Effect of oxygen on ethanol fermentation in packed-bed tapered-column reactor

Summary In ethanol production with immobilized yeast a major problem is the provision of nutrients to these highly concentrated cells. O₂ being one of the nutrients of utmost importance to yeast cells, was fed into a column packed with beads with a cell loading of more than 40 g/l. Since addition of large volume of air or O₂ to a cylindrical column reactor would aggravate the problems of pressure build up and channelling caused by the evolving CO₂ gas, a tapered-column reactor and pulsed flow of oxygen gas was used. The supplement of O₂ gas to the tapered column increased the productivity from 21.1 g ethanol x (l gel x h)^-1 to 26.7 g x (l gel x h)^-1, when the ethanol concentration at the outlet was about 80 g/l. The yield coefficient of ethanol was also increased from 0.41 g ethanol/g glucose to 0.43 after O₂ supplement was started. The effects of frequency and duration of O₂ supplement were also determined.