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Ozone Water Treatment |
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Ensuring that drinking water is safe for consumption is no longer the sole burden of municipal water providers. More water treatment dealers are attempting not only to improve water's aesthetics, but to disinfect it as well.
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Ozone can often accomplish both objectives. It can, for example, destroy microorganisms like Escherichi coli (E. coli), Cryptospondium, Poliovirus, Giardia muris and Girdia lamblia. It can also help remove iron, hydrogen sulfide and other contaminants from water.
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Ozone (O3) is low molecular weight molecule composed of three oxygen atoms arranged in a chain. It's an allotrope of oxygen (O2), meaning its composed of the same atoms combined in a different way.
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Ozone is the most powerful useful oxidant known, second only to fluorine in strength. Its high chemical reactivity arise from its unstable electron configuration that seeks electrons from other molecules. During its reaction with other molecules ozone is destroyed and the host is oxidized.
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In water, oxidizing pollutants undergo a process similar to burning. The difference is temperature; ozone is so powerful it's able to oxidize at ambient temperatures. Also, pH of water isn't directly changed when ozone is employed. This differs from other oxidizers such as chlorine, which require the use of caustic or lime to adjust the pH, thus altering overall water quality when byproducts are left in the water.
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| Generating Ozone |
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Commercially, ozone is generated by accelerating electrons between two electrically charged plates in a process called "corona discharge." The method used in most residential applications is ultraviolet (UV) light ozone generation. In this process ambient air passes through an ozone chamber where UV light disassociates oxygen molecules. They then recombine as ozone molecules.
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A filtration system may be required in conjunction with an ozone system for home water treatment. This system removes destroyed microorganisms and the matter to maintain stability and yield optimum water clarity.
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Like chlorine, ozone kills microorganisms by oxidation. In the case of chlorine, the active oxidant is hypochlorous acid (HOCI). With ozone, the ozone itself attacks the microbe. Bacteria kill rates are vastly different between ozone and chlorine because the method of kill is different. Ozone ruptures bacteria's cellular membranes, so reactivation of the cell is impossible. It may be said to act blindly because no limits to disaffection have been found in the numbers or species eliminated.
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Ozone is the most powerful useful oxidant known, second only to fluorine in strength. Its high chemical reactivity arise from its unstable electron configuration that seeks electrons from other molecules. During its reaction with other molecules ozone is destroyed and the host is oxidized.
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Chlorine treats water much slower because it must first diffuse through he cell wall of the bacterium. Thus, contact times for chlorine eliminating a microbe can be 2.5 to 55 times longer than with ozone.
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In fact, tests show ozone 3,125 times faster an oxidant than chlorine. This means that while contact time is important when sizing an ozone system to treat a particular water source, the most important variable is the quantity of ozone transferred into the water.
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To optimize the mechanism of cellular destruction, well-designed ozone systems bring bacteria into intimate contact with ozone. This is done in the ozone diffusion contact tank prior to final filtration. For whole-house ozonation, two methods of transferring ozone to water are a ceramic dispersion stone or a venturi.
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| Ozone as a Disinfectant |
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Guidelines for ozone disinfection were established in 1967 based on a series of studies done in 1964 and 1967 on Poliovirus which determined that maintaining a dissolved ozone residual of 0.3 ppm for a minimum of 4 minutes guarantees at least 99.99% virus inactivation.
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For the studies, 1 milliliter of virus suspension was added to 1 liter of water in a specially designed flask. 15 milligram does of ozone was added to the flask, which was inverted and shaken vigorously over the four minute period. Virus titration samples were obtained by diluting the total ozonated sample with a culture medium containing 10% veal serum to destroy any excess ozone.
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These studies show that each time the value of residual ozone measured in the water was below 0.3 ppm, viruses were only partially inactivated after the four or eight minute period of contact time. Having established the necessary residual ozone concentration to provide 99.99% viral inactivation at 0.3 ppm in the batch studies, researchers set up a continuous flow column apparatus within which ozone was applied to the virus containing water samples continuously. The bubbles of ozone / air rose upward while the water flowed downward.
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Under these conditions, the ozone content of the water increased in gradual stages until it reached a theoretical maximum corresponding to a balance between the various demands for it. Over a 15 year period of research, ozonation conditions have shown that in normal operation, water containing no suspended and little oxidizable matter is completely free of pathogenic bacteria after ozonation, according to the most accurate detection methods in use.
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Consequently it's safe to say that maintaining a dissolved ozone residual of 0.4 ppm (0.1 higher than tested) for a minimum of 4 minutes will ensure drinking water is of high microbial quality. Bear in mind that each disinfection application has unique features; select a supplier that can provide the right information and equipment for the job.
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