Microbial reductive dechlorination of hexachloro-1,3-butadiene in a methanogenic enrichment culture

Sequential reductive dechlorination of hexachloro-1,3-butadiene (HCBD) was achieved by a mixed, methanogenic culture enriched from a contaminated estuarine sediment. Both methanol and lactate served as carbon and electron sources. Methanol was stoichiometrically converted to methane, whereas lactate was fermented to propionate and acetate and then to methane. Lactate and propionate fermentation, as well as methanogenesis were not inhibited at 0.4 mg HCBD/l, the normal enrichment culture HCBD feeding level. At a higher initial HCBD level of 1.5 mg HCBD/l, propionate fermentation and acetoclastic methanogenesis were inhibited while, after a lag time, enhanced HCBD dechlorination rates were observed. While lactate fermentation was not inhibited at high concentrations (>25 mM) of 2-bromoethanesulfonate (BES), both propionate fermentation and methanogenesis were completely inhibited, although the HCBD dechlorination rate was not affected. Therefore, methanogens were not likely responsible for the observed dechlorination of HCBD in the enrichment culture. The predominant HCBD dechlorination products were isomers of tri- and dichloro-1,3-butadiene. Traces of a monochloro-1,3-butadiene isomer were also detected. Although extensive dechlorination of HCBD was achieved by the enrichment culture, the detoxification efficiency of this process remains unclear because the potential inhibitory effect of the HCBD transformation products is unknown.