Roles of pH in biologic production of hydrogen and volatile fatty acids from glucose by enriched anaerobic cultures.

Batch experiments were carried out to study the roles of pH in the biologic production of hydrogen and volatile fatty acids from glucose by enriched anaerobic cultures. The results showed that 95-99% of glucose in wastewater was acidified at 30 degrees C and pH 4.0-8.5. Hydrogen yield fluctuated between 1.30 and 1.57 mol of H2/mol of glucose when the reactor was operated at pH 4.0-5.0. However, a further increase in pH led to a considerable decrease in hydrogen yield, especially for the cases at pH 7.5 and 8.0. Acetate, propionate, butyrate, and ethanol were the key products of acidogenesis. Production of butyrate was favored at pH 4.0-5.0, whereas production of acetate was favored at pH 6.0-8.0. A modified Gompertz equation is able to properly describe the batch production of hydrogen from glucose. The optimum pH for the specific hydrogen production was found to be 5.5, close to 5.7, the optimum pH calculated using a semiempirical model.