title: Recirculation of process streams in fuel ethanol production from softwood based on simultaneous saccharification and fermentation.
abstract: The effect of process stream recirculation on ethanol production from steam- pretreated softwood based on simultaneous saccharification and fermentation (SSF) was investigated for two process configurations. In the first configuration, a part of the stillage stream after distillation was recycled and, in the second configuration, the liquid after SSF was recycled. The aim was to minimize the energy consumption in the distillation of the fermentation broth and in the evaporation of the stillage, as well as the use of fresh water. However, recirculation leads to an increased concentration of nonvolatiles in the first configuration, and of both volatiles and nonvolatiles in the second configuration. These substances might be inhibitory to the enzymes and the yeast in SSF. When 60% of the fresh water was replaced by stillage, the ethanol yield and the productivity were the same as for the configuration without recirculation. The ethanol production cost was reduced by 17%. In the second configuration, up to 40% of the fresh water could be replaced without affecting the final ethanol yield, although the initial ethanol productivity decreased. The ethanol production cost was reduced by 12%. At higher degrees of recirculation, fermentation was clearly inhibited, resulting in a decrease in ethanol yield while hydrolysis seemed unaffected.
authors.affiliation: Department of Chemical Engineering, Lund University, Sweden.
authors.forename: Malek
authors.initials: M
authors.lastname: Alkasrawi
authors.forename: Mats
authors.initials: M
authors.lastname: Galbe
authors.forename: Guido
authors.initials: G
authors.lastname: Zacchi
mesh_terms: D001709:Biotechnology / Q000295:instrumentation / Q000379:methods; D050260:Carbohydrate Metabolism; D002482:Cellulose / Q000378:metabolism; D003470:Culture Media; D000431:Ethanol / Q000302:isolation & purification / Q000378:metabolism*; D005285:Fermentation; D005579:Fossil Fuels; D005618:Fresh Water; D007202:Indicators and Reagents; D007700:Kinetics; D008031:Lignin / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000254:growth & development; D013458:Sulfur Dioxide; D014934:Wood
chemical_list: D003470:Culture Media; D005579:Fossil Fuels; D007202:Indicators and Reagents; D013458:Sulfur Dioxide; D000431:Ethanol; D002482:Cellulose; D008031:Lignin