Enhanced butanol production by coculture of Clostridium beijerinckii and Clostridium tyrobutyricum

•Free and immobilized-cell coculture greatly improved butanol productivity.•The highest ABE productivity was obtained in continuous immobilized-cell coculture.•This continuous coculture may be suitable for industrial ABE production. Cocultures of Clostridium beijerinckii and Clostridium tyrobutyricum in free-cell and immobilized-cell fermentation modes were investigated as a means of enhancing butanol production. The immobilized fermentation was performed in a fibrous-bed bioreactor (FBB). The results demonstrated that two-strain coculture significantly enhanced butanol production, yield and volumetric productivity compared with those in pure culture with or without butyric acid. Further, continuous immobilized-cell cocultures in two FBBs using glucose, cassava starch, or cane molasses were conducted at a dilution rate of 0.144h−1. The butanol production (6.66g/L), yield (0.18g/g), and productivity (0.96g/L/h) were obtained with cassava starch as the substrate. Meanwhile, the acetone–butanol–ethanol (ABE) yield (0.36g/g) was the highest among all processes investigated, suggesting that this continuous coculture mode may be suitable for industrial ABE production with no need for repeated sterilization and inoculation.