Biohydrogen production from rice straw hydrolyzate in a continuously external circulating bioreactor

The average hydrogen production rates (HPR) of 5.52 L/L/d (hydrogen molar yield: 0.72 mol H2/mol hexose) and 16.32 L/L/d (hydrogen molar yield: 1.02 mol H2/mol hexose) were obtained at hydraulic retention time (HRT) 8 and 4 h respectively. The value of hydrogen production rate at HRT 4 h was three times more than that at HRT 8 h. The presence of bacteria Clostridium favors the hydrogen production from the acetic acid and butyric acid metabolic pathways which were determined by DGGE analysis. The biomass could not be maintained in the CECBR by washing out of the bacteria when the feeding rate was lowered to HRT 2 h. This phenomenon resulted in less hydrogen production and ineffective degradation of hydrolyzate. But the continuously external circulating bioreactor could be steady operated at HRT 4 h with an impressive hydrogen production rate by a rice straw hydrolyzate.