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

Electrochemical Detection of Ammonia in Water Using NiCu Carbonate Hydroxide-Modified Carbon Cloth Electrodes: A Simple Sensing Method

Excessive ammonia nitrogen can potentially compromise the safety of drinking water. Therefore, developing a rapid and simple detection method for ammonia nitrogen in drinking water is of great importance. Nickel-copper hydroxides exhibit strong catalytic capabilities and are widely applied in ammonia nitrogen oxidation. In this study, a self-supported electrode made of nickel-copper carbonate hydroxide was synthesized on a carbon cloth collector via a straightforward one-step hydrothermal method for rapid ammonia nitrogen detection in water. It exhibits sensitivities of 3.9 μA μM-1 cm-2 and 3.13 μA μM-1 cm-2 within linear ranges of 1 μM to 100 μM and 100 μM to 400 μM, respectively, using a simple and rapid i-t method. The detection limit is as low as 0.62 μM, highlighting its excellent anti-interference properties against various anions and cations. The methodology's simplicity and effectiveness suggest broad applicability in water quality monitoring and environmental protection, particularly due to its significant cost-effectiveness.

Dichloramine Hydrolysis in Membrane Desalination Permeate: Mechanistic Insights and Implications for Oxidative Capacity in Potable Reuse Applications

Dichloramine (NHCl2) naturally exists in reverse osmosis (RO) permeate due to its application as an antifouling chemical in membrane-based potable reuse treatment. This study investigated mechanisms of background NHCl2 hydrolysis associated with the generation of oxidative radical species in RO permeate, established a kinetic model to predict the oxidative capacity, and examined its removal efficiency on trace organic contaminants in potable reuse. Results showed that NHCl2 hydrolysis generated transient peroxynitrite (ONOO-) and subsequently dissociated into hydroxyl radical (HO•). The maximal HO• exposure was observed at an RO permeate pH of 8.4, higher than that from typical ultraviolet (UV)-based advanced oxidation processes. The HO• exposure during NHCl2 hydrolysis also peaked at a NH2Cl-to-NHCl2 molar ratio of 1:1. The oxidative capacity rapidly degraded 1,4-dioxane, carbamazepine, atenolol, and sulfamethoxazole in RO permeate. Furthermore, background elevated carbonate in fresh RO permeate can convert HO• to carbonate radical (CO3•-). Aeration of the RO permeate removed total carbonate, significantly increased HO• exposure, and enhanced the degradation kinetics of trace organic contaminants. The kinetic model of NHCl2 hydrolysis predicted well the degradation of contaminants in RO permeate. This study provides new mechanistic insights into NHCl2 hydrolysis that contributes to the oxidative degradation of trace organic contaminants in potable reuse systems.

Multiple barriers as an efficient treatment for removing pesticides aiming direct potable reuse: A pilot scale study

Water reuse for potable purposes can represent a realistic source supply of drinking water in areas with water scarcity. Therefore, combining conventional wastewater treatment technologies with advanced technologies is necessary to remove contaminants and obtain high-quality and safe water. In this study, the pesticides and degradation products, atrazine (ATZ), hydroxyatrazine (ATZOH), deethylatrazine (DEA), deisopropylatrazine (DIA), simazine (SMZ), ametryn (AMT), diuron (DIU), 2,4-D, fipronil (FIP), fipronil sulfide (FIP-SF) and fipronil sulfone (FIP-SN) were evaluated in effluent after membrane bioreactor (MBR), effluent after advanced treatment by multiple barriers (MBR, reverse osmosis, UV/H2O2 and activated carbon), in tap water collected in the urban region of Campinas and in the Atibaia River (water supply source from city of Campinas). The pesticide concentrations in the Atibaia River and the post-MBR effluent ranged between 1 and 434 ng L-1 and 1 and 470 ng L-1, respectively. Therefore, the Atibaia River and the post-MBR effluent had the same magnitude pesticide concentrations. In the production of potable water reuse, after the multiple barriers processes, only fipronil (1 ng L-1) and atrazine (3 ng L-1) were quantified in some of the samples. In tap water from Campinas, atrazine, ATZOH, DEA, diuron, and 2,4-D were quantified in concentrations ranging between 3 and 425 ng L-1. Therefore, when comparing drinking water obtained from conventional treatment with potable water reuse, according to the pesticides studied, it is possible to conclude that the advanced treatment used on a pilot scale is promising for use in a potable water reuse plant. However, studies involving more microbiological and chemical parameters should be conducted to classify potable water reuse as drinking water.

What is the role of nitrate/nitrite in trace organic contaminants degradation and transformation during UV-based advanced oxidation processes?

The effectiveness of UV-based advanced oxidation processes (UV-AOPs) in degrading trace organic contaminants (TrOCs) can be significantly influenced by the ubiquitous presence of nitrate (NO3-) and nitrite (NO2-) in water and wastewater. Indeed, NO3-/NO2- can play multiple roles of NO3-/NO2- in UV-AOPs, leading to complexities and conflicting results observed in existing research. They can inhibit the degradation of TrOCs by scavenging reactive species and/or competitively absorbing UV light. Conversely, they can also enhance the elimination of TrOCs by generating additional •OH and reactive nitrogen species (RNS). Furthermore, the presence of NO3-/NO2- during UV-AOP treatment can affect the transformation pathways of TrOCs, potentially resulting in the nitration/nitrosation of TrOCs. The resulting nitro(so)-products are generally more toxic than the parent TrOCs and may become precursors of nitrogenous disinfection byproducts (N-DBPs) upon chlorination. Particularly, since the impact of NO3-/NO2- in UV-AOPs is largely due to the generation of RNS from NO3-/NO2- including NO•, NO2•, and peroxynitrite (ONOO-/ONOOH), this review covers the generation, properties, and detection methods of these RNS. From kinetic, mechanistic, and toxicologic perspectives, future research needs are proposed to advance the understanding of how NO3-/NO2- can be exploited to improve the performance of UV-AOPs treating TrOCs. This critical review provides a comprehensive framework outlining the multifaceted impact of NO3-/NO2- in UV-AOPs, contributing insights for basic research and practical applications of UV-AOPs containing NO3-/NO2-.

A multi-criteria decision framework for circular wastewater systems in emerging megacities of the Global South

Lima faces increasing water stress due to demographic growth, climate change and outdated water management infrastructure. Moreover, its highly centralized wastewater management system is currently unable to recover water or other resources. Hence, the primary aim of this study is to identify suitable wastewater treatment alternatives for both eutrophication mitigation and indirect potable reuse (IPR). For eutrophication mitigation, we examined MLE, Bardenpho, Step-feed, HF-MBR, and FS-MBR. For IPR, we considered secondary treatment+UF + RO + AOP or MBR + RO + AOP. These alternatives form part of a WWTP network at a district level, aiding Lima's pursuit of a circular economy approach. This perspective allows reducing environmental impacts through resource recovery, making the system more resilient to disasters and future water shortages. The methods used to assess these scenarios were Life Cycle Assessment for the environmental dimension; Life Cycle Costing for the economic perspective; and Multi-Criteria Decision Analysis to integrate both the quantitative tools aforementioned and qualitative criteria for social and techno-operational dimensions, which combined, strengthen the decision-making process. The decision-making steered towards Bardenpho for eutrophication abatement when environmental and economic criteria were prioritized or when the four criteria were equally weighted, while HF-MBR was the preferred option when techno-operational and social aspects were emphasized. In this scenario, global warming (GW) impacts ranged from 0.23 to 0.27 kg CO2eq, eutrophication mitigation varied from 6.44 to 7.29 g PO4- equivalent, and costs ranged between 0.12 and 0.17 €/m3. Conversely, HF-MBR + RO + AOP showed the best performance when IPR was sought from the outset. In the IPR scenario, GW impacts were significantly higher, at 0.46-0.51 kg CO2eq, eutrophication abatement was above 98 % and costs increased to ca. 0.44 €/m3.

Degradation of sulfonamide antibiotic via UV/MgO2 system: kinetic, application, and mechanism

In response to antibiotic residues in the water, a novel advanced oxidation technology based on MgO2 was used to remediate sulfamethazine (SMTZ) pollution in aquatic environments. Upon appropriate regulation, the remarkable removal efficiency of SMTZ was observed in a UV/MgO2 system, and the pseudo-first-order reaction constant reached 0.4074 min-1. In addition, the better performance of the UV/MgO2 system in a weak acid environment was discovered. During the removal of SMTZ, the pathways of SMTZ degradation were deduced, including nitration, ring opening, and group loss. In the mineralization exploration, the further removal of residual products of SMTZ by the UV/MgO2 system was visually demonstrated. The qualitative and quantitative researches as well as the roles of reactive species were valuated, which revealed the important role of ·O2-. Common co-existing substances in actual wastewater such as NO3- HA, Cl-, Fe2+, Co2+, and Mn2+ can slightly inhibit the degradation of SMTZ in the UV/MgO2 system. Finally, the capacity of efficient degradation of SMTZ in actual wastewater by the UV/MgO2 system was proved. The results indicated that the innovative UV/MgO2 system was of great practical application prospect in antibiotic residue wastewater remediation.

Closing Dichloramine Decomposition Nitrogen and Oxygen Mass Balances: Relative Importance of End-Products from the Reactive Nitrogen Species Pathway

In drinking water chloramination, monochloramine autodecomposition occurs in the presence of excess free ammonia through dichloramine, the decay of which was implicated in N-nitrosodimethylamine (NDMA) formation by (i) dichloramine hydrolysis to nitroxyl which reacts with itself to nitrous oxide (N2O), (ii) nitroxyl reaction with dissolved oxygen (DO) to peroxynitrite or mono/dichloramine to nitrogen gas (N2), and (iii) peroxynitrite reaction with total dimethylamine (TOTDMA) to NDMA or decomposition to nitrite/nitrate. Here, the yields of nitrogen and oxygen-containing end-products were quantified at pH 9 from NHCl2 decomposition at 200, 400, or 800 μeq Cl2·L-1 with and without 10 μM-N TOTDMA under ambient DO (∼500 μM-O) and, to limit peroxynitrite formation, low DO (≤40 μM-O). Without TOTDMA, the sum of free ammonia, monochloramine, dichloramine, N2, N2O, nitrite, and nitrate indicated nitrogen recoveries ±95% confidence intervals were not significantly different under ambient (90 ± 6%) and low (93 ± 7%) DO. With TOTDMA, nitrogen recoveries were less under ambient (82 ± 5%) than low (97 ± 7%) DO. Oxygen recoveries under ambient DO were 88-97%, and the so-called unidentified product of dichloramine decomposition formed at about three-fold greater concentration under ambient compared to low DO, like NDMA, consistent with a DO limitation. Unidentified product formation stemmed from peroxynitrite decomposition products reacting with mono/dichloramine. For a 2:2:1 nitrogen/oxygen/chlorine atom ratio and its estimated molar absorptivity, unidentified product inclusion with uncertainty may close oxygen recoveries and increase nitrogen recoveries to 98% (ambient DO) and 100% (low DO).

Bromide induced the formation of brominated halonitromethanes from aspartic acid in the UV/chlorine disinfection process

Brominated halonitromethanes (Br-HNMs) are generated in water disinfection processes and present high toxicity to human health. This work used aspartic acid (ASP) as the precursor to reveal that bromide (Br-) induced the production of Br-HNMs in the UV/chlorine disinfection process. Consequently, six Br-HNMs were identified, and their yields presented an increasing and then declining evolution over the reaction time from 0 to 15 min. Also, the total Br-HNMs yield reached the maximum of 251.1 μg L-1 at 5 min and then declined to 107.1 μg L-1. The total Br-HNMs yield increased from 2.40 to 251.14 μg L-1 with the increase of Cl2:Br- ratios from 0.25 to 3.0 by increasing free chlorine dosage with a fixed Br- concentration, and it increased from 207.59 to 251.14 μg L-1 and then decreased to 93.44 μg L-1 with the increase of Cl2:Br- ratio from 1.0 to 3.6 by increasing Br- concentration with a fixed free chlorine dosage. Besides, the total Br-HNMs yield reached the highest value (251.14 μg L-1) at pH 7.0 and the lowest value (74.20 μg L-1) at pH 8.0. Subsequently, the possible reaction mechanism of Br-HNMs generated from ASP was deduced, and the changes in toxicity of Br-HNMs also followed an increasing and then declining trend, closely relating to Br-HNMs yields and Br- utilization. This work explored and illustrated the yields, influence factors, reaction mechanisms, and toxicity of Br-HNMs formed from Br- containing ASP water during UV/chlorine disinfection, which might help to control Br-HNMs formation.

Methyl nitrate as a byproduct in advanced water treatment systems: Liquid chromatographic determination method and cause of formation

Neutral low-molecular-weight organics such as methyl nitrate that can readily pass through reverse osmosis (RO) membranes employed in potable water reuse facilities attract interest owing to public health considerations. In this study, a novel determination method based on high-performance liquid chromatography, online photochemical conversion to peroxynitrite, and luminol chemiluminescence detection was developed for methyl nitrate measurement in treated water. The maximum photochemical conversion efficiency of methyl nitrate to peroxynitrite was found to be 6.5% using a 222-nm excimer lamp. The calibration curve for the developed method was linear between 1.0 × 10-9 and 1.0 × 10-7 M, and the limit of detection was 0.3 nM (0.03 μg/L) given an injection volume of 200 μL. The methyl nitrate concentrations in RO permeate from reclaimed wastewater and product water after subsequent treatment by a UV/H2O2 advanced oxidation process (AOP) were 2.2 and 22.5 nM (0.17 and 1.7 μg/L), respectively. UV irradiation of RO permeate in the laboratory using a low-pressure Hg lamp confirmed the formation of methyl nitrate in the permeate in the absence of H2O2 and residual chloramines. This chemiluminescent detection method for methyl nitrate will promote a greater understanding of the origin and formation of this treatment byproduct in reclaimed wastewater.

Enhanced Oxidation of Antibiotics by Ferrate Mediated with Natural Organic Matter: Role of Phenolic Moieties

The increasing presence of antibiotics in water sources threatens public health and ecosystems. Various treatments have been previously applied to degrade antibiotics, yet their efficiency is commonly hindered by the presence of natural organic matter (NOM) in water. On the contrary, we show here that nine types of NOM and NOM model compounds improved the removal of trimethoprim and sulfamethoxazole by ferrate(VI) (FeVIO42-, Fe(VI)) under mild alkaline conditions. This is probably associated with the presence of phenolic moieties in NOMs, as suggested by first-order kinetics using NOM, phenol, and hydroquinone. Electron paramagnetic resonance reveals that NOM radicals are generated within milliseconds in the Fe(VI)-NOM system via single-electron transfer from NOM to Fe(VI) with the formation of Fe(V). The dominance of the Fe(V) reaction with antibiotics resulted in their enhanced removal despite concurrent reactions between Fe(V) and NOM moieties, the radicals, and water. Kinetic modeling considering Fe(V) explains the enhanced kinetics of antibiotics abatement at low phenol concentrations. Experiments with humic and fulvic acids of lake and river waters show similar results, thus supporting the enhanced abatement of antibiotics in real water situations.

A Novel Source of Radicals from UV/Dichloroisocyanurate for Surpassing Abatement of Emerging Contaminants Versus Conventional UV/Chlor(am)ine Processes

Ultraviolet (UV)/chlor(am)ine processes are emerging advanced oxidation processes (AOPs) for water decontamination and raising continuous attention. However, limitations appear in the UV/hypochlorite and UV/monochloramine for removing specific contaminants ascribed to the differences in the sorts and yields of free radicals. Here, this study reports UV/dichloroisocyanurate (NaDCC) as a novel source of radicals. NaDCC was demonstrated to be a well-balanced compound between hypochlorite and monochloramine, and it had significant UV absorption and a medium intrinsic quantum yield. The UV/NaDCC produced more substantial hydroxyl radicals (·OH) and reactive chlorine species (RCSs, including Cl·, ClO·, and Cl2·-) than conventional UV/chlor(am)ine, thereby generating a higher oxidation efficiency. The reaction mechanisms, environmental applicability, and energy requirements of the UV/NaDCC process for emerging contaminants (ECs) abatement were further investigated. The results showed that ·OH and ·NH2 attacked ECs mostly through hydrogen atom transfer (HAT) and radical adduct formation, whereas Cl· destroyed ECs mainly through HAT and single electron transfer, with ClO· playing a certain role through HAT. Kinetic model analyses revealed that the UV/NaDCC outperformed the conventional UV/chlor(am)ine in a variety of water matrices with superior degradation efficiency, significantly saving up to 96% electrical energy per order. Overall, this study first demonstrates application prospects of a novel AOP using UV/NaDCC, which can compensate for the deficiency of the conventional UV/chlor(am)ine AOPs.

Formation, toxicity, and mechanisms of halonitromethanes from poly(diallyl dimethyl ammonium chloride) during UV/monochloramine disinfection in the absence and presence of bromide ion

Bromide ion (Br^-) is known as a prevalent component in water environments, which exhibits significant impacts on halonitromethanes (HNMs) formation. This study was performed to explore and compare the formation, toxicity, and mechanisms of HNMs from poly(diallyl dimethyl ammonium chloride) (PDDACl) in the absence and presence of Br^- in the UV/monochloramine (UV/NH₂Cl) disinfection process. The results showed that chlorinated HNMs were found in the absence of Br^-, while brominated (chlorinated) HNMs and brominated HNMs were found in the presence of Br^-. Furthermore, the peaks of total HNMs were promoted by 2.0 and 2.4 times, respectively when 1.0 and 2.0 mg L^-1 Br^- were added. Also, the peaks of total HNMs were enhanced with the increase of the NH₂Cl dosage, which were reduced with the increase of pH. It should be noted that Br^- induced higher toxicity of HNMs, and the cytotoxicity and genotoxicity of HNMs with the addition of 2.0 mg L^-1 Br^- were 78.0 and 3.7 times those without the addition of Br^-, respectively. Meanwhile, both the reaction mechanisms of HNMs produced from PDDACl were speculated in the absence and presence of Br^-. Finally, different HNMs species and yields were discovered in these two real water samples compared to those in simulated waters. These findings of this work will be conducive to understanding the significance of Br^- affecting HNMs formation and toxicity in the disinfection process.

Toxicological aspect of water treated by chlorine-based advanced oxidation processes: A review

As well established in the literature, residual toxicity is an important parameter for evaluating the sanitary and environmental safety of water treatment processes, and this parameter becomes even more crucial when chlorine-based processes are applied for water treatment. Eliminating initial toxicity or preventing its increase after water treatment remains a huge challenge mainly due to the formation of highly toxic disinfection by-products (DBPs) that stem from the degradation of organic contaminants or the interaction of the chlorine-based oxidants with different matrix components. In this review, we present a comprehensive discussion regarding the toxicological aspects of water treated using chlorine-based advanced oxidation processes (AOPs) and the recent findings related to the factors influencing toxicity, and provide directions for future research in the area. The review begins by shedding light on the advances made in the application of free chlorine AOPs and the findings from studies conducted using electrochemical technologies based on free chlorine generation. We then delve into the insights and contributions brought to the fore regarding the application of NH₂Cl- and ClO₂-based treatment processes. Finally, we broaden our discussion by evaluating the toxicological assays and predictive models employed in the study of residual toxicity and provide an overview of the findings reported to date on this subject matter, while giving useful insights and directions for future research on the topic.

Visible light-driven NH2Cl activation by g-C3N4 photocatalysis producing reactive nitrogen species to degrade bisphenol A

The photolysis of monochloramine (NH₂Cl), a widely used disinfectant, under UVC irradiation produces different radicals for the micropollutant degradation. For the first time, this study demonstrates the degradation of bisphenol A (BPA) via the NH₂Cl activation by graphitic carbon nitride (g-C₃N₄) photocatalysis using visible light-LEDs at 420 nm, termed as the Vis₄₂₀/g-C₃N₄/NH₂Cl process. The process produces •NH₂, •NH₂OO, •NO and •NO₂ via the e_CB^-- and O₂^•--induced activation pathways and •NHCl and NHClOO• via the h_VB⁺-induced activation pathway. The produced reactive nitrogen species (RNS) enhanced 100% of the BPA degradation compared with the Vis₄₂₀/g-C₃N₄. Density functional theory calculations confirmed the proposed NH₂Cl activation pathways and further demonstrated that e_CB^-/O₂^•- and h_VB⁺ induced the cleavage of N-Cl and N-H bonds in NH₂Cl, respectively. The process converted 73.5% of the decomposed NH₂Cl to nitrogen-containing gas, compared with that of approximately 20% in the UVC/NH₂Cl process, leaving much less ammonia, nitrite and nitrate in water. Among different operating conditions and water matrices tested, of particular significance is natural organic matter of 5 mgDOC/L only reduced 13.1% of the BPA degradation compared against that of at least 46% reduction in the UVC/NH₂Cl process. Only 0.017-0.161 µg/L of disinfection byproducts were produced, two orders of magnitudes lower than that in the UVC/chlorine and UVC/NH₂Cl processes. The combined use of visible light-LEDs, g-C₃N₄ and NH₂Cl significantly improves the micropollutant degradation and reduces the energy consumption and byproduct formation of the NH₂Cl-based AOP.

Photolysis of chloramines in vacuum-UV and vacuum-UV/chlorine advanced oxidation processes for removal of 1,4-dioxane: Effect of water matrix, kinetic modeling, and implications for potable reuse

Advanced oxidation processes (AOPs) are a key step in eliminating persistent micropollutants in potable reuse trains. Under such conditions, chloramines are an inevitable component in the AOP feed water given their application as an antifouling agent for the upstream membrane processes. In cases when other oxidants, such as free chlorine, are to be used in the AOP treatment, the effect of background chloramines and any potential interplays between the oxidants should be considered. In this study, vacuum-UV (VUV) and VUV/Cl₂ have been proposed as promising AOP alternatives for potable reuse and the effect of chloramine photolysis has been considered on the removal of 1,4-dioxane. Results indicated that while presence of chloramine reduces the treatment efficiency in the VUV AOP, coexistence of free chlorine and chloramine oxidants significantly improves 1,4-dioxane degradation rates. Experimental data and kinetic modeling both confirmed the roles of OH^• and Cl₂^•- in 1,4-dioxane removal with 62.5% and 32.5% contribution in the VUV/Cl₂/chloramines, respectively. Among the other water matrix conditions, Cl^- was shown to improve the degradation rates while HCO₃^- suppressed the reactions by scavenging radical species. Overall, the findings of this research are informative for the design and development of VUV AOPs at small scale potable reuse facilities.

Analysis of degradation kinetic modeling and mechanism of chlorinated-halonitromethanes under UV/monochloramine treatment

Chlorinated-halonitromethanes (Cl-HNMs) including chloronitromethane (CNM), dichloronitromethane (DCNM), and trichloronitromethane (TCNM) are nitrogenous disinfection by-products, which have high cytotoxicity and genotoxicity to human. This study aimed to investigate the degradation kinetic modeling and mechanism of Cl-HNMs under monochloramine activated by ultraviolet of 254 nm (UV/NH₂Cl) treatment. The first-principle kinetic model of UV/NH₂Cl process was developed to simulate Cl-HNMs degradation. Of note, the second-order rate constants of Cl-HNMs reacting with HO• (∼10⁸ M^-1 s^-1), Cl• (k_{Cl•,CNM or DCNM} = ∼10¹⁰ M^-1 s^-1, k_Cl•,TCNM = ∼10² M^-1 s^-1), Cl₂•^- (k_{Cl•,CNM or DCNM} = ∼10⁹ M^-1 s^-1, k_Cl•,TCNM = ∼10¹ M^-1 s^-1), ClO• (∼10⁵-10⁶ M^-1 s^-1) and CO₃•^- (∼10⁶-10⁷ M^-1 s^-1) were obtained by the first-principle kinetic model. Overall, Cl-HNMs degradation under UV/NH₂Cl treatment was successfully predicted by the kinetic model under various conditions. It was found that UV (>60%) was dominant in Cl-HNMs degradation, followed by HO• (3.8%-24.5%), reactive chlorine species (RCS, 0.9%-28.8%) and CO₃•^- (0-26.1%). Among the contributions of RCS, Cl• and Cl₂•^- were main radicals in the degradation of CNM and DCNM, while ClO• was responsible for the abatement of TCNM. The minimum EE/O values under UV/NH₂Cl treatment were approximately 30% lower than those under UV treatment. Finally, the possible degradation pathways were proposed, including hemolytic/heterolytic cleavage of Cl-HNMs by UV irradiation, hydrogen abstraction/electron transfer of CNM and DCNM and adduct reaction of TCNM by free radicals. This study based on the kinetic model is beneficial to predict and control the concentrations of Cl-HNMs under UV/NH₂Cl treatment.

Influence of water matrix components on the UV/chlorine process and its reactions mechanism

The UV/chlorine system has become an attractive alternative Advanced Oxidation Process (AOP) for the removal of recalcitrant pollutants in the last decade due to the simultaneous formation of chlorine and hydroxyl radicals. However, there is no consensus regarding the results and trends obtained in previous micropollutant removal studies by AOPs, highlighting the complexity of the UV/chlorine process and the need for further research. This study investigates the degradation of acetaminophen (ACTP) by UV/chlorine and the effects of the water matrix in the reaction kinetics. In particular, the effects of natural organic matter (NOM), alkalinity and mineral salts on the kinetics and reactive species were elucidated. The complexity of the system was revealed by the analysis of the radical generation and transformation in different water matrices, applying the kinetic modelling approach to complement the scavenger tests. The higher kinetic rates of ACTP at alkaline pH provided new insights into the chlorine reactions under UV radiation, where secondary and tertiary reactive oxygen species including ozone were proven to play the major role in degradation. On the contrary, at acidic pH, reaction kinetic modelling demonstrated that ClO^• radical occurs at high concentrations in the order of 10^-10 M, being therefore the main oxidant, followed by other chlorine radicals. It is noteworthy that at alkaline pH the presence of typical inorganic ions such as carbonate had little impact on ACTP degradation, contrary to the observed reduction of degradation rates at acidic pH. The expected detrimental effect of the NOM in AOPs was also evidenced, although the use of chlorine as radical source reduces the relevance of the inner filter effect in comparison to UV/H₂O₂.

Current understanding on antibacterial mechanisms and research progress of tea polyphenols as a supplementary disinfectant for drinking water

Disinfection by-products (DBPs) generated during the disinfection of drinking water have become an urgent problem. So, tea polyphenol, a natural green disinfectant, has attracted widespread attention in recent years. This review summarizes the antibacterial mechanism of tea polyphenols and the recent findings on tea polyphenols as disinfectants for drinking water. These studies show that tea polyphenol is an antibacterial agent that works through different mechanisms and can be used as a supplementary disinfectant because of its higher lasting effect and economical cost. The dosage of tea polyphenols as a disinfectant of ultrafiltration effluent is the lowest among all the tea polyphenols disinfection methods, which can ensure the microbial safety of drinking water. This application of tea polyphenols is deemed a practical solution to solving the issue of disinfecting drinking water and reducing DBPs. However, it is necessary to further explore the influence of factors such as pipeline materials on the disinfection process and efficacy to expand the application scope of tea polyphenols. The large-scale application of tea polyphenols still needs to be fine-tuned but with new developments in tea polyphenol purification technology and the long-term need for drinking water that is safe for human consumption, tea polyphenols have good prospects for further development.

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.

Reactivity of nitrogen species with inorganic and organic compounds in water

Many studies on the reactive nitrogen species (RNS, ^●NO₂, ^●NO and ^●NH₂) with pollutants in water have been performed to understand the abatement of inorganic and organic compounds by these species, and the mechanisms of the formation of oxidative transformation products, especially nitrogenous oxidized byproducts. In this review, approaches to generate RNS in aqueous solution is first presented, followed by a summary of their reactivity with a wide range of compounds. The second-order rate constants (k, M^-1 s^-1) for the reactivity of ^●NO₂ and ^●NO with a wide range of inorganic radical and nonradical species were correlated with thermodynamic one-electron oxidation potentials (E⁰). The positive correlation between log(k) versus E⁰ suggests one-electron transfer reactions. The Hammett-type correlations were developed for the reactions of ^●NO₂ and ^●NH₂ with organic compounds, using the unsubstituted benzene as a reference molecule (i.e., Σσ_o,p,m = 0) to calculate Σσ_o,p,m = σ_o + σ_p + σ_m for each organic molecule. Linear negative correlations of log(k) with Σσ_o,p,m were obtained for both ^●NO₂ and ^●NH₂, suggesting electrophilic substitution mechanism. The correlations presented herein may assist in eliminating organic micropollutants in water treatment and reuse processes.

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.

Effects of MPUV/chlorine oxidation and coexisting bromide, ammonia, and nitrate on DBP formation potential of five typical amino acids

Disinfection byproduct (DBP) formation is a potential concern with regard to MPUV/Cl₂ application in water treatment. In this study, five typical amino acids (AAs) were selected to investigate their DBP alteration during short-term medium pressure (MP) UV/chlorine oxidation following post-chlorination relative to parallel dark controls. The five selected AAs include two potent DBP precursors (aspartic acid and tryptophan), one modest precursor (asparagine) and two poor precursors (phenylalanine and proline). MPUV/chlorine increased the total DBP formation and DBP-associated cytotoxicity of the two poor precursors phenylalanine (Phe) and proline (Pro) as well as their chlorine demands. Conversely, DBP formation and DBP-associated cytotoxicity of the three modest-to-potent DBP precursors showed the opposite changing trends due to MPUV/Cl₂ oxidation. The two aromatic AAs (tryptophan and phenylalanine) were more readily to be affected by MPUV/Cl₂ oxidation especially at acidic pH condition. Conversely, DBP formation and DBP-associated cytotoxicity of the three modest-to-potent precursors showed the opposite changing trends due to MPUV/Cl₂ oxidation. Among the measured DBPs, the absolute formation potential changes of haloacetic acids and haloacetonitriles were the most prominent. Presence of bromide increased the trihalomethane formation potential of five AAs. Ammonia-spiked samples resulted in notably higher chlorine demands but slightly reduced DBPFP. Photonitration caused increased haloacetonitrile and trichloronitromethane formation but lower overall DBP formation potential and DBP-associated cytotoxicity. Results indicated that increased DBP formation of unreactive aromatic AAs may be problematic with respect to MPUV/Cl₂ application, while the presence of inorganic ions may not contribute to further increase in calculated cytotoxicity of measured DBPs.

Misconceptions about the Chemistry of Aqueous Chlorine Atoms and HClOH•(aq), and a Revised Mechanism for the Photochemical Peroxydisulfate/Chloride Reaction

It is widely considered that aqueous chlorine atoms (Cl•) convert to the species HClOH• with a half life of about 3 µs and that this species plays an important role...