Speciation and Kinetics of Trihalomethane Formation in Drinking Water in Mexico

Water chlorination continues to be one of the most common water disinfection processes, especially in developing countries. When natural organic matter (NOM) is present, the process produces disinfection by-products (DBPs), some of them being trihalomethanes (THMs). This study determined the presence, speciation, and kinetics of THMs formation in the water supply for the northern area of the city of Toluca, Mexico. The results show that the concentrations of THMs are below the maximum allowable limits of 200 μg/L in accordance with NOM-127-SSA1-1994. Regarding THMs speciation, the presence of chloroform was more frequently observed in domestic water; furthermore, in one sample in which bromoform was present, it dominated over the chlorine species. Regarding the kinetics of THMs formation, a maximum concentration of THMs (THMs_Max) of 13.02 μg/L was obtained, and the time required to reach 50% THMs_Max ( t ₅₀) was 39.45 min.     

Formation of Trihalomethanes in Soil and Groundwater by the Release of Sodium Hypochlorite

Trihalomethanes (THMs) are formed by the reaction of reactive chlorine species, such as hypochlorous acid, with naturally occurring organic matter. THMs are also found in soil and groundwater at sites where releases of organic solvents have occurred and are often ascribed to the biological degradation chlorinated solvents. This research was prompted by the discovery of THMs in groundwater at a site with a reported discharge of sodium hypochlorite. This paper reports the formation of THMs in soil and water resulting from the reaction of sodium hypochlorite with soil. Soil samples were reacted with dilute bleach solutions (sodium hypochlorite) and the solution collected for analysis by gas chromatography/mass spectrometry. All THMs were detected in test samples after treatment. Concentrations of chloroform up to 2450 µg/L in aqueous extracts were detected compared to 40 µg/L in bleach and 1 µg/L in blank samples.     

Comparison of Fe-based and Al-based coagulants in the removal of organic and disinfection by-product precursors

Surface water is renowned for its natural organic matter, constituting approximately 45% of total dissolved organic carbon (DOC) which can be removed in water treatment plants. However, residual DOC in water can react with chlorine to form several carcinogenic disinfectant by-products (DBPs). This study aimed to examine the molecular weight of organic fractions dissolved in three different water sources that act as precursors to the formation of DBPs species. The coagulants used were Al- and Fe-based, frequently used in water treatment plants to remove organic fractions. Characterization of DOC in source water served as the first step in determining the performance of both coagulants in terms of organic properties. The results showed that the selected surface waters had similar DOC characteristics, including biopolymers, humic substances, building blocks, and a low molecular weight. These fractions contributed to the formation of trihalomethanes (THMs) and haloacetic acids (HAAs). The Fe-based coagulant was more effective than the Al-based coagulant in removing all organic fractions and reducing THMs compared to HAAs. Furthermore, one-way ANOVA analysis showed a significant difference in the average removal of organic fractions and DBP species between the Fe-based and Al-based coagulants. The Fe-based coagulant showed higher efficiency in removing biopolymers, dibromochloromethane, and chlorodibromoacetic acid than the Al-based coagulant. In contrast, the Al-based coagulant had better performance in reducing dibromo HAA and tribromo HAA. Both coagulants had no significant difference in extracting other organic fractions or DBPs species.     

Preserving Ground Water Samples With Hydrochloric Acid Does Not Result in the Formation of Chloroform

Water samples collected for the determination of volatile organic compounds (VOCs) are often preserved with hydrochloric acid (HCl) to inhibit the biotransformation of the analytes of interest until the chemical analyses can he performed. However, it is theoretically possible that residual free chlorine in the HCl can react with dissolved organic carbon (DOC) to form chloroform via the haloform reaction. Analyses of 1501 ground water samples preserved with HCl from the U.S. Geological Survey's National Water-Quality Assessment Program indicate that chloroform was the most commonly detected VOC among 60 VOCs monitored. The DOC concentrations were not significantly larger in samples with detectable chloroform than in those with no delectable chloroform, nor was there any correlation between the concentrations of chloroform and DOC. Furthermore, chloroform was detected more frequently in shallow ground water in urban areas (28.5% of the wells sampled) than in agricultural areas (1.6% of the wells sampled), which indicates that its detection was more related to urban land-use activities than to sample acidification. These data provide strong evidence that acidification with HCl does not lead to the production of significant amounts of chloroform in ground water samples. To verify these results, an acidification study was designed to measure the concentrations of all trihalomethanes (THMs) that can form as a result of HCl preservation in ground water samples and to determine if ascorbic acid (C₆H₈O₆) could inhibit this reaction if it did occur. This study showed that no THMs were formed as a result of HCl acidification, and that ascorbic acid had no discernible effect on the concentrations of THMs measured.     

Pipe Service Age Effect on Chlorine Decay in Drinking‐Water Transmission and Distribution Systems

Maintaining acceptable quality of water transported in the transmission and distribution system requires the chlorination of water beyond the treatment plant. While flowing through pipes, the chlorine concentration decreases for different reasons. Reaction with the pipe material itself and the reaction with both the biofilm and tubercles formed on the pipe wall are known as pipe wall demand. This varies with pipe parameters. The aim of this paper was to assess the impact of the service age of pipes on the chlorine wall decay constant. One hundred and fifty three pipe sections of different sizes and four different pipe materials were collected and tested for their chlorine first‐order wall decay constants. The results showed that pipe service age was an important factor that must not be ignored. For the range of the 55 years of pipe service age used in this study, the change in the wall decay ranged from 8 to 531% of the corresponding values in the recently installed pipes. The effect of service age on the wall decay constants was most evident in steel pipes. Other important findings were reached.     

Tidal residual eddies and their effect on water exchange in Puget Sound

Tidal residual eddies are one of the important hydrodynamic features in tidally dominant estuaries and coastal bays, and they could have significant effects on water exchange in a tidal system. This paper presents a modeling study of tides and tidal residual eddies in Puget Sound, a tidally dominant fjord-like estuary in the Pacific Northwest coast, using a three-dimensional finite-volume coastal ocean model. Mechanisms of vorticity generation and asymmetric distribution patterns around an island/headland were analyzed using the dynamic vorticity transfer approach and numerical experiments. Model results of Puget Sound show that a number of large twin tidal residual eddies exist in the Admiralty Inlet because of the presence of major headlands in the inlet. Simulated residual vorticities near the major headlands indicate that the clockwise tidal residual eddy (negative vorticity) is generally stronger than the anticlockwise eddy (positive vorticity) because of the effect of Coriolis force. The effect of tidal residual eddies on water exchange in Puget Sound and its subbasins was evaluated by simulations of dye transport. It was found that the strong transverse variability of residual currents in the Admiralty Inlet results in a dominant seaward transport along the eastern shore and a dominant landward transport along the western shore of the inlet. A similar transport pattern in Hood Canal is caused by the presence of tidal residual eddies near the entrance of the canal. Model results show that tidal residual currents in Whidbey Basin are small in comparison to other subbasins. A large clockwise residual circulation is formed around Vashon Island near entrance of South Sound, which can potentially constrain the water exchange between the Central Basin and South Sound.     

Minimizing the impacts of contaminant intrusion in small water distribution networks through booster chlorination optimization

Contaminant intrusion in a water distribution network (DN) has three basic pre-conditions: source of contaminant (e.g., leaky sewer), a pathway (e.g., water main leaks), and a driving force (e.g., negative pressure). The impact of intrusion can be catastrophic if residual disinfectant (chlorine) is not present. To avoid microbiological water quality failure, higher levels of secondary chlorination doses can be a possible solution, but they can produce disinfectant by-products which lead to taste and odour complaints. This study presents a methodology to identify potential intrusion points in a DN and optimize booster chlorination based on trade-offs among microbiological risk, chemical risk and life-cycle cost for booster chlorination. A point-scoring scheme was developed to identify the potential intrusion points within a DN. It utilized factors such as pollutant source (e.g., sewer characteristics), pollution pathway (water main diameter, length, age, and surrounding soil properties, etc.), consequence of contamination (e.g., population, and land use), and operational factors (e.g., water pressure) integrated through a geographical information system using advanced ArcMap 10 operations. The contaminant intrusion was modelled for E. Coli O156: H7 (a microbiological indicator) using the EPANET-MSX programmer’s toolkit. The quantitative microbial risk assessment and chemical (human health) risk assessment frameworks were adapted to estimate risk potentials. Booster chlorination locations and dosages were selected using a multi-objective genetic algorithm. The methodology was illustrated through a case study on a portion of a municipal DN.     

Application of the Response Surface Method for Optimization of Headspace Liquid Phase Microextraction of Trihalomethanes in Drinking Water

An optimized analysis method based on headspace liquid phase microextraction (HS‐LPME) and gas chromatography coupled with mass spectrometry was proposed for the determination of trihalomethanes (THMs) in drinking water. The response surface method (RSM) was used to optimize the extraction of THMs for analysis by HS‐LPME. The temperature, extraction time and NaCl concentration were found to be important extraction parameters. The coefficient of determination (R²) for the model was 94.97%. A high probability value (P < 0.0001) for the regression indicated that the model had a high level of significance. The optimum conditions were seen to be: temperature 42.0°C, NaCl concentration 0.30 g/mL, and extraction time 28 min. The response variable was the summation of the THMs chromatography peak areas and the reproducibility of this was investigated in five replicate experiments under the optimized conditions. The relative standard deviations (RSD%) of the THMs ranged from 8.0–11.6%. The limits of detection (LODs), based on a signal‐to‐noise ratio (S/N) of three ranged from 0.42–0.78 μg/L, and were lower than the maximum limits for THMs in drinking water established by the WHO.     

Carcinogenic Risk Assessment of Trihalomethanes in Major Drinking Water Sources of Baghdad City

Three standard methodological approaches used for carcinogenic risk assessment of the four trihalomethanes (THMs) species: Dibromochloromethane (CHClBr₂), Bromodichloromethane (CHCl₂Br), Bromoform (CHBr₃) and Chloroform (CHCl₃), in water collected from public water supplies which included main water source (raw water of the Tigris River), water treatment plants (treated water) and distribution system (tap water) in Baghdad City. The total concentration of THMs ranged between 13.78 and 63.1 μg/L in winter and summer respectively. The occurrence of THMs followed the given order: CHClBr₂ (36%) > CHCl₂Br (27%) > CHCl₃ (25%) > CHBr₃ (12%). The annual levels of THMs concentrations in the distribution networks of Baghdad City ranged between 12 and 97.3 μg/L in winter and summer, respectively, and followed the given order: CHClBr₂ (37%) > CHCl₂Br (33%) > CHCl₃ (21%) > CHBr³ (9%). The World Health Organization (WHO) index for additive toxicity approach was in compliant with the WHO guideline value, and does not pose any adverse toxic health impacts. The hazard index does not suggest any potential noncancer risk to the exposed population, whereas the total multi-pathway cancer risk analysis suggests that total cancer risk exceeds the USEPA acceptable level of 10–6.     

Chlorine Disinfection of Ground Water Obtained from 200M Deep Wells

The effect of chlorine concentration, ground water pH, and contact time on chlorine demand and the inactivation of coliform bacteria, Escherichia coli , was studied in the laboratory using a batch reactor under controlled environmental conditions. Ground water for this study was obtained from 200m deep wells in Bangkok, Thailand. The test results demonstrate that the kinetics of chlorine inactivation of coliforms in ground water consist of an initial rapid kill rate followed by a slower rate. Disinfection was more effective in acidic pH (5.5) than basic pH (8.5). Chlorine demand exerted by ground water increased with chlorine dose, contact time, and hydrogen ion concentration. Based on the applied chlorine dose, inactivation of E. coli by chlorine at neutral pH and room temperature was over two orders of magnitude less effective in ground water than in demand-free water. Because of the high chlorine demand exerted by this ground water, chlorine residuals leaving the treatment plant are likely to be unstable.     

Cancer risk analysis and assessment of trihalomethanes in drinking water

This study conducts risk assessment for an array of health effects that may result from exposure to disinfection by-products (DBPs). An analysis of the relationship between exposure and health-related outcomes is conducted. The trihalomethanes (THMs) species have been verified as the principal DBPs in the drinking water disinfection process. The data used in this study was collected from the Taiwan Water Corporation (TWC) from 1998 to 2002. Statistical analysis, multistage of Benchmark model, Monte Carlo simulation (MCS) and sensitive analysis were used to estimate the cancer risk analysis and assessment. This study included the statistical data analysis, epidemiology investigation and cancer risk assessment of THMs species in drinking water in Taiwan. It is more significant to establish an assessment procedure for the decision making in policy of drinking water safety predominantly.     

A catchment water balance assessment of an abrupt shift in evapotranspiration at the Hubbard Brook Experimental Forest,New Hampshire,USA

Small catchments have served as sentinels of forest ecosystem responses to changes in air quality and climate. The Hubbard Brook Experimental Forest in New Hampshire has been tracking catchment water budgets and their controls – meteorology and vegetation – since 1956. Water budgets in four reference catchments indicated an approximately 30% increase in the evapotranspiration (ET) as estimated by the difference between precipitation (P) and runoff (RO) starting in 2010 and continuing through 2019. We analyzed the annual water budgets, cumulative deviations of the daily P, RO and water budget residual (WBR = P − RO), potential ET (PET) and indicators of subsurface storage to gain greater insight into this shift in the water budgets. The PET and the subsurface storage indicators suggest that this change in WBR was primarily due to increasing ET. While multiple long-term hydrological and micrometeorological data sets were used to detect and investigate this change in ET, additional measurements of groundwater storage and soil moisture would enable better estimation of ET within the catchment water balance. Increasing the breadth of long-term measurements across small gauged catchments allows them to serve as more effective sentinels of substantial hydrologic changes like the ET increase that we observed.     

两种氮浓度对轮叶黑藻(Hydrilla verticillata)腐解过程营养盐释放及附着生物膜内氮循环基因丰度的影响

氨氮是地表水常见污染物,尤其在农业区域,氮类化肥的不合理施用会导致周边水体氮浓度迅速升高并保持较高水平.然而,当前对高氮水平下沉水植物腐败和附着氮循环微生物的影响尚不清楚.以轮叶黑藻(Hydrilla verticillata)为研究用沉水植物,在实验室内模拟水体内8和16 mg/L氮浓度下轮叶黑藻腐解过程中营养盐释放及残体表面微生物氮循环功能基因丰度的变化.研究发现水体两种氮浓度下轮叶黑藻腐解过程中残体腐解及营养盐释放速率无显著差异;与对照相比,植物腐败初期水体内碳、磷浓度迅速增加,而溶解氧浓度及氧化还原电位迅速降低,随着时间的推移上述水质指标逐步恢复至初期状态(第146天);水体荧光溶解性有机质主要包括紫外类富里酸、可见类富里酸、色氨酸类蛋白质和酪氨酸类蛋白质等类型.在5个氮循环相关基因中,氮负荷增加对轮叶黑藻残体生物膜内amo A、napA和narG的丰度有显著影响.冗余分析表明氮循环基因丰度受水体总氮浓度的影响较小,与植物总有机碳含量和水体化学需氧量及溶解氧浓度存在相关性.研究结果表明虽然当前氮水平对植物腐败过程影响不大、对氮循环基因丰度有一定影响,但是对该水生植被(尤其是植物腐败初期)和农业退水排放的管理仍需加强,以降低其对水体的影响.     

Process Performance of a Biotrickling Filter Using a Flow‐Directional‐Switching Method

Non‐uniform distribution of biomass and the accumulation of excess biomass at the inlet of a unidirectional flow biotrickling filter (UF‐BTF) may lead to severe operating problems including increasing airflow resistance in packed bed, clogging, and low contaminant removal efficiencies, even performance loss. Therefore, a flow‐directional‐switching biotrickling filter (FDS‐BTF) was designed to improve performance such as the maximum elimination capacity and elimination efficiency. Toluene was chosen as the unique carbon source for microorganism. The results indicated that the purification performance of FDS‐BTF was superior to UF‐BTF. The maximum elimination capacity of FDS‐BTF was up to 480 g/(m³ h), which was 17.1% higher than that of UF‐BTF. After a 50‐day continuous operation, FDS‐BTF attained the stable purification performance and the outlet concentrations of toluene could meet the emission standard with inlet concentrations ranging from 720 to 1100 mg/m³ for an empty bed residence time (EBRT) of 23.9 s. The average well color development in FDS‐BTF was higher than that in UF‐BTF. It indicated that FDS‐BTF could improve the metabolic activity, which may improve the uniform distribution of biomass along the length of packed bed. When two systems were shut down, 24 and 48 h, respectively, the time that FDS‐BTF and UF‐BTF needed to restore the former elimination efficiency after a shut down of 48 h were 3–4 and 9–10 h. These data indicated that the purification performance of FDS‐BTF was superior to UF‐BTF.     

Effect of Well Disinfection on Arsenic in Ground Water

Domestic water wells are routinely subjected to in situ chemical disinfection treatments to control nuisance or pathogenic bacteria. Most treatments are chlorine based and presumably cause strongly oxidizing conditions in the wellbore. Water resource managers in Wisconsin were concerned that such treatments might facilitate release of arsenic from sulfide minerals disseminated within a confined sandstone aquifer. To test this hypothesis, a well was subjected to four disinfection treatments over 9 months time. The first treatment consisted of routine pumping of the well without chemical disinfection; three subsequent treatments included chlorine disinfection and pumping. Pretreatment arsenic concentrations in well water ranged from 7.4 to 18 μg/L. Elevated arsenic concentrations up to 57 μg/L in the chemical treatment solutions purged from the well are attributed to the disintegration or dissolution of biofilms or scale. Following each of the four treatments, arsenic concentrations decreased to less than 10 μg/L during a period of pumping. Arsenic concentrations generally returned to pretreatment levels under stagnant, nonpumping conditions imposed following each treatment. Populations of iron-oxidizing, heterotrophic, and sulfate-reducing bacteria decreased following chemical treatments but were never fully eradicated from the well. Strongly oxidizing conditions were induced by the chlorine-based disinfections, but the treatments did not result in sustained increases in well water arsenic. Results suggest that disruption of biofilm and mineral deposits in the well and the water distribution system in tandem with chlorine disinfection can improve water quality in this setting.     

Wirkung der Chlorung auf die Abläufe einer Großkläranlage und ihres Vorfluters

To protect a water for the purpose of local recreation – inclusive of bathing – the effluent of an upstream clarification plant was chlorinated. Due to poorly controlled dosing, residual chlorine quantities exceeding the permissible level entered the receiving stream, its biocenosis having been considerably endangered. Detrimental effects on the chemical composition are graphically represented by the measured results for some waters – partly criteria of quality. There is explained that the self-purification capacity of the water decreased by about 30 % and that the hydrobiological species composition of periphyton was reduced by about 80 %. Finally, advice is given concerning the prevention of such damages to waters.     

Nanofiltration in Combination with Limestone Filtration for Treating a Soft Spring Water Containing High Amounts of Humic Substances

The paper presented here describes experiments with a nanofiltration pilot plant treating spring water which contains high amounts of humic substances. With this process, water components such as humic substances, iron, manganese, and aluminum may be very well removed. However, the low pH value of the NF filtrate does not conform with the German standards. This is why the pH value will be increased in a second treatment step by limestone filtration. Prior to limestone filtration, CO₂ dosage is required in order to make sure that the pH value stays below the upper limit of the German standards of 9.5. With this treatment, a drinking water results which meets the German standards and has good chemical properties with respect to corrosion. The operation of the nanofiltration pilot plant for the treatment of the very soft spring water did not require the continuous addition of chemicals in order to prevent scaling. Although the spring water entered the NF without chemical pretreatment, there was no decrease in filtrate capacity observed over a period of six months. This is in contrast to other investigations involving colour reduction from very hard surface waters. When treating very hard waters by nanofiltration, the addition of complexing agents or acid is required in order to prevent scaling of the membranes. Such intricate pretreatment procedures cause doubt of the application of nanofiltration for the treatment of hard waters in large plants. However, in the case presented here, the application of NF in combination with the hardening step is quite simple, so that the full-scale plant may be operated mainly automatically and will require only little maintenance.     

Using Chlorine Dioxide to Remove the Fouling of Ultrafiltration Membrane and Control Disinfection By‐Products

Ultrafiltration (UF) can remove natural organic matter (NOM) effectively. Moreover, chlorine dioxide (ClO₂) has been an alternative disinfectant as it forms fewer disinfection by‐products with NOM than chlorination does. Therefore, combining ClO₂ with UF may improve conventional purification processes. In this study, feed water containing humic acid with 4.07 mg/L total organic carbon (TOC) was dosed directly with various amounts of ClO₂ (0, 2, 5, 10, and 15 mg/L) before being filtered through a 5‐kDa UF membrane. With a low dose (2 mg/L ClO₂), UF removed humic acid effectively, as TOC was not detected in the permeate, and the permeate flux increased to about 80% of the initial permeate flux by cross flow. Moreover, the concentrations of ClO, ClO, and trihalomethanes in the permeate were below the United States Environmental Protection Agency guidelines.     

Visualization experiments of biodegradation in porous media and calculation of the biodegradation rate

Biodegradation in porous media is studied with carefully controlled and well-characterized experiments in model porous media constructed of etched glass. Porous media of this type allow visual observation of the phenomena that take place at pore scale. An aqueous solution of five organic pollutants (toluene, phenol, o-cresol, naphthalene and 1,2,3-trimethylbenzene) was used as a model NAPL (representing creosote). The bacteria used were Pseudomonas fluorescens, which are indigenous (even predominant) in many contaminated soils. The maximum aqueous concentrations of the specific organic substances, below which biodegradation becomes possible, were determined as a function of temperature from toxicity experiments. Visualization experiments were made under various flow velocities and organic loadings to study the morphology and thickness of the biofilm as a function of the pore size and the distance from the entrance, and the efficiency of biodegradation. The efficiency of biodegradation decreased as the aqueous concentration of NAPL at the inlet increased and/or as the flow velocity increased. The thickness of biofilm decreased as the distance from the inlet increased and/or the pore diameter decreased. A quasi-steady-state theoretical model of biodegradation was used to calculate the values of the mesoscopic biochemical rates and to predict the profile of NAPL concentration in the porous medium and the thickness of biofilm in pores. The agreement between experimental data and model predictions is quite satisfactory.     

Communicating human health risks associated with disinfection by-products in drinking water supplies: a fuzzy-based approach

Chlorine used for the disinfection of water supplies can react with naturally occurring organic compounds and form potentially harmful disinfection by-products (DBPs). A risk index for two regulated groups of chlorinated DBPs—trihalomethanes (THMs) and haloacetic acids (HAAs), using fuzzy C-means (FCM) clustering algorithm and fuzzy rule-based modeling is proposed for risk communication. The proposed index evaluates the cancer and non-cancer risks individually for THMs and HAAs using the FCM algorithm. Subsequently, two different fuzzy rule-bases were used to evaluate the overall risk-index based on cancer and non-cancer risks. The overall risk-index will provide drinking water utilities with an effective communication tool for communicating aggregated water quality compliance. Simulated DBP occurrence data obtained from the City of Quebec, Canada, is used to demonstrate the application of this methodology.