UV light output at 254 nanometres is known as UVC light (germicidal region). UVC light has the ability to inactivate all known microorganisms, bacteria, pathogens, virus and moulds, including chemically resistant organisms, such as Cryptosporidium and Giardia. UV dose is measured in mJ/cm2. Systems are typically sized in two ways: -
Validated RED Dose. The term RED – Reduction Equivalent Dose is used for validated UV systems that have undergone independent, 3rd party bioassay testing. The testing uses live surrogate microorganisms e.g. MS2 and T1 to physically test and ascertain ‘real world’ reactor performance. Validated RED doses take into account UV chamber design, hydraulic flow efficiencies, lamp positioning and intensity zones to guarantee the performance of a UV system at achieving bacterial log reductions of microorganisms e.g. a 40 RED will achieve 99.99% reduction. Safety factors such as lamp aging and quartz fouling factors are also included in the UV dose equation to provide a conservative and guaranteed performance.
Sizing a UV system is based around water quality. For sizing UV disinfection systems, water quality is measured in UVT (Ultraviolet Transmittance). This measures the clarity of the water to ultraviolet light, relative to that of distilled water (taken to be 100%). Specifically, this property is measured in a quartz cuvette at a fixed UV wavelength of 254 nm. If the water is of high quality, e.g. borehole water, the UVT will be high - around 95% UVT. If the water is low quality, e.g. river water, the UVT will be low - around 80% UVT. It is important to note that a fall in just a few % UVT can double the amount of UV intensity required to provide disinfection.
| Typical Application | Typical UVT % | Normal Required Dose |
|---|---|---|
| Drinking Water | 90% - 95% | 25 mJ/cm2 RED - 40 mJ/cm2 RED |
| Wastewater | 50% - 80% | 30 mJ/cm2 Wall Dose |
| Swimming Pools | 94% | 60 mJ/cm2 Average |
| Aquaculture | 85% - 90% | 320 mJ/cm2 Average |
| Rain Water Harvesting - Irrigation | 80% - 85% | 150 mJ/cm2 Wall Dose |
| Rain Water Harvesting - Process | 80% - 85% | 30 mJ/cm2 Wall Dose |
| Process Water - Towns Mains | 90% | 30 mJ/cm2 |
| Make-up Water - Towns Mains | 90% | 30 mJ/cm2 |
| Cooling Loops | 70% - 90% | 30 mJ/cm2 |
The use of UV light has now become standard practice in a vast range of industries, including municipal drinking water and wastewater treatment, Industrial process and manufacturing, offshore and marine and aquatics. Ultraviolet disinfection systems are used to ensure water is free from harmful organisms and is a proven, regulated and environmentally friendly technology.
In order to provide the best Ultraviolet system to suit your needs, the following variables are required to accurately size a UV system for a specific application. The following information is helpful but not essential to providing a quotation:
