Monday, May 5, 2008
7-25

SSCF of Paper Sludge Using Recombinant Xylose-Fermenting Microbes

Jiayi Zhang, Dartmouth College, 8000 Cummings Hall, Hanover, NH 03755 and Lee R. Lynd, Thayer School of Engineering, Dartmouth College, 8000 Cummings Hall, Hanover, NH 03755.

 As a cellulosic waste that in many cases does not require pretreatment, paper sludge is a potentially attractive commercial substrate as well as a model substrate for the investigation of simultaneous saccharification and co-fermentation (SSCF) featuring cellulose hydrolysis, hemicellulose hydrolysis, and fermentation of resulting sugars in an a single process step. Two recombinant xylose-utilizing strains, Zymomonas mobilis 8b and Saccharomyces cerevisiae RWB222, were studied for performance in paper sludge SSCF with a commercial Trichoderma reesei cellulase preparation under conditions producing > 40 g/L ethanol. Substrate conversion, ethanol production, and cell viability were evaluated, and the role of ethanol inhibition, mass transfer limitation, and inhibition by compounds present in paper sludge was investigated.  Formation of ethyl b-xylopyranoside, a previously-unreported byproduct, was observed in substantial amounts (corresponding to approximately 25% of hemicellulose hydrolyzed) during paper sludge SSCF. A comprehensive mathematic model was developed for SSCF, the first such model known to us.  Model validation data and use of the model for hypothesis testing will be presented, and overall conclusions about paper sludge conversion and SSCF will be drawn. 

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