Incorporating Reservoir Transfer into Treatment Optimization Decisions

The Massachusetts Water Resources Authority (MWRA) supplies unfiltered water from two large surface water reservoirs to the metropolitan Boston area, as well as to three smaller communities in central Massachusetts [the Chicopee Valley Aqueduct (CVA) communities]. Quabbin Reservoir is larger than Wachusett Reservoir, and has traditionally been used to supplement the Wachusett during the summer period. Quabbin water is also of better quality, with lower reactive natural organic matter (NOM). The MWRA began to add chlorine at Wachusett in 1997, and a new facility for adding chlorine at Quabbin for the CVA was also started up in 2000 to meet primary disinfection regulations to meet pathogen inactivation. The reaction of chlorine with NOM produces undesirable disinfection by-products (DBPs). The absorption of ultraviolet light at a wavelength of 254 nm was identified in chlorine decay studies to be the most important raw water quality parameter for predicting chlorine decay and DBP formation. This technical note summarizes the chlorine decay model for Wachusett and Quabbin water. The model is extended to ozonation of Wachusett water for the future Walnut Hill treatment plant. The models allowed the development of a trigger using UV-254 to time the Quabbin transfer to optimize treatment results. It is believed that the model for disinfectant decay and the use of UV-254 as a trigger for water treatment decisions are generalized and applicable to other water utilities.     

Effects of Bromide Ion and Natural Organic Matter Fractions on the Formation and Speciation of Chlorination By-Products

The impacts of bromide concentration and natural organic matter (NOM) characteristics on the formation and speciation of disinfection by-products (DBPs) in chlorinated NOM fractions were investigated. A total of 20 bulk water NOM fractions with a wide range of specific ultraviolet (UV) absorbance (SUVA254) values were obtained from a source water employing XAD-8 or XAD-4 resin adsorption in completely mixed batch reactors. SUVA was not a good predictor of DBP [trihalomethanes (THMs), haloacetic acids (HAAs), and adsorbable organic halogens (AOX)] formation and speciation. The destruction in the UV254 absorbance from chlorination did not correlate with DBP formation at any bromide level. NOM moieties which do not absorb UV light at 254?nm significantly contributed to DBP formation. Mass balance calculations on halogens using THMs, HAAs, and AOX data indicated that significant amounts of DBPs (>54% of AOX) other than THMs and HAAs were formed in NOM fractions with 60–110?μg/L bromide concentration. The relative occurrence of such other halogenated by-products decreased with increasing bromide concentrations up to 500?μg/L level. NOM in the studied water was more susceptible to the formation of brominated THM species as opposed to brominated HAAs. At constant dissolved organic carbon concentration, chlorine dose and pH, increasing bromide concentrations in NOM fractions increased the total concentrations of DBPs and resulted in a shift toward the formation of brominated species. Further, increasing bromide concentrations increased the spectrum of detected species (i.e., occurrence of all nine HAAs) and provided a competitive advantage to THM and HAA precursors in NOM over precursors of other DBPs.     

Predicting the Formation of Chlorinated and Brominated By-Products

Although disinfection was one of the major public health advances in the last century and continues to be so in the twenty-first century, the disinfectants themselves may react with naturally occurring materials in treated water to form unintended by-products, which may themselves pose risks. This is of particular concern with regard to the use of chlorine. Generation of disinfection by-products (DBPs) has been shown to be a function of various factors including total organic carbon concentration, type of organic precursor, chlorination level, pH, temperature, reaction time, and UV-254 absorbance. Another factor affecting DBP formation is the presence and concentration of the bromide ion in the raw or finished water. Bromine substitutes for chlorine to produce bromine-containing homologues of the more familiar chlorine species. The current list of by-products targeted for regulation contains brominated and mixed bromine-chlorine species of total trihalomethanes and haloacetic acids. These are known to form in bromide-containing waters when chlorinated. To control chlorination DBPs therefore requires an understanding of the factors that influence their formation. This paper presents a model that can be used to predict the formation of chlorinated, brominated, and mixed species compounds based on initial chlorine concentration, chlorine consumption, bromide ion concentration, and pH. The model clearly shows that higher levels of bromide in the water favor the formation of brominated compounds. Brominated compounds also form faster than chlorinated compounds.     

Secondary Benefits of Aquifer Storage and Recovery: Disinfection By-Product Control

The potential of biological processes during aquifer storage to reduce disinfection by-products (DBP), and DBP precursors were examined under controlled conditions. Finished water treated by conventional water treatment practice was pumped into a sand media column for up to 34 days of residence time. Two experiments were conducted where the finished water was chlorinated or ozonated prior to injection. Chlorination of water withdrawn from simulated aquifer storage conditions resulted in reduced formation of trihalomethane (THM) concentrations for all three treated water types. Ozonation of finished water resulted in a 70% decrease in TTHM formation. Aquifer storage of finished water resulted in a 26–28% reduction in TTHM formation and the removal of preformed THM species was as high as 40%. Overall, aquifer storage of chlorinated finished water resulted in a 44% reduction in TTHM formation when additionally chlorinated after withdrawal. Bromate formed during ozonation was reduced by approximately 54%. This study indicates that the sequencing of chlorination or ozonation with respect to aquifer storage and recovery operations can impact DBP formation.     

Hydrophobicity and Molecular Size Distribution of Unknown TOX in Drinking Water

The analysis of total organic halogen (TOX) in drinking water indicates that a substantial amount of the halogenated compounds cannot be accounted for by known specific disinfection by-products (DBPs). The primary aim of this research was to characterize the hydrophobicity and molecular size distribution of the unknown halogenated DBPs using XAD resins and ultrafiltration membranes. The impact of membrane rejection on the size analysis of unknown TOX was also investigated using chlorinated fulvic acid. Six finished waters from different locations and treatment processes were collected and fractionated into various hydrophobicity and molecular size groups. The results showed that most unknown TOX was in the size range between 0.5?kDa and 10?kDa, but it could have a wide spectrum of hydrophobicities. Simple ultrafiltration was not always reliable as a characterization tool, as it was shown to reject a significant fraction of DBPs with molecular weight (MW) lower than the membrane cutoffs. Flushing with deionized water was effective in removing these low MW compounds from the ultrafiltration cell. A significant reduction in the apparent size of unknown TOX resulted when low MW DBPs were flushed out of the cell (comparing with classic parallel ultrafiltration). Coagulation of fulvic acid also significantly reduced the apparent size of unknown TOX formed by chlorine.     

Iron Oxide Enhanced Chlorine Decay and Disinfection By-Product Formation

This study investigates the interaction of natural organic matter with iron oxide (goethite) on chlorine decay, disinfection by-product (DBP) formation, and DBP compound speciation [total trihalomethanes (TTHM4) and haloacetic acids (HAA5)]. Batch experiments were conducted with goethite, multiple finished drinking waters, variable chlorine dose, and fixed pH 8. The overall objective was to assess natural organic matter (NOM) adsorption onto goethite and its effect on chlorine decay and DBP formation. Chlorine consumption always increased in the presence of goethite and is attributed to an increase in the reactivity and/or modification of adsorbed NOM. Adsorbed NOM also led to an overall increase in TTHM4, however, HAA5 formation was suppressed during the first 2?h. Chloroform was identified as the increasing species and dichloracetic acid was identified as the suppressed species. This study clearly shows that goethite, which is the predominant iron oxide of pipe deposits, alters both chlorine decay and DBP formation and should be considered when assessing water treatment plant operations and DBP monitoring site selection.     

Temporal and Spatial Variations in Bulk Chlorine Decay within a Water Supply System

Modern water treatment must maintain an acceptable balance between the microbial safety of potable water supply, the costs of treatment, and the formation of potentially harmful disinfection by-products (DBPs). In order to achieve the optimum balance, it is essential to understand and predict both the formation of DBP and the decay of chlorine, in relation to source water, treatment processes, storage, and supply. Reported herein are new data which demonstrate the lack of durability, precision, and accuracy associated with earlier empirical chlorine decay rate equations. This work develops an improved methodology for the prediction of variation in chlorine decay rates in distribution systems enabling practical, cost-effective prediction of the effects of both seasonal variations and management interventions on chlorine levels at treatment works and in distribution systems.     

Comparative Analysis of Chlorine Dioxide, Free Chlorine and Chloramines on Bacterial Water Quality in Model Distribution Systems

Drinking water utilities may be required to change disinfectant to improve water quality and meet more stringent disinfection regulations. This research was conducted to assess and compares chlorine dioxide to free chlorine and chloramines on bacterial water quality monitored within model distribution systems (i.e., annular reactors). Following colonization with nondisinfected water, annular reactors containing either polycarbonate or cast iron coupons were treated with free chlorine, chlorine dioxide or chloramines. Two disinfectant doses (low/high) were tested for each disinfectant. Under specific environmental conditions, bacterial inactivation varied as a function of the disinfectant type and dose, sample type (bulk water versus biofilm bacteria) and coupon material. The ranking by efficiency was as follows: chlorine dioxide > chlorine > chloramines. On preformed biofilms of 106–107?cfu/cm2, the continuous application of a disinfectant led to a log removal of heterotrophic bacteria concentrations for suspended and biofilm bacteria ranging from 1.1 to 4.0, and from 0.2 to 2.5, respectively. Doubling the amount of disinfectant doses led to an additional log inactivation of 1–2.5 of heterotrophic bacteria levels. This study demonstrates that bacterial inactivation in distribution systems is governed by various inter-related parameters. The data indicate that chlorine dioxide represents a viable alternative for secondary disinfection in distribution systems.     

Modeling the Transformation of Chromophoric Natural Organic Matter during UV/H2O2 Advanced Oxidation

This research developed a differential kinetic model to predict the partial degradation of natural organic matter (NOM) during ultraviolet plus hydrogen peroxide (UV/H2O2) advanced oxidation treatment. The absorbance of 254?nm UV, representing chromophoric NOM (CNOM) was used as a surrogate to track the degradation of NOM. To obtain reaction rate constants not available in the literature, i.e., reactions between the hydroxyl radical (?OH) and NOM, experiments were conducted with “synthetic” water, using isolated Suwannee River NOM, and parameter estimation was applied to obtain the unknown model parameters. The reaction rate constant for the reaction between ?OH and total organic carbon (TOC), k?OH,TOC, was estimated at 1.14(±0.10)×104??L?mg-1?s-1, and the reaction rate constant between ?OH and CNOM, k?OH,CNOM, was estimated at 3.04(±0.33)×104??L?mol-1?s-1. The model was evaluated on two natural waters to predict the degradation of CNOM and H2O2 during UV/H2O2 treatment. Model predictions of CNOM degradation agreed well with the experimental results for UV/H2O2 treatment of the natural waters, with errors up to 6%. For the natural water with additional alkalinity, the model also predicted well the slower degradation of CNOM during UV/H2O2 treatment, owing to scavenging of ?OH by carbonate species. The model, however, underpredicted the degradation of H2O2, suggesting that, when NOM is present, mechanisms besides the photolysis of H2O2 contribute appreciably to H2O2 degradation.     

Optimal Design of Level 1 Redundant Water Distribution Networks Considering Nodal Storage

A water distribution network (WDN) is designed to meet time-varying demands with sufficient pressure, taking into consideration an appropriate demand during peak hours. Therefore, a network has inherent redundancy in the sense that under abnormal conditions such as those arising due to pipe breaks or pump failures, deficiency in supply during peak hours can be met through additional supply during off-peak periods. However, this necessitates a storage facility at the consumer end of the network, which is normally available in the form of a sump or an overhead tank in developing countries. Such a storage enables the consumer to store water during the off-peak period and then use it during the peak period. Reliability of a WDN is assessed herein considering nodal storage, and an iterative method is proposed for the optimal design of Level 1 redundant WDNs, i.e., networks that can sustain a single pipe failure without affecting consumer services either in part or in full. The method is illustrated through an example and the designs of a network with and without storage are compared. Provision of a nodal storage is found to reduce the total cost of the network.     

Lime-Soda Softening Process Modifications for Enhanced NOM Removal

In this research, a number of process modifications to the lime-soda softening process were examined, including utilization of high Mg-content lime, addition of MgCl2, and the recycling of softening sludge, in order to improve the removal of natural organic matter (NOM) and reduce the formation of disinfection byproducts (DBPs). Jar test results showed that dissolved organic carbon (DOC) removal increased and trihalomethane (THM) formation was reduced as the magnesium in hydrated lime increased, and was directly correlated with the amount of magnesium removed from the system. However, a dolomitic quick lime hydrated under atmospheric conditions resulted in less effective DOC removal due to a lack of available Mg, and subsequently, less co-precipitation of Mg(OH)2-NOM complexes. The addition of MgCl2 to the raw water also increased DOC removal and reduced THM formation in both the presence and absence of softening sludge, with DOC removal increasing as softening sludge and magnesium dosages increased. As high as 43% removal of DOC was achieved at the stoichoimetric lime-soda ash dose in the presence of 457 mg/L sludge and 7.5 mg/L MgCl2, as compared to only 13% removal in the absence of sludge and MgCl2. The recycling of softening sludge had little or no effect on the hardness and the level of inorganic elements in treated water. The results presented here provide new approaches for improving DBP precursor removal during lime-soda softening without significantly increasing lime and soda ash dosage or the generation of waste sludge.     

Case-control study of bladder cancer and water disinfection methods in Colorado

A population-based case-control study of bladder cancer and drinking water disinfection methods was conducted during 1990-1991 in Colorado. Surface water in Colorado has historically been disinfected with chlorine (chlorination) or with a combination of chlorine and ammonia (chloramination). A total of 327 histologically verified bladder cancer cases were frequency matched by age and sex to 261 other-cancer controls. Subjects were interviewed by telephone about residential and water source histories. This information was linked to data from water utility and Colorado Department of Health records to create a drinking water exposure profile. After adjustment for cigarette smoking, tap water and coffee consumption, and medical history factors by logistic regression, years of exposure to chlorinated surface water were significantly associated with risk for bladder cancer (p = 0.0007). The odds ratio for bladder cancer increased for longer durations of exposure to a level of 1.8 (95% confidence interval 1.1-2.9) for more than 30 years of exposure to chlorinated surface water compared with no exposure. The increased bladder cancer risk was similar for males and females and for nonsmokers and smokers. Levels of total trihalomethanes, nitrates, and residual chlorine were not associated with bladder cancer risk after controlling for years of exposure to chlorinated water.     

Determination of Perchlorate Rejection and Associated Inorganic Fouling (Scaling) for Reverse Osmosis and Nanofiltration Membranes under Various Operating Conditions

This study focused on perchlorate (ClO4?) rejection and flux-decline in bench-scale cross-flow flat-sheet filtration for two reverse osmosis (RO) and two nanofiltration (NF) membranes with a natural water, and addressed estimation of precipitative fouling/scaling with inorganic salts and characterizations of inorganic fouling and antiscalants. Thus the study considered tradeoffs between productivity (increased recovery and flux) versus ClO4? rejection versus membrane fouling/scaling. In this study, the rejection of water quality parameters (cations, anions, dissolved organic carbon, UVA254, total dissolved solids) and flux-decline trends for four different membranes were investigated over a various range of operating conditions (i.e., J0/k ratio and recovery). Inorganic foulants on the membrane surface were analyzed by various methods (i.e., x-ray diffraction and scanning electron microscopy), and demonstrated inhibition effects of antiscalant. With increasing recovery and J0/k ratio, high productivity (flux) was achieved, however, the rejections of perchlorate and other water quality parameters decreased and the precipitative fouling/scaling potential of membranes increased. At the same operating conditions in the presence of an antiscalant, embodying phosphonate functional groups, flux decline trends for the four membranes indicated lower scale formation supported by the results of the fouled membrane characterizations.     

Impact of Chlorinated Water Exposure on Contaminant Transport and Surface and Bulk Properties of High-Density Polyethylene and Cross-Linked Polyethylene Potable Water Pipes

The aim of this work was to determine if the aging of polyethylene (HDPE, PEX-A and PEX-B) water pipes by exposure to chlorinated water altered polar and nonpolar contaminant diffusivity and solubility by analyzing new, laboratory-aged, and exhumed water-distribution system polyethylene (PE) pipes. After 141?days of aging in pH 6.5 water with 45??mg/L free chlorine, the surface chemistry and bulk properties of PEX-A pipe were unaffected. Carbonyl bonds (σ = 1,713??cm-1) were detected on the surfaces of HDPE and PEX-B pipe, and these oxygenated surfaces became more hydrophilic, resulting in statistically significant increases in diffusion rates. All 10 contaminant and four pipe material combinations had diffusivity increases on average of 50% for polar contaminants and 5% for nonpolar contaminants. Contaminant solubility was slightly increased for aged PEX-A and slightly decreased for PEX-B pipes. Toluene and trichloromethane diffusivity and solubility values for 7- to 25-year-old buried water utility pipes were similar to values for new and laboratory-aged HDPE-based materials. Because chlorinated water exposure alters how polar contaminants interact with aged PE pipes, results of this work should be considered in future health risk assessments, water quality modeling, pipe performance, and service-life considerations.     

Reduction of Nitrate, Bromate, and Chlorate by Zero Valent Iron (Fe0)

Oxo-anions occur in drinking waters, pose potential health risks, and should be controlled. It may be possible to incorporate zero-valent iron (Fe0) into water treatment processes to remove oxo-anions. Under near neutral pH (～7) and aerobic conditions, the three oxo-anions studied (NO3?, BrO3?, ClO3?) were electrochemically reduced by Fe0 in batch and continuous-flow packed column experiments. Mass balances provided strong evidence that ammonia is the primary reduction by-product from nitrate, chloride from chlorate, and bromide from bromate. Protons were consumed during the reaction, resulting in an increase in pH (i.e., production of hydroxide). Oxo-anion removal rates decreased as follows: BrO3?>ClO3?>NO3?. Differing rates of oxo-anion removal between batch and continuous flow column tests suggested that higher solid (Fe0) to liquid ratios increase oxo-anion electrochemical reduction, and scaling up of batch kinetic data to larger scale must consider the solid–liquid ratios. The atomic structure (atomic radii, electron orbital configuration, electron affinity) of nitrogen, chlorine, and bromine elements of the oxo-anions, and the bond dissociation energy between these elements and oxygen, were good indicators for the relative rates of reduction by Fe0.     

Particulate and THM Precursor Removal with Ferric Chloride

Pilot-scale experiments were performed to investigate the effectiveness of enhanced coagulation in removing particles and trihalomethane (THM) precursors from two surface source waters: California State Project water and Colorado River water. The removal of suspended particles and natural organic matter at various ferric chloride doses and coagulation pHs was assessed through source water and filter effluent measurements of turbidity, particle count, UV254, TOC, and THM formation potential. Overall, it was found that optimal removal of particles and THM precursors by enhanced coagulation with ferric chloride is obtained at high coagulant doses (>16 mg∕L) and low pH conditions. Generally, turbidity removal is more efficient and head loss is more moderate at ambient pH compared with pH 5.5. Additionally, filter effluent particle counts were found to be consistent with residual turbidity data. The removal of THM precursors by enhanced coagulation is significantly enhanced at pH 5.5 compared with ambient pH. The reduction in THM formation potential is consistent with the trends observed for the THM precursor removal data (i.e., UV254 and TOC data). Furthermore, specific UV absorbance was used to estimate the proportion of humic substances in the raw waters. Enhanced coagulation was found to be less effective for the source water with the lower specific UV absorbance.     

Bromate Formation by Ozone-VUV in Comparison with Ozone and Ozone-UV: Effects of pH, Ozone Dose, and VUV Power

The formation of bromate by ozone–vacuum ultraviolet (VUV) (185+254??nm) process in comparison with ozone and ozone-ultraviolet (UV) (254?nm) processes of coagulated and softened water was studied. The effects of pH (7, 9, and 11), ozone dosage (1, 2, and 4?mg O3/mg C), and VUV power (30, 60, and 120?W) were investigated. Bromate concentrations formed by the ozone-VUV process were up to four and six times less than those by the ozone and ozone-UV processes, respectively. Among the variables studied, ozone dosage had the most effect on bromate formation by the ozone-VUV process. Approximately 64 and 213% increases of bromate concentration were observed when the ozone dosage was increased from 1 to 2 and 4?mg O3/mg C with VUV power of 120?W at pH 7. The bromate formation also increased as VUV power and pH increased. Hydroxyl radical exposure had a positive relationship with ozone dosage and bromate formation. Results further indicated that it might be difficult to achieve the drinking water standard for bromate and high organic matter removal concurrently.     

Spectroscopic changes in human dentine exposed to various storage solutions--short term

OBJECTIVES: Tooth storage conditions in studies of dentine have not been standardized. The objective of this investigation was to determine the effects of storage solution and time on dentine, using spectroscopic methods. METHODS: Twenty-seven dentine disks (0.75 mm thick) were prepared from freshly extracted third molars with documented histories. The teeth were sectioned parallel to the occlusal plane using a diamond saw. Specimens were analysed non-destructively for surface chemical changes using specular reflectance infra-red Fourier transform spectroscopy (SRIFTS), and changes in optical properties were measured in the ultraviolet, visible and near-infra-red spectral ranges with an integrating sphere spectrophotometer (UV/VIS/NIR) before and after storage. A minimum of five specimens were stored in distilled water with 0.02% thymol, purified and filtered water, phosphate buffered saline with 0.02% thymol, 70% ethanol or 10% buffered formalin and evaluated at 0, 1, 2, 7, 14, 21 and 28 days. After each measurement, specimens were stored in fresh solutions. IR spectra were obtained from 4400 to 400 wave-numbers (cm-1). Optical properties of reflectance and transmittance were determined from 200 to 2500 nm, and absorbance was calculated. RESULTS: Analysis of the IR spectra indicated no significant differences in collagen or mineral peak positions for any solution at any time period. There were significant differences in peak intensities of dentine stored in distilled water, purified and filtered water and phosphate-buffered saline over time in the IR spectra. Furthermore, differences in optical properties of dentine disks were detected by UV/VIS/NIR. CONCLUSION: It was concluded that changes in surface chemistry and optical properties of dentine occur as a function of storage solution and time, which must be considered when studying dentine.     

Methotrexate suppresses nitric oxide production ex vivo in macrophages from rats with adjuvant-induced arthritis

This review discusses the relation between by-products of drinking water chlorination and cancer in the light of present toxicological and epidemiologic evidence. During the chlorination of drinking water, a complex mixture of by-products forms from chlorine and the organic and inorganic compounds present in raw water. The quality and quantity of such compounds depend on the specific nature of the organic material in raw waters, the inorganic material in raw water, pH, temperature, other water treatment practices, and the chlorine timing and dose added. Chlorination by-products are important mainly when surface water is used for drinking water as more organic compounds are present in surface waters than in ground waters. The gastrointestinal and urinary tract are the cancer sites that are most often associated with the use of chlorinated surface water or with the quantity of chlorination by-products in the water-supply network. Yet the microbial quality of drinking water should not be compromised by excessive caution over the potential long-term effects of disinfection by-products because the risk of illness and death resulting from exposure to pathogens in untreated drinking water may be several orders of magnitude greater than the cancer risks from chlorination by-products.     

Estimating the Removal of Anthropogenic Organic Chemicals from Raw Drinking Water by Coagulation Flocculation

A mathematical model was developed to estimate the efficacy of coagulation–flocculation treatment for removing neutral hydrophobic organic chemicals from raw drinking water. The model assumed that the only significant removal mechanism was the destabilization and settling of organic matter containing sorbed anthropogenic organic compounds. The model was validated with standard jar tests using compounds with a range of hydrophobicities (log?Kow = 1.89?to?5.48), including contaminant candidate list chemicals, pesticides, pharmaceuticals, and endocrine disrupting chemicals. Final concentrations of test compounds after coagulation and flocculation were in good agreement with model estimations for synthetic waters composed of Aldrich (Milwaukee, WI) humic acid solutions. The final compound concentrations in coagulated natural waters from two drinking water reservoirs were about 80% lower than those estimated with the model. Overestimations of treated water concentrations by the model were attributed to an increase in sorption by natural organic matter when coiled in aluminum hydroxide flocs, compared to sorption to dispersed natural organic matter in untreated water.