Intensification of delignification and enzymatic hydrolysis of orange peel waste using ultrasound for enhanced fermentable sugar production

Abstract

The present study focuses on using orange peel as a lignocellulosic substrate for fermentable reducing sugar production with intensification studies for delignification and enzymatic hydrolysis steps. The orange peel exposed to conventional and ultrasound-assisted alkaline pretreatment under ambient temperature for delignification resulted in around 86% delignification and 92% delignification in 4 h respectively. Subsequently, the effect of the enzyme concentration, ultrasonic power and duty cycle on reducing sugar production in the enzymatic hydrolysis has been investigated. Maximum concentration of reducing sugar as 1.30 g/L was obtained in 6 h treatment under 60W as power and 70% duty cycle, which was higher and much faster as compared to the conventional method where the sugar concentration was 0.814 g/L in 24 h. Studies involving advanced oxidation pretreatment based on hydrogen peroxide, Fenton, and ozone performed under ambient temperature demonstrated that the optimum conditions for best pretreatment efficacy are 3% H2O2 loading, 0.5g as FeSO4 loading and 2 L/min as the ozone flow rate as applicable, yielding a sugar concentration of 1.528 g/L, 2.069 g/L and 0.472 g/L respectively. Overall, the work has established that application of ultrasound and advanced oxidation pretreatment benefits the delignification and subsequent enzymatic hydrolysis of orange peel waste.