The City of Clearwater, Florida, is investigating the feasibility of replenishing the brackish water interval of the Floridan aquifer system with purified water, creating an indirect potable reuse system. The City selected Tetra Tech to provide professional engineering services to assist in determining the technical and financial viability of using the multi-barrier, full advanced treatment processes for purification of reclaimed water at a capacity of three million gallons per day. The anticipated benefits include increased sustainability of existing water resources through protecting them from saltwater intrusion from the Gulf of Mexico and Tampa Bay.

The purification treatment process included ultrafiltration, reverse osmosis, and advanced oxidation. This process was followed by groundwater conditioning steps consisting of membrane contactors and post-treatment stabilization. Tetra Tech added dissolved oxygen removal to the multi-barrier processes to minimize any potential to dissolve naturally-occurring arsenic minerals in the receiving aquifer. With Tetra Tech’s assistance, the City of Clearwater was the first in Florida to demonstrate post-treatment stabilization for potable reuse. Effective post-treatment processing to condition the purified water for injection to the groundwater aquifer is critical for keeping purified water pure and to successful implementing indirect potable reuse in Florida.

Tetra Tech assisted the City of Clearwater with the operation of a full advanced treatment process pilot system to purify the reclaimed water. The initial year-long phase of pilot testing, which concluded in June 2014, is the longest pilot demonstration of this purification process by a Florida utility. Tetra Tech and the City obtained valuable operating experience and insights into the design and operation of purification and post-treatment processes. Tetra Tech’s services included data collection; review of system operations; troubleshooting; recommendations for operational adjustments and membrane cleanings; water quality sampling and monitoring; emerging constituent challenge testing; and support of the City’s public education and information program.

The City of Clearwater maintains continual coordination with regulatory agencies on policies and rule compliance. The data collected from the pilot operations has demonstrated that a combination of power treatment technologies and cutting-edge solutions in post-treatment can provide sustainable water supplies for the city’s future.

Among seven recent Florida potable reuse pilot studies, the City of Clearwater’s program was the most comprehensive water quality sampling program and most extensive microconstituent challenge study. It is the only potable reuse pilot-scale chemical post-treatment project and the only pilot to demonstrate membrane contactors, essential for removing dissolved oxygen and halting arsenic release.

Highlights

  • Tetra Tech won Best Paper Presentation at the AMTA/AWWA 2015 Membrane Technology Conference for “Groundwater Replenishment Performance and Operations: Lessons Learned During Clearwater’s One-Year Pilot.”
  • Tetra Tech won Best Paper Presentation at the Florida Section AWWA 2014 Annual Conference for “Groundwater Replenishment Performance and Operations: Lessons Learned During Clearwater’s One-Year Pilot.”