The potential of anaerobic bacteria to degrade chlorinated compounds

Chlorinated ethenes and chlorinated aromatics are often found as pollutants in sediments, groundwater, and wastewater. These compounds were long consi dered to be recalcitrant under anaerobic conditions. In the past years howe ver, dechlorination of these compounds has been found to occur under anaero bic conditions at contaminated sites and in wastewater treatment systems. T his dechlorination is mainly attributed to halo-respiring bacteria, which a re able to couple this dechlorination to energy conservation via electron t ransport coupled phosphorylation. The dechlorinating activities of the halo -respiring bacteria seem to be confined to the dechlorination of chloroethe nes and chlorinated aromatic compounds. In addition, methanogenic and aceto genic bacteria are also able to reduce the chlorinated ethenes via a-specif ic cometabolic pathways. Although these later reactions may not be importan t in the remediation of contaminated sites, they may be of substantial infl uence in the start-up of remediation processes and in the application of gr anular sludge from UASB reactors. Specific halo-respiring bacteria may be u sed to increase the dechlorination activities via bioaugmentation in the ca se that the appropriate microorganisms are not present at the contaminated site or in the sludge.