An Experimental and Multiphysics Simulations Study of Clostridium carboxidivorans sp. 624 for Acid and Alcohol Production in CO 2 /H 2
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Biotechnological advancements in carbon utilization, particularly CO 2 gas fermentation, present a sustainable alternative to energy-intensive chemical catalysis. Clostridium carboxidivorans sp. 624, a clostridial acetogen, employs the Wood-Ljungdahl pathway to fix CO 2 , producing valuable acids and alcohols. In this study, we systematically investigate the metabolic dynamics of CO 2 /H 2 fermentation, focusing on optimizing temperature and media conditions to enhance yield. Notably, batch fermentation at 25°C achieved the highest reported acetate concentration of 4.38 g/L, with butyrate and hexanoate detected at lower yields. To further optimize fermentation performance, we examined the impact of the liquid-to-gas volume ratio (V L /V G ) on product distribution. Acetate remained dominant, while V L /V G = 4 enhanced longer-chain acid production, due to improved gas solubility and substrate bioavailability. The enriched liquid phase at V L /V G = 4 also drove higher total acid (5.341 g/L) and alcohol (0.411 g/L) production. Moreover, the acid-to- alcohol ratio was 13 for V L /V G = 4, promoting alcohol conversion, while a higher ratio of 18 for V L /V G = 1 maintained an acetogenic profile. To complement the experimental insights, a kinetic model coupled with 3D computational fluid dynamics simulations was developed to elucidate spatial inhomogeneity and its impact on reaction kinetics. This comparative analysis identified key optimized parameters, including maximum reaction rates, half-saturation concentrations, and inhibition rates, which serve as critical guidelines for enhancing fermentation performance. By leveraging real-time computational modelling to refine bioreactor design, this approach facilitates the transition toward scalable CO 2 bioprocessing. These findings advance of sustainable chemical manufacturing, reinforcing CO 2 bioconversion as a strategy for carbon-negative biotechnology.
