Column studies of biodegradation of mixtures of tetrachloroethene and carbon tetrachloride

Studies of the anaerobic biodegradation of mixtures of tetrachloroethene (PCE) and carbon tetrachloride (CT) were performed in a 2 m long sand-filled column that was initially biodegrading PCE in the absence of CT. CT added to the column was rapidly biodegraded to chloroform (CF). When concentrations of CT were increased from 3.3 μM, to 6.6 μM, and finally to 13 μM the corresponding CF concentrations were 1.2, 2.3, and 3.0 μM, respectively. Dichloromethane (DCM) production also increased as CT concentrations were increased, but all DCM was biodegraded. Biodegradation of PCE was initially completely inhibited on exposure of the column to 3.3 μM CT, but within 24 days PCE biodegradation had restarted, reaching a peak recovery after 34 days. Subsequent doubling of CT inlet concentrations to 6.6 μM (2.3 μM CF) produced only partial inhibition of PCE biodegradation and recovery was faster than observed with the initial addition of CT. Further doubling of CT concentrations to 13 μM (3.0 μM CF) produced an even shorter period of elevated inhibition of PCE biodegradation. The ultimate rate and extent of PCE biodegradation were reduced however, indicating an increased inhibition of PCE biodegradation at 3.0 μM CF compared to 2.3 μM CF.