Enhanced degradation of chlorinated ethylenes in groundwater from a paint contaminated site by two-stage fluidized-bed reactor.

Abstract Groundwater, used in this study, contaminated predominantly with aromatic compounds, was biologically treated in a fluidized-bed reactor (FBR) with immobilized cells. The aromatics were completely decomposed, while cis -1,2-dichloroethylene ( cis -DCE) and trichloroethylene (TCE) were decomposed only approximately 20% and 5%, respectively. In these studies a significant improvement of the decomposition efficiency for chlorinated ethylenes was achieved by utilizing cometabolism. Methanol (MeOH) and toluene were used as the substrate in the case of one-stage reactor (Single Reactor). MeOH (187 mg l −1 ) increased the decomposition efficiency up to 40% and 60% for cis -DCE and TCE, respectively, while toluene (20 mg l −1 ) increased the decomposition efficiency of cis -DCE to 92% and the decomposition efficiency of TCE to 76%. In the case of two-stage reactor system (Reactor 1 and Reactor 2), MeOH and methane (CH 4 ) were used as the substrate. In this system, cells grown on MeOH or CH 4 in the Reactor 1 were continuously fed into Reactor 2 and groundwater was fed into Reactor 2 only. When MeOH (384 mg l −1  d −1 ) was used as substrate the decomposition efficiency of cis -DCE and TCE were 60% and 70%, respectively. Similar decomposition efficiency was observed for a small amount of CH 4 (19.3 mg l −1  d −1 ).