Evaporation

MELASAt the end of the fermentation stage, the resulting broth contains 5-6 % yeast biomass. The cells are separated by large scale continuous type separators and collected as yeast cream liquid, while the cells free fermentation broth is directed for evaporation. The cell free fermentation broth is preheated to about 90 oC by heat exchangers with the effluent and then sent to the evaporators. Here, the liquor is heated by live steam and fractionated to give about 60–55 % dry matter. The discharge from the evaporators is the vinasse. The condensed water from this stage is usually pumped back to the wastewater system. Economic considerations frequently suggest the simplest answers to the question of how to utilize vinasse produced, specifically as either fodder or fertilizer. Such uses, however, do not resolve the problem because of the large scale of yeast production. Molasses-based vinasse is characterized by high potassium content, and therefore limits its potential as farm animal fodder. Another use, particularly in the case of vinasse, consists in classifying stillage as wastewater and making it subject to anaerobic biodegradation. Vinasse contains many organic and mineral substances, including organic acids, reducing substances, glycerin and proteins. Beet molasses vinasse additionally contains betaine. The organic pollution load of beet molasses vinasse expressed as chemical oxygen demand is high and often exceeds 100 g O2/L. A recommended approach to the treatment of such effluents is to use aerobic biodegradation processes. However, the use of biodegradation for the treatment of fermentation wastewater is still subject to laboratory tests, and so far no studies on their industrial applications have been reported. The positive results of beet molasses vinasse biodegradation under aerobic mesophilic conditions encouraged our current research on the effect of aeration conditions and pH control on the progress and efficiency of biodegradation of the same stillage by a commercial mixed culture of microorganisms.