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

本研究的目的是利用天然矿物质和微生物的脱氯反应，建立有效的氯化有机化合物污染土壤的修复体系。主要研究成果如下：TCE与黄铁矿的脱氯反应在好氧条件下比在厌氧条件下进行得好。TCE通过有机酸转化为二氧化碳和氯离子。黄铁矿被氧化转化为硫酸盐和铁离子。该反应的反应速率取决于氧的浓度。硫化铁、黄铜矿等硫化物矿物在厌氧条件下进行TCE脱氯。实验中黄铁矿的反应速率最大。利用硫酸盐还原环境中获得的厌氧菌群将TCE完全脱氯为乙烷。发现产甲烷菌的控制是该菌群分解TCE的重要因素。收集和分析了几个污染地点地下水中氯代有机物衰减的长期数据。通过分析，揭示了影响衰减的主要因素。采用含土壤颗粒吸附、地下水扩散、微生物和矿物学反应分解的输运模型，预测了氯化有机化合物（如TCE）在污染场地中的行为。在此基础上，初步设计了含氯有机化合物污染土壤的修复工艺。该联合过程包括黄铁矿与污染土壤的混合和微生物群落中降解细菌的活化。在好氧和厌氧系统中，含氯芳香族化合物如氯苯也可被黄铁矿分解。这些结果说明了黄铁矿在水体系中分解二恶英及其衍生物的可能性。

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.