During the past 10 yr, a number of outbreaks of waterborne infections from Giardia lamblia another intestinal protozoan have been reported National Academy of Sciences, Most incidents in the United States that were traced to municipal water supplies involved surface water sources where disinfection appeared to be the only treatment. The cysts of this parasite are thought to be as resistant to chlorine as those of E.
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However, there seem to be no studies of the resistance of this parasite to chlorine or other disinfectants. One of the earliest references to the mechanism of inactivation of microorganisms by chlorine resulted from the work of Chang a,b. While studying the inactivation of E. This observation was associated with the increased inactivation efficiency of the undissociated hypochlorous acid. Supportive evidence for the hypothesis that permeability of the uncharged chlorine species is important in determining sensitivity to chlorine has been provided by Skvortsova and Lebedeva , Kaminski et al.
Chang a also noted that the inactivation of amoebic cysts was accompanied by microscopic damage to the cell nucleus, which was dependent on chlorine penetration. In , Rahn suggested that the inactivation of bacteria by chlorine was due to multiple injuries to the cell surface.
From their work with bacterial spores, Kulikovsky et al. Studies with Escherichia coli have shown that chlorine causes leakage of cytoplasmic material, first protein, then RNA and DNA, into the suspending menstruum. It also inhibits the biochemical activities that are associated with the bacterial cell membrane Venkobachar, ; Venkobachar et al.
Friberg observed that E. In a recent study, Haas demonstrated that chlorine caused certain bacteria and yeast to release organic matter or UV-absorbing material, presumably protein or nucleic acid or their precursors. This investigator also noted that chlorine affected the uptake and retention of potassium by these same microorganisms.
Green and Stumpf and Knox et al. Specifically, they suggested that chlorine affected the aldolase enzyme of E. Venkobachar et al. 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. Haas also observed chlorine to affect the respiration of bacteria as well as the rate of synthesis of protein and DNA.
Others have also noted that chlorine affects the nucleic acids or physically damages DNA Bocharov, ; Bocharov and Kulikovskii, ; Fetner, ; Rosenkranz, ; Shih and Lederberg, a,b. It appears that chlorine, having penetrated the cell wall, encounters the cell membrane and alters its permeability. Simultaneously or subsequently, the chlorine molecules may enter the cytoplasm and interfere with various enzymatic reactions.
It should be noted that permeases and respiratory enzymes are associated with the cytoplasmic membrane of bacteria. Chang supported the hypothesis that the rapid destruction of vegetative bacteria by chlorine was due to the extensive destruction of metabolic enzyme systems. He also addressed the subject of virus inactivation, commenting that viruses are generally more resistant to chlorine than bacteria. He associated this observation with the fact that viruses completely lack a metabolic enzyme system.
He speculated that inactivation of viruses by chlorine probably result from the denaturation of the capsid protein.
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Furthermore, since protein denaturation is more difficult to achieve than destruction of enzymatic R—S—H bonds by oxidizing agents, it is understandable why greater levels of chlorine are required to inactivate viruses than bacteria. However, from their experimental work with the bacterial virus f2, Olivieri et al. Dennis reported that the incorporation of chlorine into the f2 bacterial virus is dependent on pH and that the higher rates of incorporation occur at lower pH values.
There is limited information in the literature on the mechanism of inactivation of microorganisms by chloramines.
Nusbaum proposed that since low levels of inorganic chloramines were effective in inactivating bacteria, the mechanism of action must be essentially the same as that of hypochlorous acid on enzymes. Ingols et al. 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.
Thus, while the sulfhydryl group may be the most vulnerable to a strong oxidant like hypochlorous acid, changes in other groups produced by the weaker oxidant, monochloramine, may lead also to microbial inactivation. More recent information indicates that the destructive effects of chloramine might be associated with the effects of chloramine on nucleic acids or DNA of cells Fetner, ; Shih and Lederberg, a,b.
Nusbaum suggested that the disinfective activity of dichloramine occurs by a mechanism similar to monochloramine, but there do not appear to be any data to support this contention. Considering the mechanism of destruction or inactivation of microorganisms by chlorine and associated compounds, it is interesting to note that Fair et al.
This "multiple hit" concept supported the observation that monochloramine must alter groups other than the sulfhydryl group to be effective in the destruction of microorganisms. Thus, the action of chlorine on microbes such as bacteria and amebic cysts may involve some or all of the steps in the following sequence: penetration of the disinfectant through the cell wall followed by attack on the cell membrane the site of cellular respiration in bacteria and disruption of permeability of the cell membrane, which leads to a loss of cell constituents, thereby disrupting metabolic functions within the cell including those involving nucleic acids.
Changes in viability may result from this process. Experimental studies on virus Olivieri et al. Chlorine is the most widely used water supply disinfectant in the United States. For example, a chlorine residual of 0. According to Walton, a properly designed, constructed, and operated water treatment plant, consisting of chemical coagulation, sedimentation, filtration, and disinfection, can remove or destroy more than Although most investigations on the removal or destruction of bacteria have used E. Laboratory studies have demonstrated that that there is limited virus inactivation after the added chlorine has reacted with any ammonia that is in the water.
Most inactivation probably occurs in the first few seconds before the chlorine has completed its reaction with ammonia Olivieri et al. Recent reports of enhanced chlorine resistance of certain viral and bacterial strains should be investigated and the mechanism of increased resistance elucidated, if the reports are corroborated.
Other recommendations, applicable to other agents as well as to chlorine, are included after the evaluations of the other methods of disinfection. It is approximately 13 times more soluble in water than is oxygen.
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Ozone has a half-life in pure distilled water of approximately 40 min at pH 7. Rising temperatures increase the rate of decomposition. Because its half-life is so short, ozone must be generated on the site where it is to be used. Ozone is a powerful oxidant that reacts rapidly with most organic and many inorganic compounds. It does not convert chloride to chlorine under test conditions U.
However, bromide and iodide are oxidized to bromine and iodine. Singer and Zilli reported that oxidation of ammonia was pH-dependent. At pH 7. During disinfection, only minor amounts of ammonia are oxidized when ozone is used. Ozone's limited reaction with ammonia is desirable, but its fast reaction rate with most organic and many inorganic compounds further shortens its persistence in water. Ozone is produced on site from a stream of clean dry air or oxygen by passing an electrical discharge between electrodes that are separated by a dielectric.
Approximately twice the percent of ozone by weight is obtained if oxygen, rather than air, is used as the feed stream. Other factors affecting efficiency are the rate of gas flow, applied voltage, and the temperature of the gas. The heat that is produced during the process must be removed by cooling with either air or water. The ozone gas stream must be fed into the water to effect the transfer of ozone. The usual methods are to inject the ozone gas stream through an orifice at the bottom of a co- or countercurrent contact chamber or to aspirate the gas into a contact chamber where it is mixed with the water mechanically.
Successful design and operation of the contactor system is necessary to minimize costs of the operation. Larger capacities are obtained by adding additional units. Successful delivery of ozone to the water to be treated requires a dependable power supply and reasonably maintenance-free ozonization equipment. 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. The maintenance and repairs that are required for the specialized ozone generation equipment provide further barriers against the use of ozone by small institutions. The disinfection process is usually controlled in one of two ways: by the dosage of a specified amount of ozone or by the maintenance of a specified minimum residual for a given time.
Residual measurements in both the gas stream and water are sometimes required. Standard Methods contains descriptions of the measurement of ozone in water by the iodometric, orthotolidine-manganese sulfate, and orthotolidine-arsenite methods. Of these methods the iodometric method, which is subject to the fewest interferences, is the method of choice. Determinations must be made immediately since ozone decomposes rapidly.
In all three methods, the oxidant compounds that result from the reaction of ozone with contaminants in water may react with the test reagents, thereby indicating a higher concentration of ozone than is actually present. This is particularly true in the presence of organic matter, which results in the formation of organic peroxides. In the iodometric method this interference and others are minimized by stripping the ozone from the sample with nitrogen or air and absorbing it from this gas stream in an iodide solution. These and other methods are described in Standard Methods. Schecter developed a UV spectrophotometric method to measure the triiodide that is formed by the oxidation of iodide by ozone.
She reported a better sensitivity at low ozone concentrations 0. The effects of interferences on the direct measurement of ozone without sparging the ozone to a separate iodide solution were not indicated. These effects are noted in Standard Methods. Analytical determination of ozone in water in the presence of other oxidants is poor.
Considerable work in this area is needed. As discussed above, ozone is unstable in water with a half-life of approximately 40 min at pH 7. Many regard the half-life in water supplies at higher ambient temperatures to be 10 to 20 min. Hydrogen peroxide H 2 O 2 may also be present by dimerization of the hydroxyl radicals. There have been no studies on the disinfecting activities of these individual species except for those on hydrogen peroxide, which is a poor biocide when compared to chlorine.
Peleg concluded that evidence indicates that the dissociation species are better disinfectants than ozone. Spores of a Bacillus species were much more resistant, requiring 2 min with 0. These data were obtained at pH 7. The observed ozone residuals were reported as being constant throughout the test periods. Katzenelson et al. The ozone was determined by the method of Schecter Using washed cells of E. They measured the ozone by stripping it into iodide at the end of the contact period.
Consequently, any demand should have used up whatever ozone was needed. They did measure what they presumed to be ozone and not some breakdown product. Thus, they appear to have eliminated the ozone demand problem as much as is possible with present techniques. However, it is possible that their results reflect some effect or artifact not yet understood.
With the constant contact time of 5 min, no inactivation of vegetative cells of E. Spores of B. Burleson et al. The pH was not reported.
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In this study, the bacteria were placed in unozonized water no initial residual , and the ozone was then sparged into the water. After 15 s the ozone concentration in solution reached approximately 0. This technique does not render quantitative data. Ozone was determined by spectrophotometric measurement of iodine that was released from iodide without stripping of the ozone. The inactivation of E. Ozone was measured by the diethyl- p -phenylenediamine DPD method.
Farooq and Farooq et al. They concluded that if the ozone residual remains constant, the disinfection capability will not be affected by a change in pH. They also demonstrated that for a given dosage a rise in temperature increases the rate of inactivation, even though the ozone residual was decreased. Ozone was less soluble at higher temperature. The work of Farooq and his colleagues is in agreement with that of Morris , who observed that the disinfection capability of ozone does not change significantly with pH, at least over the normal pH range 6 to 8.
Their experimental methods were the same as those described above for bacteria. They also observed that inactivation resulted from two distinct stages rates of action. The second stage, which lasted from 1 to 5 min, still left some viruses infective. Additional work showed that the slower second stage inactivation apparently involved the inactivation of viruses that were clumped together. The single virus particles were inactivated during the first stage. After ultrasonic treatment, Coin et al.
In distilled water, nearly 1 log of the virus was inactivated in 4 min at a 4-min ozone residual of approximately 0. In river water, the inactivation was in excess of The ozone was measured by the iodide titration without stripping of the ozone. Rather large ozone demands existed in this system. The same initial residual in river water decreased to between 0. Temperature and pH were not reported. Keller et al. Inactivation of poliovirus 2 and coxsackievirus B3 in 5 min was greater than Initial ozone residuals varied from 1.
At the pilot plant, greater than Temperature and pH conditions were not reported. Ozone was measured by the iodide method without prior stripping of the ozone. The experiment was conducted in the same manner as that described above for their studies with bacteria. Evison reported data for the inactivation of a number of viruses in buffered water at pH 7. The reported ozone concentrations were evidently those measured initially and maintained by the addition of ozone during the experiment.
Ozone was measured by a colorimetric version of Palin's DPD technique. The Evison data show that more ozone or a longer time are required for inactivation than do the data of other workers. This may have resulted from the virus purification used. Her viruses were purified by low-speed centrifugation and filtration through an 0.
These cleanup procedures are neither as complete nor as thorough as those used by other investigators. The unremoved cell debris and organic matter offer protection to the virus. Either higher ozone residuals or longer contact times would be required to inactivate such preparations to the same extent as clean virus. Other data showed that the inactivation of coliphage was relatively unaffected by pH's ranging from 6.
Evison also concluded that the rate of inactivation of the coliphage by ozone was much less affected by temperature than was the inactivation by chlorine. In this study, ozone was measured by the Schecter method. Sproul et al. The initial ozone residual of 0. The experiments were conducted with the Sharpe dynamic reactor. Ozone was measured by the Schecter method. Ozone may have application as an antiparasitic agent in the treatment of water supplies but only limited information is available.
Newton and Jones reported that ozone, with 5-min residuals as low as 0. Initial ozone residuals that were required to obtain 5-min residuals of 0. Ozone was measured by titration of iodine, which was released from iodide directly in the reactors without removal of ozone by sparging.
Investigations of the inactivation of bacteria by ozone have centered on the action of ozone on the cell membrane. Scott and Lesher concluded from their work with E. Cell contents then leaked into the water. This was confirmed by Smith Prat et al. Riesser et al. 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.
Inactivation with ozone at specified ozone residuals is relatively insensitive to pH's between 6. Moreover, ozone does not react with ammonia over this same range when short detention times are used. The data on temperature are not sufficiently firm to permit conclusions concerning its effect on disinfection. Ozone must be generated on site, and the process is relatively energy intensive.
To make economic comparisons of ozone with other disinfectants, the cost of local power must be ascertained. Available kinetic data on ozone inactivation are presented in Table II These variations illustrate the difficulty of doing quantitative experimentation with ozone and microorganisms in water. Among other reasons, these difficulties are caused by undetected ozone demand in the water, poor analytical techniques for residual ozone, and nonuniformity of microorganisms from one laboratory to another.
As an example of the latter, different strains of poliovirus with different inactivation rates are used, but the inactivation data are frequently not reported as strain-specific. Furthermore, viruses frequently exist in an undetected clumped state rather than in the presumed single discrete particle state.
Because of ozone's relatively short half-life in water, another disinfectant must be added to maintain a disinfection capability in the distribution system. The most effective disinfectant, its optimum concentration, and method of addition must be determined. The disinfection process with ozone will probably be controlled by specifying the ozone residual at the beginning and end of a given contact time. Chlorine dioxide ClO 2 was first prepared in the early nineteenth century by Sir Humphrey Davey By combining potassium chlorate KClO 3 and hydrochloric acid HCl , he produced a greenish-yellow gas, which he named ''euchlorine.
The bleaching action of chlorine dioxide on wood pulp was recognized by Watt and Burgess Large quantities of chlorine dioxide are produced each day in the United States.
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Although its primary application has been the bleaching of wood pulp, it is also used extensively for bleaching and dye stripping in the textile industry and for bleaching flour, fats, oils, and waxes Gall, In the United States, chlorine dioxide was first used in at the water treatment plant in Niagara Falls, New York, to control phenolic tastes and odors arising from the presence of industrial wastes, algae, and decaying vegetation Synan et al. Granstrom and Lee surveyed water treatment plants believed to be using chlorine dioxide.
The majority of respondents plants were using it for taste and odor control. Other uses reported were algal control 7 plants , iron and manganese removal 3 plants , and disinfection 15 plants. Sussman compiled a partial listing of plants using chlorine dioxide. He reported that the compound is used primarily to control taste and odor in the United States. In England, Italy, and Switzerland, it is used for disinfection of water supplies. 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.
However, two important reactions do not occur. Chlorine dioxide per se does not react to cause the formation of trihalomethanes THM's Miltner, However, THM's will be formed if the chlorine dioxide is contaminated with chlorine. Such a situation may occur when chlorine is used in the preparation of chlorine dioxide. Chlorine dioxide does not react with ammonia, but will react with other amines Rosenblatt, The amine structure determines reactivity. Tertiary amines are more reactive with chlorine dioxide than secondary amines, which, in turn, are more reactive than primary amines.
Chlorine dioxide condenses to form an unstable liquid. Both the gas and liquid are sensitive to temperature, pressure, and light. As a result, the preparation and distribution of chlorine dioxide in bulk have not been deemed practical. It has been generated and used on site. The method of production will depend upon the amount of chlorine dioxide that is required. The reduction of sodium chlorate is the more efficient process and is generally used when large volumes and high concentrations of chlorine dioxide are needed.
Commercial processes that are used in North America for large-scale production of chlorine dioxide are based on the three reactions listed below. To reduce the sodium chlorate, each process uses a different agent: sulfur dioxide SO 2 , methanol CH 3 OH , and the chloride ion Cl -. All of these processes are used in the pulp and paper industry.
They can also be used to prepare chlorine dioxide for the large waterworks that might require several metric tons per day. Small quantities of chlorine are formed during the side reactions and intermediate reactions in these processes. A more detailed review of the chemistry that is involved in the production of chlorine dioxide from chlorate is given by Gall and Gordon et al.
Chlorine dioxide can be prepared from chlorine and sodium chlorite through the following reactions:. The theoretical weight ratio of sodium chlorite to chlorine is 1. In practice, Gall recommended a chlorite to chlorine ratio of The excess chlorine lowers the pH, thereby increasing the reaction rate and optimizing the yield of chlorine dioxide. Dowling reported that the maximum theoretical yield of chlorine dioxide was produced when the ratio was normally maintained at a minimum of 1. Alternatively, chlorine dioxide may be prepared from sodium hypochlorite NaOCl and sodium chlorite.
The sodium hypochlorite is acidified to yield hypochlorous acid HOCl , and the chlorine dioxide is generated according to Reaction Each of the methods produces a solution containing both chlorine and chlorine dioxide. Chlorine dioxide may also be prepared by the addition of a strong acid, such as sulfuric acid H 2 SO 4 or hydrochloric acid, to sodium chlorite as shown in the following reactions:.
Although some investigators have claimed that this method produces chlorine-free chlorine dioxide, Feuss and Schilling reported that chlorine is also formed. Dowling indicated that chlorine was formed even when sulfuric acid was used. Chlorine dioxide is one of the few stable nonmetallic inorganic free radicals Rosenblatt, It does not contain available chlorine in the form of hypochlorous acid or hypochlorite ion OCl -.
However, concentrations of chlorine dioxide are often reported in terms of available chlorine. A reduction to chloride results in a gain of five electrons. The weight ratio of chlorine dioxide to available chlorine is However, in water treatment practices this increased oxidizing capacity is rarely realized. The reduction of chlorine dioxide depends heavily on pH and the nature of the reducing agent. At neutral or alkaline pH, chlorine dioxide is reduced to chlorite, a net gain of one electron.
At low pH, the chlorite ClO 2 - is reduced to chloride Cl - releasing the remaining four available electrons. Chlorine dioxide may be determined iodometrically Standard Methods , , amperometrically Haller and Listek, ; Standard Methods , , spectrophotometrically Gordon et al. Several studies contain comparisons of various analytical methods and procedures for the measurement of chlorine dioxide.
Adams et al. Public Health Service Miltner, Myhrstad and Samdal noted that the DPD method Palin, , yielded consistently higher residual measurements for chlorine dioxide than those that are produced with other analytical methods. After analysis with acid chrome violet K Masschelein, , chlorine dioxide was not observed in the water of the distribution system; however, chlorite was found.
The residuals that were previously interpreted as chlorine dioxide were apparently due to chlorite. Recently, more sophisticated procedures were suggested for the determination of chlorine dioxide. Moffa et al. Stevenson et al. Under development is a sensor that shows a linear response region from about 0. The response to hypochlorous acid and chloramines was low, and the sensor does not measure chlorite or other ionized species. No one procedure appears to possess the necessary sensitivity, selectivity, and simplicity to permit reliable determinations in the treatment of water.
Each of the titration methods are prone to error because of volatilization. They are time-consuming and particularly complex when differentiation of chlorine and oxychloro species are necessary. The colorimetric procedures require strict control of pH, temperature, and reaction times and will be affected by turbidity.
In addition, the selectivity of the indicators for chlorine dioxide is questionable. The direct spectrophotometric determination of chlorine dioxide at nm is selective and rapid but is not sufficiently sensitive for use in water. Limited experience with the more recent procedures chemiluminescence and membrane amperometric probe does not permit an evaluation. In practice, the principal distinction that must be made is that between the active biocidal species hypochlorous acid, the hypochloride ion, and chlorine dioxide , the moderately biocidal species monochloramine [NH 2 Cl], dichloramine [NHCl 2 ], and nitrogen trichloride [NCl 3 ] , and the relatively nonbiocidal species chlorite and chlorate [ClO 3 - ] ions.
This is imperative when the primary purpose for the addition of chlorine dioxide is the inactivation of microorganisms. Furthermore, when the formation of THM's is to be considered, the distinction between free chlorine and chlorine dioxide becomes important. Experimental data on the efficacy of chlorine dioxide as a disinfectant became available in the early 's. McCarthy , reported that chlorine dioxide was an effective bactericide in water with a low organic content. When the levels of organic material in the water were high, chlorine dioxide was less effective.
Ridenour and Ingols reported that chlorine dioxide was at least as effective as chlorine against Escherichia coli after 30 min at similar residual concentrations. Both chlorine and chlorine dioxide residues were determined by the orthotolidine-arsenite OTA method. The bactericidal activity of chlorine dioxide was not affected by pH values from 6. Ridenour and Armbruster extended their observation to other enteric bacteria. The common waterborne pathogens were similarly inactivated with chlorine dioxide.
Ridenour et al. They indicated that less weight of chlorine dioxide than chlorine is required to inactivate the spores of Bacillus mesentericus in either demand-free water or in waters containing ammonia. 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.
In their paper Ridenour and Armbruster, , the survival measurement was quantitative, but only one contact time was used, 5. Russian investigators Bedulevich et al. Additional data were reported for Bacillus anthracis. They observed that the efficiency of chlorine dioxide decreased as the pH of the system containing the B. Early studies on disinfectant activity are difficult to interpret because the methods of preparing chlorine dioxide invariably included the addition or production of chlorine.
Analytical procedures were not sufficiently advanced to differentiate between chlorine dioxide and other oxychloro species. Thus, the quantitative analyses of stock solutions and reports of dose and residual chlorine dioxide may be in error. 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.
Many of the difficulties that were encountered during the early studies were overcome in a series of studies reported by Benarde and co-workers during the mid's. Their work on disinfection was based heavily on the improved methods of preparing and analyzing chlorine dioxide, which were reported by Granstrom and Lee They prepared chlorine dioxide by oxidizing sodium chlorite with persulfate S 2 O 8 2- under acid conditions.
The resulting chlorine dioxide was swept to a collection vessel by high purity nitrogen gas. Chlorine dioxide was measured spectrophotometrically at nm. Bernarde et al. At pH 6. Chlorine was slightly more effective at the lower dosages at the lower pH. At pH 8. Chlorine dioxide was significantly more efficient than chlorine in the presence of high levels of organic and nitrogenous material.
More recent work by Cronier in a clean system also demonstrated the excellent bactericidal activity of chlorine dioxide. Results of both studies are shown in Table II In the mid's, there were also investigations on the virucidal activity of chlorine dioxide. Ridenour and Ingols reported that chlorine dioxide was as effective as chlorine against a mouse-adapted strain of poliovirus Lansing. Again, their comparison was based upon OTA-determined residual levels of each disinfectant. Hettche and Ehlbeck found chlorine dioxide to be more effective against poliovirus than either chlorine or ozone.
In addition to the difficulties that are associated with the preparation and measurement of chlorine dioxide and chlorine, the early virus studies were also saddled with difficult and time-consuming virus test systems. Warriner showed that the rate of inactivation of poliovirus 3 increased with increasing pH at pH values of 5. Similar to the action on bacteria, the viral inactivation occurred rapidly.
When chlorine and chlorine dioxide were combined, the inactivation was synergistic. The inactivation with the two chlorine species together was more efficient at lower pH, but the presence of chlorine dioxide enhanced inactivation by chlorine at the higher pH. Cronier compared the inactivation of E. Poliovirus 1 and coxsackievirus A9 were more resistant than E. Similar to its bactericidal activity, chlorine dioxide was more effective 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.
At turbidity levels below 2. However, at 3. The bentonite at these levels appeared to offer protection to the virus. The data that are available on the efficacy of chlorine dioxide on helminths or protozoan cysts do not appear to be suitable for comparison with the action of other disinfectants. Table II-7 presents similar data for viruses.
The amount of inactivation depended on the virus that was tested. There is little information concerning the mode of action by which chlorine dioxide inactivates bacteria and viruses. Ingols and Ridenour suggested that the bactericidal effectiveness of chlorine dioxide is due to its adsorption on the cell wall with subsequent penetration into the cell where it reacts with enzymes containing sulfhydryl groups. Benarde et al. The incorporation of 14 C-labeled amino acids into protein by whole cells stopped within a few seconds after the addition of chlorine dioxide.
Subsequently, Olivieri reported a dose-response in the inhibition of protein synthesis in bacteria that had been treated with chlorine dioxide. The site of action was localized in the soluble portion enzymes of the cell extracts of treated cells without affecting the integrity of the ribosomes' function in protein synthesis.
Chlorine dioxide is an effective bactericide and virucide under the pH, temperature, and turbidity that are expected in the treatment of potable water. It should be noted that the U. Environmental Protection Agency, because of the unresolved questions on its health effects Symons et al.
A simple, selective, and sensitive test for chlorine dioxide should be developed to monitor residual concentration. Chlorine dioxide is currently used at several plants. A review of plant records and field studies on the stability and effectiveness of chlorine dioxide in the distribution system should be undertaken. More information should be obtained on the mode of action by which chlorine dioxide inactivates bacteria, viruses, and cysts.
The use of iodine as a biocide has had a long history, primarily as an antiseptic for skin wounds and mucous surfaces of the body and, to a lesser degree, as a powerful sanitizing agent in hospitals and laboratories Gershenfeld, The use of iodine as a disinfectant of drinking and swimming pool water has not been extensive, mainly because of the costs and problems that are involved in applying the dosage. Aside from the emergency iodination of small volumes for field and emergency drinking water and limited experience with swimming pool disinfection Black et al.
A persistent residual was maintained throughout the distribution system despite a finished water pH of 8. No adverse effects on health were observed among those consuming the water. Iodine is the only common halogen that is a solid at room temperature, and it possesses the highest atomic weight Of the four common halogens, it is the least soluble in water, has the lowest standard oxidation potential for reduction to halide, and reacts least readily with organic compounds.
The effect of pH on this reaction is shown in Table II The distribution of chemical species of iodine given in Table II-8 was taken from the calculations that were made by Chang from the equilibrium expression:. With iodine residuals at 0. At pH 7, the two forms are present in almost equal concentrations. Consequently, the dissociation of hypoiodous acid, which occurs at high pH's, is not important for practical purposes. However, as confirmed by the field studies in Florida, hypoiodous acid can form iodate ion by autooxidation at pH values above 9.
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 C 2 H 5 OH and potassium iodide KI to overcome the low concentration of aqueous iodine stock for solution feeders. Another method produces the required concentration of iodine by passing water through a bed of crystalline iodine saturator. This has passing water through a bed of crystalline iodine saturator.
This has been used in many small, semipublic and private home water systems. The iodinated anion exchange resin bed and the vaporization technique are not sufficiently developed to be considered for use in public water supplies. In certain circumstances, potassium iodide might be combined with an oxidation reaction to release iodine.
The chemistry is simple, and the persistence of the iodine that is generated may be much better than chlorine. This method has been used in swimming pools and for dechlorination purposes where a chlorine residual may be exchanged for an iodine residual, or an iodine residual may be provided where ozone is the primary disinfectant. Both amperometric titration and leuco crystal violet LCV colorimetric methods give acceptable results when used to measure free iodine in drinking water.
Waters containing oxidized forms of manganese interfere with the LCV method. Under unusual situations, where mixtures of chlorine, bromine, and ozone occur along with iodine, the problem of separation is difficult Standard Methods , Table II-9 shows the relative resistance of bacteria, viruses, and cysts to inactivation by iodine. Iodine was less dependent than chlorine upon the pH, temperature, contact time, and secondary reactions with nitrogenous impurities in the water. As a cysticide, iodine was poor in water with a high pH.
Consequently, the tablet that was formulated contained an acid buffer to lower the pH of the water. The tablet is not widely accepted, since color, taste, and odor problems are fairly common O'Connor and Kapoor, Chambers et al. Their results are not completely quantitative in that the reported iodine concentration is that required to inactivate all test organisms plated out after 1, 2, and 5 min of contact. This was equivalent to approximately There was definitely an observed pH effect. A summary of their work with E. This is the best available information on iodine as a bactericide.
Studies on the efficacy of iodine on viruses have shown that viruses are more resistant to disinfection than are vegetative cells of bacteria. However, when the potassium iodide concentration was raised to 0. Survival of E. Berg et al. Data on the inactivation of virus by iodine are summarized in Table II for both polio and f2. The results of inactivation studies by the various groups compare very favorably. At the pH's likely to be maintained in the distribution system pH 8. Many studies on cyst inactivation have been reported, but there are discrepancies in their results due mainly to differences in the test systems that were used.
The dose, pH, and temperature that were used in many of the studies are in doubt as are the different sources, cleaning methods for cysts, number of cysts used per test, and determination of viability. Stringer compared the resistance to iodine disinfection of Entamoeba histolytica cysts obtained from in-vitro culturing with those harvested from a human carrier and mixed amoebic cysts from monkeys.
In water at room temperature at pH 6. Large numbers of amoebic cysts from simian hosts were more readily available than cysts from human stools. They served as a reliable model for human E. The most extensive and reliable data on the cysticidal properties of iodine are found in the work of Chang and Stringer and their co-workers Change and Baxter, ; Chang et al. The only quantitative comparative study of the cysticidal properties of chlorine, bromine, and iodine believed to be published is that of Stringer, who reported a The earlier studies of others involved "total kills" and are quite dependent on the cyst density that was used.
There may be the problem of ineffective iodine residual in the distribution system where cross-connection introduction of cyst contamination is a possibility. This is due to the practice for corrosion control of maintaining water in the distribution system at approximately pH 8. At the low halogen residual levels that are usually maintained, the most cysticidal form, I 2 , would be less prevalent than hypoiodous acid. However, in the presence of excess ammonia, with which the halogens could react, bromine appears to be more effective at pH 8.
Residual iodine in water at pH 8. The cultured E. Stringer et al. The failure of a strong commercial iodine disinfectant to inactivate poliovirus Wallis et al. Fraenkel-Conrat pointed out inconsistencies in the literature regarding the virucidal properties of iodine. Hsu extracted fully active transforming DNA from iodine-inactivated Haemophilus parainfluenzae cells and just as much infectious RNA from f2 bacterial virus that had been inactivated 5 logs by iodine as from noniodinated controls.
Iodine inactivation, unlike the action of chlorine, appears to be attributable to a reaction with vital amino acids in proteins. Further experiments were conducted to determine whether sulfhydryl, tryptophanyl, histidyl, or tyrosyl groups were involved. With bacterial cells, there was a striking similarity between the kinetics of inactivation with iodine and the application of p-chloromercuribenzoic acid, a sulfhydryl reacting agent.
When sulfhydroxyl groups are the site of inactivation, a low pH should favor the reaction. With the viruses, the sulfhydroxyl group is not involved. Evidence of tyrosine's involvement came from parallel experiments showing similar patterns of inactivation curves between iodination of f2 virus and L tyrosine. Li , had shown that the presence of iodide ion and low pH iodine I 2 inhibited the iodination of tyrosine. Both poliovirus and f2 virus inactivation with iodine was inhibited by the iodide ion Cramer et al.
At pH 4. Although iodine decomposes rapidly to iodate IO 3 - and iodide at pH 10, flash mixing of iodine yielding hypoiodous acid overcomes this difficulty effectively, and the virus inactivation is complete in less than 1 min Longley, Therefore, there is evidence that iodine action, with little or no iodide present, is effected by the modification of protein without destroying DNA or RNA Brammer, ; Hsu, The mode of action of iodine in cyst penetration and inactivation has not been studied. Iodine has many features that are comparable to free chlorine and bromine as a water disinfectant, but iodamines are not formed.
Free iodine is an effective bactericide over a relatively wide range of pH. Field studies on small public water systems have shown that low levels of 0. Like other halogens, the effectiveness of iodine against bacteria and cysts is significantly reduced by high pH, but unlike bromine and chlorine it is much more effective against viruses because of the enhanced iodination of tyrosine. Currently, its use is restricted primarily to emergency disinfection of field water supplies because of its high cost and because it is difficult to apply to large systems.
The possible adverse health effects of increased iodide intake for susceptible individuals in the population must also be considered. Studies should be conducted to determine the consequences for human health of the long-term consumption of iodine in drinking water with special regard for more susceptible subgroups of the population. Bromine was first applied to water as a disinfectant in the form of liquid bromine Br 2 Henderson, , but it can also be added as bromine chloride gas BrCl Mills, or from a solid brominated ion exchange resin Mills, Oxidation of bromide Br - to bromine can also be accomplished either chemically or electrochemically.
Oxidation with aqueous chlorine gives either bromine or hypobromous acid HOBr , depending on the ratio of chlorine to bromide. Both bromine Liebhafsky, and bromine chloride Kanyaev and Shilov, hydrolyze to hypobromous acid:. Molecular bromine exists in water at moderately acid pH and high bromide concentrations since the equilibrium constant of Reaction 21 is 5.
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. From the equilibrium expression for Reaction The hypobromite ion OBr - becomes the major form of bromine above pH 8. Lower temperature decreases both of the above equilibrium values, thereby increasing the pH range where hypobromous acid is the major chemical form of bromine in water.
Bromine and bromine chloride also react with basic nitrogen compounds to form combined bromine or bromamines Galal-Gorchev and Morris, ; Johannesson, ; Johnson and Overby, :. The observed breakpoint for ammonia NH 3 solutions that have been treated with bromine is similar to that seen with chlorine. At this point, a minimum of bromamine stability occurs Inman et al. At bromine-to-ammonia ratios higher than this and in the acid pH range, nitrogen tribromide NBr 3 is stable. It is the most abundant bromamine in such aqueous solutions.
At lower bromine concentrations, dibromamine NHBr 2 can be present, but it is quite unstable. Only at alkaline pH values and very high ammonia concentrations such as those found in wastewater are significant quantities of monobromamine NH 2 Br formed. Organic bromamines are also formed, but there is little information on their forms or stability.
Bromine is produced by oxidation of bromide-rich brines that contain between 0. Bromine is then stripped with steam or air and is collected as liquid Br 2. Bromine chloride is produced by mixing equal molar quantities of pure bromine and chlorine Mills, Bromine has been applied to water as liquid Br 2. The difficulties that are encountered when handling the liquid and its corrosive nature, especially when wet, have encouraged the use of bromine chloride. Liquid bromine chloride is removed from cylinders under moderate pressure. It is then vaporized, and the gas is metered in equipment that is similar to that used for chlorine.
Like chlorine, bromine chloride is shipped as the dry liquid in steel containers. Gas feeders must be made of Teflon, Kynar, or Viton plastics because bromine chloride is more reactive than chlorine with polyvinylchloride plastics. Bromine concentrations can be measured iodometrically by procedures that are identical to those used to measure total chlorine residuals Standard Methods , None of these procedures is capable of distinguishing free bromine Br 2 , HOBr, OBr - from combined bromine bromamines or other oxidants that are capable of reacting with iodide under the slightly acid conditions used in these procedures.
However, bromate does not interfere except at low pH Kolthoff and Belcher, UV spectroscopy can be used to measure the bromamines selectively in the presence of one another and without interference from free bromine because none of the free bromine forms except Br 3 - has strong UV absorptivities Johnson and Overby, The efficacy of bromine inactivation of bacteria has been summarized by Farkas-Hinsley Vegetative cells are readily inactivated by bromine, but reports often leave the type of bromine compound and its residual concentration as uncertain.
Consequently, it is difficult to make quantitative comparisons with other disinfectants. Tanner and Pitner reported that the concentrations of hypobromous acid that are required to give ''complete kill" in 30 min are 0. This is in conflict with observations made at low pH, since high bromide should also produce bromine. The data at pH 4. Even these data, the best available, are based on the concentrations of bromine added to the solution.
It is difficult to compare the various studies on disinfection by bromine, since the chemical species of bromine present in most instances have not been measured or reported. The effect of the formation and decomposition of the bromamines on the efficacy of bacterial disinfection was first discussed by Johannesson He reported that 0. The measurements of the halogen remaining after the experiments showed very little loss. The efficacy of bromine inactivation of spores of Bacillus metiens and B. Both pairs of investigators found that the activity was markedly pH-dependent at low pH values where molecular bromine predominates.
The activity increased rapidly from pH 4 to pH 3, the lowest that was tested. The text integrates the best of recent social and cultural scholarship -- including fun material on music and movies -- into a political story, offering students the most comprehensive and complete understanding of American history available. Important Notice: Media content referenced within the product description or the product text may not be available in the ebook version.
To the Student. Supplements and Acknowledgments. The Old South Toward an American Culture. Whigs and Democrats. Antebellum Reform. The Gathering Tempest Secession and Civil War