Anaerobic Transformations of Carbon Tetrachloride: Combined Bacterial and Abiotic Processes

Abstract

Environmental transformation of chlorinated organic compounds can involve strictly abiotic reactions, direct microbial transformations, and microbially mediated reactions. Shewanella putrefaciens 200, is able to dechlorinate carbon tetrachloride (CT) under anaerobic conditions and served as a model bacterium for examining the role of inorganic components (iron minerals), natural organic matter, and solution chemistry (buffer concentration) on rates of CT transformation. Pseudo-first-order rate constants for CT degradation increased 10-fold in the presence of 150 mM Fe(III)-oxide and were linearly proportional to Fe(III)-oxide concentrations. The Fe(III)-oxide did not transform CT in the absence of S. putrefaciens. CT dechlorination in microbial batch reactors was also increased by the presence of soil containing a high concentration of natural organic matter. The same soil catalyzed CT dechlorination in the absence of S. putrefaciens when dithiothreitol was added as a reductant. Rates of CT transformation by S. putrefaciens in the absence of soil or Fe(III)-oxides were also shown to increase with increasing buffer concentration. This work suggests that the relative contribution of (i) direct microbial transformations and (ii) microbially mediated abiotic transformations by inorganic or organic sediment catalysts will vary with sediment composition and solution chemistry. Increased biotreatment rates may be possible by utilization of sediment amendments that increase abiotic transformation rates.