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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]

Graphical abstract Highlights • UV/chlorination of diatrizoate (DTZ) follows pseudo first-order kinetics. • UV/chlorination can degrade diatrizoate more effectively than UV alone. • OCl mainly contributes to the degradation of diatrizoate. • The steady-state concentration of OH was very low during UV/chlorination. Abstract The degradation kinetics of the widely used iodinated X-ray contrast medium, namely diatrizoate, was investigated during ultraviolet (UV) photolysis and UV/chlorination. Factors influencing diatrizoate degradation, such as pH, chlorine dosage, and bromide concentration, were also evaluated. Diatrizoate was not degraded during chlorination. However, the degradation of diatrizoate during UV photolysis and UV/chlorination complied with the pseudo-first-order kinetics. At pH 7, the pseudo-first-order rate constant during UV/chlorination was 9.3 times higher than that during UV photolysis. The results of a radical quenching test using excessive tert -butanol suggested that the contribution of Cl, a type of reactive chlorine species (RCS), was limited. The contributions of UV direct photolysis, hydroxyl radicals (OH), and RCS to diatrizoate degradation during UV/chlorination at pH 7 were estimated to be 12.8%, 1.2%, and 85.9%, respectively. Results of further experiment suggested that OCl primarily caused diatrizoate degradation. As the chlorine concentration gradually increased from 25 to 150 μM, the corresponding pseudo-first-order rate constant of UV/chlorination increased from 8.37 (±0.42) × 10−3 to 5.52 (±0.28) × 10−2 s−1. When the pH value was increased from 5 to 9, the rate of diatrizoate degradation reached the maximum at pH 7 and gradually decreased during UV/chlorination; however, the rate of diatrizoate degradation remained stable during UV photolysis. The degradation of diatrizoate was inhibited when the bromide concentration was increased due to the competition for chlorine between bromide and diatrizoate; thus, the generation of OCl was limited. Compared with UV irradiation, UV/chlorination could reduce the formation of iodinated trihalomethanes (I-THM) after chlorination. However, dichloroacetonitrile (C 2 HCl 2 N), which is carcinogenic, was generated during UV/chlorination. [ABSTRACT FROM AUTHOR]

Abstract: Ni2P/SiO2 catalyst with high dispersion was obtained by temperature-programmedly reducing the precursor that was prepared via a new approach. In this approach, nickel-containing silica was firstly synthesized via a sol–gel process, and phosphorus species were then supported on it through impregnation. In the precursor, the nickel species highly dispersed and the interaction between nickel and support was strong. This contributed to the resistance of Ni2P to sintering, and the resulting Ni2P particles were very small and uniform. The Ni2P/SiO2 catalyst proved to be very active and stable in the hydrodechlorination of chlorobenzene. [Copyright &y& Elsevier]

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]

• 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]

Highlights: [•] The kinetics of dinoseb chlorination can be described by a second-order model. [•] Dinoseb chlorination is subject to hydroxylation, oxidation and substitution reactions. [•] High concentrations of TCNM and CF were generated and the yields varied with Cl2/C, time and pH. [•] TCNM formation favors acid pHs during dinoseb chlorination. [Copyright &y& Elsevier]

Abstract: Chlortoluron chlorination is studied in the pH range of 3–10 at 25±1°C. The chlorination kinetics can be well described by a second-order kinetics model, first-order in chlorine and first-order in chlortoluron. The apparent rate constants were determined and found to be minimum at pH 6, maximum at pH 3 and medium at alkaline conditions. The rate constant of each predominant elementary reactions (i.e., the acid-catalyzed reaction of chlortoluron with HOCl, the reaction of chlortoluron with HOCl and the reaction of chlortoluron with OCl−) was calculated as 3.12 (± 0.10)×107 M−2 h−1, 3.11 (±0.39)×102 M−1 h−1 and 3.06 (±0.47)×103 M−1 h−1, respectively. The main chlortoluron chlorination by-products were identified by gas chromatography–mass spectrometry (GC–MS) with purge-and-trap pretreatment, ultra-performance liquid chromatography–electrospray ionization-MS and GC-electron capture detector. Six volatile disinfection by-products were identified including chloroform (CF), dichloroacetonitrile, 1,1-dichloropropanone, 1,1,1-trichloropropanone, dichloronitromethane and trichloronitromethane. Degradation pathways of chlortoluron chlorination were then proposed. High concentrations of CF were generated during chlortoluron chlorination, with maximum CF yield at circumneutral pH range in solution. [Copyright &y& Elsevier]

The degradation kinetics, pathways and disinfection by-products (DBPs) formation of iopamidol by chlorine and chloramines were investigated in this paper. The chlorination kinetics can be well described by a second-order model. The apparent second-order rate constants of iopamidol chlorination significantly increased with solution pH. The rate constants of iopamidol with HOCl and OCl − were calculated as (1.66 ± 0.09) × 10 −3 M −1 s −1 and (0.45± 0.02) M −1 s −1 , respectively. However, the chloramination of iopamidol fitted well with third-order kinetics and the maximum of the apparent rate constant occurred at pH 7. It was inferred that the free chlorine (i.e., HOCl and OCl − ) can react with iopamidol while the combined chlorine species (i.e., NH 2 Cl and NHCl 2 ) were not reactive with iopamidol. The main intermediates during chlorination or chloramination of iopamidol were identified using ultra performance liquid chromatography - electrospray ionization-mass spectrometry (UPLC-ESI-MS), and the destruction pathways including stepwise deiodination, hydroxylation as well as chlorination were then proposed. The regular and iodinated DBPs formed during chlorination and chloramination of iopamidol were measured. It was found that iodine conversion from iopamidol to toxic iodinated DBPs distinctly increased during chloramination. The results also indicated that although chloramines were much less reactive than chlorine toward iopamidol, they led to the formation of much more toxic iodinated DBPs, especially CHI 3 . [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]

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]

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]

The formation and control of haloacetamides (HAcAms) in drinking water have raised high attention due to their high genotoxicity and cytotoxicity, especially the most cytotoxic one, diiodoacetamide (DIAcAm). In this study, the degradation of DIAcAm by UV/chlorination was investigated in terms of degradation kinetics, efficiency, influencing factors, oxidation products and toxicity evaluation. Results revealed that the degradation of DIAcAm by UV/chlorine process followed pseudo-first-order kinetics, and the rate constant between DIAcAm and OH radicals was determined as 2.8 × 109 M−1 s−1. The contribution of Cl to DIAcAm degradation by UV/chlorine oxidation was negligible. Increasing chlorine dosage and decreasing pH significantly promoted the DIAcAm degradation during UV/chlorine oxidation, but the presence of bicarbonate (HCO 3 −) and natural organic matter (NOM) inhibited it. The mass balance analysis of iodine species was also evaluated during UV/chlorine oxidation of DIAcAm. In this process, with DIAcAm decreasing from 16.0 to 0.8 μM-I in 20 min, IO 3 −, I− and HOI/I 2 increased from 0 to 6.3, 6.1 and 0.5 μM-I, respectively. The increase of CHO cell viability during DIAcAm degradation indicated that the toxicity of DIAcAm could be decreased by chlorination, UV irradiation and UV/chlorine oxidation treatments, in which UV/chlorine oxidation was more effective on toxicity reduction than chlorination and UV irradiation alone. Image 1 • UV/chlorine is more effective on DIAcAm degradation than UV and chlorination alone. • Kinetics models were established for DIAcAm degradation during UV/chlorine process. • DIAcAm degradation by UV/chlorine is remarkably affected by pH, HCO 3 − and NOM. • IO 3 −, I− and HOI/I 2 can be produced during UV/chlorine oxidation of DIAcAm. • DIAcAm toxicity can be reduced significantly by UV/chlorine oxidation. [ABSTRACT FROM AUTHOR]