The sun as a role model The sun radiates light in different wavelengths (nanometer nm) to the earth. Some of this is visible light (colour spectrum) and some is not visible to the human eye. For the preparation of water, however, only ultraviolet light with a wavelength of 185 to 315 nm is of importance.
The ultraviolet rays of the sun kill off morbiferous microorganisms within seconds, thus preventing further spreading. The primary damage to the microorganisms during ultraviolet irradiation is based on a photosensitive alteration of the nucleic acids that prevents cell division. A very effective disinfection is achieved through this. The most efficient disinfection is achieved by ultraviolet rays with a wavelength of 254 nm.
Ozone (O3) is formed due to ultraviolet irradiation at 185 nm. It breaks down easily upon formation of oxygen and is thus deemed to be a good disinfectant and oxidant of many water-soluble, (partly persistent) substances.
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