This
month we have talked a bit about Ultra Violet as a disinfecting
agent for drinking water. Ultra violet has a number of advantages
over traditional disinfectants such as chlorine or chloramines
however like anything else it must be applied properly. We see a
number of customers who want to treat their water with a UV device
because it is so simple to install, easy to maintain and relatively
cheap to purchase but without doing the proper checks and tests,
you could be buying a lot of problems.
Ultra
violet light or UV, is suitable for residential, commercial and
industrial markets. Surface water from lakes, rivers or shallow
wells is typically exposed to more sources of contamination than
deeper wells. And they are also subject to wider fluctuations in
water quality due to runoff and seasonal effects. These water
sources are also a source of waterborne diseases caused by
pathogenic bacteria and viruses. These microbes can be easily
inactivated by UV.
The
mechanism of UV disinfection is the same for all UV systems.
Microbial inactivation is caused by the damaging effect of UV light
on the microbes DNA. In the case of pathogens, the resulting damage
prevents the microbe from multiplying thus destroying their ability
to infect and cause disease such as cholera, typhus and other
gastro-intestinal diseases commonly associated with contaminated
water sources.
UV
has the ability to inactivate bacteria, viruses and protozoa.
However each type of organism requires a specific "dose" for
inactivation and typically viruses require higher UV doses than
bacteria and protozoa. UV dose is the product of light intensity
and exposure time, the time the water resides in the UV reaction
chamber.
The
UV dose is usually given in units of microWatt seconds per square
centimeter. For most residences a range of 16,000-30,000 mW/cm is
acceptable and will inactivate 99.99% of all bacteria, protozoa and
viruses including cryptosporidium and giardia (Beaver
fever).
Key
factors which impact the performance of a UV system are water
quality, pretreatment and UV design.
UV
is highly effective when the water is low in iron, manganese,
hardness and has a high UV transmittance. UV transmittance is
commonly referred to as UVT and refers to the waters ability to
transmit UV light. Various organic and inorganic compounds that may
or may not be visible can absorb UV and decrease the amount of UV
energy for disinfecting. All water should be tested for UVT before
it should be considered as a disinfection method. Typically most
water with a UVT of 75% or higher is required. Your water treatment
professional can usually perform this test with the proper
analyzer.
A
comprehensive water test is an absolute necessity for sizing a UV
system. As mentioned, water quality is paramount for the successful
operation of a UV system. As elevated levels of minerals such as
iron or hardness can form a film on the UV sleeve reducing the UV
dosage below the "kill zone". Again, your water treatment
professional can test for these parameters and make any
recommendations should pretreatment be needed. In addition, all UV
manufactures require a minimum 5 micron sediment filter before the
UV system and will also recommend a carbon filter to reduce
undesirable tastes, odors and organic compounds.
You
can read more about UV on our website at edspumps.com
Drop into our store for a
free UVT test!