Sodium (Na+) concentration effects on metabolic pathway and estimation of ATP use in dark fermentation hydrogen production through stoichiometric analysis

Abstract Batch experiments were conducted to investigate the effects of Na + concentration on hydrogen production with dark fermentation. The Na + concentration was varied from 0 to 8 g/L in the mixed culture using an anaerobic sludge treated by acid. The maximum hydrogen production was achieved with 1 g-Na + /L, whereas the hydrogen production was decreased over 2 g-Na + /L due to the inhibitory of Na + . The mechanisms of Na + inhibition to the hydrogen production are studied using pure culture of Clostridium butyricum by calculating the energy balance. At a high sodium concentration, C. butyricum used a greater proportion of the ATP generated via fermentation for cell maintenance rather than for cell synthesis. Additionally, higher Na + concentrations shifted the fermentation process toward the acetate synthesis pathway instead of the butyrate pathway, and the value of Y X/ATP decreased. With high Na + concentrations, a greater ratio of hydrogen was produced via the oxidation of NADH. Excess hydrogen production decreased as the Na + concentration increased.