What is UV disinfection?
These systems work by transferring electromagnetic energy from a mercury lamp to an organism’s DNA & RNA structure by penetrating the cell wall, causing cell death and destroying the ability to reproduce. Since most microorganisms cause disease by multiplying rapidly inside the host, UV light treatment is an effective method for water disinfection. UV light simply means part of electromagnetic spectrum with wavelengths between 100 and 400 nanometers, although wavelength for disinfection is in the region of 200nm to 300nm with optimum energy intensity at 254nm.
Factors affecting efficiency of UV disinfection systems.
There are several factors affecting UV systems
- Strength of UV light. (This in turn depends on design of UV equipment, lamp age, sleeve fouling)
- Duration of treatment.
- Quality of feed water (This in turn depends on Turbidity, size of particles, humic materials, iron)
- Concentration and characteristics of microorganisms.
Effect of turbidity on UV disinfection
Turbidity can affect UV disinfection system in two ways
1- Higher turbidity levels can influence the UV dose required for disinfection and a higher dose might be required.
2- Shadowing, where the microorganisms can hide behind dirt particles and leave the UV system unaffected.
UV dose is a product of UV intensity and exposure time and optimal UV dose varies for different microorganisms although relatively low dose is required for most viruses and bacteria. In order for the UV system to work efficiently the organism needs to be directly exposed to UV light for a reasonable duration.
Turbidity or high dirt levels in water can hinder the path of light and produce what is called a shadowing affect where microorganisms can escape untreated, shielded by the dirt particles.
UV prefiltration using cartridge filtration
Since an increase in the size of particles will either directly increase the UV dose requirement for disinfection or cause shadowing, cartridge filtration is an effective pre treatment step to ensure that turbidity drops to required levels for efficient working of UV systems.
Filter cartridges from Siga filtration can provide excellent removal of sediment and debris and we recommend that a two stage filtration system is employed for high or unpredictable turbidity levels due to seasonal changes, for example surface water sources, please contact us directly for more information on this application.
acuraPromelt is an excellent sediment removal cartridge which will remove up to 99.9% of all particles at the rated pore size. A 25 micron acuraPromelt filter cartridge followed by a 5 micron filter cartridge will ensure that dirt particles are reduced to optimum levels. It should be noted that UV treatment has no residual effect and routine sample testing might be required.
Ground water on the other hand is of generally good quality and a 5 micron filter cartridge should provide sufficient reduction in turbidity.
Additional treatment stages for the removal of pesticides, chlorinated solvents and Iron/Manganese depending on water quality and source of water might be required which are outside the scope of this article.
A range of filter housings in plastic and Stainless Steel material is available for pre treatment of UV disinfection systems using cartridge filtration, please contact us for more information.