Compatibility of the flocculation of Saccharomyces uvarum and fermentation optimum conditions to improve ethanol production continuously using recycle tower bioreactor



Flocculation is an attractive feature of the yeast Saccharomyces uvarum. The usefulness of its application in the fermentation process comes from the simple separation technique of the yeast cells from the fermentation products. The benefit of the flocculation of S. uvarum is that it keeps the continuous fermentation of ethanol at a certain level as it maintains the yeast inside the bioreactor and prevents it from being washed out with the ethanol. The flocculation behavior of the yeast was studied during the production of ethanol from date syrup. Furthermore, the compatibility of the optimum conditions between flocculation and ethanol fermentation was studied. Three essential parameters were studied during the continuous ethanol production: fermentation temperature, date syrup concentration, and feeding flow rate. The statistical application of central composite design was used to identify the optimum conditions that maintain the flocculation between the yeast cells and prevent it from being washed out with the product. The minimum percentage of washout yeast from the bioreactor (9.15%) was carried out under the following conditions: a temperature of 20°C, an initial date syrup sugar concentration of 6.5% (w/v), and a feeding flow rate of 294 mL h−1. In line with the optimum conditions of the ethanol production, the conditions that gave the best ethanol productivity (7.57 g L−1 h−1) with a minimum washout yeast (19.6%) was found to be a fermentation temperature of 29°C, an initial date syrup sugar concentration of 5.5% (w/v) and a feeding flow rate of 294 mL h−1. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 308–314, 2014