| To explore the promotion mechanism of adding corn straw to coal to biomethane in the anaerobic fermentation system of coal and the feasibility of field application,and further deepen the understanding of change characteristics of products and microbial metabolism in the process of co-degradation of coal and corn straw,this paper mainly used lean coal from Wangjialing mine,coking coal from Shoushan No.1 mine,weakly coking coals of Meiyukou mine and corn straw as fermentation substrates,and the simulation experiment of biogas production by fixed fermentation of coal and corn straw was carried out under different mass ratios.The gas production characteristics of different fermentation combinations were compared and analyzed,and the optimal gas production combination of three kinds of coal and corn straw was selected.The solid-liquid products in the fermentation process were tested by FT-IR,13C-NMR,BET specific surface area,XPS,GC-MS,and three-dimensional fluorescence to analyze the degradation degree of coal and corn straw and the variation of degradation products.Through 16S r RNA sequencing and test for enzyme activity involved in lignin degradation of fermentation liquid and SEM of coal and straw,the evolution,attachment morphology and enzyme activity of flora were discussed.The microbial function and metabolic pathway were analyzed by PICRUSt and KEGG pathway.The effects of different factors on biogas production in field application were analyzed with biogas production and biomethane production as the judgement indexes.The results show that:（1）The optimal combination of lean coal,coking coal,weakly coking coal with corn straw was 2:1,3:1 and 2:1,respectively.The gas production was17.28 m L/g,14.88 m L/g and 12.51 m L/g,respectively.Higher CO2 concentration in the early stage of fermentation helps to produce biomethane.The promotion effect of corn straw on methane production by synergistic fermentation:lean coal>coking coal>weakly coking coal.（2）The transmittance of the samples of corn straw at each peak position of infrared spectrum was low.Only the total content of oxygen-containing organic carbon on the surface of lean coal increased,and the functional genes of glycolysis and fatty acid biosynthesis were more abundant.The relative abundances of lignin and phenol degradation,carbohydrate metabolism,nitrate reduction,energy metabolism and lipid metabolism were the highest,which may be part of the reason for the higher methane production of the optimal gas production combination of lean coal and corn straw.（3）Many macromolecular organic matter in the mixed fermentation substrate was degraded into small molecular substances.These small molecular organic matter and complex microbial communities and their metabolites occupied part of the pore space in coal,resulting in the decrease of specific surface area and total pore volume of residual coal.（4）The liquid products of the optimal gas production combination of lean coal and corn straw were mainly long-chain alkanes,while the optimal gas production combination of coking coal and corn straw were mainly esters and ether organic compounds.The liquid products of the optimal gas production combination of weakly coking coal and corn straw were mostly volatile fatty acids.The liquid products of the optimal gas production combination of lean coal and corn stalk were higher and more abundant.（5）Biodegradable tyrosine-like proteins and soluble microbial by-products had the highest fluorescence intensity in the fermentation liquid with low rank coal as substrate,and the content of biodegradable substrate was the highest in the mixed fermentation system of low rank coal and corn straw.（6）Archaeal communities are more susceptible to coal rank than bacterial communities.When the substrate changed from high rank coal to low rank coal,the archaea structure changed from aceticlastic to hydrogenotrophic methanogens.（7）With the increase of coal rank,the attachment amount of flora on the surface of coal gradually decreases and the attachment amount of flora on the surface of corn straw increases,indicating that if there was high rank coal in the fermentation substrate,corn straw will be preferentially degraded by flora.（8）The activity of peroxidase and polyphenol oxidase in the optimal gas production combination composed of weakly sticky coal and corn straw were low,which may be related to the inhibition of small molecular acids in liquid products.（9）The proportion of hydrogenotrophic was significantly higher than that of aceticlastic and methylotrophic,and the metabolic activity of acetic acid synthesis pathway was easily affected by coal rank.（10）The methane production of the mixed fermentation of coal and corn straw with domesticated bacteria as the source was the highest under the mixed conditions,and the inorganic minerals including calcite,montmorillonite and kaolin significantly promoted the biogas production.Corn straw can also effectively promote the gas production of high rank coal.This study provides experimental support for the promotion of corn straw on the conversion of coal to biomethane,and reveals the promotion mechanism of corn straw on biogas production process from substrate degradation and metabolic pathways,which is also an in-depth exploration of synergistic degradation and field application of mixed substrates.There are 32 figures,23 tables and 171 references. |
