Oxygen Transfer in High Solids Loading and Highly Viscous Lignocellulose Hydrolysates

High product concentration in aerobic biorefining fermentation requires high lignocellulose feedstock loading. However, the high solids content and the consequent high viscosity of the lignocellulose hydrolysate severely limit oxygen transfer and thus lead to low aerobic fermentation rate. This study first investigates the experimental measurement and the computational fluid dynamics (CFD)-based simulation of oxygen transfer properties in the high solids loading and highly viscous lignocellulose hydrolysates. The oxygen mass transfer coefficients kLa values vary with various biorefining processing parameters. A minimum threshold kLa value was required for aerobic fermentation of glucose oxidation into gluconic acid. The rheological properties of the slurry were experimentally determined, and a CFD model was established for the design of aerobic fermentation bioreactors. The kLa values between the CFD calculation and the experimental determination were in good agreement for the high solids loading and highly viscous hydrolysate slurry. The study provided important information and useful tools for achieving efficient aerobic fermentations in high solids loading and highly viscous lignocellulose hydrolysates. The measured kLa value could be applied to general aerobic fermentation using lignocellulose feedstock.