INLSA
Durban plans to become the first SA city to purify and recycle sewage water into drinking-quality tap water and officials are urging residents to comment on the proposal as soon as possible.
The plan involves producing about 12 percent of the city’s tap water supply from recycled sewage effluent – mainly in the northern suburbs and townships of the city.
The water would be disinfected and purified at the KwaMashu and Northern sewerage works, which would be upgraded to incorporate new ultra-filtration and disinfection methods.
The city is also carrying out a parallel feasibility study on purifying sea water as an alternative, but the desalination process requires large volumes of electricity that would push up treatment costs.
As part of a compulsory social and environmental impact assessment, eThekwini municipality and consultant Golder Associates placed newspaper advertisements on February 8, inviting the public to comment before March 23.
But Golder Associates consultant Rob Hounsome told The Mercury yesterday that with just nine days to go before the deadline for comment expired, there had been limited feedback from the public. However, this deadline would be extended if residents needed more time to study and comment on the plan.
According to a background information document, a Department of Water Affairs study in 2008 found the eThekwini metro area was running short of reliable water supplies and the risk of water restrictions was considered “unacceptable”.
Yet a staggering 37 percent of water bought from Umgeni Water is going astray in Durban because of leaks, theft and other “unaccounted losses”. The city recently spent millions of rand replacing large sections of old, leaky pipes and reduced pressure levels in several areas to curb leaking, but eThekwini says further water conservation strategies are unlikely to relieve the supply risks immediately.
The eThekwini senior water engineer, Bill Pfaff, said although a large new dam, Spring Grove, was being built near Mooi River, this would not relieve the water supply risk to an acceptable level in the short term. The city hoped to get approval to build and commission the new sewage purification works before 2016.
Although the toilet-to-tap water proposal was likely to draw criticism because of the “yuck” factor, Hounsome noted that Windhoek had been partially reliant on recycled sewage-to-tap water since 1968.
“General distaste for drinking treated effluent has given way to pride in the municipality’s unique, effective and efficient use of scarce water resources,” said Hounsome.
“Crucial to this public acceptance is Windhoek’s 42-year record of no waterborne disease outbreaks and no negative health effects attributable to drinking reclaimed water.”
Golder Associates’ background document says the only other SA municipality now using treated effluent for tap water is Beaufort West in the Western Cape. This R42-million scheme began producing water in January.
According to eThekwini’s water department, there would be at least three safety barriers to ensure the quality of treated effluent.
It would be treated first using conventional wastewater technology. The semi-treated clear water would then be pumped at high pressure through ultra-filtration membranes that removed suspended and dissolved solids, and bacteria.
Only pure water molecules passed through the membranes.
This ultra-filtered water would then be treated with reverse osmosis technology, which filtered the water through tiny pores, about 0.001 micrometres in diameter.
The final stage involved ultra-violet light disinfection.
Commenting on concerns that the treatment relied on high levels of technical skills and efficiency, the Golder report said Durban was among the top scorers (above 96 percent) in the 2011 national Blue Drop water quality scheme.
Nevertheless, Golder said numerous studies showed that conventional wastewater treatment plants could not remove endocrine disrupting compounds (EDCs) completely.
EDCs are derived from pharmaceutical and personal care products and can cause growth deformities, gender-bending effects and other ecological impacts, even at very low levels.
However, more advanced processes like reverse osmosis “appear to be viable for the removal of many trace contaminants, including EDCs”.
As a further safeguard, all purified effluents from the two new Durban plants would be stored for at least 12 hours after treatment so that final grab samples could be taken before the water was released into tap supplies.
For more information and to comment on the plan, the public may contact Rob Hounsome or Mfundo Ndlovu at 031 717 2790, or e-mail mndlovu@golder.co.za
