Increasing ethanol productivity during xylose fermentation by cell recycling of recombinant Saccharomyces cerevisiae

The influence of cell recycling of xylose-fermenting Saccharomycescerevisiae TMB3001 was investigated during continuous cultivation on a xylose-glucose mixture. By using cell recycling at the dilution rate (D) of 0.05 h–1, the cell-mass concentration could be increased from 2.2 g l–1 to 22 g l–1. Consequently, the volumetric ethanol productivity increased ten-fold, from 0.5 g l–1 h–1 to 5.35 g l–1 h–1. By increasing the biomass concentration, the xylose consumption rate increased from 0.75 g xylose l–1 h–1 without recycling to 1.9 g l–1 h–1 with recycling. The specific ethanol productivity was in the range of 0.23–0.26 g g–1 h–1 with or without cell recycling, showing that an increased cell-mass concentration did not influence the efficiency of the yeast.