Experimental Research On Biomethane Production From Microorganism In Situ Coalseam

In order to investigate the genetic types and formation features of biomethane in coal seams.The fresh coal samples of different coal rank were selected as the research object in this paper.The Miseq high-throughput sequencing technology was used to study the diversity of microorganism in situ coal seams.The biogas formation simulation experiments were conducted with lignite and lean coal.Through the GC-MS,illumina-miseq,ion chromatography and other testing techniques to analyze the change rules of gas components,liquid phase products,bacterial succession and inorganic ions in the process of gas generation.Based on that,the genetic types of biological methane and the genetic types of carbon dioxide and nitrogen were revealed.In order to enhance the gas-producing efficiency,the domestication of NM bacteria with coal as carbon source for 20 d was carried out step by step,the gas generation effects of acclimation were analyzed and evaluated,and the domestication mechanism of bacteria was revealed from the aspects of microbial community structure succession,microbial network relations and gene function differences.The main research results are as follows:Sequences in the Archaea domain were classified into four phyla and included members from Euryarchaeota,Thaumarchaeota,Woesearchaeota,and Pacearchaeota.The Bacteria domain included members of the phyla:Firmicutes,Proteobacteria,Bacteroidetes,Actinobacteria,Acidobacteria,Verrucomicrobia,Planctomycetes,Chloroflexi,and Nitrospirae.The hydrogen-producing bacteria was dominated by the genera:Clostridium,Enterobacter,Klebsiella,Citrobacter,and Bacillus;the methanogens included the genera:Methanorix,Methanosarcina,Methanoculleus,Methanobrevibacter,Methanobacterium,Methanofollis,and Methanomassiliicoccus.Traces of hydrogen-producing bacteria and methanogens were detected in both biogenic and nonbiogenic CBM areas.The diversity and abundance of bacteria in the biogenic CBM areas are relatively higher than in the areas without biogenic CBM.The community structure and distribution characteristics depend on coal rank,trace metal elements,temperature,depth and groundwater dynamic conditions.Biogenic gas was mainly composed of hydrogen and methane,the difference and diversity were caused by microbe-specific fermentation of substrates;as well as by the environmental conditions.The production of biological methane is accompanied by the production of nitrogen and carbon dioxide.The diversity of bacterial community and low degree of metamorphism in NM coal make the peak of biological gas production earlier than that of HB,and the species and abundance of liquid phase products are higher than that of HB.Different types of methane formation are determined by different bacterial communities and metabolic substrates in the gas generation process of NM and HB.It is worth noting that carbon dioxide is generated in different gas production stages,which can be used by hydrotrophic methanogens to generate methane in the form of HCO₃^-,small molecular substances such as alcohols,acids and methylamines were generated by hydrolysis and acidification bacteria,which were used by acetoclastic methanogens and methylotrophic methanogens to generate methane.Meanwhile,the amines generated by hydrolysis were nitrified and denitrified to form nitrogen under the action of microorganisms involved in nitrogen cycle.After 5 generations of domestication,The gene function abundance and the reading number of the bacteria in terms of Membrane transport,Cell motility and Xenbiotics biodegradation and metabolism were significantly improved with acclimation.The diversity of bacteria and archaea communities was significantly increased after domestication,and the diversity and abundance of microorganisms that can cooperate with methanogens are on the rise with the acclimation of bacteria.The methane production capacity in the fermentation system was greatly improved,and the cumulative gas production increased from 4.26ml/g to 9.26ml/g.The gas production cycle was extended from 28d to 30d.The cumulative gas production of nitrogen decreased significantly with the domestication.This study enriched the diversity of microorganisms in coal seam,and provided an experimental basis for the biogenesis of coal seam gas and MECBM.