Continuous butanol fermentation from xylose with high cell density by cell recycling system

► pH was a significant factor in continuous fermentation of butanol. ► Butanol productivity were increased dramatically by cell recycling. ► Maximum butanol productivity was obtained at a dilution rate of 0.78h−1. A continuous butanol production system with high-density Clostridium saccharoperbutylacetonicum N1-4 generated by cell recycling was established to examine the characteristics of butanol fermentation from xylose. In continuous culture without cell recycling, cell washout was avoided by maintaining pH>5.6 at a dilution rate of 0.26h−1, indicating pH control was critical to this experiment. Subsequently, continuous culture with cell recycling increased cell concentration to 17.4gL−1, which increased butanol productivity to 1.20gL−1h−1 at a dilution rate of 0.26h−1 from 0.529gL−1h−1 without cell recycling. The effect of dilution rates on butanol production was also investigated in continuous culture with cell recycling. Maximum butanol productivity (3.32gL−1h−1) was observed at a dilution rate of 0.78h−1, approximately 6-fold higher than observed in continuous culture without cell recycling (0.529gL−1h−1).