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• Synthetic water matrices as a surrogate for dissolved organic matter during ozonation. • Micropollutant abatement and product formation match for real and synthetic waters. • Bromate formation in real waters is well represented by synthetic matrices. • Synthetic matrices can be tailored for ozonation of natural water and wastewater. Ozonation is used worldwide for drinking water disinfection and increasingly also for micropollutant abatement from wastewater. Identification of transformation products formed during the ozonation of micropollutants is challenging due to several factors including (i) the reactions of both oxidants, ozone and hydroxyl radicals with the micropollutants, as well as with intermediate transformation products, (ii) effects of the water matrix on the ozone and hydroxyl radical chemistry and (iii) the generation of oxidation by-products. In this study, a simple approach to achieve realistic ozonation conditions in the absence of dissolved organic matter has been developed. It is based on composing synthetic water matrices with low-molecular-weight scavenger compounds (phenol, methanol, acetate, and carbonate) that mimic the chemical interactions of ozone and hydroxyl radicals with real water matrices. Synthetic waters composed of only four low-molecular-weight compounds successfully replicated two lake waters and two secondary wastewater effluents, matching instantaneous ozone demand, ozone and hydroxyl radical exposures in the initial phase, as well as the ozone evolution in the second phase of the ozonation process. The synthetic water matrices also reproduced the effects of temperature and pH changes observed in real waters. The abatement of two micropollutants, bezafibrate and atrazine, and the formation of the corresponding transformation products during ozonation were in agreement for synthetic and real waters. Furthermore, the kinetics and extent of bromate formation during ozonation in synthetic water were comparable to real lake water and wastewater. This supports the robustness of the proposed approach because bromate formation is very sensitive to the interplay of ozone and hydroxyl radicals. Furthermore, with the novel reaction system, a significant effect of hydroxyl radicals scavenging by carbonate on bromate formation was demonstrated. Overall, the herein-developed approach based on synthetic water matrices allows to perform realistic ozonation studies including both oxidants, ozone and hydroxyl radicals, without the constraints of using dissolved organic matter. [Display omitted] [ABSTRACT FROM AUTHOR]

Dissolved black carbon (DBC) with a hyperconjugated structure is ubiquitous in nature, and plays a crucial role in the migration and transformation of environmental contaminants due to its prominent properties of accepting electrons and sorption. However, little is known about the DBC-induced phototransformation of pharmaceutical and personal care products (PPCPs) in natural waters. Herein, the photodegradation kinetics of PPCPs were investigated in DBC solution under simulated solar irradiation and compared with those in Suwannee River natural organic matter (SRNOM) solution. The decay rates for the positively charged PPCPs (mean 1.484 ± 0.041 h -1 ) were significantly higher than those for the negatively charged PPCPs (mean 0.014 ± 0.002 h -1 ) in DBC solution due to the charge interaction. Moreover, the decay rates for the positively charged PPCPs in DBC solution were approximately 3-16 times of those in SRNOM solution due to the discrepant sorption and ability to produce bonded HO • . Finally, a microheterogeneous photodegradation mechanism of HO • -labile PPCPs in DBC solution involving the sorption and subsequent reaction with bonded HO • in the DBC microphase was proposed, which was verified using isopropanol and isopropamide as selective HO • scavengers. This work will provide useful insights into the photochemistry of DBC and also the DBC-involved phototransformation of PPCPs in aquatic environments., 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 © 2024 Elsevier Ltd. All rights reserved.)

Riparian zones are important depositional environments at the catchment scale and provide environmental services such as carbon sequestration. This zone is a highly dynamic interface for oxygen and electron exchange, which confers the basis for reactive oxygen species (ROS) production. However, the differences in soil ROS production and their impact on carbon turnover across various redox locations within the riparian zone remain to be fully elucidated. In this study, we investigated the distribution characteristics and generation mechanism of ROS in riparian soil based on soil samples collected in a three-month field monitoring experiment, with additional incubation experiments conducted to examine the effect of hydroxyl radical ( • OH) on soil organic carbon (SOC) mineralization. The obtained results demonstrated that the riverine wetland was the hotspot zone for • OH production, with the production flux of 13.05 μmol kg -1 d -1 , which was significantly higher than that in floodplain (7.29 μmol kg -1 d -1 ) and riverbank soils (8.61 μmol kg -1 d -1 ). Moreover, • OH levels displayed distinct rhythmic fluctuations, with significantly higher concentrations at low water levels compared to those at high water levels, and remained essentially flat over three cycles. The statistic analysis revealed that the ROS production was highly dependent on reduced species and microbial community structure, which function as biogeochemical batteries and electron shuttles under redox fluctuations. Furthermore, the generated • OH involved in the abiotic mineralization of SOC, contributing to 13.1‒21.8 % of total CO 2 efflux. Compared to particulate organic carbon (POC), mineral-associated organic carbon (MAOC) fractions of SOC were more susceptible to • OH attacks. The findings provide a novel insight to comprehensively assess the redox process on riparian carbon turnover., 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 © 2024 Elsevier Ltd. All rights reserved.)

The application of Fe-catalyzed periodate (PI) processes is often limited by both the narrow applicable pH range and weak reaction between Fe(III) and oxidant. Here, the biodegradable picolinic acid (PICA) was used as one kind of chelating ligands (CLs) to enhance the removal of organic pollutants (OPs) at initial pH 3.0-8.0, which displayed superior properties than the other CLs in Fe(III)/PI process. The dominant reactive species produced in the Fe(III)-PICA/PI process turned out to be high-valent iron-oxo (Fe IV =O) species and hydroxyl radical ( • OH) by quenching, sulfoxide probe transformation, and 18 O isotope-labeling tests. The relative contribution of Fe IV =O and • OH was dependent on OPs ionization potential (IP) and energy gap (ΔE). The degradation of OPs was also directly associated with their structure, the apparent rate constants correlated well with the highest occupied molecular orbital energy (E HOMO ), IP, and ΔE, and among them ΔE had a greater effect. Furthermore, Fe(III)-PICA complexes displayed excellent long-term effectiveness for OPs removal in actual water matrixes, along with the non-toxic conversion of PI, indicating a broad application perspective of Fe(III)-PICA/PI process. This study provides an efficient method to improve the performance of Fe(III)/PI process and reveals the mechanism and relationship between removal efficiency and pollutant structure., 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 © 2024 Elsevier Ltd. All rights reserved.)

• Aerobic photo-methanification of DOMs with different origins was studied. • Photo-induced CH 4 production rates were 3.57 × 10−3∼5.90 × 10−2 nmol CH 4 mg-C−1 h−1. • Contribution of •OH to photo-methanificaiton for all DOMs was about 4∼42 %. • Carbohydrate- and lipid-like substances highly associated with photo-methanification rates. • Photo-methanification contributed 0.1∼18.3 % of diffusive CH 4 flux in Lake Chaohu. Lingering inconsistencies in the global methane (CH 4) budget and ambiguity in CH 4 sources and sinks triggered efforts to identify new CH 4 formation pathways in natural ecosystems. Herein, we reported a novel mechanism of light-induced generation of hydroxyl radicals (•OH) that drove the production of CH 4 from aquatic dissolved organic matters (DOMs) under ambient conditions. A total of five DOM samples with different origins were applied to examine their potential in photo-methanification production under aerobic conditions, presenting a wide range of CH 4 production rates from 3.57 × 10−3 to 5.90 × 10−2 nmol CH 4 mg-C−1 h−1. Experiments of •OH generator and scavenger indicated that the contribution of •OH to photo-methanificaiton among different DOM samples reached about 4∼42 %. In addition, Fourier transform infrared spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry showed that the carbohydrate- and lipid-like substances containing nitrogen-bonded methyl groups, methyl ester, acetyl groups, and ketones, were the potential precursors for light-induced CH 4 production. Based on the experimental results and simulated calculations, the contribution of photo-methanification of aquatic DOMs to the diffusive CH 4 flux across the water-air interface in a typical eutrophic shallow lake (e.g., Lake Chaohu) ranged from 0.1 % to 18.3 %. This study provides a new perspective on the pathways of CH 4 formation in aquatic ecosystems and a deeper understanding on the sources and sinks of global CH 4. [Display omitted] [ABSTRACT FROM AUTHOR]

• Modelling of micropollutant degradation by ozonation in reverse osmosis concentrate. • Assessment of bromate formation during ozonation of RO concentrate. • X-ray contrast media treatment in RO concentrate by UV/persulfate oxidation. • Determination of sulfateradical and hydroxyl radical reaction rate constants of irbesartan and candesartan. This study investigated the elimination of pharmaceuticals, corrosion inhibitors, x-ray contrast media and perfluorinated compounds from reverse osmosis concentrates during ozonation and UV/persulfate processes. Second-order rate constants for the reactions of candesartan, irbesartan, methyl-benzotriazole, and chloro‑benzotriazole with sulfate radical (SO 4 ·−) were determined for the first time. Experiments were conducted in buffered pure water, in buffered water added with the matrix substituents chloride, carbonate, NOM, and reverse osmosis concentrate with spiked micropollutants (MP). UV/persulfate eliminated all MP to a higher extent than ozonation in RO concentrates due to the higher yield of oxidative species and photolytic degradation. Compounds with electron-rich moieties such as carbamazepine, diclofenac, metoprolol, and sulfamethoxazole were completely eliminated with small ozone doses (< 0.5 mg O 3 / mg DOC) and with a small fluence (< 5000 J m−2) in UV/persulfate processes. Photosensitive compounds with high reactivity towards hydroxyl radicals (·OH) and SO 4 ·− like the x-ray contrast media Iopamidol, Iohexol, and Amidotrizoic acid were successfully eliminated with a reasonable fluence in UV/persulfate, whereas these compounds persist in ozonation at common ozone dosages. However, much higher fluences and ozone dosages were required for the least reactive compounds like the class of benzotriazoles. Comparing the application of both oxidative processes to the RO concentrate, ozonation has the disadvantage of forming bromate. The energy input of both processes strongly depends on the target compounds to be eliminated. For the elimination of compounds such as sulfamethoxazole, ozonation is a feasible technique, whereas UV/persulfate is better suited for the elimination of recalcitrant compounds such as x-ray contrast media. In general, oxidative process treatment of RO concentrate could be applied to partly abate micropollutants before discharge. [Display omitted] [ABSTRACT FROM AUTHOR]

• Cl 2 •− was an important parent radical of HO• in the presence of chloride. • The k Cl2•−, HCO3− and k Cl2•−, CO32− were determined by laser flash photolysis. • The accuracy and applicability of the kinetic model were greatly improved. • Chloride could compensate the inhibitory effect of bicarbonate on HO• generation. The ultraviolet/monochloramine (UV/NH 2 Cl) process is an emerging advanced oxidation process with promising prospects in water treatment. Previous studies developed kinetic models of UV/NH 2 Cl for simulating radical concentrations and pollutant degradation. However, the reaction rate constants of Cl 2 •− with bicarbonate and carbonate (k Cl2•−, HCO3− and k Cl2•−, CO32−) were overestimated in literature. Consequently, when dosing 1 mM chloride and 1 mM bicarbonate, the current models of UV/NH 2 Cl severely under-predicted the experimental concentrations of three important radicals (i.e., hydroxyl radical (HO•), chlorine radical (Cl•), and dichloride radical (Cl 2 •−)) with great deviations (> 90 %). To investigate this issue, the transformation reactions among these three radicals in UV/NH 2 Cl were systematically studied. For the first time, it was found that in addition to Cl•, Cl 2 •− was also an important parent radical of HO• in the presence of chloride, and chloride could effectively compensate the inhibitory effect of bicarbonate on HO• generation in the system. Moreover, reactions and rate constants in current models were scrutinized from corresponding literature, and the reaction rate constants of Cl 2 •− with bicarbonate and carbonate (k Cl2•−, HCO3− and k Cl2•−, CO32−) were reevaluated to be 1.47 × 105 and 3.78 × 106 M−1s−1, respectively, by laser flash photolysis. With the newly obtained rate constants, the refined model could accurately simulate concentrations of all three radicals under different chloride and bicarbonate dosages with satisfactory deviations (< 30 %). Meanwhile, the refined model performed much better in predicting pollutant degradation and radical contribution compared with the unrefined model (with the previously estimated k Cl2•−, HCO3− and k Cl2•−, CO32−). The results of this study enhanced the accuracy and applicability of the kinetic model of UV/NH 2 Cl, and deepened the understanding of radical transformation in the process. [Display omitted] [ABSTRACT FROM AUTHOR]

Photochemical production of hydroxyl radical (·OH) from algal organic matter (AOM) collected from Lake Torrens in South Australia was examined using a sunlight simulator. The two AOM isolates featured lower molecular weight, lower chromophoric content, and lower SUVA 254 (0.7 and 0.9, L mgC−1 m−1) than the reference Suwannee River hydrophobic acid (SR-HPO), they had considerably higher apparent quantum yields ( ϕ N O M O H , 3.03 × 10−5 and 2.18 × 10−5) than SR-HPO (0.84 × 10−5). Fluorescence excitation-emission matrix (FEEM) showed that the major components in the AOM were aromatic protein-like and soluble microbial substances. Unique formulas of the two AOM isolates as compared to SR-HPO were revealed using FTICR-MS and classified into four areas, namely protein-like molecules with low O/C (H/C > 1.5, O/C: 0.2–0.4), lignin-derived moieties with low O/C (H/C:1.0–1.5, O/C: 0.1–0.3), protein-like molecules with high O/C (H/C > 1.5, O/C: 0.5–0.7), and carbohydrate derivatives (H/C > 1.5, O/C > 0.7). These unique AOM moieties characterised utilizing FEEM and FTICR-MS were tentatively postulated to contribute to the high ϕ N O M O H . To the best of our knowledge, this is the first study performed to both evaluate natural AOM as an efficient photosensitiser of ·OH and propose AOM moieties responsible for the high ϕ N O M O H . Image 1 • Algal organic matter showed higher quantum yield than Suwannee River organic matter. • Algal organic matter was characterised by FEEM and FTICR-MS. • Possible sources of higher quantum yield were proposed. [ABSTRACT FROM AUTHOR]

Catalyzed H 2 O 2 propagations (CHP) is characterized by the most robust reactivity of any of the in situ chemical oxidation (ISCO) technologies because it generates the strong oxidant hydroxyl radical along with nucleophiles + reductants, such as superoxide radical. The most common groundwater contaminants, trichloroethylene (TCE) and perchloroethylene (PCE), were used as model contaminants in evaluating the effect of hydrogen peroxide (H 2 O 2) dosage on contaminant destruction kinetics. Both TCE and PCE degradation rates increased with H 2 O 2 dosages up to 0.1 M, and then decreased with higher H 2 O 2 dosages. Parallel reactions conducted with the addition of the hydroxyl radical scavenger 2-propanol and the hydroxyl radical-specific probe nitrobenzene confirmed that hydroxyl radical is primarily responsible for TCE and PCE degradation; however, 5–20% of their degradation was attributed to a non-hydroxyl radical mechanism. Reactions conducted with the superoxide probe tetranitromethane showed that superoxide generation rates increased with increasing H 2 O 2 doses. These results were confirmed by electron spin resonance spectroscopy. Therefore, the non-hydroxyl radical pathway for TCE and PCE degradation at H 2 O 2 ≥0.5 M was likely via nucleophilic attack by superoxide. The results of this research demonstrate that contaminants present in the aqueous phase that are reactive with hydroxyl radical require only low doses of H 2 O 2 (≤0.1 M), but subsurface systems contaminated with species not reactive with hydroxyl radical (e.g., carbon tetrachloride) require H 2 O 2 concentrations ≥0.5 M. Image 1 • Catalyzed H 2 O 2 Propagations is a robust in situ chemical oxidation technology. • TCE and PCE degradation was studied using a range of H 2 O 2 dosages. • Hydroxyl radical was the predominant transforming species. • Superoxide was an additional transforming species at H 2 O 2 dosages ≥0.5 M. • High doses of H 2 O 2 are necessary only when superoxide driven treatment is needed. [ABSTRACT FROM AUTHOR]

Abstract Dissolved organic matter (DOM) plays an important role in degradation of organic pollutants by photochemically-produced reactive intermediates (RIs), such as excited triplet-states of DOM (3DOM*), singlet oxygen (1O 2) and hydroxyl radical (·OH). However, it is not clear whether DOM extracted from coastal seawaters (CS-DOM) and DOM derived from freshwaters (FW-DOM) exhibit similar effects on photodegradation of organic micropollutants. Herein, 2,4-dihydroxybenzophenone (BP-1) was adopted as a model compound to probe the effects of different DOM on photodegradation kinetics of organic micropollutants. Results show that the CS-DOM promotes the photodegradation of BP-1 mainly via the pathway involving 3DOM*; while 3DOM*, 1O 2 and ·OH are responsible for BP-1 photodegradation in the presence of the FW-DOM. Compared with the FW-DOM, the CS-DOM undergoes more photobleaching, and contains less aromatic C=C and C=O functional groups. Although 3DOM* formation quantum yields for the CS-DOM are relatively higher than those for the FW-DOM, the CS-DOM has lower rates of light absorption, leading to lower steady-state RI concentrations for the CS-DOM. BP-1 photodegradation in the presence of the CS-DOM is faster than in the presence of the FW-DOM, due to higher second-order reaction rate constants between BP-1 and CS-3DOM* and fewer antioxidants contained in the CS-DOM. Graphical abstract Image 1 Highlights • Coastal seawater DOM is mainly from autochthonous sources with low aromaticity. • Coastal seawater DOM produces low steady-state concentrations of 3DOM*, 1O 2 and ·OH. • Coastal seawater DOM and freshwater DOM can enhance photodegradation of BP-1. • Coastal seawater DOM promotes photodegradation of BP-1 via 3DOM*. • Freshwater DOM promotes phototransformation of BP-1 via 3DOM*, ·OH and 1O 2. [ABSTRACT FROM AUTHOR]

Abstract A light-weight granular mixed-quartz sand (denoted as L-GQS) combined with stirring-assisted bubble column reactor was firstly applied in catalytic ozonation of atrazine. The L-GQS, with a density of 2.36 g cm−3 and average diameter of ca. of 4 mm, was readily churned up and uniformly distributed within the solution in the reactor. The introduction of L-GQS was found to exhibit enhanced catalytic ozonation of atrazine, with the increase in degradation rate and the dissolved organic carbon (DOC) removal being more than 2-fold for the catalytic process (L-GQS dosage = 5 g L−1, [atrazine] 0 = 50 μM, [O 3 ] = 25 mg L−1, gas flow = 0.2 L min−1, at pH 7.0 and 293 K). The L-GQS settled at the bottom of the reactor after experimentation, allowing its easy separation from the solution. A complete characterization of the material (XRD, XPS, FTIR, FE-SEM/EDS, BET and pH pzc) revealed that L-GQS consisted of α-quartz, β-cristobalite, anorthoclase and small amount of iron oxy-hydroxides. Hydroxyl groups, Bronsted acid sites and Lewis acid sites on the surface of L-GQS all contributed to the atrazine adsorption, ozone decomposition and ·OH generation. The L-GQS catalyzed ozonation exhibited superior atrazine degradation and mineralization rates in a wide range of pH (3.0–9.0) and reaction temperatures (278 K–293 K). Also, an enhancement of DOC abatement was observed both in presence of natural organic matter isolates and natural water matrices (river water) when L-GQS was used. Finally, the degradation mechanism was proposed, based on the intermediates and by-products formation analyzed by LC-QTOF-MS/MS and ionic chromatography. Our results indicate that the L-GQS combined with stirring-assisted bubble column reactor could be utilized as an enhancement of ozone-based advanced oxidation processes. Graphical abstract Image 1 Highlights • L-GQS is an effective ozonation catalyst for pollutants mineralization. • The chemical and physical properties of L-GQS were characterized in detail. • L-GQS revealed excellent ·OH generation capacity in wide range of conditions. • L-GQS can be easily dispersed and separated from solution. [ABSTRACT FROM AUTHOR]

Abstract The frequent detection of propranolol, a widely used β-blocker, in wastewater effluents and surface waters has raised serious concern, due to its adverse effects on organisms. UV/hydrogen peroxide (UV/H 2 O 2) and UV/persulfate (UV/PDS) processes are efficient in eliminating propranolol in various waters, but the formation of oxidation products in these processes, as well as the assessment of their toxicity, has not been systematically addressed. In this study, we identified and compared transformation products of propranolol produced by hydroxyl radical (•OH) and sulfate radical (SO 4 •-). The electrostatic attraction enhances the reaction between SO 4 •- and the protonated form of propranolol, while •OH shows non-selectivity toward both protonated and neutral propranolol species. The hydroxylation of propranolol by •OH occurs at either amine moiety or naphthalene group while SO 4 •- favors the oxidation of the electron-rich naphthalene group. Further oxidation by •OH and SO 4 •- results in ring-opening products. Bicarbonate and chloride exert no effect on propranolol degradation. The generation of CO 3 •- and Cl-containing radicals is favorable to oxidizing naphthalene group. The acute toxicity assay of Vibrio fischeri suggests that SO 4 •- generates more toxic products than •OH, while CO 3 •- and Cl-containing radicals produce similar toxicity as SO 4 •-. High concentrations of bicarbonate in UV/H 2 O 2 increase the toxicity of treated solution. Graphical abstract Image 1 Highlights • Propranolol degradation is comparatively studied in UV/H 2 O 2 and UV/PDS. • CO 3.•- and Cl-containing radicals react with propranolol •.•OH induces hydroxylation of propranolol at either amine or naphthalene group • SO 4.•-, CO 3 •- and Cl-containing radicals attack the naphthalene group • SO 4.•-, CO 3 •- and Cl-containing radicals generate more toxic products than •OH [ABSTRACT FROM AUTHOR]

Abstract Solar irradiation of chlorine-containing waters enhances inactivation of chlorine-resistant pathogens (e.g., Cryptosporidium oocysts), through in situ formation of ozone, hydroxyl radical, and other reactive species during photolysis of free available chlorine (FAC) at UVB-UVA wavelengths of solar light (290–400 nm). However, corresponding effects on regulated disinfection byproduct (DBP) formation and associated dissolved organic matter (DOM) properties remain unclear. In this work, when compared to dark chlorination, sunlight-driven FAC photolysis over a range of conditions was found to yield higher DBP levels, depletion of DOM chromophores and fluorophores, preferential removal of phenolic groups versus carboxylic acid groups, and degradation of larger humic substances to smaller molecular weight compounds. Control experiments showed that increased DBP levels were not due to direct DOM photolysis and subsequent dark reactions with FAC, but to co-exposure of DOM to FAC and reactive species (e.g., O 3 , HO•, Cl•, Cl 2 •-, ClO•) generated by FAC photolysis. Because solar chlorine photolysis can enable inactivation of chlorine-resistant pathogens at far lower CT FAC values than chlorination alone, the increases in DBP formation inherent to this approach can likely be offset to some extent by the ability to operate at significantly decreased CT FAC. Nonetheless, these findings demonstrate that applications of solar chlorine photolysis will require careful attention to potential impacts on DBP formation. Graphical abstract Image 1 Highlights • Solar chlorine photolysis increases THM and HAA formation in DOM-containing waters. • DBP formation correlates with extensive photobleaching and decreased MW of DOM. • Photogenerated ROS, RHS, and O 3 drive DBP precursor generation and destruction. • THM and HAA levels can be maintained below MCLs in waters with low DOC and bromide. • Use of solar chlorine photolysis for disinfection requires attention to DBP impacts. [ABSTRACT FROM AUTHOR]

● High yields of DCAM and DCAA are formed during ozonation of phenicol antibiotics. ● The transformation pathways of phenicol antibiotics during ozonation are investigated. ● DCAM is completely transformed to DCAA during post-chlorination of ozonation effluent. ● The molar yield of DCAA is ∼100 % during phenicol antibiotic abatement by ozonation and post-chlorination. ● Post-chloramination of ozonation effluent increases the yields of DCAM and DCAA moderately. This study investigated the formation of dichloroacetamide (DCAM) and dichloroacetic acid (DCAA) from the abatement of three phenicol antibiotics (PABs, chloramphenicol, thiamphenicol, and florfenicol) during ozonation and post-chlor(am)ination. Results show that the three PABs have a low ozone reactivity (k O3 = 0.11‒0.12 M−1 s−1), and therefore are mainly abated through the hydrogen abstraction mechanism by hydroxyl radicals (•OH) during ozonation. During PAB degradation, the carboxamide moiety in the parent molecules can be cleaved off by •OH attack and thus gives rise to DCAM. The formed DCAM can then be further oxidized by O 3 and/or •OH to DCAA as a more stable transformation product (TP). When the three PABs were adequately abated (abatement efficiency of ∼82 %‒95 %), the molar yields of DCAM and DCAA were determined to be 2.79 %‒4.71 % and 32.9 %‒37.2 %, respectively. Furthermore, post-chloramination of the ozonation effluents increased the yields of DCAM and DCAA slightly to 4.20 %‒6.45 % and 39.0 %‒41.1 %, respectively. In comparison, post-chlorination eliminated DCAM in the solutions, but significantly increased DCAA yields to ∼100 % due to the further conversion of DCAM and other ozonation TPs to DCAA by chlorine oxidation. The results of this study indicate that high yields of DCAM and DCAA can be generated from PAB degradation during ozonation, and post-chlorination and post-chloramination will result in very different fates of DCAM and DCAA in the disinfected effluent. The formation and transformation of DCAM and DCAA during PAB degradation need to be taken into account when selecting multi-barrier treatment processes for the treatment of PAB-containing water. [Display omitted] [ABSTRACT FROM AUTHOR]

• R ct values can be estimated by organic carbon content and alkalinity of a water. • Predicting degradation by R ct is restricted to waters with low or medium alkalinity. • Carbonate radicals can contribute to degradation of purine and adenine in ozonation. • Product formation differs for guanine and antivirals depending on matrix components. Ozonation of micropollutants strongly depends on the water matrix. Natural organic matter is known to highly affect the hydroxyl radical exposure due to radical promoting and inhibiting effects. Other important matrix components in ozonation are carbonate species which scavenge hydroxyl radicals. However, additional factors such as the formation of other radicals might also play a role but are generally not covered in research or considered in modelling of micropollutant degradation. Hence, the ozonation of purine derivatives, the basic structure of various antiviral micropollutants, in different artificial water matrices is investigated in this study with focus on the impact of natural organic matter and increasing alkalinity on the degradation and product formation. The degradation of purine and adenine is inhibited by bicarbonate in the water matrix due to the anion's scavenging of hydroxyl radicals. This effect is already observed for low bicarbonate concentrations of 0.3 mM. However, formed carbonate radicals contribute to the compounds' degradation and also affect the stability of transformation products. This effect gains in relevance with increasing alkalinity and needs consideration in evaluating ozonation of very hard waters. Three ozonation products are evaluated in detail, which are affected by the matrix due to impacts on ozone stability, hydroxyl radical yield and carbonate radical formation. One product of adenine with the mass 147 was reported for the first time and only occurs in presence of matrix components. Under typical water treatment conditions rough predictions of pollutants' degradation are possible by the R ct concept using ozone and hydroxyl radical exposures. However, other reactive species such as carbonate radicals are not considered leading to deviations between modelled and experimental data at extreme conditions such as industrial wastewater. A general correlation between the R ct and the fraction f of hydroxyl radicals scavenged by bicarbonate (ln(R ct) = - 5.9 × f - 16.3) calculated from the concentration of organic matter and alkalinity was observed for various water samples allowing the estimation of micropollutant degradation during ozone treatment at moderate conditions by simple organic and inorganic carbon measurements. [Display omitted] [ABSTRACT FROM AUTHOR]

• ⋅OH and reactive phosphate species (RPS) dominate in phosphate (PB)/PMS. • [HPO 4 ⋅−] ss is 666 and 773 times higher than [⋅OH] ss and [SO 4 ⋅−] ss in PB/PMS at pH=8. • RPS selectively oxidize micropollutants with electron-donating moieties. • The degradation pathways of micropollutants in PB/PMS were proposed. • Cytotoxicity decreased during the degradation of BPA and DCF by PB/PMS. This study investigated the mechanisms of forming reactive species to degrade micropollutants through the activation of peroxymonosulfate (PMS) by phosphate, a prevalent ion in wastewater. Considering the density functional theory results, the formation of hydrogen bonds between phosphate and PMS molecules might be the crucial step in the overall reactions, which prefers producing ⋅OH and reactive phosphate species (RPS, namely H 2 PO 4 ⋅, HPO 4 ⋅−, and PO 4 ⋅2−) to yielding SO 4 ⋅−. Besides, in the phosphate (5 mM)/PMS system at pH = 8, HPO 4 ⋅− was modeled to be the dominant radical with a steady-state concentration of 3.6 × 10−12 M, which was 666 and 773 times higher than those of ⋅OH and SO 4 ⋅−. The contributions of 1O 2 , ⋅OH, SO 4 ⋅−, and RPS to the micropollutant decomposition in phosphate/PMS were studied, and RPS were found to be selective for micropollutants with electron-donating moieties (such as phenolic and aniline groups). Additionally, the degradation pathways of bisphenol A, diclofenac, ibuprofen, and atrazine in phosphate/PMS were proposed according to the detected transformation products. Cytotoxicity analysis was carried out to evaluate the potential environmental impacts resulting from the degradation of micropollutants by phosphate/PMS. This study confirmed the significance of RPS for micropollutant degradation during PMS-based treatment in phosphate-rich scenarios. [Display omitted] [ABSTRACT FROM AUTHOR]

A novel particle electrode based on antimony tailings microspheres was successfully constructed by ultrasonic immersion calcination method, and the degradation of RhB was studied in a three-dimensional electrochemical reactor (3DER). It was characterized by XRD, SEM, EDS, XPS, cyclic voltammetry and linear sweep voltammetry. When the pH value is 5.00, the dosage of Fe/Cu@antimony tailing is 1.50 g/L, the initial concentration is 100 mg/L, and the current density is 20 mA/cm 2 , the degradation efficiency is the best (99.40% for RhB and 98.81% for TOC) within 15 min. The results show that in the three-dimensional electrochemical oxidation system, electrochemical oxidation and electro Fenton oxidation occur at the same time to cause the increase of hydroxyl radicals. According to LC-MS analysis and EPR characterization, it can be found that the main degradation mechanism of RhB is that hydroxyl radicals continuously attack RhB, and realize rapid degradation of RhB through deethylation, deamination, dealkylation, decarboxylation, chromophore splitting, ring opening and mineralization. Fe/Cu@antimony tailing particles are both electrodes for electrochemical oxidation and catalysts for Fenton oxidation. The degradation effect of RhB remained at 94% after 6 cycles, and the leaching rates of Fe and Cu are only 1.20% and 0.79%, indicating that Fe/Cu@AT had significant stability. This work provides a new insight into the establishment of an efficient and stable three-dimensional electrocatalytic particle electrode., 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.)

Periodate (PI) as an oxidant has been extensively studied for organic foulants removal in advanced oxidation processes. Here PI was introduced into In 2 O 3 /Vis-LED process to enhance the formation of ·OH for promoting the degradation of organic foulants. Results showed that the addition of PI would significantly promote the removal of sulfamethoxazole (SMX) in the In 2 O 3 /Vis-LED process (from 9.26% to 100%), and ·OH was proved to be the dominant species in the system. Besides, the process exhibited non-selectivity in the removal of different organic foulants. Comparatively, various oxidants (e.g., peroxymonosulfate, peroxydisulfate, and hydrogen peroxide) did not markedly promote the removal of SMX in the In 2 O 3 /Vis-LED process. Electrochemical analyses demonstrated that PI could effectively receive photoelectrons, thus inhibiting the recombination of photogenerated electron-hole (e - /h + ) pairs. The holes then oxidized the adsorbed H 2 O to generate ·OH, and the PI converted to iodate at the same time. Additionally, the removal rate of SMX reduced from 100% to 17.2% as Vis-LED wavelengths increased from 440 to 560 nm, because of the low energy of photons produced at longer wavelengths. Notably, the species of PI do not affect its ability to accept electrons, resulting in the degradation efficiency of SMX irrespective of pH (4.0-10.0). The coexistence of inorganic cations and anions (such as Cl - , CO 3 2- /HCO 3 - , SO 4 2- , Ca 2+ , and Mg 2+ ) also had an insignificant effect on SMX degradation. Furthermore, the process also showed excellent degradation potential in real water. The proposed strategy provides a new insight for visible light-catalyzed activation of PI and guidance to explore green catalytic processes for high-efficiency removal of various organic foulants., 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.)

Advanced oxidation processes are commonly considered one of the most effective techniques to degrade refractory organic pollutants, but the limitation of a single process usually makes it insufficient to achieve the desired treatment. This work introduces, for the first time, a highly-efficient coupled advanced oxidation process, namely Electro-Oxidation-Persulfate-Electro-Fenton (EO-PS-EF). Leveraging the EO-PS-EF tri-coupling system, diverse contaminants can be highly efficiently removed with the help of reactive hydroxyl and sulfate radicals generated via homogeneous and heterogeneous bi-catalysis, as certified by radical quenching and electron spin resonance. Concerning degradation of tetracycline (TC), the EO-PS-EF system witnessed a fast pseudo-first-order reaction kinetic constant of 2.54 × 10 -3 s -1 , ten times that of a single EO system and three-to-four times that of a binary system (EO-PS or EO-EF). In addition, critical parameters (e.g., electrolyte, pH and temperature) are systematically investigated. Surprisingly, after 100 repetitive trials TC removal can still reach 100% within 30 min and no apparent morphological changes to electrode materials were observed, demonstrating its long-term stability. Finally, its universality was demonstrated with effective degradation of diverse refractory contaminants (i.e., antibiotics, dyes and pesticides)., 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. Published by Elsevier Ltd.)

Abstract In this study, we comparatively investigated the degradation of 12 trace organic chemicals (TOrCs) during UV/H 2 O 2 and UV/peroxydisulfate (PDS) processes. Second-order rate constants for the reactions of iopromide, phenytoin, caffeine, benzotriazole, and primidone with sulfate radical (SO 4 •−) were determined for the first time. Experiments were conducted in buffered pure water and wastewater effluent with spiked TOrCs. UV/PDS degraded all TOrCs more efficiently than UV/H 2 O 2 in buffered pure water due to the higher yield of SO 4 •− than that of hydroxyl radical (•OH) at the same initial molar dose of PDS and H 2 O 2 , respectively. UV/PDS showed higher selectivity toward TOrCs removal than UV/H 2 O 2 in wastewater effluent. Compounds with electron-rich moieties, such as diclofenac, venlafaxine, and metoprolol, were eliminated faster in UV/PDS whereas UV/H 2 O 2 was more efficient in degrading compounds with lower reactivity to SO 4 •−. The fluence-based rate constants ( k o b s − U V / H 2 O 2 ) of TOrCs in wastewater effluent linearly increased as a function of initial H 2 O 2 dose during UV/H 2 O 2 , possibly due to the constant scavenging impact of the wastewater matrix on •OH. However, exponential increase of k o b s − U V / P D S with increasing PDS dose was observed for most compounds during UV/PDS, suggesting the decreasing scavenging effect of the water matrix (electron-rich site of effluent organic matter (EfOM)) after initial depletion of SO 4 •− at low PDS dose. Fulvic and humic-like fluorophores appeared to be more persistent during UV/H 2 O 2 compared to aromatic protein and soluble microbial product-like fluorophores. In contrast, UV/PDS efficiently degraded all identified fluorophores and showed less selectivity toward the fluorescent EfOM components. Removal pattern of TOrCs during pilot-scale UV/PDS was consistent with lab-scale experiments, however, overall removal rates were lower due to the presence of higher concentration of EfOM and nitrite. Graphical abstract Image 1 Highlights • A comparative investigation on the efficiency of UV/H 2 O 2 and UV/PDS. • Degradation kinetics of 12 trace organic chemicals. • Higher steady state concentration of SO 4 •− compared to •OH in pure water. • Selective property of SO 4 •− favouring oxidation of electron-rich organic moieties. • Pilot-scale validation of UV/PDS in wastewater treatment plant effluent. [ABSTRACT FROM AUTHOR]

Hydroxyl radical ( • OH) based advanced oxidation technologies (AOTs) are effective for removing non‒steroidal anti−inflammatory drugs (NSAIDs) during water treatment. In this study, we systematically investigated the degradation kinetics of naproxen (NAP), a representative NSAID, with a combination of experimental and theoretical approaches. The second−order rate constant ( k ) of • OH oxidation of NAP was measured to be (4.32 ± 0.04) × 10 9  M −1  s −1 , which was in a reasonable agreement with transition state theory calculated k value (1.08 × 10 9  M −1  s −1 ) at SMD/M05–2X/6–311++G**//M05–2X/6–31+G** level of theory. The calculated result revealed that the dominant reaction intermediate is 2‒(5‒hydroxy‒6‒methoxynaphthalen‒2‒yl)propanoic acid (HMNPA) formed via radical adduct formation pathway, in which • OH addition onto the ortho site of the methoxy−substituted benzene ring is the most favorable pathway for the NAP oxidation. We further investigated the subsequent • OH oxidation of HMNPA via a kinetic modelling technique. The k value of the reaction of HMNPA and • OH was determined to be 2.22 × 10 9  M −1  s −1 , exhibiting a similar reactivity to the parent NAP. This is the first study on the kinetic and mechanistic aspects of NAP and its reaction intermediates. The current results are valuable in future study evaluating and extending the application of • OH based AOTs to degrade NAP and other NSAIDs of concern in water treatment plants. [ABSTRACT FROM AUTHOR]

Sludge cell disruption was generally considered as the rate-limiting step for the anaerobic digestion of waste activated sludge (WAS). Advanced oxidation processes and bio-electro-chemical systems were recently reported to enhance the hydrolysis of WAS and sludge cell disruption, while the cell-breaking processes of these systems remain unclear yet. In this study, an innovative Bio-electro-Fenton system was developed to pretreat the WAS sequentially with cathode Fenton process and anode anaerobic digestion. Significant cell disruption and dissolution intracellular organics were founded after the treatment. X-ray photoelectron spectroscopy (XPS) analysis and fourier transform infrared spectroscopy (FT-IR) spectra indicated that Gram-negative bacteria were more sensitive to free radicals yielded in cathode to induce a chain reaction that destroyed the lipid-contained outer membrane, while Gram-positive bacteria with thick peptidoglycan layer were liable to be biologically decomposed in the anode. Compared with the oxidation of organic matters in the cathode Fenton, the secretion of enzyme increased in the anode which was beneficial to break down the complex matters (peptidoglycans) into simples that were available for anode oxidation by exoelectrogens. The results also showed a possible prospect for the application of this sequential pretreatment in bio-electro-Fenton systems to disrupt sludge cells and enhance the anaerobic digestion. [ABSTRACT FROM AUTHOR]

The corrosion of zero valent iron (ZVI) by hydrogen peroxide (H 2 O 2 ) generates hydroxyl (⋅OH) and other radical oxygen species (ROS) that degrade organic materials. To better understand the factors that govern the ROS formation during the H 2 O 2 -induced corrosion, we investigated the degradation of an organic probe compound (acesulfame (ACE)) in slurries of ZVI powder in unbuffered laboratory water at pH 6.5 ± 0.5. Chloride ions accelerated the corrosion of ZVI by H 2 O 2 and the formation ROS and, therefore, the degradation of organic materials. Conversely, slowing corrosion by phosphate buffer inhibited ROS formation and the degradation of organic compounds. The rate of H 2 O 2 decomposition was correlated with the liberation of Fe 2+ (aq) and the ACE degradation rate. The kinetics of H 2 O 2 decomposition was pseudo-first-order and zero-order at low (<0.04 mM/mg) and high [H 2 O 2 ]/[ZVI] initial ratios, respectively, and was consistent with Langmuir kinetics. The H 2 O 2 decomposition rate was proportional to the ZVI reactive surface area (SA) and nearly independent of the extent of ZVI oxidation, the presence of a Fe 2+ (aq) chelating agent, and ⋅OH quenchers (methanol and tert -butanol). Kinetic data suggest a mechanism involving rapid cathodic reduction of H 2 O 2 at the metallic ZVI surface which causes the liberation of Fe 2+ (aq) that generate ⋅OH via the homogeneous Fenton reaction. The stoichiometric efficiency (SE) of organics degradation ranged from 0.0008% to 0.014% and increased with decreasing H 2 O 2 decomposition rate. [ABSTRACT FROM AUTHOR]

Sodium persulfate has become the most popular oxidant source for the in situ chemical oxidation (ISCO) treatment of organic contaminants in the subsurface. The most common persulfate activators, iron chelates and base, are often ineffective in initiating the generation of reactive oxygen species in field applications. In this study, glucose was investigated as a persulfate activator in systems containing varying concentrations of sodium hydroxide using nitrobenzene as a hydroxyl radical probe and hexachloroethane as a reductant + nucleophile probe. Glucose activation of persulfate increased as a function of sodium hydroxide addition, but was still effective at circumneutral pH regimes. Use of central composite rotatable experimental designs showed that hydroxyl radical and reductant + nucleophile generation rates increased as a function of persulfate at near-neutral pH regimes. Glucose activation of persulfate has the advantages over other activation pathways of more options and flexibility for effective process chemistry and of minimizing or eliminating the mass of sodium hydroxide added to the subsurface. The results of this research can be applied in the field by first evaluating glucose activation compared to base and iron chelate activation of persulfate in laboratory treatability studies. [ABSTRACT FROM AUTHOR]

Vacuum-Ultraviolet (VUV), an efficient and green method to produce hydroxyl radical (•OH), is effective in degrading numerous organic contaminants in aqueous solution. Here, we proposed an effective and simple kinetic model to describe the degradation of organic pollutants in VUV system, by taking the •OH scavenging effects of formed organic intermediates as co-existing organic matter in whole. Using benzoic acid (BA) as a •OH probe, •OH was regarded vital for pollutant degradation in VUV system, and the thus developed model successfully predicted its degradation kinetics under different conditions. Effects of typical influencing factors such as BA concentrations and UV intensity were investigated quantitatively by the model. Temperature was found to be an important influencing factor in the VUV system, and the quantum yield of •OH showed a positive linear dependence on temperature. Impacts of humic acid (HA), alkalinity, chloride, and water matrices (realistic waters) on the oxidation efficiency were also examined. BA degradation was significantly inhibited by HA due to its scavenging of •OH, but was influenced much less by the alkalinity and chloride; high oxidation efficiency was still obtained in the realistic water. The degradation kinetics of three other typical micropollutants including bisphenol A (BPA), nitrobenzene (NB) and dimethyl phthalate (DMP), and the mixture of co-existing BA, BPA and DMP were further studied, and the developed model predicted the experimental data well, especially in realistic water. It is expected that this study will provide an effective approach to predict the degradation of organic micropollutants by the promising VUV system, and broaden the application of VUV system in water treatment. [ABSTRACT FROM AUTHOR]

A massive spill of 4-methylcyclohexanemethanol (MCHM), a semi-volatile organic compound, contaminated the Elk river and forced the recent closure of tap water for nearly 300,000 residents. Typical water treatment methods are not effective for MCHM remediation, however ultrasonic irradiation leads to its rapid pseudo-first order degradation. The degradation processes were effectively modeled employing heterogeneous kinetic models with the reaction surface corresponding to the gas-liquid interface of the cavitation bubble. The Freundlich model which takes into account non-uniform distribution within the reactive zone showed the strongest correlation to the observed degradation kinetic data with R 2 > 0.99. Solute-solute clustering behavior is proposed to explain non-uniform distribution of MCHM. The results indicate the degradation occurs predominantly at the gas-liquid interface as a result of hydroxyl radical reactions and pyrolysis with primary reaction products, (4-methylcyclohexenyl) methanol and 4-methylcyclohexanone. Computational methods using density functional B3YPL/6-311G** calculations with Gaussian 09 provided insight of the hydroxyl radical and pyrolytic degradation pathways for the isomeric and conformational forms of MCHM. Our studies demonstrate that heterogeneous kinetic models and computational methods are important tools for the fundamental understanding and effective application of ultrasonically mediated degradation of MCHM which may be extended to a number of semi-volatile compounds. [ABSTRACT FROM AUTHOR]

• Reaction rate constants of EfOM and its isolated fractions with ·OH were reported. • Roles of EfOM and its fractions as initiator, promoter or inhibitor were quantified. • ·OH reaction rate of hydrophilic fraction is 10-fold higher than hydrophobic one. • Hydrophilic base dominates ozone decomposition and reaction with ·OH. Dissolved effluent organic matter (EfOM) plays an important role in ozonation decomposition and hydroxyl radical (·OH) scavenging in ozonation for the degradation of trace organic contaminants (TrOCs) in municipal secondary effluents. The properties of EfOM have been considered a major concern in this process because EfOM fractions act differently as initiator, promoter or inhibitor of ozone decomposition and ·OH scavenging, which further impacts the degradation effectiveness of TrOCs. This study isolated EfOM from three wastewater treatment plants into six fractions (HoA, HoB, HoN, HiA, HiB and HiN) to understand the reaction kinetics as a function of EfOM and its isolated fractions. Their reaction rate constants with ·OH (k EfOM-·OH), and their roles as the initiator, promoter and inhibitor in the ·OH chain reactions in ozone decomposition were further quantified. The results showed that k EfOM-·OH of hydrophilic fractions (HiF) (accounting for 17%) reached up to 10 times as high as that for hydrophobic fractions (HoF) (accounting for 83%) (7.92 × 108 M−1 s−1 versus 0.78 × 108 M−1 s−1), suggesting the dominating role of HiF in ·OH scavenging. Hydrophilic base (HiB) was the most important fraction dominating the ozone decomposition and reaction with ·OH due to its highest rate constants of initiation and promotion. This study quantifies the kinetics and contribution of EfOM fractions in ·OH scavenging, which will guide the optimization implementation of ozonation and other ·OH-mediated AOPs toward wastewater effluents. [Display omitted] [ABSTRACT FROM AUTHOR]

● The role of O 2 •− for O 3 decomposition during ozonation is evaluated by a probe-based kinetic model. ● Exposures and transient concentrations of O 2 •− are determined from abatement of CCl 4 as a probe compound. ● Relative contribution of O 2 •− to O 3 decomposition is quantitatively assessed by the model. ● This study provides evidence that O 2 •− is critical for O 3 decomposition kinetics and •OH formation. Superoxide radicals (O 2 •−) have been suggested as an important chain carrier in the radical chain reaction that promotes ozone (O 3) decomposition to hydroxyl radicals (•OH) during ozonation. However, due to the difficulty in measuring transient O 2 •− concentrations, this hypothesis has not been verified under realistic ozonation conditions during water treatment. In this study, a probe compound was used in combination with kinetic modeling to evaluate the role of O 2 •− for O 3 decomposition during ozonation of synthetic solutions with model promotors and inhibitors (methanol and acetate or tert -butanol) and natural waters (one groundwater and two surface waters). By measurement of the abatement of spiked tetrachloromethane (as a O 2 •− probe), the O 2 •− exposure during ozonation was determined. Based on the measured O 2 •− exposures, the relative contribution of O 2 •− to O 3 decomposition, in comparison to OH−, •OH, and dissolved organic matter (DOM), was quantitatively evaluated using kinetic modeling. The results show that water compositions (e.g., the concentration of promotors and inhibitors, and the O 3 reactivity of DOM) have a considerable effect on the extent of the O 2 •−-promoted radical chain reaction during ozonation. In general, the reaction with O 2 •− accounted for ∼59‒70% and ∼45‒52% of the overall O 3 decomposition during ozonation of the selected synthetic solutions and natural waters, respectively. This confirms that O 2 •− plays a critical role in promoting O 3 decomposition to •OH. Overall, this study provides new insights on the controlling factors for ozone stability during ozonation processes. [Display omitted] [ABSTRACT FROM AUTHOR]

Polyvinyl alcohol (PVA) is widely used in industry but is difficult to degrade. In this study, the synergistic effect of UV irradiation and chlorination on degradation of PVA was investigated. UV irradiation or chlorination alone did not degrade PVA. By contrast, UV/chlorine oxidation showed good efficiency for PVA degradation via generation of active free radicals, such as OH and Cl. The relative importance of these two free radicals in the oxidation process was evaluated, and it was shown that OH contributed more to PVA degradation than Cl did. The degradation of PVA followed pseudo first order kinetics. The rate constant k increased linearly from 0 min −1 to 0.3 min −1 with increasing chlorine dosage in range of 0 mg/L to 20 mg/L. However, when the chlorine dosage was increased above 20 mg/L, scavenging effect of free radicals occurred, and the degradation efficiency of PVA did not increase much more. Acidic media increased the degradation efficiency of PVA by UV/chlorine oxidation more than basic or neutral media because of the higher ratio of [HOCl]/[OCl − ], higher free radical quantum yields, and the lower free radical quenching effect under acidic conditions. Results of Fourier Transform Infrared Spectroscopy showed that carbonyl groups in degradation products were formed during UV/chlorine oxidation, and a possible degradation pathway via alcohol to carbonyl was proposed. [ABSTRACT FROM AUTHOR]

Levofloxacin (LF) is a frequently detected fluoroquinolone in surface water, and permanganate (MnO 4 − ) is a commonly used oxidant in drinking water treatment. This study investigated the impact of humic acid (HA) on LF degradation by aqueous MnO 4 − from both kinetic and mechanistic aspects. In the absence of HA, the second-order rate constant ( k ) of LF degradation by MnO 4 − was determined to be 3.9 M −1 s −1 at pH 7.5, which increased with decreasing pH. In the presence of HA, the pseudo-first-order rate constant ( k obs ) of LF degradation at pH 7.5 was significantly increased by 3.8- and 2.8-fold at [HA] o :[KMnO 4 ] o (mass ratio) = 0.5 and 1, respectively. Secondary oxidant scavenging and electron paramagnetic resonance tests indicated that HA could form a complex with Mn(III), a strongly oxidative intermediate produced in the reaction of MnO 4 − with HA, to induce the successive formation of superoxide radicals (O 2 − ) and hydroxyl radicals ( OH). The resulting OH primarily contributed to the accelerated LF degradation, and the complex [HA-Mn(III)] could account for the rest of acceleration. The degradation of LF and its byproducts during MnO 4 − oxidation was mainly through hydroxylation, dehydrogenation and carboxylation, and the presence of HA led to a stronger destruction of LF. This study helps better understand the degradation of organic micropollutants by MnO 4 − in drinking water treatment. [ABSTRACT FROM AUTHOR]

This study assessed the inactivation efficiency of plasmid-encoded antibiotic resistance genes (ARGs) both in extracellular form (e-ARG) and present within Escherichia coli (intracellular form, i-ARG) during water treatment with chlorine, UV (254 nm), and UV/H 2 O 2 . A quantitative real-time PCR (qPCR) method was used to quantify the ARG damage to amp R (850 bp) and kan R (806 bp) amplicons, both of which are located in the pUC4K plasmid. The plate count and flow cytometry methods were also used to determine the bacterial inactivation parameters, such as culturability and membrane damage, respectively. In the first part of the study, the kinetics of E. coli inactivation and ARG damage were determined in phosphate buffered solutions. The ARG damage occurred much more slowly than E. coli inactivation in all cases. To achieve 4-log reduction of ARG concentration at pH 7, the required chlorine exposure and UV fluence were 33–72 (mg × min)/L for chlorine and 50–130 mJ/cm 2 for UV and UV/H 2 O 2 . After increasing pH from 7 to 8, the rates of ARG damage decreased for chlorine, while they did not vary for UV and UV/H 2 O 2 . The i-ARGs mostly showed lower rates of damage compared to the e-ARGs due to the protective roles of cellular components against oxidants and UV. The contribution of OH radicals to i-ARG damage was negligible in UV/H 2 O 2 due to significant OH radical scavenging by cellular components. In all cases, the ARG damage rates were similar for amp R versus kan R , except for the chlorination of e-ARGs, in which the damage to amp R occurred faster than that to kan R . Chlorine and UV dose-dependent ARG inactivation levels determined in a wastewater effluent matrix could be reasonably explained by the kinetic data obtained from the phosphate buffered solutions and the expected oxidant (chlorine and OH radicals) demands by water matrix components. These results can be useful in optimizing chlorine and UV-based disinfection systems to achieve ARG inactivation. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) is an attractive metal-free catalyst that can be explored in combination with ozone treatment. Using fluorescence microscopy image analysis, we investigated the production of hydroxyl radicals (HO ) within the solid-liquid interphase for CNT-mediated catalytic ozonation. The visualized results suggest that HO was vastly generated via catalysis and accumulated within a surface region of the CNT (we defined this region as the interphase “HO zone”). In this region, using 7-hydroxycoumarin as a HO marker, the radical abundance was at least 1000 times higher than that in the aqueous bulk phase. Owing to the observed inhomogeneity of HO , the CNT/ozone system effectively decomposed perfluorooctane sulfonate that was fairly resistant to non-catalytic ozonation, and the decomposition kinetics was not much inhibited by tert-butanol as bulk-phase HO scavenger due to the remaining “HO zone” at surface region available for reaction. A longevity trial revealed the sustained formation of the interphase “HO zone” and strongly indicated that the graphitic structure may optimize the density of surface active sites responsible for the proliferation and local concentration of HO . CNT, with good catalytic efficiency, longevity and stability, is anticipated as the basis of future nanomaterials able to promote HO exposure in ozone treatment for advanced oxidation process. [ABSTRACT FROM AUTHOR]

Ozonation is an effective treatment for removing various organic pollutants from aquatic systems. The R ct concept, which is defined as the ratio of OH exposure to O 3 exposure, has been widely used to predict the removal efficiency of target compounds, but it has significant variations by water temperature and initial O 3 dose which are crucial parameters in drinking water plant. The R OH,O3 concept, which is defined as the OH exposure by O 3 consumption, was proposed as a kinetic parameter for characterization and kinetic modeling for ozonation. The R OH,O3 concept is independent of temperature and initial O 3 dose. A higher R OH,O3 value indicates a higher OH formation when the same amount of O 3 is consumed in different water samples; therefore, the OH yield from O 3 decomposition of the water samples can be compared using the R OH,O3 values. The R OH,O3 concept can also be used to characterize and model the initial ozone demand phase, and it is more convenient method compared to R ct concept. Using the R OH,O3 concept, the dynamic O 3 and OH kinetics and the removal efficiencies of iopromide and ibuprofen were well predicted ( R 2 = 0.98) over a wide range of experimental conditions ( n = 124). [ABSTRACT FROM AUTHOR]

The frequent detection of sulfamethoxazole (SMX) in wastewater and surface waters gives rise of concerns about their ecotoxicological effects and potential risks to induce antibacterial resistant genes. UV/hydrogen peroxide (UV/H 2 O 2 ) and UV/persulfate (UV/PDS) advanced oxidation processes have been demonstrated to be effective for the elimination of SMX, but there is still a need for a deeper understanding of product formations. In this study, we identified and compared the transformation products of SMX in UV, UV/H 2 O 2 and UV/PDS processes. Because of the electrophilic nature of SO 4 - , the second-order rate constant for the reaction of sulfate radical (SO 4 - ) with the anionic form of SMX was higher than that with the neutral form, while hydroxyl radical ( OH) exhibited comparable reactivity to both forms. The direct photolysis of SMX predominately occurred through cleavage of the N S bond, rearrangement of the isoxazole ring, and hydroxylation mechanisms. Hydroxylation was the dominant pathway for the reaction of OH with SMX. SO 4 - favored attack on NH 2 group of SMX to generate a nitro derivative and dimeric products. The presence of bicarbonate in UV/H 2 O 2 inhibited the formation of hydroxylated products, but promoted the formation of the nitro derivative and the dimeric products. In UV/PDS, bicarbonate increased the formation of the nitro derivative and the dimeric products, but decreased the formation of the hydroxylated dimeric products. The different effect of bicarbonate on transformation products in UV/H 2 O 2 vs. UV/PDS suggested that carbonate radical (CO 3 - ) oxidized SMX through the electron transfer mechanism similar to SO 4 - but with less oxidation capacity. Additionally, SO 4 - and CO 3 - exhibited higher reactivity to the oxazole ring than the isoxazole ring of SMX. Ecotoxicity of transformation products was estimated by ECOSAR program based on the quantitative structure-activity relationship analysis as well as by experiments using Vibrio fischeri , and these results indicated that the oxidation of SO 4 - or CO 3 - with SMX generated more toxic products than those of OH. [ABSTRACT FROM AUTHOR]

• Ozone reacts very slow with organo-phosphonate based antiscalants. • Sulfate and Hydroxyl radicals are a promising tool of organophosphonate degradation. • Bromate formation limit organophosphonate degradation in ozonation. Reverse osmosis (RO) is an advanced technology used to produce potable water from a variety of water sources, including surface water, seawater and wastewater. The yield of the product water from the RO systems is increased by the addition of antiscalants which prevent scaling from calcium and other ions. Removal of antiscalants from RO concentrate can induce the precipitation of oversaturated scale-forming substances, enable additional water recovery from RO concentrates, and reduce the risk of eutrophication after concentrate disposal into the receiving water (e.g., river water). This study aims to provide a better insight into oxidation reactions of the N -free phosphonate antiscalants 1-hydroxyethane-1,1-diphosphonic acid (HEDP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) with ozone, hydroxyl radical (•OH) and sulfate radicals (SO 4 •−). Ozone barely reacts with HEDP and PBTC at pH 7 (k < 10 M-1 s −1), while second order reaction rates of SO 4 •− and •OH were determined to be in the range 107–108 M −1 s −1. Sulfate, silicate and chloride matrices increased HEDP ozone degradation rate possibly due to metal complexation effect. Whereas carbonate and chloride hindered PBTC ozone degradation, and natural organic matter (NOM) inhibited both HEDP and PBTC degradation through scavenging of •OH. The SO 4 •−- radical based oxidation process of HEDP and PBTC is mainly inhibited by carbonate and NOM, interestingly only HEDP degradation is inhibited by chloride whereby the PBTC could not be fully degraded (degradation < 60%). The oxidation of PBTC is in real RO concentrates in both processes limited to 10% degradation, whereas HEDP could be degraded up to 60% with ozone and UV/persulfate application. [ABSTRACT FROM AUTHOR]

• Mackinawite could efficiently adsorb and degrade FQs at ambient conditions. • Dissolved oxygen participated and played an essential role on FQs degradation. • OH• and O 2 •−were generated during FeS oxidation. • Surface-bound OH• and O 2 •− were dominant ROS responsible for FQs degradation. • Mackinawite showed great potential for environmental remediation. Fluoroquinolone antibiotics (FQs) have been widely detected in the sediments due to vast production and consumption. In this study, the transformation of FQs was investigated in the presence of sediment mackinawite (FeS) under ambient conditions. Moreover, the role of dissolved oxygen was evaluated for the enhanced degradation of FQs induced by FeS. Our results demonstrated that typical FQs (i.e., flumequine, enrofloxacin and ciprofloxacin) could be efficiently adsorbed and degraded by FeS under neutral pH conditions. As indicated by the results of electron paramagnetic resonance analysis (EPR) and free radicals quenching experiments, hydroxyl radical and superoxide radical anions were identified as the dominant reactive species responsible for FQs degradation. Based on the results of product analysis and theoretical calculation, the degradation of FQs mainly occurred at the piperazine ring and quinolone structure. Our results show that FQs could be efficiently removed by FeS, which benefits understanding the transformation of antibiotics in the sediments, and even sheds light on the remediation of organic pollutants contaminated soils. [Display omitted] [ABSTRACT FROM AUTHOR]

• Dynamic electronic structure analysis is applied to reveal radical attack mechanism. • SO 4 •− has higher oxidation potential and electrophilic index than •OH. • Only SO 4 •−can react with CAF through single electron transfer reaction (SET) route. • Only •OH can react with CAF through hydrogen atom abstraction (HAA) route. • •OH shows larger energy barriers than SO 4 •− through radical adduct formation (RAF). Hydroxyl radical (•OH) and sulfate radical (SO 4 •−) produced in advanced oxidation processes (AOPs) have been widely studied for organic contaminants degradation, however, the different radical characteristics and reaction mechanisms on organics degradation are still needed. In this study, a homogeneous Co(II)/peroxymonosulfate activation system was established for caffeine (CAF) degradation, and pH was controlled to regulate the radicals production. The different attack routes driven by SO 4 •− and •OH were deeply explored by transformation products (TPs) identification and theoretical calculations. Specifically, a method on dynamic electronic structure analysis of reactants (R), transition state (TS) and intermediates (IMs) during reaction was proposed, which was applied to elucidate the underlying mechanism of CAF oxidation by •OH and SO 4 •− at the molecular orbital level. In total, SO 4 •− is kinetically more likely to attack CAF than •OH due to its higher oxidation potential and electrophilicity index. Single electron transfer reaction (SET) is only favorable for SO 4 •−due to its higher electron affinity than •OH, while only •OH can react with CAF via hydrogen atom abstraction (HAA) route. Radical adduct formation (RAF) is the most favorable route for both •OH and SO 4 •− attack according to both kinetics and thermodynamics results. These findings can significantly promote the understanding on the degradation mechanism of organic pollutants driven by •OH and SO 4 •− in AOPs. [Display omitted] [ABSTRACT FROM AUTHOR]

Advanced oxidation processes (AOPs) have been widely used in water and wastewater treatment and have shown excellent performance in remediating contaminated water. However, their oxidation byproducts, including halogenated organics, have recently attracted increasing attention. Alkyl halides are among the most important environmental pollutants in nature. Here, we report a Fenton-like reaction in which alkyl halides can form during the photodegradation of aliphatic carboxylic acids in the presence of Fe(III) and halides. Chloromethane, chloroethane, and 1-chloropropane were produced from the degradation of acetic acid, propionic acid and n-butyric acid, respectively. CH 3 Cl, CH 2 Cl 2 and CHCl 3 were all identified as the products of acetic acid with the yields of approximately 5.1%, 0.2% and 0.005%, respectively. It was demonstrated that hydroxyl radicals, halogen radicals and alkyl radicals were involved in the formation of alkyl halides. A possible mechanism of chloromethane formation was proposed based on the results. In real samples of saline water, the addition of carboxylic acid and Fe(III) significantly promoted the generation of CH 3 Cl under xenon lamp irradiation. The results indicated that the coexistence of Fe(III), halides and carboxylic acids enhanced the photochemical release of alkyl halides. The reactions described in this paper may contribute to knowledge on the mechanism of halogenated byproduct formation during AOPs., 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.)

Compounds with N , N -dimethylhydrazine moieties ((CH 3 ) 2 N-N-) form N -nitrosodimethylamine (NDMA) during ozonation, but the relevant reaction chemistry is hitherto poorly understood. This study investigated the reaction kinetics and mechanisms of NDMA formation during ozonation of unsymmetrical dimethylhydrazine (UDMH) and daminozide (DMZ) as structural model N , N -dimethylhydrazine compounds. The reaction of ozone with these NDMA precursor compounds was fast, and k O3 at pH 7 was 2 × 10 6 M −1 s −1 for UDMH and 5 × 10 5 M −1 s −1 for DMZ. Molar NDMA yields (i.e., Δ[NDMA]/Δ[precursor] × 100) were 84% and 100% for UDMH and DMZ, respectively, determined at molar ozone dose ratio ([O 3 ] 0 /[precursor] 0 ) of ≥4 in the presence of tert -butanol as hydroxyl radical ( OH) scavenger. The molar NDMA yields decreased significantly in the absence of tert -butanol, indicating OH formation and its subsequent reaction with the parent precursors forming negligible NDMA. The k OH at pH 7 was 4.9 × 10 9 M −1 s −1 and 3.4 × 10 9 M −1 s −1 for UDMH and DMZ, respectively. Reaction mechanisms are proposed in which an ozone adduct is formed at the nitrogen next to N , N -dimethylamine which decomposes via homolytic and heterolytic cleavages of the –N + -O-O-O − bond, forming NDMA as a final product. The heterolytic cleavage pathway explains the significant OH formation via radical intermediates. Overall, significant NDMA formation was found to be unavoidable during ozonation or even O 3 /H 2 O 2 treatment of waters containing N , N -dimethylhydrazine compounds due to their rapid reaction with ozone forming NDMA with high yield. Thus, source control or pre-treatment of N , N -dimethylhydrazine precursors and post-treatment of NDMA are proposed as the mitigation options. [ABSTRACT FROM AUTHOR]

Polycyclic musks (PCMs) have recently caused a worldwide environmental concern due to their bioaccumulation potential and ecotoxicological effects. Herein, the OH-initiated indirect photochemical transformation mechanism, environmental fate and ecotoxicity of PCMs (by taking tonalide as an example) were theoretically studied. Results show that tonalide can be degraded readily through OH-addition and H-abstraction pathways, with total rate constants of 6.03 × 10 9 –15.8 × 10 9 M −1 s −1 . The OH-addition pathways were dominant at low temperature (<∼287 K), whereas H-abstraction was the dominant pathway at high temperature. Further, the bioconcentration factors (BCF) and aquatic toxicities to fish of all transformation products from H-abstraction pathways were smaller than tonalide. In contrast, these values of most intermediates from OH-addition pathways were up to 8 times higher than tonalide. Particularly, the resultant phenolic product PC1 had a BCF of 5590 L/kg wet-wt, which exceeds the cutoff criterion set for the typically persistent organic pollutants as critically bioaccumulative. Notably, PC1 would mainly be produced under anaerobic aquatic conditions at low temperatures. Therefore, particular attention should be paid to the indirect photochemical products and parental PCMs, particularly the intermediates from OH-addition pathway. [ABSTRACT FROM AUTHOR]

To develop a cost-effective method for post-formation mitigation of iodinated disinfection by-products, degradation of iodoacids by UV, UV/PS (persulfate), and UV/H 2 O 2 was extensively investigated in this study. UV direct photolysis of 4 iodoacids followed first-order kinetics with rate constants in the range of 2.43 × 10 −4 −3.02 × 10 −3 cm 2 kJ −1 . The derived quantum yields (Ф 254 ) of the 4 iodoacids range from 0.13 to 0.34, respectively. A quantitative structure-activity relationship (QSAR) model was subsequently established and applied to predict the direct photolysis rates of 6 other structurally similar iodoacids whose standards are commercially unavailable. At a UV dose of 140 mJ cm −2 which is typically applied for disinfection of drinking water, the removal percentages of 4 iodoacids were only between 3.35% and 34.7%. Thus, ICH 2 CO 2 H (IAA), the most photo-recalcitrant species, was selected as the target compound for removal in the UV/PS and UV/H 2 O 2 processes. The IAA degradation rates decreased with increasing pH from 3 to 11 in both processes. Humic acid (HA) and HCO 3 − had inhibitory effects on IAA degradation in both processes. Cl − adversely affected the IAA degradation in the UV/PS process but had no effect in the UV/H 2 O 2 process. Generally, in the deionized (DI) water, surface water, treated drinking water, and secondary effluent, UV/PS process is more effective than UV/H 2 O 2 process for IAA removal, based on the same molar ratio of oxidant: IAA. SO 4 − generated in the UV/PS process yields a greater mineralization of IAA than HO in the UV/H 2 O 2 process. IO 3 − was the predominant end-product in the UV/PS process, while I − was the major end-product in the UV/H 2 O 2 process. The respective contributions of UV, HO , and SO 4 − for IAA removal in the UV/PS process were 7.8%, 14.7%, and 77.5%, respectively, at a specific condition (1.5 μM IAA, 60 μM oxidant, and pH 7). Compared to UV/H 2 O 2 process, UV/PS was also observed as more cost-effective process based on the electrical energy per order (EE/O) and chemical cost. [ABSTRACT FROM AUTHOR]

The synergistic effect of ultraviolet light (UV) and chlorine on the structural transformation of Humic Acid (HA) and formation of chloro-disinfection byproducts (DBPs) in water were investigated, with chlorination as a reference. The transformation and mineralization of HA were enhanced upon co-exposure to UV and chlorine. Electron spin resonance (ESR) studies revealed that hydroxyl radical ( OH) and chlorine radical ( Cl) were predominant active species in a pH range from 4 to 7, while Cl dominated at pH 2 and pH higher than 7. The impact of different radicals on the transformation of HA was investigated by UV 254 , fluorescence and TOC measurements. OH were found to be responsible for the removal of chromophoric groups and mineralization of HA, while Cl mainly reacted with HA and intermediates from HA degradation. Due to the competitive and synergistic reaction of OH and Cl with HA, higher removal of HA and lower formation of chloro-DBPs appeared in UV-chlorine than chlorination, thus the combined UV-chlorine processes should be a promising method for water purification. [ABSTRACT FROM AUTHOR]