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).
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