Influencing factors and degradation products of antipyrine chlorination in water with free chlorine

Degradation of antipyrine in water with activated persulfate aided with biochar of olive pomace

The degradation of antipyrine (AP) in water has been studied using persulfate activated with biochar obtained from gasification of olive pomace (BC) combined with ferric salts in the presence of UV-A radiation. Firstly, the adsorption of AP on biochar was evaluated. The data were adjusted using various kinetic models verifying that AP adsorption on BC occurs in three stages and follows pseudo-second order kinetics. Degradation tests show that the presence of iron or persulfate (PS) in binary systems with BC produces increases AP degradation when no radiation is used, reaching 75.7 % due to the ability of BC to donate electrons. On the other hand, addition of PS showed an increase in efficiency in the presence of BC (up to 79%). For ternary systems the best result was found when UVA/PS/Fe was used (100% of AP degradation in 30 min). The addition of UV-A radiation to the BC/PS system improves the degradation of the contaminant by only 6.7%, while the presence of iron in the studied conditions does not cause any improvement. A Central Composite Factorial Design of experiments was used to optimize the UVA/BC/PS/Fe system, leading to an 89.3% AP degradation rate in 90 min (k = 0.0134 min-1) under optimal conditions ([Fe(III)] = 10 mg/L, [PS] = 379 mg/L, [BC] = 500 mg/L). Although the best results were obtained for the UVA/PS/Fe process without BC, systems based on BC/PS can be considered as an alternative in cloudy days or when simple processes are selected due to economical/technical reasons.

Hypochlorite-mediated degradation and detoxification of sulfathiazole in aqueous solution and soil slurry

Although various activated sodium hypochlorite (NaClO) systems were proven to be promising strategies for recalcitrant organics treatment, the direct interaction between NaClO and pollutants without explicit activation is quite limited. In this work, a revolutionary approach to degrade sulfathiazole (STZ) in aqueous and soil slurry by single NaClO without any activator was proposed. The results demonstrated that 100% and 94.11% of STZ could be degraded by 0.025 mM and 5 mM NaClO in water and soil slurry, respectively. The elimination of STZ was shown to involve superoxide anion (O2•-), chlorine oxygen radical (ClO•), and hydroxyl radical (•OH), according to quenching experiments and the analysis of electron paramagnetic resonance. The addition of Cl-, HCO3-, SO42-, and humic acid (HA) marginally impeded the decomposition of STZ, while NO3-, Fe3+, and Mn2+ facilitated the process. The NaClO process exhibited significant removal effectiveness at a neutral initial pH. Moreover, the NaClO facilitated application in various soil samples and water matrices, and the procedure was also successful in effectively eliminating a range of sulfonamides. The suggested NaClO degradation mechanism of STZ was based on the observed intermediates, and the majority of the products exhibited lower ecotoxicity than STZ. Besides, the experiment results by using X-ray diffraction (XRD) and a fourier transform infrared spectrometer (FTIR) indicated the negligible effects on the composition and structure of soil by the treatment of NaClO. Simultaneously, the experimental results also illustrated that the bioavailability of heavy metals and the physiochemical characteristics of the soil before and after the remediation did not change to a significant extent. Following the remediation of NaClO, the phytotoxicity tests showed reduced toxicity to wheat and cucumber seeds. As a result, treating soil and water contaminated with STZ by using NaClO was a reasonably practical and eco-friendly method.

Enzymatic and non-enzymatic removal of organic micropollutants with spent mushroom substrate of Agaricus bisporus

Water bodies are increasingly contaminated with a diversity of organic micropollutants (OMPs). This impacts the quality of ecosystems due to their recalcitrant nature. In this study, we assessed the removal of OMPs by spent mushroom substrate (SMS) of the white button mushroom (Agaricus bisporus) and by its aqueous tea extract. Removal of acesulfame K, antipyrine, bentazon, caffeine, carbamazepine, chloridazon, clofibric acid, and N, N-diethyl-meta-toluamide (DEET) by SMS and its tea was between 10 and 90% and 0-26%, respectively, in a 7-day period. Sorption to SMS particles was between 0 and 29%, which can thus not explain the removal difference between SMS and its tea, the latter lacking these particles. Carbamazepine was removed most efficiently by both SMS and its tea. Removal of OMPs (except caffeine) by SMS tea was not affected by heat treatment. By contrast, heat-treatment of SMS reduced OMP removal to < 10% except for carbamazepine with a removal of 90%. These results indicate that OMP removal by SMS and its tea is mediated by both enzymatic and non-enzymatic activities. The presence of copper, manganese, and iron (0.03, 0.88, and 0.33 µg L-1, respectively) as well as H2O2 (1.5 µM) in SMS tea indicated that the Fenton reaction represents (part of) the non-enzymatic activity. Indeed, the in vitro reconstituted Fenton reaction removed OMPs > 50% better than the teas. From these data it is concluded that spent mushroom substrate of the white button mushroom, which is widely available as a waste-stream, can be used to purify water from OMPs.

Efficient elimination of phenazone by an electro-assisted Fe3+-EDDS/PS process at neutral pH: Kinetics, mechanistic insights and toxicity evaluation

The feasibility of the degradation of phenazone (PNZ), a common anti-inflammatory drug used for reducing pain and fever, in water at neutral pH by an electrochemically assisted Fe³⁺-ethylenediamine disuccinate-activated persulfate process (EC/Fe³⁺-EDDS/PS) was investigated. The efficient removal of PNZ at neutral pH condition was mainly attributed to the continuous activation of PS via electrochemically driven regenerated Fe²⁺ from a Fe³⁺-EDDS complex at the cathode. The influence of several critical parameters, including current density, Fe³⁺ concentration, EDDS to Fe³⁺ molar ratio, and PS dosage, on PNZ degradation was evaluated and optimized. Both hydroxyl radicals (•OH) and sulfate radicals (SO₄^●-) were considered major reactive species responsible for PNZ degradation. To understand the mechanistic model of action at the molecular level, the thermodynamic and kinetic behaviors of the reactions between PNZ with •OH and SO₄^●- were theoretically calculated using a density functional theory (DFT) method. The results revealed that radical adduct formation (RAF) is the most favorable pathway for the •OH-driven oxidation of PNZ, while single electron transfer (SET) appears to be the dominant pathway for the reaction of SO₄^●- with PNZ. In total, thirteen oxidation intermediates were identified, and hydroxylation, pyrazole ring opening, dephenylization, and demethylation were speculated to be the major degradation pathways. Furthermore, predicted toxicity to aquatic organisms indicated that PNZ degradation resulted in products that were less harmful. However, the developmental toxicity of PNZ and its intermediate products should be further investigated in the environment. The findings of this work demonstrate the viability of effectively removing organic contaminants in water at near-neutral pH by using EDDS chelation combined with electrochemistry in a Fe³⁺/persulfate system.

Analysis of degradation and pathways of three common antihistamine drugs by NaClO, UV, and UV-NaClO methods

Antihistamines (ANTs) are medicines to treat allergic diseases. They have been frequently detected in the natural water environment, posing potential threats to the ecological environment and human health. In this study, the degradation of three common antihistamines, loratadine, fexofenadine, and cetirizine, was estimated under different oxidation methods (NaClO, UV, and UV-NaClO). The results showed that UV-NaClO had the highest degree of degradation on the drugs under most conditions: 100% degradation for fexofenadine within 20 s at pH 7 and 10. Under UV irradiation, the degradation efficiencies of the three drugs during 150 s were all above 77% at a pH of 7. The drugs' removal by NaClO was much lower than that of the previous two methods. In addition, this study explored the contribution rates of active oxygen species in the photolysis process. Among them, the contribution of ¹O₂ to the fexofenadine and cetirizine removal rate reached 70%. Different aqueous matrices (HCO₃^-, NO₃^-, and humic acid) had varying degrees of influence on the degradation. Acute toxicity tests and ultraviolet scans of the degradation products showed that the drugs were not completely mineralized, and the toxicities of the intermediates were even higher than those of the parent drugs. There were 9, 8, and 10 chloride oxidation products of loratadine, fexofenadine, and cetirizine, respectively, and 8 photolysis products of cetirizine were identified. For cetirizine, it was found that there were three identical intermediates produced by photodegradation and NaClO oxidation.

Reaction of phenazone-type drugs and metabolites with chlorine and monochloramine

This work studies the chlorination and monochloramination reaction kinetics of two phenazone-type drugs (phenazone - Phe and propyphenazone - PrPhe) and three metabolites of phenazone-type drugs (4-formylaminoantipyrine - FAA, 4-aminoantipyrine - AA and 4-acetoamidoantipyrine - AAA). Kinetics were faster with chlorine (apparent second-order constants between 100 and 66,500 times higher) than with monochloramine. For FAA and AAA, no significant reaction was observed during monochloramination. Further, apparent rate constants decreased as the pH increased from pH 5.7 to 8.3, except during chlorination of AA. The transformation products (TPs) formed were also elucidated by liquid chromatography-high resolution mass spectrometry. The main transformation pathway for Phe and PrPhe consisted of halogenations, hydroxylations and dealkylations, while AAA and FAA were firstly transformed to AA, then followed by pyrazole ring opening and hydroxylations. The extend of the reaction was also tested in real water samples, where, in general, slower reaction kinetics were obtained during monochloramination, while the chlorination reaction showed similar half-lives to ultrapure water. Finally, acute and chronic toxicity of the TPs were estimated using two quantitative structure-activity relationship (QSAR) software (ECOSAR and TEST), showing that some TPs could be more toxic than their precursor compounds.

An activated carbon fiber supported Fe2O3@bismuth carbonate heterojunction for enhanced visible light degradation of emerging pharmaceutical pollutants

The developed Fe2O3@BC heterojunction photocatalyst supported over activated carbon fiber exhibited efficient photocatalytic activity for degradation of antipyrine under visible light irradiation.

A comparative study on phenazone degradation by sulfate radicals based processes

In this paper, a comparative study on removal of the emerging pollutant phenazone (PNZ) by two treatment processes UVA/Fe(II)/persulfate (PS) and UVA/Fe(II)/peroxymonosulfate (PMS) was conducted. The two processes showed high efficiency in PNZ degradation, followed by a reasonable mineralization. The treatment system with PMS was found to be more efficient for PNZ degradation than that with PS due to the larger amounts of radicals generated. While the treatment process UVA/Fe(II)/PS showed higher ΔTOC/ΔSMX (TOC removal per unit of PNZ decay) than UVA/Fe(II)/PMS process. The sulfate and hydroxyl radicals played dominant roles in PNZ degradation in the UVA/Fe(II)/PS and UVA/Fe(II)/PMS process, respectively. Six and seven intermediates during PNZ degradation by UVA/Fe(II)/PS and UVA/Fe(II)/PMS process were detected, respectively. Among the detected intermediates, six of them are found for the first time. It takes shorter time for toxicity elimination by UVA/Fe(II)/PS process than UVA/Fe(II)/PMS, possibly due to the lower Kow values of hydroxylated products. The results demonstrate that UVA/Fe(II)/PMS process is more efficient in PNZ degradation, while UVA/Fe(II)/PS is more efficient in detoxification of PNZ. The two sulfate radicals based processes have good potentials in degradation, mineralization and detoxification of the emerging contaminants such as PNZ.

Occurrences of pharmaceuticals and personal care products in the drinking water of Taiwan and their removal in conventional water treatment processes

Pharmaceuticals and personal care products (PPCPs) has been of concerns for their potential threats to ecosystems and human's health for decades. PPCPs have been detected in water environments worldwide and have been identified in water sources and finished water. To elucidate the potential exposure of PPCPs in drinking water, this study assessed the occurrences and treatment efficiencies of PPCPs in the drinking water of Taiwan. Raw and finished water samples collected from five main drinking water treatment plants (DWTPs) in February, June, and November 2018 were analyzed. Furthermore, laboratory-scale water treatment processes were conducted to evaluate the treatment efficiencies of these chemicals. Most of the water samples from the DWTPs had a low concentration (<30 ng/L) of PPCPs. Only samples from a DWTP was observed to have higher concentration of ibuprofen (55.6 ng/L), benzophenone (92.5 ng/L), caffeine (390.5 ng/L), and diethyltoluamide (DEET) (434.9 ng/L) in raw water than others. The results of laboratory simulations indicated that the pre-chlorination process was the key step responsible for the removal of PPCPs in conventional water treatment processes, which can remove most of the hormone treatment products, parabens, oxybenzone, and acetaminophen in water sources. However, the filtration process with anthracite as a medium could remove some of the parabens (approximately 11.9%-41.2%), hormones (approximately 18.2%-44.8%), suntan lotions (37.5%-68.8%), and naproxen (30.1%) from Milli-Q water. The removal efficiencies of the aforementioned chemicals were marginally lower in raw water. However, analgesics, caffeine, and DEET cannot be removed effectively through conventional drinking water treatment.

Solvothermal synthesis of multiwall carbon nanotubes/BiOI photocatalysts for the efficient degradation of antipyrine under visible light

Antipyrine (ANT), as a widely used relieve headache, fever anti-inflammatory pharmaceutical in medical treatment, is difficult to be removed completely in water. The application of photocatalytic removal of ANT is restricted to UV light irradiation (<5% of solar energy), and the degradation pathways of ANT require more theoretical evidence. In this study, a series of three dimensions (3D) hierarchical structure multiwall carbon nanotubes/bismuth oxyiodide (MWCNTs/BiOI) photocatalysts were systematically designed and firstly applied to remove ANT through visible light (>43% of solar energy) induced photodegradation. Consequently, the as-prepared MWCNTs/BiOI photocatalysts presented superior photocatalytic activities on ANT degradation with respect to that of BiOI under 60 min visible light irradiation (100% vs 82.2%). Especially, the enhanced photocatalytic mechanism on ANT was analyzed by morphology, optical and photo-electrochemical properties. Results revealed that the designed 3D micro-mesoporous structure could promote the diffusion of photogenerated electron-hole pairs, and the utilization of photoelectrons could be efficiently improved by MWCNTs (1.5 times). Furthermore, based on radicals scavenging experiments, the photogenerated hole (h⁺) and superoxide radical (O₂^-) were demonstrated as the dominant active species in ANT photocatalytic oxidation process. The photodegradation pathways of ANT were proposed with the calculation of frontier electron densities (FEDs) and the analysis of LC-MS/MS. This study presents a feasible approach for the high efficiency removal of trace pharmaceuticals under visible light photocatalytic process.

Chlorination of enoxacin (ENO) in the drinking water distribution system: Degradation, byproducts, and toxicity

Chlorine is widely used as a drinking water disinfectant to ensure water security. However, the transformation mechanisms of its degradation of emerging pollutants within the water distribution system (WDS) is insufficiently understood. Thus, the kinetics, degradation byproducts, and toxicity of the chlorination of enoxacin (ENO, a type of emerging pollutant) were explored in a pilot-scale WDS for the first time. It was found that the chlorination rate of ENO was higher in deionized water (DW) than in the pilot-scale WDS, and the degradation followed second-order kinetics in DW. The degradation efficiency was found to be sensitive to pH, and was highest at a pH of 7.4. The chlorination rate of ENO increased with increasing temperature in both DW and WDS. For different pipe materials, the relative performance of ENO chlorination efficiency followed the order of steel pipe > ductile iron pipe > polyethylene (PE) pipe. Seven intermediates were identified during ENO chlorination, and the primary oxidation reaction involved the cleavage of the piperazine group. Finally, it was found that the potential for chlorine toxicity in treated drinking water in the presence of ENO is higher than it is without this pollutant.

Ultraviolet absorption redshift induced direct photodegradation of halogenated parabens under simulated sunlight

As disinfection by-products of parabens, halogenated parabens are frequently detected in aquatic environments and exhibit higher persistence and toxicity than parabens themselves. An interesting phenomenon was found that UV absorption redshift (∼45 nm) occurs after halogenation of parabens at circumneutral pH, leading to overlap with the spectrum of terrestrial sunlight. This work presents the first evidence on the direct photodegradation of seven chlorinated and brominated parabens under simulated sunlight. These halogenated parabens underwent rapid direct photodegradation, distinguished from the negligible degradation of the parent compounds. The photodegradation rate depended on their forms and substituents. The deprotonation of halogenated parabens facilitated the direct photodegradation. Brominated parabens exhibited higher degradation efficiency than chlorinated parabens, and mono-halogenated parabens had higher degradation than di-halogenated parabens. The pseudo-first-order rate constants (k_obs) for brominated parabens (0.075-0.120 min^-1) were approximately 7-fold higher than those of chlorinated parabens (0.011-0.017 min^-1). A quantitative structure-activity relationship (QSAR) model suggested that the photodegradation was linearly correlated with the C-X bond energies, electronic and steric effects of halogen substituents. The photodegradation products were identified using QTOF-MS analyses and a degradation pathway was proposed. The yeast two-hybrid estrogenicity assay revealed that the estrogenic activities of the photoproducts were negligible. These findings are important for the removal of halogenated parabens and predictions of their fate and potential impacts in surface waters.

Products of methotrexate during chlorination

Methotrexate (MTX) is a cytotoxic drug widely used in the treatment of tumors, autoimmune diseases and severe asthma. jen00883This drug has been frequently detected in the aquatic environment with concentrations up to μg/L levels. The MTX present in environmental water might be transformed and removed during chlorination disinfection treatment. In this work, the fate of MTX during aqueous chlorination was investigated in laboratory batch experiments, and the transformation products of MTX were identified. Aqueous solutions of MTX (1mg/L) were chlorinated by sodium hypochlorite solution at room temperature under neutral pH conditions. Chlorinated products were pre-concentrated with solid-phase extraction (SPE) cartridges and determined by liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The reaction of MTX chlorination exhibited pseudo-first-order kinetics and the half-life time of MTX degradation was calculated to be 1.65min, when the initial chlorine concentration was 2mg/L. Two chlorinated MTX congeners, 4-amino-3-chlorinated-N10-methylpteroylglutamic (monochloro-MTX) and 4-amino-3,5-dichloro-N10-methylpteroylglutamic (dichloro-MTX) were found in the chlorinated solution. Monochloro-MTX was successfully fractionated by high performance liquid chromatography (HPLC) and its structure was further identified using ¹H nuclear magnetic resonance (NMR) analysis. The presence of the two products in real hospital wastewater was then examined and both compounds were detected. Finally, the effects of MTX and monochloro-MTX on the cell cycle progression in vitro were evaluated using zebrafish liver cell line. It was found that both compounds could inhibit the proliferation of zebrafish liver cells through S phase arrest and their effects on the cell cycle profile had no significant difference.

A systematic study on photocatalysis of antipyrine: Catalyst characterization, parameter optimization, reaction mechanism a toxicity evolution to plankton

The toxicity of antipyrine (AP) in the photodegradation using UV/CoFe₂O₄/TiO₂ was investigated by analyzing the characteristic of the catalyst, the effect of parameters (light source wavelength, catalyst dose, pH and initial AP concentration), the reaction mechanism (the organic intermediates, TOC reduction and inorganic ions release) and the newly proposed low-dosage-high-effective radical reaction approach. The catalyst shows the optimal removal efficiency under the conditions of wavelength at 350 nm, the catalyst dose at 0.5 g/L, and pH value at 5.5. Ten organic intermediates were identified, and five of them were newly reported in AP treatment process. Hydroxylation, demethylation and the cleavage of the pentacyclic ring were included in the decomposition pathways. The ring opening was certified by the 45% TOC reduction and 60% ammonia release during the process. The parent compound AP and its degradation products show positive effects on the growth of the algae. However, acute toxicity of AP was detected on brine shrimps Artemia salina. The toxicity was eliminated gradually with the decomposition of AP and the generation of the byproducts. The results indicate that the photocatalysis process is effective in AP removal, TOC reduction and toxicity elimination.

Transformation of aminopyrine in the presence of free available chlorine: Kinetics, products, and reaction pathways

Aminopyrine (AMP) has been frequently detected in the aquatic environment. In this study, the transformation mechanism of AMP by free available chlorine (FAC) oxidation was investigated. The results showed that FAC reacted with AMP rapidly, and a 74% elimination was achieved for 1.30 μM AMP after 2 min at 14.08 μM FAC dose. AMP chlorination was strongly pH-dependent, and its reaction included second- and third-order kinetic processes. Three active FAC species, including chlorine monoxide (Cl₂O), molecular chlorine (Cl₂), and hypochlorous acid (HOCl), were observed to contribute to AMP degradation. The intrinsic rate constants of each FAC species with neutral (AMP⁰) and cation (AMP⁺) species were obtained by kinetic fitting. Cl₂O exhibited the highest reactivity with AMP⁰ (k_{AMP0, Cl2O} = (4.33 ± 1.4) × 10⁹ M^-1s^-1). In addition, Cl₂ showed high reactivity (10⁶-10⁷ M^-1s^-1) in the presence of chloride, compared with HOCl (k_{AMP+, HOCl} = (5.73 ± 0.23) × 10² M^-1s^-1, k_{AMP0, HOCl} = (9.68 ± 0.96) × 10² M^-1s^-1). At pH 6.15 and 14.08 μM FAC dose without chloride addition, the contribution of Cl₂O reached to the maximum (33.3%), but in the whole pH range, HOCl was the main contributor (>66.6%) for AMP degradation. The significance of Cl₂ was noticeable in water containing chloride. Moreover, 11 transformation products were identified, and the main transformation pathways included pyrazole ring breakage, hydroxylation, dehydrogenation, and halogenation.

Antipyrine removal by TiO2 photocatalysis based on spinning disc reactor technology

The photo-degradation of the emerging contaminant antipyrine (AP) was studied and optimized in a novel photocatalytic spinning disc reactor (SDR). A heterogeneous process (UV/H₂O₂/TiO₂) was used. TiO₂ was immobilized on the surface of a glass disc using a sol-gel method. A factorial design of experiments followed by a Neural Networks fitting allowed the optimal conditions to be determined for treating 50 mg/L of AP. Under these conditions (pH = 4; [H₂O₂]₀ = 1500 mg/L; disc speed = 500 rpm; flowrate = 25 mL/s), AP was completely degraded in 120 min and regeneration of the disc allowed 10 cycles with no loss in efficiency. The value of the apparent volumetric rate constant was found to be 6.9·10^-4 s^-1 with no apparent mass transfer limitation. Based on the main intermediates identified, a mechanism is proposed for antipyrine photodegradation: Firstly, cleavage of the NN bond of penta-heterocycle leads to the formation of two aromatic acids and N-phenylpropanamide. An attack to the CN bond in the latter compound produces benzenamine. Finally, the phenyl ring of the aromatic intermediates are opened and molecular organic acids are formed.

Zr-doped TiO2 supported on delaminated clay materials for solar photocatalytic treatment of emerging pollutants

Solar light-active Zr-doped TiO₂ nanoparticles were successfully immobilized on delaminated clay materials by a one-step sol-gel route. Fixing the amount of TiO₂ at 65wt.%, this work studies the influence of Zr loading (up to 2%) on the photocatalytic activity of the resulting Zr-doped TiO₂/clay materials. The structural characterization demonstrates that all samples were formed by a delaminated clay with nanostructured anatase assembled on its surface. The Zr dopant was successfully incorporated into the anatase lattice, resulting in a slight deformation of the anatase crystal and the reduction of the band gap. These materials exhibit high surface area with a disordered mesoporous structure formed by TiO₂ particles (15-20nm) supported on a delaminated clay. They were tested in the solar photodegradation of antipyrine, usually used as an analgesic drug and selected as an example of emerging pollutant. High degradation rates have been obtained at low antipyrine concentrations and high solar irradiation intensities with the Zr-doped TiO₂/clay catalyst, more effective than the undoped one. This work demonstrates the potential application of the synthesis method for preparing novel and efficient solar-light photocatalysts based on metal-doped anatase and a delaminated clay.

Kinetics and mechanistic investigation into the degradation of naproxen by a UV/chlorine process

The degradation kinetics and mechanism of naproxen during UV/chlorine treatment were investigated.

Impact of prechlorination on organophosphorus pesticides during drinking water treatment: Removal and transformation to toxic oxon byproducts

Prechlorination is commonly used to minimize operational problems associated with biological growth as well as taste and odor control during drinking water treatment. However, prechlorination can also oxidise micropollutants into intermediate byproducts. This could impose profound effects on the safety of the finished water if the transformed byproducts are more toxic and less removable. This study investigated the effect of prechlorination on decomposition and subsequent removal of the four organophosphorus pesticides (OPPs): chlorpyrifos, diazinon, malathion and tolclofos-methyl using a simulated conventional water treatment process of powdered activated carbon assisted coagulation-sedimentation-filtration (PAC-CSF) and postchlorination. It was found that, following prechlorination, not only did the percentage of OPPs oxidation vary significantly, but also the concentration of transformed oxons, which are more toxic than their parent compounds, increased as the major identified oxidation byproducts in water. Removal of these oxons proved to be more difficult by the PAC-CSF than their parent OPPs, because they are more water soluble and more hydrophilic. Both the OPP oxidation and oxon formation increased with chlorine dose during prechlorination. Meanwhile, the continuing chlorination of OPPs by residual free chlorine during PAC-CSF further complicated the pesticide removal processes, generally resulting in a gradually increased formation of oxons. Moreover, in the final treatment stage of postchlorination, the more chlorine-reactive pesticides, malathion and diazinon, were completely oxidised and the formation of corresponding oxons was increased with the prechlorine dose. In contrast, a certain amount of the less chlorine-reactive pesticide tolclofos-methyl still remained in solution after postchlorination, accompanied by an increased formation of tolclofos-methyl oxon with prechlorine dose. Since the oxons are resistant to further oxidation and less adsorbable during the PAC-CSF process, the gross removal of these pesticides and their oxons decreased with increase of the prechlorine dose. This led to an accumulation of the more toxic oxons in the finished water, especially at higher chlorine doses during prechlorination. The significance of this work is the demonstration that, under circumstances where prechlorination is used and source water contains traces of OPPs, alternative practices should be prioritized to avoid the potential risks involved in consumption of the treated water.

Chlorination of florfenicol (FF): reaction kinetics, influencing factors and by-products formation

Florfenicol (FF) is a widely used antibiotic, which is commonly found in natural waters.

Degradation of phenazone in aqueous solution with ozone: influencing factors and degradation pathways

Oxidation kinetics and degradation pathways of phenazone (an analgesic and antipyretic drug) upon reaction with O3 were investigated. Kinetic studies on degradation of phenazone were carried out under different operating conditions such as temperature, pH, anions and H2O2 addition. Results showed that the degradation followed the pseudo-first-order kinetic model. The reaction rate constant (kobs) of phenazone reached the maximum at 20 °C (9.653×10(-3) s(-1)). The presence of NO3(-) could enhance the degradation rate, while the addition of HCO3(-), SO4(2)(-), Cl(-) and the rise of pH showed negative effects on the ozonation of phenazone. H2O2 addition increased the phenazone degradation efficiency by 45.9% with the optimal concentration of 0.135 mM. Reaction by-products were evaluated by UPLC-Q-TOF-MS, which allowed the identification of a total of 10 by-products. The transformation pathways of phenazone ozonation consisted mainly of electrophilic addition and substitution, pyrazole ring opening, hydroxylation, dephenylization and coupling. The toxicity of these intermediate products showed that they are expected not to be more toxic than phenazone, with the exception of P7 (aniline) and P10 (1,5-dimethyl-4-((1-methyl-2-phenylhydrazinyl)methoxy)-2-phenyl-1H-pyrazol-3(2H)-one).

Degradation of antipyrine by UV, UV/H₂O₂ and UV/PS

Degradation of antipyrine (AP) in water by three UV-based photolysis processes (i.e., direct UV, UV/H₂O₂, UV/persulfate (UV/PS)) was studied. For all the oxidation processes, the AP decomposition exhibited a pseudo-first-order kinetics pattern. Generally, UV/H₂O₂ and UV/PS significantly improved the degradation rate relevant to UV treatment alone. The pseudo-first-order degradation rate constants (kobs) were, to different degrees, affected by initial AP concentration, oxidant dose, pH, UV irradiation intensity, and co-existing chemicals such as humic acid, chloride, bicarbonate, carbonate and nitrate. The three oxidation processes followed the order in terms of treatment costs: UV/PS>UV>UV/H₂O₂ if the energy and chemical costs are considered. Finally, the AP degradation pathways in the UV/H₂O₂ and UV/PS processes are proposed. Results demonstrated that UV/H₂O₂ and UV/PS are potential alternatives to control water pollution caused by emerging contaminants such as AP.