Experimental Study On Combined Degradation Of Coal-formed Gas By Advanced Oxidation And Microorganisms

In order to promote the clean utilization of coal,many research achievements have been made in the degradation and hydrocarbon generation of coal seam native and exogenous microorganisms.However,the low bioconversion rate has always been the bottleneck of coal biological gasification.In the experiment of microbial degradation of coal,strong acid,alkali,high temperature and pressure are commonly used to pretreat raw coal to improve the rate of gas formation.These methods belong to high energy consumption methods,which are not conducive to the subsequent microbial gas formation.Therefore,how to break the three-dimensional reticular macromolecular structure of coal under mild conditions and improve the utilization efficiency of coal by microorganisms has become an important problem to be solved.Using self-made biogas slurry as exogenous bacteria,advanced oxidation was introduced into the simulation experiment of coal biogas.By studying the influence trend of the parameters changes of advanced oxidation on coal degradation,the experimental conditions were optimized and the subsequent biogas rate was improved.The spectral characteristics and content changes of the intermediate products were analyzed,and the change law of gas-producing intermediates with time was determined.The changes of microbial community structure in the gas-forming process were analyzed,and the functional microorganisms which played an important role in gas formation were discussed.The differences between raw coal and oxidized coal in different gas production stages were compared and analyzed,and the effect of advanced oxidation and microbial degradation of coal-formed gas was discussed.This study can provide a new idea for improving the rate of bioconversion coal and a new way for clean and efficient utilization of coal.The research contents,methods and main achievements are as follows:1.Two advanced oxidation methods,H₂O₂and microwave/ultrasound combined with H₂O₂,were used to degrade coal.The residual H₂O₂concentration in the system decreased with the increase of reaction temperature.The results show that microwave/ultrasound combined with H₂O₂system is the best way to degrade Chaohua mine?ZC coal?and Gengcun mine?YG coal?.The optimum experimental conditions are as follows:reaction temperature 80?,ultrasonic power 600 W,and the optimum reaction time of ZC and YG coal is 40 min and 60 min,respectively.In the advanced oxidation pretreatment,the methane output of pretreated medium rank coal is 1.43 times higher than that of raw coal.The methane output of pretreated low rank coal is 1.31times higher than that of raw coal.The pretreatment method can provide technical and theoretical support for further small-scale industrial applications.2.The spectral characteristics of soluble organic matter?DOM?during gas formation were analyzed.The fluorescence intensity of DOM decreased with the increase of gas production time,and the fluorescence intensity ratio of aromatic proteins?regions I?and soluble microbial metabolites?regions IV?was dominant in the whole gas production process.Tyrosine and microbial metabolites are the main components of DOM in the process of gas formation.The parallel factor?PARAFAC?model is introduced to classify and identify the three-dimensional fluorescence spectrum of DOM in coal biogenic gas,and the influence of parallel factor number on the analytical results of the model is analyzed.It is found that the three-component parallel factor analysis model is suitable for the three-dimensional fluorescence spectrum analysis of DOM in the process of coal biogas.3.In the process of gas formation,the content of soluble organic carbon?DOC?decreased.The aromatization degree and humification level of DOM change with the gas production cycle,and the content of hydrophobic organic matter increases with the increase of gas production time.In the initial stage of rapied gas production,the content of small molecular acid is higher and the corresponding methane production rate is higher.The change of saturated hydrocarbon content is not obvious in a certain period of time,because the macromolecules of coal are gradually depolymerized to form long-chain saturated hydrocarbons and microorganisms give priority to the utilization of saturated hydrocarbons in coal.There is a growth and decline relationship between saturated hydrocarbon and methane content.4.After domestication and culture,there were 185 OTU in the bacterial source.The bacterial domain?98.86%?was absolutely dominant,and a few were distributed in the archaeal domain?1.14%?.The dominant bacteria in the process of gas production are Proteiniphilum,Aminobacterium,Romboutsia,Terrisporobacter,yntrophomonas,Thauera,and Petrimonas.Most of the bacteria detected have the function of hydrolytic fermentation,and some of them have the function of hydrogen/acetic acid production,which play an important role in the first stage?hydrolytic fermentation stage?and the second stage?hydrogen production/acetic acid production stage?of coal biogas production.Methanobacterium and Methanoculleus are the dominant archaea in the process of methane production from coal.The whole gas formation process is dominated by hydrogen nutrition type,and the initial gas production process is dominated by methyl nutrition type.