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UV Systems are sized according to application requirements.
What is U.V. light:
U.V. is a proven means of addressing microbiologically contaminated waters. This simple and safe technology is suitable for small flow rates i.e. domestic applications and large flows for commercial and industrial uses.
These units produce ultraviolet light of between 200 – 295 nanometers (nm) by converting electrical energy through the use of a low pressure mercury vapour lamps. (commonly called U.V. Bulbs or U.V. Lamps.) These lamps are similar in design to standard flourescent lamps with a few exceptions. The U.V. lamp is manufactured with Quartz glass which allows for the transmittion of 90% of radiated energy. Flourescent lamps also contain a thin coating of phosphor inside the lamp which converts the U.V. to visable light.
Microorganisms encompas a wide variety of unique structures and can be grouped into five basic groups.
| Bacteria | |
| Virus | |
| Fungi | |
| Protozoa | |
| Algae |
In simplest terms, a microorganism is made up of the Cell wall, Cytoplasmic membrane and the cell’s Genetic material, nucleic acid. It is this genetic material or DNA that is targeted by U.V. light. As the light penetrates the cell wall and cytoplasmic membrane it causes a molecular rearrangement of the microorganism’s DNA and prevents it from reproducing.
If a Cell cannot reproduce it is considered dead.
How a U.V. unit works:
Water enters through the inlet port in the reactor chamber and flows around a high output U.V. lamp, this lamp emits powerful ultraviolet energy at the 253.7 nm wave length and is protected from contact with the water by a quartz sleeve. The treated water then exits through the outlet port. The design of a U.V is critical to its preformance, the flow rate through the unit must allow for proper contact time.
Factors affecting U.V.
Suspended solids:
This can cause a shielding problem in which a microbe may pass through the unit without having any direct U.V. penetration. this problem can be reduced be mechanical filtration down to at least five microns.
Iron/Manganese:
Iron will cause staining of the Quartz sleeve with levels as low as 0.03 ppm and levels of manganese should not exceed 0.05 ppm. This staining will inhibit the transmission of U.V.light through the water in the chamber. If these problems exist then pretreatment will be required.
Calcium/Magnesium:
These will cause scale to form on the quartz sleeve and will be magnified during times of low or no flow. This scale will inhibit the transmission of U.V. light through the water in the chamber. If these problems are present they can be easily remideed by the use of an ion exchange softener.
Other absorbing compounds:
Compounds such as humic and fumic acids as well as tannins will reduce the amount of U.V. energy available to penetrate through the water and alter the DNA of the molecule.
Advantages of UV lights include:
- Environmentally friendly, no dangerous chemicals to handle or store, no problems of overdosing.
- Low initial capital cost as well as reduced operating expenses when compared with similar technologies such as ozone, chlorine, etc.
- Immediate treatment process works, no need for holding tanks, long retention times, etc.
- Extremely economical, hundreds of gallons may be treated for each penny of operating cost.
- No chemicals added to the water supply – no by-products (i.e. chlorine + organics = trihalomethanes).
- No change in taste, odor, pH, or conductivity or the general chemistry of the water.
- Automatic operation without special attention or measurement, operator friendly.
- Simplicity and ease of maintenance, periodic cleaning (if applicable) and annual lamp replacement, no moving parts to wear out.
- No handling of toxic chemicals, no need for specialized storage requirements, no WHMIS requirements.
- Easy installation, only two water connections and a power connection.
- More effective against viruses than chlorine.
- Compatible with all other water processes (i.e. RO, filtration, ion exchange, etc.)
The UV system, mounted on the wall (above right) is used to maintain a bacteria-free water supply in this clean-room environment. Here, stored RO permeate is continuously recycled through the UV system to prevent biological growth.
Factors Affecting UV:
The effectiveness of a UV system in eliminating microbiological contamination is directly dependant on the physical qualities of the influent water supply.
Suspended Solids or Particulate Matter cause a shielding problem in which a microbe may pass through the sterilizer without actually having any direct UV penetration. This shielding can be reduced by the correct mechanical filtration of at least five microns in size.
Iron / Manganese will cause staining on the lamp or quartz sleeve at levels as low as 0.3 ppm of iron and 0.05 ppm of manganese. Proper pretreatment is required to eliminate this staining problem.
Calcium / Magnesium Hardness will allow scale formation on the lamp or quartz sleeve. This problem will be especially magnified during low flow (or no flow) times when the calcium and magnesium ions tie-up with carbonates and sulfates to form hard scale build-up inside the sterilizer chamber and be deposited on the lamp or sleeve.
Other Absorbing Compounds such as humic and fumic acids as well as tannins will reduce the amount of UV energy available to penetrate through the water to affect the genetic material, DNA of the molecule.
Additional Factors Affecting UV:
Temperature is a determining factor. The optimal operating temperature of the UV lamp must be near 40°C (104°F). UV levels will fluctuate with excessively high or low temperature levels. A quartz sleeve is typically employed to buffer direct lamp – water contact thereby reducing any temperature fluctuations. A typical method employed in a system without a quartz sleeve is to engineer the system to take into account these fluctuations and typically de-rate the regular flow rate by the corresponding amount.
Summary
The need for chemical-free disinfection of water can be found in all areas of water treatment whether it be residential, commercial, institutional or industrial applications. The utilization of UV light is not a cure-all for microbial contamination, nor is it the replacement for traditional cleaning and sanitizing methods. It is however, a useful tool that has proven successful in thousands of installations over a period of 50 years. UV light’s physical rather than chemical process makes it an ideal system component for ease of maintenance, low operating cost, and operator safety.
| Table 1 Typical UV Applications |
| Commercial Campgrounds Recreational Vehicles Resorts Hotels Restaurants |
| Institutional Hospitals Schools Nursing Homes Fish Hatcheries Laboratories |
| Industrial Electronics Food Packaging Breweries Bottlers Cosmetics |
Pakwater Care Services provide complete solutions for Ultra Violet (UV) Water Disinfection Systems for Domestic, Commercial and Industrial Applications.
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