EFFECT OF SUGAR CONSUMPTION ON ETHANOL FERMENTATION IN A TOWER FERMENTER PACKED WITH SELF-AGGREGATING YEAST - MATHEMATICAL-MODELING AND BEDHEIGHT PREDICTION

A strain of self-aggregating Saccharomyces uvarum was cultivated in a 6-L tower fermentor for continuous ethanol fermentation. Large aggrega tes (2-3 mm) were formed and packed in the column. The height of this packed region depends on the sugar concentration. As sugar concentrati ons were reduced to below a critical value, most of the large aggregat es disintegrated into smaller aggregates (0.1-0.2 mm). Above the packe d bed region, small aggregates and small amount of large aggregates we re fluidized and formed a well mixed region by the liquid medium and t he produced carbon dioxide. A mathematical model of a plug flow with c onsideration of axial dispersion and a Continuous Stirred Tank Reactor (CSTR) in series is proposed to describe such fermentor. The concentr ation profile of sugar can be simulated by this model. The height of t he packed bed region can then be estimated based on the predetermined critical sugar concentration. Final ethanol concentration and the prod uctivity of such fermentor can also be predicted.