Importance of measuring UV transmittance (UVT) for UV disinfection


Courtesy of Real Tech Inc.

UV disinfection systems disinfect water using UV light at the 254 nm wavelength. UV light at this wavelength actually destroys the DNA of microbiological material in the water which prevents dangerous viruses such as cryptosporidium and e-coli from reproducing and causing harm.

UV Disinfection Dose and UV Transmittance (UVT)
The effectiveness of a UV disinfection system is determined by the UV dose that the UV disinfection system is able to deliver to the water. The UV dose is dependent primarily on the combined effects of the UV light intensity, the exposure time of the system and the UV transmittance (UVT) of the water.

The intensity of the UV light source depends on the size and type of UV lamp used and the power supplied to the lamp. The exposure time of the system depends on the flow rate of the system. The flow rate is often regulated between multiple UV disinfection systems operating in parallel, and there is often a manufacturer specified maximum flow rate for the system. The UVT of the water being disinfected can significantly affect the effective UV dose delivered to the water by the UV disinfection system and it varies over time and from site to site.

UVT is related to the quantity of organics, colloidal solids and other material in the water which absorb  and scatter the UV light as it passes through the water. In a UV disinfection system, if the UVT of the water is too low, then the UV light is not able to penetrate the water as efficiently, thereby reducing the effective UV dose delivered by the system. This is why manufacturers usually state a minimum UVT for a UV disinfection system, below which the system will not function properly.

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