TRICHLOROETHYLENE AND METHANE FEEDING STRATEGIES TO SUSTAIN DEGRADATION BY METHANOTROPHIC ENRICHMENTS

Metabolite toxicity production during trichloroethylene (TCE) degradat ion by methanotrophic bacteria can lead to partial or complete inactiv ation of the TCE-degrading enrichment. The general objectives of this research were to determine if TCE and methane feeding strategies could be selected that would reduce metabolite toxicity effects and determi ne operating conditions that would sustain TCE-degrading methanotrophi c enrichments. in batch treatment of TCE with and without methane, the presence of methane doubled the amount of TCE degraded per unit bioma ss (0.051 mg TCE/mg biomass). In a closed complete-mix methanotrophic enrichment reactor continuously fed TCE and methane, reactor failure o ccurred at a loading of only 0.005 mg TCE/mg volatile suspended solids (VSS) . d. In the same type of reactor operation with intermittent TC E feeding and continuous methane feeding, TCE degradation was sustaine d at daily loadings of 0.03 mg TCE/mg VSS . d. The intermittent TCE-fe d reactor could produce an effluent TCE concentration below the drinki ng water standard (0.005 mg/L) at a higher TCE loading than the contin uous-fed system (0.03 versus 0.002 5 mg TCE/mg VSS . d). The system wi th intermittent TCE feeding provided more efficient use of methane rel ative to TCE degradation. The amount of methane consumed per unit of T CE degraded was 33 and 167 mg methane/mg TCE for the intermittent and continuous TCE-fed operations, respectively. With continuous TCE expos ure, the methanotrophic population in the continuous TCE-fed reactor c hanged to a type that is characterized by having less soluble TCE-oxid izing enzymes and slower TCE oxidation rates.