Drinking Water and Health, Volume 7 Disinfectants and Disinfectant By-Products (1987) / Chapter Skim
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2 DISINFECTION METHODS AND EFFICACY
2 DISINFECTION METHODS AND EFFICACY
Pages 4-26
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From page 4... ...
Cholera and dysentery were rampant in the 1800s, and typhoid fever was responsible for about 25,000 deaths in the United States as late as 1900 (Akin et al., 19821. Current drinking water disinfection practices in the United States provide the means to control most pathogenic bacteria, viruses, helminths, and protozoa responsible for the major waterborne diseases.
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From page 5... ...
These operations and the principal disinfection practices are briefly discussed below. The historical development of potable water treatment and more detailed aspects of disinfection have been reviewed in previous volumes of Drinking Water and Health (NRC, 1977, l980a,b)
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From page 6... ...
, and taste, odor, or color problems, both natural and anthropogenic, may cause treatment practices appropriate for one set of conditions to be inanorooriate for others. Treatment , ~ Besides disinfection, drinking water treatment practices at a given facility may include coagulation, flocculation, settling, and filtration to remove suspended particles; stripping and chemical oxidation to reduce objectionable taste, odor, or color; and precipitation, softening, pH control, or other operations designed to produce safe and aesthetically acceptable finished water from a raw water source, reliably and cost effectively.
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From page 7... ...
Inorganic and organic molecules, suspended particles, and microbiota in raw water produce what is termed "chlorine demand," because they react with and consume free chlorine, requiring a higher dose of additional chlorine for equivalent biocidal activity. Addition of chlorine beyond the chlorine-demand "breakpoint" produces a free-chlorine residual, which, together with time of exposure, forms the practical basis for determining required amounts of disinfectant.
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From page 8... ...
, are summarized in Tables 2-1 and 2-2. ALTERNATIVE METHODS The suitability of any method for drinking water disinfection can be evaluated on the basis of its efficacy against waterborne pathogens, the accuracy with which it can be monitored and controlled, its ability to provide the necessary residual biocidal activity in the distribution system, the aesthetic quality of the treated water, the applicability of the technology to large-scale operations, and the formation of toxic by-products (NRC, 1977, 1980a,b)
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From page 9... ...
Chlorine Dioxide Chlorine dioxide (C1O2) is used mainly as an industrial bleaching agent for wood pulp, textiles, flour, fats, oils, and waxes, but it has been widely used at drinking water treatment plants for taste, odor, and algal control; iron and manganese removal; and (mainly in Europe)
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From page 13... ...
of 0.10 mg of total trihalomethanes per liter set by the Environmental Protection Agency under the Safe Drinking Water Act (EPA 1979, 1980) , have caused treatment facilities in several states to increase or switch to chloramination (Hack, 19851.
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From page 14... ...
In contrast, several states continue to prohibit chloramination, as Kansas formerly did. WATERBORNE PATHOGENS Outbreaks of waterborne disease associated with drinking water from 1978 to 1984 are shown in Table 2-4.
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From page 15... ...
under defined pH and temperature conditions. Data from several investigations showing the comparative resistance of Giardia cysts and several other types of microorganisms to free chlorine in the form of hypochlorous acid are shown in Table 2-6.
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From page 16... ...
Nusbaum (1952) proposed that the mechanism of bactericidal action of monochloramine is similar to that of hypochlorous acid; that is, the chloramine molecules enter the cytoplasm and interfere with enzymatic reactions.
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From page 20... ...
The results are shown in Table 2-11. The data indicate that chlorine dioxide is considerably more effective than free chlorine but not so effective as ozone for inactivating Giardia cysts.
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From page 22... ...
Employing additional treatment processes to remove substantial numbers of cysts before disinfection is also important in order to decrease reliance on disinfection. viruses The majority of tests described in the literature pertaining to inactivation of human viruses with drinking water disinfectants have been conducted with human enteroviruses, poliovirus, Coxsackievirus, and echovirus.
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From page 23... ...
As with other viruses, the suspected resistance of this agent may be due to the dramatic differences in the rates of inactivation with free and combined chlorine. While culture methods are not available for Norwalk agent, limited information has become available from human volunteer studies.
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From page 24... ...
The data suggesting the resistance of Norwalk agent to free chlorine are difficult to interpret without a clear definition of the nature of the chlorine species present in the reaction system. The reported resistance may be due to the marked difference in the vir~cidal activity of free and combined chlorine that has been reported for other viruses (NRC, 1980a)
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From page 25... ...
1956. Recommended chlorine residuals for military water supplies.
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From page 26... ...
1984. The International Drinking Water Supply and Sanitation Decade: Review of National Baseline Data (as at 31 December 1980)
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