Hydrothermal pretreatment with microwaves: A new strategy for ensuring the sustainability of biorefineries

Lignocellulosic biomass (LCB) includes agricultural residues, crop wastes, and food wastes that are ubiquitously present and can be used as renewable resources to generate bioenergy or biofuels. Still, direct utilization of LCB to produce biofuel is not an easy task due to the recalcitrance property of LCB. The pretreatment strategy is an important step in a biorefinery to reduce biomass recalcitrance and to use it for bioenergy including value-added product generation. Microwave irradiation is procuring interest regarding LCB and waste material pretreatment over time before moving to biological transformation to biofuels. The coupling of microwave heating with water has made it the most effective treatment for biomass valorization to generate biofuel and other value-added products, turning it into the most cost-effective and eco-friendly approach. Despite its numerous advantages, scaling up microwave pretreatment from laboratory experiments to industrial applications faces several challenges. These limitations become significant hurdles in scaling up. As a result, it is necessary to focus research on cost evaluations and life cycle assessment (LCA) studies for commercialization that will benefit the bioeconomy and the environment. This review discusses microwave-assisted pretreatment significance in valorizing LCB for biofuel generation including the cost evaluation and LCA studies that have the most important role in commercializing the microwave-assisted pretreatment from lab scale to industrial scale.