Issue Papers for AwwaRF Project 3116 Strategy to Manage ...K. ozaena Adapted from Geldreich and...

Issue Papers for AwwaRF Project 3116 “Strategy to Manage and Response to Total Coliforms and E. coli in the

Distribution System” AwwaRF 3116 (to be published in 2009) provides practical guidelines to help utilities investigate, manage, and respond to total coliform and E. coli occurrences in the distribution system. The Project Team developed five issue papers to describe the status of the following relevant topics:

• Source of Coliforms and Causes of Coliform Positives, • Fate and Transport of Coliform in the Distribution System, • Evaluation of Coliform Monitoring Techniques and Comparison of Indicators, • Use and Application of Source Tracking Tools in Drinking Water, and • Tools and Methods Using Utility Data for Identifying Causes of Coliform

Occurrences. Each paper provides background information on the given topic, describes research findings, and identifies gaps in the current understanding of coliform management. Each paper is meant to serve as a “stand-alone” document, providing the reader with broad discussion of the topic. As such, repetition may be present between papers.

©2008 AwwaRF. ALL RIGHTS RESERVED

SOURCES OF COLIFORM BACTERIA AND CAUSES OF COLIFORM OCCURRENCES IN DISTRIBUTION SYSTEMS

November 2007

By: Mark W. LeChevallier, Ph.D.

Director, Innovation & Environmental Stewardship American Water

Voorhees, NJ 08043

An Issue Paper Developed for AwwaRF 3116 – Strategy to Manage and Respond to Total Coliforms and E. coli in the Distribution System

Principal Investigator: Melinda Friedman

Co-Principal Investigator: Mark LeChevallier AwwaRF Project Manager: John Albert

FINAL


AwwaRF 3116 and AwwaRF 4130 i Attachment 2 Periodic Report No. 7

Introduction to AwwaRF 3116 Issue Papers This issue paper was developed as part of AwwaRF Project 3116 Strategy to Manage and Response to Total Coliforms and E. coli in the Distribution System. AwwaRF 3116 (to be published in 2009) provides practical guidelines to help utilities investigate, manage, and respond to total coliform and E. coli occurrences in the distribution system. The Project Team developed five issue papers to describe the status of the following relevant topics:

• Source of Coliforms and Causes of Coliform Positives, • Fate and Transport of Coliform in the Distribution System, • Evaluation of Coliform Monitoring Techniques and Comparison of Indicators, • Use and Application of Source Tracking Tools in Drinking Water, and • Tools and Methods Using Utility Data for Identifying Causes of Coliform Occurrences.

Each paper provides background information on the given topic, describes research findings, and identifies gaps in the current understanding of coliform management. Each paper is meant to serve as a “stand-alone” document, providing the reader with broad discussion of the topic. As such, repetition may be present between papers.


AwwaRF 3116 and AwwaRF 4130 1 Attachment 2 Periodic Report No. 7

SOURCES OF COLIFORM BACTERIA AND CAUSES OF COLIFORM OCCURRENCES IN DISTRIBUTION SYSTEMS

SCOPE AND OBJECTIVES The objective of this “white paper” is to review the relevant literature pertaining to the sources and causes of coliform bacterial occurrence in drinking water. The paper is complementary to the companion paper on fate and transport of coliform bacteria. Because the two topics are clearly linked there is some inevitable overlap, but efforts have been made to try to minimize this. This paper focuses on the principle mechanisms by which coliform bacteria occur in finished drinking water; break through treatment, regrowth, or recontamination after treatment. The companion paper on fate and transport of coliform bacteria focuses on how these organisms survive disinfection and are transported through the distribution system. Because coliform bacteria are similar in physiology and survival to many hetrotrophic plate count (HPC) bacteria (like Pseudomonas spp.), some HPC results are used to illustrate some principles related to growth and survival, however, where possible comparative data are provided for coliform bacteria.

SOURCES OF COLIFORM BACTERIA Total coliform bacteria (a subset of Gram-negative bacteria) are used primarily as a measure of water supply treatment effectiveness and can occasionally be found in water supplies. Origins of total coliform bacteria can include untreated surface and groundwater, vegetation, soils, insects, and animal and human fecal material. Typical coliform bacteria found in drinking water systems include Klebsiella pneumoniae, Enterobacter aerogenes, Enterobacter cloacae, and Citrobacter freundii. Other typical species and genera are shown in Table 1.

Table 1 Coliform Isolates Typically Found in Drinking Water

Citrobacter C. freundii C. diversus

Escherichia E. coli

Enterobacter E. aerogenes E. agglomerans E. cloacae

Klebsiella K. pneumonia K. oxytoca K. rhinoscleromatis K. ozaena

Adapted from Geldreich and LeChevallier, 1999. ©1999. The McGraw-Hill Companies, Inc. Thermotolerant coliforms (capable of growth at 44.5 oC), also termed “fecal coliforms” have a higher association with fecal pollution than total coliforms. Escherichia coli, however, is considered even more directly related to fecal pollution as it is commonly found in the intestinal track of warm-blooded animals. Although most fecal coliform and E. coli strains are not pathogenic, some strains are invasive for intestinal cells and can produce heat-labile or heat-stable toxins (AWWA, 2006).



MECHANISMS OF COLIFORM OCCURRENCE

Fundamentally, there are three basic mechanisms by which coliform bacteria occur in treated drinking water: (1) coliforms break through the treatment process from the source water supply, (2) coliforms regrow, typically in biofilms, from very low initial levels, and (3) organisms result from a recontamination of the treated water within the distribution pipeline system. These mechanisms are incorporated in the concept of multiple barriers for water treatment, the cornerstone of sanitary engineering. These barriers are selected to duplicate removal capabilities by succeeding process steps. In this way, sufficient backup systems are available to permit continuous operation in the face of normal mechanical failures. Traditionally, the barriers have included:

• Source water protection • Coagulation, flocculation, sedimentation • Filtration • Disinfection • Protection of the distribution system

For the past several decades, drinking water regulations have largely focused on the primary treatment process for controlling coliforms in potable water supplies. The Surface Water Treatment Rule (SWTR), the Total Coliform Rule, the Interim Enhanced SWTR, the Long-Term 1 and the proposed Long-Term 2 SWTR, and the Groundwater Rule have emphasized turbidity reduction and/or adequate disinfection as principal components for microbial treatment (USEPA, 1989a,b, 1990, 1991, 1996, 1998, 2000) (Groundwater systems may or may not include the coagulation, flocculation, sedimentation or filtration steps; depending on source water quality). When properly applied, these regulations can control most microbes of concern, with the some uncertainty for Cryptosporidium (Aboytes and LeChevallier, 2004).

PRIMARY TREATMENT The “multiple barrier” and “hazard analysis and critical control points” concepts of water treatment are used to provide a framework for evaluating microbial control measures. These approaches have value because they focus attention on key process steps (e.g., coagulation, filtration, and disinfection), important for ensuring the microbial safety of water. Many of the current water treatment practices already employ these concepts (e.g., CT values for disinfection, or effluent turbidity monitoring), although it is likely that future regulations will continue to codify these approaches. Processes for removal of microbes from water include pretreatment, coagulation/flocculation/ sedimentation, and filtration. Pretreatment can broadly be defined as any process to modify microbial water quality prior to, or at the entry of, the treatment plant. Pretreatment processes include application of roughing filters, microstrainers, off-stream storage, or bank infiltration, each with a particular function and water quality benefit. These pretreatment processes have a range of applications, from removal of algal cells or pretreatment of high turbidity spikes, to effective removal of coliforms, viruses and protozoan cysts.



For conventional treatment processes, proper chemical coagulation is critical for effective removal of microbes including coliform bacteria. When properly performed, coagulation, flocculation, and sedimentation can result in 1-2 log removals of bacteria (including coliforms), viruses, and protozoa. High-rate clarification using solids contact clarification, ballasted-floc, or contact clarification systems can be as, or more, effective than conventional basins for removal of microbes. Dissolved air flotation can be particularly effective for removal of algal cells and Cryptosporidium oocysts. Lime softening can provide good treatment for coliform bacteria through a combination of inactivation by high pH and removal by sedimentation. Granular media filtration is widely used in drinking water treatment, and removes coliforms through a combination of physical-hydrodynamic properties and surface and solution chemistry. Without proper chemical pretreatment, rapid rate filtration works as a simple strainer and is not an effective barrier for microbial pathogens. Under optimal conditions the combination of coagulation, flocculation, sedimentation, and granular media filtration can result in 4 logs or better removal of protozoan pathogens. Slow sand filtration works through a combination of biological and physical-chemical interactions. The biological layer, termed, schmutzdecke, is an important component for effective removal of microbial pathogens by slow sand filtration. Precoat filtration was initially developed as a portable unit to remove Entamoeba histolytica, a protozoan parasite. In precoat filtration, water is forced under pressure or by vacuum through a uniformly thin layer of filtering material, typically diatomaceous earth. As with granular media filtration, proper chemical conditioning of the water improves the treatment efficiency of precoat filtration. In contrast, membrane filtration removes microbial pathogens primarily by size exclusion (without the need for coagulation), with effective removal of microbes larger than the membrane pore size. Studies have shown that at various times during a filter run cycle, both before and immediately after backwashing, particles enter distribution water (Amirtharajah and Wetstein, 1980). Robeck et al. (1962) demonstrated that bacterial and viral penetration through a granular filter accompanied floc breakthrough. Bucklin et al. (1991) reported coliform bacterial counts as high as 60 cfu/100 mL during the filter ripening period following backwash. Significantly, filter turbidity values never exceeded 0.4 NTU and the coliform bacteria were only detected on media designed to detect injured coliforms (mT7 agar). Similar results were reported by McFeters et al. (1986) where injured coliform bacteria were detected in the treatment plant effluent, but became detectable on conventional media after resuscitation in the distribution system. Coliform bacteria have been detected in some filter media. Camper et al. (1986), examined the fines released from carbon filters and found that over 17% of the samples (MPN analyses) contained carbon particles colonized with coliform bacteria. In some instances, high levels of coliform bacteria (1,194 coliforms per sample) were recovered from the carbon fines. Significantly, 28% of the coliform organisms exhibited the fecal biotype. Similar results have been reported by Stewart et al. (1988) and although few coliform bacteria were detected in their system, on one occasion a fecal coliform (Klebsiella pneumoniae) was found attached to carbon particles released from the GAC filter. However, Camper et al. (1986) report that none of the systems they studied which released colonized carbon particles had a history of coliform problems.



Oxidants may be added to water for a variety of purposes, including control of taste and odor compounds, removal of iron and manganese, Zebra Mussel control, and particle removal, among others. For coliform bacteria, application of strong oxidizing compounds such as chlorine, chlorine dioxide, or ozone will also result in cellular inactivation through a variety of chemical pathways. Principle factors that influence inactivation efficiency are the disinfectant concentration, contact time, temperature, and pH. The concept of disinfectant concentration and contact time is integral to the practical application of the CT concept (disinfectant concentration multiplied by the contact time). CT data for free chlorine, chlorine dioxide, ozone for E. coli indicate that all are capable of rapid inactivation of coliform bacteria (Table 2). Monochloramine will inactivate coliform bacteria more slowly. Ultraviolet light (UV) inactivates microorganisms through reactions with microbial nucleic acids, and is particularly effective for control of Cryptosporidium and many vegetative cells including coliform bacteria (Hijnen et al. 2006).

Table 2 Comparative Efficiency of Disinfectants for the Production of

99% Bacterial Inactivation in Oxidant Demand-Free Systems1

Escherichia coli HPC Bacteria

Disinfectant Agent

pH Temperature (°C)

CT (mg⋅min)/L

pH Temperature (°C)

CT (mg⋅min)/L

Hypochlorous acid 6.0 5 0.04 7.0 1-2 0.08 ± 0.02 Hypochlorite ion 10.0 5 0.92 8.5 1-2 3.3 ± 1.0 Chlorine dioxide 6.5 20 0.18 7.0 1-2 0.13 ± 0.02 6.5 15 0.38 8.5 1-2 0.19 ± 0.06 7.0 25 0.28 Monochloramine 9.0 15 64 7.0 1-2 94.0 ± 7.0 8.5 1-2 278 ± 46.0

1 Adapted from LeChevallier et al. (LeChevallier et. al., 1988) Available research has shown that increased resistance to disinfection may result from the attachment of microorganisms to or the association of microorganisms with various surfaces, including macroinvertebrates (Crustacea, Nematoda, Platyhelminthes and Insecta) (Levy et. al., 1984,Tracy et. al., 1966), turbidity particles (,LeChevallier et. al., 1981,Ridgway and Olson, 1982), algae (Silverman et. al., 1983), carbon fines (Camper et. al., 1986,LeChevallier et. al., 1984) and glass (Olivieri et. al., 1985). Ridgway and Olson (Ridgway and Olson, 1982) have shown that the majority of viable bacteria in chlorinated drinking water are attached to particles. Presumably, microbes entrapped in particles or adsorbed onto surfaces (Figure 1) are shielded from disinfection and are not inactivated (LeChevallier et al., 1988).



Figure 1. Examples of biofilms on particle surfaces.

GROWTH Growth is the increase in bacterial numbers in the distribution system due to cell reproduction. Significant growth always occurs at the expense of an organic or inorganic substrate. Most coliform growth is thought to occur in biofilms on distribution pipe surfaces (Figure 1). Biofilm refers to an organic or inorganic deposit consisting of microorganisms, microbial products, and detritus at a surface (Marshall, 1976; Characklis, 1981; Safe Drinking Water Committee, 1982). Biofilms may occur on pipe surfaces, sediments, inorganic tubercles (a nodular or knobby outgrowth on a pipe surface), suspended particles, or virtually any substratum immersed in the aquatic environment. (LeChevallier, 2005) Biofilms in drinking water pipe networks can be responsible for a wide range of water quality and operational problems. Biofilms contribute to loss of distribution system disinfectant residuals, increased bacterial levels, reduction of dissolved oxygen, taste, and odor changes, red or black water problems due to iron or sulfate-reducing bacteria, microbial-influenced corrosion, hydraulic roughness, and reduced materials life (Characklis and Marshall, 1990).

Microorganisms in biofilms can include bacteria (including coccoid [round], rod-shaped, filamentous, and appendaged bacteria), fungi, and higher organisms such as nematodes, larvae, and Crustacea. Recently, researchers have shown that viruses and parasites such as Cryptosporidium can be trapped in biofilms (Quignon, et al. 1997; Piriou et al., 2000). Although viruses and Cryptosporidium do not grow in a biofilm, they can attach to biofilms after a contamination event. Therefore, it is important to thoroughly flush the distribution system to remove these organisms following a contamination event.

Coliform growth may be related to (1) environmental factors such as temperature and rainfall, (2) the availability of nutrients, (3) the ineffectiveness of disinfectant residuals, (4) corrosion and sediment accumulation, (5) hydraulic effects (Table 3). These

Table 3. Factors associated with coliform growth/occurrence in drinking water: • Treatment process, filtration • Temperature • Disinfectant type, concentration • Biodegradable organic matter • Pipe material, corrosion • Water chemistry • System maintenance, flushing • Flow velocity, reversal, hydraulic shear



factors have been summarized in a number of reviews (LeChevallier, 1990; LeChevallier et al., 1996; Volk and LeChevallier, 2000).

Treatment Processes The types of processes used to treat source water can greatly impact the biological stability of drinking water supplies. Groundwaters are typically stable (e.g., little change in bacterial levels) due to the natural percolation of water through the soil environment. However, the presence of methane, ferrous iron, reduced sulfur compounds, hydrogen gas, manganese, ammonia, and nitrite can serve as either carbon or energy sources that can promote growth of certain microbes (Hutchinson and Ridgway, 1977). In some cases, excess ammonia levels have been related to serious bacterial growth problems (Rittmann and Snoeyink, 1984; Wolfe et al., 1988). Surface water treatment processes, including the type of coagulant, clarification process, filter media, and disinfection regime, can alter the biological stability of treated water (Volk and LeChevallier, 2000). Application of nano-membrane filtration can be effective for removal of many inorganic and large molecular weight carbon molecules, but small molecular weight substances may serve as nutrients for coliform growth (Escobar and Randall, 1999). Unfiltered surface water supplies were found to be particularly susceptible to coliform growth (LeChevallier et al., 1996). Temperature On average, the occurrences of coliform bacteria are significantly higher when water temperatures are > 59oF (15oC) (Figure 2). However, the minimum temperature at which coliform activity is observed varies from system to system. Systems that typically experienced cold water may have increases in coliform occurrences when water temperatures were near 50oF (10oC). The strains of coliform bacteria in these systems may be better adapted to grow at lower temperatures (psychrophiles).

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cfu/100 mL

% Positive

Figure 2. Relationship between monthly average water temperature and coliform occurrence.

From (LeChevallier et al., 1996, Reprinted with permission from the American Society for Microbiology)



Disinfectant Residual and Disinfectant Level Systems that maintain low or no disinfectant residual may experience occurrences of coliform bacteria. LeChevallier et al. (1996) recommended maintaining at the far ends of the distribution system at least 0.2 mg/L free chlorine or 0.5 mg/L chloramines to limit coliform occurrences. Additionally, the type of disinfectant can influence coliform occurrences. LeChevallier et al. (1996) reported that systems that used free chlorine had 0.97% of 33,196 samples containing coliform bacteria, while 0.51% of 35,159 samples from chloraminated systems contained coliform bacteria (statistically different at p


during months when coliforms were not recovered on the standard m-Endo medium. Conversion of the disinfectant to chloramines in June 1993 resulted in dramatic decreases in coliform occurrences measured by both m-Endo and m-T7 media, and the bacteria were not detected in the finished drinking water for the 3 years following the change (Norton and LeChevallier, 1997). In addition to the type of disinfectant used, the residual maintained at the end of the distribution system was also associated with coliform occurrences (LeChevallier et al., 1996). Figure 4 shows that results of a utility in Utah that experienced coliform occurrences when free chlorine levels were 0.2 mg/L.



AOC and BDOC Levels AOC is determined using a bioassay (Van der Kooij, 1990, 1992) and measures the microbial response to biodegradable materials in water. The presence of biodegradable organic matter (BOM) in water has been associated with coliform growth in drinking water. BOM is commonly measured as AOC or biodegradable dissolved organic carbon (BDOC). AOC levels (Figure 6) in 940 North American drinking water systems ranged from 20 to 214 µg/L, median 100 µg/L (LeChevallier et al., 1996; Volk and LeChevallier, 2000). BDOC is the difference in the concentration of DOC before and after bacterial growth in a sample and measures the amount of nutrient readily available for bacterial growth (Joret and Levi, 1986). Levels of BDOC in 30 North American water systems (Figure 7) ranged from 0 to 1.7 mg/L, with a median level of 0.38 mg/L (Volk and LeChevallier, 2000).

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Percent Occurrence

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BD

OC

mg/

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Figure 5. BDOC levels in 30 North American water systems

1 11 21 31 41 51 61 71 81 91

Number of Utilities

0

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100

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200

250

AO

C (µ

g/L)

P17 NOX Total AOC

Figure 4. AOC levels in 94 North American water systems. Utilities are numbered 1 through 94 along x axis. Source: Volk and LeChevallier 2000. Reprinted with permission from the American Water Works Association.



High levels of AOC can stimulate coliform growth in distribution system biofilms (LeChevallier et al., 1996; Volk and LeChevallier, 2000). On average, free chlorinated systems with AOC levels greater than 100 μg/L had 82% more coliform-positive samples, and the coliform densities were 19 times higher than in free chlorinated systems with average AOC levels less than 99 μg/L. However, high levels of AOC alone do not dictate the occurrence of coliform bacteria in drinking water but are only one factor. Figure 8 illustrates a decision tree that graphically depicts combinations of threshold values above which the probability of coliform occurrence is increased (Volk and LeChevallier, 2000). As more of the threshold values are

exceeded (temperature, AOC level, disinfectant residual), the probability of coliform occurrences is increased. In systems that do not maintain a disinfectant residual, very low AOC levels (15oC, AOC levels >100 µg/L, and disinfectant residual


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U tica, N YO ldequipm entfa ils

Tem porarylim einterruption

O perational problem spH contro l incom plete

Newequipm entInsta llationincom ple te

Corrosion contro l consistent

Figure 11. Example of improved corrosion control for limiting

coliform occurrences.

Corrosion Control and Pipe Materials Corrosion of iron pipes can influence the effectiveness of chlorine-based disinfectants for inactivation of biofilm bacteria (LeChevallier et al., 1990, 1993). Therefore, the choice of pipe material and the accumulation of corrosion products can dramatically impact the ability to control the effects of biofilms in drinking water systems. Figure 9 shows average monthly corrosion rates (in milles [thousandth of an inch] per year) from a system in Illinois (Volk et al., 2000). The conventional plant effluent corrosion rate showed marked seasonal variations. Corrosion rates were highest during the summer months when, traditionally, the incidence of coliform occurrences is the highest. Increasing the phosphate dose during the summer months (test data) lowered the corrosion rate. Similar seasonal variations have been observed in other systems (Norton and LeChevallier, 1997). This variation in corrosion rates is important because the corrosion products react with residual chlorine, preventing the biocide from penetrating the biofilm and controlling coliform growth. Studies have shown that free chlorine is impacted to a greater extent than monochloramine, although the effectiveness of both disinfectants is impaired if corrosion rates are not controlled (LeChevallier et al., 1990, 1993). Increasing the phosphate-based corrosion inhibitor dose, especially during the summer months, can help reduce corrosion rates (Figure 9). Full-scale studies have shown higher coliform occurrences when corrosion rates increased, especially during the summer months (Figure 10). Figure 11 shows the results for another system where a series of improvements were necessary to reliably feed lime for corrosion control. When corrosion control was consistent, coliform levels were low, but increased during a temporary interruption of the lime feed. In addition to the level of generalized corrosion, localized pitting can also provide a protective habitat for bacterial proliferation. The pitting of certain metal pipes can be accelerated by high levels of

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phat

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Figure 9. Increasing phosphate levels can reduce

corrosion rates. Abbreviations: PE, plant effluent; Test, side stream test reactor; PO4, phosphate residual.

Figure 10. Relationship between corrosion rates and

coliform occurrences.



Figure 7. Localized pitting corrosion can provide a habitat for coliform bacteria. Source: LeChevallier 1993. Reprinted with permission from the American Water Works Association

chloride and sulfate. The ratio of chloride and sulfate to bicarbonate levels is known as the Larson index and can indicate the propensity for pitting corrosion (Figure 12). Research has shown (LeChevallier et al. 1993) that consideration of the level of generalized corrosion, Larson index, corrosion inhibitor, and disinfectant residual is necessary to accurately predict the inactivation of biofilm bacteria (Table 5).

Studies have shown that the Larson index can vary seasonally in drinking water systems, with the highest levels occurring during the summer months (LeChevallier et al. 1993). Factors that can influence the Larson index include anything that increases chloride or sulfate levels (chlorine disinfection, aluminum or ferric salts) or changes the alkalinity of the water (lime, soda ash, and sodium bicarbonate have a positive influence; hydrofluosilicic acid, chlorine gas, and certain coagulants depress alkalinity).

Table 5. Multiple Linear Regression Model for Monochloramine Disinfection of Biofilm Bacteria

Coefficient

Standard Error

t-

Statistic

Significance Level

Log reduction viable counts= Intercept

-1.0734

0.5685

-1.888

0.0816

Log Larson Index

-0.5808

0.1963

-2.958

0.0111

Log Corrosion Rate

-0.4820

0.3205

-1.504

0.1566

Log Monochloramine

2.0086

0.9226

2.177

0.0485

Phosphate Level

0.1445

0.0336

4.295

0.0009

Corrected R-Squared:

0.746

F test:

13.474

Model is based on 18 observations

Adapted from LeChevallier et al. 1993. Reprinted with permission from the American Water Works Association Distribution system maintenance, cleaning, relining of corroded pipes, and flushing of accumulated sediments and debris can help reduce the habitats where bacteria grow in water systems. However, these procedures must be routinely implemented, because they do not change the underlying mechanisms by which bacteria were initially growing in the water supply. In one study (LeChevallier et al., 1987), coliform bacteria reappeared within 1 week after flushing a section of a distribution system, presumably because the organisms were

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Corrosion control improved

Figure 8. Example of improved distribution system

flushing, corrosion control, and tank maintenance for control of coliform regrowth.



growing in other parts of the pipe network. Figure 13 demonstrates one utility experience with a comprehensive coliform control plan. Implementation of increased chlorine residuals, improved corrosion control, annual flushing and storage tank maintenance were all necessary to reduce the occurrences of coliform bacteria. Residence Time and Hydraulic Effects Whenever drinking water stagnates, microbial water quality degrades. Therefore, an increase in hydraulic residence time is an important factor related to coliform growth. With long residence times, chlorine residual tends to dissipate, water temperatures rise, and bacterial levels increase. Increases in coliform occurrences have been related to distribution systems with a large number of storage tanks (LeChevallier et al., 1996; Hanson et al., 1987). Stagnation of water in service lines can also result in high bacterial counts at the customers’ tap (Brazos et al., 1985; LeChevallier et al., 1987). When water velocity slows in these areas, sediments can precipitate, creating habitats for coliform growth. Donlan and Pipes (1988) showed that water velocity had an inverse relationship on biofilm counts. Increasing reservoir turnover, looping dead-end pipes, and flushing stagnant zones can help reduce hydraulic residence times. Occasionally, mistakenly closed valves can create artificial dead-end pipelines. A routine flushing and valve maintenance program is helpful for identifying closed valves and improving the circulation in the distribution system.

Reversal of water flows within the distribution system can shear biofilms and water hammer can dislodge tubercles from pipe surfaces (Lehtola et al. 2006). Opheim et al. (1988) found that bacterial levels in an experimental pipe system increased 10 fold when flows were started and stopped. Larger releases of bacteria were noted when the system was exposed to physical and vibrational forces.

DISTRIBUTION SYSTEM RECONTAMINATION Cross-Connection A cross-connection is any mechanism by which nonpotable water contaminates treated drinking water supplies. A cross-connection has been defined as “any unprotected actual or potential connection or structural arrangement between a public or private potable water system, and any other source or system through which it is possible to introduce into any part of the potable system any used water, industrial fluids, gas, or substance other than the intended potable water with which the potable system is supplied” (USC FCCCHR, 1993). Backflow is any unwanted flow of nonpotable water or other substances from any domestic, industrial, or institutional piping system back into the potable water distribution system. Backflow may be due to backsiphonage (a backflow caused by negative or subatmospheric pressure in the supply piping) or backpressure (a flow caused when a potable system is connected to a nonpotable supply operating under a higher pressure). Cross-connections and backflow have been identified as potentially significant contributors to the spread of waterborne disease and illness (USEPA, 2002). The US Environmental Protection



Agency (USEPA) compiled information on 469 backflow incidents that occurred in the United States between 1970 and 2001. For data compiled between 1981 and 1998, 57 cases were investigated by the US Centers for Disease Control and Prevention and it was found that cross-connections resulted in identified waterborne disease outbreaks of 9,734 illnesses. These included 20 outbreaks (6,333 cases of illness) caused by microbiological contamination, 15 outbreaks (679 cases of illness) caused by chemical contamination, and 22 outbreaks (2,722 cases of illness) where the contaminant was not reported. The majority of documented cross-connection events are recognized because they resulted in illness, typically gastrointestinal disorders, but a few cross connection events resulted in deaths. Contamination of an unchlorinated groundwater system by Escherichia coli O157:H7 in Cabool, Missouri, from December 1989 to January 1990 from sewage entering broken water pipes resulted in 243 known cases of diarrhea, 32 hospitalizations, and 4 deaths (Geldreich, 1996). Hydraulic modeling supported the hypothesis that localized low pressures created by the main breaks provided opportunities for back-siphonage of sewage from the deteriorated sewer system. Freezing temperatures caused blockages in 43 water meters, and partially submerged meter boxes could have allowed contaminated water to enter the system during repairs. In another instance, intensive flushing of the distribution system in Gideon, Missouri, during November to December 1993 was speculated to cause low pressures that allowed water to move from contaminated storage tanks into the pipe network. The storage tanks were in disrepair and contaminated by bird feces containing Salmonella typhimurium. The outbreak resulted in 27 laboratory-confirmed illnesses, 13 hospitalizations, and 2 deaths (Geldreich, 1996). Still many more cross connection go unrecognized because they cause little or no observable change in water quality. This low level of contamination may frequently be the cause of sporadic coliform occurrences. Figure 14 illustrates sites that experienced backflow through “backflow recording” water meters. Approximately 5% of the utility meters experience reversed flow when a major water line broke. Approximately 1% of the meters recorded flows greater than 10 gallons over a 15 minute interval. The utility reported no coliform detections during this time, but the frequency of monitoring is typically insufficient to capture such events. Cross-connections may be avoided by using devices or procedures designed to prevent backflow of water into the distribution system. For example, air gaps (a physical separation of the supply pipe by at least 1 inch above the overflow rim of the receiving receptacle) provide the greatest

Figure 9. Backflow locations recorded using backflow recording water meters. Blue flags (4%) represent sites

with backflows >0.1 gallons/15 min interval. Green flags (1%) represent sites with backflows >10 gallons/15 min

interval.



protection against backflow. Backflow devices and assemblies include atmospheric vacuum breakers, dual check valves, pressure vacuum breakers, dual check valve assemblies, and reduced pressure principle backflow assemblies (USEPA, 2002). However, these devices are only truly effective when they are part of an active cross-connection control program that includes training and certification, public education, testing and repair, record keeping, and enforcement. Although laws in some areas require installation of backflow preventers in all new construction, many areas have no such restriction. And even though most water utilities have some type of cross-connection control program, low levels of cross connection routinely occur. One water supply system in Indiana canvassed door-to-door looking for cross-connections and found a number of them, particularly in areas that were once serviced by individual wells. Although the volume of water introduced into a system by cross connections is unknown, it certainly has an impact on microbial water quality. An important reason for maintaining a disinfectant residual in distribution systems is to inactivate microorganisms that may enter the system following primary treatment. Because of the expansive nature of the distribution system, with many miles of pipe, storage tanks, interconnections with industrial users, and the potential for tampering and vandalism, opportunities for contamination do occur. Despite the best efforts to repair main breaks using good sanitary procedures, main breaks are an opportunity for contamination to enter the distribution system. Utilities typically isolate the affected section, super chlorinate, and flush the repaired pipe. However, flushing velocities may not always be achievable to remove all contaminated debris and microbiological tests performed to check the final water quality may not detect contaminating organisms. McFeters et al. (1986) reported high levels of injured coliform bacteria, not detectable by standard coliform techniques, following the repair of a main break. Resampling of the site one week later showed persistence of high levels of the coliform bacteria, detectable only using m-T7 agar, a medium specially designed to recover chlorine-injured coliforms. Installation of backflow devices to prevent the entry of contaminated water is an important distribution system barrier. Due to cost considerations, backflow devices are primarily installed on commercial service lines where the facility uses potentially hazardous substances. Examples of such facilities include hospitals, mortuaries, dry cleaners, industrial users, etc. It is not common that all service connections have backflow devices, so the possibility of back-siphonage exists at these points. In addition, installation of backflow devices for all service connections would make routine checking of the devices nearly impossible and without routine inspection the proper functioning of the units cannot be determined. Even when backflow devices have been installed, contamination events have occurred. It was the failure of a backflow check valve that allowed water stored for fire protection to enter the Cabool, Missouri distribution system (Geldreich, 1996). A broken vent in the storage tank allowed birds to enter and contaminate the water with Salmonella. Three people died due to Salmonella infection. Intrusion



A pressure transient in a drinking water pipeline is caused by an abrupt change in the water’s velocity. This event is sometimes termed surge or water hammer. Negative pressure transients create the opportunity for backsiphonage or backpressure of nonpotable water from domestic, industrial, or institutional piping into the distribution system. Intrusion refers to the flow of nonpotable water into mains through leakage points, submerged air valves, faulty seals, or other openings. As such, intrusion is defined as a specialized backflow situation that occurs in an otherwise pressurized system (LeChevallier et al. 2003). Pipes located below the water table are subject to pressure from the exterior water (depending on the height of the water table above the pipe). Thus, an opportunity exists for water on the outside of the pipe to intrude into the pipe under low or negative pressure conditions within the pipe. Water may also intrude into a distribution system by means other than pipelines. It has been speculated that faulty joint seals may leak under certain circumstances when exposed to negative pressures (Grigory, 2002). Engineering standards (Recommended Standards for Water Works, 1997) specify that all air release valves (and similar appurtenances) be designed with above-grade venting (this venting should be tamper-proof to prevent deliberate contamination of the system) or be modified in a way to prevent the flooding of the vault (e.g., via drainage or a pump). Karim et al. (2003) reported on a study that examined 66 soil and water samples collected from eight utilities in six states. The samples were collected immediately adjacent to drinking water pipelines. Total coliform and fecal coliform bacteria were detected in water and soil in about half of the samples, indicating the presence of fecal contamination. Viruses were detected using culturable methods in 12% of the soil and water samples and by molecular methods in 19% of the soil samples and 47% of the water samples. When these data were combined, 56% of the samples were positive for viruses either in the water or the soil. Sequence analysis showed that these viruses were predominantly enteroviruses (the vaccine strain of Poliovirus), but Norwalk and Hepatitis A viruses were also detected, providing clear evidence of human fecal contamination immediately exterior to the pipe. These data may not be surprising considering that engineering standards call for a minimum separation of 10 feet between drinking water and sewer pipelines, although separations can be as small as 18 inches if the drinking water pipe is located at an elevation that is higher than the sewer pipe (Recommended Standards for Water Works, 1997). However, frequently in urban areas water and sewer lines can be found side-by-side (Figure 15).

Figure 10. Example of a leaking water main next to a cracked sewer line. Source Karim et al. 2003. Reprinted with permission from the American Water Works Association



Problems with low or negative pressure transients have been reported in the literature (Walski and Lutes, 1994; Qaqish et al., 1995). Using pressure data loggers, LeChevallier et al. (2003) documented the production of negative pressure transients in a number of systems and concluded that negative pressures provide a potential portal for entry of nonpotable water into potable water distribution pipelines. Routine pressure monitoring of a distribution systems have shown that negative pressure events frequently occur following power outages at pumping stations (LeChevallier et al. 2003, Gullick et al. 2005). Measures to mitigate pressure transients are well described and include slow valve closure times, avoiding check valve slam, minimized resonance, air vessels, surge tanks, pressure relief valves, surge anticipation valves, air release valves, combination two-way air valves, vacuum break valves, check valves, surge suppressors, and by-pass lines with check valves. A surge tank or standpipe provides water when system pressure decreases and can also absorb pressure increases. Four common types of surge tanks include pneumatic or closed tank, open standpipe, a feed tank with a check valve, and a bladder tank. If water is stored in the tank for long periods of time the water quality may degrade and proper operation and maintenance is required to prevent poor quality water from entering the distribution system. These results emphasize the need to maintain an effective disinfectant residual in all parts of the distribution system as a barrier against intruded pathogens. Efforts to reduce distribution system pipeline leakage are beneficial not only from a water conservation standpoint but also to minimize the potential for intrusion of contaminants into potable water supplies. Repair of leaking sewer lines should also be a top priority, not only to minimize the occurrence of pathogens near drinking water pipelines but to prevent these sources of contamination from being transported to groundwater supplies and receiving streams, particularly under wet weather conditions. High-speed pressure data loggers would probably benefit distribution system monitoring, because they appear to be more sensitive, particularly for low pressure events. Surge modeling can be used to determine the potential vulnerability of a system to negative pressures (Kirmeyer et al., 2001). Modeling is able to identify zones in the distribution system most prone to negative pressure events (Fleming et al. 2005). These areas would then be prioritized for maintenance of a disinfectant residual, leak detection and control, main replacement, and rehabilitation of nearby sewer systems.

Negative for > 16 sec;as low as –10.1 psi (-69 kPa)

Figure 11. Examples of a negative pressure transient following a power outage. Source: LeChevallier et al. 2003. Reprinted with permission from the IWA Publishing



Storage tanks

Finished water storage facilities are an important component of the distribution system “barrier”. Historically, finished water storage facilities have been designed to equalize water demands, reduce pressure fluctuations in the distribution system; and provide reserves for fire fighting, power outages and other emergencies. Many storage facilities operate to provide adequate pressure and are kept full for emergency conditions. This emphasis on hydraulic considerations may result in storage facilities operating water storage capacity much grater than what is needed for non-emergency use. Some storage facilities have been designed such that the high water level is below the hydraulic grade line of the system, making it very difficult to turnover the tank and resulting in very old water that can affect water quality. Coliform contamination from birds or insects is a major water quality problem in storage tanks. One Missouri tank inspection firm reported 20 to 25 percent of tanks have serious sanitary defects and eighty to ninety percent of the tanks have various minor flaws that could lead to sanitary problems (Zelch 2002). Many sanitary defects result from design problems with roof hatch systems and vents that do not provide a watertight seal. These gaps allow spiders, bird droppings and other contaminants to enter the tank. Zelch (2002) reports a trend of positive total coliform bacteria occurrences in the fall due to water turnover. The warm water that has aged in the tank all summer is discharged to the system and is often suspected as the cause of total coliform occurrences. In 2000, a City in Massachusetts detected total coliform bacteria in one of their six finished water storage facilities (Correia, 2002). The tank inspector discovered an open access hatch and other signs of vandalism. When the tanks were cleaned, they had several inches of accumulated sediment and it was hypothesized that the sediment was the cause of widespread total coliform occurrences in the distribution system (Correia, 2002). Similar problems were reported for tanks in a water district in Maine where many roof shingles were missing and large gaps were present in the tank roofs that resulted in two feet of accumulated sediment (Hunt 2002). Operational conditions that may encourage bacterial colonization include prolonged storage time, reduced flow velocities and infrequent cleaning. Because outlet structures are frequently located above the reservoir floor, accumulation of sediments can occur. These sediments comprise significant amounts of assimilable organic material that support bacterial growth in the distribution network. Slime or biofilm development in cement structures may develop on cement mortars with plastic additives, on sealers such as epoxy resin, bitumen, and PVC film, and on areas of cement erosion (Schoenen 1986). Metal structures are also subject to microbial activity in areas of corrosion and at seam and joint construction bonds. Porous materials such as brick and wood used in reservoirs are particularly suited for microbial colonization and may be difficult to clean by flushing or disinfection treatment. Redwood used in wooden storage tanks resulted in the growth of environmental strains of Klebsiella that colonize the wood tissues of the trees. New redwood tanks were the source of Klebsiella and caused massive biofilms on the inner surfaces of the tank (Seidler et al. 1977). Disinfection and scraping the wood staves was ineffective in eliminating the bacteria because the organisms persist deep inside the wood pores utilizing the wood sugars (cyclitols) as a nutrient



source. Today, most wooden tanks have been eliminated or sealed, but the episode highlights the importance of water contact materials. Uncovered storage reservoirs also provide an opportunity for contaminant entry from bird and other animal excrement or surface water runoff (LeChevallier et al. 1997). Reservoirs with floating covers are susceptible to coliform contamination and regrowth from untreated water that collects on the cover surface. Surface water collected on the floating cover of one storage reservoir contained fecal coliform bacteria counts as high as 13,000 per 100 mL and total coliform bacteria counts as high as 33,000 per 100 mL (Kirmeyer et al. 2000). Main Replacement and Repairs Contaminants can enter the distribution system during pipeline construction and repair through introduction of soil and contaminated water, construction debris, or dirt and dust accumulated inside pipes during transport and storage. Contaminated sediment introduction during pipe repairs was the suspected cause of persistent coliform occurrences in a dead-end area of a Canadian distribution system studied by Gauthier et al (1999). McFeters et al. (1986) reported injured coliform bacteria in 82 to 100% of new and repaired distribution system mains. Significantly, one week after a main break was repaired, all 11 coliforms samples were still positive using m-T7 agar (a medium to detect injured coliform bacteria) whereas the standard m-Endo medium showed no growth. Haas et al. (1999) reported for 16% of the utilities surveyed, that 1% of the first samples taken following new main disinfection showed a positive result for total coliform. The researchers conducted laboratory and field experiments to examine the theoretical and practical basis for water main disinfection practice, and found that the standard disinfection practices appears to be conservative based on a target of a 4-log inactivation of HPC organisms that might be washed from the pipe surface. Nevertheless, Geldreich (1996) points out that no amount of disinfection will be effective if a substantial amount of sediment or debris is present in the pipeline. Frequently the flushing velocity of a repaired pipe is not always sufficient (often too low) to totally remove soil and sediment contamination. In the cases of larger pipelines, use of cleaning devices such as poly pigs or foam swabs can be effective for removing debris. For new construction such devices can be placed in the first section of pipe and be pushed through the pipeline when the system is first pressurized. In Halifax, Nova Scotia, persistent coliform occurrences wee traced to pieces of wood construction material embedded into the pipe surface (Geldreich 1996). AWWA has published standards for water main disinfection (AWWA C651-99) that requires disinfection with an application of chlorine at a prescribed concentration for a prescribed contact time, followed by bacterial testing of the water for confirmation of effectiveness. The standard permits three methods of pipe disinfection for new construction and repairs: tablet, continuous feed, and slug:

• The tablet method involves cementing calcium hypochlorite tablets at intervals along the pipe crown as pipe is being installed, so that when it is initially charged with water the tablets will dissolve to yield an average chlorine concentration of 25 mg/L for 24 hours.



• The continuous feed method fills a main with water with chlorine of a dose of at least 25 mg/L, and held for 24 hours, after which there should be a tested chlorine residual of at least 10 mg/L.

• The slug method entails flowing water through the pipeline with a slug of high chlorine

of at least 50 mg/L, so that the pipe is exposed to this high concentration for three hours. Ellison (2003) conducted a review of pipeline cleaning methods for potable water mains to remove loose sediment, biofilm, and scales (friable or hard scales and tubercles). Methods for pipe cleaning and repairs are shown in Table 6. Conventional or spot flushing generally involves opening hydrants in an affected area to purge contaminated water from the system. This is a common method when coliform occurrences are thought to be due to localized low chlorine residuals. Unidirectional flushing involves the closure of valves and opening of hydrants in fashion so that the flow is concentrated in a limited number of pipes, with flow velocities maximized so that shear velocity near the pipe wall is maximized. It is intended to be done in a progressive fashion, proceeding outward from the source of water in the system so that flushing water is drawn from previously flushed reaches. This type of flushing is recommended for biofilm control. Air scouring, swabbing, abrasive pigging and chemical cleaning are aggressive techniques to remove corrosion tubercles, biofilms, and sediments. Mechanical cleaning and lining is typically applied to old, tuberculated, cast iron water mains and are typically followed by an in-situ application of a thin cement mortar or epoxy lining to lasting protection. Structural linings reinforce the pipe integrity as well as provide a renovated interior surface.

SUMMARY AND CONCLUSIONS This white paper has summarized the three principle mechanisms by which coliform bacteria occur in treated drinking water:

(1) coliforms break through the treatment process from the source water supply, (2) coliforms regrow, typically in biofilms, from very low initial levels, or (3) coliforms result from recontamination of the treated water within the distribution pipeline

system. Determining the relative contribution of each of these routes can be difficult without extensive analysis and historical data. Coliform penetration through primary treatment can accompany lapses in coagulation, flocculation, sedimentation, or filtration. In these cases, increases in finished water turbidity or particle counts in the finished water can be a preliminary indictor of a treatment failure. Coliform bacteria may also be released during filter ripening or by passage of fined through

Table 6. Summary of Pipe Cleaning and Repair Procedures • Conventional or spot flushing • Unidirectional flushing • Air scouring • Swabbing • Abrasive pigging • Chemical cleaning • Jetting or balling (primarily sewer) • Mechanical cleaning and lining

(nonstructural, cement or epoxy applied linings)

• Structural linings



treatment. Although disinfectants are generally capable of inactivating coliform bacteria, attachment of the bacteria to particles can dramatically increase their resistance. Therefore, the key factors to controlling coliform penetration through primary treatment is the production of low turbidity (


REFERENCES Aboytes, R., G.D. Di Giovanni, F. A. Abrams, C. Rheinecker, W. McElroy, N. Shaw, and M. W. LeChevallier. 2004. Detection of Infectious Cryptosporidium in filtered drinking water. JAWWA 96(9): 88-98. Amirtharajah, A. and D.P. Wetstein. 1980. Initial Degradation of Effluent Quality During Fitration. Journal American Water Works Association, 72:9:518. American Water Works Association. 1999. ANSI/AWWA 651-99 - AWWA Standard for Disinfecting Water Mains. Denver, CO: AWWA. AWWA. 2006. Waterborne Pathogens; Manual of Water Supply Practices – M48, Second Edition. American Water Works Association, Denver, Co. Brazos, B. J. O'Connor, J.T. and Abcouwer, S. 1985. Kinetics of chlorine depletion and microbial growth in household plumbing systems. Proc. AWWA Water Quality Tech. Conf. Houston, TX. Bucklin K.E., G. A. McFeters, and A. Amirtharajah. 1991. Penetration of coliforms through municipal drinking water filters. Wat. Res. 25(8):1013-1017. Camper, A. K., M. W. LeChevallier, S. C. Broadaway, and G. A. McFeters. 1986. Bacteria associated with granular activated carbon particles in drinking water. Appl. Environ. Microbiol. 52:434-438. Characklis, W.G. 1981. Fouling biofilm development: a process analysis. Biotechnol. Bioengin. 23: 1923-1960. Characklis, W.G. and Marshall, K.C. 1990. Biofilms. John Wiley & Sons, Inc. New York. Chen, X. and Stewart, P.S. 1996. Chlorine penetration into artificial biofilm is limited by a reaction-diffusion interaction. Environ. Sci. Technol. 30(6), 2078–2083. Correia, L. 2002. City of Fall River, Massachusetts. Personal Communication. 508.324.2723. De Beer, D., Srinivasan, R. and Stewart, P.S. 1994. Direct measurement of chlorine penetration into biofilms during disinfection. Appl. Environ. Microbiol. 60(12), 4339–4344. Donlan, R.M. and Pipes, W.O. 1988. Selected drinking water characteristics and attached microbial population density. J. Am. Water Works. Assoc. 80(11): 70-76. Ellison, D., S. J. Duranceau, S. Ancel, G. Deagle, and R. McCoy. 2003. Investigation of Pipe Cleaning Methods (#90938). AWWA Research Foundation and the American Water Works Association, Denver, CO.



Escobar, I.C., and A.A. Randall. 1999. Influence of NF on Distribution System Biostability. Jour. AWWA, 91(6):76-89. Fleming, K.K., R.W. Gullick, J.P. Dugandzic, and M. W. LeChevallier. 2005. Using Distribution System Modeling to Identify the Potential for Low Pressure Surge Events. AWWA Water Quality and Technology Conference, Quebec City, Quebec, November 6-10, 2005. Gauthier V., Besner M.C., Trépanier M., Barbeau B., Millette R., Chapleau R. and Prévost M. 1999. Understanding the microbial quality of drinking water using distribution system structure information and hydraulic modeling. In Proc. AWWA WQTC, Tampa, Fl. Geldreich, E.E., 1996. Microbial Quality of Water Supply in Distribution Systems. Lewis Publishers, Boca Raton, Florida. Geldreich, E.E. and LeChevallier, M.W. 1999. Microbial water quality in distribution systems. In Water Quality and Treatment, 5th edition (ed. R.D. Letterman), pp. 18.1–18.49, McGraw-Hill, New York. Grigory, S. 2002. Time for Leak Free Water Systems. www.grigory.com/WaterpipeSeal.htm. Gullick, R.W., M.W. LeChevallier, J. Case, D.J. Wood, J.E. Funk, and M.J. Friedman. 2005. Application of pressure monitoring and modeling to detect and minimize low pressure events in distribution systems. J. Water Supply & Technol. – AQUA 54(2): 65-81. Haas, C. N., M. Gupta, G. A. Burlingame, R. B. Chitluru, and W. O.Pipes. 1999. Bacterial levels of new mains. J. Amer. Water Works Assoc. 91(5):78–84. Hanson, H.F. Mueller, L.M. Hasted, S.S. and Goff, D.R. 1987. Deterioration of water quality in distribution systems. American Water Works Association, Denver, CO. Hijnen, W.A.M., E. F. Beerendonj, and G. J. Medema. Inactivation credit of UV radiation for virus, bacteria and protozoan (oo)cysts in water: a review. Water Research 40:3-22. Hunt, T. 2002. Personal Communication with K. Martel. 207-443-2391. Hutchinson, M. and Rigway, J.W. 1977. Microbiological aspects of drinking water supplies. Aquatic Microbiology (F.A. Skinner and J.M. Shewan, editors). Acedic Press, London, UK. Joret, J.C. and Levi, Y. 1986. Méthode rapide d’évaluation du carbone éliminable des eaux par voie biologique. Trib. Cebedeau 510(39), 3–9. Karim, M, M. Abbaszadegan, and M.W. LeChevallier. 2003. Potential for pathogen intrusion during pressure transients. JAWWA 95(5): 134-146. Kirmeyer, G., M. Friedman, J. Clement, A. Sandvig, P. F. Noran, K. D. Martel, D. Smith, M. LeChevallier, C. Volk, J. Dyksen, and R. Cushing. 2000. Guidance Manual for Maintaining



Distribution System Water Quality. AWWA Research Foundation and the American Water Works Association, Denver, CO. Kirmeyer, G.J., M. Friedman, K. Martel, D. Howie, M. LeChevallier, M. Abbaszadegan, M. Karim, J. Funk, J. Harbour. 2001. Pathogen Intrusion into the Distribution System. AWWA Research Foundation and the American Water Works Association, Denver, CO. LeChevallier, M.W. 1990. Coliform regrowth in drinking water: a review. J. Amer. Water Works Assoc. 82(11): 74-86. LeChevallier, M.W. 1991. Biocides and the current status of biofouling control in water systems. In Proceedings of an International Workshop on Industrial Biofouling and Biocorrosion, pp. 113–132, Springer-Verlag, New York. LeChevallier, M.W., T.M. Evans and R.J. Seidler. 1981. Effect of turbidity on chlorination efficiency and bacterial persistence in drinking water. Appl. Environ. Microbiol. 42: 159 167. LeChevallier, M.W., T.S. Hassenauer, A.K. Camper and G.A. McFeters. 1984. Disinfection of bacteria attached to granular activated carbon. Appl. Environ. Microbiol. 48: 918 928. LeChevallier, M.W. Babcock, T.M. and Lee, R.G. 1987. Examination and characterization of distribution system biofilms. Appl. Environ. Microbiol. 53: 2714-2724. LeChevallier, M.W. Cameron, S.C. and McFeters, G.A. 1983. New medium for improved recovery of coliform bacteria from drinking water. Appl. Environ. Microbiol.45: 484-492. LeChevallier, M.W., C.D. Cawthon and R.G. Lee. 1988. Factors promoting survival of bacteria in chlorinated water supplies. Appl. Environ. Microbiol. 54: 649 654. LeChevallier, M. W., C. D. Lowry, and R. G. Lee. 1990. Disinfecting biofilms in a model distribution system. J. Amer. Water Works Assoc. 82(7): 87 99. LeChevallier, M.W., Lowry, C.D., Lee, R.G. and Gibbon, D.L. 1993. Examining the Relationship between iron corrosion and the disinfection of biofilm bacteria. J. Am. Water Works Assoc. 85(7), 111–123. LeChevallier, M. W., N. J. Welch, and D. B. Smith. 1996. Full Scale Studies of Factors Related to Coliform Regrowth in Drinking Water. Appl. Environ. Microbiol. 62(7): 2201-2211. LeChevallier, M.W., W.D. Norton, and T.B. Atherholt. 1997. Protozoa in Open Finished Reservoirs. J. Amer. Water Works Assoc., 89(9): 84-96. LeChevallier, M. W., R. W. Gullick, M. R. Karim, M. Friedman, and J. E. Funk. 2003. The potential for health risks from intrusion of contaminants into distribution systems from pressure transients. J. Water and Health 1(1) 3-14.



Lehtola M. J., M. Laxander, I. T. Miettinen, A. Hirvonen, T. Vartiainen, and P. J. Martikainen. 2006. The effects of changing water flow velocity on the formation of biofilms and water quality in pilot distribution system consisting of copper or polyethylene pipes. Water Res. 40(11): 2151-2160. Levy, R. V., R. D. Cheetham, and F. L. Hart. 1984. Occurrence of Macroinvertebrates in a Public Drinking Water Supply, p. 1-14. National Technical Information Service, Cincinnati, OH. Marshall, K.C. 1976. Interfaces in Microbial Ecology. Harvard University Press, Cambridge, MA, and London, England. McFeters, G.A., J.F. Kippen and M.W. LeChevallier. 1986. Injured coliforms in drinking water. Appl. Environ. Microbiol. 51: 1 5. Norton, C.D. and LeChevallier, M.W. 1997. Chloramination: its effect on distribution system water quality. J. Am. Water Works Assoc. 89(7), 66–77. Olivieri, V. P., A. E. Bakalian, K. W. Bossung, and E. D. Lowther. 1985. Recurrent Coliforms in Water Distribution Systems in the Presence of Free Residual Chlorine. Lewis Publishers Inc., Chelsea, MI. Opheim, D. Grochowski, J. and Smith, D. 1988. Isolation of coliforms from water main tubercles, N-6. Abst. Annual Meet. Amer. Soc. Microbiol. p. 245. Piriou, P., Helmi, K., Jousset, M., Castel, N., Guillot, E. and Kiene, L. 2000. Impact of biofilm on C. parvum persistence in distribution systems. In Proceedings of an International Distribution System Research Symposium, 10–11 June, American Water Works Association, Denver, CO. Qaqish, A., D.E. Guastella, J.H. Dillingham, and D.V. Chase. 1995. Control of Hydraulic Transients in Large Water Transmission Mains, p 507-526, AWWA Annual Conference Proceedings - Engineering and Operations, Anaheim, CA, June 18-22, 1995 American Water Works Association, Denver, CO. Quignon, F., Sardin, M., Kiene, L. and Schwartzbrod, L. 1997. Poliovirus-1 inactivation and interaction with biofilm: a pilot-scale study. Appl. Environ. Microbiol. 63(3), 978–982. Ridgway, H. F. and B. H. Olson. 1982. Chlorine resistance patterns of bacteria from two drinking water distribution systems. Appl. Environ. Microbiol. 44(4):972-987. Rittmann, B. E. and V. L. Snoeyink. 1984. Achieving biologically stable drinking water. J. Amer. Water Works Assoc. 76 (10): 106-114. Robeck, G.G., N.A. Clarke, and K.A. Dostal. 1962. Effectiveness of Water Treatment Processes in Virus Removal. J. Amer. Water Works Assoc. 54(10): 1275-1290.



Safe Drinking Water Committee. 1982. Biological quality of water in the distribution system. Drinking Water and Health, Vol. 4. National Academy Press, Washington, DC. Schoenen, D. 1986. Microbial Growth Due to Materials Used in Drinking Water Systems. Biotechnology, Vol. 8, (H.J. Rehm & G. Reed, editors), VCH Verlagsgesellschaft, Weinheim. Seidler, R.J., J.E. Morrow, and S.T. Bagley. 1977. Klebsielleae in drinking water emanating from redwood tanks. Appl. Environ. Microbiol. 33 : 893-900. Silverman, G. S., L. A. Nagy, and B. H. Olson. 1983. Variations in particulate matter, algae, and bacteria in an uncovered, finished-drinking water reservoir. J. Amer. Water Works Assoc. 75(4):191-195. Stewart M.H., R.L. Wolfe, and E.G. Means. 1990. Assessment of the bacteriological activity associated with granular activated carbon treatment of drinking water. Appl. Environ. Microbiol. 56(12): 3822-3829. Stewart, P. S., G. A. McFeters, and C. T. Huang. 2000. Biofilm control by antimicrobial agents, p. in press. In J. D. Bryers (ed.), Biofilms. John Wiley & Sons, New York. Tracy, H. W., V. M. Camarena, and F. Wing. 1966. Coliform persistence in highly chlorinated waters. J. Amer. Water Works Assoc. 58:1151-1159. USC FCCCHR. 1993. Manual of Cross Connection Control, 9th ed. University of Southern California Foundation for Cross Connection Control and Hydraulic Research. Los Angeles, CA. US Environmental Protection Agency. 1989a. Drinking water; national primary drinking water regulations; filtration, disinfection; turbidity, Giardia lamblia, viruses, Legionella, and heterotrophic bacteria; final rule. Federal Register 54:27486--541. US Environmental Protection Agency. 1989b. Drinking water; national primary drinking water regulations; total coliforms (including fecal coliforms and E. coli); final rule. Federal Register 1989;54:27544--68. US Environmental Protection Agency. 1990. Drinking water; national primary drinking water regulations; total coliforms; corrections and technical amendments; final rule. Federal Register 55:25064--5. US Environmental Protection Agency. 1991. Drinking water regulations: maximum contaminant level goals and national primary drinking water regulations for lead and copper; final rule. Federal Register 56:26460--4. US Environmental Protection Agency. 1996. National primary drinking water regulations: monitoring requirements for public drinking water supplies; final rule. Federal Register 61:24353--88.



US Environmental Protection Agency. 1998. National primary drinking water regulations: interim enhanced surface water treatment; final rule. Federal Register 63:69477--521. US Environmental Protection Agency. 2000. Stage 2 microbial and disinfection byproduct Federal Advisory Committee agreement in principle. Federal Register 65(251): 83015-83024. US Environmental Protection Agency. 2002. Potential Contamination Due to Cross Connections and Baclflow and the Associated health Risks: an issues paper. EPA Office of Groundwater and Drinking Water. http://www.epa.gov/safewater/tcr/pdf/ccrwhite.pdf. van der Kooij, D. 1990. Assimilable organic carbon (AOC) in drinking water. In Drinking Water Microbiology (ed G.A. McFeters), pp. 57–87, Springer-Verlag, New York. van der Kooij, D. 1992. Assimilable organic carbon as an indicator of bacterial regrowth. J. Am. Water Works Assoc. 84, 57–65. Volk, C.J. and LeChevallier, M.W. 2000. Assessing biodegradable organic matter. J. Am. Water Works Assoc. 92(5), 64–76. Volk, C., Renner, C. and Joret, J.C. 1992. The measurement of BDOC: an index of bacterial regrowth potential in water. Rev. Sci. Eau 5(n special), 189–205. Walski, T.M. and T.L. Lutes. 1994. Hydraulic Transients Cause Low-Pressure Problems. JAWWA 86(12): 24-32. Wolfe, R.L., Means, E.G., Davis, M.K. and Barrett, S. 1988. 1988. Biological Nitrification in Covered Reservoirs Containing Chloraminated Water. JAWWA. 80(9): 109-114. Zelch, C. 2002. Tomcat Consultants, Missouri. Personal Communication with K. Martel. 573- 764-5255.


FATE AND TRANSPORT OF COLIFORM BACTERIA IN THE DISTRIBUTION SYSTEM

November 2007

By: Mark W. LeChevallier, Ph.D.

Director, Innovation & Environmental Stewardship American Water

Voorhees, NJ

An Issue Paper Developed for AwwaRF 3116 – Strategy to Manage and Respond to Total Coliforms and E. coli in the Distribution System

Principal Investigator: Melinda Friedman

Co-Principal Investigator: Mark LeChevallier AwwaRF Project Manager: John Albert

FINAL



Introduction to AwwaRF 3116 Issue Papers This issue paper was developed as part of AwwaRF Project 3116 Strategy to Manage and Response to Total Coliforms and E. coli in the Distribution System. AwwaRF 3116 (to be published in 2009) provides practical guidelines to help utilities investigate, manage, and respond to total coliform and E. coli occurrences in the distribution system. The Project Team developed five issue papers to describe the status of the following relevant topics:

• Source of Coliforms and Causes of Coliform Positives, • Fate and Transport of Coliform in the Distribution System, • Evaluation of Coliform Monitoring Techniques and Comparison of Indicators, • Use and Application of Source Tracking Tools in Drinking Water, and • Tools and Methods Using Utility Data for Identifying Causes of Coliform Occurrences.

Each paper provides background information on the given topic, describes research findings, and identifies gaps in the current understanding of coliform management. Each paper is meant to serve as a “stand-alone” document, providing the reader with broad discussion of the topic. As such, repetition may be present between papers.



FATE AND TRANSPORT OF COLIFORM BACTERIA IN THE DISTRIBUTION SYSTEM

SCOPE AND OBJECTIVES The objective of this “issue paper” is to review the relevant literature pertaining to the fate and transport coliform bacteria in drinking water. The paper is complementary to the companion papers on sources and causes of coliform bacteria in distribution systems; and tools and methods using utility data for identifying causes of coliform occurrences. Because the topics are clearly linked, and for completeness sake, there is some inevitable overlap but efforts have been made to try to minimize this. This paper focuses on the principle mechanisms by which coliform bacteria survive and even grow in finished drinking water; are resistant to disinfectant residuals, and are transported through the distribution system. The sources and causes of coliform bacteria paper focuses on the primary mechanisms by which coliform bacteria occur in treated drinking water: (1) coliforms break through the treatment process, (2) coliforms growth in biofilms, and (3) recontaminate the distribution pipeline system. The treatment of models is more extensive in the tools and methods paper since selection of the modeling tool is critical part of the data mining effort. Because coliform bacteria are similar in physiology and survival to many hetrotrophic plate count (HPC) bacteria (like Pseudomonas spp.), some HPC results are used to illustrate some principles related to growth and survival, however, where possible comparative data are provided for coliform bacteria. INTRODUCTION Distribution systems are complex ecosystems with differing ecology for water, pipe surfaces, and sediments. For the most part these ecosystems are poorly characterized, so it is no surprise that water utilities are frequently puzzled by the sporadic occurrences of coliform bacteria in drinking water pipelines. Given the miles and miles of distribution system mains, the variety of pipe, valve, coating, and gasket materials, the chemical and biological modification of these surfaces by mineral scales, deposits, corrosion, and biofilms, the accumulation of sediments and post precipitation chemicals in pipes and storage tanks, and variations in hydraulic flow rates, detention time, chemical water quality characteristics throughout the system; one begins to grasp the complexity of drinking water systems. This is not to mention that the ecology is constantly changing with seasonal effects of water temperature and system demand, but also short term variations in source water quality, precipitation and treatment efficacy. From a microbial perspective, the ecology of the distribution system can change millimeter by millimeter throughout the system and the microbial water quality can be altered by a single bacterial microcolony whose cells can detach and colonize downstream locations. Research has suggested that a single tubercle colonized by coliform bacteria can result in detectable indicator bacterial levels in downstream water samples (LeChevallier et al. 1987).



From the time a surface is first placed into water, organic and inorganic materials begin to accumulate on the surface and a biofilm begins to develop. Biofilm refers to an organic or inorganic deposit consisting of microorganisms, microbial products, and detritus on a surface (Marshall, 1976; Characklis, 1981). Therefore, biofilms exist in all distribution systems; the impact of biofilms on water quality is determined by growth rate and metabolic activity and their resistance to disinfection. Given this complexity, the water operator should view the distribution system as a dynamic, multifaceted, and living ecosystem rather than a monolithic structure. The acknowledgement of this complexity will allow the operator to realize that virtually everything that happens in a distribution affects the physicochemical quality of the water. IMPACT OF PIPE MATERIAL From the time that water flows into a pipe system, the pipe material has a profound impact on the microbial characteristics of water. Armstrong et al. (1982) characterized microbial populations by the level of multiple antibiotic resistance and showed that a shift in microbial populations (evidenced by a shift in multiple antibiotic resistance profiles) occurred as soon as raw water entered a pipeline. Increasing levels of treatment further influenced the levels of multiple antibiotic resistance. The authors speculated that because antibiotic resistance is frequently associated with plasmids that confer resistance to heavy metals, the possession of these traits improved the survival of the bacteria on metallic pipelines. The pipe surface itself has a profound influence on the composition and activity of biofilm populations. Studies have shown that biofilms developed more quickly on iron pipe surfaces than on plastic polyvinyl chloride (PVC) pipes, despite the fact that adequate corrosion control was applied, the water was biologically treated to reduce AOC levels, and chlorine residuals were consistently maintained (Camper, 1996; Haas et al., 1983). In general, the larger surface-to-volume ratio in smaller diameter pipes (compared to larger pipes) results in a greater impact of biofilm bacteria on bulk water quality. The greater surface area of small pipes also increases reaction rates that deplete chlorine residuals.

In addition to influencing the development of biofilms, the pipe surface has also been shown to affect the composition of the microbial communities present within the biofilm (Figure 1). Iron pipes have been shown to support a more diverse microbial population than did PVC pipes (Norton and LeChevallier, 2000). It has been speculated that corrosion of the pipe surface could provide a source of electrons that would serve as an energy source for microbial growth. Bacteria that possess hyrdrogenase enzymes that would catalyze such a process have been found in biofilm bacteria (Norton and LeChevallier, 2000). Iron surfaces can also bind and accumulate humic carbon compounds that can be slowly biodegraded and serve as a nutrient source to stimulate bacterial growth on iron pipe surfaces (Camper et al. 1996, 2000). Victoreen (1980) crushed and ground tubercles from distribution system pipes and found that the surface properties of the particles stimulated coliform growth. Unlined cast iron pipes are a frequent source of bacterial problems and systems with a greater proportion of these pipes tend to have higher rates of coliform occurrences (LeChevallier et al. 1996). In the New Jersey American,



Swimming River system, high levels of coliform bacteria were found only in iron tubercles (LeChevallier et al., 1987). These tubercles were found in a 28-year-old cement-lined ductile iron main, where parts of the lining had broken away. Coliform bacteria in the iron tubercle had the same biochemical profile as organisms isolated from the water column.

Stenotrophomonas74.0%

Other - Gram -1.0%

Nocardia20.0%

Agrobacterium4.0%

Other - Gram +1.0%

Acidovorax24.0%

Stenotrophomonas4.0%Pseudomonas

16.0%

Other - Gram -8.0%

Xanthobacter22.0%

Nocardia26.0%

Figure 1. Microbial populations isolated from PVC (A) or iron pipe (B) surfaces. Source: Norton and LeChevallier

2000. Reprinted with permission from the American Society for Microbiology Some pipe materials may leach constituents that support coliform growth. For example, pipe gaskets and elastic sealants (containing polyamide and silicone) can be a source of nutrients for bacterial proliferation. Colbourne et al. (1984) reported that Legionella were associated with certain rubber gaskets. Organisms associated with joint-packing materials include Pseudomonas aeruginosa, Chromobacter spp., Enterobacter aerogenes, and Klebsiella pneumoniae (Schoenen, 1986; Geldreich and LeChevallier, 1999). Pump lubricants should be non-nutritive to avoid bacterial growth in treated water (White and LeChevallier, 1993). Coating compounds for storage reservoirs and standpipes can contribute to organic polymers and solvents that may support regrowth of heterotrophic bacteria (Schoenen, 1986; Thofern et al., 1987). Liner materials may contain bitumen, chlorinated rubber, epoxy resin, or tar-epoxy resin combinations that can support bacterial regrowth (Schoenen, 1986). PVC pipes and coating materials may leach stabilizers that can result in coliform growth. Studies performed in the United Kingdom showed coliform isolations were four times higher when samples were collected from plastic taps than from metallic faucets (cited in Geldreich and LeChevallier, 1999). Although procedures are available to evaluate the growth stimulation of different materials (Bellen et al., 1993); these tests are not universally applied.

A.

B.



The pipe substratum also has a major influence on disinfection efficiency. (LeChevallier et al., 1990, 1993) examined the disinfection efficiency of free chlorine and monochloramine for controlling biofilm organisms in a model pipe system. Bacteria grown on galvanized, copper, or PVC pipe surfaces were readily inactivated by a 1-mg/L residual of free chlorine or monochloramine (Figure 2). Biofilms grown on iron pipes treated with free chlorine doses as high as 4 mg/L (3-mg/L residual) for two weeks did not show significant changes in viability, but if treated with 4 mg/L of monochloramine for two weeks, these biofilms exhibited a more than 3-log die-off. Accumulation of corrosion products on iron pipes was found to interfere with free chlorine disinfection (LeChevallier et al., 1990, 1993).

LeChevallier et al. (1990) suggested that there was a threshold level at which monochloramine was effective for controlling biofilms on iron pipes. Under the experimental conditions tested, a 1.0- mg/L monochloramine residual was necessary to inactivate attached bacteria. The Hackensack Water Company converted to chloramine in its distribution system in 1982 (Fung 1989) and initially maintained a 2-mg/L chloramine residual, but because of sporadic occurrences of presumptive coliforms and evidence of nitrification in the distribution system, the company increased the chloramine dose to 3.0 mg/L in 1986. In that year, only a few coliform bacteria were recovered during the summer months. In August 1986, chloramine doses were increased to 4.0 mg/L (average distribution system residuals ranged from 2 to 3 mg/L) and no coliform or nitrification problems were reported for at least a four-year period afterwards (LeChevallier et al., 1990). Utilities experiencing coliform regrowth problems often maintain high free chlorine residuals in the distribution system in an effort to control bacteria (Earnhardt 1980, Reilley and Kippen 1983, Oliveri et al. 1985, LeChevallier et al. 1987). In general, free chlorine residuals ranging from 3 to 6 mg/L have been necessary to control coliform regrowth. However, Earnhardt (1980) reported recovering 51 coliform bacteria/100mL in samples containing between 10 and 12 mg/L free chlorine.

Corrosion of an iron pipe protects biofilm bacteria from disinfection because the corrosion products react with chlorine disinfectants and prevents the biocide from penetrating the biofilm layer. Even low levels of corrosion, i.e., 3 mpy) affected monochloramine disinfection. The type of corrosion influences the efficiency of disinfection of the biofilm. Increases in the ratio of chloride and sulfate to bicarbonate (the Larson index) have been shown to be associated with pitting corrosion, which appears to interfere with disinfection more than general corrosion. Multiple linear regression models were able to predict approximately 75 percent of the variation in biofilm inactivation. Therefore,

Iron Galvanized Copper PVC0

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7

Dec

reas

e L

og V

iabl

e C

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(CFU

/cm

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Free 1 mg/LMono 1 mg/LFree 4 mg/LMono 4 mg/L

Figure 2. Impact of pipe material on disinfection of biofilm bacteria. Free, free chlorine; Mono, monochloramine. Source: LeChevallier et al. 1990, 1993. Reprinted with permission from the American Water Works Association



water utilities monitor and control corrosion rates and Larson indexes to levels as low as feasible (LeChevallier et al., 1993). Corrosion control will improve the effectiveness of chlorine disinfection, increase maintenance of chlorine residuals, and help control bacterial levels in potable water supplies. Lowther and Moser (9) suggested that corrosion may have been related to the occurrence of coliform bacteria in the Seymour, Ind., distribution system. They reported decreased coliform levels a few weeks after application of zinc orthophosphate. Zinc orthophosphate has also been successfully used to control coliforms at other Indiana operations (unpublished data). Martin et al. (1982) reported that adding lime to treated water supplies was an effective method of pH and bacterial control. The authors presented data that suggested that high pH levels (pH 9.0) were bactericidal. In both of these situations, reduced corrosivity of the water could have resulted in improved free chlorine disinfection of biofilm organisms.

The impact of pipe surfaces affects more than just coliform bacteria. The reported resistance of mycobacteria to zinc and copper (Kirschner et al., 1992) may aid the development of biofilms on co

Issue Papers for AwwaRF Project 3116 Strategy to Manage ...K. ozaena Adapted from Geldreich and...

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