Ultraviolet Disinfection Worksheet

A NATIONAL DRINKING WATER CLEARINGHOUSE FACT SHEET

Ultraviolet Disinfection
Summary
Using ultraviolet (UV) light for drinking water disinfection dates back to 1916 in the U.S. Over the years, UV costs have declined as researchers develop and use new UV methods to disinfect water and wastewater. Currently, several states have developed regulations that allow systems to disinfect their drinking water supplies with UV light. Running a UV light system requires a basic level of operator skill and relatively clean source water. On the down side, however, UV offers no residual disinfection within the distribution system.

What is UV disinfection? UV light, which continues to be a reliable means of disinfection, involves exposing contaminated
UV achieves 1-log reduction of Giardia lamblia at an intensity of 80-120 mWs/cm2, and 4-log reduction of viruses at an intensity of 90-140 mWs/cm2. Only recently has the scientific community begun to accept UV as a highly effective tool for Cryptosporidium control. UV light disinfection does not form any significant disinfection byproducts, nor does it cause any significant increase in assimilable organic carbon (AOC). Research has confirmed that UV effectiveness is relatively insensitive to temperature and pH differences. In addition, researchers found that UV application does not convert nitrates to nitrites, or bromide to bromines or bromates. Recent pilot studies show that UV-treated drinking water inhibits bacterial growth and replication in the distribution system; however, conditions within distribution systems, such as leaks, still require additional residual disinfection (e.g., free chlorine). The advantages of using UV, rather than chemical disinfection, include: • Has no known toxic or significant nontoxic byproducts; • Has no danger of overdosing; • Removes some organic contaminants; • Has no volatile organic compound (VOC) emissions or toxic air emissions; • Has no onsite smell and no smell in the final water product; • Requires very little contact time (seconds versus minutes for chemical disinfection); • Does not require storage of hazardous material; • Requires minimal space for equipment and
“Tech Briefs’’ drinking water treatment fact sheets have been a regular feature in the National Drinking Water Clearinghouse (NDWC) newsletter On Tap for more than four years. NDWC Technical Assistance Specialist Mohamed Lahlou, Ph.D., researches, compiles, and writes these very popular items. A package of the Tech Briefs is now available as a product. A three ring binder holds all the current Tech Briefs in print. New selections can be easily added to the package as they become available. To order this product, call the NDWC at the numbers listed below and ask for item #DWPKPE71. The item is free.

To order, call the NDWC at [phone] or [phone]. You also may order online at [e-mail] or download fact sheets from our Web site at www.ndwc.wvu.edu.
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(Additional copies of fact sheets are free; however, postal charges may be added.) For further information, to comment on this fact sheet, or to suggest topics, call Dr. Lahlou at one of the above numbers or contact him via e-mail at [e-mail].

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FIFTEEN• SEPTEMBER