| Landfill cover soils oxidize a considerable fraction of the methane, play a role in greenhouse gas reduction. Knowing the mechanism of methane oxidation clearly distinguishing the biological characteristics of bio-cover material effectively and analyzing the microbial community structure thoroughly in landfill cover soil are the important part of the research on methane emission. So a series of studies were carried out. These research mainly include evaluating biological characteristics of bio-cover material, prediction on methane oxidation, fitting kinetics of methane oxidation and analyzing methanotrophs community structure. The details are as follows.A bioreactor was set up using landfill cover soils, and a simulation model of methane transport and transformation process was developed that incorporates Monod equation and gas diffusion model in fixed-bed. There was an excellent agreement between the model and the experimental data. Therefore, the model is highly applicable to the description on the process of methane transport and transformation in bioreactor. Finally, half-saturation constant KS was 0.0066~0.0163 g·L-1 indicating that these landfill cover soils had excellent affinity and oxidizability for methane. The model will provide guidance for the screening of cover material and contribute to getting accurate parameters.Then expansion Process of oxygen was analyzed by the method of simulating in landfill cover soil, and oxygen diffusion model was obtained which could be fitted by exponential equation(0.8941<R2<0.9975). In addition, potential of methane oxidation in different landfill cover depths was also investigated by analysis on organic carbon and monitoring of methane concentration, results indicate that the most intensive methane oxidation occurred at the layer of 0.05~0.25 m. Oxygen consumption flux model in landfill cover was derived on the basis of Fick law and axial dispersion model, and results showed that there was no significant difference between fitted values by oxygen consumption flux model and derived values by Biological oxidation empirical equation of methane. Based on above model, methane consumption flux model was derived finally, and the prediction was consistent with the detection. These achievements provided new ideas and theoretical basis for revealing biogas expansion process of landfill cover soil, intensifying methane oxidation capability and predicting methane emission.Based on the system of real time online monitoring system the distribution regularity of biogas in landfill cover was taken under various methane fluxes(0~2000 g﹒m-2﹒d-1). The result show that rate of methane oxidation and methane flux are positively correlated relationship, while efficiency of methane oxidation and methane flux are negative correlation. In addition, the kinetics of methane oxidation was fitted in dynamic condition by CH4-O2 dual-substrate model, and half-saturation constant Km was 0.157%~0.729% which increases with depth. Compared with Km in static condition, the deviations of that in dynamic condition were 1.1%-1.6%. Then, methanotrophs community structure was analyzed by high throughput sequencing for original soil and that in simulated landfill cover. The indicated that the abundance and diversity were significant increase after enrichment, and methanotrophs Methylobacter and Methylococcales dominated in simulated landfill cover soil. Distribution of methylobacter and concertration of oxygen are positively correlated relationship. Distribution of other methanotrophs show no significant difference in different depths. These achievements will contribute to accurately understanding the methane oxidation law and provide essential data for studying on microbial community structure in landfill cover.Impact on biological function of landfill cover soil which enriched by methane in presence of t-1, 2-DCE, c-1, 2-DCE, TCE and PCE was studied. The results shown that PCE can promote the methane oxidation when the quantity of that less than 3.4 mg, and TCE have no influence on methane oxidation when the quantity of TCE less than 4.4. With the increase of t-1, 2-DCE and c-1, 2-DCE concentration, inhibiting effect on methane oxidation was remarkable at initial reaction stage, and rapidity of methane consumption occurred in disinhibition at the later step. It demonstrated that chlorinated hydrocarbon and methane were competitor during the biological reaction and degradation products of chlorinated hydrocarbon can inhibit activity of microbial enzyme. The study give a guidance for enhancing methane oxidation and biodegradation of chlorinated hydrocarbon by landfill cover soil. |
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