Anaerobic biotransformation of polychlorinated methane and ethene under various redox conditions

Two sets of batch-type experiments with different concentrations of acetate as the auxiliary substrate was performed under various redox conditions to evaluate the effects of the redox potential of the environment and substrate concentration on the biotransformation of carbon tetrachloride (CT) and tetrachloroethylene (PCE). Experimental results indicated that the redox potential of the environment is a more influential environmental factor than the substrate concentration in affecting the biotransformability of the chlorinated hydrocarbons. Disappearances 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 and 70 mV were also identified for the obvious biotransformation (> 30%) of PCE and CT, respectively. Substrate concentration effect was emphasized only when the redox potential of the microcosms was below the threshold value. The strong-electron-acceptor-inhibition hypothesis based on the thermodynamic rules provides an explanation for the difference of the biotransformability between PCE and CT under different redox potential conditions. A lower redox potential provided a relatively higher electron activity, thereby facilitating dechlorination reaction more readily. A higher substrate concentration produced more biomass than a lower substrate concentration. Results in this study have provided further insight into the foundation of in-situ bioremediation practices. Furthermore, more accurately controlling the redox potential of the environment would yield a higher remediation efficiency for the groundwater contaminated with chlorinated hydrocarbons.