Inhibitory effect of acetic acid on dark-fermentative hydrogen production

This study examined the working mechanisms of acetic acid inhibition on dark fermentative hydrogen production. It was found that undissociated acetic acid (UAA) concentration was the critical factor in acetic acid inhibition. Hydrogen production activity decreased by 50 % and 90 % when UAA concentrations was 76.3 mg/L (1.27 mmol/L) and 686.7 mg/L (11.44 mmol/L), respectively. Dominant microbes were changed from genus Clostridium_sensu_stricto_1 to genus Inhella, Aquabacterium and Caulobacter under the stress of acetic acid inhibition. Functional enzyme analysis showed that acetic acid inhibited the hydrogen production by activating the lactate formation pathway when UAA concentration was below the inhibition threshold, while by impairing most hydrogen-producing pathways when UAA concentration was over the inhibition threshold. In brief, acetic acid inhibited the hydrogen production by altering the dominant microbial community and regulating the metabolic pathways, controlling the UAA concentration would be a good strategy to alleviate the acetic acid inhibition.