Microbial production of a biofuel (acetone-butanol-ethanol) in a continuous bioreactor: impact of bleed and simultaneous product removal.

Acetone butanol ethanol (ABE) was produced in an integrated continuous one-stage fermentation and gas stripping product recovery system using Clostridium beijerinckii BA101 and fermentation gases (CO(2) and H(2)). In this system, the bioreactor was fed with a concentrated sugar solution (250-500 g L(-1) glucose). The bioreactor was bled semi-continuously to avoid accumulation of inhibitory chemicals and products. The continuous system was operated for 504 h (21 days) after which the fermentation was intentionally terminated. The bioreactor produced 461.3 g ABE from 1,125.0 g total sugar in 1 L culture volume as compared to a control batch process in which 18.4 g ABE was produced from 47.3 g sugar. These results demonstrate that ABE fermentation can be operated in an integrated continuous one-stage fermentation and product recovery system for a long period of time, if butanol and other microbial metabolites in the bioreactor are kept below threshold of toxicity.