BIODEGRADATION OF CIS-1,2-DICHLORO-ETHYLENE AT LOW CONCENTRATIONS WITH METHANE-OXIDIZING BACTERIA IN A BIOFILM REACTOR

This work focuses on the kinetics of cis-1,2-dichloro-ethylene (c-DCE) biodegradation at very low concentrations (mu g/l range) in an aerobi c fixed-film reactor inoculated with a mixed culture of methane-oxidiz ing bacteria. Analysis of dissolved components (oxygen, methane, c-DCE ) were performed by membrane-inlet mass-spectrometry allowing an on-li ne control of the reactor performance. The c-DCE degradation rate cons tant k(x)/K-s ranged from 0.1 to 5.5 x 10(-2)m(3)d(-1)g(x)(-1), depend ing on the c-DCE concentration. However, this degradation rate was und erestimated because the amount of active biomass in the biofilm was sm all (15% to 20% of the total biofilm dry weight). Toxicity effects wer e observed when the c-DCE initial concentration was above 100 mu g/l, leading to a decrease of the c-DCE and methane removal rate. Analysis showed the formation of an intermediate compound subsequent to the c-D CE degradation. Preliminary analysis suggested that it was c-DCE-epoxi de. This degradation product or its metabolites seem to be the cause o f the deactivation of the cells. However, the toxic effect could be co unterbalanced, and the c-DCE degradation rate could be partly sustaine d if methane was supplied continuously in the reactor so that inactiva ted cells were replaced. These results are of practical interest for g roundwater restoration or for waterworks since concentrations generall y encountered in contaminated aquifers are in the mu g/l range. Copyri ght (C) 1996 Elsevier Science Ltd