ASABE Technical Library - Abstract

Abstract. The main problem of hydrogen production via anaerobic formation is the very low production rate due to severe hydrogen-consuming reaction. Hydrogen partial pressure is a major factor influencing reactions of hydrogen production and consumption. To study it, H₂ was mixed with N₂ to sparge the fermentation broth with initial concentrations of 20%, 40%, 60%, 80% and 100%. The results showed that H₂ concentration can change the pathway of glucose degradation. With increasing H₂ concentration in sparging gas, the pathway transfered from propionic acid (HPr) and butyric acid (HBu) production to HPr production. When the H₂ concentration was 20% and the N₂ concentration was 80%, the production rates of HPr and HBu were the highest, which were 0.76, 0.41 mmol/mmol glucose _consumed·d, respectively, and accounted for 100% of total soluble metabolic products. When the H₂ concentration in sparging gas was more than 40%, production rates of HPr and HBu decreased and glucose degradation was inhibited. In addition, due to HPr type fermentation and high hydrogen partial pressure, acetogenesis were not feasible thermodynamically, resulting in low production rate of H₂ during the whole fermentation process. When the initial H₂ concentration in sparging gas was 40%, the production rate of the H₂ was the highest, which was 0.42 mol/mol glucose _consumed.d. The theoretical production rate of H₂ calculated by the productions of soluble metabolic products was less than the actual value. It resulted from the co-existence of thomoacetogenesis and acetic acid oxidation due to the bidirectionality of homoacetogens, establishing a new symbiotic relationship.