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

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 0.26 h−1, indicating pH control was critical to this experiment. Subsequently, continuous culture with cell recycling increased cell concentration to 17.4 g L−1, which increased butanol productivity to 1.20 g L−1 h−1 at a dilution rate of 0.26 h−1 from 0.529 g L−1 h−1 without cell recycling. The effect of dilution rates on butanol production was also investigated in continuous culture with cell recycling. Maximum butanol productivity (3.32 g L−1 h−1) was observed at a dilution rate of 0.78 h−1, approximately 6-fold higher than observed in continuous culture without cell recycling (0.529 g L−1 h−1).