Energy security, environmental concerns, and business opportunities in the emerging bio-economy have generated strong interest in the production of n-butanol by fermentation. The acetone butanol ethanol (ABE or solvent) batch fermentation process is product limiting because butanol, even at low concentrations, inhibits the growth of fermenting microorganisms resulting in (i) low ABE yield, usually 0.33, (ii) use of dilute sugar solutions as substrates, (iii) low concentration of butanol in the bioreactor, (iv) energy intensive recovery of butanol due to low concentration in the fermentation broth, and (v) generation of large effluent streams. Indeed, the inhibitory property of butanol largely accounts for the long batch fermentation time (60-72 h) thus resulting in low ABE productivity. The cumulative effects of these factors hamper the energy efficient production of butanol and hence scale-up and commercialization. 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