Germicidal effect

UV radiation destroys the genetic structure of microorganisms and inhibits their ability to replicate thus causing their death. In nature germicidal ultraviolet is a part of the sun's radiation however, most germicidal radiation (UV-C) does not reach earth.

Modern technologies can be used to convert electrical power into germicidal ultraviolet in an efficient manner. One of these technologies is a mercury gas-discharge lamp that generates UV-C radiation, which can be used to inactivate microorganisms by destroying DNA.

UV radiation in particular UV-C effectively kills airborne, surface and water living bacteria, viruses and cysts. Especially important is the fact that UV radiation destroys some types of viruses that are resistant to conventional chlorination. One of the characteristics of UV lamps is the ability to selectively radiate at 254 nm close to the optimum wavelength of 260 nm (see below) and not to emit radiation that generates ozone or other carcinogenic substances.

Germicidal ultraviolet does not change the chemical composition and flavour of water in contrast to reagent methods of disinfection (chlorination, ozonation). Resistivity of microorganism to UV radiation strongly depends on its type. Most sensitive to UV radiation are viruses and bacteria in vegetative forms (bacillus, coccus), for example, well know microorganisms such as Salmonella typhosa, Vibrio cholerae, Shigella dysenteriae, Hepatitis virus, Mycobacterium tuberculisis.

Alarger UV dose is required to inactivate Lamblia cysts and Cryptosporidium oocysts, while the largest UV dose is necessary to destroy spores. It is always possible to choose a UV dose that provides proper disinfection in any particular case, since there is no negative overdosing effect.

Best performance

Inactivation efficiency of UV radiation is demonstrated by the so-called germicidal curve that shows relative quantity of destroyed microorganisms versus wavelength of UV radiation. The germicidal effect of ultraviolet radiation is considerable in the 205-315 nanometer range of the spectrum, with the maximum disinfection efficiency achieved at 260 nm. The spectral distribution of radiation from mercury low-pressure germicidal lamps used in LIT UV systems is peaks at 254 nm, which is very close to the optimal disinfection wavelength. LIT UV units provide reliable disinfection over a wide range of water quality parameters due to the margin of UV dose. Ultraviolet radiation only takes about 3-5 seconds to kill most bacteria and viruses in treated water.