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2 Disinfection Methods and Efficacy CURRENT PRACTICES More than 1.5 billion people in developing nations are still without safe drinking water. Waterborne diseases such as typhoid, cholera, dysentery, amebiasis, salmonellosis, shigellosis, and hepatitis A are still estimated to be responsible for the deaths of more than 30,000 people daily (IRC, 19841. In that context, the United Nations General Assembly has declared 1981-1990 as the International Drinking Water Supply and Sanitation Decade (WHO, 19841. In the last century, major outbreaks of waterborne diseases also occurred in the United States and other affluent nations. 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 pro- vide the means to control most pathogenic bacteria, viruses, helminths, and protozoa responsible for the major waterborne diseases. Some out- breaks still occur in this country (Figure 2-1) owing to continuing problems involving consumption of untreated water, errors of insufficient or inter- rupted disinfection, failures to maintain adequate levels of residual dis- infectant in potable water distribution systems, and/or breaches in the systems (Akin et al., 19821. Moreover, as discussed later in this chapter, the etiology of waterborne disease has changed dramatically since the early l900s; most outbreaks in recent years have been caused by viruses and protozoan cysts that are generally more resistant to disinfection than are pathogenic bacteria, the primary targets of concern in past decades. 4

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Disinfection Methods and Efficacy 5 `~, 50 ye cc m ~ 40 o 10 o it, .?:?.:?:':?:.?:~.2. =='/~;'/m'1~''1 /c / ~ / c / ~ I / c' I / ~ / ~ / ~ / I ~ / FIGURE 2-1 Average annual number of waterborne disease outbreaks occulting in the United States from 1920 through 1979. From Akin et al. (1982), with permission. :::- -:~. ~- .:~::,~,,., :.:.::. :~ .. ,. us o / u) / Q ,u, so ~ ~ Regardless of the method employed, disinfection is only one of the requirements of a potable water supply system. Disinfection requirements and efficacy are often highly interrelated with other water supply and treatment operations. A complete system of potable water supply opera- tions may be considered in three general phases: collection, treatment, and distribution. 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). Collection Surface and groundwater sources of potable water vary locally in terms of their physical, chemical, particulate, biological, and aesthetic charac- teristics. Each characteristic may be an important factor in water supply operations, including disinfection. Water quantity, temperature, pH, sus- pended particulates, solid aggregates, dissolved inorganic constituents (e.g., hardness, ferrous ions, nitrites, and ammonia), nonparticulate organic

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6 DRINKING WATER AND HEALTH constituents (e.g., fulvic and humic acids), microbiota (e.g., bacteria, viruses, protozoa, helminths, and algae), and taste, odor, or color prob- lems, both natural and anthropogenic, may cause treatment practices ap- propriate for one set of conditions to be inanorooriate for others. Treatment , ~ Besides disinfection, drinking water treatment practices at a given fa- cility 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 con- trol, or other operations designed to produce safe and aesthetically ac- ceptable finished water from a raw water source, reliably and cost effectively. More than 1.2 million tons of about 60 bulk chemicals were used for potable water treatment in the United States in 1981; chemicals used for disinfection and oxidation amounted to about 42% of that total (Rehwoldt, 19821. The biocidal efficacy of a chemical or physical disinfectant can depend on the method of application as well as the methods and staging of other treatment practices. Thorough mixing is important to ensure uniform dis- persal and exposure of pathogens to the disinfectant. Pretreatment is often important to minimize solid particles and aggregates that would shield pathogens from the disinfectant. If the disinfectant is chemical, pretreat- ment such as sedimentation of suspended matter, coagulation with alum, or filtration may also be needed to reduce potential reactants that would, in effect, consume a disinfectant, thereby reducing the biocidal efficacy of a given dosage. Distribution A drinking water distribution system is more than a means of trans- porting finished water to the tap. It also acts as a storage system and a potential source of inorganic, organic, and biological contamination that must be considered in the design and operation of a potable water supply system. The distribution system imposes a requirement that adequate post- disinfection residuals continue biocidal activity. CHLORINATION Chlorination has been the predominant method of drinking water dis- infection in the United States for more than 70 years. When concerns about the formation of trihalomethanes and other halogenated hydrocarbon by-products began to stimulate the reexamination of chlorination practices

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Disinfection Methods and Efficacy 7 in the early 1970s, chlorine was being used to disinfect about 95% of the potable water supplied in the United States (Morris, 19711. Chlorine, a strong oxidizing and disinfecting agent, is an effective microbiocide against most waterborne pathogens. It is inexpensive and relatively convenient to produce, store, transport, and use. Nonetheless, because it is a gas at room temperature it can present safety problems, especially during transportation and storage. Its high solubility in water makes it easy to apply in controlled amounts either as chlorine gas, which readily dissolves in water at room temperature, or as a salt of hypochlorite, which is formed by the reaction of chlorine and water as follows: C12 + H2O = HOCl + H+ + Cl HOCl + H2O = H+ + OCl During chlorination, the relative concentrations of the hypochlorous acid (HOC1) and hypochlorite ions (OCl-), together termed "free chlor- ine," are determined mainly by measurement of pH. HOCl, a more ef- fective biocide than OCl-, dissociates into OCl- between a pH of 7.0 and 8.0, the range in which most potable water undergoes treatment (Figure 2-24. 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. Sedimentation, coagulation, filtration, aeration, or any other practices that remove chlorine-demanding substances before chlorination reduce the amount of chlorine required to produce equivalent disinfection. Such prac- tices may also remove humic acids and other organic precursors before chlorination, thereby reducing the formation of trihalomethanes and other by-products of concern (NRC, 19771. Postdisinfection biocidal activity persists in a chlorinated drinking water distribution system. This residual activity, an important advantage of chlo- rination, is primarily due to the reaction of hypochlorous acid with am- monia and amines in raw water to form chloramines, which are less effective as biocides but persist longer than chlorine. The mechanism of chlorine's highly effective biocidal action against indicator bacteria appears to involve alteration of cell membrane perme- ability and disruption of enzymatic reactions within the cell (NRC, 1980a). The relative efficacies of HOC1, OCl -, and chloramines against bacteria, viruses, and protozoan cysts, compared with those of several

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~ DRINKING WATER AND HEALTH boor ~ 80 60 40 20 o O - 20C OC 1 1 1 1 \41 4 5 6 7 8 9 10 11 pH 20 40 _ - - o 60 80 100 FIGURE 2-2 Effect of pH on quantities of hypochlorous acid (HOC1) and hypochlonte ion (OC1-) that are present in water (NRC, 1980a). alternative disinfectants (see next section), 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). Cost may also be a factor, although the costs of several alternative disinfection methods compared by Clark (1981) did not vary by more than threefold to fourfold. Also relevant are the comparative hazards of production, use, transport, disposal, and cleanup. Restricting itself to toxicological and technological criteria, the Safe Drinking Water Committee has previously (NRC, 1980a) judged three of

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Disinfection Methods and Efficacy 9 the many possible alternatives to chlorine to be suitable for primary or secondary drinking water disinfection: ozone, chlorine dioxide, and chlor- amines (Table 2-31. Ozone Ozone (03) is a strong oxidizing gas that reacts rapidly with most organic (and many inorganic) molecules. Its short half-life in water, approximately 10 to 30 minutes in practical treatment applications, requires ozone to be generated on-site for use as a disinfectant. Ozone does not produce a disinfecting residual, so a second disinfectant must usually be added to the treated water to furnish the necessary protection in the distribution system. Ozone is used as the primary disinfectant in many drinking water treat- ment plants, mostly in Europe and Canada. Small-scale applications have been limited in the past owing to maintenance and repair requirements for a reliable power source; but the large-scale technology is well established, and both the reliability and efficiency of ozone technology are improving rapidly. A typical ozone disinfection system consists of modular solid- state generators, air predrying equipment (necessary to produce ozone efficiently), and contactors designed to produce good mixing with the water being treated. Ozone is an efficient biocide that appears to attack the double bonds of fatty acids in bacterial cell walls and the protein capsid of viruses (NRC, 1980a). Its overall efficacy against waterborne pathogens is summarized in Table 2-1. 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) disinfection. Since C1O2 is unstable; sensitive to temperature, pressure, and light; and ex- plosive in air at concentrations of about 4% or more, it is usually generated and used on-site to avoid problems of bulk storage and distribution. C1O2 is highly effective as a biocide against bacteria and viruses under the temperature, pH, and turbidity conditions of drinking water treatment (Table 2-11. ChIoramination Although chloramines are less effective than free chlorine as biocides (Table 2-1), they are more persistent and do not react to form trihalo

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11 D ,_ - C~: O ~s D O ~ + + + + + + + ~C~ + + + + + + + + + + + + + + + + + + + + + + + + + + ~o ~c) C~ Ct ~O - ~ ~V C<' ~ 3~ ~: ~ ~c, ~<,, ~ 3 0 ,,, ~ . ~,= _ ~ ~c~ ~ t4 . :: ~ ~ ~o Z u~ .O _. ~ O ~ ~ 0 ~c~ 0 ~ 0 . _ < < E O ~o m o - o tl . ~ ._ .> Ct - ._ o ._ D 30 _._ v~ _~ +~ ._ c~ . ~. _ .~ ._0 CtD C~ . _C~ 03 ._ ~3 e~ 0 + - ._ c' o ._ o + + ._ ;> ._ . ~ - _ e~ _ ~ 1 - ~ 0 _ . _ - ~ x 0 ~ - + + ct Z c' + ~ ce ~o C,' ce . ~ c~ Ct Ct ~ ~ ~r Ct C~ o o e~ Ct o C~ o = s~ C~ ~0 ~ e,~ . O ~: .^ 00 ~ ~ ;^ ~ O c: ._ ~ _ _ ~ Ct O ._ ~ ~ ~ O ~ Ct ~ O Ct ~; C) ~ D t O C~ c) 3 ~ O ~ O c: ~ ~: o Ct ~ ~ ~ 3 ~ ~ ce .' _ e, D ~ s:: ~ ~ V V =: )_ ~ - 3 ~ ,.~ = 50 ~ ~ Ce s =.= O. C) L., t- ~ m Li,~

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12 a, so 1 Ct C:: ._ Cal Cal ._ Cal so o o so C) ._ o o o ._ Cd .> C) ._ U) 4- C) ._ C~ ._ o Ct C~ L~ s~ Ct C~ C~ m ~ ;^ C~ C~ . O ~ . Ct _ Ct _ ~ ~ ca . o . O ~ Ct _ O -o .~ . C~ ~ S := O _ X ~ 0 00 ~_ a~ o 00 1 O ~ C~ O O O O ~ O - ~ _ O O O _ _ - O ~ O ~ O ~ ~ _ C~ O O O V~ O O O O . . . . . . . . ~ ~ ~ ~ ~ ~ ~ o ~C~ o 0 0 0 00 0 ~ 0 0 U~ U~ C ~C~_ c~ _ 0 00 0 ~ . . . . . ~ C~ ~ 0 oo oo oo oo 0 0 ~ 0 0 ~ ~ ~ ~ ~U~ . . . . . . . . . . 0 0 0 0 0 0 0 0 0 ~U~ C~ 1 1 _ ~ O ~ ~ 0 0 _ _ c~ _ c~ c-~ c- 0 0 0 0 U~ V~ . . . .. . C) Ct 0 ca ~ ._ 0 ~0 ~c ._ 0 0 ~ ~ 0 ;^ ~ ~ :r: ~ 0 ~ 3 o "S: C.) Ct - ~ Ct Ct s~ ~ C) C) ~ - o _ U, o ._ _ ~ D - ~ 3 C') 5~ ._ O r _ C~ - _ _ Ct Ct _ ~ 0c ~ c O ~ C~ S C) S~ ;> 3 ~o . ~ C) Ct 3 t4 . ~ Ct ~ .~ ~o 3 o ~o ~ o - ~ C) o 3 :: e~ , - 3 ~ Ct Ct ._ C.) X .- C) '~ o ~k ~d o o ~ ._ C) ~ . C.) 3 . 't 3 = ~ C) ;,- - - ~ ._ ~ . ~ ~ ,_ V .- E- C~ V~ ~ ~ <,, _ C~ _ o ~ U ~o o r~ ~ t_ ON ~ ._ ~ o C) -, ._ C~ ~ ~ ._ ~ ~ ~ o "o ~s m ~ ~: .s Ct - o C) ._ .= C) - - C~ - o U, ._ - ._ - . ~ - _ _ ~ . ~ ~ .= ^ C~D _% ._ Ct 0 ~ ~ 0 _ ~ ~ O ~ . _ Z ~ C) o o Lt ~ V) C) Ct

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Disinfection Methods and Efficacy 13 TABLE 2-3 Status of Possible Methods of Drinking Water Disinfectiona Suitability Suitability for Disinfection as Inactivating Drinking Water Agent Agent Limitations Disinfectionb Ozone Chlorine Yes Efficacy decreases with Yes increasing pH; affected by ammonia or organic nitrogen Yes On-site generation Yes required; no residual; other disinfectant needed for residual Chlorine dioxide Yes On-site generation Yes required; interim MCL 1.0 mg/liter Iodine Yes Biocidal activity No sensitive to pH Bromine Yes Lack of technological No experience; activity may be pH sensitive Chloramines No Mediocre bactericide; Not poor virucide Ferrate Yes Moderate bactericide; No good virucide; residual unstable; lack of technological experience High pH conditions No Poor biocide No Hydrogen peroxide No Poor biocide No Ionizing radiation Yes Lack of technological No experience Potassium permanganate No Poor biocide No Silver No Poor biocide; MCL No 0.05 mg/liter UV light Yes Adequate biocide; no No residual; use limited by equipment maintenance considerations aData from NRC (1980a), p. 1 18. bThis evaluation relates solely to the suitability for controlling infectious disease transmission. See Conclusions. CChloramines may have use as a secondary disinfectant in the distribution system in view of their persistence. methanes. Concerns about halogenated by-products of chlorination, and the maximum contaminant level (MCL) of 0.10 mg of total trihalometh- anes 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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14 DRINKING WATER AND HEALTH Kansas now requires the use of ammonia to convert all the free-chlorine residual to chloramines following 30 minutes of chlorination. The Met- ropolitan Water District of Southern California has changed from chlo- r~nation to chloramination for distribution system disinfection. 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. During this time, 261 outbreaks were observed, with almost 72,000 cases. The average annual number of outbreaks corresponded to 37, with more than lO,OOO cases. The etiology of disease found in drinking water has changed dramati- cally since the early l900s. While the early diseases associated with drinking water were those with a bacterial etiology, the more recent out- breaks appear to be dominated by gastrointestinal illness associated with viruses and protozoa. The agents associated with the waterborne outbreaks for 1984 are shown in Table 2-5. The data in the table are dominated by acute gastrointestinal illness, which was responsible for nine outbreaks, with 426 cases. Despite the fact that no agent was identifiable in these episodes of waterborne illness, a significant percentage of these outbreaks is believed to be caused by Norwalk or Norwalk-like virus (Kaplan et al., 1982; Kappus et al., 1982; Taylor et al., 1981; Wilson et al., 19821. In 1983, three outbreaks with 164 cases were due to hepatitis A virus (CDC, 1984), while in 1984 only one outbreak with seven cases was reported TABLE 2-4 Disease Associated with Drinking Water, 1978-1984a Number of Outbreaks According to Water Source Non- Number of Year Community community Private Total Cases 1978 10 18 4 32 11,435 1979 23 14 4 41 9,720 1980 23 22 5 50 20,008 1981 14 16 2 32 4,430 1982 22 12 6 40 3,456 1983 29 6 5 40 20,905 1984 13 4 9 26 1,755 TOTAL 134 92 35 261 71,709 Average 37 10,244 aData from CDC (1985).

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i6 DRINKING WATER AND HEALTH TABLE 2-6 C t Products for 99% Inactivation of Various Microorganisms by Free Chlorine at 5C, pH 6.0 Chlorine ConcentrationTime Microorganism (mg/liter)(min) C t Reference - E. cold 0.10.4 0.4 Scarpino et al. (1972) Poliovirus 1 1.01.7 1.7 Scarpino et al. (1972) E. histolyticaa 5.018 90 Snow (1956) cysts G. Iambliab 1.050 50 Jarroll et al. (1981) cysts 2.040 80 Ja~Toll et al. (1981) 4.020 80 Ja~Toll et al. (1981) 8.09 72 Ja~Toll et al. (1981) G. IambliaC 2.530 75 Rice et al. (1982) cysts G. Iambliab 2.5100 250a Rice et al. (1982) cysts G. muris 2.5100 250a Rice et al. (1982) cysts aExtrapolated data. bCysts from asymptomatic carriers. CCysts from symptomatic earners. represented by Escherichia colt. C t results for G. Iamblia, based on cysts from the same source using different chlorine concentrations and exposure times, are similar. The results also indicate that G. Iamblia from different sources may vary in resistance and that G. muris cysts are similar in resistance to G. Iamblia cysts. Additional data showing the effects of temperature and pH on cyst inactivation by free chlorine are presented in Table 2-7 (G. Iamblia) and Table 2-8 (G. muris). For cysts of both species, the general decrease in inactivation rates at lower temperatures is evident. The decrease in free- chlorine efficiency with increasing pH is due to the shift from the more effective hypochlorous acid form to the less effective hypochlorite form. Table 2-9 presents data on inactivation of G. muris by chloramine. The results point up the lower disinfection efficiency of chloramine. The dif- ferences between free- and combined-chlorine efficiency appear to be greater at higher temperatures. The literature on mechanisms of inactivation of other microorganisms by monochloramines is limited. Nusbaum (1952) proposed that the mech- anism of bactericidal action of monochloramine is similar to that of hy- pochlorous acid; that is, the chloramine molecules enter the cytoplasm and interfere with enzymatic reactions. Ingold (1969) suggested that mono

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17 - - go, _) . ~ . o o ._ as > so Cal C) o m Cal C) ~ ~ .O Z O ~ Ct C) Cal ~ O a .O u, o oo ~ TIC a_ SO C ~ ~ _ ~ ~ _ ~ '_ ~ I 00 ~ as ~ ax ~- - ~ _ _ _ ~. . . . . . . . . _ ~ ~ Ct e~5 ct cut cat ct _ Cal ~ ~ ~ ~ ~ ~ ~ - ____--___ .O g g g ~ g ~ ~ ~ ~ - 00 _ _ _ ~ ~ ~ o o ~ ~ ~D \0 ~ - ~ ~ ~ ~ O - - v v v o ~ ~ v~ ~ ~ ~o - u~ c~ ~ oo - - ~ ~ u~ ~ ~ ~ l l l l ~ ~ ~ ~ - - c~ ~ o ~ V_ _ V V o ~ CN ~ oo _ ~ ~ _ _ 1 1 1 1 1 1 ~o ~ ~ ~ ~ ~ ~ ~o ~ oo o o o o o o . . . . . . oo oo oo 1 1 1 1 1 1 o o o ~ ~ U~ ~ ~ V) . . . . . . . . . . _ ~ ~ C~ ~ ~ _ _ _ \0 ~D ~ oo ~ ~ oo \0 ~ oo _ _ _

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18 . ~ Cal U) Co .~ At; .~ o o Cal ._ C) sol o Cat o . oo m 5) 5 -7 ~ ~ O Ct C,7 so ._ C) hi Cal ~- ~ I_ .s ~ ~ O Cal Cal ~ c: C) ~ ~ . _ O ~ TIC o Cal EM of Do cry Ch is - - ~ AD . . ~ oo - - oo _ A, ~) _ t_ _ _ ~ D ~ ~0 = C~ oo ~ ~ ~ CS -, oo o0 oo Ce _ _ _ ~ >, ;^ ~ ~ ~ ~ ._ ._ ~ ,~ ~ ~ ~ ~ - ~ ~ ~ O o0 0 0 0 ~ ~ ~D ~ ~ ~ ~ ~ ~ ~ o ~ - ~ ~ - o - o oo ~ ~ ~ t- 1 1 1 11 1 1 o crN oo ~ - r~ ~ u~ ~ oo c~ - - ~- - oo o (3N o t - ~ ~ ~ 1 1 1 1 ~ ~ o ~ ~ ~ u~ ~ u ~- ~ ~ o ~ . . . Ko ~ ~ - - - 1 1 1 o cn ~ o o - ~ ~ ~ ~ - o ~ - ~ - ~ t - t 1 1 1 1 1 1 1 (o - ~ ~ ~ ~ ~ c~ - o o o - . . - - ) ~ ~ ~ ~ ~ ~ oo a~ - ~: o . - c~ c) . - o e ~ o - ~ o ~ .- ~ c~ ~ = o ~ ~ - ~ D O ~ _ _ ~ O O =, - O ~ ._ ~ ~ ._ O ~ C~ ~ ~ _ D Ct ~ O -O - ~ O ~ ~_ _ E_ C) ;> ._ ~ ~ ._ _ C) _ ._ Ct 0D O ~ ._ _ _4 _ O ~ _ ^ S - Ct c: ~ 8 ~ ^ - _ ~ (t o m C~ ~o <: C~ V, O = ~ Ct C~ C) '< ~a~ V

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19 is: C) 5 go: (L) s Do o PA ~ .s Ct o Cal Cal Cq ~ c O Z ._ . . Cal _ C X Z O I, ~.0 v Son ~~ . 0~ m o Cal ~ -0 ~ ~ ~ ~ ~ ~ A_ A_ _ A_ A_ _` ~ ~ of i,, ~ ~ ~ ED ED ~ ~ \0 ~ ~ ~ _- A_ A_ _ _ 00 of 00 00 00 00 00 00 at cr ~ cr. ~ ~ ~ ox Go oo oo on oo ________ _____ So ~ ~ S S. $, ~ .= .= .~ ~ .= .= . .= .= con c) c) D ~ D ID V V V V V V V V ~ Pt P~ Pt P~ c~ c~ cn u, c~ O O O O O O O O ~ ~ ~ C) ~ ZZZZZZZz>(~> c~ ~ ~ ~ ~ ~ c~ ~ _ c~ - d' t~ ~ ~ O O O O O a~` - c~ ~ a, oo - oo c~ ~ ~- ~ ~t ~ ~ ~ - - ~ 00 t- ~ O. ') _ _ _ O O ~O~- - 00 ~C) C~00 0 ON ~ ~ oO ^ - ) - ) ~ ~ ~_ _ 1 1 1 1 1 1 1 1 1 1 1 0 ~ ~ v~ _ cr~ ~ ~ ~ 0 ON O O - , c~ ~ a~` ~ - ~ ~ oo O c~ 0 - 1 ~t ~ ~ - ] - - - 00 ~t ~ O~ ~ _ _ _ .C:~ v.~ ~ `~C~ t- ~ ~) - ~O ax ~ ~ c~ ~ v ~oo _ _ 1 1 1 1 1 1 1 1 1 1 1 oo ~o ~ ~ ~ oo ~ oo ~ r~ 0 00 ~ C~ C~ \0 ~ ~ ~ O O 00 _ ~ C~ _ _ ~ _ ~ ~ 00 - - C ~( ~0 t_ ~ ~ _ C ~- - 00 1 1 1 1 1 1 1 1 1 1 1 U ~- O. - 00 ~ 00 0 ________~-) ~In ~n ~ ~ . . . . . 00 ~ ~ ~ 00 ~ 00 ~ 00 O O oo oo oo - ', ~ Ir, - - - - - - - oo - ~o oo a~ - o .- e o c~ . - . - e~ c) . 3 ~ ~ O ~ _ O ~ _ O O ~ s~ ~ ~ O ~ ._ ~ O oc ^ O ~ ;^ ._ C~ ;> ._ ~: o 3 o C~ {:q - . ' ~ o ~ _ C~ ~ ~o . ~ P~ o e~ ~ . O V Ct o ._ o . - ._ o~ 3 - ._ ._ o ._ D

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20 DRINKING WATER AND HEALTH chloramine was known to oxidize sulfhydryl groups immediately and irreversibly. On the other hand, Jacangelo and Olivieri (1985) have shown that monochloramine reacts rapidly with several amino acids including cystine. In the presence of excess monochloramine, reactions with other amino acids may also occur. A less rapid reaction, but still more rapid than with other amino acids, occurs between monochloramine and aspara- gine, aspartic acid, histidine, lysine, and tyrosine (Jacangelo and Olivieri, 19851. The inactivation of enzymes that occurs during monochloramine oxidation is believed to be the lethal event in the killing of bacteria. Nucleic acids, particularly deoxyribonucleic acid (DNA), react com- paratively rapidly with monochloramine. The purine and pyrimidine bases react with monochloramine about 0.6 times as rapidly as the nucleosides (Jacangelo and Olivieri, 19851. Scission of the nucleic acid polymer, rather than substitution reactions on the purine or pyrimidine bases, is believed to be responsible for the inactivation of DNA or ribonucleic acid (RNA). In a study carried out by Shih and Lederberg (1976), when monochlor- amine was applied to Bacillus subtilis cells in viva or to the extracted bacterial DNA, it caused double- and single-strand breaks. Comparative inactivation of G. muris and other types of microorganisms by ozone is shown in Table 2-10. The overall resistance pattern is similar to that for chlorine, with cyst resistance being approximately 1 order of magnitude higher than that for poliovirus 1 and 2 to 3 orders of magnitude higher than that for E. colt. The much lower C t products also point up the much higher efficiency of ozone compared with chlorine. Inactivation of G. muris cysts by chlorine dioxide has been studied by one group of researchers (A. J. Rubin, Professor of Civil Engineering, The Ohio State University, Columbus, Ohio, personal communication, 1986~. The results are shown in Table 2-11. The data indicate that chlorine dioxide is considerably more effective than free chlorine but not so ef- fective as ozone for inactivating Giardia cysts. The use of ultraviolet (UV) radiation for low-maintenance, cost-effec- tive disinfection in small water supply systems is under active consider- ation. The results of laboratory studies on the effectiveness of UV radiation against G. Iamblia cysts (Rice and Hoff, 1981) indicate that at the max- imum dose used (63,000 ~W-sec/cm2), less than 80% of the cysts were inactivated, whereas a dose of 3,000 ~W-sec/cm2 inactivated 99.9% of an exposed E. cold population. This is very significant when one considers that the maximum designed dose range of many commercially available UV treatment units is 25,000 to 35,000 ~W-sec/cm2. Other studies in progress confirm the high resistance of Giardia cysts to UV radiation (Carlson et al., 19851. The results of recent studies indicate that, contrary to our general impres- sions 10 years ago, Giardia cysts can be inactivated by drinking water

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21 v~ oo ~ ~ - - oo oo - - ~: o o c~ ;^ .~ ~: cd - c~ ~ - o - o - ~ o . o o ~ - ~ - ~: - s~ ,~o4 c~ - 'e . o - m C} S C) C) - ~.~ D s~ s ~C) Z O ~ e~ _ _ Ct Ct _ _ C) ~ O C~ - C C) :d oo - - - o '_ _ '_ _` U~ ~ U~ o0 oo oo oo ~ ~ C~ _ _ _ _ ~, ~ ~ _ _ Ct Ct _ _ C) ~ . . . _ _ _ Ct Ct C _ _ _ C) C) ~ C~ ~ ~ =: ~ ~ ~: ~: Ct Ct Ct Ct Ct ~ ~ ;^ Ct Ct Ct Ct Ct ~ ~ ~ ~ ~: Ct Ct Ct Ct C5 's ~ ~ ~ ~ C5 e~ C~ Ct Ct C) C) C) C) C~ ._ ._ ._ ._ ._ 3 3 3 3 3 _ _ _ ~ C - ) ~ ~ - , ~ ~ o ~ ~ o O ~D ~ ~ ~ ~ ~c~ o o o o O ~1 1 1 1 1 1 o ~. .. . . . . . ~ o o o - o o o o s.- ~ - -o ts =.- aO~ ~o ~ C) Ct a . e~ S~ -0 ~ . 00 . . . . . O O O O O ~ ~ ~ . . . . . a~ ~ ~ oo oo ~1 1 1 1 1 O ~ ~ ~ O ~ ~ O . . . . . . . . O O ~ . . . . . ~n O O O 0 0 1 1 1 1 1 O O ~ {~} C~) O O O O O O . . O O . . . ~ ~ ~ ~ ~ ~ r~ _ _ ~, Ir, ~ ~) ~) ~ C~ .~5 .3 ~ .S:3 - L, . . . . . C: ~ ;3 ~ C3

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22 DRINKING WATER AND HEALTH TABLE 2-11 C t Products for 99% Inactivation of G. muris Cysts by Chlorine Dioxide Range Disin fectant Number Temper- Cvncen- of ature tration Time Mean Expen (C) pH (mg/liter) (min) Ct Ct meets Reference 5 7 0.11-5.55 1.3-168 7.2-17.6 11.0 5 Rubin (1986)a 25 7 0.22-1.13 3.3-28.8 3.7-6.2 5.0 5 Rubin (1986)a 25 9 0.16-0.82 2.1-19.2 1.7-3.7 2.8 4 Rubin (1986)a aA. J. Rubin, Professor of Civil Engineering, The Ohio State University, Columbus, Ohio, personal communication, 1986. disinfectants. The order of efficacy of disinfectants conventionally used for drinking water treatment is ozone > chlorine dioxide > free chlorine > chloramine. Giardia cysts are among the most resistant pathogens known, however, and the disinfection step must be conducted rigorously under well-controlled conditions. This is especially important during pe- riods when water temperatures are low. 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. While the data collected about these viruses are useful, data on the viruses that are responsible for the diseases observed in drinking water are even more important. Culture methods for hepatitis A virus have recently become available, and several have been reported (Grabow et al., 1983; Peterson et al., 1983~. Recent information is summarized in Table 2-12 in the light of other information for the human enteroviruses. The information is presented as the product of the disinfection concentration times the contact time necessary for 99% inactivation. The data on the human enteroviruses were taken from an earlier summary (NRC, 1980a). The C t product for poliovirus was about 1 to 2 and 10.5 for hypochlorous acid and hypochlorite ion, respectively. The C t product estimated from the data reported by Peterson et al. (1983) for 99% inactivation of hepatitis A virus was about 60 at pH 7 (a mixture of hypochlorous acid and hypochlorite ion). The C t for 99% inactivation is at best a crude estimate and was approximated from data presented for the sero

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Disinfection Methods and Efficacy 23 TABLE 2-12 The Inactivation of Selected Viruses with Chlorine Disinfectants Test Temper Micro- Disin- ature organism fectant pH (C)C t Reference E. cold HOC1 6.0 50.04 NRC (1980a) OCl- 10.0 50.92 NRC (1980a) NH2C1 9.0 5175.00 NRC (1980a) Poliovirus 1 HOC1 6.0 51-2 NRC (1980a) OC1- 10.0 510.5 NRC (1980a) NH2C1 9.0 15900.0 NRC (1980a) Rotovirus HOC1 a a0.25 NRC (1980a) OC1- a a1.4 NRC (1980a) NH2C1 a aa Hepatitis A HOCl 7.0 5Gob Peterson et al. (1983) HOC1 6.0 a<0.32C Grabow et al. (1983) OC1- 10.0 a<1.04C Grabow et al. (1983) NH2C1 a Norwalk agent HOCl/OCl- 7.4 25a Keswick et al. (1985) aNot reported. bC t estimated from animal infectivity data. CC t estimated from disinfection curves. Chlorine residual data suggested that the test mixtures contained significant demand. Concentration used for calculation was the dose reported. conversion of marmoset monkeys (Saguinus spp. ). Grabow et al. ( 1983) reported that the infectious hepatitis agent was much more sensitive to chlorine. Hepatitis A virus was titrated with a multiple-tube dilution procedure coupled with a radioimmune assay that allowed the deter- mination of the probable number of viruses during disinfection with chlorine. The C t product for 99% inactivation of hepatitis A virus from their graphic presentation was <0.32 for hypochlorous acid at pH 6.0 and <1.04 for hypochlorite ion at pH 10.0. The study reported comparative data for other microorganisms, and the hepatitis A virus did not appear to be particularly resistant to chlorine. The conditions normally specified for the disinfection of drinking water with free chlo- rine would successfully inactivate hepatitis A virus. The C t products reported for 99% inactivation of poliovirus by combined chlorine are considerably higher, and C t products as high as 900 have been re- ported. No data are available at present on the inactivation of hepatitis A virus by the combined forms of chlorine. 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. Keswick et al. (1985) reported that Norwalk agent appeared to be more resistant

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24 DRINKING WATER AND HEALTH to chlorine than two strains of rotovirus, one strain of poliovirus, and F2 bacterial virus. Close inspection of the reported data shows that for chlorine doses of 3.75 to 6.25 mg/liter, the majority of the chlorine was in the combined form. Free chlorine was observed after 30 minutes in the ro- tovirus and poliovirus trials, and these viruses were not recovered. How- ever. after 30 minutes no free chlorine was found in the Norwalk trial, and only trace quantities of free chlorine were found in the F2 trial. In each case the viruses were not completely inactivated. 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). REFERENCES Akin, E. W., J. C. Hoff, and E. C. Lippy. 1982. Waterborne outbreak control: Which disinfectant? Environ. Health Perspect. 46:7- 12. Barrett, S. E., M. K. Davis, and M. J. McGuire. 1985. Blending chloraminated and chlor- inated waters. J. Am. Water Works Assoc. 77(1):50-61. Carlson, D. A., R. W. Seabloom, F. B. DeWalle, T. F. Wetzler, J. Engeset, R. Butler, S. Wangsuphuchart, and S. Wang. 1985. Ultraviolet Disinfection of Water for Small Water Supplies. Doc. No. EPA/600/2-85/092. Water Engineering Research Laboratory, U. S. Environmental Protection Agency, Cincinnati, Ohio. [125 pp.] CDC (Centers for Disease Control). 1984. Water-Related Disease Outbreaks. Annual Sum- mary 1983. Centers for Disease Control, Public Health Service, U.S. Department of Health and Human Services, Atlanta, Ga. [19 pp.] CDC (Centers for Disease Control). 1985. Water-Related Disease Outbreaks. Annual Sum- mary 1984. Centers for Disease Control, Public Health Service, U.S. Department of Health and Human Services, Atlanta, Ga. [19 pp.] Clark, R. M. 1981. Evaluating costs and benefits of alternative disinfectants. J. Am. Water Works Assoc. 73:89-94. EPA (U.S. Environmental Protection Agency). 1979. National interim primary drinking water regulations; control of trihalomethanes in drinking water; final rule. Fed. Regist. 44:68624-68707. EPA (U.S. Environmental Protection Agency). 1980. National interim primary drinking water regulations; control of trihalomethanes in drinking water; correction. Fed Regist. 45: 15542-15547. Grabow, W. O. K., V. Gauss-Muller, O. W. Prozesky, and F. Deinhardt. 1983. Inacti- vation of hepatitis A virus and indicator organisms in water by free chlorine residuals. Appl. Environ. Microbiol. 46:619-624. Hack, D. J. 1985. State regulation of chloramination. J. Am. Water Works Assoc. 77(1):46- 49. Ingold, C. K. 1969. Structure and Mechanism in Organic Chemistry, 2nd ed. Cornell University Press, Ithaca, N.Y. 1,266 pp. IRC (International Reference Centre for Community Water Supply and Sanitation). 1984. IRC at a Glance. IRC, The Hague, The Netherlands. 20 pp.

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Disinfection Methods and Efficacy 25 Jacangelo, J. G., and V. P. Olivieri. 1985. Aspects of the mode of action of monochlor- amine. Pp. 575-586 in R. L. Jolley, R. J. Bull, W. P. Davis, S. Katz, M. H. Roberts, Jr., and V. A. Jacobs, eds. Water Chlorination: Chemistry, Environmental Impact and Health Effects, Vol. 5. Lewis Publishers, Chelsea, Mich. Jarroll, E. L., A. K. gingham, and E. A. Meyer. 1981. Effect of chlorine on Giardia lamblia cyst viability. Appl. Environ. Microbiol. 41:483-487. Jarroll, E. L., J. C. Hoff, and E. A. Meyer. 1984. Resistance of cysts to disinfection agents. Pp. 311-328 in S. L. Erlandsen and E. A. Meyer. Giardia and Giardiasis: Biology, Pathogenesis, and Epidemiology. Plenum, New York Kaplan, J. E., R. A. Goodman, L. B. Schonberger, E. C. Lippy, and G. W. Gary. 1982. Gastroenteritis due to Norwalk virus: An outbreak associated with a municipal water system. J. Infect. Dis. 146:190-197. Kappus, K. D., J. S. Marks, R. C. Holman, J. K. Bryant, C. Baker, G. W. Gary, and H. B. Greenberg. 1982. An outbreak of Norwalk gastroenteritis associated with swim- ming in a pool and secondary person-to-person transmission. Am. J. Epidemiol. 116:834 839. Katzenelson, E., B. Kletter, and H. I. Shuval. 1974. Inactivation kinetics of viruses and bacteria in water by use of ozone. J. Am. Water Works Assoc. 66:725-729. Keswick, B. H., T. K. Satterwhite, P. C. Johnson, H. L. DuPont, S. L. Secor, J. A. Bitsura, G. W. Gary, and J. C. Hoff. 1985. Inactivation of Norwalk virus in drinking water by chlorine. Appl. Environ. Microbiol. 50:261-264. Morris, J. C. 1971. Chlorination and disinfection State of the art. J. Am. Water Works Assoc. 63:769-774. NRC (National Research Council). 1977. Drinking Water and Health. National Academy of Sciences, Washington, D.C. 939 pp. NRC (National Research Council). 1980a. Drinking Water and Health, Vol. 2. National Academy Press, Washington, D.C. 393 pp. NRC (National Research Council). 1980b. Drinking Water and Health, Vol. 3. National Academy Press, Washington, D.C. 415 pp. Nusbaum, I. 1952. Sewage chlorination mechanism: A survey of fundamental factors. Water Sewage Works 99:295-297. Peterson, D. A., T. R. Hurley, J. C. Hoff, and L. G. Wolfe. 1983. Effect of chlorine treatment on infectivity of hepatitis A virus. Appl. Environ. Microbiol. 45:223-227. Rehwoldt, R. 1982. Water chemicals codex. Environ. Sci. Technol. 16:616A-618A. Rice, E. W., and J. C. Hoff. 1981. Inactivation of Giardia lamblia cysts by ultraviolet irradiation. Appl. Environ. Microbiol. 42:546-547. Rice, E. W., J. C. Hoff, and F. W. Schaefer III. 1982. Inactivation of Giardia cysts by chlorine. Appl. Environ. Microbiol. 43:250-251. Roy, D., R. S. Englebrecht, and E. S. K. Chian. 1982. Comparative inactivation of six enteroviruses by ozone. J. Am. Water Works Assoc. 74:660-664. Scarpino, P. V., G. Berg, S. L. Chang, D. Dahling, and M. Lucas. 1972. A comparative study of the inactivation of viruses in water by chlorine. Water Res. 6:959-965. Shih, K. L., and J. Lederberg. 1976. Chloramine mutagenesis in Bacillus subtilis. Science 192:1141- 1143. Snow, W. B. 1956. Recommended chlorine residuals for military water supplies. J. Am. Water Works Assoc. 48: 1510- 1514. Taylor, J. W., G. W. Gary, Jr., and H. B. Greenberg. 1981. Norwalk-related viral gas- troenteritis due to contaminated drinking water. Am. J. Epidemiol. 114:584-592.

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26 DRINKING WATER AND HEALTH WHO (World Health Organization). 1984. The International Drinking Water Supply and Sanitation Decade: Review of National Baseline Data (as at 31 December 1980). WHO Offset Publication No. 85. World Health Organization, Geneva. 169 pp. Wickramanayake, G. B., A. J. Rubin, and O. J. Sproul. 1984. Inactivation of Naegleria and Giardia cysts in water by ozonation. J. Water Pollut. Control. Fed. 56:983-988. Wickramanayake, G. B., A. J. Rubin, and O. J. Sproul. 1985. Effects of ozone and storage temperature on Giardia cysts. J. Am. Water Works Assoc. 77(8):74-77. Wilson, R., L. J. Anderson, R. C. Holman, G. W. Gary, and H. B. Greenberg. 1982. Waterborne gastroenteritis due to the Norwalk agent: Clinical and epidemiologic inves- tigation. Am. J. Public Health 72:72-74.