Ozonation using microbubbles formed by electric fields

Abstract

Abstract The use of ozone in water and wastewater treatment systems has been shown to be a process that is limited by mass transfer. The most effective way to overcome this limitation is to increase the interfacial area available for mass transfer by decreasing the size of the ozone gas bubbles that are dispersed in solution. Electrostatic spraying (ES) of ozone into water was investigated in this work as a method of increasing the rate of mass transfer of ozone into a solution and thereby increasing the rate of phenol oxidation. The studies were conducted in a 30 cm column of 7.5 cm internal diameter, using deionized water and phenol as the solution phase and an ozone–oxygen mixture, generated by a corona-discharge ozone generator, as the gas phase. Results were obtained for ES at input power levels ranging from 0 to 4 kV and compared with two different pore-size bubble diffusers (10–15 μm and 40–60 μm). It was determined that the rate of mass transfer could be increased by as much as 40% when the applied voltage was increased from 0 to 4 kV as a result of the smaller bubbles generated by ES. In addition, ES was shown to be more effective than the medium-pore-size (10–15 μm) bubble diffuser; the best results were achieved at low gas flow rates. Phenol oxidation rates were also compared for ES and the medium-pore-size bubble diffuser, and the results indicate that the increased mass transfer rate achieved by ES enhances the rate of removal of phenol from solution.