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.     

The effects of combined ozonation and filtration on disinfection by-product formation

The effects of combined ozonation and membrane filtration on the removal of the natural organic matter (NOM) and the formation of disinfection by-products (DBPs) were investigated. Ozonation/filtration resulted in a reduction of up to 50% in the dissolved organic carbon (DOC) concentration. Furthermore, humic substances were converted to non-humic substances, with changes in the humic and non-humic substance concentrations of up to −50% and +20%, respectively. Ozonation/filtration resulted in the formation of partially oxidized compounds from NOM that were less reactive with chlorine, decreasing the concentration of simulated distribution system total trihalomethanes (SDS TTHMs) and simulated distribution system halo acetic acids (SDS HAAs) by up to 80% and 65%, respectively. Reducing the molecular weight cut-off (MWCO) of the membranes resulted in reductions in the concentrations of SDS TTHMs and SDS HAAs. Using a membrane with a 5 kD MWCO, the minimum gaseous ozone concentration required to bring about effective NOM degradation and meet regulatory requirements for chlorinated DBPs was 2.5 g/m³.     

Evidence for alternative exhaled elimination profiles of disinfection by-products and potential markers of airway responses to swimming in a chlorinated pool environment

Chlorine-based disinfectants protect pool water from pathogen contamination but produce potentially harmful halogenated disinfection by-products (DBPs). This study characterized the bioaccumulation and elimination of exhaled DBPs post-swimming and investigated changes in exhaled breath profiles associated with chlorinated pool exposure. Nineteen participants provided alveolar-enriched breath samples prior to and 5, 90, 300, 510, and 600 minutes post-swimming. Known DBPs associated with chlorinated water were quantitated by thermal desorption-gas chromatography-mass spectrometry. Two distinct exhaled DBP elimination profiles were observed. Most participants (84%) reported peak concentrations immediately post-swimming that reduced exponentially. A sub-group exhibited a previously unobserved and delayed washout profile with peak levels at 90 minutes post-exposure. Metabolomic investigations tentatively identified two candidate biomarkers associated with swimming pool exposure, demonstrating an upregulation in the hours after exposure. These data demonstrated a hitherto undescribed exhaled DBP elimination profile in a small number of participants which contrasts previous findings of uniform accumulation and exponential elimination. This sub-group which exhibited delayed peak-exhaled concentrations suggests the uptake, processing, and immediate elimination of DBPs are not ubiquitous across individuals as previously understood. Additionally, non-targeted metabolomics highlighted extended buildup of compounds tentatively associated with swimming in a chlorinated pool environment that may indicate airway responses to DBP exposure.     

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.     

含氮消毒副产物卤代酰胺的生成特性与控制研究进展

卤代酰胺(haloamides)具有极强的致癌、致崎和致突变性,是饮用水处理领域开始关注的一种新型含氮卤代消毒副产物.这类物质分子质量小、结构简单、可水解,具有很强的极性和亲水性,可广泛存在于消毒后的出厂水中.卤代酰胺的产生受到温度、pH值、消毒剂含量的影响,但生成机制非常复杂,尚未有相关理论能完全解释其产生规律.鉴于其较强的"三致"特性,对它的物理特性、产生条件及控制手段进行研究是目前消毒副产物领域的一个重要方向.介绍了卤代酰胺的特性、检测方法,对其控制手段的最新研究进展进行了重点说明,指出通过控制其前体物的方法来控制卤代酰胺的产生是该领域的研究重点.     

Characterization of algal organic matter and formation of DBPs from chlor(am)ination

The frequent occurrence of algal blooms in drinking water reservoirs causes problems to water supply, one of which is the release of algal organic matter in high concentrations to affect drinking water quality. Algal organic matter, including extracellular organic matter (EOM) and intracellular organic matter (IOM), was characterized. The formation of a variety of disinfection by-products (DBPs) in chlorination and chloramination of EOM, IOM and algal cells was evaluated. Natural organic matter (NOM) isolated from Suwannee River was also studied for comparison. EOM and IOM were rich in organic nitrogen, which consisted of high (over 10 kDa) and low (70–1000 Da) molecular weight (MW) organic matter, whilst the MW of organic carbon in EOM and IOM was relatively lower. IOM had a higher fraction of total organic nitrogen, with larger proportions of higher MW and more hydrophobic contents than did EOM. IOM also contained higher fractions of free amino acids but lower fractions of aliphatic amines than did EOM. During chlorination of EOM and IOM, organic chloramines were first formed and then became undetectable after 1 d. Chlorination of EOM and IOM produced more nitrogenous DBPs (N-DBPs) and haloaldehydes and less carbonaceous DBPs (C-DBPs) than did chlorination of NOM. Organic chloramines were found after 3-d chloramination of EOM and IOM. The amounts of N-DBPs and C-DBPs formed from chloramination of EOM or IOM were much less than that from NOM. EOM produced less DBPs (except for trichloronitromethane) than did IOM and algal cells in chlorination and chloramination.     

The effects of UV disinfection on drinking water quality in distribution systems

UV treatment is a cost-effective disinfection process for drinking water, but concerned to have negative effects on water quality in distribution system by changed DOM structure. In the study, the authors evaluated the effects of UV disinfection on the water quality in the distribution system by investigating structure of DOM, concentration of AOC, chlorine demand and DBP formation before and after UV disinfection process. Although UV treatment did not affect concentration of AOC and characteristics of DOM (e.g., DOC, UV_254, SUVA₂₅₄, the ratio of hydrophilic/hydrophobic fractions, and distribution of molecular weight) significantly, the increase of low molecular fraction was observed after UV treatment, in dry season. Chlorine demand and THMFP are also increased with chlorination of UV treated water. This implies that UV irradiation can cleave DOM, but molecular weights of broken DOM are not low enough to be used directly by microorganisms in distribution system. Nonetheless, modification of DOM structure can affect water quality of distribution system as it can increase chlorine demands and DBPs formation by post-chlorination.     

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.     

Volatile disinfection by-product analysis from chlorinated indoor swimming pools

Chlorination of indoor swimming pools is practiced for disinfection and oxidation of reduced compounds that are introduced to water by swimmers. However, there is growing concern associated with formation for chlorinated disinfection by-products (DBPs) in these settings. Volatile DBPs are of particular concern because they may promote respiratory ailments and other adverse health effects among swimmers and patrons of indoor pool facilities. To examine the scope of this issue, water samples were collected from 11 pools over a 6 month period and analyzed for free chlorine and their volatile DBP content. Eleven volatile DBPs were identified: monochloramine (NH₂Cl), dichloramine (NHCl₂), trichloramine (NCl₃), chloroform (CHCl₃), bromoform (CHBr₃), dichlorobromomethane (CHBrCl₂), dibromochloromethane (CHBr₂Cl), cyanogen chloride (CNCl), cyanogen bromide (CNBr), dichloroacetonitrile (CNCHCl₂), and dichloromethylamine (CH₃NCl₂). Of these 11 DBPs, 10 were identified as regularly occurring, with CHBrCl₂ only appearing sporadically. Pool water samples were analyzed for residual chlorine compounds using the DPD colorimetric method and by membrane introduction mass spectrometry (MIMS). These two methods were chosen as complementary measures of residual chlorine, and to allow for comparisons between the methods. The DPD method was demonstrated to consistently overestimate inorganic chloramine content in swimming pools. Pairwise correlations among the measured volatile DBPs allowed identification of dichloromethylamine and dichloroacetonitrile as potential swimming pool water quality indicator compounds.     

Disinfection by-products (DBPs) in drinking water and predictive models for their occurrence: a review

Disinfection for drinking water reduces the risk of pathogenic infection but may pose chemical threat to human health due to disinfection residues and their by-products (DBPs) when the organic and inorganic precursors are present in water. More than 250 DBPs have been identified, but the behavioural profile of only approximately 20 DBPs are adequately known. In the last 2 decades, many modelling attempts have been made to predict the occurrence of DBPs in drinking water. Models have been developed based on data generated in laboratory-scaled and field-scaled investigations. The objective of this paper is to review DBPs predictive models, identify their advantages and limitations, and examine their potential applications as decision-making tools for water treatment analysis, epidemiological studies and regulatory concerns. The paper concludes with a discussion about the future research needs in this area.     

Measurement of dissolved organic nitrogen forms in wastewater effluents: concentrations, size distribution and NDMA formation potential

Dissolved organic nitrogen (DON), which may act as a nutrient and a disinfection by-product precursor, accounts for most of the dissolved nitrogen in nitrified-denitrified wastewater effluents. To gain insight into the behavior of wastewater-derived DON in engineered and natural systems, samples from treatment plants employing a range of different processes were characterized by several different methods. Dissolved free and combined amino acids accounted for the majority of the identifiable DON. Combined amino acids typically accounted for less than 10-20% of the wastewater-derived DON. Other organic-nitrogen containing species such as EDTA and humic substances from the water source only accounted for a few percent of the remaining DON. The remaining DON mainly consisted of hydrophilic, low-molecular weight compounds, capable of passing through a 1 kDa ultrafilter. This fraction of the DON also contained most of the precursors of N-nitrosodimethylamine (NDMA). The chemical properties of wastewater-derived DON pose challenges to designers of wastewater treatment plants because most physical and chemical treatment processes will not remove low-molecular weight, hydrophilic compounds.     

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。     

饮用水中溶解性有机氮类化合物的控制研究进展

水中溶解性有机氮类化合物(Dissolved Organic Nitrogen,DON)是水中溶解性有机物(DOM)的重要组成部分.与溶解性有机碳化合物(DOC)性质相似,DON可导致耗氯量增加、膜污染、产生消毒副产物等问题.尤为需要关注的是,DON在氯化过程中将产生强致癌性的卤化硝基甲烷与亚硝胺化合物(如NDMA)等,对水质安全构成重大威胁.因此,对水中溶解性有机氮的控制成为目前饮用水领域关注的新问题之一.系统介绍了原水中DON的含量、种类、分子组成、存在形式等,同时对DON控制方法进行了阐述.鉴于DON含量较小、种类繁多、亲水性强,常规净水工艺很难有效控制其浓度,水厂可通过强化混凝、膜处理、吸附与氧化来改善对DON的去除效果.     

再生水用于地下回灌的加氯消毒研究

针对城市污水厂二级出水用于地下回灌的两种深度处理工艺,确定了达到消毒要求的加氯量,并且研究了加氯消毒对有关水质参数DOC、AOX、CHCl3、CCl4、UV254等的影响。研究发现,有效氯投加量在8mg/L左右时,水中细菌总数与总大肠菌群数均能达到我国饮用水卫生标准。加氯后水的DOC值变化不大,AOX值则有较明显的增大,CHCl3浓度略有增加,CCl4基本维持在加氯前的水平,UV254值也较加氯前有所增大。研究结果还表明,粒状活性炭处理工艺在污水深度处理流程中对去除消毒副产物（AOX）及其前驱物发挥着重要的作用。     

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.     

Identification and understanding of fouling in low-pressure membrane (MF/UF) filtration by natural organic matter (NOM)

An understanding of natural organic matter (NOM) as a membrane foulant and the behavior of NOM components in low-pressure membrane fouling are needed to provide a basis for appropriate selection and operation of membrane technology for drinking water treatment. Fouling by NOM was investigated by employing several innovative chemical and morphological analyses.

Source (feed) waters with a high hydrophilic (HPI) fraction content of NOM resulted in significant flux decline. Macromolecules of a relatively hydrophilic character (e.g. polysaccharides) were effectively rejected by low-pressure membranes, suggesting that macromolecular compounds and/or colloidal organic matter in the hydrophilic NOM fraction may be a problematic foulant of low-pressure membranes. Moreover, the significant organic fouling that is contributed by polysaccharides and/or proteins in macromolecular and/or colloidal forms depends on molecular shape (structure) as well as size (i.e. molecular weight). More significant flux decline was observed in microfiltration (MF) compared to ultrafiltration (UF) membrane filtration. MF membrane fouling may be caused by pore blockage associated with large (macromolecular) hydrophilic molecules and/or organic colloids. In the case of UF membranes, the flux decline may be caused by sequential or simultaneous processes of surface (gel layer) coverage during filtration. Morphological analyses support the notion that membrane roughness may be considered as a more important factor in membrane fouling by controlling interaction between molecules and the membrane surface, compared to the hydrophobic/hydrophilic character of membranes. Membrane fouling mechanisms are not only a function of membrane type (MF versus UF) but also depend on source (feed) water characteristics.     

Seasonal variations of disinfection by-product precursors profile and their removal through surface water treatment plants

A sampling program has been undertaken to investigate the variations of disinfection by-products (DBPs) formation and nature and fate of natural organic matter (NOM) through water treatment plants in Istanbul. Specific focus has been given to the effect seasonal changes on the formation of DBPs and organic precursors levels. Water samples were collected from the three reservoirs inlet and within three major water treatment plants of Istanbul, Turkey. Changes in the dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV(254)), specific ultraviolet absorbance (SUVA), trihalomethane formation potential (THMFP), and haloacetic acids formation potential (HAAFP) were measured for both the treated and raw water samples. The variations of THM and HAA concentrations within treatment processes were monitored and also successfully assessed. The reactivity of the organic matter changed throughout the year with the lowest reactivity (THMFP and HAAFP) in winter, increasing in spring and reaching a maximum in fall season. This corresponded to the water being easier to treat in fall and an increase in the proportion of hydrophobic content. Understanding the seasonal changes in organic matter character and their reactivity with treatment chemicals should lead to a better optimization of the treatment processes and a more consistent water quality.     

饮用水氯消毒生成DBPs的影响因素及其控制工艺

阐述了饮用水消毒副产物(DBPs)产生的影响因素,分析了天然有机物(NOM)、温度、pH、接触时间、氯用量和余氯浓度等各种因素对产生DBPs种类和数量的影响,提出了控制DBPs应从去除其前体物NOM,改变消毒工艺或采用新的消毒剂以及去除已生成的DBPs三方面入手.     

预臭氧化对有机物混凝的影响

消毒副产物是饮用水安全保障技术面临的重大课题,消毒副产物前驱物的去除方法有很多种,预臭氧化就是其中的一种,但是预臭氧化对后续的混凝的影响目前尚没有统一的结论。本文采用化学极性树脂分级技术为试验手段,研完了预臭氧化对混凝去除天然有机物效果的影响,对水中有机物的各成分分布进行了表征,对预臭氧化影响混凝的机理进行初步的探讨。通过树脂分级试验发现,预臭氧化使得原水中憎水中性有机物显著增加。不经预臭氧化的原水经过混凝后DOC的含量都有所下降,DOC的去除率从高到低的顺序依次为：憎水中性有机物、憎水碱性有机物、憎水酸性有机物、弱憎水酸性有机物和亲水性有机物。臭氧投加量为1．1mg／L时,憎水中性有机物的去除率大幅度提高,去除率为95％左右;臭氧投加量为4．4mg／L时,憎水酸性有机物、弱憎水酸性有机物及其它亲水性有机物的去除率都有不同程度的提高,强憎水性有机物的去除率变化不大。     

Characterization of natural organic matter in conventional water treatment processes for selection of treatment processes focused on DBPs control

Natural organic matter (NOM) from raw and process waters at a conventional water treatment plant was isolated into hydrophobic and hydrophilic fractions by physicochemical fractionation methods to investigate its characteristics. Formation potential of trihalomethanes (THMs) was highly influenced by the hydrophobic fraction, whereas haloacetic acids formation potential (HAAFP) depended more on the hydrophilic fraction. However the hydrophobic fraction was removed more than the hydrophilic fraction through conventional water treatment. Therefore residual hydrophilic NOM after conventional treatment needs to be removed to reduce HAAFP. Feasible additional processes are required to be evaluated by comparing preferential removal efficiency of hydrophilic NOM through pilot tests. The structural and chemical characteristics of hydrophobic NOM (i.e., humic substances (HS)) were further investigated to know how they are influenced by conventional treatment. The phenolic fraction in the hydrophobic NOM was mainly removed compared to the carboxylic fraction through water treatment, and a higher formation potential of THMs resulted from NOM with a higher phenolic content. The Fourier-transform infrared (FT-IR) and proton nuclear magnetic resonance ((1)H-NMR) employed for characterization of NOM through water treatment were insightful revealing that their results were quite close to each other. Decreases of ratio of UV absorbance at 253 and 203 nm, respectively (A(253)/A(203) ratio) and trihalomethane formation potential/dissolved organic carbon (THMFP/DOC) showed consistent trends; therefore, the A(253)/A(203) ratio may be a good indicator of tendency for the formation potential of disinfection by-products (DBPs).