Enhanced Thermophilic Hydrogen Production by an Enriched Novel Acetic-Acid-Type Fermentative Bacterium from Inoculum Sludge with Nonheat Pretreatment

Biological hydrogen production from renewable biomass based on anaerobic dark fermentation is an environmentally friendly process. However, the hydrogen production efficiency was not ideal and the start-up time was always long for dark fermentation systems, which limits the development of biohydrogen production. In this study, a novel mild preculture method which regulates substrate concentration without controlling pH was used to enhance hydrogen production efficiency and accelerate the start-up process under thermophilic conditions. We regulated the substrate concentration from 2000 to 8000 mg COD/L without controlling the pH and performed a nonheat pretreatment (>90 degrees C) of inoculum sludge at 55 degrees C using an SBR anaerobic reactor. The reaction process of hydrogen production was divided into eight stages according to different COD concentrations. The experimental results indicated that the reactor quickly became stable on the 12th day, while the maximum hydrogen yield of 3.68 mol of H-2/mol of glucose was obtained in the fifth stage, with the optimal COD of 5500 mg/L, and the maximum COD removal efficiency of 39.61% was achieved in the fourth stage, with a COD of 5000 mg/L. Microorganism community structure analysis showed that Thermoanaerobacterium was the dominant species throughout the process of hydrogen production. In particular, a novel hydrogen-producing bacterium of acetic-acid-type fermentation, Thermoanaerobacterium thermosaccharolyticum strain CT72, was successfully enriched and exhibited excellent capacity for hydrogen production under thermophilic conditions.