Helios© UV Systems

Transmission of UV-light at 254nm is a widely used method in both clean and wastewater applications (APHA, 2012). Water transparency is commonly used as an indicator of general water quality and is described by UVA, which represents the amount of light absorbed by particles within a sample. The removal of carbon-based compounds (e.g. NVOC, COD and fluorescent organic matter) resulted in visually cleaner water. UVT is used to define water clarity.

Water clarity was determined in terms of UVA and/or UV transmittance (UVT%), measuring directly the absorbance of water samples at 254 nm using a 10 mm quartz cuvette.

UVA = A254nm = -Log(I / I0)                
Equation 1

%UVT = 100 x 10-UVA
Equation 2

Where I = light intensity at the detector (light out) and I0 = intensity of the light incident before the sample (light in).

Sizing UV Systems

Typical UVT values and recommended UV doses for several water treatment applications.

NOTE: The required UV dose for each facility will differentiate depending on the water matrix and the established water treatment technology.

Typical ApplicationTypical UVT %Normal Required Dose
Drinking Water90% – 95%40 mJ/cm²
Waste Water50% – 80%20 – 30 mJ/cm² Average
Swimming Pools95%60 mJ/cm² Average
Aquaculture75% – 95%40 – 320 mJ/cm² Average