The advantages of ozone are:
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Safe and easy in use
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Low maintenance costs
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Ozone is produced on-site and requires no storage of dangerous chemicals
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Ozone requires no additional disinfectants
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No cocktail of disinfectants necessary. Micro-organism can not get resistant to ozone after prolonged use of ozone
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High efficiency as disinfectant. A residual ozone concentration of 0.1 to 0.2 ppm is in most cases very effective in keeping the cooling tower and the cooling circuit clean.
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Very effective in removing biofilms
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Higher efficiency of heat exchangers due to reduced biofilm formation
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Due to good biofilm removal capacities very effective against Legionella
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No chlorinated compounds. Very low corrosion rates in the system.
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No persistent chemicals or disinfectants in bleed. Ozone breaks down to oxygen.
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In some cases ozone can replace disinfectants and also dispergents and inhibitors
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In many cases a higher concentration factor is possible
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Lower operational costs and in many cases a lower overall costs
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Ozone is effective in a wide pH range
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Also effective for mussel growth
In the design of a proper ozone disinfected cooling tower, one needs to take care of the following points
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Suppletion water with high hardness and / or high COD levels is less suitable for ozone based cooling towers
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Retention time in the system. The half time of ozone is normally less than 10 minutes in cooling systems. To assure an adequate residual ozone concentration it is necessary to start with an adequate begin concentration.
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Dead spots. Because ozone depletes to oxygen, spots with little circulation have to be prevented.
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Temperature. The solubility of ozone and the half life time of ozone decreases at higher temperatures. This limits the temperature of the cooling water in which ozone can be used. This limit is in most cases around the 45°C.
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Material. The materials used in the cooling tower need to be ozone resistant.
Legionella
In the prevention and control of legionnaires disease (legionella) causing microbes, ozone has taken an eminent roll. The specific characteristics of the disinfectant make sure ozone gets the job done where others fail.
Biofilm in the piping can protect legionella from most of the disinfectants.
Environmentally friendly solution for this problem is the use of ozone disinfection for new and existing cooling towers.
Biofilm
A biofilm is a layer of microorganisms contained in a matrix (slime layer), which forms on surfaces in contact with water. Incorporation of pathogens in biofilms can protect the pathogens from concentrations of biocides that would otherwise kill or inhibit those organisms freely suspended in water.
Biofilms provide a safe haven for organisms like listeria, E. coli and legionella where they can reproduce to levels where contamination of products passing through that water becomes inevitable.
