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lv Biological Quality of Water in the Distribution System One objective of the physical and chemical treatment of water intended for public consumption is to reduce the levels of total coliforms to less than 1 coliform/100 ml. Such treatment has proved to be an effective bar- rier against transmission of infectious disease by water. Commonly used processes such as coagulation, sedimentation, sand filtration, and disin- fection yield a water essentially free of disease-causing viruses, bacterial and protozoa. The system of pipes, valves, and connections designed to distribute the water to the consumer is disinfected but not sterilized during construc- tion. Thus, drinking water is not sterile and may contain living material that may influence water quality in the distribution network. In a well-designed, -constructed, and -operated water distribution sys- tem, changes in water quality will be minimal, and water provided to the consumer will be similar to that leaving the treatment plant. In poorly de- signed, constructed, and operated water systems, water quality will deteri- orate in the distribution system and result in consumer complaints. In the worst cases, outbreaks of disease may result. BIOLOGICAL MATERIAL IN WATER DISTRIBUTION SYSTEMS The nature of the biological material in water distribution systems results from a complex series of physical, chemical, and biological reactions (Fig- ure IV-11. Living organisms and nutrients may enter the distribution sys 108

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Biological Quality of Water in the Distribution System 109 tern with the raw water, during the treatment processes, or from sources such as leaks, cross-connections, back-siphonages, and open reservoirs. Growth may occur at or near the pipe surface, the interface of suspended particulates, and within the water itself. The chemical and biological products leave the distribution system at the consumer's tap. Biofilms Fouling refers to the undesirable formation of inorganic and/or organic deposits on pipe surfaces. These deposits can induce water quality changes, increase the rate of corrosion at the surface, and increase the fluid frictional resistance at the surface. There are several types of fouling and combinations thereof: crystalline or precipitation fouling, corrosion fouling, particulate fouling, chemical reaction fouling, and biological fouling (biofouling). Biofouling can result from development of an organic film (biofilm) consisting of microorgan- isms and their products and from assorted detritus. Development of an understanding of biofouling from field observations has been limited because of the interaction of several contributing rate processes. The mechanisms of fouling biofilm accumulation may be de- scribed as the net result of the following: Transport and accumulation of materialfrom the bulk fluid to the surface. Materials can be soluble (microbial nutrients and organic salts) or particulate matter (viable microorganisms, their detritus, or inorganic particles). Microbial growth within the film. Microbial growth in the biofilm and extracellular polymers produced by the microorganisms contribute to the biofilm deposit and promote adherence of inorganic suspended solids. Fluid shear stress at the surface of the film. Such forces can limit the overall extent of the fouling deposit by reentraining attached material. The reentrained material can result in significant water quality changes in the pipe. Surface material and roughness of the pipe. Surface properties of the pipe can influence micro-mixing near the pipe wall and corrosion pro- cesses. Some metal surfaces may release toxic components into the biofilm inhibiting growth and/or attachment. Some metals produce loosely held oxide films under the biofilms. When the oxide film sloughs, the biofilm is also removed. Fouling control procedures. Chlorine, the most commonly used disin- fecting chemical, oxidizes biofilm polymers causing disruption and partial removal in the shear stress field. Inactivation of a portion of the microbial

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112 DRINKING WATER AND HEALTH population also occurs. Altered biofilm "roughness" and decreased viable cell numbers will influence "regrowth" rates of the biofilm. Chlorine is also capable of accelerating corrosion processes. There can be no doubt that biofilms in water supply distribution sys- tems alter water quality. The following changes, or their combination, can occur in the distribution system as a result of biofilm processes: decrease in chlorine residual (Larson, 1966; O'Connor et al., 1975~; increased bacterial counts resulting from loss of chlorine residual (Larson, 1966; O'Connor et al., 1975~; increased bacterial counts or "regrowth" in the distribution system resulting from detachment of bacteria from the biofilm (Becker, 1975; Russell, 1976~; reduction in dissolved oxygen content resulting from microbial activ- ity in the biofilm (O'Connor et al., 1975~; taste and odor changes resulting from products of microbial metabo- lism within the biofilm or their reaction with chlorine (O'Connor et al.. 1975; Silvey et al., 19751; "red water" resulting from the activity of iron bacteria (Larson, 1966; O'Connor et al., 1975; Russell, 1976~; "black water" resulting from the activity of sulfate-reducing bacteria in anaerobic microenvironments within the conduits (Larson, 1966; Lee and O'Connor, 1975~; and increased "hydraulic roughness," which increases turbulence in the conduit. Increased turbulence increases mass transfer rates at the conduit wall, influencing corrosion rates, leaching rates, and detachment of bacte- ria from the biofilm (Picologlou et al., 1980~. BlOFILM HORTON face; film. Biofilm formation is the net result of several physical, chemical, and bio- logical processes including the following: transport of solutes to the wetted surface; adsorption of solutes at the wetted surface; transport of particles (including microbial cells) to the wetted sur attachment of microorganisms to the surface; and metabolism and growth of microorganisms immobilized in the bio

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Biological Quality of Water in the Distribution System 113 The rate of water flow and the concentration of growth-limiting nutri- ents (i.e., substrate) are the primary environmental variables influencing the rate and extent of biofilm formation. A general discussion of biofilm formation follows, with special attention to problems encountered in water supply distribution systems. The formation of biofilm begins with transport to and adsorption of or- ganic solutes at the pipe wall. The organic material may be of microbial origin or a component of the raw water supply. Algae and bacteria in the water treatment plant' on the open reservoirs, or within the conduits pro- duce relatively high-molecular-weight organic compounds, primarily poly- saccharide in nature. Raw waters frequently contain organic compounds such as tannins or lignins. These polyelectrolytes are surface active and adsorb readily, thereby conditioning the surface. Generally, the polyelec- trolytes and the conduit surface are both negatively charged, and firm ad- sorption of the polyelectrolyte to the surface is mediated by inorganic cat- ions such as calcium, magnesium, and iron. Microbial cells are transported to the conditioned surface where they at- tach. Research by Marshall et al. (1971) and Zobell (1943) suggests the ex- istence of a two-stage attachment process: reversible adhesion followed by an irreversible attachment. Reversible adhesion refers to an initially weak adhesion of a cell that can still exhibit Brownian motion. Conversely, irre- versible attachment is a permanent bonding to the surface, usually aided by the production of extracellular polymers. Marshall (1976) and Corpe (1978) have implicated polysaccharides and glycoproteins in irreversible attachment. Attached microorganisms assimilate nutrients, synthesize biomass, and produce extracellular products. In many cases, the rate of assimilation of nutrients is limited by the diffusion of nutrients through the biofilm. As a result, a significant concentration gradient exists between the bulk fluid and the pipe wall. When nutrients cannot penetrate the lower layers of the biofilm, the microorganisms in that region lyse. If dissolved oxygen be- comes depleted in the biofilm, denitrification and sulfate reduction will occur when nitrate and sulfate are present. The sulfate-reducing organ- isms have been implicated in accelerated corrosion of pipelines. At any point in its development, portions of biofilm peel away from the pipe surface and are reentrained in the fluid flow. Detachment is a contin- uous process of biofilm removal. It is highly dependent on hydrodynamic conditions and is characterized by particle sizes similar to microbial cell diameters. As the biofilm grows thicker, the fluid shear stress at the bio- film interface generally increases and the potential for substrate oxygen or nutrient limitation in the deeper portions is great. These limitations may weaken the biofilm matrix and cause detachment. When the flow is turbu

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114 DRINKING WATER AND HEALTH lent, the rate at which the biofilm detaches increases as the thickness of the biofilm increases (Trulear and Characklis, 19791. For a given biofilm thickness' detachment rate increases with increasing fluid shear stress. Sloughing, a random massive removal of biofilm, is generally attributed to oxygen/nutrient depletion deep within the biofilms. Sloughing occurs more frequently with thicker, dense films characteristic of laminar flow systems and results in the reentrainment of large aggregates of biofilm. The detached material consists of microbial cells. their extracellular products, and any other adsorbed or entrapped material within the bio- film. The rate of water flow and the concentration of growth-limiting nutrient (i.e., substrate) significantly influence the rate and extent of biofilm devel- opment. For example, high rate of water flow and high concentrations increase transport rate of soluble substrate to the pipe wall; high concentrations of substrate increase the rate of metabolic pro- cesses within the biofilm; high rates of water flow and low concentrations of substrate result in thinner biofilms; and high rates of water flow increase the detachment of material from the biofilm. PROPERTIES AND COMPOSITION Microorganisms, primarily bacteria, adhere to surfaces ranging from the human tooth and intestine to the metal surface of power plant condenser tubes exposed to turbulent flows of water. The microorganisms "stick" by means of extracellular polymer fibers, which are fabricated and oriented by the cell and extend from the cell surface to form a tangled matrix termed a "glycocalyx" (Costerton et al., 19781. The fibers may conserve and concentrate extracellular enzymes that are necessary for preparing substrate molecules for ingestion, especially high molecular weight or par- ticulate substrate frequently found in natural waters. The biofilm surface is highly adsorptive, especially because of its poly- electrolyte nature, and can collect significant quantities of silt, clay, or other detritus in natural waters. Biofilms can also accumulate large amounts of heavy metals (Dugan and Pickrum, 1972~. Physical, chemical, and biological properties of biofilms are dependent on the environment to which the attachment surface is exposed. The phys- ical and chemical microenvironments combine to select the prevalent mi- croorganisms which, in turn, modify the microenvironment of the surface.

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Biological Quality of Water in the Distribution System 115 As colonization proceeds and a biofilm develops, concentration gradients develop within the biofilm and "average" biofilm properties change. PHYSICAL PROPERTIES The most fundamental biofilm properties are volume (thickness) and mass. In turbulent flow systems. wet biofilm thickness seldom exceeds 1,000 mm (Picologlou et al., 1980~. In laminar flow, biofilms can be sev- eral millimeters thick. The biofilm mass can be determined from the wet biofilm thickness if the biofilm dry mass density is known. Biofilm dry mass density reflects the attached dry mass per unit wet biofilm volume. Measured mass values in turbulent flow systems range from 10 to 50 ma/ cm3. In laminar flow, higher values have been observed (Hoehn and Ray, 1973~. Biofilm density increases with increasing turbulence (Characklis 1980) and increasing substrate loading (Trulear and Characklis. 1979~. The increase in biofilm density with increasing turbulence may be caused by one of the following phenomena: selective attachment of only certain microbial species from the avail- able population; microbial metabolic response to environmental stress; and "squeezing" of loosely bound water from the. biofilm by fluid pres- sure forces. The relatively low densities of biofilm mass compare well with observed water content of biofilm (Characklis, 1973, 1980; Nimmons, 1979~. The transport properties of biofilm are of critical importance in assess- ing its effects on mass, heat, and transfer of momentum. Diffusion coeffi- cients for various compounds through microbial aggregates have been re- ported in the literature, mostly for microbial floe particles. Matson and Characklis (1976) reported variation in the diffusion coefficient for glu- cose and oxygen with growth rate and carbon-to-nitrogen ratio. The diffu- sion coefficient of biofilms is most probably related to its density. In-situ theological measurements indicate that the biofilm is viscoelastic with a relatively high viscous modulus (Characklis, 1980~. The thermal conduc- tivity of biofilm is not significantly different from that of water (Charack- lis, 1980~. CHEMICAL PROPERTIES The inorganic composition of biofilms undoubtedly varies with the chemi- cal composition of the bulk water and probably affects the physical and

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Biological Quality of Water in the Distribution System 117 biological structure of the film. Calcium, magnesium, and iron affect intermolecular bonding of biofilm polymers, which are primarily responsi- ble for the structural integrity of the deposit. Experimentally, ethylenedi- aminetetraacetic acid (EDTA) is effective in detaching biofilm (Charack- lis, 1980~. Table IV-1 shows the range of inorganic composition observed in selected biofilms. Very little is known about the interaction between biological fouling and inorganic scaling (primarily calcium precipitation on the pipe wall). The combined process probably occurs in many water distribution systems. The organic composition of the biofilm is strongly related to the energy and carbon sources available for metabolism. Herbert (1961) and Schaech- ter et al. (1958) demonstrated the effect of environment and microbial growth rate on the composition of the cells and their extracellular prod- ucts. For example, nitrogen limitation can result in production of copious quantities of microbial extracellular polysaccharides. Table IV-2 presents data on the composition of biofilms developed in the field and in the labo- ratory. Other chemical analyses of biofilm from laboratory systems indi- cate relatively high levels of polysaccharide in the biofilm (Bryers and Characklis, 19801. BIOLOGICAL PROPERTIES The organisms that colonize the attachment surface strongly influence the rate at which biofilm develops and its chemical and physical properties. However, organism-organism and organism-environment interactions un- doubtedly shift population distributions during biofilm accumulation. Several investigators have observed a succession of various microbial species during biofouling (Corpe. 1978; Marshall, 1976~. The first visible signs of microbial activity on a surface are usually small "colonies" of cells distributed randomly on the surface. If biofilm devel- opment continues, the colonies grow together forming a relatively uniform biofilm. The viable cell numbers are relatively low in comparison to the volume of biofilm. The cells occupy from 1% to 10% of the biofilm in di- lute nutrient solutions (Characklis. 1980~. Jones et al. (1969) presented photomicrographs to corroborate these data in natural and laboratory sys- tems. Allen and Geldreich (1977) have measured bacterial populations ex- ceeding 105 organisms per gram of deposit from a distribution pipeline. These deposits consisted of sediment accumulations and "encrustations." Figure IV-2 contains electron micrographs of encrustations collected from water distribution systems across the United States (Allen et al., 1979, 1980). A number of different genera of bacteria and fungi have been observed

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126 DRINKING WATER AND HEALTH tion following construction and repair generally requires repeated high doses of chlorine before the system can be placed into service. Cross-Connections Cross-connections and back-siphonages provide another opportunity for large amounts of biological material to enter the distribution system. These events generally result in noticable change in water quality, includ- ing turbidity, increased content of solids, and undesirable tastes and odors. In many cases, cross-connections are not obvious and the resulting changes in water quality are not detected by the consumer. Often, small intermittent flows through cross-connections can back-siphon and be re- sponsible for outbreaks of disease. CONTROL OF BIOLOGICAL CONTAMINATION Chlorination has been the predominant means of controlling fouling bio- film formation in water distribution systems. Figure IV-3 illustrates the effectiveness of these processes in a segment of a water distribution con- duit. There are three basic steps: Chlorine species entering the pipe segment react with chlorine-de- manding components (viable cells and chemical compounds) in the bulk water. Chlorine species are transported through the bulk water to the water- biofilm interface. Chlorine species diffuse and react within the biofilm releasing soluble and particulate matter into the bulk water. Since both "solid" and liquid phases are required, the chlorine-biofilm reaction is a heterogeneous process. Therefore, physical transport of reac- tants and products in each phase becomes important since transport limi- tations can significantly affect the rate of the overall process. Transport of Chlorine WATER PHASE The rate at which chlorine is transported to the biofilm depends on the concentration of chlorine in the bulk water and the intensity of the turbu- lence.

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128 DRINKING WATER AND HEALTH The concentration of chlorine in the bulk water is related to the rate of its application minus the chlorine demand of the water. If the chlorine concentration at the biofilm interface is the same as its concentration in the bulk water, then the chlorine concentration in the water drives the re- actions of chlorine within the biofilm. If chlorine reacts with biofilm rela- tively rapidly, the concentration at the interface will be low and the physi- cal transport of the chlorine may limit the rate of the overall process within the biofilm. By increasing the intensity of the turbulence through increased flow rate both the transport rates in the bulk water and the concentration at the in- terface will increase. In bulk water, chlorine is transported primarily by eddy diffusion. BIOFILM The transport of chlorine in biofilms occurs primarily by molecular diffu- sion. Since the composition of biofilms is from 96% to 99% water, the dif- fusivity of chlorine in biofilm is probably similar to its diffusivity in water. In biofilms of higher density or in those containing microbial matter asso- ciated with inorganic scale, tubercules, or sediment deposits, diffusion of chlorine may be relatively slow. Chlorine reacts with various organic and reduced inorganic components within the biofilm, and it disrupts cellular material and inactivates cells in the biofilm to some extent. Its greatest apparent effect is its reaction with the extracellular polymers (primarily polysaccharides), which are respon- sible for the physical integrity of the biofilm (Characklis and Dydek, 1976~. Bacterial floes or biofilms that are rich in polysaccharide material ex- hibit a more rapid and ultimately greater chlorine demand (Characklis and Dydek, 1976~. One possible explanation is that hypochlorite ion at- tacks glucose polysaccharides with extensive oxidation at the C2 and C3 positions of D-glucose units, which results in cleavage of the C2-C3 bond (Hullinger, 1964; Whistler et al., 1956~. Depolymerization can result from the inductive effects of this oxidation, from direct oxidative cleavage of the glucosidic bond, or from degradation of the intermediate carbonyl com- pound. The reaction of chlorine with biofilm produces an immediate response in the bulk water by increasing turbidity and the soluble organic constitu- ents (Characklis and Dydek, 19761. A significant removal of biofilm is evi- denced by a decrease in biofilm thickness and a decrease in fluid frictional resistance (Characklis, 1980; Characklis and Dydek, 1976; Norrman et al., 1977~. Inactivation of the biofilm with a nonoxidizing poison does not result in any biofilm removal (Characklis and Dydek, 1976~. The results

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Biological Quality of Water in the Distribution System 129 suggest that hypochlorite ion oxidizes the polysaccharides in the biofilm resulting in depolymerization, dissolution, and detachment. Characklis et al. (1980) reported that biofilm detachment resulting from chlorination is much higher between pH 7.5 and 8.5 than between pH 6 and 7. These data correspond well with data for chlorination of poly- saccharides such as starch, which is optimum at pH > 7 (Whistler and Schweiger, 19571. On the other hand, disinfection with chlorine is more effective at lower pH (approximately pH 6-71. Similar data are not avail- able for monochloramine, dichloramine, or other N-chloro compounds. Fluid shear forces may play a major role in the removal of biofilm. Norrman et al. (1977) measured a higher rate of chlorine uptake by bio- films when the fluid shear stress was greater. The authors suggested that these greater shear forces disrupted the biofilm during chlorination, thereby reentraining reaction products and exposing new surfaces for chlorine reaction. Characklis et al. ( 1980) observed that the detachment of biofilm resulting from chlorination increased with increasing fluid stress. In summary, when chlorine contacts biofilm, the following occurs: de- tachment of biofilm, dissolution of biofilm components, and consumption of chlorine. Limited observations suggest that the following factors influ- ence the rate of the chlorine-biofilm reaction: Transport of chlorine from the water to the water-biofilm interface. Transport rate increases with increasing chlorine concentration and tur- bulence. Transport of chlorine within the biofilm or deposit. Transport rate can be increased by increasing the chlorine concentration at the water-bio- film interface. Reaction of chlorine within the biofilm, especially the abiotic compo- nents. Detachment and reentrainment of reacted biofilm primarily due to fluid shear stress. Appropriate chlorine residuals are difficult to maintain throughout the distribution system on a continuing basis. Consequently. biofilms may fre- quently exist in various locations in the pipe network. Therefore, more studies should be conducted to define these fundamental process rates and the factors that influence them. DISPERSED GROWTH Finished water leaving a properly operated water treatment plant is rela- tively free of biological activity. Pipe networks designed specifically to minimize water stagnation and dead ends and regular cleaning and flush

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130 DRINKING WATER AND HEALTH ing programs are used to control contamination after treatment. In addi- tion, chlorine and chloramines have been used almost exclusively as the residual disinfectants in water distribution systems. Control of chlorination during the early days of water disinfection was based on the applied dose of chlorine. It was soon recognized that the dose of chlorine alone was not adequate to ensure good microbial inactivation. Folwell (1917) pointed out that "the only safe rule is to test the germicidal effect of different doses on the water in question." The concept of residual chlorination was suggested by Wolman and Enslow (1919~. They recom- mended that the amount of chlorine applied should be based on the amount of chlorine consumed by the water at 20C for 5 minutes (chlorine demand) plus an additional 0.2 mg/liter. However, they specifically did not recommend the maintenance of a chlorine residual in the distribution system because of anticipated taste and odor problems. By the 1930's ammonia was sometimes added to reduce the tastes and odors produced by the chlorine. Baylis (1935) noted that the chlorammo- niation process yielded a stable chlorine residual that produced minimum complaints and reduced bacterial growth in the distribution system. The practice of maintaining a chlorine residual throughout the distribution system was gradually adopted, and by 1941 the American Water Works Association water quality and treatment manual noted that the chlorine- ammonia treatment prevented the formation of tastes and odors in the distribution system and reduced the number of complaints pertaining to "red-water" in the dead ends of the system. However, the chlorammonia- tion process was quite ineffective in eliminating taste and odors in unfil- tered water supplies. As the reaction between chlorine and ammonia became better understood and the superior disinfecting activity of free chlorine was recognized, the practice of maintaining a free chlorine resid- ual in the distribution system evolved. The 1950 American Water Works Association water quality and treatment manual noted that high chlorina- tion rates reduced bacterial content and eliminated some tastes and odors. The value of residual chlorine in the distribution system has received considerable attention. At the request of the Department of the Army, the National Academy of Sciences/National Research Council (NAS/NRC) prepared the following statement in 1958: Residual chlorine in the concentrations routinely employed in water utility practice will not ordinarily disinfect any sizeable amounts of contaminators material enter- ing the system, though this will depend on the amount of dilution occurring at the point of contamination, on the type and concentration of residual chlorine and on the time-of-flow interval between the point of contamination and the nearest con- sumer.... The NAS-NRC does not consider maintenance of a residual satisfactory

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Biological Quality of Water in the Distribution System 131 substitute for good design, construction and supervision of a water distribution sys- tem, nor does it feel that the presence of a residual in the system constitutes a guar- antee of water potability. It was the opinion of the NAS/NRC committee responsible for this state- ment that the establishment of a universal standard for maintaining resid- ual chlorine in the water in distribution systems was not desirable. Al- though the military had no policy concerning residual chlorine, all services recommended that chlorination be accomplished to levels of free resid- uals. More recently Coene (1963) reported that the presence of some type of chlorine residual reduces the coliform content. In 1970, the results of a survey of community water supplies supported Coene's study (McCabe et al., 19701. Buelow and Walton (1971) reported that the maintenance of a chlorine residual throughout the water system was effective in meeting the bacterial standards. Geldreich et al. (1972) showed that chlorine residuals were effective in controlling bacterial populations within the distribution lines. Snead et al. (1980) confirmed the earlier results and reported that the chlorine residual was the single most important factor influencing the level of microorganisms found in samples collected from distribution networks in Baltimore and Frederick, Maryland. Cross-connections and back-siphonages have been implicated in nu- merous outbreaks attributed to waterborne microorganisms (Craun et al., 1976; McCabe et al., 19701. Snead et al. (1980) evaluated the protec- tion afforded the water consumer by the maintenance of a free or com- bined chlorine residual when tap water was challenged with sewage con- taining enteric bacteria and viruses. An initial free chlorine residual was more effective than an equivalent initial combined chlorine residual. At pH 8.0, an initial free chlorine residual of 0.7 mg/liter, and a challenge of 1.0~o sewage by volume. investigators observed inactivation of enteric bacteria at 3 logs or greater ~ > 99.9~o kill). Viral inactivation under these conditions was 2 logs (~99% kill.) SUMMARY AND CONCLUSIONS Living organisms can enter the water distribution system through insuffi- ciently treated raw water, in-line reservoirs, and imperfections in the pipe- line network. Microbial activity occurs predominantly at the pipe wall where nutrients gather in high concentrations. Flow rate, ratio of surface area to volume, and nutrient concentration all influence the microbial ac- tivity both at the wall and in the bulk water.

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132 DRINKING WATER AND HEALTH Microbial processes within the distribution system can significantly in- crease hydraulic roughness and corrosion in the pipes. Microbial activity can result in undesirable tastes and odors, "black" water (sulfide), and "red" water (iron). Detached portions of biofilms in the pipes provides a continuing source of microorganisms in the distribution system. Disinfectant residual, usually chlorine, provides a relatively effective barrier to the growth of microorganisms in both the bulk water and the biofilm. Chlorine is also effective in removing existing biofilms and pro- viding some protection against contamination of the water after treat- ment. Distribution networks are dynamic systems. The flow rates and compo- sition of water in the pipelines vary with the length of time they are in the system and the magnitude of the network as a result of changes in raw water characteristics, water treatment processes, reactions within the pipes, and water demand. Because chlorine residual is open low or even absent in some portions of the distribution system, microorganisms may proliferate. Enteric pathogens are rarely found in distribution systems containing adequately disinfected water. REFERENCES Ackerman, T.V., and E.J. Lynde. 1944. Effect of storage reservoir detritus on ground- water. J. Am. Water Works Assoc. 36:315-322. Allen, M.J., and E.E. Geldreich. 1977. Distribution line sediments and bacterial regrowth. Paper 3B-I in Water Quality in the Distribution System, Proceedings, American Water Works Association Water Quality Technology Conference, Dec. 4-7, Kansas City, Mo. American Water Works Association, Denver, Colo. 6 pp. Allen, M.J., E.E. Geldreich, and R.H. Taylor. 1979. The occurrence of microorganisms in water main encrustations. Pp. 1 13-1 17 in Advances in Laboratory Techniques for Quality Control. Presented at the 7th Annual American Water Works Association Water Quality Technology Conference, Dec. 9-12, 1979, Philadelphia, Pa. American Water Works As- sociation, Denver, Colo. Allen, Ad., R.H. Taylor, and E.E. Geldreich. 1980. The occurrence of microorganisms in water main encrustations. J. Am. Water Works Assoc. 72:614-625. American Water Works Association Committee on Tastes and Odors. 1970. Research on tastes and odors. J. Am. Water Works Assoc. 62:S9-62. Arnold, G. E. 1936. Crenothrix chokes conduits. Eng. News- Rec. 1 16: 774-775. Baylis, J.R. 193S. Elimination of Taste and Odor in Water. McGraw-Hill Book Co., New York. 375 pp. Becker, R.J. 1975. Bacterial regrowth within the distribution system. Paper 2B-4 in Water Quality, Proceedings, American Water Works Association Water Quality Technology Conference, Dec. 8-9, Atlanta, Ga. American Water Works Association and the Ameri- can Water Works Association Research Foundation, Denver, Colo. 10 pp.

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Biological Quality of Water in the Distribution System 133 Bryers, J.D., and W.G. Characklis. 1980. Measurement of primary biofilm formation. Pp. 169-183 in J.F. Garey, ed. Condenser Biofouling Control. Ann Arbor Science Publishers, Inc., Ann Arbor, Mich. Beulou, R.W., and G. Walton. 1971. Bacteriological quality vs. residual chlorine. J. Am. Water Works Assoc. 63:28. Beul`~u, R.W., R.H. Taylor, E.E. Geldreich, A. Goodenkouf, L. Wilwerding, F. Holdren, M. Hutchinson, and l.H. Nelson. 1976. Disinfection of new water mains. J. Am. Water Works Assoc. 68:283. Characklis, W.G. 1973. Attached microbial growths. 1. Attachment and growth. Water Res. 7:1113-1127. Characklis, W.G. 1980. Biofilm Development and Destruction. Final Report. Prepared by Rice University, Houston, Texas. EPRI CS-1554. Electric Power Research Institute, Palo Alto, Calif. 283 pp. Characklis, W.G., and S.T. Dydek. 1976. The influence of carbon nitrogen ratio on the chlorination of microbial aggregates. Water Res.. 10:515-S22. Characklis, W.G., M.G. Trulear, N. Stathopoulos, and L-C. Chang. 1980. Oxidation and destruction of microbial films. Pp. 349-368 in R.J. Jolley, W.A. Brungs, and R.B. Cum- ming, eds. Water Chlorination: Environmental Impact and Health Effects. Vol. 3. Pro- ceedings of the 3rd Conference held in Colorado Springs. Colo., Oct. 28-Nov. 1, 1979. Ann Arbor Science Publishers, Ann Arbor, Mich. Clark, J.A., and J.E. Pagel. 1977. Pollution indicator bacteria associated with municipal rau and drinking water supplies. Can. J. Microbiol. 23:465-470. Coene, R.F. 1963. Relationship between Residual Chlorine and Coliform Density in Water Distribution Systems. M.S. Thesis, Oregon State University, Co~vallis. Oreg. Corpe, W.A. 1978. Ecology of microbial attachment and grouth on solid surfaces. Pp. 57-65 in R.M. Gerhold, ed. Microbiology of Power Plant Thermal Effluents. Proceedings of the Symposium. The University of lowa, lo~a City. Costerton, J.W. 1979. The mechanism of primary fouling of submerged surfaces by bacteria. Condenser Biofouling Control Symposium, Electric Power Research institute, Atlanta, Ga. Costerton, ].W., G.G. Geesey, and K.J. Cheng. 1978. Hou bacteria stick. Sci. Am. 238(1): 86-95. Craun, G.F., L.J. McCabe, and J.M. Hughes. 1976. Waterborne disease outbreaks in the US-1971-1974. J. Am. Water Works Assoc. 68:420-424. Derby, R.L. 1947. Control of slime grouths in transmission lines. J. Am. Water Works Assoc. 39: 1107-11 14. Dugan, P.R., and H.M. Pickrum. 1972. Removal of mineral ions from water by microbially produced polymers. Pp. 1019-1038 in Proceedings of the 27th Industrial Waste Confer- ence, May 2, 3, and 4, 1972, Purdue University. Lafayette, Ind. Folwell. A.P. 1917. Water-Supply Engineering. John Wiley & Sons, New York. 562 pp. Geldreich, E.E. 1980. Microbiological processes in ~ater supply distribution. Presented at an American Society for Microbiology Seminar. Microbial Problems in Potable Water Distribution, May 14, 1980, Miami Beach, Fla. 22 pp. Geldreich, E.E., H.D. Nash, D.J. Reasoner, and R.H. Taylor. 1972. The necessity of con- trolling bacterial populations in potable waters: Community water supply. J. Am. Water. Works Assoc. 64:596-602. Geldreich, E.E., R.H. Taylor, and M.J. Allen. 1974. Bacteriological considerations in the installation and repair of ~ ater mains. Paper VIII- I in Water Quality. Proceedings. American Water Works Association Water Quality Technology Conference. Dec. 2-3,

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134 DRINKING WATER AND HEALTH 1974, Dallas. Tex. American Water Works Association and the American Water Works Association Research Foundation, Denver. Colo. 5 pp. Gunsalus, I.C., and R.Y. Stanier, eds. 1960. Bacteria-Structure. Vol. 1. Academic Press, New York. 34 pp. Hejkal, T.W., F.M. Wellings, P.A. LaRock, and A.L. Lewis. 1979. Survival of poliovirus within organic solids during chlorination. Appl. Environ. Microbial. 38:114-118. Herbert, D. 1961. The chemical composition of micro-organisms as ~ function of their envi- ronment. Pp. 391-416 in Microbial Reaction to Environment. Eleventh Symposium of the Society for General Microbiology held at the Royal institution, London, April 1961. The University Press, Cambridge, England. Hoehn, R.C., and A.D. Ray. 1973. Effects of thickness on bacterial film. J. Water Pollut. Control. Fed. 45:2302-2320. Hoff, J.C. 1978. The relationship of turbidity to disinfection of potable water. Pp. 103-117 in C.W. Hendricks, ed. Evaluation of the Microbiology Standards for Drinking Water. EPA- 570/9-78-OOC. U.S. Environmental Protection Agency, Washington, D.C. Hullinger, C.H. 1964. Oxidation. [74] Hypochlorite-oxidized starch. Pp. 313-315 in R.L. Whistler, R.J. Smith, and J.N. BeMiller. eds. Methods in Carbohydrate Chemistry. Aca- demic Press, inc., Neu York. Hutchinson, M. 1971. The disinfection of new water mains. Chem. Ind. No. 1:139-142. Hutchinson, M., and R.W. Collingwood. 1974. WRA MEDLUBE, A Bactericidal Lubricant for Assembly of Push-Fit Pipe Joints. TP 110. The Water Research Association, Medmen- ham, England. Jones, H.C., I.L. Roth, and W.M. Sanders, Ill. 1969. Electron microscopic study of a slime layer. J. Bacteriol. 99:316-325. Kooijmans, L.H. 1966. Occurrence, significance and control of organisms in distribution systems. Pp. C5-C32 in International Water Supply Congress and Exhibition. Vol. 1. General Reports and Papers on Special Subjects. 7th Congress, 3rd to 7th Oct. 1966, Bar- celona. International Water Supply Association, Barcelona, Spain. Kornegay, B.H., and J.F. Andrews. 1968. Kinetics of fixed-film biological reactors. J. Water Pollut. Control Fed. 40: R460-R468. Larson, T.E. 1966. Deterioration of water quality in distribution systems. J. Am. Water Works Assoc. 58: 1307- 1316. Lee, S.H., and J.T. O'Connor. 1975. Biologically mediated deterioration of water quality in distribution systems. Paper No. 22-6. Presented at the American Water Works Associa- tion Annual Conference, Minneapolis, Minn. 9 pp. Lippy, E.C. 1979. Reservoir Water Quality studies. Pp. 5A-1 in Proceedings, American Water Works Association Water Quality Technology Conference. American Water Works Association, Denver, Colo. Lippy, E.C., and J. Erb. 1976. Gastrointestinal illness at Sewickley, Pa. J. Am. Water Works Assoc. 68:606-610. Mackenthun, K.M., and L.E. Keup. 1970. Biological problems encountered in water sup- plies. J. Am. Water Works Assoc. 62:520-526. Marshall, K.C. 1976. Interfaces in Microbial Ecology. Harvard University Press, Cam- bridge, Mass. 156 pp. Marshall, K.C., R. Stout, and R. Mitchell. 1971. Mechanisms of the initial events in the sorption of marine bacteria to surfaces. J. Gen. Microbiol. 68:337-348. Matson, J.V., and W.G. Characklis. 1976. Diffusion into microbial aggregates. Water Res. 10:877-885. McCabe, L.J., J.M. Symons, R.D. Lee, and G.G. Robeck. 1970. Survey of community water supply systems. J. Am. Water Works Assoc. 62:670-687.

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Biological Quality of Water in the Distribution System 135 Minkus, A.J. 1954. Deterioration of the hydraulic capacity of pipelines. J. N. Engl. Water Works Assoc. 68: 1-10. National Academs of Sciences. 1958. Revised Statement on Maintaining a Trace of Residual Chlorine in Water Distribution Systems. Prepared for the Subcommittee on Water Supply of the Committee on Sanitar Engineering and the Environment, National Academy of Sciences-National Research Council, Washington, D.C. 4 pp. Nimmons, M.J. 1979. Heat Transfer Effects in Turbulent Flou Due to Biofilm Develop- ment. M.S. Thesis, Rice University, Houston, Tex. 119 pp. Norrman, G., W.G. Characklis. and J.D. Braces. 1977. Control of microbial fouling in cir- cular tubes with chlorine. Dot. Ind. Microbial. 18:581-590. O'Connor, J.T., L. Hash, and A.B. Eduards. 1975. Deterioration of Hater quality in distri- bution systems. J. Am. Water Works Assoc. 67:113-116. Picologlc~u, B.F., N. Zelver, and W.G. Characklis. 1980. Biofilm growth and hydraulic per- formancc. J. Hydraulics Dis . 106: 733-746. Pollard, A.L., and H.E. House. 1959. An unusual deposit in a hydraulic tunnel. J. Power Di`.85:163-171. Ridg~ay, H.F., and B.H. Olson. 1981. Scanning electron microscope evidence for bacterial colonization of a drinking-~ater distribution system. Appl. Environ. Microbiol. 41:274- 287. Ridguay,J., R.G. Ainsuorth. and R.D. Guilliam. 1978. Water quality changes-Chemical and microbiological studies. In Proceedings of the Conference on Water Distribution Sys- tems. Water Research Centre, Medmenham, England. Russell, G.A. 1976. Deterioration of Hater quality in distribution systems-Dimensions of the problem. Pp. 5-11 in Proceedings, 18th Annual Public Water Supply Conference, Water Treatment, Part 1. University of Illinois, College of Engineering. Urbana, Ill. Schaechter, M., O. Maale, and N.O. Kjeldg~ard. 1958. Dependency on medium and tem- perature of cell size and chemical composition during balanced grow th of Sal,,'a''cll`' typhinturiu'?t. J. Gen. Microbiol. 19:592-606. Silvey, J.K.G., D.E. Henley, R. Hoehn, and W.C. Nunez. 1975. Musty-earthy odors and their biological control. Paper 4B- I in Water Quality, Proceedings. American Water Works Association Water Quality Technology Conference, Dec. 8-9. Atlanta, Ga. Ameri- can Water Works Association and the American Water Works Association Research Foundation, Denver, Colo. Snead, M.C., V.P. Olivieri, K. Kawata, and C.W. Kruse. 1980. Effectiveness of chlorine residuals in inactivation of bacteria and viruses introduced by post-treatment contamina- tion. Water Res. 14:403-408. Tracey, H.W., V.M. Camarena, and F. Wing. 1966. Coliform persistence in highly chlori- nated Haters. J. Am. Water Works Assoc. 58:1151-1159. Trulear, M.G., and W.G. Characklis. 1979. Dynamics of biofilm processes. Pp. 838-853 in Proceedings of the 34th industrial Waste Conference, May 8. 9, and 10, 1979. Purdue University, Lafayette, Ind. Ann Arbor Science Publishers, Inc., Ann Arbor, Mich. Victoreen, H.T. 1969. Soil bacteria and color problem in distribution systems. J. Am. Water Works Assoc. 61:429-431. Victoreen, H.T. 1974. Control of water quality in transmission and distribution mains. J. Am. Water Works Assoc. 66:369-370. Water Research Centre. 1977. Deterioration of Bacteriological Quality of Water During Dis- tribution. Notes on Water Research No. 6. Water Research Centre, Medmenham, Eng- land. 4 pp. Whistler, R.L., and R. Schweiger. 1957. Oxidation of amylopectin with hypochlorite at dif- ferent hydrogen-ion concentrations. J. Am. Chem. Soc. 79:6460-6464.

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136 DRINKING WATER AND HEALTH Whistler, R.L., E.G. Linke, and S.J. Kazeniac. 1956. Action of alkaline hypochlorite on corn-starch amylose and methyl 4-0-methyl-D-glucopyranosides. J. Am. Chem. Soc. 78: 4704-4709. Wiederhold, W. 1949. Uber den Einsluss van Rohrablagerungen auf den hydraulischen Druckabsall. GOOF, Gas Wasserfach, 90:634-641. Wolman, A., and L.H. Enslow. 1919. Chlorine absorption and the chlorination of water. J and. Eng. Chem. I 1: 209-213. Zobell, C.E. 1943. The effect of solid surfaces upon bacterial activity. J. Bacteriol. 46:39-56. Washington, D.C. 187 pp.