MICROBIAL HEXACHLOROBENZENE DECHLORINATION UNDER 3 REDUCING CONDITIONS

The potential dechlorination of hexachlorobenzene (HCB) in medium by 1 ,2,3-trichlorobenzene (TCB)-adapted mixed culture under three reducing conditions was investigated. It was found that strongest to weakest H CB dechlolination occurred in the order of methanogenic conditions > s ulfate-reducing conditions > denitrifying conditions. Under denitrifyi ng conditions, no dechlorination was observed during the first 20 days of incubation. Biotransformation occurred in this older: HCB --> pent achlorobenzene (PCB) --> 1,2,3,5-tetrachlorobenzene (TeCB) --> 1,3,5-T CB + 1,2,4-TCB --> 1,3-dichlorobenzene (DCB). HCB dechlorination was d elayed following treatment with ferric chloride and manganese dioxide, but enhanced by the addition of lactate and pyruvate under methanogen ic or sulfate-reducing conditions; the addition of acetate had no sign ificant effect on HCB dechlorination under arty of the three reducing conditions. Sequential dechlorination was observed at concentrations o f 2-50 mg/L, but at a significantly slower rate at the highest concent rations. (C) 1998 Elsevier Science Ltd. All rights reserved.