Microbial Community Structure And Methanogenesis Metabolism In Anaerobic Digestion Of Domestic Waste

The domestic landfill disposal process produces methane through anaerobic digestion.Methane production is the core of resource recovery of anaerobic digestion of domestic waste,but microbial flora is rarely studied in methane production process.It is of great significance to study the structure and function of bacterial flora and methaneproducing flora in the process of anaerobic digestion of domestic waste to perfect the theory of anaerobic digestion technology.In this study,anaerobic digestion experiments were carried out using domestic waste inoculated with sludge to monitor environmental parameters and gas production during the operation of the system.The structure and function of methanogenic bacteria and archaea were characterized by real-time fluorescent quantitative PCR and metagenomic analysis,and the methanogenic pathway was studied by natural stable carbon isotope analysis.The main research conclusions are as follows:(1)The pH values in the pre-operation(6-12 days)and late(20-25 days)of the system are 5.5 and 6.5,respectively,which is suitable for the metabolic activities of fermentation acid-producing bacteria and methane-producing archaea.The low organic load in anaerobic digestion of domestic waste results in lower concentrations of total ammonia nitrogen(up to 100 mg/L)and volatile fatty acids(up to 1050 mg/L)produced by the system.Gompertz model fitting results also show that low organic load of domestic waste anaerobic digestion of methane production delay period is longer than food waste.(2)In anaerobic digestion of domestic waste,Firmicutes and Proteobacteria in bacterial flora form hydrolytic acidification systems and always dominate.The genus Methanosarcina,Methanothrix and Methanobacterium account for a combined 94.1% of methane-producing archaea.The results of redundancy analysis between microorganisms and environmental factors show that acetic acid concentration and methane yield are the key factors affecting methane-producing archaea,and there is a clear positive correlation between the two environmental factors.The results of metagenomic analysis show that the relative abundance of functional genes in the accelerated methane production stage is significantly higher than that of anaerobic acidification,and acetoclastic methanogenesis is the main way to produce methane.Combined with the gas production of the system and the gene abundance of methane production function,it is found that the physical and chemical index of the system will lag behind the change of functional gene abundance.(3)The analysis of natural stable carbon isotopes is consistent with the results of macrogenomic analysis,that is,the metabolic pathway of acetoclastic methanogenesis has always been dominant in anaerobic digestion.The metabolic activity of acetoclastic methanogenesis archaea is strongest when the methane production stage is accelerated,and as the substrate acetic acid is gradually consumed,its methane production contribution begins to decrease and gradually stabilized.