Transformation of iopamidol and atrazine by peroxymonosulfate under catalysis of a composite iron corrosion product (Fe/Fe3O4): Electron transfer, active species and reaction pathways

Abstract

Cast iron pipes are commonly applied in drinking water distribution systems (DWDSs); peroxymonosulfate (PMS) is a promising alternative for drinking water disinfection; organic micropollutants is still present in drinking water after waterworks' treatment. However, iron corrosion products may affect the reactions between a disinfectant and organic micropollutants. The study investigated the transformation of iopamidol (IPM) and atrazine (ATZ) by PMS under the catalysis of a composite iron corrosion product (Fe/Fe3O4). The pseudo-first-order rate constants (k) for the degradation of IPM and ATZ were 1.47 and 1.03 min-1, respectively. Electron paramagnetic resonance (EPR) experiments indicated that PMS was effectively activated to yield sulfate radical (SO4•-) and hydroxyl radical (HO•), mainly via the reduction by Fe component, dissolved Fe2+ and generated Feocta2+. SO4•- contributed more than HO• to the degradation of IPM and ATZ, and the radical yield achieved 0.97 mol/mol. The k values reached maximum with Fe/Fe3O4 and PMS doses of 2.5 g L-1 and 25 mg L-1, respectively. The optimum mass fraction of Fe3O4 in Fe/Fe3O4 (MFmag) and pH were 10% and 7.0, respectively. The k values increased with increasing temperature, while decreased in the presence of water matrix. Most of the iodine released from IPM was oxidized to IO3-, and NH4+ was the dominant species of nitrogen released from ATZ. The identification of transformation intermediates showed that the radical chain reactions of IPM was mainly initiated from single electron transfer and radical adduct formation, while those of ATZ was primarily initiated from hydrogen atom abstraction and radical adduct formation.