Formation equation of halogenated organic compounds when water is chlorinated

Various halogenated organic compounds are formed by chlorination of water. In this study, formation of organic compounds halogenated from a reagent humic acid and extract of a leaf mold were examined under various conditions. The following overall formation equation was obtained from empirical data under the practical wide range when free chlorine remained.

[TOX]=k_TOX[TOC][Cl₂]_ot^β.

Here, [TOX] is the concentration of total organic halogen after t h in units of mg chlorine per liter; [TOC] and [Cl₂]_o are concentrations of total organic carbon and dosed chlorine in units of mg per liter; k_TOX is the rate constant and and β are parameters. From the values of k_TOX, and β, the character of organic substances i.e. precursor of halogenated organic compounds, in water can be evaluated. The values k_TOX, and β for humic acid are 0.053, 0.28 and 0.13, and the values for extract of the leaf mold are 0.032, 0.36 and 0.15, respectively. The activation energies are 10 kJ mol⁻¹ and 11 kJ mol⁻¹ for the reactions of humic acid and leaf mold extract, respectively.     

Correlation of humic substance trihalomethane formation potential and adsorption behavior to molecular weight distribution in raw and chemically treated waters

The molecular weight distributions (MWDs) of several commercially prepared humic and fulvic acids and organic matter present in natural waters were analyzed by gel chromatography. The responses of these substances to treatment by alum coagulation, lime softening, and activated carbon adsorption were also analyzed, as were their trihalomethane formation potentials before and after each treatment. The treatability characteristics and trihalomethane formation properties of the different organic substances were then related to their respective MWDs. Differences in the MWDs were found to effect differences in the behavior of lumped parameter measures of organic matter (such as TOC) with respect to the several treatment operations. The treatments in turn were observed to alter the MWDs of the organic substances as well as their phenomenological behavior in subsequent process operations.     

Characterization of aquatic humic substances

Aquatic natural organic matter (NOM) is composed of a large variety of compounds. In this study, NOM from Uzquiza Reservoir in Burgos (Spain) was fractionated using a resin adsorption procedure, and three humic substances – natural fulvic and humic acids (NFA and NHA, respectively) extracted from the mentioned reservoir and a commercially supplied humic acid (CHA) – were characterized by molecular weight (MW) distribution, elemental composition, organic acidity and ultraviolet and infrared spectroscopy. The results indicate that Uzquiza Reservoir NOM is mainly composed of fulvic acids (45%) and low MW hydrophilic acids (27%). MWs obtained are in the following order: CHA (4500 Da)>NHA (2500 Da)>NFA (1000 Da). Both humic acids (CHA and NHA) have the highest specific UV absorbance values (SUVA, an aromaticity indicator) whereas NFA shows a higher total and carboxylic acidity, which is in accordance with its higher solubility in water. Infrared spectra confirm these results.     

Multivariate statistical relationships between routine water plant data and trihalomethane levels. Implications for studies of human health

Routine water treatment plant data were used to construct a mathematical/statistical model of trihalomethane formation during lime-soda ash softening. Chemical characteristics of the raw water, such as temperature and color, and several treatment parameters, including chlorine dose, were significant predictors for chloroform and total trihalomethanes. The pattern of prediction was notably different for the brominated species. The results of this preliminary study support the view that routine water plant data can be used to estimate retrospectively, and with accuracy, trihalomethane levels for past time periods in which only the routine plant data are available. Possible limitations of the approach and the prospects for improving epidemiologic health effects studies of trihalomethanes in drinking water are discussed.     

Testing and validation of a multiple nonlinear regression model for predicting trihalomethane formation potential

This paper summarizes a testing and validation analysis of a previously developed model for predicting trihalomethane formation potential (THMFP) in chlorinated waters containing THM precursors. The original model, in the form of a nonlinear multiple regression equation, tended to overpredict THM formation potential at lower chlorine concentrations and underpredict at higher chlorine concentrations. The model proved to be more accurate in simulating THM formation potential in waters with moderate levels of organic carbon/THM precursors. While the model did not provide a high degree of predictive accuracy, the general format of the nonlinear model represents a rational framework for developing source specific models applicable to a given water source.     

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。     

Sorption of trichloroethylene by organo-clays in the presence of humic substances

We examined trichloroethylene sorption by organo-clays [hexadecyltrimethylammonium (HDTMA) and didodecyldimethylammonium (DDDMA) exchanged smectites (SWy-1 and SAz-1)] in aqueous solutions both in the presence and absence of humic substances (Aldrich humic acid and peat fulvic acid). The results indicated the uptake of humic substances by organo-clays and the effects of humic substances on trichloroethylene sorption by organo-clays were dependent on the type of organo-clay and humic substance. Selection of an appropriate combination of clay and organic cation can optimize the removal of trichloroethylene as well as humic substances from aqueous solutions by organo-clays. Organo-clays may be an alternative to activated carbon sorbents in some specific water treatment processes.     

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.     

Dissolved and particulate humic substances in water channels in the historic centre of Venice

The presence of humic substances, both in solution and as particulate, was studied in channels of the historic centre of Venice. The amount of particulate, its composition (organic and inorganic fraction) and the ratio between organic matter and humic substances were also considered. The sampling campaign was planned in 2001-02 from November to May. Three samplings in 20 stations representative of a large typical urban area were performed. The results obtained show that the composition of the particulate is variable, whereas the concentration of both dissolved and particulate humic substances is relatively homogeneous. Fulvic acids present in particulate are less homogeneous than dissolved forms; furthermore, the humification rate of organic matter is variable. Humic acids are absent, both in particulate and in dissolved forms.     

Contact flocculation-filtration of humic substances

Contact flocculation-filtration of humic dispersions with alum in medium grain (0.62 mm) sand gave short runs to breakthrough, while in coarse (1.2 mm) media clarification was inefficient. Alum with cationic polymer gave in coarse media acceptable runs, but shorter then for mineral dispersions. Analysis of results by parameters of existing filtration models showed that using the Ives-Iwasaki model and plotting filtration coefficient λ vs specific deposit σ gave different λ_max for different polymer dose, plot of λ_max vs dose goes through maximum at optimum dose.Plotting the cube root of headloss vs square root of specific deposit gave a straight line corresponding to Shektman formula.Analysis by Adin-Rebhun model showed that for contact flocculation-filtration humic dispersions attachment coefficient k₁ was similar to, detachment k₂ was many fold higher then and theoretical maximum mass capacity much lower then in case of mineral dispersions.Calculations showed that the solid content and the density of alumo-organic deposits in bed are much lower than of alumo-mineral deposits. Polymers and minerals increase the solid content, the density of deposits and the mass capacity of filter beds.     

Binding of organic solutes to dissolved humic substances and its effects on adsorption and transport in the aquatic environment

Humic substances constitute a major fraction of dissolved organic matter in natural water and effluents. Their effect on the adsorption of organic contaminants to aquifer material was elucidated, and a model was proposed for the adsorption of organic solutes to aquifer solids in the presence of dissolved humic substances. The model is based on the assumption that organic solute binds to dissolved humic substances in a reversible manner to form a solute-humate complex. Following binding, both free and bound fractions of the organic solute are independently adsorbed onto the solid phase. In order to evaluate the validity of the model, the following parameters were determined: (1) the adsorption coefficient of the organic solute to clay; (2) the binding constant of the solute-humate complex; and (3) the adsorption of humic acid (HA) to clay, assuming that the solute-humate complex is adsorbed similarly to humic acid itself. Using these parameters in the model enabled the effect of dissolved humic substances on adsorption to be evaluated. Experimental results obtained for the adsorption of fluoranthene (a model compound of the PAH group) to clay in the presence of dissolved HA were compared with calculated values derived from the model described above. The sensitivity of the model to various parameters was evaluated and a prediction was made with respect to the effect of dissolved humic substances on the adsorption of a variety of organic solutes. It appears that dissolved humic substances solubilize organic solutes which have higher adsorption coefficients to clay than humic substances, but increase the adsorption of solutes having lower adsorption coefficients relative to humic substances.     

Reduction of dissolved organic matter and trihalomethane formation potential during laboratory-scale soil-aquifer treatment

Dissolved organic matter (DOM) in recovered groundwater from soil-aquifer treatment (SAT) has the potential to generate harmful disinfection by-products. This study investigated the reduction of mass and trihalomethane formation potential (THMFP) of DOM fractions from secondary effluent during laboratory-scale SAT. Using XAD-8 and XAD-4 resins, DOM was fractionated into three fractions: hydrophobic acid (HPO-A), transphilic acid (TPI-A) and hydrophilic fraction (HPI). HPO-A was removed by 61.1%, TPI-A by 54.9% and HPI by 75.0% as dissolved organic carbon (DOC) during the laboratory-scale SAT, respectively. The reduction of THMFP from HPO-A, TPI-A and HPI was 27.24, 26.24 and 36.08%, respectively. Specific THMFP for each DOM fraction increased across the soil columns. HPO-A was found to be the major precursor of THMs. THMFP was strongly correlated to ultraviolet light at 254 nm (UV-254) for HPO-A and HPI, while the relationship between THMFP and UV-254 for TPI-A was significantly poor.     

Changes of trihalomethane formation potentials in the tone river

The changes of trihalomethane formation potentials (THMFPs) in the Tone River were examined. There were clear differences not in THMFPs but in THMFP loading (THMFP × flow rate) between the winter and the summer. The ratio of THMFP loading caused by artificial pollution was estimated. This ratio increased sharply with increases in watershed area and reached about 80% for a watershed area of about 2000 km² (with a population density of about 65 persons km²). Further, two formulas were obtained to estimate the THMFP and THMFP loading of the Tone River in the future.     

氯化消毒副产物的控制研究进展

探讨了CDBPs的形成机理,总结了目前国内外控制CDBPs的方法,并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,以确保饮用水的安全性。     

The stabilization of dispersed mineral particles by adsorption of humic substances

The coagulation of suspended silica and kaolinite particles by electrolytes was studied by a photometric technique in the presence of three different humic extracts derived from surface and groundwaters. The organic substances stabilize the dispersions with increasing dosages due to the adsorption of fractions of the dissolved organic carbon. Adsorption isotherms reveal the favorable uptake of high-molecular-weight substances and the role of pH and electrolyte content. Stabilization is primarily caused by adsorbed neutral molecules. The adsorption model developed, describes the isotherm data based on three different fractions and can be used to predict the stabilization effects, if precipitation of calcium humate can be excluded. Colloid stability is thereby determined by the free surface of particles and can be understood in relation to the action of synthetic polymeric stabilizers.     

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.     

Effect of bromide ions on genotoxicity of halogenated by-products from chlorination of humic acid in water

Genotoxicity of halogenated by-products obtained by chlorination of humic acid in water was evaluated in the presence of bromide ions (Br⁻). After the halogenated humic acid solution was made to flow through CSP800 cartridge, absorbed substances were eluted with dimethyl sulfoxide or acetone, and subjected to mutagenicity assays and to analysis of trihalomethanes (THMs). Mutagenic activity was measured by Ames tests using S. typhimurium TA100 strain without metabolic activation, and by the frequencies of micronuclei formation using cultured Chinese hamster lung cells (CHL/IU) in vitro. A powerful effect of bromide ions in chlorinated humic acid solutions was observed on the reverse mutation and micronuclei formations. The formations of total THMs and more brominated THMs were also enhanced in the presence of bromide ions. The ratio of [Br⁻/Cl⁻] regulated the composition and concentrations of THMs intensely, and the rate of substitution of Br⁻ was greater than that of chloride ions (Cl⁻). The increments of the mutagenicity and total THMs formed in chlorinated solutions were observed in parallel with the concentration of Br⁻ or Cl⁻. From the observations, it was concluded that the increasing mutagenicity might be caused by the increasing chlorinated and/or brominated by-products.     

Copper catalysis in chloroform formation during water chlorination

The seminal work of Rook initiated a considerable body of research regarding the formation of trihalomethanes (THMs) and other by-products of chlorine-based disinfection. Since that time, a broad spectrum of compounds has been identified as precursors to THM formation. More recently, it has been demonstrated that the presence of copper in solution enhances THM formation. Copper is known to catalyze a number of reactions that are similar to the conventional haloform reaction. A study was therefore initiated to investigate the specific role played by copper in the formation of chloroform during chlorination of water supplies. Aqueous solutions containing a number of known THM precursors were chlorinated in the presence and absence of copper, and subjected to time-course monitoring of chloroform concentration. The results of experiments with humic acid demonstrated an apparent catalytic effect on the part of copper in chloroform formation. To examine the role of copper in greater detail, a series of experiments involving aqueous solutions of pure compounds of humic substance structural units was conducted. Of the pure compounds investigated as THM precursors, only citric acid demonstrated enhanced chloroform formation in the presence of copper. A detailed matrix of experiments conducted with citric acid as a precursor demonstrated that copper, at environmentally relevant concentrations, can have a profound effect on chloroform formation. Based on previously published information regarding the mechanism of chloroform formation from citric acid and the results of these experiments, it is hypothesized that copper promotes chloroform formation from chlorination of citric acid through catalysis of oxidative decarboxylation, and the subsequent chlorination of beta-ketoglutaric acid.     

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.     

Electrochemical determination and characterization of surface active substances in freshwaters

Surface active material has been analyzed in samples of different freshwater systems: river water, groundwater and tap water, by electrochemical methods based on the measurement of the adsorption effects at the mercury electrode. Two electrochemical methods were used: the measurement of the suppression of the polarographic maxima and a.c. polarography. A rough characterization of predominant surface active compounds was performed through a comparison of the shape and the intensity of the electrochemical responses with those obtained with different model surfactants. It was found that humic substances represent predominant surface active substances in freshwater systems. The total surfactant activity corresponds to approx. 0.5–20 mg dm^?3 of humic substances.Anionic detergents were analyzed by the spectrophotometric methylene blue method. The highest values (100–300 μg dm^?3) were found in river water samples which were taken downstream from the city location. The total surfactant activity values of river water samples as measured by the electrochemical methods were only exceptionally influenced by the presence of detergents.