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 te trachloride (CT) were investigated at 35 degrees C under low concentra tion of acetic acid as the auxiliary substrate to evaluate the concent ration effect of the auxiliary substrate on the biotransformation of t he chlorinated hydrocarbons. Data shown in this study demonstrated tha t concentration of acetic acid could change the dechlorination capabil ity of the microorganisms and, thus, influence the biotransformation o f chlorinated hydrocarbons. The rate of the biotransformation of CT an d TCA in the concentration range of 100-1000 mu g/l increased progress ively with the increase of the substrate concentration ranged from 0 t o 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 observ ed in 85 days, depending on the concentrations of both the primary sub strate and the chlorinated compound. These removal efficiencies corres ponded to second-order rate coefficients of 0.0006-0.0041 1/mg-VSS/d a nd 2.75 x 10(-5) to 2.97 x 10(-4) 1/mg-VSS/d for CT and TCA, respectiv ely. Available substrate supply is essential for the dechlorination of chlorinated compounds which is demonstrated by the experimental resul ts showing the effects of the substrate concentration and the compound concentration. Also, the difference between the oxidation-reduction p otentials of these two chlorinated hydrocarbons gives a possible expla nation for the difference of the biotransformabilities of CT and TCA u nder some substrate conditions.