Bioproducts from sulfite pulping : Bioconversion of sugar streams from pulp , sludge , and spent sulfite liquor

The production of singleand mixed-sugar streams and their conversion to bioproducts were studied using sulfite pulping streams as feedstocks. Sulfite pulp, sludge, and spent sulfite liquor (SSL) were utilized because they are concurrently generated alongside of bleached pulp, and because the pulping process renders pretreatment unnecessary. SSL, comprised of mostly monomeric hexose and pentose sugars, was directly fermented to ethanol and xylitol with Candida guilliermondii. Single-sugar streams were generated through hydrolysis of pulp and sludge in buffered water, followed by fermentation to ethanol with Saccharomyces cerevisiae. Mixed-sugar streams were generated through both SHF and SSF of pulp and sludge in SSL using S. cerevisiae. Direct fermentation of SSL to ethanol and xylitol produced yields consistent with that of a synthetic sugar control (89.5%, 40.3%, respectively). The best utilization of pulp was determined to be as a single-sugar stream, derived from SHF in water, which yielded a cellulose to ethanol conversion of 62.2% of the theoretical maximum (28.3 g/L). Sludge produced the highest yield when mixed with SSL during SSF (50.0%, 23.7 g/L). Sulfite pulp, sludge, and SSL currently represent untapped industrial resources for the production of singleand mixed-sugar streams from which high-value bioproducts can be made.