In-situ Remediation of Contaminated Soil with Chlorinated Organic Compounds using Natural Activity

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The purpose of this study was to develop remediation system for contaminated soils with chlorinated organic compounds using effectively with dechlorination reactions with natural minerals and microorganisms. Main research results are as follows.1. Dechlorination reaction of TCE with pyrite progressed well in aerobic condition rather than in anaerobic condition. TCE was converted to carbon dioxide and chlorine ion via organic acids. Pyrite was oxidized and converted to sulfate and iron ion. Reaction rate of this reaction depended on the oxygen concentration.2. TCE dechlorination with sulfide minerals such as iron sulfide, chalcopyrite and so on progressed in anaerobic condition. Pyrite gave maximum reaction rate in the experiment.3. TCE was completely dechlorinated to ethane by anaerobic microbial consortium obtained from sulfate reducing environment. It was found that control of methane producing bacteria was important factor for the TCE decomposition by this consortium.4. Long-term data for the attenuation of chlorinated organic compounds in groundwater in several contaminated sites were collected and analyzed. Main factor of the attenuation was revealed by the analysis.5. Behavior of chlorinated organic compounds such as TCE in the contaminated site was predicted using transport model containing adsorption to soil particles, diffusion in groundwater and decomposition with microbial and mineralogical reaction of the compounds.6. From these results, soil remediation process contaminated with chlorinated organic compounds was basically designed. The combined process consists of mixing of pyrite with the contaminated soil and activation of degrading bacteria in the microbial community.7. Chlorinated aromatic compounds such as chlorobenzenes were also decomposed by pyrite in aerobic and anaerobic systems. These results indicate the possibility of decomposition of dioxins and their derivatives by pyrite in aqueous system.