H2 production via dark fermentation of soybean molasses: Elucidating the role of homoacetogenesis and endogenous substrate microorganisms by kinetic and microbial analysis

Soybean molasses has been the subject of research aimed at transforming it into products with increased value and energy potential. Using this substrate in an anaerobic bioreactor at 30 °C, the study discovered challenges for stable biohydrogen production. Stable H2 was achieved with a productivity of 14.3 mmol-H2.m−3.d−1 and a yield of 0.93 mmol-H2.g-Carb−1 at 26 kg-COD.m−3.d−1, after a start-up strategy with sucrose feeding for biomass adaptation. Thermodynamic analysis, kinetic modeling and microbial composition analysis revealed a complex biochemical process that could not be established with only monitoring data analysis. The analyses indicated a scenario in which homoacetogenesis consumed up to 59.9 % of the hydrogen produced. Furthermore, microbial analysis of soybean molasses suggests its role as an inoculum source. Lactobacillus and Caproiciproducens were the predominant genera identified during the system's reduced hydrogen yield. Significant obstacles to achieving high hydrogen production in mesophilic conditions using soybean molasses included: (i) the presence of endogenous microorganisms in this substrate, which changed the consortia of hydrogen-producing microorganisms established during sucrose adaptation start-up, and (ii) the probable occurrence of homoacetogenesis. Nevertheless, suggestions for future research on this by-product were discussed, offering insights into how to overcome these challenges.