The role of hydrogenotrophic methanogens in an acidogenic reactor

•pH reduction has negative impacts on hydrogenotrophic methanogen in acidogenic phase.•Hydrogenotrophic methanogen is essential in regulating hydrogen content in biogas.•Hydrogen can affect the production of volatile fatty acids in acidogenic phase.•VFA production was recovered after recovery of hydrogenotrophic methanogen population.•Methane was mainly produced from hydrogenotrophic methanogenesis in acidogenic phase.

A laboratory-scale acidogenic anaerobic sequencing batch reactor was set up to test the effect of pH change on microbial community structure of the reactor biomass and process performance. No immediate performance change on acidogenesis was observed after the pH change. However, as the hydrogenotrophic methanogen population decreased, hydrogen content in biogas increased followed by a sharp decrease in volatile fatty acids (VFAs) with acetic acid (HAc) in particular. Recovery of reactor performance following pH correction was only apparent after recovery of hydrogenotrophic methanogen population. These suggested hydrogenotrophic methanogens played a very important role in performance of the acidogenic process.