Impact of pulsed ultrasound on bacteria reduction of natural waters

There is a limited work on the use of pulsed ultrasound for water disinfection particularly the case of natural water. Hence, pulsed ultrasound disinfection of natural water was thoroughly investigated in this study along with continuous ultrasound as a standard for comparison. Total coliform measurements were applied to evaluate treatment efficiency. Factorial design of 2(3) for the tested experimental factors such as power, treatment time and operational mode was applied. Two levels of power with 40% and 70% amplitudes, treatment time of 5 and 15 min and operational modes of continuous and pulsed with On to Off ratio (R) of 0.1:0.6 s were investigated. Results showed that increasing power and treatment time or both increases total coliform reduction, whereas switching from continuous to pulsed mode in combination with power and treatment time has negative effect on total coliform reduction. A regression model for predicting total coliform reduction under different operating conditions was developed and validated. Energy and cost analyses applying electrical and calorimetric powers were conducted to serve as selection guidelines for the choosing optimum parameters of ultrasound disinfection. The outcome of these analyses indicated that low power level, short treatment time, and high R ratios are the most effective operating parameters. (C) 2015 Elsevier B.V. All rights reserved.