Enhancing butanol production by Clostridium beijerinckii through cathodic electrofermentation approach

Biobutanol, produced by solventogenic bacteria like Clostridium beijerinckii through acetone, butanol, and ethanol (ABE) fermentation, is a promising green alternative to fossil fuels. However, this ABE fermentation suffers drawbacks, such as a relatively low productivity that limits its industrial deployment. Electro-fermentation (EF) can modify the intracellular ratio of oxidized nicotinamide adenine dinucleotide to reduced nicotinamide (NAD⁺/NADH), a critical factor for butanol synthesis by C. beijerinckii, thus allowing higher product titers (or productivity) to be reached. RESULTS: The present study focuses on glucose-based ABE-EF at laboratory-scale. Three replicate EF reactors (300 mL) were constructed and used to grow C. beijerinckii. Different cathode materials were electrochemically characterized and tested. The effect of voltage application on process productivity was assessed by performing chronoamperometry tests at constant cathode potential (E_cat), ranging from −0,7 to −1,0 V vs Ag/AgCl. These trials were compared with a benchmark ABE fermentation that was performed without voltage application. Poising E_cat at −0,8 V vs Ag/AgCl resulted in the optimal EF scenario. In these conditions, the specific growth rate of bacteria was 73% higher than the benchmark ABE fermentation, with a productivity of 125,6 mg-butanol/L/h, a process yield of 0,15 g-butanol/g-glucose, and a selectivity for butanol of 87% (34%, 25%, and 11% higher than the benchmark fermentation, respectively). The addition of 0,5 mM neutral red as redox mediator in the broth led to a further improvement of butanol productivity (152,9 mg L h⁻¹), requiring a very low energy consumption of 0,02 kWh/kg-butanol to run the EF process. CONCLUSION: Applying EF enhances the ABE fermentation in terms of butanol production, selectivity, and energy consumption.