BIOFILM REACTORS FOR TREATMENT OF GAS STREAMS CONTAINING CHLORINATED SOLVENTS

Air streams contaminated with chlorinated solvents are increasingly common as by-products of air-stripping and soil-vapor-extraction operations. This research investigated treatment of such gas streams with a bioreactor that supported the growth of methanotrophic bacteria. These bacteria cometabolize many chlorinated solvents. Trichloroethylene (TCE) and 1.2-dichloroethane (DCA) were selected as model contaminants. Removals ranged from 20% to 80% at influent concentrations of 300-1,000 mug/L of air and packed-bed gas-resident times of 5-12 min. Biofilm models were able to describe bioreactor performance well. Pseudo-first-order rate constants from reactor modeling were considerably smaller than those measured in batch systems, suggesting that much of the biofilm was inactive, which also was supported by methane-removal data. Enzyme competition between methane and chlorinated solvents and toxicity from chlorinated solvent metabolites both appeared significant.