Valorization of Sugar-Ethanol Industry Waste Vinasse for Increased Second-Generation Ethanol Production Using Spathaspora passalidarum Yeast Strains

Abstract

In this study, sugarcane bagasse hydrolysate supplemented with different proportions of sugar-ethanol industrial waste (vinasse) was used to optimize fermentative ethanol production using two Spathaspora passalidarum yeast strains isolated from decaying wood in Amazonian biome. The bagasse samples were pretreated chemically and enzymatically before using a binary factorial experimental design. The factorial design was carried out in two stages; in the first, a 24 factorial design was done to assess the effects of pretreated sugarcane bagasse hydrolysate and vinasse, ammonium sulfate concentration, yeast biomass concentration, and two different strains of yeast, S. passalidarum; in the second stage, a 23 factorial design was done to provide a more detailed analysis of the effects of vinasse supplementation on the fermentation process—this time, by modifying the ratio of sugarcane bagasse hydrolysate and vinasse and, more significantly, the same factor—biomass concentration. The results showed that the most significant factors for increasing bioethanol production in the 24 factorial design proved to be the following: inoculum and hydrolyzed bagasse supplementation with vinasse (the optimal being 75:25), followed by yeast concentration (optimal at 14% w/v cell wet weight) and then the type of strain used (S. passalidarum UFMG-HMD-14.1). The use of only hydrolyzed bagasse without vinasse (23 factorial design) had no significant influence on the results, nor did varying the concentration of nitrogen. This increase in ethanol production, which allows the same amount of ethanol productivity through a reduction in the carbon source, suggests it can lead to an improved final use for vinasse.