A Chinese expert has recently found a new way of dealing with the mounting sludge produced in sewage treatment and dumped in city suburbs amid rapid urbanization process.
Weng Huanxin, a professor with the Environmental and Biological Geochemistry Institute of the Zhejiang University, east China's Zhejiang Province, has developed a method of transferring sludge into innoxious materials for bricks and cement at a low cost.
Sludge is threatening to besiege more than 700 cities in China. Beijing alone produces 1,000 tons of sludge a day, Shanghai 700 tons and Shenzhen 300 tons.
It is estimated that China's sludge amount will rise at an annual rate of 10 to 15 percent in the following years. Beijing is expected to discharge more than 2 million tons of sewage every day in 2008, which is likely to yield more than 2,000 tons of sludge if all the sewage is treated.
Most of the sludge is just piled up in open air or land filled, which occupies too much land and may cause pollution. Direct burning will produce toxic fumes.
According to Weng's new technology, sludge can be dried at a low temperature, under which toxic components are permanently fixed and won't volatilize any more. It is then made into hard bean-sized granules.
The granules, mixed with clays, can be burnt into light-weight bricks. Since each granule contains 1,500 kilocalories of heat, they themselves can contribute to burning and help save fuels.
Meanwhile, small holes emerging inside the granules after burning will reduce the weight of bricks and enhance their resistance against pressure.
Weng said that a production line using the new technology to deal with 100 tons of sludge a day will help save about 1 million yuan (US$125,000) of landfill cost.
Statistics show that accumulating sludge is also plaguing the United States and European countries. The United States will see its sludge amount to 8.2 million tons in 2010, and Britain produces about 1.1 million tons of thickened sludge every year.
(Xinhua News Agency September 11, 2006)
