ABSTRACT
The application of biotechnological processes for the treatment of effluents has a long tradition. Activated sludge systems are used for the removal of easily degradable organics from municipal and industrial waste water, and composting is a standard technique for the treatment of solid organic waste. During the last 15 years, there has been an increasing interest in the development of similar processes for the treatment of waste streams or the cleanup of sites that are contaminated with chemicals of synthetic origin (xenobiotics). However, in many cases these chemicals appear to be resistant to microbial degradation, a problem that was first encountered in the sixties with the environmental persistence of organochlorine insecticides but holds as well for many other agrochemicals, various solvents, waste products and chemical intermediates. Such chemicals are often chlorinated, for example shortchain chloroethylenes, highly chlorinated alkanes and alkenes, PCB's, chlorinated dioxins and dibenzofurans, and chlorobenzenes.
