Fe­(II) is an excellent promoter for advanced oxidation processes (AOPs) because of its environmental ubiquity and low toxicity. This study is among the first to characterize the reaction of peracetic acid (PAA) with Fe­(II) ion and apply the Fe­(II)/PAA AOP for degradation of micropollutants. PAA reacts with Fe­(II) (k = 1.10 × 105–1.56 × 104 M–1 s–1 at pH 3.0–8.1) much more rapidly than H2O2 and outperforms the coexistent H2O2 for reaction with Fe­(II). While PAA alone showed minimal reactivity with methylene blue, naproxen, and bisphenol-A, significant abatement (48–98%) of compounds was observed by Fe­(II)/PAA at initial pH of 3.0–8.2. The micropollutant degradation by Fe­(II)/PAA exhibited two kinetic phases (very rapid then slow) related to PAA and H2O2, respectively. Based on experimental evidence, formation of carbon-centered radicals (CH3C­(O)­O•, CH3C­(O)•, and •CH3), •OH, and Fe­(IV) reactive intermediate species from the PAA and Fe­(II) reactions in the presence of H2O2 is hypothesized. The carbon-centered radicals and/or Fe­(IV) likely played an important role in micropollutant degradation in the initial kinetic phase, while •OH was important in the second reaction phase. The transformation products of micropollutants showed lower model-predicted toxicity than their parent compounds. This study significantly advances the understanding of PAA and Fe­(II) reaction and demonstrates Fe­(II)/PAA to be a feasible advanced oxidation technology.

Peracetic acid (PAA) is increasingly used as an alternative disinfectant and its advanced oxidation processes (AOPs) could be useful for pollutant degradation. Co­(II) or Co­(III) can activate PAA to produce acetyloxyl (CH3C­(O)­O•) and acetylperoxyl (CH3C­(O)­OO•) radicals with little •OH radical formation, and Co­(II)/Co­(III) is cycled. For the first time, this study determined the reaction rates of PAA with Co­(II) (k PAA,Co(II) = 1.70 × 101 to 6.67 × 102 M–1·s–1) and Co­(III) (k PAA,Co(III) = 3.91 × 100 to 4.57 × 102 M–1·s–1) ions over the initial pH 3.0–8.2 and evaluated 30 different aromatic organic compounds for degradation by Co/PAA. In-depth investigation confirmed that CH3C­(O)­OO• is the key reactive species under Co/PAA for compound degradation. Assessing the structure–activity relationship between compounds’ molecular descriptors and pseudo-first-order degradation rate constants (k′PAA• in s–1) by Co/PAA showed the number of ring atoms, E HOMO, softness, and ionization potential to be the most influential, strongly suggesting the electron transfer mechanism from aromatic compounds to the acetylperoxyl radical. The radical production and compound degradation in Co/PAA are most efficient in the intermediate pH range and can be influenced by water matrix constituents of bicarbonate, phosphate, and humic acids. These results significantly improve the knowledge regarding the acetylperoxyl radical from PAA and will be useful for further development and applications of PAA-based AOPs.

As an emerging oxidant and disinfectant, peracetic acid (PAA) has increasingly been used in wastewater treatment and the food and medical industries and has attracted greater research interest. To better understand reactions initiated by PAA, this paper is among the first to comprehensively review the reactivity of PAA with respect to organic compounds of various structures. The reactivities of PAA with respect to 123 organic compounds are compiled from the literature and new experiments, and possible reaction pathways and products are discussed. Overall, PAA is an electrophile with high selectivity in reaction. The second-order rate constants of PAA oxidation of organic compounds vary by nearly 10 orders of magnitude, from 3.2 × 10 −6 to >1.0 × 10 5 M −1 s −1 , which are much larger than those of H 2 O 2 coexisting in PAA solutions. Electron-donating groups of compounds increase the reactivity with respect to PAA, evidenced by the strong negative correlations between rate constants and substituent constants [Hammett (σ) or Taft (σ*)] of compounds. Sulfur moieties show exceptionally high reactivity with respect to PAA. Limited studies have shown that generally oxygen-added reaction products are formed from PAA oxidation. This critical review provides a useful foundation for advancing our understanding of the fate of organic compounds in wastewater treatment including PAA and identifies further research needs to evaluate a broader range of compounds and their oxidation products and toxicity.

Ferrate(VI) and peracetic acid (PAA) are two oxidants of growing importance in water treatment. Recently, our group found that simultaneous application of ferrate(VI) and PAA led to much faster degradation of micropollutants compared to that by a single oxidant, and this paper systematically evaluated the underlying mechanisms. First, we used benzoic acid and methyl phenyl sulfoxide as probe compounds and concluded that Fe(IV)/Fe(V) was the main reactive species, while organic radicalshad negligible contribution. Second, we removed the coexistent hydrogen peroxide (H 2 O 2 ) in PAA stock solution with free chlorine and, to our surprise, found the second-order reaction rate constant between ferrate(VI) and PAA to be only about 1.44 ± 0.12 M −1 s −1 while that of H 2 O 2 was as high as (2.01 ± 0.12) × 10 1 M −1 s −1 at pH 9.0. Finally, further experiments on ferrate(VI)-bisulfite and ferrate(VI)-2,2′azino-bis(3-ethylbenzothiazoline-6-sulfonic)acid systems confirmed that PAA was not an activator for ferrate(VI). Rather, PAA could enhance the oxidation capacity of Fe(IV)/Fe(V), making their oxidation outcompete self-decay. This study, for the first time, reveals the ability of PAA to promote electron transfer efficiency between highvalent metals and organic contaminants and confirms the benefits of co-application of ferrate(VI) and PAA for alkaline wastewater treatment.

This paper presents an advanced oxidation process (AOP) of peracetic acid (PAA) and ruthenium(III) (Ru(III)) to oxidize micropollutants in water. Studies of PAA−Ru(III) oxidation of sulfamethoxazole (SMX), a sulfonamide antibiotic, in 0.5−20.0 mM phosphate solution at different pH values (5.0− 9.0) showed an optimum pH of 7.0 with a complete transformation of SMX in 2.0 min. At pH 7.0, other metal ions (i.e., Fe(II), Fe(III), Mn(II), Mn(III), Co(II), Cu(II), and Ni(II)) in 10 mM phosphate could activate PAA to oxidize SMX only up to 20%. The PAA−Ru(III) oxidation process was also unaffected by the presence of chloride and carbonate ions in solution. Electron paramagnetic resonance (EPR) measurements and quenching experiments showed the dominant involvement of the acetyl(per)oxyl radicals (i.e., CH 3 C(O)O • and CH 3 C(O)OO • ) for degrading SMX in the PAA−Ru(III) oxidation process. The transformation pathways of SMX by PAA−Ru(III) were proposed based on the identified intermediates. Tests with other pharmaceuticals demonstrated that the PAA−Ru(III) oxidation system could remove efficiently a wide range of pharmaceuticals (9 compounds) in the presence of phosphate ions in 2.0 min at neutral pH. The knowledge gained herein on the effective role of Ru(III) to activate PAA to oxidize micropollutants may aid in developing Ru(III)containing catalysts for PAA-based AOPs.