Co-optimization of sugar yield and input energy by the stepwise reduction of agitation rate during lignocellulose hydrolysis

• The effect of agitation on enzymatic hydrolysis of corncob was investigated.
• Cellulase was obviously deactivated under high agitation rate.
• A control strategy with stepwise reduction in agitation rates was proposed.
• Optimal strategy yields more glucose than most of continuous agitation.

To ensure effective enzyme transfer and energy saving, the mixing control is a key issue for efficient hydrolysis of lignocellulose at high solid loading. The effect of agitation on enzymatic hydrolysis of pretreated corncob was investigated in this work. Cellulase was obviously deactivated under the agitated condition in the absence of substrate. Increasing from 0 rpm to 150 rpm, high agitation rates increased initial hydrolysis rates and final sugar concentration. However, the excessively high agitation rate at 200 rpm had a significant negative effect on hydrolysis efficiency at the solid loadings from 2% to 15%. Rapid mixing was required only to promote cellulase diffusion within the first 6 h of hydrolysis; afterwards, a smaller mixing energy was required to maintain high hydrolysis efficiency. Based on the hydrolysis rates at different agitation rates, a control strategy with stepwise reduction in agitation rates was proposed. After 72 h of hydrolysis, the glucose yield (54.92 g/L) using the optimal strategy approached that using high-rate continuous agitation (57.34 g/L) at a solid loading of 10% and was greater than those using low-rate continuous agitation. Thus, the stepwise reduction of agitation rate could be beneficial because it could save energy while producing a high sugar concentration, especially for a high solid loading reaction system.