tech update Industrial UV he use of (UV) has become standard practice in most industrial processes. T If the water is used as a product or as part of the process, spoilage organisms cause nuisance and potential harm to people or stock, and a product recall can lead to lasting damage to market reputation.

By Jon McClean UV light was first discovered in 1801. It took more than The use of UV is now extended to the dechlorina- 100 years to develop lamps and power supplies to allow the tion and dechloramination of water, as well as selectively application of the technology on an industrial scale when removing a wide variety of endocrine disrupting chemi- a drinking water plant treating 0.2 mgd of potable water cal compounds, pesticides and other contaminants such briefly used UV light in Marseilles, France, in 1910. as N-Nitrosodimethylamine. The general application of chlorine to drinking water after World War I led to UV only being used in a munici- How does it Work? pal application where chlorine could not be used. UV light is a nonintrusive method of ensuring that UV light was routinely used to address vitamin defi- organisms in water, wastewater and other process flu- ciencies caused by poor diets during the war years in ids are rendered inert. Light at 260 nm has the ability to Europe, and in 1937 the directors cause permanent damage to the DNA contained in all of Sherwood Colliery, Mansfield, living species. The damage to the DNA occurs in a few England, installed a “Light Corridor” picoseconds and is permanent at a UV dose of 40 mJcm-2, that miners walked down after show- which is a usual UV dose. ering and before dressing, as a means No organisms can demonstrate any immunity to of providing artificial to UV; however, a number of organisms such as Listeria those working underground to over- Monocytogenes, Cryptosporidium Parvuum and Giardia come vitamin deficiencies. are now chlorine immune, with others demonstrating UV light was successfully used for increased tolerance. The incidence of organisms such as medical and therapeutic applications methicillin-resistant staphylococcus aureus becoming toler- from the 1940s until the mid 1980s, ant to antibiotics is well documented. when clinical drugs became widely UV does not alter the pH, color, taste, odor or the available and were able to address root physical property of water. While this is one of its main causes rather than merely dealing with benefits, it can also be a crucial drawback. UV offers no a symptom. residual protection, and the fluid can be subsequently Industrially, the use of UV light reinfected if the plant design or housekeeping is poor. developed as a number of process Pipe dead legs, biofilm and other process barriers users of water, such as breweries and such as GAC contactors or submicron filters can all be pharmaceutical plants, adopted UV as microbial breeding grounds. The technology should a means of extending submicron filter be part of a multibarrier approach, and plant operators runs or preventing spoilage. should periodically sanitize with steam or a chemical In many industries, UV was the only clean-in-place regime. available means of ensuring the water The UV light is created by a low-pressure, high-output was free from harmful organisms, such lamp, or by a medium-pressure lamp. The low-pressure, as fish farms, crab grow-outs or shellfish high-output lamps use an amalgam of mercury to produce depuration. Early UV systems lacked a single (monochromatic) line output at 254 nm. These meaningful UV monitors, optical foul- lamps operate independently of fluid temperature, and ing was not easy to remove and high their main advantage is the electrical efficiency, which can prices meant the technology did not be up to 40%. Medium-pressure lamps are used where gain widespread acceptance until the 1970s. footprint is more important than electrical efficiency. One of the newer applications for UV light By 2000, a number of key drivers had led to the tech- These types of lamps are 12% to 15% efficient, and the is the dechlorination of potable or reuse nology being readily incorporated into most process users’ large amount of heat () energy emitted causes sig- water that is increasingly being supplied as water treatment facilities. The main drivers were the flight nificant fouling issues. a lower cost alternative to potable water. from chemical-based regimes, pressure to extend shelf The large amount of visible light also emitted does cause life, increasing immunity to conventional disinfectants by algal growth, which can be an issue when using UV to emerging pathogens and increased chlorine intolerance of dechlorinate reuse water. The medium-pressure lamps are many membranes. polychromatic, and produce a continuous spectral output The use of UV today has been extended to disin- from 190 nm to the long- visible light and infra- fect brines, marinades and fruit juices, and increasingly red parts of the spectrum. expensive water has led many users to reuse and reclaim Electronic ballasts are used to continuously vary the their discharges or to partner with a local municipal lamp output, compensate for lamp aging and ensure that a water provider and accept municipal reuse for industrial uniform UV dose is delivered to the fluid. and other nonpotable applications. Wipers are used to keep the optical path free from

22 WATER QUALITY PRODUCTS

222_TechUpDate_UV_0708.indd2_TechUpDate_UV_0708.indd 2222 66/18/08/18/08 110:24:440:24:44 AMAM fouling. Iron and calcium will foul the quartz sleeves, and play an important role, often when used in conjunction often these mechanical wiping systems need chemical assis- with a catalyst or accelerant. tance to clean the quartz. A UV monitor camera is used to continuously measure the amount of UV light being emit- Some Drawbacks ted from the lamp and through the quartz sleeve. When used to dechlorinate poor transmittance reuse water, UV light can cause algal growth inside pipelines. This New Applications is caused by the system geometry permitting long-wavelength One of the newer applications for UV light is the dechlo- light to travel extended distances. As the penetration depth rination of potable or reuse water that is increasingly being increases, all of the germicidal light will be absorbed by the supplied as a lower cost alternative to potable water. The fluid, leaving visible light that stimulates algal growth. This New applications local municipal water provider will usually add chlorine or problem can be overcome by modifying the chamber geom- chloramines to ensure the reuse water remains free from etry to prevent the passage of long wavelength visible light or for UV in industrial pathogens. Chemical dechlorination regimes often lead to by treating the immediate connecting pipe walls. fouling of RO membranes and have fallen out of favor. The algae growth can become so profound that large water treatment UV light is able to render organisms nonviable by break- clumps break off and can actually break the quartz sleeves. ing bonds in their DNA so selective are able This problem can be overcome, but illustrates the selection of to cleave the bonds in the chlorine and chloramine spe- a qualified vendor and a degree of application understanding. cies. This type of photolysis also delivers a high disinfection dose, which is a secondary benefit. The Future The use of UV in swimming pools is well documented Water will continue to be used in a very wide variety and standard practice, with hundreds of pools in the U.S., of industrial processes, and as it becomes more expensive, LearnMore! For more information Europe and Asia now using UV systems. industrial users will be encouraged to reuse their waste. related to this article, visit the web at A dose of 90 mJcm-2 is normally required to sufficiently The flight from chemical regimes will continue—driven www.wqpmag.com/lm.cfm/wq070809 reduce the combined chlorine (chloramine) load, and it by costs and risks (both terrorist attacks and disinfection also ensures high removal of any waterborne organisms. As byproducts)—so UV will continue to gain popularity. For more information on this subject, with chloramines, the mechanisms for the removal of chlo- Energy will become a far more urgent issue, and energy- write in 1019 on the reader service card. rine depend on a number of factors such as water pH, water efficient designs and lamps will gain favor over less efficient chemistry and the level of removal required. technologies. wqp UV has been successfully used to remove ozone from ultrapure water systems for many years, and as new Jon McClean was president of Aquionics, Inc. McClean can contaminants such as Urea emerge, the technology will be reached by e-mail at [email protected].

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