Search

• UV/PMS and PMS-UV contributed similar SMX removal but different DBP formation potentials. • PMS-UV with a short time interval reduced TCNM formation risk. • High PMS dose in PMS-UV increased TCNM formation risk obviously. • PMS-UV in alkaline conditions enhanced SMX removal and reduced DBP risk except TCM. UV/peroxymonosulfate (UV/PMS) advanced oxidation process has attracted significant attention for removal of micropollutants in water. However, during practical water treatment applications, the PMS treatment must be performed before the UV treatment to achieve full contact. In this study, sulfamethoxazole (SMX) was selected as the target micropollutant. Four different operational approaches, including UV alone, PMS alone, simultaneous UV/PMS and sequential PMS-UV, were compared for their differences in SMX removal and disinfection by-product (DBP) formation potentials during chlorine-driven disinfection. Among the four approaches, UV/PMS and PMS-UV achieved over 90% removal efficiencies for SMX without substantial differences. For raw water, the trichloronitromethane (TCNM) formation potential after treatment with PMS-UV was lower than that after UV/PMS treatment. The time interval over which the PMS-UV process was conducted had little effect on the final removal efficiency for SMX. However, a brief (5 min) pre-PMS treatment significantly reduced the TCNM formation potential and the genotoxicity from DBPs. The formation risk for TCNM during chlorination increased markedly with increasing PMS dosages, and the appropriate dosage under these experimental conditions was suggested to be 0.5–1.0 mmol/L. Under alkaline conditions, PMS-UV treatment can enhance SMX degradation as well as dramatically reduced the formation potentials for haloketones, haloacetonitriles and halonitromethanes. This study suggests that proper optimization of UV/PMS processes can remove SMX and reduce its DBP formation. [Display omitted]. [ABSTRACT FROM AUTHOR]

Deep eutectic solvents (DESs) have emerged as a new type of promising ionic solvents with a broad range of potential applications. Although their ecotoxicological profile is still poorly known, DESs are generally regarded as “green” because they are composed of ammonium salts and H-bond donors (HBDs) which are considered to be eco-friendly. In this work, cholinium-based DESs comprised of choline chloride (ChCl) and choline acetate (ChAc) as the salt and urea (U), acetamide (A), glycerol (G) and ethylene glycol (EG) as the HBD were evaluated for their toxic effects on different living organisms such as Escherichia coli (a bacterium), Allium sativum (garlic, a plant) and hydra (an invertebrate), and their biodegradabilities were assessed by means of closed bottle tests. These DESs possessed an anti-bacterial property and exhibited inhibitory effects on the test organisms adopted, depending on the composition and concentration of the DES. The mechanism for the impact of DESs and their components on different living organisms can be associated to their interactions with the cellular membranes. Not all DESs can be considered readily biodegradable. By extending the limited knowledge about the toxicity and biodegradation of this particular solvent family, this investigation on DESs provides insight into our structure-based understanding of their ecotoxicological behavior. [ABSTRACT FROM AUTHOR]

• The characteristics of mixed chlorine/chloramine species were summarized. • Analysis methods of mixed chlorine/chloramine species and limitation are reviewed. • Concomitant issues of chlorine/chloramine species conversion were identified. • Control strategies for alleviating mixed chlorine/chloramines were proposed. • Future research directions of mixed chlorine/chloramine species were recommended. Mixed chlorine/chloramines are commonly occurring in real drinking water distribution systems (DWDSs) but often overlooked. This review provides a comprehensive overview of the occurrences, characteristics, analysis methods, and control strategies of mixed chlorine/chloramines in DWDSs. The characteristics of mixed chlorine/chloramine species are summarized for treated water in drinking water treatment plants (DWTPs), secondary disinfection facilities, and DWDSs where different disinfectants could be blended. The key to differentiating and quantifying mixed chlorine/chloramine species is to separate organic chloramines (OCs) from di/tri-chloramines and overcome certain interferences. The complex interactions between water matrixes and chlorine/chloramine species could accelerate pipeline corrosions, enhance emerging disinfection by-products risks, lead to off-flavors in drinking water, and induce bio-instability issues (such as nitrification, microorganism regrowth, and promotion of horizontal gene-transfers). Three promising strategies for alleviating mixed chlorine/chloramine species are recommended, which include (i) removing precursors intensively and reconditioning the treated water, (ii) combining UV irradiation to eliminate undesired chlorine/chloramines species, and (iii) strengthening monitoring, operation, and maintenance management of DWDSs. Finally, the challenges for gaining insights into the mechanisms of mixed chlorine/chloramine species conversion are discussed and promising research directions are proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Pulsed ultraviolet (UV) irradiation has presented enhanced inactivation efficiency in water disinfection and food decontamination. As an emerging UV source, UV light-emitting diodes (UV-LEDs) are an attractive alternative for pulsed irradiation because they can be turned on and off with a high and adjustable frequency. In this study, disinfection efficiencies of pulsed and continuous UV-LED irradiation were compared for Escherichia coli (E. coli) inactivation in water using a high power 285 nm LED and low power 265 and 280 nm LEDs. Factors including various duty cycles, pulse frequencies and UV irradiances were evaluated. The log-inactivation of E. coli increased substantially as the duty cycle decreased from 100% to 5% at the same UV dose. For 265 and 280 nm LEDs, the log-inactivation enhancements of pulsed UV irradiation were similar. When a higher irradiance was applied, the energy efficiency enhancement of pulsed UV irradiation became more obvious. The log-inactivation of E. coli enhanced remarkably using high current pulsed irradiation of 280 nm LEDs. Compared to continuous UV irradiation, pulsed UV-LED irradiation is an attractive alternative for E. coli inactivation in water considering energy efficiency. Graphical abstract Unlabelled Image Highlights • E. coli inactivation was enhanced using pulsed UVC-LED irradiation. • Log-inactivation increased substantially as duty cycle decreased from 100% to 5%. • Inactivation enhancement of pulsed UV were similar for 280 and 265 nm LEDs. • High current pulsed irradiation showed remarkable inactivation enhancement. [ABSTRACT FROM AUTHOR]

Abstract Ultraviolet (UV) irradiation has been widely used in drinking water treatment processes, but its influence on the formation of disinfection by-products (DBPs), especially the emerging iodinated trihalomethanes (I-THMs) during post-chloramination remains unclear. This study evaluated the impact of low pressure (LP) UV treatment on the formation of I-THMs during post-chloramination through two pathways. The first pathway is through the transition of DOM structure and composition during UV-chloramination, resulting significant increase of I-THM formation with increasing UV dosage in different dissolved organic matter (DOM)-containing water (49.7%–90.5% at 1160 mJ/cm2). With the application of excitation emission matrix-parallel factor analysis (EEM-PARAFAC), we found that I-THM formation in UV-chloraminated water correlated well with two ratios of three PARAFAC humic-like components (C3/C2 and C1/C2, R2 = 0.958–1.000), suggesting that the ratios of fluorescent components can be used as reliable indicators for I-THM formation. Moreover, the shift in these fluorescent components is crucial for I-THM formation during UV-chloramination. Another pathway for UV irradiation to affect I-THM formation during post-chloramination is through the transformation of iodine species. Large amounts of reactive iodine species (HOI/I 2 and I 3 −) can be generated directly in the mixed iodine system by UV light, leading to the enhancement of iodine utilization factor (IUF) (up to 0.040) after post-chloramination. These results suggest that UV application to DOM-containing water may induce changes in organic precursors and iodine species so as to enhance I-THM formation during post-chloramination. Graphical abstract Image 1 Highlights • UV irradiation increased I-THM formation significantly during post-chloramination. • The transition of DOM structure were elucidated using EEM-PARAFAC and GPC analyses. • The ratios of three fluorescent components after UV-chloramination correlated well with I-THM formation. • UV irradiation enhanced iodine utilization factor (IUF) remarkably during post-chloramination. • Large amounts of reactive iodine species were generated directly in the mixed iodine system by UV irradiation. [ABSTRACT FROM AUTHOR]

Combining pre-oxidation with activated carbon adsorption was explored as an ideal approach for removing iodine from water source to eliminate the formation of Iodinated trihalomethanes (I-THMs). Compared with permanganate and monochloramine, chlorine is more suitable as pre-oxidant to obtain higher active iodine species (HOI/I 2). Active iodine species adsorption using both powdered activated carbon (PAC) and granular activated carbon (GAC) can be well fitted the pseudo-second-order kinetic model indicating that chemical adsorption was the dominant mechanism for HOI/I 2 adsorption. The average pore size of activated carbons was the most strongly correlated with the adsorption capacity (R2 > 0.98), followed by methylene blue (R2 > 0.76), pore volume (R2 > 0.70) and iodine number (R2 > 0.67). Moreover, three models, including intraparticle diffusion, Byod kinetic, and diffusion-chemisorption were used to illustrate the mechanisms of HOI/I 2 adsorption. Chemical adsorption was the dominant mechanism for HOI/I 2 adsorption. In summary, at the molar ratio of [NaClO] and [I−] as 1.2, pre-chloriantion time of 5 min, subsequently dosage of 15 mg/L of PAC E with 20 min adsorption can remove 79.8% iodine. In addition, the combined process can eliminate 61%–87.2% of I-THMs in the subsequent chlor(am)ination. The results indicate that pre-chlorination combined with PAC can effectively removed HOI/I 2 and attenuate I-THMs formation in the subsequent disinfection process. [Display omitted] • Optimizing prechlorination can enhance HOI/I 2 formation, facilitating subsequent adsorption. • Active iodine species (HOI/I 2) were chemically adsorpted by PACs and GACs. • HOI/I 2 adsorption followed pseudo-second-order kinetics. • Film diffusion was the rate-limiting process for HOI/I 2 adsorption on activated carbon. • Pre-chlorination with PAC adsorption can effectively remove HOI/I 2 and attenuate I-THM formation. [ABSTRACT FROM AUTHOR]

· Mn(VII)-Fe(III)/PMS process showed excellent coagulation and oxidation performance. · NOM in raw water can mediate the redox cycle of iron. · The synergistic effect of NOM, Fe and Mn can promote the activation of PMS. · SO 4 •− was the main active species in the Mn(VII)-Fe(III)/PMS process. To improve the performance of the conventional coagulation process, a permanganate (Mn(VII)) pre-oxidation combined with Fe(III)/peroxymonosulfate (PMS) coagulation process (Mn(VII)-Fe(III)/PMS) that can significantly improve the removal of dissolved organic carbon (DOC), turbidity, and micropollutants is proposed in this study. Compared with conventional Fe(III) coagulation, the Mn(VII)-Fe(III)/PMS process can also significantly enhance the removal of iohexol and sulfamethoxazole in raw water. During this process, the primary reduction product, Mn(IV), after Mn(VII) pre-oxidation was adsorbed on the floc surfaces and involved in the Fe(III)/PMS process. The natural organic matter (NOM) in raw water mediated the redox cycle of iron. The synergistic effect of NOM, Fe, and Mn facilitated the redox cycle of Mn(III)/Mn(IV) and Fe(III)/Fe(II) to promote the activation of PMS. The sulfate radical (SO 4 •−) played an important role in the degradation of micropollutants. The formation potential of the detected volatile disinfection by-product (DBP) during the subsequent chlorination was reduced by 21.9% after the Mn(VII)-Fe(III)/PMS process. This study demonstrated the promising application of the Mn(VII)-Fe(III)/PMS process for coagulation and micropollutant control and illustrated the reaction mechanism. This study provides guidance for improving conventional drinking water treatment processes. [Display omitted] [ABSTRACT FROM AUTHOR]

• Benzoquinone (BQ) can accelerate emerging organic contaminants degradation by Mn(VII). • Semiquinone radicals can act as ligands to stabilize Mn(III) to form Mn(III)-L. • The presence of BQ promoted the in-situ formation MnO 2. • 1O 2 , Mn(III)-L and MnO 2 contributed to the accelerated degradation of BPA in the Mn(VII)/BQ system. • Semiquinone radicals inhibited BPA self-coupling and promote mineralization. Permanganate (Mn(VII)) is widely used as a mild oxidant in water treatment. However, the reaction rates of some emerging contaminants with Mn(VII) are extremely low. In this study, benzoquinone (BQ), a redox mediator with the important component in dissolved organic matter (DOM), enhanced the oxidation of bisphenol A (BPA) by Mn(VII) in a wide pH range of 4.0-10.0. The redox cycle of BQ would produce semiquinone radicals, which could act as ligands to stabilize the formed Mn(III) in the system to promote the oxidation of BPA. Notably, the presence of BQ might promote the formation of MnO 2. A novel mechanism was proposed that singlet oxygen (1O 2), Mn(III)-ligands (Mn(III)-L) and in-situ formed MnO 2 were the main contributors to accelerate BPA degradation in the Mn(VII)/BQ system. Under acidic conditions, the in-situ formed MnO 2 involved in the redox reaction and part of the Mn(IV) was reduced to Mn(III), indicating that the electron transfer of BQ promoted the formation of active Mn species and enhanced the Mn(VII) oxidation performance. Semiquinone radicals generated by BQ transformation would couple with the hydrogen substitution products of BPA to inhibit BPA self-coupling and promote the ring-opening reactions of BPA. Mn(VII)/BQ had better effect in raw water than in pure water, indicating that the Mn(VII)/BQ system has high potential for practical application. This study provided insights into the role of DOM in enhancing the Mn(VII) oxidation in water treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

Background Accumulating evidence suggests that microRNA-590 (miR-590) has protective effects on cardiovascular diseases, but the mechanism is unknown. Interestingly, previous studies from our laboratory and others have shown that macrophage-derived lipoprotein lipase (LPL) might accelerate atherosclerosis by promoting lipid accumulation and inflammatory response. However, the regulation of LPL at the post-transcriptional level by microRNAs has not been fully understood. In this study, we explored whether miR-590 affects the expression of LPL and its potential subsequent effects on lipid accumulation and pro-inflammatory cytokine secretion in human THP-1 macrophages. Methods and results Using bioinformatics analyses and dual-luciferase reporter assays, we found that miR-590 directly inhibited LPL protein and mRNA expression by targeting LPL 3′UTR. LPL Activity Assays showed that miR-590 reduced LPL activity in the culture media. Oil Red O staining and high-performance liquid chromatography assays showed that miR-590 had inhibitory effects on the lipid accumulation in human THP-1 macrophages. We also illustrated that miR-590 alleviated pro-inflammatory cytokine secretion in human THP-1 macrophages as measured by ELISA. With the method of small interfering RNA, we found that LPL siRNA can inhibit the miR-590 inhibitor-induced increase in lipid accumulation and secretion of pro-inflammatory cytokines in oxLDL-treated human THP-1 macrophages. Conclusions MiR-590 attenuates lipid accumulation and pro-inflammatory cytokine secretion by targeting LPL gene in human THP-1 macrophages. Therefore, targeting miR-590 may offer a promising strategy to treat atherosclerotic cardiovascular diseases. [ABSTRACT FROM AUTHOR]

Pyrimidine and purine bases (adenine, cytosine, guanine and thymine) are important precursors of organic chloramines (OC) and disinfection by-products (DBPs) during chlor(am)ination. In this study, OC and DBP formation derived from pyrimidine and purine bases during chlor(am)ination, post-chlor(am)ination after pretreated by UV alone and UV/chlorination were systematically investigated with ultraviolet light-emitting diodes (UV-LEDs, 265 and 275 nm) and low pressure mercury lamp (LPUV, 254 nm). The results revealed that higher OC formation was observed during chlorination than that during chloramination of pyrimidine and purine bases. The degradation of pyrimidine and purine bases followed the pseudo-first-order kinetics. Both solution pH and UV wavelength played vital influence on the degradation of pyrimidine and purine bases. In terms of fluence-based rate constants (k obs), the degradation rates of pyrimidine and purine bases decreased in the order of 275 nm > 265 nm > 254 nm in alkaline conditions. The synergistic effects of k obs, chlorine, k obs, •OH and k obs, RCS contributed to the differences of pyrimidine and purine bases degradation at different pH values and UV wavelengths. A vital suppression of OC formation was observed during post-chlorination after pretreated by 275 nm UV-LED/chlorination. In addition, compared with LPUV (254 nm), less DBP formation was observed at UV-LED (275 nm), especially during the UV/chlorine process. The phenomena obtained in this study indicated that 275 nm UV-LED combined with chlorine could be a preferred method to promote pyrimidine and purine bases degradation and control OC and DBP formation in practical water treatment. [Display omitted] • Higher levels of OC were observed during chlorination of pyrimidine and purine bases. • k obs of pyrimidine and purine bases during UV/chlorine process decreased in the order of 275 > 265 > 254 nm at pH > 7.0. • k obs, chlorine, k obs, •OH and k obs, RCS presented synergistic effects of on the removal of pyrimidine and purine bases. • UV/chlorine pretreatment significantly suppressed OC formation, but also enhanced the DBP formation. [ABSTRACT FROM AUTHOR]

Abstract: In this study, granular activated carbon (GAC) coated with cetyltrimethyl ammonium chloride (GAC-CTAC) was synthesized to remove perchlorate from water. Bench scale kinetics and adsorption isotherm tests were performed to evaluate the effects of factors affecting the adsorption efficiency, including the CTAC content, solution pH and ionic strength (I). When the content of CTAC on GAC increased from 0.031 to 0.16mmol/g, the rate constant in the pseudo-second order reaction was decreased from 46.35 to 23.24h·g/mmol, and the K value in the Freundlich equation was increased from 0.087 to 0.20mmol/g correspondingly. Typically, GAC-CTAC exhibited a higher adsorption capacity than GAC, which highlighted the key role of CTAC. The optimum perchlorate removal by GAC or GAC-CTAC was observed at pH 2–3, equivalent to pHpzc determined by zeta potential measurement. The adsorption capacity of perchlorate onto GAC-CTAC at pH 2.5 (0.36mmol/g) was 3.8 times as high as that onto GAC-CTAC at pH 5.6 (0.094mmol/g). Ionic strength appeared to significantly inhibit the perchlorate adsorption on GAC-CTAC. Finally, our results demonstrated that the primary mechanisms for the adsorption of perchlorate on GAC-CTAC were associated with electrostatic interaction, surface complexation and ion exchange. [Copyright &y& Elsevier]

Abstract: This study was to investigate granular activated carbon (GAC) adsorption of two algal odorants in water, dimethyl trisulfide and β-cyclocitral. Among the four isotherm models (Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich), Freundlich isotherm showed the best fitting with the equilibrium data in terms of the coefficient of determination (R2) and Chi-square (χ 2). Based on the parameters determined in the Freundlich isotherm equations for GAC adsorption of a single odorant, we successfully predicted the GAC adsorption behavior in a bisolute solution using the Ideal Solution Adsorption (IAS) model. In the kinetics study of the two odorants adsorption by GAC, pseudo first-order and pseudo second-order kinetic models both well fit the experimental data. The calculated Gibbs free-energy changes for GAC adsorption of dimethyl trisulfide and β-cyclocitral were −3.61 and −4.24kJ/mol at 298K, respectively. The pH effects on GAC adsorption of dimethyl trisulfide and β-cyclocitral were different. Alkaline condition (pH >10) favored GAC adsorption of dimethyl trisulfide, however, adsorption of the β-cyclocitral was not significantly influenced by pH (2–13). The presence of natural organic matter (NOM) hindered adsorption of dimethyl trisulfide and β-cyclocitral to different degrees. Low molecular weight NOM fractions (particularly <1000) showed the significant inhibiting effect in the GAC adsorption. [ABSTRACT FROM AUTHOR]

• Chlor(am)ination-derived odors have extremely low odor threshold concentrations. • The formation pathways of typical chlor(am)ination-derived odors are summarized. • Detection methods of typical chlor(am)ination-derived odors are reviewed. • Combination methods can effectively remove chlor(am)ination-derived odors. • Future development of chlor(am)ination-derived odors is proposed. Odors and tastes have become universal problems related to drinking water quality. In addition to the typical odor problems caused by algae or microorganisms, the occurrence of odors derived from drinking water disinfection have attracted attention. The chlor(am)ination-derived odor substances have certain toxicity and odor-causing characteristics, and would enter the tap water through water distribution systems, directly affecting drinking water safety and customer experience. This study provided a comprehensive overview of the occurrence, detection, and control of odor substances derived from drinking water chlor(am)ination disinfection. The occurrence and formation mechanisms of several typical types of disinfection derived odor substances were summarized, including haloanisoles, N- chloroaldimines, iodotrihalomethanes, and halophenoles. They are mainly derived from specific precursors such as halophenols, anisoles, and amino acids species during the disinfection or distribution networks. In addition, the change of disinfectant during chlor(am)ination was also one of the causes of disinfection odors. Due to the extremely low odor threshold concentrations (OTCs) of these odor substances, the effective sample pre-enrichment for instrument identification and quantification are essential. The control strategies of odor problems mainly include adsorption, chemical oxidation, and combined processes such as ozonation and biological activated carbon processes (O 3 /BAC) and ultraviolet-based advanced oxidation processes (UV-AOPs). Finally, the challenges and possible future research directions in this research field were discussed and proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

Iopamidol is a commonly used iodinated X-ray contrast media in medical field, and its residue in water can react with disinfectants to form highly toxic iodinated disinfection by-products (I-DBPs). This study investigated the degradation of iopamidol and formation of DBPs, especially iodinated trihalomethanes (I-THMs), during ferrate (Fe(VI)) pre-oxidation and subsequent chlor(am)ination under raw water background. It was found that iopamidol degradation efficiency in raw water by Fe(VI) at pH 9 could reach about 80%, which was much higher than that at pH 5 and pH 7 (both about 25%). With Fe(VI) dose increasing, iopamidol removal efficiency increased obviously. During the iopamidol degradation by Fe(VI), IO 3 − was the dominant product among all the iodine species. After pre-treated by Fe(VI), yields of THM4 and I-THMs can be reduced in subsequent chlor(am)ination. Besides, pH was a crucial factor for Fe(VI) pre-oxidition controlling DBPs. With the pH increasing from 5 to 9, the yield of THM4 kept increasing in subsequent chlorination but showed the highest amount at pH 6 in subsequent chloramination. The yield of I-THMs increased first and then decreased with the increase of pH in both subsequent chlorination and chloramination. I-THM concentrations in chlorinated samples were lower than chloraminated ones under acidic conditions but became higher under neutral and alkaline conditions. The total CTI of THMs during Fe(VI)-chloramination was higher than that during Fe(VI)-chlorination under neutral condition, but sharply decreased under alkaline conditions. In summary, Fe(VI)-chloramination subsequent treatment under alkaline conditions should be an effective method for iopamidol removal and DBP control. [Display omitted] • Iopamidol removal efficiency by Fe(VI) is higher at pH > 7 than that at pH ≤ 7. • IO 3 − was a dominant iodine product during iopamidol degradation by Fe(VI). • Fe(VI)-chloramination is effective in reducing THMs under alkaline conditions. • The toxicity contribution of CHI 3 is the highest in Fe(VI)-chloramination. [ABSTRACT FROM AUTHOR]

• IO 3 − can be reduced by e aq − in mixed IO 3 −/I− system under UV irradiation. • Acid pHs and high I− concentration promoted the IO 3 − transformation to RIS. • Mixed IO 3 −/I− system enhanced I-THM formation in UV/post-chloramination. • Humic substances promoted I-THM formation in a mixed IO 3 −/I− system. This study investigated the mechanisms of mixed IO 3 −/I− system under UV irradiation in drinking water and compared the iodinated trihalomethanes (I-THMs) formation of a mixed IO 3 −/I− system to that of single I− and IO 3 − systems during subsequent chloramination. The effects of initial I−/IO 3 − molar ratio, pH, and UV intensity on a mixed IO 3 −/I− system were studied. The introduction of I− enhanced the conversion rate of IO 3 − to reactive iodine species (RIS). Besides, IO 3 − degradation rate increased with the increase of initial I− concentration and UV intensity and the decrease of pH value. In a mixed IO 3 −/I− system, IO 3 − could undergo direct photolysis and photoreduction by hydrated electron (e aq −). Moreover, the enhancement of I-THM formation in a mixed IO 3 −/I− system during subsequent chloramination was observed. The I-THM yields in a mixed IO 3 −/I− system were higher than the sum of I-THMs produced in a single IO 3 − and I− systems at all the evaluated initial I− concentrations and pH values. The difference between I-THM formation in a mixed IO 3 −/I− system and the sum of I-THMs in a single IO 3 − and I− systems increased with the increase of initial I− concentration. As the initial pH decreased from 9 to 5, the difference of I-THM yields enhanced, while the total I-THM yield of a mixed IO 3 −/I− system and single I− and IO 3 − systems decreased slightly. Besides, IO 3 −-I−-containing water with DOC concentration of 2.5-4.5 mg-C/L, which mainly contained humic-acid substances, had a higher risk in I-THMs formation than individual I−-containing and IO 3 −-containing water. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The conversion mechanisms of chlorine species (including free chlorine, monochloramine (NH 2 Cl), dichloramine, and total chlorine), nitrogen species (including ammonium (NH 4 +), nitrate (NO 3 −), and nitrite (NO 2 −)) as well as the formation of disinfection by-products (DBPs) in a UV-activated mixed chlorine/chloramines system in water were investigated in this work. The consumption rates of free chlorine and NH 2 Cl were significantly promoted in a HOCl/NH 2 Cl coexisting system, especially in the presence of UV irradiation. Moreover, the transformation forms of nitrogen in both ultrapure and HA-containing waters were considerably affected by UV irradiation and the mass ratio of free chlorine to NH 2 Cl. NO 3 − and NO 2 − can be easily produced under UV irradiation, and the removal efficiency of total nitrogen with UV was obvious higher than that without UV when the initial ratio of HOCl/NH 2 Cl was less than 1. The roles of different radicals in the degradation of free chlorine, NH 2 Cl and NH 4 + were also considered in such a UV-activated mixed chlorine/chloramines system. The results indicated that OH• was important to the consumption of free chlorine and NH 2 Cl, and showed negligible influence on the consumption of NH 4 +. Besides, the changes of DOC and UV 254 in HA-containing water in UV-activated mixed chlorine/chloramines system indicated that the removal efficiency of DOC (24%) was much lower than that of UV 254 (94%). The formation of DBPs in a mixed chlorine/chloramines system was also evaluated. The yields of DBPs decreased significantly as the mass ratio of HOCl/NH 2 Cl varied from 1 : 0 to 0 : 1. Moreover, compared to the conditions without UV irradiation, higher DBPs yields and DBP-associated calculated toxicity were observed during the UV-activated mixed chlorine/chloramine process. Image 1 • UV-activated mixed HOCl/NH 2 Cl promoted the consumption of free chlorine and NH 2 Cl. • UV-activated mixed HOCl/NH 2 Cl enhanced the formation of NO 2 − and NO 3 −. • OH• was important to the consumption of free chlorine and NH 2 Cl, but not NH 4 +. • Higher DBPs yields were observed in the UV-activated mixed HOCl/NH 2 Cl system. [ABSTRACT FROM AUTHOR]