Continuous ethanol production from molasses at 45°C using alginate-immobilized Kluyveromyces marxianus IMB3 in a continuous-flow bioreactor

The thermotolerant, ethanol-producing yeast strain Kluyveromyces marxianus IMB3 was immobilized in calcium alginate and used in a continuous flow bioreactor to produce ethanol from molasses at 45 degrees C. The molasses was diluted to yield a number of final sugar concentrations and the effect of molasses sugar concentration on ethanol production by the continuous system was examined. Although maximum ethanol concentrations were obtained using sugar concentrations of 140 g/l, within 10 h of introducing the feed to the column bioreactors, those ethanol concentrations subsequently decreased to lower levels over a 48 h period. Examination of viable yeast cell number within the immobilization matrix indicated a dramatic reduction over this time period. At lower molasses concentrations, ethanol production by the continuous flow system remained relatively constant over this time period. In addition, the effect of residence time on ethanol production by the continuous flow bioreactor was examined at a fixed molasses sugar concentration (120 g/l) and a residence time of 0.66 h was found to be optimal on the basis of volumetric productivity. Efficiencies of the continuous flow bioreactor configuration used in these studies ranged from 31-76%.