of their treatment works and equipment availability, vandalism and theft of cables.

The phosphate released into the rivers is a contributing factor that causes the hyacinth problem in Hartbeespoort Dam.

Read more in Daily Maverick: Harties vs the hyacinth (Part 1) – The toxic dangers lurking under cover of an invasive weed

In the bioreactors, they only add chemicals (ferric chloride) if their biological process fails.

water treatment works Bioreactors in Driefontein Wastewater Treatment Works, where non-harmful bacteria are grown so it can remove harmful nutrients in the sewerage. (Photo: Julia Evans)



Ngwenya explained that “our process is mainly biological. We rely on the good bacteria that’s already in the system to treat the water.”

In other words, this part of the treatment makes use of non-harmful microorganisms to remove nutrients they don’t want in the final effluent (excess nitrate, phosphorus).

water treatment works The aeration zone of the bioreactor, which is used to introduce oxygen to the microorganisms so they can remove the nutrients Phosphate and Ammonia. (Photo: Julia Evans)


Secondary treatment: 


The Secondary Clarifiers separate the mixed liquor solids from the clear treated effluent.

water treatment works Secondary clarifiers, which separate the suspended solids from the clear treated effluent. (Photo: Julia Evans)



The treated effluent flows to the downstream disinfection process, the final phase of the liquid treatment, where the effluent is disinfected using calcium hypochlorite (chlorine-based product) to disinfect and remove e-coli. 

water treatment works The final phase - the effluent is disinfected using calcium a chlorine-based product to disinfect and remove e-coli. (Photo: Julia Evans)



Finally, the fully treated effluent is released into the Crocodile River.

water treatment works The treated effluent is released into the Crocodile River, before ending up in Hartbeespoort Dam. (Photo: Julia Evans)


Tertiary treatment:


The sludge — a by-product of the wastewater treatment process — does not go to waste.

The dried-out sludge is used as compost for nearby farmers. (Photo: Julia Evans)



The dewatered sludge, a byproduct of treating sewerage, in the sludge drying bed, which solar-dried and composted and taken to local farmers. (Photo: Julia Evans)



The sludge is dewatered and taken to drying beds; the sludge is solar-dried, composted and taken off-site to agricultural land, as it has nutrients that help plants grow. DM

To read all about Daily Maverick's recent The Gathering: Earth Edition, click here.

https://www.youtube.com/watch?v=REeWvTRUpMk

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