Bioconversion of paper sludge with low cellulosic content to ethanol by separate hydrolysis and fermentation

Abstract

The purpose of the present work was to evaluate the possibility of converting paper sludge into ethanol using xylose-fermenting yeast SHY07-1 in separate hydrolysis and fermentation. In the enzymatic hydrolysis step, sludge on 2% (w/v, expressed in terms of total carbohydrate mass) substrate consistency was incubated with the filter-sterilized enzyme solutions (Celluclast 1.5 L on a dosage of 15 FPU/g cellulose and Novozyme™188 on a dosage of 30 CBU/g cellulose) without any pretreatment, and a total degree of saccharification of 99.65% was achieved under certain conditions. The hydrolysate produced from enzymatically-digested paper sludge (on a consistency of 2% (w/v, expressed in terms of total carbohydrate mass) was fermented by yeast SHY07-1 without prior detoxification and nutrient supplementation, and xylose was consumed well. A final ethanol concentration of 14.18 g/L was achieved, corresponding to an ethanol yield of 0.49 g/g with a fermentation efficiency of 97.68%. The results indicate that paper sludge can be enzymatically hydrolyzed with high degree of saccharification and the hydrolysate can be fermented efficiently to ethanol by using xylose-fermenting yeast SHY07-1. Key words : Paper sludge, separate hydrolysis and fermentation, ethanol, cellulase.