Chemical oxidation of organic matter in secondary-treated municipal wastewater by using methods involving ozone, ultraviolet radiation and TiO2 catalyst

The efficiencies of chemical oxidation of organic matter in genuine secondary-treated municipal wastewater by using O₃, O₃/UV, O₃/TiO₂, UV/TiO₂ and O₃/UV/TiO₂ methods were compared experimentally. Effects of carbonates on these efficiencies were also investigated. Elimination of carbonates from the water increased TOC reduction efficiency of all the methods. The effect of the carbonates on the O₃ method was less significant than that on the other methods. The O₃/UV method was the most effective for reducing TOC under both carbonate-present and decarbonated conditions. The catalytic ozone process (O₃/TiO₂) showed a tendency to increase the ozonation efficiency at the beginning of the reaction under the decarbonated condition, but the addition of the TiO₂ catalyst inhibited the ozonation under the carbonate-present condition. The photocatalytic oxidation process (UV/TiO₂) did not reduce TOC as much as the other methods, but it could reduce TOC over a long time. And the O₃/UV/TiO₂ method did not show a synergistic effect of ozonation and photocatalytic oxidation. Furthermore, zonation prior to coagulation increased TOC reduction efficiency of coagulation, but this effect was also affected by the carbonates in water.