Disinfection byproduct formation in reverse-osmosis concentrated and lyophilized natural organic matter from a drinking water source

Drinking water treatment and disinfection byproduct (DBP) research can be complicated by natural organic matter (NOM) temporal variability. NOM preservation by lyophilization (freeze-drying) has been long practiced to address this issue; however, its applicability for drinking water research has been limited because the selected NOM sources are atypical of most drinking water sources. The purpose of this research was to demonstrate that reconstituted NOM from a lyophilized reverse-osmosis (RO) concentrate of a typical drinking water source closely represents DBP formation in the original NOM. A preliminary experiment assessed DBP formation kinetics and yields in concentrated NOM, which demonstrated that chlorine decays faster in concentrate, in some cases leading to altered DBP speciation. Potential changes in NOM reactivity caused by lyophilization were evaluated by chlorination of lyophilized and reconstituted NOM, its parent RO concentrate, and the source water. Bromide lost during RO concentration was replaced by adding potassium bromide prior to chlorination. Although total measured DBP formation tended to decrease slightly and unidentified halogenated organic formation tended to increase slightly as a result of RO concentration, the changes associated with lyophilization were minor. In lyophilized NOM reconstituted back to source water TOC levels and then chlorinated, the concentrations of 19 of 21 measured DBPs, constituting 96% of the total identified DBP mass, were statistically indistinguishable from those in the chlorinated source water. Furthermore, the concentrations of 16 of 21 DBPs in lyophilized NOM reconstituted back to the RO concentrate TOC levels, constituting 86% DBP mass, were statistically indistinguishable from those in the RO concentrate. This study suggests that lyophilization can be used to preserve concentrated NOM without substantially altering the precursors to DBP formation.     

氯化消毒条件及污水水质对生成THMs、HAAs的影响

系统地研究了消毒务件和水质在城市污水氯化消毒过程中对生成三卤甲烷和卤乙酸的影响。结果表明，投氯量对三卤甲烷和卤乙酸生成量的影响最大，投氯量为40mg／L时的生成量分别约是投氯量为5mg／L时的30倍和70倍。三卤甲烷浓度随反应时间和温度无明显变化，而卤乙酸浓度在反应2h后达到峰值并在之后逐渐降低，且随温度的升高呈下降趋势。pH对两类副产物生成的影响几乎相反，近中性条件下的三卤甲烷生成量最多而卤乙酸生成量最少。水中氨氮浓度的增加会导致三卤甲烷生成量略有下降，而卤乙酸浓度却大幅上升。溴离子浓度升高将导致三卤甲烷和卤乙酸生成量显著增加，其中三氯甲烷浓度下降，三溴甲烷浓度显著上升，混合取代的三卤甲烷浓度先增加后减少。与此类似，二氯乙酸和三氯乙酸浓度随溴离子浓度的增加而减少，含溴卤乙酸浓度则有不同程度的增加。反应温度、反应时间、pH和氨氮对污水消毒副产物生成的影响与已报道的饮用水消毒中的作用规律存在显著差异，甚至截然相反，这为有针对性地选取消毒工艺参数提供了依据。     

Comparison of the disinfection by-product formation potential of treated waters exposed to chlorine and monochloramine

The formation of disinfection by-products (DBPs) from chlorination and monochloramination of treated drinking waters was determined. Samples were collected after treatment at 11 water treatment works but before exposure to chlorine or monochloramine. Formation potential tests were carried out to determine the DBPs formed by chlorination and monochloramination. DBPs measured were trihalomethanes (THMs), haloacetic acids (HAAs), halonitromethanes (HNMs), haloacetonitriles (HANs), haloaldehydes (HAs), haloketones (HKs) and iodo-THMs (i-THMs). All waters had the potential to form significant levels of all the DBPs measured. Compared to chlorine, monochloramination generally resulted in lower concentrations of DBPs with the exception of 1,1-dichloropropanone. The concentrations of THMs correlated well with the HAAs formed. The impact of bromine on the speciation of the DBPs was determined. The literature findings that higher bromide levels lead to higher concentrations of brominated DBPS were confirmed.     

Low trihalomethane formation in Korean drinking water

Organics in water have the potential to generate harmful disinfection by-products (DBPs) such as trihalomethanes (THMs) during the chlorination process. To clarify the regulatory implications of Korean THMs levels which appear to be significantly lower than those in the US where the Stage 1 and 2 D/DBPs rule has been promulgated, the characteristics of THMs formation were investigated on five major river waters in Korea. Water samples were taken from 12 water treatment plants on five major rivers that serve as drinking water sources for more than 90% of the Korean population. Trihalomethane formation potential (THMFP), total organic halide formation potential (TOXFP) and ultraviolet absorbance at 254 nm (UV(254)) were determined and compared with those from US data. A survey of existing data [J Korean Soc Water Qual; 16(4) 2000b 431-443] provided evidence that THMs levels in treated drinking water in Korea were one-third of those reported in the US. The lower THMs levels were mainly attributable to the differences in the level and THMFP of dissolved organic carbon (DOC). The DOC levels and the THMFP normalized to DOC were approximately 60% of those in the US. Results which combined could quantitatively account for the lower THMs levels (i.e. 0.6 x 0.6 approximately 1/3) in Korea. The observed Korean THMs levels were over-predicted by the THMs model () developed in the US. The level of THMFP was found to be similar if normalized for aromaticity as measured by UV(254). These findings suggest that: (i) the case for more stringent THMs control is not likely to be a high priority among issues of drinking water quality in Korea; and (ii) significant variation of THMFP level may exist over different geographic regions; hence (iii) independent THMs models should be developed to make accurate predictions for different regions.     

Bioanalytical and chemical assessment of the disinfection by-product formation potential: Role of organic matter

Disinfection by-products (DBP) formed from natural organic matter and disinfectants like chlorine and chloramine may cause adverse health effects. Here, we evaluate how the quantity and quality of natural organic matter and other precursors influence the formation of DBPs during chlorination and chloramination using a comprehensive approach including chemical analysis of regulated and emerging DBPs, total organic halogen quantification, organic matter characterisation and bioanalytical tools. In vitro bioassays allow us to assess the hazard potential of DBPs early in the chain of cellular events, when the DBPs react with their molecular target(s) and activate stress response and defence mechanisms. Given the reactive properties of known DBPs, a suite of bioassays targeting reactive modes of toxic action including genotoxicity and sensitive early warning endpoints such as protein damage and oxidative stress were evaluated in addition to cytotoxicity. Coagulated surface water was collected from three different drinking water treatment plants, along with reverse osmosis permeate from a desalination plant, and DBP formation potential was assessed after chlorination and chloramination. While effects were low or below the limit of detection before disinfection, the observed effects and DBP levels increased after disinfection and were generally higher after chlorination than after chloramination, indicating that chlorination forms higher concentrations of DBPs or more potent DBPs in the studied waters. Bacterial cytotoxicity, assessed using the bioluminescence inhibition assay, and induction of the oxidative stress response were the most sensitive endpoints, followed by genotoxicity. Source waters with higher dissolved organic carbon levels induced increased DBP formation and caused greater effects in the endpoints related to DNA damage repair, glutathione conjugation/protein damage and the Nrf2 oxidative stress response pathway after disinfection. Fractionation studies indicated that all molecular weight fractions of organic carbon contributed to the DBP formation potential, with the humic rich fractions forming the greatest amount of DBPs, while the low molecular weight fractions formed more brominated DBPs due to the high bromide to organic carbon ratio. The presence of higher bromide concentrations also led to a higher fraction of brominated DBPs as well as proportionally higher effects. This study demonstrates how a suite of analytical and bioanalytical tools can be used to effectively characterise the precursors and formation potential of DBPs.     

臭氧/氯消毒中藻类有机物生成消毒副产物的特征

饮用水源地藻华会释放大量藻类有机物(AOM),AOM与氯消毒剂反应生成的消毒副产物(DBPs)会给饮用水用户带来不容忽视的健康风险。为此,探究了臭氧/氯消毒对AOM结构和DBPs生成的影响。结果表明,臭氧氧化能有效去除AOM中芳香蛋白和酚类、叶绿素a、藻蓝蛋白结构物质,但是对腐殖酸类结构的去除效果相对较差。DBPs生成总量随臭氧投加浓度的升高而增加,其中主要是三氯甲烷(TCM);卤代乙腈和卤代酮的生成总量随臭氧投加浓度的变化趋势不明显。延长臭氧接触时间会明显增加1 h氯化中TCM的生成量,氯化24 h时DBPs生成总量与臭氧接触时间无关。在臭氧/氯消毒过程中,AOM的DBPs生成潜能低于天然有机物(NOM)。AOM有利于一溴一氯乙腈的生成,而NOM会生成更多的二氯乙腈。     

Differential absorbance study of effects of temperature on chlorine consumption and formation of disinfection by-products in chlorinated water

Effects of chlorine dose, reaction time and temperature on the formation of disinfection by-products (DBPs) and corresponding changes in the absorbance of natural organic matter (NOM) in chlorinated water were examined in this study. Although variations of chlorination parameters, notably those of temperature that was varied from 3 to 35 degrees C, influenced the kinetics of chlorine consumption and DBP release, correlations between chlorine consumption, concentrations of trihalomethanes (THMs), haloacetonitriles (HANs), other DBP species and, on the other hand, intensity of differential absorbance at 272nm remained unaffected. THM and HAN speciation was correlated with the differential absorbance, indicating preferential incorporation of bromine at the initial phases of halogenation that correspond to low DeltaA(272) values. Because the DeltaA(272) parameter is a strong indicator of the formation of DBP species and chlorine decay, optimization of chlorination operations and DBPs control based on this parameter can be beneficial for many water utilities, especially those with pronounced variability of water temperature and residence times.     

Multivariate distributions of disinfection by-products in chlorinated drinking water

Drinking water disinfection by-product (DBP) occurrence research is important in supporting risk assessment and regulatory performance assessment. Recent DBP occurrence surveys have expanded their scope to include non-regulated priority DBPs as well as regulated DBPs. This study applies a Box-Cox transformed multivariate normal model and data augmentation methods for left-censored and missing observations to US EPA Information Collection Rule (ICR) drinking water data to describe the variability in the trihalomethane (THM4), trihaloacetic acid (THAA), dihaloacetic acid (DHAA), and dihaloacetonitrile (DHAN) DBP classes, the relationship between class-sum and the occurrence of individual DBPs within these classes. Inferences about bromine incorporation in these classes are then compared to those made by Obolensky and Singer (2005). Results reported herein show that class-based and individual DBP concentrations are strongly related to bromine substitution, and that speciation and bromine substitution patterns are consistent across DBP classes. In addition, the multiple imputation approach employed reveals that uncertainties related to missing and left-censored DBPs have important implications for understanding bromine substitution in the THAA class. These concerns should be considered through alternative approaches to DBP regulation in subsequent Stage II D/DBP assessment and revisions, where appropriate.     

Model development for predicting changes in DBP exposure concentrations during indoor handling of tap water

Disinfection by-products (DBPs) in municipal drinking water are a matter of concern because of their possible risks to human health. Risk assessment studies often use measurements of DBPs in water distribution systems, whereas populations are typically exposed to the indoor tap water. Further to this, consumers often employ several indoor strategies to handle tap water (e.g., storing in a refrigerator, boiling, filtering, etc.) prior to use. The indoor handling of municipal water may have implications on DBPs' exposure assessment. This study investigates and develops models to predict the effects of various indoor handling strategies on trihalomethanes (THMs) and haloacetic acids (HAAs). Linear and nonlinear models are developed to predict changes in THM and HAA concentrations due to various indoor water manipulation strategies. The models are capable of assessing representative exposure concentrations of THMs and HAAs as a result of indoor handling, which might be useful in gaining a better understanding of exposure and risks from DBPs in municipal drinking water.     

Electrochemical removal of bromide and reduction of THM formation potential in drinking water

Trihalomethanes (THMs), a by-product of the chlorination of natural waters containing dissolved organic carbon and bromide, are the focus of considerable public health concern and regulation due to their potential as a carcinogen by ingestion. This paper presents a promising new water treatment process that lowers the concentration of bromide in drinking water and thus, lowers the THM formation potential. Bromide is oxidized by electrolysis to bromine and then the bromine apparently volatilized. The electrolyzed water, when chlorinated, produces measurably lower amounts of THMs and proportionately fewer brominated THMs, which are of greater public health concern than the chlorinated THMs. Removing bromide should also reduce the formation of other disinfection by-products such as bromate and haloacetic acids.     

Evaluation of bromine substitution factors of DBPs during chlorination and chloramination

Bromine substitution factor (BSF) was used to quantify the effects of disinfectant dose, reaction time, pH, and temperature on the bromine substitution of disinfection byproducts (DBPs) during chlorination and chloramination. The BSF is defined as the ratio of the bromine incorporated into a given class of DBPs to the total concentration of chlorine and bromine in that class. Four classes of DBPs were evaluated: trihalomethanes (THMs), dihaloacetonitriles (DHANs), dihaloacetic acids (DHAAs) and trihaloacetic acids (THAAs). The results showed that the BSFs of the four classes of DBPs generally decreased with increasing reaction time and temperature during chlorination at neutral pH. The BSFs peaked at a low chlorine dose (1 mg/L) and decreased when the chlorine dose further increased. The BSFs of chlorination DBPs at neutral pH are in the order of DHAN > THM & DHAA > THAA. DHAAs formed by chloramines exhibited distinctly different bromine substitution patterns compared to chlorination DHAAs. Brominated DBP formation was generally less affected by the pH change compared to chlorinated DBP formation.     

The formation of halogen-specific TOX from chlorination and chloramination of natural organic matter isolates

The formation of disinfection by-products (DBPs) is a public health concern. An important way to evaluate the presence of DBPs is in terms of the total organic halogen (TOX), which can be further specified into total organic chlorine (TOCl), bromine (TOBr), and iodine (TOI). The formation and distribution of halogen-specific TOX during chlorination and chloramination of natural organic matter (NOM) isolates in the presence of bromide and iodide ions were studied. As expected, chloramination produced significantly less TOX than chlorination. TOCl was the dominant species formed in both chlorination and chloramination. TOI was always produced in chloramination, but not in chlorination when high chlorine dose was used, due to the limited presence of HOI in chlorination as a result of the oxidation of iodide to iodate in the presence of excess chlorine. The formation of TOI during chloramination increased as the initial iodide ion concentration increased, with a maximum of ∼60% of the initial iodide ion becoming incorporated into NOM. Iodine incorporation in NOM was consistently higher than bromine incorporation, demonstrating that the competitive reactions between bromine and iodine species in chloramination favoured the formation of HOI and thus TOI, rather than TOBr. Correlations between the aromatic character of the NOM isolates (SUVA₂₅₄ and % aromatic C) and the concentrations of overall TOX and halogen-specific TOX in chloramination were observed. This indicates that the aromatic moieties in NOM, as indicated by SUVA₂₅₄ and % aromatic C, play an important role in the formation of overall TOX and halogen-specific TOX in chloramination. THMs comprised only a fraction of TOX, up to 7% in chloramination and up to 47% in chlorination. Although chloramine produces less TOX than chlorine, it formed proportionally more non-THM DBPs than chlorine. These non-THM DBPs are mostly unknown, corresponding to unknown health risks. Considering the higher potential for formation of iodinated DBPs and unknown DBPs associated with the use of chloramine, water utilities need to carefully balance the risks and benefits of using chloramine as an alternative disinfectant to chlorine in order to satisfy guideline values for THMs.     

Formation of chlorination by-products in waters with low SUVA--correlations with SUVA and differential UV spectroscopy

The formation of THMs and HAAs after chlorination of bulk water fractions of low-SUVA (specific UV absorbance) surface waters was investigated, and the applicability of SUVA and differential UV spectroscopy for monitoring THMs and HAAs in such waters was evaluated. Samples from two reservoirs were fractionated employing XAD-8, XAD-4, MIEX resin and granular activated carbon adsorption. A total of 83 bulk water NOM fractions (i.e., the remaining solutions after contact with the adsorbent or resin at various doses) were obtained and chlorinated. The majority of NOM in both waters was found to have average molecular weights <2000 Da and SUVA values <2L/mg Cm, indicating that NOM in the tested waters contained dominantly lower molecular weight fractions and low aromaticity. SUVA did not correlate well with the formation and speciation of THMs and HAAs, suggesting that SUVA does not capture the reactive sites on NOM moieties responsible for DBP formation in low-SUVA waters. Similarly, no correlations were found among THMs/HAAs formations and differential UV spectroscopy, indicating the formation of DBPs independent of destruction in UV-absorbing sites. In all fractions, concentrations of THMs were higher than those of HAAs. Chlorinated DBP species were dominant over brominated ones due to low bromide concentrations. The results overall suggested that low- or non-UV-absorbing NOM moieties play important roles in the formation of DBPs in waters with low SUVA, low DOC and low bromide levels.     

Disinfection by-products and their precursors in a water treatment plant in North China: Seasonal changes and fraction analysis

A one-year-long monitoring project was conducted to assay the concentrations of THMs, HAAs and their formation potential along the conventional process in a water treatment plant in North China. Subsequent investigations of organic matter fractionation and the contribution of the algae to the precursor were also conducted to trace the source of the DBPs. The results showed that the concentration of DBPs and their formation potential varied with the seasons. The highest concentrations of THMs and the highest HAAs formation potential, each almost 500 microg/L, were detected in autumn and the lowest were in spring, no more than 100 microg/L. Both organic matter and algae were found to be important DBP precursors. The hydrophobic acid fraction in dissolved organic matter has the highest formation potential for both THM and HAA. Algae contribute about 20% to 50% of the total formation potential during an algal bloom. The efficiency of each unit process for DBPs and precursors was also assayed. Unfortunately, the conventional drinking water treatment process is limited in its efficiency for precursor removal. The pre-chlorination and filtration process had a negative effect on DBP or precursor removal.     

Occurrence and control of nitrogenous disinfection by-products in drinking water--a review

The presence of nitrogenous disinfection by-products (N-DBPs), including nitrosamines, cyanogen halides, haloacetonitriles, haloacetamides and halonitromethanes, in drinking water is of concern due to their high genotoxicity and cytotoxicity compared with regulated DBPs. Occurrence of N-DBPs is likely to increase if water sources become impacted by wastewater and algae. Moreover, a shift from chlorination to chloramination, an option for water providers wanting to reduce regulated DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs), can also increase certain N-DBPs. This paper provides a critical review of the occurrence and control of N-DBPs. Data collated from surveys undertaken in the United States and Scotland were used to calculate that the sum of analysed halonitromethanes represented 3-4% of the mass of THMs on a median basis; with Pearson product moment correlation coefficients of 0.78 and 0.83 between formation of dihaloacetonitriles and that of THMs and HAAs respectively. The impact of water treatment processes on N-DBP formation is complex and variable. While coagulation and filtration are of moderate efficacy for the removal of N-DBP precursors, such as amino acids and amines, biofiltration, if used prior to disinfection, is particularly successful at removing cyanogen halide precursors. Oxidation before final disinfection can increase halonitromethane formation and decrease N-nitrosodimethylamine, and chloramination is likely to increase cyanogen halides and NDMA relative to chlorination.     

Modeling DBPs formation in drinking water in residential plumbing pipes and hot water tanks

Disinfection byproducts (DBPs) in municipal supply water are a concern because of their possible risks to human health. Risk assessment studies often use DBP data in water distribution systems (WDS). However, DBPs in tap water may be different because of stagnation of the water in plumbing pipes (PP) and heating in hot water tanks (HWT). This study investigated occurrences and developed predictive models for DBPs in the PP and the HWT of six houses from three municipal water systems in Quebec (Canada) in a year-round study. Trihalomethanes (THMs) in PP and HWT were observed to be 1.4-1.8 and 1.9-2.7 times the THMs in the WDS, respectively. Haloacetic acid (HAAs) in PP and HWT were observed to be variable (PP/WDS = 0.23-2.24; HWT/WDS = 0.53-2.61). Using DBPs occurrence data from these systems, three types of linear models (main factors; main factors, interactions and higher orders; logarithmic) and two types of nonlinear models (three parameters Logistic and four parameters Weibull) were investigated to predict DBPs in the PP and HWT. Significant factors affecting DBPs formation in the PP and HWT were identified through numerical and graphical techniques. The R² values of the models varied between 0.77 and 0.96, indicating excellent predictive ability for THMs and HAAs in the PP and the HWT. The models were found to be statistically significant. The models were validated using additional data. These models can be used to predict DBPs increase from WDS (water entry point of house) to the PP and HWT, and could thereby help gain a better understanding of human exposure to DBPs and their associated risks.     

A comparison of disinfection by-products found in chlorinated and chloraminated drinking waters in Scotland

Seven water treatment works were selected to compare disinfection by-products (DBPs) formed when using chlorination and chloramination. DBPs measured included trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), trihalonitromethane, iodinated THMs and nitrosamines. Generally treatment works that used chloramination were able to meet the European THM regulatory limit of 100 μg L⁻¹ whereas the chlorinated works found it significantly more difficult. There were no significant differences in the levels of nitrogenous DBPs between the treatment works using chlorination or chloramination with the exception of the nitrosamine N-nitrosodimethylamine (NDMA) which was present at one treatment works in one season.     

Trihalomethane exposures in indoor swimming pools: a level III fugacity model

The potential for generation of disinfection byproducts (DBPs) in swimming pools is high due to the concentrations of chlorine required to maintain adequate disinfection, and the presence of organics introduced by the swimmers. Health Canada set guidelines for trihalomethanes (THMs) in drinking water; however, no such guideline exists for swimming pool waters. Exposure occurs through ingestion, inhalation and dermal contact in swimming pools. In this research, a multimedia model is developed to evaluate exposure concentrations of THMs in the air and water of an indoor swimming pool. THM water concentration data were obtained from 15 indoor swimming pool facilities in Quebec (Canada). A level III fugacity model is used to estimate inhalation, dermal contact and ingestion exposure doses. The results of the proposed model will be useful to perform a human health risk assessment and develop risk management strategies including developing health-based guidelines for disinfection practices and the design of ventilation system for indoor swimming pools.     

Considerations for improving the accuracy of exposure to disinfection by-products by ingestion in epidemiologic studies

Disinfection by-product (DBP) exposure characterization studies are often based on the analysis of a limited number of samples collected from a distribution system (DS) in which DBP levels are variable over time and space. A compositing technique was developed to simplify the sample collection procedures for integrating over temporal variations in DBPs measured in terms of trihalomethanes (THMs), haloacetic acids (HAAs), and total organic halogen (TOX). Over the course of 5 days analysis, the single composited sample was within 94-100% of the average THM concentration in all grab samples, 92-105% of HAAs, and 130% of the TOX concentration. Additionally, temporal variability factors such as timing of sample collection and the handling of tap water prior to consumption were found to influence DBP levels in consumers' drinking water. Included in our study of home water use are the effects of boiling which removed up to 98% of THMs and point of use (POU) devices which all showed DBP removal but differed depending on the device used. These factors should be taken into consideration in DBP exposure characterization for epidemiologic studies.     

Natural organic matter and DBP formation potential in Alaskan water supplies

Disinfection by-products (DBP) are formed when natural organic matter (NOM) in water reacts with a disinfectant, usually chlorine. DBPs are a health risk element and regulated under the Safe Drinking Water Act. A study was conducted to evaluate the characteristics of NOM that contribute to DBPs in 17 different drinking water systems in Alaska. In order to determine the nature of the organic matter contributing to DBPs, DBP formation potential was compared with standard water quality parameters such as UV-254, color and dissolved organic carbon (DOC), as well as pyrolysis-gas chromatography/mass spectrometry (GC/MS). Results showed strong correlations between UV-254 and DBP formation potential for all waters studied. DOC, on the other hand, was less strongly correlated to DBP formation potential. Unlike previous studies, the total trihalomethane and haloacetic acid formation potentials were equal on a mass concentration basis for the waters studied. Pyrolysis-GC/MS indicated that NOM contributing to DBPs were primarily phenolic compounds. This finding was consistent with previous studies; however, unlike other studies, no correlation was found between aliphatic compounds in the raw waters and DBP formation potential.