(467a) Ethanol Production by Bioconversion of Softwood Prehydrolysates Supplemented with Pulp Mill Sludges

Eighty percent of the hemicellulose fraction of pulp mill feedstock is released into black liquor during kraft pulping process. In pulping process, the black liquor is burned to recover chemicals and generate steam and electricity. It is technically feasible to remove part of the hemicellulose before pulping keeping the quality of pulp unaffected. The hemicellulose portion of the pulp mill feedstock can be selectively converted to soluble sugars (termed as prehydrolysate) by water or mild acid hydrolysis. The prehydrolysate thus prepared contain pentose, hexose, and their oligomers. In this study, bioconversion of the prehydrolysate to ethanol was investigated using Saccharomyces cerevisiae. The prehydrolysate produced from wood also contain toxins, primarily organic acid, lignin and sugar degradation products. These toxins strongly inhibit microbial action. The prehydrolysate was therefore detoxified by over-liming and by addition of peroxide. The detoxified prehydroysate was further treated with pectinase to hydrolyze the mannose oligomers to monomer. After these treatments, the hysrolyzate was efficiently converted to ethanol. Use of mixture of prehydrolysate and pulp mill sludge as the fermentation feed has given significant increase of the ethanol concentration in the bioreactor over that of prehydrolysate fermentation.