Boosting light-utilization efficiency and long-term hydrogen production in pilot-scale Photo-fermentation: Biomass substrate and hybrid lighting approach

The utilization of biomass as a substrate for photo-fermentation represents an environmentally sustainable approach for clean biohydrogen production. However, large-scale application of industrialization process is constrained by high feedstock costs and limited light utilization efficiency. In this study, a 70 L semi-continuous combined tubular photo-fermentation system was successfully built, and R. sphaeroides HY01 was used to produce hydrogen and volatile fatty acids from corn straw hydrolysate on an outdoor pilot scale. The system start-up stage could achieve a total hydrogen yield of 113.7 mL H2/g corn straw in this approach. During the semi-continuous operation, the peak hydrogen production rate of 92.3 ± 3.5 mL H2/(L·d) and the light conversion efficiency of 1.73% were obtained under the optimal hydrogen production conditions. Notably, the innovative hybrid solar-artificial lighting system enhanced light conversion efficiency by 9.6% and the hydrogen production rate by 17.1% compared to artificial lighting alone, addresses a critical challenge in photobioreactor design. Furthermore, metabolic flux analysis revealed concentration-dependent substrate regulation, with elevated loading redirecting carbon flow toward volatile fatty acids. These results establish the feasibility of outdoor photo-fermentation using biomass while identifying optimal operational parameters for balancing hydrogen yield and long-term system stability in pilot-scale.