Neonicotinoids removal by associated binary, tertiary and quaternary advanced oxidation processes: Synergistic effects, kinetics and mineralization.

The degradation of four representative neonicotinoids, namely Thiamethoxam, Imidacloprid, Acetamiprid and Thiacloprid, was carried out by the sequential association of different advanced oxidation processes, including Ozonation, Electro-chemical Oxidation, Ultrasound, Ultraviolet radiation, and their different possible associations. There are no published papers in the literature on the removal of this type of insecticides through these associated oxidation processes. Single oxidation processes did not achieve total pollutants removal in less than 3 h (only UV radiation treatment obtain a total removal of Thiamethoxan in 150 min, but with mineralization below 15% TOC). For double sequential processes, Electro-oxidation-Ozone treatment obtains a total removal of Imidacloprid in 120 min and an increase of mineralization to 50% TOC. Three or four sequential processes are recommended to improve degradation and mineralization rates in a significant way, Electro-oxidation-Ozone-UV treatment obtains a total removal of Thiamethoxan in 80 min with mineralization over 75% TOC. These results confirm important synergistic effects which were quantified. The global trend indicates that Thiamethoxam is the most oxidizable neonicotinoid, whereas Acetamiprid is the most recalcitrant compound. The degradation rate of each neonicotinoid followed pseudo-first-order kinetics and the different oxidation pathways were also quantified from a kinetic point of view.