Optimization of biohydrogen production using acid pretreated corn stover hydrolysate followed by nickel nanoparticle addition

The dilute acid hydrolysis using corn stover (CS) to produce reducible sugars was optimized by the response surface methodology. The electron-equivalent balances of the main metabolites during the dark fermentation (DF) using acid hydrolysate were investigated to identify the evolutions of the electron sinks over the course of DF. The additions of nickel ion and Ni⁰ nanoparticles (NPs) were found to effectively enhance the hydrogen production at experimental conditions. The optimal condition (HCl 2.5 wt%, hydrolyzing duration 105 minutes, pH=5, S/B=3.5, Ni⁰ NPs=10 mg/L^-1) was achieved with Y_H2/S reaching 1.18 (mol.mol^-1-glucose). The Y_H2/S increased from 0.7 (mol.mol^-1-glucose) to 1.18 (mol.mol^-1-glucose) reaching 40% hydrogen yield increase when Ni⁰ NPs was added to the fermentation broth. Among the investigated significant soluble metabolites, the butyric acid was found to serve as the largest e-sink in the electron-equivalent balance. The additions of Ni⁰ NPs at low level (below 10 mg/L) were found to appreciably increase the hydrogen production. The increased pH and substrate to biomass ratio were found to skew the metabolic balance from hydrogen production to the biosynthesis (an increase of biomass). The proposed anaerobic digestion model with consideration of the inhibitory factors model presents a good agreement with the experimental data. The chemical addition such as nickel ions, Ni⁰ NPs was found to be a practical approach in enhancing biohydrogen production using CS acid hydrolysate as cultivation broth.