Biodegradation of guar gum and its enhancing effect on biogas production from coal

To investigate the effects of biodegradation of guar gum and its products on the production of biogas from coal, experiments on biogas production from coal were carried out using guar gum at different concentrations. The effects of the changes in biogas production, the biodegradation characteristics of guar gum, and the structure of microbial community on coal-to-biogas conversion were investigated. When both coal and guar gum were used for fermentation, the biomethane production was >79.10% higher than the sum of biomethane produced using each of the substrates. The biodegradation of guar gum caused the dissolved organic matter in the reaction system to increase. After biodegradation, some of the functional groups such as -OH, C-H, and C-C were dissociated from guar gum, resulting in the increase of the surface roughness. Moreover, the contents of hydrogen, carbon and oxygen decreased from 6.82%, 43.03%, and 42.46% to below 3%, 18%, and 28%, respectively. Desulfovibrio has a certain negative effect on the biodegradation, but the addition of guar gum could reduce its amount in the reaction system. In addition, guar gum was found to be beneficial to the growth and reproduction of hydrogenotrophic methanogens. The pathway for methane production was converted from acetic acid or methyl reduction to CO2 reduction. This work provides significant information on the gel breaking of guar gum fracturing fluid by microorganisms in in situ coal seam.