SUPPRESSION OF HYDROGEN CONSUMING BACTERIA IN ANAEROBIC HYDROGEN FERMENTATION

Severe loss or hydrogen occurred in most anaerobic hydrogen fermentation reactors. Several selected methods were applied to suppress the consumption of hydrogen and increase the potential of production. As the first trial, pH shock was applied. The pH of reactor was dropped nearly to 3.0 by stopping alkalinity supply and on]y feeding glucose (5 g/L-d). As the pH was increase to $4.8{\pm}0.2,$ the degradation pathway was derived to solventogenesis resulting in disappearance of hydrogen in the headspace. In the aspect of bacterial community, methanogens weren't detected after 22 and 35 day, respectively. Even though, however, there was no methanogenic bacterium detected with fluorescence in-situ hybridization (FISH) method, hydrogen loss still occurred in the reactor showing a continuous increase of acetate when the pH was increased to $5.5{\pm}0.2$. This result was suggesting the possibility of the survival of spore fanning acetogenic bacteria enduring the severely acidic pH. As an alternative and additive method, nitrate was added in a batch experiment. It resulted in the increase of maximum hydrogen fraction from 29 (blank) to 61 % $(500\;mg\;NO_3/L)$. However, unfortunately, the loss of hydrogen occurred right after the depletion of nitrate by denitrification. In order to prevent the loss entangled with acetate formation, $CO_2$ scavenging in the headspace was applied to the hydrogen fermentation with heat-treated sludge since it was the primer of acetogenesis. As the $CO_2$ scavenging was applied, the maximum fraction of hydrogen was enhanced from 68 % to 87 %. And the loss of hydrogen could be protected effectively.