Developmental study on trichloroethylene degradation by a bioreactor

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1. Characterization of liquid-solid phase trichloroethylene (TCE) degradation by Methylocystis sp. M (strain M) immobilized in Ca alginate was studied to maximize the degradation rate. The results obtained were as follows. (1) In order to get the cells of strain M possessing high specific activity for TCE degradation, elimination of Cu (almost to zero) in the medium and harvesting the cells at the end of the log phase were very important. (2 ) Kinetics constants (V max and Ks) and optimum conditions for TCE degradation (pH, temperature, DO) by immobilized cells were cleared. (3) The half life of the degradability of strain M was relatively short, and which was caused by the toxicity of intermediates formed by TCE degradation in the cells. (4) Inactivated cells by the intracellular toxicity were reactivated by incubation with methane or methanol, suggesting that the immobilized cells was possible to be repeatedly used in the TCE degradation. (5) Under the optimum conditions obtained, semicontinuous TCE degradation in a 5L bioreactor showed that the total amount of approximately 13mg TCE could be degraded in 120h.2. We also studied on the gas-solid phase TCE degradation system by the immobilized cells. The gaseous TCE of 0.3ppm, which was fed continuous into the glass-column bioreactor, was almost completely degraded in about 50h. The maximum TCE concentration to be degraded by this reactor was 100ppm, suggesting that, as the gaseous TCE concentration exhausted from ducts of TCE treatment facilities was too high (300-500ppm), the gaseous TCE was necessary to be diluted and be applied to the bioreactor.