Bioethanol production from Eucalyptus grandis using novel low-cost nutrient supplements in fermentation

Abstract

The conversion of Eucalyptus biomass to ethanol via fermentation is beset with challenges including efficient sugar utilisation, the presence of inhibitors, expensive nutrients, and low yields. To address some of these challenges, this study evaluated Thermosacc Dry® and GSF335 xylose recombinant yeast in fermentations using acid pretreated Eucalyptus grandis fibre and hydrolysates. These fermentations were supplemented with novel and low-cost nutrients. Contrary to previous reports, the inclusion of trace metals in saccharification and hydrolysis fermentations of whole slurries did not eliminate the inhibitory effects of acetic acid. Elevated levels of xylitol and acetic acid suggested a redirection of carbon flux to redress redox imbalances in both yeast types. Using GSF335 propagated in xylose-enriched liquors, and Nutri-Plex Plus™, diammonium phosphate, or crude dried spent yeast as nitrogen sources, saccharification and hydrolysis fermentations produced ethanol yields ranging from 141.4 to 145.6 kg t−1 dry weight E.grandis. Inclusion of yeast hulls and trace metals in simultaneous saccharification and fermentations yielded 175.6 kg ethanol t−1 dry weight E.grandis, corresponding to a 64.4% conversion efficiency. Results from this study support the use of novel low-cost waste by-products as nutrient supplements in bioethanol production from Eucalyptus biomass. Furthermore, they have implications for the production of bioethanol from other lignocellulosic materials and warrant further investigation.