The synergistic effect of ozonation and photocatalysis on color removal from reused water

In this study, the treatment efficiency of different AOPs (UV/O₃, UV/TiO₂ and UV/TiO₂/O₃) was compared for the reduction of color and trace organics remained in the actual-treated wastewater using a laboratory scale recirculating ozonation photocatalytic system. Color, A₂₅₄ (the organics absorption at the wavelength of 254 nm), and total organic carbon (TOC) were characterized to assess the process efficiency. The effects of ozone dose, circulation flow rate, UV intensity, ozone input flow rate, ozonation procedure, as well as UV light source on the process efficiency were also investigated. The results showed that the combined ozonation and photocatalytic process (UV/TiO₂/O₃) is more efficient than ozonation (UV/O₃) or photocatalysis (UV/TiO₂) alone, particularly in total mineralization of TOCs. It was evident that a synergistic effect occurred in the combined ozonation and photocatalytic process. The ozone dose and ozonation procedure were found to have a significant impact on the process efficiency whereas circulation flow rate, UV intensity, ozone input flow rate, and UV light source had relatively less effect. The color removal rate was significantly increased with the increase of O₃ dose. The co-treatment of ozonation and photocatalytic oxidation increased TOC removal rate by nearly 50% compared to the process when ozonation was used as a pre-treatment for photocatalysis. This was due to the synergistic effect between photocatalysis and ozonation.