What to do with sewage sludge?

segunda-feira, 18 de janeiro de 2010

In recent years China has developed into one of the world’s biggest markets for sewage treatment. According to the Chinese Ministry of Environmental Protection, over 20 billion euros was invested by the end of 2008 in around 1,550 sewage plants in the People’s Republic. Together these facilities process 86 million tons of sewage each day. ‘Despite the high level of expenditure on cleaning the main rivers and lakes, not a great deal of progress has been made,’ said Wu Xiaoqing, Vice Minister of the Ministry of Environmental Protection. ‘Water pollution is now holding back further economic development in China – and it has become a key environmental factor endangering the health of the population.’

Still largely unsolved, for example, is the issue of sewage sludge: China is continuing to look for suitable disposal solutions for this unpopular side product of sewage treatment. ‘One problem is that in some cases it is not the operators of sewage treatment plants that are not responsible for disposal of the sewage sludge, but instead the local Environmental Protection Bureau (EPB). The sewage plant operators thus have only a limited influence on how it is disposed of – and vice versa, the EPB has little influence on the quality of the sludge presented to them,’ explained Günter Traub, one of the China experts at the KfW Entwicklungsbank of Frankfurt am Main, Germany.

‘One important step towards clearer regulations was the passing of a series of directives in 2007. They help in categorizing sewage sludge and defining the possible applications for the different types,’ explained Michael Leinhos, Managing Director of Kocks Consult of Koblenz, Germany, a company engaged in planning and consultation in the sewage market, including in China. ‘For example, sewage sludge can now only be dumped if it has at least 40-percent dry content, a level that is comparatively very high. This protects the dump operators from stability problems, for example.’ With the systems currently being used to drain sludge, via centrifuges – sometimes with the addition of auxiliary agents to aid the process – only around 20- to 25-percent dry content can be achieved.

The use of sewage sludge as a fertilizer in agriculture or in landscaping work is also strictly regulated by the new package of directives. The limiting factors here are the levels of heavy metals or other harmful substances in the sludge. ‘In the main centers of population in China, however, the sewage sludge is so severely polluted that it can under no circumstances be used in agriculture, and in some cases not even be disposed of in regular dumps,’ said Traub. ‘In the case of this sludge, virtually the only way of dealing with it is combustion.’

As a result, in at least four of the eight new sewage treatment projects considered for funding by the KfW in the last two years, combustion of sludge in coal-fired power stations is part of the plan. All the projects are currently in the tender phase, or already under construction. ‘The first combined combustion plant funded by us is scheduled to go into operation at the end of this year,’ said Traub. Leinhos also forecasts: ‘Because of a lack of real alternatives, co-combustion will probably be a main way of treating Chinese sewage sludge.’

Against this background, new openings are emerging for foreign suppliers of environmental technology, particularly in sewage drainage and drying, as well as in the processing of flue gas in combustion plant.

Environmental Expert