Complete degradation of chlorinated ethenes and its intermediates through sequential anaerobic/aerobic biodegradation in simulated groundwater columns (complete degradation of chlorinated ethenes)

This study evaluated the effectiveness of sequential anaerobic/aerobic biodegradation of tetrachloroethene (PCE) and its intermediates,cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC). Two sand columns were operated in series. The first column simulated the up-gradient side of a groundwater system, was operated under anaerobic conditions, and was continuously fed the target contaminant, PCE (42 mu M). The second column simulated the down-gradient side of the groundwater system and was operated under aerobic conditions, using low concentrations of hydrogen peroxide as the dissolved oxygen source. After 15 days of operation, cDCE was detected at the end of the first, anaerobic column, at concentrations of 7.02-15.57 mu M. After 36 days of operation, VC (7.32 mu M) was also detected at the end of the first column. cDCE and VC then migrated into the second, aerobic column. Results showed that cDCE and VC were almost completely aerobically biodegraded in the second column, with removal efficiencies of up to 97% and 95%, respectively. This study also used batch experiments to compare cDCE removal efficiencies between aerobic metabolism using cDCE as the only substrate, and aerobic cometabolism using methane and cDCE as primary and secondary substrates. Results showed that aerobic cometabolism of cDCE was inhibited at cDCE concentrations greater than 50 mg/L. This inhibition effect was not obvious under aerobic metabolism using cDCE as the only substrate. Results of a Michaelis-Menten/Monod kinetics analysis showed that when cDCE concentrations were greater than 20 mg/L, cDCE could be biodegraded more effectively under aerobic metabolism than under aerobic cometabolism.