Disinfection of wastewater using a 20-kHz ultrasound unit

The present study explored the application of a 20-kHz ultrasound unit for the disinfection of domestic wastewater. Experiments were conducted in batch with an ultrasound probe. The disinfection efficiency of fecal coliform increased with ultrasound power input from 0.003 log kill/min at 70 W/L to 1.8 log kill/min at 1250 W/L. Disinfection data are well-described by the Chick-Watson disinfection model (coefficient of dilution, n = 2.0) using ultrasound power in place of chemical concentration. Water quality did not affect disinfection efficiency significantly. Temperature increases experienced with ultrasonic treatment were significant. Attempts to control the temperature resulted in a marked decrease in disinfection efficiency. Experiments devised to quantify the role of thermal mechanisms revealed that of the total kill produced by ultrasound approximately 52% was attributed to heat, 36% to mechanical stresses associated with ultrasonically induced cavitation, and 12% to uncharacterized synergistic effects. Successful scale-up was demonstrated using a 9.3-L pilot-scale ultrasound unit, operated under flow-through conditions.