Degradation efficiencies of selected organic pesticides in aqueous solution using various advanced oxidation techniques

Abstract

The pervasive contamination of water resources by persistent organic pesticides necessitates the development of efficient water purification technologies. This study aims to evaluate and compare the performance of five different oxidation techniques (KMnO₄, NaClO, K₂S₂O₈ (PS), Fenton, and UV/PS processes) for the simultaneous removal of six typical organic pesticides (cyromazine, dinotefuran, chloridazon, atrazine, diuron, and tebuconazole) from aqueous solutions. Experimental trials were systematically conducted across a range of oxidant concentrations and solution pH conditions, with degradation kinetics analyzed using pseudo-first-order kinetic models. Molecular reactivity was further probed using density functional theory (DFT) to identify key degradation sites. Results demonstrated that conventional oxidants (KMnO₄, NaClO, K₂S₂O₈) exhibited limited removal efficiency for organic pesticides ( removal rate < 50 %), which is attributed to the structural recalcitrance and reactive oxygen species (ROS) competition of the selected pesticides in mixed pesticide aqueous solution. The Fenton process achieved moderate removal (60 %–85 %) under acidic conditions (pH=3) but required strict H₂O₂/Fe²⁺ stoichiometry (mass ratio 2:1) and generated operational challenges from sludge formation. In contrast, the UV/PS process demonstrated exceptional removal efficiencies (> 95 %) for selected organic pesticides at neutral pH, even with a minimal K₂S₂O₈ dosage of 2.0 mg·L⁻¹, supported by rapid reaction kinetics. DFT calculations revealed chlorine atoms as nucleophilic hotspots for ROS attack, while pyridine rings impeded degradation via steric hindrance. These findings highlight the UV/PS process as a scalable and pH–neutral technology for the effective removal of multiple pesticides, providing valuable insights for optimizing water treatment protocols in complex matrices.