Rate controlling processes in the transformation of tetrachloroethylene and carbon tetrachloride under iron reducing and sulfate reducing conditions

While in situ dechlorination of chlorinated aliphatic contaminants such as tetrachloroethylene (PCE) and carbon tetrachloride (CT) has been studied extensively, rate controlling processes in the transformation of these compounds remain uncertain. The objectives of this work were (1) to compare the relative rates of abiotic and microbial transformation of PCE and CT in microcosms designed to simulate natural conditions, and (2) for CT, to measure the relative rates of reactive mineral formation and CT transformation by these reactive minerals. While the rates of microbial dechlorination exceeded the rates of abiotic dechlorination of PCE in the microcosms, the opposite trend was observed for CT. The times required for microbial sulfate reduction, the first step in formation of many reactive minerals, were significantly longer than those required for transformation of CT by these reactive minerals, indicating possible rate control of abiotic CT transformation by microbial respiration under natural conditions.