ANAEROBIC BIOTRANSFORMATION OF POLYCHLORINATED METHANE AND ETHENE UNDER VARIOUS REDOX CONDITIONS

Two sets of batch-type experiments with different concentrations of ac etate as the auxiliary substrate was performed under various redox con ditions to evaluate the effects of the redox potential of the environm ent and substrate concentration on the biotransformation of carbon tet rachloride (CT) and tetrachloroethylene (PCE). Experimental results in dicated that the redox potential of the environment is a more influent ial environmental factor than the substrate concentration in affecting the biotransformability of the chlorinated hydrocarbons. Disappearanc es of 20 to 62 % and 22 to 99.9% of the original concentrations of PCE and CT, respectively, were observed with the redox potentials of the microcosms ranging from 188 to -263 mV. The threshold values of -60 an d 70 mV were also identified for the obvious biotransformation (> 30%) of PCE and CT, respectively, Substrate concentration effect was empha sized only when the redox potential of the microcosms was below the th reshold value. The strong-electron-acceptor-inhibition hypothesis base d on the thermodynamic rules provides an explanation for the differenc e of the biotransformability between PCE and CT under different redox potential conditions. A lower redox potential provided a relatively hi gher electron activity, thereby facilitating dechlorination reaction m ore readily. A higher substrate concentration produced more biomass th an a lower substrate concentration. Results in this study have provide d further insight into the foundation of in-situ bioremediation practi ces. Furthermore, more accurately controlling the redox potential of t he environment would yield a higher remediation efficiency for the gro undwater contaminated with chlorinated hydrocarbons.