Anaerobic conversion of chlorobenzene and benzene to CH4 and CO2 in bioaugmented microcosms

Chlorobenzene is a widespread groundwater contaminant found at many industrial sites. Reductive dechlorination of chlorobenzene requires input of electron donor and results in problematic accumulation of benzene, which is more toxic than chlorobenzene. We hypothesized that coupling a culture capable of reductive dechlorination of chlorobenzene to benzene with a second benzene-degrading methanogenic culture would completely detoxify chlorobenzene. To this end, active chlorobenzene-dechlorinating microcosms that were producing benzene were inoculated with a previously described enriched methanogenic benzene-degrading consortium. The combination resulted in the transformation of chlorobenzene via benzene to the nontoxic degradation products, CO2 and CH4. Sustainable degradation of chlorobenzene and benzene was observed in the microcosms and was further confirmed by shifts in the carbon isotopic ratios of chlorobenzene and benzene during degradation. Moreover, we could show that benzene derived electrons fueled chlorobenzene dechlorination removing the need to provide exogenous electron donor. The results have promising implications for sustainable bioremediation of sites contaminated with chlorinated benzenes and benzene.