UV Pre-treatment

In order for any UV disinfection system to be effective, the quality of the incoming water needs to be to a certain standard.

When a UV disinfection system is specified for each unique application, the following project characteristics need to be taken into consideration.

  • UV dose required
  • UV transmission of water or liquid (UVT)
  • Peak flow

Having the above information allows UV-Guard to select the UV disinfection system best suited to a certain application. If we know what UV dose is required, we can establish which system will achieve this at the desired peak flow rate and UVT value.

UVT is a measure of how well germicidal UV-C light will penetrate a given water or liquid. UVT is an extremely powerful parameter as it encompasses several water quality characteristics such Turbidity, Total Suspended Solids (TSS), Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). All of which may contribute to UV light being absorbed or scattered. It must be noted that UVT does not exactly correlate to these characteristics as there are other factors involved.

UVT alone cannot be relied on to ensure effective UV water treatment. TSS in excess of 10 mg/L, or Turbidity >5 NTU may lead to pathogens hiding behind the suspended particles in the water, preventing them from receiving the required UV light exposure. This is also known as ‘shielding’.

Iron, Manganese and water Hardness are also important as high levels can result in a UV disinfection system’s lamp protective quartz (quartz sleeve, thimble or tube) becoming fouled, in addition to absorption and scattering. This results in UV light from the lamp being unable to pass the fouled quartz, consequently UV disinfection of the water is significantly reduced or non-existent. High levels of hardness in the water can be overcome by using quartz tube wiping systems. However, where hardness levels are in excess of 120ppm, and no wiping system is supplied, additional treatment methods are recommended.

UV-Guard will measure or assume a UVT value for your application, and will factor this into our system recommendation. For other pre-treatment conditions, refer to the below treatment recommendation guide.

 

Water Condition Max Value (mg/L, ppm) Recommendation
Total Suspended Solids (TSS) 10 5-10 micron pre-filtration
Hardness 120 Water softener, auto wiping system or regular quartz cleaning
Manganese 0.05
Iron 0.3

 

Please note that the above table reflects values for effective UV water treatment. It does not take into consideration regulatory or other process water quality requirements.