Monday, April 30, 2007

Pretreatment, hydrolysis and fermentation of brewer's spent grain

Kripa Rao, Sasidhar Varanasi, Dong-shik Kim, Constance Schall, and Anantha Ramprasad Dadi. Department of Chemical & Environmental Engineering, The University of Toledo, 3062 Nitschke Hall, 2801 West Bancroft Street, Toledo, OH 43606

Discharge of waste streams food related industries usually require further processing and the associated costs would reduce the profitability of these companies. Many food processing wastes form valuable low/no cost sources of lignocellulosic biomass. Producing fuels and chemicals from these waste streams has the potential to significantly improve the economies of these industries. Herein, we study the utilization of barley spent grains (BSG) from breweries for ethanol production.  In particular, we studied (1) pretreatment of BSG (a lignocellulose) by hydrothermal treatment to render the cellulos.e and hemicellulose portions more hydrolysable (2) saccharification of the treated BSG by latest generation of enzymes to render the polymeric sugars to monomeric sugars, and (3) fermentation of these monomeric hexoses and pentoses by yeast/bacteria for production of ethanol. Hydrothermal pretreatment is a facile technique capable of converting hemicellulose to soluble oligomers and for solubilizing lignin from biomass without using chemicals. Further, the physico-chemical nature of the biomass determines the optimal enzyme mix necessary to achieve maximal saccharification of cellulose and hemicellulose components.  We observe that for BSG the following combination of Genencore enzymes provides optimal hydrolysis:  Cellulase (GC 220), ß glucosidase (Novo 188), Multifect Xylanase, and Pectinase. Finally, we attempted fermentation of the saccharified mass with the microorganisms: Bakers Yeast (Saccharomyces Cervisiae), Pichia Stipitis (yeast for fermenting C5 sugars) and E Coli KO11 (a genetically modified E Coli capable of fermenting both C6 and C5 sugars). The result of all these experiments with BSG feedstock will be presented and discussed.