Bioconversion of different paper sludge to ethanol by yeast using separate hydrolysis and fermentation

The objective of the present work was to evaluate the possibility of converting three different kinds of paper sludge (PS) into ethanol using xylose-fermenting yeast SHY07-1 and common yeast SHY08-3 in separate hydrolysis and fermentation (SHF). Effects of pH, temperature and enzyme loading on saccharification of different PS were investigated and the enzymatic hydrolysis performance of chemical pulping PS was superior to that of deinking PS. The hydrolysate produced from enzymatically-digested PS (on a consistency of 6% (w/v, expressed in terms of total carbohydrate mass)) was fermented by yeast without prior detoxification and nutrient supplementation. A final ethanol concentration of 34.72 and 29.29 g/L was achieved by SHY07-1 and SHY08-3 separately, corresponding to an ethanol yield of 0.42 and 0.41 g/g with a fermentation efficiency of 80.84% and 68.18%. The results indicate that PS can be enzymatically hydrolyzed without pretreatment and the hydrolysate can be fermented efficiently to ethanol by using xylose-fermenting yeast SHY07-1.