Enhanced degradation of emerging contaminants by Far-UVC photolysis of peracetic acid: Synergistic effect and mechanisms.

Krypton chloride (KrCl*) excimer lamps (222 nm) are used as a promising irradiation source to drive ultraviolet-based advanced oxidation processes (UV-AOPs) in water treatment. In this study, the UV222/peracetic acid (PAA) process is implemented as a novel UV-AOPs for the degradation of emerging contaminants (ECs) in water. The results demonstrate that UV222/PAA process exhibits excellent degradation performance for carbamazepine (CBZ), with a removal rate of 90.8 % within 45 min. Notably, the degradation of CBZ in the UV222/PAA process (90.8 %) was significantly higher than that in the UV254/PAA process (15.1 %) at the same UV dose. The UV222/PAA process exhibits superior electrical energy per order (EE/O) performance while reducing resource consumption associated with the high-energy UV254/PAA process. Quenching experiments and electron paramagnetic resonance (EPR) detection confirm that HO• play a dominant role in the reaction. The contributions of direct photolysis, HO•, and other active species (RO• and 1O2) are estimated to be 5 %, 88 %, and 7 %, respectively. In addition, the effects of Cl-, HCO3-, and humic acid (HA) on the degradation of CBZ are evaluated. The presence of relatively low concentrations of Cl-, HCO3-, and HA can inhibit CBZ degradation. The UV222/PAA oxidation process could also effectively degrade several other ECs (i.e., iohexol, sulfamethoxazole, acetochlor, ibuprofen), indicating the potential application of this process in pollutant removal. These findings will propel the development of the UV222/PAA process and provide valuable insights for its application in water treatment.

Wavelength dependency and photosensitizer effects in UV-LED photodegradation of iohexol.

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 (kobs) 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 ClO2-, NO3-and HA due to the formation of various reactive species. In the presence of NO3-, the kobs 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.

Degradation kinetics and disinfection by-products formation of benzophenone-4 during UV/persulfate process.

The degradation kinetics, reaction pathways, and disinfection by-products formation of an organic UV filter, benzophenone-4 (BP4) during UV/persulfate oxidation were investigated. BP4 can hardly be degraded by UV alone, but can be effectively decomposed by UV/persulfate following pseudo-first order kinetics. BP4 degradation rate was enhanced with increasing persulfate dosage and decreasing pH from 8 to 5. However, the degradation rate of BP4 at pH 9 was higher than that at pH 8 because of the presence of phenolic group in BP4 structure. and SO4-⋅ were confirmed as the major contributors to BP4 decomposition in radical scavenging experiments, and the second-order rate constants between HO⋅ and BP4 as well as those between SO4-⋅ and BP4 were estimated by establishing and solving a kinetic model. The presence of Br- and humic acid inhibited the decomposition of BP4, while NO3- promoted it. The mineralisation of BP4 was only 9.1% at the persulfate concentration of 50 µM. Six degradation intermediates were identified for the promulgation of the reaction pathways of BP4 during UV/persulfate oxidation were proposed as a result. In addition, the formation of DBP in the sequential chlorination was evaluated at different persulfate dosages, pH values, and water matrix. The results of this study can provide essential knowledge for the effective control of DBP formation with reducing potential hazard to provide safe drinking water to the public.

BP4 can be effectively degraded by UV/persulfate process, following pseudo-first order kinetics.OH⋅ and SO4−⋅ were identified as the main contributors to BP4 degradation during UV/persulfate process.The degradation pathways of BP4 during UV/persulfate process were proposed.Initial persulfate concentration and solution pH both affected the yield of DBPs.The higher toxic DBPs can be generated in the presence of Br− or NO3−.

Comparison of four pre-oxidants coupled powdered activated carbon adsorption for odor compounds and algae removal: Kinetics, process optimization, and formation of disinfection byproducts.

Pre-oxidation and powdered activate carbon (PAC) are usually used to remove algae and odorants in drinking waterworks. However, the influence of interaction between oxidants and PAC on the treatment performance are scarcely known. This study systematically investigated the combination schemes of four oxidants (KMnO4, NaClO, ClO2, and O3) and PAC on the inactivation of Microcystis aeruginosa cells and removal of four frequently detected odorants in raw water (diethyl disulfide (DEDS), 2,2'-oxybis(1chloropropane) (DCIP), 2-methylisoborneol (2-MIB) and geosmin (GSM)). O3 showed highest pseudo-first-order removal rate for all four compounds and NaClO exhibited highest inactivation rates for the cell viability and Chlorophyll a (Chl-a). The Freundlich model fitted well for the adsorption of DEDS and DCIP by PAC. When treated by combined oxidation/PAC, the removal ratio of algae cells and odorants were lower (at least 1.6 times) than the sum of removal ratios obtained in oxidation or PAC adsorption alone. Among these four oxidants, the highest synchronous control efficiency of odorants (52 %) and algae (66 %) was achieved by NaClO/PAC. Prolonging the dosage time interval promoted the removal rates. The pre-PAC/post-oxidation processes possessed comparable efficiency for the removal of odorants and algae cells comparing with pre-oxidation/post-PAC process, but significantly inhibited formation of disinfection byproducts (DBPs), especially for the formation of C-DBPs (for NaClO and ClO2), bromate (for O3) and chlorate/chlorite (for ClO2). This study could provide a better understanding of improving in-situ operation of the combined pre-treatments of oxidation and PAC for source water.

Insight into mixed chlorine/chloramines conversion and associated water quality variability in drinking water distribution systems.

Mixed chlorine/chloramines are common in drinking water distribution systems (DWDSs); however, their transformation and impact on chemical and microbial characteristics are not well understood. We systematically investigated water quality parameters associated with mixed chlorine/chloramine species conversion in 192 samples (including raw, finished, and tap water) collected throughout the year in a city in East China. Various chlorine/chloramine species (free chlorine, monochloramine [NH2Cl], dichloramine [NHCl2], and organic chloramines [OC]) were detected in both chlorinated and chloraminated DWDSs. NHCl2 + OC increased with transport distance along the pipeline network. The maximum proportion of NHCl2 + OC in over total chlorine in tap water reached 66 % and 38 % from chlorinated and chloraminated DWDSs, respectively. Both free chlorine and NH2Cl showed a rapid decay in the water pipe systems, but NHCl2 and OC were more persistent. Correlations between chlorine/chloramine species and physicochemical parameters were established. Models for predicting the sum of chloroform/TCM, bromodichloromethane/BDCM, chlorodibromomethane/CBDM, and bromoform/TBM (THM4) (R2 = 0.56) and haloacetic acids (HAAs) (R2 = 0.65) exhibited greater accuracy based on machine learning tuned with chlorine/chloramine species, particularly NHCl2 + OC. The predominant bacterial communities in mixed chlorine/chloramine systems were those resistant to chlorine or chloramine such as proteobacteria. NH2Cl was the most significant explanatory factor (28.1 %) for the variation in microbial community assemblage in chloraminated DWDSs. Although residual free chlorine and NHCl2 + OC, accounted for a smaller proportion of chlorine species in chloraminated DWDSs, they played an essential role (12.4 % and 9.1 %, respectively) in the microbial community structure.

Sequential combination of pre-chlorination and powdered activated carbon adsorption on iodine removal and I-THMs control in drinking water.

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/I2). 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/I2 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/I2 adsorption. Chemical adsorption was the dominant mechanism for HOI/I2 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/I2 and attenuate I-THMs formation in the subsequent disinfection process.

Enhanced coagulation and oxidation by the Mn(VII)-Fe(III)/peroxymonosulfate process: Performance and mechanisms.

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 (SO4•-) 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.

Occurrence of fungal spores in drinking water: A review of pathogenicity, odor, chlorine resistance and control strategies.

Fungi in drinking water have been long neglected due to the lack of convenient analysis methods, widely accepted regulations and efficient control strategies. However, in the last few decades, fungi in drinking water have been widely recognized as opportunity pathogens that cause serious damage to the health of immune-compromised individuals. In drinking water treatment plants, fungal spores are more resistant to chlorine disinfection than bacteria and viruses, which can regrow in drinking water distribution systems and subsequently pose health threats to water consumers. In addition, fungi in drinking water may represent an ignored source of taste and odor (T&O). This review identified 74 genera of fungi isolated from drinking water and presented their detailed taxonomy, sources and biomass levels in drinking water systems. The typical pathways of exposure of water-borne fungi and the main effects on human health are clarified. The fungi producing T&O compounds and their products are summarized. Data on free chlorine or monochloramine inactivation of fungal spores and other pathogens are compared. At the first time, we suggested four chlorine-resistant mechanisms including aggregation to tolerate chlorine, strong cell walls, cellular responses to oxidative stress and antioxidation of melanin, which are instructive for the future fungi control attempts. Finally, the inactivation performance of fungal spores by various technologies are comprehensively analyzed. The purpose of this study is to provide an overview of fungi distribution and risks in drinking water, provide insight into the chlorine resistance mechanisms of fungal spores and propose approaches for the control of fungi in drinking water.

Chlorine dioxide-based oxidation processes for water purification：A review.

Chlorine dioxide (ClO2) 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 ClO2-based oxidation processes used in water treatment. A systematic review of scientific information and experimental data on ClO2-based water purification procedures is presented. Concerning ClO2-based oxidation derivative problems, the pros and cons of ClO2-based combined processes are assessed and disinfection by-product (DBP) control approaches are proposed. The kinetic and mechanistic data on ClO2 reactivity towards micropollutants are discussed. ClO2 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 ClO2. Future applications include the combination of ClO2 with ferrous ions, activated carbon, ozone, UV, visible light, or persulfate processes. The combined process can reduce by-product generation while still ensuring ClO2 sterilization and disinfection. Overall, this research could provide useful information and new insights into the application of ClO2-based technologies.

Micropollutant removal and disinfection byproduct control by sequential peroxymonosulfate-UV treatment in water: A case study with sulfamethoxazole.

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.

Insight into the formation of iodinated trihalomethanes during chlorination, monochloramination, and dichloramination of iodide-containing water.

In this study, the formation of iodinated trihalomethanes (I-THMs) was systematically evaluated and compared for three treatment processes - (i) chlorination, (ii) monochloramine, and (iii) dichloramination - under different pH conditions. The results demonstrated that I-THM formation decreased in the order of monochloramination > dichloramination > chlorination in acidic and neutral pH. However, the generation of I-THMs increased in the dichloramination < chlorination < monochloramination order in alkaline condition. Specifically, the formation of I-THMs increased as pH increased from 5 to 9 during chlorination and monochloramination processes, while the maximum I-THM formation occurred at pH 7 during dichloramination. The discrepancy could be mainly related to the stability of the three chlor (am) ine disinfectants at different pH conditions. Moreover, in order to gain a thorough insight into the mechanisms of I-THM formation during dichloramination, further investigation was conducted on the influencing factors of DOC concentration and Br-/I- molar ratio. I-THM formation exhibited an increasing and then decreasing trend as the concentration of DOC increased from 1 to 7 mg-C/L, while the yield of I-THMs increased with increasing Br-/I- molar ratio from 5:0 to 5:10. During the three processes mentioned above, similar I-THM formation results were also obtained in real water, which indicates that the excessive generation of I-THMs should be paid special attention during the disinfection of iodide-containing water.

Enhanced degradation of emerging contaminants by permanganate/quinone process: Case study with bisphenol A.

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 MnO2. A novel mechanism was proposed that singlet oxygen (1O2), Mn(III)-ligands (Mn(III)-L) and in-situ formed MnO2 were the main contributors to accelerate BPA degradation in the Mn(VII)/BQ system. Under acidic conditions, the in-situ formed MnO2 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.

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

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

Enhanced formation of iodinated trihalomethanes in a mixed chlorine/chloramine system and attenuation by UV-activated process.

Iodinated trihalomethanes (I-THMs) have drawn increasing concerns due to their higher toxicity than those of their chlorinated and brominated analogues. In this study, I-THM formation was firstly evaluated for three treatment scenarios - (i) chlorine alone, (ii) chloramine alone, and (iii) mixed chlorine/chloramine - in the presence and absence of UV irradiation for the iodide-containing humic acid solution or natural water. The results indicated that I-THM formation decreased in the order of mixed chlorination/chloramination > chloramination > > chlorination, which fitted the trend of toxicity evaluation results using Chinese hamster ovary cells. Conversely, total organic halide concentration decreased in the order of chlorination > > chloramination ≈ mixed chlorination/chloramination. Besides, I-THM formation can be efficiently controlled in a UV-activated mixed chlorine/chloramine system. Influencing factors including pH values and Br-/I- molar ratios were also systematically investigated in a mixed chlorine/chloramine system. Enhanced I-THM formation was observed with increasing pH values (6.0-8.0) and Br-/I- molar ratios (1: 1-10: 1). The results obtained in this study can provide new insights into the increasing risk of I-THM formation in a mixed chlorine/chloramine system and the effective control of I-THMs in the iodide-containing water using UV irradiation.

Formation and control of organic chloramines and disinfection by-products during the degradation of pyrimidines and purines by UV/chlorine process in water.

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 (kobs), 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 kobs, chlorine,kobs, •OH and kobs, 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.

The formation, analysis, and control of chlor(am)ination-derived odor problems: A review.

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 (O3/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.

The application of UV-C laser in persulfate activation for micropollutant removal: Case study with iodinated X-ray contrast medias.

A novel light source UV-C laser was applied in persulfate (PS) activation to effectively remove iodinated X-ray contrast medias (ICMs) including iohexol (IOX), iopamidol (IPM) and diatrizoate (DTZ) in this study. Significant ICMs degradation was observed in UV-C laser/PS systems with pseudo first-order rate constants of 0.022-0.067 s-1. Sulfate radicals (SO4•-) were the main active species in the three ICMs degradation, and the steady-state concentrations ([SO4•-]ss) were 3.629 × 10-11 M (IOX), 1.702 × 10-11 M (IPM) and 1.148 × 10-11 M (DTZ), respectively. Under the high intensity of UV-C laser, the optimal reaction efficiency was achieved at pH = 7.0 with PS concentration of 1.0 mM, and the degradation efficiency for IOX reached 93.8% within only 40 s. Both bicarbonate and chloride ions could inhibit the three ICMs degradation and the inhibition rate increased with the increase of ions concentration. The kinetic models were established and the steady-state concentrations of radicals were calculated. Density functional theory (DFT) calculations combined with experiments were used to derive the reaction pathways for three ICMs. Cyclic voltammetry measurements detected a lower redox potential peak in IOX degradation, revealing the existence of electron shuttles under the UV-C laser irradiation to promote the redox reaction. This study is the first report of UV-C laser activation of persulfate. It is a new advanced oxidation process mediated by very effective photolysis and active species formation.

Degradation kinetics of prometryn and formation of disinfection by-products during chlorination.

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 (kapp) appeared at pH 5 with the observed rate constant (kobs) as 190. 08 h-1; the minimum value of kapp reached at pH 9 with kobs 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.

Photodegradation pathway of iodate and formation of I-THMs during subsequent chloramination in iodate-iodide-containing water.

This study investigated the mechanisms of mixed IO3-/I- system under UV irradiation in drinking water and compared the iodinated trihalomethanes (I-THMs) formation of a mixed IO3-/I- system to that of single I- and IO3- systems during subsequent chloramination. The effects of initial I-/IO3- molar ratio, pH, and UV intensity on a mixed IO3-/I- system were studied. The introduction of I- enhanced the conversion rate of IO3- to reactive iodine species (RIS). Besides, IO3- degradation rate increased with the increase of initial I- concentration and UV intensity and the decrease of pH value. In a mixed IO3-/I- system, IO3- could undergo direct photolysis and photoreduction by hydrated electron (eaq-). Moreover, the enhancement of I-THM formation in a mixed IO3-/I- system during subsequent chloramination was observed. The I-THM yields in a mixed IO3-/I- system were higher than the sum of I-THMs produced in a single IO3- and I- systems at all the evaluated initial I- concentrations and pH values. The difference between I-THM formation in a mixed IO3-/I- system and the sum of I-THMs in a single IO3- 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 IO3-/I- system and single I- and IO3- systems decreased slightly. Besides, IO3--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 IO3--containing water.

Iodinated trihalomethanes formation in iopamidol-contained water during ferrate/chlor(am)ination treatment.

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), IO3- 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.