The Effects of Applied Potential and Carbon Donor on Succinic Acid Production via Electro-Fermentation

This study was conducted to understand how applied potential modulates metabolic flux toward succinic acid during xylose electro-fermentation by Actinobacillus succinogenes under varying feed concentrations (15, 20, 25 g/L). Electro-fermentations were conducted with applied potential at -1.5 V and -2.5 V and compared to open circuit control. Product distribution and carbon balance were quantified to assess the effect of potential on pathway routing. Results showed that applied potential consistently reduced formic acid and increased succinic acid selectivity. At 20 g/L xylose, the highest succinic acid yield was 0.80 mol/mol at -2.5 V, a 28.88% increase compared to that of the control (0.62 mol/mol). Formic acid and acetic acid yields were 0.73 and 0.60 mol/mol, representing a 48.83% and 16.09% reduction, respectively. The carbon allocation to succinic acid was 51% with a total carbon recovery of 81%. In addition, the effects of 10 g/L and 15 g/L NaHCO₃, as well as 10 g/L NaHCO₃ supplemented with gaseous CO_2, were evaluated at 15 g/L xylose and -2.5 V. Supplementation with gaseous CO₂ increased succinic acid yield from 0.74 to 0.85 mol/mol and improved total carbon recovery from 75% to 84%. Collectively, these findings show that applied potential, in combination with bicarbonate or CO₂ supply, can be strategically employed to improve succinic acid production.