Modeling of trihalomethane cometabolism in nitrifying biofilters

The computer program AQUASIM was used to model biofilter experiments seeded with Lake Austin, Texas mixed-culture nitrifiers. These biofilters degraded four trihalomethanes (THMs) (trichloromethane (TCM) or chloroform, bromodichloromethane (BDCM), dibromochloromethane (DBCM), tribromomethane (TBM) or bromoform) commonly found in treated drinking water. Apparent steady-state data from the biofilter experiments and supporting batch experiments were used to estimate kinetic parameters for TCM, DBCM and ammonia degradation. Subsequently, the model was verified against other experimental biofilter data. To allow for full-scale simulations, BDCM and TBM rate constants were estimated using data from batch kinetic studies. Finally, the model was used to simulate full-scale filter performance under different filter surface loading rates and THM speciation seen in practice. Overall, total THM removals ranged from 16% to 54% in these simulations with influent total THM concentrations of 75-82microg/L, which illustrates the potential of THM cometabolism to have a significant impact on treated water quality.     

Performance and biofilm activity of nitrifying biofilters removing trihalomethanes

Nitrifying biofilters seeded with three different mixed-culture sources removed trichloromethane (TCM) and dibromochloromethane (DBCM) with removals reaching 18% for TCM and 75% for DBCM. In addition, resuspended biofilm removed TCM, bromodichloromethane (BDCM), DBCM, and tribromomethane (TBM) in backwash batch kinetic tests, demonstrating that the biofilters contained organisms capable of biotransforming the four regulated trihalomethanes (THMs) commonly found in treated drinking water. Upon the initial and subsequent increased TCM addition, total ammonia nitrogen (TOTNH₃) removal decreased and then reestablished, indicating an adjustment by the biofilm bacteria. In addition, changes in DBCM removal indicated a change in activity related to DBCM. The backwash batch kinetic tests provided a useful tool to evaluate the biofilm’s bacteria. Based on these experiments, the biofilters contained bacteria with similar THM removal kinetics to those seen in previous batch kinetic experiments. Overall, performance or selection does not seem based specifically on nutrients, source water, or source cultures and most likely results from THM product toxicity, and the use of GAC media appeared to offer benefits over anthracite for biofilter stability and long-term performance, although the reasons for this advantage are not apparent based on research to date.     

Cometabolism of trihalomethanes by mixed culture nitrifiers

Three mixed-culture nitrifier sources degraded low concentrations (25-450 microg/L) of four trihalomethanes (THMs) (trichloromethane (TCM) or chloroform, bromodichloromethane (BDCM), dibromochloromethane (DBCM), tribromomethane (TBM) or bromoform) commonly found in treated drinking water. Individual THM rate constants (k1THM) increased with increasing THM bromine-substitution with TBM>DBCM>BDCM>TCM and were comparable to previous studies with the pure culture nitrifier, Nitrosomonas europaea. A decrease in temperature resulted in a decrease in both ammonia and THM degradation rates with ammonia rates affected to a greater extent than THM degradation rates. The significant effect of temperature indicates that seasonal variations in water temperature should be a consideration for technology implementation. Product toxicity, measured by transformation capacity (T(c)), was similar to that observed with N. europaea. Because both rate constants and product toxicities increase with increasing THM bromine-substitution, a water's THM speciation is an important consideration for process implementation during drinking water treatment. Even though a given water is kinetically favored, the resulting THM product toxicity may not allow stable treatment process performance.     

Determination of dichloroacetic acid and trichloroacetic acid in drinking water by acidic methanol esterification and headspace gas chromatography

A simple and rapid headspace method for gas chromatographic determination of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) in drinking water was developed. Acidic methanol esterification followed by a headspace technique using a capillary column gas chromatograph (GC) equipped with an electron capture detector (ECD) was applied to determine the levels of DCAA and TCAA in drinking water. The major advantages of this method are the use of acidic methanol as the derivatization agent instead of the hazardous diazomethane, and esterification is carried out in water instead of organic solvent. DCAA and TCAA methyl esters produced in the reaction were determined directly by a headspace GC/ECD method. The linear correlation coefficients at concentrations ranging from 0 to 60 microg/L were 0.992 and 0.996 for DCAA and TCAA, respectively. The relative standard deviations (RSD, %) for the determination of DCAA and TCAA in drinking water were 15 and 21.3%, respectively (n=3). The detection limits of this method were 3 and 0.5 microg/L for DCAA and TCAA, respectively, and the recovery was 68-103.2% for DCAA and TCAA.     

Investigating effects of bromide ions on trihalomethanes and developing model for predicting bromodichloromethane in drinking water

Chlorination for drinking water can form brominated trihalomethanes (THMs) in the presence of bromide ions. Recent studies have reported that bromodichloromethane (BDCM) has a stronger association with stillbirths and neural tube defects than other THMs species. In this paper, the results of an experimental investigation into the factors forming THMs in the presence of bromide ions are presented. The experiments were conducted using synthetic water samples with different characteristics (e.g., pH, temperature, dissolve organic content). Different combinations of these characteristics were considered in the experimental program. The results showed that increased bromide ion concentrations led to increases in the formation of total THMs, with higher BDCM and dibromochloromethane (DBCM), and lower chloroform formation. By increasing the pH from 6 to 8.5, increased chloroform and decreased BDCM and DBCM formation were observed. Higher bromide ions to chlorine ratios increased BDCM and DBCM and decreased chloroform formation, while higher temperatures increased BDCM, DBCM and chloroform formation. In most cases, bromoform (CHBr₃) concentrations were found to be below the detection limit. Significant factors influencing BDCM formation were identified using a statistical analysis. A model for BDCM formation was estimated from 44 experiments and statistical adequacy was assessed using appropriate diagnostics, including residual plots and an R² of 0.97. The model was validated using external data from 17 water supply systems in Newfoundland, Canada. The predictive performance of the model was found to be excellent, and the resulting model could be used to predict BDCM formation in drinking water and to perform risk-cost balance analyses for best management practices.     

Decomposition of trihaloacetic acids and formation of the corresponding trihalomethanes in drinking water

The decomposition of trihaloacetic acids [bromodichloroacetic acid (BDCAA), dibromochloroacetic acid (DBCAA), tribromoacetic acid (TBAA)], and the formation of the corresponding trihalomethanes [bromodichloromethane (BDCM), dibromochloromethane (DBCM), tribromomethane (TBM)] were studied. Like TBAA, the two mixed chlorobromo-species, BDCAA and DBCAA, were found to decompose to form BDCM and DBCM, respectively, via a decarboxylation pathway. The decomposition of BDCAA, DBCAA and TBAA in water at neutral pH follows a first-order reaction, with rate constants of 0.0011, 0.0062 and 0.040 day(-1) at 23 degrees C, respectively; and 0.000028, 0.00014 and 0.0016 day(-1) at 4 degrees C, respectively. The activation energies for the decomposition reaction of BDCAA, DBCAA and TBAA in water at neutral pH were found to be 35.0, 34.5 and 29.2 kcal/mol, respectively. The effect of pH in the range of 6-9 and the effect of a drinking water matrix on the decomposition of BDCAA, DBCAA, and TBAA in water were found to be insignificant. Measurement and health implications due to decomposition of trihaloacetic acids and formation of the corresponding trihalomethanes were discussed. By applying the technique of quantitative structure-activity relationships (QSAR), the decomposition rate constants of six iodinated trihaloacetic acids were estimated.     

Correlations between differential absorbance and the formation of individual DBPs

This study examined correlations between the differential absorbance at 272nm (deltaA272) and the formation of disinfection by-products (DBPs) in chlorinated water from the Tolt River, a water source for Seattle, WA. The DBPs investigated included chloroform (CHCl3), dichlorobromomethane (CHCl2Br), mono-, di- and trichloroacetic acids (MCAA, DCAA, and TCAA, respectively), chloral hydrate (CH), dichloroacetonitrile (DCAN) and 1,1,1-trichloropropanone (TCP). Whereas the kinetics of DBP formation are complex and are non-linear, the same DBP data represented as a function of deltaA272 are quite simple. Absorbance decreases when the water is chlorinated, i.e., deltaA272 is always negative. The DBP vs. -deltaA272 correlations can almost always be quantified by linear equations, at least above some threshold value of -deltaA272, with R2 values > 0.95. The only DBP that did not follow this trend was CH, for which an exponential relationship better described the data. TCP and DCAN were unstable at pH 7 and 8, but at pH 6 linear correlations between their concentrations and -deltaA272 were as strong as those for the more stable DBPs. The threshold -deltaA272 value is approximately the same for many of the DBPs studied, supporting the hypothesis that individual DBPs are released following the formation of a common intermediate, or at least a small group of similar intermediates. The DBP vs. -deltaA272 correlations may have practical value since they provide an alternative approach for monitoring the formation of individual DBP species on-line, but the generality of the relationships needs to be further examined.     

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.     

Effects of indoor drinking water handling on trihalomethanes and haloacetic acids

In this study, different tap water handling strategies were investigated to evaluate the effects on two principal chlorinated DBPs, trihalomethanes (THMs) and haloacetic acids (HAAs). Tap water samples collected in the Quebec City (Canada) distribution system on a spatio-temporal basis were subjected to diverse indoor handling scenarios: storing water in the refrigerator, boiling water followed by storage and, finally, filtering water with a point-of-use commercial pitcher also followed by storage. In the first two cases, the use of covered and uncovered pitchers was investigated separately, while in the last case, both the use of new and used filters was compared. In all cases, maximum storage time was 48h. Results demonstrated that in some cases, water handling scenarios have considerable effect, and in other cases, little or no effect. Removal of THM concentrations by simple storage was high (on average 30%) and very high by boiling and filtering with subsequent storage in the refrigerator (on average, 87% and 92%, respectively). In scenarios where water was stored in uncovered pitchers (with or without previous boiling and filtering), the THM decrease was higher for increased storage times. However, storage did not have any effect on HAAs, whereas boiling decreased levels of trichloroacetic acid (TCAA) (on average 42%) and increased levels of dichloroacetic acid (DCAA) (on average 35%), resulting in unchanged average levels of total HAAs. The use of the filtration pitcher decreased HAA levels dramatically (on average 66%). Percentages of change in chlorinated DBPs in the different scenarios varied according to initial concentrations in tap water (baseline water), that is, according to the spatio-temporal variations of these substances in the distribution system. On the basis of these results, the paper discusses implications regarding public health protection and exposure assessment for epidemiological studies.     

Chlorination disinfection by-products, public health risk tradeoffs and me

Since 1974 when trihalomethanes (THMs) were first reported as disinfection by-products (DBPs) in drinking water, there has been an enormous research effort directed at understanding how DBPs are formed in the chlorination or chloramination of drinking water, how these chlorination DBPs can be minimized and whether they pose a public health risk, mainly in the form of cancer or adverse reproductive outcomes. Driven by continuing analytical advances, the original DBPs, the THMs, have been expanded to include over 600 DBPs that have now been reported in drinking water. The historical risk assessment context which presumed cancer could be mainly attributed to exposure to environmental carcinogens played a major role in defining regulatory responses to chlorination DBPs which, in turn, strongly influenced the DBP research agenda. There are now more than 30 years of drinking water quality, treatment and health effects research, including more than 60 epidemiology studies on human populations, directed at the chlorination DBP issue. These provide considerable scope to reflect on what we know now, how our understanding has changed, what those changes mean for public health risk management overall and where we should look to better understand and manage this issue in the future.     

The effect of boiling water on disinfection by-product exposure

Chloraminated and chlorinated waters containing bromide were used to determine the impact of boiling on disinfection by-product (DBP) concentrations. No significant changes were detected in the concentrations of the dihalogenated haloacetic acids (DXAAs) (i.e., dichloro-, bromochloro-, dibromoacetic acid) upon boiling of chloraminated water, whereas the levels of the trihalogenated haloacetic acids (TXAAs) (i.e., trichloro- (TCAA), bromodichloro- (BDCAA), dibromochloroacetic acid (DBCAA)) decreased over time (e.g., 9-37% for TCAA). Increased DXAA concentrations (58-68%) were detected in the boiled chlorinated sample, which likely resulted from residual chlorine reacting with DXAA precursors. TCAA concentration was unchanged after boiling chlorinated water for 1 min, but a 30% reduction was observed after 5 min of boiling. BDCAA concentrations decreased 57% upon boiling for 1 min and were completely removed after 2 min of boiling, whereas DBCAA was removed after boiling chlorinated water for 1 min. Trihalomethane concentrations were reduced in both chloraminated (74-98%) and chlorinated (64-98%) water upon boiling. Boiling chloraminated water for 1 min reduced chloroform concentration by 75%. Chloroform was reduced by only 34% in chlorinated water after a 1 min boil, which indicates that simultaneous formation and volatilization of chloroform was occurring. Most of the remaining DBPs (e.g. haloketones, chloral hydrate, haloacetonitriles) were removed by at least 90% after 1 min of boiling in both samples. These data suggest that other mechanisms (e.g., hydrolysis) may have been responsible for removal of the non-volatile DBPs and further highlight the importance of examining individual species when estimating thermal effects on DBP concentrations.     

Formation, adsorption and separation of high molecular weight disinfection byproducts resulting from chlorination of aquatic humic substances

A significant portion of the unidentified disinfection byproducts (DBPs) in chlorinated drinking water can be attributed to high molecular weight (MW)-chlorinated DBPs (above 500 Da) that may have adverse health effects. In this work, issues on the formation, adsorption and separation of high MW-chlorinated DBPs were investigated by introducing radioactive (36)Cl into humic substance samples. The results show that the amount of high MW-chlorinated DBPs during chlorination decreased with the increase of contact time from 1 to 120 h, increased with the increase of pH from 5.5 to 9.5, and was less in the ultrafiltered samples from Suwannee River fulvic acid than from Suwannee River humic acid. The high MW-chlorinated DBPs were found to be effectively adsorbed by activated carbon and be possibly reduced to Cl(-) by activated carbon, but not to be readily desorbed from the activated carbon. Those high MW-chlorinated DBPs were demonstrated to be incapable of resolution into discrete peaks by any of the three liquid chromatography columns studied. The significant implications of these results are discussed.     

不同离子对Dinoseb氯化降解及消毒副产物生成的影响

以水体中常见的污染物地乐酚(Dinoseb)为研究对象,分析了水中4种不同离子(Br^-、NH4⁺、NO3^-、NO2^-)背景浓度下Dinoseb氯化动力学及生成消毒副产物(DBPs)的情况。结果表明,4种离子对Dinoseb氯化反应的影响顺序为:Br^->NH4⁺>NO2^->NO3^-。产生的消毒副产物主要有三氯甲烷(CF)、三氯硝基甲烷(TCNM)、二氯乙腈(DCAN)、三氯丙酮(TCP)、二氯一溴甲烷(DCBM)等,其中TCNM浓度最高,Dinoseb是TCNM的典型前体物。当水中有Br^-存在时,Dinoseb降解反应非常复杂,降解速率不符合拟一级反应规律,还会产生大量溴代THMs,如二氯一溴甲烷(DCBM)、一氯二溴甲烷(DBCM)、三溴甲烷(TBM)等,它们的浓度均随着Br^-/Cl2值的增加而迅速增加,浓度高低顺序为:DCBM>DBCM>TBM>CF。在相同p H值下,Dinoseb的氯化降解速率随着Br^-浓度的增大而增加;在相同Br^-浓度下,pH值越低,Dinoseb的氯化反应速率越快。与Br^-相比,pH值是更重要的氯化速率影响因素。当水体中有NH4⁺存在时,TCNM产率会提高较多;NO3^-对Dinoseb的氯化反应有一定的抑制作用,各DBPs浓度都有降低;NO2^-可以被水中的次氯酸氧化成NO3^-,消耗水中部分次氯酸,DBPs浓度总体都会降低。     

THM, HAA and CNCl formation from UV irradiation and chlor(am)ination of selected organic waters

The formation of disinfection by-products (DBPs), including chloroform, dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), and cyanogen chloride (CNCl) after sequential exposure of four organic waters to UV irradiation via either low- or medium-pressure lamps and free chlorine (or preformed monochloramine) under practical conditions was simulated. Statistically significant changes in the DBP formation from chlorination due to the additional UV irradiation are commonly observed under testing conditions, although some of these changes are not practically significant. The impacts from UV exposure were found to be most significant in chloroform formation (up to 40 microg/L) among the four tested DBPs. Organics from rivers were more sensitive to UV alteration than was the organic drawn from soil. This difference could not be explained by the specific UV absorbance (SUVA) values. In most cases, irradiation with the medium-pressure UV lamp gave similar or slightly larger changes in DBP yields, compared with the corresponding trials using the low-pressure lamp. Different application sequences could significantly change the relative quantities of DBPs but no general trend was identified. Case-specific evaluation of the formation of chloroform and CNCl is necessary.     

The impact of bromide on the formation of neutral and acidic disinfection by-products (DBPs) in Mediterranean chlorinated drinking water

By using the Grob closed loop stripping analysis technique a wide variety of disinfection by-products (DBPs) was determined, in finished drinking water of 15 important cities of Greece distributed in the southern, northern, west continental land and in the islands of Aegean and Ionian Seas. Trihalomethanes, haloacetonitriles, haloacetic acids, chloropicrin, halogenated ketons and chloral hydrate were the main DBPs determined. In chlorinated drinking water of coastal cities brominated DBPs were most abundant than their chlorinated homologues due to the higher bromide concentration in raw waters of these areas. Factor analysis with principal component extraction of the results demonstrated a clear differentiation between the examined drinking waters on the basis of their DBPs content and vicinity to the sea.     

Potential impact of chlorination of Sandy bottom swimming areas on drinking water sources

The concentrations of trihalomethanes and haloacetic acids, disinfection by‐products (DBPs) of chlorine, were measured in sandy bottom swimming areas to determine their potential impact on surface and ground water that are sources of drinking water. Total trihalomethanes and individual haloacetic acid concentrations in several swimming area samples were higher than the drinking water standards (current and proposed). Individual trihalomethanes (except bromoform) also exceeded ground and surface water release standards. No release standard exists for haloacetic acids. The DBPs, while exceeding standards, would be diluted by the ground water and microbially degraded prior to reaching the drinking water plant. So while DBPs from swimming areas contributed to groundwater concentrations, the current drinking water standards could still be met using source waters impacted by chlorinated swimming areas. It is suggested, though, that any release of chlorinated DBPs to surface and ground water be minimized to obtain the highest quality water sources for drinking water.     

Formation and fate of haloacetic acids (HAAs) within the water treatment plant

Most research on the occurrence of chlorinated disinfection by-products (DBPs) in drinking water has focused on trihalomethane (THM) formation and evolution, in particular within distribution systems. In this research, we investigated the variability of the occurrence of haloacetic acids (HAAs) during the treatment process in two facilities where surface water is pre-chlorinated before being treated by conventional physico-chemical processes. The investigation focused on both seasonal and point-to-point fluctuations of HAAs. In both facilities, samples were collected weekly during 1 complete year at four points in order to generate robust data on HAAs and on complementary parameters. The results showed that the initial formation of HAAs was the highest and the most variable in the plant where levels of DBP precursor indicators and the pre-chlorination dose were both higher and more variable. Subsequent formation of HAAs from the pre-chlorination point until the settled water occurred due to remaining levels of residual chlorine and DBP precursors. However, HAA levels and in particular dichloroacetic acid (DCAA) (the preponderant HAA species in the waters under study) decreased dramatically during filtration, very probably because of biodegradation within the filter. The effect of filtration on DCAA fate was season-dependant, with the highest degradation in warm water periods and practically no variation during winter. Statistical modeling was applied to empirically identify the operational factors responsible for HAA formation and fate. Model performance to identify HAA variability in waters following pre-chlorination was much better than for water following filtration, which is due to the lack of information on mechanisms and conditions favoring DCAA degradation.     

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。     

Formation of carbonaceous and nitrogenous disinfection by-products from the chlorination of Microcystis aeruginosa

Formation of carbonaceous disinfection by-products (C-DBPs), including trihalomethanes (THMs), haloacetic acids (HAAs), haloketones (HKs), chloral hydrate (CH), and nitrogenous disinfection by-products (N-DBPs), including haloacetonitriles (HANs) and trichloronitromethane (TCNM) from chlorination of Microcystis aeruginosa, a blue-green algae, under different conditions was investigated. Factors evaluated include contact time, chlorine dosages, pH, temperature, ammonia concentrations and algae growth stages. Increased reaction time, chlorine dosage and temperature improved the formation of the relatively stable C-DBPs (e.g., THM, HAA, and CH) and TCNM. Formation of dichloroacetonitrile (DCAN) followed an increasing and then decreasing pattern with prolonged reaction time and increased chlorine dosages. pH affected DBP formation differently, with THM increasing, HKs decreasing, and other DBPs having maximum concentrations at certain pH values. The addition of ammonia significantly reduced the formation of most DBPs, but TCNM formation was not affected and 1,1-dichloropropanone (1,1-DCP) formation was higher with the addition of ammonia. Most DBPs increased as the growth period of algal cells increased. Chlorination of algal cells of higher organic nitrogen content generated higher concentrations of N-DBPs (e.g., HANs and TCNM) and CH, comparable DCAA concentration but much lower concentrations of other C-DBPs (e.g., THM, TCAA and HKs) than did natural organic matter (NOM).     

An electrospray ionization-tandem mass spectrometry method for identifying chlorinated drinking water disinfection byproducts

Identification of chlorinated drinking water disinfection byproducts (DBPs) was investigated by using electrospray ionization-mass spectrometry/mass spectrometry (ESI-MS/MS). Chlorine-containing compounds were found to form chloride ion fragments by MS/MS, which can be used as a 'fingerprint' for chlorinated DBPs. Instrumental parameters that affect the formation of chloride ions by ESI-MS/MS were examined, and appropriate conditions for use in finding specific structural information were evaluated. The results show that maximizing the formation of chloride ions by MS/MS required a relatively high collision energy and collision gas pressure; also, limiting the scan range to m/z 30-40 allowed improved sensitivity for detection; but obtaining structural information required the use of lower collision energies. The conditions obtained were demonstrated to be effective in identifying chlorinated DBPs in a standard sample with relatively low concentrations of each component and in a chlorinated humic substance sample. Sample pretreatment techniques including ultrafiltration and size exclusion chromatography appeared to be helpful for identifying highly polar or high molecular weight chlorine-containing DBPs by ESI-MS/MS.