INHIBITION AND STIMULATION OF TRICHLOROETHYLENE BIODEGRADATION IN MICROAEROPHILIC MICROCOSMS

Abstract

The possibility of increasing the biotransformation rate of trichloroethylene (TCE) in ground water and subsurface environments by nutrient addition to microcosms was studied. Three sets of microcosms made of sediment and water were prepared under a nitrogen atmosphere to preserve microacrophilic conditions; each set contained one of the following nutrients: sulfate, methane or ethylene. A control set of microcosms without nutrients was also prepared. The addition of methane was found to increase the biotransformation rate of TCE, allowing the depletion of 99.6% of the TCE in 6 months of incubation, with a lag time of 3 months. In the control microcosms, with no added nutrient, 78% of the TCE was depleted in 6 months of incubation. However, in the microcosms to which sulfate or ethylene was added, the half-life of TCE was appreciably increased. This indicates that methane addition increased the ability of the indigenous microorganisms to biodegrade TCE under microaerophilic conditions, and that sulfate addition inhibited the organisms responsible for the biotransformation of TCE or their biodegrading ability. The effect of ethylene was ambiguous; bacterial growth did not occur in sediment-water cultures supplied with ethylene as the sole carbon source. Hence ethylene either inhibited growth of indigenous bacteria or was not a suitable carbon source. The microcosm experiments suggest that biotransformation resulted from the action of methylotrophs, coexisting in microhabitats with methanogens, which cometabolize the chlorinated ethenes with methane.