1. Water Bottling Plants
  2. Make-Up Water for Hospitals
  3. Cooling Tower Recirculation Loops
  4. DI Sterilization Loops for electronics/semiconductors)
  5. Food Processing
  6. Fish Hatcheries
  7. Laboratories
  8. Textiles
  9. Marine & Offshore Platforms
  10. Cosmetics Manufacturing
  11. Pharmaceuticals
  12. Liquid Syrups
  13. Dozens of Other Applications

(typical in-line UV system with intensity monitor and alarm)


(skip the technical discussions - take me directly to the equipment and specification sheets)

For many years chlorination has been the standard method of water disinfection. Recent studies have shown that water chlorination causes several environmental problems. Residuals and byproducts can be toxic to aquatic life in receiving waters. Some by-products of chlorination may be carcinogenic, and may require removal in a drinking water treatment; plant. Also, it has been discovered that chlorination is much less effective in virus destruction than in killing bacteria .

Until the onset of the "energy crisis" of the 1970's, chlorination was the most cost-effective disinfection technique. Because chlorination production is energy intensive and because energy costs have -,increased freight rates, the price of chlorine at the plant site has risen substantially in recent years. This trend is likely to continue. Potential gaseous chlorination safety problems have caused come communities, e.g., New York City and San Francisco, to choose hypochlorite which is much more costly than gaseous chlorine.

The above problems with chlorination have caused consulting engineers, users, and regulatory agencies to-actively pursue alternatives for water disinfection. Ultraviolet light is currently the leading candidate for water disinfection. It has the following inherent advantages over all other disinfection methods:

1. No chemical consumption-eliminates large scale storage, transportation and handling, and potential safety hazards.

2. Low contact time-no contact basin is necessary and space requirements are reduced.

3. No harmful by-products are formed.

4. A minimum of, or no, moving parts - high reliability.

5. Low energy requirements

Ultraviolet disinfection, thus, solves the environmental and safety problems, and is cost-effective as well.

Ultraviolet disinfection of water employs low-pressure mercury lamps. They generate short-wave ultraviolet in the region of 2537 Angstroms which is lethal to microorganisms including bacteria, protozoa, viruses, molds, yeasts, fungi, nemotode eggs, and algae. The mechanism of microorganism destruction is currently believed to be that ultraviolet causes molecular rearrangements in DNA and RHA, which in turn blocks replication.

When micro-organisms are subjected to ultraviolet light, a constant fraction of the number present die in each time increment (4). The fraction of the initial number of micro-organisms present at a given time is called the survival ratio. The fraction killed is one minus the survival ratio. The mathematical expression of these facts is shown below:

Survival Ratio = Nt/No = e-KIt


No = The number initially present

Nt = The number surviving at time

t = The time of exposure

I = the intensity (more correctly, scalar irradiance of ultraviolet light impinging on the microorganisms)

K = A constant which depends upon the type of micro-organisms and wavelength of ultraviolet light.

The above equation indicates that for each given micro-organism and UY wavelength, the fraction killed depends upon the product of UV light intensity and exposure time. This product is known as the "dosage". It is the single most important parameter for rating UV disinfection equipment.

The validity of this mathematical expression has been proven over a thousand fold range in intensity. The expression fails at only low values of intensity, which would not probably be found in a properly designed ultraviolet unit.

UV dosage requirement varies with the type of micro-organism. Dosage requirements for bacteria range from 2,500 to 22,000 microwatt-second/cm2. Yeast dosage requirements range from 6,600 to 17,600 microwatt-second/ cm2. Mold spore, fungi, and algae dosage renuirements range from 11,000 to 330,000 micowatt-second/cm2.

Viruses, with the exception of the tobacco mosaic (not normally found in water) have dosage requirements in the same range as bacteria. Protozoa and nematode egss have extremely high dosage requirements.

There is no universally accepted minimum dosage requirement for ultraviolet disinfection systems. In 1966, the U.S. Public Health Service published a policy statement which contained a drinking water disinfection dosage requirement of 16,000 microwatt-second/cm2 (5). This statement has formed the basis for several standards published throughout the world.

A dosage requirement has not yet been developed for wastewater. However, fecal coliform bacteria are the customary indicator micro-organisms used in judging the efficiency of water disinfection. The destruction dosage for fecal coliform is 6,600 microwatt-second/cm2 .

The basic design problem in any ultraviolet system to efficiently and reliably deliver the required dosage to micro-organisms suspended in the fluid. There are essentially two basic design concepts in current use to accomplish this task. One employs flow over a submerged bank of germicidal lamps with quartz sleeves. Fluid flows through Teflon tubes surrounded by germicidal lamps in the other design concept.

Quartz Tube Systems with Shellside flow

Most substances are not penetrated by short-wave ultraviolet rays. Water is one of the few liquids which allows a significant penetration. Quartz is one of the few solid materials that is virtually transparent to short-wave ultraviolet. It is used in the manufacture of germicidal lamps and as a material of construction in many commercial ultraviolet systems.

Quartz tubes tend to be brittle, fragile and difficult to seal. Complicated in-place cleaning systems must usually be installed to keep the quartz surface free from fouling materials.

In a conventional quartz ultraviolet disinfection unit, water flows over a bank of quartz sleeves similar to flow in the shell-side of a shell-and-tube heat exchanger. Inside each quartz sleeve is a germicidal lamp. A separate o-ring seal is made at the end of each quartz sleeve. The outer shell is usually constructed of either stainless steel andized aluminum, or polyvinyl chloride. Quartz UV systems are designed for either pressurized or gravity water flow.

Unless the quartz ultraviolet system is disinfecting an ultra-pure water source, the quartz sleeves readily foul with suspended and dissolved matter in the water. Therefore, it is necessary to employ a technique to remove the fouling matter on an almost continuous basis to preserve the high UV transmittance of quartz and the disinfection capability of the system.

Two, non-chemical, cleaning methods have been used with limited success. The first is a mechanical wiper system, in which a wiper periodically scrapes fouling deposits off of the outer surface of the quartz sleeves. For this technique to work effectively, very close toler ances are required on quartz sleeve outer diameter and alignment. Close tolerances are also required on the wiper system as well. These severe tolerance requirements add to manufacturing expense and tend to be difficult to achieve with large tube bundles.

Teflon Tube Flow Systems

In the early 1970's it was discovered that FEP Teflon was also an excellent transmitter of 253.7 nm ultraviolet light . Data obtained over fifteen years of continuous testing by DuPont indicated that Teflon was also very stable to solar ultraviolet (minimum 290 nm). Shorter term tests (five years) indicated that Teflon is virtually unaffected by the shorter germicidal wave length light. Teflon, an deal material to contain a wastewater during disinfection, has the following advantages:

1. It has a high transmission of 253.7 nm ultraviolet light - approximately 80 percent transmission with wall thicknesses used in disinfection systems.

2. Teflon is chemically inert. Teflon tubes are not attacked by substances present in water or wastewater.

3. It is non-wetting and has an extremely low-friction co-efficient. Tefton tubes are usually not fouled by substances present in water or wastewater. If fouling should occur, chemical cleaning can be used to easily remove deposits.

4. Teflon is an approved material by the U.S. Food and Drug Administration for use with food and beverages.

5. It is virtually unaffected by ultraviolet rays.

In the Teflon tube flow system, the fluid to be disinfected flows through Teflon tubes. To achieve large flow capacities, these tubes can be connected in parallel to large diameter headers. Systems of several million gallons per day capacity can then be built as a single unit.

Banks of germicidal lamps are placed in between the tubes so that each tube is exposed to ultraviolet light from alt sides. The lamps are mounted on a frame which can be slid out for easy lamp replacement.

Aluminum, which is an excellent reflector for ultraviolet, forms the outer casing. Unabsorbed ultraviolet, which strikes the enclosure walls, is mostly re-reflected and is eventually absorbed by the water. This design is extremely efficient in the utilization of ultraviolet energy emitted by the germicidal lamps.

From the preceding, it is obvious that an essential aspect of effective application of ultraviolet irradiation involves maintaining an optimal dose of radiant energy. Manufacturers of ultraviolet irradiation equipment provide ratings related to the maximum water flow rates which may be attempted, above which the radiant dose will be inadequate.

While there will be some variations among different makes and models, most ultraviolet disinfection equipment of the type used for hemodialysis and other purified water systems are designed to provide a radiant dose of 30 000 microwatt-sec/cm2, which is well in excess of that needed for the destruction of most, but not all, types of water-born bacteria.

In this regard, it should be recognized that an inadequate dose of radiant energy may result if the mercury vapor lamps are not periodically replaced, if the water contains materials which absorb or prevent the light from reaching the bacteria, or if the quartz sleeve becomes coated.

It should also be pointed out that, for many commercial units, a continuous flow of water is required to prevent overheating of the ultraviolet lamps. If such overheating is allowed to occur, the wavelength of ultraviolet light emitted may change to a point at which it is no longer bactericidal and, when flow is resumed, initial volumes of effluent water may be bacterially contaminated.

It has been reported that certain bacterial species are resistant to ultraviolet irradiation and, unless controlled by other means, may proliferate to excessive levels. A further disadvantage of ultraviolet irradiators is their ineffectiveness for the removal of endotoxin. The inability of ultraviolet irradiation to remove endotoxin may preclude its use in some medical situations, or other appicatiors in whch more stringent control of these contaminants is necessary.

Ultraviolet irradiation equipment is convenient to operate, routine use requiring only that they be electrically switched "on", and may be helpful in suppressing bacterial growth in purified water distribution systems in which upstream equipment, such as reverse osmosis, provides the primary means for their removal.

Submicron filtration is also frequently used, as a secondary means of bacterial control. The capabilities of ultraviolet irradiation and submicron filtration are both limited in that neither remove endotoxin and only destroy or eliminate bacteria within the equipment itself. Ultraviolet irradiation may actually cause endotoxin levels to increase as a result of bacterial destruction.

Also, since ultraviolet irradiation has no downstream bactericidal effects, it should be used in combination with regular chemical disinfection procedures. In this manner organisms are chemically eliminated from the entire system, after which ultraviolet irradiation prevents rapid multiplication of bacteria which may penetrate the reverse osmosis equipment.

Users of ultraviolet irradiation equipment should recognize the need for regular maintenance, including lamp replacement and cleaning. Ultraviolet lamps are typically designed to operate for one year, during which time radiant output will progressively decrease.

Thus, at a minimum, the lamps must be replaced annually. Most manufacturers also provide, at additional cost, monitors to detect loss of lamp radiant energy output and these provide a more accurate indication of the need for lamp replacement than reliance on calendar-based replacement schedules.

We trust that this short overview of Ultraviolet Technology is useful to you as an end user or as a water dealer. Your comments and suggestions are always appreciated.



 Model Inlet/Outlet Size(NPT) Maximum Capacity Clear Fresh Water # of Lamps

Electrical Power(Amps)

@ 120VAC

Electrical Power(Amps)


 1S  1"  10 GPM  1  0.6  0.3
 2S  1-1/2"  30 GPM  2  1.1  0.6
 2L  2"  40 GPM  2  1.6  0.9
 4S  1-1/2"  40 GPM  4  2.1  1.1
 4L  2"  80 GPM  4  3.2  1.7
 6S  2"  60 GPM  6  3.2  1.7
 6L  2"  110 GPM  6  4.8  2.6
 8L  4"  160 GPM  8  6.4  3.5
 12L  4"  220 GPM  12  9.6  5.2


*All enclosures are NEMA 3R; Operating Pressure is 125 psi maximum






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