UV sterilizers are an innovative technology that deactivate bacteria, viruses, and other microbiological water contaminants without the use of chemicals.
A great way to understand a UV sterilizer is to consider the effect of ordinary sunlight when we spend too much time outdoors in the sun – we can get a sunburn and our skin can be damaged. UV water disinfection is a similar process, except that it is dramatically more powerful than sunlight. A special lamp, surrounded by a quartz glass sleeve inside the stainless-steel chamber that the water flows through, produces concentrated UV light at a specific wavelength tested to be the most damaging to microorganisms. Inside the chamber, the microbes are exposed to the UV light which damages their DNA. Once the DNA of the organism is damaged, the microorganism is unable to regulate its functions and reproduce. It either dies or is no longer able to reproduce and cause illness. We call this inactivation.
Just as the extent of your sunburn can vary depending on how much time you spend in the sun and the intensity of the sunlight, the amount of UV light the contaminants are exposed to determines the effectiveness of the UV sterilizer. This is known as the UV dose. The 2 factors that contribute to UV dose are the exposure time (which is directly related to the flow rate of the water through the UV chamber), and the intensity of the UV light (related to the effectiveness and design of the UV lamp and chamber, the age of the lamp, the clarity of the sleeve, and the clarity of the water being treated). We refer to the clarity of the water as UV transmittance or UVT. It is important to note that water with a high level of organics can sometimes appear virtually clear but have poor UVT (since many organics can absorb UV light). We recommend that you have the UVT of your water tested to ensure you are getting the right level of UV treatment.
UV Dose = UV Intensity x Exposure Time (Flow Rate)
To ensure a high UV intensity, it is important that the UV sleeve be cleaned periodically and that the water is properly pre-treated to remove minerals that can foul the UV sleeve (hardness, iron, and manganese). It is also important to pre-treat to remove sediment as well as organics and tannins that could absorb UV light. Pre-filtration of sediment to a minimum level of 5 microns is required by all UV manufacturers.
As a UV lamp ages, the intensity of the UV light it produces will decline. UV manufacturers test the performance of their UV systems to ensure that they are capable of safely treating the water based on the UV output of their lamp at the end of its stated life. Beyond this point, the UV lamp might still be illuminated, but the specific wavelength of UV light might not be intense enough to safely sterilize the water. This is why it is very important to replace the UV lamp based on the manufacturer’s stated lamp life. Most UV lamps have a service life of 9,000 hours or 1 year.
Many of our competitors advertise the capacity of their UV sterilizers based on a dosage of 30 mJ/cm2. We provide this information for comparative purposes, however, we strongly recommend that you size your UV sterilizer based on a dosage of 40 mJ/cm2. This ensures better disinfection when the UVT is less than optimal and provides extra protection against more resistant viruses. See our UV dose chart for a list of UV dosage levels required to treat for common bacteria and other waterborne pathogens.
With proper pre-treatment and scheduled lamp replacement, UV disinfection is a highly effective and economical means of disinfecting drinking water. It is the most popular disinfection technology for well water and other private water supplies. It is also growing in popularity as a whole house treatment for homes connected to a city water supply as homeowners seek additional assurance that their water supply is safe, especially in light of recent prominent infrastructure failures in the news across the country.
UV Systems and Parts Available from Darrington Water Conditioning