Ozone Treatment of Water
Ozone is an unstable gas, comprising of three oxygen atoms. Ozone is produced by subjecting oxygen molecules to high electrical voltages. It is often used to treat water since it has a greater disinfection effectiveness in removing virus and bacteria present in water when compared to chlorination. Ozone is also known to reduce the concentration of iron, sulfur and manganese and eliminate odor and taste problems. Ozone oxides the manganese, sulfur and iron into insoluble metal oxides or elemental sulfur. These insoluble particles are later removed by filtration. The process of using ozone to treat water is commonly known as ozonation.
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Formation of Ozone
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Oxygen is converted to ozone using energy. This process is carried out by ultraviolet radiation in a UV-type ozone generator or by an electrical discharge field as in a CD (corona discharge) type ozone generator. In addition to these commercial methods, ozone may also be generated through chemical or electrolytic methods. UV type ozone generators are used when the quantity of water to be treated is less, while the CD type is used for larger volumes of water.
Ozonation Process
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Clean air is passed through the high voltage electric discharge which creates approximately 1 percent ozone. Raw water is then passed through a venturi throat which creates a vacuum and pulls the ozone gas into water. Air is then bubbled up through the water that needs to be treated. Ozone reacts with the metals present in the water to form insoluble metal oxides which are later removed by filtration.
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Performance of Ozonation Process
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The performance of the ozonation process is dependent on the susceptibility of bacteria, virus and other microorganisms to ozone, concentration of ozone and the amount of time the microorganisms are in contact with ozone in the water.
Benefits of Ozonation
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Ozone is highly effective in eliminating the Cryptosporidium bacteria and other naturally occurring microorganisms present in water. Unlike ultraviolet and chlorine disinfection systems, there is no re-growth of microbes after ozonation. Ozonation is also known to reduce the formation of trihalomethanes, which are a result of interactions between naturally occurring materials in the source water and chlorine. The main advantage of using ozone is that it does not use any chemicals to treat water. Ozone also has a very high oxidizing power with very short reaction periods.
Disadvantages of Ozonation
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Disadvantages of using ozonation are many. The process can generate harmful by-products like bromates, aldehydes, and ketones. Operational and maintenance costs are also very high for Ozonation systems. The Ozonation process also does not provide residual protection and often secondary disinfection is necessary.
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