Transformation of an Amine Moiety of Atenolol during Water Treatment with Chlorine/UV: Reaction Kinetics, Products, and Mechanisms

Formation and toxicity alteration of halonitromethanes from Chlorella vulgaris during UV/chloramination process involving bromide ion

Frequent algal blooms cause algal cells and their algal organic matter (AOM) to become critical precursors of disinfection by-products (DBPs) during water treatment. The presence of bromide ion (Br-) in water has been demonstrated to affect the formation laws and species distribution of DBPs. However, few researchers have addressed the formation and toxicity alteration of halonitromethanes (HNMs) from algae during disinfection in the presence of Br-. Therefore, in this work, Chlorella vulgaris was selected as a representative algal precursor to investigate the formation and toxicity alteration of HNMs during UV/chloramination involving Br-. The results showed that the formation concentration of HNMs increased and then decreased during UV/chloramination. The intracellular organic matter of Chlorella vulgaris was more susceptible to form HNMs than the extracellular organic matter. When the Br-: Cl2 mass ratio was raised from 0.004 to 0.08, the peak of HNMs total concentration increased 33.99%, and the cytotoxicity index and genotoxicity index of HNMs increased 67.94% and 22.80%. Besides, the formation concentration and toxicity of HNMs increased with increasing Chlorella vulgaris concentration but decreased with increasing solution pH. Possible formation pathways of HNMs from Chlorella vulgaris during UV/chloramination involving Br- were proposed based on the alteration of nitrogen species and fluorescence spectrum analysis. Furthermore, the formation laws of HNMs from Chlorella vulgaris in real water samples were similar to those in deionized water samples. This study contributes to a better comprehension of HNMs formation from Chlorella vulgaris and provides valuable information for water managers to reduce hazards associated with the formation of HNMs.

Chlorination of antiviral drug ribavirin: Kinetics, nontargeted identification, and concomitant toxicity evolution

Residual antiviral drugs in wastewater may increase the risk of generating transformation products (TPs) during wastewater treatment. Therefore, chlorination behavior and toxicity evolution are essential to understand the secondary ecological risk associated with their TPs. Herein, chlorination kinetics, transformation pathways, and secondary risks of ribavirin (RBV), one of the most commonly used broad-spectrum antivirals, were investigated. The pH-dependent second-order rate constants k increased from 0.18 M-1·s-1 (pH 5.8) to 1.53 M-1·s-1 (pH 8.0) due to neutral RBV and ClO- as dominant species. 12 TPs were identified using high-resolution mass spectrometry in a nontargeted approach, of which 6 TPs were reported for the first time, and their chlorination pathways were elucidated. The luminescence inhibition rate of Vibrio fischeri exposed to chlorinated RBV solution was positively correlated with initial free active chlorine, probably due to the accumulation of toxic TPs. Quantitative structure-activity relationship prediction identified 7 TPs with elevated toxicity, concentrating on developmental toxicity and bioconcentration factors, which explained the increased toxicity of chlorinated RBV. Overall, this study highlights the urgent need to minimize the discharge of toxic chlorinated TPs into aquatic environments and contributes to environmental risk control in future pandemics and regions with high consumption of antivirals.

Advanced oxidation of recalcitrant chromophores in full-scale MBR effluent for non-potable reuse of leachate co-treated municipal wastewater

Wastewater non-potable reuse involves further processing of secondary effluent to a quality level acceptable for reuse and is a promising solution to combating water scarcity. Recalcitrant chromophores in landfill leachate challenge the water quality for non-potable reuse when leachate is co-treated with municipal wastewater. In this study, we first use multivariate statistical analysis to reveal that leachate is an important source (with a Pearson's coefficient of 0.82) of recalcitrant chromophores in the full-scale membrane bioreactor (MBR) effluent. We then evaluate the removal efficacies of chromophores by chlorination, breakpoint chlorination, and the chlorination-UV/chlorine advanced oxidation treatment. Conventional chlorination and breakpoint chlorination only partially remove chromophores, leaving a colour level exceeding the standards for non-potable reuse (>20 Hazen units). We demonstrate that pre-chlorination (with an initial chlorine dosing of 20 mg/L as Cl2) followed by UV radiation (with a UV fluence of 500 mJ/cm2) effectively degraded recalcitrant chromophores (>90%). By quantifying the electron donating capacity (EDC) and radical scavenging capacity (RSC) of the reclaimed water, we demonstrate that pre-chlorination reduces EDC and RSC by up to 64%, increases UV transmittance by 32%, and increases radical yields from UV photolysis of chlorine by 1.7-2.2 times. The findings advance fundamental understanding of the alteration of dissolved coloured substances by (photo)chlorination treatment and provide implications for applying advanced oxidation processes in treating wastewater effluents towards sustainable non-potable reuse.

Unexpected side reactions dominate the oxidative transformation of aromatic amines in the Co(II)/peracetic acid system

Aromatic amines (AAs), ubiquitous in industrial applications, pose significant environmental hazards due to their resistance to conventional wastewater treatments. Peracetic acid (PAA)-based advanced oxidation processes (AOPs) have been proposed as effective strategies for addressing persistent AA contaminants. While the organic radicals generated in these systems are believed to be selective and highly oxidative, acetate residue complicates the evaluation of AA removal efficiency. In this work, we explored transformation pathways of AAs in a representative Co(II)-catalyzed PAA system, revealing five side reactions (i.e. nitrosation, nitration, coupling, dimerization, and acetylation) that yield 17 predominantly stable and toxic by-products. The dominant reactive species was demonstrated as Co-OOC(O)CH3, which hardly facilitated ring-opening reactions. Our findings highlight the potential risks associated with PAA-based AOPs for AA degradation and provide insights into selecting suitable catalytic systems aimed at efficient and by-product-free degradation of pollutants containing aromatic -NH2.

Portable and reversible smart labels for non-destructive detection of seafood freshness via amine-response fluorescent ionic liquids

Herein, a functionalized ionic liquid (IL) 7-HDCP (7-hydroxycoumarin-quaternary phosphorus) was developed as NH3 trapping agents and fluorescent indicators to achieve in-time and on-site detection of seafood freshness. Interestingly, the IL displayed remarkable blue fluorescence "turn-on" enhancement to gaseous amine due to excellent amine solubility. By FTIR and 1H NMR spectrogram, this fluorescence "turn-on" phenomenon originated from the weak hydrogen bonding between the ester group of the coumarin functional group and the ammonia molecule. Moreover, the IL exhibited a rapid response (<11 s), prominent sensitivity (0.12 ppm), excellent selectivity (10 interfering substances) and outstanding reversibility (>22 cycles). Benefiting from ion characters, 7-HDCP obtained advantages of easy-to-fabricate and easy-to-use, which was fabricated by one-step simple immersion without aggregation-caused quenching phenomenon. This portable and sensitive smart label made of ion probes facilitates the timely and on-site NH3 detection in the early deterioration stages of aquatic products, enabling "early detection, early warning, and early treatment".

Formation Mechanisms of Nitro Products from Transformation of Aliphatic Amines by UV/Chlorine Treatment

Formation of nitrogenous disinfection byproducts from aliphatic amines is a widespread concern owing to the serious health risks associated with them. However, the mechanisms of transforming aliphatic amines and forming nitro products in the UV/chlorine process have rarely been discussed, which are investigated in this work. Initially, secondary amines (R1R2NH) are transformed into secondary organic chloramines (R1R2NCl) via chlorination. Subsequently, radicals, such as HO• and Cl•, are found to contribute predominantly to such transformations. The rate constants at which HO•, Cl•, and Cl2•- react with R1R2NCl are (2.4-5.1) × 109, (1.5-3.8) × 109, and (1.2-6.1) × 107 M-1 s-1, respectively. Consequently, R1R2NCl are transformed into primary amines (R1NH2/R2NH2) and chlorinated primary amines (R1NHCl/R2NHCl and R1NCl2/R2NCl2) by excess chlorine. Furthermore, primarily driven by UV photolysis, chlorinated primary amines can be transformed into nitroalkanes with conversion rates of ∼10%. Dissolved oxygen and free chlorine play crucial roles in forming nitroalkanes, and post-chlorination can further form chloronitroalkanes, such as trichloronitromethane (TCNM). Radicals are involved in forming TCNM in the UV/chlorine process. This study provides new insights into the mechanisms of transforming aliphatic amines and forming nitro products using the UV/chlorine process.

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

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

Impact of water matrices on oxidation effects and mechanisms of pharmaceuticals by ultraviolet-based advanced oxidation technologies: A review

The binding between water components (dissolved organic matters, anions and cations) and pharmaceuticals influences the migration and transformation of pollutants. Herein, the impact of water matrices on drug degradation, as well as the electrical energy demands during UV, UV/catalysts, UV/O₃, UV/H₂O₂-based, UV/persulfate and UV/chlorine processes were systemically evaluated. The enhancement effects of water constituents are due to the powerful reactive species formation, the recombination reduction of electrons and holes of catalyst and the catalyst regeneration; the inhibition results from the light attenuation, quenching effects of the excited states of target pollutants and reactive species, the stable complexations generation and the catalyst deactivation. The transformation pathways of the same pollutant in various AOPs have high similarities. At the same time, each oxidant also can act as a special nucleophile or electrophile, depending on the functional groups of the target compound. The electrical energy per order (EEO) of drugs degradation may follow the order of EEO_UV > EEO_UV/catalyst > EEO_UV/H2O2 > EEO_UV/PS > EEO_UV/chlorine or EEO_UV/O3. Meanwhile, it is crucial to balance the cost-benefit assessment and toxic by-products formation, and the comparison of the contaminant degradation pathways and productions in the presence of different water matrices is still lacking.

Organic chloramines attenuation and disinfection by-product formation during UV, chlorination and UV/chlorine processes

Organic chloramines (OCs) have become one of the research focuses in the field of drinking water treatment due to its limited oxidation and sterilization ability as well as potential cytotoxicity and genetic toxicity to the public. Among widespread OCs, produced by chlorinating cytosine are a typical one exists during chlorine disinfection. OCs degradation during UV, chlorination and UV/chlorine processes were systematically investigated. UV irradiation at 254 nm could effectively degrade OCs by 96.6% after 60 min, mainly because N-Cl bond had significant UV absorption at 250-280 nm leading to the generation of Cl• and HO•. Direct chlorination had poor removal of OCs with the OCs concentration increased first and then decreased as time went by. On the other hand, the removal of OCs during UV/chlorination was much higher than that during chlorination, but was worse than that during UV alone. pH had a minor effect on OCs decomposition via UV irradiation, whereas the effect was pronounced in the chlorination and UV chlorine processes. UV wavelength can affect the degradation of OCs with efficiency decreased in the order of UV 254 > UV 265 > UV 275. The total yields of disinfection by-products (DBPs) during the degradation of OCs followed UV/chlorine > UV > chlorination. CH and DCAA were the two dominant types of DBPs among detected 7 DBPs. DBPs yield followed the order of UV254 > UV265 > UV275 at pH 6.0 and 7.0. After UV 265 irradiation, DBPs yield slightly decreased by 2.4%, 3.0% and 6.6% with the pH increased from 6.0 to 9.0. The results can provide theoretical basis for effective control of OCs in drinking water.

Antibiotics degradation by UV/chlor(am)ine advanced oxidation processes: A comprehensive review

Antibiotics are emerging contaminants in aquatic environments which pose serious risks to the ecological environment and human health. Advanced oxidation processes (AOPs) based on ultraviolet (UV) light have good application prospects for antibiotic degradation. As new and developing UV-AOPs, UV/chlorine and derived UV/chloramine processes have attracted increasing attention due to the production of highly reactive radicals (e.g., hydroxyl radical, reactive chlorine species, and reactive nitrogen species) and also because they can provide long-lasting disinfection. In this review, the main reaction pathways of radicals formed during the UV/chlor (am)ine process are proposed. The degradation efficiency, influencing factors, generation of disinfection by-products (DBPs), and changes in toxicity that occur during antibiotic degradation by UV/chlor (am)ine are reviewed. Based on the statistics and analysis of published results, the effects caused by energy consumption, defined as electrical energy per order (EE/O), increase in the following order: UV/chlorine < UV/peroxydisulfate (PDS)< UV/H₂O₂ < UV/persulfate (PS) < 265 nm and 285 nm UV-LED/chlorine (EE/O). Some inherent problems that affect the UV/chlor (am)ine processes and prospects for future research are proposed. The use of UV/chlor (am)ine AOPs is a rich field of research and has promising future applications, and this review provides a theoretical basis for that.

Exploring Pathways and Mechanisms for Dichloroacetonitrile Formation from Typical Amino Compounds during UV/Chlorine Treatment

The formation of disinfection byproducts (DBPs) during UV/chlorine treatment, especially nitrogenous DBPs, is not well understood. This study investigated the formation mechanisms for dichloroacetonitrile (DCAN) from typical amino compounds during UV/chlorine treatment. Compared to chlorination, the yields of DCAN increase by 88-240% during UV/chlorine treatment from real waters, while the yields of DCAN from amino compounds increase by 3.3-5724 times. Amino compounds with electron-withdrawing side chains show much higher DCAN formation than those with electron-donating side chains. Phenylethylamine, l- phenylalanine, and l-phenylalanyl-l-phenylalanine were selected to represent amines, amino acids, and peptides, respectively, to investigate the formation pathways for DCAN during UV/chlorine treatment. First, chlorination of amines, amino acids, and peptides rapidly forms N-chloramines via chlorine substitution. Then, UV photolysis but not radicals promotes the transformation from N-chloramines to N-chloroaldimines and then to phenylacetonitrile, with yields of 5.4, 51.0, and 19.8% from chlorinated phenylethylamine, l-phenylalanine, and l-phenylalanyl-l-phenylalanine to phenylacetonitrile, respectively. Finally, phenylacetonitrile is transformed to DCAN with conversion ratios of 14.2-25.6%, which is attributed to radical oxidation, as indicated by scavenging experiments and density functional theory calculations. This study elucidates the pathways and mechanisms for DCAN formation from typical amino compounds during UV/chlorine treatment.

Rapid Conversion of Co2+ to Co3+ by Introducing Oxygen Vacancies in Co3O4 Nanowire Anodes for Nitrogen Removal with Highly Efficient H2 Recovery in Urine Treatment

Urine is a nitrogenous waste biomass but can be used as an appealing alternative substrate for H₂ recovery. However, urine electrolysis suffers from sluggish kinetics and requires alkaline condition. Herein, we report a novel system to decompose urine to H₂ and N₂ under neutral conditions mediated by Cl^• using oxygen-vacancy-rich Co₃O₄ nanowire (O_v-Co₃O₄) anodes and CuO nanowire cathodes. The Co²⁺/Co³⁺ cycle in Co₃O₄ activates Cl^- in urine to Cl^•, which rapidly and selectively converts urea into N₂. Thus, electron transfer is boosted for H₂ production, eliminating the kinetic limitations. The shuttle of Co²⁺ to Co³⁺ is the key step for Cl^• yield, which is accelerated due to the introduction of O_v. Electrochemical analysis shows that O_v induces positive charge on the Co center; therefore, Co²⁺ loses electrons more efficiently to form Co³⁺. H₂ production in this system reaches 716 μmol h^-1, which is 320% that of non-radical-mediated urine electrolysis. The utilization of O_v-Co₃O₄ further enhances H₂ generation, which is 490 and 210% those of noble Pt and RuO₂, respectively. Moreover, urine is effectively degraded in 90 min with the total nitrogen removal of 95.4%, and N₂ is the final product. This work provides new insights for efficient and low-cost recovery of H₂ and urine remediation.

Sensitivity Analysis with the Monte Carlo Method and Prediction of Atenolol Removal Using Modified Multiwalled Carbon Nanotubes Based on the Response Surface Method: Isotherm and Kinetics Studies

Atenolol (ATN) is a β-blocker drug extensively used to treat arrhythmias and high blood pressure. Because the human body cannot metabolize it completely, this drug has been commonly found in many environmental matrices. In the present study, the response surface method (RSM) was used for adsorption prediction of ATN on modified multiwalled carbon nanotubes (M-MWCNTs) by NaOCl and ultrasonic. The sensitivity analysis was done by the Monte Carlo method. Sensitivity analysis was performed to determine the effective parameter by the Monte Carlo simulator. Statistical analysis of variance (ANOVA) was performed by using the nonlinear second-order model of RSM. The influential parameters including contact time (min), adsorbent dosage (g/L), pH, and the initial concentration (mg/L) of ATN were investigated, and optimal conditions were determined. Kinetic of ATN adsorption on M-MWCNTs was evaluated using pseudo-first, pseudo-second-order, and intraparticle diffusion models. Equilibrium isotherms for this system were analyzed by the ISOFIT software. As per our result, optimum conditions in the adsorption experiments were pH 7, 60 min of contact time, 0.5 mg/L ATN initial concentration, and 150 mg/L adsorbent dose. In terms of ATN removal efficiency, coefficients of R2 and adjusted R2 were 0.999 and 0.998, respectively. Sensitivity analysis also showed that contact time has the greatest effect on increasing the removal of ATN. Pseudo-first-order (R2 value of 0.99) was the best kinetic model for the adsorption of ATN, and for isotherm, BET (AICC value of 3.27) was the best model that fit the experimental data. According to the obtained results from sensitive analysis, time was the most important parameter, and after that, the adsorbent dose and pH affect positively on ATN removal efficiency. It can be concluded that the modified multiwalled carbon nanotubes can be applied as one of the best adsorbents to remove ATN from the aqueous solution.

Micropollutant abatement by the UV/chloramine process in potable water reuse: A review

The need in using reclaimed water increased significantly to address the water shortage and its continuing quality deterioration in sustaining societal development. Degrading micropollutants in wastewater treatment plant effluents is one of the most important tasks in supplying safe drinking water, which is often achieved by full advanced treatment technologies (FATs), including reverse osmosis (RO) and the UV-based advanced oxidation process (AOP). As an emerging AOP, UV/chloramine process shows many noteworthy advantages in the scenario of potable water reuse, including membrane biological fouling control by chloramine, producing highly reactive radicals (e.g., Cl^•, HO^•, Cl₂^•-, and reactive nitrogen-containing species) to degrade the RO permeated pollutants, and acting as long-lasting disinfectant in the potable water distribution system. In addition, chloramine is often designedly produced by taking advantage of the ammonia in source. Thus, UV/chloramine processes gather much attention from researcher and published papers on UV/chloramine process have drastically increased since 2016, which were thoroughly reviewed in this paper. The fundamentals of chloramine photolysis, including the photolysis kinetics, the quantum yield, the generation and transformation of radicals and the final products, were scrutinized. Further, the impacts of reaction conditions such as pH, chloramine dosage and water matrix on the degradation of micropollutants by the UV/chloramine process are discussed. Moreover, the formation potential of disinfection by-products is debated. The opportunity of application of the UV/chloramine process in real-world practice is also presented, emphasizing the need for extensive efforts to remove currently prevalent knowledge roadblocks.

Accurate experimental characterization of the labile N–Cl bond in N-chloro-N′-(p-fluorophenyl)-benzamidine crystal at 17.5 K

Very low temperature can preserve the photolabile N–Cl bond in a N-chloro-N-benzamidine derivative long enough to carry on an accurate experimental X-ray charge density study.

Activation of organic chloramine by UV photolysis: A non-negligible oxidant for micro-pollutant abatement and disinfection by-product formation

Due to the wide-presence of organic amines in natural waters, organic chloramines are commonly formed during (pre-)chlorination. With the increasing application of UV disinfection in water treatment, both the activation mechanism of organic chloramine by UV photolysis and its subsequent impact on water quality are not clear. Using sarcosine (Sar) as an amine group-containing compound, it was found that organic chloramines (i.e., Cl-Sar) would be firstly formed during chlorination even in the presence of natural organic matter. Compared with self-decay of Cl-Sar, UV photolysis accelerated Cl-Sar decomposition and induced NCl bond cleavage. Using metoprolol (MTP) as a model micro-pollutant, UV-activated Cl-Sar (UV/Cl-Sar) can accelerate micro-pollutant degradation, attributed to reactive radicals formation. HO^• and Cl^• were important contributors, with a total contribution of 45%‒64%. Moreover, the degradation rate of MTP by UV/Cl-Sar was pH-dependent, which monotonically increased from 0.044 to 0.065 min^‒1 under pHs 5.5‒8.5. Although the activation of organic chloramine by UV could accelerate micro-pollutant degradation, UV/Cl-Sar treatment could also enhance disinfection by-products formation. Trichloromethane (TCM) formation was observed during MTP degradation by UV/Cl-Sar. After post-chlorination, TCM, 1,1-dichloropropanone, 1,1,1-trichloropropanone, and dichloroacetonitrile were detected. Their individual and total concentrations were all positively proportional to UV/Cl-Sar treatment time. The total concentration with 30 min treatment (66.93 μg L^‒1) was about 2.3 times that with 1 min treatment (28.76 μg L^‒1). Finally, the accelerated effect was verified with Cl-glycine and Cl-alanine. It is expected to unravel the non-negligible role of organic chloramine on water quality during UV disinfection.

Efficient Hydrogen Generation and Total Nitrogen Removal for Urine Treatment in a Neutral Solution Based on a Self-Driving Nano Photoelectrocatalytic System

Urine is the main source of nitrogen pollution, while urea is a hydrogen-enriched carrier that has been ignored. Decomposition of urea to H2 and N2 is of great significance. Unfortunately, direct urea oxidation suffers from sluggish kinetics, and needs strong alkaline condition. Herein, we developed a self-driving nano photoelectrocatalytic (PEC) system to efficiently produce hydrogen and remove total nitrogen (TN) for urine treatment under neutral pH conditions. TiO2/WO3 nanosheets were used as photoanode to generate chlorine radicals (Cl•) to convert urea-nitrogen to N2, which can promote hydrogen generation, due to the kinetic advantage of Cl-/Cl• cyclic catalysis. Copper nanowire electrodes (Cu NWs/CF) were employed as the cathode to produce hydrogen and simultaneously eliminate the over-oxidized nitrate-nitrogen. The self-driving was achieved based on a self-bias photoanode, consisting of confronted TiO2/WO3 nanosheets and a rear Si photovoltaic cell (Si PVC). The experiment results showed that hydrogen generation with Cl• is 2.03 times higher than in urine treatment without Cl•, generating hydrogen at 66.71 μmol h-1. At the same time, this system achieved a decomposition rate of 98.33% for urea in 2 h, with a reaction rate constant of 0.0359 min-1. The removal rate of total nitrogen and total organic carbon (TOC) reached 75.3% and 48.4% in 2 h, respectively. This study proposes an efficient and potential urine treatment and energy recovery method in neutral solution.

UV254 irradiation of N-chloro-α-amino acids: Kinetics, mechanisms, and N-DBP formation potentials

This study explores the degradation kinetics and mechanisms of N-chloro-α-amino acids and the changes in the formation potential of nitrogenous disinfection byproducts (N-DBPs) upon UV₂₅₄ irradiation. UV₂₅₄ irradiation significantly accelerated the degradation of all the tested N-chloro-α-amino acids compared to those in the dark. Both direct photolysis-induced cleavage of the N-Cl bonds and radical oxidation (e.g., Cl^• and Cl₂^•-) involved reactions that contributed to their enhanced degradation. The fluence-based photolysis rate constants of the N-chloro-α-amino acids varied in the range of (1.06-5.47) × 10^-3 cm² mJ^-1 at pH 6.0 and (0.74-2.79) × 10^-3 cm² mJ^-1 at pH 8.0. The apparent quantum yields (Φ_app) of the majority of the N-chloro-α-amino acids were in the range of 0.41-0.95 at pH 6.0 and 0.22-0.79 at pH 8.0, except N-chloroaspartic acid, N-chlorohistidine, and N-chloroalanine. UV₂₅₄ irradiation significantly enhanced the formation of trichloronitromethane (TCNM) from the tested N-chloro-α-amino acids after post-chlorination, but exhibited various effects on the formation of dichloroacetonitrile (DCAN). A longer UV₂₅₄ irradiation time generated more TCNM, and a lower pH produced more DCAN from the N-chloro-α-amino acids. The degradation pathways of N-chlorotyrosine, as a representative N-chloro-α-amino acid, are proposed, and the β-scission and 1,2-H shift pathways led to the formation of different precursors of TCNM and DCAN. The results of this study improve our understanding of the fate of N-chloro-α-amino acids under UV₂₅₄ irradiation and post-chlorination.

Photolysis of N-chlorourea and its effect on urea removal in a combined pre-chlorination and UV254 process

Urea is one of the most important nitrogenous organic pollutants in water, and its removal attracts attention because of a growing concern related to water eutrophication. Urea has previously been considered to be largely unaffected by the UV-chlorine process. However, N-chlorourea, an intermediate of urea chlorination, has been shown to absorb ultraviolet radiation, and as such its photolysis is possible. Experiments were conducted to quantify the kinetics of N-chlorourea degradation under UV₂₅₄ irradiation. The results showed that about 92% of N-chlorourea was degraded under UV₂₅₄ irradiation. Ammonia and nitrate were detected as the primary nitrogen containing products of the photolysis of N-chlorourea. Solution pH ranging from 3.0 to 7.5 influenced the distribution of these products but not on the degradation rate. Based on these data, a possible pathway of photodegradation of N-chlorourea under UV₂₅₄ is proposed. The degradation of urea was also achieved by the photolysis of N-chlorourea during the combined pre-chlorination and UV₂₅₄ process. Insights gained in this study may be useful for exploring the potential of combined pre-chlorination and UV₂₅₄ process on urea removal in water treatment.

Antibiotics in coastal aquaculture waters: Occurrence and elimination efficiency in oxidative water treatment processes

The influents and effluents of coastal flow-through aquacultures in Korea were monitored for four selected antibiotics (amoxicillin-AMX, florfenicol-FLO, oxolinic acid-OXO, and oxytetracycline-OTC). A number of 177 samples were obtained from 16 aquaculture facilities for a monitoring period of two years. OTC was detected in 93 samples with a median concentration of 116 ng/L. OXO, FLO, and AMX were also detected in 36, 34, and 22 samples with median concentrations of 90, 44, and 63 ng/L, respectively. After antibiotics were applied to fish tanks, the aquaculture effluents were found to contain antibiotics up to several hundred μg/L, indicating that some control measures are required. Bench-scale experiments showed that chlorine and ozone fully eliminated AMX and OTC but not FLO at ≤2 mg/L of oxidant dosage. Reactive halogen species formed in the marine water matrix enhanced the antibiotic degradation. UV₂₅₄ most effectively eliminated FLO, achieving 60-70 % elimination at 1000 mJ/cm² of UV fluence. Sequential use of chlorine followed by UV₂₅₄ demonstrated significant elimination of all four selected antibiotics. The obtained kinetic information for the reactions of these oxidants and UV with the antibiotics and marine aquaculture water constituents could be useful for designing and optimizing the aquaculture water treatment processes.

Nitrogen conversion from ammonia to trichloronitromethane: Potential risk during UV/chlorine process

In this study, the potential formation of trichloronitromethane (TCNM) from model organic compounds in ammonia-containing water treated by UV/chlorine process was evaluated. Monochloramine generated from the reaction of chlorine and ammonia can be photolyzed to produce NO₂^- and reactive nitrogen species (RNS), which play important roles in the formation of TCNM during the subsequent chlorination. The results showed that increase of nitrogen to chlorine molar ratio (from 0 to 1.0) and pH (from 6.5 to 8.0) enhanced the formation of TCNM, mainly due to the increased yield of NO₂^- and RNS from the photolyzed monochloramine. The formation of TCNM was interestingly found to be linearly correlated with Hammett constants of the model precursors, which is theoretically related to the rate constants of RNS with model compounds. Enhanced formation of TCNM was also observed during the treatment of natural organic matter by UV/chlorine process in ammonia-containing water. The toxicity assessment showed that TCNM significantly increased the genotoxicity of formed DBPs. Furthermore, the electrophilic substitution reaction of ^•NO₂ was proved to more likely occur on the ortho and para position of phenol according to the calculation of Gaussian program, and a possible reaction pathway of phenol and ^•NO₂ was proposed based on the calculated results.