Pathways And Microbiological Characterization Of Coalbed Biomethane Production And Oxidation

Coalbed methane?CBM?is unconventional natural gas produced by geological reaction or microbial degradation during coalification.The reserves of CBM in China are 3-3.7×10¹³ m³,biogenic CBM accounts for 15-30%.Coal is rich in hydrocarbons and has low biodegradability.Anaerobic degradation of hydrocarbon requires various microbial groups,which results the progress of research on coal biodegradation slow.Methane oxidizing bacteria widely exist in coal seam environment,and the research on coal seam methane oxidation is still scarce.Coalbed methane in Erlian Basin and Hailaer area has been proved to contain biogenic coalbed methane,which may be produced continuously.In this paper,the microbial communities of coal seam water in situ in Erlian Basin and Hailaer area were detected by high-throughput sequencing.Combined with the simulated degradation experiments of coal,short-chain fatty acid and methanogenic precursors,the metabolic function of coal seam water and key microbial groups in coal degradation process were studied.Finally,the verification experiments of anaerobic oxidation of coal seam water methane were carried out.The experimental conclusions were as follows:?1?Methanobacterium?relative abundance 6.6-98.2%?is the dominant methanogenic archaea detected in the raw coal seam water of Erlian basin and Hailar area,with an average relative abundance of 61.6%.Methylomonas or/and Methylobacter?relative abundance 6.0-38.1%?are the dominant bacteria in 77.8%of coal seam water,with an average relative abundance of 20.3%.?2?Oil sediment flaro domesticated by coal can degrade lignite?R_o=0.3%?and bituminous coal?R_o=1.5%?and can not degrade anthracite?R_o=3.0%?.Under 35?and 55?culturing conditions,the gas production potential of 2 g lignite respectively is 103.89±20.92?mol and 50.91±32.94?mol,and the gas production potential of 2 g bituminous coal respectively is 35.60±22.73?mol and 81.33±30.64?mol?352 days of incubation?.The microbial community structure was significantly correlated with enrichment culture's temperature,and the substrate difference?coal maturity?had a significant impact on the microbial community structure at 35?.The dominant archaea were Methanothermobacter?relative abundance 72.5-82.8%?,Methanosaeta?relative abundance 16.2-36.1%?and Methanosarcina?relative abundance 25.5-41.1%?.Clostridium XI?relative abundance 7.8-70.4%?and Enterobacteriaceae?relative abundance 9.03-31.1%?were the dominant bacteria in the culture system at 35?.Clostridia?relative abundance 5.1-34.9%?and Thermoanaerobacteraceae?relative abundance 5.3-13.4%?were the dominant bacteria in the culture system at 55?.?3?Coalbed water's microbes in Erlian Basin and Hailaer area has the ability to metabolize acetic acid,propionic acid and butanoic acid to produce methane.The maximum specific producing methane rates of acetic acid,propionic acid and butanoic acid are 0.14-0.29 day^-1,0.08-0.13 day^-1 and 0.19-0.42day^-1,respectively.After enrichment,the community structure of archaea was significantly correlated with the source of coal seam water,while the community structure of bacteria was significantly correlated with the substrate.Methanosarcina?relative abundance 7.9-51.25%?and Methanocalculus?relative abundance 13.53-63.43%?were the dominant Archaea in Erlian Basin,while Methanosarcina?relative abundance 29.7-66.5%?and Methanobacterium?relative abundance24.28-57.36%?were the dominant Archaea in Hailar Basin.Desulfovibrio?relative abundance 35.0-39.2%?,Syntrophobacter?relative abundance 38.13-75.45%?and Syntrophomonas?relative abundance 4.16-21.13%?were significantly enriched in the treatment with acetic acid,propionic acid and butyric acid as substrates,respectively.?4?Erlian Basin coalbed water's methane production pathway was significantly correlated with the types of substrates;the dominant archaea in alcohols and hydrogen/carbon dioxide and formic acid treatment groups were Methanobacterium or/and Methanocorpusculum?relative abundance was4.9-91.7%?,with an average relative abundance of 80.6%;and the dominant archaea in different methyl-substrate treatment group was different.The dominant archaea in dimethylamine,methanol and methanol/hydrogen treatment is Methanolobus?relative abundance 15.7-32.9%?,the dominant archaea in disulfide treatment is Methanomethylovorans?relative abundance 35.2%?.?5?The original coal seam water has the ability of anaerobic oxidation of methane.Under the condition that nitrate and sulfate as electron acceptors,the metabolic rates are 0.068±0.013umol·day^-1·ml^-1 and 0.077±0.040 umol·day^-1·ml^-1.Compared with the control group,Bacteroidetes(relative abundance?20.8%?,Ectothiorhodospiraceae?relative abundance 27.5%?,Rhodobacter?relative abundance 13.1%?were significantly enriched in nitrate treatment group,while Clostries XI?relative abundance 15.2%?,Desulfarus?relative abundance 6.9%?and Bacteroidales?relative abundance 8.8%?were significantly enriched in sulfate treatment group.