Bidding, Testing, and Start-Up of a Reuse UV Disinfection System in Florida

Authors:

  • Josefin M. Edeback and Melanie Mann, Hazen and Sawyer

This paper presents a case study of an ultraviolet (UV) disinfection system for reuse at the Falkenburg Advanced Wastewater Treatment Plant (AWTP) in Hillsborough County (County), Florida. The bidding approach, on-site fouling study results, development of a UV Operating Protocol required by the Florida Department of Environmental Protection (FDEP), and performance testing results are summarized. The Falkenburg AWTP is designed to achieve both high level disinfection and biological nutrient removal (BNR). The plant is permitted to discharge treated effluent to two disposal systems: a surface water discharge system and a public access reuse system. The Falkenburg AWTP expansion will be completed in January 2009 and will increase the plant’s capacity from 9.0 MGD to 12.0 MGD annual average daily flow (AADF). The plant expansion includes replacing the existing gaseous chlorine disinfection system with a UV disinfection system, as part of a County-wide effort to convert all wastewater disinfection systems to UV disinfection.

The construction bid documents included plans and specifications for two horizontal UV systems and one vertical UV system, one of which would be installed in an existing chlorine contact basin. The UV system was required to provide a validated UV dose of 100 mJ/cm2 at the maximum day flow of 16.7 mgd with one channel out of service. The lowest responsible bid was based on the Trojan 3000 Plus low pressure, high output (LPHO) system, and this system was installed.

Bid documentation included submitting the lamp fouling factor and the number of UV lamps required based on that fouling factor. The Trojan scope was based on a fouling factor of 0.95. The County required the UV manufacturer to provide a pilot unit for a six month test to determine a site-specific fouling factor. The sleeve transmittance data from this testing is summarized in Table 1, and shows the fouling factor was 0.984 after 180 days of testing. The number of lamps provided for the project was not reduced as a result of the on-site fouling test. If the site-specific fouling factor had been less than that used by the manufacturer in the bid, additional lamps would have been required.

FDEP required the County to submit a revised operating protocol for the new reuse UV disinfection system prior to placing the system in service. The UV protocol includes general operating information including operator protocol for a reject response and was submitted to and accepted by FDEP. The Falkenburg UV operating protocol will be a guide for other plants owned by the County when they convert to UV disinfection.

The thirty-day performance testing performed included measurements of head loss and power consumption, and intensive water quality testing of UV influent and effluent. FDEP required the testing to be restarted because of one instance when the system provided an operational dose less than 100 mJ/cm2. The system control program was adjusted to use a target operational UV dose of 104 mJ/cm2 instead of 100 mJ/cm2. Final performance test results will be complete in December 2008.

For a copy of the full paper, please contact the author at mmann@hazenandsawyer.com

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