Enhancing overall energy conversion through innovative coupling of photo-fermentation biohydrogen and anaerobic biomethane stages.

Biohydrogen and biomethane co-production via photo-fermentation and anaerobic digestion would improve the energy conversion efficiency (ECE) by further utilizing organic matter remained in the liquid and slag of photo-fermentation biohydrogen production. In this study, the effect of connection time between photo-fermentation and anaerobic digestion on biohydrogen and biomethane production as well as bacterial community was evaluated. Among the tested conditions, the 60 h connection time yielded the highest hydrogen and methane production (256.56 mL and 1,233.3 mL, respectively), with relatively stable performance observed within the 48-72 h window. The ECE increased from 3.72% for photo-fermentation alone to 53.49% for hydrogen and methane co-production at 60 h. Connecting methane fermentation within this optimal window can not only improve ECE but also further extend the economic value of the industry compared to individual photo-fermentation biohydrogen production. These results show that combining biohydrogen and biomethane production processes promotes bioenergy recovery from biomass and supports renewable energy development.