Continuous ethanol production by yeast immobilized on to channeled alumina beads

Abstract

Vertical and near-horizontal (15° angle) packed-bed columns were compared for continuous ethanol fermentation using an alcohol- and glucose-tolerant Saccharomyces cerevisiae strain immobilized on to channeled alumina beads (5·0 × 10 9 cells g −1 beads). Spaces between beads (1·0–6·5 mm) and angle (15°) of near-horizontal reactor columns (with six ports in each) efficiently removed CO 2 and increased ethanol productivity. Malt-glucose-yeast-extract broth containing 16·7% glucose at 35°C fed at a dilution rate of 3· h −1 to thw two horizontal columns (in series) yielded maximum ethanol productivity of 40·0 g liter −1 h −1. Feedstock flow rate and other factors (temperature, pH, nutrients, and glucose levels) affected productivities. The immobilized-cell system showed operational stability for >3 months without plugging, and could be stored for at least one year with no loss of bioreactor performance. Scanning electron micrographs of the beads revealed large numbers of yeast-cells attached on to internal and external surfaces of beads.