Ozonation of Para-Substituted Phenolic Compounds Yields p-Benzoquinones, Other Cyclic α,β-Unsaturated Ketones, and Substituted Catechols

Fabrication of porous and defect-rich BiOI/MWCNTs photocatalyst by Ar plasma-etching for emerging pollutants degradation

Carbon material modification and defect engineering are indispensable for bolstering the photocatalytic effectiveness of bismuth halide oxide (BiOX). In this study, a novel porous and defect-rich Ar-CB-2 photocatalyst was synthesized for emerging pollutants degradation. Leveraging the interfacial coupling effect of multi-walled carbon nanotubes (MWCNTs), we expanded the absorption spectrum of BiOI nanosheets and significantly suppressed the recombination of charge carriers. Introducing defects via Argon (Ar) plasma-etching further bolstered the adsorption efficacy and electron transfer properties of photocatalyst. In comparison to the pristine BiOI and CB-2, the Ar-CB-2 photocatalyst demonstrated superior photodegradation efficiency, with the first-order reaction rates for the photodegradation of tetracycline (TC) and bisphenol A (BPA) increasing by 2.83 and 4.53 times, respectively. Further probe experiments revealed that the steady-state concentrations of ·O2- and 1O2 in the Ar-CB-2/light system were enhanced by a factor of 1.67 and 1.28 compared to CB-2/light system. This result confirmed that the porous and defect-rich structure of Ar-CB-2 inhibited electron-hole recombination and boosted photocatalyst-oxygen interaction, swiftly transforming O2 into active oxygen species, thus accelerating their production. Furthermore, the possible degradation pathways for TC and BPA in the Ar-CB-2/light system were predicted. Overall, these findings offered a groundbreaking approach to the development of highly effective photocatalysts, capable of swiftly breaking down emerging pollutants.

Formation and toxicity contribution of chlorinated and dechlorinated halobenzoquinones from dichlorophenols after ozonation

Halobenzoquinones (HBQs) are a class of disinfection byproducts with high cytotoxicity and potential carcinogenicity, which have been widely detected in chlorination of drinking water and swimming pool water. However, to date, the formation of HBQs upon ozonation and the HBQ precursors have been overlooked. This study investigated the formation of chlorinated and dechlorinated HBQs from six dichlorophenol (DCP) isomers. The monomeric and dimeric HBQs were identified in all the ozonation effluents, exhibiting 1-100 times higher toxicity levels than their precursors. The sum of detected HBQs intensity had a satisfactory linear relation with the maximum toxic unit (R2 = 0.9657), indicating the primary toxicity contribution to the increased overall toxicity of effluents. Based on density functional theory calculations, when ozone attacks the para carbon to the hydroxyl group of 2,3-DCP, the probability of producing chlorinated HBQs is 80.41 %, indicating that the para carbon attack mainly resulted in the formation of monomeric HBQs. 2,3-dichlorophenoxy radicals were successfully detected in ozonated 2,3-DCP effluent through electron paramagnetic resonance and further validated using theoretical calculation, revealing the formation pathway of dimeric HBQs. The results indicate that chlorinated phenols, regardless of the positions of chlorine substitution, can potentially serve as precursors for both chlorinated and dechlorinated HBQs formation during ozonation.

Chlorination of Emerging Contaminants for Application in Potable Wastewater Reuse: Disinfection Byproduct Formation, Estrogen Activity, and Cytotoxicity

With increasing water scarcity, many utilities are considering the potable reuse of wastewater as a source of drinking water. However, not all chemicals are removed in conventional wastewater treatment, and disinfection byproducts (DBPs) can form from these contaminants when disinfectants are applied during or after reuse treatment, especially if applied upstream of advanced treatment processes to control biofouling. We investigated the chlorination of seven priority emerging contaminants (17β-estradiol, estrone, 17α-ethinylestradiol, bisphenol A (BPA), diclofenac, p-nonylphenol, and triclosan) in ultrapure water, and we also investigated the impact of chlorination on real samples from different treatment stages of an advanced reuse plant to evaluate the role of chlorination on the associated cytotoxicity and estrogenicity. Many DBPs were tentatively identified via liquid chromatography (LC)- and gas chromatography (GC)-high resolution mass spectrometry, including 28 not previously reported. These encompassed chlorinated, brominated, and oxidized analogs of the parent compounds as well as smaller halogenated molecules. Chlorinated BPA was the least cytotoxic of the DBPs formed but was highly estrogenic, whereas chlorinated hormones were highly cytotoxic. Estrogenicity decreased by ∼4-6 orders of magnitude for 17β-estradiol and estrone following chlorination but increased 2 orders of magnitude for diclofenac. Estrogenicity of chlorinated BPA and p-nonylphenol were ∼50% of the natural/synthetic hormones. Potential seasonal differences in estrogen activity of unreacted vs reacted advanced wastewater treatment field samples were observed.

Hydrogen Peroxide Formation during Ozonation of Olefins and Phenol: Mechanistic Insights from Oxygen Isotope Signatures

Mitigation of undesired byproducts from ozonation of dissolved organic matter (DOM) such as aldehydes and ketones is currently hampered by limited knowledge of their precursors and formation pathways. Here, the stable oxygen isotope composition of H2O2 formed simultaneously with these byproducts was studied to determine if it can reveal this missing information. A newly developed procedure, which quantitatively transforms H2O2 to O2 for subsequent 18O/16O ratio analysis, was used to determine the δ18O of H2O2 generated from ozonated model compounds (olefins and phenol, pH 3-8). A constant enrichment of 18O in H2O2 with a δ18O value of ∼59‰ implies that 16O-16O bonds are cleaved preferentially in the intermediate Criegee ozonide, which is commonly formed from olefins. H2O2 from the ozonation of acrylic acid and phenol at pH 7 resulted in lower 18O enrichment (δ18O = 47-49‰). For acrylic acid, enhancement of one of the two pathways followed by a carbonyl-H2O2 equilibrium was responsible for the smaller δ18O of H2O2. During phenol ozonation at pH 7, various competing reactions leading to H2O2 via an intermediate ozone adduct are hypothesized to cause lower δ18O in H2O2. These insights provide a first step toward supporting pH-dependent H2O2 precursor elucidation in DOM.

Thiol Reactome: A Nontargeted Strategy to Precisely Identify Thiol Reactive Drinking Water Disinfection Byproducts

The precise identification of predominant toxic disinfection byproducts (DBPs) from disinfected water is a longstanding challenge. We propose a new acellular analytical strategy, the 'Thiol Reactome', to identify thiol-reactive DBPs by employing a thiol probe and nontargeted mass spectrometry (MS) analysis. Disinfected/oxidized water samples had reduced cellular oxidative stress responses of 46 ± 23% in Nrf2 reporter cells when preincubated with glutathione (GSH). This supports thiol-reactive DBPs as the predominant drivers of oxidative stress. This method was benchmarked using seven classes of DBPs including haloacetonitriles, which preferentially reacted with GSH via substitution or addition depending on the number of halogens present. The method was then applied to chemically disinfected/oxidized waters, and 181 tentative DBP-GSH reaction products were detected. The formulas of 24 high abundance DBP-GSH adducts were predicted, among which nitrogenous-DBPs (11) and unsaturated carbonyls (4) were the predominant compound classes. Two major unsaturated carbonyl-GSH adducts, GSH-acrolein and GSH-acrylic acid, were confirmed by their authentic standards. These two adducts were unexpectedly formed from larger native DBPs when reacting with GSH. This study demonstrated the "Thiol Reactome" as an effective acellular assay to precisely identify and broadly capture toxic DBPs from water mixtures.

Predicting Transformation Products during Aqueous Oxidation Processes: Current State and Outlook

Water quality and its impacts on human and ecosystem health presents tremendous global challenges. While oxidative water treatment can solve many of these problems related to hygiene and micropollutants, identifying and predicting transformation products from a large variety of micropollutants induced by dosed chemical oxidants and in situ formed radicals is still a major challenge. To this end, a better understanding of the formed transformation products and their potential toxicity is needed. Currently, no theoretical tools alone can predict oxidatively induced transformation products in aqueous systems. Coupling experimental and theoretical studies has advanced the understanding of reaction kinetics and mechanisms significantly. This perspective article highlights the key progress made concerning experimental and computational approaches to predict transformation products. Knowledge gaps are identified, and the research required to advance the predictive capability is discussed.

One-Electron Oxidant-Induced Transformations of Aromatic Alcohol to Ketone Moieties in Dissolved Organic Matter Increase Trichloromethane Formation

Radicals in advanced oxidation processes (AOPs) degrade micropollutants during water and wastewater treatment, but the transformation of dissolved organic matter (DOM) may be equally important. Ketone moieties in DOM are known disinfection byproduct precursors, but ketones themselves are intermediates produced during AOPs. We found that aromatic alcohols in DOM underwent transformation to ketones by one-electron oxidants (using SO4•- as a representative), and the formed ketones significantly increased trichloromethane (CHCl3) formation potential (FP) upon subsequent chlorination. CHCl3-FPs from aromatic ketones (Ar-CO-CH3, average of 22 mol/mol) were 6-24 times of CHCl3-FPs from aromatic alcohols (Ar-CH(OH)-CH3, average of 0.85 mol/mol). At a typical SO4•- exposure of 7.0 × 10-12 M·s, CHCl3-FPs from aromatic alcohol transformation increased by 24.8%-112% with an average increase of 53.4%. Notably, SO4•- oxidation of aliphatic alcohols resulted in minute changes in CHCl3-FPs due to their low reactivities with SO4•- (∼107 M-1 s-1). Other one-electron oxidants (Cl2•-, Br2•-,and CO3•-) are present in AOPs and also lead to aromatic alcohol-ketone transformations similar to SO4•-. This study highlights that subtle changes in DOM physicochemical properties due to one-electron oxidants can greatly affect the reactivity with free chlorine and the formation of chlorinated byproducts.

Redox-directed identification of toxic transformation products during ozonation of aromatics

The toxicity assessment of transformation products (TPs) formed in oxidative water treatment is crucial but challenging because of their low concentration, structural diversity, and mixture complexity. Here, this study developed a novel redox-directed approach for identification of toxic TPs without the individual toxicity and concentration information. This approach based on sodium borohydride reduction comprised an integrated process of toxicological evaluation, fluorescence excitation-emission matrix characterization, high-resolution mass spectrometry detection, followed by ecological toxicity assessment of identified TPs. The redox-directed identification of primary causative toxicants was experimentally tested for the increased nonspecific toxicity observations in the ozonated effluents of model aromatics. Reduction reaction caused a remarkable decrease in toxicity and increase in fluorescence intensity, obtaining a good linear relation between them. More than ten monomeric or dimeric p-benzoquinone (p-BQ) TPs were identified in the ozonated effluents. The occurrence of the p-BQ TPs was further verified through parallel sodium sulfite reduction and actual wastewater ozonation experiments. In vitro bioassays of luminescent bacteria, as well as in silico genotoxicity and cytotoxicity predictions, indicate that the toxicity of p-BQ TPs is significantly higher than that of their precursors and other TPs. These together demonstrated that the identified p-BQ TPs are primary toxicity contributors. The redox-directed approach facilitated the revelation of primary toxicity contribution, illustrating emerging p-BQs are a concern for aquatic ecosystem safety in the oxidative treatment of aromatics-contaminated wastewater.

Tire-rubber related pollutant 6-PPD quinone: A review of its transformation, environmental distribution, bioavailability, and toxicity

The antioxidant 6-PPD has been widely used to prevent cracking and thermal oxidative degradation and to extend the service life of tire rubber. 6-PPD quinone (6-PPDQ) is formed via the reaction of 6-PPD with O3. Due to its acute lethality in coho salmon, 6-PPDQ has become an emerging pollutant of increasing concern. In this review, we provide a critical overview of the generation, environmental distribution, bioavailability, and potential toxicity of 6-PPDQ. The transformation pathways from 6-PPD to 6-PPDQ include the N-1,3-dimethylbutyl-N-phenyl quinone diamine (QDI), intermediate phenol, and semiquinone radical pathways. 6-PPDQ has been frequently detected in water, dust, air particles, soil, and sediments, indicating its large-scale and potentially global pollution trend. 6-PPDQ is bioavailable to both aquatic animals and mammals and acute exposure to 6-PPDQ can be lethal to some organisms. Exposure to 6-PPDQ at environmentally relevant concentrations could induce several types of toxicity, including neurotoxicity, intestinal toxicity, and reproductive toxicity. This review also identifies and discusses knowledge gaps and research needs for the study of 6-PPDQ. This review facilitates a better understanding of the environmental occurrence and exposure risk of 6-PPDQ.

Guidance document on the impact of water treatment processes on residues of active substances or their metabolites in water abstracted for the production of drinking water

This guidance document provides a tiered framework for risk assessors and facilitates risk managers in making decisions concerning the approval of active substances (AS) that are chemicals in plant protection products (PPPs) and biocidal products, and authorisation of the products. Based on the approaches presented in this document, a conclusion can be drawn on the impact of water treatment processes on residues of the AS or its metabolites in surface water and/or groundwater abstracted for the production of drinking water, i.e. the formation of transformation products (TPs). This guidance enables the identification of actual public health concerns from exposure to harmful compounds generated during the processing of water for the production of drinking water, and it focuses on water treatment methods commonly used in the European Union (EU). The tiered framework determines whether residues from PPP use or residues from biocidal product use can be present in water at water abstraction locations. Approaches, including experimental methods, are described that can be used to assess whether harmful TPs may form during water treatment and, if so, how to assess the impact of exposure to these water treatment TPs (tTPs) and other residues including environmental TPs (eTPs) on human and domesticated animal health through the consumption of TPs via drinking water. The types of studies or information that would be required are described while avoiding vertebrate testing as much as possible. The framework integrates the use of weight-of-evidence and, when possible alternative (new approach) methods to avoid as far as possible the need for additional testing.

Decoupling Optical Response and Photochemical Formation of Singlet Oxygen in Size Isolated Fractions of Ozonated Dissolved Organic Matter

The complex effects of ozonation on the photophysical and size-based properties of dissolved organic matter (DOM) were investigated using two DOM isolates, Suwannee River Fulvic Acid (SRFA) and Pony Lake Fulvic Acid (PLFA). A size exclusion chromatography system paired with absorbance, fluorescence, and total organic carbon detection was used to determine the fluorescence quantum yield (Φ_f) as a function of the apparent molecular weight (AMW). Size-based fractions of each isolate were collected and irradiated to measure singlet oxygen (¹O₂) quantum yield (Φ_1O2). Φ_f decreased with ozonation in low AMW fractions, while increasing in high AMW fractions. Φ_1O2 increased with ozone dose in low AMW fractions from ∼2 to ∼7% and ∼3 to ∼11% for PLFA and SRFA, respectively, indicating that these are the most photoreactive fractions of DOM. Decreases in Φ_f and concomitant increases in Φ_1O2 in low AMW fractions indicated that chemical transformations occurred, likely including the conversion of phenols to quinones, particularly in SRFA. Results further suggest that the photoactive and fluorescent fractions of DOM are likely independent pools of chromophores from different AMW fractions. In PLFA, a linear response in Φ_1O2, specific UV absorbance at wavelength 254 nm (SUVA₂₅₄), and Φ_f with ozonation indicated the equal distribution of ozone-reactive moieties.

Transformation Products of Tire Rubber Antioxidant 6PPD in Heterogeneous Gas-Phase Ozonation: Identification and Environmental Occurrence

6PPD, a tire rubber antioxidant, poses substantial ecological risks because it can form a highly toxic quinone transformation product (TP), 6PPD-quinone (6PPDQ), during exposure to gas-phase ozone. Important data gaps exist regarding the structures, reaction mechanisms, and environmental occurrence of TPs from 6PPD ozonation. To address these data gaps, gas-phase ozonation of 6PPD was conducted over 24-168 h and ozonation TPs were characterized using high-resolution mass spectrometry. The probable structures were proposed for 23 TPs with 5 subsequently standard-verified. Consistent with prior findings, 6PPDQ (C18H22N2O2) was one of the major TPs in 6PPD ozonation (∼1 to 19% yield). Notably, 6PPDQ was not observed during ozonation of 6QDI (N-(1,3-dimethylbutyl)-N'-phenyl-p-quinonediimine), indicating that 6PPDQ formation does not proceed through 6QDI or associated 6QDI TPs. Other major 6PPD TPs included multiple C18H22N2O and C18H22N2O2 isomers, with presumptive N-oxide, N,N'-dioxide, and orthoquinone structures. Standard-verified TPs were quantified in roadway-impacted environmental samples, with total concentrations of 130 ± 3.2 μg/g in methanol extracts of tire tread wear particles (TWPs), 34 ± 4 μg/g-TWP in aqueous TWP leachates, 2700 ± 1500 ng/L in roadway runoff, and 1900 ± 1200 ng/L in roadway-impacted creeks. These data demonstrate that 6PPD TPs are likely an important and ubiquitous class of contaminants in roadway-impacted environments.

Computational Studies of Rubber Ozonation Explain the Effectiveness of 6PPD as an Antidegradant and the Mechanism of Its Quinone Formation

The discovery that the commercial rubber antidegradant 6PPD reacts with ozone (O₃) to produce a highly toxic quinone (6PPDQ) spurred a significant research effort into nontoxic alternatives. This work has been hampered by lack of a detailed understanding of the mechanism of protection that 6PPD affords rubber compounds against ozone. Herein, we report high-level density functional theory studies into early steps of rubber and PPD (p-phenylenediamine) ozonation, identifying key steps that contribute to the antiozonant activity of PPDs. In this, we establish that our density functional theory approach can achieve chemical accuracy for many ozonation reactions, which are notoriously difficult to model. Using adiabatic energy decomposition analysis, we examine and dispel the notion that one-electron charge transfer initiates ozonation in these systems, as is sometimes argued. Instead, we find direct interaction between O₃ and the PPD aromatic ring is kinetically accessible and that this motif is more significant than interactions with PPD nitrogens. The former pathway results in a hydroxylated PPD intermediate, which reacts further with O₃ to afford 6PPD hydroquinone and, ultimately, 6PPDQ. This mechanism directly links the toxicity of 6PPDQ to the antiozonant function of 6PPD. These results have significant implications for development of alternative antiozonants, which are discussed.

Enzymatic post-treatment of ozonation: laccase-mediated removal of the by-products of acetaminophen ozonation

Ozonation is a powerful technique to remove micropollutants from wastewater. As chemical oxidation of wastewater comes with the formation of varying, possibly persistent and toxic by-products, post-treatment of the ozonated effluent is routinely suggested. This study explored an enzymatic treatment of ozonation products using the laccase from Trametes versicolor. A high-performance liquid chromatography coupled with high-resolution mass spectrometry (HPLC-HRMS) analysis revealed that the major by-products were effectively degraded by the enzymatic post-treatment. The enzymatic removal of the by-products reduced the ecotoxicity of the ozonation effluent, as monitored by the inhibition of Aliivibrio fischeri. The ecotoxicity was more effectively reduced by enzymatic post-oxidation at pH 7 than at the activity maximum of the laccase at pH 5. A mechanistic HPLC-HRMS and UV/Vis spectroscopic analysis revealed that acidic conditions favored rapid conversion of the phenolic by-products to dead-end products in the absence of nucleophiles. In contrast, the polymerization to harmless insoluble polymers was favored at neutral conditions. Hence, coupling ozonation with laccase-catalyzed post-oxidation at neutral conditions, which are present in wastewater effluents, is suggested as a new resource-efficient method to remove persistent micropollutants while excluding the emission of potentially harmful by-products.

Ozonation of lake water and wastewater: Identification of carbonous and nitrogenous carbonyl-containing oxidation byproducts by non-target screening

Ozonation of drinking water and wastewater is accompanied by the formation of disinfection byproducts (DBPs) such as low molecular weight aldehydes and ketones from the reactions of ozone with dissolved organic matter (DOM). By applying a recently developed non-target workflow, 178 carbonous and nitrogenous carbonyl compounds were detected during bench-scale ozonation of two lake waters and three secondary wastewater effluent samples and full-scale ozonation of secondary treated wastewater effluent. An overlapping subset of carbonyl compounds (20%) was detected in all water types. Moreover, wastewater effluents showed a significantly higher fraction of N-containing carbonyl compounds (30%) compared to lake water (17%). All carbonyl compounds can be classified in 5 main formation trends as a function of increasing specific ozone doses. Formation trends upon ozonation and comparison of results in presence and absence of the ^•OH radical scavenger DMSO in combination with kinetic and mechanistic information allowed to elucidate potential carbonyl structures. A link between the detected carbonyl compounds and their precursors was established by ozonating six model compounds (phenol, 4-ethylphenol, 4-methoxyphenol, sorbic acid, 3-buten-2-ol and acetylacetone). About one third of the detected carbonous carbonyl compounds detected in real waters was also detected by ozonating model compounds. Evaluation of the non-target analysis data revealed the identity of 15 carbonyl compounds, including hydroxylated aldehydes and ketones (e.g. hydroxyacetone, confidence level (CL) = 1), unsaturated dicarbonyls (e.g. acrolein, CL = 1; 2-butene-1,4-dial, CL = 1; 4-oxobut-2-enoic acid, CL = 2) and also a nitrogen-containing carbonyl compound (2-oxo-propanamide, CL =1). Overall, this study shows the formation of versatile carbonous and nitrogenous carbonyl compounds upon ozonation involving ozone and ^•OH reactions. Carbonyl compounds with unknown toxicity might be formed, and it could be demonstrated that acrolein, malondialdehyde, methyl glyoxal, 2-butene-1,4-dial and 4-oxo-pentenal are degraded during biological post-treatment.

Impact of chlorination and ozonation of dissolved organic matter on its photo-induced production of long-lived photooxidants and excited triplet states

Recent studies suggested that long-lived photooxidants (LLPO), which are reactive intermediates formed during irradiation of dissolved organic matter (DOM), may consist of phenoxyl radicals derived from phenolic moieties of the DOM. Besides the well-studied excited triplet states of chromophoric DOM (³CDOM*), LLPO presumably are important photooxidants for the transformation of electron-rich contaminants in surface waters. The main objective of this study was to further test the potential role of phenoxyl radical as LLPO. Suwannee River fulvic acid (SRFA) as a model DOM was pre-oxidised using the phenol-reactive oxidants chlorine and ozone, followed by its characterization by the specific UV absorption at 254 nm (SUVA₂₅₄), the ratio of absorbance at λ = 254 nm and λ = 365 nm (E2:E3), and the electron donating capacity (EDC). Subsequently, the photoreactivity of pre-oxidized SRFA was tested using 3,4-dimethoxyphenol (DMOP) as a LLPO probe compound at two initial concentrations ([DMOP]₀ = 0.1 and 5.0 μM). Linear inter-correlations were observed for the relative changes in SUVA₂₅₄, E2:E3, and EDC for increasing oxidant doses. Pseudo-first-order transformation rate constants normalized to the changing SRFA absorption rate (i.e., k_0.1^obs/r_CDOM^absand k_5.0^obs/r_CDOM^abs, for 0.1 and 5.0 µM, respectively) exhibited the following distinct trends: The LLPO-dominated k_0.1^obs/r_CDOM^absratio decreased with increasing oxidant dose and with decreasing SUVA₂₅₄ and EDC, while the ³CDOM*-dominated k_5.0^obs/r_CDOM^absratio positively correlated with E2:E3. Finally, it was concluded that precursors of ³CDOM* and LLPO are chemically modified differently by pre-oxidation of DOM, and LLPO precursors likely consist of phenolic moieties of DOM, suggesting phenoxyl radicals as LLPO.

Comparison of nitrate formation mechanisms from free amino acids and amines during ozonation: a computational study

Nitrate as a potential surrogate parameter for abatement of micropollutants, oxidant exposure, and characterizing oxidant-reactive DON during ozonation has attracted extensive attention, however, understanding of its formation mechanisms is still limited. In this study, nitrate formation mechanisms from amino acids (AAs) and amines during ozonation were investigated by the DFT method. The results indicate that N-ozonation initially occurs to produce competitive nitroso- and N,N-dihydroxy intermediates, and the former is preferred for both AAs and primary amines. Then, oxime and nitroalkane are generated during further ozonation, which are the important last intermediate products for nitrate formation from the respective AAs and amines. Moreover, the ozonation of the above important intermediates is the nitrate yield-controlling step, where the relatively higher reactivity of the CN moiety in the oxime compared to the general C_α atom in the nitroalkane explains why the nitrate yields of most AAs are higher than those from general amines, and it is the larger number of released C_α^- anions, which are the real reaction sites attacked by ozone, that leads to the higher nitrate yield for nitroalkane with an electron-withdrawing group bound to the C_α atom. The good relationship between nitrate yields and activation free energies of the rate-limiting step (ΔG≠rls) and nitrate yield-controlling step (ΔG≠nycs) for the respective AAs and amines verifies the reliability of the proposed mechanisms. Additionally, the bond dissociation energy of C_α-H in the nitroalkanes formed from amines was found to be a good parameter to evaluate the reactivity of the amines. The findings here are helpful for further understanding nitrate formation mechanisms and predicting nitrate precursors during ozonation.

Formation of carbonyl compounds during ozonation of lake water and wastewater: Development of a non-target screening method and quantification of target compounds

Ozonation of natural waters is typically associated with the formation of carbonyl compounds (aldehydes, ketones and ketoacids), a main class of organic disinfection byproducts (DBPs). However, the detection of carbonyl compounds in water and wastewater is challenged by multiple difficulties inherent to their physicochemical properties. A non-target screening method involving the derivatisation of carbonyl compounds with p-toluenesulfonylhydrazine (TSH) followed by their analysis using liquid chromatography coupled to electrospray ionisation high-resolution mass spectrometry (LC-ESI-HRMS) and an advanced non-target screening and data processing workflow was developed. The workflow was applied to investigate the formation of carbonyl compounds during ozonation of different water types including lake water, aqueous solutions containing Suwannee River Fulvic acid (SRFA), and wastewater. A higher sensitivity for most target carbonyl compounds was achieved compared to previous derivatisation methods. Moreover, the method allowed the identification of known and unknown carbonyl compounds. 8 out of 17 target carbonyl compounds were consistently detected above limits of quantification (LOQs) in most ozonated samples. Generally, the concentrations of the 8 detected target compounds decreased in the order: formaldehyde > acetaldehyde > glyoxylic acid > pyruvic acid > glutaraldehyde > 2,3-butanedione > glyoxal > 1-acetyl-1-cyclohexene. The DOC concentration-normalised formation of carbonyl compounds during ozonation was higher in wastewater and SRFA-containing water than in lake water. The specific ozone doses and the type of the dissolved organic matter (DOM) played a predominant role for the extent of formation of carbonyl compounds. Five formation trends were distinguished for different carbonyl compounds. Some compounds were produced continuously upon ozonation even at high ozone doses, while others reached a maximum concentration at a certain ozone dose above which they decreased. Concentrations of target and peak areas of non-target carbonyl compounds during full-scale ozonation at a wastewater treatment plant showed an increase as a function of the specific ozone dose (sum of 8 target compounds ∼ 280 µg/L at 1 mgO₃/mgC), followed by a significant decrease after biological sand filtration (> 64-94% abatement for the different compounds). This highlights the biodegradability of target and non-target carbonyl compounds and the importance of biological post-treatment.

Oxidative treatment of NOM by selective oxidants in drinking water treatment and its impact on DBP formation in postchlorination

Natural organic matter (NOM), as a ubiquitous component in aqueous environments, has raised continuous scientific concerns due to its role as an organic precursor to disinfection by-products (DBPs) in the subsequent chlorination process. Selective oxidants, including ozone (O₃), chlorine dioxide (ClO₂), permanganate (Mn(VII)), and ferrate (Fe(VI)) are widely used in the preoxidation stage in drinking water treatment. The selective reactivity of those oxidants toward NOM is expected to alternate NOM properties and consequently DBP formation in postchlorination. Despite extensive studies on the interactions of NOM with selective oxidants, there is currently a lack of an overview of this area. To fill this gap, this study presents the current knowledge of the modification of NOM properties by selective oxidants and its impact on DBP formation in postchlorination. The NOM property changes in three aspects, including bulk property (e.g., total organic carbon, ultraviolet absorbance), fractional constituent (e.g., molecular size, hydrophilicity/hydrophobicity), and elemental composition (e.g., functional group) by the four selective oxidants (i.e., O₃, ClO₂, Mn(VII), and Fe(VI)) were discussed. Thereafter, the impacts of alteration of NOM properties by those selective oxidants on DBP formation in the subsequent chlorination were summarized, wherein the key influencing factors were discussed. Finally, the future perspectives in this area were forwarded, which highlighted the significance of process optimization, the attention to the less studied but more toxic DBPs, and the need for the identification of unknown DBPs. This review presented a state-of-the-art knowledge pool of the fate of NOM in oxidation and chlorination processes, promoted our understanding of the relationship between NOM properties and DBP formation, and identified further research needs in this area.

Ozone mechanism, kinetics, and toxicity studies of halophenols: Theoretical calculation combined with toxicity experiment

Aromatic disinfection by-products (DBPs), which are generally more toxic than aliphatic DBPs, have attracted increasing attention. The toxicity of 13 typical halophenols on Scenedesmus obliquus was experimentally investigated, and the ozonation mechanism and kinetics of representative halophenols were further studied by quantum chemical calculations. The results showed that the EC₅₀ values of halophenols ranged from 2.74 to 60.23 mg/L, and their toxicity ranked as follows: di-halogenated phenols > mono-halogenated phenols, mixed halogen-substituted phenols > single halogen-substituted phenols, and iodophenols > bromophenols > chlorophenols. The toxicity of halophenols was well described by the electronegativity index (ω) as lg(EC₅₀)^-1 = 6.228ω - 3.869, indicating halophenols capturing electrons as their potential toxicity mechanism. The reactions of O₃ with halophenolate anions were dominated by three mechanisms: 1,3-dipolar cycloaddition, oxygen addition, and single electron transfer. The kinetic calculation indicated that O₃ oxidized aqueous halophenols by reacting with halophenolate anions with the reaction rate constants as high as (0.91-3.47) × 10¹⁰ M^-1 s^-1. The number of halogen substituents affected the k_{O3, cal} values of halophenolate anions, which are in the order of 2,4-dihalophenolate anions >4-halophenolate anions > 2,4,6-trihalophenolate anions. During the ozonation of 2,4,6-tribromophenol (246TBP), the toxic products (dimers and brominated benzoquinones) could be synergistically degraded by O₃ and HO^•. Thus, ozonation is feasible as a strategy to degrade aromatic DBPs.

Identification of chlorinated products from tyrosine and tyrosyl dipeptides during chlorination: a computational study

Chlorinated amino acids and peptides, as the model modified protein structures relevant to pathogen inactivation and an emerging class of disinfection byproducts (DBPs) with potential health risks to humans, have attracted much attention. However, due to a large variety of peptides (over 600) identified in source water and most of them featuring multiple reaction sites, it is a huge challenge to identify all the chlorinated amino acids and peptides. As a good complement to the experiment, quantum chemical computation can be used to uncover the chlorination sites and chlorinated products. In this study, frequently detected tyrosine (Tyr) and tyrosine-amide (Tyr-Am) as well as N-acetyl-tyrosine (NacTyr) were chosen as the model amino acid and model dipeptides, respectively. The results indicate that the kinetic reactivity order of reactive sites with estimated apparent rate constants (k_obs-est, in M^-1 s^-1) is amino N (10^7-8) ≫ mono-chlorinated amino N (10^1-3) >/≈ phenol ortho-C (10^0-3) ≫ meta-C (10^-3), and phenol ortho-C5 (10^2-3) > ortho-C3 (10^0-2) for dipeptides, while in thermodynamics, phenol C sites are more favorable than amino N sites. Moreover, due to the smaller differences of k_obs-est values between the mono-chlorinated amino N and the phenol ortho-C sites in tyrosyl dipeptides compared to free Tyr, more kinds of C-chloro-tyrosyl dipeptides are likely to be generated. Additionally, a structure-kinetic reactivity relationship study reveals good correlations between lg k_obs-est and NPA charges and BDEs of protons released from amino/hydroxyl groups in tyrosyl compounds rather than FED² (HOMO). The results are helpful to further understand the reactivity of various reaction sites in peptides and identify chlorinated products from tyrosyl peptides during chlorination.

Reactions of bisphenol F and bisphenol S with ozone and hydroxyl radical: Kinetics and mechanisms

Bisphenol F (BPF) and bisphenol S (BPS) are the most employed substitutes of bisphenol A (BPA), after being restricted by legislation in different countries because of its endocrine disrupting behaviour. In the present work, a deep study was performed about the reactivity of BPF and BPS with ozone and hydroxyl radical. Firstly, the second order rate constants of ozone with the di-protonated, mono-protonated and deprotonated species of both bisphenols were determined to be 2.38 × 10⁴, 1.31 × 10⁹ and 1.43 × 10⁹ M^-1 s^-1 for BPF and 5.01, 2.82 × 10⁷ and 1.09 × 10⁹ M^-1 s^-1 for BPS. Then, the second order rate constants for the reaction of hydroxyl radical with BPF and BPS were established through UV/H₂O₂ and UV experiments at pH 7, resulting in the values of 8.60 × 10⁹ and 6.60 × 10⁹ M^-1 s^-1, respectively. Finally, a study regarding the transformation products (TPs) from the reaction of both bisphenols with molecular ozone and hydroxyl radical was also performed. Hydroxylation in the ortho position of the phenol rings was observed as main degradation pathway. Additionally, most of the TPs were accumulated over the reactions at relatively high oxidant doses.

Further transformation of the primary ozonation products of tramadol- and venlafaxine N-oxide: Mechanistic and structural considerations

Ozonation has been used to effectively remove micropollutants from the secondary effluent in several wastewater treatment plants. It is known that ozonation transforms tertiary amine compounds into their respective N-oxides, however in an earlier study a mass balance could not be closed at elevated ozone concentrations, leading to the assumption that more ozonation products are possible. This study was conducted to elucidate which (hitherto unknown) ozonation products can be formed from venlafaxine and tramadol when ozonating wastewater. Ozonation experiments were performed with tramadol and venlafaxine N-oxide in two different set-ups. Both tramadol- and venlafaxine N-oxide degraded during ozonation in pure (deionized) water in both semi-continuous and batch mode ozonation set-ups. 13 and 17 new transformation products were detected from tramadol- and venlafaxine N-oxide respectively, using high resolution mass spectrometry with ESI(+) ionization. Empirical chemical formulas were proposed based on the determination of the exact masses and interpretation of the product ion spectra. These transformation products result from the addition of one to three oxygen atoms and removal of C, -CH₂, C₂H₂, C₃H₆, etc., from the parent molecule, respectively. Quenching experiments suggested that most of the transformation products originated from the direct reaction with ozone (eight for tramadol N-oxide and ten for venlafaxine N-oxide), whereas fewer products originated from the reaction with OH radicals (three for tramadol N-oxide and three for venlafaxine N-oxide). Reaction mechanisms and chemical structures of products are proposed, based on the available active sites and past literature on ozone reaction mechanisms. The experimental results are compared to theory and literature on ozone reactive sites and ozone reaction mechanisms. All in all this shows that there can be multiple ozonation products, and ozonation pathways can be complex, even if initially only one ozonation product is formed.

Unveiling the pH-Dependent Yields of H2O2 and OH by Aqueous-Phase Ozonolysis of m-Cresol in the Atmosphere

Hydrogen peroxide (H₂O₂) and hydroxyl radical (OH) are important oxidants in the atmospheric aqueous phase such as cloud droplets and deliquescent aerosol particles, playing a significant role in the chemical transformation of organic and inorganic pollutants in the atmosphere. Atmospheric aqueous-phase chemistry has been considered to be a source of H₂O₂ and OH. However, our understanding of the mechanisms of their formation in atmospheric waters is still incomplete. Here, we show that the aqueous-phase reaction of dissolved ozone (O₃) with substituted phenols such as m-cresol represents an important source of H₂O₂ and OH exhibiting pH-dependent yields. Intriguingly, the formation of H₂O₂ through the ring-opening mechanism is strongly promoted under lower pH conditions (pH 2.5-3.5), while higher pH favors the ring-retaining pathways yielding OH. The rate constant of the reaction of O₃ with m-cresol increases with increasing pH. The reaction products formed during the ozonolysis of m-cresol are analyzed by an Orbitrap mass spectrometer, and reaction pathways are suggested based on the identified product compounds. This study indicates that aqueous-phase ozonolysis of phenolic compounds might be an alternative source of H₂O₂ and OH in the cloud, rain, and liquid water of aerosol particles; thus, it should be considered in future model studies.

Ozonation of organic compounds in water and wastewater: A critical review

Ozonation has been applied in water treatment for more than a century, first for disinfection, later for oxidation of inorganic and organic pollutants. In recent years, ozone has been increasingly applied for enhanced municipal wastewater treatment for ecosystem protection and for potable water reuse. These applications triggered significant research efforts on the abatement efficiency of organic contaminants and the ensuing formation of transformation products. This endeavor was accompanied by developments in analytical and computational chemistry, which allowed to improve the mechanistic understanding of ozone reactions. This critical review assesses the challenges of ozonation of impaired water qualities such as wastewaters and provides an up-to-date compilation of the recent kinetic and mechanistic findings of ozone reactions with dissolved organic matter, various functional groups (olefins, aromatic compounds, heterocyclic compounds, aliphatic nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, carbanions, β-diketones) and antibiotic resistance genes.

Overlooked environmental risks deriving from aqueous transformation of bisphenol alternatives: Integration of chemical and toxicological insights

Owing to the widespread prevalence and ecotoxicity of bisphenol alternatives such as bisphenol S, bisphenol F, and bisphenol AF, the past decade has witnessed the publication of a remarkable number of studies related to their transformation and remediation in natural waters. However, the reactivity, removal efficiency, transformation products (TPs), and mechanisms of such emerging pollutants by different treatment processes have not been well elucidated. Particularly, the transformation-driven environmental risks have been mostly overlooked. Therefore, we present a review to address these issues from chemical and toxicological viewpoints. Four degradation systems can be largely classified as catalytic persulfate (PS) oxidation, non-catalytic oxidation, photolysis and photocatalysis, and biodegradation. It was found that bisphenol alternatives possess distinct reactivities with different oxidizing species, with the highest performance for hydroxyl radicals. All systems exhibit superior elimination efficiency for these compounds. The inadequate mineralization suggests the formation of recalcitrant TPs, from which the overall reaction pathways are proposed. The combined experimental and in silico analysis indicates that many TPs have developmental toxicity, endocrine-disrupting effects, and genotoxicity. Notably, catalytic PS systems and non-catalytic oxidation result in the formation of coupling products as well as halogenated TPs with higher acute and chronic toxicity and lower biodegradability than the parent compounds. In contrast, photolysis and photocatalysis generate hydroxylated and bond-cleavage TPs with less toxicity. Overall, this review highlights the secondary environmental risks from the transformation of bisphenol alternatives by conventional and emerging treatment processes. Finally, future perspectives are recommended to address the knowledge gaps of these contaminants in aquatic ecosystems.

Reaction kinetics and degradation efficiency of halogenated methylparabens during ozonation and UV/H2O2 treatment of drinking water and wastewater effluent

This study investigated the reaction kinetics and degradation efficiency of methylparaben and its halogenated products (Cl-, Br-, Cl,Cl-, Br,Cl-, and Br,Br-methylparabens) during ozonation and UV₂₅₄/H₂O₂ treatment. Second-order rate constants for reactions of the parabens with ozone and ^•OH were [Formula: see text] = 10⁷ - 10⁸ M^-1 s^-1 and [Formula: see text] = (2.3 - 4.3)× 10⁹ M^-1 s^-1 at pH 7. Species-specific [Formula: see text] values of the protonated and deprotonated parabens were closely related to phenol ring substituent effects via quantitative structure-activity relationships with other substituted phenols. The UV photolysis rate of the parabens [k_UV = (2.4 - 7.2)× 10^-4 cm² mJ^-1] depended on the halogenation state of the paraben and solution pH, from which species-specific quantum yields were also determined. In simulated treatments of drinking water and wastewater effluent, the parabens were efficiently eliminated during ozonation, requiring a specific ozone dose of > 0.26 gO₃/gDOC for > 97% degradation. During UV/H₂O₂ treatment with 10 mg L^-1 H₂O₂, the degradation levels were > 90% at a UV fluence of 2000 mJ cm^-2, except for Cl,Cl-methylparaben. Kinetic models based on the obtained reaction kinetic parameters could successfully predict the degradation levels of the parabens. Overall, ozonation and UV/H₂O₂ were effective in controlling parabens and their halogenated products during advanced water treatment.

Identification of unknown disinfection byproducts in drinking water produced from Taihu Lake source water

Although disinfection byproducts (DBPs) in drinking water have been suggested as a cancer causing factor, the causative compounds have not yet been clarified. In this study, we used liquid chromatography quadrupole-time-of-flight spectrometry (LC-QTOF MS) to identify the unknown disinfection byproducts (DBPs) in drinking water produced from Taihu Lake source water, which is known as a convergence point for the anthropogenic pollutants discharged from intensive industrial activities in the surrounding regions. In total, 91 formulas of DBPs were discovered through LC-QTOF MS nontarget screen, 81 of which have not yet been reported. Among the 91 molecules, 56 only contain bromine, 15 only contain chlorine and 20 DBPs have both bromine and chlorine atoms. Finally, five DBPs including 2,4,6-tribromophenol, 2,6-dibromo-4-chlorophenol, 2,6-dichloro-4-bromophenol, 4-bromo-2,6-di-tert-butylphenol and 3,6-dibromocarbazole were confirmed using standards. The former three compounds mainly formed in the predisinfection step (maximum concentration, 0.2-2.6 µg/L), while the latter two formed in the disinfection step (maximum concentration, 18.2-33.6 ng/L). In addition, 19 possible precursors of the discovered DBPs were detected, with the aromatic compounds being a major group. 2,6-di-tert-butylphenol as the precursor of 4-bromo-2,6-di-tert-butylphenol was confirmed with standard, with a concentration of 20.3 µg/L in raw water. The results of this study show that brominated DBPs which are possibly formed from industrial pollutants are relevant DBP species in drinking water produced form Taihu source water, suggesting protection of Taihu Lake source water is important to control the DBP risks.

Prediction of reaction mechanism for OH radical-mediated phenol oxidation using quantum chemical calculation

Understanding the reaction mechanism of OH•-mediated oxidation of organic micropollutants (OMPs) contributes to the assessment and development of advanced oxidation processes (AOPs) for removal of OMPs in water environment. In this study, a theoretical approach using quantum chemical calculation (QCC) was employed to investigate the prediction accuracy of the reaction mechanism (i.e., reaction site and rate) for OH•-mediated oxidation of phenol, where the hydroquinone and catechol are generated as transformation products (TPs) via radical and electrophilic reactions. We compared three different levels of theory (Hartree-Fock, B3LYP, and M06-2X) with 6-311 + G (2d,2p)/SMD, and the reaction site and rate constants were predicted by the Fukui function and transition state theory, respectively. Overall, the prediction accuracy of the TPs formation mechanism was the highest in the calculations using M06-2X. For example, the initial OH• addition to phenol was predicted to occur with a probability of 77% for the ortho position and 23% for the para position, which was consistent with the experimental observation. By applying the transition state theory, the rate constants toward TPs formation pathway can be reasonably reproduced, suggesting that M06-2X has an effective function for polycyclic reactions. However, the observed discrepancies in rate constants are inferred from dispersion effects and the multi-reference property in the computational system or derived from mismatch of target reactions between theoretical calculations and experiments. Overall, this study provides an insight into QCC application for investigating the formation mechanism of TPs in AOPs for removal of OMPs in water environment.

Linking reaction rate constants and isotope fractionation of ozonation reactions using phenols as probes

Ozonation is nowadays a widely used method in drinking water treatment for disinfection and pollutant control. However, transformation products of ozonation can be more toxic than their parent compounds. Therefore, the knowledge of the reaction mechanisms and product formation is essential for a safe application. Different analytical methods such as high-resolution mass spectrometry (HRMS) and compound-specific isotope analysis (CSIA) can be applied to elucidate products and primary attack positions of oxidation agents such as ozone. During the investigation of the ozonation of phenolic compounds in water by CSIA, a reaction rate depending carbon isotope fractionation was observed. The fractionation strongly depends on the phenol speciation. With decreasing pH values and reaction rates <10⁵ M^-1 s^-1, the isotope enrichment factor ε increases (ε is between -5.2 and -1.0‰). For faster reactions (>10⁵ M^-1 s^-1), the carbon isotope enrichment was not significant anymore (ε is between -1.0 and 0‰). Based on these data a concept to correlate isotope enrichment factors with kinetic data for aromatic compounds is proposed. The additional investigation of aliphatic double and triple bonds did not fit this correlation suggesting different rate-limiting steps. However, double and triple bond showed a similar enrichment factor, which implies the same rate-limiting step in the reaction with ozone, the monodentate addition of ozone.

Fe-Mn doped powdered activated carbon pellet as ozone catalyst for cost-effective phenolic wastewater treatment: Mechanism studies and phenol by-products elimination

A novel bimetallic doped PAC (Fe-Mn/PAC) pellet was prepared with a facile sol-gel method and used as an ozone catalyst for phenolic wastewater (PWW) treatment. Adoption of Fe-Mn/PAC pellet in microbubble ozonation enhanced the 1-h chemical oxygen demand (COD) and phenol removal in PWW to 79% and 95%, respectively. With ozone dosage of 10 mg/L, 1 g/L Fe-Mn/PAC pellet exhibited ozone conversion of 92%. In comparison to microbubble ozonation process, Fe-Mn/PAC induced microbubble-catalytic ozonation process promoted ozone decomposition rate by 1.9 times. In terms of ^•OH production, Fe-Mn/PAC pellet enhanced ^•OH exposure by 10 times, with a R_ct value of 2.92 × 10 ^-8. R_ct kinetic model also suggested that Fe-Mn/PAC pellet obtained higher kinetic rate constants for initiating and promoting ^•OH generation. Usage of Fe-Mn/PAC pellet in microbubble ozonation for phenolic wastewater treatment also reduced the total ozone consumption by 70%. In Fe-Mn/PAC induced microbubble-catalytic ozonation process, the ratio between ozone consumption and COD removal (ΔO₃/ΔCOD) was 0.91. Fe-Mn/PAC pellet characterization with X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) and X-ray powder diffraction (XRD) analysis revealed successful doping of Fe-Mn on PAC substrate and larger numbers of carbon-oxygen/hydroxyl surface groups, which played key roles in ozone decomposition and ^•OH production.

Application of UV absorbance and electron-donating capacity as surrogates for micropollutant abatement during full-scale ozonation of secondary-treated wastewater

Ozonation of secondary-treated wastewater for the abatement of micropollutants requires a reliable control of ozone doses. Changes in the UV absorbance of dissolved organic matter (DOM) during ozonation allow to estimate micropollutant abatement on-line and were therefore identified as feed-back control parameter. In this study, the suitability of the electron-donating capacity (EDC) as an additional surrogate parameter which is independent of optical DOM properties was evaluated during full-scale ozonation. For this purpose, a recently developed EDC analyzer was enhanced to enable continuous on-line EDC and UV absorbance measurements. During a multi-week monitoring campaign at the wastewater treatment plant of Zurich, Switzerland, specific ozone doses were varied from 0.13 to 0.91 mgO3⋅mgDOC-1 and selected micropollutants with different ozone reactivities were analyzed by LC-MS in conjunction with bromate analysis by IC-MS. In agreement with previous laboratory studies, the relative residual UV absorbance and EDC both decreased exponentially as a function of the specific ozone dose and, in comparison to the residual UV absorbance, residual EDC values showed a more pronounced decrease at low specific ozone doses ≤0.34 mgO3⋅mgDOC-1. Logistic regression models allowed to estimate relative residual micropollutant concentrations in the ozonation effluent using either the residual UV absorbance or EDC as explanatory variable. Averaging those models along the explanatory variables allowed to estimate target values in relative residual UV absorbances and EDC for specific micropollutant abatement targets. In addition, both parameters allowed to identify conditions with elevated conversions of bromide to bromate. Taken together, these findings show that the integration of relative residual EDC values as a second control parameter can improve existing absorbance-based ozonation control systems to meet micropollutant abatement targets, particularly for treatment systems where low ozone doses are applied.

Taping into the super power and magic appeal of ultrasound coupled with EDTA on degradation of 2,4,6-TCP by Fe0 based advanced oxidation processes

Chlorophenol is a widely used organic compound, and the environmental and health problems caused by it have being worsened in recent years. This study used 2,4,6-trichlorophenol (2,4,6-TCP) as the target pollutant, and employed ultrasound (US) enhanced zero-valent iron (Fe⁰)/EDTA/air system (FEA), namely US/FEA, to remove 2,4,6-TCP. The influence of single factor experimental conditions such as EDTA concentration, Fe⁰ dosage, US power, pH and pollutant concentration on the removal efficiency of 2,4,6-TCP was investigated, and the optimal reaction conditions were determined. The mechanism of reactive oxygen species (ROS) produced by US/FEA was explored. The degradation process and removal mechanism of 2,4,6-TCP in the US/FEA were discussed through the determination and analysis of intermediate products. The results showed that US could continuously activate and renew the Fe⁰ surface, accelerate its oxidation and corrosion process, and then continuously and stably produce sufficient amounts of Fe²⁺ and Fe³⁺. Ultrasonic cavitation effect could reduce the difficulty of O₂ activation reaction, and promote the production of sufficient H₂O₂. The addition of EDTA made the system have a wide range of pH applications, and its performance under neutral and alkaline conditions was also superior. The ROS of US/FEA included ·OH, O₂^·- and Fe(IV), where Fe(IV) was the main contributor to the removal of 2,4,6-TCP. In addition, the degradation of 2,4,6-TCP had two processes including dechlorination and benzene ring opening. First, 2,4,6-TCP was dechlorinated and degraded into phenol. And then, phenol was degraded into small molecular acids by ring-opening, and finally it was mineralized into CO₂ and H₂O completely. US/FEA is a promising technology for high-efficiency degradation of organic matter and deep environmental purification.

Evaluation of Oxidation Process by Ozonation and Glucose Oxidase Enzyme on the Degradation of Benzoquinone in Wheat Flour

Background:

Wheat flour is an important food ingredient for humans, which is the basic ingredient of bread and other bakery products.

Objective:

This study aimed to assess the effect of adding Glucose Oxidase (GOX), and exposure to ozone gas on methyl-1, 4-benzoquinone (MBQ), and ethyl-1, 4-benzoquinone (EBQ) secreted by Tribolium castaneum in flour.

Methods:

The flour contaminated by MBQ and EBQ was treated with ozone gas at (10, 20, and 40 ppm) with exposure times (15, 30, and 45 min). Similarly, GOX was added to flour at (10, 15, and 20 ppm), leaving the dough for periods between 10 and 45 min after treatments. The MBQ and EBQ determined by HPLC, and the UV-Visible Spectrophotometer and Fourier Transform Infrared Spectroscopy (FTIR) were used to describe the changes that occurred in the main structure of EBQ after ozonation at 40 ppm for 45 min.

Results:

The results indicated that adding GOX enzyme to the flour at level 20 ppm degrade the MBQ to 13.7, 20.23, and 39.6 after 15, 30, and 45 min from mixing time, respectively. On the other hnad, the EBQ degrades to 13.6, 18.9, and 35.9%. In contrast, the percentages of degradation of MBQ and EBQ increases after ozonation at 40 ppm for 45min were 84.1 and 78.8%, respectively. The results obtained by UV–vis spectroscopy and FTIR reflect that many oxidation products formed as aldehydes, ketones, and carboxylic acids.

Conclusion:

In general, ozonation was a reliable treatment for the degradation of benzoquinone in flour.

Abatement technology of endocrine-disrupting chemicals (EDCs) by means of enhanced coagulation and ozonation for wastewater reuse

In this study, we have investigated the purification efficiency during enhanced coagulation, ozone oxidation and their combined processes for the removal of trace amounts of EDCs in different DOM matrices. The results indicated that the maximum removal efficiency of EDCs occurred at or near pH 7.0 when measured over a pH range of 4.0-10.0. The addition of natural colloids had a two-part influence. While the floc generated by polyaluminium chloride (PAC) significantly increased in size from 198.0 μm to 290.4 μm with a simultaneous improvement in the removal efficiency of EDCs, the floc size generated by polyferric sulfate (PFS) had no worthwhile change except for a slight decrement. The removal efficiency of EDCs and the decrease in spectral parameters including UVA254, UVA280 and humic-like fluorescence during ozonation processes with and without pre-coagulation were investigated. During the ozonation process, efficient elimination of target EDCs are achieved at low O₃ doses (O₃/dissolved organic carbon (DOC) < 0.2) in different water matrices. The pH-titration differential absorbance spectra technique further demonstrated that the high reactivity of O₃ to EDCs is owing to their phenolic moieties. In addition, when mgO₃/mgDOC ratio reaches to ~0.40, >90% of estrogenic activity was eliminated. In a nutshell, ozonation with pre-coagulation together leads to considerably higher abatement of EDCs and estradiol (E2) equivalent values (EEQ) at the same ozone dosage than ozonation only process for wastewater treatment.

Formation control of bromate and trihalomethanes during ozonation of bromide-containing water with chemical addition: Hydrogen peroxide or ammonia?

To ensure the safety of drinking water, ozone (O₃) has been extensively applied in drinking water treatment plants to further remove natural organic matter (NOM). However, the surface water and groundwater near the coastal areas often contain high concentrations of bromide ion (Br^-). Considering the risk of bromate (BrO₃^-) formation in ozonation of the sand-filtered water, the inhibitory efficiencies of hydrogen peroxide (H₂O₂) and ammonia (NH₃) on BrO₃^- formation during ozonation process were compared. The addition of H₂O₂ effectively inhibited BrO₃^- formation at an initial Br^- concentration amended to 350 µg/L. The inhibition efficiencies reached 59.6 and 100% when the mass ratio of H₂O₂/O₃ was 0.25 and > 0.5, respectively. The UV₂₅₄ and total organic carbon (TOC) also decreased after adding H₂O₂, while the formation potential of trihalomethanes (THMsFP) increased especially in subsequent chlorination process at a low dose of H₂O₂. To control the formation of both BrO₃^- and THMs, a relatively large dose of O₃ and a high ratio of H₂O₂/O₃were generally needed. NH₃ addition inhibited BrO₃^- formation when the background ammonia nitrogen (NH₃N) concentration was low. There was no significant correlation between BrO₃^- inhibition efficiency and NH₃ dose, and a small amount of NH₃N (0.2 mg/L) could obviously inhibit BrO₃^- formation. The oxidation of NOM seemed unaffected by NH₃ addition, and the structure of NOM reflected by synchronous fluorescence (SF) scanning remained almost unchanged before and after adding NH₃. Considering the formation of BrO₃^- and THMs, the optimal dose of NH₃ was suggested to be 0.5 mg/L.

Oxidant-reactive carbonous moieties in dissolved organic matter: Selective quantification by oxidative titration using chlorine dioxide and ozone

The application of oxidants for disinfection or micropollutant abatement during drinking water and wastewater treatment is accompanied by oxidation of matrix components such as dissolved organic matter (DOM). To improve predictions of the efficiency of oxidation processes and the formation of oxidation products, methods to determine concentrations of oxidant-reactive phenolic, olefinic or amine-type DOM moieties are critical. Here, a novel selective oxidative titration approach is presented, which is based on reaction kinetics of oxidation reactions towards certain DOM moieties. Phenolic moieties were determined by oxidative titration with ClO₂ and O₃ for five DOM isolates and two secondary wastewater effluent samples. The determined concentrations of phenolic moieties correlated with the electron-donating capacity (EDC) and the formation of inorganic ClO₂-byproducts (HOCl, ClO₂^-, ClO₃^-). ClO₂-byproduct yields from phenol and DOM isolates and changes due to the application of molecular tagging for phenols revealed a better understanding of oxidant-reactive structures within DOM. Overall, oxidative titrations with ClO₂ and O₃ provide a novel and promising tool to quantify oxidant-reactive moieties in complex mixtures such as DOM and can be expanded to other matrices or oxidants.

Oxidation of 51 micropollutants during drinking water ozonation: Formation of transformation products and their fate during biological post-filtration

Micropollutants (MP) with varying ozone-reactive moieties were spiked to lake water in the influent of a drinking water pilot plant consisting of an ozonation followed by a biological sand filtration. During ozonation, 227 transformation products (OTPs) from 39 of the spiked 51 MPs were detected after solid phase extraction by liquid chromatography high-resolution mass spectrometry (LC-HRMS/MS). Based on the MS/MS data, tentative molecular structures are proposed. Reaction mechanisms for the formation of a large number of OTPs are suggested by combination of the kinetics of formation and abatement and state-of-the-art knowledge on ozone and hydroxyl radical chemistry. OTPs forming as primary or higher generation products from the oxidation of MPs could be differentiated. However, some expected products from the reactions of ozone with activated aromatic compounds and olefins were not detected with the applied analytical procedure. 187 OTPs were present in the sand filtration in sufficiently high concentrations to elucidate their fate in this treatment step. 35 of these OTPs (19%) were abated in the sand filtration step, most likely due to biodegradation. Only 24 (13%) of the OTPs were abated more efficiently than the parent compounds, with a dependency on the functional group of the parent MPs and OTPs. Overall, this study provides evidence, that the common assumption that OTPs are easily abated in biological post-treatment is not generally valid. Nevertheless, it is unknown how the OTPs, which escaped detection, would have behaved in the biological post-treatment.

Implications of hydrogen peroxide on bromate depression during seawater ozonation

The presence of hydrogen peroxide (H₂O₂) in ozonation process can resist the formation of carcinogenic bromate (BrO₃¯) efficiently, and the bromate depression is closely related with background water qualities, especially in high bromide-containing seawater. In this study, the freshwater and seawater were selected to investigate the effects of H₂O₂ on ozone (O₃) decomposition kinetics, bromide transformation and bromate depression, and the evolutions of BrO₃¯ under different scavengers were explored to speculate the primary bromate formation pathways. The results showed that the initial O₃ half-live period (t_1/2-O₃) in seawater was only one-sixth of that in freshwater, and its attenuation rate increased analogously with the increase of H₂O₂ concentration in both freshwater and seawater. The H₂O₂ could promote the formation of BrO₃¯ via hydroxyl radical (•OH) based bromate pathways, nevertheless higher concentration of H₂O₂ facilitated the reduction of HOBr/OBr¯ back to Br¯, resulting in 87.0% and 73.2% of BrO₃¯ retardment in freshwater and seawater, respectively. The suppression ratios of BrO₃¯ were up to 48.4% and 35.3% in freshwater with the addition of •OH and •O₂¯ scavengers, and the corresponding depressions in seawater decreased to 35.3% and 12.7%, indicating that •OH was dominant on bromate formation when the concentration of residual ozone was adequate to generate some bromine intermediates, meanwhile H₂O₂ and •O₂¯ functioned as the key reductants for bromate depression. Based on these results, the Br¯ transformation mechanisms via O₃, •OH, H₂O₂, and •O₂¯ reactions were speculated, and the feasibility of H₂O₂-ozonation was verified for the treatment of high Br¯-containing seawater.

Selective Reactivity and Oxidation of Dissolved Organic Matter by Manganese Oxides

Dissolved organic matter (DOM) varies widely across natural and engineered systems, but little is known about the influence of DOM composition on its reactivity with manganese oxides. Here, we investigate bulk and molecular transformations of 30 diverse DOM samples after reaction with acid birnessite (MnO₂), a strong oxidant that may react with DOM in Mn-rich environments or engineered treatment systems. The reaction of DOM with acid birnessite reduces Mn and forms DOM that is generally more aliphatic and lower in apparent molecular weight. However, the extent of reaction depends on the water type (e.g., wastewater, rivers) and highly aromatic DOM undergoes greater changes. Despite the variability in reactivity due to the DOM composition, aqueous products attributable to the oxidation of phenolic precursors are identified in waters analyzed by high-resolution mass spectrometry. The number of matched product formulas correlates significantly with indicators of DOM aromaticity, such as double-bond equivalents (p = 2.43 × 10^-4). At the molecular level, highly aromatic, lignin-like carbon reacts selectively with acid birnessite in all samples despite the variability in initial DOM composition, resulting in the formation of a wide range of aqueous products. These findings demonstrate that DOM oxidation occurs in diverse waters but also suggest that reactivity with acid birnessite and the composition of the resulting aqueous DOM pool are composition-dependent and linked to the DOM source and initial aromaticity.

Catalytic ozonation for metoprolol and ibuprofen removal over different MnO2 nanocrystals: Efficiency, transformation and mechanism

Manganese dioxide has been widely recognized as catalyst in catalytic ozonation for organic pollutants removal from wastewater in recent decades. However, few studies focus on the structure-activity relationship of MnO₂ and catalytic ozonation mechanism in water. In the present study, the oxidative reactivity of three different crystal phases of MnO₂ corresponding to α-MnO₂, β-MnO₂ and γ-MnO₂ towards metoprolol (MET) and ibuprofen (IBU) were evaluated. α-MnO₂ was found to contain the most abundant oxygen vacancy and readily reducible surface adsorbed oxygen (O^2-, O^-, OH^-), which facilitated an increase of ozone utilization and the highest catalytic performance with 99% degradation efficiency for IBU and MET. α-MnO₂ was then selected to investigate the optimum key operating parameters with a result of catalyst dosage 0.1 g/L, ozone dosage 1 mg/min and an initial pH 7. The introduction of α-MnO₂ promoted reactive oxygen species (O^2-, O^-, OH^-) generation which played significant roles in IBU degradation. Probable degradation pathways of MET and IBU were proposed according to the organic intermediates identified and the reaction sites based on density function theory (DFT) calculations. The present study deepened our understanding on the MnO₂ catalyzed ozonation and provided reference to enhance the process efficiency.

Toxic effects of substituted p-benzoquinones and hydroquinones in in vitro bioassays are altered by reactions with the cell assay medium

Substituted para-benzoquinones and hydroquinones are ubiquitous transformation products that arise during oxidative water treatment of phenolic precursors, for example through ozonation or chlorination. The benzoquinone structural motive is associated with mutagenicity and carcinogenicity, and also with induction of the oxidative stress response through the Nrf2 pathway. For either endpoint, toxicological data for differently substituted compounds are scarce. In this study, oxidative stress response, as indicated by the AREc32 in vitro bioassay, was induced by differently substituted para-benzoquinones, but also by the corresponding hydroquinones. Bioassays that indicate defense against genotoxicity (p53RE-bla) and DNA repair activity (UmuC) were not activated by these compounds. Stability tests conducted under incubation conditions, but in the absence of cell lines, showed that tested para-benzoquinones reacted rapidly with constituents of the incubation medium. Compounds were abated already in phosphate buffer, but even faster in biological media, with reactions attributed to amino- and thiol-groups of peptides, proteins, and free amino acids. The products of these reactions were often the corresponding substituted hydroquinones. Conversely, differently substituted hydroquinones were quantitatively oxidized to p-benzoquinones over the course of the incubation. The observed induction of the oxidative stress response was attributed to hydroquinones that are presumably oxidized to benzoquinones inside the cells. Despite the instability of the tested compounds in the incubation medium, the AREc32 in vitro bioassay could be used as an unspecific sum parameter to detect para-benzoquinones and hydroquinones in oxidatively treated waters.

Formation of transformation products during ozonation of secondary wastewater effluent and their fate in post-treatment: From laboratory- to full-scale

Ozonation is increasingly applied in water and wastewater treatment for the abatement of micropollutants (MPs). However, the transformation products formed during ozonation (OTPs) and their fate in biological or sorptive post-treatments is largely unknown. In this project, a high-throughput approach, combining laboratory ozonation experiments and detection by liquid chromatography high-resolution mass spectrometry (LC-HR-MS/MS), was developed and applied to identify OTPs formed during ozonation of wastewater effluent for a large number of relevant MPs (total 87). For the laboratory ozonation experiments, a simplified experimental solution, consisting of surrogate organic matter (methanol and acetate), was created, which produced ozonation conditions similar to realistic conditions in terms of ozone and hydroxyl radical exposures. The 87 selected parent MPs were divided into 19 mixtures, which enabled the identification of OTPs with an optimized number of experiments. The following two approaches were considered to identify OTPs. (1) A screening of LC-HR-MS signal formation in these experiments was performed and revealed a list of 1749 potential OTP candidate signals associated to 70 parent MPs. This list can be used in future suspect screening studies. (2) A screening was performed for signals that were formed in both batch experiments and in samples of wastewater treatment plants (WWTPs). This second approach was ultimately more time-efficient and was applied to four different WWTPs with ozonation (specific ozone doses in the range 0.23-0.55 gO₃/gDOC), leading to the identification of 84 relevant OTPs of 40 parent MPs in wastewater effluent. Chemical structures could be proposed for 83 OTPs through the interpretation of MS/MS spectra and expert knowledge in ozone chemistry. Forty-eight OTPs (58%) have not been reported previously. The fate of the verified OTPs was studied in different post-treatment steps. During sand filtration, 87-89% of the OTPs were stable. In granular activated carbon (GAC) filters, OTPs were abated with decreasing efficiency with increasing run times of the filters. For example, in a GAC filter with 16,000 bed volumes, 53% of the OTPs were abated, while in a GAC filter with 35,000 bed volumes, 40% of the OTPs were abated. The highest abatement (87% of OTPs) was observed when 13 mg/L powdered activated carbon (PAC) was dosed onto a sand filter.

Efficient degradation of clofibric acid by heterogeneous catalytic ozonation using CoFe2O4 catalyst in water

CoFe₂O₄ (Cobalt ferrite, CF) nanoparticles were prepared, well characterized and applied as efficient solid catalyst in catalytic ozonation, named CF/O₃ process, for the removal of emerging organic contaminants (EOCs). The degradation and mineralization of clofibric acid (CA) in CF/O₃ process were dramatically enhanced in comparison with those under the O₃ system. Surface hydroxyl groups (HGs) were considered as an important factor for ozone decomposition and the reactive oxygen species (ROS) on the catalyst surface were mainly responsible for CA elimination. The contribution and formation of ROS, including hydroxyl radicals (^•OH), especially superoxide radicals (O₂^•-), singlet oxygen (¹O₂), and hydrogen peroxide (H₂O₂) were evaluated, and a rational mechanism was elucidated accordingly. Probable degradation pathway of CA was proposed according to the organic intermediates identified. The acute toxicity of the treated solution increased during the first 15 min and then declined rapidly and nearly disappeared as the reaction proceeded. In addition, acceptable catalytic performance of CF/O₃ can be obtained for the treatment of other EOCs and the treatment of natural surface water spiked with CA. This work presents an efficient and promising catalytic ozonation technique for the elimination of EOCs in complex water matrices.

Reduction of bromate by zero valent iron (ZVI) enhances formation of brominated disinfection by-products during chlorination

Bromate (BrO₃^-) is a predominant undesired toxic disinfection by-product (DBP) during ozonation of bromide-containing waters. The reduction of BrO₃^- by zero valent iron (ZVI) and its effect on formation of organic halogenated DBPs during chlorination were investigated in this study. The presence of ZVI could reduce BrO₃^- to bromide (Br^-), and Br^- formed could be transformed to free bromine (HOBr/OBr^-) during chlorination, further leading to organic brominated (Br-) DBPs formation. Formation of DBPs during chlorination, including trihalomethanes (THMs) and haloacetonitriles (HANs) was detected under different conditions. The results showed that when ZVI dosage increased from 0 to 1 g L^-1, the formation of Br-DBPs (e.g., TBM and DBCM) was significantly improved, while the formation of Cl-DBPs (e.g., TCM, TCAN and DCAN) reduced. Higher ZVI dosage exhibited inhibitory effect on Br-DBPs formation due to the competition between ZVI and free chlorine (HOCl/OCl^-). The bromine substitution factor (BSF) of THMs significantly decreased from 0.61 ± 0.06 to 0.22 ± 0.02, as the pH was raised from 5.0 to 9.0. Besides, the increase of initial BrO₃^- concentration significantly improved the formation of Br-DBPs and decreased the formation of Cl-DBPs, leading to an obvious rise on the BSF of THMs. As the initial concentration of HOCl increased, all THMs and HANs gradually increased. Moreover, the analysis based on the cytotoxicity index (CTI) of the determined DBPs showed that reduction of BrO₃^- by ZVI during chlorination had certain risks in real water sources, which should be paid attention to in the application.

Singlet Oxygen Quantum Yields in Environmental Waters

Singlet oxygen (¹O₂) is a reactive oxygen species produced in sunlit waters via energy transfer from the triplet states of natural sensitizers. There has been an increasing interest in measuring apparent ¹O₂ quantum yields (Φ_Δ) of aquatic and atmospheric organic matter samples, driven in part by the fact that this parameter can be used for environmental fate modeling of organic contaminants and to advance our understanding of dissolved organic matter photophysics. However, the lack of reproducibility across research groups and publications remains a challenge that significantly limits the usability of literature data. In the first part of this review, we critically evaluate the experimental techniques that have been used to determine Φ_Δ values of natural organic matter, we identify and quantify sources of errors that potentially explain the large variability in the literature, and we provide general experimental recommendations for future studies. In the second part, we provide a qualitative overview of known Φ_Δ trends as a function of organic matter type, isolation and extraction procedures, bulk water chemistry parameters, molecular and spectroscopic organic matter features, chemical treatments, wavelength, season, and location. This review is supplemented with a comprehensive database of Φ_Δ values of environmental samples.

FeOx@GAC catalyzed microbubble ozonation coupled with biological process for industrial phenolic wastewater treatment: Catalytic performance, biological process screening and microbial characteristics

Phenolic compounds are common ccontaminants in industrial effluents. In this study, a combined catalytic microbubble ozonation and biological process was developed and applied for efficient industrial phenolic wastewater (PWW) treatment. Catalytic activity of an iron-oxides (FeO_x) doped granular activated carbon (GAC) catalyst (FeO_x@GAC) in microbubble ozonation for PWW treatment was investigated. The results demonstrated that the FeO_x@GAC catalyzed microbubble ozonation (O₃/FeO_x@GAC) obtained significantly higher reaction rate constant (k₁ = 0.023 min^-1) in TOC removal compared to the bare GAC catalyzed microbubble ozonation (O₃/GAC, k₁ = 0.013 min^-1) and ordinary microbubble ozonation (k₁ = 0.008 min^-1). Destruction rate constant of phenolic compounds (k₂) was improved from 0.014 min^-1 (ordinary microbubble ozonation) to 0.025 min^-1 (O₃/FeO_x@GAC). The 60-min pretreatment of PWW by O₃/FeO_x@GAC process enhanced BOD₅/COD ratio from 0.31 to 0.76 and reduced the acute bio-toxicity by 79.2%. Screening and characterization of biological post-treatment processes were conducted among activated sludge process (ASP), up-flow anaerobic sludge blanket (UASB) and membrane bioreactor (MBR). UASB and ASP showed limited phenolic compounds removal of 35.4% and 57.0% with lower bio-toxicity resistance than MBR (94.9% phenolic compounds removal). The combined process O₃/FeO_x@GAC-MBR was thus developed and achieved high COD removal (98.0%) and phenolic compounds degradation (99.4%). PWW pretreatment by O₃/FeO_x@GAC process decreased membrane fouling rate of MBR by 88.2% by reducing proteins/polysaccharides accumulation in both extracellular polymeric substances and soluble microbial products. 16S rRNA high-throughput sequencing revealed the predominance of phylum Proteobacteria, class Alphaproteobacteria and genera Mycobacterium, Gordonia, Pedomicrobium & Defluviimonas in biological PWW treatment bio-systems. Pearson correlation coefficient and ANOVA analysis verified that Mycobacterium possessed high bio-toxicity resistance and was the main contributor to the biodegradation of phenolic compounds.

Reactivity-directed analysis - a novel approach for the identification of toxic organic electrophiles in drinking water

Drinking water consumption results in exposure to complex mixtures of organic chemicals, including natural and anthropogenic chemicals and compounds formed during drinking water treatment such as disinfection by-products. The complexity of drinking water contaminant mixtures has hindered efforts to assess associated health impacts. Existing approaches focus primarily on individual chemicals and/or the evaluation of mixtures, without providing information about the chemicals causing the toxic effect. Thus, there is a need for the development of novel strategies to evaluate chemical mixtures and provide insights into the species responsible for the observed toxic effects. This critical review introduces the application of a novel approach called Reactivity-Directed Analysis (RDA) to assess and identify organic electrophiles, the largest group of known environmental toxicants. In contrast to existing in vivo and in vitro approaches, RDA utilizes in chemico methodologies that investigate the reaction of organic electrophiles with nucleophilic biomolecules, including proteins and DNA. This review summarizes the existing knowledge about the presence of electrophiles in drinking water, with a particular focus on their formation in oxidative treatment systems with ozone, advanced oxidation processes, and UV light, as well as disinfectants such as chlorine, chloramines and chlorine dioxide. This summary is followed by an overview of existing RDA approaches and their application for the assessment of aqueous environmental matrices, with an emphasis on drinking water. RDA can be applied beyond drinking water, however, to evaluate source waters and wastewater for human and environmental health risks. Finally, future research demands for the detection and identification of electrophiles in drinking water via RDA are outlined.

A ubiquitous tire rubber-derived chemical induces acute mortality in coho salmon

In U.S. Pacific Northwest coho salmon (Oncorhynchus kisutch), stormwater exposure annually causes unexplained acute mortality when adult salmon migrate to urban creeks to reproduce. By investigating this phenomenon, we identified a highly toxic quinone transformation product of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), a globally ubiquitous tire rubber antioxidant. Retrospective analysis of representative roadway runoff and stormwater-affected creeks of the U.S. West Coast indicated widespread occurrence of 6PPD-quinone (<0.3 to 19 micrograms per liter) at toxic concentrations (median lethal concentration of 0.8 ± 0.16 micrograms per liter). These results reveal unanticipated risks of 6PPD antioxidants to an aquatic species and imply toxicological relevance for dissipated tire rubber residues.

Efficiency of pre-oxidation of natural organic matter for the mitigation of disinfection byproducts: Electron donating capacity and UV absorbance as surrogate parameters

Pre-oxidation is often used before disinfection with chlorine to decrease the reactivity of the water matrix and mitigate the formation of regulated disinfection byproducts (DBPs). This study provides insights on the impact of oxidative pre-treatment with chlorine dioxide (ClO₂), ozone (O₃), ferrate (Fe(VI)) and permanganate (Mn(VII)) on Suwannee River Natural Organic Matter (SRNOM) properties characterized by the UV absorbance at 254 nm (UV₂₅₄) and the electron donating capacity (EDC). Changes in NOM reactivity and abatement of DBP precursors are also assessed. The impact of pre-oxidants (based on molar concentration) on UV₂₅₄ abatement ranked in the order O₃ > Mn(VII) > Fe(VI)/ClO₂, while the efficiency of pre-oxidation on EDC abatement followed the order Mn(VII) > ClO₂ > Fe(VI) > O₃ and two phases were observed. At low specific ClO₂, Fe(VI) and Mn(VII) doses corresponding to < 50% EDC abatement, a limited relative abatement of UV₂₅₄ compared to the EDC was observed (~ 8% EDC abatement per 1% UV₂₅₄ abatement). This suggests the oxidation of phenolic-type moieties to quinone-type moieties which absorb UV₂₅₄ and don't contribute to EDC. At higher oxidant doses (> 50% EDC abatement), a similar abatement of EDC and UV₂₅₄ (~ 0.9-1.2% EDC abatement per 1% UV₂₅₄ abatement) suggested aromatic ring cleavage. In comparison to the other oxidants, O₃ abated the relative UV₂₅₄ more effectively, due to a more efficient cleavage of aromatic rings. For a pre-oxidation with Mn(VII), ClO₂ and Fe(VI), similar correlations between the EDC abatement and the chlorine demand or the adsorbable organic halide (AOX) formation were obtained. In contrast, O₃ pre-treatment led to a lower chlorine demand and AOX formation for equivalent EDC abatement. For all oxidants_, trihalomethane formation was poorly correlated with both EDC and UV_254. The EDC abatement was found to be a pre-oxidant-independent surrogate for haloacetonitrile formation. These results emphasize the benefits of combining EDC and UV₂₅₄ measurement to understand and monitor oxidant-induced changes of NOM and assessing DBP formation.