Monday, June 11, 2012

How UV Works

UV systems expose water to the light from a special lamp. The light is at a specific wavelength, capable of killing common bacteria. The percentage of organisms killed depends on the intensity of the UV light, the contact time that the water has with the light, and the amount of suspended solid particles in the water. The system adds nothing to the water, produces no tastes or odors, and typically requires only a few seconds of exposure to be effective. Treatment of the water occurs as the water passes into the light. The light penetration into water is shallow, usually only 2 to 3 inches.
Scientifically ExplainedUltraviolet light kills microorganisms by damaging the DNA. UV radiation disrupts the chemical bonds that hold the atoms of DNA together in the microorganism. If the damage is severe enough, the bacteria cannot repair the damage and will die. Longer exposure to UV light is necessary to ensure complete kill-off of all microorganisms. Unlike chemical treatments, UV-treated water does not resist re-contamination.  

Importance of Pre-Filtration - 
As always - Test your water source! You must know what to treat in order to treat properly. Suspended solid particles in the water can shield organisms from the light. The untreated water entering the unit must be completely clear and free from any sediment or turbidity to allow all of the bacteria to be contacted by the light. The use of a Chemsorb backwash filter will remove any sediment down to 5 microns.  

In addition, inorganic constituents such as iron should be less than 0.3 ppm, a Nelsen AIO Air Injection Oxidizing Filter System will remove up to 8 ppm of iron. Hardness should be less than 120 ppm (7 grains per gallon) for the UV unit to effectively treat the water. Water with a high hardness (calcium and magnesium) may also coat the sleeve with scale (a whitish deposit of hardness), which may require routine cleaning or addition of a water softener. UV devices are often combined with other technologies such as sediment filters, iron filters, ion exchange units, and reverse osmosis systems to remove particles prior to UV disinfection. UV is often the last device in the treatment series of devices), following reverse osmosis, water softening, and filtration. The UV unit can either be a point-of-entry system, treating all the water entering the house, or a point-of-use device, treating water from a single tap as a final disinfection method.
UV Transmittance:  Perhaps the most overlooked, yet most critical UV performance factor when assessing an application's UV requirement/demand, is the water's "UV Transmittance" which is expressed in percent (0-100%). %UVT is the measured value between a known UV light source (@ 254 nm) and what is measured by a calibrated detector through a 1 cm thick sample of the water to be treated. The measured value (%UVT) is expressed as the total amount of UV light energy available to treat the water. The higher the % value the greater the UV dose will be. UV light that is absorbed by substances in the water is unavailable to inactivate microorganisms. When more UV light is absorbed (i.e. low %UVT), greater UV capacity will be required to compensate for the loss due to absorption. Specifying UV equipment properly can not legitimately take place without first identifying the %UVT.

The UV unit should be located as close as possible to the point of use because any part of the plumbing system could be contaminated with bacteria. Before using a UV system for the first time, disinfect the entire plumbing system with chlorine.
Regardless of the quality of the equipment purchased, it will not perform satisfactorily unless maintained. 
  • Sleeve Cleaning - Minerals in the water slowly form a coating on the sleeve. This coating must be removed because it reduces the amount of UV light reaching the water, thereby reducing purification performance. 
  • Lamp Replacement - The amount of UV light created by the lamp decreases over time, requiring that the lamp be replaced every 12 months.     
The treated water should be tested for coliform bacteria on a monthly basis for at least the first six months of the device's use. If bacteria are present in the treated water, the lamp intensity should be checked and the entire plumbing system should be shock chlorinated.
For additional help and information on UV pre-treatment and UV disinfection, give your sales person a call!

No comments:

Post a Comment