Bioethanol production from autohydrolyzed Eucalyptus globulus by Simultaneous Saccharification and Fermentation operating at high solids loading

Abstract

Eucalyptus globulus wood samples were subjected to non-isothermal autohydrolysis in order to solubilize hemicelluloses, leading to treated solids of increased cellulose content and enzyme digestibility. Autohydrolyzed solids obtained under a variety of operational conditions were assayed as substrates for bioethanol production by Simultaneous Saccharification and Fermentation (SSF). SSF was optimized using the Response Surface Methodology. The experimental plan included as independent variables the autohydrolysis severity (So defined as the logarithm of the severity factor), the liquor to solid ratio and the enzyme to substrate ratio. The dependent variables considered were the maximum ethanol concentration achieved in individual experiments, the volumetric productivity, the maximum ethanol conversion, the yield of solids after SSF and the cellulose recovery in solids coming from SSF. Operating at high solids loading (So=4.67, LSR=4g/g, ESR=16FPU/g), media containing up to 67.4g ethanol/L and corresponding to 91% of the stoichiometric amount calculated from the cellulose content of wood were obtained. Wood processing resulted in the generation of soluble products from hemicelluloses, in the generation of up to 291L ethanol/1000kg oven-dry wood from cellulose, and in a solid material mainly made up of lignin.