The effects of Fe0 and Ni0 nanoparticles versus Fe2+ and Ni2+ ions on dark hydrogen fermentation

The effects of Fe0 and Ni0 nanoparticles (NPs) versus Fe2+ and Ni2+ ions on the efficiency of mesophilic dark hydrogen fermentation from glucose were investigated using the heat-shock pretreated anaerobic sludge. The initial glucose concentration and the pH of the reactors were 5 g/L and 5.5, respectively, and the concentrations of the supplemented metals were varied between 0 and 50 mg/L. The hydrogen and biogas yields of the control test were 247 and 391 mL/g VS, respectively. The results showed that the effect of Ni2+ ions on the hydrogen yield was highly significant (P < 0.01), improving the hydrogen yield by 55%. The effects of Fe0 NPs and Fe2+ ions were significant too (P < 0.05), enhancing the hydrogen yield by 37% and 15%, respectively, whereas the effect of Ni0 NPs was insignificant (P > 0.05). The analysis of the soluble metabolites revealed that the hydrogen fermentative yield was mainly affected by ethanol and propionate production, while the production of butyrate favored the hydrogen fermentation.