Bulletin 71

Bulletin 71

UV Applications and Drinking Water

Germicidal ultraviolet energy is primarily intended for the destruction of bacteria and other microorganisms in air, liquids or on surfaces.  The most effective germicidal wavelength is at 253.7 nm for destroying microorganisms, mold spores, protozoa, viruses and yeast.

 Ultraviolet germicidal energy has been used for years to destroy bacteria in water.  The intensity of ultraviolet is expressed in microwatt seconds per square centimeter and is the product of the lamp in watts, exposure time and the volume of water being treated.

 As we all know, fresh water is a precious resource and may not always be safe to drink.  Fresh water may be contaminated by sewage, septic tanks, industrial and other wastes.  It must be emphasized that the clearest looking, best tasting water can be unsafe for human consumption and may cause infectious hepatitis, dysentery, infectious jaundice, typhoid fever and a host of other diseases.  Constant vigilance is necessary to keep drinking water safe.

 There are some items that need to be understood for proper consideration of a drinking water system.  These are discussed as follows:

EXPOSURE

 About 95% of the ultraviolet radiation from the UV lamp is emitted at the 253.7 nanometer wavelength, which is the region in the spectrum nearest the peak of germicidal effectiveness.  The power of a UV lamp is usually described in two ways: that of intensity and that of output.

 1.      Intensity is the density, or strength, of the ultraviolet light rays at a point a specific distance from the lamp.  Intensity is usually expressed in microwatts per square centimeter, which is a product of energy, time and area.

2.      Output is the volume, or total amount, of ultraviolet light rays being emitted by the lamp in all directions.  Output is usually expressed in watts of 253.7 radiation.

 High intensities of UV for a short period of time, or low intensities for a long period of time, are fundamentally equal in lethal action on microorganisms.  All Full-Pure Liquid Purifiers use high intensity lamps to accomplish their lethal action quickly and efficiently.

UV TRANSMISSION CHARACTERISTICS

 Successful treatment of water and other transparent liquids with UV depends on a number of factors, such as clarity, absorption of ultraviolet, amount of suspended matter, flow rates, temperature and, of course, the type or kind of microbial contamination.

 The transmission characteristics of UV on liquids is dependent on the depth of the liquid.  It's interesting to note that the ultraviolet intensity through liquids decreases logarithmically with the distance from the lamp.  In addition, the absorption coefficient further relates itself to the presence of minute traces of iron compounds and organic matter.

 The physical requirements of less than 10 NTU of turbidity, 15 TCU of color and 0.2 ppm of iron should be met prior to installing a Full-Pure UV Liquid Purifier.  In addition, prefiltering of suspended matter to at least 5 microns in size is recommended for residential water supplies.

 Table II in the following section reflects the percent of transmission of ultraviolet on water of various absorption coefficients.  As a matter of interest, for average tap water the absorption coefficient is 0.008.  Cloudy water can be 0.50 or less.  Obviously, the transmission capability of the liquid to be purified must be known for proper sizing.

 Most significant, waterborne miroorganisms are destroyed by dosages of less than 10,000 micro-watt seconds/cm² (mw/sec/cm²), however . . .

 The U.S. Public Health Service has published criteria stating that acceptability of an ultraviolet disinfecting unit is contingent on imparting a minimum dosage of 16,000 mw/sec/cm².

         ALL FULLER UV UNITS NEARLY DOUBLE THIS MINIMUM DOSAGE.

 When used as directed, Fuller UV Liquid Purifiers will provide a minimum dosage of 30,000 mw/sec/cm^2.  The Fuller product line is manufactured in various sizes to accommodate different flow rates for a "single pass through" or a recirculation system, as in industrial storage tanks, hot tubs, spas and swimming pools.

 In order for the ultraviolet rays to kill bacteria, they must directly strike the microorganism, and each microorganism must absorb a specific amount of energy to be destroyed.  The dosage necessary to inactivate a microorganism is a product of time and intensity.  The destruction is accomplished quickly and effectively in all Full-Pure Liquid Purifiers.

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