Sequential anaerobic/aerobic biodegradation of chlorinated ethenes

Chlorinated solvents, such as tetrachloroethylene and trichloroethylene, are common contaminants of soil. They are readily transported in ground water, causing wide-spread aquifer contamination. Experiments were performed to demonstrate the feasibility of in situ biodegradation of tetrachloroethylene and trichloroethylene. The process involves controlled addition of nutrients to the ground water to stimulate the activity of naturally occurring bacteria. A twenty-three liter laboratory aquifer simulator was constructed, filled with soil and amended ground water was recirculated through the soil. Methanogenic conditions were brought about in the reactor within 15 days. Tetrachloroethylene and trichloroethylene were shown to degrade rapidly to dichloroethylene. Oxygen was then introduced and the oxidation of dichloroethylene by methanotrophic bacteria was accomplished. Results showed that chlorinated ethenes could be completely biodegraded under sequential anaerobic and aerobic condition.