Hydrothermal Pretreatment Unlocks Waste Paper’s Sugar Potential: Enhanced Enzymatic Saccharification via Lignin Removal and Cellulose Decrystallization

Waste paper, with its high cellulose and hemicellulose content, represents a promising bioresource for producing fermentable sugars in biorefining processes. In this study, five types of waste paper were analyzed for cellulose content, and tissue paper (TP), exhibiting the highest cellulose content, was selected for hydrothermal pretreatment. Optimal pretreatment conditions were determined through single-factor experiments: 160 °C, water as the solvent, and a retention time of 50 min, corresponding to a severity factor (SF) of 3.47. Under these conditions, the reducing sugar yield from pretreated TP reached 0.61 g sugar/g paper, a 38.64% increase compared to untreated TP. The enhancement was attributed to lignin solubilization, disruption of crystalline cellulose regions, and increased specific surface area. These findings demonstrate the effectiveness of hydrothermal pretreatment in improving the enzymatic digestibility of waste paper for biorefining applications.