REDUCTIVE DECHLORINATION OF TETRACHLOROETHYLENE BY A CHLOROBENZOATE-ENRICHED BIOFILM REACTOR

This study evaluates the potential and technical feasibility of treating chloroaliphatics, common groundwater contaminants, using a specialized microbial consortium under fixed-film conditions. The reactor was developed using 3-chlorobenzoate (3-CB) as a substrate under anaerobic conditions and the enrichment that harbored an unusual dechlorinator, Desulfomonile tiedjei DCB-1. The dechlorination rate of both PCE and 3-CB increased with increasing flow rates up to 50 mL/h. The maximum observed dechlorination rates of PCE and 3-CB fed at 6.0 and 1000 mu M were 2.0 and 414 mu mol L h(-1), respectively. This corresponds to a PCE consumption rate of 3.7 nmol h(-1) (mg of protein)(-1) [88.9 mu mol (g of protein)(-1) day(-1)]. The rate of PCE dechlorination increased from 2.0 to 10.3 mu mol L(-1) h(-1) when the influent PCE was increased from 6.0 to 120 mu M, respectively; however, concentrations of 60 mu M and above damaged reactor performance. PCE was mainly converted to TCE and cis- and trans-DCE at all the tested flow rates. Vinyl chloride (VC) was never detected, thus suggesting dechlorination of PCE to nonchlorinated products. Although the PCE dechlorination activity of the biofilm was dependent on 3-CB, the activity could be sustained for 4-5 days on cheaper substrates such as acetate or benzoate after a 1-day pulse feeding of 3-CB. In addition to PCE dechlorination, the biofilm also dechlorinated other compounds such as chloroform (CF) and 1,1,2-trichloroethane (1,1,2-TCA). The present study is important, since D. tiedjei was previousely shown to dechlorinate many other chloroaromatic and aliphatic compounds.