EFFECTS OF ELECTRON-DONOR, DISSOLVED-OXYGEN, AND OXIDATION-REDUCTION POTENTIAL BIODEGRADATION OF CARBON-TETRACHLORIDE BY ESCHERICHIA-COLI K-12

Carbon tetrachloride (CT) is recalcitrant to spontaneous degradation. To achieve efficient biodegradation of CT, conditions Favorable for de chlorination should be created. Oxidation-reduction potential (ORP) an d dissolved oxygen (DO) were found to be important environmental facto rs in optimizing CT bioremediation. A desired oxidation-reduction envi ronment was obtained by controlling medium composition and/or adding e xternal reducing agents. Environmental modification resulted in greate r than 80% removal of CT by Escherichia coli K-12 at a CT initial conc entration of 300 mu g/L within 300 hours under the conditions of this study. The degradation followed pseudo-first-order kinetics. A substan tially improved overall substrate removal rate constant, K, hence a mo re 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 agen t 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 thi s study yield higher and more consistent CT biodegradation rates than those reported in the literature for the same type culture of microorg anisms. This underscores the significance of DO and ORP as conditions for optimizing CT biodegradation. These findings are important in term s of field application, which is commonly limited by site-specific env ironmental conditions.