Spatial Diversity of Chlorine Residual in a Drinking Water Distribution System

Chlorine residuals of drinking water have long been recognized as an excellent indicator for studying water quality in the distribution network. This research applied factor analysis and cluster analysis to determine the spatial diversity of chlorine residual in the distribution system of Feng-Yuan city. Thirteen sampling sites were established. From the results of factor analysis, the sampling sites of the study area could be classified into three groups: residential zone, mixed zone, and commercial zone. The spatial diversity of chlorine residual was found to correlate with the daily lifestyle of the inhabitants and the commercial activities. From the results of cluster analysis, the sampling sites of the study area could also be classified into three groups: high-chlorine-level zone, medium-chlorine-level zone, and low-chlorine-level zone. By combining the results of factor analysis and cluster analysis, the worst case scenarios for drinking water quality in the distribution network also could be determined.     

Inactivation of Adenovirus Types 2, 5, and 41 in Drinking Water by UV Light, Free Chlorine, and Monochloramine

A bench-scale study was conducted to determine the inactivation of adenovirus (Ad) types 2, 5, and 41 by ultraviolet (UV) light, chlorine, and monochloramine. The motivation for this study was to determine whether UV disinfection followed by chlorine or monochloramine for a very short contact time (e.g., a minute) could satisfy regulatory requirements for four-log virus inactivation. In order to overcome the difficulty Ad 41 presents for enumeration of the virus in cell culture, a technique was used that combined immunofluorescent staining of viral antigen with traditional scoring of cytopathic effect. A UV dose of 40?mJ/cm2 (millijoules per square centimeter) (applied using a collimated beam apparatus) achieved approximately one-log inactivation of adenovirus types 2, 5 and 41, confirming previous research. Ad 41 was found to be more UV resistant to UV light than Ad 2 or Ad 5 at UV doses >70?mJ/cm2 to a statistically significant degree (95% confidence); however, at lower UV doses there were no statistically significant differences. Experiments with Ad 5 and Ad 41 at 5°C and pH 8.5 showed that chlorine was very effective against Ad 5 and Ad 41, with a product of disinfectant concentration and contact time (CT) of 0.22?mg min/L providing four-log inactivation. Monochloramine was less effective against these adenoviruses, with a CT of 350?mg min/L required to achieve 2.5-log inactivation of Ad 5 and 41 at 5°C and pH 8.5.     

Modeling Discoloration in Potable Water Distribution Systems

Discoloration of potable water supplied to customer taps is one of the biggest causes of water quality related customer complaints. At present, understanding of the fundamental processes that cause discoloration is limited and the modeling of events unfeasible. This paper describes the development, verification, and validation of a novel cohesive transport modeling approach to simulate discoloration within distribution systems. The model is based on the principal that strength characteristics of fine particulate material accumulated at the pipe walls are conditioned by the shear stress of the usual daily hydraulics. Discoloration occurs when the flow through the systems changes, exceeding the peak daily value. Fieldwork results from two sites are presented in detail: Site 1 demonstrates model application including sensitivity and parameter dependence, while data from Site 2 is used to investigate the hypothesis that daily hydraulic forces condition the material layers within the pipes. Model simulations are also presented for a selection of other field sites to demonstrate the wider applicability of the model.     

Removal of Antibiotics from Surface and Distilled Water in Conventional Water Treatment Processes

Conventional drinking water treatment processes were evaluated under typical water treatment plant conditions to determine their effectiveness in the removal of seven common antibiotics: carbadox, sulfachlorpyridazine, sulfadimethoxine, sulfamerazine, sulfamethazine, sulfathiazole, and trimethoprim. Experiments were conducted using synthetic solutions prepared by spiking both distilled/deionized water and Missouri River water with the studied compounds. Sorption on Calgon WPH powdered activated carbon, reverse osmosis, and oxidation with chlorine and ozone under typical plant conditions were all shown to be effective in removing the studied antibiotics. Conversely, coagulation/flocculation/sedimentation with alum and iron salts, excess lime/soda ash softening, ultraviolet irradiation at disinfection dosages, and ion exchange were all relatively ineffective methods of antibiotic removal. This study shows that the studied antibiotics could be effectively removed using processes already in use in many water treatment plants. Additional work is needed on by-product formation and the removal of other classes of antibiotics.     

Modeling the Impact of Microbial Intrusion on Secondary Disinfection in a Drinking Water Distribution System

The purpose of this study was to quantify the potential level of protection that secondary disinfection may provide in response to an intrusion event. Although several uncertainties exist regarding intrusion events, this study presents an analysis of the inactivation provided by disinfectant residuals by using a distribution system model, inactivation and disinfectant decay models, and conservative assumptions based on available data. A variety of conditions were modeled, including a range of water quality parameters (pH, temperature); inactivation of two microorganisms, Giardia and E. coli O157:H7; and intrusion water dilution ratios. Despite the assumptions inherent in the model, several generalizations were derived from the study. A free chlorine residual of 0.5?mg/L may be insufficient to provide adequate control of disinfectant-resistant Giardia even at low pH (6.5) and high temperature (25°C) conditions that enhance chlorine effectiveness. For E. coli, an organism of “average” disinfectant resistance relative to others, a residual of 0.5?mg/L may provide ample protection against intrusion even assuming that the chlorine residual is reduced within several minutes, such as would be predicted to occur with sewage intrusion at levels below 1% of the total flow. Importantly, chloramines may have a negligible benefit in terms of protecting against intrusion for even relatively susceptible organisms such as E. coli. Consequently, systems should consider protection against intrusion when choosing their secondary disinfectant.     

Efficacy of Chlorine Dioxide as a Disinfectant for Bacillus Spores in Drinking-Water Biofilms

This paper presents results describing the effectiveness of chlorine dioxide penetration into a drinking-water distribution system biofilm/corrosion matrix and decontamination of adhered Bacillus globigii spores, a surrogate for Bacillus anthracis. Biofilm and corrosion products were developed using biofilm annular reactors containing oxidized scaled, iron coupons. Reactors were inoculated with B. globigii spores after biofilm development, and decontamination was undertaken with bulk-phase chlorine dioxide concentrations of 5, 10, 15, and 25??mg/L. Initial biofilm viable B. globigii spore densities of 106??CFU/cm2 were reduced to 50 to 300??CFU/cm2 at chlorine dioxide concentrations of 25 and 15??mg/L, respectively, within 6?days. B. globigii spore distribution throughout the biofilm/corrosion matrix depth and the change in viable spore count during chlorine dioxide disinfection were examined using a microslicing technique. Four layers of 360?μm thickness were sliced, and these showed that B. globigii spores were equally distributed throughout the biofilm/corrosion matrix depth. Furthermore, chlorine dioxide acted on all layers simultaneously, but spores still persisted in the deepest layer of the biofilm/corrosion matrix after 6?days of disinfection at 15 and 25??mg/L chlorine dioxide.     

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.     

Modeling and Control of Vinyl Chloride in Drinking Water Distribution Systems

In water distribution systems containing PVC pipe manufactured in the “early era” (prior to 1977), vinyl chloride can leach into drinking water resulting in vinyl chloride concentrations exceeding the 2 μg?L?1 maximum contaminant level. Field testing of dead-end segments of water distribution systems consisting of early-era PVC pipe was conducted to examine their initial intrapipe vinyl chloride monomer (VCM) concentrations based on a Fickian-diffusion-based leaching model. The experiments showed a wide range of VCM concentrations within early-era PVC pipe ranging from less than 50 to more than 600 mg?kg?1. Based on the diffusion modeling approach, a protocol was designed that provides a means for utility managers to calibrate the model for specific dead-end lines. The paper delineates procedures to determine which dead ends require flushing to control vinyl chloride, examines the effects of system parameters such as temperature on vinyl chloride leaching, and provides a method to devise flush schedules and volumes. Through a properly designed, tested, and maintained flush protocol such as that developed in this research, public water systems with dead-end lines consisting of early-era PVC pipe can control vinyl chloride concentrations using either manual or automatic flush valves.     

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.     

Iron Corrosion Scales: Model for Scale Growth, Iron Release, and Colored Water Formation

This paper was presented in part by V. L. Snoeyink as the Simon W. Freese Lecture at the 2002 Canadian Society of Civil Engineers/Environmental and Water Resources Institute of ASCE Environmental Engineering Conference in Niagara Falls, Ontario, Canada, July 22, 2002. The interactions of corroded iron pipe surfaces with water are of importance because they can lead to serious water quality degradation and material deterioration. A conceptual model has been developed in this paper to describe the formation and growth of iron scales, and their reactions that lead to colored water problems. Most corrosion scales have characteristic structural features, such as a loosely held top surface layer, a shell-like layer(s), and a porous core. According to this model corrosion scales are expected to grow from inside the scale via the corrosion reaction, i.e., the conversion of iron metal to ferrous ion. The average oxidation state of iron increases with distance from the pipe wall. The scale structure and scale reactions permit the ferrous iron to be released to the bulk water, where it undergoes conversion to particulate ferric iron, which is the cause of colored water. Scale structure and composition play important roles in the reactions of iron scales that lead to iron release, and water quality control to decrease the porosity of the scale is an important means of reducing iron release. It is anticipated that the conceptual model presented here will be used as a basis for changing water quality to minimize colored water formation, and as a guide for further research.     

Modeling Residual Chlorine Response to a Microbial Contamination Event in Drinking Water Distribution Systems

Changes in chlorine residual concentrations in water distribution systems could be used as an indicator of microbial contamination. Consideration is given on how to model the behavior of chlorine within the distribution system following a microbial contamination event. Existing multispecies models require knowledge of specific reaction kinetics that are unlikely to be known. A method to parameterize a rate expression describing microbially induced chlorine decay over a wide range of conditions based on a limited number of batch experiments is described. This method is integrated into EPANET-MSX using the programmer’s toolkit. The model was used to simulate a series of microbial contamination events in a small community distribution system. Results of these simulations showed that changes in chlorine induced by microbial contaminants can be observed throughout a network at nodes downstream from and distant to the contaminated node. Some factors that promote or inhibit the transport of these chlorine demand signals are species-specific reaction kinetics, the chlorine concentration at the time and location of contamination, and the system’s unique demand patterns and architecture.     

Nitrification Modeling in Pilot-Scale Chloraminated Drinking Water Distribution Systems

A suspended growth nitrification model was developed to describe nitrification dynamics in terms of chloramine, ammonia, nitrite, nitrate, and nitrifying bacteria concentrations in pilot-scale chloraminated drinking water systems. The model provided a semimechanistic base to study the regrowth and persistence of nitrifiers in chloraminated distribution systems. Results showed that the developed suspended growth model, without a biofilm nitrification component, was able to simulate and predict nitrification episodes in the pilot-scale systems. In the restricted low nutrient drinking water environment, growth kinetic parameters for nitrifiers were estimated to be significantly lower than ranges reported in the literature. The maximum specific growth rate and ammonia half-saturation constant for ammonia oxidizing bacteria were estimated to be 0.46?day?1and 0.023?mg NH3–N/L, respectively. In addition, an estimated reaction rate of 70±32?L/(mg?HPC?day) between chloramines and soluble microbial products suggests that heterotrophic growth can be a significant contributor to chloramine decay in some chloraminated distribution systems.     

Modified Larsons Ratio Incorporating Temperature, Water Age, and Electroneutrality Effects on Red Water Release

Corrosion indices have a historical as well as practical relevance in drinking water treatment. The development of reliable indicators of corrosion related problems, like red water, is an ongoing process in the drinking water industry. Due to the complexity of interaction among the physical, chemical, and biological reactions taking place within a typical distribution system, mechanistic models are difficult to formulate. Even if such a model was available, fitting it to actual field conditions would still be an empirical process. Corrosion indices give simplistic generalizations to complex corrosion phenomena. A modified form of the Larson Ratio that includes the effects of temperature and hydraulic retention time is proposed based on apparent color release data available from a 2 year pilot distribution system study.     

Effect of ClO2 Pretreatment on Subsequent Water Treatment Processes

The effect of chlorine dioxide (ClO2) pretreatment on subsequent treatment processes (coagulation, flocculation, sedimentation, filtration, and ozonation) was studied at pilot-scale at the Upper San Leandro Water Treatment Plant near Oakland, Calif. Potential impacts of ClO2 on the distribution system were also studied at bench scale using simulated distribution system (SDS) tests. Pilot trials were conducted with one train operating without ClO2 pretreatment (Train 1) and the other with a ClO2 dose of between 0.6 and 1.0?mg/L (Train 2). Comparison between Trains 1 and 2 showed that ClO2 pretreatment resulted in a 0.1–0.2 NTU decrease in settled water turbidity when compared to no pretreatment. ClO2 pretreatment also resulted in a small (0.01?cm?1) decrease in ultraviolet absorbance at 254?nm. Following sedimentation, about 60% of the applied ClO2 formed chlorite (ClO2?), with 10–20% forming chlorate (ClO3?). Ozonation immediately converted all residual ClO2 and ClO2? to ClO3?. There was no significant difference in the performance of the filters between the two trains in terms of headloss, particle count, and turbidity. Bench-scale SDS tests indicated that chlorine dioxide preoxidation did not affect subsequent chloramine stability or concentrations of trihalomethanes, haloacetic acids, or adsorbable organic halides in the distribution system.     

Chromium Redox Chemistry in Drinking Water Systems

In order to understand the redox chemistry of chromium at low concentrations (100?μg/L) under conditions typically found in drinking water systems, three reductants and four oxidants were tested in three different waters at pH 5, 7, and 9. In the absence of any oxidant or reductant, Cr(VI) was stable at all three pHs, while Cr(III) precipitated out of solution at pH 9 and greatly impacted the reduction reactions. Stannous chloride was more effective than sodium sulfite or sodium sulfide for reducing Cr(VI) to Cr(III). Sulfide is not likely to be used as a reductant due to the long reaction time (120?h) to achieve the same reduction as SnCl2, while sulfite may be effective at higher doses. The oxidation of Cr(III) by dissolved oxygen and chloramine was very slow, while Cl2 and KMnO4 were effective oxidants under many conditions. A Cl2 residual in a drinking water distribution system may oxidize any soluble Cr(III) to Cr(VI) because of the long contact time, so Cr treatment strategies will need to remove both Cr(III) and Cr(VI).     

Quality Modeling of Water Distribution Systems Using Sensitivity Equations

In this paper, unsteady water quality modeling and the associated sensitivity equations are solved for water distribution systems. A new solution algorithm is proposed, designed for slow varying velocity and based on a time splitting method to separate and solve efficiently each phenomenon such as advection and chemical reaction. This numerical approach allows simultaneous solution of both the direct problem and the sensitivity equations. Special attention is given to the treatment of advection, which is handled with a total variation diminishing scheme. The general model presented in this study permits global sensitivity analysis of the system to be performed and its efficiency is illustrated on two pipe networks. The importance of the sensitivity analysis is shown as part of the calibration process on a real network.     

Institutional Analysis of Infrastructure Problems: Case Study of Water Quality in Distribution Systems

Civil engineers working with public infrastructure face institutional problems, but they are hard to explain and no effective methodology for analyzing them has been available to civil engineers. As applied to public infrastructure, the term “institution” includes more than agencies and organizations, and extends to laws, customs, and management behaviors. A methodology for institutional analysis should provide a systematic way to answer questions about infrastructure that include: what are the laws and controls; what are the incentives; who has control and which roles; and what is the management culture? The methodology is presented and a case study of institutional problems with water quality in distribution systems identifies technical issues and gaps in institutional arrangements that inhibit solutions to them: fragmented authority, inadequate legal controls stemming from poor technical understanding, faulty incentive structures, management cultures, and unclear roles and responsibilities, made worse by difficulties in enabling the players to undertake their responsibilities. It was evident from the case study that unless institutional problems are addressed, progress is not possible on the technical and management issues. Whereas the elements of institutional analysis are not new, the methodology offers a repeatable way to structure the analysis.     

Treating High-Turbidity Water Using Full-Scale Floc Blanket Clarifiers

Dynamic responses of the blanket in full-scale flat-bottom type floc blanket clarifiers at the PingTsan Water Works, Taiwan Water Supply Corporation, were monitored given a step-change in coagulant (polyaluminum chloride, PACl) dosage. The blankets in the clarifiers were easily washed out using the conventional coagulation-clarification process (the “single-stage process”), seriously threatening drinking water quality. Consequently, the PingTsan Water Works included a pretreatment stage before the single-stage process to enhance treatment efficiency. The performance of this full-scale “two-stage process” for treating high-turbidity storm water was monitored on November 9 to 10, 2000. The two-stage process achieved a stable blanket and good quality clarified water that was insensitive to variation in raw water turbidity or PACl dose. Pilot tests were also conducted on October 6 to 7, 2001 to reveal performance differences between the single-stage and two-stage processes in dealing with high-turbidity water. The single-stage process yielded a blanket that was sensitive to PACl change. Not only was the produced blanket easily washed out when the PACl dose was step-decreased, it was also slow to recover when the chemical dosage was returned to its original value. The blanket yielded by the two-stage process was more robust to low coagulant dose, and recovered more easily when coagulant supply was increased. Applying the two-stage process to achieve the same effluent quality from single-stage process could significantly reduce total PACl dosage.     

Steady-State Water Quality Analysis for Pipe Network Systems

In 1993 P. F. Boulos and T. Altman developed an efficient explicit scheme for determining steady state water quality in a distribution system for conservative and zero-order reacting constituents. This approach is extended here to first- and second-order reactions and a general reaction relationship is discussed. Mass balance relationships and nonconservative reaction kinetics lead to a general matrix for constituent analysis. The directed graph that results in steady flow conditions permits single equations to be solved sequentially providing the water quality distribution throughout the system. The method can be used to solve for linear and nonlinear conditions and is demonstrated for first-order decay and growth and second-order decay on a 13-pipe system.