Difference of metabolic functions in biomethane produced fromdifferent rank coals

In order to investigate the coupling relationship between biomethane production and microbial metabolic function from the biogas production experiments of different coals，lignite，long flame coal，gas coal and coking coal were selected to test the biomethane content and 16S rRNA metabolic function in fermentation process. With the help of the modified Gompertz model，the characteristics of biomethane production potential from different coals，the expression of metabolic function metabolic function expression and their correlation were analyzed. The results show that the cumulative biogas production from long flame coal as substrate is significantly higher than that of other experimental groups，and its biomethane production increased by 10.82%，38.88% and 73.49% compared with lignite，gas coal and coking coal，respectively. The fitting results of modified Gompertz model show that the biomethane production potential of the long flame coal experimental group is the largest，and with the increase of the coal rank，the lag time is gradually increasing. The relative abundance of microbial metabolic functions in the long flame coal experimental group was significantly higher than that in other experimental groups，which was almost consistent with the results of biomethane production. There was a great linear relationship between the maximum methane production potential and the two metabolic functions (coenzyme transport and metabolism，carbohydrate transport and metabolism) (R2=0.727,R2=0.945). The prediction results of functional genes show that the abundance of aspartate 4-decarboxylase，glutamate dehydro genase，aspartate aminotransferase and sarcosine oxidase involved in amino acid formation and transformation，3-oxoyl-［acyl carrier protein］ reductase and acetylcoenzyme A carboxylase involved in fatty acid and functional genes involved in biofilm synthesis was the largest in the long flame coal experimental group，which provided more precursor substance for the synthesis of volatile fatty acids (VFA) in the fermentation system，and also improved the resistance and tolerance of cells to environmental pressure.