Oxidative removal of metronidazole from aqueous solution by thermally activated persulfate process: kinetics and mechanisms

Abstract

Metronidazole (MNZ) is widely used in clinical applications and animal feed as an antibiotic agent and additive, respectively. Widespread occurrence of MNZ in wastewater treatment and hospital effluents has been reported. In this study, the mechanism of MNZ degradation in aqueous solutions via thermally activated persulfate (TAP) process was established under different conditions. The kinetic model was derived for MNZ degradation and followed pseudo-first-order reaction kinetics and was consistent with the model fitted by experimental data (R ² > 98.8%). The rate constant increased with the initial dosage of persulfate, as well as the temperature, and the yielding apparent activation energy was 23.9 kcal mol⁻¹. The pH of the solutions did not have significant effect on MNZ degradation. The degradation efficiency of MNZ reached 96.6% within 180 min for an initial MNZ concentration of 100 mg L⁻¹ under the optional condition of [PS]₀ = 20 mM, T = 60 °C, and unadjusted pH. \( {SO}_4^{\cdotp -} \) and HO ^· were confirmed using electron paramagnetic resonance (EPR) spectra during TAP process. Radical quenching study revealed that \( {SO}_4^{\cdotp -} \) was mainly responsible for MNZ degradation at an unadjusted pH. MNZ mineralization evaluation showed that the removal efficiency of total organic carbon (TOC) reached more than 97.2%.