The Study Of Anaerobic Oxidation Of Methane In Landfill Site

Methane is an important greenhouse gas which is lower than carbon dioxide, controlling methane emission is a necessary measure to alleviate the greenhouse effect. Biological oxidation is an important way to reduce methane emission. It was thought that the oxidation of methane only occurred under aerobic conditions. With the development of anaerobic oxidation of methane(AOM) in recent years, the function of methane in anaerobic environment is gradually transformed into the function of source sink. AOM is gradually being discovered and studied by coupling different electron acceptor in different habitats. But for the coexistence of the multi electron acceptor landfill habitat, AOM lacks direct evidence, kinetics and microbiological mechanism is unknown.In this paper, through the analysis of landfill waste sampling, the microbiological evidence of AOM in landfill site was obtained, and it was proved that the electron acceptor coupling method of AOM in landfill site was anaerobic oxidation of methane(S-DAMO) coupled with ferric iron(Fe-DAMO), anaerobic oxidation of methane(S-DAMO) coupled with sulfate and anaerobic oxidation of methane(S-DAMO) coupled with nitrate. The dynamic model of Fe-DAMO, S-DAMO and N-DAMO process was obtained by static shaking flask experiment. The influence of environmental factors on the process of Fe-DAMO, S-DAMO and N-DAMO was analyzed based on orthogonal experiment. Build landfill reactor which is based on the treatment of leachate and aerobic treatment to improve the efficiency of electron acceptor return and evaluate contribution of AOM to the landfill methane emission reduction. The specific experimental results were as follows:(1) In the process of Fe-DAMO, the degradation rate of methane was related to the concentration of methane, it had nothing to do with the concentration of ferric iron. The reaction accords with the first order kinetic model, the reaction rate constant of 89 μmol·kg-1d-1. The reaction between S-DAMO and N-DAMO was positively correlated with the concentration of methane and electron acceptor. In the double substrates on the Mimen equation fitting effect was good. The distribution of S-DAMO and N-DAMO reaction rate constant were 170 mol·kg-1d-1 and 204 μmol·kg-1d-1.(2) In the process of orthogonal experiment, the main environmental factors which influence the coupling of different electron acceptor AOM reaction were temperature, pH, water content and organic matter. In the process of Fe-DAMO, the sequence effect of environmental factors on AOM process from high to low were pH, water content, temperature and organic matter, When the temperature was 26.44 degrees Celsius, pH were equal to 5.27, the moisture content was 19.29%, the organic matter was 19.76g/kg, the oxidation rate of Fe-DAMO reached the maximum. In the process of S-DAMO, the sequence effect of environmental factors on AOM process from high to low were pH, organic matter, temperature and moisture content. When the temperature was 37.19 degrees Celsius, pH was equal to 7.27, the water content was 16.24%, the organic matter was 11.99g/kg, the oxidation rate of S-DAMO reached the maximum. In the process of N-DAMO, the sequence effect of environmental factors on AOM process from high to low were organic matter, pH, temperature and moisture content. When the temperature was 28.68 degrees Celsius, pH was equal to 8.32, the water content was 21.07%, the organic matter was 22.40g/kg, the oxidation rate of N-DAMO reached the maximum. So it was significant to pay attention to the value of the environmental factors according to the content of the electron acceptor in the field of the electron acceptor in the landfill site.(3) After aerobic treatment, the ferrous iron rapidly converted to ferric iron in the leachate, they reached stable state on the second day. When the reactor runned to the seventh day, the ferrous iron had not been detected in the leachate. While the leachate sulfide conversion process was relatively slow. The initial concentration of sulfate increased from 120mg/L to 151mg/L. Because of nitrification-denitrification in the process of aerobic treatment of leachate. Most ammonia nitrogen were converted to nitrogen. So the content of nitrate was low. However, leachate treatment test could prove that, the reduction of the electron acceptor substance was oxidized into AOM by electron acceptor after the process of aerobic treatment of leachate, which provided a prerequisite for landfill methane sinks.(4) According to the kinetic fitting results, The excess of three kinds of electron acceptor(ferric iron, sulfate and nitrate) were recharged in the simulation of landfill reactor. The result showed that the efficiency of the reduction of methane with different electron acceptor in the soil of the unit mass was more than 90%. In the case of methane flux of 3.3×10-2mol/m2, the oxidation efficiency of methane could reach 2.97×10-2mol/m at least. Therefore, under the condition of 10 meters high in the landfill. the amount of methane that could be reduced by anaerobic methane sinks was 0.297 mol. Compared with aerobic methane oxidation, although the rate is low, the depth of the landfill was large and the area of anaerobic oxidation of methane was large. The artificial control of electron acceptor could be returned to the irrigation. The reduction of methane emission accompanys with the reduction of leachate, so it has good application prospects.