Effects of seed sludge on fermentative characteristics and microbial community structures in thermophilic hydrogen fermentation of starch

In this work, effects of seed sludge on thermophilic hydrogen fermentation were investigated. Five different kinds of sludge were separately inoculated in completely stirred tank reactors (CSTRs), without any pretreatment. The reactors were operated in parallel with starch as substrate under thermophilic condition (55 °C) at a hydraulic retention time (HRT) of 24 h for 50 days. Stable hydrogen production was achieved in all reactors. The highest hydrogen yield (2.32 mol H2/mol glucose) was obtained from the reactor seeded with thermophilically digested activated sludge. The stoichiometric equation of hydrogen fermentation calculated using the data obtained in this study was expressed as follows: starch ([C6H10O5]n) → 2.32n H2 + 2.14n CO2 + 0.50n acetate + 0.63n butyrate + 0.11n cell (C5H7NO2). Microbial community structure was analyzed by polymerase chain reaction–denaturing gel gradient electrophoresis (PCR–DGGE) and 16S rRNA gene cloning. Close relatives of the Thermoanaerobacterium were found to be the most predominated one in all reactors.