Ultraviolet Light (UV) is a type of electromagnetic radiation often used in use in high purity water solutions, industrial water treatment and municipal water treatment and disinfection. UV is just a small portion of the spectrum which includes visible light, radio waves, and microwaves- all at different wavelengths. UV light wavelengths are between 100-400 nanometers (nm) whereas visible light is between 400-700 nm. UV light is invisible to the human eye.
The benefits of UV light on germs was discovered as early as 1887. Research shows that UV light at certain wavelengths (200-300 nm) Inactivates most microorganisms so they are unable to reproduce. If the organisms cannot reproduce, they are unable to infect. This in turn prevents outbreaks of illness.
UV devices can range in size from a single water bottle all the way to a full commercial system treating millions of gallons of water a day. One significant disadvantage to using UV light is that it does not provide a residual (the effect that remains in the water without a repeat of light). This means that if the water is to be stored, it would need a chemical disinfection such as chlorine or iodine- which provides a long lasting disinfectant residual effect.
254 nm ultraviolet lamps destruct the DNA in bacteria. These are typically placed after deionization tanks in a system.
185 nm ultraviolet lamps are typically placed in a system before deionization tanks. These remove TOC (Total Oxidizable Carbon).
Apart from the disinfecting effect, TOC degradation gains primary importance when applying UV technology in the field of ultrapure water, in order to further scale down the TOC concentration achieved by pre-treatment to the values required for ultrapure water. The TOC plays a crucial role when assessing the organic quality of ultrapure water. Since it cannot be measured directly, conductivity is relied upon as a parameter.
UV oxidation makes use of the effect that UV irradiation, especially at a wave length of 185nm, generates hydroxyl radicals from water. These radicals oxidize the organic constituents down to CO2 and H2O. Thus the UV reactor is used for degradation and the determination of TOC at the same time. Special UV lamps are applied in the reactors, which, apart from the wave length of 254nm relevant to disinfection, also emit UV irradiation of 185nm required for TOC degradation.
An important criterion for the design of UV systems is, apart from the qualitative property of the UV lamp, to emit a wave length of 185nm, i.e. irradiation H [J/m²], which is at 1,200 J/m² and higher (e.g. up to 4,000 J/m² in microelectronics) for TOC degradation in ultrapure water systems.