Investigation of bioethanol production from grape pomace

In this study, bioethanol production from grape pomace has been studied by different yeast strains (Saccharomyces cerevisiae NRRL Y-12632 and Saccharomyces cerevisiae) in a batch system. The experimental studies consisted of three main stages: determination of some properties of grape pomace used, obtaining of hydrolysate with high reduced sugar by hydrolysis of grape pomace, and bioethanol production by fermentation. It has been determined that the grape pomace studied contains approximately 46 % holocellulose (cellulose+hemicellulose). Acidic hydrolysis method which is common for hydrolysis of lignocellulosic materials has been used. The hydrolysis conditions have been optimized by central composite design (CCD). Independent variables were solid (grape pomace) concentration, acid concentration, temperature, and hydrolysis time. Response variable was also reduced sugar concentration. Response surface method (RSM) experiments have been carried out in 250 ml volume of flasks with 50 ml working volume. The optimum conditions obtained from results of hydrolysis experiments of grape pomace have been determined temperature of 92,5 °C, solid concentration of 77,5 g/L, acid concentration 1,25 % (v/v), and time of 85 minutes. In these conditions, reduced sugar concentration obtained was 34,128 g/L. Fermentation studies have been performed in 250 ml volume of flasks with 50 ml working volume, under oxygen free media, at the temperature of 30 °C, 150 rpm, and in a batch rector. Both yeast strains studied have been grown in YPD nutrition media. The fermentation experiments carried out during the 72 h and the samples for sugar and alcohol analyses have been taken at specific time interval. Sugar and alcohol concentrations have been measured by DNS and gas chromatography (GC) technique, respectively. In the result of the fermentation carried out by Saccharomyces cerevisiae, typical theoretical yield values have been determined. The heights value of bioethanol yield obtained from grape pomace by Saccharomyces cerevisiae is 70 %. The value of bioethanol yield obtained from grape pomace with Saccharomyces cerevisiae NRRL Y-12632 is also 89 %. This result shows that Saccharomyces cerevisiae NRRL Y-12632 is more resistant to the inhibitory agents in the hydrolysate medium obtained from grape pomace by acidic hydrolysis method. Keywords: Bioethanol, Fermentation, Grape pomace, S. cerevisiae, S. cerevisiae NRRL Y-12632, Optimization.