Role of L-cysteine and iron oxide nanoparticle in affecting hydrogen yield potential and electronic distribution in biohydrogen production from dark fermentation effluents by photo-fermentation

Dark fermentation effluent is a potential substrate for hydrogen production by photosynthetic bacteria(PSB). Influences of adding L-cysteine and Fe₃O₄ nanoparticles (NPs) on hydrogen production performance and electronic distribution from dark fermentation effluents (DFEs) during photo fermentation hydrogen production(PFHP) process were experimentally studied, as well as the critical kinetic analysis. L-cysteine addition can promote flocculability and cell growth rates of PSB HAU-M1 while addition of 300 mg/L L-cysteine and 100 mg/L Fe₃O₄ NPs can peak H₂ yield from the DFEs, resulting in 29.94% and 29.23% substrate electrons were diverted to H_2, respectively. Controlling the adding time interval of L-cysteine and Fe₃O₄ NPs can improve the activity of nitrogenase without weakening flocculation and increase the hydrogen production, the maximum hydrogen yield of 234.55 ± 7.5 mL was obtained at 12 h interval time, 35.94% substrate electrons diverted towards bio-hydrogen generation, and the corresponding nitrogenase activity increased by 2.12 times as comparing to the control. The modified Gompertz and Han-Levenspiel models were employed to model the effect of the L-cysteine and Fe₃O₄ NPs on hydrogen production, the predicted critical L-cysteine and Fe₃O₄ NPs concentrations were 4630.87 and 1969.18 mg/L, respectively.