Exposure times and energy densities for ultrasonic disinfection of Escherichia coli, Pseudomonas aeruginosa, Enterococcus avium, and sewage

Abstract

We investigated the disinfection of sewage and several bacterial pure cultures relevant to sewage using ultrasound produced by the magnetostrictive material, TERFENOL-D. Particular attention was paid to measuring the ultrasonic exposure time and energy density required to kill bacteria. Ultrasonic power was measured and recorded during the treatments, and bacterial kill curves were constructed based on both exposure time and total energy. In 100 mL of synthetic graywater medium, bacterial pure cultures required from ~5 to 16 min per log kill at moderate intensity (~25 W·cm–2), while a sewage sample took several times longer to experience a 90% kill. The effects of intensity, horn size, sonication medium, and vessel geometry and volume on exposure time and energy density were explored. Intensity, horn size, and the sonication medium had significant effects on bacterial kill by ultrasound, but vessel geometry did not. The volume of the liquid being treated and the treatment time were correlated, indicating that the volume of the disinfection zone was smaller than the volume of the liquid being treated.