Medium optimization and fermentation regulation strategies for enhancing CO2 conversion to acetic acid coupled with H2 by Clostridium ljungdahlii

Abstract:

Clostridium ljungdahlii can reduce CO₂ to acetic acid via the Wood-Ljungdahl pathway using H₂ as an energy source and CO₂ as a carbon source, and it is a key chassis for realizing resource utilization of CO₂. Acetic acid, as a bulk basic organic chemical raw material, has a large market demand and wide application scenarios. Moreover, the syngas fermentation route is green and low-carbon, with mild reaction conditions, making it an ideal direction for replacing traditional petroleum-based processes. However, during the fermentation process, it encountered problems such as slow growth, low biomass, and low acetic acid production. Therefore, in this study, the strain C. ljungdahlii SL40, which was obtained through laboratory adaptive evolution, was selected as the object of investigation. Through optimization of the culture medium and regulation of key fermentation processes, its acetic acid synthesis capacity was enhanced. Single-factor experiments integrated with response surface methodology were used to optimize the culture conditions. The optimal parameters were determined as follows: H₂: CO₂=60%: 40% (V/V), yeast extract 4.0 g/L, FeSO₄ 16 mg/L, culture temperature 37 ℃. Further experiments were conducted in a 5 L fermentation tank to investigate the effects of aeration rate and pH on the product. The results showed that increasing the aeration rate from 0.8 L/min to 1.5 L/min significantly promoted the production of acetic acid, raising the acetic acid concentration from 20.740 g/L to 25.950 g/L. When pH was controlled at 5.85, the acetic acid concentration was further increased to 36.570 g/L. Through systematic optimization, this study effectively broke through the key bottlenecks such as low biomass and low gas utilization rate in the autotrophic fermentation of the strain and significantly improved the acetic acid yield. These findings provide a feasible path for the directed conversion of CO₂ to produce high value-added chemicals and has good industrial application potential.