(351c) Enhancing Biological CO2 Conversion to Ethanol By Clostridium Ragsdalei: Insights from Batch and Continuous Operations

Biological conversion of CO₂ into biofuels offers a promising avenue for both greenhouse gas mitigation and resource utilization. This study investigates the conversion of CO₂ into ethanol by Clostridium ragsdalei P11 in 3-L stirred tank reactors operated in both batch and continuous modes using a gas mix H₂:CO₂:N₂ (60:20:20). Enzyme activities in the acetyl-CoA pathway, including carbon monoxide dehydrogenase (CODH), hydrogenase (H₂ase), formate dehydrogenase (FDH) and alcohol dehydrogenase (ADH), were evaluated. Results demonstrate that strain P11 produces 7.0 g/L ethanol from CO₂ in batch fermentations. During batch fermentation, H₂ and CO₂ conversion efficiencies were 60% and 40%, respectively. The supplementation of CO to CO₂ improved ethanol production. Continuous CO₂ fermentation with CO supplementation yielded 22 g/L ethanol. Increased activity of CODH and H₂ase was observed during the initial growth phase, while the rise in ADH activity closely correlated with ethanol production. Enzyme activities exhibited a 3.6-7 fold increase during continuous compared to batch fermentations. These findings highlight the robust potential of strain P11 for CO₂ conversion into ethanol and provide a promising groundwork for further optimizing CO₂ fermentation processes.