Mechanistic investigations on the removal of diclofenac sodium by UV/S2O8 2−/Fe2+, UV/HSO5 −/Fe2+ and UV/H2O2/Fe2+-based advanced oxidation processes

Abstract

ABSTRACT This study reports the comparative removal of an emerging contaminant diclofenac sodium (DCF) by UV-254 nm-based advanced oxidation processes (AOPs), i.e. UV/S2O8 2−/Fe2+, UV/HSO5 −/Fe2+ and UV/H2O2/Fe2+ processes. The results demonstrated that by applying [DCF]0 = 0.30 mM and [H2O2]0 = [S2O8 2−]0 = [HSO5 −]0 = 3 mM, k app values were 0.082, 0.166, 0.221, 0.485 and 2.014 min−1 for UV-only, UV/Fe2+, UV/H2O2/Fe2+, UV/S2O8 2−/Fe2+ and UV/HSO5 −/Fe2+ processes, respectively. At different [DCF]0 from 0.30 to 0.90 mM, the degradation rate was increased from 0.01 mM min−1 to 0.12 mM min−1, while the corresponding k app values were decreased from 2.01 min−1 to 1.04 min−1. The removal performance of the applied AOP was significantly influenced by the presence of natural water contaminants (NO3 −, Cl−, HCO3 −, SO4 2− and humic acid (HA)) and [pH]0. The inhibition of these natural water contaminants on the removal of DCF by UV/HSO5−/Fe2+ process was in the order of HA > NO2 − > SO4 2− > HCO3 − ≈ Cl− > NO3 −. Furthermore, seven (07) degradation products (DPs) of DCF were explored by UPLC-MS/MS and accordingly degradation pathways of DCF were suggested. The practical applications of the proposed AOPs towards the removal of DCF were further strengthened by calculating total organic carbon removal and toxicity assessment.