Thermophilic dark fermentation fast start-up of hydrogen production with substrate concentration regulation and moderate pretreatment inoculum

Abstract

Accelerating start-up of thermophilic dark fermentation would improve hydrogen production efficiency was investigated. To find an efficient method for accelerating start-up and explore the effect of inoculum type for hydrogen production system, three thermophilic hydrogen production EGSB (expanded granular sludge bed) reactors equipped with flocculent or granular sludge using different startup modes were constructed in this study. Among three reactors under butyric acid type of fermentation, EGSB3 (startup mode: pretreated granular sludge as inoculum and regulated substrate concentration) was the most efficient one with shortest start-up time (13 days) and maximum hydrogen production (1.64 mol H2/mol glucose). EGSB1 (startup mode: pretreated flocculent sludge as inoculum and regulated substrate concentration) was started up in 27 days at 1.27 mol H2/mol glucose in maximum. While EGSB2 (startup mode: original granular sludge as inoculum and without regulating substrate concentration) took 46 days for start-up and the 1.6 mol H2/mol glucose hydrogen producing rate was obtained. After start-up, the dominant hydrogen production bacteria were Thermoanaerobacterium thermosaccharolyticum strain TG57 in three reactors. EGSB3 reactor owned the most proportion with 53.21 % than others. In all, mild pretreatment and regulating substrate concentration for granular sludge would be benefit for fast startup of thermophilic dark fermentation hydrogen production leading to shortest startup time, high hydrogen production efficiency and most functional microorganism.