such as glazed surfaces [4]. The most part of the work
was carried out at the laboratory and pilot reactors.
2.1 Principle of the photocatalysis
The principle of the water treatment by heterogeneous photocatalysis uses the excitation by the ultraviolet light of a
semiconductor in the form of solid particles settings in contact with water to be treated [5]. The heterogeneous
photocatalysis is started by the semiconductor material irradiation with photons of energy adapted to the solid. It
allows fast oxidation until the complete mineralization of many organic compounds, nitrogenized, etc. adsorbed on
catalyst. It is necessary indeed that there is mass transfer of the pollutant of the liquid phase towards the surface of
catalyst so that there can be reaction and adsorption is the first stage necessary to any heterogeneous catalytic
reaction.
Concerning the effectiveness of the technique like means of cleaning up of water on the scale of the laboratory or
industrial, the kinetics of degradation depends on five principals factors those would have to be optimized [6, 2]:
1. Catalyst mass when this last is powder
2. The wavelength and light radiation
3. Intensity of the light radiation
4. Pollutant Initial concentration
5. Geometry and dimensions of the reactor
2. 2. The catalyst
A catalyst is a solid which has the property to accelerate the reaction rate of a chemical conversion
thermodynamically possible. The catalyst is found unaltered at the end of the reaction.
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If the catalyst is a solid, it is able to create active intermediaries of a different type: in fact the adsorbed species by
rupture of the intermolecular connections, form connections with surface. The heterogeneous catalysis is primarily a
phenomenon of surface. The choice of a semiconductor in proceeds photocatalytic appears limited in consequence
of the very selective criteria like the catalytic activity, insolubility, not - toxicity and stability in the darkness in
contact with the reactional medium and under the irradiation. These considerations are significant water treatment
process. The catalyst is generally used in the form of powder in suspension. They can also be attached or
incorporated in motionless supports. The processes using this type of photocatalyst make it possible to avoid the
stages of filtration or decantation and resuspension of a powder photocatalyst.
Because of the important advantages that presents TiO2 is used the most for the purification of water. Among these
advantages we can include the most important [2]:
• Stable, not very expensive, not toxic;
• The use of additives is not necessary;
• The most effective catalyst;
• Support the photodegradation of a broad range of pollutants of interior at ambient temperature.