Recycling wastewater an option to counter water scarcity
Recycling sewage into potable, drinking water is an extensive and complicated process, but it could be part of the solution for water-scarce South Africa in future.
The issue has come into the spotlight since the World Health Organisation (WHO) published its ‘Potable Reuse Guidance for Producing Safe Drinking Water 2017’ report.
Water solutions provider Proxa technical director Wimpie van der Merwe told delegates at the Water Desalination Symposium, in Cape Town, that potable reuse schemes would be complex. Proponents would need to have sufficient resources and capabilities to implement it successfully.
“I can see many, many debates around it in future. It needs to be handled with care and managed very carefully. For the public, it is still an emotional issue,” he said.
The WHO report said potable reuse represents a realistic, practical and relatively climate-independent source of drinking water. It can provide large volumes of drinking water from wastewater available from established collection systems in both coastal and inland locations.
The use of potable water is growing exponentially in other countries. Singapore is a leader in the space. It has four plants that reuse sewage, providing 40% of the country’s potable water.
Potable reuse schemes were pioneered in Windhoek in 1969. The system is also being used in Australia and parts of the US, besides other countries.
While desalination is a growing and popular option to supplement dams, Van der Merwe said desalination comes with certain risks, including noise, traffic, land-use, energy consumption and brine disposal concerns.
Van der Merwe explained that various processes had to be undertaken to convert wastewater into potable water.
“The first . . . thing is to take out the macropollutants and adjust the physical properties. You also need to take out the micropollutants and endocrine disruptors present in pharmaceuticals and personal care products,” explained Van der Merwe.
He said there were more than 4 000 suspected contaminants. Out of these, the WHO has identified 50 key components.
“If we want to ensure public safety, we will need several processes. Not one single process can guarantee compliance,” Van der Merwe stressed.
Steps would involve reducing the residual nutrients, removing suspended solids, reducing dissolved solids, reducing trace components, and disinfecting and stabilising the water.
The WHO says there is growing acceptance of treating wastewater into potable water, which is typically less expensive than seawater desalination. But it has pointed out several challenges.
One of them is that municipal wastewater systems collect pathogens, which include bacteria and viruses.
“Source wastewaters are very poor quality with high concentrations of microbial pathogens and can potentially contain a broad range of chemical contaminants. It generally includes the use of complex treatment processes and a high level of technical expertise and understanding,” says the report.
Desalination company Ion Exchange Safic CEO and executive director Gourish Chakravorty, meanwhile, told delegates at the summit that communities’ attitudes would also need to shift.
“Recycled wastewater can be better for the community and be more sustainable, but you have to change the perception in the community. You need to say used water not wastewater,” he suggests.
Green Cape Sector Development Agency water sector analyst Bridget Fundikwa, meanwhile, pointed out that businesses in the Western Cape were showing an increasing interest in saving industrial water for reuse.
“The drought situation in the Western Cape has been a big wake-up call for most companies.”
But Fundikwa said surveys and interviews had indicated that smaller and medium-sized companies, in particular, had called for incentives to invest in processes that would allow industrial water to be used again, or 'repurposed'.
She said Green Cape saw the water crisis as an opportunity.
“Let’s leverage this increased interest in water for financially rational, low regret, resilient investments.”