By Thomas M. Hargy

Alert: An international organization is making a concerted effort to expose the U.S. public to ultraviolet light.

In fact, the International Ultraviolet Association (IUVA) has initiated a series of ultraviolet (UV) disinfection one-day regional workshops to further education on the benefits of UV use in water treatment and other applications. The purpose of the workshops is to give water treatment personnel, regulators, engineers, and the interested public, an opportunity to hear experts in the field of UV disinfection present the latest information on the technology.

The first of these workshops—for the Northeast/Mid-Atlantic region—was held June 4, 2002, and co-sponsored by IUVA, the New York State Energy Research and Development Authority, the New York State Department of Health, and the host facility—the State University of New York at Albany.

Attacking protozoa
A complete overview of UV technology was provided, including fundamentals of the physics of UV and by what mechanism it’s capable of disinfecting microorganisms. Dose requirements for various waterborne pathogens were presented, indicating bacteria cells and protozoa (Cryptosporidium, Giardia and Microsporidia) are quite sensitive to UV. The referenced research found these microorganisms could be inactivated by 4 log (99.99 percent) following exposure to 5 to 20 milliJoules per square centimeter (mJ/cm2), while bacteria spores and viruses would require 30 to over 100 mJ/cm2 for that same level of disinfection. The most UV-resistant waterborne microorganism appears to be the enteric virus, Adenovirus, which has been found to require over 150 mJ/cm2 for 4-log inactivation.

Various types of UV lamps and reactors were compared, and plant engineering and design considerations discussed. The value of gathering extensive water quality data, especially on UV transmittance—well ahead of any planned installation—was emphasized. As water quality to be treated is the major influence on design costs, locating UV reactors downstream of filtration in a water treatment system was highly recommended.

Choosing an alternative
Monitoring the performance of UV systems entails procedures unique among disinfection technologies. Because UV disinfection offers no residual, alternatives to direct sampling must be used for treatment monitoring and dose verification. Reactor validation by biodosimetry (bioassay) was explained as a process where the dose response of non-pathogenic organisms, such as Bacillus subtilis spores or coliphage MS2, is determined in a precisely controlled laboratory setting. Subsequently, a stock of these organisms is injected over a period of time into an operating UV reactor, and inlet and outlet samples are collected and analyzed. The inactivation achieved in the reactor is compared against that from the laboratory-generated dose response curve, and the delivered dose can then be inferred.

A review of the status of UV relative to current and upcoming regulations noted that the U.S. Environmental Protection Agency (USEPA) has recognized UV as a compliance technology for disinfection of viruses under the upcoming Ground Water Rule (GWR), the final proposal for which is expected in March 2003 in advance of a statutory deadline of July 2003 (for details on UV and the GWR, see pp. 30235, 30237&30239: www.epa.gov/fedrgstr/EPA-WATER/2000/May/Day-10/w10763.htm). In addition, UV is considered a critical tool for disinfection of Cryptosporidium while minimizing disinfection by-products—two goals of the proposed Long Term 2 Enhanced Surface Water Treatment Rule, which is slated for promulgation late next year. A draft UV guidance manual to assist with implementation is being prepared. The present, pre-proposal draft rules are now available on the Internet (at www.epa.gov/safewater/lt2/st2eswtr.html) and the next draft rules and draft guidance are scheduled to be available in December, a year ahead of the final promulgation. Presently, statistical treatments of existing UV Cryptosporidium disinfection data suggest that a dose of roughly 18 mJ/cm2 provides a 90 percent probability of 3-log inactivation of the protozoan pathogen. Total costs (including annual operating costs and amortized capital costs over a 20-year period) of UV disinfection designed to provide over twice that dose were projected to be one-third to one-tenth of those for only 1- or 2-log Cryptosporidium inactivation by ozone. This cost advantage was greatest for systems treating less than 1 million gallons per day (mgd).

Q&A session
In the first of two panel discussions, attendees (regulators, public health officials, utility managers and operators, engineers, manufacturers’ representatives and academic personnel) had the opportunity to question federal and state officials on how UV will be regulated as it becomes incorporated into more and more drinking water treatment systems.

A second panel was composed of engineers, consultants and utility representatives currently involved in bringing UV on-line at water treatment plants in the Northeast. The range of these experiences extended from smaller utilities of 20 mgd or less to systems as large as New York City’s proposed UV disinfection plant, which may incorporate over 60 reactors. Each reactor would be capable of handling 40 mgd for an overall capacity in excess of 2 billion gallons per day on the unfiltered water supply. Questions to this panel focused on how UV would fit into the various site-specific conditions. Interest in a national or regional UV testing facility was expressed. Such a center would facilitate reactor validation, allowing the testing to be undertaken prior to actual installation at a given utility.

Conclusion
Future IUVA regional workshops are being planned. The Southeast workshop will be held Sept. 6, 2002, at the University of South Florida. Conferences in the Southwest, Midwest and Ontario, Canada, are also being planned. For details on these workshops and others as they become available, click on “Upcoming Meetings” on the IUVA website—www.iuva.org

About the author
Tom Hargy is senior scientist at Clancy Environmental Consultants of St. Albans, Vt., which provides analytical and research and development services to the drinking water, wastewater and high purity water industries. A member of the International Ultraviolet Association and American Water Works Association, he’s also on the WC&P Technical Review Committee. Hargy can be reached at (802) 527-2460, (802) 524-3909 (fax) or email: thargy@clancyenv.com

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