high titer ethanol production from sporl-pretreated lodgepole pine by simultaneous enzymatic saccharification and combined fermentation

lodgepole wood chips were pretreated by sulfite pretreatment to overcome recalcitrance of lignocelluloses (sporl) at 25% solids loading and 180 °c for 20 min with sulfuric acid and sodium bisulfite charges of 2.2 and 8 wt/wt% on an oven-dry wood basis, respectively. the pretreated wood chips were disk-milled with pretreatment spent liquor and water, and the solid fraction was separated from the liquor stream. the liquor was neutralized and concentrated through vacuum evaporation. quasi-simultaneous enzymatic saccharification of the cellulosic solids and combined fermentation with the concentrated liquor was conducted at up to 20% total solids loading. fed-batching of the solids facilitated liquefaction and saccharification, as well as managing instantaneous inhibitor concentrations. at a commercial cellulase (ctec2) loading of only 9 fpu or 0.06 ml/g untreated wood, a maximum ethanol titer of 47.4 g/l was achieved, resulting in a calculated yield of 285 l/tonne of wood using saccharomyces cerevisiae yrh400 at 35 °c and ph 5.5.