Long-Term Biodegradation of Trichloroethylene Influenced by Bioaugmentation and Dissolved Oxygen in Aquifer Microcosms

Aerobic trichloroethylene (TCE) biodegradation was investigated in small-column aquifer microcosms repeatedly fed solutions containing 6.5 mg/L phenol or 15 mg/L lactate and 250 μg/L TCE every two to three days. The effectiveness of TCE cometabolism by an indigenous phenol-fed microbial population declined significantly during a 280-day experiment. This behavior, possibly due to the negative selective pressure of TCE cometabolism, which leads to the formation of toxic products, has not been observed previously in shorter term TCE transformation experiments. The addition of microorganisms Burkholderia cepacia G4 or PR1301 to microcosms along with phenol or lactate initially allowed for substantial TCE degradation but led to the eventual depletion of dissolved oxygen and a decline in TCE transformation. After termination of bioaugmentation, dissolved oxygen levels recovered in all microcosms and those microcosms that continued to receive phenol returned to or surpassed previous TCE transformation levels, while unfed and lactate-fed microcosms lost degradative activity. The introduced organisms, however, did not appear to be responsible for the recovered TCE degradation in the phenol-fed, formerly bioaugmented microcosms. The source of activity in these microcosms was not identified but is likely to have been efficient TCE-transforming indigenous organisms selected by the operating conditions within the microcosms.