Effect of the accuracy of pH control on hydrogen fermentation

pH, known as the most important parameter in H-2 fermentation, cannot be precisely controlled in a scaled-up fermenter as in a lab fermenter. In the preset work, to assess the effect of pH control accuracy on H-2 fermentation, the pH was controlled at 6.0 +/- 0.1, 6.0 +/- 0.3, 6.0 +/- 0.5, 6.0 +/- 0.7, and 6.0 +/- 0.9 during batch fermentation of food waste. Up to deviation of +/- 0.3, a high H-2 yield of 1.67-1.73 mol H-2/mol hexose(added) was attained with producing butyrate as a major metabolite (>70% of total organic acids produced). A huge drop of H-2 production, however, was observed at deviation >+/- 0.5 with lowered substrate utilization and increased production of lactate. Next generation sequencing results showed that Clostridium was found to be the dominant genus (76.4% of total number of sequences) at deviation of +/- 0.1, whereas the dominant genus was changed to lactic acid bacteria such as Streptococcus and Lactobacillus with increase of deviation value. (C) 2014 Elsevier Ltd. All rights reserved.