UVA and UVT are essentially just different representations of the same physical phenomenon. They can be related by a simple mathematical expression which indicates an inverse logarithmic relationship between UVA and UVT.
UVA = 2 – log10 UVT
Since UVT and UVA are related mathematically, no actual information is lost in choosing one parameter over the other. UVT is a measure of how much UV light is able to penetrate through a water sample. The less UV light that is transmitted through the water, the lower the UVT. UVA is a measure of the absorbance of UV light by matter in the water. The less UV light transmitted through the water, the higher the UVA.
UVA254 FOR ORGANICS APPLICATIONS
UV254 is directly proportional to the concentration of organic matter in water, therefore UV254 is generally the measurement of choice for most applications. For drinking water treatment, many source waters contain natural organic matter (NOM) that must be removed. UV254 is a simple and effective monitoring tool that helps treatment plant operators control and monitor processes that target organics removal such as coagulation or granular activated carbon (GAC). UV254 is also biased toward the reactive fraction of NOM that tend to form higher disinfection byproduct (DBP) levels, therefore UV254 is also a good indicator to monitor DBP formation potential throughout the plant.
UVT FOR UV DISINFECTION APPLICATIONS
UVT is an important measurement for the UV disinfection process. UV disinfection is a treatment process where UV light is used to inactivate pathogenic microorganisms in water or wastewater. Understanding water quality conditions and the capacity of UV light able to penetrate the water via UVT enables the system to determine the UV dose or lamp output settings require for proper disinfection of the water. UVT is also useful prior to the installation of a UV disinfection system to determine the expected UVT water quality range for design purposes.