Optimization of Alkaline Pretreatment and Structural Insights for Converting Eucalyptus Sawdust and Sugarcane Bagasse into Cellulosic Sugars.

The efficient conversion of lignocellulosic biomass into fermentable sugars is critical for the sustainable production of biofuels and bioproducts. This study optimized mild alkaline pretreatment conditions for eucalyptus sawdust (ES) and sugarcane bagasse (SCB) using a Response Surface Methodology-Central Composite Rotational Design (RSM-CCRD). The effects of NaOH concentration, solid loading, temperature, and retention time on enzymatic hydrolysis efficiency were evaluated. Optimal pretreatment conditions (7.5% NaOH, 5% solid loading, 90 °C, 8 h) led to a tenfold increase in total reducing sugars (TRS) from ES (40.4 g/L) after 72 h, while SCB exhibited a higher hydrolysis efficiency (89.2%) and TRS (60.8 g/L) after enzymatic hydrolysis. Structural analyses using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) revealed enhanced cellulose accessibility and lignin modification in pretreated SCB, whereas ES remained more recalcitrant due to its higher lignin content. These findings demonstrate the effectiveness of mild alkaline pretreatment for SCB and highlight the need for more aggressive conditions to improve the digestibility of hardwood biomass. This study contributes to optimizing pretreatment strategies to enhance sugar release from agro-industrial residues, supporting lignocellulosic biorefinery development.