NaOH-urea pretreatment of corn stover under outdoor cold conditions for enhanced biodegradability and anaerobic methane yield.

Lignocellulosic biomass, including corn stover, offers substantial potential for sustainable methane production through anaerobic digestion, yet its recalcitrant structure limits efficiency and contributes to environmental waste. This study investigated the optimization of outdoor freezing temperature NaOH-urea pretreatment to address gaps in outdoor application and resource efficiency. The objectives included evaluating the effects of storage period, NaOH-urea concentration, and solid-to-liquid ratios on substrate composition and digestion performance. The methods involved preparing NaOH-urea solutions, pretreating corn stover under outdoor conditions (-20 ± 5 °C for up to 90 days), conducting batch and continuous anaerobic digestion assays, and analyzing structural changes via fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The results revealed 64.9% lignin removal, an increase in cellulose crystallinity from 55.3% to 78.8%, and methane yields increasing from 151 mL/g VS in untreated samples to 252 mL/g VS in pretreated samples, with kinetic modeling indicating faster production rates. These outcomes demonstrate enhanced substrate biodegradability and process efficiency, support scalable bioenergy systems, reduce energy demands in cold regions, and contribute to renewable energy policies.