Effect of gas sparging on continuous fermentative hydrogen production

摘要

The effect of gas sparging on continuous fermentative H_2 production was investigated in completely stirred-tank reactors (CSTR) using internal biogas, N_2 and CO_2 with various flow rates (100, 200, 300 and 400 ml/min). The sparging with external gases of N_2 and CO_2 showed higher H_2 yield than the control of no sparging and internal biogas sparging. It indicated that the decrease of H_2 partial pressure by external gas sparging had a beneficial effect on H_2 fermentation. Especially, CO_2 sparging was more effective in the reactor performance than N_2 sparging, accompanied by higher production of H_2 and butyrate. The best performance was obtained by CO_2 sparging at 300 ml/min, resulting in the highest H_2 yield of 1.68 mol H_2/mol hexose_(consumed) and the maximum specific H_2 production rate of 6.89 L H_2/g VSS/day. Compared to N_2 sparging, there might be another positive effect in CO_2 sparging apart from lowering H_2 partial pressure. High CO_2 partial pressure had little effect on H_2-producing bacteria but inhibitory effect on other microorganisms such as acetogens and lactic acid bacteria which were competitive with H_2-producing bacteria. Only H_2-producng bacteria, such as Clostridium tyrobutyricum, C. proteolyticum and C. acidisoli were isolated under CO_2 sparging conditions based on 16S rDNA analysis by PCR-DGGE.