Ultraviolet radiation can cleanly and rapidly destroy many organic contaminants \u2014 but it\u2019s most useful when properly applied.<\/p>\n
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| Between \u00a0 the rising costs of electricity and growing consumer demand for \u201cgreen\u201d water \u00a0 treatment solutions, ultraviolet (UV) radiation is becoming an increasingly \u00a0 popular tool for disinfecting pools and spas.<\/p>\n However, like any sanitation technology, UV isn\u2019t an end-all solution \u2014 its \u00a0 effects are rapid but limited, and it often requires help from other types of \u00a0 sanitizers.<\/p>\n Here, we talk with professional chemists about the exact nature of UV, the \u00a0 means by which it sanitizes, and the most effective ways of implementing it. \u00a0 A fuller, more detailed understanding of these principles will inform \u00a0 decisions about where and how to apply UV for maximum effectiveness.<\/p>\n What is UV?<\/strong> As with most artificial light, UV is produced by a bulb designed to generate \u00a0 radiation in a specific range of wavelengths. \u201cThere are medium pressure and \u00a0 low pressure UV lamps, and each one produces a different range of UV \u00a0 wavelengths,\u201d says Ellen Meyer, the Charleston, Tenn.-based tech service \u00a0 manager for Lonza.<\/p>\n Shorter wavelengths indicate higher energy, and the UV range is subdivided \u00a0 along a sort of energy scale, progressing from UVA (315 to 400 nm) to UVB \u00a0 (280 to 315 nm) to UVC (200 to 280 nm) to high-energy radiation known as \u00a0 vacuum UV (100 to 200 nm). Most UV radiation is at least somewhat effective \u00a0 at killing microorganisms and breaking down organic compounds, but the \u00a0 high-energy radiation of vacuum UV is the most powerful \u2014 and thus, the most \u00a0 deadly to microbes. Still, even lower-energy UV is effective at deactivating \u00a0 many organisms that resist the disinfection effects of chlorine.<\/p>\n Like other kinds of light, UV travels fast and doesn\u2019t hang around \u2014 a \u00a0 property that has its ups and downs. On the positive side, this means UV \u00a0 reaches its entire target area almost instantly, and destroys the organic \u00a0 contaminants it touches in a matter of seconds. The downside is, UV can\u2019t \u00a0 diffuse throughout the water the way, say, chlorine can \u2014 so its \u00a0 effectiveness is limited to the path along which it\u2019s projected, and it can\u2019t \u00a0 maintain a sanitizer residual in the pool.<\/p>\n Thus, some kind of additional sanitizer is a must in pools using UV. \u201cEven in \u00a0 Europe, where UV and UV-generated ozone are commonplace, additional chlorine \u00a0 is required by health authorities,\u201d says Corinne Lehr, assistant professor at \u00a0 the California Polytechnic State University Department of Chemistry and \u00a0 Biochemistry in San Luis Obispo, Calif.<\/p>\n Another significant concern in UV-sanitized pools is the replacement and \u00a0 disposal of bulbs. \u201cThe bulbs have to be replaced every six to nine months, \u00a0 and that costs $750 to $1500 every time,\u201d says Jeff Jones, the Dallas-based \u00a0 North American sales director of the residential pool division at Del Ozone. \u00a0 In addition, Jones points out that the bulbs contain the chemical mercury, \u00a0 whose disposal many cities regulate closely.<\/p>\n What does UV do?<\/strong> A predominant explanation for UV\u2019s damage to microbes hinges on the damage \u00a0 this radiation causes to DNA \u2014 the self-replicating molecule necessary for \u00a0 life to reproduce. \u201cOnce an organism\u2019s DNA is sufficiently damaged, that \u00a0 organism can\u2019t reproduce anymore,\u201d Meyer explains. \u201cSo even if you were to \u00a0 swallow some of the organism, it won\u2019t be able to grow and reproduce and \u00a0 cause an infection \u2014 you\u2019ve pretty much disarmed it.\u201d<\/p>\n But UV\u2019s effects may also play more immediate roles in microbe destruction. \u00a0 \u201cSimilarly to how UV gives us sunburns, it can cause physical damage to \u00a0 microbes,\u201d Lehr says. \u201cBut that damage can be even more serious to them \u2014 it \u00a0 can kill them.\u201d<\/p>\n The degree to which UV inactivates or kills an organism depends on multiple \u00a0 factors, including the wavelength of the UV and the biological makeup of the \u00a0 organism. The chart above details some kill and inactivation figures for \u00a0 several common microorganisms under UVA radiation.<\/p>\n Along these same lines, UV can be used to destroy other organic contaminants, \u00a0 like the chloramines that form when chlorine reacts with bather wastes in the \u00a0 water. The only problem is, the molecular pieces of some chloramines stick \u00a0 around in the water, and may re-form into their original compounds if they\u2019re \u00a0 not filtered out quickly enough \u2014 as can be seen in the charts to the right.<\/p>\n In the first chart, levels of monochloramine (NH2<\/sub>Cl) and nitrogen \u00a0 trichloride (NCl3<\/sub>) are both lower after UV than before UV, but the \u00a0 level of dichloramine (NHCl2<\/sub>) can sometimes be slightly higher. In \u00a0 the second chart, it\u2019s equally clear that even after a dose of UV, some of \u00a0 the chloramines have re-formed, and their levels have actually risen. \u201cSo you \u00a0 actually see more of certain disinfection byproducts with UV than you do \u00a0 without it,\u201d Meyer says.<\/p>\n How can UV be used effectively?<\/strong> Some microorganisms, such as the notorious cryptosporidium<\/em>, are highly \u00a0 resistant to chlorine, because they produce hard shells known as cysts. \u00a0 Others, such as black algae, produce slimy coats called biofilms, which also \u00a0 can be tricky for chlorine to penetrate.<\/p>\n However, UV is often highly effective at breaking down these defenses. By \u00a0 combining UV with chlorine, it\u2019s possible to cut through the organisms\u2019 \u00a0 protective layers and attack their vulnerable bodies and DNA \u2014 then oxidize \u00a0 and destroy the remaining organic contaminants. This \u201cone-two punch\u201d can keep \u00a0 even a large public pool free from infectious and otherwise annoying \u00a0 invaders.<\/p>\n It\u2019s also important to note than UV rays only attack organic matter in areas \u00a0 they can directly reach \u2014 so if corners of the pool are \u201cin shadow,\u201d so to \u00a0 speak, other disinfection methods will be necessary for keeping those areas \u00a0 clear of algae and bacterial growth.<\/p>\n To ensure that the UV lamp is as effective as possible, it pays to examine \u00a0 the shape of the pool carefully, and place the lamp in a location where its \u00a0 rays will reach as many surfaces as possible. Another alternative is to \u00a0 install an inline UV system, which bathes a closed chamber in UV light as \u00a0 water continually flows through it.<\/p>\n Finally, it\u2019s worth mentioning that UV won\u2019t have an effect against metal \u00a0 stains or phosphates \u2014 these issues will need to be treated with other \u00a0 chemical solutions, such as sequestrants and phosphate removers. However, if \u00a0 levels of these chemicals are kept within acceptable ranges, UV will prove a \u00a0 powerful ally against any unwanted microbes that try to move in.<\/p>\n The bottom line is, there\u2019s no end-all system for treating a pool \u2014 no \u00a0 perfect solution that kills every organism in the water, produces no \u00a0 disinfection byproducts, and operates in a way that\u2019s completely safe and green. \u00a0 Still, the highest priority is to keep swimmers free from infection and \u00a0 irritation \u2014 even if the best way to do that is different for every pool. A \u00a0 working understanding of how UV disinfection can fit into an overall \u00a0 sanitation scheme will inform much clearer decisions about how best to apply \u00a0 this technology.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Source: Ben Thomas- Pool and Spa News | 1.27.2012<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":" Ultraviolet radiation can cleanly and rapidly destroy many organic contaminants \u2014 but it\u2019s most useful when properly applied. Between \u00a0 the rising costs of electricity and growing consumer demand for \u201cgreen\u201d water \u00a0 treatment solutions, ultraviolet (UV) radiation is … Continue reading |