Ultraviolet Radiation Yields Promising Results
Further Research Necessary to Address Unanswered Questions

In order to provide an additional level of protection against Cryptosporidium, many water utilities across the nation are taking a look at ultraviolet radiation (UV). Many experts consider a multi-barrier approach involving UV radiation as a leading choice for combating treatment-resistant Cryptosporidium. UV penetrates the pathogen’s outer cellular membrane, passes through the cell body and reaches the DNA to alter genetic material. It does not kill pathogens; rather, it sterilizes the invading organisms with "germicidal wavelengths" of similar strength to those found in fluorescent light.

UV in Water Disinfection

Although the technology has been used for 75 years in Europe, UV drinking water treatment is relatively new in the United States. UV can successfully sterilize smaller quantities of water and, as such, is being used in 50 systems in this country (the largest serving 30,000 residents in Fort Benton, Montana). During the next three years, UV disinfection will be tested in larger systems such as Atlanta, Salt Lake City, Austin, Phoenix and St. Louis.

Efficiency Vs. Effectiveness

Perhaps the most important benefit of UV treatment is its ability to deactivate Cryptosporidium by penetrating its cellular membrane and sterilizing the pathogen. In addition, the EPA’s "Guidance Manual on Alternative Disinfectants and Oxidants" states that UV radiation quickly dissipates into water to be absorbed or reflected off material within the water. As a result, no residual is produced, giving the water a chemical-free taste and odor. This lack of a residual has its pluses and minuses. It is attractive because disinfection byproducts do not form; however, a secondary chemical disinfectant remains necessary to maintain residual protection against recontamination and regrowth of bacteria throughout the distribution system.

Once water leaves the facility, it can become contaminated by corroded and broken pipes. The country’s largest water distributors average 500 breaks a year, which can lead to recontamination of the water. Thus, a residual disinfectant is required to protect water from the treatment plant to the tap. For these reasons, UV should be used with chlorine or chloramines as a disinfectant in the distribution system.

There are many variables of UV strength, which can alter its effectiveness. Water composition is the most important because murky, dirty water blocks the UV rays and diminishes their strength. Other variables include water color and regular maintenance.

According to the EPA, sufficient dosages of UV can disinfect water to the degree required. Yet, the EPA recognizes that the doses needed to inactivate the many microorganisms found in water may not yet be adequately defined. Systems may need to be designed to inactivate the most resistant known organisms (e.g., Adenoviruses are currently the most resistant to UV inactivation). While UV can effectively disable harmful elements in water, its efficiency, especially regarding larger systems, is not known.

The Future of UV

UV disinfection has many assets but many questions remain that can only be answered through additional research. James P. Malley, president of the International UV Association and an environmental engineering professor at the University of New Hampshire, notes, "It would be a mistake for the water industry to widely apply UV for the treatment of surface waters for Giardia and Cryptosporidium inactivation until several key research issues are resolved." These issues include: verification of UV’s ability to inactive Cryptosporidium, the efficacy of removal/inactivation of Giardia lamblia cysts, the long-term performance of sensors, the best placement of UV technologies in a system, the type of UV dosage needed and the cleaning techniques and frequencies required.

For more information on ultraviolet radiation, visit the EPA’s website at http://www.epa.gov/ogwdw000/mdbp/pdf/alter/chapt_8.pdf. Adobe Acrobat Reader is required to read this file. Click here to download Reader for free.