The Characteristics Of Biochemical Metabolism And Isotopes During Collaborative Methane Production Of Lignite And Straw

As a kind of clean energy,biogas plays an important role under the background of serious air pollution and gradual depletion of fossil energy.Coal bio-gasification is a hot issue in the research field of energy.At the same time,in view of the complexity and difficult degradation of coal macromolecular structure,the biotransformation of coal is also a difficult problem faced by the scientific community.As a typical low rank coal,the synergistic degradation of lignite and waste straw biomass is an important potential way to improve the production of biomethane,but the mechanism of synergistic fermentation of lignite and straw is not clear.In view of that,this thesis makes full use of the theoretical knowledge of coal structural chemistry,microbiology,multivariate statistics and isotopic geochemistry to study the flora metabolism and isotopic characteristics in the process of co-fermentation of lignite and straw.Based on the systematically summarizing and comparing of the characteristics and differences in the aspects of the solid substrate,liquid product,flora structure and gas-phase isotope distribution among collaborative fermentation,single lignite fermentation and single straw fermentation,the deep-seated reasons for promoting biomethane production by collaborative fermentation of lignite and straw were found out,so as to provide theoretical support for the bio-gasification and utilization of lignite and straw.The main research results are as follows:（1）The promotion effect of co-fermentation of lignite and straw on biomethane production was clarified.The research results show that collaborative fermentation of lignite and straw had an obvious promoting effect on the production of biomethane.The cumulative biomethane production of collaborative fermentation group increased by 462.69%and126.60%compared with that of single lignite fermentation group and single wheat straw fermentation group.Compared with single lignite fermentation group and single rice straw fermentation group,the cumulative biogenic methane production of collaborative fermentation group increased by 617.97%and 135.79%.（2）The differences of liquid-phase biochemical characteristics between collaborative fermentation group and single substrate anaerobic fermentation group were monitored.The collaborative fermentation group tends to have a higher availability of the organic matter in the liquid phase and is much closer to the suitable p H for methane production.The collaborative fermentation of lignite and straw can adjust the C/H ratio.Research also showed that the addition of lignite can reduce the ammonia concentration and acid concentration,improve the flora structure and enhance the activity of cellular potassium channel,so as to promote the collaborative fermentation of methane production.（3）The synergistic degradation characteristics of solid substrate in anaerobic fermentation was analyzed.The change trends of C/H or C/O in lignite and straw constituted a complementary relationship.Compared with single substrate fermentation group,the relative content of C-C/C-H bond of lignite and straw in collaborative fermentation group decreased significantly;the degree of coal branching increased more,and the degree of aromatization of coal further weakened.The crystallinity of straw further increased after degradation in the collaborative fermentation group.The adsorption of microorganisms on straw is better than that of lignite,so that straw may provide a more suitable living environment for microorganisms in the process of co-fermentation,so as to promote gas production.（4）The characteristics of different metabolites between collaborative fermentation and single substrate fermentation were discussed.The number of differential metabolites detected between collaborative fermentation and single lignite fermentation is more than that between collaborative fermentation and single straw fermentation.Most differential metabolites between collaborative fermentation and single lignite fermentation showed the characteristics of differential up-regulation;most differential metabolites between co-fermentation and single straw fermentation showed the characteristics of differential down-regulation.In KEGG topology analysis,under the condition of the greatest importance and p（27）0.05,the differential metabolites between the collaborative fermentation group and the single lignite or single straw fermentation group are 16-Hydroxyhexadecanoic acid,（s）-10,16-Dihydroxyhexadecanoic acid,Sucrose,Levan,P-Salicic acid,Vanillin,Isophenoxazine,5-Hydroxy-L-tryptophan,Indole-3-acetic acid.（5）The differences of microbial community characteristics between collaborative fermentation and single substrate fermentation were found out.The number of species in collaborative fermentation group was the largest,and the anaerobic fermentation system mainly contains bacteria and archaea,in which bacteria occupy an obvious advantage.The presence of lignite increased the abundance of methanogenic archaea and the presence of straw increased the abundance of bacteria.The methanogenic archaea in the reaction system were mainly Methanosarcina and Methanoculleus.（6）The differences of gene functional groups and metabolic pathways between collaborative fermentation group and single substrate fermentation group were found out.In the collaborative fermentation group,the gene sequences annotated with energy production and conversion,lipid transport and metabolism,transcription,inorganic ion transport and metabolism,and signal transduction mechanisms were increased,and the gene abundance of some key CAZy metabolizing enzymes and glycolytic metabolizing enzymes was enhanced,which is conducive to improve methane production.The results of gene abundance annotation of methanogenic metabolic pathway showed that hydrogenotrophic and acetotrophic pathways are two key methanogenic pathways.The acetotrophic pathway at the fermentation peak is more competitive than hydrogenotrophic pathway.Compared with the single lignite fermentation group,the relative proportion of acetotrophic pathway in the single straw fermentation group and collaborative fermentation group increased significantly in the peak period,so as to promote methane production in the mixed fermentation process after adding straw.（7）The proportion of methanogenesis metabolic pathway in different substrate fermentation systems was quantitatively calculated based onδ¹³C-CH₄,δ¹³C-CO₂ andδD-CH₄.The results of δ¹³C-CH₄,δ¹³C-CO₂ andδD-CH₄ showed that the collaborative fermentation system tended to produce lower stable isotopes of methane.Acetotrophic pathway was the main pathway in different substrate systems.Overall,the proportion of carbon dioxide reduction pathway（hydrogenotrophic pathway）in collaborative fermentation system is higher than that in single substrate fermentation system,and the quantitative proportion of different metabolic pathways in collaborative and single substrate fermentation shows the opposite trend.In the middle of fermentation,the proportion of carbon dioxide reduction pathway in collaborative substrate fermentation system decreased significantly.