Rapid and continuous degradation of diclofenac by Fe(II)-activated persulfate combined with bisulfite

Abstract

The improvement on diclofenac (DCF) degradation by Fe(II)-activated persulfate (PS) combined with bisulfite (BS) was investigated. It was observed that the introduction of BS in Fe(II)/PS process enhanced the circulation of Fe(III/II) and kept Fe(II) at a high concentration, resulting a rapid and continuous DCF degradation. The initial pH, reagent dosages and reaction temperature played important roles on DCF removal in BS/Fe(II)/PS process. The main iron species in this system were FeHSO3+, Fe2+ and FeOHSO3H+, and their variation trends were calculated by the software of MINITEQ 3.1. Based on the alcohols quenching experiments, SO4− was confirmed to be the prominent reactive radical for DCF oxidation in BS/Fe(II)/PS process. Moreover, the probable DCF degradation mechanism was proposed based on the detected intermediate products and density functional theory (DFT) calculation. The BS/Fe(II)/PS system presented a synergistic effect for rapid and steady DCF degradation through the occurred cycle of Fe(II/III) (i.e., oxidation of Fe(II) by PS and then reduction of Fe(III) by BS) and solved the drawbacks of slow initial reaction of Fe(II)/BS and weak durability of Fe(II)/PS. This study could provide an effective and environmentally friendly approach to sewage treatment.