Enhanced ethanol fermentation in a pervaporation membrane bioreactor with the convenient permeate vapor recovery

• Continuous and complete coupling of ethanol fermentation and pervaporation.
• Second cell growth feature.
• Enhanced ethanol fermentation performance.
• Convenient permeate vapor recovery and refining without refrigeration unit.

A continuous and closed-circulating fermentation (CCCF) system with a pervaporation membrane bioreactor was built for ethanol fermentation without a refrigeration unit to condense the permeate vapor. Two runs of experiment with a feature of complete and continuous coupling of fermentation and pervaporation were carried out, lasting for 192 h and 264 h, respectively. The experimental measurement indicated that the enhanced fermentation could be achieved with additional advantages of convenient permeate recovery and energy saving of the process. During the second experiment, the average cell concentration, glucose consumption rate, ethanol productivity, ethanol yield and total ethanol amount produced reached 19.8 g L−1, 6.06 g L−1 h−1, 2.31 g L−1 h−1, 0.38, and 609.8 g L−1, respectively. During the continuous fermentation process, ethanol removal in situ promoted the cell second growth obviously, but the accumulation of the secondary metabolites in the broth became the main inhibitor against the cell growth and fermentation.