Anaerobic Microbial Reductive Dehalogenation of Chlorinated Ethenes

The current knowledge on microbial reductive dechlorination of chlorinated ethenes (CEs) and its application are discussed. Physiological studies on CEs dechlorinating microorganisms indicate that a distinction can be made between cometabolic dechlorination and halorespiration. Whereas cometabolic dechlorination is a coincidental and nonspecific side reaction, catalyzed by several methanogenic and acetogenic bacteria, halorespiration is a specific enzymatic reaction from which metabolic energy can be gained. In contrast to the well-studied biological dechlorination of PCE to cis-DCE, little is known about the biology of the further dechlorination from cis-DCE to ethene. Bacteria performing the latter reaction have not yet been isolated. Microbial reductive dechlorination can be applied to the in situ bioremediation of CEs contaminated sites. From laboratory and field studies, it has become clear that the dechlorination of tetrachloroethene (PCE) to cis-clichloroethene (cis-DCE) occurs rapidly and can be stimulated relatively easily. However, complete reduction to ethene appears to be a slower process that is more difficult to achieve.