Development and Evaluation of Semicontinuous Slurry Microcosms to Simulate in Situ Biodegradation of Trichloroethylene in Contaminated Aquifers

Trichloroethylene (TCE) was efficiently biodegraded in situ by aerobic cometabolism at the Moffett Federal Airfield test site, in the presence of phenol or toluene (Hopkins et al. Appl. Environ. Microbiol . 1993, 59, 2277; Hopkins et al. Environ. Sci. Technol . 1993, 27, 2542; Hopkins, G. D.; McCarty, P. L. Environ. Sci. Technol. 1995, 29, 1628). Using uncontaminated soil from this site as an inoculum, a semicontinuous slurry microcosm method was developed that reproduced in situ TCE degradation rates. The slurry method was then applied to evaluate the in situ TCE biodegradation potential at Edwards Air Force Base where full-scale application was contemplated. With 0.66 mg/L TCE and either 9.7 mg/L toluene or 13.4 mg/L phenol in the exchange fluid, steady state TCE removals varied between 87 and 99%, depending upon sample depth. Toluene and phenol growth yields based upon oxygen to substrate ratios were 0.77 and 0.59 g/g during the start-up phase and 0.52 and 0.36 g/g during steady state TCE removal, respectively. The TCE degradation rate constant ratio, k c / K c, was similar for the two substrates. Steady state TCE removals varied little in a given microcosm over 1 year of operation. In the Moffett and Edwards microcosms as well as at Moffett Federal Airfield (Fries et al. Appl. Environ. Technol. 1997, 63, 1523), toluene o -monooxygenase was the dominant TCE-oxidizing enzyme present.