ABSTRACT
All white light contains ultraviolet (UV) light. The UV light for use in water disinfection in depuration plants is generated by low pressure mercury vapor bulbs, creating short-wave radiation at a wavelength of 254 nm. In a UV treatment system, water is disinfected by exposure to this radiation at a specific dose rate or intensity. The UV light disinfects by damaging the DNA and RNA of pathogenic organisms. In practice, water flows through an irradiation chamber known as a photoreactor. The selection of flow rate for an effective resident time for the area under the bulb is a function of the intensity of the UV tube. Some stainless steel quartz units have been prone to rust, causing iron salts to dissolve into the process water and absorb UV energy. A problem with the quartz units was that incomplete drainage of the reactor tube allowed growth of algae which was subsequently resuspended upon restart.
