Intensification of enzymatic hydrolysis of waste newspaper using ultrasound for fermentable sugar production

• Use of sustainable feedstock in terms of waste newspaper.
• Intensification of enzymatic hydrolysis using ultrasound.
• Understanding into effect of different operating parameters.
• Kinetic model fitting for the enzymatic hydrolysis.

An effective conversion of lignocellulose into fermentable sugars is a key step in producing bioethanol in an eco-friendly and cost effective manner. In this study, the effect of ultrasound on enzymatic hydrolysis of newspaper, a potential feedstock for bioethanol production due to its high cellulosic content, was investigated. The effect of substrate loading, enzyme loading, temperature, ultrasonic power and duty cycle on the hydrolysis has been studied. Optimum conditions for conventional enzymatic hydrolysis were substrate loading of 5% (w/v), enzyme loading of 0.14% (w/v), temperature of 323 K, and under these conditions and 72 h of hydrolysis, reducing sugar yield of 11.569 g/L was obtained. In case of ultrasound-assisted enzymatic hydrolysis approach, optimum conditions obtained were substrate loading of 3% (w/v), enzyme loading of 0.8% (w/v), sonication power of 60 W, duty cycle of 70%, hydrolysis time of 6.5 h and the reducing sugar yield obtained under these conditions was 27.6 g/L. Approximately 2.4 times increase in the release of reducing sugar concentration was obtained by the ultrasound-assisted enzymatic hydrolysis approach. Results indicate that there is a synergistic effect obtained from the combination of ultrasound and enzymes which lowers the diffusion-limiting barrier to enzyme/substrate binding and results in an increase in reaction rate. The experimental data were also fitted in a simple three parameter kinetic model.