Ultrasound-Based Technologies for Agricultural Waste Biomass Valorization: Mechanism, Recent Technical Advances, Limitations, and Future Aspect

Bioenergy attracts great attention as a renewable energy source; on the one hand, environmental pollution caused by agricultural waste biomass can be solved; on the other hand, the additional values of agricultural products will be boosted. Hence, efficient processing technologies are essential to agricultural waste biomass valorization. Ultrasound has been termed a novel technology and proved to be a very effective physical processing method. It is closely related to ultrasonic propagation properties and processing mechanisms. Deep eutectic solvent (DES) can promote agricultural waste biomass valorization because of high extracting efficiency from different components of plant-based materials with other exceptional advantages, including low value, simple synthesis, tiny volatility, preferable solubility, better biodegradability, and little toxicity. The combined utilization of ultrasound and DES can make the high-value applications of agricultural waste biomass and is conducive to the practicability of commercial-scale extraction. This chapter will present the fundamentals of ultrasound-based processing, including the processing mechanism, cavitation bubble behavior, and affecting factors. Subsequently, recent ultrasound-based technical advances in the fields, such as pretreatment, extraction, hydrolyzation, homogenization, fermentation, nanocrystallization, and catalysis, will be introduced, analyzed, and concluded. Finally, limitations and future perspectives on ultrasound-based technologies and DES will be predicted for further agricultural waste biomass valorization.