Microbial dechlorination of hexachlorobenzene in anaerobic sewage sludge

From this study of the dechlorination of hexachlorobenzene (ICB) in municip al sewage sludge by an anaerobic mixed culture, we determined the dechlorin ation rate to be 0.29 mg/L/day under the optimal incubation conditions of p H 7.0, 30 degrees C temperature, and a concentration of total solids at 26. 8 g/L. In addition, we found that dechlorination did not occur during agita tion. Biotransformation occurred along a pathway of HCB --> pentachlorobenz ene (QCB) --> 1,2,3,4-tetrachlorobenzene (TeCB) + 1,2,3,5-TeCB --> 1,2,4-tr ichlorobenzene (TCB) + 1,2,3-TCB + 1,3,5-TCB --> 1,2-dichlorobenzene (DCB) + 1,4-DCB. Sequential dechlorination was observed within a substrate concen tration range of 2-50 mg/L, but slowed down significantly at concentrations of 50 mg/L or higher. High-to-low dechlorination rates under three reducin g conditions were identified as methanogenic conditions (0.30 mg/L/day) > s ulfate-reducing conditions (0.12 mg/L/day) > denitrifying conditions (0.08 mg/L/day). (C) 1998 Elsevier Science Ltd. All rights reserved.