Spent Yeast Valorisation as a Supplementation Source for Cellulosic Ethanol Fermentation
摘要
In the present work, pretreated Eucalyptus globulus bark was used as raw material for cellulosic ethanol production, and spent yeast was integrated as a supplementation source for the fermentation media. Several supplementation alternatives including the commercial yeast extract (YE) were evaluated. The spent yeast from the own cellulosic ethanol fermentation was assessed as a supplementation alternative and three methods were performed to produce laboratory yeast extract (labYE): (I) lysis by autoclave; (II) autolysis followed by heating; (III) plasmolysis. The 2.5 g L-1 labYE from method II combined with salts, proved to be an excellent supplementation source for fermentation media, providing a maximum ethanol concentration of about 48.7 g L -1, corresponding to productivity and conversion efficiency of about 2.03 g L -1 h -1 and 77.5%, respectively. This fermentation performance was similar to the attained, using 2.25 g L-1 of urea combined with 0.625 g L-1 of commercial YE, and also the 2.5 g L-1 Lipnus® 45 supplementation. In contrast, the supplement Fermaid® O redirected glucose consumption more towards biomass growth rather than ethanol production. Supplementation with 3.0 g L-1 of urea as the sole nitrogen source also significantly decreased conversion efficiency and productivity. The fermentation performance of labYE was also validated at the 5 L-bioreactor scale. The purpose of replacing a costly nitrogen source and maintaining an excellent fermentation performance by upgrading spent yeast represents new business opportunities for the cellulosic ethanol market after a good techno-economic assessment. This valorization pathway contributes to a growing responsible and sustainable industrialization according to the circular economy model.
Graphical Abstract