Trichloroethylene elimination assay by naural consortia of heterotrophic and methanotrophic bacteria

Abstract

Xenobiotic compounds generated from the various industrial activities are toxic and could affect the natural ecosystem. So far biological processes have been used for treatment of those compounds. It has been reported that xenobiotic compounds can be degraded in pure cultures of methanotrophic bacteria. Therefore, the aim of this study is to demonstrate the capacity of several natural consortia of heterotrophic and methanotrophic bacteria in degradation of trichloroethylene (TCE). Treatability of TCE was studied using 3 different consortia of heterotrophic and methanotrophic bacteria. After a first culture with methane and contact with TCE, all the consortia tested showed a biological TCE degradation efficiency between 29 and 43%. Using acetylene as MMO inhibitor, the implication of this enzyme on the three inocula was demonstrated very well. It was found that the toxicity threshold of TCE to the tested bacteria fell into a range of 30 to 40 mg/l. At not toxic TCE concentration of 5 and 10 mg/l, the maximal TCE specific activity was observed after an incubation of 15 minutes. This initial degradation rate could be used as indicator of the efficiency of a natural inoculum for TCE degradation. The impact of the initial TCE and biomass concentration on the TCE degradation kinetics was also evaluated. In the experiments, the TCE degradation was subject to first order kinetics. The maximum specific degradation rate of TCE was estimated at 48.9 mg TCE/mg SST.h. These experiments clearly demonstrate that methanotrophic bacteria are ubiquitous in the environment, and a lot of them can degrade TCE. This shows good perspectives for in situ treatment of TCE-contaminated sites by enrichment of the methanotrophic natural populations.