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How Does UV Water Treatment Work?
A UV water purifier works quite simply by exposing your water to certain wavelengths of ultraviolet light, typically 254 nm. This light damages the nucleic acids and DNA in the cells, so they can no longer work correctly. UV light doesn't necessarily kill microorganisms, but it is very effective at inactivating them and preventing them from replicating and producing colonies. Keep in mind that the only thing that microorganisms do in life is replicate and make colonies, which is why we get sick if we consume them in large amounts through our drinking water. In other words, we don't have to worry about microorganisms that cannot replicate. These organisms can enter our system and will pass right through without causing any illness.
As you probably know, DNA is the genetic coding found in all living things. Within each DNA strand there are different sequence codes, with each sequence coding for different characteristics. UV light can be damaging to DNA – in fact, the reason that it's a good idea to wear sunscreen when you're outside is because the UV light in the sun's rays can damage the DNA in your skin cells, causing them to reproduce incorrectly and leading to skin cancer.
Because microorganisms are very simple creatures, their DNA is primarily coded for replication. At the 254 nm wavelength, the light from a UV water purifier is absorbed quite readily in one spot in the DNA strand causing it to break the bond. This then causes the microorganism to become sterile, no longer able to replicate.
What Does "Disinfection" Really Mean?
The term "disinfection" refers to the process of destroying or preventing the growth of disease carrying microorganisms. But what does this really mean? There are two main types of disinfection: chemical and physical. Chemical disinfection requires a substance to be added to the water (or other material) to kill or inactivate microorganisms. Chlorine, for example, is a very commonly used disinfectant for water treatment. Physical disinfection, on the other hand, treats the substance being disinfected but does not add anything to it. Boiling water, for example, will kill many dangerous bacteria and leave the water safe to drink.
Chemical disinfectants have been used very successfully for many years, but they carry a number of risks. Chlorine, for example, is used by many water treatment plants because it's relatively inexpensive and very effective. However, chlorine and chloramines (a related chemical disinfectant), often react with other compounds in the water to form trihalomethanes (THMs), which are carcinogens. Many people also find that chlorine treated water has a particular smell and taste that they find objectionable.
Physical disinfectants are often preferred over chemical means because they don't add anything to the water that could produce dangerous byproducts. There are challenges with physical methods, however – after all, you wouldn't want to always have to boil all of the water in your home before you use it! UV water treatment has come a long way in recent years, and most people find that it's far superior to chemical means for treating water in their homes or businesses. Note that these systems are sometimes called "UV water sterilizer systems, " but this is misleading; it's nearly impossible to prove complete sterilization, but well-designed UV systems can kill or inactivate 99.99% of many dangerous microorganisms.
Advantages and Disadvantages of UV Water Treatment
UV water purifier systems can be very effective for treating water that contains many types of bacteria, viruses, and other microorganisms, but it's not right for every situation. Even the best UV systems have pluses and minuses that you'll need to consider when choosing the water treatment plan that's right for you. If you need assistance, our Certified Water Specialists are just a phone call away at 1-800-608-8792.
- Physical disinfection adds no potentially harmful chemicals
- Virtually instantaneous disinfection, requiring no holding tanks like chlorination does
- No change in taste, odor, pH or conductivity of treated water
- No handling of toxic chemicals, including special storage requirements
- No disinfection by-products (e.g. THMs)
- Very low power consumption
- No removal of beneficial minerals
- Very low setup cost and low operational expense when compared to other technologies
- Environmentally friendly
- Universally accepted treatment process for potable and non-potable supplies
- Automatic, unattended operation
- Easy maintenance, with no moving parts to wear out
- Safe to use
- More effective against cysts than chlorine
- Water must be pretreated for a UV water filter to work effectively
- Power is required; during a power outage, the system will not work
- UV lamp should be changed yearly
- No residual protection – once the water leaves the UV water purifier, it could become reinfected
- UV water treatment works best with high quality water with little or no sediment
Ultraviolet light is an extremely effective treatment technology, but for a UV water purification system to work properly, water quality plays a very important role. LUMINOR recommends the following when it comes to pretreatment:
- UV Transmittance - 75% or greater
- Iron - less than 0.3 ppm (mg/l)
- Manganese - less than 0.05 ppm (mg/l)
- Tannins - less than 0.1 ppm (mg/l)
- Hardness - less than 7 gpg (120 mg/l)
- Turbidity - less than 1 NTU
You can purchase the best UV water purifier system available on the market today, but if it's not installed correctly, or misapplied, then you're spending your money for nothing! Modern UV water treatment systems are designed for years of trouble-free operation; however, you must remember that the system is treating your water in your specific application. If you do not follow the manufacturer's installation and maintenance instructions exactly, then how can the product work as it was designed? The following are some installation tips and suggestions for a trouble-free operation:
- When possible, install the UV reactor in the vertical position with the inlet at the bottom of the reactor.
- Disinfect the distribution system (the pipes) with household bleach for a full 30 minutes to destroy any microbiological contaminants in the system and flush before using the water.
- Always install a 5 micron prefilter with every UV water treatment system.
- Install the UV system as your last piece of treatment equipment.
- Ensure the UV water filter is installed prior to the hot water heater and before any branch lines to ensure complete disinfection within the home.
- Leave enough space to remove the lamp and/or quartz sleeve from the system.
- Never undersize a system. Always move to the next larger size if in doubt.
- Install your UV water purifier on a separate ground fault interrupter (GFCI) circuit.
- Use unions in case the system needs to be removed from your home.
- Follow the recommended pretreatment requirements to the letter!
- Do not ignore any alarms or warnings from the system.
- Change your UV lamp every year.
- Test your water regularly for microbiological contaminants.
Just as there are many different kinds of microorganisms that can be found in drinking water, there are different levels of UV energy (dose) required to inactivate each one. For example, E.coli bacteria will require a slightly different dose of UV light to inactivate than Cryptosporidium, as they are genetically different. The good news is that typical bacteriological contaminants that are found in water are all easily inactivated using UV light. E. coli, for example, is inactivated at a dose of 6.6 mJ/cm² and both Giardia lamblia and Cryptosporidium are eradicated at dose levels less than 10 mJ/cm².
Although UV water treatment is effective against nearly all forms of bacteriological contaminants, viruses typically require the highest dose level for complete destruction. In some cases, such as Adenovirus, a UV dose of 165 mJ/cm² is required for inactivation. As this dose is typically much higher than what traditional UV systems are rated for, a multi-barrier approach (using chlorine or chloramine in addition to UV) is typically used to address the virus inactivation (typically used in municipal applications).
The term UV dose, or more simply just "dose, " refers to the total amount of radiant energy products by a UV light source inside a system. It is the product of intensity "I", (expressed as energy per unit surface area) and the residence time, "T". Dose can be shown in many units, but the most common are in mJ/cm² or W/m². As dose is a product of two units multiplied together, one can easily see how the adjustment of one of these variables will adjust the corresponding dose. This is why many UV water filter systems are rated at different dose levels depending upon the stated flow rate (the "T" portion or residence time).
The dose levels produced by a UV water purifier are typically represented at three distinct levels. The first is based on an old US Public Health document outlining a UV dose of 16, 000 µWsec/cm² (or 16 mJ/cm² under the newer units where 1000 µWsec/cm² equals 1 mJ/cm²). Over the past few years, a UV dose of 30 mJ/cm² has become the industry standard used by many UV water treatment system manufacturers, including Viqua and Luminor. A UV dose of 40 mJ/cm² has been adopted by NSF and consequently by many U.S. states as the new "standard" for dose levels. Whatever dose level you may choose for your system, it is important to remember that this can be achieved by simply controlling the flow of the unit with an optional flow restrictor.
The History of UV Disinfection
In the late 1800s and early 1900s, scientists discovered that sunlight had dramatic ability to destroy and provide for an effective means of treating bacterial infections. Further research lead to the first full-scale UV disinfection system, created in France in 1910. While early systems were not always reliable, by the 1950s, UV water purification was being used in several countries in Europe. With continued improvements and developments, including those that lowered operating costs, thousands of UV water treatment plants were operating by the beginning of the 21st century across the continent.