Search

Peracetic acid combined ultraviolet (UV/PAA) process has garnered growing attention as a promising advanced oxidation process (AOP) for wastewater treatment, but the corresponding transformation of ubiquitous dissolved organic matter (DOM) under this AOP remains unknown. This study systematically investigated the changes in characteristics and composition of DOM under UV/PAA, as well as the underlying mechanisms by multiple spectroscopic analyses and Fourier transform ion cyclotron resonance mass spectrometry. UV/PAA treatment dramatically decreased aromaticity, apparent molecular weight, and fluorescent abundance of DOM with the production of more oxidized and saturated compounds. The reactive species (i.e., · OH and CH 3 C(O)O · /CH 3 C(O)OO · ) in UV/PAA contributed primarily to DOM changes but showed different reaction selectivity and mechanisms. · OH reacts with DOM components and mainly yields oxygenation products via a radical addition pathway. Comparatively, the electron transfer route is more likely to occur in CH 3 C(O)O · /CH 3 C(O)OO · -induced DOM transformation. Aside from oxygenation products, electron transfer could exclusively generate decarboxylation products and distinguishes CH 3 C(O)O · /CH 3 C(O)OO · -based AOPs from · OH-based AOPs. These findings significantly improve knowledge of DOM alterations under UV/PAA AOP at both the bulk and molecular levels., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

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 (CH 3 C(O)O • ) and acetylperoxyl (CH 3 C(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 × 10 1 to 6.67 × 10 2 M -1 ·s -1 ) and Co(III) ( k PAA,Co(III) = 3.91 × 10 0 to 4.57 × 10 2 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 CH 3 C(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.

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 × 10 5 -1.56 × 10 4 M -1 s -1 at pH 3.0-8.1) much more rapidly than H 2 O 2 and outperforms the coexistent H 2 O 2 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 H 2 O 2 , respectively. Based on experimental evidence, formation of carbon-centered radicals (CH 3 C(O)O • , CH 3 C(O) • , and • CH 3 ), • OH, and Fe(IV) reactive intermediate species from the PAA and Fe(II) reactions in the presence of H 2 O 2 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.

• Homogenous Co(II)/PAA system is efficient for organic pollutants degradation. • CH 3 CO 3 • is the major reactive species in Co(II)/PAA process under neutral condition. • Hydrogen atom abstraction is the most favorable route for CH 3 CO 3 • attack on phenol. • Direct experimental and theoretical results both support the HAA mechanism. • Phenoxy radical is proposed to be the primary reaction intermediate after CH 3 CO 3 • attack. Peracetic acid (PAA) has been widely used as an alternative disinfectant in wastewater treatment, and PAA-based advanced oxidation processes (AOPs) have drawn increasing attention recently. Among the generated reactive species after PAA activation, acetylperoxyl radical (CH 3 CO 3 •) plays an important role in organic compounds degradation. However, little is known about the reaction mechanism on CH 3 CO 3 • attack due to the challenging of experimental analysis. In this study, a homogeneous PAA activation system was built up using Co(II) as an activator at neutral pH to generate CH 3 CO 3 • for phenol degradation. More importantly, reaction mechanism on CH 3 CO 3 •-driven oxidation of phenol is elucidated at the molecular level. CH 3 CO 3 • with lower electrophilicity index but much larger Waals molecular volume holds different phenol oxidation route compared with the conventional •OH. Direct evidences on CH 3 CO 3 • formation and attack mechanism are provided through integrated experimental and theoretical results, indicating that hydrogen atom abstraction (HAA) is the most favorable route in the initial step of CH 3 CO 3 •-driven phenol oxidation. HAA reaction step is found to produce phenoxy radicals with a low energy barrier of 4.78 kcal mol−1 and free energy change of -12.21 kcal mol−1. The generated phenoxy radicals will undergo further dimerization to form 4-phenoxyphenol and corresponding hydroxylated products, or react with CH 3 CO 3 • to generate catechol and hydroquinone. These results significantly promote the understanding of CH 3 CO 3 •-driven organic pollutant degradation and are useful for further development of PAA-based AOPs in environmental applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Peracetic acid (PAA) is a disinfection oxidant used in many industries including wastewater treatment. β -Lactams, a group of widely prescribed antibiotics, are frequently detected in wastewater effluents and surface waters. The reaction kinetics and transformation of seven β -lactams (cefalexin (CFX), cefadroxil (CFR), cefapirin (CFP), cephalothin (CFT), ampicillin (AMP), amoxicillin (AMX) and penicillin G (PG)) toward PAA were investigated to elucidate the behavior of β -lactams during PAA oxidation processes. The reaction follows second-order kinetics and is much faster at pH 5 and 7 than at pH 9 due to speciation of PAA. Reactivity to PAA follows the order of CFR ∼ CFX > AMP ∼ AMX > CFT ∼ CFP ∼ PG and is related to β -lactam's nucleophilicity. The thioether sulfur of β -lactams is attacked by PAA to generate sulfoxide products. Presence of the phenylglycinyl amino group on β -lactams can significantly influence electron distribution and the highest occupied molecular orbital (HOMO) location and energy in ways that enhance the reactivity to PAA. Reaction rate constants obtained in clean water matrix can be used to accurately model the decay of β -lactams by PAA in surface water matrix and only slightly overestimate the decay in wastewater matrix. Results of this study indicate that the oxidative transformation of β -lactams by PAA can be expected under appropriate wastewater treatment conditions. [ABSTRACT FROM AUTHOR]

• A systematic EPR method to accurately identify radicals in UV-AOPs was presented. • EPR method on identification of SO 4 ·− without the interference of ·OH was proposed. • Alkoxy and alkyl radicals produced in UV/peracetic acid system were identified. • Iodine-related radicals and hydrated electron in UV/IO 4 − system were identified. • Key characteristics on various DMPO-radical adducts in EPR spectrum were summarized. Accurate identification of radicals in advanced oxidation processes (AOPs) is important to study the mechanisms on radical production and subsequent oxidation-reduction reaction. The commonly applied radical quenching experiments cannot provide direct evidences on generation and evolution of radicals in AOPs, while electron paramagnetic resonance (EPR) is a cutting-edge technology to identify radicals based on spectral characteristics. However, the complexity of EPR spectrum brings uncertainty and inconsistency to radical identification and mechanism clarification. This work presented a comprehensive study on identification of radicals by in-situ EPR analysis in four typical UV-based homogenous AOPs, including UV/H 2 O 2 , UV/peroxodisulfate (and peroxymonosulfate), UV/peracetic acid and UV/IO 4 − systems. Radical formation mechanism was also clarified based on EPR results. A reliable EPR method using organic solvents was proposed to identify alkoxy and alkyl radicals (CH 3 C(=O)OO·, CH 3 C(=O)O· and ·CH 3) in UV/PAA system. Two activation pathways for radical production were proposed in UV/IO 4 − system, in which the produced IO 3 ·, IO 4 ·, ·OH and hydrated electron were precisely detected. It is interesting that addition of specific organic solvents can effectively identify oxygen-center and carbon-center radicals. A key parameter in EPR spectrum for 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin adduct, A H , is ranked as: ·CH 3 (23 G) >·OH (15 G) >IO 3 · (12.9 G) >O 2 ·− (11 G) ≥·OOH (9–11 G) ≥IO 4 · (9–10 G) ≥SO 4 ·− (9–10 G) >CH 3 C(=O)OO· (8.5 G) > CH 3 C(=O)O· (7.5 G). This study will give a systematic method on identification of radicals in AOPs, and shed light on the insightful understanding of radical production mechanism. [Display omitted] [ABSTRACT FROM AUTHOR]