Enhanced degradation of iopamidol by peroxymonosulfate catalyzed by two pipe corrosion products (CuO and δ-MnO2)

Abstract

Peroxymonosulfate (PMS) is a promising alternative for drinking water disinfection; also many organic micropollutants may be present in drinking water sources nowadays. However, pipe corrosion products (PCPs) may impact the reactions between a disinfectant and organic micropollutants in water distribution systems. This study investigated iopamidol (IPM) degradation by PMS under catalysis of two PCPs (i.e., CuO and δ-MnO2). The pseudo-first-order rate constant of IPM degradation in the CuO/PMS system (CuPS) was 3.7 times of that in the δ-MnO2/PMS system (MnPS), with values of 0.218 and 0.059 min−1, respectively. Sulfate radical (SO4−) was the major contributor to IPM degradation in the CuPS, while hydroxyl radical (HO) also played an important role in the MnPS. The radical yield ratio was 0.89 and 0.69 mol/mol in the CuPS and MnPS, respectively. The IPM degradation rate increased with increasing PMS dose, and reached a maximum with a PCP dose of 1.0 and 1.5 g L−1 in the CuPS and MnPS, respectively. The highest degradation efficiency was achieved at pH 7.0 in the two systems. The water matrix (i.e., natural organic matter, alkalinity and chloride) had detrimental effects on IPM degradation to different degrees. The majority of the iodine released from IPM was oxidized to iodate (IO3−) and a small fraction of the initial total organic iodine was transformed to iodoform (CHI3). The IPM degradation by PMS mainly proceeded through two pathways: (1) amide hydrolysis of side chain A, amino oxidation, and amide hydrolysis of side chains B and B′ in sequence; and (2) deiodination reactions.