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[Display omitted] • A novel MV-mediated CEF system is proposed for efficient butanol production. • Methyl viologen supplement inhibits H 2 formation and enhances butanol production. • Exogenous butyric acid enhances butanol production in the MV-mediated CEF system. • Butanol selectivity from co-substrates of glucose and butyric acid achieves 90.44%. Butanol production by solventogenic Clostridia shows great potential to combat the energy crisis, but is still challenged by low butanol selectivity and high downstream cost. In this study, a novel cathodic electro-fermentation (CEF) system mediated by methyl viologen (MV) was proposed and sequentially optimized to obtain highly selective butanol production. Under the optimal conditions (−0.60 V cathode potential, 0.50 mM MV, 30 g/L glucose), 7.17 ± 0.55 g/L butanol production were achieved with the yield of 0.32 ± 0.02 g/g. With the supplement of 4 g/L butyric acid as co-substrate, butanol production further improved to 13.14 ± 1.14 g/L with butanol yield and selectivity as high as 0.43 ± 0.01 g/g and 90.44 ± 1.66%, respectively. The polarized electrode enabled the unbalanced fermentation towards butanol formation and MV further inhibited hydrogen production, both of which contributed to the high-level butanol production and selectivity. The MV-mediated CEF system is a promising approach for cost-effective bio-butanol production. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel NR-mediated CEF system of Clostridium beijerinckii was constructed. • The enhanced H 2 yield of 206.53 mL/g was 71.4% higher than the open circuit system. • The enhanced butanol yield of 0.30 g/g was 172.7% higher than the OC system. • The polarized electrode was responsible for the effective H 2 production. • The additional neutral red induced more carbon source and electrons to form butanol. To enhance the co-production of butanol and hydrogen by the acetone-butanol-ethanol (ABE) fermentation of Clostridium beijerinckii , a novel cathodic electro-fermentation (CEF) system was constructed with neutral red (NR) as electron mediator. With the mediation of NR, production of butanol and hydrogen from glucose in the CEF system achieved 5.49 ± 0.28 g/L and 3.74 ± 0.16 L/L, 569.5% and 325.0% higher than that in the open circuit (OC) system, respectively. The butanol and hydrogen yield of 0.30 ± 0.02 g/g and 206.53 ± 8.20 mL/g was 172.7% and 71.4% higher than that in the OC system, respectively. The effective co-production of butanol and hydrogen in the NR-mediated CEF system was attributed to the cooperation of the introduced polarized electrode and the additional NR. With the control of the polarized electrode, a feasible ORP was available for the effective hydrogen production. And the additional NR had induced more carbon source and electrons to the synthesis of butanol. [ABSTRACT FROM AUTHOR]