UV light is split into four main categories, UVA, UVB, UVC and Vacuum UV. 200 to 280 nanometers is the most effective range for pathogen destruction, and is known as the germicidal spectrum, 254 nanometers being the most effective value.
UVC light has the ability to cause permanent damage to a wide range of nuisance
micro-organisms by breaking their cell walls and disrupting their DNA.
Advantages:
· Micro-organisms are inactivated in seconds
· No chemicals
· No hazardous by-products
· Inactivates bacteria, virus and cysts
Disadvantages:
· UV sterilisers must be preceded by filtration down to 5 microns
· UV is reliant on the water being clear enough for the transmission of UV light
· UV provides no residual disinfection to prevent recontamination downstream of UV
For these reasons, UV is a common technology for treatment of clean potable water close to the point of use. For water distribution networks alternative or additional treatment is recommended.
Unit design, lamp efficiency, UV intensity and flow rate all affect the efficiency of a UV.
The amount of UV energy that water is exposed to is called the dosage rate, and is typically quoted in mj/cm2. The dosage rate varies greatly between suppliers. When comparing UV units, make sure you are comparing flow rates at the same dosage rate.
See also: UV Disinfection
For wastewater, special designs are required. Please enquire.