Effect of substrate concentration on fermentative hydrogen production from sweet sorghum extract

The present study focuses on the influence of substrate concentration on the fermentative hydrogen production from the sugars of sweet sorghum extract, in a continuous stirred tank bioreactor. The reactor was operated at a Hydraulic Retention Time of 12 h and substrate concentrations ranging from 9895 to 20990 mg/L, in glucose equivalents. The maximum hydrogen production rate and yield were obtained at the concentration of 17000 mg carbohydrates/L and were 2.93 ± 0.09 L H2 /L reactor /d and 0.74 ± 0.02 mol H2 / mol glucose consumed or 8.81 ± 0.02 LH2 / kg sweet sorghum, respectively. The main metabolic product at all steady states was butyric acid while ethanol production was high at high substrate
concentrations. The experiments showed that the hydrogen productivity depends significantly on the initial carbohydrates concentration which also influences the distribution of the metabolic products.