Optimizing Inoculation Conditions for a Two-Strain Fermentation of H2 Production

In order to improve the H2-production of Bacillus cereus (B. cereus) and Brevundimonas naejangsanensis (B. naejangsanensis) by dark fermentation and provide the preferred inoculation conditions for better understanding the process of a co-culture fermentative hydrogen production by both strains, initial inoculation conditions for the single fermentation of both strains were optimized. Results showed that the preferred initial inoculation conditions are 15 h (4.62 × 106 CFU/mL) and 96 h (5.00 × 107 CFU/mL). At the end of fermentation, the highest H2 yield is 1.93 mol H2/mol glucose consumed and 1.98 mol H2/mol glucose consumed, respectively. The corresponding substrate consumption rates are 62.64% and 53.25%. Results also showed that inoculated seed liquid in the early stage of the deceleration growth phase has the capacity of both the effective utilization of starch and production of hydrogen for B. cereus, and that in the late stage of the deceleration growth phase has the similar effect for B. naejangsanensis. The time required to decompose starch to soluble sugar of B. cereus is faster 24 h than that of B. naejangsanensis. When metabolic pathway shifted to produce lactic and propionic acid, hydrogen production decreased, elevated acetic and butyric acid concentrations correlated with higher hydrogen production. Butyric acid-type fermentation is dominating during the fermentation process of both strains. B. cereus demonstrated superior performance for starch-based hydrogen production.