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.