Sterilization of Underwater Bacteria by Ozone Bubble Pulsed Discharge

Electric discharge is going to be applied to bactericidal inactivation in water without chemical dosing. In this article, the sterilization experiments of simulated reused water from an industrial washing machine were conducted by three different treatment methods: 1) air bubble pulsed discharge (ABPD); 2) O3 alone; and 3) ozone bubble pulsed discharge (OBPD). The results showed that: 1) the highest sterilization effect was obtained by OBPD treatment and 2) since the number of sterilized bacteria by OBPD treatment was larger than the sum of the number of sterilized bacteria by ABPD treatment and that of by O3 alone treatment, the synergistic effect by OBPD treatment exists. In order to clarify the decisive factor of synergistic effect by OBPD treatment, we measured dissolved O3 concentration, pH, ${\mathrm {NO}}_{\mathbf {3}}^{\mathbf {-}}$ concentration, emission intensities of O radical, and H2O2 concentration. As a result, dissolved O3 concentrations were less than 0.02 mg/L in all conditions, there was no difference in pH from ${\mathrm {NO}}_{\mathbf {3}}^{\mathbf {-}}$ between ABPD treatment and OBPD treatment, there was no difference between emission intensities from O radical generated by ABPD treatment and OBPD treatment, the highest H2O2 concentration was obtained by OBPD treatment, and the number of sterilized bacteria by H2O2 (5.82 mg/L) with O3 (100 ppm) bubble was larger than the sum of the number of sterilized bacteria by H2O2 (5.82 mg/L) with air bubble and O3 alone treatment. From these results, we conclude that the H2O2 concentration increase and the AOP by O3/H2O2 are the decisive factor of the synergistic effect by OBPD treatment.