Occurrence and simulation of trihalomethanes in swimming pool water: A simple prediction method based on DOC and mass balance

Disinfection by-product formation potential in response to variability in dissolved organic matter and nutrient inputs: Insights from a mesocosm study

Changes in rainfall patterns driven by climate change affect the transport of dissolved organic matter (DOM) and nutrients through runoff to freshwater systems. This presents challenges for drinking water providers. DOM, which is a heterogeneous mix of organic molecules, serves as a critical precursor for disinfection by-products (DBPs) which are associated with adverse health effects. Predicting DBP formation is complex due to changes in DOM concentration and composition in source waters, intensified by altered rainfall frequency and intensity. We employed a novel mesocosm approach to investigate the response of DBP precursors to variability in DOM composition and inorganic nutrients, such as nitrogen and phosphorus, export to lakes. Three distinct pulse event scenarios, mimicking extreme, intermittent, and continuous runoff were studied. Simultaneous experiments were conducted at two boreal lakes with distinct DOM composition, as reflected in their color (brown and clear lakes), and bromide content, using standardized methods. Results showed primarily site-specific changes in DBP precursors, some heavily influenced by runoff variability. Intermittent and daily pulse events in the clear-water mesocosms exhibited higher haloacetonitriles (HANs) formation potential linked to freshly produced protein-like DOM enhanced by light availability. In contrast, trihalomethanes (THMs), associated with humic-like DOM, showed no significant differences between pulse events in the brown-water mesocosms. Elevated bromide concentration in the clear mesocosms critically influenced THMs speciation and concentrations. These findings contribute to understanding how changing precipitation patterns impact the dynamics of DBP formation, thereby offering insights for monitoring the mobilization and alterations of DBP precursors within catchment areas and lake ecosystems.

Advances and research needs for disinfection byproducts control strategies in swimming pools

The control of disinfection byproducts (DBPs) in swimming pools is of great significance due to the non-negligible toxicity and widespread existence of DBPs. However, the management of DBPs remains challenging as the removal and regulation of DBPs is a multifactorial phenomenon in pools. This study summarized recent studies on the removal and regulation of DBPs, and further proposed some research needs. Specifically, the removal of DBPs was divided into the direct removal of the generated DBPs and the indirect removal by inhibiting DBP formation. Inhibiting DBP formation seems to be the more effective and economically practical strategy, which can be achieved mainly by reducing precursors, improving disinfection technology, and optimizing water quality parameters. Alternative disinfection technologies to chlorine disinfection have attracted increasing attention, while their applicability in pools requires further investigation. The regulation of DBPs was discussed in terms of improving the standards on DBPs and their preccursors. The development of online monitoring technology for DBPs is essential for implementing the standard. Overall, this study makes a significant contribution to the control of DBPs in pool water by updating the latest research advances and providing detailed perspectives.

Modelling chloroform in indoor swimming pool air and water: the influences of internal air circulation and occupants

The release of chloroform from water to air in an indoor swimming pool (ISP) exhibits complex physicochemical interactions among many variables, including environmental conditions, occupant activities, and geometry of the ISP. By combining the relevant variables, a structured mathematical model, the double-layer air compartment (DLAC) model, was developed to predict the level of chloroform in ISP air. A physical parameter, the indoor airflow recycle ratio (R), was incorporated into the DLAC model due to internal airflow circulation resulting in the ISP structural configuration. The theoretical R-value for a specific indoor airflow rate (v_y) can be found by fitting the predicted residence time distribution (RTD) to the simulated RTD from computational fluid dynamics (CFD), showing a positive linear relationship with v_y. The mechanical energies induced by occupant activities were converted into a lumped overall mass-transfer coefficient to account for the enhanced mass transfer of chloroform from the water into the air and mixing in ISP air. The DLAC model predicted that chloroform air concentrations were statistically less accurate without considering the influence of R compared with the online open-path Fourier transform infrared measurements. A novel index, the magnitude of emission (MOE) from swimmers, was linked to the level of chloroform in ISP water. The capability of the DLAC model associated with the MOE concept may facilitate upgrading the hygiene management of ISPs, including the ability to administer necessary chlorine additives in pool water and monitor the chloroform in ISP air.

Halogenated By-Products in Chlorinated Indoor Swimming Pools: A Long-Term Monitoring and Empirical Modeling Study

Monitoring the disinfection process and swimming pool water quality is essential for the prevention of microbial infections and associated diseases. However, carcinogenic and chronic-toxic disinfection by-products (DBPs) are formed with reactions between disinfectants and organic/inorganic matters. DBP precursors in swimming pools originate from anthropogenic sources (body secretions, personal care products, pharmaceuticals, etc.) or chemicals used in pools. Temporal (48 weeks) water quality trends of trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and halonitromethanes (HNMs) in two swimming pools (SP-A and SP-B) and precursor-DBP relationships were investigated in this study. Weekly samples were taken from swimming pools, and several physical/chemical water quality parameters, absorbable organic halides (AOX), and DBPs were determined. THMs and HAAs were the most detected DBP groups in pool water. While chloroform was determined to be the dominant THM compound, dichloroacetic acid and trichloroacetic acid were the dominant HAA compounds. The average AOX concentrations were measured to be 304 and 746 μg/L as Cl^- in SP-A and SP-B, respectively. Although the amount of AOX from unknown chlorinated by-products in SP-A did not vary temporally, a significant increase in unknown DBP concentrations in SP-B was observed over time. AOX concentrations of chlorinated pool waters were determined to be an important parameter that can be used to estimate DBP concentrations.

Within-day variation and health risk assessment of trihalomethanes (THMs) in a chlorinated indoor swimming pool in China

Trihalomethanes (THMs) are the most common species of disinfection by-products (DBPs) in swimming pools and have received widespread attention due to their risk to public health. However, studies examining within-day variation and the carcinogenic health risks from exposure to THMs in indoor swimming pools are limited. Our study aimed to detect the within-day variation of four THMs categories and carcinogenic health risk in indoor swimming pool water in Taiyuan, China, and to examine the correlations between THMs and environmental parameters. Our results showed chloroform (TCM) was the most abundant component in THMs with median concentrations from 0.038-0.118 μg/m³. TCM and THMs were significantly positively correlated with FCl and significantly negatively correlated with the cumulative number of swimmers (CNS) in the swimming pool. The concentration of total THMs and TCM, lifetime average daily doses (LADD) of TCM, and the total lifetime cancer risks (ELCR) values of THMs declined with time with the highest level occurring at 8:00 am. ELCR values of THMs were in the range of 1.368 × 10^-5-1.968 × 10^-5, which exceeded the negligible risk level (10^-6) defined by US EPA. Our results suggest that THM occurrence and the carcinogenic health risks in pool water varied temporally. Exposure to pool water THMs may pose a carcinogenic risk to human health, especially at the pool's opening time.

A new computer-based index for swimming pools' environmental health assessment in big data environment by consensus-based fuzzy group decision-making models

Swimming pools are popularly used for sport and recreational purposes worldwide. These places influence swimmers' health as they are considered public places. This study attempted to introduce a process mining framework which analyzes the environmental health status in swimming pools. In this context, a new numerical index namely Swimming Pool Environmental Health Index (SPEHI) was developed through which, big data extracted from checklists of environmental health inspection of swimming pools were analyzed in fuzzy environment. The methodology comprises MCDM (Multi- Criteria Decision-Making) approach including fuzzy TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) and fuzzy OWA (Ordered Weighting Average). The performance of this index was evaluated through an applied example on 12 swimming pools in Shiraz, Iran that was run for a three-year sequence from 2015 to 2017. Among 30 evaluation criteria used in this index, the greatest (0.61) and lowest (0.35) group weights were dedicated to "Residual chlorine biological water quality" and "existence of drinking water facilities", respectively. For the study area, SPEHI showed a wide range of environmental health conditions between 37.8 (Relatively good) to 98.19 (Excellent). The extended index could shrink swimming pool's big data to concise values which are interpretable for health experts and managers of sport sector. It helps figuring out the trends of hygiene conditions in a swimming pool over the time and easy access to compare a city's swimming pools as well. The methodology is flexible in structure and thus, it could be applied for other sporting places.

The Occurrence of N-nitrosodimethylamine (NDMA) in Swimming Pools: An Overview

The occurrence of several disinfectant byproducts has been investigated in swimming pools. Until now, there are only a few studies on nitrosamine, particularly N-nitrosodimethylamine in swimming pool water. This could be due to the lack of a suitable method that is sensitive enough for the measurement of N-nitrosodimethylamine in pool waters. Other disinfectant byproducts formed in pool water widely documented are trihalomethanes, haloacetic acids, halonitromethanes, and chloramines but inadequate information on N-nitrosodimethylamine. This paper provides a review of the nitrogenous disinfectant byproduct in swimming pools and its health implications. Anthropogenic substances introduced by swimmers such as sweat, lotions, and urine contribute to the formation of N-nitrosodimethylamine. The reaction of secondary amines such as dimethylamine with mono/dichloroamines produced dimethyl hydrazine and further undergo oxidation to form N-nitrosodimethylamine. The reaction of chlorine and other disinfectants with these anthropogenic sources in swimming pools cause cancer and asthma in human tissues. Thus, the assessment of N-nitrosodimethylamine in the swimming pool is less well documented. Therefore, the health consequences, mutagenic, and genotoxic potentials of N-nitrosodimethylamine should be the focus of more research studies.

The role of biofilms on the formation and decay of disinfection by-products in chlor(am)inated water distribution systems

This study investigated the role of biofilms on the formation and decay of disinfection by-products (DBPs) in chlorine (Cl₂) or monochloramine (NH₂Cl) disinfected reactors under the conditions related to drinking water distribution systems (DWDSs). Biofilm analysis results revealed that at 0.5 mg/L of disinfectant residual, both Cl₂ and NH₂Cl were not effective to remove biofilms. As the disinfectant residual increased, biofilms could be eradicated by Cl₂, while remaining biofilms were still present even under the highest allowable NH₂Cl dose (4 mg/L) for 25 days. Low DBP formation was observed under the recommended minimum Cl₂ residual (0.5 mg/L), which could be attributed to limited Cl₂ reactions with biofilms, as well as a combination of the volatilization and biodegradation of DBPs. However, when Cl₂ residuals reached 2 mg/L, DBP concentrations in bulk water increased sharply beyond the DBP formation of the feed solution, with trihalomethanes and haloacetic acids being the most prevalent DBP species. The sharp increase was temporary for 15 days because of the removal of biofilms. For unregulated DBPs, high levels of haloacetonitriles were observed as attached biofilms reacted with the increased Cl₂ dose and provided an additional organic nitrogen source for nitrogenous DBP formation. When maximum Cl₂ residual (4 mg/L) was applied, no further increase of DBPs was observed because of biofilm eradication. For NH₂Cl disinfection, the DBP levels were much lower than those of Cl₂ disinfection, with small differences in DBP formation for different NH₂Cl residuals. Overall, this study provides insights into optimizing disinfection protocols for water utilities by balancing the benefits of disinfection application for biofilm control with minimized toxic DBP formation in DWDSs.

Human health risk estimation and predictive modeling of halogenated disinfection by- products (chloroform) in swimming pool waters: a case study of Dhanbad, Jharkhand, India

Disinfection is an important process to make the water free from harmful pathogenic substances, but sometimes it results in the formation of harmful by-products. Development of predictive models is required to define the concentration of THMs in pool water. Majority of studies reported inhalation to be the most significant THMs exposure route which is more likely to be dependent upon the concentration of THMs in pool water and in air. THMs concentration in the analyzed pool water samples and in air was found to be 197.18 ± 16.31 μg L-1 and 0.033 μg m3-1, respectively. Statistical parameters such as high correlation coefficients, high R2 values, low standard error, and low mean square error of prediction indicated the validity of MLR based linear model over non-linear model. Therefore, linear model can be most suitably used to pre-assess and predict the THMs levels in swimming pool water. Risk estimation studies was conducted by using the united states environmental protection agency (USEPA) Swimmer Exposure Assessment Model (SWIMODEL). The lifetime time cancer risk values related to chloroform exceeded 10-6 for both the sub-population. Inhalation exposure leads to maximum risk and contributed up to 99% to total cancer risk. Risk due to other exposure pathways like accidental ingestion and skin contact was found to be negligible and insignificant. Monte Carlo simulation results revealed that the simulated THMs risk values for the studied exposure pathways lies within ±3.1% of the average risk values obtained using SWIMODEL. Hence, the risk estimates obtained using SWIMODEL seemed to be appropriate in determining the potential risk exposure of THMs on human health. Variation in input parameters like body weight (BW) and skin surface area (SA) leads to difference in risk estimates for the studied population. Non cancer risk was found to be insignificant as represented by low hazard quotient (HQ < 1) values. Through monitoring and regulations on control of THMs in swimming pool water is required to minimize the risk associated.

Assessment of exposure of children swimmers to trihalomethanes in an indoor swimming pool

This study aimed to understand the exposure levels of trihalomethanes (THMs) in an indoor swimming pool and calculate the risks of exposure to THMs, based on the presence of each THM species, of children swimmers aged 6-17, in Beijing, China. We obtained exposure factors for the children through questionnaires and measured THM concentrations through laboratory tests, and we combined the results with an exposure model to calculate the risks, with consideration of different exposure routes (oral ingestion, inhalation and dermal absorption). In terms of exposure factors for the swimmers aged 6-17, the average body weight, exposure duration, exposure frequency, swimming time, shower time, changing time, warm-up exercise and rest time, skin surface area and ingestion rate of pool water were 40.46 kg, 2.70 years, 96 events/year, 64.03 min/event, 17.04 min/event, 15.31 min/event, 12.71 min/event, 1.37 m² and 48.93 ml/event, respectively. The THM concentrations in swimming pool water, shower water, swimming pool air and locker room air were 67.17 μg/L, 12.64 μg/L, 358.66 μg/m³ and 40.98 μg/m³, respectively. The average cancer risk of THMs was 5.44 × 10^-6, which is an unacceptable risk according to the United State Environmental Protection Agency (USEPA) Guidelines. The average hazard index was 0.007, i.e., less than 1, indicating that the noncancer risk was acceptable. Chloroform (TCM) was the main substance in four species of THMs and inhalation exposure was the main exposure pathway. The risk of cancer and noncancer from inhalation exposure to THMs accounts for 97-99% of the total risk. As a result, the disease control authorities and administrative department should pay attention to the health and safety of swimming facilities and, at the same time, establish standards for THMs in the air through further research.

Characterization of organic matter by HRMS in surface waters: Effects of chlorination on molecular fingerprints and correlation with DBP formation potential

In order to understand and minimize the formation of halogenated disinfection by-products (DBPs), it is important to investigate how dissolved organic matter (DOM) contributes to their generation. In the present study, we analysed the DOM profile of water samples from the Barcelona catchment area by high resolution mass spectrometry (HRMS) and we studied the changes after chlorination. Chlorination produced significant changes in the DOM, decreased the average m/z and Kendrick mass defect (KMD) of their spectra and decreased the number and abundance of lignin-like features. The Van Krevelen (VK) fingerprint exhibited several noticeable changes, including the appearance of highly oxidized peaks in the tannin-like region (average O/C, 0.78 ± 0.08), the appearance of features with low H/C and the disappearance of more than half of the lipids-like features. Up to 657 halogenated peaks were generated during sample chlorination, most of which in the condensed hydrocarbons-like and the lignin-like region of the VK diagram. Around 200 features were found to be strongly correlated (ρ ≥ 0.795) to the formation potential of trihalomethanes (THMs) and 5 were correlated with the formation potential of haloacetonitrile (HANs). They all were plotted in the lignin fraction of the VK diagram, but both groups of features exhibited different nitrogen content: those features related to HANs FP had at least one nitrogen atoms in their structures, whilst those related to THMs did not.

+Chlorination by-products in indoor swimming pools: Development of a pilot pool unit and impact of operating parameters

Chlorine addition in swimming pools ensures the microbiological quality of the water and the bathers' safety. However, water chlorination is associated with disinfection byproducts (DBP) formation and adverse health effects. The impact of operating parameters and innovative water treatment systems on DBPs levels has been reported in several studies, but sampling campaign in real pools remain difficult to carry out, mainly due to unexpected attendance variations. This study presents the development of a pilot pool plant allowing to perform experiments under controlled and reproducible conditions. Bathers inputs were simulated both for the organic load and for the mechanical agitation of water. Two sampling campaigns were performed during the building of the pilot, before and after the hall was closed. Key operating parameters such as chlorine dose, water temperature and attendance were controlled and monitored. DBP levels in the pilot plant were representative of French indoor swimming pools and the impact of bathers' activity was visible on volatile DBPs. Furthermore, correlations could be stated between operating parameters and DBP levels. Stripping effectively reduced volatile DBP concentrations in water. Moreover, energy consumption data, which are usually very scarce in experimental studies, showed the influence of heat pump consumption on the global energy consumption.

Body fluid analog chlorination: Application to the determination of disinfection byproduct formation kinetics in swimming pool water

Disinfection by-products (DBPs) are formed in swimming pools by the reactions of bather inputs with the disinfectant. Although a wide range of molecules has been identified within DBPs, only few kinetic rates have been reported. This study investigates the kinetics of chlorine consumption, chloroform formation and dichloroacetonitrile formation caused by human releases. Since the flux and main components of human inputs have been determined and formalized through Body Fluid Analogs (BFAs), it is possible to model the DBPs formation kinetics by studying a limited number of precursor molecules. For each parameter the individual contributions of BFA components have been quantified and kinetic rates have been determined, based on reaction mechanisms proposed in the literature. With a molar consumption of 4 mol Cl₂/mol, urea is confirmed as the major chlorine consumer in the BFA because of its high concentration in human releases. The higher reactivity of ammonia is however highlighted. Citric acid is responsible for most of the chloroform produced during BFA chlorination. Chloroform formation is relatively slow with a limiting rate constant determined at 5.50 × 10^-3 L/mol/sec. L-histidine is the only precursor for dichloroacetonitrile in the BFA. This DBP is rapidly formed and its degradation by hydrolysis and by reaction with hypochlorite shortens its lifetime in the basin. Reaction rates of dichloroacetonitrile formation by L-histidine chlorination have been established based on the latest chlorination mechanisms proposed. Moreover, this study shows that the reactivity toward chlorine differs whether L-histidine is isolated or mixed with BFA components.

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.

Impact of Different Combinations of Water Treatment Processes on the Concentration of Disinfection Byproducts and Their Precursors in Swimming Pool Water

To mitigate microbial activity in swimming pools and to ensure hygienic safety for bathers, pool systems have a recirculating water system ensuring continuous water treatment and disinfection by chlorination. A major drawback associated with the use of chlorine as disinfectant is its potential to react with precursor substances present in pool water to form harmful disinfection byproducts (DBPs). In this study, different combinations of conventional and advanced treatment processes were applied to lower the concentration of DBPs and their precursors in pool water by using a pilot-scale swimming pool model operated under reproducible and fully controlled conditions. The quality of the pool water was determined after stationary concentrations of dissolved organic carbon (DOC) were reached. The relative removal of DOC (Δc c_in^-1) across the considered treatment trains ranged between 0.1  ±  2.9% and 7.70  ±  4.5%, where conventional water treatment (coagulation and sand filtration combined with granular activated carbon (GAC) filtration) was revealed to be the most effective. Microbial processes in the deeper, chlorine-free regions of the GAC filter have been found to play an important role in the degradation of organic substances. Almost all treatment combinations were capable of removing trihalomethanes to some degree and trichloramine and dichloroacetonitrile almost completely. However, the results demonstrated that effective removal of DBPs across the treatment train does not necessarily result in low DBP concentrations in the basin of a pool. This raises the importance of the DBP formation potential of the organic precursors, which has been shown to depend strongly on the treatment concept applied. Irrespective of the filtration technique employed, treatment combinations employing UV irradiation as a second treatment step revealed higher concentrations of volatile DBPs in the pool compared to those employing GAC filtration as a second treatment step. In the particular case of trichloramine, results confirm that its removal across the treatment train is not a feasible mitigation strategy because it cannot compensate for the fast formation in the basin.

Variability of residual chlorine in swimming pool water and determination of chlorine consumption for maintaining hygienic safety of bathers with a simple mass balance model

Trial-and-error chlorination as a conventional practice for swimming pool water disinfection may fail to consistently maintain the pool's residual chlorine within regulatory limits. This study explored the variability of residual chlorine and other common water quality parameters of two sample swimming pools and examined the potential of using a mass balance model for proactive determination of chlorine consumption to better secure the hygienic safety of bathers. A lightly loaded Pool 1 with a normalized bather load of 0.038 bather/m³/day and a heavily loaded Pool 2 with a normalized bather load of 0.36 bather/m³/day showed great variances in residual free and combined chlorine control by trial-and-error methods due to dynamic pool uses. A mass balance model based on chemical and physical chlorine consumption mechanisms was found to be statistically valid using field data obtained from Pool 1. The chlorine consumption per capita coefficient was determined to be 4120 mg/bather. The predictive method based on chlorine demand has a potential to be used as a complementary approach to the existing trial-and-error chlorination practices for swimming pool water disinfection. The research is useful for pool maintenance to proactively determine the required chlorine dosage for compliance of pool regulations.

An exploration of disinfection by-products formation and governing factors in chlorinated swimming pool water

This paper investigates disinfection by-products (DBPs) formation and their relationship with governing factors in chlorinated swimming pools. The study compares concentrations of DBPs with WHO guidelines for drinking water quality recommended to screen swimming pool water quality. The statistical analysis is based on a global database of 188 swimming pools accumulated from 42 peer-reviewed journal publications from 16 countries. The mean and standard deviation of dichloroacetic acid and trichloroacetic acid were estimated as 282 ± 437 and 326 ± 517 μg L^-1, respectively, which most often surpassed the WHO guidelines. Similarly, more than half of the examined pools had higher values of chloral hydrate (102 ± 128 μg L^-1). The concentration of total chloramines (650 ± 490 μg L^-1) was well above the WHO guidelines in all reported cases. Nevertheless, the reported values remained below the guidelines for most of the studied pools in the case of total trihalomethanes (134 ± 160 μg L^-1), dichloroacetonitrile (12 ± 12 μg L^-1) and dibromoacetonitrile (8 ± 11 μg L^-1). Total organic carbon, free residual chlorine, temperature, pH, total nitrogen and bromide ions play a pivotal role in DBPs formation processes. Therefore, proper management of these governing factors could significantly reduce DBPs formation, thereby, contributing towards a healthy swimming pool environment.