Search

Nanofiltration (NF) membranes, which can consistently offer safe and reliable water quality, have become increasingly popular in drinking water treatment. In this study, the conventional (coagulation-sedimentation-sand filtration) and ozonation-biologically activated carbon filtration (O3-BAC) advanced treatment processes at a full-scale drinking water treatment plant (DWTP) were combined with a pilot-scale NF process for treatment of Taihu Lake water. The results showed that the "conventional + O3-BAC + NF" combined processes had superior effects on removing natural organic matter (NOM), Br−, and other common water quality parameters (e.g., turbidity, conductivity, TDS, and total hardness) with efficiencies of 88.8–99.8%, for which the NF process played a critical role. The conventional plus O3-BAC processes effectively removed formation potential of chlorinated disinfection by-products (Cl-DBPFPs, by 28.0–46.6%), but had poorer effect in reducing formation potential of brominated DBPs (Br-DBPFPs, by −2637.2–17.3%). NOM concentrations (characterized by dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV254), and/or fluorescent components) were the driving factors for most DBPFP species, while elevation of [Br−]/[DOC] ratio likely resulted in enhanced formation of brominated trihalomethanes (THMs) during chlorination of the BAC effluent. By adding the pilot-scale NF process, the "conventional + O3-BAC + NF" treatment train effectively controlled DBPFP, yielding the removal efficiencies of Cl-DBPFP and Br-DBPFP as 77.6–100% and 33.5–100%, respectively, with monochloroacetic acid, mono-bromo-acetic acid, and tribromomethane formation potentials (MCAA-FP, MBAA-FP, and TBM-FP) not detected in the final effluent. Low temperature in the winter season might be the primary reason for the rapid increase of transmembrane pressure when operating the NF membrane under flux of 25 L/(m2·h), which could be largely delayed by lowering the flux to 20 L/(m2·h). Characterization of the membrane cleaning solutions showed that macromolecular biopolymers (6000 Da–4000K Da) such as polysaccharides and proteins were the main contributors to membrane fouling. [ABSTRACT FROM AUTHOR]

Disinfection by-products (DBPs) are prevalent contaminants in drinking water and are primarily linked to issues regarding water quality. These contaminants have been associated with various adverse health effects. Among different treatment processes, nanofiltration (NF) has demonstrated superior performance in effectively reducing the levels of DBPs compared to conventional processes and ozone-biological activated carbon (O 3 -BAC) processes. In this experiment, we systematically investigated the performance of three advanced membrane filtration treatment schemes, namely "sand filter + nanofiltration" (SF + NF), "sand filter + ozone-biological activated carbon + nanofiltration" (SF + O 3 -BAC + NF), and "ultrafiltration + nanofiltration" (UF + NF), in terms of their ability to control disinfection by-product (DBP) formation in treated water, analyzed the source and fate of DBP precursors during chlorination, and elucidated the role of precursor molecular weight distribution during membrane filtration in relation to DBP formation potential (DBPFP). The results indicated that each treatment process reduced DBPFP, as measured by trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP), with the SF + O 3 -BAC + NF process being the most effective (14.27 μg/L and 14.88 μg/L), followed by the SF + NF process (21.04 μg/L and 16.29 μg/L) and the UF + NF process (26.26 μg/L and 21.75 μg/L). Tyrosine, tryptophan, and soluble microbial products were identified as the major DBP precursors during chlorination, with their fluorescence intensity decreasing gradually as water treatment progressed. Additionally, while large molecular weight organics (60–100,000 KDa) played a minor role in DBPFP, small molecular weight organics (0.2–5 KDa) were highlighted as key contributors to DBPFP, and medium molecular weight organics (5–60 KDa) could adhere to the membrane surface and reduce DBPFP. Based on these findings, the combined NF process can be reasonably selected for controlling DBP formation, with potential long-term benefits for human health. [Display omitted] • The SF + NF, SF + O 3 -BAC + NF, and UF + NF processes help eliminate TCM and DCAA precursors. • Proteins and soluble microbial products are the main precursors for DBP formation. • Small molecular weight organics (0.2–5 KDa) are particularly likely to form DBPs. • The process chosen should consider energy consumption and economic factors. [ABSTRACT FROM AUTHOR]

The degradation rates and kinetics of one commonly used iodinated contrast medium, iohexol, were investigated and compared during ultraviolet (UV) photolysis, UV/H 2 O 2 and UV/ S 2 O 8 2 − advanced oxidation processes (AOPs). Results indicate that the iohexol degradation rate increased in the order of UV/H 2 O 2 < UV irradiation < UV/ S 2 O 8 2 − and followed pseudo-first-order kinetics. Increasing persulfate concentration significantly increased iohexol degradation rate, whereas increasing H 2 O 2 concentration caused reverse effect. Radical scavenging test results show that UV photolysis, OH and radicals all contributed to iohexol degradation during UV/ S 2 O 8 2 − , but OH was the main contributor during UV/H 2 O 2 and was consumed by excess H 2 O 2. The kinetic models of iohexol degradation by both AOPs were developed, and the reaction rate constants with OH and were calculated as 5.73 (±0.02) × 108 and 3.91 (±0.01) × 1010 M−1 s−1, respectively. Iohexol degradation rate remained stable at pH 5–9 during UV irradiation and UV/H 2 O 2 , but gradually decreased at pH 5–7 and remained stable at pH 7–9 during UV/ S 2 O 8 2 −. The presence of anions displayed inhibitory effects on iohexol degradation during UV/ S 2 O 8 2 − in the order of Cl − > HCO 3 − ≫ S O 4 2 − . UV/ S 2 O 8 2 − AOP exhibited high degradation efficiency and stability on the basis of UV irradiation, which can be applied as a promising degradation method for iohexol. UV/ S 2 O 8 2 − AOP can effectively mineralize iohexol to CO 2 but promoted the generation of toxic iodoform (CHI 3), and the subsequent chlorination had the potential to reduce the content of disinfection by-products; therefore, further evaluation of possible environmental hazards is warranted. • The degradation efficiency of iohexol increased in the order of UV/H 2 O 2 < UV irradiation < UV/ S 2 O 8 2 − . • The iohexol degradation by UV/H 2 O 2 oxidation was mainly contributed by OH radical without UV photolysis. • The rate constants of iohexol reacting with OH and · S O 4 − were calculated as 5.73 (±0.02) × 108 and 3.91 × 1010 (±0.01) M−1 s−1, respectively. • pH has a negligible impact on iohexol degradation during UV irradiation and slight influence during UV/ and UV/H 2 O 2. • Higher concentrations of chloride and bicarbonate (≥2 mM) inhibited iohexol degradation. [ABSTRACT FROM AUTHOR]

A common nitrogen-containing herbicide, metribuzin, was studied for the effect of pH, bromide and ammonium concentrations as well as temperature on its degradation kinetics and disinfection by-product (DBP) formation during chlorination. Metribuzin chlorination can be well described by a second-order kinetic model, and the rate constants of the acid-catalyzed and HOCl oxidizing charged metribuzin (metribuzin + ) were calculated as 7.72 (±0.90) × 10 8  M −2 min −1 and 8.22 (±4.00) × 10 3  M −1 min −1 , respectively. Metribuzin degradation rate increased with increasing bromide concentration or decreasing ammonium concentration. A kinetic model of metribuzin chlorination in the presence of bromide and ammonium, respectively, was developed in this study, and the rate constant for the reaction of HOBr and metribuzin + was calculated as 2.44 (±2.30) × 10 5  M −1   min −1 . Moreover, the formation and distribution of chlorinated DBPs were analyzed. Chloroform was the major volatile degradation product with the molar yield of 0.86% under the circumneutral condition, and its formation increased gradually with the increase of reaction time and pH. However, the formation of dichloroacetonitrile, 1,1-dichloro-2-propanone, 1,1-trichloro-2-propanone and trichloronitromethane climbed up and then declined with increasing reaction time and pH. The formation of brominated DBPs increased with increasing bromide to chlorine molar ratio, especially for dibromochloromethane. The rate constants of metribuzin chlorination increased with increasing temperature, and the activation energy was estimated as 22.83 kJ mol −1 . In sum, special attention should be paid during metribuzin chlorination at alkaline conditions, especially in the presence of bromide, which would cause the formation of more toxic brmoninated DBPs than their chlorinated analogs. [ABSTRACT FROM AUTHOR]

The raw waters from the Yellow River and the Danjiangkou Reservoir are the two most important sources of water in the water-receiving areas of the south-to-north water diversion project (SNWDP). This paper compared the constitution of dissolved organic matter (DOM) in the two waters based on XAD resins isolation, ultrafiltration fractionation, and the disinfection by-product formation potential of each fraction. The dissolved organic carbon (DOC), UV254, trihalomethanes, and nitrogenous disinfection by-product (N-DBP) formation potential of the raw water from the Yellow River were higher than those from the Danjiangkou Reservoir. The molecular weight (MW) < 1 kDa fraction contained the most DOM and dominated the major THM formation potential (THMFP) and N-DBP formation potential (N-DBPFP) in both waters. The hydrophilic fraction possessed the highest proportion in the Yellow River water, while the transphilic fraction was predominant in the Danjiangkou Reservoir water. In both waters, the hydrophobic fraction owned the highest THMFP and the hydrophilic fraction contained the highest N-DBPFP. Meanwhile, the molecular weight (MW) < 1 kDa and hydrophilic fractions contributed more bromated THMFP than the other fractions. Very toxic bromoform, bromochloroacetonitrile, and dibromoacetonitrile were only detected in DOM fractions from the Yellow River water. Therefore, the hydrophobic/hydrophilic organic compounds with low MW in both raw waters and bromide in Yellow River water should receive attention during the upgrading and reforming of drinking water treatment processes for adapting waters with different qualities in the water-receiving areas of SNWDP. [ABSTRACT FROM AUTHOR]

The kinetics of bensulfuron-methyl chlorination were studied at pH 4–9 at room temperature (25 ± 1 °C), which can be described well by a second-order kinetic model, first-order in chlorine and first-order in bensulfuron-methyl concentrations. Bensulfuron-methyl reacted very rapidly with aqueous chlorine with the maximum reaction rate constant at pH 6 and minimum at pH 9. The superior reactions were the reactions between HOCl and ionized/nonionized bensulfuron-methyl. The reaction factors including bromide and ammonium concentrations as well as temperature were also evaluated. It was found that bromide accelerated the chlorination of bensulfuron-methyl and the reaction rate increased linearly with the increase of bromide concentration. In contrast, the presence of ammonium inhibited the degradation of bensulfuron-methyl due to its quick conversion of chlorine to chloramines. Bensulfuron-methyl chlorination is an endothermic reaction with the activation energy being estimated as 13.74 kJ/mol using the Arrhenius equation. Four volatile disinfection by-products (DBPs) were identified after bensulfuron-methyl chlorination, including chloroform, dichloroacetonitrile, 1,1,1-trichloroacetone and nitrotrichloromethane. Trihalomethanes were the dominant species with a maximum reached at pH 8, which could cause potential risks to public health during bensulfuron-methyl chlorination, especially with the presence of bromide because the concentration and species of brominated DBPs increased with increasing bromide concentration. [ABSTRACT FROM AUTHOR]

This study investigated the degradation kinetics, formation of disinfection by-products (DBPs), and degradation pathways during monochloramination of oxytetracycline (OTC). The degradation kinetics can be well described by a second-order kinetic model, first-order in monochloramine (NH2Cl), and first-order in OTC. Reaction of OTC with NH2Cl shows a high reactivity, with the apparent rate constant of 17.64/M/s at pH 7. The apparent rate constant declined as pH increased from 5 to 10. Six DBPs were detected during monochloramination of OTC, including chloroform (CF), 1,1-dichloro-2-propanone (1,1-DCP), 1,1,1-trichloro-2-propanone (1,1,1-TCP), dichloroacetonitrile (DCAN), trichloronitromethane (TCNM), and N-nitrosodimethlyamine (NDMA). CF, DCAN and NDMA had the maximum yields at neutral pH, while 1,1-DCP and 1,1,1-TCP had the maximum yields at pH 4. However, TCNM concentration increased as pH increased. Degradation pathways of OTC monochloramination were then proposed. Hydroxylation and Cl-substitution are found to be the dominant mechanisms in monochloramination of OTC. [ABSTRACT FROM AUTHOR]

Prometryn is a herbicide that is widely used and frequently detected in aqueous environment and soil. Prometryn is chemically stable, biologically toxic, and easily to accumulate in living bodies, which can cause accumulate in the environment and acute and chronic toxicity to living creatures. In this study, factors affecting the degradation kinetics of prometryn chlorination were studied, including solution pH, bromide and ammonium concentrations, and temperature. Prometryn reacted quickly with aqueous chlorine following the pseudo-first-order kinetics. The maximum pseudo-first-order rate constant (k app) appeared at pH 5 with the observed rate constant (k obs) as 190. 08 h−1; the minimum value of k app reached at pH 9 with k obs as 5.26 h−1. The presence of Br− and increase of temperature both accelerated the degradation rate of prometryn during chlorination. The activation energy was calculated as 31.80 kJ/mol. Meanwhile 6 disinfection by-products (DBPs) were detected, namely: chloroform (CF), trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), dichloroacetone, trichloronitromethane (TCNM), and trichloroacetone. Solution pH significantly affected the formation and distribution of DBPs. CF was the most formed carbonated DBP (C-DBP) with the maximum of 217.9 μg/L at pH 8, and its formation was significantly higher in alkaline conditions. For nitrogenated DBPs (N-DBPs), the yields of DCAN and TCAN were significantly higher in acidic conditions, while the maximum of TCNM achieved in neutral conditions. Because the toxicity of N-DBPs is higher than that of C-DBPs, the pH should be controlled in neutral or slight alkaline conditions during prometryn chlorination to effectively control DBP formation and reduce the related toxicity. [Display omitted] • Prometryn chlorination followed pseudo-first-order kinetics. • The highest prometryn degradation rate happened at pH 5. • Br− promote prometryn degradation during chlorination, while NH 4 + inhibited it. • The degradation rate of prometryn increased with increasing temperature. • Solution pH should be controlled at around 7 to reduce the toxicity of DBPs. [ABSTRACT FROM AUTHOR]

• The chlorination of iohexol folllowed second-order kinetics. • The chloramination of iohexol followed pseudo-tertiary kinetics with the highest rate constant at pH 7. • NH 4 + promoted iohexol degradation during chlorination, while Br- inhibited that during chloramination. • In the presence of Br-, the formation of CHBrI 2 was significant during iohexol chlorination. • Iodine conversion to iodinated DBPs increased significantly during iohexol chloramination. In this study, the degradation kinetics, and the formation of disinfection byproducts (DBPs) during iohexol chlor(am)ination were studied. The chlorination kinetics can be described using a second-order model. As the pH of the solution increased, the apparent second-order rate constant of iohexol chlorination increased considerably. The reaction rate constants of iohexol with HOCl and OCl− were calculated as (3.75 ± 0.70) × 10 - 4 and (1.39 ± 1.19) × 10 - 4 M−1 s−1, respectively. In addition, the chloramination of iohexol followed tertiary kinetics, and the maximum apparent rate constant of 3.78 × 10 - 6 M−1 s−1 occurred at pH 7. NH 4 + can promote the degradation of iohexol during chlorination, whereas Br− inhibits iohexol degradation during chloramination. The formation of conventional carbonated DBPs and emerging nitrogenated DBPs during chlor(am)ination of iohexol was measured. However, in the presence of bromide, the conversion of iohexol to toxic iodinated DBPs increased significantly during chlorination, and chlorination resulted in higher formation of toxic I-DBP compared to chloramination. Therefore, chloramine disinfection is preferred for treating raw water containing high bromide concentrations in terms of DBP formation control. [ABSTRACT FROM AUTHOR]

• Heat-activated persulfate can effectively remove iohexol, but mineralization was almost negligible. • Raising temperature can significantly improve the degradation rate of iohexol, especially in the beginning 5 min. • Hydroxyl radical contributed more to the iohexol degradation than sulfate radical. • Higher concentrations of chloride (≥1 mM), bicarbonate (≥5 mM), and humic acid (≥5 mg/L) inhibited iohexol degradation. • Iodide was generated during iohexol degradation. In this study, we investigated the degradation kinetics of a commonly used iodinated contrast medium, iohexol, by using heat-activated persulfate. The results indicate that the iohexol concentration can be effectively reduced with a removal percentage higher than 85% despite the long reaction time (2–3 h). The iohexol disappearance fitted well with the pseudo-first-order kinetic model. The persulfate consumption almost reached the maximum value during the initial 5 min of the reaction. Subsequently, persulfate was no longer consumed, which resulted in a decrease in the reaction rate. The pseudo-first-order rate constant of iohexol degradation significantly increased with temperature but decreased with an increase in pH from 5 to 9. The results of the quenching experiments performed using ethanol and tert-butanol indicate that the role of hydroxyl radicals was more important than that of sulfate radicals in iohexol degradation during heat-activated persulfate oxidation. However, without heat activation, persulfate did not react with iohexol. Therefore, the effect of pH on the HO· concentration dominated the effect of pH on iohexol degradation. High concentrations of bicarbonate (≥5 mM), chloride (≥1 mM), and dissolved natural organic matter (≥5 mg/L) inhibited the degradation of iohexol due to the consumption of sulfate and hydroxyl radicals. The mineralization percentage was only 3.8% (no considerable improvement) when the temperature was increased to 80 °C. The molecular structures of the intermediates contained iodine with molecular weights higher than 377 Da. Moreover, the generation of iodide was detected. The experimental results suggest that special attention should be paid to the risk of the formation of disinfection by-products in the subsequent chlorine disinfection process when treating natural water containing iohexol through heat-activated persulfate oxidation. [ABSTRACT FROM AUTHOR]

• 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]

This study compared the formation of iodinated trihalomethanes (I-THMs) from iodide-containing raw waters oxidized by chlorine, chlorine dioxide (ClO 2 ) and potassium permanganate (KMnO 4 ) at different oxidant concentrations, reaction times, pHs, initial iodide concentrations and bromide to iodide mass ratios. Among the six investigated I-THMs, iodoform was the major species formed during the oxidation using chlorine, ClO 2 and KMnO 4 . When oxidant concentration increased from 0.1 to 3.0 mg/L, the formation of I-THMs increased and then decreased for chlorine and ClO 2 , but kept increasing for KMnO 4 . As the reaction time went by, I-THM concentration increased to a plateau within 10 h (ClO 2 within only 1 h, especially) for all the three oxidants. I-THM formation gradually increased from pH 3.0 to 9.0 and remained stable at pH values higher than 7.5 for chlorine; however, for ClO 2 and KMnO 4 the highest I-THM formation showed at pH 7.0 and 7.5, respectively. As initial iodide concentration increased from 20 to 800 μg/L, the total amount and species of I-THMs increased for the three oxidants. Iodide contributed to I-THM formation much more significantly than bromide. [ABSTRACT FROM AUTHOR]

• Direct photolysis of iohexol had significant dependence of UV wavelength spectral. • Distinctive photogenerated intermediates were observed with different photosensitizers. • Reactive sites and transformation pathways of iohexol were proposed. • Iohexol elimination and DBP yields by UV-LED irradiation followed the order of 255 > 265 > 275 > 285 nm. Iodinated X-ray contrast media (ICM) are ubiquitously present in water sources and challenging to eliminate using conventional processes, posing a significant risk to aquatic ecosystems. Ultraviolet light-emitting diodes (UV-LED) emerge as a promising technology for transforming micropollutants in water, boasting advantages such as diverse wavelengths, elimination of chemical additives, and no induction of microorganisms' resistance to disinfectants. The research reveals that iohexol (IOX) degradation escalates as UV wavelength decreases, attributed to enhanced photon utilization efficiency. Pseudo-first-order rate constants (k obs) were determined as 3.70, 2.60, 1.31 and 0.65 cm2 J−1 at UV-LED wavelengths of 255, 265, 275 and 285 nm, respectively. The optical properties of dissolved organic matter (DOM) and anions undeniably influence the UV-LED photolysis process through photon competition and the generation of reactive substances. The influence of Cl− on IOX degradation was insignificant at UV-LED 255, but it promoted IOX degradation at 265, 275 and 285 nm. IOX degradation was accelerated by ClO 2 −, NO 3 −and HA due to the formation of various reactive species. In the presence of NO 3 −, the k obs of IOX followed the order: 265 > 255 > 275 > 285 nm. Photosensitizers altered the spectral dependence of IOX, and the intermediate photoactivity products were detected using electron spin resonance. The transformation pathways of IOX were determined through density functional theory calculations and experiments. Disinfection by-products (DBPs) yields of IOX during UV-LED irradiation decreased as the wavelength increased: 255 > 265 > 275 > 285 nm. The cytotoxicity index value decreased as the UV-LED wavelength increased from 255 to 285 nm. These findings are crucial for selecting the most efficient wavelength for UV-LED degradation of ICM and will benefit future water purification design. [Display omitted] [ABSTRACT FROM AUTHOR]

The efficiency of the ultraviolet (UV)/chlorine process strongly depends on UV wavelength because chlorine photolysis and its subsequent radical formation are highly wavelength-dependent. This study compared the degradation of humic acid (HA) during the UV/chlorine process by low pressure mercury lamp (LPUV, 254 nm) and ultraviolet light-emitting diode (UV-LED, 275 and 310 nm). The results indicated that HA degradation followed the pseudo-first-order kinetics, and the fluence-based degradation rate constants (k obs) were significantly affected by UV wavelength and solution pH. HA degradation decreased greatly with increasing solution pH during the UV/chlorine process at 254 nm, while the opposite trend was observed at 275 and 310 nm. In the meantime, k obs decreased in the order of 275 nm > 254 nm > 310 nm at pH > 7.0. The changes of chlorine molar absorption coefficients at different UV wavelengths resulted in the variation of chlorine photodecay rates (k obs, chlorine), and the synergistic effects of k obs, chlorine and chlorine quantum yields (Φ chlorine) affected HA reduction. The formation of disinfection by-products (DBPs) during the UV/chlorine process was also evaluated. A significant suppression on DBP formation and DBP-associated calculated theoretical cytotoxicity were observed at 275 nm high UV fluence and alkaline pHs. These findings in this study demonstrate that UV wavelength at 275 nm is more suitable for HA degradation by the UV/chlorine advanced oxidation process in practical applications. Image 1 • HA degradation rate constants were significantly affected by UV wavelength in the UV/chlorine process. • The UV/chlorine process was more efficient at 275 nm than 254 and 310 nm at alkaline conditions. • Effective mitigation of DBPs and toxicity was achieved at 275 nm at high UV fluence. • DBP-associated cytotoxicity decreased in the order of 254 > 310 > 275 nm at high UV fluence in the presence of Br−. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Dual-wavelength synergy can significantly accelerate iopamidol degradation during UV-LED and UV-LED/chlorine processes. • Dual-wavelength irradiation can promote the photolysis of chlorine. • Maximum k obs for iopamidol degradation occurred at pH 7.0 during UV-LED/chlorine process. • HO· and RCSs are the major radical species for iopamidol degradation during UV-LED/chlorine process. • I-THM formation decreased in Milli-Q water while increased in real water with increasing irradiation time. Abstract This study revealed the iopamidol degradation performance and the synergistic effect of dual-wavelength ultraviolet light-emitting diodes (UV-LEDs). It was found that the dual-wavelength irradiation (265 and 280 nm) can promote iopamidol degradation during both UV-LED alone and UV-LED/chlorine processes (p < 0.05). The effects of key experimental parameters including pH, chlorine dosage and water matrix during UV-LED/chlorine process were evaluated. Peak degradation rate was observed at pH 7.0 due to the combined effects of the quantum yield of aquatic chlorine photolysis (Φ chlorine) and absorptivity of chlorine. The destruction pathways of iopamidol in the UV-LED/chlorine process were proposed by Ultra Performance Liquid Chromatography-Electrospray Ionization-mass spectrometry. Additionally, an opposite trend of iodinated trihalomethane (I-THM) formation during subsequent chlorination between Milli-Q and real waters with prolonging irradiation time was observed, while other detected disinfection by-product (DBP) formation showed the same variation in Milli-Q and real waters. The UV-LED/chlorine treatment using dual-wavelength can enhance iopamidol degradation significantly, but it also promoted I-THM formation in real water, indicating the need for evaluating DBPs before the application of UV-LED/chlorine process in drinking water treatment. [ABSTRACT FROM AUTHOR]

Acrylamide is a monomer of polyacrylamide, which is widely used in the water treatment process as a flocculant. The degradation kinetics and formation of disinfection by-products (DBPs) during acrylamide chlorination were investigated in this study. The reaction between chlorine and acrylamide followed a pseudo-first-order kinetics. A kinetic model regarding acrylamide chlorination was established and the rate constants of each predominant elementary reaction (i.e., the base-catalyzed reaction of acrylamide with ClO − as well as the reactions of acrylamide with HOCl and ClO − ) were calculated as 7.89 × 10 7 M − 2 h − 1 , 7.72 × 10 1 M − 1 h − 1 , and 1.65 × 10 3 M − 1 h − 1 , respectively. The presence of Br − in water led to the formation of HOBr and accelerated the rate of acrylamide degradation by chlorine. The reaction rate constant of acrylamide with HOBr was calculated as 1.33 × 10 3 M − 1 h − 1 . The degradation pathways of acrylamide chlorination were proposed according to the intermediates identified using ultra-performance liquid chromatography and electrospray ionization-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). Five chlorinated DBPs including chloroform (CF), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), dichloroacetamide (DCAcAm), and trichloroacetamide (TCAcAm) were identified during acrylamide chlorination. The formation of CF, DCAN, DCAcAm, and TCAcAm kept increasing, while that of TCAN increased and then decreased with increasing reaction time. As the chlorine dosage increased from 0.75 to 4.5 mM, DCAN became the dominant DBP. Large amounts of CF, DCAN, and TCAN were formed at basic pHs. The hydrolysis of DCAN and TCAN led to the formation of DCAcAm and TCAcAm, respectively. The results of this study elucidated that acrylamide can be a precursor for the formation of haloacetonitriles (HANs) and haloacetamides (HAcAms) during drinking water treatment. [ABSTRACT FROM AUTHOR]

This study investigated the effect of several factors on the formation of disinfection byproducts (DBPs) including trihalomethanes (THMs), haloacetonitriles (HANs) and halonitromethanes (HNMs) during UV-chlor(am)ination of the water collected after filtration unit in a drinking water treatment plant. In general, THM formation was higher during UV-chlorination while HAN and HNM formation were higher during UV-chloramination. Higher Medium pressure (MP) UV dose resulted in more DBP formation. The value of pH affected DBP formation differently. THMs decreased with increasing pH during UV-chlorination but remained stable during UV-chloramination. HNMs increased as pH increased from 5 to 7 but decreased as pH further increased to 9 during UV-chlorination. On the other hand, HNM formation decreased with increasing pH during UV-chloramination. However, pH had little impact on HAN formation. The nitrate concentration had negligible impact on the formation of THM, HAN and HNM during both UV-chlor(am)ination. Increasing bromide concentration improved THM and HAN formation, decreased HNM formation, and shifted DBPs to more brominated species in the three categories. MP UV irradiation enhanced the formation of DBPs compared to low pressure UV during both UV-chlor(am)ination, especially for nitrogenated DBPs. [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]

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. [Display omitted] • Stable organic chloramines were produced during cytosine chlorination. • UV irradiation can effectively degrade the generated organic chloramine. • The concentrations of DOC and TN in the solution were negligibly changed during chlorination. • OCs photodecay efficiency decreased in the order of 254 nm > 265 nm > 275 nm. • DBPs yield from OCs followed the order of UV/chlorine > UV > chlorination. [ABSTRACT FROM AUTHOR]

Chlorine dioxide (ClO 2) has emerged as a broad-spectrum, safe, and effective disinfectant due to its high oxidation efficiency and reduced formation of organochlorinated by-products during application. This article provides an updated overview of ClO 2 -based oxidation processes used in water treatment. A systematic review of scientific information and experimental data on ClO 2 -based water purification procedures is presented. Concerning ClO 2 -based oxidation derivative problems, the pros and cons of ClO 2 -based combined processes are assessed and disinfection by-product (DBP) control approaches are proposed. The kinetic and mechanistic data on ClO 2 reactivity towards micropollutants are discussed. ClO 2 selectively reacts with electron-rich moieties (anilines, phenols, olefins, and amines) and eliminates certain inorganic ions and microorganisms with high efficiency. The formation of chlorite and chlorate during the oxidation process is a crucial concern when utilizing ClO 2. Future applications include the combination of ClO 2 with ferrous ions, activated carbon, ozone, UV, visible light, or persulfate processes. The combined process can reduce by-product generation while still ensuring ClO 2 sterilization and disinfection. Overall, this research could provide useful information and new insights into the application of ClO 2 -based technologies. [Display omitted] • ClO 2 application derivative problems and DBPs control methods are discussed. • UV/ClO 2 process can achieve high-efficiency disinfection and reuse ClO 2 -. • The mechanistic information on combination process based on ClO 2 is analyzed. • The pros and cons of ClO 2 -based treatments are evaluated. • Challenges and perspectives for future development are proposed. [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: This study was to explore the formation of iodinated disinfection by-products (I-DBPs), including iodoform (CHI3), iodoacetic acid (IAA) and triiodoacetic acid (TIAA), when iodide-containing artificial synthesized waters and raw waters are in contact with chlorine dioxide (ClO2). Among the investigated I-DBPs, CHI3 was the major species during ClO2 oxidation in artificial synthesized waters. Impact factors were evaluated, including the concentrations of ClO2, iodide (I–), dissolved organic carbon (DOC) and pH. Formation of CHI3, IAA and TIAA followed an increasing and then decreasing pattern with increased ClO2 or DOC concentration. I-DBPs yield was significantly affected by solution pH. High concentrations of I-DBPs were generated under circumneutral conditions with the maximum formation at pH 8. The increase of I– concentration can increase I-DBPs yields, but the increment was suppressed when I– concentration was higher than 50 μM. When 100 μg/L I–and ClO2 (7.5–44.4 μM) were spiked to the raw water samples from Yangshupu and Minhang drinking water treatment plant, certain amounts of CHI3 and IAA were found under pH 7 and the concentrations were strongly correlated with ClO2 dosage and water qualities, however, no TIAA was detected. Finally, we investigated I-DBPs formation of 18 model compounds, including 4 carboxylic acids, 5 phenols and 8 amino acids, treating with ClO2 when I– was present. Results showed that most of these model compounds could form a considerable amount of I-DBPs, especially for propanoic acid, butanoic acid, resorcinol, hydroquinone, alanine, glutamic acid, phenylalanine and serine. [Copyright &y& Elsevier]

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]

In recent years, ultraviolet (UV) irradiation coupled with chlor(am)ination process is ubiquitous in secondary water supply systems in many cities of China. However, the disinfection by-products (DBPs) formation in a UV-activated mixed chlorine/chloramine system (MCCS) still remains unclear. In this study, the DBPs formation in a UV-activated MCCS was systematically investigated, considering influencing factors including the mass ratios of free chlorine to NH 2 Cl, UV irradiation, pH values, NOM types, Br− concentration and toxicity of the DBPs. Results indicated that DBPs formation decreased remarkably as mass ratio of free chlorine to NH 2 Cl changed from 5:0 to 0:5. The DBPs formation in humic acid (HA)-containing water was the highest, followed by those in fulvic acid (FA) and algal organic matter (AOM). Besides, better control of the DBP-related calculated toxicity can be achieved in acidic conditions regardless of the UV irradiation. Furthermore, in the presence of Br−, a significant reduction of DBPs formation could be achieved in a UV-activated MCCS. The findings also demonstrated that DBPs formation in real water can be effectively reduced at high UV fluence in a MCCS. ga1 • Mass ratio of HOCl/NH 2 Cl and UV irradiation significantly affected DBPs formation. • UV-activated MCC process reduced DBPs formation in alkaline conditions. • UV irradiation could control DBPs formation in Br−-containing water during MCC process. • MCC process achieved DBPs control in real water at high UV fluence. [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]

The effect of bromide and iodide on the transformation of humic acid (HA) and algal organic matter (AOM), and the formation of disinfection by-products (DBPs) during UV/chlorination were investigated. Experimental results indicated that the halides effectively inhibited mineralization, with multiple changes in organic molecule transformation due to differences in formation and speciation of reactive halogen species and free halogen. As a consequence, bromide and iodide also played important roles in DBP formation. The DBP yields in HA-containing water during UV/chlorination decreased in the order of iodide loaded > freshwater ≫ bromide loaded, whereas DBP formation in AOM-containing water decreased remarkably with halides added (freshwater > bromide loaded ≫ iodide loaded) at high UV fluence. Moreover, Pearson correlation analysis exhibited weaker correlation between DBPs and water parameters in AOM-containing water, while DBPs in HA-containing water exhibited better correlation with water parameters. For both simulated waters, the theoretical toxicity was calculated and peaked in bromide-containing water, whereas the calculated toxicity in iodide-containing water was comparable or slightly higher than that in freshwater. Therefore, UV/chlorine treatment may achieve good quality water with reduced DBP-associated toxicity in freshwater or iodide-containing water (iodide only), but careful consideration is needed when purifying source waters containing bromide (bromide only), especially for AOM/bromide-containing water. Image 1 • HA and AOM transformation was affected by halides during UV/chlorination. • DBP formation varied with the addition of Br− and I−. • DBP formed from HA decreased in the order of I− loaded > freshwater > Br− loaded. • Halides mitigated DBP formation from AOM (freshwater > Br− loaded ≫ I− loaded). • The highest DBP-associated cytotoxicity was observed in the presence of Br−. [ABSTRACT FROM AUTHOR]

• This study first compared different disinfection processes for controlling DBPs in rainwater. • The application of chloramine could control the yields of C-DBPs, but not N-DBPs in rainwater. • K 2 FeO 4 exerted effective control of most identified DBPs in rainwater. • UV-related AOPs could control DBP formation as well as cyto- and genotoxicity. • UV/PS was more effective to reduce DOC and alter DOM in rainwater than UV/H 2 O 2. With increasing shortage of clean water, rainwater has been considered as a precious alternative drinking water source. The processes applied to rainwater treatment are responsible for the safety of drinking water. Therefore, we systematically compared different disinfection processes to evaluate the control of disinfection by-product (DBP) formation and integrated cyto- and genotoxicity of the treated rainwater for the first time. The evaluated disinfection processes included chlorination and chloramination, pre-oxidation by potassium permanganate (KMnO 4) and potassium ferrate (K 2 FeO 4), ultraviolet/hydrogen peroxide (UV/H 2 O 2), and ultraviolet/persulfate (UV/PS) processes. The results revealed that chloramination was effective for controlling the formation of carbonaceous DBPs (C-DBPs), but not nitrogenous DBPs (N-DBPs). Compared to KMnO 4 pre-oxidation, better reduction of almost all DBPs was observed during K 2 FeO 4 pre-oxidation. According to the calculation of cytotoxicity index (CTI) and genotoxicity index (GTI), cyto- and genotoxicity of the samples decreased obviously at the dosage of ≥ 2.0 mg/L KMnO 4 and K 2 FeO 4. The control of the cyto- and genotoxicity of the formed DBPs from the two UV-related AOPs was more effective at the dosage of ≥ 1.0 mM PS and ≥ 5.0 mM H 2 O 2. Moreover, UV/PS was much more powerful to alter the structure of DBP precursors in rainwater. [ABSTRACT FROM AUTHOR]