Impact of electrochemical reducing power on homoacetogenesis.

Homoacetogenesis was performed in a microbial electrosynthesis single-chamber reactor at open and closed circuits modes. The aim is to investigate how an applied reducing power affects acetic acid synthesis and H gas-liquid mass transfer. At a cathode voltage of -175 mV vs. Ag/AgCl (3.0 NaCl), the acetic acid synthesis rate ramped up to 0.225 mmol Lh due to additional electrons and protons liberation from carbon-free sources such as water and ammonium via anodic oxidation. The study sets a new lowest benchmark that acetic acid can be bioelectrochemical synthesized at - 175 mV. The applied reducing power did not increase the H gas-liquid mass transfer because the direct electron transfer from cathode to microorganisms reduced the demand for H in the fermentation medium. Microbial analysis shows a high presence of Veillonellaceae spore-forming clostridia, which are identified as homoacetogens.