Bioethanol Production from Glycerol by Mixed Culture System

Abstract

Glycerol, a by-product from biodiesel industry, is a promising feedstock for subsequent bioconversion to higher-value products. Potential application of a mixed microbial consortium on the fermentative conversion of glycerol to ethanol was demonstrated in this study. Maximum ethanol concentration of 11.1 g l-1 was produced after 72 h fermentation from the initial pure glycerol concentration of 45 g l-1, at 30 ̊C, and pH 7 under anaerobic conditions, corresponding to the ethanol production rate and yield of 0.34 g l-1 h-1, and 0.81 mol ethanolmol-1 glycerol, respectively. The microbial consortium yielded lower ethanol concentration (6.5 g l-1) but similar ethanol yield (0.85 mol ethanol mol-1 glycerol) when crude glycerol of 45 g l-1 was fermented at the same condition. At the optimum fermentative condition of the pure glycerol, phylogenetic analysis of microbial consortium based on 16S rRNA gene sequences indicated that Gammaproteobacteria represented 95% of the microbial diversity in the consortium while the rest belonged to Betaproteobacteria. The consortium was dominated by bacteria closely related to genera Enterobacter and Klebsiella, which could play the role on conversion of glycerol to ethanol in this system.