Enhanced butanol production by modulation of electron flow in Clostridium acetobutylicum B3 immobilized by surface adsorption

► NAD(P)H that had escaped from the fermentation as H2 limited the butanol yield. ► NAD(P)H regulation in C. acetobutylicum B3 by methyl viologen increased the butanol yield by 37.8%. ► C. acetobutylicum B3 cells were immobilized on a cotton towel by surface adsorption. ► The butanol tolerance of the immobilized cells was significantly improved. ► An average of 15.6 g/L butanol was achieved within 12 h in repeated batch fermentation.