Fate of organics during soil-aquifer treatment: sustainability of removals in the field

A 5-year program of study was conducted at the Sweetwater Recharge Facilities (SRF) to assess the performance of surface spreading operations for organics attenuation during field-scale soil-aquifer treatment (SAT) of municipal wastewater. Studies were conducted utilizing both mature (approximately 10 yr old) and new infiltration basins. Removals of dissolved organic carbon (DOC) were robust, averaging >90 percent during percolation through the local 37-m vadose zone. The hydrophilic (most polar) fraction of DOC was preferentially removed during SAT; removals were attributed primarily to biodegradation. Reductions in trihalomethane formation potential (THMFP) averaged 91 percent across the vadose zone profile. The reactivity (specific THMFP) of post-SAT organic residuals with chlorine decreased slightly from pre-SAT levels (60 vs. 72 microg THM per mg DOC, respectively). Variations in the duration of wetting/drying periods did not significantly impact organic removal efficiencies.     

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.     

The effect of advanced treatment on chlorine decay in metallic pipes

Experiments were run to measure what effect advanced treatment might have on the kinetics of chlorine and chloramine decay in metallic pipes that comprise many drinking water distribution systems. A recirculating loop of 6-in diameter unlined ductile iron pipe was used to simulate turbulent flow conditions in a pipe with significant corrosion and tubercle buildup. Conventionally treated test water was subjected to either ozonation, carbon adsorption (GAC), reverse osmosis (RO) or no further treatment before being chlorinated and introduced into the pipeline simulator. Results showed that overall chlorine decay in the simulator was consistently dominated by wall reactions whose first-order rate constants were an order of magnitude higher than those for the bulk water. With free chlorine, the wall rate constants for ozonated and GAC-treated water were about twice those of conventional or RO-treated water. This behavior is believed due to the effect that changes in the organic content of water have on its ability to complex iron and the effect that changes in water conductivity have on pipe wall corrosion. Tests run with chloraminated water showed no statistically significant effect of treatment type and had wall rate constants that were only 40 to 70% as high as those using free chlorine.     

Bacterial dynamics in the drinking water distribution system of Brussels

Water samples and pipe coupons were collected from the Brussel's drinking water distribution system (DS). A treated surface water and various groundwaters feed this DS. Parameters related to bacterial regrowth have been measured on these samples: temperature, concentrations of free residual chlorine, concentration of biodegradable dissolved organic carbon (BDOC), abundance of suspended bacteria, densities of fixed bacteria and levels of bacterial activity. Results showed that groundwaters were less susceptible to favor bacterial regrowth in the DS pipes. Treated surface water and mixed waters had the highest potential of bacterial regrowth in the DS dead ends. Results also showed that the potential regrowth induced by the distribution of a treated surface water could be reduced if: (1) the BDOC levels were below 0.25 mg C/l at the outlet of the surface water treatment plant; (2) a significant free chlorine residual was present within the whole DS. Second-stage biological filtration using granular activated carbon is now under construction at the surface water treatment plant feeding a part of this DS. This treatment implementation should reduce BDOC levels and chlorine demand of the treated surface water and will further reduce the slight regrowth phenomena observed in this DS.     

双水源对置供水管网中三卤甲烷变化规律浅析

为有效控制供水管网中的三卤甲烷浓度,考察了以太湖和阳澄湖为双水源的管网水中三卤甲烷的变化趋势。采集S市分别经过A水厂(以太湖为水源)和B水厂(以阳澄湖为水源)处理后的供水管网水样,探讨三卤甲烷和余氯浓度随供水距离的变化规律,并进行了三卤甲烷-余氯和三卤甲烷-供水距离的线性回归分析。结果表明,在A、B水厂单独供水管网中,三卤甲烷随供水距离的增加而升高,余氯浓度随供水距离的增加而降低;在A、B水厂同时供水的对置供水管网中,三卤甲烷浓度由A水厂到B水厂呈现先升高后降低的变化规律,而余氯浓度则呈现先降低后增加的变化规律,对置供水管网中10 km处为水力交接点,此处余氯浓度最低,三卤甲烷浓度最高。经线性回归分析发现,三卤甲烷浓度与余氯浓度和供水距离之间存在显著的相关性,并且温度对模型的影响较大。     

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.     

Minimizing biofilm in the presence of iron oxides and humic substances

Based upon circumstantial evidence linking elevated coliform bacteria counts in drinking water distribution systems with unlined cast iron pipe, it was hypothesized that adsorption of humic substances by iron oxide containing corrosion products (CPs) can stimulate and/or support biofilm development. Using porous media consisting of iron-oxide-coated glass beads (IOCBs) or actual iron CPs, experiments were performed to evaluate the effectiveness of different corrosion control and disinfection treatments in reducing biofilm when humic substances were the carbon source. Free chlorine was the most effective treatment in minimizing biofilm. Addition of phosphate alone did not significantly reduce biofilm using the CPs, but there was weak evidence it did using the IOCBs. The combination of free chlorine and phosphate was more effective at minimizing biofilm than free chlorine alone when CPs were the media. The presence of humic substances was a major factor when considering biofilm minimization based on results of experiments using both types of iron oxide media. The combination of humic substances and CPs led to an increase in biofilm biomass when free chlorine was not present, similar to conditions that could occur at distribution system dead-ends. Treatment to raise the pH to 9 did not reduce biofilm in experiments using both media, and actually increased biofilm in the experiment using CPs under the conditions tested.     

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.     

O3/BAC对氯化消毒副产物的控制作用

采用臭氧化—生物活性炭(O3／BAC)深度处理工艺去除水中消毒副产物前质的试验结果表明，该工艺能够有效去除水中消毒副产物前质，可控制氯化消毒副产物的生成，其中主臭氧化对三卤甲烷前质和卤乙酸前质均具有很好的去除效果，生物活性炭对卤乙酸前质表现出较好的去除效果，但对三卤甲烷前质的去除效果有限；藻类、有机物等在滤层的累积使得砂滤池在同一工作周期中的不同阶段对水中三卤甲烷前质的去除效果有所不同，因而需要合理设置砂滤池的反冲洗周期。臭氧化—生物活性炭工艺充分发挥了臭氧化和生物活性炭两种技术的优点，并相互促进和补充，能够充分保障饮用水的安全性。     

Combined toxicity of free chlorine, chloramine and temperature to stage I larvae of the American lobster Homarus americanus

The differential effects of free chlorine and chloramine on stage I larvae of the American lobster Homarus americanus have been investigated in continuous flow bioassay units. Applied chloramine was more toxic than corresponding concentrations of applied free chlorine to lobster larvae with estimated lc₅₀ values at 25° of 16.30 mg/l applied free chlorine and 2.02 mg/l applied chloramine. The synergistic effect of temperature on the toxicity of both free chlorine and chloramine has also been demonstrated. Exposure to applied free chlorine at 20° resulted in no significant mortality of test organisms, whereas exposure at 30° resulted in an estimated lc₅₀ value of 2.50 mg/l. Applied chloramine was considerably more toxic with an estimated lc₅₀ value at 20° of 4.08 mg/l and at 30° of 0.56 mg/l.The action of each toxicant appeared to be an alteration of standard metabolic activity as revealed by changes in respiration rates during and after exposure to applied free chlorine and chloramine. Initial respiratory stress was detected during exposure to 0.05 mg/l applied chloramine and 5.00 mg/l applied free chlorine. Reductions in respiration rates 48 h after exposure were observed with exposure to all concentrations tested, similar results being obtained following exposure to 0.05 mg/l applied chloramine and 0.10 mg/l applied free chlorine. These results are indicative of the need for information in addition to that obtained in standard bioassays for an adequate assessment of chlorine toxicity.The apparent chlorine demand of the seawater used in this study was determined after removal of particulate and dissolved organics and ammonia. Approximately 18% of the applied level of free chlorine and chloramine was recovered as residuals, measured by amperometric titration; however, no reason for this low recovery has been determined. Until it has been established that undetected chlorine and chloramine in seawater do not result in the production of toxic compounds, both applied and residual levels should be reported in toxicity studies.     

DBP formation kinetics in a simulated distribution system

Little is known about how the growth of halogenated disinfection by-products (DBPs) in drinking water is affected by time spent in a distribution system. Experiments were performed to compare the rate of trihalomethane and haloacetic acid production in a simulated pipe environment to that observed for the same water held in glass bottles. Results showed that although the rate of chlorine consumption in the pipe was much greater than in the bottle, there was no decrease in the amount of haloacetic acids produced and that trihalomethane levels actually increased by an average of 15%. Separate tests confirmed that this increase was due to a reservoir of organic precursor material associated with deposits on the pipe wall. This work suggests that the rate of DBP production in a distribution system will not necessarily be reduced by increased chlorine consumption due to non-DBP producing reactions with deposits on the pipe wall.     

Rapid free chlorine decay in the presence of Cu(OH)2: chemistry and practical implications

A rapid reaction between free chlorine and the cupric hydroxide [Cu(OH)₂] solids commonly found on pipe walls in premise plumbing can convert free chlorine to chloride and rapidly age Cu(OH)₂ to tenorite (CuO). This reaction has important practical implications for maintaining free chlorine residuals in premise plumbing, commissioning of new copper pipe systems, and maintaining low levels of copper in potable water. The reaction stoichiometry between chlorine and Cu(OH)₂ is consistent with formation of CuO through a metastable Cu(III) intermediate, although definitive mechanistic understanding requires future research. Natural levels of silica in water (0-30 mg/L), orthophosphate, and higher pH interfere with the rate of this reaction.     

Equilibrium adsorption of fulvic acids on activated carbon and its dependance on preozonization of solutions

The impact of ozonization on the equilibrium adsorption of fulvic acids (FA) on activated carbon has been studied. The possibility of multicomponent approach to describe the adsorption equilibrium by using two hypothetical components: weakly and strongly adsorbable fractions of FA was examined. The ozone treatment was shown to equalize the ability of FA fractions to adsorption as compared with the unozonized solution. It was established that the variation of the free energy of adsorption of FA destruction products correlated with changes of the share of organic carbon, subjected to biological impact, in the total organic carbon. The efficiency prediction of the ozone treatment of solutions of natural organic compounds prior to their filtration through the biologically activated carbon can be expediently performed by determining the variation of the free energy of adsorption.     

Effects of activated carbon on the reactions of combined chlorine with phenols

In the presence of ammonia, prechlorination in drinking water treatment results in contact of combined chlorine (monochloramine) with activated carbon, which is used to remove organic compounds from water. Monochloramine reacts very slowly with phenolic compounds in aqueous solution, giving low yields of chlorinated phenols. When monochloramine reacts with phenols adsorbed on granular activated carbon (GAC), however, several oxidized products, principally hydroxylated biphenyls, are formed. Some of the hydroxylated biphenyls are chlorinated (hydroxylated PCBs). Their formation is particularly important because of their potential toxicity. Such compounds are major reaction products from chlorophenol, but they are also formed in small amounts from nonchlorinated phenols. Most of the monochloramine-GAC-phenolic compound reaction products are also produced in similar reactions with free chlorine, indicating that similar reaction mechanisms (free radical mechanisms) take place on carbon's surface. No organic compounds are produced from the reaction of monochloramine with GAC alone.     

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.     

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.     

Disinfection by-product formation after biologically assisted GAC treatment of water supplies with different bromide and DOC content

Chlorination of drinking water in the presence of bromide and dissolved organic carbon (DOC) leads to the formation of brominated and chlorinated disinfection by-products (DBP). The concentration of bromide ions in the raw water is a significant factor in the speciation of DBP formed, and causes shifts in trihalomethane (THM) formation from chlorinated to brominated species. Drinking water treatment techniques that remove organic contaminants without affecting bromide ion concentrations cause increases in the brominated THM. For the present study, three water supplies containing different DOC and ambient bromide concentrations were filtered through biologically assisted granular activated carbon (BGAC). Similar to adsorption and coagulation treatment, this treatment does not remove bromide from drinking water; also, THMFP (trihalomethane formation potential) analysis indicated that the chlorinated effluent contained higher concentrations of brominated THM in comparison to the influent. Although BGAC may increase the brominated THM, which may be more toxic than the chlorinated THM, the overall reduction of THMFP by DOC removal far exceeds this negative change, thereby producing a much less toxic finished drinking water. This work is part of a study to make high DOC surface waters on the Canadian prairie safe and palatable for small volume users (individuals or small communities).     

Aqueous chlorination of carbamazepine: Kinetic study and transformation product identification

Carbamazepine reactivity and fate during chlorination was investigated in this study. From a kinetic standpoint, a third-order reaction (first-order relative to the CBZ concentration and second-order relative to the free chlorine concentration) was observed at neutral and slightly acidic pH, whereas a second-order reaction (first order relative to the CBZ concentration and first order relative to the free chlorine concentration) was noted under alkaline conditions. In order to gain insight into the observed pH-dependence of the reaction order, elementary reactions (i.e. reactions of Cl₂, Cl₂O, HOCl with CBZ and of ClO⁻ with CBZ or of HOCl with the ionized form of CBZ) were highlighted and second order rate constants of each of them were calculated. Close correlations between the experimental and modeled values were obtained under these conditions. Cl₂ and Cl₂O were the main chlorination agents at neutral and acidic pH. These results indicate that, for a 1 mg/L free chlorine concentration and 1–10 mg/L chloride concentration at pH 7, halflives about 52–69 days can be expected. A low reactivity of chlorine with CBZ could thus occur under the chlorination steps used during water treatment. From a mechanistic viewpoint, several transformation products were observed during carbamazepine chlorination. As previously described for the chlorination of polynuclear aromatic or unsaturated compounds, we proposed monohydroxylated, epoxide, diols or chlorinated alcohol derivatives of CBZ for the chemical structures of these degradation products. Most of these compounds seem to accumulate in solution in the presence of excess chlorine.     

Chlorination of model drinking water biofilm: implications for growth and organic carbon removal

The influence of chlorine on biofilm in low organic carbon environments typical of drinking water or industrial process water was examined by comparing biomass and kinetic parameters for biofilm growth in a chlorinated reactor to those in a non-chlorinated control. Mixed-population heterotrophic biofilms were developed in rotating annular reactors under low concentration, carbon-limited conditions (< 2 mg/L as carbon) using three substrate groups (amino acids, carbohydrates and humic substances). Reactors were operated in parallel under identical conditions with the exception that chlorine was added to one reactor at a dose sufficient to maintain a free chlorine residual of 0.09-0.15 mg/L in the effluent. The presence of free chlorine resulted in development of less biofilm biomass compared to the control for all substrates investigated. However, specific growth and organic carbon removal rates were on the average five times greater for chlorinated biofilm compared to the control. Observed yield values were less for chlorinated biofilm. Although chlorinated biofilm's specific organic carbon removal rate was high, the low observed yield indicated organic carbon was being utilized for purposes other than creating new cell biomass. The impacts of free chlorine on mixed-population biofilms in low-nutrient environments were different depending upon the available substrate. Biofilms grown using amino acids exhibited the least difference between control and chlorinated kinetic parameters; biofilm grown using carbohydrates had the greatest differences. These findings are particularly relevant to the fundamental kinetic parameters used in models of biofilm growth in piping systems that distribute chlorinated, low-carbon-concentration water.     

Fractionation of dissolved organic matter from surface waters using macroporous resins

To obtain fractions enriched with biodegradable dissolved organic carbon (BDOC) or with organic compounds responsible for the chlorine demand (CID) and for trihalomethane formation potential (THMFP), Seine river water samples were percolated on various macroporous resins (anionic, cationic and non-ionic) and compared with granulated activated carbon (GAC). In addition, measurement of UV absorbance at 254 nm and the fluorescence index (λ_excitation 320 nm) had allowed to follow up the retention of dissolved organic matter by the different adsorbants. In contrast to cationic and non-ionic resins, anionic resins confirm their excellent retention capacity of organic compounds responsible for UV 254 absorbance and fluorescence index. The relative values of BDOC/DOC ratio (mg-C/mg-C) are slightly increased in the effluents of anionic resins, indicating that they retain a little preferentially the refractory fraction instead of the biodegradable fraction. There is no significant difference between the ratio of CID/DOC (mg-Cl₂/mg-C) in influent and effluent of anionic resins. Cationic resin has a low capacity for retention of DOC, but they seem to retain significantly the organic compounds responsible for CID. The capability of anionic resins to retain THMFP is similar to that of GAC.