ENRICHMENT AND PROPERTIES OF A 1,2,4-TRICHLOROBENZENE-DECHLORINATING METHANOGENIC MICROBIAL CONSORTIUM

A methanogenic microbial consortium capable of reductively dechlorinat ing 1,2,4-trichlorobenzene (1,2,4-TCB) was enriched from a mixture of polluted sediments, 1,2,4-TCB was dechlorinated via 1,4-dichlorobenzen e (1,4-DCB) to chlorobenzene (CB), Lactate, which was used as an elect ron donor during the enrichment, was converted via propionate and acet ate to methane. Glucose, ethanol, methanol, propionate, acetate, and h ydrogen were also suitable electron donors for dechlorination, whereas formate was not. The addition of 5% (wt/vol) sterile Rhine River sand was necessary to maintain the dechlorinating activity of the consorti um, The addition of 2-bromoethanesulfonic acid (BrES) inhibited methan ogenesis completely but had no effect on the dechlorination of 1,2,4-T CB. The consortium was also able to dechlorinate other chlorinated ben zenes via various simultaneous pathways to 1,3,5-TCB, 1,2-DCB, 1,3-DCB , or CB as an end product. The addition of BrES inhibited several of t he simultaneously occurring dechlorination pathways of 1,2,3,4- and 1, 2,3,5-tetrachlorobenzene and of pentachlorobenzene, which resulted in the formation of CB as the only final product. Hexachlorobenzene and p olychlorinated biphenyls (PCBs) were dechlorinated after a lag phase o f ca. 15 days, showing a dechlorination pattern that is different from those observed for lower chlorinated benzenes: only chlorines with tw o adjacent chlorines were removed. The results show that the consortiu m possesses at least three distinct dechlorination activities toward c hlorinated benzenes and PCBs.