Reaction of Amino Acids with Ferrate(VI): Impact of the Carboxylic Group on the Primary Amine Oxidation Kinetics and Mechanism.

Ferrate (Fe(VI)) is a novel oxidant that can be used to mitigate disinfection byproduct (DBP) precursors. However, the reaction of Fe(VI) with organic nitrogen, which is a potential precursor of potent nitrogenous DBPs, remains largely unexplored. The present work aimed to identify the kinetics and products for the reaction of Fe(VI) with primary amines, notably amino acids. A new kinetic model involving ionizable intermediates was proposed and can describe the unusual pH effect on the Fe(VI) reactivity toward primary amines and amino acids. The Fe(VI) oxidation of phenylalanine produced a mixture of nitrile, nitrite/nitrate, amide, and ammonia, while nitroalkane was an additional product in the case of glycine. The product distribution for amino acids significantly differed from that of uncarboxylated primary amines that mainly generate nitriles. A general reaction pathway for primary amines and amino acids was proposed and notably involved the formation of imines, the degradation of which was affected by the presence of a carboxylic group. In comparison, ozonation led to higher yields of nitroalkanes that could be readily converted to potent halonitroalkanes during chlor(am)ination. Based on this study, Fe(VI) can effectively mitigate primary amine-based, nitrogenous DBP precursors with little formation of toxic halonitroalkanes.

Kinetic modelling of the bromine-ammonia system: Formation and decomposition of bromamines.

Bromamines i.e. monobromamine (NH2Br), dibromamine (NHBr2), and tribromamine (NBr3) can be formed during oxidative treatment of waters containing bromide and ammonia. The formation and decomposition of bromamines in aqueous solution was investigated and a comprehensive kinetic model of the bromine-ammonia system was developed at 23 ± 1 °C. Determination of rate constants and model validation were primarily performed at pH 8.0 - 8.3 for subsequent application to seawater disinfection. The rate constant of NHBr2 self-decomposition was determined by second-order rate law linearization with k9 = 5.5 (± 0.8) M-1s-1 at pH 8.10. The rate constant of NBr3 self-decomposition increased proportionately to the concentration of hydroxide ions (OH-) according to the equation k10 = 4.4 (± 0.1) × 107. [OH-] over the pH range 6.0 - 8.5, which gave k10 = 56 (± 1) M-1s-1 at pH 8.10. The rate constants of NHBr2 and NBr3 formation were obtained by fitting model-predicted data to the experimental results and were found to be k3 = 2.3 (± 0.2) × 104M-1s-1 and k5 = 4.0 (± 0.6) × 103M-1s-1, respectively at pH 8.10. NBr3 was also found to react with NHBr2 with k11 = 3.4 (± 0.2) × 103M-1s-1 at pH 8.10. A kinetic model was proposed based on these experimental rate constants and literature values, which provided a good prediction of bromamines formation and decomposition for various initial bromine and ammonia concentrations. The kinetic model was also used to accurately predict the total oxidant concentration and the speciation of bromamines during breakpoint bromination. This study provides kinetic data to model more complex oxidative systems such as seawater chlorination in the presence of ammonia.

Kinetic and mechanistic understanding of chlorite oxidation during chlorination: Optimization of ClO2 pre-oxidation for disinfection byproduct control.

Chlorine dioxide (ClO2) applications to drinking water are limited by the formation of chlorite (ClO2-) which is regulated in many countries. However, when ClO2 is used as a pre-oxidant, ClO2- can be oxidized by chlorine during subsequent disinfection. In this study, a kinetic model for the reaction of chlorine with ClO2- was developed to predict the fate of ClO2- during chlorine disinfection. The reaction of ClO2- with chlorine was found to be highly pH-dependent with formation of ClO3- and ClO2 in ultrapure water. In presence of dissolved organic matter (DOM), 60-70% of the ClO2- was transformed to ClO3- during chlorination, while the in situ regenerated ClO2 was quickly consumed by reaction with DOM. The remaining 30-40% of the ClO2- first reacted to ClO2 which then formed chlorine from the DOM-ClO2 reaction. Since only part of the ClO2- was transformed to ClO3-, the sum of the molar concentrations of oxychlorine species (ClO2- + ClO3-) decreased during chlorination. By kinetic modelling, the ClO2- concentration after 24 h of chlorination was accurately predicted in synthetic waters but was largely overestimated in natural waters, possibly due to a ClO2- decay enhanced by high concentrations of chloride and in situ formed bromine from bromide. Understanding the chlorine-ClO2- reaction mechanism and the corresponding kinetics allows to potentially apply higher ClO2 doses during the pre-oxidation step, thus improving disinfection byproduct mitigation while keeping ClO2-, and if required, ClO3- below the regulatory limits. In addition, ClO2 was demonstrated to efficiently degrade haloacetonitrile precursors, either when used as pre-oxidant or when regenerated in situ during chlorination.

Brominated trihalamines in chlorinated seawaters: Quantification of tribromamine and identification of bromochloramines by Membrane Introduction Mass Spectrometry.

During chlorination of seawater, the presence of bromide and ammonia alters the speciation of the oxidant and lead to the formation of chlorinated and brominated amines. This can affect the effectiveness of the disinfection treatment and the formation of disinfection by-products released to the environment. In this study, a Membrane Introduction Mass Spectrometry (MIMS) analytical method was developed to differentiate brominated trihalamines (i.e. tribromamine NBr3, dibromochloramine NBr2Cl and bromodichloramine NBrCl2) in synthetic and natural chlorinated seawater. A mass-to-charge ratio of m/z = 253 corresponding to the parent ion was used for the quantification of NBr3 in absence of organic matter and the signal of the fragment at m/z = 177 was chosen in presence of high concentration of organic matter. Limits of detection were 0.23 µM (49 µg Cl2/L) and 0.18 µM (38 µg Cl2/L) for m/z 253 and m/z 177, respectively. Both NBr2Cl and NBrCl2 were monitored in chlorinated seawaters with their respective parent ion at m/z = 207 and m/z = 163 but were not quantified. MIMS results also showed that reaction of brominated trihalamines with natural organic matter (NOM) was a minor pathway for 1-2 mg C/L compared to their auto-decomposition in natural or synthetic seawater. Overall, MIMS was able to unambiguously differentiate and monitor brominated trihalamines for the first time in chlorinated seawater, which was not possible by using UV measurement, titration and colorimetric methods.

Chemical analysis of fresh and aged Australian e-cigarette liquids.

OBJECTIVES: To assess the chemical composition of electronic cigarette liquids (e-liquids) sold in Australia, in both their fresh and aged forms. DESIGN, SETTING: Gas chromatography-mass spectrometry analysis of commercial e-liquids sold in Australia (online and physical stores). MAIN OUTCOME MEASURES: Chemical composition of 65 Australian e-liquids - excipients/solvents, flavouring chemicals, other known e-liquid constituents (including nicotine), and polycyclic aromatic hydrocarbons - before and after an accelerated ageing process that simulated the effects of vaping. RESULTS: The measured levels of propylene glycol and glycerol often diverged from those recorded on the e-liquid label. All e-liquids contained one or more potentially harmful chemicals, including benzaldehyde, menthol, trans-cinnamaldehyde, and polycyclic aromatic hydrocarbons. Nicotine or nicotyrine were detected in a small proportion of e-liquids at extremely low concentrations. CONCLUSIONS: Australian e-liquids contain a wide variety of chemicals for which information on inhalation toxicity is not available. Further analyses are required to assess the potential long term effects of e-cigarette use on health.

Kinetic and mechanistic investigations of the decomposition of bromamines in the presence of Cu(II).

This study demonstrates that Cu(II) can significantly enhance the decomposition rate of bromamines. Apparent second order rate constants of 2.31 ± 0.01 M-1s-1 and 0.36 ± 0.01 M-1s-1 at pH 7.5 were determined for the reaction of Cu(II) with bromamines and the self-decomposition of bromamines, respectively. Increasing the pH from 6.0 to 8.5, the rate of bromamines self-decomposition decreased while the rate of Cu(II)-catalysed decomposition of bromamines increased. Species-specific rate constants indicated that Cu(OH)2 was the most reactive copper species towards NH2Br and NHBr2. Experiments were carried out with 15N-labelled bromamines to analyse the nitrogenous degradation products of bromamines in the presence and absence of Cu(II). Nitrogen gas (N2) was found to be the major product from the self-decomposition of bromamines, with N2O, NO2-, and NO3- as additional minor products. When Cu(II) was present, the product distribution changed and NO2- and N2O became significant, while N2 and NO3- were produced at low levels. Increasing the Cu(II) concentration from 1.0 to 5.0 mg/L increased the N2O production while decreased the NO2- formation. Based on these results, a mechanism for Cu(II)-catalysed decomposition of bromamines is proposed. This work provides new insights related to the chemistry of bromamines in chloraminated drinking water distribution systems where copper is present.

Identification and quantification of chloramines, bromamines and bromochloramine by Membrane Introduction Mass Spectrometry (MIMS).

A Membrane Introduction Mass Spectrometry (MIMS) method was developed to differentiate and quantify the different chlorinated and brominated-amines, present in drinking water during chloramination. The representative mass to charge ratios (m/z) of 53, 85, 97, 175 and 131 corresponding to the mass of the parent compounds were selected to monitor NH2Cl, NHCl2, NH2Br, NHBr2 and NHBrCl and the detection limits were found to be 0.034, 0.034, 0.10, 0.12 and 0.36 mg/L as Cl2, respectively. NHCl2, NHBr2 and NHBrCl fragments interfere with the analysis/quantification of NH2Cl and NH2Br via protonation reactions at hot metal surfaces inside the mass spectrometer. To accurately quantify NH2Cl or NH2Br in mixtures of NH2Cl/NHCl2 or NH2Br/NHBr2, the interference from NHCl2 or NHBr2 was subtracted to the signal of the parent compound. If NHBrCl is present, NH2Br and NH2Cl cannot be accurately quantified since the interference from the NHBrCl fragment cannot be distinguished from the signal of the parent compound. Under drinking water conditions, the interference from NHBrCl on NH2Cl was negligible. The different halamines were monitored and quantified for the first time in two surface waters and one seawater that were chloraminated to mimic a realistic disinfection scenario.

Effect of copper oxide on monochloramine decomposition in bromide-containing waters.

Copper oxide (CuO), a common corrosion product found in copper pipes, has been shown to catalyse the decay of different oxidants in drinking water, including chlorine, bromine, iodine, and chlorine dioxide. However, its impact on monochloramine (NH2Cl), a disinfectant commonly used in long distribution system worldwide is still unknown. In this study, the effect of CuO on NH2Cl decay in the absence or presence of bromide was investigated. Results showed that in the presence of CuO and the absence of bromide, NH2Cl slightly decayed under acidic conditions. When bromide was present in NH2Cl solutions, the total oxidant concentration (sum of the different bromo-chloro-amines) was significantly decreased by CuO. This was primarily due to the degradation of bromochloramine (NHBrCl) by CuO which was evidenced by membrane inlet mass spectrometry. The decomposition rate of the total oxidant was similar for different CuO dosages (0.02-0.2 g/L) but increased with increasing bromide concentration (0-80 µM) and decreasing pH (6.5-8). An apparent second-order rate constant of 0.73 M-1 s-1 was determined with respect to NH2Cl and bromide concentrations for a CuO concentration of 0.05 g/L. Our findings suggest that, during water transportation in copper pipes or in distribution systems where copper oxide is present, special attention should be given to the stability of chloramines when bromide-containing waters are chloraminated.

Efficiency of pre-oxidation of natural organic matter for the mitigation of disinfection byproducts: Electron donating capacity and UV absorbance as surrogate parameters.

Pre-oxidation is often used before disinfection with chlorine to decrease the reactivity of the water matrix and mitigate the formation of regulated disinfection byproducts (DBPs). This study provides insights on the impact of oxidative pre-treatment with chlorine dioxide (ClO2), ozone (O3), ferrate (Fe(VI)) and permanganate (Mn(VII)) on Suwannee River Natural Organic Matter (SRNOM) properties characterized by the UV absorbance at 254 nm (UV254) and the electron donating capacity (EDC). Changes in NOM reactivity and abatement of DBP precursors are also assessed. The impact of pre-oxidants (based on molar concentration) on UV254 abatement ranked in the order O3 > Mn(VII) > Fe(VI)/ClO2, while the efficiency of pre-oxidation on EDC abatement followed the order Mn(VII) > ClO2 > Fe(VI) > O3 and two phases were observed. At low specific ClO2, Fe(VI) and Mn(VII) doses corresponding to < 50% EDC abatement, a limited relative abatement of UV254 compared to the EDC was observed (~ 8% EDC abatement per 1% UV254 abatement). This suggests the oxidation of phenolic-type moieties to quinone-type moieties which absorb UV254 and don't contribute to EDC. At higher oxidant doses (> 50% EDC abatement), a similar abatement of EDC and UV254 (~ 0.9-1.2% EDC abatement per 1% UV254 abatement) suggested aromatic ring cleavage. In comparison to the other oxidants, O3 abated the relative UV254 more effectively, due to a more efficient cleavage of aromatic rings. For a pre-oxidation with Mn(VII), ClO2 and Fe(VI), similar correlations between the EDC abatement and the chlorine demand or the adsorbable organic halide (AOX) formation were obtained. In contrast, O3 pre-treatment led to a lower chlorine demand and AOX formation for equivalent EDC abatement. For all oxidants, trihalomethane formation was poorly correlated with both EDC and UV254. The EDC abatement was found to be a pre-oxidant-independent surrogate for haloacetonitrile formation. These results emphasize the benefits of combining EDC and UV254 measurement to understand and monitor oxidant-induced changes of NOM and assessing DBP formation.

Tracking down carbon inputs underground from an arid zone Australian calcrete.

Freshwater ecosystems play a key role in shaping the global carbon cycle and maintaining the ecological balance that sustains biodiversity worldwide. Surficial water bodies are often interconnected with groundwater, forming a physical continuum, and their interaction has been reported as a crucial driver for organic matter (OM) inputs in groundwater systems. However, despite the growing concerns related to increasing anthropogenic pressure and effects of global change to groundwater environments, our understanding of the dynamics regulating subterranean carbon flows is still sparse. We traced carbon composition and transformations in an arid zone calcrete aquifer using a novel multidisciplinary approach that combined isotopic analyses of dissolved organic carbon (DOC) and inorganic carbon (DIC) (δ13CDOC, δ13CDIC, 14CDOC and 14CDIC) with fluorescence spectroscopy (Chromophoric Dissolved OM (CDOM) characterisation) and metabarcoding analyses (taxonomic and functional genomics on bacterial 16S rRNA). To compare dynamics linked to potential aquifer recharge processes, water samples were collected from two boreholes under contrasting rainfall: low rainfall ((LR), dry season) and high rainfall ((HR), wet season). Our isotopic results indicate limited changes and dominance of modern terrestrial carbon in the upper part (northeast) of the bore field, but correlation between HR and increased old and 13C-enriched DOC in the lower area (southwest). CDOM results show a shift from terrestrially to microbially derived compounds after rainfall in the same lower field bore, which was also sampled for microbial genetics. Functional genomic results showed increased genes coding for degradative pathways-dominated by those related to aromatic compound metabolisms-during HR. Our results indicate that rainfall leads to different responses in different parts of the bore field, with an increase in old carbon sources and microbial processing in the lower part of the field. We hypothesise that this may be due to increasing salinity, either due to mobilisation of Cl- from the soil, or infiltration from the downstream salt lake during HR. This study is the first to use a multi-technique assessment using stable and radioactive isotopes together with functional genomics to probe the principal organic biogeochemical pathways regulating an arid zone calcrete system. Further investigations involving extensive sampling from diverse groundwater ecosystems will allow better understanding of the microbiological pathways sustaining the ecological functioning of subterranean biota.

Mechanistic and Kinetic Understanding of the UV254 Photolysis of Chlorine and Bromine Species in Water and Formation of Oxyhalides.

This study investigated the UV254 photolysis of free available chlorine and bromine species in water. The intrinsic quantum yields for •OH and X• (X = Cl or Br) generation were determined by model fitting of formaldehyde formation using a tert-butanol assay to be 0.61/0.45 for HOCl/OCl- and 0.32/0.43 for HOBr/OBr-. The steady-state •OH concentration in UV/HOX was higher than that in UV/OX- by a factor of 23.3 and 7.8 for Cl and Br, respectively. This was attributed to the different •OH consumption rate by HOCl versus OCl-, while for HOBr/OBr-, both the •OH formation and consumption rates were implied. This was supported by a k of 1.4 × 108 M-1 s-1 for the •OH reaction with HOCl, which was >14 times less than the k for •OH reactions with OCl-, HOBr, and OBr-. Formation of ClO3- and BrO3- was found to be significant with apparent quantum yields of 0.12-0.23. A detailed mechanistic study on the formation of XO3- including a new pathway involving XO• is presented, which has important implications as the level of XO3- can exceed the regulation (BrO3-) or guideline (ClO3-) values during UV/halogen oxidant water treatment. Our new kinetic models well simulate the experimental results for the halogen oxidant decomposition, probe compound degradation, and formation of ClO3- and BrO3-.

Alternative application of preformed monochloramine as a drinking water disinfectant for redosing in long drinking water distribution system servicing remote locations.

Chloramine is the disinfectant of choice for long drinking water distribution systems since it is more stable than chlorine, therefore providing a longer lasting disinfectant residual and producing less disinfection byproducts. However, to deliver safe drinking water in remote areas, redosing stations are used where (mostly) chlorine is added to the water to re-establish a disinfectant residual. In this study, the use of a highly concentrated preformed monochloramine solution instead of chlorine for redosing in tanks or reservoirs along extensive distribution systems was investigated. This will avoid unwanted reactions due to chlorine reactivity (formation of disinfection byproducts) and increase the disinfectant stability. Highly concentrated monochloramine solutions (15 mM, 1 gCl2 L-1) are most stable at high pH (10) and low temperature. It was found that the current kinetic model used for drinking water application was not accurate for highly concentrated monochloramine. A simplified kinetic model was developed and successfully used to predict monochloramine stability in our conditions. This will assist water utilities for application of preformed concentrated monochloramine allowing monochloramine redosing in long drinking water distribution systems. Hydrazine, a compound of health concern, might form at high monochloramine concentrations and high pH and needs to be carefully controlled.

Impact of DOM source and character on the degradation of primidone by UV/chlorine: Reaction kinetics and disinfection by-product formation.

The presence of Dissolved Organic Matter (DOM) can exert a strong influence on the effectiveness of the UV/chlorine process. This study examined the impact of five DOM isolates with different characteristics on the degradation kinetics of model contaminant primidone (PM) during UV/chlorine treatment. The formation of Disinfection By-Products (DBPs) from DOM after 15-min UV/chlorine treatment followed by 24 h chlorination was investigated and compared with chlorination alone. The use of chemical probes and radical scavengers revealed that •OH and ClO• were the main radical species responsible for the loss of PM at acidic and alkaline conditions, respectively. All tested DOM isolates significantly inhibited the decay of PM. A strong negative correlation (>0.93) was observed between the decay rate constants of PM and SUVA of DOM isolates, except for EfOM isolate, which induced the strongest inhibitory effect due to its higher abundance in sulfur-containing functional groups (i.e., sink of •OH/Cl• radicals). Compared with chlorination, the formation of Adsorbable Organic Chlorine (AOCl) and Trichloromethane (TCM) during the UV/Chlorine process was enhanced and hindered for low SUVA isolates and high SUVA DOM, respectively. However, Dichloroacetonitrile (DCAN) formation was generally lower for all isolates except for Ribou Reservoir DOM at pH 8.4 because of its high reactive nitrogenous DBP precursors at caustic conditions. However, when normalized to the chlorine consumed, the UV/Chlorine process always led to a lower DBPs formation compared with chlorination alone.

Ozone combined with ceramic membranes for water treatment: Impact on HO radical formation and mitigation of bromate.

The beneficial effect of combining ozone with ceramic membrane filtration (CMF) to enhance membrane flux performances during water treatment (e.g., wastewater and drinking water) could be related to the formation of hydroxyl (HO) radicals from the interaction of ozone with ceramic membrane. To explore this effect, para-chlorobenzoic acid was used to probe HO radical activity during a combined ozone/CMF process using a 0.1 µm pore size membrane supplied by Metawater, Japan. Tests were then extended to explore the impact on bromate formation downstream CMF, a well-known undesirable by-product from ozone use in water treatment. Ozone reduction by the membrane and its module appeared to be more associated with physical degassing, but a noticeable formation of HO radicals was observed during the interaction of ozone with the ceramic membrane. CMF treatment of ozonated potable water containing bromide showed a reduced bromate formation of 50% when the water was recirculated to the filtration module containing the ceramic membrane, compared to the experiment performed with an empty module. Single pass experiments showed bromate mitigation of around 10%. The mitigation of bromate formation was attributed to reduced overall ozone exposure by deagassing effect, but also potentially from suppression of the oxidation of Br- and HOBr/BrO- to BrO3- due to the catalytic degradation of ozone via a HO radical pathway.

500 days of swimmers: the chemical water quality of swimming pool waters from the beginning.

Many studies of disinfection by-products (DBPs) in pools have focused on haloacetic acids, trihalomethanes, and chloramines, with less studies investigating the occurrence of other DBPs, such as haloketones, haloacetaldehydes, haloacetonitriles, halonitromethanes, and haloacetamides. Furthermore, while many studies have achieved a broadscreen analysis across several pools, fewer studies have followed the water quality of pools over time, with information regarding the production and fate of DBPs in pools over extended periods (e.g. > 1 year) being limited. This study reports the occurrence of 39 DBPs and several general water quality parameters in two newly built and filled swimming pools over 15 months, where investigations began prior to opening. DBP concentrations measured in this study were generally similar to or higher than those previously reported in chlorinated pools, with concentrations of chloroacetic acid, dichloroacetic acid, trichloroacetic acid, and chloral hydrate (trichloroacetaldehyde) in some samples being higher than previously reported maximum concentrations. Considering both pools, lower concentrations of DBPs were measured in the pool where a steady state non-purgeable organic carbon concentration was achieved, highlighting the importance of the establishment of a steady state balance of mineralisation versus addition of organic carbon to reduce precursors for DBP formation in pools. Pools were found to exhibit significantly higher estimated cytotoxicity than their filling water, which reflects the significantly higher concentrations of DBPs measured in the pools in comparison to the filling water. Chloral hydrate accounted for up to 99% the total estimated cytotoxicity and was found to be correlated to the number of pool entries, suggesting that swimmers may be a potential source of chloral hydrate precursors in pools. The presence and subsequent peak of non-purgeable organic carbon and DBPs prior to, and soon after, opening suggest that the building process and/or new pool infrastructure may have had a significant impact on the chemical water quality, particularly on DBP formation. This study includes the first quantification of bromochloroacetaldehyde, bromodichloroacetaldehyde, bromochloronitromethane, and dichloronitromethane in chlorinated swimming pools, and provides important new knowledge on the long-term trends of DBPs in pools.

Occurrence of disinfection by-products in swimming pools and the estimated resulting cytotoxicity.

Swimming pools are disinfected to protect against the risk of microbial disease, however, the formation of disinfection by-products (DBPs) is an unwanted consequence. While many studies have reported the occurrence of commonly investigated DBPs (trihalomethanes and haloacetic acids) in pools, few studies have investigated emerging DBP classes, such as the haloketones or haloacetaldehydes, and the nitrogenous haloacetamides, halonitromethanes, haloacetonitriles and N-nitrosamines. This study investigated the occurrence of sixty four DBPs from the eight aforementioned DBP classes in pools employing different treatment methods. Approximately 70% of the DBPs were detected in at least one of the pools, with most concentrations being equal to or greater than those previously reported. Chloral hydrate (trichloroacetaldehyde) was one of many DBPs detected in all chlorinated waters (202 to 1313 µg/L), and, on a molar basis, was the predominant DBP. Several other DBPs, namely chloroacetic acid, dichloroacetic acid, trichloroacetic acid, dichloroacetamide, dibromoacetamide, dibromochloroacetamide and trichloroacetamide, and many of the N-nitrosamines, were measured at concentrations greater than previously reported: up to 200 to 479 µg/L for the haloacetic acids, 56 to 736 µg/L for the haloacetamides and up to 1093 ng/L for some N-nitrosamines. The higher disinfectant residuals required to be employed in Australian pools, and poor pool management (e.g. of chlorine residual and pH) are likely factors contributing to these relatively high DBP concentrations. Where possible, the cytotoxicity values of the investigated DBPs were evaluated, with chloral hydrate representing over 90% of the total chronic cytotoxicity despite only representing up to 64% of the total molar DBP concentration. This study is the first report of bromodichloroacetaldehyde and bromochloroacetaldehyde in pools and is the first investigation of N-nitrosamines in a brominated pool. Furthermore, this work aids in understanding DBPs in both chlorine and bromine treated pools, the latter being the subject of only limited previous studies.

In Situ Formation of Free Chlorine During ClO2 Treatment: Implications on the Formation of Disinfection Byproducts.

Chlorine dioxide (ClO2) is commonly used as an alternative disinfectant to chlorine in drinking water treatment because it produces limited concentrations of halogenated organic disinfection byproducts. During drinking water treatment, the primary ClO2 byproducts are the chlorite (50-70%) and the chlorate ions (0-30%). However, a significant portion of the ClO2 remains unaccounted for. This study demonstrates that when ClO2 was reacting with phenol, one mole of free available chlorine (FAC) was produced per two moles of consumed ClO2. The in situ formed FAC completed the mass balance on Cl for inorganic ClO2 byproducts (FAC + ClO2- + ClO3-). When reacting with organic matter extracts at near neutral conditions (pH 6.5-8.1), ClO2 also yielded a significant amount of FAC (up to 25%). Up to 27% of this in situ formed FAC was incorporated in organic matter forming adsorbable organic chlorine, which accounted for up to 7% of the initial ClO2 dose. Only low concentrations of regulated trihalomethanes were produced because of an efficient mitigation of their precursors by ClO2 oxidation. Conversely, dichloroacetonitrile formation from ClO2-induced generation of FAC was higher than from addition of FAC in absence of ClO2. Overall, these findings provide important information on the formation of FAC and disinfection byproducts during drinking water treatment with ClO2.

Method Development for Quantification of Bromochloramine Using Membrane Introduction Mass Spectrometry.

During chloramination of bromide-containing waters, the main brominated amine formed is bromochloramine (NHBrCl). To date, there is no analytical method, free of interference, allowing its accurate quantification. The major reason is that it is not possible to produce a pure NHBrCl solution. In this study, we report a method allowing the accurate quantification of NHBrCl with membrane introduction mass spectrometry (MIMS). First, the molar absorption coefficient for NHBrCl was determined by quantifying NHBrCl as 2,4,6-tribromophenol by HPLC-UV and comparing the results with the direct UV response at 320 nm. A molar absorption coefficient of 304 M-1cm-1 was obtained. The results obtained by direct UV measurements were compared to the MIMS signal recorded at m/ z 131 corresponding to the mass of the molecular ion and used to establish a calibration curve. A limit of detection of 2.9 µM (378 µg/L) was determined. MIMS is the only method enabling the unambiguous quantification of NHBrCl, as it is based on m/ z 131, while with other analytical techniques, other halamines can interfere, i.e., overlapping peaks with direct UV measurements and reaction of several halamines with colorimetric reagents or phenols. While the detection limit is not quite low enough to measure NHBrCl in actual drinking water, this analytical method will benefit the scientific community by allowing further mechanistic studies on the contribution of NHBrCl to the formation of toxic disinfection by-products.