Fermentative High-Titer Ethanol Production from Douglas-Fir Forest Residue Without Detoxification Using SPORL: High SO2 Loading at Low Temperature

Abstract

Abstract This study evaluated high sulfur dioxide (SO2) loading in applying Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL) to Douglas-fir forest residue (FS-10) for ethanol production through yeast fermentation. Three pretreatments were conducted at 140°C with a targeted total SO2 loading of 32 wt% on wood, or 80 g/L in the pretreatment liquor. Magnesium was used as the metal base with a targeted combined SO2 loading of 4.4 wt% on wood. A pretreatment duration of approximately 60 min was found sufficient to effectively remove the strong recalcitrance of FS-10 with ultra-low degradation of sugar to furans. Pretreatment mixing was performed through either a rotating digester or liquor circulation, and was found to have no significant effect on pretreatment performance. The ultra-low furan formation facilitated enzymatic saccharification and fermentation at total solids loading of 20% without detoxification. At cellulase loading of 35 mL/kg FS-10, a maximal ethanol yield of 322...