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| How does Ultraviolet Energy work? |
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Ultraviolet or UV energy is found in the electromagnetic spectrum between visible light and x-rays can be described as invisible radiation. In order to kill microorganism, the UV rays must actually strike cell. UV rays penetrate the outer cell membrane, passes through the cell body and disrupt its DNA preventing reproduction. It is a physical treatment, not chemical, so it doesn’t alter the water chemistry. UV adds nothing to the water such as undesirable color, odor, taste or flavor and neither does it generate harmful by-products. |
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The degree of inactivation by ultraviolet radiation is directly related to the UV dosage applied to the water. The dosage, a product of UV intensity and exposure time, is measured in microwatt second per square centimeter. The accompanying table lists dosage requirements to destroy common microorganisms. Most UV units are designed to provide a dosage greater than 30,000 µW/cm2 after one year continuous operation. |
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| UV System for water disinfection |
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Special low-pressure mercury vapor lamps produce UV radiation at 253.7nm, the optimal wavelength for disinfection. The UV lamp never contact the water, it is either housed in a glass sleeve inside the water chamber or mounted external to the water which flows through transparent Teflon tubes. |
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| In this method water flow through the SS Chamber and gets in contact with submerged bank of germicidal lamps housed within quartz Sleevet. |
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Some ultra pure water system use 185nm UV lamps for reducing TOC (total organic carbon). It is possible to achieve 99.9% reduction in certain applications and with proper maintenance. UV treatment renders the rinse water cleaner and virtually devoid of the undesirable TOC. In order for a UV unit to successfully disinfect water, the following variables must be considered. |
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| “Point” Disinfection |
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UV rays only kill bacteria at one point in a watering system and do not provide any residual germicidal effect downstream. If just one bacteria passes through unharmed, there is nothing to prevent it from attaching to downstream piping surfaces and proliferating. Bacteria cells are not removed in a UV unit but are converted into pyrogens. The killed microorganism and any other contaminants in the water are food source for any bacteria that do survive downstream of the UV unit. Therefore UV system always installed at the end use. |
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UV/Chlorine/Ozone |
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| Methods |
Ultraviolet |
Chlorination |
Ozone |
| Destruction |
Physical |
Chemical |
Chemical |
| Capital cost |
Low |
Medium |
High |
| Operating cost |
Low |
Medium |
High |
| Maintenance cost |
Low |
Medium |
High |
| Maintenance frequency |
Low |
Medium |
High |
| Disinfection Performance |
Excellent |
Very Good |
Unpredictable |
| Contact time |
1-5 Seconds |
25-45 minutes |
5-10 minutes |
| Personal Hazards |
Low |
Medium |
High |
| Toxic Chemicals |
No |
Yes |
Yes |
| Water Chemistry change |
No |
Yes |
Yes |
| Residual effect |
No |
Yes |
Yes |
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