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Ultraviolet Sterilizers: Use in Filtration Systems

Bob Fenner

UVs can help prevent the spread of disease & more

Ultraviolet (U.V.) radiation is sometimes employed in water purification systems for tropical freshwater, marine, cool water and pond systems. U.V. sterilization can be very effective in reducing free-floating algae, bacteria and other microscopic planktonic organisms.

U.V. and near U.V. radiation, 295 to 400 nm (nanometers) has also been documented to aid in oxidation of organics, phosphate and nitrogenous compounds through the adjunctive production of ozone (O3).

Though the disease reducing benefits above are considerable in producing and maintaining a favorable environment, U.V. sterilization should not be relied on as the principal part of a filtration system. U.V. purification is a very useful addition to an otherwise appropriate filtration system.

This article describes the pros and cons of U.V. use and appropriate application in cold water and tropical recirculated (closed) aquatic systems.

Cons:

U.V. light is indiscriminate in the destruction of free-floating micro-organisms. It kills "good guys" as well as bad. These beneficial microbes are absolutely necessary in almost all captive environments. For this reason: 1) Initial, break-in periods of new aquatic set-ups are run without the U.V being turned on. 2) It is suggested that U.V.s be left off in conjunction with some therapeutic treatments and used with others.

Organisms maintained in a "well-filtered", strongly U.V. sterilized system seem to develop a type of acquired immune deficiency syndrome. Like the boy-in-a-bubble, organisms kept in an almost sterile environment seem to lose their ability to ward off infectious diseases. Now, let me explain the qualifiers placed upon the terms above. A) There are no captive systems that result in 100% effective kill of all micro-organisms. B) This loss of apparent immunity occurs over long periods of time in a highly variable, non-selective manner. C) This "syndrome has, to my knowledge, never been scientifically documented; therefore my use of the word seems from my personal and second-hand experiences.

Application:

U.V. purification is widely used in many industries; medical, recreational swimming, alcoholic beverages and drinking water among others.

U.V. light is a natural part of electro-magnetic-radiation (EMR) produced by the sun. U.V. lamps generate more of these frequencies of light at a low cost.

There are sizes, fittings and models of U.V.s for virtually any aquatic application; aquaria, pools, ponds and recirculating multiple tank systems.

The water going through the U.V. sterilizer should first be run through biological filtration and mechanically filtered to remove particulates. Allowing air bubbles or any solid matter to pass through the contact chamber is contra-indicated. For this reason, using an air-lift system as a means of moving water through the U.V. is a bad idea. It is suggested that if a heat-exchanger and/or separate chemical filtration is utilized that these come before the U.V.. In other words, the U.V. system should be the last part of the filtration system to have water passed through before returning to the live-holding systems.

The reasons for this are several and mostly obvious. The most important are:

1) To remove as much "other stuff" from the water so that the U.V> radiation will operate with highest efficiency.

2) Beneficial microbes will be preserved and their activity promoted.

An Idealized Filtration System

Flow Rates:

Dwell time, the amount of time a given quantity of water is exposed to a given concentration of radiation may be calculated at about twenty gallons per hour flow per watt U.V.. This value or more watts per unit unit is adequate for providing a good kill rate per pass and will substantially reduce planktonic micro-organisms and organics concentrations.

The beneficial effects of U.V. are enhanced by utilizing the filter system order described above and by arranging for as complete a circulation pattern as possible in your live-holding system.

More vigorous flows are not necessarily to be avoided, but reducing dwell time will result in loss of efficiency per pass. This might lead to increased spread of infectious disease.

Passing all the water in the system though the filter mechanisms once or more an hour is ideal.

Sleeves:

Most U.V. lamps are engineered to operate at around 72 degrees Fahrenheit. Cooler water systems or systems with debris or pressure that might damage the lamps can be fitted with sleeves of quartz of Teflon.

These jackets require periodic inspection and cleaning as for the lamps in tropical systems that come in direct contact with the water.

Plumbing By-Pass:

To facilitate cleaning and lamp replacement, the following layout is offered:

Valves A and B can be closed after opening C, allowing continuous operation of the system during U.V. shutdown. Multiple U.V. systems can be cut in parallel to aid in cleaning one at a time.

Maintenance:

Regular, routine up-keep is necessary to assure peak performance.

Sleeves &/or bulbs should be removed from their contact chambers and cleaned once a month or so. Generally, this can be accomplished by simply wiping with a clean, dry cloth or towel. If necessary, slime may be removed by wiping with rubbing alcohol.

To Build or Buy a U.V.?

Depending on the size and complexity of the system in question, an adequate U.V. might cost as little as $100.00 to buy and $70.00 to build, with the ratio of cost to savings improving with the size of the system. This guesstimate, of course, figures no charge for your tools and your time to search for, collect and assemble the necessary components.

To Build: A simple do-it-yourself model is described below; assembled with easy to find parts and solvent.

Parts:

1+ fluorescent fixture(s); connectors, ballast, switch, cord, wire.

1+ germicidal (U.V.) lamp; from medical, pet fish business.

Some plastic (PVC, ABS) pipe of adequate diameter to allow insertion of lamp, possibly sleeve and permit water flow.

Some fittings; tees, reducers, barbs if necessary.

2+ compression fittings for water-tight sealing of lamp and/or sleeve. Possibly quartz or Teflon tubing for sleeve(s).

A pumping source for pushing/pulling water through the U.V..

Buying a U.V.: Features to look for:

1) Remoteable ballast; to position it in a heat and water-damage free pace.

2) Indicator light; to check for "on" operation.

3) Automatic on feature; to turn the U.V. back on in the event of a temporary power loss.

4) Couplings that are easily fitted to your system.

5) Sleeving at little or no additional cost.

6) Guarantees/warrantees.

7) All non-corrosive, water-contact surfaces.

8) Ask other user's regarding their success/failure, in particular with leakage and ease of use with given brand names and models.

References:

Drew, C. 1970. How To Build an Ultra-Violet Germicidal Filter. Modern Aquarium, December 1970.

Fujita, Grant 1987. Nishikigoi Book. Electrical Purification, p.107

Kennedy, Ron & Rosemay, 1986. Electronic U.V. Filter. In The Associated Koi Club's of America's, KOI BOOK, p. 85 & 86

Webb, R.B. & Brown, M.S., 1982. Genetic Damage in Escherichia coli K12 AB2480 by Broad Spectrum Near-Ultraviolet Radiation. Science, Vol 215, 19 Feb. 1982, AAAS

Thanks to John Epps @ Aquanetics, San Diego for use of his companies literature and illustrations.

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