Study On Co-degradation Of Pretreatment Low Rank Coal With Ultrasound Assists Oxidation And Sawdust To Produce Biomethane

The extensive research on microbial degradation of coal to produce methane has laid an important theoretical and application foundation for further promoting the industrialization process of coal-formed gas and realizing the sustainable development of low-carbon economy.However,the utilization efficiency of coal and the low activity of microorganisms are still important factors in the low production of biogas,and these drawbacks have always limited the large-scale production and utilization of coal.In order to explore the method of improving the biodegradation efficiency of low-grade coal and increasing the production of material gas,this study used ultrasonic assisted oxidation method to pretreat low-order coal.By changing the ultrasonic conditions,the effects of reaction time,temperature and power on the pretreatment effect of low-order coal were discussed,and the biomethane generation pathway and production increase effect of raw coal,residual coal and filtrate were analyzed;the effect of sawdust on the production of low-order coal biomethane and the effect of different mass ratio sawdust and coal on methane production were analyzed;the best mass ratio of sawdust and coal sample(1:1)was obtained according to the previous experiment,and the co-degradation gas production experiment was carried out with the residual coal and filtrate obtained by sonication respectively.The effect of residual coal and filtrate and sawdust co-degradation on methane production was analyzed,and the changes in volatile fatty acid(VFA)content,p H change and microbial community structure of the fermentation broth during the reaction process were preliminarily determined to determine the types of methanogenic bacteria in each gas production stage,and the methanogenic pathways in each gas production stage were judged according to the changes in the hydrocarbon isotope composition in each gas production point.The conclusion is as follows:(1)The optimal condition for ultrasonic pretreatment is a temperature of 66 °C,a reaction time of 96 min,and an ultrasonic power of 466 W.After pretreatment,the complex macromolecular structure in the coal is destroyed,and the oxygen-containing groups such as carboxylic acid and carboxyl groups are reduced,which is related to the use of microorganisms;the structure of the coal body changes after the raw coal is pretreated,the porosity increases,and the specific surface area of the contact between the microorganism and the coal sample is increased.After pretreatment,the low-grade coal significantly improved the utilization efficiency of microorganisms,increased the production of biomethane,and increased the methane production of residual coal and filtrate relative to raw coal,which was increased by 12.11% and 8.39% respectively,and the methane production of residual coal and filtrate was added to increase by126% relative to raw coal methane production.(2)Moderate amount of sawdust can effectively improve the biomethane yield of low-order coal,when the ratio of sawdust to low-grade coal mass is 1:1,the biomethane yield is the largest,which is 385.21 μmol/g,which is 43.29% higher than that of the control group degraded by low-order coal alone;when the quality of sawdust and low-grade coal is 2:1,the biomethane yield decreases.Scanning electron microscopy analysis results show that after the co-degradation of sawdust and loworder coal,the pore structure on the surface of sawdust becomes larger,and the specific surface area of coal particles and sawdust contact increases;the addition of sawdust affects the utilization effect of microorganisms on aromatic hydrocarbons and carboxyl groups,and improves the degradation capacity of hydrolyzed bacteria and methanogenic bacteria in microorganisms to coal.(3)The co-degradation of residual coal and filtrate with sawdust can significantly shorten the methane-producing cycle and increase methane production,the methaneproducing cycle is shortened from 28 d to 21 d,and the degradation of methane yield of lower-order coal alone is increased by 224.67% and 171.44%,respectively;according to the change of VFA content and p H value in the fermentation broth,it is found that in the process of microbial degradation of coal gas production,it is mainly dominated by phytonutical methanogene of acetic acid;the change in the composition of biomethane hydrocarbon isotopes can be seen.In this study,biomethane is mainly completed by acetic acid fermentation pathway,and the change trend of hydrocarbon isotopes of methane in the late gas production period can be speculated that there is carbon dioxide hydrogen reduction genesis biomethane in the gas production process.