Permanganate (Mn(VII)) has been widely applied as an oxidant in water treatment plants. However, compared with ozone, Fenton, and other advanced oxidation processes, the reaction rates of some trace organic contaminants (TrOCs) with Mn(VII) are relatively low. Therefore, further studies on the strategies for enhancing the oxidation of organic contaminants by Mn(VII) are valuable. In this work, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), as an electron shuttle, enhanced Mn(VII) oxidation toward various TrOCs (i.e., bisphenol A (BPA), phenol, estrone, sulfisoxazole, etc.). TEMPO sped up the oxidative kinetics of BPA by Mn(VII) greatly, and this enhancement was observed at a wide pH range of 4.0−11.0. The exact mechanism of TEMPO in Mn(VII) oxidation was described briefly as follows: (i) TEMPO was oxidized by Mn(VII) to its oxoammonium cation (TEMPO + ) by electron transfer, which was the reactive species responsible for the accelerated degradation of TrOCs and (ii) TEMPO + could decompose TrOCs rapidly with itself back to TEMPO or TEMPOH (TEMPO hydroxylamine). To further illustrate the interaction between TEMPO and target TrOCs, we explored the transformation pathways of BPA in Mn(VII)/ TEMPO oxidation. Compared to Mn(VII) alone, adding TEMPO into the Mn(VII) solution significantly suppressed BPA's selfcoupling and promoted hydroxylation, ring-opening, and decarboxylation. Moreover, the Mn(VII)/TEMPO system was promising for the abatement of TrOCs in real waters for humic acid, and ubiquitous cations/anions had no adverse or even beneficial impact on the Mn(VII)/TEMPO system.

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Ferrate (Fe(VI), K 2 FeO 4 ) has attracted much attention in water treatment for its high redox potential, especially under acidic conditions. Although interests have been arising in the performance of Fe(VI) at pH below 7.0, a contradicting trend of second order reaction rates (k app ) was observed at acidic conditions, and the reactive species (i.e., high-valent iron species or hydroxyl radicals (HO • )) of Fe(VI) oxidation at acidic pH remains unclear. Thus, the kinetics of Fe(VI) oxidizing bisphenol A (BPA) under a wide pH range was reinvestigated. The k app value of Fe(VI) with BPA strongly depends on pH, which increased from 7.31 × 10 1 to 2.44 × 10 3 M −1 s −1 with pH decreasing from 10.0 to 3.0. Moreover, high-valent iron species were identified as the reactive species, i.e., Fe(VI), Fe(V), and Fe(IV), in both alkaline and acidic solutions, while HO • was identified as the secondary reactive species at acidic conditions with negligible contribution. Theoretical calculation was used to predict the reactive sites, and similar degradation products of BPA were identified under both acidic and alkaline conditions, ascribed to the similar reactive species. Toxicity assessment based on the Toxicity Estimation Software Tool suggested that Fe(VI) can alleviate the bioaccumulation toxicity efficiently. Humic acid (0.2−2.0 mgC L −1 ) and ubiquitous anions (1.0 mM) showed no obvious adverse effect on Fe(VI) oxidation while 1.0 mM Fe 3+ or Cu 2+ could accelerate it, and Fe(VI) showed a promising performance for the abatement of BPA in real waters.