Ozone, a triatomic allotrope of oxygen, is produced industrially in an electric discharge field generator from dry air or oxygen at the site of use. The ozone generator produces an ozone-air or ozone-oxygen mixture containing 1 and 2% ozone by weight. This gas mixture is introduced into the water by injection or diffusion into a well-baffled mixing chamber or scrubber, or by spraying the water into an ozone atmosphere.

Ozone is a powerful oxidizing agent. The mechanism of its bactericidal action is believed to be diffusion through the cell membrane followed by the irreversible oxidation of cell enzymes. Disinfection is unusually rapid and requires only low ozone concentrations.

The viricidal action of ozone is even faster than its bactericidal effect. The mechanism by which the virus is destroyed is not yet understood. Ozone is also more effective than chlorine against spores and cysts such as Endamoeba histolytica.

Disinfection, color, taste, and odor control can be accomplished in a single treatment step by ozonation. Ozone reacts rapidly with all oxidizable organic and inorganic materials present in the water.

The ozone dosage necessary for disinfection depends on pollutant concentration in the raw water. An ozone dose of 0.2 to 0.3 ppm is usually sufficient for bactericidal action only. The ozone dosage necessary for secondary activated wastewater treatment effluent disinfection is 6 or more ppm. Ozonation leaves no disinfection residue, and therefore ozonation should be followed by chlorination in drinking water supply treatment applications. To obtain optimum drinking water, raw water should first be ozonated to remove color, odor, and taste and to destroy bacteria, viruses and other organisms. Then the water should be chlorinated lightly to prevent recontamination.

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