Simultaneous production of high-concentration sugar and purity lignin from wheat straw via ball-milling assisted DES pretreatment for high-loading enzymatic hydrolysis

The challenge in lignocellulose valorization is achieving high-concentrated sugar with low enzyme input while concurrently obtaining high-value lignin. To address this, we developed a green pretreatment strategy using ball-milling assisted deep eutectic solvent (composed of choline chloride, ethylene glycol, and oxalic acid) on wheat straw. Under optimized pretreatment conditions (110 °C, 1:10 (m/v), 2.5 h), 82% lignin and 99% hemicellulose were removed. Glucose concentration reached 220 g/L after 120 h of enzymatic hydrolysis with 10 FPU/g cellulase and 2.5% PEG 6000, which was 7.3% higher than the result obtained without PEG 6000. This is one of the highest glucose concentrations reported for fed-batch enzymatic hydrolysis at such low enzyme loading (10 FPU/g). This high glucose concentration resulted from substrate modifications (reduced hydrophobicity, enhanced specific surface area, and exposure of more reducing ends) that created optimal attack sites for cellulase. The fed-batch strategy further improved hydrolysis efficiency by increasing free water and restricting cellulase adsorption by lignin. Meanwhile, lignin with high purity (97.6%) and uniform molecular weight was obtained. Unlike most existing pretreatment strategies that prioritize either sugar yield or lignin quality, this study achieved the co-production of high-concentration sugar and high-purity lignin, thereby advancing a sustainable biorefinery for lignocellulose valorization.