Ultra-violet (UV) treatment is the disinfection process of passing water by a special light source. Immersed in the water in a protective transparent sleeve, the special light source emits UV waves that can inactivate harmful microorganisms. This method of treatment is growing in popularity because it does not necessarily require the addition of chemicals.

UV systems alone are neither intended to treat water that is visually contaminated nor intended to convert wastewater to safe, microbiologically potable water.

The ultra-violet rays, similar to the sun’s UV but stronger, alter the nucleic acid (DNA) of viruses, bacteria, molds or parasites, so that they cannot reproduce and are considered inactivated. UV treatment does not alter the water chemically as nothing is added except energy. It should be noted that inactivated microorganisms are not removed from the water. UV treatment does not remove dirt and particles, metals such as lead or iron, or hard minerals such as calcium. Other devices are required to remove particles, metals and minerals,

http://www.cmhc-schl.gc.ca/en/co/maho/wawa/wawa_002.cfm

The UV Effluent System is based on a flow through open channel arrangement, which is incorporated in either stainless steel channels supplied by Willand, or concrete channels supplied by other parties.

The effluent system uses medium pressure UV mercury discharge lamps, which enables variable lamp power output to be included, extending lamp life and increasing energy efficiency by means of UV dose control

Each system features banks of medium pressure UV lamps, divided into independently removable lamp support racks that can be removed without necessitating system shut down.

http://www.lenntech.com/systems/uv/effluent/uv-effluent.htm