RD 140/2003 establishes the obligation to treat and control water intended for human consumption. For this, chlorine is the most used disinfectant agent, but not the only nor the best. The disinfecting power of ozone is about 3,000 times greater and faster. Treating drinking water with ozone therefore has a series of advantages over treatment with chlorine.
Firstly, due to the strong oxidizing power, the quality of ozone disinfection is much higher than that achieved with chlorine treatment. In this way, viruses, bacteria and generally chlorine-resistant microorganisms are eliminated. Also thanks to this high oxidation potential we are able to precipitate heavy metals that can be found in solution and eliminate organic compounds, pesticides, and all types of strange odors and flavors that the water may contain. Another of the important advantages of using ozone over chlorine is the speed with which it acts, which allows us to carry out very effective treatments in a few seconds or minutes when a much longer contact time is necessary to carry out a disinfection treatment with chlorine.
The main effects of ozonation of drinking water
- 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 is as follows:
Disinfection and viral inactivation
- Bacteria and viral inactivation are related to the concentration of ozone in the water and its duration of contact with the microorganisms. Bacteria are the most quickly destroyed. E-Coli bacteria are destroyed by ozone concentrations of a little more than 0.1 mg/liter and a contact duration of 15 seconds at temperatures of 25 ºC and 30 ºC. Streptococcus tecalis are destroyed much more easily. At ozone concentrations of approximately 0.025 mg/liter, 99.9% inactivation is achieved in 20 seconds or less at both temperatures. Viruses are more resistant than bacteria. Pioneering studies by French Public Health scientists in the 1960s have shown that poliovirus types I, II and III are inactivated by exposure to dissolved ozone concentrations of 0.4 mg/liter for a contact period of four minutes.
Oxidation of inorganics
- In the case of iron, manganese, and various arsenic compounds, oxidation occurs very quickly, leaving insoluble compounds that can be easily removed by means of an activated carbon filter. Sulfide ions are oxidized to sulfate ions, a harmless substance.
Organic oxidation
- Ozone is a very powerful agent in the treatment of organic materials. Organics are natural (wetting and fumic acids) or synthetic (detergents, pesticides) in essence. Some organics react with ozone very quickly until destruction, within minutes or even seconds (phenol, formic acid), while others react more slowly with ozone (wetting and fumic acids, various pesticides, trichlorethane etc.). In some cases, organic materials are only partially oxidized with ozone. A main advantage of partial oxidation of organic materials is that when partially oxidized, the organic materials become much more polarized than originally, producing complex insoluble materials that can be removed with activated carbon filters.
Turbidity removal
- Turbidity from water is removed by ozonation through a combination of chemical oxidation and charge neutralization. The colloidal particles that cause turbidity are kept in suspension by negatively charged particles that are neutralized by ozone. Ozone also destroys colloidal materials through the oxidation of organic materials.
Elimination of odors, colors and flavors
- The oxidation of organic matter, heavy metals, sulfides and foreign substances produces the suppression of foreign flavors and odors that the water may contain, providing an improvement in the quality and appearance of the water, making it more suitable for consumption and enjoyment.
Ozone water treatment
- The technique is fundamentally based on achieving an adequate contact time of water, with the appropriate amount of ozone. Concentrations of between 0.5 and 0.8 mg/l of ozone for about three or four minutes are sufficient to achieve exceptional, disinfected water quality. After treatment, the ozone decomposes into oxygen after several minutes, leaving no type of residual, but consequently, there will be no disinfectant residual that could prevent bacteriological growth. In cases where it is necessary to ensure that the drinking water has been freshly treated with ozone, the ozonation system will be carried out in a tank with a recirculation flow, where the appropriate ozone production will be added using a venturi injector. This amount of ozone and therefore, the concentration of residual ozone in the tank depends, firstly, on the production characteristics of the equipment, and secondly, on its operating and shutdown time. That is, using the timer, it is possible to increase and decrease the production and shutdown time, achieving a higher or lower ozone concentration in a steady state. For more complex regulation and control systems, a residual ozone measurement probe can be installed in the water that acts directly on the equipment's production to reach the pre-established setpoint as the ideal ozone concentration in the water.
- Depending on the type of installation and demand, there may be many other possibilities, such as injecting ozone directly into the pipe through a by-pass.
- In short, an ozone treatment allows us to enjoy excellent quality water free of pathogenic microorganisms and in the absence of chlorine and all the problems that this biocidal agent entails.
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