Ultraviolet (UV) Sterilization – Technical Information

To Achieve Successful Germicidal Disinfection
in a “Continuous-flow” Aquatic Life Support System

Achieving successful “germicidal disinfection” can only be accomplished by directly exposing the living target microorganism to the specific spectral area of UV-C for a predetermined amount of time UV dose). Ultraviolet light consists of four specific spectral areas: Vacuum UV, UV-C, UV-B and UV-A (see the Light Spectrum Chart below). However, the established “Germicidal Action Spectrum” lies between 240-280 nm. The peak wavelength of 264 nm is the most lethal to a living organism’s DNA, and prevents it from reproducing.

Familiarizing ourselves with the microorganisms we are targeting for disinfection will help us understand the complexities of “germicidal disinfection”. Microorganisms, like any other living creature, are totally unique unto themselves. An individual microorganism’s uniqueness is determined by its size, life cycle, and physical makeup, which explains why each requires a specific and different UV dose.

The diagram below demonstrates the complex life cycle of the warm water parasite “Cryptocaryon” (also known as “salt water white spot”).

This diagram illustrates the four stages of this lethal protozoa’s life. The “theront stage,” identifiable by the organism’s size (25-60 µm) and free-swimming characteristic, is the stage most conducive to achieving successful UV treatment. The Microorganism Chart, shown below, lists a wide variety of bacteria, protozoa, and viruses commonly found in continuous-flow aquatic life support systems. Each microorganism listed is accompanied by its established UV dose.

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, all of which require their own specific UV-C dose. A microorganism’s size plays a significant roll in the UV dose required to irradiate it. Protozoa are often many times larger than bacteria and therefore require a much higher UV dose.

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 following charts demonstrate how a lower %UVT parallels a diminished UV dose when operating our model CLP6780-A8 (3-260 Watt Amalgam UV Lamps) at a flow rate of 150 GPM. Notice the distinct drop in UV dose when considering a slightly lower %UVT.

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UV Benefits:

UV treatment takes place only inside the UV exposure chamber and leaves no residue downstream, and is therefore harmless to the animals in the pool. UV sterilization is a proven solution to harmful waterborne pathogens commonly associated with aquatic recirculating systems. (In contrast, chlorine/bromine leaves a residue in the water that can irritate the skin and eye tissue of mammals, reptiles, and birds. Even Ozone is capable of causing severe tissue damage and possibly death in fish and invertebrates, if it is not measured and controlled properly.)

UV Limitations:

Exposure time between the waterborne microorganism and the UV-C light is critical to achieving successful UV disinfection. The condition of the application’s water (%UVT) will determine how well the UV-C light penetrates through it. 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 any mechanical filtration.

The pivotal component of any UV sterilizer is its UV lamp. Critical performance characteristics include: output performance, arc length, and useful lamp life. The power source (ballast) operates the lamp and must match its specific operating parameters (operating current and input watts). The UV reactor is essentially the space that houses the UV lamp field; the dimensions of which are based upon the lamp’s operating specifications.

Our design incorporates “Third-Party Validated” engineering criteria into a uniform, industrial grade housing for years of dependable and efficient operation. Optimal UV Sterilizer Design Criteria:

• Optimal UV Lamp Performance, plus
• Ballast(s) that are specifically matched to the UV lamp’s operating requirements, plus
• UV Lamp Array that utilizes the lamp’s output to its maximum potential.

UV equipment design is the result of a calculated balance between equipment size, cost, and performance. Many of our competitors realize the consumer’s sensitivity to the size and cost of this equipment and try to capitalize on it by over-rating their UVs. Some use a “compact” approach while grossly exaggerating the equipment's true capacity. Compact UVs are sold on both the hobbyist and commercial levels to the detriment of the consumers since they are paying for UV protection they never receive. This problem is a by-product of unregulated product and marketing claims. Unfortunately, consumers bear the burden.

WMT provides UV lamp performance data sheets which substantiate our recommendations. These include:

1. Flow rate calculations based upon the Bolton Photosciences, Inc. UV Calc Modeling Program (same program that is recognized by the EPA),
2. Lamp dimensions
3. UV-C output
4. End-of-useful-lamp life

NOTE: Beware of companies that “cannot divulge” this critical information. It is not proprietary.

• Medium-Pressure Lamps produce 10 times more HEAT (1,600°F) than Low-Pressure Lamps (180°F max.).
• Medium-Pressure Lamps produce the majority of their UV Output in the UV-A and UV-B spectral areas (well outside the specific UV-C “Germicidal Spectrum”).
• Low-Pressure UV lamps produce 33-40% of their UV Output in the UV-C action spectrum, which is unmatched by Medium-Pressure Lamps (maximum 7-13%).
• Our high quality T5 Standard-Output, T5 HO and Amalgam UV lamps deliver an unmatched 9,000 hours of continual operation while retaining >80% efficiency, as opposed to Medium-Pressure Lamps’ typical life of between 700 to 4,000 hours while retaining as little as 60% efficiency.
• Low-Pressure Lamps’ “cost of ownership” is far LESS EXPENSIVE than Medium-Pressure Lamps, due to Medium-Pressure Lamps' short lamp life. Short lamp life requires that they be replaced much more frequently.
• In order to obtain the maximum life from a Medium-Pressure Lamp the lamp’s operating temperature must constantly be monitored and controlled. This increased level of control adds a higher level of sophistication & expense to the UV system.

Low-Pressure UV lamps are made of either soft-glass or hard-quartz glass. The difference between the two types of glass is that hard quartz glass is more resistant to solarization than inferior soft glass. Solarization is a by-product of UV lamp operation. During lamp operation, the mercury that is used to create the UV energy reacts with the applied electrical arc which, over time, forms a very gradual plating of mercury oxide onto the inside surface of the lamp’s glass envelope. This mercury oxide by-product reaction absorbs UV light, therefore reducing the UV-C light transmission through the lamp’s glass envelope.

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All UV lamps convert a percentage of their “Input Watts” (the electrical power that drives them) into UV-C Output “Germicidal Watts”. UV-C light is the spectral (Germicidal Action Spectrum/240-280 nm) wavelength used to render “living microorganisms” incapable of reproducing. The comparison chart below demonstrates a significant contrast in UV-C output between Low-Pressure “Soft Glass” and “Hard Quartz Glass” UV Lamps. “Hard Quartz Glass” UV Lamps are preferred due to their exceptional input Watt to UV-C Output Watt conversion performance. At the beginning of this evaluation Medium-Pressure lamps were eliminated due to their poor UV-C output (7%-13% of initial input watts) but are still shown here for sake of comparison.

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Practically all UV lamps in use today are affected by the temperature of their immediate environment! The temperature at which the lamp operates affects the UV-C output and can decrease it by as much as one percent per 1.5°F of temperature change from the lamp’s nominal operating temperature. Thermally protecting the lamp can be accomplished by using one of the two known methods. The first method is to sheath the lamp inside a transparent hard quartz glass sleeve. The quartz sleeve will isolate/insulate the lamp from the water by creating a protective temperature zone around the lamp. This is the preferred method.

The second method is to flow the water through a transparent quartz glass reactor with the lamp(s) positioned just outside and around the reactor. This method becomes considerably complex due to the sensitive control of air temperature around the lamp(s). In addition, the travel path of light photons is distorted due to the curvature of the quartz reactor. There is no creditable data supporting this method.

The “UV Lamp Operating Temperature Chart” below identifies the optimum lamp operating temperature as well as optimum application water temperature parameters for the various types of Low-Pressure UV Lamps.

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• Note: The Medium-Pressure UV Lamp is not recommended for Aquatic Life Support applications due to its extreme operating temperature which causes a high incidence of quartz sleeve fouling and requires the use of complex sleeve wiper systems.

• Soft Glass, Low-Pressure/Low-Output UV Lamps offer less UV-C Output, a shorter useful lamp life and a narrower Application Water Temperature Tolerance than the hard quartz glass UV Lamp styles, therefore, we focus primarily on the preferred Hard Quartz Glass Low-Pressure UV Lamps.