Effects of electron donor, dissolved oxygen, and oxidation–reduction potential biodegradation of carbon tetrachloride by Escherichia coli K‐12

Abstract

Carbon tetrachloride (CT) is recalcitrant to spontaneous degradation. To achieve efficient biodegradation of CT, conditions favorable for dechlorination should be created. Oxidation–reduction potential (ORP) and dissolved oxygen (DO) were found to be important environmental factors in optimizing CT bioremediation. A desired oxidation‐reduction environment was obtained by controlling medium composition and/or adding external reducing agents. Environmental modification resulted in greater than 80% removal of CT by Escherichia coli K‐12 at a CT initial concentration of 300 μg/L within 300 hours under the conditions of this study. The degradation followed pseudo‐first‐order kinetics. A substantially improved overall substrate removal rate constant, K, hence a more efficient CT removal, are observed at −162 mV < ORP < −50 mV under the conditions of the study. The trend of decreasing K observed at ORP of approximately −160 mv is caused by inhibition of the reducing agent titanium (III) citrate on E. coli K‐12 at its higher concentrations. At trace DO levels, ORP was found to be a more reliable and feasible parameter for CT biodegradation correlation. Results obtained from this study yield higher and more consistent CT biodegradation rates than those reported in the literature for the same type culture of microorganisms. This underscores the significance of DO and ORP as conditions for optimizing CT biodegradation. These findings are important in terms of field application, which is commonly limited by site‐specific environmental conditions.