Ultraviolet (UV) radiation is an electromagnetic radiation with a wavelength shorter than visible light. If microorganisms (bacteria, viruses, parasites) are exposed to ultraviolet radiation, the absorption of photons occurs and triggers a photochemical reaction. The main cellular component which is disrupted by UV radiation are nucleic acids. In the case when suitable wavelength ranges and sufficiently high doses of UV radiation are used, such radiation causes damage to microorganisms, leading to their inactivation, i.e. loss of their reproductive ability (reproductive cells death). Such inactivated organisms does not possess no further risk of infection.
When using the minimum dose of 400 J/m2 of UV radiation (at wavelength λ = 254nm), it is possible, according to the current state of knowledge, to achieve a 99.99% reduction of microorganisms contained in the water and also any bacteria recover systems are destroyed.
Advantages of water UV disinfection
- no chemical dosing needed
- very short reaction times (fractions of seconds)
- when used correctly, no changes in the water composition occur
- microbicidal effect is not dependent on pH and temperature, unlike in chemical disinfection processes
- according to the current state of knowledge, better effect against resistant forms of pathogens (such as cryptosporidium oocysts) is achieved, unlike with any chemical methods of disinfection
Disadvantages of water UV disinfection
- unlike in chemical disinfection methods (chlorine, ozone), no direct measurement of the UV dose is possible during the practical use
- effective only at the area of direct exposure, no lasting effect (as for example in water systém)
General assumptions of water disinfection
- there is no universally applicable method suitable to all operating conditions from the current approved methods of disinfection (chlorination, ozonization, UV disinfection)
- choice of method must match to individual requirements
- disinfection must always take a place as the last stage of water treatment
- water must not have any turbidity to accomplish appropriate microbicidal effect and thus the reliable disinfection (this applies to all methods, especially for UV disinfecting
UV radiation is used for disinfection of the the drinking water in a groundwater and surface water treatment, in drinking water treatment facilities at the point of consumption, in hot water distribution systems, medical facilities, and in the other technological applications.