Ultrasound as a Green Processing Technology for Pretreatment and Conversion of Biomass into Biofuels

Abstract

In the past decades, a great deal of attention has been focused on mechanical, thermal or chemical pretreatments of lignocellulosic and algal biomass for the production of biofuel. This chapter is focused on the potential of ultrasound (US) technology in pretreating the biomass to enhance the conversion of cellulose to fermentable sugars and also the disintegration and component extraction of microalgae for the generation of bioethanol or biogas. In addition, US can supplement existing biomass pretreatment methods to greatly enhance their performance and their efficacy. Low frequency ultrasound (LFU, 20–100 kHz) is commonly used in biomass processing, particularly in processes that require intense physical effects such as cell disruption and polymer degradation. High frequency ultrasound (HFU, 400 kHz–2 MHz) recently attracted considerable interest as potential alternative technique for pretreating both the lignocellulosic and algal biomass for sustainable biofuel production. HFU is gaining increasing importance because of its environmentally sound and energy-saving production method since it demands lower energy input for the conversion of biomass. It not only saves time and energy but also lowers the chemical/enzyme dosage and hence novel and considered to be a new sustainable and environmentally-friendly green technique. Although many studies have shown the promise of ultrasound in the cell breakdown for enhanced enzymatic hydrolysis, there is limited information in the application of HFU on biomass pretreatment processes. This chapter provides an overview on the fundamentals of US, the critical parameters that control the conversion of biomass, challenges involved with the application of US in the biomass conversion and its future perspectives.