The Influence of Hydrogen Concentration in Sparging Gas on Hydrogen Production and Consumption via Anaerobic Fermentation

Abstract

Abstract. The main problem of hydrogen production via anaerobic fermentation is the very low production rate due to severe hydrogen-consuming reactions. Hydrogen partial pressure is a major factor influencing reactions of hydrogen production and consumption. To study the influence of H2 concentration on hydrogen production and consumption, H2 was mixed with N2 at initial concentrations of 20%, 40%, 60%, 80%, and 100% to sparge the fermentation broth. The results showed that H2 concentration had significant influence on these reactions, changing the pathway of glucose hydrolysis and acidification. With increasing H2 concentration in the sparging gas, the pathway of glucose acidogenesis hydrolysis transferred from mixed acid production (propionic acid and butyric acid) to propionic acid production. When the H2 concentration was 20% and the N2 concentration was 80%, the production rates of propionic acid and butyric acid were highest (0.76 and 0.41 mmol mmol-1 glucose consumed d-1, respectively) and accounted for 100% of total soluble metabolic products. When the H2 concentration in the sparging gas was more than 40%, the production rates of propionic acid and butyric acid decreased, and glucose degradation was inhibited. In addition, due to propionic acid type fermentation and high hydrogen partial pressure, acetogenesis was not feasible thermodynamically, resulting in a low production rate of H2 during the whole fermentation process. When the initial H2 concentration in the sparging gas was 40%, the production rate of H2 was highest, (0.42 mol mol-1 glucose consumed d-1). In addition, the theoretical production rate of H2 calculated from the production of soluble metabolic products was less than the actual value. This resulted from the co-existence of homoacetogenesis and acetic acid oxidation due to the bidirectionality of homoacetogens, establishing a new symbiotic relationship. Keywords: Anaerobic fermentation, Hydrogen consumption, Hydrogen partial pressure, Hydrogen production, Sparging.