Drinking Water and Health, Volume 4 (1982) / Chapter Skim
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IV Biological Quality of Water in the Distribution System
IV Biological Quality of Water in the Distribution System
Pages 108-136
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From page 108... ...
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 system, changes in water quality will be minimal, and water provided to the consumer will be similar to that leaving the treatment plant.
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From page 109... ...
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.
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From page 112... ...
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 activity in the biofilm (O'Connor et al., 1975~; · taste and odor changes resulting from products of microbial metabolism 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.
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From page 113... ...
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 produce relatively high-molecular-weight organic compounds, primarily polysaccharide in nature.
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From page 114... ...
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 processes 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.
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From page 115... ...
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.
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From page 117... ...
. The combined process probably occurs in many water distribution systems.
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From page 119... ...
Increases in the frictional resistance when the water flow rate is constant increases the fluid stress at the biofilm-water interface. The result is an increase in the rates at which nutrients and particles (including microbial cells)
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From page 122... ...
122 Cal A ._ 3 ._ C~ ._ G)
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From page 123... ...
ct c} c)
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From page 124... ...
. This living material can enter the distribution network in many ways: through raw water, treated water, reservoirs, tanks, and imperfections and perturbations in the water distribution system.
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From page 125... ...
Construction and Repair Microorganisms and nutrients supporting microbial growth may gain access to water distribution systems during installation and repair of components (Buelow et curl., 1976; Geldreich et al., 1974~. During these processes, unprotected pipe sections may become contaminated by soil, sewage, storm runoff, animal feces, and debris and can therefore contribute heavy loads of microorganims to the pipe network directly.
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From page 126... ...
Figure IV-3 illustrates the effectiveness of these processes in a segment of a water distribution conduit. There are three basic steps: · Chlorine species entering the pipe segment react with chlorine-demanding components (viable cells and chemical compounds)
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From page 128... ...
If chlorine reacts with biofilm relatively rapidly, the concentration at the interface will be low and the physical 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 interface will increase.
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From page 129... ...
· 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.
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From page 130... ...
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 chlorineammonia 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 chlorammoniation process was quite ineffective in eliminating taste and odors in unfiltered water supplies.
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From page 131... ...
SUMMARY AND CONCLUSIONS Living organisms can enter the water distribution system through insufficiently treated raw water, in-line reservoirs, and imperfections in the pipeline network. Microbial activity occurs predominantly at the pipe wall where nutrients gather in high concentrations.
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From page 132... ...
Paper 2B-4 in Water Quality, Proceedings, American Water Works Association Water Quality Technology Conference, Dec. 8-9, Atlanta, Ga.
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From page 133... ...
American Water Works Association Water Quality Technology Conference.
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From page 134... ...
Pp. 5A-1 in Proceedings, American Water Works Association Water Quality Technology Conference.
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From page 135... ...
Paper 4B- I in Water Quality, Proceedings. American Water Works Association Water Quality Technology Conference, Dec.
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From page 136... ...
1949. Uber den Einsluss van Rohrablagerungen auf den hydraulischen Druckabsall.
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