Simultaneous hydrogen and ethanol production from a mixture of glucose and xylose using extreme thermophiles II: Effect of hydraulic retention time

In this study, biofuels (hydrogen and ethanol) fermentation from glucose and xylose by extreme thermophiles in an Up-flow Anaerobic Sludge Bed (UASB) reactor was successfully demonstrated. Autoclaved methanogenic granules were used as carriers for the extreme thermophiles. High yields of hydrogen and ethanol were achieved at various HRTs from 24 h to 6 h. The highest hydrogen production rate of 121 ± 23 mL/(L h) and highest ethanol production rate of 6.7 ± 1.2 mmol/(L h) were observed at HRT = 12 h. The highest simultaneous hydrogen and ethanol yields were 0.58 ± 0.11 mol H2/(mol hexose) and 0.72 ± 0.13 mol ethanol/(mol hexose), reaching a total energy yield of 1151 kJ/mol hexose. The substrate conversion efficiency was maintained over 90% at three HRTs (24, 18, and 12 h).