4. Conclusions
Continuous fermentation with the asporogenous C. acetobutylicumATCC55025 immobilized in a fibrous bed bioreactor was studied forn -butanol production from glucose and butyric acid. At a high dilution rate of 1.88 h-1, butanol production at a high productivity of 16.8 g/L∙h, more than 80 times of that in batch free-cell fermentation, was obtained. Although butyric acid strongly inhibited cell growth, butyric acid added in the feed medium helped maintain stable butanol production and improved butanol yield from glucose by ~20%. The risk of contamination by commensal bacteria was reduced by butyric acid and butanol, allowing the continuous process to operate for an extended period over 30 days.