Pretreatment of Corncob with Typical Anaerobic Digestion-Derived Organic Acids for Improving Enzymatic Saccharification and Bioethanol Production

The transition to renewable energy is essential for mitigating greenhouse gas emissions and advancing carbon neutrality. Lignocellulosic biomass offers an abundant and sustainable feedstock for biofuel production, but its inherent recalcitrance demands effective pretreatment to enable enzymatic saccharification. This study evaluated five commercial organic acids typical of anaerobic digestion (AD) effluents, namely acetic, propionic, butyric, valeric, and caproic acids, for corncob pretreatment. Compared with untreated corncob, which gave a glucose yield of only 23%, all acid pretreatments substantially enhanced enzymatic hydrolysis. A strong correlation between xylan removal and total sugar yield (R2 = 0.98) confirmed that hemicellulose solubilization is the primary factor governing digestibility in typical AD-derived organic acid pretreatment. Among the conditions tested, pretreatment with 2.5% butyric acid at 180 °C for 45 min was optimal, removing 91.84% xylan and 53.10% lignin while retaining 75.24% glucan, which led to a near-complete glucose release during subsequent enzymatic hydrolysis at 2% solid loading with cellulase (15 FPU/g substrate). Fermentation of the butyric acid-pretreated hydrolysate via separate hydrolysis and fermentation produced 43.32 g/L ethanol with ~99% glucose consumption. In this case, the final ethanol yield from consumed sugars was 79.8% of the theoretical yield. These findings demonstrate that typical AD-derived pure organic acids serve as effective pretreatment agents, offering a promising route for lignocellulose valorization and biofuel production within a circular biorefinery framework.