Enhancement of Biomethane Generation from Coal by Anaerobically Co-Degrading with Biological and Chemical Products of Straw Treatment

Co-degradation of coal and straw is an effective way to enhance the generation of biogenic coalbed methane (CBM). However, solid straw is not easily injected into coal seam and the complex and rigid structure of straw also makes the direct degradation inefficient. Therefore, straw was biologically and chemically treated, here, to obtain a liquid product which was further co-degraded with coal to produce methane. The results showed that the methane productions in co-degradations of coal and liquid products were all higher than that from coal. The highest methane production was observed in co-degradation of coal and biological liquid products with fresh microflora (MRC1) which was about 600 μmol and even higher than that in co-degradation of coal and straw. Organic acids were dominant in all liquid products whose contents ranged from 25.4 to 73.1%, and were positively related with methane productions in co-degradation. After co-degradation, the microbial community in MRC1 was closer to the original microflora, and the coal sample was degraded deeper than after cultivation with only coal as revealed by FTIR results. These results suggested that the liquefaction of straw by pretreatment can perfectly solve the injection and degradation limitation in co-degradation, and organic acids would be the essential factors in the interaction between coal and straw. Based on that, a new method was proposed to enhance biogenic CBM generation in coal seam or goaf by injecting microorganisms and liquid products or organic acids associated with rice straw.