Wednesday, April 11, 2012
Toilet Water Can Be Purified
In this file picture, sewage gushes from a pipe into the Umhlatuzana River.
Experts say that residents are already drinking water containing many pollutants,
\despite their reluctance to entertain the idea of drinking water recycled from sewage effluent.
Yuck! This is the response in most instances to the proposal to recycle water from sewage effluent.
But experts warn that there are already substances in our water supply that might draw similar reaction – and we drink it anyway.
Durban plans to become the first South African city to purify and recycle sewage into quality tap water. 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.
Dr Jo Barnes, a senior lecturer in epidemiology and community health in the faculty of health sciences at the University of Stellenbosch, said it was worth remembering that all water on Earth had been used before.
“The treatment cycle is just much longer for water harvested from nature, while the water directly harvested from households is still very polluted. The major difference is that household wastewater needs aggressive purification.”
The concern in many minds, she said, was that all engineering systems had the potential to fail at some point.
“Water from nature can also be unclean, but less so than household wastewater. It is the close proximity between use, dirtying and re-use in the household wastewater scenario that concerns many people.”
The acting head of the city’s health unit, Dr Ayo Olowolagba, said South Africa’s water was internationally highly ranked for its quality – but even this water contained chemicals, in their permissible amounts. “Nothing is pure, from the air we breathe, to the food we eat – but our water still meets national and international standards.”
People’s perceptions had little to do with reality. Even the bottled water people often consumed was no better in terms of chemical content, compared with tap water, he said.
“We have strict monitoring systems in place. If there is a problem, we let the public know. There’s no hidden agenda.”
South Africa, he said, was a water-scarce country, so the municipality had to prepare for any eventuality. “This is part of that plan.”
Barnes said there were stringent limits for many harmful substances in drinking water purified by municipalities.
“The purification works in most cities are still in reasonable shape, but the purification works in many smaller municipalities, especially in rural areas, are not functioning properly at all.
So, the harmful substances already in drinking water and distributed to consumers depends on the sophistication and functioning of the relevant works.”
She said there were some substances that were difficult or very expensive to remove.
“Two harmful organisms that can make people ill are Cryptosporidium and Giardia. Both can cause serious diarrhoea and vomiting. But they are resistant to chlorine – the disinfectant most often used to purify water.”
Barnes said there were also some compounds such as those containing nano particles (extremely small particles) that were difficult to remove, even for sophisticated purification works. She said there had been well-documented instances of such outbreaks of waterborne disease.
“But, it depends, among other things, on how clean a municipal system can get the water.
Another factor to remember is that the quality of the purified water is usually tested as it leaves the purification works.”
But this water still has to reach the consumers. In towns where the distribution systems (pipes, etc.) are in poor repair or leaking, even initially clean water can get re-contaminated, making people ill.
Barnes said with waterborne disease from contaminated drinking water, the contaminated batch of water had long passed through the system.
She said no large-scale processes were 100 percent safe, but alternatives could sometimes carry worse risks.
“Not purifying water carries an even bigger risk. As far as health aspects are concerned, these decisions are about balancing the risk of distributing contaminated water against the health effects if people do not have enough water to clean themselves and their living quarters. That also carries risk.”
Money was also a factor in the water purification process, she said. “‘Black’ water, or water containing toilet waste is the dirtiest and most dangerous of all the various water waste streams, and needs the most sophisticated and costly systems to clean.
Since water containing human waste always carries health risks, this purification system should be very safe and well maintained.”
“‘Grey’ water – water originating from baths and showers, for instance – was much less contaminated and therefore easier to purify. “I would certainly consider re-using such ‘grey’ water long before trying to clean ‘black’ water.”
A spokesman for the South African Bureau of Standards (SABS), Verna Schutte, said the SABS was the administrative tool on supplying the standard and had no jurisdiction on the quality of drinking water to the consumer.
“SABS is not responsible for water quality. An SABS standard is available through the input of water authorities on allowed limits for drinking water,” she said.
Environmental research campaigner Dr Rico Euripidou of NGO groundWork said the process of purifying and converting sewage water into drinking water was neither uncommon nor publicly rejected where it was a necessity, “in water-scarce countries such as Singapore, the western US, UK, Australia and even closer to home, in Namibia”.
The principle, he said, was that once purified, drinking water was generally free of pathogens common to sewage.
“In fact, the general quality of water in the Inanda Dam prior to purification would contain many ‘sewage pathogens’ as does the uMngeni River, etc. This is one of the main reasons we fail to get Blue Flag status for our beaches. Canals and failures at sewage treatment works means raw sewage makes its way to the sea.”
He said many chemical substances that might be harmful to health such as endocrine disruptors and some pthalates (substances added to plastics to increase their flexibility) were not routinely tested in drinking water.
Lushendrie Naidu, South Durban Community Environmental Alliance projects officer, applauded the move, saying that if the country were to face a water shortage in the next couple of years, this might be the only solution.
By Kamcilla Pillay@iol.co.za/Daily News