In an integrated biorefinery approach, aspen wood is being converted concurrently to ethanol and pulp for papermaking. Prior to pulping, a portion of the hemicellulose was extracted from aspen wood chips by hot water pretreatment (150°C, 4.5 hours). The resulting hemicellulose extract was acid hydrolyzed to monomeric sugars and then adjusted to pH 7 by addition of calcium hydroxide. The resulting sugar solution (27g/L xylose, 1 g/L glucose, 0.5 g/L arabinose) was then used for fermentation without further detoxification steps. The fermentations were conducted in batch with Escherichia coli FBR5 at cell densities between 2.1 g/L and 44 g/L cell dry weight. At the highest cell density, all sugars were consumed within 80 minutes resulting in 11.1 g/L ethanol, corresponding to a yield of 0.4g ethanol/g total sugar. The volumetric ethanol production rate was 7.2g/L*h. These results were used as the basis for designing a continuous fermenter with membrane-assisted cell recycle. Data on the performance of this continuous reactor will also be presented.