Methods for mitigation of bio-oil extract toxicity

Levoglucosan (1,6-anhydro-β-d-glucopyranose) and other anhydrosugars can be produced in significant quantities during fast pyrolysis of lignocellulosic material. Levoglucosan can be extracted and hydrolyzed to produce fermentable glucose, however co-extraction of fermentation inhibitors can reduce ethanol yields. This work was aimed at evaluating various methods for mitigating the toxicity of bio-oil aqueous extract. Among the detoxification techniques tested, it was found that overliming and solvent extraction were able to improve the fermentability of bio-oil hydrolyzates. Overliming was able to increase the yield of ethanol from bio-oil hydrolyzate by 0.19 ± 0.01 (g ethanol/g glucose) at 50% volume hydrolyzate and 0.45 ± 0.05 (g ethanol/g glucose) at 40% volume hydrolyzate. A number of extractants were examined and the best solvent was tri-n-octylamine with co-solvent 1-octanol. It was able to selectively (100% glucose retention) remove at least 90 ± 6.8% of acetic acid, which was the targeted inhibitor in bio-oil hydrolyzate. This increased the ethanol yield by 0.24 (g ethanol/g glucose) at 40% volume of hydrolyzate. In addition, a technique called adaptive evolution of yeasts was applied, which was capable of increasing the ethanol yield by up to 39% when compared with the unadapted parental strains.