Effect of substrate concentration on the biotransformation of carbon tetrachloride and 1,1,1-trichloroethane under anaerobic condition

The biotransformabilities of 1,1,1-trichloroethane (TCA) and carbon tetrachloride (CT) were investigated at 35°C under low concentration of acetic acid as the auxiliary substrate to evaluate the concentration effect of the auxiliary substrate on the biotransformation of the chlorinated hydrocarbons. Data shown in this study demonstrated that concentration of acetic acid could change the dechlorination capability of the microorganisms and, thus, influence the biotransformation of chlorinated hydrocarbons. The rate of the biotransformation of CT and TCA in the concentration range of 100–1000 μg/l increased progressively with the increase of the substrate concentration ranged from 0 to 30 mg/l. Nearly complete biotransformation of CT was obtained in 32 days. TCA was degraded slower than CT and removal of 20–91% was observed in 85 days, depending on the concentrations of both the primary substrate and the chlorinated compound. These removal efficiencies corresponded to second-order rate coefficients of 0.0006–0.0041 l/mg-VSS/d and 2.75 × 10−5 to 2.97 × 10−4l/mg-VSS/d for CT and TCA, respectively. Available substrate supply is essential for the dechlorination of chlorinated compounds which is demonstrated by the experimental results showing the effects of the substrate concentration and the compound concentration. Also, the difference between the oxidation-reduction potentials of these two chlorinated hydrocarbons gives a possible explanation for the difference of the biotransformabilities of CT and TCA under some substrate conditions.