Approach for Achieving Sustainable Operation of the 2-bgd Catskill-Delaware UV Disinfection Facility

Last Modified: Nov 18, 2009


  • Matthew T. Valade, P.E., Steven Farabaugh– Hazen and Sawyer
  • Paul D. Smith, P.E. – New York City Department of Environmental Protection
  • Gary Kroll, P.E. – CDM

Recent advances in testing methods are being applied to the validation of NYC’s Catskill-Delaware UV equipment. These advanced methods will allow the full scale facility to operate in a more sustainable manner with up to 60% reduction in operating power requirements (and corresponding reduction in CO2 emissions) and savings over $1 million annually.

The design of the Catskill-Delaware UV disinfection facility has been on-going since 2001 and has been conducted concurrent with the development of the LT2ESWTR. The intent of the LT2 Rule is to ensure protection of public health, particularly regarding infection by Cryptosporidium. NYCDEP has specifically undertaken the design and construction of the Cat-Del UV facility in order to meet the requirements of LT2. Because the design and LT2 rule development were performed concurrently, relatively conservative design criteria were required in order to ensure the UV disinfection facility would meet the requirements of the anticipated rule. Specifically, these design criteria are the dose and capacity of the UV reactor, both of which directly affect the size of the UV units and therefore the footprint of the UV disinfection facility.

Until recently, the industry standard in the United States for establishing disinfection effectiveness through validation testing of a UV reactor was through using a surrogate microbe of MS-2. Other countries have used various other surrogates, although it was felt that MS-2 was the easiest and best surrogate to use to conservatively estimate disinfection effectiveness for larger capacity UV units. Only recently (i.e. post-2005) have other, more efficient surrogates (i.e. reduce the RED bias) been identified and used for validating UV equipment in the US. Prior to the final draft of the Guidance Manual being published, requirements for an RED close to 40 mJ/cm2 were expected to be required to achieve 3-log inactivation of Cryptosporidium. Therefore, 40 mJ/cm2 was used as the design basis for the Catskill-Delaware UV facility design. However, final revisions of the Guidance Manual were made in 2006 changing how the RED bias was determined and allowing for validation with surrogates, such as Q-beta, that could significantly reduce the RED bias of a UV unit. More recently, advances in the application of non-biological surrogates such as dyed microspheres (DMS) which provided a greater understanding of the treatment characteristics of a reactor have been made.

NYCDEP is currently conducting additional validation testing with DMS and other surrogates that will allow for increased certainty of the applied dose, while reducing the power required to achieve proper disinfection by over 2,400 kW-hrs per day – enough energy to power over 1,000 homes. This paper will present the approach NYC is taking to ensure a sustainable operation of the Cat-Del facility and results of the validation testing. Recommendations will be made to help other utilities considering UV treatment design and operate in the most efficient way possible.

For a copy of the full paper, please contact the author at

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