Ozone

The ozone is a chemical compound comprising 3 atoms of Oxygène ( O₃ ). Its structure is a resonance between three states. Metastable in the environmental conditions, ozone tends to break up naturally into Dioxygène. With room temperature, it is a pale water gas. It is liquefied with -111,9  °C in the form of a particularly unstable liquid dark blue and is solidified with -192,5  °C.

One produces ozone by electric shock in dioxygene. Ozone reacts with the alkaline metals and alkaline-earth metals to form Ozonide S ($M\; +\; O\_3\; \backslash \; rightarrow\; MO\_3$), unstable and reacting with the Eau to form dioxygene. This succession of chemical reactions explains for the greatest part the character of Polluant which is allotted to ozone when it is present in the atmosphere close to the ground.

Contrary to odorless dioxygene, ozone is perceived by the human Odorat; its odor is very characteristic, slightly prickly. Breathed in great quantity, it is toxic.

Discovered

Ozone was discovered in May 1840 by the Swiss chemist Christian Schönbein. It thus named it by referring to the Greek root ozein (to exhale an odor, to feel). The relation between ozone and the oxides of nitrogen was highlighted in the years 1970 by Paul Josef Crutzen, Nobel Prize of Chemistry 1995.

Ozone in the atmosphere

See also: Layer of ozone

In high the Atmosphere of the Earth, the layer of ozone is an ozone concentration which filters part of the ultraviolet rays emitted by the Sun, ultra-violets in particular responsible for Cancer S of the Peau. This protective coating is threatened by pollution, in particular by the gas emissions CFC (Chlorofluorocarbone), which go up in the upper atmosphere and catalyze the destruction of ozone there, being thus at the origin of the hole in the layer of ozone. Like measuring instrument, one can note the instrument GOMOS satellite ENVISAT.

See also: tropospheric Ozone

Ozone is also very present around the great agglomerations which provide the precursors of them, in particular the Dioxide nitrogen NO₂, by their atmospheric pollution. At the time of the Heat wave S, one finds ozone in great quantity in the low layers of the atmosphere, especially around the urban centres. It is mainly produced there by the reaction of the Hydrocarbure S unburnt residues and nitrogen the oxides of exhaust fumes of the vehicles with the Oxygène of the air under the influence of solar light. At the time of strong temperatures, its evacuation towards the roadbases of the atmosphere is braked, which can involve health issues at the fragile people.

Industrial production

On an industrial scale, ozone is produced by using ultraviolet radiations short wavelengths emitted by a mercury discharge lamp or by the process of cold discharge (discharge corona) which uses a high Electric field. The apparatus of discharge consists of two plates of Métal separated by a layer from air and a Isolant electric of constant dielectric high, like the Mica or glass borosilicate. A high potential difference is applied between the two plates, which involves the dissociation of the Molécule S of Oxygène of the layer of air and their ozone recombination. A crown can be present but the electric field is maintained at a value lower than that which would involve the appearance of an electric arc and a plasma.

In laboratory, ozone can be produced by electrolysis by using a battery of 9V, a Cathode of Graphite, a Anode of Platine and the sulphuric Acid like electrolyte. The half-reactions which take place are:

3:00 ₂O → O₃ + 6:00 ⁺ + 6e^- ΔE^o = - 1.53 V

6:00 ⁺ + 6e^- → 3:00 ₂ ΔE^o = 0 V

2:00 ₂O → O₂ + 4:00 ⁺ + 4e^- ΔE^o = -1. 23 V

Three equivalent water are used to produce an equivalent of ozone. This reaction is in competition with that of oxygen formation.

Use in the water treatment

Purification of drinking water

Ozone presents a series of advantages compared to the Chlore for the water treatment, which explains why it is employed in spite of the often significant cost of an installation of ozonization of water. These advantages are the suivants :

• it does not remain present in the eau  ;
• it does not cause the appearance of organochlorinated products, which can be cancérigènes  ;
• it does not leave bad little appreciated taste of the consumers of Drinking water.

But it leaves a negligible blue trace in water.

Ozone is employed in the water treatment for several fonctions :

• oxidation of iron;
• improvement of the performance of sand filters;
• improvement of flocculation (called " ozofloculation")
• disinfection of water;
• elimination of harmful organic compounds, as private individuals pesticides and weedkillers. For this application ozone is in general injected upstream filter activated carbon.

Waste water

Ozone is used in processes of treatment of waste water, in particular to make digestible by bacteria DCO known as " dure" , and for the disinfection of water at exit of purification plants (treatment known as tertiary ). These applications require the control of several technologies: ozonization, but also bio-engines. Sometimes the performance of ozone can be improved by combining ozonization by a treatment UV with high amount of irradiation. One then speaks about proceeded of oxidation advanced .

Industrial uses of ozone

Importance of the industrial applications of ozone

The use of ozone in the water treatment remains currently the industrial application prévalente. However a series of other applications were developed during the 2 last decades, primarily in substitution of chlorine.

Motivations of the use of ozone

Ozone is oxidizing and a one disinfecting powerful. It has certain advantages by reports/ratios to other oxidants usually used in industry, in particular chlorine. The main advantage is the absence of remanence : ozone being chemically unstable, there do not remain oxidant traces or derivative products on the treated products.

Laundry

This application is very widespread in the Anglo-Saxon countries and little in continental Europe. Ozone is used primarily for the washing of white linen in the commercial installations.

Agribusiness industry

Ozone is employed in the agroalimentary one for two quite distinct applications:

• the ozonization of cold rooms;
• the washing of food products to ozonée water.

Micro-electronics

The Wafer S intended for the manufacture of integrated circuits are washed with water ozonée with for objective the elimination of possible organic matter traces.

Paper mill

Ozone is employed like bleaching alternate with chlorine, and for the treatment of waste water of Papeterie.

Cleaning of the conduits

Ozonée water is simple means to implement for the destruction of biofilms in conduits.

See too

• Ozone on the level of the ground

• Ozonothérapie
• Layer of ozone

External bonds

ozone

• international Card of toxicological safety
• Card of the INRS
• Air pollution by ozone and health summarized of GreenFacts of scientific reports/ratios of WHO
• Forecast of ozone Forecasts and observations of the quality of the air in France and Europe
• International Ozone Association - European African Asian Australasian Group
• HTTP: /ozone.ch/librairie/manuel/ Handbook of purification of water: Ebook with lélécharger, contains a broad section on the measurement of ozone and the use of ozone in water treatment.
• HTTP: /www.ozontherapie-aerzte.ch: Association of the Swiss doctors for the therapeutic use of ozone

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