Recent Advancements and Prospects of Using Cavitation-Assisted Pretreatment of Lignocellulosic Biomass for Production of Biofuels

The cavitation phenomenon has been evaluated for several different industrial applications. More recently, cavitation has been used for biomass pretreatment, a fundamental step in biorefineries, required to modify the lignocellulosic biomass structure and composition, favoring subsequent enzymatic hydrolysis of the carbohydrates. The use of cavitation for this application has been resulting in advantages such as high efficiency and low process time. However, to be used in biorefineries, an adequate addressing of cavitation-assisted pretreatment strategies is fundamental, aiming to profitable yield and productivity of the processes at industrial scale. In the developing biorefineries, different alternatives of cavitation pretreatments and operation modes have been considered and systematically evaluated, mainly taking into account variables such as time of pretreatment, temperature, and solid:liquid ratio. Ultrasonic and hydrodynamic cavitation systems have been used for the pretreatment of lignocellulosic biomass under different conditions. Ultrasound has been more studied, and a number of different lignocellulosic materials have been pretreated under diverse ultrasound frequencies combined with other pretreatment technologies. Hydrodynamic cavitation studies for this application are more recent, presenting advantages such as easier scale-up, with orifice plate-based reactors as the most commonly used. Considering cavitation-assisted pretreatment is a promising alternative for biorefineries, this chapter discusses the main advances in this research area. The main cavitation reactors and the different approaches are also discussed, including the authors’ investigations presenting specific advances for hydrodynamic cavitation pretreatment. An overview of different approaches for cavitation pretreatments was presented, focusing on current techniques, advancements, and future prospects.