Applications of advanced oxidation processes (electro-Fenton and sono-electro-Fenton) for degradation of diazinon insecticide from aqueous solutions: optimization and modeling using RSM-CCD, influencing factors, evaluation of toxicity, and degradation pathway

Diazinon (DZ), an organophosphorus pesticide, has a large consumption for agricultural activities, which its discharge into groundwater and surface is associated with serious concerns for the animal and plants. Thus, the degradation of the mentioned pesticide from an aqueous environment was examined in the electro-Fenton (EF) and sono-electro-Fenton process (SEF) process using SS316/beta-PbO2 anode. To characterize the synthesized anode, the analyses, e.g., XRD, SEM, and EDX, were used. The central composite design (CCD) was the method used to assess the effect of selected parameters (DZ concentration = 25-75 mg/L, voltage = 5-15 V, pH = 3-9, and electrolysis time = 20-80 min) and their interactions on the DZ degradation in the evaluated system. Detecting the intermediates of DZ degradation was carried out by LC-MS analysis, and its degradation pathways were proposed. To conduct the toxicity tests for inlet and outlet, the growth inhibition percentage of Pseudomonas aeruginosa and Staphylococcus aureus was estimated. SEF process could represent the DZ degradation, COD, and TOC removal efficiencies of 92.2%, 73.2%, and 67.4%, respectively. According to kinetic studies, the pseudo-first-order kinetic (R-2 > 0.99) was detected to be an adequate model for the enlightenment of data of the degradation of DZ by the evaluated system. Finally, DZ is converted into carbon dioxide (CO2( and water (H2O). The results of this study showed that the degradation and mineralization of DZ using the SEF process were successfully carried out.