Disinfection By-Product Formation during Long-Term Water Storage in Alaska

In many areas of Northern and Western Alaska, small streams and shallow lakes serve as community raw water supplies. These water supplies freeze completely during winter. In order to supply drinking water during the 6–9 month winter, communities store water that was treated during summer. A chlorine residual is maintained in the stored water. Raw water sources derived from surface water may be heavily laden with dissolved organic matter. At utilities where organic matter escapes treatment, the potential for accumulation of disinfection by-products (DBPs) during storage is a significant health concern. The following study was performed to evaluate this potential threat. Water was collected from five operating utilities, four that normally store water for 6–9 months and one that produces drinking water year-round. Raw, filtered (i.e., unchlorinated) and “finished” (i.e., filtered and chlorinated) water samples were collected during the summer pumping season and stored in the laboratory for 8 months. In order to mimic practice in the field, the chlorine residual was maintained in the finished water for the full storage period. While the concentration of DBPs in the finished water varied over the study period, there was not a statistically significant trend from the third to the eighth month of storage. The observed DBP values were strongly a function of the type of treatment system used. Those systems passing more organic matter had higher DBP values throughout the storage period. The ultraviolet absorbance at 254 nanometers ?start(UV254)end? decreased continuously in the finished water coincident with chlorine consumption. ?startUV254end?, often used as a surrogate for DBPs, remained constant during the entire storage periodin raw and filtered water samples. Filtered water that was stored prior to chlorination accumulated fewer DBPs than finished water that was continuously chlorinated during the storage period. This result suggests that storing filtered water instead of finished water for long periods would limit DBP exposure to consumers. This conclusion was based on a comparison of DBP formation potentials (i.e., raw and filtered water) to DBPs (i.e., finished water). It is important to note that DBP formation potentials are based on a ?start24?hend?chlorine contact time. If long term storage were provided for filtered water, a smaller volume of secondary storage would still be needed to provide contact time for disinfection.     

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.     

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.     

Evaluation of Bacillus Spore Survival and Surface Morphology Following Chlorine and Ultraviolet Disinfection in Water

The objective of this paper is to evaluate the change in Bacillus subtilis spore survival and dimensions following ultraviolet and chlorine disinfection in water. Disinfection was monitored by using tools such as atomic force microscopy (AFM), particle sizing by the electrozone sensing technique and fluorescence of spores after staining with an optical brightener. Results indicated that there was a change in the adsorbed fluorescence following chlorine; however, the magnitude of this change was only approximately twofold at 90% of spore kill. In addition, changes in spore particle-size distribution following chlorine occur at above 99.9% of spore kill. Even the roughness (RMS), width, and length of spores as measured by AFM change only after about 99% of spore killing with chlorine. Use of optical brighteners, AFM, and sizing are not sensitive enough for detecting the disinfection of chlorine-resistant spores and as expected no changes occurred with ultraviolet treated spores. Even though, these techniques may have the potential for determining oxidative disinfection and for the development of monitors and sensors of chemical disinfection for chlorine-sensitive microorganisms.     

MS2 Inactivation by Chloride-Assisted Electrochemical Disinfection

An electrochemical (EC) disinfection system employing an iridium–antimony–tin-coated titanium anode and direct current was used to inactivate bacteriophage MS2 in synthetic solutions with sodium chloride addition. The inactivation data fit the modified Chick–Watson (n ≠ 1) model well. The model indicates that, although better disinfection could be achieved with increases in salt content, contact time, and applied current, these three parameters influence the EC disinfection of MS2 in distinct manners and to different degrees. Compared with chlorination, our EC disinfection system exhibited superior inactivation capability especially with a longer contact time or in the presence of ammonium. The formation of trihalomethanes and haloacetic acids in the EC system was smaller than that from chlorination but a large formation of chlorate ions was observed. These differences indicate that the EC system is likely to produce other potent oxidants that enhance inactivation and alter disinfection by-product formation.     

Evaluation of Characterization Techniques for Iron Pipe Corrosion Products and Iron Oxide Thin Films

A common problem faced by drinking water studies is that of properly characterizing the corrosion products (CP) in iron pipes or synthetic Fe (hydr)oxides used to simulate the iron pipe used in municipal drinking-water systems. The present work compares the relative applicability of a suite of imaging and analytical techniques for the characterization of CPs and synthetic Fe oxide thin films and provide an overview of the type of data that each instrument can provide as well as their limitations to help researchers and consultants choose the best technique for a given task. Crushed CP from a water distribution system and synthetic Fe oxide thin films formed on glass surfaces were chosen as test samples for this evaluation. The CP and synthetic Fe oxide thin films were analyzed by atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive spectroscopy, time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray powder diffractometry (XRD), grazing incident diffractometry (GID), transmission electron microscopy (TEM), selected area electron diffraction, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared, M?ssbauer spectroscopy, Brunauer–Emmett–Teller N2 adsorption and Fe concentration was determined by the ferrozine method. XRD and GID were found to be the most suitable techniques for identification of the mineralogical composition of CP and synthetic Fe oxide thin films, respectively. AFM and a combined ToF-SIMS–AFM approach proved excellent for roughness and depth profiling analysis of synthetic Fe oxide thin films, respectively. Corrosion products were difficult to study by AFM due to their surface roughness, while synthetic Fe oxide thin films resisted most spectroscopic methods due to their limited thickness (118?nm). XPS analysis is not recommended for mixtures of Fe (hydr)oxides due to their spectral similarities. SEM and TEM provided great detail on mineralogical morphology.     

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.     

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.     

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.     

Degradation of Lindane by Zero-Valent Iron Nanoparticles

Thus far, zero-valent iron has been studied mostly for the degradation of structurally simple one- and two-carbon halogenated organic contaminants such as chlorinated methanes, ethanes, and ethenes. In this research, laboratory synthesized particles of nanoscale iron were explored to degrade lindane, also known as γ-hexachlorocyclohexane, a formerly widely utilized pesticide and well-documented persistent organic pollutant. In general, lindane disappeared from aqueous solution within 24?h in the presence of nanoiron concentrations ranging from 0.015?to?0.39?g/L. By comparison, approximately 40% of the initial lindane dose remained in solution after 24?h in the presence of 0.53?g/L of larger microscale iron particles. However, the surface area normalized first-order rate constants were all within the same order of magnitude regardless of dose or iron type. A key reaction intermediate, γ-3,4,5,6-tetrachlorocyclohexene from dihaloelimination of lindane was identified and quantified. Trace levels of additional degradation products including benzene and biphenyl were detected but only in the high concentration experiments conducted in 50% ethanol. While up to 80% of the chlorine from the lindane molecules ended as chloride in water, only 38% of the expected chloride concentration was observed for the microscale iron experiment. This work together with previous published studies on the degradation of polychlorinated biphenyl, chlorinated benzenes, and phenols suggest that zero-valent iron nanoparticles can be effective in the treatment of more structurally complex and environmentally persistent organic pollutants such as lindane.     

Disinfection By-Product Precursor Adsorption as Function of GAC Properties: Case Study

Four different granular activated carbons (GACs) were tested at the bench scale for the adsorption of disinfection by-product (DBP) precursors and were found to be spent at different rates for the Lincoln (Nebraska) water system. This study examined the value of several physical and chemical tests for ranking the potential of different GACs for DBP precursor removal for one water utility. The surface area in the micro- and mesopore range and tannin adsorption were found to be useful indicators of DBP precursor adsorption potential. GACs with the largest surface in the 5?to?50?? pore-width range were able to treat the largest amount of water before being spent. A high value obtained in the tannin adsorption test was observed for the GACs that treated large water volumes.     

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.     

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.     

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.     

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.     

High-Density Polyethylene Membrane Containing Fe0 as a Contaminant Barrier

To improve the performance of polymer-based containment barriers with respect to the breakthrough of chlorinated solvents, a high-density polyethylene (HDPE) membrane containing zero-valent iron (Fe0) nanoparticles was developed as a reactive barrier. The performance of the reactive membrane was evaluated by challenging it with carbon tetrachloride in a diaphragm cell apparatus. In a Fe0/HDPE system, reaction between carbon tetrachloride and Fe0 did not occur due to a lack of water in the polymer matrix. A glycerol-modified Fe0/HDPE membrane successfully increased the lag time before breakthrough by 13–16 fold compared to HDPE alone. Calculations estimate that only 2.5–3.0% of the Fe0 initially present in the membrane reacted before breakthrough of carbon tetrachloride. Extrapolations of these results to practical situations with larger membrane thicknesses and lower contaminant concentrations predict lag times on the order of years.     

Arsenic Removal by a Colloidal Iron Oxide Coated Sand

A novel treatment process for arsenic removal from contaminated groundwater has been developed for use as a reactive barrier or a small drinking water treatment unit. In this study, modified porous media was made by the deposition of colloidal iron oxide onto sand grains at intermediate pH and ionic strength. Kd values from column experiments were 0.016–0.37?L/kg for As(III) and 0.023–0.85?L/kg for As(V), being lower than those of batch experiments (0.50 and 1.30?L/kg for As(III) and As(V), respectively) due to lower availability of surface adsorption sites in the packed column. Media-independent Kd values reflect the enhancement of arsenic adsorption with an increase of colloidal iron oxide coated sand fraction, apparently due to adsorption equilibration during arsenic transport under the same flow column conditions. The heterogeneous composition of two groundwater samples also reduced arsenic adsorption. Therefore, arsenic elution near the initial breakthrough was regulated by available adsorption surface in a porous coated sand media as well as the effects of competing oxyanions. The exhaustion of adsorption capacity near the critical contamination level is sensitive to geochemical and remedial properties of the contaminants.     

Hydraulic Calibration and Fluence Determination of Model Ultraviolet Disinfection System

The objective of this project was to determine the impact hydraulic dispersion has on the calibration of a flow-though model ultraviolet (UV)-disinfection system with chemical actinometry (potassium ferrioxalate) and MS 2 bacteriophage. Fluence was supplied by a medium-pressure ultraviolet lamp to a quartz tube (19 mm diameter) situated in a ventilated galvanized casing. The UV lamp was attached to a vertical position guide, for UV fluence to be varied by positioning the UV lamp at various vertical heights above the quartz tube. Water was pumped through the quartz tube at rates of 100–300 mL/min. An in-line pipe mixer was installed prior to the UV system to ensure adequate mixing with the bulk liquid and chemical actinometer and to mitigate jet formation within the quartz tube. Tracer studies were conducted with and without the in-line mixer using potassium chloride (3 mM). Dispersion coefficients were obtained from the tracer study and incorporated into an axial-dispersion model to determine the rate coefficient of potassium ferrioxalate in the model UV system. A numerical model was used to determine the fluence supplied by the lamp with a reduction in exposure time. After dispersion and kinetics are accounted for within the UV system, the model predicted UV fluence that was in general agreement with UV design curves for inactivation MS 2 bacteriophage. The differences in the design curves and the fluence–response model in the present investigation were found to be related to the experimental errors introduced from using a flowing system and because a medium pressure lamp was used in the present investigation.     

Impact of Booster Chlorination on Chlorine Decay and THM Production: Simulated Analysis

The effect of conventional and booster chlorination on chlorine residuals and trihalomethane (THM) formation in drinking water distribution systems was modeled using the EPANET hydraulic modeling software. The model results suggest that booster chlorination may allow utilities to meet disinfection goals better by carrying chlorine residuals to remote points in the distribution system while lowering the total mass of chlorine applied to the system. The model results suggest that booster chlorination may provide the greatest advantages to points in the distribution system located near storage tanks by providing a more consistent chlorine residual and possibly reducing THM formation. A new version of the EPANET model, the EPANET Multispecies model, was also used to compare chlorine decay due to reactions in the bulk fluid and reactions occurring at the pipe wall. The results suggest that chlorine decay due to wall reactions can be very significant at remote points in the distribution system. Additionally, if THMs are assumed to form primarily through reactions in the bulk fluid, use of the new EPANET Multispecies software allows for calculation of THM formation based solely on chlorine reactions in the bulk fluid rather than on overall chlorine decay.