SANDHILL WRF

Project Background & Challenges

As the county seat of Osceola County just south of Orlando, Kissimee is best known for its proximity to the many amusement and theme parks in the area including Universal Studios and Walt Disney World. Kissimmee, situated on the north shore of Lake Thohopekaliga, obtains water and wastewater serviced from the Sandhill Water Reclamation Facility (WRF) of Toho Water Authority. As the largest provider in Osceola County, Toho water serves upwards of 160,000 citizens in the greater Kissimmee metropolitan area.

The Sandhill WRF needed to be expanded due to the substantial population growth over the past couple of decades and due to anticipated growth in the coming years. Town officials worked with Carollo Engineering alongside construction manager Wharton-Smith  to determine that a 50% expansion was necessary – increasing from 6 MGD to 9 MGD. Upgrading the former AEROSTRIP flat panel aeration system to meet the new capacity, the treatment impact for the plant was targeted at removing 1.62 million KG/year BOD and 321,000 KG/year NH3.

How the Plant Worked

In an ongoing effort to minimize excessive nutrients in their effluent, the Sandhill WRF is designed to have four total basins, with seven different aerated zones with different diffuser densities. Each basin uses a four-stage Bardenpho process that required multiple tank zones operating with settings of AOAO – Anoxic, Aerobic/Oxygenated, Second Anoxic, and Small Reaeration/Oxygenation steps for nitrogen removal. Additional zones within the tanks were also designated as swing zones, to be used only when needed. Given the complexities of the existing operation, and the different diffuser densities depending on the basin, the seemingly simple upgrade to accomplish the new parameters of the WRF was actually going to be quite a challenge.

The EDI Solution

The Carollo Engineering team set out to determine the ideal solution and their design incorporated EDI FlexAir Pro MiniPanel Diffusers in an MP3 model as the primary technology to address the needs of the plant. The high-efficiency and high-density diffusers, supplied with EPDM (ethylene propylene diene monomer) micropore membranes, were chosen due to their easier maintenance, chemical resistance, and added UV protection ideal for municipal applications like Sandhill. Since some of the zones had mixers, creating high water velocity in the mixer zones, EDI also supplied diffuser end-supports and pipe support side-bracing, so the system could withstand the higher turbulence. In-basin piping was made of Schedule 80 PVC and mounted with Type 316 stainless steel, for added corrosion-resistance and durability. In total, 1,068 units of MP3 diffuser arms were supplied for the basin upgrade.

Site Construction

In order to keep the water reclamation facility online during the renovation process, Wharton-Smith worked with the team at Sandhill to schedule the work in stages. The plan was to essentially take one tank offline at a time which is not an easy feat, especially while also maintaining compliance with local effluent regulations. The first basin was completed in May 2022, with the next basin (Basin 3) completed in July 2023. The third basin, Basin 2, reached its completion in August 2023 while Basin 4 was not part of the upgrade project, so there weren’t significant changes made there at this time. Some diffuser locations had to be removed due to pillars in the tank, but it was determined that the system had enough aeration capacity to make up for this reduction.

Upgraded System Performance

Ever since the upgrade was completed in August 2023, all systems have been running smoothly, and the Sandhill WRF continues to minimize nutrients in their effluent. It is efficient facilities like Sandhill, and providers like Toho Water, that help to address nutrient pollution in our communities, reducing nitrogen and phosphorus in our waterways and water supply.

Quote from Shane Howard, the Chief Operator at Toho Water’s Sandhill WRF:

“We are really pleased with the efforts of the EDI team, pulling together a solution for our expansion,” says Shane Howard, Chief Operator at Sandhill WRF. “We were able to maintain operations during the entire process, which was critical. And with the upgrades now complete, we are meeting our discharge requirements and minimizing the amount of nutrients in our effluent. They did a terrific job.”