Effects of the substrate and cell concentration on bio-hydrogen production from ground wheat by combined dark and photo-fermentation

Effects of the substrate and cell concentration on bio-hydrogen production from ground wheat solution were investigated in combined dark-light fermentations. The ratio of the dark to light bacteria concentration (D/L)was kept constant at 1/10 while the wheat powder (WP)concentration was changed between 2.5 and 20 g L?1 with a total cell concentration of 0.41 g L?1 in the first set of experiments. Cell concentration was changed between 0.5 and 5 g L?1 in the second set of experiments while the wheat powder concentration was constant at 5 g L?1 with a D/L ratio of 1/7. The highest cumulative hydrogen (135 ml)and formation rate (3.44 ml H2 h?1)were obtained with the 20 g L?1 wheat powder concentration. However, the highest yield (63.9 ml g?1 starch)was obtained with the 2.5 g L?1 wheat powder. In variable cell concentration experiments, the highest cumulative hydrogen (118 ml)and yield (156.8 ml H2 g?1 starch)were obtained with 1.1 g L?1 cell concentration yielding an optimal biomass/substrate ratio of 0.22 g cells/g WP.