Forward osmosis membrane bioreactor for sustainable hydrogen production from waste molasses

The current study evaluates the feasibility of a forward osmosis membrane bioreactor (FO-MBR) for dark fermentation, aiming at simultaneous biohydrogen production and wastewater treatment. Optimal microbial inoculation was achieved via heat-treated activated sludge, enriching Clostridium sensu stricto 1 and yielding up to 2.21 mol H₂.(mol hexose)⁻¹ in batch mode. In continuous operation, a substrate concentration of 4.4 g L⁻¹ and a hydraulic retention time (HRT) of 12 h delivered the best results, producing 1.51 mol H₂.(mol hexose_supplied)⁻¹. The FO-MBR, configured with a 1.1 m² hollow fiber side-stream membrane module and operated under dynamic HRT (2.5–12 h) dependent on membrane flux, was integrated with intermittent CSTR (Continuous stirred tank reactor) operation to counter metabolite accumulation. This system outperformed a conventional CSTR, achieving a hydrogen yield of 1.78 mol H₂.(mol hexose_supplied)⁻¹. Remarkable treatment efficiencies were observed with BOD₅, COD, and TOC removal rates of 95.32 %, 99.02 %, and 99.10 %, respectively, and an 83.8 % reduction in total waste volume. Additionally, the FO-MBR demonstrated strong antifouling performance, with 96.14 % water flux recovery achieved after a brief 5 min hydraulic rinse following 47.5 h of continuous high-strength broth exposure. These results highlight the FO-MBR system's ability as a sustainable and high-performance alternative for integrated hydrogen production and effluent treatment. Further studies are recommended to address long-term fouling control and metabolite management for industrial scalability.