Advances in Microwave-Aided Pretreatment of Lignocellulosic Biomass for Improved Enzymatic Hydrolysis: A Sustainable Approach to Bioethanol Production

The production of bioethanol from lignocellulosic biomass could serve as an excellent alternative to fossil fuels. However, the structural complexity of its biomass hinders its efficiency. Effective pretreatment techniques have been established to improve its hydrolysis and increase sugar yield. Among the pretreatment methods employed in lignocellulosic biomass hydrolysis, microwave-assisted pretreatment (MAP) has gained attention for its rapid heating, energy efficiency, and reduced environmental impact. This review highlights the importance of MAP over conventional heating. It examines recent advances in MAP, focusing on dielectric fundamentals for the conversion of lignocellulosic biomass and on the effectiveness of MAP in deconstructing the cellulose-hemicellulose-lignin matrix. Several studies have shown that MAP significantly improves enzymatic accessibility, reduces pretreatment time, and minimizes the formation of inhibitory compounds. The work further reviews the combination of MAP with chemical agents, such as alkaline or acidic solutions, which enhances biomass digestibility, and highlights key process parameters that influence pretreatment efficiency and subsequent bioethanol yield, including microwave power, irradiation time, and biomass particle size. Despite the benefits of MAP, challenges such as high initial costs and industrial scalability persist, necessitating further research to optimize process conditions and reactor designs. It is therefore imperative to integrate MAP with other pretreatment strategies, including techno-economic analysis (TEA) and life cycle assessment (LCA), to explore its application in biorefineries and thereby enhance its feasibility for large-scale bioethanol production. When these challenges are addressed, MAP has excellent potential to develop a sustainable, economically viable biofuel industry.