Anaerobic Degradation of Halogenated 1- and 2-Carbon Organic Compounds

Trihalomethanes, trichloroethylene, and tetrachloroethylene at concentrations commonly found in surface water and groundwater were incubated aerobically in the presence of primary sewage bacterial cultures and anaerobically in the presence of mixed methanogenic bacterial cultures. No aerobic conditions were found under which these compounds could be degraded. Anaerobic degradation was observed for the trihalomethanes, but the 2-carbon chlorine-substituted aliphatic compounds remained unchanged or were degraded only slightly. The brominated trihalomethanes were degraded rapidly in both anaerobic sterile controls and seeded cultures, indicating a chemical mechanism. However, the rate of decomposition increased in the presence of microbial activity. Chloroform degradation was much slower, occurred only in anaerobically seeded cultures, and appears to be biologically mediated. However, a combination of chemical and biological mechanisms cannot be rejected. These batch culture results are consistent with field evidence of long-term degradation of trihalomethanes during groundwater recharge of advanced- treated sewage effluent.