Hydrogen gas production from cheese whey powder (CWP) solution by thermophilic dark fermentation

Hydrogen gas production from cheese whey powder (CWP) solution by thermophilic dark fermentation was investigated at 55 °C. Experiments were performed at different initial total sugar concentrations varying between 5.2 and 28.5 g L⁻¹ with a constant initial bacteria concentration of 1 g L⁻¹. The highest cumulative hydrogen evolution (257 mL) was obtained with 20 g L⁻¹ total sugar (substrate) concentration within 360 h while the highest H₂ formation rate (2.55 mL h⁻¹) and yield (1.03 mol H₂ mol⁻¹ glucose) were obtained at 5.2 and 9.5 g L⁻¹ substrate concentrations, respectively. The specific H₂ production rate (SHPR = 4.5 mL h⁻¹ g⁻¹cells) reached the highest level at 20 g L⁻¹ total sugar concentration. Total volatile fatty acid (TVFA) concentration increased with increasing initial total sugar content and reached the highest level (14.15 g L⁻¹) at 28.5 g L⁻¹ initial substrate concentration. The experimental data was correlated with the Gompertz equation and the constants were determined. The optimum initial total sugar concentration was 20 g L⁻¹ above which substrate and product (VFA) inhibitions were observed.