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Ultraviolet irradiation uses a specific wavelength of light to sterilize water, air, and objects without producing toxic by-products. A germicidal lamp emitting a wavelength of 254 nm is effective against bacteria, viruses, parasites, fungi, and spores. However, the water must be clear, and the microorganisms must be in direct contact with the UV light rays. UV irradiation is being used more frequently for purification due to public concern about the toxic byproducts of chlorine treatment. It is particularly useful for homes that draw their supply from wells, lakes, or streams.
Ultraviolet irradiation is the sterilization of water, air or objects through the use of a particular wavelength of ultraviolet light. This is a common way of disinfecting wastewater and drinking water for homes and institutions. This disinfection method does not produce the toxic by-products that can be produced by water chlorination.
Ultraviolet radiation is not visible to the naked eye and emits shorter wavelengths than visible light. These wavelengths are measured in nanometers (nm). There are several types of ultraviolet (UV) light, and each has different wavelengths. Sunlight emits all of this, but the shortwave ultraviolet (UVC) light used in ultraviolet disinfection is shielded by the earth’s atmosphere. Therefore, microorganisms have no resistance against it.
A typical UV disinfection system is a special quartz glass mercury vapor lamp that emits a wavelength of 254 nm, known as a germicidal lamp. The maximum wavelength at which DNA absorbs is 260 nm. Therefore, at 254 nm, the DNA of microorganisms is damaged and they cannot reproduce. This ultraviolet irradiation does not kill them, but they are irreparably damaged. Such a UV sterilizer is effective against bacteria, viruses, parasites, fungi and spores.
For ultraviolet irradiation to be successful, the microorganism must be in direct contact with the UV light rays. Also, for a UV water purifier to work, the water cannot be cloudy. If it is cloudy, it must first be filtered or treated with activated carbon. It’s important that the light stays strong, so lamp maintenance is an important part of an ultraviolet system. Home units should have an alarm that sounds a warning if the lamp is malfunctioning.
Given public concern about the toxic byproducts of chlorine treatment, ultraviolet irradiation is being used more frequently for purification of both drinking water and wastewater. One problem is that there is no residue in the water to continue disinfection after the light has penetrated. Therefore, if the water becomes contaminated after the initial treatment, it will remain contaminated. For this reason, the Ultraviolet Water Purifier should be located close to the place of final use, to minimize any possibility of subsequent contamination. In domestic units, ultraviolet irradiation is often the final step in a process which may also include some other form of treatment, such as water softening or reverse osmosis.
Ultraviolet irradiation is particularly useful in treating the water of homes that draw their supply from wells, lakes or streams. People who are concerned about the effects of chlorine byproducts typically dechlorinate their water and use UV irradiation to disinfect it after this treatment. Commercial establishments often find it easier to use a UV disinfection system than to chlorinate their water. Bottled water is also often disinfected this way.
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