More than 40 percent of South Africa's dams suffer eutrophication, when the water becomes nutrient-rich and algae multiply, releasing cyanobacterial toxins harmful to the liver and nervous systems of humans, domestic animals and wildlife.
Failing water treatment plants that allow inadequately treated sewage back into the environment are being blamed for eutrophication, which is regarded as the most serious threat to the country's already stressed water resources.
The 2009 Green Drop Report by the Department of Water Affairs found that over 55 percent of South Africa's wastewater treatment plants were in need of "drastic improvement." Its 2010 report found that only 32 of around 850 wastewater treatment plants - about three percent - were considered completely compliant with safe discharge standards.
Sector analysts agree the problem is aging water infrastructure, coupled with the rapid expansion of water services since the demise of apartheid in 1994, which have been hastened by a shortage of skills and the poor management of wastewater treatment plants.
The Council for Scientific and Industrial Research (CSIR), a South African scientific and technology research unit, has said the country's freshwater resource will be depleted by 2030 if current practices towards water remained unchanged.
The World Health Organization notes on its website that the effect of "cyanobacterial toxins varies according to the type of toxin and the type of water or water-related exposure (drinking, skin contact, etc). Humans are affected by a range of symptoms, including skin irritation, stomach cramps, vomiting, nausea, diarrhoea, fever, sore throat, headache, muscle and joint pain, blisters of the mouth and liver damage."
The increase in eutrophication is being compounded by industrial effluents, soil erosion and agriculture - which accounts for about 60 percent of South Africa's water consumption - through the use of fertilizers.
In a field on the outskirts of Du Noon, a poor township about 15km north of Cape Town, there is a 50-metre-long pool with two small reed-covered islands that mimic the mechanics of a wetland, removing nutrients, trace metals, and hazardous compounds from the storm water runoff of what has become an open toilet for nearby residents. The cleansed water then flows back into a nearby river where, perversely, inadequately treated sewage re-pollutes it.
|This technology provides a proven, immediately implementable means of reducing a range of problem elements and compounds present in wastewater|
The technology, developed in the United States, replicates freshwater islands composed of tightly-knit roots, peat, and detritus. In wetlands 80 percent of the biological action is performed by aggregates of micro-organisms attached to all submerged surfaces, called biofilm.
The matrix structure of the floating islands provides a greater surface area for biofilm to grow, so they are 150 times more efficient than those of a conventional wetland. One square metre of a bio-island is equivalent to 150 square metres of conventional wetland - a compact format suited to urban environments.
"The most important part of the islands is the organisms that grow on the matrix - the bacterial biofilm. In six weeks to three months it's taking out nutrients, trace metals, pharmaceuticals like oestrogen, antibiotics, everything is going into the biofilm and being sequestered," said Bill Harding, the aquatic ecologist who installed the system.
"This technology provides a proven, immediately implementable means of reducing a range of problem elements and compounds present in wastewater.”
Capacity issues in South Africa make the technology particularly suitable. "There's no maintenance - you put it in, and it immediately starts operating. Basically, you're restoring the skeleton for a biological engine," Harding told IRIN.
"We're not saying you can replace a wastewater treatment plant [with floating island technology]," he said. "But at the right scale, [this technology] can reduce the outflow of phosphates from wastewater treatments by about 30 percent."
The start-up cost of the matrix material is about US$185 per square metre, and so far uptake in South Africa has been limited to the private sector - a proposed bus station in Du Noon, farms, and individuals - but widescale use could stimulate employment in the local production of matrix components.
More islands needed
"Bio-islands can definitely play a role in purifying the water. They give you the water fleas and plankton that play an important role in keeping [algae] blooms under control," Paul Oberholster, a chief researcher at the CSIR, told IRIN. "But it's still a short-term solution. We need to address the causes, look at managing erosion and the overuse of fertilizers in the agriculture sector."
One of the authors of the 2010 CSIR report on water, Oberholster stressed the need to "put policy into practice" in the existing wastewater treatment system, and to create new policies that limit the amount of phosphates dumped into the system, especially the quantity of fertilizers in agricultural runoff, and the level of phosphates in detergents.
According to the CSIR, rehabilitating municipal water and sanitation infrastructure would cost about R83 billion (US$11 billion).