Preventing water wars?

2011-03-11 00:00

IN addition to dire warnings about “water wars”, a former director general in the then Department of Water Affairs and Forestry, Mike Muller, was quoted in media saying that it’s time to start panicking about water supplies, otherwise we are headed for a major crisis in 2020. He singled out eTheKwini Metropolitan Municipality as “the most vulnerable metro at the moment — they’ve been living a charmed life”. The metro “should” have run out of water during the World Cup and it “should” run out of water during the UN climate change talks later this year, but would “probably get away with it”, Muller said (News24, February 19, 2011).

Umgeni Water (UW) supplies bulk water to both the eThekwini and Msunduzi municipalities. Msunduzi’s potable water comes from the Midmar waterworks, while UW supplies the eThekwini municipal area from Inanda, Albert Falls and Nagle dams. This is treated at Durban Heights and Wiggins waterworks and gravity-fed from there to eThekwini infrastructure for supply to consumers.

In an initiative called the Umlaas Road New Water Project, UW has been investigating ways to supplement water supply to the Umlaas Road reservoir, which supplies the uMgungundlovu as well as the eThekwini municipal area. One of these is “direct reuse”, which would turn treated wastewater into drinking water and pump it to Umlaas Road reservoir to be blended with water from Midmar Dam.

UW has built three membrane bioreactor (MBR) demonstration treatment plants at Darvill wastewater treatment works near Sobantu. Since the start of 2010 it has been conducting experiments on treating wastewater using membrane technology. The demonstration-scale MBR plants are capable of producing up to 2 500 ℓ an hour of water recycled from sewage. There are parallel investigations under way into the production of potable water from wastewater and into this technology’s potential to improve the quality of the effluent that the Darvill plant produces. Even if it’s decided not to produce drinking water at Darvill, UW could use this technology to improve the quality of the water the works discharges into the Msunduzi River, which eventually ends up as drinking water via Inanda Dam.

UW knows that it’s possible to produce drinking water from wastewater: the technology is in use and the oldest such plant in the world, operating since 1969, is in Windhoek, Namibia. Scientists know that it’s even possible to produce potable water to World Health Organisation standards that are higher than South Africa’s SANS 241 standards. What UW does not know is whether it’s financially viable to do it on a large scale in the local context.

UW is benefiting from looking into membrane technology at a fairly late stage in its development when it is much more advanced and cheaper than when first introduced. The MBR demonstration plants are fitted with different types of membranes for comparison purposes, including tubular, hollow-fibre and flat-sheet membranes in submerged and external applications. These membrane systems are imported from Austria, Holland and the United States, and are installed by international suppliers and maintained with the assistance of local contractors. MBR plants are highly automated processes that require little intervention and undertake chemical cleaning of the membranes automatically. Local expertise and personnel are reportedly more than capable of maintaining a plant like this. Additional treatment technologies such as ozonation and ultra-violet light will be added to the process train later this year (see box).

The pilot project will run until July 2013 and it will be three years before UW can say whether it’s a good idea or not. After that, higher authorities will make the decision about whether to go ahead and build an advanced treatment plant at Darvill. If the project goes ahead, there will first be the budgeting process, and then the design and construction phases. “At the absolute minimum we are talking five years before we could be producing potable water from wastewater here. The critical factors in making or breaking the project will be the economic feasibility of the project and overall public acceptance for the project,” said UW corporate stakeholder manager, Shami Harichunder.

As part of the investigations into wastewater-to-potable water reclamation, UW contracted independent consultancies to conduct a public participation process in the form of an environmental focus group (EFG). Key stakeholders were invited to identify, discuss and debate the socioeconomic and biophysical environmental issues associated with water reuse in the local context. They were also presented with the results of studies into issues associated with a reuse plant, like the quality of the water produced, and the social and environmental impact on and water quality and quantity issues in the Msunduzi River.

After considering the data gathered, the EFG concluded that the reuse investigations should continue because “the benefit of this project is that wastewater is a guaranteed source of water”. However, they also identified several hydrological, technological and social issues that required more investigation, including “the yuck factor”. This is the consumer response and possible resistance to the idea of drinking water produced from recycled wastewater.

UW is aware that community education and managing public perception would be important to the success of wastewater reuse, if it is to be implemented in future.

Consumers have to accept that whether it’s in five years or 50 years, they are going to have to drink water recycled from wastewater because that’s the reality of this water-scarce country.

THE pilot scale reclamation-reuse plant to be constructed later this year comprises several treatment steps that remove pollutants from the wastewater, including organic and inorganic solids, bacteria, viruses and contaminants of emerging concern (CEC) e.g. endocrine disrupting compounds (EDCs).

Different advanced treatment technologies and configurations are to be tested to ascertain the most appropriate combination of technologies. In order to minimise risk a multiple-barrier approach is adopted to ensure that if one barrier fails the next barrier will provide a backup. The steps of the process would include:

• multiple membranes to remove solids;

Ozonation to inactivate pathogenic microorganisms and destroy tastes and odours causing compounds;

• a biological active and granular activated carbon filter to remove dissolved organics and CECs;

• a nano filtration membrane to remove any remaining solids and pathogens; and

• ultra-violet light to disinfect the water.

 

— Source: Umgeni Water Workshop report, Phelamanga Projects, September 2010

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