REMOVAL OF TETRACHLOROETHYLENE IN AN ANAEROBIC COLUMN BIOREACTOR

Removal of tetrachloroethylene (perchloroethylene; C2Cl4) by microbial consortia from two sites with different C2Cl4 exposure histories was examined in a bench-scale anaerobic column bioreactor. It was hypothes ized that optimal removal would be observed in the reactor packed with sediments having an extensive exposure history. Microbial consortia w ere enriched from hyporheic-zone (HZ) sediments from the Portneuf aqui fer near Pocatello, Idaho, and from industrial-zone (IZ) sediments fro m a highly contaminated aquifer in Portland, Oregon. Lactate and aceta te were the electron donors during experiments conducted over 9 and 7 months for HZ and IZ sediments, respectively. In the HZ bioreactor, th e retention time ranged from 31 h to 81 h, and inlet C2Cl4 concentrati ons ranged from 0.1 ppm to 1.0 ppm. Dechlorination of C2Cl4 averaged 6 0% and reached a maximum of 78%. An increase in C:N from 27:1 to 500:1 corresponded to an 18% increase in removal efficiency. Trichloroethyl ene production corresponded to decreased effluent C2Cl4; further inter mediates were not detected. In the IZ bioreactor, the retention time v aried from 34 h to 115 h, the inlet C2Cl4 concentration was 1.0 ppm. C 2Cl4 removal averaged 70% with a maximum of 98%. Trichloroethylene and cis-dichloroethylene were detected in the effluent. Increases in C:N from 50:1 to 250:1 enhanced dechlorination activity.