Fermentation of liquefacted hydrothermally pretreated sweet sorghum bagasse to ethanol at high-solids content.

The ability of sweet sorghum bagasse to be utilized as feedstock for ethanol production at high initial dry matter concentration was investigated. In order to achieve high enzymatic hydrolysis yield, a hydrothermal pretreatment prior to liquefaction and saccharification was applied. Response surface methodology had been employed in order to optimize the pretreatment step, taking into account the yield of cellulose hydrolysis. Liquefaction of the pretreated bagasse was performed at a specially designed liquefaction chamber at 50 °C for either 12 or 24h using an enzyme loading of 10 FPU/g · DM and 18% DM. Fermentation of liquefacted bagasse was not affected by liquefaction duration and leaded to an ethanol production of 41.43 g/L and a volumetric productivity of 1.88 g/Lh. The addition of extra enzymes at the start up of SSF enhanced both ethanol concentration and volumetric productivity by 16% and 17% after 12 and 24h saccharification, respectively.