Natural Attenuation of Chlorinated Solvents byMicrobial Activities at a Contaminated Site in Takahata

摘要

There are many sites contaminated by chlorinated solvents all over Japan.Recently, monitored natural attenuation (MNA) has been developed to clean up thosechemicals. MNA utilizes attenuating processes including biodegradation, dispersion,dilution, sorption, volatilization, and chemical or biological stabilization of contaminants.Natural attenuation of chlorinated solvents, such as tetrachloroethylene and trichloroethylenein contaminated groundwater in Takahata town, was studied. The correlationbetween natural attenuation behaviors was investigated in order to understand the mechanismsinvolved in natural attenuation process and to forecast future conditions. The degradationbehaviors of chlorinated solvents were different between each well. Thechemical components in the groundwater of the degradation with by-products showedlower redox potential, dissolved oxygen and higher heavy metals such as iron and manganese.These anaerobic reducing ambient is suitable for the bacteria concerned with thereductive dechlorination. Although in certain cases, vinyl chloride or ethylene can beobserved. In this site, the higher degradation product was 1,2-cis-dichloroethylene whilevinyl chloride and ethylene only appeared in a very low concentration. Those resultssuggest that only a small proportion of bacteria have the ability to degrade1,2-cis-dichloroethylene to ethylene. To improve the biodegradation process toward theformation of ethylene, the effectiveness of different medium conditions was evaluated.