(103i) Enhancing Biohydrogen Production from Untreated Lignocellulosic Biomass through Bioreactor Design

Biological hydrogen production from lignocellulosic biomass offers a sustainable approach by simultaneously reducing organic waste and generating renewable energy. Among the available biohydrogen production methods, dark fermentation is particularly attractive because it can efficiently valorize waste lignocellulosic biomass, energy crops, and wet waste streams. However, this process is hindered by the structural complexity of lignocellulose and its inherent recalcitrance to enzymatic degradation, thereby necessitating additional pretreatment steps. Clostridium thermocellum has a unique ability to form cellulosomes on its cell surface, anchored to the cell wall or cytoplasmic membrane, which house a wide array of hydrolytic enzymes. This organism produces hydrogen under anaerobic cultivation, making it a promising platform for lignocellulosic biohydrogen production. Nonetheless, the direct use of non-pretreated biomass (i.e., solid biomass) is limited by mixing and mass transfer challenges, particularly in conventional Rushton impeller bioreactors. Achieving homogeneous mixing is therefore critical, as it strongly influences the physical properties and flow behavior of such feedstocks. At the same time, realizing commercially viable production rates requires balancing biomass loading and throughput with uniform mixing conditions, which are essential for effective enzyme dispersion and the efficient removal of hydrogen and other metabolites in continuous operation. To address these challenges, we simulated the flow behavior of corn stover using Computational Fluid Dynamics (CFD) with different impeller morphologies and subsequently designed a customized bioreactor to demonstrate the potential for enhanced hydrogen production. In parallel, we investigated the effects of varying loadings and particle sizes of raw milled biomass on biohydrogen production. We also examined cellulose and hemicellulose solubilization from solid lignocellulosic biomass using the C. thermocellum KJC19-9 strain, genetically engineered for the co-utilization of cellulose and hemicellulose sugars (e.g., xylose). The process achieved higher hydrogen yields with increased biomass concentrations, although the overall solubilization ratio remained approximately 65% for glucan and 70% for xylan. In addition, smaller biomass particle sizes supported higher hydrogen production, with 0.5 mm particles yielding 3.61 L H₂/L compared to 3.53 L H₂/L for 2.0 mm particles, though the difference was not statistically significant.

References

1. Chou, K.J., Croft, T., Hebdon, S.D., Magnusson, L.R., Xiong, W., Reyes, L.H., Chen, X., Miller, E.J., Riley, D.M., Dupuis, S. and Laramore, K.A., 2024. Engineering the cellulolytic bacterium, Clostridium thermocellum, to co-utilize hemicellulose. Metabolic Engineering, 83, pp.193-205.
2. Kim, C., Wolf, I., Dou, C., Magnusson, L., Maness, P.C., Chou, K.J., Singer, S. and Sundstrom, E., 2023. Coupling gas purging with inorganic carbon supply to enhance biohydrogen production with Clostridium thermocellum. Chemical Engineering Journal, 456, p.141028.

Keywords

Biohydrogen, Lignocellulosic biomass, Clostrodium themocellum, Dark fermentation, scale-up