Improvement of Ethanol Fermentation from Oligosaccharides in Spent Sulfite Liquor with Pichia stipitis by Combined Calcium Oxide and Ion Exchange Resin Treatments

The objective of this study was to develop an effective method for the removal of inhibitory compounds without decreasing oligosaccharides in spent sulfite liquor (SSL). The oligosaccharide fermentation was subsequently conducted by using Pichia stipitis, which is one of the feasible strains that can produce ethanol from oligosaccharides. The effect of inhibitory compounds on ethanol fermentation from cellobiose by P. stipitis was investigated. No ethanol was produced from cellobiose in the presence of more than 5 g/L of acetic acid. At 1 g/L of acetic acid, 2.6 g/L of ethanol was obtained after 40 h of fermentation. The removal of acetic acid in the SSL by the combined CaO and ion exchange resin treatments was also studied. The acetic acid concentration of softwood SSL was decreased from 5.2 to 0.9 g/L without decreasing oligosaccharides concentration by the combined method. Finally, the improvement of ethanol fermentation from oligosaccharides in the SSL by using the combined CaO and ion exchange resin treatments was studied. 1.3 g/L of ethanol was obtained from the SSL treated by the combined methods, while 6.5 g/L of total oligosaccharides were consumed. No ethanol was obtained from the untreated SSL.