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UV disinfection is a method of using ultraviolet radiation to kill micro-organisms that may be living in water, thereby making it safe to drink. To purify water in this way, mercury arc lamps are often used to generate ultraviolet light. The light penetrates the cell walls of bacteria, parasites, viruses, and other living contaminants, altering their DNA. Depending on the intensity of the radiation and the length of exposure, this either kills them or prevents them from reproducing. The same technique may be used to sanitize wastewater.
In one method of UV disinfection, UV lamps are housed inside quartz tubes and placed over or around the flowing water. Quartz is one of the few solids that ultraviolet radiation can penetrate, allowing the surrounding water to be exposed to the purifying rays. The drawback of this system is that substances dissolved in the water tend to collect on the exposed walls of the quartz tubing, blocking the radiation from escaping into the water.
Another method of UV disinfection uses banks of UV lamps surrounded by Teflon® tubes. Teflon® is an excellent conductor of ultraviolet radiation, so as water flows through these tubes, it is exposed to the light from all sides and sanitized. Often, these Teflon® tube systems are surrounded by an aluminum casing, which reflects any UV light that isn't absorbed back into the water. Unlike quartz, Teflon® usually does not collect impurities that can block the radiation.
Both methods are preferable to hydrogen peroxide or chlorine disinfection because they use no chemicals. This means that no chemical residue is left in the purified water, and the environment is not exposed to harmful chemicals. However, because of the chemicals they leave behind, these more traditional methods of water disinfection methods offer some residual sanitizing, which UV disinfection does not.
UV disinfection is not as effective on cloudy water, because bacteria and other contaminants can hide in larger particles and avoid exposure to the radiation. This type of disinfection is also dependent on properly functioning equipment. Water must flow continuously to prevent the system from overheating, which could shift the frequency of the radiation to outside the anti-microbial range. Likewise, lamps must be replaced regularly to ensure they are putting out the correct amount of radiation.
The cost of UV disinfection is comparable to that of chlorine disinfection. As the technology for UV lamps and sanitization systems improves, the cost will likely drop further, encouraging more people to use ultraviolet water purifiers. This, in turn, may increase the competition among manufacturers and distributors of these systems, keeping the price low and making UV disinfection one of the top water sanitization methods.
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