Trichloroethylene and methane feeding strategies to sustain degradation by methanotrophic enrichments

Abstract

Metabolite toxicity production during trichloroethylene (TCE) degradation by methanotrophic bacteria can lead to partial or complete inactivation 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 determine operating conditions that would sustain TCE‐degrading methanotrophic enrichments. In batch treatment of TCE with and without methane, the presence of methane doubled the amount of TCE degraded per unit biomass (0.051 mg TCE/mg biomass). In a closed complete‐mix methanotrophic enrichment reactor continuously fed TCE and methane, reactor failure occurred at a loading of only 0.005 mg TCE/mg volatile suspended solids (VSS) · d. In the same type of reactor operation with intermittent TCE feeding and continuous methane feeding, TCE degradation was sustained at daily loadings of 0.03 mg TCE/mg VSS · d. The intermittent TCE‐fed reactor could produce an effluent TCE concentration below the drinking water standard (0.005 mg/L) at a higher TCE loading than the continuous‐fed system (0.03 versus 0.0025 mg TCE/mg VSS · d). The system with intermittent TCE feeding provided more efficient use of methane relative to TCE degradation. The amount of methane consumed per unit of TCE degraded was 33 and 167 mg methane/mg TCE for the intermittent and continuous TCE‐fed operations, respectively. With continuous TCE exposure, the methanotrophic population in the continuous TCE‐fed reactor changed to a type that is characterized by having less soluble TCE‐oxidizing enzymes and slower TCE oxidation rates.