AWWA ACE59869

AWWA ACE59869 Low Pressure over Medium Pressure - The New York City UV Decision
Conference Proceeding by American Water Works Association, 06/17/2004

Fahey, Richard J.; Valade, Matthew T.; Kroll, Gary R.; Potorti, Donna; Kessler, Deborah E.; Borsykowsky, Michael

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The Catskill and Delaware watersheds supply New York City with up to 90% of its daily waterdemand of 1.2 billion gallons of water. Due to the high raw water quality of these unfiltered suppliesand an extensive watershed protection program, the New York City Department of EnvironmentalProtection (NYCDEP) has been granted a Filtration Avoidance Determination (FAD) by the US Environmental Protection Agency (USEPA). Aspart of the FAD, NYCDEP must proceed with the design and installation of ultraviolet (UV) disinfectionfacilities. The purpose of this paper is to review the selection of a lamp technology for the UVfacility and discuss the unique series of challenges that had to be addressed in the process.The design of a UV disinfection facility for New York City's Catskill and Delaware supplies posesseveral unique design challenges due to the scale of the facility (2,020 mgd), the properties of theunfiltered surface water sources, gravity flow system, and the relative infancy of UV technology inthe U.S. drinking water industry, as regulations continue to evolve. A major challenge has been toidentify manufacturers capable of producing a UV system with a unit capacity of 40 mgd, a size thathas never been built before.During the development of the UV facility design concept, both low pressure high output (LPHO)and medium pressure (MP) systems were evaluated and deemed feasible for providing thedisinfection level needed to meet the anticipated regulations for inactivation of Cryptosporidium.Considerable research and evaluation was conducted on the relative merits and drawbacks of the twosystems, including a series of meetings with potential manufacturers, canvassing of other users, andsite visits to large operating facilities. While no 40-mgd UV unit has ever been constructed, unitscapable of treating about 20 mgd for microbial inactivation are now in service.The paper details the primary features of LPHO and MP systems, outlines their primary advantagesand disadvantages, and presents how New York City arrived at the decision to proceed with the LPHOlamp technology for its Catskill/Delaware UV disinfection facility. Includes tables, figures.