UV-C irradiation enhanced ozonation for the treatment of hazardous insecticide methomyl

Decomposition of hazardous methomyl via ozonation (OZ) and ultraviolet photolysis OZ (UV-OZ) processes was studied. The decomposition efficiencies of methomyl (ηmet) and total organic carbon (ηTOC) were determined to measure the oxidative destruction ability. In the OZ process with pH 7 and 10, methomyl can be decomposed completely at the applied ozone dosage per volume of liquid (mA,in) of 300 mg L−1. At mA,in of 3600 mg L−1 with pH values controlled at 2, 7 and 10, the ηTOC values are 13, 26 and 43%, respectively, showing the great influence of pH value on the ηTOC for the OZ process. Combining the UV-C radiation in the OZ process can promote the decomposition of O3 to form OH˙ radical which has higher oxidizing ability than O3 and can further decompose the acidic intermediates, thus increasing the ηTOC. At mA,in of 3600 mg L−1 and UV-C lamp irradiation power of 16 W with controlled pH values at 2, 7 and 10 in the UV-OZ process, the ηTOC values are close to that (72%) without controlling the pH value. The results indicate that the UV-C radiation can enhance the mineralization with insignificant effect of pH value.