Ultraviolet light, UV, is a disinfection technology that relies entirely on lightwaves.
How it works:
UV light at the 254 nm wavelength penetrates the cell membrane of the microorganism. The UV energy permanently alters the DNA structure of the microorganism in a process called thymine dimerization. The microorganism is rendered unable to reproduce or infect.
Efficacy of UV light for microbial disinfection peaks at the wavelength of 254 nm. Above and below this wavelength, effectiveness is quite diminished.
Advantages of UV light technology:
Triggers a nearly instant reaction.
No disinfection byproducts. (Chlorination, by contrast, creates THMs.)
No hazards introduced, such as the handling and disposal of chemicals.
No alteration of water chemistry, no effect on taste, odor, color or pH.
Extensively used in environmentally sensitive and qualitatively critical applications, such as food and beverage, pharmaceutical, and semiconductor manufacturing.
No post-treatment residual.
Subject to water quality: Turbidity, color and suspended solids affect penetration of lightwaves.
No effect on water quality factors such as suspended solids although ideal for destruction of organics and chemicals.
Most microorganisms require relatively low levels of UV energy to be rendered inactive - under 10 mJ/cm2 (10,000 μWsec/cm2).
States call for varying standards. In New York State, a minimum safety factor of 4x - 40 mJ/cm2 - is required at the end of UV lamp life (EOL).