In this study, the effects of iron and nickel zero-valent nanoparticles on hydrogen production in a biorefinery with gaseous products were investigated. Glucose, starch, cellulose, sugarcane bagasse and rice straw were used as substrate. Sulfuric acid pretreatment was applied to alter the structure of the substrate and to make it ready for fermentation. Acidic pretreatment efficiently improved the hydrogen production yield. Iron nanoparticles (Fe 0 ) significantly improved the hydrogen production from glucose by 37% (p 0.05), while nickel nanoparticles (Ni 0 ) had no significant effect on the hydrogen yield. The maximum hydrogen production from cellulose (45.7 mL/g VS) was obtained after supplementation of Fe 0 and Ni 0 of 5 and 12.5 mg/L, respectively. The maximum hydrogen production from sugarcane bagasse of 114.1 mL/g VS (32% higher than control test) was achieved after Fe 0 and Ni 0 supplementation of 5 and 12.5 mg/L, respectively. Moreover, the maximum hydrogen production from rice straw of 103.5 mL/g VS (51% higher than the control test) was obtained after Fe 0 and Ni 0 supplementation of 12.5 and 5 mg/L, respectively. Analysis of the produced soluble metabolites showed that the major effects of supplemented Fe 0 and Ni 0 (at optimum concentrations) were enhancement in butyrate (desirable byproduct) fermentation and inhibition of ethanol and lactate (undesirable byproducts) fermentation. The maximum recovered energy from cellulose, sugarcane bagasse and rice straw (in sequential hydrogen and methane production processes) were 9.61, 11.57 and 7.1 MJ/Kg, respectively. Keywords: Anaerobic digestion, dark fermentation, Fe 0 nanoparticles, Ni 0 nanoparticles, pretreatment.
