Ultrasonic Stimulation of Co-Immobilized Saccharomyces cerevisiae Cells and β-Galactosidase Enzyme for Enhanced Ethanol Production from Whey Ultrafiltration Permeate

Low energy ultrasound irradiation (20 kHz, 1.0 W·L) was applied to enhance bioethanol production from whey ultrafiltration permeate by co-immobilized Saccharomyces cerevisiae cells and β-galactosidese enzyme. Sugar utilization and ethanol formation were investigated as a function of hydraulic retention time (HRT) between 12 and 36 h. Maximum ethanol production under HRT of 36 h was 26.30 g·L with ultrasound exposure, and 23.60 g·L without. Maximum ethanol yield was 0.532 g·g lactose in the fermentation process with ultrasound irradiation, and 0.511 g·g without. For the continuously operating bioreactors, the maximum rates of sugar utilization were 98.9 and 92.4% for the yeast with and without ultrasound exposure, respectively. These results highlight the positive effect of low-intensity ultrasounds in bioethanol fermentation from whey permeates, raising new perspectives for its disposal.