Prehydrolysis of Eucalyptus globulus Labill. hemicelluloses prior to pulping and fermentation of the hydrolysates with the yeast Pichia stipitis 10th EWLP, Stockholm, Sweden, August 25–28, 2008

The aim of this work was to evaluate the potential of Eucalyptus globulus hemicelluloses, mainly xylan, for bioethanol production. Hemicelluloses have been removed prior to pulping by auto-hydrolysis and an acid-catalysed hydrolysis. As the hydrolysates obtained were rich in xylose, the yeast Pichia stipitis was selected for fermentation. It was confirmed that the yeast performance is strongly dependent on pH and the presence of inhibitors, such as lignin. The addition of Ca(OH)2 was successful for lowering the concentration of inhibitors and adjusting the pH. The strain was grown in culture media with increasing volumetric percentages of treated hydrolysates up to 100% (v/v), supplemented with nutrients other than the carbon and energy source. This methodology shortened the lag phase of fermentation and improved the performance of yeast. Maximum ethanol concentration (12 geth l-1), productivity (0.22 geth l-1 h-1), and yield (0.48 geth gxyl eqs -1) were achieved with treated acid-hydrolysates. These results are similar to those obtained by a synthetic medium with an equivalent xylose concentration.