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Formation of Haloforms During Chlorination of Natural Waters
... 1 Chlorine and chloramine (NH 2 Cl) are currently the most popular disinfectants used around the world. In the United States, disinfectant residuals are regulated by the U.S. Environmental Protection Agency (EPA) to not exceed 4.0 mg/L to improve public health protection by reducing exposure to disinfection byproducts (DBPs). 2 While chemical disinfectants inactivate pathogenic microorganisms, disinfectants react with dissolved organic matter and/or halide ions (e.g., bromide and iodide) to form DBPs. 3 DBPs are a ubiquitous source of chemical exposure and have been associated with serious health impacts in human epidemiologic studies. 4−10 DBP exposure from drinking water comes from ingestion, inhalation, and dermal absorption. ...
... 27,29,31 Previous studies show that increasing iodide concentrations in source water generally shifts the speciation of halogenated DBPs from chlorinated to iodinated species. 18,27,31,32 From a toxicological point of view, the oxidation of HOI to IO 3 − is preferred because ingested IO 3 − is quickly reduced to I − by glutathione, and therefore may be considered as nontoxic. 27 While chlorination generally results in rapid formation of IO 3 − , chloramination favors the formation of organic I − DBPs, 18,27,31,33,34 particularly when the free chlorine contact time is short before ammonia addition to form chloramines. 18,32,35 When the I − concentration is high, organic I-DBPs can also form during chlorination. ...
Iodized table salt provides iodide that is essential for health. However, during cooking, we found that chloramine residuals in tap water can react with iodide in table salt and organic matter in pasta to form iodinated disinfection byproducts (I-DBPs). While naturally occurring iodide in source waters is known to react with chloramine and dissolved organic carbon (e.g., humic acid) during the treatment of drinking water, this is the first study to investigate I-DBP formation from cooking real food with iodized table salt and chloraminated tap water. Matrix effects from the pasta posed an analytical challenge, necessitating the development of a new method for sensitive and reproducible measurements. The optimized method utilized sample cleanup with Captiva EMR-Lipid sorbent, extraction with ethyl acetate, standard addition calibration, and analysis using gas chromatography (GC)-mass spectrometry (MS)/MS. Using this method, seven I-DBPs, including six iodo-trihalomethanes (I-THMs) and iodoacetonitrile, were detected when iodized table salt was used to cook pasta, while no I-DBPs were formed with Kosher or Himalayan salts. Total I-THM levels of 11.1 ng/g in pasta combined with cooking water were measured, with triiodomethane and chlorodiiodomethane dominant, at 6.7 and 1.3 ng/g, respectively. Calculated cytotoxicity and genotoxicity of I-THMs for the pasta with cooking water were 126- and 18-fold, respectively, compared to the corresponding chloraminated tap water. However, when the cooked pasta was separated (strained) from the pasta water, chlorodiiodomethane was the dominant I-THM, and lower levels of total I-THMs (retaining 30% of the I-THMs) and calculated toxicity were observed. This study highlights an overlooked source of exposure to toxic I-DBPs. At the same time, the formation of I-DBPs can be avoided by boiling the pasta without a lid and adding iodized salt after cooking.
... Trihalomethanes (THM) are the most common disinfection byproducts of drinking water, resulting in reactions of free chlorine with organic matter (Rook, 1974 Consequently, the occurrence of many dangerous disinfection byproducts (DBPs) is a considerable concern worldwide (Prasad, 2020), mainly when considering that the most used disinfection methods involve the use of chlorine. The use of high concentrations of chlorine leads to the production of DBPs Thus, the objective of this study was to evaluate different chlorine concentrations in water for sanitizing Nile tilapia llets on the formation of trihalomethanes in fresh and frozen stored llets. ...
Fish is a food with high nutritional value, but its quickly perishable nature requires a hygiene process to maintain product quality and increase shelf life. The objective of this study was to evaluate different chlorine concentrations in water for sanitizing Nile tilapia fillets on the formation of trihalomethanes (THM) in fresh and frozen stored fish fillets. A completely randomized experimental design was used, in a 2×3 split-plot arrangement, with 15 replications; the plots consisted of fresh and frozen fish fillets, and the subplots consisted of the three chlorine concentrations in the water for sanitizing the fillets (100, 175, and 250 mg L-1). Fresh fish analysis showed the following variations in THM levels: 1.4 to 6.8 μg kg-1 (chloroform), 0.5 to 3.2 μg kg-1 (bromodichloromethane), and 0.4 to 1.2 μg kg-1 (dibromochloromethane). Bromoform ranged from 3.7 μg kg-1 to undetected levels in the different tested storage times. Frozen fish analyses showed concentrations ranging from 2.1 to 5.2 μg kg-1 (chloroform) and 0.6 to 2.0 μg kg-1 (bromodichloromethane), while dibromochloromethane and bromoform levels were below the technique's quantification limits in all storage times. THM formation depends on the chlorine concentration in the washing water and the storage time and temperature; fresh fish presented higher THM levels than frozen fish.
... However, while disinfectants effectively inactivate or eliminate harmful microorganisms, their strong oxidizing properties can trigger unavoidable reactions with natural organic matters (NOMs) and bromide and iodide compounds present in water, leading to the formation of disinfection byproducts (DBPs) [5] that pose health risks. For instance, during chlorine disinfection of drinking water, trihalomethanes (THMs) and haloacetic acids (HAAs) [6,7] are produced, which are known to be carcinogenic and reproductively toxic [8,9]. Notably, the chlorination reactions of wastewater also lead to the formation of a substantial number of DBPs, which are generally more toxic than the parent compounds and even more resistant to subsequent degradation. ...
In the face of ongoing water pollution challenges, the intricate interplay between dissolved organic matter and disinfectants like chlorine gives rise to potentially harmful disinfection byproducts (DBPs) during water treatment. The exploration of DBP formation originating from amino acids (AA) is a critical focus of global research. Aromatic DBPs, in particular, have garnered considerable attention due to their markedly higher toxicity compared to their aliphatic counterparts. This work seeks to advance the understanding of DBP formation by investigating chlorination disinfection and kinetics using tyrosine (Tyr), phenylalanine (Phe), and tryptophan (Trp) as precursors. Via rigorous experiments, a total of 15 distinct DBPs with accurate molecular structures were successfully identified. The chlorination of all three AAs yielded highly toxic chlorophenylacetonitriles (CPANs), and the disinfectant dosage and pH value of the reaction system potentially influence chlorination kinetics. Notably, Phe exhibited the highest degradation rate compared to Tyr and Trp, at both the CAA:CHOCl ratio of within 1:2 and a wide pH range (6.0 to 9.0). Additionally, a neutral pH environment triggered the maximal reaction rates of the three AAs, while an acidic condition may reduce their reactivity. Overall, this study aims to augment the DBP database and foster a deeper comprehension of the DBP formation and relevant kinetics underlying the chlorination of aromatic AAs.
... It contains a versatile range of NOM (2.1-44.1 mg/L), which raises a significant challenge of forming potentially hazardous disinfection by-products (DBPs), especially Trihalomethane (THMs), during the chlorination process (Karimi Pasandideh et al. 2016;Park et al. 2019). These THMs compounds include chloroform (CHCl 3 ) (CF), dibromochloromethane (CHClBr 2 ) (DBCM), bromodichloromethane (CHCl 2 Br) (BDCM), and bromoform (CHBr 3 ) (BF), which increased the risk of carcinogenicity and mutagenicity in human beings and identified as Class B carcinogens (Rook 1974;Clark et al. 1986). Many researchers reported an elevated range of THMs in the drinking water of Kolkata (466 μg/l), Dhanbad (503 μg/l) (Minashree Kumari 2014), Delhi (311-377 μg/l) (Hasan et al. 2010), Varanasi (380.9 μg/l), Raipur (324.3 μg/l), and Bhubaneswar (319.7 μg/l) (Mahato and Gupta 2020), Bokaro (594 μg/l) (Mishra et al. 2014), which exceeded the guideline value of USEPA (80 μg/), WHO (300 μg/l), and BIS (200 μg/l). ...
The study explored the GIS-based trends analysis for various trihalomethane (THMs) compounds, namely chloroform (CF), dibromochloromethane (DBCM), bromodichloromethane (BDCM), and bromoform (BF) in Indian drinking supplies. Five water treatment plants (WTPs) were selected to establish the concentration and spatial distribution. THMs compounds were estimated using the liquid–liquid extraction method by vigorous pentane: water mixture agitation, with gas chromatography equipped with electron-capture detection (ECD). Higher concentrations of CF (319.85 to 380.72 μg/l) were observed when source waters were subject to elevated organic matter levels. GIS-based spatial distribution of various THMs compounds indicated CF was most prevalent in chlorinated drinking water. The formation of THMs is then rooted in operational and geographic factors. The observed trends analysis will help the researchers and scientists, including water professionals, to confiscate the problems of THMs and improve the water quality in the WTPs from future perspectives.
... ¯ [1,2,3,4] . ...
The objective of the present work is to determine the operating conditions of an
activated carbon filter, based on the characteristics of breakthrough curves. This aims to
properly design and operate fixed-bed adsorption processes. We apply the concept of the
mass transfer zone (MTZ) that helps to obtain the evolutions of the operating parameters of
the fixed-bed. Charcoal activated (0.2-0.6 mm) purchased from POCH SA (Poland) was
studied.
Breakthrough curves have been studied on four different particle sizes of the
adsorbent (A, B, C, D) with diameter ranges (1000-2000), (500-1000), (250-500), (125-
250)µm respectively, and three initial concentrations of phenol (20, 40, 60ppm). The
experimental data were analyzed by calculating fractional capacity (F), the height of
(MTZ) (HZ), the number of unit transfer equivalent (NZ). The amount of phenol
eliminated by the bed of activated carbon at the breakthrough (ABP). The results of the
study show that granular sizes (C, D) were more effective than (A, B).
... Electrolysis, ozone, and ultraviolet (UV) lamps are used to sterilize water; however, chlorine generated by both electrolysis and ozone may have negative effects on plants (Buck et al., 2002;Graham et al., 2009). In contrast, sterilization via UV lamps has attracted attention as an alternative technique to chlorine for water disinfection, as chlorine has been associated with the promotion of chlorine-resistant microbial pathogens and the generation of toxic byproducts such as trihalomethanes (Rook, 1974;Boorman et al., 1999;Luo et al., 2021). However, since the "Minamata Convention on Mercury" greatly limited worldwide manufacture, import, and export of mercury products after 2020 (United Nations Environmental Program 2019), an alternative technique to mercury-containing UV lamps for sterilization is required. ...
The reutilization of hydroponic nutrient solutions in agriculture is important for increasing the utility of limited water resources. It is necessary to remove the contaminating plant pathogen before reusing the culture solution. Damping-off, caused by Pythium aphanidermatum, is a major disease in hydroponic and soil cultivation systems. Strategies to control P. aphanidermatum primarily involve chemical fungicides that are not effective in hydroponic cultivation systems. Therefore, novel methods are needed to control this pathogen. In this study, we investigated the inhibitory effects of ultraviolet-light emitting diode (UV-LED) irradiation (265, 280, and 300 nm) on P. aphanidermatum. UV-LED irradiation significantly and permanently inhibited the growth of P. aphanidermatum mycelia in water. Fungal DNA degradation was observed as early as 5 min after irradiation with UV-LED (280 nm), and fungal mycelia were unable to infect cucumber plants after being irradiated for 5 min with UV-LED (280 nm). These results suggest that UV-LED irradiation can control damping-off caused by P. aphanidermatum and be used for the recycling of hydroponic nutrient solutions.
... Since the beginning of the 20th century a large number of disinfecting reagents was proposed, i.e. chlorine, hypochlorite, hypobromite, chloramine, ozone, etc. After discovering formation of chloroform as a disinfection by-product (DBP) (Rook, 1974(Rook, , 1976, many efforts were focused to study transformations of organic compounds during water preparation, to reveal new DBPs and their toxic effects on humans (Plewa et al., 2004;Plewa et al., 2008;Plewa et al., 2010;Richardson et al., 2007;Richardson and Ternes, 2018;Yang and Zhang, 2016). According to recent estimations, the number of identified DBPs exceeds 700 (Richardson and Postigo, 2016;Richardson and Ternes, 2018) or even over 800 (Yang and Zhang, 2016;Usman et al., 2023) compounds. ...
Among numerous disinfection by-products (DBP) forming during aqueous chlorination nitrogen containing species are of special concern due to their toxicological properties. Nevertheless, corresponding reaction products of these natural and anthropogenic compounds are not sufficiently studied so far. An interesting reaction involves dealkylation of the substituted amine moiety. Here we present the results of the comparative study of one-electron oxidation and aqueous chlorination of several aliphatic and aromatic amines. The reaction products were reliably identified with gas chromatography – high resolution mass spectrometry (GC-HRMS), high pressure liquid chromatography – electrospray ionization high resolution mass spectrometry HPLC-ESI/HRMS), and electrochemistry - electrospray ionization high resolution mass spectrometry (EC-ESI/HRMS). Certain similarities dealing with the formation of the corresponding aldehydes and substitution of alkyl groups at the nitrogen atom for hydrogen were shown for the studied processes. The mechanism of the substituted amines’ aqueous chlorination involving one-electron oxidation is proposed and confirmed by the array of the observed reaction products. Alternative reactions taking place in conditions of aqueous chlorination, i.e. aromatic electrophilic substitution, may successfully compete with dealkylation and produce major products.
... Trihalomethanes (THMs) were the first DBPs discovered in 1974 in the Netherlands and the USA [11,12]. These early discoveries used non-target screening with gas chromatography coupled to mass spectrometry (GC-MS), driven by the scientists' curiosity regarding the identity of the unknown chromatographic peaks observed in chlorinated drinking water extracts. ...
Disinfection by-products (DBPs), formed during drinking water treatment, are ubiquitous in disinfected drinking water and are generally found at levels 1,000-fold higher than other emerging contaminants like pharmaceuticals and per- and poly-fluoroalkyl substances (PFAS). More than 700 DBP structures are known, yet ~70% of the halogenated organics are still unknown in chlorinated drinking water. Moreover, it is currently not known which DBPs are responsible for the adverse human health effects observed in human epidemiologic studies. Thus, non-target screening strategies are critical. Popular screening strategies include gas chromatography (GC) and liquid chromatography (LC) coupled with high-resolution mass spectrometry (HRMS). GCxGC-MS is also sometimes used for complex samples. Other novel screening methods include supercritical fluid chromatography (SFC)-MS, a new thiol reactome method, a stable isotope labeling approach, precursor ion scan, and precursor ion exclusion, along with custom software and a new database to conduct suspect screening of chlorination by-products of emerging contaminants. Halogen-specific total organic halogen also continues to be an important tool to assess the total concentration of halogenated DBPs, including known DBPs and unknown DBPs, not yet identified. This review article details these DBP screening strategies, with a particular focus on new papers reported in the last 5 years.
... Among all the THM species, chloroform is always present in the highest concentration covering almost 90% of the total concentration of THMs (Durmishi et al., 2015). Rook (1974) discovered that chlorinated drinking water can produce halogenated DBPs, now considered a subordinate health risk (Rook, 1976). ...
The reactions between natural organic matter, anthropogenic contaminants, ions, and disinfectants lead to the formation of disinfection by-products (DBPs) such as trihalomethanes (THMs) in drinking water. The formation of THMs is strongly related to the chlorination of water. The study’s central objective was to compare the concentration of THMs in twenty developed and developing countries and their disinfection techniques. The THM concentration in 11 developed and 9 developing countries ranged from 0.5 µg/L (Germany) to 215 µg/L (Russia) and 3 µg/L (China) to 439.2 µg/L (Bangladesh), respectively. The developed country has partially succeeded in reducing THM concentration in drinking water, whereas significant steps are needed in developing countries to reduce the existing high THM concentration. The concentration of THMs in water varies among these countries because of the different water sources, water quality, environmental conditions, and efficiency of water treatment technologies. A meaningful relationship has been observed between the properties of water and the THM formation. The use of chemical disinfectants will result in new forms of DBPs that are undesirable due to their carcinogenic and mutagenic effects on human health. The DBP guidelines by various national and international agencies have helped to control and manage the THM concentration in drinking water. However, these regulatory standards are not continuously monitored. Therefore, the formation of these compounds should be prevented either by removing THMs forming precursors or by using an integrated approach for controlling THM formation by implementing advanced water treatment technology. Extensive research is desirable in domains like THM minimization strategies which are easy to deploy, scalable, and cost-effective.
Graphical abstract
... Some of these halocarbons have been shown to be mutagenic. 9,10 Historically leaks have been identified by various means in petroleum refineries, petrochemical plants, or gas plants. ...
This paper describes a quick and easy method which can be used to identify exchangers which have hydrocarbon leaks into cooling water. The severity of the leak can also be determined. The method involves the use of a portable, explosion proof flame ionization detector to measure volatile hydrocarbons off-gassing from the cooling water which exits an exchanger. The lower limit of detectability is in the part per million range. One case history is described herein.
... In 1900, cholera spread was ended in the Western world by applying chlorination in the municipality-supplied water. However, in 1974 some researchers discovered that NOM reacted with chlorine and formed trihalomethanes, and the concentration reached 160 µg/L [83,84]. It has been proven that DBPs affect the human body when exposed to public water supplies and swimming pools [36,85]. ...
The supply of safe drinking water to rural communities has always been challenging, unlike in most large cities where government authorities have constructed central water supply systems. In many rural areas, primary water sources such as surface water and groundwater are at risk of contamination with rapid agricultural and industrial growth and climate change-related issues. Rainwater harvesting is an ancient practice for rural communities, and the momentum around its use is continually growing in recent years. However, the lack of sustainable treatment facilities on a small scale encourages dwellers to consume harvested rainwater (HRW) without any treatment even though drinking untreated HRW may have multiple health impacts in many cases. There are several methods of treating HRW. While chlorination is extensively used to disinfect water in large volumes, e.g., central drinking water supply systems), it has not been widely adopted for treating water on a small scale. We present a scoping review to explore whether chlorination could be a viable option for disinfecting HRW at a domestic level. It is found that inadequate treatment prior to chlorine disinfection could produce chlorine disinfection byproducts (DBPs). Limited data on DBP concentrations in HRW are available to assess its health implications. Based on this review, it is argued that chlorination could be an option for treating HRW at a domestic level when limitations associated with this method (such as safe storage, appropriate sustainable technology, and lessening DBPs by lowering total organic carbon before chlorination through other treatment methods) are resolved.
... Interest in studying organic substances in drinking water began in 1974 with the detection of haloforms or trihalomethanes by Rook J. during the quality control of water treatment at the Berenplaat, Netherlands [4]. THMs as synthetic organic compounds are created by replacement of three hydrogen atoms in the methane molecule with the atoms of the halogen elements. ...
Trihalomethanes (THMs) are created as a result of the reaction between chlorine used to disinfect drinking water and natural organic matter in water. At high levels, THMs have been associated with cancer. As a consequence, THMs must be constantly monitored. They are mainly determined by the method of gas chromatography, which is a more difficult procedure and at a higher cost. In recent years, however, mathematical models have been used to predict THMs. These models work by measuring some physico-chemical parameters of drinking water, those values of these parameters are replaced in mathematical models and the THMs content in drinking water can be predicted. The main purpose of this paper was to predict the content of THMs in the drinking water of the city of Kumanova. The measured parameters were: temperature, residual chlorine, pH, electrical conductivity, chemical oxygen, total dissolved solids and chlorides. Measurements were made during the spring season 2022 in the four sampling points. Ten mathematical models were used for prediction and of them the average value with standard deviation of THM was 26.9532 ± 10.03 μg/L. From the result we can conclude that content of THM does not pose a risk to the health of the population.
... During the past century, the introduction of chlorine disinfection of municipal drinking water in high-income countries nearly eliminated outbreaks of typhoid, cholera and other waterborne diseases 1 . During the 1970s, researchers discovered that chloroform and other trihalomethanes (THMs) form at concentrations of up to ~160 μg l −1 from the reactions of the chlorine disinfectant with dissolved organic matter (DOM) 2,3 . Subsequent epidemiological studies indicated that consumers exposed to elevated concentrations of THMs in tap water exhibited increased risk of bladder cancer [4][5][6] . ...
... Reactions of chlorine to NOM and the corresponding formation of DBPs were first reported by Rook [14], with an increasing number of DBPs subsequently reported [15]. Broadly, the most common DBP types are trihalomethanes (THMs) and haloacetic acids (HAAs) which constitute approximately 34 % of total organic halides [15,16], and are widely regulated. ...
... The discussion about the generation of DBPs began in the 1970s with the detection of chloroform and other trihalomethanes (THMs) during the chlorination of natural waters containing dissolved organic matter (DOM) (Rook, 1974). Epidemiological investigations conducted after this discovery suggested that the consumption of chlorinated tap water with elevated concentrations of THMs could have diverse adverse effects on human health. ...
As well established in the literature, residual toxicity is an important parameter for evaluating the sanitary and environmental safety of water treatment processes, and this parameter becomes even more crucial when chlorine-based processes are applied for water treatment. Eliminating initial toxicity or preventing its increase after water treatment remains a huge challenge mainly due to the formation of highly toxic disinfection by-products (DBPs) that stem from the degradation of organic contaminants or the interaction of the chlorine-based oxidants with different matrix components. In this review, we present a comprehensive discussion regarding the toxicological aspects of water treated using chlorine-based advanced oxidation processes (AOPs) and the recent findings related to the factors influencing toxicity, and provide directions for future research in the area. The review begins by shedding light on the advances made in the application of free chlorine AOPs and the findings from studies conducted using electrochemical technologies based on free chlorine generation. We then delve into the insights and contributions brought to the fore regarding the application of NH2Cl- and ClO2-based treatment processes. Finally, we broaden our discussion by evaluating the toxicological assays and predictive models employed in the study of residual toxicity and provide an overview of the findings reported to date on this subject matter, while giving useful insights and directions for future research on the topic.
... There have been more than 700 species of DBPs identified since their discovery in the early 1970s (Rook, 1974). Epidemiological studies and water toxicity research have shown that increased exposure to DBPs is correlated with an increased risk of colon, bladder, and rectum cancers (Bove et al., 2007;Bull et al., 1995;Cantor et al., 2010;Costet et al., 2011;King et al., 2000;King & Marrett, 1996;Koivusalo et al., 1997;McGeehin et al., 1993;Morris et al., 1992;Rahman et al., 2010;Villanueva et al., 2004Villanueva et al., , 2007. ...
The formation of disinfection byproducts (DBPs) in finished drinking water is an ongoing challenge for public health agencies and water utilities. The Fourth Unregulated Contaminant Monitoring Rule data were used to assess the prevalence and drivers of haloacetic acids (HAAs)—a class of DBPs—in New York State's (NYS) public water systems, with a focus on total measured (HAA9), regulated (HAA5), brominated (HAA6Br), and unregulated (HAA4) HAAs. The concentrations of all HAA groups in NYS are found to be similar to those nationally, with HAA4 composing approximately 20% of HAA9. Concentrations of all HAA groups are lowest in groundwater and highest in surface waters across NYS systems. Higher total organic carbon (TOC) concentrations lead to elevated HAA9 and HAA5, while higher bromide concentrations favor more HAA4 and HAA6Br. HAA4 concentrations are well predicted with pre‐oxidation/disinfection types, HAA5, TOC, and bromide concentrations, with an adjusted R2 of 70%.
... Interest in studying organic substances in drinking water began in 1974 with the detection of haloforms or trihalomethanes by Rook J. during the quality control of water treatment at the Berenplaat, Netherlands [4]. THMs as synthetic organic compounds are created by replacement of three hydrogen atoms in the methane molecule with the atoms of the halogen elements. ...
Trihalomethanes (THMs) are the main disinfection byproducts created when chlorine reacts with organic matter of the drinking water. THMs in high concentrations are harmful and can be carcinogenic for the liver, pancreas, nervous system, development organs, whereas in women can cause miscarriage. Therefore, THMs recently have concerned very much the scientific community and the general public. Consequently, THMs must be constantly monitored. THMs mainly are determined by the gas chromatography method, which is a difficult procedure and very costly. To avoid this, in the past years the use of mathematical models for prediction of THMs in drinking water is practiced. By fast measuring of the values of some simple parameters of drinking water quality and replacing them in the mathematical models we can predict the THMs content. The aim of this article was the prediction of the THMs content in drinking water in the city of Struga for the spring of 2021 in four sampling points S1, S2, S3 and S4. The measured parameters and their average values with standard deviation were: water temperature (13.56± 1.17 ºC), residual chlorine (0.20 0.00 mg/L), pH (7.58 0.03), electrical conductivity (250.89 9.37 μS/cm), chemical oxygen demand (1.53 0.06 mg/L), total dissolved solids, (407.67 2.89 mg/L) and chlorides (5.26 0.32 mg/L), respectively. These values are then placed in mathematical models and with calculation is predicted the THMs content in drinking water. For prediction were used ten mathematical models and the average value of the THMs with standard deviation was 27.40 ± 10.67 μg/L). From the results we can conclude that the used models for THMs prediction have resulted successful and this content of THMs pose no risk to public health.
... Several DBPs are a major health concern because of their carcinogenic properties [90]. As previously reported, trihalomethanes (THMs) were discovered as the first chemical class of DBPs in 1974 [91]. To date, more than 600 DBPs have been identified, and among these, the haloacetaldehydes (HALs) are the third-largest group by weight of identified DBPs in drinking water [89,[92][93][94][95]. ...
... [2][3][4][5][6] Nearly one thousand kinds of DBPs have been detected and reported since trichloromethane was discovered in chlorinated water in 1974. [7][8][9] Among them, carbonaceous DBPs (C-DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs) have always received the most attention over the past decades. 10,11 Compared to common C-DBPs under regulation, nitrogenous DBPs (N-DBPs) at low concentrations of μg L −1 , e.g., halonitromethanes (HNMs), haloacetamides (HAcAms), haloacetonitriles (HANs), and N-nitrosamines (NAs), exhibit extremely higher cytotoxicity and genotoxicity and therefore have aroused increasing concerns. ...
Tryptophan was selected as the precursor for the investigation on the formation of brominated halonitromethanes (Br-HNMs) in the presence of bromide during UV/chlorine disinfection.
... The application of O 3 in (waste)water treatment can be used for the removal of micropollutants (Lee and von Gunten, 2012), abatement of taste and odor compounds (Glaze et al., 1990), and disinfection purposes (Morrison et al., 2022;Von Gunten, 2003a). O 3 has been used for water disinfection since the beginning of the last century and has gained increasing interest after discovering that the application of chlorination may result in the formation of undesired taste and odor compounds and harmful DBPs (Rook, 1974). The reaction mechanisms and the application of O 3 for water and wastewater treatment have been reviewed frequently over the last decades (Glaze et al., 1987;Lawrence and Cappelli, 1977;von Gunten, 2018von Gunten, , 2003bvon Gunten, , 2003avon Sonntag and von Gunten, 2012). ...
Water disinfection during drinking water production is one of the most important processes to ensure safe drinking water, which is gaining even more importance due to the increasing impact of climate change. With specific reaction partners, chemical oxidants can form secondary oxidants, which can cause additional damage to bacteria. Cases in point are chlorine dioxide which forms free available chlorine (e.g., in the reaction with phenol) and ozone which can form hydroxyl radicals (e.g., during the reaction with natural organic matter). The present work reviews the complex interplay of all these reactive species which can occur in disinfection processes and their potential to affect disinfection processes. A quantitative overview of their disinfection strength based on inactivation kinetics and typical exposures is provided. By unifying the current data for different oxidants it was observable that cultivated wild strains (e.g., from wastewater treatment plants) are in general more resistant towards chemical oxidants compared to lab-cultivated strains from the same bacterium. Furthermore, it could be shown that for selective strains chlorine dioxide is the strongest disinfectant (highest maximum inactivation), however as a broadband disinfectant ozone showed the highest strength (highest average inactivation). Details in inactivation mechanisms regarding possible target structures and reaction mechanisms are provided. Thereby the formation of secondary oxidants and their role in inactivation of pathogens is decently discussed. Eventually, possible defense responses of bacteria and additional effects which can occur in vivo are discussed.
... DBPs form complex mixtures (Richardson et al., 2007), which constitute a methodological research challenge (Villanueva et al., 2014). Since the first identification of chloroform in drinking water in the 1970's (Bellar et al., 1974;Rook, 1974), total THMs have been typically used as a DBP surrogate, particularly when the disinfectant is chlorine. Other widespread byproducts of chlorination are haloacetic acids, which are regulated in a few countries (Poleneni, 2020). ...
Background
Trihalomethanes (THM), a major class of disinfection by-products, are widespread and are associated with adverse health effects. We conducted a global evaluation of current THM regulations and concentrations in drinking water.
Methods
We included 120 countries (∼7,000 million inhabitants in 2016), representing 94% of the world population. We searched for country regulations and THM routine monitoring data using a questionnaire addressed to referent contacts. Scientific and grey literature was reviewed where contacts were not identified or declined participation. We obtained or estimated annual average THM concentrations, weighted to the population served when possible.
Results
Drinking water regulations were ascertained for 116/120 (97%) countries, with 89/116 (77%) including THM regulations. Routine monitoring was implemented in 47/89 (53%) of countries with THM regulations. THM data with a varying population coverage was obtained for 69/120 (58%) countries consisting of ∼5,600 million inhabitants (76% of world's population in 2016). Population coverage was ≥90% in 14 countries, mostly in the Global North, 50-89% in 19 countries, 11-49% among 21 countries, and ≤10% in 14 countries including India, China, Russian Federation and Nigeria (40% of world's population).
Discussion
An enormous gap exists in THM regulatory status, routine monitoring practice, reporting and data availability among countries, especially between high- vs. low- and middle-income countries (LMICs). More efforts are warranted to regulate and systematically assess chemical quality of drinking water, centralise, harmonise, and openly report data, particularly in LMICs.
... Disinfection by-products (DBPs) are formed at the same time as the disinfectants are added at raw water [1,2]. Their training formation in the network continued when there was a presence of natural organic matter (NOM) in sufficient amount and residual disinfectant [3,4]. The infectious diseases of water origin in our society are eliminated mainly by the disinfection of drinking water. ...
... Traces of sodium hypochlorite increased during the pandemic with the increase in disinfectants usage and became part of landfill leachate. It reacts with water to form hypochlorous acid and with bromine to form hypobromous acid (Rook 1974). These two acids combined with natural organic matter form genotoxic and carcinogenic disinfection by-products (Medeiros et al. 2019). ...
The COVID-19 pandemic affected public health, economy, social life, and the environment. It infected and killed millions of people around the world. Most of the recent literature has focused on the medications to combat this virus, including antivirals and vaccines, but studies about its effect on the environment are still rare, particularly on the water sector. Most of the studies concentrate on the effect of water availability on COVID-19, the effect of the used medications on the water, and the probability of transmission of SARS-CoV-2 through water. Herein, we have summarized the effects of COVID-19 on the water sector from many perspectives. We show different methods to detect the effect of the pandemic on water and also methods to investigate the presence of the virus or its RNA in the water. We also show the different effects of its presence in the wastewater, the probability of transmission, the detection of different variants, and the prediction of new waves. We also show the disadvantages and advantages of the pandemic in the water sector. We finally suggest some recommendations to face this pandemic and the future pandemics for the governments and water policymakers, water treatment plants, general population, and researchers. The aim of this review is to show the different aspects of the pandemic in order to give a general idea about what must be done in order to minimize its effect and any probable pandemic in the future.
... Depending on the local quality of the raw water and following the so-called multiple-barrier principle, several treatment steps are usually combined to ensure the highest level of safety for the finished drinking water [1,3,44,77]. The widespread implementation of pre-and post-treatments (before and after the oxidation step) has been fostered by the need to reduce the occurrence of harmful DBPs, known since the 70 s to be formed from NOM during oxidation [78,79]. Pre-treatments primarily aim at reducing the concentration of NOM and other organics precursors of DBPs, while post-treatment aims at removing DBPs potentially formed. ...
Oxidative treatment methods are valuable tools for the microbial safety of drinking water. However, the reaction of oxidants with natural substances or anthropogenic contaminants present in the raw water can potentially lead to the formation of harmful transformation products (TPs). The present paper proposes a tiered approach for the risk evaluation of TPs formed from pesticide residues during drinking water treatment. First, the concentrations of pesticide residues in raw water used for drinking water production are evaluated (step 1). Substances with a predicted concentration in raw water above 0.1 µg/L proceed further to a reactivity assessment, examining the behavior in water treatment plants (step 2). Using information available in the scientific literature, prediction of structural elements in the TPs can be made and allow a worst-case assessment based on the Threshold of Toxicological Concern (TTC) (step 3). If concerns remain, experiments may be conducted to simulate water treatment (step 4). Because of their complexity and variability, experiments for the simulation of water treatment should focus on prioritized substances of potential concern. The test conditions should be realistic (i.e., close to EU-representative conditions in waterworks) and ozonation and chlorination should be combined with pre- and post-treatment steps, as is normally the case in European waterworks. As a first screening option, we propose to test the toxicity of the reaction mixture. If the treated water shows an enhanced toxicity, further experiments can be conducted to identify and quantify the major TPs (step 5). We propose to define major TPs as substances present at more than 10% of the initially applied test substance. For major TPs, a tiered dietary risk assessment is conducted, starting with the TTC concept, and continuing with toxicity testing of the TP, according to EFSA and ECHA and internationally agreed guidance.
... Federal legislation in the 1970s, including the Clean Water Act of 1972 [27] and the Safe Drinking Water Act of 1974 [28] led to the regulation of a broad range of water quality constituents of concern in drinking water supplies and in treated drinking water. Coincident with this period, researchers demonstrated the formation of THMs during chlorination [29,30], a conventional treatment process for disinfecting drinking water. Later investigations suggested a potential relationship between THM occurrence and increased incidence of cancer among exposed populations [31]. ...
This paper presents the history and evolution of the California Department of Water Resources’ Municipal Water Quality Investigations (MWQI) program. This program tracks source water quality in the Sacramento–San Joaquin Delta (Delta) for drinking water supply for nearly two-thirds of California. The program provides early warning of changing conditions in source water quality, provides data and knowledge-based support for operational decision making, and provides scientific support to a variety of urban water users. This retrospective (i) documents program formation, (ii) describes its evolution in response to regulations and technological advances in water treatment and field monitoring, and (iii) notes how the development of federal drinking water quality regulations such as the Disinfection By-Products Rule impacted the program. The MWQI program is believed to be the first drinking water supply program in the United States to conduct continuous, real-time monitoring of organic carbon, bromide, and other anions and to report these data on the internet. In addition to its regular use for operational decision making, the data may be used for evaluating long-term trends and responses to specific changes in the Delta and its watershed. Future program directions will likely be guided by factors that may trigger changes in treatment plant processes and operations, such as emerging contaminants, changes in land and water management practices, permanent Delta island flooding, sea level rise, and climate change. While this retrospective focuses on one region, its multi-decade interplay of science, treatment and monitoring technology, and regulations (as well as practical aspects of managing such a large-scale program) are broadly relevant to professionals engaged in drinking water quality management in other urbanized and developed regions of the world.
This study reports the trihalomethanes generated during disinfection within the water distribution network of Delhi, India. For 12 months study period tap water samples were collected (n = 216) from the command areas of nine water treatment plants to provide a comprehensive picture of spatial and seasonal variation of trihalomethanes in the city. The mean concentrations of chloroform, bromodichloromethane, dibromochloromethane, bromoform were 34.62 ± 13.09 μg/l, 25.39 ± 11.75 μg/l, 15.83 ± 9.66 μg/l, 1.74 ± 1.51 μg/l respectively, the total trihalomethanes concentration ranged between 11.41–175.54 μg/l. Chloroform was prevalent accounting 45% in total trihalomethanes followed by bromodichloromethane, dibromochloromethane, bromoform accounting 33%, 20%, and 2% respectively. Trihalomethanes concentrations were found to be increasing during summer season and got decreased in the winter and post-monsoon season. Total trihalomethanes levels were found to be highest at Chandrawal water treatment plant command area (85.35–148.38 μg/l) and lowest at Okhla water treatment plant command area (11.41–63.38 μg/l). In many samples trihalomethanes concentrations were discovered to be higher than the allowable limit specified by Indian Standards. A strong relationship between trihalomethanes formation with total organic carbon (r = 0.934) and residual chlorine (r = 0.801) accentuate its capability for monitoring disinfection by-products in the distribution network. Results showed that considerable levels of trihalomethanes are generated in the study area, therefore the competent authorities must take the appropriate steps to regularly monitor the trihalomethanes in drinking water. The findings of this study may help to provide operators with invaluable information on drinking water quality and open up several chances to enhance water quality management.
Water is a vital element which supplies essential nutrients to the plants and animals on Earth and without water no life will exist on Earth. The raw water is conventionally treated by processes such as coagulation, flocculation, sedimentation, and filtration, followed by disinfection before supplying the treated water to the consumers. Disease-causing pathogens enter the water supply network through leakages thus contaminating water which may cause illness. During disinfection process disinfectants like chlorine and chloramine are used to kill the disease-causing microorganisms. When chlorine combines with the natural organic matter (NOM) in raw water, disinfection by-products (DBPs) are created. This led researchers to discover more DBPs formed in drinking water and to find their harmful health effects. According to a USEPA assessment, the four THMs are likely human carcinogens for chloroform, bromodichloromethane, bromoform, and dibromochloromethane, respectively. A few animals’ toxicity studies have reported a strong relationship between the DBPs and carcinogenic diseases. THMs were first regulated by the United States Environmental Protection Agency (USEPA) at 100 μg/L (ppb) in drinking water in 1979. In 1998, the Stage 1 Disinfection By-Products Rule limited THMs to 80 μg/L and for the first time regulated haloaceticacids (HAAs), chlorate, chlorite, and bromate. Since then, many countries have regulated the DBPs. There are several ways to manage DBP concentrations, including eliminating the precursor NOM before adding chlorine, removing DBPs once they have formed, or utilising other disinfectants.
World’s population is growing rapidly and it will touch 10 million by the end of 2050. Availability of clean and safe water for all is a global challenge. Disinfection of water is the most important step in water treatment to ensure the inactivation of pathogens from water. There are many techniques/materials available for disinfection of water. However, there are also many challenges associated with successful implementation of methods of disinfection including cost, type of pathogens, and other health implications caused due to formation of disinfection byproducts during the disinfection process. In this chapter, the background of water disinfection techniques as well as recent trends of the area has been discussed in detail with an objective to suggest safer strategies for water disinfection. Disinfection by-products often lead to health implications due to their long-lasting and toxic behavior. There are many other factors including pH, residence period, temperature, natural organic matter, and other water characteristics that significantly affect the efficiency of disinfectants and fate of disinfection by-products. Some by-products are carcinogenic, reproductive toxicants as well as mutagenic in nature. However, with advancements in disinfection techniques formation of toxic by-products can be avoided during water treatment. These methods have been discussed in the chapter along with the challenges and knowledge gaps to provide a basic outlook for future research in the development of safer disinfection alternatives.
Most of the natural sources of water around the world are not always suitable for drinking without treatment. Microorganisms can be found in raw water from rivers, lakes, ponds and groundwater. Pathogens present in water can be transmitted through a drinking water distribution system, causing waterborne disease to those who consume it. Disinfection is a crucial water treatment method as it ensures that water is free of pathogenic microorganisms causing water-borne diseases. In order to combat waterborne diseases, different disinfection methods are used to inactivate pathogens. The main aim of this paper is discussed different methods of disinfection, their suitability, limitation, factors influencing disinfection process, Chlorine by products and impacts of chlorine by products impacts on human beings.
Chlorine dioxide (ClO2) is an oxidant applied in water treatment processes that is very effective for disinfection and abatement of inorganic and organic pollutants. Thereby phenol is the most important reaction partner of ClO2 in reactions of natural organic matter (NOM) and in pollutant degradation. It was previously reported that with specific reaction partners (e.g., phenol), free available chlorine (FAC) could form as another byproduct next to chlorite (ClO2-). This study investigates the impact of different functional groups attached to the aromatic ring of phenol on the formation of inorganic byproducts (i.e., FAC, ClO2-, chloride, and chlorate) and the overall reaction mechanism. The majority of the investigated compounds reacted with a 2:1 stoichiometry and formed 50% ClO2- and 50% FAC, regardless of the position and kind of the groups attached to the aromatic ring. The only functional groups strongly influencing the FAC formation in the ClO2 reaction with phenols were hydroxyl- and amino-substituents in ortho- and para-positions, causing 100% ClO2- and 0% FAC formation. Additionally, this class of compounds showed a pH-dependent stoichiometric ratio due to pH-dependent autoxidation. Overall, FAC is an important secondary oxidant in ClO2 based treatment processes. Synergetic effects in pollutant control and disinfection might be observable; however, the formation of halogenated byproducts needs to be considered as well.
Spray aeration is a comparatively low‐cost option to reduce trihalomethane (THM) concentrations in distribution system storage. The effect of spray aeration on unregulated, toxic disinfection by‐products was investigated in a bench‐scale apparatus in closed‐tank and open‐tank experiments. In the closed‐tank experiments, initially over 90% of THMs, trichloroacetonitrile, and chloropicrin were removed, while 36% of dihaloacetonitriles were removed. However, due to the buildup of concentrations in the tank headspace, removal rates for all compounds decreased significantly with time, falling to 44% removal of THMs, 76% removal of trichloroacetonitrile, and 58% removal of chloropicrin. Removal of dihaloacetonitriles decreased to zero. In the open‐tank experiments, THM removal rates were high and did not decrease with time. Considering the results with open and closed tanks as approximate bounds for performance expected under real‐world conditions in storage tanks, the findings suggest that spray aeration may not significantly reduce haloacetonitrile‐related toxicity while halonitromethane‐related toxicity may be reduced.
Ambroxol hydrochloride (AMB) and bromhexine hydrochloride (BRO) are classic expectorants and bronchosecretolytic pharmaceuticals. In 2022, both AMB and BRO were recommended by medical emergency department of China to alleviate cough and expectoration for symptoms caused by COVID-19. The reaction characteristics and mechanism of AMB/BRO with chlorine disinfectant in the disinfection process were investigated in this study. The reaction of chlorine with AMB/BRO were well described by a second-order kinetics model, first-order in both AMB/BRO and chlorine. The second order rate reaction constant of AMB and BRO with chlorine at pH 7.0 were 1.15 × 102 M-1s-1 and 2.03 × 102 M-1s-1, respectively. During chlorination, a new class of aromatic nitrogenous disinfection by-products (DBPs) including 2-chloro-4, 6-dibromoaniline and 2, 4, 6-tribromoaniline were identified as the intermediate aromatic DBPs by gas chromatography-mass spectrometry. The effect of chlorine dosage, pH, and contact time on the formation of 2-chloro-4, 6-dibromoaniline and 2, 4, 6-tribromoaniline were evaluated. In addition, it was found that bromine in AMB/BRO were vital bromine source to greatly promote the formation of classic brominated DBPs, with the highest Br-THMs yields of 23.8% and 37.8%, respectively. This study inspired that bromine in brominated organic compounds may be an important bromine source of brominated DBPs.
The formation of disinfection byproducts (DBPs) during the water disinfection process has attracted extensive attention due to their potential toxicity. Emerging organic micropollutants (EOMPs) are now ubiquitous in the water environments, and they have been confirmed that could be the precursors for many DBPs during chlorine-based disinfection processes (Cl-DPs). Although there are increasing studies on the formation of DBPs from EOMPs during Cl-DPs, there is still a lack of review paper on this hotspot. In this review, the typical Cl-DPs and their corresponding mechanisms were introduced first. Then, the DBPs formation in the presence of different EOMPs (e.g., pharmaceuticals and personal care products, endocrine disrupting chemicals, and brominated flame retardants) during Cl-DPs were discussed and highlighted, including the pathways, mechanisms, and influencing factors. Moreover, the DBPs detection and control methods have also been summarized and discussed. Finally, future studies and challenges of controlling DBPs formation were proposed. This review gave a comprehensive understanding of DBPs formation from EOMPs during Cl-DPs, and more studies are needed in the future to balance the EOMPs removal against corresponding DBPs formation during disinfection processes.
In a few studies focusing on premise plumbing, water quality parameters were compared between LEED-certified and non-certified buildings. However, in those studies, the building characteristics were different, which can cause variations in comparison attempts. This study's purpose is to identify the effects of building type on premise plumbing water quality. For this purpose, temperature, pH, free chlorine residuals, total organic carbon, and trihalomethanes (THMs) were sampled from four drinking fountains of a combined LEED-certified and non-certified building. Although some influential factors on water quality (e.g., location of buildings, distributed water quality) were isolated for a better comparison, variations in parameters and total THMs were observed resulting from the plumbing age differences in the buildings. The findings of this study point out the impacts of the plumbing pipe age on water chemistry and emphasize the consideration of piping age as a factor in water quality comparisons between LEED-certified and non-certified buildings.
Observations of the effects of solar ultraviolet (UV) radiation on human health and human tissues were made as early as the 5th century BC, but much of the formal knowledge base related to photochemistry and photochemical reactors has emerged within the last century. The laws of photochemistry (Grotthus‐Draper [1st Law]; Stark‐Einstein [2nd Law]; Bunsen‐Roscoe [3rd Law]) were established by a group of remarkable scientists who also had interesting personalities. They established the foundational principles of photochemistry that inform our current understanding and application of photochemistry, including those based on UV radiation. Their actions and observations taught many important lessons, either intentionally or unintentionally. These fundamental principles are critical to our understanding of natural photochemical processes, such as photosynthesis, atmospheric chemistry, and vision. In a similar manner, the laws of photochemistry also define the foundation of “engineered” photochemical processes, including such diverse applications as photography and disinfection. Municipal‐scale applications were initiated in the early 1900s and involved reactor systems that employed principles that are still in use today. Since that time, applications of UV radiation have expanded, largely based on improvements in our collective understanding of photochemistry and photochemical reactors.
Natural organic matter (NOM), as a ubiquitous component in aqueous environments, has raised continuous scientific concerns due to its role as an organic precursor to disinfection by-products (DBPs) in the subsequent chlorination process. Selective oxidants, including ozone (O3), chlorine dioxide (ClO2), permanganate (Mn(VII)), and ferrate (Fe(VI)) are widely used in the preoxidation stage in drinking water treatment. The selective reactivity of those oxidants toward NOM is expected to alternate NOM properties and consequently DBP formation in postchlorination. Despite extensive studies on the interactions of NOM with selective oxidants, there is currently a lack of an overview of this area. To fill this gap, this study presents the current knowledge of the modification of NOM properties by selective oxidants and its impact on DBP formation in postchlorination. The NOM property changes in three aspects, including bulk property (e.g., total organic carbon, ultraviolet absorbance), fractional constituent (e.g., molecular size, hydrophilicity/hydrophobicity), and elemental composition (e.g., functional group) by the four selective oxidants (i.e., O3, ClO2, Mn(VII), and Fe(VI)) were discussed. Thereafter, the impacts of alteration of NOM properties by those selective oxidants on DBP formation in the subsequent chlorination were summarized, wherein the key influencing factors were discussed. Finally, the future perspectives in this area were forwarded, which highlighted the significance of process optimization, the attention to the less studied but more toxic DBPs, and the need for the identification of unknown DBPs. This review presented a state-of-the-art knowledge pool of the fate of NOM in oxidation and chlorination processes, promoted our understanding of the relationship between NOM properties and DBP formation, and identified further research needs in this area.
Recent data showing fast degradation of the emerging disinfection by‐product 2,6‐dichloro‐1,4‐benzoquinone (DCBQ) in the presence of free chlorine seem incompatible with the high concentrations reported in drinking water distribution systems. The current study was conducted to reconcile this apparent incompatibility. Laboratory tests showed that the published protocol for DCBQ preservation, addition of formic acid without conventional reducing agents, was problematic. Formic acid does not rapidly reduce free chlorine, allowing chlorine residuals to persist during sample workup and analysis. Acidic conditions from formic acid addition along with a persistent free chlorine residual catalyzed additional DCBQ formation when organic precursors were present. This led to large positive analytical bias during formation potential testing using raw water and model precursors. DCBQ levels previously reported using the formic acid preservation method are likely to show a strong positive bias. For future testing, we recommend the use of glycine or arsenite followed by formic acid.
Oxidative treatment of drinking water has been practiced for more than a century. UV-based advanced oxidation processes (UV-AOPs) have emerged as promising oxidative treatment technologies to eliminate recalcitrant chemicals and biological contaminants in drinking water. UV-AOPs inevitably alter the properties of natural organic matter (NOM) and affect the disinfection byproduct (DBP) formation in the post-disinfection. This paper provides a state-of-the-art review on the effects of UV-AOPs on the changes of NOM properties and the consequent impacts on DBP formation in the post-chlorination process. A tutorial review to the connotations of NOM properties (e.g., bulk properties, fractional constituents, and molecular structures) and the associated state-of-the-art analytical methods are firstly presented. The impacts of different radical-based AOPs on the changes of NOM properties together with the underlying NOM-radical reaction mechanisms are discussed. The impacts of alteration of NOM properties on DBP formation in the post-chlorination process are then reviewed. The current knowledge gaps and future research needs are finally presented, with emphases on the needs to strengthen the comparability of research data in literature, the accuracy in quantifying the reactive moieties of NOM, and the awareness of unknown DBPs in oxidative water treatment processes. The review and discussion improve the fundamental understanding of NOM-radical and NOM-chlorine chemistry. They also provide useful implications on the engineering design and operation of next-generation drinking water treatment plants.
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