Bio-hydrogen production from rice straw via ferrous sulphate and nickel chloride inclusion: A pathway to enhanced efficiency

Present research has investigated the efficient conversion of rice straw (RS) biomass into bio-hydrogen using mixed microbial consortia. Batch experiments were performed to analyse the influence of various parameters such as pH, substrate concentration, temperature, iron [Fe2+], and nickel [Ni2+] on bio-hydrogen production. Acidic and alkaline pretreatment on RS was performed to compare the bio-hydrogen production where higher hydrogen production was observed in case of alkaline pretreated RS in batch mode. The optimum conditions for the maximum bio-hydrogen production on the alkaline RS (75 g/L) were temperature of 37 °C, [Ni2+] 37.5 mg/L and [Fe2+] 150 mg/L at pH 7.0. Further, the maximum cumulative volume of bio-hydrogen and hydrogen yield obtained were 702.41 ± 27.40 mL and 0.82 mol H2/g of substrate, respectively. Additionally, the use of [Fe2+] and [Ni2+] shifted the metabolic pathway from acetate to higher butyrate production. However, higher substrate concentrations were advantageous to produce ethanol. Result showed 11% increase in the bio-hydrogen production by supplementing the [Fe2+] and [Ni2+], with an average highest hydrogen yield of 0.85 mol H2/g of substrate, in the lab scale fermenter. The maximum hydrogen production potential (P), production rate (Rm), and lag time (λ) obtained were: 807.90 ± 34.13 mL, 13.65 ± 1.22 mL/h, and: 8.74 ± 2.43 h, respectively, and well fitted by the modified Gompertz equation with a high r2 (0.996). The present study confirmed that the pretreatment of substrate plays a key role in the efficient conversion of RS waste into bio-hydrogen production.