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.     

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.     

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.     

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.     

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.     

Human health risk assessment of chlorinated disinfection by-products in drinking water using a probabilistic approach

The presence of chlorinated disinfection by-products (DBPs) in drinking water is a public health issue, due to their possible adverse health effects on humans. To gauge the risk of chlorinated DBPs on human health, a risk assessment of chloroform (trichloromethane (TCM)), bromodichloromethane (BDCM), dibromochloromethane (DBCM), bromoform (tribromomethane (TBM)), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) in drinking water was carried out using probabilistic techniques. Literature data on exposure concentrations from more than 15 different countries and adverse health effects on test animals as well as human epidemiological studies were used. The risk assessment showed no overlap between the highest human exposure dose (EXP(D)) and the lowest human equivalent dose (HED) from animal test data, for TCM, BDCM, DBCM, TBM, DCAA and TCAA. All the HED values were approximately 10(4)-10(5) times higher than the 95th percentiles of EXP(D). However, from the human epidemiology data, there was a positive overlap between the highest EXP(D) and the lifetime average daily doses (LADD(H)) for TCM, BDCM, DCAA and TCAA. This suggests that there are possible adverse health risks such as a small increased incidence of cancers in males and developmental effects on infants. However, the epidemiological data comprised several risk factors and exposure classification levels which may affect the overall results.     

Kinetics of reactions between chlorine and the cyanobacterial toxins microcystins

Blooms of cyanobacteria can give rise to the production of toxins which contaminate drinking water sources. Among the oxidants and disinfectants typically applied in waterworks, chlorine has been found to be effective for the degradation of microcystins. In the present study, unknown second-order rate constants for the reactions of microcystin-LR (MC-LR), -RR and -YR with chlorine were determined over a wide pH range. It was found that an increase of pH has a negative effect on the microcystin degradation rate. Apparent second-order rate constant for the chlorination of MC-LR at 20 degrees C varied from 475 M(-1)s(-1) at pH 4.8 to 9.8 M(-1)s(-1) at pH 8.8. From these apparent second-order rate constants, rate constants for the reactions of MC-LR with hypochlorous acid (HOCl) and hypochlorite (ClO-) were evaluated. Half-life times ranged from minutes at pH 6 to 1 h at pH 8 for a constant residual chlorine concentration of 1.0-0.5 mgl(-1), typical of oxidation pre-treatment and final disinfection. Similar reactivity with chlorine was found for MC-RR and MC-YR. Therefore, chlorination is a feasible option for microcystin degradation during oxidation and disinfection processes, and can be applied in drinking water treatment in case of cyanobacterial toxin risk if the pH is kept below 8.     

Chlorination of humic substances in aqueous solution: Yields of volatile and major non-volatile organic halides

In this paper, we present the study of the effect of chlorination contact time, of the chlorine/carbon ratio and of the bromide concentration on the major halogenated products in the case of chlorinated humic substance solutions at neutral pH. The yields of chloroform, of trichloroacetic acid and of dichloro-acetic acid increase with the increase in reaction time and in chlorine dosage. Various values for the yield are given for chlorinated commercial humic acid solutions and for chlorinated solutions of aquatic fulvic and humic acids. The simultaneous presence of trihalomethanes precursors and bromides in the solution leads to the formation of organo-brominated products. Total trihalomethanes increase with the increase of bromide concentration.     

Effect of acid speciation on solid waste liquefaction in an anaerobic acid digester

Laboratory scale experiments were carried out to evaluate and determine the suitable working conditions for the enhancement of volatile fatty acids (VFAs) production with the stabilization of solid pineapple waste (peel) simultaneously when operating two-phase anaerobic digestion. It was found that acid production, enhanced when the digester was operated at neutral pH. VFAs, could be obtained at about 50 g/kg-waste within 14 days when operating at pH 6.5-7.5 compared to 33 g/kg-waste for digester operated at pH 5.0-6.0 for 32 days. The total volatile solid reduction of 42-48% was obtained with a 51-57% volume reduction at neutral pH. The effect of undissociated acids on the activity of acetogenic bacteria was also studied. The inhibitory level of undissociated acids for acidogenesis was found to be about 2300, 650, and 120 mg/L at pH 5, 6, and 7, respectively. The results revealed that at low pH, undissociated acids are inhibitory. It was found that for efficient operation of two-phase anaerobic digestion, both VFAs concentration and pH should be controlled.     

Evaluation of bromine substitution factors of DBPs during chlorination and chloramination

Bromine substitution factor (BSF) was used to quantify the effects of disinfectant dose, reaction time, pH, and temperature on the bromine substitution of disinfection byproducts (DBPs) during chlorination and chloramination. The BSF is defined as the ratio of the bromine incorporated into a given class of DBPs to the total concentration of chlorine and bromine in that class. Four classes of DBPs were evaluated: trihalomethanes (THMs), dihaloacetonitriles (DHANs), dihaloacetic acids (DHAAs) and trihaloacetic acids (THAAs). The results showed that the BSFs of the four classes of DBPs generally decreased with increasing reaction time and temperature during chlorination at neutral pH. The BSFs peaked at a low chlorine dose (1 mg/L) and decreased when the chlorine dose further increased. The BSFs of chlorination DBPs at neutral pH are in the order of DHAN > THM & DHAA > THAA. DHAAs formed by chloramines exhibited distinctly different bromine substitution patterns compared to chlorination DHAAs. Brominated DBP formation was generally less affected by the pH change compared to chlorinated DBP formation.     

不同分子质量区间腐殖酸的氯化反应特性研究

以自配的腐殖酸水样为研究对象,投加次氯酸钠对其进行消毒,考察了消毒过程中三卤甲烷、卤乙酸的生成量及DOC、UV254、A410、A465/A656的变化情况。结果表明,分子质量为50—100ku的腐殖酸为生成三卤甲烷和卤乙酸的最主要前体物;消毒反应后,各分子质量区间腐殖酸的DOC、UV254和A410都有不同程度的下降,且对小分子质量腐殖酸的DOC、UV254和A410的去除率高于对大分子质量腐殖酸的;A465／A656的变化表明消毒过程中腐殖酸的分子质量呈下降趋势。     

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.     

Reactivity of mucohalic acids in water

One group of disinfection byproducts of increasing interest are the halogenated furanones, which are formed in the chlorination of drinking water. Among these halofuranones is mucochloric acid (MCA, 3,4-dichloro-5-hydroxyfuran-2(5H)-one), and mucobromic acid (MBA, 3,4-dibromo-5-hydroxyfuran-2(5H)-one). Both mucohalic acids (MXA) are direct genotoxins and potential carcinogens, with the capacity to alkylate the DNA bases guanosine, adenosine and cytosine, and they have been measured in concentrations ranging up to 700 ng/l in tap water. MCA and MBA react in basic aqueous medium to form mucoxyhalic acids (4-halo-3,5-hydroxyfuran-2(5H)-one). Since: i) this reaction may represent the first step in the abiotic decomposition of mucohalic acids, ii) mucoxyhalic acids have been proposed as possible intermediates in the reaction of MXA with DNA, a kinetic study of the reaction mechanism is of interest. Here, the following conclusions were drawn: a) At moderately basic pH, the reaction of mucohalic acids with OH⁻ to form mucoxyhalic acids is kinetically significant. b) The nucleophilic attack of hydroxide ions on MXA occurs through a combination of two paths: one of them is first-order in hydroxide whereas the other is second-order and are proposed to occur through the deprotonation of the hydrate of MXA. c) The hydration constants of mucohalic acids −0.23 and 0.17 for MCA and MBA respectively - corresponds to the very significant hydrate concentrations. Since hydrates are not electrophilic, these values imply a decrease in the alkylating capacity of mucohalic acids.     

The Use of Bone Charcoal in the Treatment of Rural Water Supplies

As a result of the Water Act of 1989 on the quality of water intended for human consumption, a number of small spring sources in Yorkshire were the subject of legal undertakings for remedial action to reduce the concentration of trihalomethanes in the distribution system. The trihalomethanes are formed when the colour in these waters, which is made up of predominantly fulvic and humic acids, is chlorinated. Therefore, in order to solve the problem of trihalomethanes in treated water, colour removal was necessary.
The paper describes the use of bone charcoal in slow sand filters to remove colour from rural water supplies. It covers six months pilot-plant work which was undertaken at Marsett water-treatment works (near Richmond), and the implementation at other plants within Yorkshire. low-rate filtration through bone charcoal ensured that the colour and trihalomethane concentrations in filtered water complied with EC standards, and the material coped well with rapid changes in raw water quality.     

Simultaneous degradation of disinfection byproducts and earthy-musty odorants by the UV/H2O2 advanced oxidation process

Advanced treatment technologies that control multiple contaminants are beneficial to drinking water treatment. This research applied UV/H₂O₂ for the simultaneous degradation of geosmin, 2-methylisoborneol, four trihalomethanes and six haloacetic acids. Experiments were conducted in de-ionized water at 24 ± 1.0 °C with ng/L amounts of odorants and μg/L amounts of disinfection byproducts. UV was applied with and without 6 mg/L H₂O_2. The results demonstrated that brominated trihalomethanes and brominated haloacetic acids were degraded to a greater extent than geosmin and 2-methylisoborneol. Tribromomethane and dibromochloromethane were degraded by 99% and 80% respectively at the UV dose of 1200 mJ/cm² with 6 mg/L H₂O₂, whereas 90% of the geosmin and 60% of the 2-methylisoborneol were removed. Tribromoacetic acid and dibromoacetic acid were degraded by 99% and 80% respectively under the same conditions. Concentrations of trichloromethane and chlorinated haloacetic acids were not substantially reduced under these conditions and were not effectively removed at doses designed to remove geosmin and 2-methylisoborneol. Brominated compounds were degraded primarily by direct photolysis and cleavage of the C-Br bond with pseudo first order rate constants ranging from 10⁻³ to 10⁻² s⁻¹. Geosmin and 2-methylisoborneol were primarily degraded by reaction with hydroxyl radical with direct photolysis as a minor factor. Perchlorinated disinfection byproducts were degraded by reaction with hydroxyl radicals. These results indicate that the UV/H₂O₂ can be applied to effectively control both odorants and brominated disinfection byproducts.     

氯化消毒条件及污水水质对生成THMs、HAAs的影响

系统地研究了消毒务件和水质在城市污水氯化消毒过程中对生成三卤甲烷和卤乙酸的影响。结果表明，投氯量对三卤甲烷和卤乙酸生成量的影响最大，投氯量为40mg／L时的生成量分别约是投氯量为5mg／L时的30倍和70倍。三卤甲烷浓度随反应时间和温度无明显变化，而卤乙酸浓度在反应2h后达到峰值并在之后逐渐降低，且随温度的升高呈下降趋势。pH对两类副产物生成的影响几乎相反，近中性条件下的三卤甲烷生成量最多而卤乙酸生成量最少。水中氨氮浓度的增加会导致三卤甲烷生成量略有下降，而卤乙酸浓度却大幅上升。溴离子浓度升高将导致三卤甲烷和卤乙酸生成量显著增加，其中三氯甲烷浓度下降，三溴甲烷浓度显著上升，混合取代的三卤甲烷浓度先增加后减少。与此类似，二氯乙酸和三氯乙酸浓度随溴离子浓度的增加而减少，含溴卤乙酸浓度则有不同程度的增加。反应温度、反应时间、pH和氨氮对污水消毒副产物生成的影响与已报道的饮用水消毒中的作用规律存在显著差异，甚至截然相反，这为有针对性地选取消毒工艺参数提供了依据。     

Selective optimization in thermophilic acidogenesis of cheese-whey wastewater to acetic and butyric acids: partial acidification and methanation

For partial acidogenesis of cheese-whey wastewater, a set of experiments were carried out to produce short-chain volatile fatty acids (VFA) in laboratory-scale continuously stirred tank reactors (CSTR). The maximum rate of acetic and butyric acid production associated with simultaneous changes in hydraulic retention time (HRT), pH, and temperature was investigated, in which the degree of acidification of the whey to the short-chain VFAs was less than 20% of the influent chemical oxygen demand (COD) concentration. Response surface methodology was successfully applied to determine the optimum physiological conditions where the maximum rates of acetic and butyric acid production occurred. These were 0.40-day HRT, pH 6.0 at 54.1 degrees C and 0.22-day HRT, pH 6.5 at 51.9 degrees C, respectively.The optimum conditions for acetic acid production were selected for partial acidification of cheese-whey wastewater because of a higher rate in combined productions of acetic and butyric acids than that at optimum conditions for butyric acid production. A thermophilic two-phase process with the partial acidification followed by a methanation step was operated. Performance of the two-phase process was compared to the single-phase anaerobic system. The two-phase process clearly showed a better performance in management of cheese-whey wastewater over the single-phase system. Maximum rate of COD removal and the rate of methane production in the two-phase process were, respectively, 116% and 43% higher than those of the single-phase system.     

Acidogenic fermentation of proteinaceous sewage sludge: Effect of pH

Proteinaceous sewage sludge represents the sludge in which the protein content exceeds the carbohydrate content, accounts for a considerable part of sewage sludge. In this study, volatile fatty acids (VFA) production and synthesis pathway as well as bacterial community in acidogenic fermentation of proteinaceous sewage sludge under different pH conditions were investigated. The results indicated that the alkaline pH improved the solubilization and biodegradation of proteins in the sludge. The soluble protein concentration at pH 11.0 was 67.88% higher than that at pH 3.0. Its biodegradation efficiencies were reduced with a decrease in pH. The pH influenced not only the total VFA production yield, but also the percentage of individual VFA. The total VFA yield at pH 9.0 was 10.70 times of that at pH 3.0. The metabolic conversion pathway of proteins to VFA in acidogenic fermentation systems was investigated using a stoichiometry approach. The Stickland reaction was found to be the main pathway for the VFA accumulation from the decomposition of proteins. pH also significantly influenced the biodiversity and bacterial community in the system. The abundance of microorganisms under alkaline or acidic pH conditions was less than that under neutral pH condition, suggesting that most anaerobic fermentative microorganisms could not tolerate the hostile environment. The terminal restriction fragment length polymorphism analysis showed that, when the pH was reduced from 12.0 to 7.0 and finally to 3.0, the dominant bacterial genuses and percentage of the total microorganisms were Granulicatella genus (65%), Clostridium genus (28%) and Bacillus genus (71%), respectively.     

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。     

Kinetics of the oxidation of cylindrospermopsin and anatoxin-a with chlorine, monochloramine and permanganate

Cyanobacteria produce toxins that may contaminate drinking water sources. Among others, the presence of the alkaloid toxins cylindrospermopsin (CYN) and anatoxin-a (ANTX) constitutes a considerable threat to human health due to the acute and chronic toxicity of these compounds. In the present study, not previously reported second-order rate constants for the reactions of CYN and ANTX with chlorine and monochloramine and of CYN with potassium permanganate were determined and the influence of pH and temperature was established for the most reactive cases. It was found that the reactivity of CYN with chlorine presents a maximum at pH 7 (rate constant of 1265 M(-1)s(-1)). However, the oxidation of CYN with chloramine and permanganate are rather slow processes, with rate constants <1 M(-1)s(-1). The first chlorination product of CYN was found to be 5-chloro-CYN (5-Cl-CYN), which reacts with chlorine 10-20 times slower than the parent compound. The reactivity of ANTX with chlorine and chloramines is also very low (k<1M(-1)s(-1)). The elimination of CYN and ANTX in surface water was also investigated. A chlorine dose of 1.5 mg l(-1) was enough to oxidize CYN almost completely. However, 3 mg l(-1) of chlorine was able to remove only 8% of ANTX, leading to a total formation of trihalomethanes (TTHM) at a concentration of 150 microg l(-1). Therefore, chlorination is a feasible option for CYN degradation during oxidation and disinfection processes but not for ANTX removal. The permanganate dose required for CYN oxidation is very high and not applicable in waterworks.