Modeling monochloramine loss in the presence of natural organic matter

A group of emerging heterocyclic nitrogenous disinfection byproducts: Formation and cytotoxicity of halopyridinols in drinking water

Recently, a new group of halopyridinol disinfection byproducts (DBPs) was reported in drinking water. The in vivo developmental and acute toxicity assays have shown that they were more toxic than a few commonly known aliphatic DBPs such as bromoform and iodoacetic acid. However, many pyridinol DBPs with the same main structures but different halogen substitutions were still unknown due to complicated water quality conditions and various disinfection methods applied in drinking water treatment plants. Studies on their transformation mechanisms in drinking water disinfection were quite limited. In this study, comprehensive detection and identification of halopyridinols were conducted, and five new halopyridinols were first reported, including 2-chloro-3-pyridinol, 2,6-dichloro-3-pyridinol, 2-bromo-5-chloro-3-pyridinol, 2,4,6-trichloro-3-pyridinol and 2,5,6-trichloro-3-pyridinol. Formation conditions and mechanisms of the halopyridinols were explored, and results showed that chlorination promoted their formation compared with chloramination. Halopyridinols were intermediate DBPs that could undergo further transformation/degradation with increasing contact time, disinfectant dose, bromide concentration, and pH. The in vitro cytotoxicity of the halopyridinols was evaluated using human hepatocellular carcinoma cells. Results showed that the cytotoxicity of 3,5,6-trichloro-2-pyridinol was the highest (EC50 = 474.3 μM), which was 13.0 and 1.6 times higher than that of 2-bromo-3-pyridinol (EC50 = 6214.5 μM) and tribromomethane (EC50 = 753.6 μM), respectively.

Locally enhanced mixed-order model for chloramine decay in drinking water disinfection

Chloramine is the second most popular disinfectant and is widely used in the disinfection of drinking water. For chloramine disinfection, some standards require the total chlorine concentration to be maintained in an appropriate range in the water distribution system. Therefore, exploring the mechanism of chloramine decay and deriving an accurate chloramine decay model helps to optimize the disinfection process and ensure water quality safety. This paper proposed a locally enhanced mixed-order(LEM) model consisting of the first order model and the mixed order model to describe chloramine auto-decomposition and decays caused by other reactions respectively. Via proving the parameter a and k2 related to temperatures instead of initial chloramine concentration, the model had been further simplified. Nine chloramine decay experiments with different initial chloramine concentrations and temperatures were designed and carried out to evaluate the new model performance for chloramine decay simulation. The research results showed that the simplified LEM model could simulate the whole process of chloramine decay well. Its accuracy evaluation indexes (R2 and SSE) were better than that obtained from the first order model and the mixed order model. This paper proposed a simple and accurate method to simulate the process of chloramine decay and had a guiding significance for water quality safety assurance.

Is monochloramine pre-oxidation a viable strategy for enhancing the treatment efficiency of algae-laden water with conventional drinking water treatment process?

Algal blooms worldwide pose many challenges to drinking water production. Pre-oxidation with NaClO, KMnO4, or ozone is commonly used to enhance algal removal in conventional drinking water treatment processes. However, these currently utilized oxidation methods often result in significant algal cell lysis or impede the operation of the subsequent units. Higher algal removal with pre-chlorination in algal solutions prepared with natural water, compared to those prepared with ultrapure water, has been observed. In the present studies, preliminary findings indicate that ammonium in natural water alters chlorine species to NH2Cl, leading to improved treatment efficiency. NH2Cl with 1.5-3.0 mg∙L-1 as Cl2 with an oxidation time of 3-7 h significantly enhancing algal removal by coagulation. The selective oxidation of surface-absorbed organic matter (S-AOM) by NH2Cl, followed by the subsequent peeling off of this material from the algal surface, leading to an increase in zeta potential from -20.2 mV to -3.8 mV, constitutes the primary mechanism of enhanced algal removal through coagulation. These peeled S-AOM retained their large molecular weight and acted as polymer aids. Compared with NaClO and KMnO4, NH2Cl displays the best performance in improving algal removal, avoiding cell lysis, and decreasing the potential for nitrogenous disinfection byproducts formation under the reaction conditions used in this study. Notably, in major Chinese cities, water purification plants commonly rely on suburban lakes or reservoirs as water sources, necessitating the transportation of raw water over long distances for times up to several hours. These conditions favor the implementation of NH2Cl pre-oxidation. The collective results indicate the potential of NH2Cl oxidation as a viable pretreatment strategy for algal contamination during water treatment processes.

Comparison of monochloramination and chlorination of 1,3-diphenylguandine (DPG): Kinetics, transformation products, and cell-based in-vitro testing

As a widely used secondary vulcanization accelerator in the rubber industry, 1,3-diphenylguanidine (DPG) poses risks to human health and the environment. To compare and comprehend the disinfection process of DPG, this work investigates the reaction kinetics, toxicity, and transformation products (TPs) of DPG during chlorination and monochloramination. It has been revealed that the reactivity of monochloramine is significantly slower compared to chlorination of DPG, with the maximum efficiency observed at pH 7 to pH 8. Cytotoxicity assessment using HepG2 and THP-1 cells reveals that cytotoxicity hierarchy is as follows: chlorine TPs > monochloramine TPs > DPG. Moreover, oxidant-to-DPG molar ratios 10 and 20 lead to higher cytotoxicity in both chlorination and monochloramination compared to ratio 5 and 100. Additionally, cell bioenergetics experiments demonstrate that chlorine and monochloramine TPs induce mitochondrial dysfunction and enhance glycolytic function in HepG2 cells. The genotoxic response from p53 signaling further suggested genotoxic effects of certain TPs. Furthermore, analysis of TPs using high-resolution mass spectrometry (HRMS) identifies ten TPs, with chlorination yielding more TPs than monochloramination. Generally, a chlorine or monochloramine molar ratio to DPG of 10-20 results in an increased formation of TPs and heightened cytotoxicity. Notably, higher oxidant molar ratios increased the formation of monoguanidine TPs and DPG hydroxylation during chlorination, whereas monochloramination lead to DPG substitution predominantly generating chlorinated DPG due to weaker oxidation effects. These findings provide valuable information for the appropriate treatment of DPG and disinfection processes in water facilities to mitigate potential risks to human health and the ecosystem.

Machine-learning-assisted prediction and optimized kinetic modelling of residual chlorine decay for enhanced water quality management

The quality of water changes from source to tap, presenting challenges in maintaining consistent water quality across the system. Predicting water quality in distribution systems, including disinfectant residual loss and by-product formation, has been the subject of research since the early 1990s. Although numerous models have been proposed to predict residual chlorine decay, disputes exist among researchers and experts over the superiority of certain models. Accordingly, this study modified the existing process-based bulk decay models by replacing the initial Total Residual Chlorine (TRC) concentration parameter with TRC demand, leading to an improvement in the models' performance. The modification resulted in a 38.03%, 28.02%, 23.11%, and 33.29% average improvement in Mean Squared Error (MSE) values for the First Order Model (FOM), Parallel First Order Model (PFOM), Second Order Model (SOM), and Parallel Second Order Model (PSOM), respectively. The study also introduced an online predictive method based on a Machine Learning (ML) algorithm that predicts the first-order TRC bulk decay rate by using water quality parameters as inputs. A Gaussian Process Regression (GPR) model was used to predict the kinetic parameters in FOM, which accurately predicted the test sets for most of the cases. In addition, a new methodology was proposed in this study for predicting TRC in water distribution systems that incorporates the variability of source natural organic matter, operational actions, and water demands. This method seeks to develop high-fidelity and robust water quality predictions that provide operational decision support for optimized distribution system management. In conclusion, this study emphasizes the importance of understanding water quality changes from source to tap and the challenges of maintaining consistent water quality across the system. The study suggests modifying existing models and introducing a novel methodology for predicting residual chlorine in water distribution systems that can improve water quality management and, ultimately, better public health outcomes.

Sub-lethal toxicity of five disinfection by-products on microalgae determined by flow cytometry - Lines of evidence for adverse outcome pathways

Standardised tests are often used to determine the ecotoxicity of chemicals and focus mainly on one or a few generic endpoints (e.g. mortality, growth), but information on the sub-cellular processes leading to these effects remain usually partial or missing. Flow cytometry (FCM) can be a practical tool to study the physiological responses of individual cells (such as microalgae) exposed to a stress via the use of fluorochromes and their morphology and natural autofluorescence. This work aimed to assess the effects of five chlorine-based disinfection by-products (DBPs) taken individually on growth and sub-cellular endpoints of the green microalgae Raphidocelis subcapitata. These five DBPs, characteristic of a chlorinated effluent, are the following monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), bromochloroacetic acid (BCAA) and 1,1-dichloropropan-2-one (1,1-DCP). Results showed that 1,1-DCP had the strongest effect on growth inhibition (EC50 = 1.8 mg.L-1), followed by MCAA, TCAA, BCAA and DCAA (EC50 of 10.1, 15.7, 27.3 and 64.5 mg.L-1 respectively). Neutral lipid content, reactive oxygen species (ROS) formation, red autofluorescence, green autofluorescence, size and intracellular complexity were significantly affected by the exposure to the five DBPs. Only mitochondrial membrane potential did not show any variation. Important cellular damages (>10%) were observed for only two of the chemicals (BCAA and 1,1-DCP) and were probably due to ROS formation. The most sensitive and informative sub-lethal parameter studied was metabolic activity (esterase activity), for which three types of response were observed. Combining all this information, an adverse outcome pathways framework was proposed to explain the effect of the targeted chemicals on R. subcapitata. Based on these results, both FCM sub-cellular analysis and conventional endpoint of algal toxicity were found to be complementary approaches.

Microbiological risks increased by ammonia-oxidizing bacteria under global warming: The neglected issue in chloraminated drinking water distribution system

A rising outbreak of waterborne diseases caused by global warming requires higher microbial stability in the drinking water distribution system (DWDS). Chloramine disinfection is gaining popularity in this context due to its good persistent stability and fewer disinfection byproducts. However, the microbiological risks may be significantly magnified by ammonia-oxidizing bacteria (AOB) in distribution systems during global warming, which is rarely noticed. Hence, this work mainly focuses on AOB to explore its impact on water quality biosafety in the context of global warming. Research indicates that global warming-induced high temperatures can directly or indirectly promote the growth of AOB, thus leading to nitrification. Further, its metabolites or cellular residues can be used as substrates for the growth of heterotrophic bacteria (e.g., waterborne pathogens). Thus, biofilm may be more persistent in the pipelines due to the presence of AOB. Breakpoint chlorination is usually applied to control such situations. However, switching between this strategy and chloramine disinfection would result in even more severe nitrification and other adverse effects. Based on the elevated microbiological risks in DWDS, the following aspects should be paid attention to in future research: (1) to understand the response of nitrifying bacteria to high temperatures and the possible association between AOB and pathogenic growth, (2) to reveal the mechanisms of AOB-mediated biofilm formation under high-temperature stress, and (3) to develop new technologies to prevent and control the occurrence of nitrification in drinking water distribution system.

Evaluation of Preformed Monochloramine Reactivity with Processed Natural Organic Matter and Scaling Methodology Development for Concentrated Waters

To evaluate natural organic matter (NOM) processing impacts on preformed monochloramine (PM) reactivity and as a first step in creating concentrated disinfection byproduct (DBP) mixtures from PM, a rational methodology was developed to proportionally scale PM NOM-related demand in unconcentrated source waters to waters with concentrated NOM. Multiple NOM preparations were evaluated, including a liquid concentrate and reconstituted lyophilized solid material. Published kinetic models were evaluated and used to develop a focused reaction scheme (FRS) that was relatively simple to implement and focused on monochloramine loss, including considerations for inorganic chloramine stability (i.e., autodecomposition) and bromide and iodide impacts. The FRS included critical reaction pathways and accurately simulated (without modification) monochloramine experimental data with and without bromide and iodide present over a range of PM-dosed NOM-free waters. For NOM-containing waters, addition of two NOM reactions in the FRS allowed (i) apportioning monochloramine loss to either inorganic or NOM-related reactions and (ii) selecting experiment conditions to provide an equivalent monochloramine NOM-related demand in unconcentrated and concentrated waters. The methodology provides a framework for future experimentation to evaluate DBP scaling and their speciation in concentrated water matrices when providing an equivalent NOM-related monochloramine demand in unconcentrated and concentrated matrices.

Investigation of Chloramines, Disinfection Byproducts, and Nitrification in Chloraminated Drinking Water Distribution Systems

Four chloraminated drinking water distribution systems (CDWDSs) required to maintain numeric versus "detectable" residuals were spatially and temporally sampled for water quality and associated trihalomethane (THM) and haloacetic acid (HAA) formation. Monochloramine decreased from entry point (EP) to maximum residence time (MRT) samples while THMs and HAAs initially increased and then stabilized or slightly decreased. Subsequently, EP and MRT samples were used in laboratory-held studies to further evaluate disinfectant residual stability, chloramine speciation, and nitrification occurrence. MRT water exhibited a faster monochloramine concentration decline compared to EP water, indicating a decreasing disinfectant residual stability from increasing water age through distribution. Using a simple technique based on published inorganic chloramine chemistry, samples were also investigated for nondisinfectant positive interference (NDPI) on total chlorine measurements. NDPI concentrations represented up to 100% of the total chlorine concentration when total chlorine concentrations decreased to 0.05 mg-Cl2/L, indicating little to no effective disinfectant residual remained.

Multiple Roles of Dissolved Organic Matter in Advanced Oxidation Processes

Advanced oxidation processes (AOPs) can degrade a wide range of trace organic contaminants (TrOCs) to improve the quality of potable water or discharged wastewater effluents. Their effectiveness is impacted, however, by the dissolved organic matter (DOM) that is ubiquitous in all water sources. During the application of an AOP, DOM can scavenge radicals and/or block light penetration, therefore impacting their effectiveness toward contaminant transformation. The multiple ways in which different types or sources of DOM can impact oxidative water purification processes are critically reviewed. DOM can inhibit the degradation of TrOCs, but it can also enhance the formation and reactivity of useful radicals for contaminants elimination and alter the transformation pathways of contaminants. An in-depth analysis highlights the inhibitory effect of DOM on the degradation efficiency of TrOCs based on DOM's structure and optical properties and its reactivity toward oxidants as well as the synergistic contribution of DOM to the transformation of TrOCs from the analysis of DOM's redox properties and DOM's transient intermediates. AOPs can alter DOM structure properties as well as and influence types, mechanisms, and extent of oxidation byproducts formation. Research needs are proposed to advance practical understanding of how DOM can be exploited to improve oxidative water purification.

Joint majorization of waterworks and secondary chlorination points considering the chloric odor and economic investment in the DWDS using machine learning and optimization algorithms

The traditional methods of increasing the chlorine disinfectant dosage in the drinking water distribution system (DWDS) to control microorganisms and improve the safety of drinking water quality are subjected to several challenges. One noticeable problem is the unpleasant odor generated by chlorine and chloramines. However, the generally proposed chlorine dosage optimization model ignores the chloric odor distribution in the DWDS. This study proposes a comprehensive multi-parameter water quality model and aims to balance the trade-offs between: (i) minimize the flavor profile analysis (FPA) degree of the chloric odor produced by chlorine and chloramines in the DWDS, and (ii) minimize the economic investment (chlorine dosage and operation cost). EPANET and back propagation (BP) network integrated with the Borg algorithm were employed as innovative approaches to simulate the chlorine, chloramines, and chloric odor intensity in the DWDS. Moreover, the application of the multi-parameter model was demonstrated in a real-world DWDS case study. 0.5 mg-Cl₂/L (mg/L) chlorine at 8 secondary chlorination points was added to the DWDS as an optimized chlorine dosing scheme considering the olfactory and financial objective functions simultaneously. When switching to a superior water source, the FPA of the chloric odor in DWDS increased by a maximum of 1.4 at most if the initial chlorine dosage remained as before. To avoid the occurrence of chloric odor and also control the residual free chlorine (residual chlorine) at a suitable value, the initial and secondary chlorine dosages were optimized to 0.4 mg/L and 0.3 mg/L, respectively. Under this condition, the initial chlorine dosage was reduced by 50% compared to the original operation scheme in City J, China, the qualification rate of the residual chlorine reached 97.2%, basically consistent with that before water source switching, and the chloric odor intensity of the DWDS was controlled below FPA 3.4.

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.

Development and Comparison of Water Quality Network Model and Data Analytics Model for Monochloramine Decay Prediction

The conventional drinking water treatment process involves disinfecting water at the final stage of treatment to ensure water is microbiologically safe at customer taps. Monochloramine is a popular disinfectant used in many water distribution systems (WDSs) worldwide. Understanding the factors that impact monochloramine decay in the WDS is critical for maintaining disinfection at the customer tap. While monochloramine residue moves through a WDS, it decays via several pathways including chemical, microbiological, and wall decay processes. The decay profile in these pathways is often site-specific and depends on various factors including treated water characteristics. In a water quality network model, the decay of a chemical species is often modelled using two parameters that represent bulk and wall decay kinetics. Typical bulk decay characteristics of monochloramine for a specific WDS can be easily established in the laboratory using grab sample tests, while in a real situation, wall decay is difficult to quantify. In this study, we compared two different approaches to model monochloramine decay in a WDS. In the first approach, the wall decay parameter was quantified using a parameter optimisation technique with monochloramine concentrations at different network locations simulated using a water quality network model. In the second approach, a data analytics model was developed using a machine learning algorithm. For both approaches, the model predicted monochloramine concentrations closely matched the observed data. Our study suggests that the data analytics model has a relatively higher accuracy in predicting monochloramine residual concentrations in a WDS.

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.

Comparison of Techniques for Maintaining Adequate Disinfectant Residuals in a Full-Scale Water Distribution Network

The present work provides a numerical comparison of different techniques that can be adopted to guarantee sufficient disinfectant residuals in a water distribution network (WDN) when chlorine or chloramine is used as disinfectant. First, while considering chlorine as a disinfectant, the implementation of booster stations in bulk areas and continuous outflows at dead-end nodes was considered. Afterward, the comparison between continuous and intermittent outflows was performed. The water volume being the same, water is provided through blowoffs for 24 h or for limited durations, respectively. Finally, the extent to which the results change was analyzed when chloramine is used instead of chlorine. The methodology is based on the use of the flow routing/water quality modeling software EPANET and its multispecies extension EPANET-MSX on a full-scale WDN. The results show that all the operational measures analyzed are effective to tackle the problem of low disinfectant residuals in WDN. Booster stations are effective to obtain a more uniform distribution of disinfectant throughout the WDN, while nodal blowoffs seem to be a necessary solution for the numerous and scattered dead-end nodes of WDN. The use of chloramine yielded a decrease in the number of blowoffs to open and in blowoff outflows.

Formation of nitrosamines during chloramination of two algae species in source water-Microcystis aeruginosa and Cyclotella meneghiniana

The contribution of two algae species, Microcystis aeruginosa (M. aeruginosa) and Cyclotella meneghiniana (C. meneghiniana), to the formation of nitrosamines (NAs) during chloramination in drinking water treatment was investigated. A variety of factors including contact time, algae cell concentration, chloramine dosages, and algal cell components (cell debris (CD), intracellular organic matter (IOM), and extracellular organic matter (EOM)) were evaluated for influencing the formation of different NAs, such as N-Nitrosodiethylamine (NDMA), N-Nitrosomethylethylamine (NMEA), N-Nitrosodibutylamine (NDBA), N-Nitrosodi-n-propylamine (NDPA), and N-nitrosopyridine (NPyr). In addition, NAs formation from Chlorophyll-a and Microcystin-LR (MC-LR) after chloramination was studied. These results showed that the increase of reaction time and algae cell concentration enhanced the formation potential of five types of NAs from both algae species, except for the NDMA formation from C. meneghiniana, which increased first and then decreased with increased reaction time. The generation of NDMA was detected as the dominated type of NAs. The formation of total NAs from both algae species followed same pattern of increasing first and then decreasing with the increase of chloramine dosage. The largest NAs formation potential (NAsFP) of M. aeruginosa and C. meneghiniana showed at 1.5 mM and 1.0 mM monochloramine, respectively. Moreover, the impacts of algae cellular components on the formation potential of NAs followed the order of IOM > EOM ≫ CD and IOM ≫ CD > EOM for M. aeruginosa and C. meneghiniana, respectively, indicating that IOM was the main source of NAs precursors for both algae. Furthermore, EEM analysis before and after chloramination confirmed that the soluble microbial products (SMPs) and protein-like substances were the main cellular components that contributed to NAs formation for both algae. The NAs formation potential of Microcystin-LR was much higher than that of Chlorophyll-a chloramination.

A probabilistic model for assessing uncertainty and sensitivity in the prediction of monochloramine loss in French river waters

Monochloramine (NH₂Cl) is increasingly used as alternative disinfectant to free chlorine in industrial plants. After use in cooling systems, the waters are released to the environment and residual NH₂Cl may be discharged into the receiving waters. As NH₂Cl is suspected to exhibit toxicity towards aquatic organisms, a proper risk assessment of its occurrence in environmental waters is needed to prevent adverse effects on wildlife. For this purpose, a comprehensive model simulating monochloramine loss in natural riverine waters was developed. This model incorporates the following processes: (i) autodecomposition; (ii) reaction with nitrite and bromide; (iii) oxidation with Dissolved Organic Carbon (DOC); (iv) oxidation with organic fraction of Suspended Particulate Matter (SPM); (v) reactions in bottom sediments and (vi) volatilization. The model was also designed to conduct uncertainty and sensitivity analysis. It was tested on several French rivers submitted to discharges of monochloraminated effluents and on several seasonal conditions. Uncertainty analysis allowed evaluation of confidence intervals related to NH₂Cl half-lives in natural waters. It was shown that simulation intervals are in good agreement with experimental data obtained on the same rivers. Sensitivity analysis using an EFAST variance decomposition approach allowed identification of the most influential parameters on half-life determination. It was shown that the kinetic rate describing rapid reaction of NH₂Cl with DOC is by far the most sensitive parameter, demonstrating the predominance of such reactions in the loss process. Variables or parameters involved in temperature dependence (temperature and activation energy) can also significantly influence model results. To a lesser extent, wind velocity is the most sensitive parameter explaining uncertainty in the prediction of volatilization, with a high level of interactions with other parameters, showing that loss through volatilization can be essential in some specific conditions only. This study then identified the most important research priorities for improving the prediction of NH₂Cl half-lives in natural rivers.

Comprehensive review on iodinated X-ray contrast media: Complete fate, occurrence, and formation of disinfection byproducts

Iodinated contrast media (ICM) are drugs which are used in medical examinations for organ imaging purposes. Wastewater treatment plants (WWTPs) have shown incapability to remove ICM, and as a consequence, ICM and their transformation products (TPs) have been detected in environmental waters. ICM show limited biotransformation and low sorption potential. ICM can act as iodine source and can react with commonly used disinfectants such as chlorine in presence of organic matter to yield iodinated disinfection byproducts (IDBPs) which are more cytotoxic and genotoxic than conventionally known disinfection byproducts (DBPs). Even highly efficient advanced treatment systems have failed to completely mineralize ICM, and TPs that are more toxic than parent ICM are produced. This raises issues regarding the efficacy of existing treatment technologies and serious concern over disinfection of ICM containing waters. Realizing this, the current review aims to capture the attention of scientific community on areas of less focus. The review features in depth knowledge regarding complete environmental fate of ICM along with their existing treatment options.

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.

Formation of disinfection by-products in a UV-activated mixed chlorine/chloramine system

In recent years, ultraviolet (UV) irradiation coupled with chlor(am)ination process is ubiquitous in secondary water supply systems in many cities of China. However, the disinfection by-products (DBPs) formation in a UV-activated mixed chlorine/chloramine system (MCCS) still remains unclear. In this study, the DBPs formation in a UV-activated MCCS was systematically investigated, considering influencing factors including the mass ratios of free chlorine to NH₂Cl, UV irradiation, pH values, NOM types, Br^- concentration and toxicity of the DBPs. Results indicated that DBPs formation decreased remarkably as mass ratio of free chlorine to NH₂Cl changed from 5:0 to 0:5. The DBPs formation in humic acid (HA)-containing water was the highest, followed by those in fulvic acid (FA) and algal organic matter (AOM). Besides, better control of the DBP-related calculated toxicity can be achieved in acidic conditions regardless of the UV irradiation. Furthermore, in the presence of Br^-, a significant reduction of DBPs formation could be achieved in a UV-activated MCCS. The findings also demonstrated that DBPs formation in real water can be effectively reduced at high UV fluence in a MCCS.

Simplified chemical chloramine decay model for water distribution systems

This paper, presents a simplified model for predicting chemical chloramine loss in ultrapure water as a function of various measurable parameters, which otherwise requires the simulation of a complex mechanistic model involving the implementation of a number of ordinary differential equations (ODE), using specialised software. The complexity of the mechanistic model is evidenced by its lack of use outside chemical reaction modelling academics. We developed a simplified model as a single-line equation with eight fixed coefficients to predict the first-order decay coefficient. The developed model accurately predicts the first-order chloramine decay coefficient as a function of the water pH (7.5-8.5), chlorine-to-ammonia mass ratio (3.0-4.5), initial chloramine dose (1.5-5.0 mg/L), and alkalinity (up to 200 mg/L CaCO₃) at 25 °C in ultrapure water samples. The user either has to input all the above mentioned water quality parameters or can evaluate the relative effect of water quality parameters individually or collectively, by using a relative model. The decay coefficient for temperature between 4 and 35 °C can be obtained by applying Arrhenius equation. To predict the chloramine profile, the initial chloramine concentration has to be decreased slightly (4% when pH < 7.8 to no adjustment at pH > 8.2) before the first order model is applied. Such a model will help in adding the effect of other parameters such as NOM, bromide, and microbiological decay in the future to facilitate easy adaptation by the water utilities.

Mechanistic study on chlorine/nitrogen transformation and disinfection by-product generation in a UV-activated mixed chlorine/chloramines system

The conversion mechanisms of chlorine species (including free chlorine, monochloramine (NH₂Cl), dichloramine, and total chlorine), nitrogen species (including ammonium (NH₄⁺), nitrate (NO₃^-), and nitrite (NO₂^-)) as well as the formation of disinfection by-products (DBPs) in a UV-activated mixed chlorine/chloramines system in water were investigated in this work. The consumption rates of free chlorine and NH₂Cl were significantly promoted in a HOCl/NH₂Cl coexisting system, especially in the presence of UV irradiation. Moreover, the transformation forms of nitrogen in both ultrapure and HA-containing waters were considerably affected by UV irradiation and the mass ratio of free chlorine to NH₂Cl. NO₃^- and NO₂^- can be easily produced under UV irradiation, and the removal efficiency of total nitrogen with UV was obvious higher than that without UV when the initial ratio of HOCl/NH₂Cl was less than 1. The roles of different radicals in the degradation of free chlorine, NH₂Cl and NH₄⁺ were also considered in such a UV-activated mixed chlorine/chloramines system. The results indicated that OH• was important to the consumption of free chlorine and NH₂Cl, and showed negligible influence on the consumption of NH₄⁺. Besides, the changes of DOC and UV₂₅₄ in HA-containing water in UV-activated mixed chlorine/chloramines system indicated that the removal efficiency of DOC (24%) was much lower than that of UV₂₅₄ (94%). The formation of DBPs in a mixed chlorine/chloramines system was also evaluated. The yields of DBPs decreased significantly as the mass ratio of HOCl/NH₂Cl varied from 1 : 0 to 0 : 1. Moreover, compared to the conditions without UV irradiation, higher DBPs yields and DBP-associated calculated toxicity were observed during the UV-activated mixed chlorine/chloramine process.

Nitrification in Premise Plumbing: A Review

Nitrification is a major issue that utilities must address if they utilize chloramines as a secondary disinfectant. Nitrification is the oxidation of free ammonia to nitrite which is then further oxidized to nitrate. Free ammonia is found in drinking water systems as a result of overfeeding at the water treatment plant (WTP) or as a result of the decomposition of monochloramine. Premise plumbing systems (i.e., the plumbing systems within buildings and homes) are characterized by irregular usage patterns, high water age, high temperature, and high surface-to-volume ratios. These characteristics create ideal conditions for increased chloramine decay, bacterial growth, and nitrification. This review discusses factors within premise plumbing that are likely to influence nitrification, and vice versa. Factors influencing, or influenced by, nitrification include the rate at which chloramine residual decays, microbial regrowth, corrosion of pipe materials, and water conservation practices. From a regulatory standpoint, the greatest impact of nitrification within premise plumbing is likely to be a result of increased lead levels during Lead and Copper Rule (LCR) sampling. Other drinking water regulations related to nitrifying parameters are monitored in a manner to reduce premise plumbing impacts. One way to potentially control nitrification in premise plumbing systems is through the development of building management plans.

Effect of bromide on NDMA formation during chloramination of model precursor compounds and natural waters

In this work, we investigated the effect of bromide ion (Br^-) on NDMA formation using model precursor compounds, wastewater effluents and surface waters. Previous studies showed that Br^- reacts with chloramines and forms bromochloramine, a reactive compound responsible for NDMA formation enhancement. Some limitations of those studies were the highest Br^- concentrations used, and the limited number of precursors considered. Here, we observed enhancement of NDMA formation from most of the model precursor compounds within the Br^- range (0-1000 μg/L) but this effect was suppressed in the presence of NOM. Also, NDMA formation was favored at pH 8 in the presence of Br^- compared to pH 6. Nevertheless, Br^- suppressed NDMA formation in wastewater effluent samples at low monochloramine doses while no effects were observed in surface waters.

Comparison of the yields of mono-, Di- and tri-chlorinated HAAs and THMs in chlorination and chloramination based on experimental and quantum-chemical data

Thermodynamic and kinetic aspects of the formation of trihalomethanes and haloacetic acids determined based on the quantum chemical (QC) simulations were compared in this study with the experimental data generated using the differential spectroscopy approach in chlorination and chloramination. The ratios of the slopes of the correlations between -DlnA₃₅₀ values and individual DBPs concentrations (S_NH2Cl/S_HOCl) were observed to be linearly correlated with the ratios of the Gibbs free energies (ΔG_NH2Cl/ΔG_HOCl) of the corresponding reactions of chloramine and chlorine with acetaldehyde which was used as a model DBP precursor in QC simulations. Further QC examination of the kinetics of chlorination and chloramination of the model compound acetoacetic acid showed that the activation energy of reactions between monochloramine that directly participates in substitution reactions to form mono-, di and tri-halogenated intermediates are 2-3 times higher than those of HOCl formed via the hydrolysis monochloramine. This result confirms that the interactions of chloramine with NOM and ensuing DBP formation are primarily mediated by the free chlorine released as a result of the hydrolysis of monochloramine while direct halogenation of NOM by monochloramine is likely to provide a small contribution to DBP formation.

Chloramination of iodide-containing waters: Formation of iodinated disinfection byproducts and toxicity correlation with total organic halides of treated waters

The formation of iodinated disinfection byproducts (I-DBPs) in drinking waters is of a concern due to their higher cyto- and genotoxicity than their chlorinated and brominated analogues. This study investigated the formation of I-DBPs under chloramination conditions using preformed chloramine and associated cyto- and geno-toxicities obtained with Chinese Hamster Ovary (CHO) cell assay. Cyto- and geno-toxicity of the samples were also calculated using DBP toxicity index values and correlated with total organic halide (TOX) formation. In low iodide (I^-) (0.32 μM, 40 μg L^-1) water, increasing dissolved organic carbon (DOC) concentration of selected waters from 0.1 to 0.25 mg L^-1 increased the formation of iodinated trihalomethanes (I-THMs), while further increases from 0.25 to 4 mg L^-1 produced an opposite trend. In high iodide water (3.2 μM, 400 μg L^-1), increasing DOC from 0.5 to 4 mg L^-1 gradually increased the I-THM formation, while a decrease was observed at 5.4 mg L^-1 DOC. Iodoform was the most influenced species from the changes in DOC concentration. While increasing the initial iodide concentration from 0 to 5 μM increased the formation of iodoform, it did not make any considerable impact on the formation of other I-THMs. The measured cytotoxicity of samples was significantly correlated with increasing DOC concentration. Unknown TOCl and TOI showed a high correlation with measured cytotoxicity, while calculated total organic chlorine (TOCl) and total organic iodine (TOI) did not correlate. The comparison of measured and calculated cytotoxicity values showed that the calculated values do not always represent the overall cytotoxicity, since the formation of unknown DBPs are not taken into consideration during the toxicity calculations.

Determination of monochloramine dissipation kinetics in various surface water qualities under relevant environmental conditions - Consequences regarding environmental risk assessment

A total 190 experiments were performed to study the dissipation kinetics of monochloramine (NH₂Cl, CAS no 10599-90-3) in surface water samples from six rivers (Loire, Rhône, Meuse, Garonne, Seine and Moselle) and an artificial reservoir (Mirgenbach), all located in France. Experiments were conducted in an open reactor, under relevant controlled environmental conditions. The impact of various parameters such as initial NH₂Cl concentration, temperature, pH, presence of sediments, sampling site and collection period was investigated. It was found that NH₂Cl dissipated rapidly without any lag phase, and that decay follows an apparent first-order kinetics (r² > 0.99). Presence of sediment greatly accelerated decay. Half-lives were generally <1 h in river water in presence of natural sediment, but of several hours without sediment. The impact of pH was low for the normal river water pH range. However, increase in temperature significantly accelerated decay. The combination of high initial NH₂Cl concentrations and elevated temperatures generally gives half-lives similar to those obtained at lower temperatures and lower concentrations. Short half-lives (0.06 to 1.50 h) were found in all the surface waters examined, regardless of geographic location of sampling site or collection period, indicating no temporal or site-specific effects on NH₂Cl dissipation. Decay was slightly faster at lower initial concentrations, which supports extrapolation of half-lives measured in this study to a wide range of environmental concentrations. It can thus be assumed that NH₂Cl degradation in river and reservoir waters is mainly determined by presence of sediments and temperature.

Modeling chloramine decay in full-scale drinking water supply systems

Chloramines are commonly used as secondary disinfectants in drinking water treatment, providing a residual for disinfection as drinking water moves to consumers. Chloramines are inherently unstable, undergoing autodecomposition reactions even in the absence of reactive substances. In the presence of natural organic matter (NOM), chloramine loss accelerates due to additional reaction pathways. In this study, batch reaction models for chloramine loss due to autodecomposition and the presence of NOM were developed. A case study was carried out for the Town of Cary, North Carolina. A hydraulic model of Cary's distribution system was developed and calibrated using the EPANET toolkit with operational and water demand data supplied by Cary. Then, water age from the hydraulic model was used together with the batch model of chloramine decay to successfully predict chloramine concentrations spatially and temporally throughout the network. The capabilities of the EPANET-MSX toolkit to model chloramine loss in a distribution network are explored. PRACTITIONER POINTS: A batch reaction model of chloramine decay over time due to autodecomposition reactions and additional reactions with NOM was developed and validated. A hydraulic model of the Town of Cary's water distribution network was developed and calibrated using operational and water demand data. Water age reported by the calibrated hydraulic model was used in conjunction with the batch reaction model of chloramine decay to successfully predict chloramine concentrations spatially and temporally throughout the network.

Chlorinated Cyanurates in Drinking Water: Measurement Bias, Stability, and Disinfectant Byproduct Formation

Two chlorinated cyanurates, commonly referred to as dichlor (anhydrous sodium dichloroisocyanurate or sodium dichloroisocyanurate dihydrate) and trichlor (trichloroisocyanuric acid) may be approved for use in United States drinking water systems as chlorine sources. One complication with dichlor or trichlor's application in drinking water is that the actual free chlorine concentration in these systems cannot be quantified accurately by currently approved methods. Based on known water chemistry, two hypothesized advantages of dichlor or trichlor use are potential increased residual chlorine stability and decreased regulated disinfectant byproduct (DBP) formation. To inform these practical considerations, the current research investigated measurement bias in N,N-diethyl-p-phenylenediamine (colorimetric and portable parallel analyzer), indophenol, amperometric titration, and amperometric electrode free chlorine methods. In addition, hold studies using a surface water and dosed with either free chlorine only, dichlor, or trichlor provided the first side-by-side comparisons of disinfectant residual stability and regulated DBP formation.

Effects of ion species on the disinfection byproduct formation in artificial and real water

Disinfection byproducts (DBPs) have attracted extensive attention due to their cytotoxicity and genotoxicity. This study investigates the effects of different ions on DBP formation during chlorination and chloramination in artificial and real water samples. Compared with chlorination, chloramination can reduce the formation of DBPs. K⁺ only reduce the formation of DBPs during chloramination. Ca²⁺ forms less DBPs than Mg²⁺ does during chlorination and chloramination due to the stronger binding effect. Al³⁺ and their hydroxide colloids have a significant effect on DBP formation. Anions have no significant effect on DBP formation. Due to the difference between the real and artificial water samples, the large amount of NH₄⁺ in the real water will form chloramine during chlorination. Furthermore, the effects of different ion in the chlorination will have the same tendency during chlorination. In the wastewater with high ionic strength, the effects of salts are mostly ignored. Studying the effects of different ions on DBP formation is important in controlling the content of DBPs in the disinfection process.

Monochloramine dissipation in storm sewer systems: field testing and model development

Monochloramine (NH₂Cl), as the dominant disinfectant in drinking water chloramination, can provide long-term disinfection in distribution systems. However, NH₂Cl can also be discharged into storm sewer systems and cause stormwater contamination through outdoor tap water uses. In storm sewer systems, NH₂Cl dissipation can occur by three pathways: (i) auto-decomposition, (ii) chemical reaction with stormwater components, and (iii) biological dissipation. In this research, a field NH₂Cl dissipation test was conducted with continuous tap water discharge into a storm sewer. The results showed a fast decrease of NH₂Cl concentration from the discharge point to the sampling point at the beginning of the discharge period, while the rate of decrease decreased as time passed. Based on the various pathways involved in NH₂Cl decay and the field testing results, a kinetic model was developed. To describe the variation of the NH₂Cl dissipation rates during the field testing, a time coefficient f_T was introduced, and the relationship between f_T and time was determined. After calibration through the f_T coefficient, the kinetic model described the field NH₂Cl dissipation process well. The model developed in this research can assist in the regulation of tap water outdoor discharge and contribute to the protection of the aquatic environment.

Effects of feed water NOM variation on chloramine demand from chloramine-decaying soluble microbial products during rechloramination

Earlier, we reported on soluble microbial products-mediated chloramine decay in nitrifying waters. However, we neither separated the agent(s) nor identified the factors that enhanced the production of chloramine-decaying soluble microbial products (cSMPs). Experiments were conducted by feeding reactor sets (each consisting of five reactors connected in series) with treated water (3-8 mg-DOC.L^-1) obtained from a water treatment plant. The reactors simulated various nitrifying conditions that are experienced in a chloraminated system. In unfiltered samples obtained from nitrified reactors, about 89-93% of the dosed chloramine decayed within 40 h. The cSMP-mediated decay accounted for 21-39% of all chloramine decay in the samples from 0 to 5 mg-C.L^-1 fed reactors and 15% in the samples from 7 to 8 mg-C.L^-1 fed reactors. Microbial processes (mediated by nitrifiers and/or heterotrophs) and biomass-associated microbial products (BMPs) in insoluble form accounted for 13-21% for the reactors fed with 0-5 mg-C.L^-1 and 34% for those fed with 7-8 mg-C.L^-1. The cSMPs were separable with a 30 kDa cut-off membrane but not with 50 or 100 kDa membranes, i.e., they were above 30 kDa but below 50 kDa in size, and were confirmed to be a protein(s). The protein(s) accelerated chloramine decay by accelerating chloramine auto-decomposition and nitrite oxidation. As opposed to the traditional belief, unknown factors accounted for approximately 34-53% in commonly encountered re-chloraminated nitrifying waters (2-5 mg-DOC.L^-1). Understanding the identity and role of these factors - such as cSMPs, BMPs, heterotrophs - will lead to a better control of chloramine.

Web-based applications to simulate drinking water inorganic chloramine chemistry

Two web-based applications (WBAs) relevant to drinking water practice are presented to simulate (1) inorganic chloramine formation and stability, including an example inorganic chloramine demand reaction for organic matter and (2) breakpoint curves. The model underlying both WBAs is a well-established inorganic chloramine formation and decay model. The WBAs were developed to be freely accessible over the Internet as web pages (https://usepaord.shinyapps.io/Unified-Combo/ and https://usepaord.shinyapps.io/Breakpoint-Curve/), providing drinking water practitioners (e.g., operators, regulators, engineers, professors, and students) learning tools to explore inorganic chloramine chemistry in an interactive manner without requiring proprietary software or user modeling expertise. The WBAs allow the user to specify two side-by-side simulations, providing a direct comparison of impacts associated with changing simulation conditions (e.g., free chlorine, free ammonia, and total organic carbon concentrations; pH; total alkalinity; and temperature). Once completed, the user may download simulation data to use offline. The WBAs' implementation, validation, and example simulations are described.

Monochloramine loss mechanisms and dissolved organic matter characterization in stormwater

Monochloramine (NH₂Cl) is widely used for secondary disinfection by water utilities. However, Edmonton field stormwater sampling results have shown that NH₂Cl, because of its long-lasting property, can cause stormwater contamination through outdoor potable water uses during the summer season. To protect water sources, it is important to understand NH₂Cl dissipation mechanisms in stormwater. Natural organic matter (NOM) is the dominant species that contributes to NH₂Cl decay in stormwater. In this research, it is proposed that NOM reacted with both NH₂Cl and free chlorine through rapid and long-term reactions during NH₂Cl dissipation. Based on this assumption, a kinetic model was developed and applied to estimate the NH₂Cl decay in real stormwater samples, and the modeling results matched experimental data well under all the conditions. Further, the stormwater dissolved organic matter (SWDOM) collected from different neighborhoods was analyzed by Fourier transform infrared (FTIR) and fluorescence excitation-emission matrix (EEM) techniques. Humic substances were found to be dominant in SWDOM, and the samples from different neighborhoods had similar organic constituents. After reaction with excess NH₂Cl, 25%-41% SWDOM fluorophores converted to inorganic components, while most of DOM remained in organic form. Humic substances as the major components in SWDON, are the dominant precursors of disinfection by-products in chloramination. Therefore, the potential reaction products of stormwater humic substances with NH₂Cl should also be of concern. This research provided a useful method to estimate the NH₂Cl dissipation in stormwater, and the methodology can also be applied for stormwater NH₂Cl decay studies in other cities. Further, it is believed the SWDOM analysis in this research will contribute to future studies of NH₂Cl NOM reaction mechanisms in both storm sewers and drinking water distribution systems.

Formation of DBPs and halogen-specific TOX in the presence of iopamidol and chlorinated oxidants

Iopamidol is a known direct precursor to iodinated and chlorinated DBP formation; however, the influence of iopamidol on both iodo/chloro-DBP formation has yet to be fully investigated. This study investigated the effect of iopamidol on the formation and speciation of halogen-specific total organic halogen (TOX), as well as iodo/chloro-DBPs, in the presence of 3 source waters (SWs) from Northeast Ohio and chlorinated oxidants. Chlorination and chloramination of SWs were carried out at pH 6.5-9.0 and, different iopamidol and dissolved organic carbon (DOC) concentrations. Total organic iodine (TOI) loss was approximately equal (22-35%) regardless of SW. Total organic chlorine (TOCl) increased in all SWs and was substantially higher in the higher SUVA₂₅₄ SWs. Iopamidol was a direct precursor to chloroform (CHCl₃), trichloroacetic acid (TCAA), and dichloroiodomethane (CHCl₂I) formation. While CHCl₃ and TCAA exhibited different formation trends with varying iopamidol concentrations, CHCl₂I increased with increasing iopamidol and DOC concentrations. Low concentrations of iodo-acids were detected without discernible trends. Total trihalomethanes (THMs), total haloacetic acids (HAAs), TOCl, and unknown TOCl (UTOCl) were correlated with fluorescence regional volumes and SUVA₂₅₄. The yields of all these species showed a strong positive correlation with fulvic, humic, and combined humic and fulvic regions, as well as SUVA₂₅₄. Iopamidol was then compared to the 3 SWs with respect to DBP yield. Although the SUVA₂₅₄ of iopamidol was relatively high, it did not produce high yields of THMs and HAAs compared to the 3 SWs. However, chlorination of iopamidol did result in high yields of TOCl and UTOCl.

The Henry's constant of monochloramine

Monochloramine is a secondary disinfectant used in drinking water and is also formed in chlorinated wastewater. While known to hydrolyze over time and react with dissolved organic matter, its partitioning between the aqueous and gas phase has not been extensively studied. Preliminary experiments demonstrated that monochloramine concentrations in solutions open to the atmosphere or actively aerated decreased more rapidly than in sealed solutions, indicating significant losses to the atmosphere. For example, a monochloramine solution open to the atmosphere yielded a loss rate constant of 0.08 d^-1, a value twice that for sealed samples without headspace (0.04 d^-1) where loss occurs exclusively as a result of hydrolysis. A solution aerated at 10 mL s^-1 had a loss rate constant nearly 10× greater than that for hydrolysis alone (0.35 d^-1). To better understand partitioning of monochloramine to the gas phase and potential for volatilization, the dimensionless Henry's law constants of monochloramine (K_H) were determined using an equilibrium headspace technique at five different temperatures (11, 16, 21, 27, and 32 °C). The resulting values ranged from 8 × 10^-3 to 4 × 10^-2, indicating a semi-volatile compound, and were found to be consistent with quantitative structure activity relationship predictions. At 20 °C, monochloramine exhibits a dimensionless Henry's constant of about 1.7 × 10^-2 which is 35 times greater than ammonia but comparable to the Henry's constant of inorganic semi-volatile compounds such sulfur dioxide. The Henry's constant values for monochloramine suggests that volatilization could be a relevant loss process in open systems such as rivers receiving chlorinated wastewater effluent, swimming pools and cooling towers.

Field data analysis of active chlorine-containing stormwater samples

Many municipalities in Canada and all over the world use chloramination for drinking water secondary disinfection to avoid DBPs formation from conventional chlorination. However, the long-lasting monochloramine (NH₂Cl) disinfectant can pose a significant risk to aquatic life through its introduction into municipal storm sewer systems and thus fresh water sources by residential, commercial, and industrial water uses. To establish general total active chlorine (TAC) concentrations in discharges from storm sewers, the TAC concentration was measured in stormwater samples in Edmonton, Alberta, Canada, during the summers of 2015 and 2016 under both dry and wet weather conditions. The field-sampling results showed TAC concentration variations from 0.02 to 0.77 mg/L in summer 2015, which exceeds the discharge effluent limit of 0.02 mg/L. As compared to 2015, the TAC concentrations were significantly lower during the summer 2016 (0-0.24 mg/L), for which it is believed that the higher precipitation during summer 2016 reduced outdoor tap water uses. Since many other cities also use chloramines as disinfectants for drinking water disinfection, the TAC analysis from Edmonton may prove useful for other regions as well. Other physicochemical and biological characteristics of stormwater and storm sewer biofilm samples were also analyzed, and no significant difference was found during these two years. Higher density of AOB and NOB detected in the storm sewer biofilm of residential areas - as compared with other areas - generally correlated to high concentrations of ammonium and nitrite in this region in both of the two years, and they may have contributed to the TAC decay in the storm sewers. The NH₂Cl decay laboratory experiments illustrate that dissolved organic carbon (DOC) concentration is the dominant factor in determining the NH₂Cl decay rate in stormwater samples. The high DOC concentrations detected from a downstream industrial sampling location may contribute to a high stormwater NH₂Cl decay rate in this area.

Comparison of the effects of chloramine and chlorine on the aromaticity of dissolved organic matter and yields of disinfection by-products

This study compared effects of chlorination and chloramination on the chromophores of dissolved organic matter (DOM) and attendant formation of disinfection by-products (DBPs) in raw and treated surface waters. Comparison of the differential absorbance spectra of chloraminated and chlorinated waters shows that interactions of chloramine with DOM chromophores result in changes that are in many respects similar to those observed for chlorine although the extent of degradation of DOM chromophores and the attendant decrease of DOM aromaticity by chloramine are less pronounced than that caused by free chlorine. The degradation of DOM chromophores caused by the examined disinfectants indicated that in both cases a gradual decrease of DOM took place. Decreases of DOM aromaticity estimated based on the changes of DOM absorbance at 254 or 280 nm were correlated with chlorine consumption in a similar way for both examined disinfectants. Correlations between changes of DOM absorbance and yields of dihaloacetic acids (DHAA) were also similar for chlorination and chloramination. This was interpreted to indicate that the generation of DHAA proceeds via the degradation of the reactive sites associated with DOM chromophores irrespective of whether these sites are engaged by chlorine or chloramine. Correlations between the decrease of DOM aromaticity and formation of other DBP (e.g. trihalomethanes - THM, trihaloacetic acids - THAA and dihaloacetonitriles - DHAN) for chloramine and chlorine were also observed but, as opposed to the observations for DHAA, the correlations between degradation of DOM aromaticity and yields of THM, THAA or DHAN were different for chlorination and chloramination.

Chlor(am)ination of iopamidol: Kinetics, pathways and disinfection by-products formation

The degradation kinetics, pathways and disinfection by-products (DBPs) formation of iopamidol by chlorine and chloramines were investigated in this paper. The chlorination kinetics can be well described by a second-order model. The apparent second-order rate constants of iopamidol chlorination significantly increased with solution pH. The rate constants of iopamidol with HOCl and OCl^- were calculated as (1.66 ± 0.09) × 10^-3 M^-1 s^-1 and (0.45± 0.02) M^-1 s^-1, respectively. However, the chloramination of iopamidol fitted well with third-order kinetics and the maximum of the apparent rate constant occurred at pH 7. It was inferred that the free chlorine (i.e., HOCl and OCl^-) can react with iopamidol while the combined chlorine species (i.e., NH₂Cl and NHCl₂) were not reactive with iopamidol. The main intermediates during chlorination or chloramination of iopamidol were identified using ultra performance liquid chromatography - electrospray ionization-mass spectrometry (UPLC-ESI-MS), and the destruction pathways including stepwise deiodination, hydroxylation as well as chlorination were then proposed. The regular and iodinated DBPs formed during chlorination and chloramination of iopamidol were measured. It was found that iodine conversion from iopamidol to toxic iodinated DBPs distinctly increased during chloramination. The results also indicated that although chloramines were much less reactive than chlorine toward iopamidol, they led to the formation of much more toxic iodinated DBPs, especially CHI₃.

Formation and reactivity of inorganic and organic chloramines and bromamines during oxidative water treatment

The formation and further reactions of halamines during oxidative water treatment can be relevant for water quality. In this study, we investigated the formation and reactivity of several inorganic and organic halamines (monochloramine, N-chloromethylamine, N-chlorodimethylamine, monobromamine, dibromamine, N-bromomethylamine, N,N-dibromomethylamine, and N-bromodimethylamine) by kinetic experiments, transformation product analysis, and quantum chemical computations. Kinetic model simulations were conducted to evaluate the relevance of halamines for various water treatment scenarios. Halamines were quickly formed from the reaction of chlorine and bromine with ammonia or organic amines. Species-specific second-order rate constants for the reaction of chlorine and bromine with ammonia, methyl- and dimethylamine were in the order of 10⁶-10⁸ M^-1s^-1. The formed halamines were found to be reactive towards phenolic compounds, forming halogenated phenols via electrophilic aromatic substitution (phenol and resorcinol) or quinones via electron transfer (catechol and hydroquinone). At near neutral pH, apparent second-order rate constants for these reactions were in the order of 10^-4-10^-1 M^-1s^-1 for chloramines and 10¹-10² M^-1s^-1 for bromamines. Quantum chemical computations were used to determine previously unknown aqueous pK_a values, gas phase bond dissociation energies (BDE) and partial atomic charges of the halamines, allowing a better understanding of their reactivities. Kinetic model simulations, based on the results of this study, showed that during chlorination inorganic and organic chloramines are the main halamines formed. However, their further reactions with organic matter are outcompeted kinetically by chlorine. During ozonation, mainly inorganic bromamines are formed, since ozone quickly oxidizes organic amines. The further reactions of bromamine are typically outcompeted by ozone and thus generally of minor importance. The use of peracetic acid for saline ballast water treatment can result in the formation of substantial amounts of bromamines, which can react with dissolved organic matter and contribute to the formation of brominated products.

Mechanistic Study on the Formation of Cl-/Br-/I-Trihalomethanes during Chlorination/Chloramination Combined with a Theoretical Cytotoxicity Evaluation

Chlorination followed by chloramination can be used to mitigate the formation of potentially toxic iodinated disinfection byproducts (I-DBPs) while controlling the formation of regulated chloro-bromo-DBPs (Cl-/Br-DBPs). Water samples containing dissolved organic matter (DOM) isolates were subjected to 3 disinfection scenarios: NH2Cl, prechlorination followed by ammonia addition, and HOCl alone. A theoretical cytotoxicity evaluation was carried out based on the trihalomethanes (THMs) formed. This study demonstrates that the presence of bromide not only enhances the yield and rate of iodate formation, it also increases the formation of brominated I-THM precursors. A shift in the speciation from CHCl2I to the more toxic CHBr2I, as well as increased iodine incorporation in THMs, was observed in the presence of bromide. For low bromide concentrations, a decrease in I-THM formation and theoretical cytotoxicity was achieved only for high prechlorination times, while for high bromide concentrations, a short prechlorination time enabled the full conversion of iodide to iodate. For low DOM concentrations or DOM with low reactivity, Br-/I-THMs were preferentially formed for short prechlorination times, inducing high cytotoxicity. However, for high chlorine exposures, the cytotoxicity induced by the formation of regulated THMs might outweigh the benefit of I-THM mitigation. For high DOM concentrations or DOM with higher reactivity, mixed I-THMs were formed together with high concentrations of regulated THMs. In this case, based on the cytotoxicity of the THMs formed, the use of NH2Cl is recommended.

Effectiveness of breakpoint chlorination to reduce accelerated chemical chloramine decay in severely nitrified bulk waters

Rectifying the accelerated chloramine decay after the onset of nitrification is a major challenge for water utilities that employ chloramine as a disinfectant. Recently, the evidence of soluble microbial products (SMPs) accelerating chloramine decay beyond traditionally known means was reported. After the onset of nitrification, with an intention to inactivate nitrifying bacteria and thus maintaining disinfectant residuals, breakpoint chlorination followed by re-chloramination is usually practiced by water utilities. However, what actually breakpoint chlorination does beyond known effects is not known, especially in light of the new finding of SMPs. In this study, experiments were conducted using severely nitrified chloraminated water samples (chloramine residuals <0.5 mg Cl2 L−1, nitrite residuals >0.1 mg N L−1 and an order of magnitude higher chloramine decay rate compared to normal decay) obtained from two laboratory scale systems operated by feeding natural organic matter (NOM) containing and NOM free waters. Results showed that the accelerated decay of chloramine as a result of SMPs can be eliminated by spiking higher free chlorine residuals (about 0.92 ± 0.03 to 1.16 ± 0.12 mg Cl2 L−1) than the stoichiometric requirement for breakpoint chlorination and nitrite oxidation. Further, accelerated initial chlorine decay showed chlorine preferentially reacts with nitrite and ammonia before destroying SMPs. This study, clearly demonstrated there is an additional demand from SMPs that needs to be satisfied to effectively recover disinfection residuals in subsequent re-chloramination.

Chlorination and chloramination of tetracycline antibiotics: disinfection by-products formation and influential factors

Formation of disinfection by-products (DBPs) from chlorination and chloramination of tetracycline antibiotics (TCs) was comprehensively investigated. It was demonstrated that a connection existed between the transformation of TCs and the formation of chloroform (CHCl3), carbon tetrachloride (CCl4), dichloroacetonitrile (DCAN) and dichloroacetone (DCAce). Factors evaluated included chlorine (Cl2) and chloramine(NH2Cl) dosage, reaction time, solution pH and disinfection modes. Increased Cl2/NH2Cl dosage and reaction time improved the formation of CHCl3 and DCAce. Formation of DCAN followed an increasing and then decreasing pattern with increasing Cl2 dosage and prolonged reaction time. pH affected DBPs formation differently, with CHCl3 and DCAN decreasing in chlorination, and having maximum concentrations at pH 7 in chloramination. The total concentrations of DBPs obeyed the following order: chlorination>chloramination>pre-chlorination (0.5h)>pre-chlorination (1h)>pre-chlorination (2h).

Integrated chemical and toxicological investigation of UV-chlorine/chloramine drinking water treatment

As the use of alternative drinking water treatment increases, it is important to understand potential public health implications associated with these processes. The objective of this study was to evaluate the formation of disinfection byproducts (DBPs) and cytotoxicity of natural organic matter (NOM) concentrates treated with chlorine, chloramine, and medium pressure ultraviolet (UV) irradiation followed by chlorine or chloramine, with and without nitrate or iodide spiking. The use of concentrated NOM conserved volatile DBPs and allowed for direct analysis of the treated water. Treatment with UV prior to chlorine in ambient (unspiked) samples did not affect cytotoxicity as measured using an in vitro normal human colon cell (NCM460) assay, compared to chlorination alone when toxicity is expressed on the basis of dissolved organic carbon (DOC). Nitrate-spiked UV+chlorine treatment produced greater cytotoxicity than nitrate-spiked chlorine alone or ambient UV+chlorine samples, on both a DOC and total organic halogen basis. Samples treated with UV+chloramine were more cytotoxic than those treated with only chloramine using either dose metric. This study demonstrated the combination of cytotoxicity and DBP measurements for process evaluation in drinking water treatment. The results highlight the importance of dose metric when considering the relative toxicity of complex DBP mixtures formed under different disinfection scenarios.

Formation of brominated disinfection byproducts during Chloramination of drinking water: new polar species and overall kinetics

The formation of brominated disinfection byproducts (Br-DBPs), which are generally significantly more cytotoxic and genotoxic than their chlorinated analogues, in chloramination has not been fully examined. In this work, the formation of new polar Br-DBPs in simulated drinking waters was examined using state-of-the-art ultraperformance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry. As many as 29 aliphatic, aromatic, or nitrogenous polar Br-DBPs were detected in chloramination, and five of them (including 2,4,6-tribromoresorcinol, 2,6-dibromo-4-nitrophenol, 2,2,4-tribromo-5-hydroxy-4-cyclopentene-1,3-dione, 2,2,4-dibromochloro-5-hydroxy-4-cyclopentene-1,3-dione, and 2,2,4-bromodichloro-5-hydroxy-4-cyclopentene-1,3-dione) were tentatively identified. Unlike chlorination, chloramination favored the formation of aromatic and nitrogenous polar Br-DBPs and was mild enough to allow polar intermediate Br-DBPs to accumulate. To further explore the formation mechanism of Br-DBPs in chloramination, a quantitative empirical model involving 33 major reactions was developed to describe the overall kinetics. According to the modeling results, bromochloramine and monobromamine were the major species responsible for 54.2-58.1% and 41.7-45.7%, respectively, of the formed Br-DBPs, while hypobromous acid accounted for only 0.2% of the formed Br-DBPs; direct reactions between monochloramine and natural organic matter accounted for the majority of the formed chlorinated DBPs (93.7-95.1%); hypochlorous acid and hypobromous acid in the chloramination were at ng/L or subng/L levels, which were not enough to cause polar intermediate Br-DBPs to decompose.

Assessment and management of the performance risk of a pilot reclaimed water disinfection process

Chlorination disinfection has been widely used in reclaimed water treatment plants to ensure water quality. In order to assess the downstream quality risk of a running reclaimed water disinfection process, a set of dynamic equations was developed to simulate reactions in the disinfection process concerning variables of bacteria, chemical oxygen demand (COD), ammonia and monochloramine. The model was calibrated by the observations obtained from a pilot disinfection process which was designed to simulate the actual process in a reclaimed water treatment plant. A Monte Carlo algorithm was applied to calculate the predictive effluent quality distributions that were used in the established hierarchical assessment system for the downstream quality risk, and the key factors affecting the downstream quality risk were defined using the Regional Sensitivity Analysis method. The results showed that the seasonal upstream quality variation caused considerable downstream quality risk; the effluent ammonia was significantly influenced by its upstream concentration; the upstream COD was a key factor determining the process effluent risk of bacterial, COD and residual disinfectant indexes; and lower COD and ammonia concentrations in the influent would mean better downstream quality.

Disinfection by-products formation and precursors transformation during chlorination and chloramination of highly-polluted source water: significance of ammonia

Many studies have demonstrated the different trends of disinfection by-products (DBPs) formation between chlorination and chloramination. However, the reactions between precursors and disinfectants are widely assumed to be "black box" and the reasons for abovementioned difference are not well illustrated. This study focused on source water with high levels of natural organic matter (NOM) and bromide, and compared the transformation of NOM specific characteristics and the ratios of specific DBPs as an equivalent of chlorine to total organic halogen (TOX) among three disinfection scenarios of chlorination, chloramination and chlorine-chloramine sequential treatment (Cl2-NH2Cl process). A three-reaction-phrases model was proposed thereafter to illustrate the major reactions involved in, i.e., stage-I: rapid consumption of fast reactive sites (DOC1), which transformed to slow reactive sites (DOC2) and measured DBPs, i.e., trihalomethanes, haloacetic acids, etc; stage-II: oxidation and/or halogenation of DOC2 into unknown TOX (UTOX) intermediates; stage-III: oxidation of UTOX intermediates into measured DBPs. The effect of ammonia was also quantified. Ammonia is observed to inhibit the formation of measured DBPs by 68-92%, 94-99%, and 92-95% of that in chlorination in Stage-I, II, and III, respectively, and the formation of UTOX is reduced by 2-80%, 60-94%, and 82-93% accordingly. These effects lead to the steady accumulation of DBPs intermediates such as UTOX, and to the elevated UTOX/TOX during chloramination and Cl2-NH2Cl process thereafter. The results illustrate the mechanism of ammonia participating in DBPs formation, and are valuable to fill in the gap between the transformation of precursors and the formation of different DBPs.

Formation of haloacetic acids from dissolved organic matter fractions during chloramination

The objective of this study was to investigate the roles of dissolved organic matter (DOM) fractions, pH and bromide concentration in the formation of haloacetic acids (HAA) during chloramination. DOM from two surface waters with a low (2.9 L/mg-m) and high (5.1 L/mg-m) specific UV absorbance (SUVA(254)) values was isolated and fractionated into three fractions based on the hydrophobicity [i.e., hydrophobic (HPO), transphilic (TPH) and hydrophilic (HPI)]. DOM mass balances and DBP reactivity checks were performed to characterize the effects of isolation and fractionation steps. The fractions were chloraminated at three pHs and three bromide concentrations. The results showed that pH was the most important factor controlling HAA formation and speciation. The HAA yields significantly decreased with increase in pH from 6.3 to 9.0. The impact of bromide in the formation of brominated HAA species also became less important with increasing pH, and no brominated specie was detectable at pH 9. HPO fractions of the two source waters consistently showed higher HAA yields than TPH and HPI fractions. On the other hand, HPI fractions showed higher bromine incorporation than HPO and TPH fractions. To maintain higher and relatively stable combined chlorine residuals while reducing HAA formation, water utilities may consider keeping pH above 7.5 as one strategy. This will also lower the formation of brominated HAA species which have been shown to be more cyto- and geno-toxic than their chlorinated analogs.