Fed-batch strategies for saccharification of pilot-scale mild-acid and alkali pretreated sugarcane bagasse: Effects of solid loading and surfactant addition

High-solid enzymatic hydrolysis of lignocellulosic biomass is a key approach for high titer and reduced downstream costs in second generation ethanol production. Combining a pilot-scale (80 L reactor) mild acid pretreatment and an alkali pretreatment of sugarcane bagasse (SCB) with fed-batch strategies for high-solid enzymatic hydrolysis, more than 150 g/L of glucose was found in the hydrolysate. The best result of the fed-batch study (2.03 g/L/h of glucose productivity) was obtained with a total solids content of 27%w/w (being 20%w/w of solids added at 0 h), and the addition of the total amount of the non-ionic surfactant PEG 4000 and the enzymes solely at the beginning of the reaction. A semi-simultaneous saccharification and fermentation strategy of the pretreated SCB (with the yeast inoculum occurring after 12 h of a single hydrolysis stage at most proper conditions for the cellulases) resulted in 62 g/L of ethanol after 48 h, and a productivity of up to 6.6 g/L/h. The strategy here reported indicates that it is possible to achieve ethanol titers suitable for industrial distilleries avoiding mass transfer limitations that incur in operational problems during high-solid enzymatic hydrolysis.