Study On Oxidation Activity And Community Structure Of Methanotrophs In Waste Biocover Soil Under Trichloroethylene Stress

Since various pollutants in landfill gas (LFG) are involved in the CH4oxidation in landfill cover soils. One of the main volative organic compounds-trichlorethylene (TCE) in LFG was selected as the target pollutant, waste biocover soil (WBS) with high CH4oxidation activity developed in our lab was used as the study objective, the removal effiency of CH4and TCE and methanotroph community in WBS under TCE stress were investigated in this study. The main conclusion obtained was as follows.(1) The adsorption capacity of TCE on WBS increased with the increasing TCE concentration in the headspace. And the time for the adsorption equilibrium was also prolonged. The adsorption equilibrium for TCE on WBS was achieved within24h under the initial gaseous TCE concentration below7000ppmv. The adsorption isotherm of TCE adsorption on WBS was well fitted with linear model, and the equation was Cs=0.0144·Ce, indicating that the adsorption of TCE on WBS was conformed to allocation principles.(2) The adsorption of TCE on WBS in this study was affected by temperature, soil moisture content and particle size. Of them, temperature is the dominant factor, followed by soil moisture content and particle size. The adsorption capacity of TCE increased with the decreasing temperature and soil moisture content. Study on the adsorption capacity of TCE on compost, sludge, sand, landfill cover soil (LCS) and WBS showed that compost had the highest adsorption capacity of TCE, followed by sludge and WBS. LCS and sand had the lower adsorption capacity of TCE. A positive correlation between the adsorption capacity of TCE and the organic content of experimental material was observed (r=0.707, P=0.01).(3) The CH4oxidation activity of WBS was affected under gaseous TCE stress. The inhibitory effect was not obvious under low TCE concentration. When the initial TCE concentration was higher than500ppmv, CH4oxidation activity of WBS was significantly inhibited. When the initial TCE concentration increased to7000ppmv, the CH4oxidation rate of WBS was very low.(4) When the initial concentrations of CH4and O2were set to10%and21%, respectively, the CH4oxidation activity was inhibited in WBS and LCS when the gaseous TCE was～50ppmv during the experiment of54days. The higher CH4oxidation activity occurred in WBS compared to LCS. The inhibitory effect was not obvious in WBS at low TCE concentration, and significant inhibition was only observed in the treatment of50ppmv TCE during the long experimental period. TCE was degraded in both soils in the presence of CH4. The TCE degradation rate increased with the increasing TCE concentration. Of the two soils, WBS showed a higher TCE degradation capacity.(5) The average abundance of methanotrophs assessed by quantification of pmoA in WBS was about two orders of magnitudes higher than in LCS during the whole experiment. Type Ⅰ methanotrophs (Methylocaldum, Methylosarcina and Methylobacter) and type Ⅱ methanotrophs(Methylocystis) were abundant in both soils. Among them, type Ⅰ methanotrophs Methylocaldum and Methylobacter dominated in WBS, while type Ⅱ methanotrophs Methylocystis predominated in LCS. Statistical analysis showed that the relative abundance of Methylobacter had a significant positive correlation (r=0.89) with TCE degradation rates in WBS, suggesting that Methylobacter might be tolerant to TCE and/or play an important role in the TCE degradation in WBS.