Optimization of media composition for hydrogen gas production from hydrolyzed wheat starch by dark fermentation

Effects of N/C, P/C and Fe(II)/C ratios in fermentation medium on biohydrogen production by dark fermentation of acid-hydrolyzed wheat starch was investigated. The powdered wheat was autoclaved at pH = 3 and 90 °C for 15 min and the resulting sugar solution was fermented after external addition of N, P and Fe(II) to overcome nutrient limitations. Box–Wilson statistical experiment design was used by considering the N/C (0–0.05, w w⁻¹), P/C (0–0.02) and Fe(II)/C (0–0.03) ratios as the independent variables while the hydrogen yield and specific hydrogen production rate (SHPR) were the objective functions to be optimized. A quadratic response function was used to correlate the response functions with the independent variables. Low levels of the variables (N/C < 0.02, P/C < 0.01, Fe(II)/C < 0.01) resulted in low hydrogen yield and SHPR due to nutrient limitations and high levels of nutrients caused inhibitions. The optimum conditions yielding the maximum hydrogen yield (Y = 2.84 mol H₂ mol⁻¹ glucose) were N/C = 0.02, P/C = 0.008 and Fe(II)/C = 0.015. The maximum SHPR (96 mL H₂ g⁻¹ biomass h⁻¹) was obtained at N/C = 0.025, P/C = 0.008 and Fe(II)/C = 0.015 (w w⁻¹).