Bioremediation of Mixed Chlorinated Solvents by Combining Two Biogeochemical Processes
Chloroethenes are a class of chlorinated solvents which cause extensive soil and groundwater contamination worldwide. They can be detoxified by anaerobic dehalogenating bacteria, in the process of reductive dechlorination. However, chloroethenes are often found mixed with chloromethanes, a class of solvents which inhibit the enzymatic detoxification of chloroethenes by dehalogenating strains. Iron sulfides are powerful chemical reductants for the dechlorination of chloromethanes, and can be generated through the metabolism of iron- and sulfate-reducing bacteria. In this study, a sulfate reducing bacterium was used to produce iron sulfide in the presence of moderate levels of tetrachloroethene and carbon tetrachloride to examine the ability of a sulfate reducing organism to drive reduction of a chloromethane in the presence of chloroethene.
Cultures of the sulfate-reducer Desulfovibrio vulgaris were established in the presence of 100 µM each of tetrachloroethene and carbon tetrachloride. Growth, sulfide formation and chlorinated solvents and their dechlorinated products were monitored. The effects of amorphous iron oxide and cyanocobalamin on the fate of chlorinated solvents compared with unamended control cultures were investigated.
Following growth and sulfide formation, carbon tetrachloride was dechlorinated mostly to carbon disulfide while tetrachloroethene was dechlorinated to trichloroethene and acetylene. Dechlorination rates were enhanced both by the presence of iron and cyanocobalamin separately, and significantly increased when both were present.
This study illustrates the potential to use sulfate reducing bacteria in zones of mixed chlorinated solvent groundwater pollution in order to produce iron sulfide minerals. Their cyanocobalamin-catalyzed action on chloromethanes, coupled with that of dehalogenating strains on chloroethenes is a promising strategy for the bioremediation of such contaminated areas."