Differences of methanogenesis between mesophilic and thermophilic in situ biogas-upgrading systems by hydrogen addition

To investigate the differences in microbial community structure between mesophilic and thermophilic in situ biogas-upgrading systems by H 2 addition, two reactors (35 °C and 55 °C) were run for four stages according to different H 2 addition rates (H 2 /CO 2 of 0:1, 1:1, and 4:1) and mixing mode (intermittent and continuous). 16S rRNA gene-sequencing technology was applied to analyze microbial community structure. The results showed that the temperature is a crucial factor in impacting succession of microbial community structure and the H 2 utilization pathway. For mesophilic digestion, most of added H 2 was consumed indirectly by the combination of homoacetogens and strict aceticlastic methanogens. In the thermophilic system, most of added H 2 may be used for microbial cell growth, and part of H 2 was utilized directly by strict hydrogenotrophic methanogens and facultative aceticlastic methanogens. Continuous stirring was harmful to the stabilization of mesophilic system, but not to the thermophilic one.