UV disinfection

Worldwide people are aware of the necessity to protect nature. One key element in protecting the environment is to assure industrial activities are done in a sustainable way.

In the past, nature usually managed to evolve and protect itself, however, man now needs to step in and find effective solutions to avoid pollution. Today more and more technologies are developed to accomplish sustainable solutions.

One of these sustainable solutions is water disinfection by ultraviolet (UV) radiation. It is certainly the most reliable and environmentally friendly method of water disinfection. The acceptance and popularity of UV disinfection applications is currently growing rapidly throughout the world.

Germicidal effect

UV-c radiation destroys the genetic structure of micro-organisms and inhibits their ability to replicate thus preventing the formation of harmful colonies causing their death. In nature, germicidal ultraviolet radiation is a part of the sun's radiation but most germicidal radiation (UV-C) does not reach the earth.

Modern technologies can be used to convert electrical energy 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 micro-organisms by destroying their DNA.

UV radiation, in particular UV-C, effectively inactivates aerosol, surface and water-living bacteria, viruses and cysts. What’s more, UV radiation also destroys some types of viruses that are resistant to conventional chemical disinfection technologies. One of the characteristics of high efficient UV lamps is their ability to selectively radiate at 254 nm, which is close to the optimal germicidal wavelength of 260 nm (see below), whilst not emitting radiation that generates ozone or other carcinogenic substances.

Germicidal ultraviolet does not change the chemical composition or flavour of the water unlike chemical reagent based disinfection methods (chlorination, ozonation). The receptive sensitivity of micro-organism to UV radiation is very dependent on its type. Viruses and bacteria in vegetative forms (e.g.: bacillus, coccus) are the most susceptible to UV radiation; these include infamous bacteria such as Mycobacterium tuberculisis, Salmonella typhosa, Shigella dysenteriae, Vibrio cholerae and Hepatitis virus.

A higher UV dose is required to inactivate Lamblia cysts and Cryptosporidium oocysts and the highest UV doses are necessary to destroy spores. It is always possible to select an UV dose that provides appropriate disinfection for any given situation because there are no negative effects from overdosing.

UV radiation’s inactivation is demonstrated by the so-called germicidal curve that plots the relative quantity of destroyed micro-organisms against the UV radiation’s wavelength. The germicidal effect of UV radiation is highest in the 205-315 nanometer range of the spectrum with the maximum disinfection efficiency occurring at 260 nm. The spectral distribution of radiation from the mercury low-pressure germicidal lamps used in LIT UV systems 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 high energy level of the UV dose. In general Ultraviolet radiation for approximate 3-5 seconds results in a lethal UV dose to inactivate most bacteria and viruses in the treated water, air or surfaces.