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 (eta(met)) and total organic carbon (eta(TOC)) 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 (m(A,in)) of 300 mg L-1. At m(A,in) of 3600 mg L-1 with pH values controlled at 2, 7 and 10, the eta(TOC) values are 13, 26 and 43%, respectively, showing the great influence of pH value on the eta(TOC) for the OZ process. Combining the UV-C radiation in the OZ process can promote the decomposition of O-3 to form OH center dot radical which has higher oxidizing ability than O-3 and can further decompose the acidic intermediates, thus increasing the eta(TOC). At m(A,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 eta(TOC) 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. (C) 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.