Biomass Anaerobic Digestion Process And Effect Research Based On Hydrothermal Pretreatment And Accelerator

On October 24,2021,the State Council issued the"carbon peak action plan before2030",which proposed to develop biogas according to local conditions.China’s abun-dant biomass resources can be used as raw materials for production.Through anaerobic digestion technology,it can not only alleviate the ecological and environmental prob-lems caused by a large number of biomass,but also produce clean energy such as me-thane and promote the green and sustainable development of society.However,due to the complex and stubborn structure of biomass in the anaerobic digestion process,the hydrolysis rate was limited,which affects the methane yield and makes the biomass utilization rate low.Therefore,how to destroy the stubborn structure of biomass,im-prove the hydrolysis rate and methane production,develop new and efficient anaerobic digestion of biomass and realize the application of large-scale biogas production from biomass is the top priority of biomass treatment technology.Based on the above con-siderations,this study carried out hydrothermal pretreatment of the typical biomass of Sycamore deciduous,and added biochar（BC）,zero-valent iron（Fe~0）,carbon-loaded zero-valent iron（BC/Fe~0）,lithium iron phosphate（LiFePO₄）,carbon-supported lithium iron phosphate（BC/LiFePO₄）and other accelerators,a series of studies were carried out on the influence and mechanism of hydrothermal pretreatment and accelerators on biomass anaerobic digestion.The main findings are as follows:（1）The single-factor rotation method was used to explore the effect of hydrother-mal parameters on the anaerobic digestion of Sycamore deciduous hydrothermal liquid-phase products,and the parameters were optimized by energy balance calculation.The hydrothermal pretreatment played a positive role in the generation of methane.The op-timal hydrothermal parameters determined by the liquid phase product anaerobic diges-tion experiment were the solid-liquid ratio of 6%,the hydrothermal time of 2.0 h,and the hydrothermal temperature of 180°C.Under the optimal parameters,the cumulative methane production of Sycamore deciduous hydrothermal liquid products for anaerobic digestion reached 132.2 m L/g VS,which were 1.06 and 1.76 times that of solid-liquid mixed phase and non-hydrothermal treatment,respectively.The energy balance calcu-lation result is 3.251 k J/g_biomass,and the T90 is basically within 7 days,which has ex-tremely important practical significance for the industrialization of biomass.The changes of VFAs and SCOD contents indicated that hydrothermal pretreatment could promote the degradation and solubilization of liquid-phase products during anaerobic digestion,and the degradation rate of SCOD in each experimental group reached more than 80%.In the process of anaerobic digestion,the utilization of phosphorus was ob-vious,and the change of nitrogen was more regular,but the nitrogen removal rate of the experimental group with high VFAs was relatively high.（2）A certain amount of BC,Fe~0,BC/Fe~0,LiFePO₄,BC/LiFePO₄ was added to the hydrothermal liquid phase and solid-liquid mixed phase anaerobic digestion system re-spectively to further improve the methane yield and explore its role in the anaerobic digestion process mechanism.The use of accelerators increased the hydrolysis rate to a certain extent,shortened the lag period of anaerobic digestion,and promoted methane production.In the solid-liquid mixed phase anaerobic digestion experiment,Fe~0 had the best promotion effect,and the methane production was 1.30 times that of the blank experimental group.In the liquid phase anaerobic digestion experiment,LiFePO₄ had the best promotion effect,and the methane production was 1.38 times that of the blank experimental group.In the whole process experiment,the methane production of the LiFePO₄+liquid phase experimental group reached 112.8 m L/g VS,which was 1.29 and2.12 times that of the Fe~0+solid-liquid mixed phase experimental group and the liquid phase experimental group,respectively.Meta-whole genome sequencing showed that the promoter significantly enhanced the diversity and richness of the microbial com-munity,and significantly increased the relative abundance of hydrolytic acidifiers and methanogens.The relative abundance of hydrolytic and fermentative bacteria such as Proteobacteria and Chloroflexi in LiFePO₄+liquid phase experimental group reached49.49%;the relative abundance of acidifying bacteria such as Bacteroidetes and Fir-micutes in Fe~0+solid-liquid mixed phase experimental group reached 30.45%;LiFePO₄and Fe~0 experimental group Euryarchaeota and other methane-producing groups The relative abundance of bacterial flora reached 3.68%.The cyclic voltammetry and AC impedance analysis of microbial preparation electrodes in the anaerobic digestion hy-drolysis acidification stage and methanogenic stage with different promoters were re-spectively extracted,and it was found that Fe~0 had the most obvious effect on hydrolysis and acidification bacteria,and LiFePO₄ had the most obvious effect on methanogenic bacteria.（3）The hydrothermal solid-phase and liquid-phase products of Sycamore decidu-ous leaves were analyzed to explore the mechanism of hydrothermal pretreatment.In the solid phase analysis,elemental analysis found that the C content and high calorific value of the sample gradually increased with the optimization of hydrothermal param-eters,which improved the fuel utilization level of the solid phase product.SEM,XRD and FTIR analysis showed that hydrothermal pretreatment can destroy the dense struc-ture of Sycamore leaves,which is more conducive to the contact between enzymes and microorganisms.In the liquid phase analysis,by exploring the changes of SCOD,VFAs,nitrogen and phosphorus under different hydrothermal parameters,we found that hy-drothermal pretreatment could break the cell wall of Sycamore deciduous leaves,re-lease intracellular substances,and provide some nutrients for the anaerobic digestion system.