Synergistic Effect of Ultraviolet and Power Ultrasonic on Reclaimed Water Disinfection

Power ultrasound (US) has been employed to enhance the effect of ultraviolet (UV) disinfection, and the mechanism was investigated based on molecular biology. The experiment result showed that there was a good linear correlation between the UV irradiation dose and inactivation rate of E.Coli. By orthogonal test, ultrasound power, action time and volume of bacterial liquid had no statistical significance to inactivation rate, and the greatest factor was the volume of bacterial liquid, then the ultrasound power, and then the action time. The optimal conditions found were: volume 50 mL; power 600 W; time 20 S. Under the optimal operating point that 200 W US for 20S, the inactivation rate was 0.22 log units in 200 mL bacterial liquid. The inactivation rate in the synergistic system between the optimal operating condition and UV was bigger than which in the independent effect of ultrasound plus UV, which demonstrated that the ultrasound pretreatment under optimal operating point can strengthen the effect of UV disinfection. The electronic microscope photograph and the gel electrophoretic map indicated that the ultrasound could not destroy the DNA but only change the cell structure. This study also utilized the specific recognition to the thymine dimmer of T₄ endonuclease V to investigate the mechanism of the optimal condition.