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 h1, indicating pH control was critical to this experiment. Subsequently, continuous
culture with cell recycling increased cell concentration to 17.4 g L1, which increased butanol productivity
to 1.20 g L1 h1 at a dilution rate of 0.26 h1 from 0.529 g L1 h1 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 L1 h1) was observed at a dilution rate of 0.78 h1, approximately
6-fold higher than observed in continuous culture without cell recycling (0.529 g L1 h1).