Successful conversion of corn stover into microbial lipids at high solids loading by Rhodosporidium toruloides at pilot scale

Lignocellulosic biomass (LCB) offers potential feedstocks for biofuels. As it generally involves processes including pretreatment, hydrolysis, and fermentation, LCB-based biorefinery at higher solids loading may improve substrate concentration and reduce operational costs, yet its scaling-up remains a challenge. Here, efficient conversion of corn stover (CS) at high solids loading into microbial lipids was demonstrated in a 1 000 L pilot-scale bioreactor using Rhodosporidium toruloides CGMCC 2.1389. The process employed lab-optimized conditions, including alkaline storage pretreatment of CS (AS-CS) with 6% NaOH for over 60 d at room temperature. The AS-CS (100 kg) was steamed in the 1000 L bioreactor at 121 °C for 1 h at a solids loading of 20%, followed by subsequent removal of alkaline black liquor (ABL) using squeeze technology. The leftover residues were hydrolysed by enzymes with a total reducing sugar (TRS) recovery of 93.6%. The lipid production in the 1 000 L bioreactor resulted in a lipid titer of 10.6 g/L and a yield of 0.194 g/g (based on consumed TRS). The mass flow analysis suggested that 89.6% of cellulose and 95.5% of hemicelluloses were released to produce lipids with little lignin by-products, avoiding their toxic effects on lipid production. The developed process in this work offers a promising avenue for industrial conversion of LCB into microbial lipids.