The aerobic bioreactor landfill technology is one of the most common and effective technologies in waste sanitary landfill. It uses leachate aeration and recharge to make the landfill a composite "purification reactor", which can accelerate the microbial degradation of organic matter and remove pollutants such as ammonia and nitrogen. However, the use of this technology in mineralized waste landfills has the problem of low organic matter content and the inability to completely remove nitrogen. Moreover, the methane produced in the lower layers of the landfill both increases the "greenhouse effect" and has the potential risk of explosion.
Cao Qin, a member of the Liu Xiaofeng team at the Chengdu Institute of Biology, Chinese Academy of Sciences, found in the previous study that the oxidation of methane in mineralized landfills can effectively couple the denitrification of nitrate. In addition, under different oxygen concentration conditions, the types of microorganisms participating in their coupling reaction are different. Therefore, a more in-depth study of its coupling microbes and collaboration mechanism through isotope tracing technology and high-throughput sequencing technology. Through isotope tracing experiments, it was found that under micro-oxygen conditions, methane first reacts with oxygen to produce extracellular organic products, such as acetic acid and citric acid. In turn, these organic products act as a carbon source to denitrify with nitrate and generate trace amounts of N2O. Under anoxic conditions, methane will perform methane fermentation to produce richer organic intermediates, which will denitrify by coupling with nitrate. Through high-throughput sequencing and analysis, it was found that the main functional microorganisms performing microoxygen methane oxidative coupling denitrification are methane oxidizing bacteria Methylomonas and methylotrophic denitrifying bacteria Methylotenera. The main functional microorganisms that perform anoxic methane oxidation coupled denitrification are the methane oxidizing bacteria Methylomonas and the non-methyl vegetative denitrifying bacteria Thermomonas. Research at home and abroad mainly focuses on aerobic methane oxidative coupling denitrification, and reports that its products are mainly CO2 and N2. The findings of this study provide more theoretical basis for oxidative coupled denitrification of methane under microaerobic and anoxic conditions, and expand the carbon and nitrogen cycles in mineralized waste landfills.
The research was supported by the National Natural Science Foundation of China (51478448) and the Open Fund of the Key Laboratory of the Center for Applied and Environmental Microbiology (KLCAS-2017-9). Related scientific research results "Stable-isotopic analysis and high-throughput pyrosequencing reveal the coupling process and bacteria in microaerobic and hypoxic methane oxidation coupled to denitrification" were published in the journal Environmental Pollution.
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