Extrusion followed by ultrasound as a chemical-free pretreatment method to enhance enzymatic hydrolysis of rice hull for fermentable sugars production

The rice hull is an abundant and renewable biomass resource, which contains rich carbohydrates and can be used as an alternative energy source. In order to exploit and utilize the biomass energy in rice hull, extrusion and ultrasound technologies were used to pretreat the rice hull. Response surface method (RSM) was used to optimize the extrusion conditions, and the optimum extrusion condition were obtained as the follows: material diameter, 60 mesh; material moisture, 29 %; extrusion temperature, 143 degrees C; screw speed, 350 rpm. Under the conditions, the expansion degree of rice hull was 2.16. After extrusion, the rice hull was subjected to ultrasound pretreatment for 1.5 h at 40 KHz/500 W. After this above, cellulase, beta-glucosidase, and hemicellulose were used to hydrolyze the rice hull. And 77.50 % of conversion of total cellulose and hemicellulose was obtained. The yield for reducing sugars, glucose, and xylose was 381.59, 291.59, and 88.87 mg/g rice hull, respectively.