R ＆ D of treatment of soil contaminated with chlorinated organic compounds by combined method of chemical dehalogenation and microbial degradation

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Highly chlorinated compounds are generally recalcitrant for the microbialdegradation, and tend to accumulate in the environment such as soil and groundwater. In this study, we attempted to develop a combined method of chemical dechlorination and following microbial degradation of highly chlorinated chemicals such as polychlorinated biphenyls (PCB) and tetrachloroethylene (PCE), compounds known as serious environmental pollutants over the world. For PCB, the base catalyzed decomposition method was employed as a chemical treatment. By this method as high as 99.79-99.98% dechlorination was achieved from KC300 and KC400, and large amounts of biphenyl accumulated in an oil reservor, in which a small amount of lightly chlorinated PCB (1-3 chlorines) were detected. These PCBs were subjected to the microbial degradation to get a small amount of chlorinated benzoic acids as the final products. For PCE, we have isolated an anaerobic bacterium strain Y51 belonging to genus Deuslfitobacterium. Strain Y51 dehalogenated PCE to cis-1,2-dichrloroethene via trichloroethene by the process of "dehalorespiration" using PCE as a final electron acceptor. The resting cells of Y51 (OD 1.0 at 600 nm) dechlorinated PCE at the concentrations of as low as 0.01 and as high as 160 mg/L within 10 hr. The addition of elemetal iron toward the soil contaminated with PCE led to the dehalogenation of PCE. Then strain Y51 was introduced into the same soil, resulting in the more efficient dehalogenation. Ethylene and ethane were detected as the final dechlorination products.