Effect of initial total solids and substrate-to-inoculum ratio on biohydrogen production via dry fermentation of organic fraction of municipal solid waste

Dry fermentation of organic waste has emerged as a promising strategy for sustainable waste valorization, especially for hydrogen (H 2 ) generation under water-limited conditions. This study investigated the influence of total solids (TS) content and substrate-to-inoculum (S/I) ratio on hydrogen and metabolite production during dry fermentation of the organic fraction of municipal solid waste (OFMSW). TS content ranged from 21.8% to 30.3%, while S/I ratios varied from 7.0 to 46.8. Batch experiments were conducted at 37 °C and an initial pH of 7.5, using thermally pretreated anaerobic sludge as inoculum. Both TS content and S/I ratio significantly affected hydrogen production (p < 0.05). Higher TS content promoted hydrogen production, reaching 5.5 ± 0.1 L H 2 /L_reactor with a yield of 35.9 ± 0.1 mL H 2 /g VS. The combination of 30.3% TS and an S/I ratio of 40.2 further increased hydrogen production to 6.2 ± 0.8 L H 2 /L reactor , corresponding to a yield of 40.3 ± 0.8 mL/g VS. Butyrate, acetate, and propionate were the main fermentation products. These findings demonstrate that competitive hydrogen production can be achieved during OFMSW dry fermentation without substrate dilution, underscoring the process's potential as a water-efficient strategy for sustainable bioenergy recovery from municipal solid waste.