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.

Trichloroethene degradation in a two-step system bymethylosinus trichosporium OB3b. Optimization of system performance: Use of formate and methane

“…These include mixed tanks (Oldenhuis, 1992;Walter et al, 1997), expanded-bed reactors (Fennell et al, 1993;Phelps et al, 1990Phelps et al, , 1991, packedbed biofilm reactors (Speitel and McLay, 1993;Strand et al, 1991;Strandberg et al, 1989), sequencing biofilm reactors (Fitch et al, 1996a;Speitel and Segar, 1995;Speitel and Leonard, 1992), and a rotating disc biofilm reactor (Arvin, 1991). In most designs competitive inhibition between growth substrate and contaminants leads to poor performance.…”

Methane monooxygenases: central enzymes in methanotrophy with promising biotechnological applications

“…In several studies the broad oxidation spectrum of sMMO for toxic and nondegradable compound has been employed, most notably for TCE degradation. In situ bioremediation based on the degradation of compounds, such as TCE, in the form of biological treatments with mixed methanotrophic communities enriched from the environment has been thoroughly investigated in several studies (Taylor 1993 ; Sutfin and Ramey 1997 ; Walter et al 1997 ). Pure methanotrophic cultures can be used for ex situ bioremediation, where in a single-stage bioreactor, the MMO-producing biocatalysts are grown and used for biodegradation within the one reactor.…”

Sustained Degradation of Trichloroethylene in a Suspended Growth Gas Treatment Reactor by an Actinomycetes Enrichment

“…In addition, the daily TCE feeding period for both reactors was changed to 22 h instead of 24 h to provide a 2-h recovery period each day for possible repair of cell damage due to the presence of inhibitory metabolites. Previous work had shown improved TCE degradation capacity with intermittent TCE feeding (20).…”