title: Use of dynamic step response for control of fed-batch conversion of lignocellulosic hydrolyzates to ethanol.
abstract: Optimization of fed-batch conversion of lignocellulosic hydrolyzates by the yeast Saccharomyces cerevisiae was studied. The feed rate was controlled using a step response strategy, in which the carbon dioxide evolution rate was used as input variable. The performance of the control strategy was examined using both an untreated and a detoxified dilute acid hydrolyzate, and the performance was compared to that obtained with a synthetic medium. In batch cultivation of the untreated hydrolyzate, only 23% of the hexose sugars were assimilated. However, by using the feed-back controlled fed-batch technique, it was possible to obtain complete conversion of the hexose sugars. Furthermore, the maximal specific ethanol productivity (q(E,max)) increased more than 10-fold, from 0.06 to 0.70 g g(-1) h(-1). In addition, the viability of the yeast cells decreased by more than 99% in batch cultivation, whereas a viability of more than 40% could be maintained during fed-batch cultivation. In contrast to untreated hydrolyzate, it was possible to convert the sugars in the detoxified hydrolyzate also in batch cultivation. However, a 50% higher specific ethanol productivity was obtained using fed-batch cultivation. During batch cultivation of both untreated and detoxified hydrolyzate a gradual decrease in specific ethanol productivity was observed. This decrease could largely be avoided in fed-batch cultivations.
authors.affiliation: Department of Chemical Engineering II, Lund University of Technology, P.O. Box 124, SE-22100 Lund, Sweden. anneli.nilsson@chemeng.lth.se
authors.forename: A
authors.initials: A
authors.lastname: Nilsson
authors.forename: M J
authors.initials: MJ
authors.lastname: Taherzadeh
authors.forename: G
authors.initials: G
authors.lastname: Lidén
mesh_terms: D002482:Cellulose / Q000378:metabolism*; D003470:Culture Media; D000431:Ethanol / Q000378:metabolism*; D006868:Hydrolysis; D008031:Lignin / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*
chemical_list: D003470:Culture Media; C036909:lignocellulose; D000431:Ethanol; D002482:Cellulose; D008031:Lignin