Selective syngas fermentation to acetate under acidic and psychrophilic conditions using mixed anaerobic culture

[Display omitted] •Bioreactor operated at 28 °C/20 °C with pH 5.5 to 4.5 using mixed culture.•Lower temperature and pH led to increased electron yields to acetate.•The highest H2 and CO consumption was at 20 °C and pH 4.5.•Methanogens were not completely suppressed under any conditions.•Different microbial genera dominated distinct experimental periods. Syngas fermentation to acetate offers a promising solution for its valorisation, particularly when syngas contains a high N2 concentration, which otherwise impedes the utilisation of syngas biomethanation gaseous product in cogeneration or upgrading units. In this study, continuous lab-scale syngas fermentation assessing the effects of acidic pH and psychrophilic conditions (28 °C and 20 °C) on bioconversion efficiency and anaerobic consortium diversity was studied. The results showed that as temperature and pH decrease, acetate yield increases. The highest H2 and CO consumption rates were observed at 20 °C and pH 4.5, reaching 48.4 mmol/(L·d) and 31.5 mmol/(L·d), respectively, and methanogenic activity was not completely suppressed. The microbial community composition indicated an enhanced abundance of acetate-producing bacteria and hydrogenotrophic methanogens at 28 °C. The PICRUSt2 prediction of metabolic potential indicated that temperature and pH changes appear to have a more pronounced impact on acetotrophic methanogenesis genes than carbon dioxide-based methanogenesis genes.