Optimization of 2G ethanol production from sugarcane bagasse: Upscaling of soda pretreatment with redox mediator followed by fed-batch enzymatic hydrolysis and co-fermentation

This study presents the upscaling of soda pretreatment of sugarcane bagasse (SB) using a new redox mediator (2-hydroxynaphthalene-1,4-dione) obtained from renewable resources, which does not affect enzymatic hydrolysis and fermentation. Upscaling was performed from a 0.5 L batch static stainless steel reactor to a 20 L pulp digester with forced liquor circulation, analogous to digestors used in the pulp and paper industry. Enzymatic hydrolysis of the pretreated material was optimized using the fed-batch method and was then carried out on a larger scale. The fed-batch method, combined with addition of 1 % (v v⁻¹) Tween 80, enabled the solids load to be increased from 10 % to 15 % (w v⁻¹), with an enzyme load of only 3.00 FPU g⁻¹. This led to a maximum total reducing sugars concentration of ∼142 g L⁻¹ after 72 h of hydrolysis. Co-fermentation of C5 and C6 sugar-rich hydrolysate by a consortium of CERLEV 47 (Saccharomyces cerevisiae) and CERLEV 1015 (Pichia guilliermondii) led to a maximum 2G ethanol production of 61.3 g L⁻¹ (308 L ethanol per ton of SB). Mass and energy balances demonstrated that the combustion of black liquor, a byproduct of the soda pretreatment, could satisfy the energy demands of the pretreatment, enzymatic hydrolysis, and fermentation, with an energy of 21.11 MJ using the surplus SB (80 %) from 1G ethanol production. This finding indicated that the developed process was robust and had the potential to enhance total 2G ethanol production. This study supports the feasibility of an integrated 1G/2G biorefinery by improving energy efficiency, economic viability, and environmental sustainability.