Short ozonation for effective removal and detoxification of fermentation inhibitors resulting from thermal pretreatment

Common pretreatment methods for bioethanol production from lignocellulosic biomass are carried out under acidic conditions at high temperatures and result in formation of by-products, such as formic acid, levulinic acid, furfural and HMF (5-hydroxymethylfurfural). These by-products have an inhibitory effect on yeasts, reducing yeast growth and fermentation, and thus ethanol production. In this study, the inhibitory dose of these by-products was investigated along with the use of short ozonation as a means of their detoxification. When the effect of ozone was tested directly on yeasts (without inhibitors), they exhibited tolerance to ozone, suggesting the utilization of ozonation in simultaneous saccharification and fermentation. Fifteen minutes of ozonation removed over 90% of the inhibitory effect originating from 50 mM furfural, 50 mM formic acid, 25 mM HMF, and 100 mM levulinic acid. Thermal pretreatment and enzymatic hydrolysis of pine sawdust resulted in inhibition of microaerobic yeast growth. This inhibition was relieved after short ozonation; however, continuous ozonation has motivated further inhibition, suggesting the formation of additional inhibitory compounds. The results demonstrate the applicability of short ozonation as a practical approach for removing by-products’ inhibitory effects originating from thermal pretreatment of lignocellulosic waste.