Domestication Of Methanogenic Bacteria In Medium-Low Temperature Anaerobic Digestion Of Coal By Conductive Materials And Microbial Electrolytic Cell

China has experienced more than 40 years of coalbed methane development,and more than 22000 coalbed methane wells have been constructed.However,the commercial production rate of coalbed methane wells is still less than one third.Therefore,it is urgent to explore a set of effective stimulation technology.Coalbed gas bioengineering has been paid more and more attention due to its dual effects of increasing CBM production and reducing carbon emission.At present,most coalbed methane development in China was concentrated in the shallow 1000 m,and a considerable part of reservoir temperature is concentrated in 15℃to 30℃.If microbial fracturing fluid is used to increase production,this temperature range will lead to the phenomenons of low bacterial activity,slow metabolism and low gas production.Therefore,in this paper,two methods of adding conductive materials and applying electric field were used to carry out generational domestication of anaerobic digestion bacteria to improve methane production at medium and low temperatures.Compared respectively before and after domestication biological methane production in anaerobic digestion system,intermediate key liquid products,microbial community structure and the changes of surface functional groups of coal residue after fermentation under low temperature conditions in two different ways to methane-producing bacteria domesticated mechanism,in order to meet the coalbed methane production function of biological engineering,the following conclusions are drawn:（1）In the medium-low temperature（15℃-30℃）,the addition of conductive materials and applying electric field domestication enhanced the activity of methanogenic bacteria in the anaerobic digestion system,and improved the degradation ability of bacteria to coal.Polymers or monomer compounds in coal fell into the fermentation liquid and were decomposed into alcohols and fatty acids.These metabolites were further degraded to form simple compounds needed by methanogens,which in turn produce methane.（2）The addition of graphene oxide domestication stimulated the enrichment of electroactive methanogenic bacteria,especially the abundance of Geobacter and Methanosarcina,which play a major role in DIET,was significantly increased.Electrons generated by Geobacter oxidized organic matter were transferred to Methanosarcina via an electronic connection device called graphene oxide for the consumption of acetic acid/CO₂to produce CH₄.（3）After domestication of methanogenic bacteria with nano-pyrite,the expressions of some genes related to Geobacter were upregulated,such as pil A and omc S.The relative abundance of coding genes of metabolic enzymes in CO₂reducing methane pathway was the highest among the three pathways.In the corresponding archaea community structure,the abundance of Methanosarcina was greatly increased,and more Methanosarcina was enriched through domestication to reduce CO₂and produce methane.（4）The glycolysis and monosaccharide metabolic pathways during hydrolysis were significantly enhanced after acclimation by the applied electric field.The abundance of genes involved in benzoic acid metabolism was significantly increased,leading to a higher conversion rate of benzoic acid during digestion.After applied electric field domestication,methane metabolism was enhanced,and the abundance of functional genes involved in acetic acid fermentation and common pathways,as well as genes involved in the synthesis of CO₂reductase,was significantly increased.The relative abundance of coding genes of metabolic enzymes in the hydrogen-trophic methanogenic pathway was the highest among the three pathways,and the hydrogen-trophic methanogenic pathway was mainly used in anaerobic fermentation system.With the operation of the system,the relative abundance of bacteria（Geobacter and Methanosarcina）that can participate in DIET is greatly increased,as well as the relative abundance of protein-coding genes involved in electron transfer between bacteria that provide electrons and methanogens that receive electrons.It indicates that DIET between microorganisms was enhanced after acclimation by applied electric field,which promotes the production of biomethane.There are 47 pictures,14 tables and 121references.