초록
<P><B>Abstract</B></P> <P>Continuous removal of ethanol during production by the anaerobic bacterium <I>Zymomonas mobilis</I> mitigated ethanol inhibition. Ethanol inhibited its own production at a concentration of >20gL<SUP>−1</SUP>. Ethanol productivity was enhanced by continuous <I>in situ</I> extraction with water-immiscible organic solvents. Several solvents were evaluated for biocompatibility with <I>Z. mobilis</I> and the ability to extract ethanol from a batch fermentation. <I>In situ</I> batch extractive fermentations were carried out in a 2-L stirred bioreactor (1:1 volume ratio of solvent and fermentation broth) with an optimal glucose concentration of 150gL<SUP>−1</SUP>, 35°C, and an agitation speed of 150rpm. Oleyl alcohol, iso-octadecanol and 2-octyl-1-dodecanol were the three solvents that were most compatible with <I>Z. mobilis</I>. With these solvents, the cell viability relative to control (no solvent) was 1.48±0.40, 1.03±0.18 and 1.05±0.07, respectively, after two days of exposure. All solvents tested improved the final biomass concentration, the glucose consumption and ethanol production relative to control, but iso-octadecanol was clearly the most effective solvent. Using iso-octadecanol, the maximum ethanol concentration of 75±3gL<SUP>−1</SUP> was attained. This was nearly 1.25-fold that of the control fermentation. For this solvent, the ethanol yield on glucose was 0.485±0.005gg<SUP>−1</SUP> compared to a yield of 0.468±0.005gg<SUP>−1</SUP> for the control culture.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An extractive fermentation enhanced the productivity of bioethanol. </LI> <LI> Continuous extraction of ethanol reduced its inhibitory effect. </LI> <LI> Suitable nontoxic extraction solvents were identified. </LI> <LI> Kinetics of the conventional and the extractive fermentations were compared. </LI> <LI> A high-gravity operation was used to reduce the size of the fermenter. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>