Research On Characteristics And Mechanism Of Methane Production By Co-digestion Of Multi-source Biomass Waste

As one of the most populous countries in the world,China’s solid waste output is increasing with the rapid economic development.Biomass waste accounts for a large proportion of solid waste,and its resource utilization can not only reduce environmental pollution but also alleviate the energy crisis.Anaerobic digestion technology has significant advantages in biomass waste treatment,which can not only reduce waste but also generate clean energy,bringing environmental,economic,and social benefits.However,the gas production efficiency of anaerobic digestion is greatly affected by the type of substrates and substrate to inoculum(S/I)ratio,and improper selection can easily lead to failure of the digestion process.In view of this,this thesis took garden waste,food waste,and tofu residue as the research objects and carried out anaerobic mono-digestion with different S/I ratios and anaerobic co-digestion with different feedstocks’ mixing ratios under mesophilic conditions.The co-digestion performance index(CPI)was used to evaluate the gas production effect of the co-substrates,and the microbial diversity of the samples in the experimental group with better gas production was analyzed.The purpose of this research was to determine the interaction of the three substrates in the anaerobic digestion process,to clarify their methane production characteristics and microbial community structure changes,and to provide a theoretical basis and case support for further expanding the types of feedstocks for anaerobic digestion and optimizing the co-digestion process.The main conclusions of this study are summarized as follows:(1)In the anaerobic mono-digestion of garden waste,food waste,and tofu residue,the cumulative methane production increased with the decrease of substrate/inoculum ratio.The maximum cumulative methane production was 279.23 m L/g VS,594.58 m L/g VS,and 360.77 m L/g VS,respectively.The excessive mono-substrate of easily hydrolyzed food waste and tofu residue would lead to acidification of the digestion system and a rapid decline in p H.(2)The anaerobic co-digestion of the three substrates could effectively alleviate the acidification problem and improve the buffering capacity of the digestion system.When the mixture ratio of garden waste,food waste,and tofu residue was 3: 4: 3,the cumulative methane yield was the highest,which was 370.54 m L/g VS.The effect of feedstock content on cumulative methane production was significant.With the change of substrate mixing ratio,there were both synergistic effects(CPI=1.09)and antagonistic effects(CPI=0.89).When the proportion of food waste reached 40%,there was a synergistic effect,while when the proportion of tofu residue≥40%,there might be an antagonistic effect.(3)The modified Gompertz model fitted the experimental data well,especially for anaerobic co-digestion.And the addition of garden waste had a considerable effect on shortening the lag phase.(4)The composition of the microbial community in the anaerobic digestion system varied with the types of substrates.The addition of food waste and tofu residue was beneficial to the enrichment of Methanosarcina,while the addition of garden waste changed the relative abundance of Methanosaeta.