Oxygen was produced from VPSA oxygen concentrators. VPSA oxygen concentrator system. Two of these systems are in place, with a LOX system for back-up to provide consistent ozone. Cutaway demo of the pipeline delivering water from the water treatment plant. One of the interesting things to learn about at these plants is water conservation. The water level in Lake Mead is at one of the lowest levels in history right now. While there is sufficient water for all, water usage is a constant concern. A new water intake is getting installed and built in the lake in case the existing water intake is no longer useful due to dropping water levels.
For more information about the International Ozone Association, or questions about membership, follow the link below:. International Ozone Association Website. Read full article HERE. There are constant microbiological threats in our daily lives; unfortunately, our drinking water and the recreational water that we play in are not excluded from where these threats reside. Among those preying on unsuspecting humans is the protozoan parasite — cryptosporidium crypto. Crypto is one of the toughest microbes faced in water treatment, however, by the power of the molecule, ozone can eliminate it.
Ozone, molecularly known as O 3 , is a sanitizer and is relentless in its attack of organic microbes bacteria, viruses, cysts, etc. Through a process known as lysing, ozone breaks down cell walls or membranes, where it can then destroy the nucleus of the microbe. In addition to sanitation, ozone is well known for the oxidizing of inorganic material that could be present in water, such as metals e. Although there are a few stronger oxidizers, ozone is the strongest that is readily available for commercial or residential use see Figure 1. In fact, it is 1. While leaving no off tastes, chemical by-products or residues, ozone is widely used in bottled water plants, wineries, breweries and food processing plants all over the world.
Furthermore, because of this higher oxidation strength, ozone cannot build up a tolerance to microbes unlike other sanitizers, such as chlorine. Learn more about water treatment with ozone here. Did you know the most common industrial use for ozone is drinking water? If you are new to the world of ozone it may surprise you how prevalent the use of ozone is throughout the United States. Today, there are more than major water treatment plants in the United States that incorporate the use of ozone in their processes.
It is projected that by the number of plants using ozone will reach There is a very good chance that the water you are drinking has been treated with ozone prior to your consumption. Ozone was initially used in the United States in in Whiting, IN for water disinfection in the water treatment process.
In , ozone was given GRAS approval for use in bottled water. This opened up the use of ozone for disinfection in the bottled water industry. Today, the majority of bottled water companies use ozone to ensure pure water that is pathogen free for consumers. Read more about ozone use in bottled water. Looking ahead, ozone may also be used for the removal of micro-pollutants, such as pharmaceuticals in the water, personal care products, and endocrine disruptors.
Ozone is currently used in waste-water disinfection for these purposes and it is possible the use of ozone will be carried over into drinking water plants in the future. Weymouth plant in La Verne is final treatment facility to receive ozone upgrade. Metropolitan General Manager Jeffrey Kightlinger called ozone treatment the most beneficial and cost-effective way to improve and protect the quality of drinking water served to 19 million Southern Californians. We believe that both of the updates will provide a great solution to your ozone monitoring needs.
This kit uses colorimetic tubes for easy ozone readings. This is a great all inclusive kit. This unit is easy to use and an accurate way to measure ozone in water. The improved vacuvials use a safety tip to ensure no broken glass is left after the vial is broken. Instruction videos have been created with simple step by step instructions on using each device. These videos can be view here:. K — Ozone Test Kit — http: I — Dissolved Ozone Meter — http: For more information on the K or I, or any of our ozone equipment, please call or e-mail us toda y.
Ozone is dissolved into water to create aqueous ozone for many applications. This page is a general overview of the methods and devices to dissolve ozone into water, along with a few helpful tips for the novice ozone user. Ozone cannot be stored, therefore it must be generated on-site and dissolved into water on-site at the rate of consumption. Ozone is generated as a gas that must be dissolved into water. A mixing device will be necessary for ozone gas to dissolve into water efficiently.
There are many variables to consider when determining the proper mixing device for a given application. The information provided below serves to provide a better understanding of the variables that may affect your application. Bubble diffusion is the oldest and simplest method for dissolving ozone into water. This is essentially a porous device used for breaking the gas into small bubbles at the bottom of a water column to allow the bubbles to slowly rise to the top of the column and dissolve into water.
The pore size of the diffuser will affect the size of gas bubble that is created with the bubble diffuser. Two smaller bubbles will have greater surface area than one bubble of the same gas volume.
Crypto is one of the toughest microbes faced in water treatment.
Greater surface area will achieve improved contact with the gas bubble and water, therefore increasing the rate of mass transfer of ozone into water. It is important when choosing a bubble diffuser to find the smallest pore size possible. The height of the water column that ozone is bubbled into will affect the mass transfer efficiency greatly. The diffuser should be placed at the bottom of the column, this way the gas bubble must travel the greatest distance within the water column prior to escaping into the head space.
Taller columns will lengthen the time duration that the bubble is in contact with the water and can dissolve into the water. More importantly, taller columns will create a higher pressure at the bottom of the column. This high pressure will exert greater force on the surface of the bubble and force more gas into solution. Bubble diffusers can dissolve ozone into water efficiently; however, a fine pore diffuser must be used with a very tall water column.
Ozone Water Disinfection | Ozonetech
This may not be practical in a given application. Fine pore diffusers can also plug with contaminates easier and cause poor long term performance. When designing a water treatment system using bubble diffuser keep safety in mind as high levels of un-dissolved ozone may escape from the head-space of the water. A venturi injector combines a method for ozone injection and provides good mass transfer efficiency in one device.
A venturi injector requires a pressure differential across the device to create a vacuum to pull ozone gas into the device. Then, using mixing vanes the gas is thoroughly mixed with the water. A venturi injector creates the very small bubbles desired for great mass transfer, and a violent mixing action to dissolve gas into water. For a Venturi Injector to work properly there must be a pressure differential between the inlet and outlet of the device.
This usually requires a separate water pump to increase the water pressure at the inlet of the venturi injector. It is then important that the outlet of the venturi injector is not obstructed or impeded in any way. We suggest placing pressure gauges directly at the inlet and outlet of the venturi injector. This will help with troubleshooting and determine the effectiveness of the device.
Using a venturi injector will require a method of removing the un-dissolved oxygen and ozone from the water. Unlike the bubble diffuser where the bubbles will naturally rise to the head-space and escape the piping system used with a venturi injector has no method of removing this un-dissolved gas, one must be provided. A contact tank is a popular method, there are also de-gas chambers and columns that can be used. If an off-gas system is not used the excess gas bubbles that may carry residual ozone can off-gas in undesirable locations causing safety concerns.
Also, this excess gas may volatilize some of the dissolved ozone back into the gaseous form. Venturi injectors become an integral part of the plumbing system in use. A pump is commonly placed prior to the injector, a tank after the injector. A by-pass loop is also commonly used to allow regulation of water flow through the injector and greater flexibility.
Venturi injector sizing is a function of the water flow rate through the device. Water pressure will also play a factor in the determination of the venturi injector sizing. When using a venturi injector it is necessary to use a device to ensure water cannot flow from the venturi injector to the Ozone Generator. There are many devices used for this task: Static mixers are any static device designed for the sole purpose of mixing two flows together.
In our application we are mixing ozone gas with water, therefore the same principle of breaking the bubbles up into the smallest possible bubbles is the goal with the static mixer. There are a variety of static mixers on the market, some go by trade names. While there may be a variety of static mixers on the market they all serve the same function, dissolving ozone gas into water.
A static mixer is sized based on the velocity of water through the mixer. Each static mixer has vanes or mixing devices inside that require a specific velocity of water past those devices to achieve the desired results. This sizing will translate to water flow rate for our purposes. Each mixer should be sold and marketed with a range of flow rates that the mixer will work well with. Ozone can be injected upstream of the static mixer using a tee or any other device to force ozone gas into the water stream. Then, the static mixer can be used to break up the gas into small fine bubbles to dissolve into water efficiently.
Essentially a static mixer can be used in place of a venturi injector, this can be helpful when energy savings are desired due to the lack of necessary pressure differential. 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 Diagrammatic representation of completed breakpoint reaction. From Morris, , personal communication. 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. When chlorine is added to water, it reacts with any reducing agents and ammonia that are present. It is believed that chlorine reacts first with the reducing agents. Since the chlorine is destroyed, no measurable residual is produced. Following the oxidation of these reducing agents, e. The quantity of monochloramine and dichloroamine that is formed is determined primarily by the pH of the water and the ratio of chlorine to ammonia. When the ratio by weight is less than 5: With additional chlorine, the ratio of chlorine to ammonia changes with the result that the monochloramines are converted to dichloramines Reaction 4.
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 N 2 O , nitrogen trichloride NCl 3 , and nitrogen N 2. The reactions leading to the formation of these oxidized forms of nitrogen destroy the combined available chlorine residual so that the measurable residual in the water actually decreases.
Upon completion of the oxidation of all the chloramines, the addition of more chlorine creates the breakpoint phenomenon. At the breakpoint dosage, some resistant chloramines may still be present, but at such small concentrations that they are unimportant. As pointed out by Morris , the occurrence of reactions giving rise to the ''breakpoint" is most rapid in the pH range 7. At greater and lesser pH values, it becomes slower and less distinct, e. In the pH range 7. Standard Methods lists six acceptable methods for the determination of chlorine residuals in natural and treated waters: Nitrogen trichloride does not interfere with the LCV procedure for free chlorine.
The sample color and turbidity may interfere with all colorimetric procedures. Thus, a compensation must be made. Also, organic contaminants in the sample may produce a false-free chlorine reading in most colorimetric methods. Standard Methods contains data on the precision and accuracy of the methods used in the measurement of chlorine. These data were obtained from participating laboratories by the Analytical Reference Service , , which then operated in an agency that preceded the Environmental Protection Agency.
However, as noted in Standard Methods , these results are valuable only for comparison of the methods tested, and many factors, such as analytical skill, recognition of known interferences, and inherent limitations, determine the reliability of any given method. Moreover, some oxidizing agents, including free halogens other than chlorine, will appear quantitatively as free chlorine.
This is also true of chlorine dioxide. Also, some nitrogen trichloride may be measured as free chlorine. The actions of interfering substances should be familiar to the analyst because they affect a particular method. Although orthotolidine i. Research studies on disinfection are restricted by the limitations that are inherent in the methods themselves or by poor selection of methods by the investigator.
The chemical conditions of the test water have not always been well-defined. The types of titratable chlorine, i. In fact, reports prior to the 's have been especially difficult to interpret, because reliable test methods for distinguishing between free and combined chlorine, between hypochlorous acid and hypochlorite ion, and between mono- and dichloramine in solution were not developed until the 's.
For example, many earlier researchers claimed to have tested mono- and dichloramine by controlling the pH and the ratio of chlorine to nitrogen. They used methods such as the orthotolidine or thiosulfate titrations to determine total chlorine residual. Much of this early work is now questionable, since it was not possible to detect free chlorine contamination in their chloramine solutions or the quantitative ratios between the mono- and dichloramine tested.
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. The pH determines the relative amounts of each species. However, inorganic chloramines will be formed if the background level of ammonia in the water supply is significant or if ammonia is intentionally added during treatment. If such is the case, monochloramine would predominate due to the alkaline pH of most finished water see Figure II In , Feng proposed that the active forms of chlorine would exhibit disinfection properties in the following descending order:.
Butterfield et al. They proposed that to study the disinfectant capacity of any chlorine species, the test medium must meet certain exacting criteria. It must be nontoxic to bacteria except for the variables under study such as chlorine and pH, well buffered at the desired pH, free of all ammonia and organic matter capable of forming chlorine-addition products, free of background chlorine, and of such a nature that calculated additions of chlorine are recoverable after 5 min without a loss in residual and that free chlorine must still be present several hours after contact.
Most studies of combined chlorine have dealt with poorly defined mixtures of mono- and dichloramine. Also, test conditions have often been inadequately defined, poorly controlled, or both. They used different levels of free chlorine at pH values ranging from 7. Their work is of great importance, since very few other studies have been conducted that dealt with the action of disinfectants on pathogens. Generally, they found that the primary factors governing the bactericidal efficacy of free available chlorine and combined available chlorine were:.
Thus, the test bacteria will be killed more rapidly at lower pH values and at higher temperatures. At higher concentrations of chlorine, i. A similar pH effect was noted for S. Unfortunately, Butterfield et al. The cells probably carried trace amounts of albumenoid nitrogen from the slants to the test flasks, thereby creating the small chlorine demand that the investigators had tried so carefully to avoid. The effect of such a trace amount of chlorine demand would be most apparent in test solutions with very low chlorine levels. In studies using approximately 0. This might indicate interference at the low levels due to the formation of combined chlorine.
Under very exact controlled test conditions of pH and temperature and using chlorine demand-free buffer systems, Scarpino et al. Their studies, which totally eliminated any form of combined chlorine from the test solutions, indicated that hypochlorous acid was approximately 50 times more effective than the hypochlorite ion as a bactericide. Fair et al. They reported that hypochlorous acid was times as bactericidal as hypochlorite ion.
In , Butterfield summarized previous results on the bactericidal properties of chloramines and free chlorine in water at pH values ranging from 6. The test bacteria included strains of Escherichia coli, Enterobacter aerogenes, Pseudomonas aeruginosa, Salmonella typhi, and Shigella dysenteriae.
Although he admitted that adequate tests for separate determination of free and combined chlorine forms were not used in these studies, the solutions were vigorously prepared to ensure the exclusions of free chlorine. Since no free chlorine was reported and should not have been found, according to the authors , the min readings of total residual chlorine were also those of total chloramine levels. No distinction could be made between monochloramine and dichloramine. However, he estimated that at pH 6. The balance was believed to be dichloramine.
Butterfield and his associates Butterfield, ; Butterfield et al. However, only 0. The bactericidal effects of monochloramine alone were confirmed by Siders et al. Since E. Chang calculated that 1. In carefully conceived studies, Esposito et al. Inactivation of various microorganisms with dichloramine NHCl 2 at pH 4.
Ozone Water Disinfection
From Esposito, From a review of the literature and an analysis of the data, Chang calculated that the relative bactericidal efficiency of dichloramine to monochloramine was 3. However, Esposito and Esposito et al. They found that dichloramine was 35 times more bactericidal than was monochloramine, not 3. They observed that dichloramine was a better bactericide than monochloramine. These chlorine derivatives exhibit some bactericidal activity, but markedly less than either free chlorine or the inorganic chloramines Feng, ; Nusbaum, In summary, the bactericidal efficiency of hypochlorous acid, the hypochlorite ion, monochloramine, and dichloramine have been accurately defined in recent years by investigators using rigidly controlled test conditions.
The order of disinfection efficiency presented by Feng has been confirmed. In reviewing disinfection of enteroviruses in water, Clarke and Chang excluded all studies on the inactivation of viruses by chlorine that were conducted before Their justification for this exclusion was the failure of these studies to differentiate between free and combined chlorine.
Furthermore, they attributed the irregular virucidal results of some studies to the use of animal inoculation methods for assaying virus concentrations. For these same reasons, those studies have been omitted in this report. The advent of viral propogation techniques using tissue cultures Enders et al. Generally, enteroviruses are more resistant to free chlorine than are the enteric bacteria Chang, ; Clarke and Kabler, ; Scarpino et al. For example, in what was probably the first well-defined study, Clarke and Kabler used purified coxsackievirus A2 to investigate viral inactivation in water by free chlorine.
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. They measured virus recoveries by using suckling mice and the LD 50 quantitation procedure. Their results indicated that inactivation times for the virus increased with increasing pH 6. They estimated that approximately 7 to 46 times as much free chlorine was required to obtain comparable inactivation of coxsackievirus A2 as was required for a suspension of E.
For instance, Butterfield et al. At approximately the same pH and temperature ranges, Clarke and Kabler observed Thus, Clarke and Kabler's work showed that 7 times as much free chlorine was required to inactivate the test coxsackievirus compared to the time necessary to kill the bacterium E. In a subsequent study, Clarke et al. At pH 6, most of the free chlorine should have been present as hypochlorous acid.
Increasing the pH to 7. At that pH, the free chlorine should have been a mixture containing predominantly hypochlorous acid and significant levels of hypochlorite ion. Both Weidenkopf and Clarke et al. At these pH's, the free chlorine should have been present as mixtures of both hypochlorous acid and hypochlorite ion, but predominantly as the ion. After comparing these studies, Clarke et al. The same percentage of the adenovirus was inactivated in approximately one-third of that time by the same concentration of hypochlorous acid. Under the same conditions, 8.
From Clarke et al. Clarke and Kabler and Clarke et al. Kelly and Sanderson reported that each of six enteric viruses possessed a different sensitivity to chlorine. Their results suggested that the inactivation of enteric viruses in water at pH 7. With combined chlorine in water, a concentration of at least 9. Poliovirus 1 strain MK was the most resistant strain tested and coxsackievirus B5 the most sensitive. Poliovirus 1 Mahoney strain , poliovirus 2, coxsackievirus B1, and poliovirus 3 were intermediate in resistance. The virucidal efficiency of hypochlorous acid was more than 50 times greater than that of the chloramines Kelley and Sanderson, , Liu et al.
They used Potomac River water that had been partially treated by coagulation with alum and filtration through sand. Chlorine was added to the water at one dosage, 0.
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The final pH was 7. There was a wide range of resistance to chlorine by the viruses. The most sensitive virus was reovirus type 1, which required 2. The most resistant, as judged by extrapolating the experimental data, was poliovirus 2, which required 40 min for the same degree of inactivation. Using actual experimental data, the most resistant virus was echovirus 12, which required a contact time of greater than 60 min for However, assuming a min contact time, most of the viruses tested at pH 7.
Using six of the same virus strains studied by Liu et al. The suspending medium was buffered, chlorine demand-free, distilled-deionized water. Each virus stock was also prepared so as to be chlorine demand-free. Because of the use of two different buffer systems, i. The kinetics of inactivation of poliovirus 1 at pH 7. The results shown in Table II-1 indicate that there is a significant difference in the time required for two logs inactivation for the various viruses at pH 6. In every case, the rate of inactivation at pH The rank ordering in Table II-1 shows that there is also a wide range of sensitivity of related viruses to chlorine disinfection.
For example, at pH There are several cases in which the relative sensitivity to chlorine was altered rank ordering between pH 6. This observation can be seen more clearly in Table II-2 in which the time required for two logs of inactivation of the various viruses and the ratio of inactivation times at pH 6. Even at pH 7. Viral inactivation rates with chloramines have been found to be much slower than with free chlorine. For example, Kelly and Sanderson studied the effects of chlorine on several enteric viruses.
At the same temperature and pH, combined chlorine at 0. Although most viral inactivation studies with chloramines have not differentiated between mono- and dichloramine Kelly and Sanderson, ; Lothrop and Sproul, , Kelly and Sanderson , noted that viral inactivation by chloramines proceeds more rapidly at pH than at pH This tendency indicates that dichloramine may be more virucidal than monochloramine since its proportion increases with increased hydrogen ion concentration. In , Chang proposed that 5. Subsequently, Siders et al.
Similarly, coxsackievirus A9 was approximately 4 times more resistant than E. Siders' data can be compared to Chang's theory on the disinfectant capacity of monochloramine. However, examination of the data of Siders et al. Therefore, it appears that Chang slightly overestimated the virucidal capacity of monochloramine. Some studies, mostly in the field of wastewater treatment, have shown that ova and larvae of the helminth parasites that affect humans and that could occur in U.
They can survive concentrations and exposure periods considerably in excess of those used in the treatment of municipal water supplies. In studies of various free-living nematodes, Chang et al. 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. There have been a number of studies on the effectiveness of chlorine in destroying or inactivating cysts of the protozoan parasite, Entamoeba histolytica , in water, especially during the early 's Brady et al. Varied results reflect primarily the different experimental conditions and techniques that were used.
The presence of organic matter, pH, and temperature, as well as the concentration and form of chlorine and exposure period, have been shown to exert an influence on disinfection. However, the consensus is that, compared with bacteria, these cysts are rather resistant to current chlorination procedures, but are much less resistant than helminths. Brady et al. Chang b , also using a culture technique, studied the cysticidal effectiveness of calcium hypochlorite solution, chloramines, and gaseous chlorine in tap water as well as the effects of pH and organic matter on the biocidal activity.
At contact periods of up to 30 min, gaseous chlorine was the most powerful, hypochlorite solution slightly less so, and chloramines the least. Increase in pH and organic matter reduced cysticidal efficacy. For comparison with Brady et al. Recently, Stringer et al. Using chlorine gas bubbled into buffered distilled water as stock, they obtained In "secondary treated sewage effluent," Stringer et al.
In keeping with these findings, it is unlikely that the chlorine residuals generally maintained in distribution systems provide much protection against E. 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. 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.
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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. 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: 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. 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: 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. 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.
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: 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 1: 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.