With the 1990s concerns about the “greenhouse effect”, interest in $H_2$ has increased as a promising alternative to fossil fuel because it is a clean and environmentally friendly fuel with high energy yield. This work aimed to investigate the effect of gas sparging on continuous $H_2$ fermentative production. Continuous-flow stirred-tank reactors (CSTR) were operated using different sparging gases (internal biogas, $CO_2$ and $N_2$) at various flow rates (100, 200, 300 and 400 ml/min).
External gas sparging showed more stable and higher $H_2$ production than internal biogas sparging or without sparging over the operation period. It suggested that the decrease of $H_2$ partial pressure by external gas sparging had a beneficial effect on $H_2$ fermentation. Especially, in spite of low glucose removal and biomass concentration, $CO_2$ sparging showed better performance than $N_2$ sparging, accompanied by high composition of butyrate which was the main metabolic product of $H_2$ fermentation by Clostridium sp. The best performance was obtained by $CO_2$ sparging at 300 ml/min, resulting in the highest $H_2$ yield of 1.68 mol $H_2/mol$ hexoseconsumed which were higher than reported values.
These results suggested that high partial pressure of $CO_2$ had little effect on $H_2$ -producing bacteria but inhibitory effect on other microorganisms like lactic acid bacteria and acetogens which were competitive with $H_2$ -producing bacteria.