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 Explained - Ultraviolet
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.
Maintenance
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!
