Drinking Water Disinfection Processes Research Articles

Profiling organic pollutants in environmental water by dansylation-based non-targeted liquid chromatography-high resolution mass spectrometry analysis

Monitoring organic pollutants in rainwater is important to understand relations between air pollutants and water safety. Non-targeted liquid chromatography–mass spectrometry (LC–MS) is a powerful tool but because of big differences of pollutants in polarity, ionization efficiency, and low concentrations, it is challenging to detect all pollutants in a single analysis. Chemical derivatization is a widely adapted strategy to fractionate complex samples with enhanced sensitivity and selectivity. Herein, we propose the usage of dansylation as a chemical derivatization method to improve both LC retention and MS ionization of organic pollutants containing amine, hydroxyl, and carboxyl for non-targeted LC–MS analysis. We first evaluated the labeling coverage of dansylation to organic pollutants in water matrix. Using dansyl chloride (DnsCl) and dansyl hydrazine (DnsHz) to label 100 amine- and hydroxyl-containing compounds and 100 carboxyl compounds, respectively, we found DnsCl and DnsHz had over 60% labeling coverage for 8 categories of compounds. Then dansylation was applied to label the rainwater, source water, disinfected rainwater, and drinking water samples. To facilitate the annotation of dansylated compounds, we also established a web-based tool termed DansylFinder. Using DansylFinder, 3889, 5813, 6077, and 4050 tentative annotations were found in rainwater, source water, disinfected rainwater, and drinking water samples by dansylation-based non-targeted LC-HRMS analysis. Four hundred fifty four were persistently detected in all water samples, suggesting significant organic overlaps of the four water samples. In addition, two degradation pathways reported in drinking water disinfection process were also detected in disinfected rainwater, suggesting rainwater is a potential path for air pollutants to infiltrate drinking water system.

N-nitrosamines induced gender-dimorphic effects on infant rats at environmental levels

The safety of drinking water has always been a concern for people all over the world. N-nitrosamines (NAs), a kind of nitrogenous disinfection by-products (N-DBPs), are generally detected as a mixture in drinking water at home and abroad. Studies have shown that individual NAs posed strong carcinogenicity at high concentrations. However, health risks of NAs at environmental levels (concentrations in drinking water) are still unclear. Therefore, the potential health risks of environmentally relevant NAs exposure in drinking water needs to be conducted. In this study, blood biochemical analysis and metabolomics based on nuclear magnetic resonance (NMR) were performed to comprehensively investigate NAs induced metabolic disturbance in infant rats at environmental levels. Results of blood biochemical indices analysis indicated that AST in the serum of male rats in NAs-treated group exhibited a significant gender-specific difference. Multivariate statistics showed that two and eight significantly disturbed metabolic pathways were identified in the serum samples of NAs-treated male and female rats, respectively. In the urine samples of NAs-treated female rats, glycine, serine, and threonine metabolism pathway was significantly disturbed; while three significantly disturbed metabolic pathways were found in the urine of NAs-treated male rats. Finally, results of spearman correlation coefficients suggested that the disturbances of metabolism profile in serum and urine were correlated with changes in the gut microbiota (data derived from our published paper). Data presented here aimed to generate new health risk data of NAs mixture exposure at environmental levels and provide theoretical support for drinking water safety management. Environmental implicationN-nitrosamines (NAs) are a kind of nitrogenous disinfection by-products (N-DBPs) generated during drinking water disinfection processes. Herein, health risks of NAs at environmental levels (concentrations in drinking water) are investigated using blood biochemical analysis and nuclear magnetic resonance (NMR)-based metabolomics. Results confirmed NAs induced gender-specific on the metabolism in rat and the disturbances of metabolism profile in serum and urine were correlated with changes in the gut microbiota. Data presented here aimed to generate new health risk data of NAs mixture exposure at environmental levels and provide theoretical support for drinking water safety management.

Convenient recycling and efficient photocatalytic degradation of disinfection by-products by in-situ growth MOF on PET

Drinking water disinfection processes have made remarkable contributions to keeping drinking water safe. However, these processes can lead to the formation of numerous harmful disinfection by-products (DBPs). Therefore, it is crucial to implement effective measures to minimize the production of DBPs. Herein, PET@PDA@NH2-MIL-53(Fe) (PNM) composite was successfully prepared via surface etching and solvothermal method. The material exhibited excellent photocatalytic activity for DBPs and their precursors at the photo-Fenton system formed by PNM and trace H2O2, which system achieved 99% degradation of 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) in 30 min, and more than 98% and 95% degradation of phenol and bisphenol A (BPA) in 60 min. The PNM shows more than 90% degradation of DBPs even in real water. Based on free radical trapping experiments, a possible catalytic mechanism was proposed. ·OH and holes were the main active species in the catalytic process. Meanwhile, using UPLC-QTOF and GC–MS to identify intermediate degradation products and Toxtree software to assess toxicity. The PNM maintained a degradation rate over 95% after 5 cycles which demonstrates a remarkable recyclability. This study achieves the reuse of waste PET and opens a new way in exploring the development of eco-friendly photocatalytic materials.

Method for establishing predictive models for total organic halogen based on piecewise interpolation and machine learning

In disinfection by-product (DBP) research, the parameter ‘total organic halogen’ (TOX) is a significant aggregate indicator and reports the total content of halogenated DBP in water, determined in a single experimental process. TOX modeling can facilitate the prediction, diagnosis, and control of the drinking water disinfection process. The modeling approach is often based on the reaction mechanisms of the disinfection process. However, building an accurate TOX model is difficult due to the complexity and nonlinearity of the disinfection reaction mechanisms, and many simplifications have been made in the modeling process, resulting in poor adaptability of the TOX model in practical applications. Machine learning algorithms are data-driven modeling methods that can achieve high prediction accuracy and are simple and convenient to apply. However, in practical experiments, the TOX dataset is often small (usually < 10 points), making TOX modeling through machine learning algorithms particularly difficult. To solve this issue, this study established a method using piecewise interpolation to expand the TOX dataset and subsequently machine learning algorithms to establish the model. Three common machine learning algorithms, backpropagation neural network, radial basis function neural network, and support vector machine, were used to evaluate the data expansion method. The modeling of TOX for a chloramination and chlorination disinfection process shows that this method can achieve satisfactory results regarding sensitivity and accuracy. All the models provided favorable predictions, with relatively high correlation coefficients (> 0.99) and low mean square errors (< 5.31 × 10−5).

Structural, electronic and optical properties of ZnO and TiO2 nanoparticles for wastewater treatment: A first-principles study

Water quality deteriorates when industrial and human activities increase. This means that toxins must be removed from industrial and domestic wastewater. In the context of nanotechnology, anchoring TiO2 and ZnO nanoparticles on clay has also been shown to be potential sequesters and has been examined for wastewater treatment. This paper presents a thorough investigation of the structural, electronic, and optical featuresof ZnO & TiO2 nanoparticles using the GGA-PBE functional within the framework of density functional theory (DFT). For ZnO and TiO2 nanoparticles, there is excellent agreement between the calculated lattice parameters and the findings of the experiments. Electronic structure calculations confirm that both ZnO and TiO2 are semiconducting in nature. The density of states calculation reveals that the conduction band in TiO2 is primarily derived from hybridization between Ti-3d states and O-2p states, whereas the valence band is derived from mixing between Ti-3d and O-2p states. Further, ZnO, O-2p, andZn-3d states, primarily contributed to the valence band, while Zn-4 s and Zn-3p states mainly contributed to the conduction band. Since drinking water disinfection processes frequently involve ultraviolet (UV) absorption based advanced oxidation process. Investigations of the optical properties of these two materials suggest that ZnO and TiO2 show great potential as strong UV-absorbing and photocatalytic materials, and can be utilized as microbial disinfectants during wastewater treatment.

Effect of ozone–tea polyphenols as a drinking water disinfection process on antibiotic resistance genes

Abstract In recent years, the wide spread of antibiotic resistance genes (ARGs) has brought tremendous risk to the biological safety of drinking water. With the increasing demand for drinking water quality, ARGs have been regarded as a new pollutant that may cause serious public health problems. A large number of studies have shown that the disinfection process of drinking water treatment plants can remove ARGs. However, the effects of traditional disinfection methods on ARGs have their own disadvantages. Tea polyphenols have attracted more and more researchers’ attention as a green, efficient and non-disinfection by-products disinfectant. The effect of the ozone–tea polyphenols disinfection process on ARGs in filtered effluent of waterworks was analyzed by using metagenomic sequencing. The result shows that the ozone–tea polyphenols disinfection process is suitable for specific raw water containing more tetracycline, sulfonamide, β-lactam, and aminoglycoside resistance genes, and the removal rate of total resistance genes in water is higher than the traditional disinfection process. The effect of the ozone–tea polyphenols disinfection process on ARGs is to reduce the transfer of ARGs by destroying ARGs molecules and inhibiting the proliferation of ARGs host cells. As an assistant disinfectant, tea polyphenols have significance for the ability to remove ARGs during traditional disinfection.

Degradation of 2,6-dichloro-1,4-benzoquinone by UV/H2O2/O3 treatment: Effectiveness, water matrix effects, and degradation mechanism

2,6-dichloro-1,4-benzoquinone (DCBQ), a typical representative of Halobenzoquinones, is an emerging aromatic disinfection by-product (DBP) with high toxicity and carcinogenicity, generated commonly through the chlorination in the drinking water disinfection process while there is still a lack of research on its removal. In this study, the effects of ultraviolet-based advanced oxidation processes (UV-AOPs) on the degradation of DCBQ were evaluated. The results showed that UV-AOPs are effective in degrading DCBQ. The removal of DCBQ by UV/H2O2/O3 was more significant than by UV/H2O2 or UV/O3, achieving a 96.7% removal rate at both the O3 and H2O2 doses of 1 mg/L. The results also indicated the alkaline and weakly acidic environments could facilitate the degradation of DCBQ, inorganic anions could inhibit DCBQ degradation and the degree of inhibition increased as the matrix concentration increased. The degradation of DCBQ was inhibited more by the CO32− than the other matrix components, such as Cl− and NO3−. It was shown by the density functional theory simulations and the ultrahigh-performance liquid chromatography (UPLC) - Orbitrap mass spectra that the electrons in DCBQ are mainly on the chlorine atom connected to the carboatomic ring and that OH• can attack the chlorine atom to cause de-chlorination. The DCBQ degradation pathway may involve the oxidation of DCBQ to 3-hydroxy-2,6-DCBQ (HO–DCBQ) and 3,5-dichloro-1,2,4-pyrogallol, the further degradation of intermediate products by OH• to dechlorinated forms of HO–DCBQ and DCBQ.

Degradation of nano-sized polystyrene plastics by ozonation or chlorination in drinking water disinfection processes

The presence of nanoplastics in drinking water inducing inevitable exposure to human beings has aroused considerable attention. It is worth evaluating the degradation and even mineralization of nanoplastics in drinking water treatment plants designed for guaranteeing drinking water safety. Herein we mainly focus on the decomposition of nano-sized polystyrene plastics by two commonly used disinfection techniques, namely ozonation and chlorination. At recommended dosage for disinfection, ozonation achieves 99.9% molecular weight (MW) degradation and 42.7% mineralization of nano-sized polystyrene plastics in 240 min, while chlorination only attains 7.1% MW degradation and 4.3% mineralization. The overwhelming MW degradation is concentrated in first 30 min with 96.3% for ozonation and 4.2% for chlorination. With the proceeding of ozonation, the surface of nano-sized polystyrene plastics becomes rough and the particle size is decreased, during which the introduction of oxygen-containing groups on the surface of nano-sized polystyrene plastics increases the hydrophilicity of plastics, thus contributing to the further oxidative degradation to produce formic acid, phenol, acetophenone, hydroquinone and other products. However chlorination cannot roughen the surface of nano-sized polystyrene plastics, and only destroys a small amount of C-C bonds in main chain to form shorter chains polymers. This finding shows ozonation other than chlorination is available and effective for degradation of nano-sized polystyrene plastics, indicating that ozonation could be employed as a potential technique to tackle nanoplastics pollution in drinking water treatment plants.

Multispecies Interactions in Biofilms and Implications to Safety of Drinking Water Distribution System

In the aquatic environment, microorganisms are predominantly organized as biofilms. Biofilms are formed by the aggregation of microbial cells and are surrounded by a matrix of extracellular polymeric substances (EPS) secreted by the microbial cells. Biofilms are attached to various surfaces, such as the living tissues, indwelling medical devices, and piping of the industrial potable water system. Biofilms formed from a single species has been extensively studied. However, there is an increased research focus on multispecies biofilms in recent years. It is important to assess the microbial mechanisms underlying the regulation of multispecies biofilm formation to determine the drinking water microbial composition. These mechanisms contribute to the predominance of the best-adapted species in an aquatic environment. This review focuses on the interactions in the multispecies biofilms, such as coaggregation, co-metabolism, cross-species protection, jamming of quorum sensing, lateral gene transfer, synergism, and antagonism. Further, this review explores the dynamics and the factors favoring biofilm formation and pathogen transmission within the drinking water distribution systems. The understanding of the physiology and biodiversity of microbial species in the biofilm may aid in the development of novel biofilm control and drinking water disinfection processes.

Integrating terrestrial and aquatic processes toward watershed scale modeling of dissolved organic carbon fluxes

Dissolved organic carbon (DOC) is not only a critical component of global and regional carbon budgets, but also an important precursor for carcinogenic disinfection byproducts (DBP) generated during drinking water disinfection process. The lack of process based watershed scale model for carbon cycling has been a limiting factor impeding effective watershed management to control DOC fluxes to source waters. Here, we integrated terrestrial and aquatic carbon processes into the widely tested Soil and Water Assessment Tool (SWAT) watershed model to enable watershed-scale DOC modeling (referred to as SWAT-DOC hereafter). The modifications to SWAT mainly fall into two groups: (1) DOC production in soils and its transport to aquatic environment by different hydrologic processes, and (2) riverine transformation of DOC and their interactions with particular organic carbon (POC), inorganic carbon and algae (floating and bottom). We tested the new SWAT-DOC model in the Cannonsville watershed, which is part of the New York City (NYC) water supply system, using long-term DOC load data (from 1998 to 2012) derived from 1399 DOC samplings. The calibration and verification results indicate that SWAT-DOC achieved satisfactory performance for both streamflow and DOC at daily and monthly temporal scales. The parameter sensitivity analysis indicates that DOC loads in the Cannonsville watershed are controlled by the DOC production in soils and its transport in both terrestrial and aquatic environments. Further model uncertainty analysis indicates high uncertainties associated with peak DOC loads, which are attributed to underestimation of high streamflows. Therefore, future efforts to enhance SWAT-DOC to better represent runoff generation processes hold promise to further improve DOC load simulation. Overall, the wide use of SWAT and the satisfactory performance of SWAT-DOC make it a useful tool for DOC modeling and mitigation at the watershed scale.

The toxic potentials and focus of disinfection byproducts based on the human embryonic kidney (HEK293) cell model

Disinfection byproducts (DBPs) are inevitably generated during drinking water disinfection processes, and their hazards have not been well characterized. Because they plausibly cause toxicological and pathological damage to human kidney, we selected the human embryonic kidney (HEK293) cell, instead of the commonly used CHO cell, as a model to investigate the toxic potential and target of 10 DBPs, including 3 haloacetamides, 2 trihaloacetaldehydes and 5 iodomethanes. Based on the chronic toxicity parameter EC10 of the cell viability test, we obtained a toxic rank of the tested DBPs different from previous studies and calculated their risk quotients by combining their actual concentrations in drinking water systems. Then, dichloroacetamide (DCAM), trichloroacetaldehyde (TCAL), and bromochloroiodomethane (BCIM) were selected to conduct multiple mechanistic bioassays, including cellular lactate dehydrogenase (LDH) assay, ATP metabolism, ROS production, mitochondria-derived apoptosis and qRT-PCR assay. All bioassays revealed the effects of interrupting the molecular, physiological and biochemical processes relevant to mitochondrial functions, such as oxidative respiration, apoptosis, and energy metabolism. Our study improved the human risk assessment of DBPs with the help of a convenient model and parameter and revealed that mitochondrion is a potential toxic focus of DBPs exposure at the cellular level.

MS2 coliphage and E. coli UVB inactivation rates in optically clear water: dose, dose rate and temperature dependence.

Natural ultraviolet irradiance disinfection is known to play a significant role in both natural wastewater treatment systems and drinking water disinfection processes, while the influence of ultraviolet B (UVB) delivering method on sunlight disinfection outcome is still unclear. This study aims to determine the effects of environmentally relevant temperatures, UVB doses (J m-2) and dose rates (W m-2) on the inactivation and log reduction values (LRVs) of the F-RNA coliphage MS2 and Escherichia coli in optically clear water. E. coli and MS2 were separately incubated and irradiated at five different doses of UVB light that delivered using six UVB dose rates. The results of the study demonstrate that the UVB dose delivering method (combination of dose rate and exposure time) influences inactivation and LRVs of E. coli and MS2 at all UVB doses investigated (up to seven-fold difference). Two phases were identified within the UVB dose rate, UVB inactivation or LRV curves for both organisms; a UVB dose rate limited inactivation phase and a dose rate saturation inactivation phase. The results contribute to a better understanding of UVB disinfection in the environment and natural wastewater treatment systems, potentially improving the design and operation of high rate algal ponds.

Chlorination and chloramination of benzophenone-3 and benzophenone-4 UV filters

The objective of this research was to explore the fundamental reactions between chlorine/chloramine and 2-hydroxyl-4-methoxyl benzophenone (BP3)/2-hydroxyl-4-methoxyl benzophenone-sulfonic acid (BP4), which were the most common reactions in benzophenone-type UV filters during drinking water treatment processes. Both BP3 and BP4 could react with free chlorine and chloramine, with reactions following pseudo-first-order kinetics in excess of chlorine (HClO) and chloramine (NH2Cl). Generally, chlorination was more rapid than chloramination. BP4 was less reactive than BP3 toward both chlorine and chloramine, due to the presence of an electron-accepting sulfonate group. Therefore, BP3 had a significantly higher disinfection by-products (DBP) formation potential than BP4. Chlorination of BP3 and BP4 generated remarkably higher levels of DBPs than chloramination, with high pH conditions facilitating the formation of chloroform but inhibiting the formation of haloacetic acid (HAAs). Comparison of the reaction behavior of two different BP-type UV filters, i.e., BP3 and BP4, revealed that certain functional groups significantly affected the reactivity of BP-type UV filters in chlorination and chloramination processes. This contribution may provide new insights into the reaction behavior of UV filters during drinking water disinfection process using chlorine and/or chloramine as disinfectant, and provide guidelines for drinking water safety management.

Role of ammonia on haloacetonitriles and halonitromethanes formation during Ultraviolet irradiation followed by chlorination/chloramination

Combination of ultraviolet (UV) disinfection and chlorination became a common multi-barrier approach taken by water utilities against microbial pathogens in drinking water disinfection. Halogenated disinfection byproducts (DBPs) have been monitored and regulated in drinking water under various jurisdictions around the world for decades. More recently, several nitrogenous DBPs (N-DBPs), like haloacetonitriles (HANs) and halonitromethanes (HNMs), have been identified in chlorinated drinking waters, whose precursors are N-containing organic compounds of various origins and structures. Rising concerns over the N-DBPs formation due to their more potent genotoxic and cytotoxic activity than the regulated carbonaceous-DBPs have prompted extensive research on drinking water disinfection processes. To examine the effect of ammonia nitrogen (NH3-N) on N-DBPs formation during UV disinfection of drinking water followed by chlorination/chloramination, as a first attempt, synthetic waters prepared by humic acid with different NH3-N concentrations were exposed to UV dose up to 300 mJ/cm2 from either low pressure (LP) or medium pressure (MP) lamps, followed by chlorination/chloramination. To investigate trends, the study employed synthetic waters with elevated precursor concentrations and disinfectant exposures to generate significant byproduct formation possible. LP UV treatment had no obvious effect on N-DBP formation, whereas MP UV irradiation produced more dichloroacetonitrile (DCAN). The existence of ammonia (≤1 mg/L-N) increased DCAN concentration in high organics synthetic waters under varying MP UV doses, respectively. In high organics synthetic water samples exposed to a MP UV dose of 300 mJ/cm2 DCAN reached a maximum yield of 13.7 μg/L in the presence of 0.5 mg/L NH3-N, whereas lower yields were observed at NH3-N ≥ 2 mg/L, i.e. 2.9 μg /L and 1.8 μg/L at 2 and 10 mg/L NH3-N, respectively.

Chemically modified chitosan polymers for bromate removal

Bromate is a harmful byproduct formed during drinking water disinfection processes. In this work, adsorption of bromate by natural chitosan and its chemically modified polymers has been investigated. Bromate adsorption was found between 22.73 mg/g and 43.48 mg/g. Adsorbents were analysed by Fourier transform infrared-ATR spectroscopy. It is suggested that chemical adsorption is the main bromate adsorption mechanism. By fitting theoretical results to experimental data, it is shown that the Langmuir adsorption model and the second-order kinetic model are more applicable to explain the adsorption process. Furthermore, increased bromate adsorption is found at high temperature and at low pH, while coexisting ions have little influence at low concentrations.

Rural Drinking Water Disinfection Technology and Research Progress of Application

With the living standards improvement of rural residents, people pay more attention to the safety of drinking water in China. As the final step in drinking water treatment, disinfection technology has received much attention. At present, drinking water disinfection process is mainly involved in chlorine disinfection, chlorine dioxide disinfection, chloramine disinfection, disinfection of potassium permanganate, ozone disinfection and ultraviolet disinfection. However, due to limitations in rural economic conditions and management level, only ozone disinfection and ultraviolet disinfection are suitable for rural areas in China. This paper described some of the application problems and limitations in drinking water disinfection process, as well as the select principle in rural areas. The principle, research status, trends and issues in application of ozone and ultraviolet disinfection technology were emphatically introduced. Finally, the development of drinking water disinfection technologies was discussed.

Palladium Nanoparticles Encapsulated in Core–Shell Silica: A Structured Hydrogenation Catalyst with Enhanced Activity for Reduction of Oxyanion Water Pollutants

Noble metal nanoparticles have been applied to mediate catalytic removal of toxic oxyanions and halogenated hydrocarbons in contaminated water using H2 as a clean and sustainable reductant. However, activity loss by nanoparticle aggregation and difficulty of nanoparticle recovery are two major challenges to widespread technology adoption. Herein, we report the synthesis of a core–shell-structured catalyst with encapsulated Pd nanoparticles and its enhanced catalytic activity in reduction of bromate (BrO3–), a regulated carcinogenic oxyanion produced during drinking water disinfection process, using 1 atm H2 at room temperature. The catalyst material consists of a nonporous silica core decorated with preformed octahedral Pd nanoparticles that were further encapsulated within an ordered mesoporous silica shell (i.e., SiO2@Pd@mSiO2). Well-defined mesopores (2.3 nm) provide a physical barrier to prevent Pd nanoparticle (∼6 nm) movement, aggregation, and detachment from the support into water. Compared to free...

Determination of secondary and tertiary amines as N-nitrosamine precursors in drinking water system using ultra-fast liquid chromatography–tandem mass spectrometry

N-Nitrosamines are potent mutagenic and carcinogenic emerging water disinfection by-products (DBPs). The most effective strategy to control the formation of these DBPs is minimizing their precursors from source water. Secondary and tertiary amines are dominating precursors of N-nitrosamines formation during drinking water disinfection process. Therefore, the screening and removal of these amines in source water are very essential for preventing the formation of N-nitrosamines. A rapid, simple, and sensitive ultrafast liquid chromatography–tandem mass spectrometry (UFLC-MS/MS) method has been developed in this study to determine seven amines, including dimethylamine, ethylmethylamine, diethylamine, dipropylamine, trimethylamine, 3-(dimethylaminomethyl)indole, and 4-dimethylaminoantipyrine, as major precursors of N-nitrosamines in drinking water system. No sample preparation process is needed except a simple filtration. Separation and detection can be achieved in 11min per sample. The method detection limits of selected amines are ranging from 0.02μg/L to 1μg/L except EMA (5μg/L), and good calibration linearity was achieved. The developed method was applied to determine the selected precursors in source water and drinking water samples collected from Midwest area of the United States. In most of water samples, the concentrations of selected precursors of N-nitrosamines were below their method detection limits. Dimethylamine was detected in some of water samples at the concentration up to 25.4μg/L.

Nano-silver in drinking water and drinking water sources: stability and influences on disinfection by-product formation

Nano-silver is increasingly used in consumer products from washing machines and refrigerators to devices marketed for the disinfection of drinking water or recreational water. The nano-silver in these products may be released, ending up in surface water bodies which may be used as drinking water sources. Little information is available about the stability of the nano-silver in sources of drinking water, its fate during drinking water disinfection processes, and its interaction with disinfection agents and disinfection by-products (DBPs). This study aims to investigate the stability of nano-silver in drinking water sources and in the finished drinking water when chlorine and chloramines are used for disinfection and to observe changes in the composition of DBPs formed when nano-silver is present in the source water. A dispersion of nano-silver particles (10 nm; PVP-coated) was used to spike untreated Ottawa River water, treated Ottawa River water, organic-free water, and a groundwater at concentrations of 5 mg/L. The diluted dispersions were kept under stirred and non-stirred conditions for up to 9 months and analyzed weekly using UV absorption to assess the stability of the nano-silver particles. In a separate experiment, Ottawa River water containing nano-silver particles (at 0.1 and 1 mg/L concentration, respectively) was disinfected by adding sodium hypochlorite (a chlorinating agent) in sufficient amounts to maintain a free chlorine residual of approximately 0.4 mg/L after 24 h. The disinfected drinking water was then quenched with ascorbic acid and analyzed for 34 neutral DBPs (trihalomethanes, haloacetonitriles, haloacetaldehydes, 1,1 dichloro-2-propanone, 1,1,1 trichloro-2-propanone, chloropicrin, and cyanogen chloride). The results were compared to the profile of DBPs obtained under the same conditions in the absence of nano-silver and in the presence of an equivalent concentration of Ag+ ions (as AgNO3). The stability of the nano-silver dispersions in untreated Ottawa River water, with a dissolved organic carbon concentration of 6 mg/L, was significantly higher than the stability of the nano-silver dispersions in distilled, organic-free water. Nano-silver particles suspended in the groundwater agglomerated and were quickly and quantitatively removed from the solution. Our data confirm previous observations that natural dissolved organic matter stabilizes nano-silver particles, while the high-ionic strength of groundwater appears to favor their agglomeration and precipitation. As expected, nano-silver was not stable in Ottawa River water through the chlorination process, but survived for many days when added to the Ottawa River water after treatment with chlorine or chloramines. Stirring appeared to have minimal effect on nano-silver stability in untreated and treated Ottawa River water. The profile of DBPs formed in the presence of nAg differed significantly from the profile of DBPs formed in the absence of nAg only at the 1 mg/L nAg concentration. The differences observed consisted mainly in reduced formation of some brominated DBPs and a small increase in the formation of cyanogen chloride. The reduced formation of brominated congeners may be explained by the decrease in available bromide due to the presence of Ag+ ions. It should be noted that a concentration of 1 mg/L is significantly higher than nAg concentrations that would be expected to be present in surface waters, but these results could be significant for the disinfection of some wastewaters with comparably high nano-silver concentrations.

Improving methodological aspects of the analysis of five regulated haloacetic acids in water samples by solid-phase extraction, ion-pair liquid chromatography and electrospray tandem mass spectrometry

Haloacetic acids (HAAs) are organic pollutants originated from the drinking water disinfection process, which ought to be controlled and minimized. In this work a method for monitoring haloacetic acids (HAAs) in water samples is proposed, which can be used in quality control laboratories using the techniques most frequently available. Among its main advantages we may highlight its automated character, including minimal steps of sample preparation, and above all, its improved selectivity and sensitivity in the analysis of real samples. Five haloacetic acids (HAA5) were analyzed using solid-phase extraction (SPE) combined with ion-pair liquid chromatography and tandem mass spectrometry. For the optimization of the chromatographic separation, two amines (triethylamine, TEA and dibutylamine, DBA) as ion pair reagents were compared, and a better selectivity and sensitivity was obtained using DBA, especially for monohaloacetic acids. SPE conditions were optimized using different polymeric adsorbents.The electrospray source parameters were studied for maximum precursor ion accumulation, while the collision cell energy of the triple quadrupole mass spectrometer was adjusted for optimum fragmentation. Precursor ions detected were deprotonated, dimeric and decarboxylated ions. The major product ions formed were: ionized halogen atom (chloride and bromide) and decarboxylated ions. After enrichment of the HAAs in Lichrolut EN adsorbent, the limits of detection obtained by LC–MS/MS analysis (between 0.04 and 0.3ngmL−1) were comparable to those obtained by GC–MS after derivatization. Linearity with good correlation coefficients was obtained over two orders of magnitude irrespective of the compound. Adequate recoveries were achieved (60–102%), and the repeatability and intermediate precision were in the range of 2.4–6.6% and 3.8–14.8%, respectively. In order to demonstrate the usefulness of the method for routine HAAs monitoring, different types of water samples were analyzed. In swimming pool water samples the ∑HAAs were determined between 76 and 154ngmL−1.