Waste composting method rated "un-ecological"

Austrian environment agency finds high air emissions from "mechanical-biological" treatment

A composting technique used to treat and reduce the organic content of municipal wastes before it is landfilled is "unecological" and should be replaced by incineration, the Austrian environment agency has concluded. The agency is proposing strict environmental controls on the process after a study concluded that it produced "unacceptable" levels of air emissions.

In Austria and Germany, "mechanical-biological" treatment (MBT) plants are used to treat a significant proportion of unrecovered municipal waste before landfilling. About one-third of such wastes are incinerated. The composting method reduces the organic content of the waste by aerating and adding bacteria. It is favoured by many local authorities as a more environmentally friendly system than incineration, and also as a generator of local employment.

But according to a study published by the Austrian environment agency this week, MBT plants emit "unacceptable" levels of volatile organic compounds, ammonia, methane and heavy metals such as mercury. Some plants have no measures in place to clean the off-gas while those that use "biofilters" are "not yielding the required degree of cleaning," the study concluded. The agency has called on the government to impose strict emissions limits to counter the problem.

The agency also says that MBT plants are incapable of reducing the organic content enough to meet the requirements of a legal target to take effect from 2004. Under Austria's 1996 waste law, the total organic content of waste going to landfill will be limited to 5%.

Under an exemption in the law for the composting technique, waste from MBT plants with a higher organic content will still be allowed to be landfilled as long as the waste's total energy content is no more than 6,000 kilojoules per kilogram. However, Isabella Kossina of the environment agency told ENDS Daily that only 30-50% of MBT residues met this standard, so the majority would have to be incinerated before landfilling anyway.

Any decision to maintain the use of MBT in Austria now would be "political" rather than "ecological," Ms Kossina said. The agency's position will be noted in Germany, where an identical 5% organic content limit for landfilled waste will enter into force in 2005. German environment minister Jürgen Trittin is currently deliberating over whether to allow MBT as an alternative to incineration for pre-treatment before landfilling (ENDS Daily 31 May).

Follow Up:
Austrian environment agency, tel: +43 1 313 040.

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