UV TECHNOLOGY
Over 100 years ago it was discovered that micro-organisms respond to light. Further investigation led to the discovery of Ultraviolet (UV) light.
UV light falls between visible light and X-rays in the electromagnetic spectrum. UV light between 200 and 300 nanometres (nm) is UV-C and has strong germicidal properties. UV disinfection is a physical process that can inactivate micro-organisms (including those that are chlorine-resistant) in water and other liquids by disrupting the DNA of the organism and preventing reproduction and DNA repair. UV disinfection of water dates back to 1910 when the first system was used in Marseille, France.
UV DOSE AND SYSTEM SELECTION
UV Dose
The level of a micro-organism’s inactivation by means of UV-C light depends on the UV dose applied and the micro-organism’s susceptibility to this UV dose. The UV dose varies for different micro-organisms and is calculated from intensity (UV power) and time (flow rate). The UV dose is typically measured in mJ/cm².
UV System Sizing
UV systems are typically sized in two ways:
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By calculation (with or without CFD modelling): This method ensures that all points within the UV chamber receive a minimum UV dose.
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By validation: Validated UV systems have undergone independent 3rd party testing. The term RED (Reduction Equivalent Dose) is used for the UV dose that applies to validated UV systems. Further information is given under UV SYSTEM VALIDATION below.
Transmittance and System Sizing
One of the key design parameters for UV system sizing, is the ultraviolet transmittance (UVT) of the liquid. This measures the ability of UV light to pass through the liquid. The UVT is determined relative to that of distilled water, which has a UVT value of 100%. The UVT is measured in a 1cm quartz cell at a wavelength of 254 nm.
A high UVT allows the UV light to easily penetrate the liquid. A low UVT will require additional power or UV lamps to achieve the same UV dose performance.
UV System Validation
Validation is a method of testing UV equipment to determine how effective and efficient the equipment is in inactivating various organisms at a range of flows and different water qualities. For a system to be validated, it must undergo independent, 3rd party bioassay testing using a recognised test standard. The testing uses live surrogate microorganisms to determine ‘real world’ reactor performance. A validated RED dose takes into account UV chamber design, hydraulic flow efficiencies, lamp positioning and intensity zones to ensure the performance of a UV system. Safety factors such as lamp ageing and quartz fouling factors are taken into account in the UV dose equation. Validation testing for atg UV Technology UV systems is carried out in accordance with the United States Environmental Protection Agencies (US EPA) UVDGM 2006. The EPA method is one of the most modern and rigorous testing regimes in the world.
HOW UV-C LIGHT IS USED IN THE TREATMENT OF WATER AND OTHER LIQUIDS
UV light is a chemical-free and non-intrusive method of inactivating micro-organisms. For industrial product and process water, as well as other liquids, these micro-organisms can be harmful to humans and cause spoilage and a reduction in product shelf life. For municipal drinking water, harmful organisms can also be disinfected.
For practical applications UV-C light is produced by commercially manufactured UV lamps. One or more of these lamps are installed in a UV chamber, which is installed in the fluid distribution network. As a liquid or water is passed through the UV chamber, it is exposed to the UV-C light generated by the UV lamps.
UV disinfection has many beneficial properties and advantages. UV does not affect the taste, pH or colour of the fluid being disinfected. It is often used where conventional chlorine disinfection cannot be applied.
Correctly specified UV systems can also be used to de-chlorinate or de-ozonate process water and to assist in the removal of TOC from ultra-pure water.
