Biodegradation of cis-1,2-dichloro-ethylene at low concentrations with methane-oxidizing bacteria in a biofilm reactor Original Research Article

This work focuses on the kinetics of cis-1,2-dichloro-ethylene (c-DCE) biodegradation at very low concentrations (μg/l range) in an aerobic fixed-film reactor inoculated with a mixed culture of methane-oxidizing bacteria. Analysis of dissolved components (oxygen, methane, c-DCE) were performed by membrane-inlet mass-spectrometry allowing an on-line control of the reactor performance. The c-DCE degradation rate constant kx/Ks ranged from from 0.1 to 5.5 × 10−2m3d−1g−1x, depending on the c-DCE concentration. However, this degradation rate was underestimated because the amount of active biomass in the biofilm was small (15% to 20% of the total biofilm dry weight). Toxicity effects were observed when the c-DCE initial concentration was above 100 μg/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-DCE degradation. Preliminary analysis suggested that it was c-DCE-epoxide. This degradation product or its metabolites seem to be the cause of the deactivation of the cells. However, the toxic effect could be counterbalanced, and the c-DCE degradation rate could be partly sustained if methane was supplied continuously in the reactor so that inactivated cells were replaced. These results are of practical interest for groundwater restoration or for waterworks since concentrations generally encountered in contaminated aquifers are in the μg/l range.