Biohydrogen production from sugarcane bagasse hydrolysate: effects of pH, S/X, Fe2+, and magnetite nanoparticles.

Batch dark fermentation experiments were conducted to investigate the effects of initial pH, substrate-to-biomass (S/X) ratio, and concentrations of Fe2+ and magnetite nanoparticles on biohydrogen production from sugarcane bagasse (SCB) hydrolysate. By applying the response surface methodology, the optimum condition of steam-acid hydrolysis was 0.64% (v/v) H2SO4 for 55.7 min, which obtained a sugar yield of 274 mg g-1. The maximum hydrogen yield (HY) of 0.874 mol (mol glucose-1) was detected at the optimum pH of 5.0 and S/X ratio of 0.5 g chemical oxygen demand (COD, g VSS-1). The addition of Fe2+ 200 mg L-1 and magnetite nanoparticles 200 mg L-1 to the inoculum enhanced the HY by 62.1% and 69.6%, respectively. The kinetics of hydrogen production was estimated by fitting the experimental data to the modified Gompertz model. The inhibitory effects of adding Fe2+ and magnetite nanoparticles to the fermentative hydrogen production were examined by applying Andrew's inhibition model. COD mass balance and full stoichiometric reactions, including soluble metabolic products, cell synthesis, and H2 production, indicated the reliability of the experimental results. A qPCR-based analysis was conducted to assess the microbial community structure using Enterobacteriaceae, Clostridium spp., and hydrogenase-specific gene activity. Results from the microbial analysis revealed the dominance of hydrogen producers in the inoculum immobilized on magnetite nanoparticles, followed by the inoculum supplemented with Fe2+ concentration. Graphical abstract ᅟ.