Proper ultrasound treatment increases ethanol production from simultaneous saccharification and fermentation of sugarcane bagasse

Abstract

This study presents the effect of ultrasound (24 kHz) on enzyme production, enzymatic hydrolysis and simultaneous saccharification and fermentation (SSF) of sugarcane bagasse (SCB) for ethanol production. Trichoderma reesei cells were cultivated with SCB to induce the required enzymes and were subjected to ultrasound to enhance the enzyme secretion. Intracellular and cell wall bound β-glucosidase released into the extracellular extract fulfilled the bioconversion of cellulose into glucose. The hydrolysis and SSF were also investigated after treatment with ultrasound at various amplitudes and times to analyse the impact of ultrasound on the enzyme structure and biomass morphology. Ultrasound showed an effect on the secondary structural configuration of enzyme and biomass destabilization. Under optimized conditions, an ultrasound treatment at 60% amplitude gave the maximum yield of 92% (92.62% for scale up) reducing sugar and 90% (91.14% for scale up) ethanol with a power consumption of 5.4 × 10³ and 3 × 10⁴ J g⁻¹ (4.9 × 10² and 12.3 × 10² J g⁻¹ for scale up), respectively. The contents of inhibitors present in the hydrolysate were well below the inhibitory levels which led to the high ethanol yield. Thus, ultrasound improved the sugars and ethanol yield by improving the biological mechanisms. The novelty of this work is the demonstration of improved secretion of a T. reesei multienzyme complex by ultrasound leading to an efficiently integrated hydrolysis process.