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The
EA Approach to Successful UV Sterilization |
Successful ultraviolet disinfection lies in the
details; Science combined with Established Engineering
Guidelines. Ultraviolet sterilization is unmatched
in its efficiency, simplicity and dependability
when applied as a microorganism disinfectant. Understanding
the science, the effect that UV-C light has over
a living microorganism is only the beginning. Learning
and following the established engineering guidelines
provides control and an objective…to achieve
successful germicidal disinfection. |
The
Objective
To render unwanted or harmful waterborne microorganisms
incapable of reproducing using ultraviolet light
(specifically the spectral area of UV-C). Ultraviolet
light is a spectrum of light
just below the range visible to the human eye (see
“Light Spectrum” Chart). UV light is
divided into four distinct spectral areas and they
are Vacuum UV (100 – 200 nm), UV-C (200 –
280 nm), UV-B (280 – 315 nm) and UV-A (315
– 400 nm). These spectral areas are very specific.
UV-C (200 – 280 nm) is the most lethal range
as a germicidal disinfectant (capable of altering
a living microorganism’s DNA, keeping it from
reproducing). UV-C, with 264 nanometers being the
peak germicidal wavelength, is known as the germicidal
spectrum. |
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UV
Benefits & Limitations
It is critical to first identify the microorganism.
Each type of microorganism requires a specific
UV-C radiation exposure rate to successfully complete
the disinfection process. The targeted microorganism
must be directly exposed to the UV-C radiation
long enough for the radiation to penetrate the
microorganism's cell wall. However, it takes only
seconds for UV-C light rays to inactivate waterborne
microorganisms by breaking through the microorganism's
cell wall and disrupting their DNA. This often
totally destroys the organism, or at the very
least will impair its ability to reproduce.
Benefits:
Germicidal disinfection (directly exposing living
microorganisms to UV-C light) is unmatched by
ozone or chlorine for simplicity and safety. Chlorine/bromine
leaves a residual in the water that can irritate
the skin and eye tissue of mammals, reptiles and
birds. Ozone, if not measured and controlled properly,
is capable of causing severe tissue damage, even
death with fish and invertebrates. In contrast,
UV treatment only takes place inside the UV exposure
chamber and leaves no residual downstream, and
therefore is harmless to the animals in the pool.
UV sterilization is a proven solution to waterborne
pathogens commonly associated with aquatic re-circulating
systems.
Limitations: UV Sterilization
treatment takes place inside the UV exposure housing.
Exposure time between the waterborne microorganism
and the UV-C light is critical in achieving successful
UV disinfection. The condition of the application’s
water will determine how well the UV-C light penetrates
through it (UV transmittance). UV-C is absorbed
by the targeted microorganism or by other organic
waterborne particles. It is for this reason that
UV equipment should be positioned after the mechanical
filter. |
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Target
Microorganism
The
size, biological make up and life cycle of a microorganism
all play a critical part in successful germicidal
disinfection. By way of comparison, there are
approximately 65,000 known protozoa and only 4,500
bacteria of which all require their own specific
UV-C dose. A microorganism’s size plays
a significant roll in the UV dose required to
irradiate it. Protozoa is often many times larger
than bacteria and therefore requires a much higher
UV dose
(See Charts 1 & 2 on below).
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Life
cycle is another critical factor that requires consideration
when applying UV sterilization,
the marine parasite cryptocaryon (salt water white spot)
is an excellent example of how complex a microorganism’s
life cycle can be. Cryptocaryon has a four part life
cycle. A warm water parasite, cryptocaryon can be lethal
to many species of marine fish. Diagram A is very descriptive,
showing the many characteristics of this microorganism.
Regarding treatment;
the aquaculture community has waged battles against
cryptocaryon and have lost, specifically at the encysted
(Tomont) stage simply due to its evasiveness by attaching
itself to substrate. Disease outbreaks still occur even
with filtering the water column using extremely fast
flow rates.
Prerequisites
of achieving successful UV disinfection: Identify the
“Target Microorganism”,
consider its physical and life cycle characteristics,
determine its required UV dose, determine
the condition of the water to be treated (water temperature
& UV Transmissibility). Contact a
reputable UV manufacturer, ask questions regarding their
equipment’s capacity, share your
needs and then select the UV sterilizer model that best
suits your application requirements.
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