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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.

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.


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).


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.