초록
<P><B>Abstract</B></P> <P>Immobilized cell hollow fiber membrane bioreactor (ICHFMB) was designed and operated to mitigate the effect of lignocellulose derived inhibitors during fermentation of synthetic lignocellulosic hydrolysate by <I>Zymomonas mobilis</I>. The individual inhibitors – vanillin, syringaldehyde, 5-hydroxymethylfurfural and 4-hydroxy-3-methoxycinnamaldehyde, exhibited toxicity on suspended cells, whereas simultaneous exposure to multiple inhibitors was detrimental for the cells. In contrast, the immobilized cells showed excellent growth and glucose uptake in the presence of these inhibitors, and the microorganisms achieved 95% of the theoretical ethanol yield under highly inhibitory conditions. ICHFMB performance could be improved significantly by increasing the flow rate of the hydrolysate over the membranes, and by increasing the number of membranes, indicating that diffusion through the membranes was an important factor during the fermentation. <I>Z. mobilis</I> showed gradual acclimatization to the presence of inhibitors as they were slowly released from the membrane pores into suspension, and enhanced glucose uptake rate and ethanol productivity. Cell immobilization within the membranes was also found to be very stable as the ICHFMB performance did not deteriorate during 20 consecutive runs under identical conditions. These results indicate that ICHFMB can be promising in lignocellulosic bioethanol production under inhibitory conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> <I>Zymomonas mobilis</I> was immobilized in macroporous hollow fiber membranes. </LI> <LI> Immobilized cells showed excellent tolerance to lignocellulose-derived inhibitors. </LI> <LI> Sorption of inhibitors on membranes reduced their effective concentrations. </LI> <LI> Cells achieved 95% theoretical ethanol yield under inhibitory conditions. </LI> <LI> Cell immobilization was stable under 20 consecutive batch runs over 10 days. </LI> </UL> </P>