Impact of gas diffusion electrodes (GDEs) was evaluated in enhancing the CO2bio-availability for its transformation to C4-organics, especially to alcohols using selective mixed culture.
Observed current density was more stable (9–11 A/m2) than submerged experiments reported and significantly varied with pH and respective CO2 solubility. Uncontrolled operating pH (starting with 8.0) showed its impact on shifting/triggering alternate metabolic pathways to increase the carbon length (butyric acid) as well as producing more reduced end products, i.e. alcohols. During the experiments, CO2 was transformed initially to a mixture of volatile fatty acids dominated with formic and acetic acids, and upon their accumulation, ethanol and butanol production was triggered. Overall, 21 g/l of alcohols and 13 g/l of organic acids were accumulated in 90 days with a coulombic efficiency (CE) of 49%.
Ethanol and butanol occupied respectively about 45% and 16% of total products, indicating larger potential of this technology.