Selective removal of acetic acid from hardwood-spent sulfite liquor using a mutant yeast

The hexoses in spent sulfite liquor can be converted to ethanol by yeasts, but conversion to ethanol of the pentose D-xylose in lignocellulosic hydrolysates is inhibited generally by the presence of acetic acid. The feasibility of a yeast-based process for selective removal of the acetic acid in hardwood-spent sulfite liquor was demonstrated The process depends on the use of a mutant of Saccharomyces cerevisiae that grows on acetic acid but not on D-xylose, D-glucose, D-mannose, or p-fructose. The process could be used to decrease the concentration of acetic acid in hardwood liquor within 24 h to levels that no longer inhibit bioconversion of xylose to ethanol. Indications of the conversion of D-xylose to ethanol in the acetic acid-depleted liquor rt ere the ability of several D-xylose-fermenting yeasts to use essentially all of the sugars and produce as much as 73% of the theoretical amount of ethanol within 24 h. The process might be generally applicable to obviation of acetic acid inhibition effects in ethanol production from hemicellulose hydrolysates.