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.     

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.     

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.     

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.     

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.     

Electrochemical Wastewater Disinfection: Identification of Its Principal Germicidal Actions

Laboratory experiments were carried out to investigate the mechanisms of electrochemical (EC) wastewater disinfection. Artificial wastewater contaminated by Escherichia coli (E. coli) culture, and which contained different salts of NaCl, Na2SO4, and NaNO3, was used as the test medium. The experimental results do not favor the hypotheses that the EC bactericidal action was due to cell destruction by the electric field and the production of persulfate. In comparison to direct chlorination, the EC process displayed a much stronger disinfecting capability than that of electrochlorination assumed for EC disinfection. Observations with scanning electron microscopy on the E. coli bacteria of wastewater treated by different means of disinfection suggested that the cells were likely killed during the EC treatment by chemical products with oxidizing and germicidal powers similar to that of ozone and much stronger than that of chlorine. All of the findings support the theory that the major killing function of EC disinfection is provided by short-lived and high-energy intermediate EC products, such as free radicals.     

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.     

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.     

Trihalomethane and Haloacetic Acid Disinfection By-Products in Full-Scale Drinking Water Systems

Trihalomethane (THM), haloacetic acid (HAA5), and total organic carbon (TOC) data provided by the Missouri Dept. of Natural Resources for drinking water treatment systems in the State of Missouri was analyzed for the years 1997–2001. These data indicated that a significant portion of systems exceeded the current regulatory limits of 80 and 60?μg/L for THM and HAA5 in these years. The vast majority of the treatment plants exceeding the regulatory limits were small plants with service populations less than 10,000 people. No significant temporal trend in either THM or HAA5 was noted for the years 1997–2001. This work suggests that the proposed use of a locational running annual average may have a significant effect on compliance. The use of chloramines (combined chlorine) versus free chlorine (HOCl/OCl?) as a residual disinfectant was shown to significantly reduce both THM and HAA5 in systems that treat their own water (primary systems), but did not have a significant effect in systems which purchase their water from primary systems (secondary systems). Comparison of finished water at the treatment plant versus in the distribution system suggested that a majority of THM and HAA5 may be produced within the plant as opposed to the distribution system. Hence, reducing these chlorinated disinfection byproducts within the treatment plant itself should be a key focus for achieving compliance, and supports Environmental Protection Agency disinfection byproducts compliance guidelines using enhanced coagulation.     

Verification of Full-Scale Ozone Contactor Inactivation Performance Using Biodosimetry

A biodosimetric technique was used to verify the concentration-contact time (CT) values [CT10, CT integrated disinfection design framework (CT-IDDF), CT segregated flow analysis (CT-SFA)] of the ozone contactors of the DesBaillets water treatment plant (Montreal), using indigenous aerobic spore formers (ASFs) as indicators of disinfection efficiency. ASF measurement in ozonated water was performed using a large water sample concentration method. Four assays, completed over a 6-week period, involved the implementation of biodosimetric calibration curves using an ozone pilot apparatus and followed by full-scale verifications. ASF inactivation kinetics were well described by a simple Chick–Watson model. The most accurate data also indicated that the CT10 underestimates the effective CT (by 1.2–1.9-fold), whereas the CT-IDDF and CT-SFA overestimate it (by 1.0–1.7-fold and 0.9–1.5-fold, respectively). Underestimation from CT10 was more pronounced with increased ozone dose while overestimation from CT-IDDF and CT-SFA is most likely due to the difficulty in obtaining a representative ozone residual profile within the contactor. The use of segregated flow analysis provided the best estimate of disinfection performance. Biodosimetry is useful in measuring the effective CT transferred, in verifying model predictions, and in determining the influence of water quality on microbial inactivation.     

Trihalomethane Species Forecast Using Optimization Methods: Genetic Algorithms and Simulated Annealing

Chlorination is an effective method for disinfection of drinking water. Yet chlorine is a strong oxidizing agent and easily reacts with both organic and inorganic materials. Trihalomethanes (THMs), formed as a by-product of chlorination, are carcinogenic to humans. Models can be derived from linear and nonlinear multiregression analyses to predict the THM species concentration of empirical reaction kinetic equations. The main objective of this study is to predict the concentrations of THM species by minimizing the nonlinear function, representing the errors between the measured and calculated THM concentrations, using the genetic algorithm (GA) and simulated annealing (SA). Additionally, two modifications of SA are employed. The solutions obtained from GA and SA are compared with the measured values and those obtained from a generalized reduced gradient method (GRG2). The results indicate that the proposed heuristic methods are capable of optimizing the nonlinear problem. The predicted concentrations may provide useful information for controlling the chlorination dosage necessary to assure the safety of water drinking.     

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.     

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.     

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.     

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.     

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.     

Remediation of TCE-Contaminated Groundwater in a Sandy Aquifer Using Pulsed Air Sparging: Laboratory and Numerical Studies

The objective of this study was to investigate, through laboratory and numerical investigations, the effectiveness of a pulsed air sparging system for remediation of groundwater contaminated with trichloroethylene (TCE) in a sandy aquifer. In laboratory experiments, air was pulsed into TCE source zone on a daily basis in order to remediate TCE-contaminated groundwater. Most dissolved TCE was removed at the end of experiments although its concentrations fluctuated due to the air pulsing. The measured gaseous phase TCE concentration increased whereas the aqueous phase TCE concentration decreased during air sparging pulses. Experimental data were assessed by using a numerical code STOMP (subsurface transport over multiphases) with some modification based on the TCE dissolution kinetics. The unmeasured residual TCE mass was predicted through numerical simulations. Results show that aqueous concentrations for TCE are still much higher than the maximum contaminant level in spite of successful removal of 95% of residual TCE. It may imply that it would be more appropriate to apply air sparging combined with other remediation technologies such as bioremediation for remediation of TCE-contaminated groundwater.     

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.     

A New Kinetic Model for Ultraviolet Disinfection of Greywater

Ultraviolet (UV) disinfection of greywater has a number of advantages for small scale applications, but the UV disinfection efficiency can be impeded by high levels of particulates and chemicals in the greywater, micro-organism aggregation, and the geometry between the UV lamp and surrounding sleeve leading to suboptimal flow paths through the lamp assembly. Most process models for UV systems are empirical in nature and do not adequately represent the distribution of UV dose that is actually delivered to micro-organisms in a continuous flow system. This paper presents a model which incorporates: (1) variations in micro-organism sensitivity to UV radiation, (2) the variation of dose received in the UV reactor chamber, and (3) the shielding effect of part of the micro-organism population by the presence of particulates. The model is capable of predicting the asymptotic decay observed in bacterial survival curves when organisms are exposed to a UV dose in a greywater matrix and has been calibrated using experimental data on a series of synthetic greywaters of differing composition and validated against a series of real greywater samples. The model compares favorably to other UV disinfection models and allows the influence of water quality parameters such as turbidity, suspended solids, and UV absorbance to be examined. This allows water quality limits to be defined beyond which the UV disinfection of greywater becomes ineffective. Acceptable performance criteria are established for low power UV systems for the treatment of greywater, which have implications for the selection of suitable annular UV reactors.     

Impact of Particle Aggregated Microbes on UV Disinfection. I: Evaluation of Spore–Clay Aggregates and Suspended Spores

Aggregation of microbes with particles can reduce the effectiveness of ultraviolet (UV) disinfection. This study evaluated the comparative impact of dispersed spores, dispersed spores mixed with clay particles (nonaggregated), spore–spore aggregates, and spore–clay aggregates on UV disinfection performance in simulated drinking waters. Aggregates were induced by flocculation with alum and characterized by particle size analysis (count, volume, and surface area) of dispersed and aggregated systems, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. It was concluded that spores within aggregates of the spore–clay system were protected from UV irradiation compared to nonaggregated spores and the difference between these systems was found to be statistically significant throughout the UV range tested. In addition SEM-EDX analysis suggested that aggregate composition is nonhomogeneous with respect to the ratio of spores and clay particles among aggregates. It was estimated that 30–50% of the spores in the aggregates tested were protected from UV irradiation.