发表时间：2013-10-08 15:08:56 编辑：管理员 来源：thejakartaglobe.com, By Brendon Bosworth 访问量统计：4
The Umgeni River system supplies drinking water to about five million people in the city of Durban, South Africa. But demand for water has outstripped supply for the past seven years. Pictured here is Howick Falls, which lies on the Umgeni River. (IPS Photo)
KwaZulu-Natal, South Africa.
In a few years, residents of the eThekwini municipality in the port city of Durban, South Africa could be drinking water that was once flushed down their toilets. Authorities are planning to introduce a system that would recycle some of the municipality’s sewage and purify it to drinking quality.
“We’re going through a crucial water shortage, which is increased by the water demand of eThekwini,” Speedy Moodliar, the municipality’s senior manager of planning for water and sanitation, told IPS.
The municipality relies on the Umgeni river system for water. But demand on the system, which supplies drinking water to about five million people and fuels industry in the economic hubs of Durban and Pietermaritzburg, a town 66 kilometers from the coast, has outstripped supply for the past seven years.
To boost supply in future, the South African government has proposed building a dam with a capacity of 250 million cubic meters on the uMkhomazi river, the third-largest river in KwaZulu-Natal, and transferring water to the Umgeni system.
But this solution would take until 2024 to implement at the earliest, said Moodliar. “Between now and when the uMkhomazi [project] comes online, [wastewater] reuse will be our mitigation measure,” he said.
In dry countries like Israel, Egypt, and Australia, treated wastewater is used for industry, landscaping and agriculture. But few countries put it directly into their drinking water supplies.
Singapore uses purified wastewater to meet 30 percent of its water needs, although just a small percentage goes to drinking water and the majority is used by industry. Citizens of Windhoek, the capital of South Africa’s arid northwestern neighbor Namibia, have been drinking recycled wastewater for over 40 years.
In 2011, the Beaufort West municipality, which serves close to 50,000 people, began treating its sewage for use as drinking water after a vicious drought, making it the first in South Africa to do so.
According to a 2012 World Bank report, few cities in Africa have functioning wastewater treatment plants and “only a small proportion of wastewater is collected, and an even smaller fraction is treated.”
The eThekwini municipality plans to upgrade two of its existing, underperforming wastewater treatment plants, the KwaMashu and Northern treatment works, Moodliar said.
A three-stage system that uses filtration, reverse osmosis, ultraviolet light and chlorination would be used get the water to drinking quality. The treated water would also be stored and tested before being released.
The purified water would be mixed with conventional drinking water at a ratio of 30 percent to 70 percent , Moodliar said. It would feed the municipality’s northern regions, including Umhlanga, Durban North, Reservoir Hills, and KwaMashu.
Reusing wastewater in this way will add 116 megaliters of tap water to the municipality’s supply daily — enough to fill more than 46 Olympic-size swimming pools, or roughly 13 percent of the municipality’s current daily consumption. It would provide an estimated seven years of water security.
While it will cost more to produce drinking water through wastewater recycling — about 75 cents per kiloliter compared to 50 cents per kiloliter for conventional treatment — the municipality sees it as “the best fit,” said Moodliar.
The municipality has touted the effectiveness and safety of the proposed system, but there has been opposition to the plan, including the submission of a 5,000-signature petition from the public.
Citizens have raised concerns about the safety of drinking the reused water. “Recycling of toilet water to drinking water is a death sentence to the general public because of health implications,” wrote Jennifer Bohus in an email to Golder Associates, the firm that produced the basic assessment report for the wastewater recycling proposal.
The municipality, however, maintains that the water will be fit to drink.
“The technology is advanced enough that the quality of the water being returned is high,” Graham Jewitt, director of the Centre for Water Resources Research at the University of KwaZulu-Natal, and chair of water resources management for state-owned Umgeni Water, told IPS. “Many cities all round the world use recycled water.”
“About 14 percent of water use in South Africa is actually water that’s being reused, most of it indirectly,” Niel van Wyk, chief engineer at the Department of Water Affairs, told IPS.
Citizens who opposed the plan also said the municipality, which loses 36 percent of its water annually, largely through leaks and illegal connections, should focus on fixing leaking pipes. Others proposed investment in seawater desalination plants.
The potential for sucking seawater from the Indian Ocean and converting it to freshwater for the region is currently under investigation. But the process of seawater desalination, which involves pumping saltwater at high-pressure through a semi-permeable membrane that retains the salt, and allows water to pass through, remains costly.
Umgeni Water, the state-owned company that is the largest supplier of bulk potable water in KwaZulu-Natal, is doing a feasibility study for two desalination plants: one on the south coast, adjacent to the Lovu River, and one on the north coast near Tongaat, Shami Harichunder, corporate stakeholder manager for Umgeni Water, told IPS.
If built, these plants would be the largest desalination operations in the country, each capable of producing 150 megaliters of water per day. By comparison, the largest desalination plant in South Africa, in Mossel Bay on the Southern Cape, produces a tenth of that amount.
One of the proposed plants could cost as much as $300 million, according to Harichunder. Necessary technological components, like high-pressure pumps, are expensive, he said.
Desalination plants, however, can be built more quickly than large dams and transfer infrastructure, and also have the potential to be scaled up in future if needed, said the Department of Water Affairs’ van Wyk.
Umgeni Water’s feasibility study will be complete by December of this year.