Empirical rate equation for trihalomethane formation with chlorination of humic substances in water

Trihalomethane (THM) in drinking water is formed by chlorination of humic substances. In this study, the rates of THM formation in aqueous solution of humic acid were examined under various conditions. The following rate equation was obtained empirically. [THM] = k (pH − a)[TOC][Cl₂]₀^mtⁿ.

Here, [THM] is the concentration of total THM after t h, [TOC] and [Cl₂]₀ are the concentrations of total organic carbon and chlorine dose, k is the rate constant and a, m and n are parameters. The values of k, a, m and n for humic acid as reagent were obtained as 8.2 × 10⁻⁴ (l^mmg^−mh⁻ⁿ), 2.8, 0.25 and 0.36, respectively. The activation energy was obtained as 37 kJ mol⁻¹. Further, it was proved that the above equation could be applied to the rates of THM formation from precursors in actual river and lake waters.     

Understanding data requirements for trihalomethane formation modelling in water supply systems

Tighter regulatory standards for trihalomethanes in drinking water have been introduced in many countries in response to improved epidemiological evidence. This has led to the need to model better the THM concentrations in water distribution systems in order to manage efficiently economic, chemical and microbiological factors. THM modelling is a challenging process given the complex chemistry and dependence on river catchment, water treatment works and distribution system characteristics. It is demonstrated that a good understanding of the system from raw water to tap is needed if cost effective models of appropriate fidelity are to be produced. For appropriate systems models can incorporate, through empirical relationships, raw water quality variations based on river flow predictions, aspects of unit process management decision making variables as well as distribution system characteristics. In many systems model fidelity and hence efficient management is constrained by a lack of knowledge of system response.     

饮用水中氯化消毒副产物的控制研究进展

探讨了DBPs的形成机理及其种类,然后介绍了DBPs对人体的健康风险,并总结了目前国内外控制DBPs的方法,为饮用水高效安全消毒技术的进一步研究提出了意见和建议。     

自由氯、氯胺和顺序氯化对饮用水消毒效果的试验研究

研究了自由氯、氯胺和顺序氯化三种消毒方式对大肠埃希氏菌和粪肠球菌的灭活效果.结果表明,自由氯浓度越高,对细菌的灭活速率和最终灭活率越大;氯胺浓度越高,对细菌的灭活速率和最终灭活率越大;顺序氯化消毒效果优于单独使用自由氯或氯胺时的消毒效果.同时,还探讨了pH和温度对三种消毒方式的影响.     

Production of lipophilic volatile organohalogen materials during laboratory chlorination of some waste water and polluted river water samples from Yugoslavia

Water chlorination leads to the generation of various halogenated products of natural and waste water organic mater. In natural surface water humic matter usually makes the greatest part of the total organic matter. However, in the river water polluted with various organic wastes, other organic matter is also present in significant concentrations. The investigation of the relationship between the concentration of organic matter in the samples of waste water and heavily polluted river waters in Yugoslavia on one side, and the production of the lipophilic volatile organohalogen materials during the process of their chlorination on the other side is described. The production of the halomethanes and other ECD response materials during the chlorination of water samples in laboratory conditions is compared with the concentrations of organic materials in water samples. From the obtained linear correlation coefficients, possibilities of predicting amounts of organohalides during the chlorination process by using several very simple methods for the organic materials estimation in the investigated water samples are discussed and compared.     

Speciation and variation in the occurrence of haloacetic acids in three water supply systems in England

An investigation into the speciation and occurrence of nine haloacetic acids (HAAs) was conducted during the period of April 2007 to March 2008 and involved three drinking water supply systems in England, which were chosen to represent a range of source water conditions; these were an upland surface water, a lowland surface water and a groundwater. Samples were collected seasonally from the water treatment plants and at different locations in the distribution systems. The highest HAA concentrations occurred in the upland surface water system, with an average total HAA concentration of 21.3 μg/L. The lowest HAA levels were observed in the groundwater source, with a mean concentration of 0.6 μg/L. Seasonal variations were significant in the HAA concentrations; the highest total HAA concentrations were found during the autumn, when the concentrations were approximately two times higher than in winter and spring. HAA speciation varied among the water sources, with dichloroacetic acid and trichloroacetic acid dominant in the lowland surface water system and brominated species dominant in the upland surface water system. There was a strong correlation between trihalomethanes and HAAs when considering all samples from the three systems in the same data set (r ²=0.88); however, the correlation was poor/moderate when considering each system independently.     

Chemometric modeling and prediction of trihalomethane formation in Barcelona's water works plant

Formation and occurrence of trihalomethanes (CHCl3, CHBr3, CHCl2Br, and CHBr2Cl) are investigated in water chlorination disinfection processes in the Barcelona's water works plant (WWP). Twenty-three WWP variables were measured and investigated for correlation with trihalomethane formation. Multivariate statistical methods including principal component analysis (PCA), multilinear regression (MLR), stepwise MLR (SWR), principal component regression (PCR) and partial least squares regression (PLSR) have been used and compared to model and predict the complex behavior observed for the measured trihalomethane concentrations. The results, obtained by PCA as well as the evaluation of the statistical significance of the coefficients in the linear regression vectors, revealed that the most important WWP variables for trihalomethane formation were: water temperature, total organic carbon, added chlorine concentrations, UV absorbance and turbidity at different sites of the WWP, as well as other variables like wells supply flow levels and carbon filters age. Overall, MLR and PLSR methods performed the best and gave similar good predictive properties. Best results were obtained for the total sum of trihalomethane concentrations, TTHM, with average modeling and prediction relative errors of 12% and 16%, respectively. Among the individual trihalomethanes, the concentrations of CHBr3 were the worst predicted ones with average modeling and prediction relative errors between 21-25% and 29-31%, respectively, followed by CHCl2Br with 23-26% and 25-27%. Better predictions were obtained for the concentrations of CHBr2Cl with relative modeling and prediction errors varying between 14-17% and 21%, and for the concentrations of CHCl3 with 21-24% and 23-25% errors, respectively.     

Variations in trihalomethane levels in three French water distribution systems and the development of a predictive model

Epidemiological studies have demonstrated that chlorination by-products in drinking water may cause some types of cancer in humans. However, due to differences in methodology between the various studies, it is not possible to establish a dose-response relationship. This shortcoming is due primarily to uncertainties about how exposure is measured—made difficult by the great number of compounds present—the exposure routes involved and the variation in concentrations in water distribution systems. This is especially true for trihalomethanes for which concentrations can double between the water treatment plant and the consumer tap.The aim of this study is to describe the behaviour of trihalomethanes in three French water distribution systems and develop a mathematical model to predict concentrations in the water distribution system using data collected from treated water at the plant (i.e. the entrance of the distribution system).In 2006 and 2007, samples were taken successively from treated water at the plant and at several points in the water distribution system in three French cities. In addition to the concentrations of the four trihalomethanes (chloroform, dichlorobromomethane, chlorodibromomethane, bromoform), many other parameters involved in their formation that affect their concentration were also measured.The average trihalomethane concentration in the three water distribution systems ranged from 21.6 μg/L to 59.9 μg/L. The increase in trihalomethanes between the treated water at the plant and a given point in the water distribution system varied by a factor of 1.1-5.7 over all of the samples. A log-log linear regression model was constructed to predict THM concentrations in the water distribution system. The five variables used were trihalomethane concentration and free residual chlorine for treated water at the plant, two variables that characterize the reactivity of organic matter (specific UV absorbance (SUVA), an indicator developed for the free chlorine consumption in the treatment plant before distribution δ) and water residence time in the distribution system.French regulations impose a minimum trihalomethane level for drinking water and most tests are performed on treated water at the plant. Applied in this context, the model developed here helps better to understand trihalomethane exposure in the French population, particularly useful for epidemiological studies.     

氟化物在我国饮用水水源和饮用水中的分布调查及健康影响

综述了氟化物和人体健康的关系,以及世界各国和地区饮用水中氟化物浓度标准限值的规定,分析了我国不同类型、不同地区、不同流域的水源水和出厂水中的氟化物浓度的分布、超标、超检(检出并超过标准值的50％)和检出情况,并针对这些分析结果提出了关于标准限值的修订及今后进一步研究的方向.     

Continuous flow method for determination of total trihalomethanes in drinking water with membrane-separation

A double-tube separation system with an inner tube of microporous poly(tetrafluoroethylene) (PTFE) and an outer tube of PTFE, is proposed for the continuous determination of TTHMs (total trihalomethanes) in drinking water. The TTHMs in the sample after mixing sodium sulfite solution, are separated with the double-tube system at 50°C and are mixed with alkaline nicotinamide solution, and then heated to 98°C. After cooling in an ice bath, the reaction product is fed to a fluorometer and the fluorescence intensity excited at 372 nm is measured at 467 nm. There was no interference from unknown species existing in drinking water and river water by using the membrane separation system. A response was obtained within 8 min. The detection limit (S/N = 3) was 0.8 μg/1. The present method was applied to the determination of the TTHMs in drinking water.     

Carbohydrates as trihalomethanes precursors. Influence of pH and the presence of Cl(-) and Br(-) on trihalomethane formation potential

Upon chlorination carbohydrates can give trihalomethanes (THMs). In the present work, we have studied the influence of pH, chloride or bromide concentration on the formation of THMs from carbohydrates. We have observed that THMs are not formed at acidic pH, while basic pH values only increase slightly the THM content, although the consumption of chlorine increases up to 100% with respect to pH 8. The presence of chloride in ppm increases the THM formation from carbohydrates without influence of the chlorine consumption. In the same manner, the presence of bromide ions in ppb also increases remarkably the THMs formed upon chlorination of saccharides. Even more, we have observed that at bromide concentrations below 100ppb, complete incorporation of bromide in THMs occurs. Overall, the results obtained show that saccharides widely present in natural waters can give rise to significant THM concentrations in the disinfection process by chlorine.     

Tap water quality and performance of point-of-use treatment devices in Cairo, Egypt

Tap water quality was examined in six sampling events over a 2-year period in a residential community of Greater Cairo, Egypt. The sampling sites chosen had a granular activated carbon (GAC), reverse osmosis (RO) or distillation point-of-use (POU) treatment device so that the performance of these units for standard water quality parameters could be evaluated. Tap water satisfied Egyptian and international drinking water standards and guidelines for the majority of samples analysed. Exceptions were the violation of international limits for lead in 10 samples, and total trihalomethane (TTHM) levels that occasionally exceeded drinking water limits. Only the RO and distillation units achieved removal of total dissolved solids (TDS), alkalinity and hardness. However, GAC units are considerably less costly in the local market. All three POU units exhibited potential reduction of chemical contaminants such as trihalomethanes (THMs), improved taste via chlorine removal and improvement in clarity. Realization of these benefits, however, is conditioned upon proper operation and maintenance of the device.     

Ozonation of water containing chlorine or chloramines. Reaction products and kinetics

Ozone reacts with free aqueous chlorine when present as hypochlorite ion (OCl⁻) with a second order rate constant of 120 ± 15 M⁻¹ s⁻¹ at 20°C. About 77% of the chlorine reacts to produce Cl⁻ and 23% is oxidized to ClO⁻₃. No ClO⁻₄ is formed. Conversion of chlorine to monochloramine reduces the ozone reaction rate to 26 ± 4 M⁻¹ s⁻¹, independent of pH, NH₂Cl is transformed quantitatively to NO⁻₃ and Cl⁻ by O₃. Rate data for other chloramines are also presented. The direct reaction of ozone with chlorine accounts for a significant amount of the chlorine and ozone demand found when the two oxidants are used in combination under water works conditions.     

饮用水消毒方式及影响因素探讨

对生活饮用水中常用的几种消毒方法进行了介绍,讨论了液氯、二氧化氯、氯胺和紫外线消毒工艺的原理、优点、缺点及影响因素,以指导相关人员合理选择消毒工艺,保障饮水安全。     

A pilot plant evaluation of the Magnetic Ion EXchange® process for the removal of dissolved organic carbon at Draycote water treatment works

Natural organic matter (NOM) in water sources is undesirable for customers because it reacts with chlorine to form trihalomethanes (THMs), which can be harmful to health, and other organochlorine compounds that can cause taste complaints. A new Magnetic Ion EXchange process (MIEX^® DOC) has been reported as being successful in removing NOM from raw water. The aim of this research was (a) to evaluate the performance of the MIEX^® process in removing NOM from hard, lowland water on a pilot plant scale and (b) to compare the performance of the MIEX^® process with low pH coagulation DAF, in particular, with respect to reducing THM levels. A 45 and 40% reduction in the amount of NOM and in the levels of THMs, respectively, in chlorine‐dosed water was achieved when the MIEX^® process was used with dissolved air flotation (DAF).     

我国饮用水水质标准发展及与国际标准的对比

本文结合国际水质标准,与我国现行的GB5749-2006生活饮用水卫生标准进行了比较分析,介绍了我国饮用水标准的发展过程,重点介绍了强制性国家GB5749-2006生活饮用水卫生标准,并提出了指导性建议。     

Microscale fluctuation assay coupled with Sep-PakR concentration as a rapid and sensitive method for screening mutagens in drinking water

A sensitive short-term mutagenicity test, the microscale fluctuation test has been coupled with a concentration method based on adsorption on Sep-Pak^R C₁₈ cartridges as a method for screening drinking water mutagens. Comparison with XAD-2 concentration method showed that Sep-Pak adsorbed 5 times higher quantity of organics but was slightly less efficient for adsorbing TOX.Microscale fluctuation test was found to be more sensitive than Ames test by testing known direct-acting mutagens and concentrates of drinking water. Samples derived from conventional treatment including chlorination from eight surface water supplies in Norway were concentrated at pH 2 by adsorption on the disposable columns. The adsorbates were tested at different doses by the microscale fluctuation assay. The mutagenic properties of drinking water samples were also related to total organic carbon (TOC), total organic halogen (TOX) and trihalomethanes (THM) concentrations. Dose-related mutagenic responses were found for all the samples with S. typhimurium TA 100 and TA98 strains without metabolic activation. Good relationship was found between mutagenicity data and TOX and THM results. The method showed to be simple, rapid and suitable for routine screening of mutagens in drinking water.     

Empirical model for disappearance of free oxidants in natural water with wide salinity and ammonia ranges

An empirical model for the disappearance rates of chlorine-induced free oxidants was developed. Both in seawater and river water, the disappearance of free oxidants occurred in two stages (stage I and II). The disappearance of free oxidants in stage II was considered to be the consumption by organic substances in natural water. The disappearance rate could be empirically explained by a second-order reaction of oxidants. The observed rate constant was decreased with the increase of the oxidant concentration after subtracting the decrease in stage I from the chlorine dose in natural water. Especially in seawater, the maximum persistence of oxidants could be estimated by the self-decomposition rate of hypobromite which was the disappearance rate in artificial seawater, and the rate constant was obtained as a function of bromide concentration. The disappearance in stage I, which was very rapid, was considered to be the reactions with reactive inorganic and organic substances in natural water. The minimum decrease, which was led to the maximum persistence in stage II, could be approximately expressed as the consumption by ammonia. Using our proposed model, the maximum persistence of free oxidants in natural water with wide salinity and ammonia ranges could be estimated.     

Comparison of two partially activated carbon fabrics for the removal of chlorine and other impurities from water

Experimental studies were undertaken at the University of Birmingham to investigate and compare the use of two partially activated carbon fabrics for the removal of chlorine and other impurities from potable water in domestic point-of-use water filters. Since the implementation of the EEC drinking water quality directive in July 1985, there has been a marketing surge in domestic water filters, generally aimed at improving taste (the taste of chlorine is frequently cited). The fabrics were observed to be very effective at removing chlorine from water; their dechlorinating powers were significantly superior to that of the granular activated carbon used for comparison. The fabrics were observed to be much less effective at removing phenol, methylene blue and colour.     

Implications of sequential use of UV and ozone for drinking water quality

The formation of bromate levels exceeding the drinking water standard of 10 microg L-1 may impose the reduction of ozone doses used in the treatment of drinking water. This paper illustrates the procedure of evaluating the use of reduced ozone doses while implementing an additional UV disinfection step for an actual drinking water treatment plant. Ozonation was performed at low ozone doses in bench-scale experiments with a pretreated river water from the Paris area (France). At the low ozone dose of 0.5 mg L-1, bromate formation could be kept below 0.4 microg L-1, while inactivation of vegetative bacteria and UV-resistant viruses was calculated to exceed 5 log units, and a substantial decoloration (31% of the absorption at lambda=254 nm) was achieved. Based on the measured transient ozone and OH radical concentrations, the oxidation of micropollutants was calculated. Fast reacting micropollutants containing phenol, amine or double bond moieties, such as sulfamethoxazole, diclofenac and 17-alpha-ethinylestradiol, were completely oxidized. Slow-reacting synthetic micropollutants, e.g., atrazine, iopromide and methyl tertiary butyl ether (MTBE), were oxidized by only 20%, 20% and 10%, respectively, and the taste and odor compounds 2-methylisoborneol (MIB) and geosmin by 40% and 50%, respectively. The addition of an UV treatment step to the existing treatment train, which should guarantee disinfection of ozone-resistant pathogenic microorganisms, including Cryptosporidium parvum oocysts, has negligible effects on water matrix components but may induce significant transformation of micropollutants. Overall, the combination of ozonation at reduced doses and UV treatment leads to an improved water quality with regard to disinfection, oxidation of micropollutants and minimization of bromate.