About 80 percent of the sludge remaining after sewage treatment is not properly handled and has itself become a source of pollution, industry statistics has suggested.

A sewage treatment plant in China. [File photo]

Nearly 2,200 tons of sludge is produced each year in the country, but 80 percent is dumped or even piled up in the open air, according to the 2011 Market Analysis Report of Sludge Treatment in China issued by h2o-china.com, the website of China's water industry.

Sludge, the byproduct of sewage treatment plants, comes from organic matter in sewage. But dealing with the hazardous waste is far from safe, industry experts said.

"If not treated scientifically, sludge will become the source of secondary pollution, affecting water, soil, groundwater and the environment as a whole," said Ma Jun, director of the Beijing-based Institute of Public and Environmental Affairs.

"In addition, sludge must be fully dehydrated. Dry mud is smaller in weight and size, and its level of harm will decrease," Ma said. "If it is not fully dehydrated, groundwater will be polluted after sludge is put in a landfill, and it will cause chemical reactions in the soil."

China Daily phoned three sewage treatment plants in Beijing on Thursday. Two phone calls went unanswered, and the other factory refused to reveal its sewage treatment capacity and how it deals with sludge.

Official information shows that sludge has a dual nature, containing nutrient substances, such as nitrogen and phosphorus, as well as harmful substances, including viruses, microbes, parasites, eggs and heavy metals.

Sludge treatment processes include sludge concentration, digestion, dehydration, fermentation, drying and incineration. Plants do not lack the technology, but are held back by high operating costs, according to Fu Tao, director of the Water Policy Research Center at Tsinghua University.

Local governments are responsible for pollution abatement under the Environmental Protection Law, but both experts contacted by China Daily believed the current improper handling shows local governments' dereliction of duty.

"The central government allocates money to local governments to establish sewage treatment plants, but local governments lack enthusiasm in investing in the operation of the plants, not to mention the treatment of sludge, which is in the later stage," said Gu Haibing, professor in public management at Renmin University of China.

"It will save a great deal of money if local governments don't deal with the sludge," Ma said.

"The fact that nobody oversees the local environmental pollution situation makes them lack the motivation."

Ma called for an integrated system of sewage treatment, saying sludge disposal should be considered in the entire process, rather than being left out at the tail end.

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