Validating, Controlling, and Operating New York City’s Cat-Del UV Facility

Last Modified: Nov 18, 2009


  • Steven Farabaugh, Matthew Valade, P.E. – Hazen and Sawyer
  • Gary R. Kroll, P.E. – CDM
  • Deborah E. Keesler, P.E. – New York City Department of Environmental Protection

New York City has completed final design and has initiated construction of a 2,020-mgd UV Disinfection Facility for its Catskill and Delaware water supplies. The UV facility will contain 56 LPHO UV units and is designed to provide up to 99.9-percent (3-log) inactivation of Cryptosporidium to meet current and possible future regulatory requirements for unfiltered water supplies.

This paper will present the details for how the facility was designed to ensure that all two billion gallons per day would be effectively disinfected including:

• The UV unit validation and protocol
• Instrumentation and control philosophy of the Cat-Del UV units
• Facility design and flow control
CFD modeling of Cat-Del UV units

The Cat-Del UV units are designed to deliver a dose of 40 mJ/cm2 at 40 mgd at a design UVT of 87 percent (5th percentile value of historical data) at end of lamp life conditions. Full-scale validation of test units and CFD modeling of the design was successfully conducted prior to the plant final design and the UV system supplier pre-selection. The UV units were validated under a full range of flow rates, water quality (i.e. UV transmittances), target doses, lamp configurations and power settings to define the envelope of operating conditions under which the UV unit meets the regulatory dose. The UV unit LCP will deliver the required regulated dose by operating individual banks of lamps based on the UV unit flow setpoint, UVT, and varying the lamp output (all banks of lamps in a UV unit always operate at the same output) from 60 to 100 percent based on the UVT and flow.

The UV facility is separated into 4 modules of 14 UV units. The flow through the UV Facility is controlled by sixteen 84-inch energy dissipation (ED) valves which are arranged so that 4 valves are dedicated to each UV module. The plant will provide controlled conveyance of UV treated water to both the Catskill and Delaware Aqueducts for delivery to its New York City consumers. The modules operate independently of each other but all units in a module operate at the same flow setpoint.

The dose algorithm (developed by the UV manufacturer based on the validation data) will be used to predict a theoretical maximum flow capacity for a UV unit which will set the maximum flow capacity for the units and the module. The plant control logic will determine each module’s flow setpoint and the N+1 strategy will determine the number of UV units online in a module. Each of the UV units has a 48-inch control butterfly valve, controlled by the UV unit control panel, which trims the flow through the units within a module to meet the UV unit flow setpoint. CFD and surge modeling of the system revealed that careful flow control measures were required to ensure the UV system could be safely and properly operated without endangering public health.

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

Hear about new publications with our email newsletter

We will never share your details with anyone else.


Newsletter Newsletter

Horizons Summer 2018 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

View previous issues »