The UV light represent a part of the solar light and falls within the range of wave lengths between 400nm and 100nm. This range is immediately inferior to the light visible by the human eye, and immediately superior to the x-rays one.
The water's disinfection mechanism through the UV radiation allows to suppress microorganisms, to inhibit their reproduction and so to guarantee for the bacteria to became completely innocuous.
The UV light kills bacteria and viruses thanks to a photochemistry reaction which affect directly the viruses and bacteria's DNA destroying their genetic information.
This reaction is the reason behind the water's treatment and disinfection ‘s techniques. The used method is focused on a natural process, with no need for using chemical additives.The efficiency and goodness of a UV system in the water's disinfection are measured in terms of bacteria reduction. Therefore, every system is designed to reduce the number of bacteria to an acceptable level, which depends from the peculiar application.
The disinfection levels are not all the same, there are different factors to consider such as:
The microorganisms' sensitivity to the UV radiation vary from species to species and is measured with a specific inactivation grade to the different number of radiations.
It is worth notice that in order to have microorganisms' inactivation levels of about 4, 5 orders of magnitude, is sufficient to have irradiation which correspond to less than 12 mJ/cm2
The germicidal UV radiation is produced by mercury vapor lamps which radiate the UV to a 254nm wavelength. Lamps can be at a low or medium pressure or amalgam lamps.
According to the different quartz glass used for the lamp's body, the low pressure and amalgam lamps radiate a light in the amount of 254nm and 185nm.
The best wavelength in order to disinfect the water are close to 260nm. UV lamp never touches the water, it's closed in a quartz glass cover or assembled out of the water that flows through a transparent pipe.
We have a very efficient disinfection thanks to this technology when the particles suspended in the water are a few, because otherwise they can protect the UV light's microorganisms. In which case is better to pre-filter the water in order to improve the action of the light and remove the bigger microorganisms.
Another key factor to consider when an installation is designed is the flow velocity: if the flow is too fast, the water will pass through with no sufficient UV exposition, if the flow is too slow, the heat could gather itself and damage the UV lamp.