Electrochemical and photo-assisted electrochemical treatment of the pesticide imidacloprid in aqueous solution by the Fenton process: Effect of operational parameters

The aim of this study was to compare the degradation efficiency (DE%) of imidacloprid as a model pesticide by electro-Fenton (EF) and photoelectro-Fenton processes (PEF) using undivided three-electrode electrochemical cell and UV irradiation in a batch mode. The potential of the working electrode (graphite) was fixed at -1.0 V versus the saturated calomel electrode. The selected operating conditions for treatment of imidacloprid (20 mg/L) were: pH 2.8, Fe²⁺ concentration of 0.36 mM and Na₂SO₄ concentration of 0.15 M as the background electrolyte, which produced a DE% of 59.23 and 80.49 % for EF and PEF after 180 min, respectively. Considerable synergistic effect between EF and UV processes was observed due to the regeneration of Fe²⁺ ions and more production of hydroxyl radicals (^·OH). Besides, accumulation of the electro-generated H₂O₂ in the electrochemical system as the source of ^·OH radicals was confirmed. Moreover, total organic carbon measurements under the optimized condition demonstrated that 50.73 and 67.15 % of the organic substrates were mineralized after 300 min of the treatment by the EF and PEF, respectively. Eventually, the experimental results revealed that the degradation and mineralization rates of the pesticide followed pseudo-first-order kinetics; however, the rate constants of the mineralization were lower than the degradation ones owing to the generated intermediates, which required more treatment during the processes.