Drinking Water and Health, Volume 2 (1980) / Chapter Skim
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II. The Disinfection of Drinking Water
II. The Disinfection of Drinking Water
Pages 5-138
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From page 5... ...
Chlorination is the most widely used method for disinfecting water supplies in the United States. The near universal adoption of this method can be attributed to its convenience and to its highly satisfactory performance as a disinfectant, which has been established by decades of use.
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From page 6... ...
Available information on the obvious major candidates for drinking water disinfection chlorine, ozone, chlorine dioxide, iodine, and bromine—is then evaluated for each method individually in the following sections. Other less obvious possibilities are also examined to see if they have been overlooked unjustly in previous studies or if it might be profitable to conduct further experimentation on them.
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From page 7... ...
The analytical methods that are described in this report are those that are most likely to be used by persons involved in disinfection research or water treatment. A review of all existing analytical methods, some of which may be more sophisticated than those described below, would be impractical within the constraints of time and space available and is not within the scope of this document.
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From page 8... ...
Water, particularly surface waters, may also contain synthetic organic molecules whose demand for disinfectant will be determined by their structure. Ammonia and amines in raw water will react with chlorine to yield chloramines that do have some biocidal activity, unlike most products of these side reactions.
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From page 9... ...
Prechlorination to a free chlorine residual is practiced early in the treatment sequence as one method to alter taste- and odor-producing compounds, to suppress growth of organisms in the treatment plant, to remove iron and manganese, and to reduce the interference of organic compounds in the coagulation process. The necessity for these treatments or others is determined by the characteristics of the raw water.
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From page 10... ...
Residual measurements are important and useful in controlling the disinfection process. By knowing the residual-time relationship that is required to inactivate pathogenic or infectious agents, one can adjust the dosage of the disinfecting agent to achieve the residual that is required for effective disinfection with a given contact time.
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From page 11... ...
These qualities might include discoloration of water from potassium permanganate (KMnO4) or iodine or problems of taste and odor from excessive chlorine.
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From page 12... ...
The overwhelming majority of the literature on water disinfection concerns the inactivation of model microorganisms rather than the pathogens. These disinfectant model microorganisms have generally been nonpathogenic microorganisms that are as similar as possible to the pathogen and behave in a similar manner when exposed to the disinfectant.
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From page 13... ...
cold were more resistant to free chlorine than were Salmonella typhi strains. At pH values of 6.5 and 7.0, strains of S
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From page 14... ...
They found enteric viruses to be most resistant to free chlorine followed by RNA phages, E colt, and the T phages.
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From page 15... ...
They observed that the yeast was more resistant to free chlorine than were poliovirus 1 and the enteric bacteria under all conditions tested. The acid-fast bacilli were most resistant.
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From page 16... ...
Naturally occurring cells that were grown in distilled water reacted quite differently to chemical and physical stresses than did cells grown on standard laboratory culture media. For example, naturally occurring cells of P
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From page 17... ...
Despite the questions that have been raised by differences in the behavior of organisms under both laboratory and field conditions, valuable comparative information can be obtained from studies of disinfectants that are conducted in similar laboratory systems. CHLORINE AND CHLORAMINES Chlorine is a strong oxidizing disinfectant that has been used to treat drinking water supplies for more than 60 yr.
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From page 18... ...
The dissociation of hypochlorous acid is dependent chiefly upon pH and, to a much lesser extent, temperature, with almost lOO~o hypochlorous acid present at pH 5 and almost lOO~o hypochlorite ion present at pH 10 (Figure II-1~. Free available chlorine refers to the concentration of hypochlorous acid and hypochlorite ion, as well as any molecular chlorine existing in a chlorinated water.
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From page 19... ...
The organic chloramines that are produced (see below) are considered encompassed in the term '~combined available chlorine." Although inorganic chloramines are less effective oxidizing and disinfecting agents than hypochlorous acid and hypochlorite ion, they are more stable.
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From page 20... ...
When chlorine is added to water with no chlorine demand, a linear relationship is established between the chlorine dosage and the free chlorine residual (Figure II-3~.
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From page 21... ...
However, when increasing amounts of chlorine are added to water containing reducing agents and ammonia, the so-called breakpoint phenomenon occurs. The breakpoint is that dosage of chlorine that produces the first detectable amount of free available chlorine residual.
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From page 22... ...
When all of the ammonia has been reacted, a free available chlorine residual begins to develop. As the concentration increases, the previously formed chloramines are oxidized to nitrous oxide (N2O)
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From page 23... ...
This is also true of chlorine dioxide. Also, some nitrogen bichloride may be measured as free chlorine.
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From page 24... ...
Some more contemporary studies have lacked quantitated information on chlorine residual and/or types of chlorine present in the test systems. Biocidal Activity In the absence of reducing agents, inorganic ammonia, and organic amines, the addition of chlorine to municipal water supplies will result in free available residual chlorine, represented by the hypochlorous acid or hypochlorite ion.
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From page 25... ...
colt, Enterobacter aerogenes, Pseudomonas aeruginosa, Salmonella typhi, and Shigella dysenteriae. They used different levels of free chlorine at pH values ranging from 7.0 to 10.7 and two temperature ranges 2°C to 5°C and 20°C to 25°C.
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From page 26... ...
In their chlorination studies, they noted the following decreasing order of resistance to free chlorine at pH values of 6, 7, and 10 and at 5°C and 20°C: acid-fast bacteria > yeasts > poliovirus > Salmonella typhimurium > E coli.
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From page 27... ...
Chloramines were determined using orthotolidine; readings made after 10 to 30 s at 20°C gave free chlorine levels, and those after standing for 10 min at 20°C were recorded as total residual chlorine. Since no free chlorine was reported (and should not have been found, according to the authors)
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From page 28... ...
Organic Chloramines These chlorine derivatives exhibit some bactericidal activity, but markedly less than either free chlorine or the inorganic chloramines (Fen", 1966; Nusbaum, 1952~. In summary, the bactericidal efficiency of hypochlorous acid, the hypochlorite ion, monochloramine, and dichloramine have been accu.
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From page 29... ...
They carefully controlled their free chlorine residuals with a modified form of the orthotolidine test to determine total chlorine and an orthotolidine-arsenite method for free chlorine. (Combined chlorine was then calculated as the difference between "total" and "free" chlorine readings.)
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From page 30... ...
coli, a 99-s contact time was required when the system was dosed with 0.1 mg/liter free chlorine as hypochlorous acid. The same percentage of the adenovirus was inactivated in approximately one-third of that time by the same concentration of hypochlorous acid.
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From page 31... ...
(1971) studied the manner in which 20 strains of human enteric viruses responded to free chlorine.
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From page 32... ...
32 ._ ~ o is o on +1 C.)
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From page 33... ...
However, assuming a 20-min contact time, most of the viruses tested at pH 7.8 and 2°C would have been 99.99% inactivated with a free chlorine residual of 0.5 mg/liter. Using six of the same virus strains studied by Liu et al.
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From page 34... ...
c Time required at pH 10.0 Time required at pH 6.0 0.3 mg/liter free chlorine inactivated 99.9% of all test viruses in 8 min. At the same temperature and pH, combined chlorine at 0.7 mg/liter and at least 4 hr of contact time were needed to achieve 99.7% inactivation of the test viruses.
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From page 35... ...
Free chlorine residuals as high as 95 to 100 mg/liter for 5 min killed only 40~50~o of the nematodes. Thus, it may be speculated that all the helminths, including their larvae, may approach the degree of resistance to chlorine that had been demonstrated by the free-living nematodes.
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From page 36... ...
Using chlorine gas bubbled into buffered distilled water as stock, they obtained 99.9% cyst inactivation (as measured by excystment capability) after 15 min exposure to 2 mg/liter free chlorine in "clean water" at pH 6.
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From page 37... ...
The latter effect was attributed to inhibition of the respiratory enzyme rather than to a deficiency in phosphate uptake. However, it is unclear whether free or combined chlorine was used in these studies.
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From page 38... ...
Such oxidation would have resulted in the rapid inactivation of the bacteria. They hypothesized that since monochloramine required higher concentrations and longer contact times to destroy bacteria completely and could not readily and irreversibly oxidize the sulfhydryl groups of the glucose oxidation enzymes, its ability to inactivate microorganisms should be attributed to changes in enzymes that may not be involved in the inactivation of the organism by hypochlorous acid.
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From page 39... ...
Summary Chlorine is the most widely used water supply disinfectant in the United States. Depending upon the predominant species of chlorine, hypochlorous acid, and/or hypochlorite ion, disinfection with chlorine can achieve greater than 99.9% destruction of bacteria.
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From page 41... ...
41 oo r~ - ~ oo ~ - ~ ~ c~ ~ o ~ o)
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From page 42... ...
Ozone has a half-life in pure distilled water of approximately 40 min at pH 7.6, but this decreases to 10 min at pH 8.5 (Stumm, 1958)
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From page 43... ...
Ozone has been used in a great number of water treatment plants throughout the world. However, in small institutions and private residences, its use appears limited, because it requires dependable power supplies and, usually, a second disinfectant to furnish a disinfecting residual in the system.
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From page 44... ...
. Hydrogen peroxide (H2O2)
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From page 45... ...
(1976~. For 99% inactivation with 0.1 mg/liter of initial ozone residuals, contact times of 16.5 and 21 s were required at pH 6 and 10, respectively.
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From page 46... ...
, who observed that the disinfection capability of ozone does not change significantly with pH, at least over the normal pH range (6 to 8.5) of water supplies.
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From page 47... ...
Inactivation of poliovirus 2 and coxsackievirus B3 in 5 min was greater than 99.9% in the batch tests when the ozone residual was between 0.8 and 1.7 mg/liter at the end of the 5-min contact period. Initial ozone residuals varied from 1.6 to 2.8 mg/liter.
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From page 48... ...
Ozone may have application as an antiparasitic agent in the treatment of water supplies but only limited information is available. Newton and Jones (1949)
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From page 49... ...
An electrophoretic study showed complete loss of viral proteins in a poliovirus 2 sample that had showed an inactivation of 7 logs in 20 min. Summary and Conclusions Inactivation with ozone at specified ozone residuals is relatively insensitive to pH's between 6.0 and 8.5.
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From page 50... ...
50 ~~ ·s ·~ o go · · c~ oN o w A, Ad a)
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From page 51... ...
surveyed water treatment plants believed to be using chlorine dioxide.
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From page 52... ...
In England, Italy, and Switzerland, it is used for disinfection of water supplies. The Chemistry of Chlorine Dioxide in Water Chlorine dioxide reacts with a wide variety of organic and inorganic chemicals under conditions that are usually found in water treatment systems (Stevens et al., 1978~.
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From page 53... ...
The sodium hypochlorite is acidified to yield hypochlorous acid (HOC1) , and the chlorine dioxide is generated according to Reaction 10.
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From page 54... ...
Analytical Methods Chlorine dioxide is one of the few stable nonmetallic inorganic free radicals (Rosenblatt, 1978~. It does not contain available chlorine in the form of hypochlorous acid or hypochlorite ion (OC1-~.
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From page 55... ...
procedures for free chlorine, chlorine dioxide, and chlorite. They reported DPD to be the most reliable, as did Dowling (1974)
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From page 56... ...
In the waters containing ammonia, chlorine had to be applied beyond breakpoint before efficient sporicidal activity was observed. The work of Ridenour and colleagues is not discussed in depth because the small amounts of free chlorine that are produced during the generation of chlorine dioxide are not distinguished from the chlorine dioxide by the OTA method that they used for both stock solutions and residual determination.
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From page 57... ...
This suggests that the initial and residual concentrations of chlorine dioxide were probably lower than reported values and that the comparative bactericidal efficiency would suffer accordingly. In addition, the older investigations did not take into account the volatility of chlorine dioxide.
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From page 58... ...
C 0.50 0.98 0.49 7.0 5 0.80 0.58 0.41 7.0 5 0.30 1.3 0.39 7.0 15 0.50 0.75 0.38 7.0 15 0.80 0.47 0.38 7.0 15 0.30 0.98 0.29 7.0 25 0.50 0.55 0.28 7.0 25 0.80 0.35 0.28 7.0 25 a Concentration of chlorine dioxide times contact time. b Data from Bernarde en al., 1967a.
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From page 59... ...
Similar to its bactericidal activity, chlorine dioxide was more elective as a virucide at higher pH. Cronier also reported that on a weight basis, it was similar to hypochlorous acid and better than hypochlorite ion, monochloramine, and dichloramine.
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From page 60... ...
Table II-7 presents similar data for viruses. Increased chlorine dioxide concentration, temperature, and pH decreased the contact time that was required to produce 99% inactivation of the viruses.
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From page 61... ...
of the cell extracts of treated cells without affecting the integrity of the ribosomes' function in protein synthesis. Conclusion Chlorine dioxide is an effective bactericide and virucide under the pH, temperature, and turbidity that are expected in the treatment of potable water.
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From page 62... ...
A persistent residual was maintained throughout the distribution system despite a finished water pH of 8.0 to 9.5. No adverse effects on health were observed among those consuming the water.
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From page 63... ...
Production and Application Iodine may be added to a municipal water supply by several procedures. One method is to employ nonhazardous solvents and solubilizing agents such as ethyl alcohol (C2H5OH)
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From page 64... ...
Under unusual situations, where mixtures of chlorine, bromine, and ozone occur along with iodine, the problem of separation is difficult (Standard Methods, 1976~. Biocidal Activity Table II-9 shows the relative resistance of bacteria, viruses, and cysts to inactivation by iodine.
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From page 65... ...
mg/liter of iodine, which is extremely high compared to the amount that is possibly needed for public water supplies. The tablet is not widely accepted, since color, taste, and odor problems are fairly common (O'Connor and Kapoor, 1970~.
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From page 66... ...
However, when the potassium iodide concentration was raised to 0.5 M, bacterial inactivation was 4 logs in 1 min while virus inactivation was only 0.5 log in 1 hr (Figure II-6~.
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From page 67... ...
, iodine is a vastly more effective virucide. than combined chlorine and is not far removed from the activity range of free chlorine.
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From page 68... ...
68 .g ~ Can o ~o o C~ Cal c - o Cal an U)
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From page 69... ...
Table II-12 shows the time in minutes required for 9~3'o inactivation of simian cysts with residuals of bromine, chlorine, and iodine in water at pH 6.0, 7.0, and 8.0 and a temperature of 30°C. At pH 8.0, iodine is inferior to free bromine and chlorine.
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From page 70... ...
70 c~~ O4 _ a i) ceS ~ ~ ~ ~ =^ ·= C ~ 8 _ =6 O~ ~ o ~ .= .E o O D m .g ~ ,7§ 3 .E o Cot ~ CS ~ —o ~ To Z ·§ ·= Cat C C ~ _ o _ ._ be.> a' ~ o mm _ rot a vat rat 0 ~ ~ ~ 0 ~ ~ 0 0 _ ~ ~ ~ 0 0 0 0 0 0 _ ~ 00 _ ~ or ~ ~ ~ ~ ~ 0 _ _ ~ ~ So of 0 So ~ _ _ ooze ooO Cat ~ ~ ~ ~ ~ fib Oslo for _ _ ~ ~ ~ ~ _ dC, 0 ~ ~ 0 0 Us _ _ _ _ ~ - } 0 0 0 0 0 0 .
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From page 71... ...
inhibited the iodination of tyrosine. Both poliovirus and f2 virus inactivation with iodine was inhibited by the iodide ion
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From page 72... ...
The mode of action of iodine in cyst penetration and inactivation has not been studied. Conclusions Iodine has many features that are comparable to free chlorine and bromine as a water disinfectant, but iodamines are not formed.
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From page 73... ...
Like chlorine, bromine chloride has a much higher hydrolysis constant than this, so it does not exist as the molecular form in appreciable concentrations under conditions of water treatment. The ratio of molecular bromine to hypobromous acid depends on both pH and bromide concentration.
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From page 74... ...
Bromine chloride is produced by mixing equal molar q~antities of pure bromine and chlorine (Mills, 1975~. It condenses to liquid bromine chloride below 5°C at 1 atm pressure or above 30 psig at 25°C.
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From page 75... ...
Gas feeders must be made of Teflon, Kynar, or Viton plastics because bromine chloride is more reactive than chlorine with polyvinylchloride plastics. Analytical Methods Bromine concentrations can be measured iodometrically by procedures that are identical to those used to measure total chlorine residuals (`Standard Methods, 1976~.
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From page 76... ...
Before the ammonia is added to the solution, hypobromous acid is the ma~or chemical form. When the ammonia nitrogen reaches 1 mg/liter, nitrogen tribromide predominates.
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From page 77... ...
b initial bromine concentration 20 mg/liter. c Concentration of bromine times contact time.
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From page 78... ...
t of 0.35 to inactivate 99% of this phage at 0°C. Compared to hypobromous acid, molecular bromine was approximately 3 times as fast, requiring Br2 at c .
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From page 79... ...
t of 0.06 was required for 99% inactivation with hypobromous acid. The inactivation of single poliovirus particles in buffered, distilled water and constant residual concentrations for the other major bromine chemical forms have also been studied by Floyd et al.
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From page 80... ...
Hypobromous acid (HOBr) Hypobromous acid Hypobromous acid 0.06 1.2 0.19 0.03 0.01 0.24 0.21 7.0 7.0 5.0 2 10 20 10.0 7.0 7.0 7.0 a Concentration of compound times contact time.
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From page 81... ...
After comparing the activity of chlorine, bromine, and iodine against spores, Marks and Strandskov (1950) noted that Brz was 9 times more effective than hypobromous acid and that the hypobromite ion and tribromide ion (Bra-)
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From page 82... ...
Ferrates are strong oxidizing agents that have a redox potential of-2.2 V or 0.7 V in acid and base, respectively flood, 1958~. The Chemistry of Ferrate in Water Aqueous solutions of potassium Serrate are unstable and decompose to yield oxygen (02)
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From page 83... ...
with potassium permanganate (KMnO41. Subsequent recrystallization yields a crystalline solid with greater than 90% purity (Schreyer et al., 1950~.
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From page 84... ...
extended Gilbert's disinfection studies to include enteric pathogens and Gram-positive bacteria and evaluated the effects of pH and temperature. The rate of E
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From page 85... ...
Mechanism of Action No studies have elucidated the mechanism of inactivation caused by ferrate. Conclusions While not as biocidal as the free halogens, chlorine dioxide, or ozone, ferrate appears to be similar to or slightly better than the chloramines as a bactericide and more active as a virucide than the chloramines.
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From page 86... ...
A few, very large water treatment plants produce their own calcium hydroxide by calcining their water-softening sludge. Hydroxide (OH-)
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From page 87... ...
Even in distilled water, calcium carbonate may precipitate if calcium hydroxide is used to raise the pH and if sufficient carbon dioxide enters the water during the experiment. These precipitates provide opportunities for adsorption and coagulation of microorganisms and will cause an increased removal over that obtained from the pH effect alone without the precipitate.
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From page 89... ...
(1968) reported that little or no poliovius 1 was inactivated in distilled water at pH 11.2 at room temperature in 90 min when calcium hydroxide or sodium hydroxide was used to increase the pH.
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From page 90... ...
showed the inactivation of echovirus 7 AGKP8A1 at 25°C in a dilution water medium (Standard Methods, 1960~. They used sodium hydroxide to adjust pH (see Table II-l9~.
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From page 91... ...
Studies are needed to determine the pH values required for inactivation of protozoans, a broader and more representative group of viruses, and a larger group of enteric bacteria. HYDROGEN PEROXIDE Hydrogen peroxide (H2O2)
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From page 92... ...
worked with Escherichia colt, Salmonella typhi, and Staphylococcus aureus in pure culture and as a mixture of bacteria. They also studied the effect of hydrogen peroxide concentrations (from 30 to 60 mg/liter)
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From page 93... ...
or increasing temperature from 24°C to 76°C significantly reduced the required inactivation time. Several studies on virus inactivation by hydrogen peroxide have been reported.
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From page 94... ...
Parallel studies using chlorine and hydrogen peroxide, separately and in conjunction, should be conducted. IONIZING RADIATION Ionizing radiation may be electromagnetic or particulate.
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From page 95... ...
Biocidal Activity EFFICACY AGAINST BACTERIA The first study of ionizing radiation in the treatment of water was reported by Dunn (19531. In addition to reviewing the literature and providing some discussion on ionizing radiation, he studied the use of a 1,000-Ci source of cobalt-60 (providing gamma rays)
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From page 96... ...
(1956) exposed pure cultures of bacteria that were suspended in double distilled water and sterile settled sewage.
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From page 97... ...
EFFICACY AGAINST PARASITES The WIT study (1977) appears to be the only one in which the effect of ionizing radiation on both protozoa and helminths was investigated; however, no quantitative data were reported.
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From page 98... ...
POTASSIUM PERMANGANATE Potassium permanganate (KMnO`) is a strong oxidizing agent, which was first used as a municipal water treatment chemical by Sir Alexander Houston of the London Metropolitan Water Board in 1913.
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From page 99... ...
and studied the effect of potassium permanganate at doses of 1 to 16 mg/liter at pH values of 5.9, 7.4, and 9.2, temperatures of 0°C and 20°C, and contact times of 4 to 120 min. They concluded that bacterial inactivation was relatively ineffective, but slightly better at the higher temperature, and
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From page 100... ...
100 o o ·= In 'a He - o cO 1 · u, I' o so ~2 o :~: a _ a .~ ~ i; Cal ~ _ ~ ~E ~ ~ ~ ~ .O Came CO I' X To _ 0 0 cry V)
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From page 101... ...
They provide few clear-cut quantitative data on biocidal activity of the compound. Information is lacking on the effect of potassium permanganate on protozoans and helminths in water.
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From page 102... ...
Production and Application In water treatment, silver has been applied principally by dissolving the metal or by incorporating a silver compound in a filter medium, often an activated carbon filter. Romans (1954)
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From page 103... ...
Analytical Methods Until recently there have been no satisfactory techniques for measuring silver at the ,ug/liter level. Using a dithizone calorimetric method, the minimum detectable quantity of silver is 200 ,ug/liter (Standard Methods, 1976~.
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From page 104... ...
In most studies of the disinfection of water with silver, Escherichia cold has been the test organism. Wuhrmann and Zobrist also tested a Salmonella species and found it to be at least as sensitive as E
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From page 105... ...
This would explain the relatively long contact times that are required for antibacterial activity at the concentrations that are normally used.
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From page 106... ...
Until some of the uncertainties regarding silver are resolved, it would be prudent to use it as a drinking water disinfectant only in situations where substantial factors of safety can be provided and where the bactericidal electiveness of the procedure can be monitored." Silver and its compounds are weak, costly disinfectants that are unsuitable for use in municipal drinking water supplies. To achieve acceptable disinfection in a reasonable time would require concentrations exceeding the MCL of 0.05 mg/liter.
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From page 107... ...
Furthermore, it must operate at atmospheric pressure. Tubular reactors are more common in water treatment because they are sealed and operate under pressure.
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From page 108... ...
Recently, attempts have been made to correct the decrease in intensity with depth in studies of wastewater disinfection where this problem is acute (Roeber and Hoot, 1975; Severin, 1978; Venosa et al., 1978~. These studies have shown that the usual water quality indices, such as chemical oxygen demand (COD)
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From page 109... ...
The Disinfection of Drinking Water 109 Biocidal Dose The biocidal dose of UV energy consists of the intensity of UV energy that is absorbed at the reactive site within the microbe over the time of interaction. The biocidal dose is then a function of the energy input from the UV source into the solution, dispersion of the energy as a function of distance from the source, the depth of the fluid between the organisms and the source as well as its absorptivity, and, finally, the losses and reflection of UV light within the contactor.
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From page 110... ...
However, this is not a major problem, because disinfection can be controlled by adjusting the contact time and the UV energy that is transmitted through the solution. The major disadvantage is the lack of a tracer for ensuring the integrity of the distribution system.
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From page 111... ...
The Disinfection of Drinking Water 111 TABLE Il-24 Ultraviolet Energy Necessary to Inactivate Various Orga~smsa Test Microorganism Lethal Dose, (~W.s/~2) Eschericf~ia cold Staphylococcus aureus Serratia marcescens Sarcina lutea Bacillus globiggii spores T3 coliphage Poliovirus Vaccinia virus Sernliki Forrest virus EMC virus 360 210 290 1,250 1,300 160 780 30 470 650 a Data from Morns, 1972.
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From page 112... ...
The biocidal activity of various disinfectants can be compared conveniently through the numerical value of the product (c .
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From page 113... ...
Chlorination, ozonization, and the use of chlorine dioxide come closest to meeting the criteria desired. At this time none of the other possibilities considered can substitute for techniques presently used to disinfect drinking water.
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From page 116... ...
116 I_ Ct 3 on .G ._ o CO 5 o o .
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From page 119... ...
It should be determined if any data are available from treatment plants on the effectiveness of ozone or chlorine dioxide in disease prevention, where these methods of disinfection are not used sequentially or, in the case 'of ozone, with subsequent chlorination. If such data, free of complications, are available, they should be compared with the records on the efficacy of chlorination disinfection.
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From page 120... ...
1943. Influence of pH and temperature on the survival of coliforms and enteric pathogens when exposed to free chlorine.
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From page 121... ...
1977. Ozone, Chlorine Dioxide, and Chloramines as Alternatives to Chlorine for Disinfection of Drinking Water: State of the Art.
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From page 122... ...
1960. Survival and protection against chlorination of human enteric pathogens in free living nematodes isolated from water supplies.
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From page 123... ...
1974. Effectiveness of hypochlorous acid and hypochlorite ion in destruction of viruses and bacteria.
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From page 124... ...
1977. Ozone, Chlorine Dioxide, and Chloramines as Alternatives to Chlorine for Disinfection of Drinking Water: State of the Art.
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From page 125... ...
Proceedings First International Symposium on Ozone for Water and Wastewater Treatment. International Ozone Institute, Waterbury, Conn.
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From page 126... ...
1974. Chlorine dioxide in potable water treatment.
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From page 127... ...
1948. Chemical properties of chlorine dioxide in water treatment.
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From page 128... ...
1978. Use of chlorine dioxide in water and wastewater treatment.
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From page 129... ...
1959. Effectiveness of iodine for the disinfection of swimming pool water.
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From page 130... ...
1950. The dissociation constant of hypobromous acid.
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From page 131... ...
Chemistry of Water Supply, Treatment, and Distribution. Ann Arbor Science Publishers, Inc., Ann Arbor, Mich.
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From page 132... ...
American Society of Civil Engineers, New York. Standard Methods for the Examination of Water and Wastewater, 11th ea., p.
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From page 133... ...
1973. Investigations on rhinovirus inactivation by hydrogen peroxide.
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From page 134... ...
1963. Potassium permanganate oxidation of organic contaminants in water supplies.
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From page 135... ...
1963. Potassium permanganate in water treatment.
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From page 136... ...
1975. The disinfection of sewage treatment plant effluents using ultraviolet light.
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From page 137... ...
Paper presented to Annual Meeting, Water Pollution Control Federation, Anaheim, Calif. Venosa, A.D., H.W.
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