BIODEGRADATION KINETICS OF CHLORINATED ALIPHATIC-HYDROCARBONS WITH METHANE OXIDIZING BACTERIA IN AN AEROBIC FIXED BIOFILM REACTOR

This paper describes the kinetics of aerobic biological degradation of chlorinated aliphatic hydrocarbons, specifically trichloroethene (TCE), 1,1,1-trichloroethane (TCA), cis-1,2-dichloroethene (c-1,2-DCE) and trans-1,2-dichloroethene (t-1,2-DCE). The kinetics were determined by using a completely mixed laboratory biofilm reactor seeded with methane-oxidizing (methanotrophic) bacteria originally obtained from an aquifer contaminated with chlorinated hydrocarbons. The contaminant degradation followed first order kinetics in the concentration range 0-1 mg/l. TCA was degraded with the same reaction rate as TCE. In other studies with methanotrophic bacteria TCA appear to be non-biodegradable. In general, the degradation of TCE, TCA and c-1,2-DCE was relatively slow at 20-24-degrees-C, whereas t-1,2-DCE was transformed relatively fast. The growth of methane oxidizing bacteria in the biofilm was studied. The biofilm thickness increased linearly for a constant loading of methane. The formation of c-1,2-DCE epoxide was presumably an intermediate from c-1,2-DCE degradation, and t-1,2-DCE epoxide was probably formed from t-1,2-DCE. This work indicates that in order to make the aerobic degradation of the chlorinated hydrocarbons practically feasible methods are required for increasing the biodegradation rate of TCE, TCA and c-1,2-DCE.