Influence of oxygen partial pressure on homoacetogenesis and promotion of acetic acid accumulation through low pH regulation under microaerobic conditions

Homoacetogenesis is an important pathway for bio-utilization of CO₂; however, oxygen is a key environmental influencing factor. This study explored the impact of different initial oxygen partial pressures (OPPs) on homoacetogenesis, while implementing low pH regulation enhanced acetic acid (HAc) accumulation under microaerobic conditions. Results indicated that cumulative HAc production increased by 18.2% in 5% OPP group, whereas decreases of 31.3% and 56.0% were observed in 10% and 20% OPP groups, respectively, compared to the control group. However, hydrogenotrophic methanogens adapted to microaerobic environment and competed with homoacetogens for CO₂, thus limiting homoacetogenesis. Controlling influent pH 5.0 per cycle increased cumulative HAc production by 18.3% and 18.2% in 5% and 10% OPP groups, respectively, compared with the control group. Consequently, regulating low pH effectively inhibited methanogenic activity under microaerobic conditions, thus increasing HAc production. This study was expected to expand the practical application of homoacetogenesis in bio-utilization of CO₂.