Effect of gas sparging on continuous fermentative hydrogen production

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 CO2 with various flow rates (100, 200, 300 and 400 ml/min). The sparging with external gases of N-2 and CO2 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, CO2 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 CO2 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 CO2 sparging apart from lowering H-2 partial pressure. High CO2 partial pressure had little effect on H-2-produrcing 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 CO2 sparging conditions based on 16S rDNA analysis by PCR-DGGE. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.