Sequential anaerobic-aerobic biodegradation of tetrachloroethene (PCE)

The objective of this study was to evaluate the feasibility of a sequential anaerobic-aerobic microbial process for in-situ bioremediation of aquifers contaminated with tetrachloroethene (PCE). Two laboratory-scale columns (2 m in length and 4.1 cm inside diameter) were used to examine the feasibility of this concept. The anaerobic soil column inoculated with biomass obtained from an anaerobic digester, was operated with low concentrations of PCE (2–5 mg/L) and methanol. After acclimation, the column was continuously operated with incrementally increased concentrations of PCE for about 2.5 years. The microbial community developed in the column exhibited a sustained dechlorination of up to 120 mg/L of PCE to vinyl chloride (VC) and ethene (ETH). This is the first demonstration of complete removal of PCE at concentrations as high as 120 mg/L in a continuously operating system at room temperature. The change in PCE:methanol ratios was found to have little effect on the breakdown of PCE and trichloroethene (TCE) but the conversion of VC to ETH was much more sensitive and VC accumulated when the PCE:methanol mass ratio dropped below one. Elimination of PCE from the system for a 5-month period did not result in the loss of degradation capacity of the culture.; The aerobic column was inoculated with microorganisms obtained from a local pond. After developing a methanotrophic culture, effluent from the anaerobic column was pumped to this column A pulsing strategy was employed to handle the competitive inhibition between methane and VC. Concentrations of VC above 10 mg/L inhibited both methane utilization and VC degradation. After reducing the methanol concentrations in the inlet of the anaerobic column, methane fluxes to the aerobic column were decreased. With these inlet conditions, methane was consumed in the lower section of the aerobic column and VC was degraded in the upper zones where the methane concentrations were minimal.; Biomass preservation/bioaugmentation studies in microcosm systems showed that storage under refrigerated conditions at 4°C could be used for short-term preservation of PCE dechlorinating biomass.; Various electron donors were compared for their abilities to support the dechlorination of PCE. Butyric acid was found to be the most effective electron donor for degradation of PCE at a PCE:electron donor ratio of 1:2 on an electron equivalent basis.; Microscopic studies revealed the presence of seven morphotypes in the PCE degrading community. Metabolic activities at different sections of the anaerobic column correlated with differences in community structure based on FAME analysis. DNA fingerprinting showed differences between consortia from different zones of the column.