UC Davis

Ethanol produced from renewable biomass, such as lignocellulosic feedstock, is one of the alternative energy resources that can be environmentally friendly. However, physical and chemical barriers caused by the close association of the main components of lignocellulosic biomass, as well as starch, hinder the hydrolysis of cellulose and hemicellulose in lignocellulose as well as amylase and amylopectin in starch to fermentable sugars. One of the main goals of pretreatment for enzymatic hydrolysis is to increase the enzyme accessibility for improving digestibility of cellulose and starch. Ultrasound irradiation applied to cellulosic materials and starch-based feedstock was found to enhance the efficiency of hydrolysis and subsequently increase the sugar yield. Prior research conducted on applying ultrasonic technology for cellulose and starch pretreatment has considered a variety of effects on physical and chemical characteristics, hydrolysis efficiency and ethanol yield. This paper reviews the application of ultrasound irradiation to cellulose and starch prior to and during hydrolysis in terms of sugar and ethanol yields. It also addresses characteristics such as accessibility, crystallinity, degree of polymerization, morphological structure, swelling power, particle size and viscosity as influenced by ultrasonic treatment. © 2014 Elsevier Ltd.