Effect of hydraulic retention time on the hydrogen yield and population of Clostridium in hydrogen fermentation of glucose

The conversion of glucose to hydrogen was evaluated using continuous stirred tank reactor at pH 5.5 with various hydraulic retention times (HRT) at 30°C. Furthermore, the population dynamics of hydrogen-producing bacteria was surveyed by fluorescence in-situ hybridization using probe Clost IV targeting the genus Clostridium based on 16S rRNA. It was clear that positive correlation was observed between the cells quantified with probe Clost IV and hydrogen yield of the respective sludge. The numbers of hydrogen-producing bacteria were decreased gradually with increasing HRT, were 9.2 × 108, 8.2 × 108, 2.8 × 108, and 6.2 × 107 cell/mL at HRT 6, 8, 12, and 14 h, respectively. The hydrogen yield was 1.4–1.5 mol H2/mol glucose at the optimum HRT range 6–8 h. It is considered that the percentage of the hydrogen-producing bacteria to total bacteria is useful parameter for evaluation of hydrogen production process.