Learn about the Importance of water quality when selecting a UV System

The Importance of Water Quality When Selecting a UV System

The nature and quality of the water to be disinfected is critical, not only in selecting an appropriate UV system, but also in deciding if UV disinfection is even possible or suitable at all. Of all water quality parameters, Ultraviolet Transmissivity (UVT) is the most important. This is because the UVT of the water will determine how well the UVC light will penetrate the water in order that the pathogens in the water may be exposed to sufficient UVC light to be inactivated. The UVT of the water is determined by taking a water sample in a quartz cuvette and passing UV light at 254nm through the sample. The percentage of UV light that penetrates this sample is referred to as the sample’s “UVT”. Most typically, the cuvette used has a path length of 10mm, in which case the UVT reading is referred to as being “T10”. The UVT of the sample is critical for a very simple reason; although parameters such as BOD, COD, turbidity and TSS all influence the extent to which UVC light penetrates the water, they are all effectively accounted for by the single UVT reading. Of all other water quality parameters apart from UVT, Total Suspended Solids (TSS) and Total Dissolved Solids (TDS)/Salinity are also important. TSS is important because anything in excess of 20mg/l TSS can result in a phenomenon known as “shielding” whereby the pathogens can be “shielded” from the UVC light by the particles suspended within the water. TDS/Salinity is important because at very high levels, attention must be paid to the materials of construction of the UV system itself so as to avoid excessive corrosion.

Author:

Graham Smith. Fluidquip Australia Pty Ltd.