FREQUENTLY ASKED  QUESTIONS

What is Ultraviolet Light Disinfection?

What are the Advantages of UV Disinfection?

What are Common UV Applications?

How does UV Disinfection Work?

What Factors Affect the Effectiveness of UV Disinfection?

Are there Special Installation and Maintenance Considerations?

What is Ultraviolet Light Disinfection?

Ultraviolet disinfection is a means of killing or rendering harmless microorganisms in a dedicated environment. These microorganisms can range from bacteria and viruses to algae and protozoa. UV disinfection is used in air and water purification, sewage treatment protection of food and beverages, and many other disinfection and sterilization applications. A major advantage of UV treatment is that it is capable of disinfecting water faster than chlorine without cumbersome retention tanks and harmful chemicals. UV treatment systems are also extremely cost efficient!

Ultraviolet disinfection systems are mysterious to many people - how can "light" kill bacteria? But the truth is it can. Ultraviolet (UV) technology has been around for 50 years, and its effectiveness has been well documented both scientifically and commercially. It is nature's own disinfection/purification method. With consumers becoming more concerned about chlorine and other chemical contamination of drinking water, more dealers are prescribing the ultraviolet solution suitable for both small flow residential applications as well as large flow commercial projects.

Following are the advantages of UV sterilization:

• Environmentally friendly, no dangerous chemicals to handle or store, no problems of overdosing.  
• Universally accepted disinfection system for potable and non-potable water systems.  
• Low initial capital cost as well as reduced operating expenses when compared with similar technologies such as ozone, chlorine, etc.  
• Immediate treatment process, no need for holding tanks, long retention times, etc.  
• Extremely economical, hundreds of gallons may be treated for each penny of operating cost.  
• Low power consumption.  
• No chemicals added to the water supply - no by-products (i.e. chlorine + organics = trihalomethanes).   
• Safe to use.  
• No removal of beneficial minerals.  
• No change in taste, odor, pH or conductivity nor the general chemistry of the water.  
• Automatic operation without special attention or measurement, operator friendly.  
• Simplicity and ease of maintenance, TWT Deposit Control System prevents scale formation of quartz sleeve, annual lamp replacement, no moving parts to wear out.  
• No handling of toxic chemicals, no need for specialized storage requirements, no OHSA 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.).

One of the most common uses of ultraviolet sterilization is the disinfection of domestic water supplies due to contaminated wells. Coupled with appropriate pre-treatment equipment, UV provides an economical, efficient and user-friendly means of producing potable water. The following list shows a few more areas where ultraviolet technology is currently in use:

surface water, groundwater, cisterns, breweries, hospitals, restaurants, vending, cosmetics, bakeries, schools, boiler feed water, laboratories, wineries, dairies, farms, hydroponics, spas, canneries, food products, distilleries, fish hatcheries, water softeners, bottled water plants, pharmaceuticals, mortgage approvals, electronics, aquaria, boats and RV's, printing, buffer processing, petro-chemical, photography, and pre- and post-reverse osmosis.

Ultraviolet is one energy region of the electromagnetic spectrum, which lies between the x-ray region and the visible region. UV itself lies in the ranges of 200 nanometers (nm) to 390 nanometers (nm). Optimum UV germicidal action occurs at 260 nm.

Since natural germicidal UV from the sun is screened out by the earth's atmosphere, we must look to alternative means of producing UV light. This is accomplished through the conversion of electrical energy in a low pressure mercury vapor "hard glass" quartz lamp. Electrons flow through the ionized mercury vapor between the electrodes of the lamp, which then creates UV light.

As UV light penetrates through the cell wall and cytoplasmic membrane, it causes a molecular rearrangement of the microorganism's DNA, which prevents it from reproducing. If the cell cannot reproduce, it is considered dead.

Because UV does not leave any measurable residual in the water it is recommended that the UV sterilizer be installed as the final step of treatment and located as close as possible to the final distribution system. Once the quality of your water source has been determined, you will need to look at things that will inhibit the UV from functioning properly (e.g., iron manganese, TDS, turbidity, and suspended solids).

Iron and manganese will cause staining on the quartz sleeve and prevent the UV energy from transmitting into the water at levels as low as 0.03 ppm of iron and 0.05 ppm of manganese. Proper pre-treatment with a sediment filter and Triangular Wave Deposit Control System is required to eliminate this staining problem.

Total Dissolved Solids (TDS) should not exceed approximately 500 ppm (about 8 grains of hardness). There are many factors that make up this equation such as the particular make-up of the dissolved solids and how fast they absorb the available UV energy. Calcium and magnesium, in high amounts, have a tendency to build up on the quartz sleeve, again impeding the UV energy from penetrating the water. A Triangular Wave Deposit Control System will handle TDS before it becomes a problem for the UV system.

Turbidity is the inability of light to travel through water. Turbidity makes water cloudy and aesthetically unpleasant. In the case of UV, levels over 1 NTU can shield microorganisms from the UV energy, making the process ineffective. Suspended Solids need to be reduced to a maximum of 5 microns in size. Larger solids have the potential of harboring or encompassing the microorganisms and preventing the necessary UV exposure. Pre-filtration is a must on all UV applications to effectively destroy microorganisms to a 99.9% kill rate.

An additional factors affecting UV is temperature. The optimal operating temperature of a UV lamp must be near 40 ⁰C (104 ⁰F). UV levels fluctuate with temperature levels. Typically a quartz sleeve is installed to buffer direct lamp-water contact thereby reducing any temperature fluctuations.

Are there Special Installation and Maintenance Considerations?

Install a Triangular Wave Deposit Control System just upstream of the UV disinfection system to protect the UV system from scale and iron deposits.  Scale and iron deposits on the quartz tube of the UV system eventually will block the UV light from treating killing the microbes in the water.

Once the application has been determined, you should find a location that offers easy access for service. You will need to have access to the pre-filters, to the UV chamber for annual lamp changes and inspection of the quartz sleeve. You will want to locate near an electrical outlet.

*Note: Using a UV system and a pump on the same electrical line may cause problems with and shorten the life of the UV lamp and ballast.  For best results, the use of a separate electrical line should be considered, depending upon the specifics of your site; please consult your electrician, if necessary.

UV units should be installed on the cold water line before any branch lines and should be the last point of treatment. All points of the distribution system after the sterilizer must be chemically "shocked" to ensure that the system is free from any downstream microbial contamination.

Lamps should be changed as lamp output monitor indicates, but at least every 10 to 12 months.  Note: depending upon systems purchased, lamp output monitors are optional, but recommended.

Filter changes are done according to the water quality, but usually it is three to six months.

Quartz sleeves should be inspected at least every 6 months.  If minor deposits have formed, the sleeves should be wiped down with a soapy solution.  Do not leave fingerprints on the quartz sleeve!

For proper operation and disinfection, it is imperative to follow the manufacturer's guidelines on water quality and operational procedures on associated process equipment as well as on the UV equipment.

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