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Ozonation is one of the many methods used for the disinfection of water. It is a technology substantially more effective than others.

  • Used to treat ground and surface water in many European cities for years
  • First ozone treatment plant was opened in Paris, France in 1906.
  • Now, more than 2,000 municipal water treatment plants worldwide use ozone.
  • Industry standard for disinfecting bottled water.

Ozone, also referred to as triatomic oxygen, is an unstable gas having life in water of minutes. Oxygen, which is normally bi-atomic, becomes ozone through the addition of a third unstable atom.

Ozone, because of its instability, cannot be generated and stored for future use. It must be generated and used for treatment immediately. It is created by one of two generation methods: Ultraviolet radiation or corona discharge. Of the two, corona discharge produces the substantially higher ozone concentration needed for the removal of complex impurities. Generated ozone is pumped into the water through a stone of fine porosity, creating very small bubbles which rise slowly through the water. The slower the bubbles rise through the water, the greater the amount of ozone transferred to the water.

Most critically for water quality, ozonation does not add chemicals to the water as does chlorine, chlorine dioxide, permanganate, etc. As the ozone passes through the water, the third unstable atom detaches, attacks, and destroys impurities in the water. The residue in the water is pure oxygen, which quickly dissipates in a few minutes. Any excess dissolved ozone which is not needed for treatment, reverts to simple oxygen in approximately 20-30 minutes.

The primary effects of ozonation of drinking water are:

  • Bacterial disinfection and viral inactivation.
  • Oxidation of inorganics such as iron, manganese, organically bound heavy metals, cyanides, sulfides and nitrates.
  • Oxidation of organics such as detergents, pesticides, herbicides, phenols, taste and odor caused by impurities.

The action of ozone in each of these cases follows:

Disinfection and Viral Inactivation
The extent of bacteria destruction and viral inactivation is related to the concentration of ozone in the water and its contact time with the microorganisms. Bacteria are the most rapidly destroyed. E-Coli bacteria are destroyed by ozone concentrations of just over .01 mg/liter and contact time of 15 second at temperatures of 25 degrees C (77 degrees F) and 30 degrees C (86 degrees F).* Streptococcus fecalis are much more easily destroyed. At ozone concentrations of about 0.025 mg/liter, 99.99% inactivation is obtained in 20 seconds or less at both temperatures. Viruses are more resistant than bacteria. Poliovirus types I, II and III are inactivated by exposure to concentrations of dissolved ozone of 0.4 mg/liter over a four minute contact period.

Oxidation of Inorganics
In the case of iron, manganese and the several arsenite or arsenate compounds, oxidation takes place very rapidly, leaving insoluble compounds which are easily removed by an activated carbon filter. Sulfide ions are oxidized sequentially to sulfate ions, an innocuous substance. The first stage of this oxidation is very rapid, quickly and efficiently removing any sulfurous odors. Nitrite ions are oxidized to nitrate ions, which are stable and innocuous.

Oxidation of Organics
Ozone if a very powerful agent in treating organic materials. Organics are either natural (humic and fulvic acids) or synthetic (detergents , pesticides) in nature. Some organics react with ozone very rapidly to destruction, within minutes or even seconds (phenol, formic acid), whereas other react more slowly with ozone (humic, fulvic acids, several pesticides, trichloroethane, etc.) In some cases, organic materials are only partially oxidized with ozone. A major advantage of partial oxidation of organic materials is that in becoming partially oxidized, the organic materials become much more polar than originally, producing complex insoluble materials which are removed by activated carbon filters.

* Ozone in Water Treatment: Applications and Engineering; 1991 printing; Lewis publishers.

 
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