SUSTAINABLE BIOETHANOL PRODUCTION FROM LIGNOCELLULOSIC BIOMASS VIA GREEN AND EMERGING TECHNOLOGIES: A FOCUS ON PRETREATMENT AND HYDROLYSIS
The growing urgency to reduce reliance on fossil fuels and lower greenhouse gas emissions has intensified interest in second-generation bioethanol derived from lignocellulosic biomass (LCB). This research responds to the need for more sustainable and economically viable bioethanol production processes by exploring innovative pretreatment and hydrolysis methods that reduce energy input, eliminate harsh chemicals, and enhance process efficiency. Using a milled softwood mixture as feedstock, the study investigates the synergistic integration of microwave-assisted deep eutectic solvent (DES) pretreatment, oxalic acid-based hydrolysis, and mechano-chemical processing.
The optimized microwave-assisted DES pretreatment using choline chloride and formic acid achieved over 90% delignification and hemicellulose removal while retaining more than 90% of cellulose. This green, rapid, and selective method enabled the recovery of high-purity lignin and improved the accessibility of cellulose for downstream processing. Hydrolysis of the pretreated biomass using oxalic acid and microwave irradiation yielded up to 79% cumulative glucose without generating fermentation inhibitors, allowing direct conversion to ethanol using Saccharomyces cerevisiae with a 43% fermentation efficiency.
Further enhancement was achieved by incorporating short-duration ball milling, which significantly reduced cellulose crystallinity and improved hydrolysis performance. The combined treatment resulted in 93% glucose selectivity and 97% ethanol fermentation efficiency, demonstrating strong industrial potential. A preliminary energy analysis confirmed the energy savings of the integrated approach compared to conventional methods.
Overall, this work offers a scalable, low-impact strategy for sustainable bioethanol production and contributes to advancing renewable energy technologies aligned with circular economy principles.
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