Abstract
This study was conducted to explore the effectiveness of thermally enhanced in situ bioremediation of the groundwater contaminated with chlorinated ethenes in reducing the treatment time. First, the soilcolumn experiments were used to evaluate the effects of elevated temperatures on the dechlorination of tetrachloroethene under semi-static flow conditions. Then, a field test of thermally enhanced in situ bioremediation of the groundwater contaminated with chlorinated ethenes in Japan was conducted using groundwater circulation. The abundance of Dehalococcoides, the bacteria responsible for the dechlorination of cis-1, 2-dichloroethene and vinyl chloride to ethene, increased rapidly at 30°C than at 15°C in the column experiments. This increase greatly improved dechlorination performance of cis-1, 2-dichloroethene and vinyl chloride. In the field test, the temperature and nutrient concentrations (as total carbon) in the contaminated aquifer were controlled at 23°C–30°C and above 100 mg/L, respectively, through repeated injection and pumping during the demonstration period. The chlorinated ethenes in the groundwater decreased to below the groundwater standards after 378 days. The total chlorinated ethene removal rate obtained in the field test was higher than those obtained in previous studies of in situ bioremediation without thermal treatment. The results demonstrated the effectiveness of thermally enhanced in situ bioremediation of groundwater contaminated with chlorinated ethenes in Japan.
