In this study, we compared the decontamination kinetics of various target compounds and the oxidation by-products (bromate and chlorate) of PMS, PDS, and H₂O₂ under UV irradiation (UV/PMS, UV/PDS, UV/H₂O₂). Probes of different reactivity with hydroxyl and sulfate radicals, such as benzoic acid (BA), nitrobenzene (NB), and trichloromethane (TCM), were selected to compare the decontamination efficiency of the three oxidation systems. Experiments were performed under acidic, neutral, and alkaline pH conditions to obtain a full-scale comparison of UV/peroxides. Furthermore, the decontamination efficiency was also compared in the presence of common radical scavengers in water bodies [bicarbonate, carbonate, and natural organic matter (NOM)]. Finally, the formation of oxidation by-products, bromate, and chlorate, was also monitored in comparison in pure water and tap water. Results showed that UV/H₂O₂ showed higher decontamination efficiency than UV/PDS and UV/PMS for BA degradation while UV/H₂O₂ and UV/PMS showed better decontamination performance than UV/PDS for NB degradation under acidic and neutral conditions. UV/PMS was the most efficient among the three processes for BA and NB degradation under alkaline conditions, while UV/PDS was the most efficient for TCM degradation under all pH conditions. In pure water, both bromate and chlorate were formed in UV/PDS, small amounts of bromate and rare chlorate were observed in UV/PMS, and no detectable bromate and chlorate were formed in UV/H₂O_2. In tap water, no bromate and chlorate were detectable for all three systems.

Peroxodisulfate (PDS), peroxymonosulfate (PMS), and hydrogen peroxide (H₂O₂) might coexist in a persulfate system. It leads to the mutual interference in concentration determination due to their similar structures. Simultaneous detection of the three peroxides involves limited reporting. Herein, a multi-step iodometry was established to simultaneously determine the concentrations of PDS, PMS, and H₂O₂ coexisting in a solution. Firstly, molybdate–NaHCO₃-buffered iodometry was proposed to uplift the overall detection of peroxides since the recovery rate of H₂O₂ was unexpectedly lower in the peroxide mixture than in the single H₂O₂ solution with reported NaHCO₃-buffered iodometry. Then, multi-step iodometry was proposed based on the established molybdate–NaHCO₃-buffered iodometry using the combination with catalase and revised acetate-buffered iodometry (pH 3). The multi-step iodometry determined the coexisting PMS, PDS, and H₂O₂ with the recovery rate of 95–105% and a standard deviation of ≤7% of two replicates at the individual centration of 13–500 μmol∙L⁻¹. The recovery rates of peroxides were within 95–105% at pH 3–11 and within 90–110% in the presence of Cl⁻ (0–150 mg∙L⁻¹), F⁻ (0–1.5 mg∙L⁻¹), SO₄²⁻ (0–150 mg∙L⁻¹), or NO₃⁻ (0–20 mg∙L⁻¹). The recovery rate of H₂O₂ was lowered down to 91% or 87% in the sample containing 100 mg/L Ca²⁺ or Mg²⁺, respectively, but was lifted up to 100% or 93% once pretreated by adding 0.11–1.06 g∙L⁻¹ Na₂CO₃. In the background of tap water, surface water, and ground water, peroxides were all detected in 90–110%, which indicates the applicability of multi-step iodometry in real waters.