Microbial Population and Degradation Activity Changes Monitored During a Chlorinated Solvent Biovent Demonstration

Microbial populations and degradation activity increased significantly during a chlorinated solvent bioventing bioremediation effort using propane at Dover Air Force Base in Delaware. The propane injection resulted in degradation of a mixture of chlorinated solvents, including trichloroethylene (TCE), cis-dichloroethylene (c-DCE), and 1,1,1-trichloroethane (TCA). In only 20 d, the propane injection resulted in decreases of TCE and c-DCE of > 98%, and a decrease in TCA in soil gas by ~ 70%. The degradation of the TCA may not have occurred with a methane, butane, toluene, or phenol injection. These decreases in chlorinated solvent concentrations were accompanied by large increases in propane-utilizing bacteria that ranged from below detection levels prior to the injection to ~1% of the ending total aerobic heterotrophic population by the end of the propane injection. Thus, a proportional increase occurred as heterotrophic counts increased a hundredfold. Microbial TCE degradation activity, as measured in microcosms, also increased with the propane injection. The highest rates of degradation were observed in microcosms with propane and nutrients, indicating the potential for higher field rates of degradation with nutrient additions.