Continuous ethanol fermentation with cell recycling using flocculating yeast

Abstract

Flocculating yeast IR-2 was isolated from a fermented food of Indonesia. In addition to the flocculation activity, the fermentation activity of the yeast was excellent compared to several other flocculating strains. Continuous ethanol fermentation with cell recycling was done using a system of two tower fermentors and one setler, and high productivities were obtained with a model medium of sugar-cane juice, i.e., with the total sugar (T.S.) 12.5% medium, 34.6 g/l.h for 54.8 g-ethanol/l and with the T.S. 15.1% medium, 28.6 g/l.h for 67.7 g-ethanol/l were obtained. Aeration of the culture increased the ethanol productivity greatly. Using the T.S. 18.1% medium with aeration, 26.3 g/l.h for 80.4 g-ethanol/l was achieved. In each case, the conversion ratio of fermentable sugar was higher than 98% and the ethanol yield was about 90% or more. The flocculation activity of the cells was stable through the 80 days of the experimental period of continuous fermentation under various conditions. Those productivities were evaluated as 6 to 8 times that of the conventional batch fermentation process with cell re-use (Melle-Boinot process), which is widely employed in Brazil.