Batch dark fermentation of powdered wheat starch to hydrogen gas: Effects of the initial substrate and biomass concentrations

Powdered wheat solution was fermented batchwise for bio-hydrogen production using heat-treated anaerobic-acidogenic sludge as the inoculum at initial pH of 7.0 and temperature of 37 °C. In order to determine the most suitable wheat powder (WP) and cell concentrations yielding the highest hydrogen formation, initial WP concentration was varied between 5 and 30 g L−1 at a constant initial biomass concentration (2.6 g L−1). The initial biomass concentration was varied between 0.5 and 5.0 g L−1 at constant WP concentration of 20 g L−1 in another set of experiments. Cumulative bio-hydrogen formation, hydrogen yield and the formation rate were maximum at the WP concentration of 20 g L−1. Higher WP concentrations resulted in lower fermentation performance probably due to substrate and product (VFA) inhibition. Similarly, hydrogen formation rate and the yield were maximum with a biomass concentration of 2.5 g L−1. Higher biomass concentrations resulted in lower hydrogen yield and formation rates due to product inhibition. The optimum initial biomass/substrate ratio maximizing the hydrogen yield and formation rate was found to be 0.125 g biomass g−1 WP. A kinetic model was developed for bio-hydrogen formation from powdered wheat starch and the constants were determined by regression analysis.