D-xylulose fermentation by free and immobilized Saccharomyces cerevisiae cells

D-xylulose fermentation by free Saccharomyces cerevisiae cells in batch fermentation and by alginate entrapped cells in continuous fermentation was studied. At high cell densities volumetric ethanol productivities of 0.18 and 0.27 gl^-1h^-1 were obtained by free and immobilized cells, respectively, under anaerobic conditions. This productivity could not, however, be maintained continuously due to the death of cells. The anaerobic columns stabilized at a productivity level of 0.15 gl^-1 h^-1 and the aerobic column at 0.25 gl^-1h^-1.