Improving the dissolved oxygen level in high solids loading cellulosic sugar acids fermentation by restructuring the biorefinery chain

Abstract

Industrial production of biochemicals and biofuels from lignocellulose feedstock frequently requires aerobic fermentation with high dissolved oxygen demand. Efficient oxygen transfer from the air phase to the liquid phase has been considered as a great challenge due to the high viscosity and solid particles derived from the high solids loading lignocellulosic slurry. Here we presented a solution for aerobic sugar acids (gluconic acid and xylonic acid) fermentation by Gluconobacter oxydans in 30% (w/w) solids loading corn stover hydrolysate without solid/liquid separation. The biorefinery chain was restructured by conducting enzymatic hydrolysis before the submerged biodetoxification instead of solid-state biodetoxification. The viscosity of corn stover slurry decreased to ∼0.03 Pa·s after submerged biodetoxification and the gas-liquid oxygen transfer coefficient (kLa) reached 50.0 at the aeration rate of 0.1 vvm and agitation rate of 500 rpm, which is more efficient for sugar acids conversion than that using solid-state biodetoxified corn stover hydrolysate (only 8.8 kLa at 2.4 vvm, 500 rpm). The cellulosic sugar acids titer reached 156.0 ± 6.9 g/L at 0.1 vvm with 92.9% of the theoretical yield in the restructured biorefinery chain. The techno-economic analysis showed that the minimum selling prices of sugar acids produced by this restructured biorefinery chain was $351.7/ton which was 12.9% lower than that produced by the general biorefinery chain. This efficient process setting including one-pot hydrolysis, submerged biodetoxification, and fermentation provides a practical technical route for lignocellulose-based aerobic fermentation under high solids loading.