Microbial dechlorination of hexachlorobenzene in anaerobic sewage sludge

From this study of the dechlorination of hexachlorobenzene (ICB) in municipal sewage sludge by an anaerobic mixed culture, we determined the dechlorination rate to be 0.29 mg/L/day under the optimal incubation conditions of pH 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 agitation. Biotransformation occurred along a pathway of HCB --> pentachlorobenzene (QCB) --> 1,2,3,4-tetrachlorobenzene (TeCB) + 1,2,3,5-TeCB --> 1,2,4-trichlorobenzene (TCB) + 1,2,3-TCB + 1,3,5-TCB --> 1,2-dichlorobenzene (DCB) + 1,4-DCB. Sequential dechlorination was observed within a substrate concentration 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 reducing conditions were identified as methanogenic conditions (0.30 mg/L/day) > sulfate-reducing conditions (0.12 mg/L/day) > denitrifying conditions (0.08 mg/L/day). (C) 1998 Elsevier Science Ltd. All rights reserved.