Biogas production and microbial community shift through neutral pH control during the anaerobic digestion of pig manure

•Biogas production and methane content in pH 7.0 system were higher than others.•Organic matter degradation rate was highest in pH 7.0 system.•The major genus at pH 7.0 was Methanocorpusculum.•The major genus at pH 6.0 and 8.0 was Methanosarcina.

Laboratory-scale reactors, in which the pH could be auto-adjusted, were employed to investigate the mesophilic methane fermentation with pig manure (7.8% total solids) at pH 6.0, 7.0, and 8.0. Results showed that the performance of anaerobic digestion was strongly dependent on pH value. Biogas production and methane content at neutral pH 7.0 were significantly higher (16,607 mL, 51.81%) than those at pH 6.0 (6916 mL, 42.9%) and 8.0 (9739 mL, 35.6%). Denaturing gradient gel electrophoresis fingerprinting and Shannon’s index indicated that the samples contained highly diverse microbial communities. The major genus at pH 7.0 was Methanocorpusculum, compared with that was Methanosarcina at both pH 6.0 and 8.0. Our research revealed that cultures maintained at pH 7.0 could support increased biogas production, which has significant implications for the scale-up biogas engineering.