Study On The Cultivation And Mechanism Of Efficient Microflora For Degrading Lignite To Produce Methane

Microbially Enhanced Coal Bed Methane(MECo M)can improve CBM reserves and extends the service life of CBM wells by using microorganisms to convert coal into methane,which is a clean and efficient technology.At present,the role of fungi in the process of biological CBM generation is not distinct,although fungi have great potential in the degradation of refractory organic compounds and the solubilization of low rank coal.In this paper,the mixture of fungi and methanogens were enriched from the produced water of coalbed methane wells in Qinshui Basin.The culture factors of methanogenic microflora were optimized,and the mechanism of conversion of coal to methane under pulverized coal and lump coal was studied by using high-throughput sequencing,GC-MS,LC-MS,metabonomics and ¹³C-NMR.In order to increase methane production,phenanthrene-degrading fungi were riched from produced water and two schemes of pretreatment and mixed culture were established to enhance the biodegradation of aromatic structure in coal and studied the mechanism of increasing methane production.The main results of this paper were as following:(1)After enrichment,the methane production of fungi-methanogens microflora was stable at about 147?mol/g coal.The optimal culture conditions were as follows:35°C,p H=9,salinity0.50-1.00%,solid-liquid ratio 1:60,trace elements and vitamins 0.10%.(2)Under the condition of pulverized coal,at day 0-7,the relative abundance of two coal-degrading fungi:Penicillium and Dicyma was higher,aromatic CH₃,methylene carbons,protonated aromatic carbons and aromatic bridgehead carbons in coal were degraded,and a large of fatty acids were produced.At day 7-28,the proportion of Penicillium and Dicyma were decreased,and the proportion of protonated aromatic carbons,oxy-aromatic carbons,aliphatic CH₃,methylene carbons,methine and quaternary carbons in coal were decreased,as well as,fatty acids were consumed as methanogenic substrates.(3)Under the condition of lump coal,Dicyma,Simplicillium and Penicillium were the dominant fungi at day 7,Volatile fatty acids(VFAs)were the most abundant intermediate metabolites,the changes of methane yield and p H were related to the abundance of VFAs.At day 7-28,the activities of Dicyma and Simplicillium and the content of VFAs decreased significantly.A large of microfractures and plant tissue pores were observed on the surface of lignite,which could allow microorganisms to enter the interior of coal and result in the changes of surface and internal of residual coal structure were consistent.Volatile component,fixed carbon,C,H,and O in coal were degraded and oxygen-containing functional groups and carboxyl carbons in coal were degraded to form methane.(4)Compared with the condition of pulverized coal,due to the expansion of coal size,solid-to-liquid ratio and culture volume,the inhibition effect on microorganisms is enhanced under the condition of lump coal,which resulted in the lower relative abundance of Penicillium at day 7,as well as,the decline of microbial diversity and the biodegradation of aromatic structure in coal after methane production,and further limits the methane yield under lump coal condition.(5)The degradation rate of Phenanthrene-degrading fungi(PF)was 43.99%±9.36%,and the protonated aromatic carbons in coal were effectively degraded after 7 days of degradation by PF.Compared with the control group(MM)which only inoculated methanogenic microflora,mixed culture(PM)and pretreatment(PP)significantly improved methane production by 29.40%and 39.52%,respectively.The activity of Aspergillus and Penicillium and the yield of VFAs were significantly increased,after the addition of functional fungi at day 0-7.At day 7 to the end of methanogenesis,PF was gradually assimilated by the methanogenic microflora,microbial community structure of PP and PM tended to be consistent with MM,and VFAs were depleted.The decrease of aliphatic CH₃,oxy-aromatic carbons,and carboxyl carbons in PP and PM might be related to higher methane production.The above results indicated that the degradation of lignite by fungi was more active in the early stage under different scales and schemes.Fungi transformed coal into VFAs to produce methane,while aromatic carbons in coal were difficult to degrade.The key to increase methane yield was to improve the activity of coal-solubilizing fungi,promote the degradation of aromatic structure and the production of VFAs at the early stage.The phenanthrene-degrading fungi riched in this paper can effectively promote the degradation of aromatic structure in coal,which significantly improved the biodegradation of coal and methane yield,which provided a feasible scheme for the future field application to increase yield of biological CBM.