Hybrid filters in STAs could increase phosphorus reduction in water from Kissimmee River

Posted 5/31/21

OKEECHOBEE COUNTY -- Thousands of acres of stormwater treatment areas (STAs) combined with a new technology could help remove phosphorus from Kissimmee River water

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Hybrid filters in STAs could increase phosphorus reduction in water from Kissimmee River

Posted


OKEECHOBEE COUNTY -- Thousands of acres of stormwater treatment areas (STAs) combined with a new technology could help remove phosphorus from Kissimmee River water before it reaches Lake Okeechobee.

At their May 13 meeting, the South Florida Water Management District Governing Board, agreed to move forward with negotiations on a contract with Ecosystem Investment Partners (EIP) on a project to be built on two Okeechobee County ranches adjacent to the Kissimmee River.

The area in green is Rio Rancho. The area in purple is Fernandez Family Trust property
The area in green is Rio Rancho. The area in purple is Fernandez Family Trust property

EIP acquired the properties from Rio Rancho Corporation and Fernandez Family Trust.

Jennifer Reynolds, South Florida Water Management District (SFWMD) Ecosystem Restoration and Capital Projects Division Director, said the cost of the project would not exceed $300 million.

EIP has proposed a Hybrid STA which includes approximately 3,100 acres of traditional STA cells as well as 10 acres of Phosphorous Elimination System (PES), explained EIP Senior Program Manager Kyle Graham.

PES is used in the project to remove nutrients from Doctors Lake
PES is used in the project to remove nutrients from Doctors Lake

PES is a relatively new technology that is currently being utilized by the St. Johns River Water Management District in their Doctors Lake Phosphorus Removal Pilot Project at Clay County Utility Authority’s Fleming Island Regional Wastewater Plant, he continued. At Doctors Lake, PES is being used to remove nutrients from wastewater.

“PES is vegetated high rate vertical filter that adsorbs phosphorus,” explained Graham. The PES will be built into a series of cells which allows a portion of the system to remain in operation while a cell is being refurbished. Over time, like any filter, the rate of phosphorus removal will decrease, and the PES will be removed and replaced. The exhausted media will be organic rich and contain plenty of plant-available phosphorus. This material can be incorporated into a top soil mix for gardening, used as agriculture soil amendment or a grass surface top course – thus displacing in part the need for traditional phosphorus fertilizer application, he added.

“There are many applications to beneficially reusing this product,” he pointed out.

“Similar to existing STAs we anticipate the vegetation within the STA cells will be comprised of a combination of emergent aquatic vegetation as well as submerged aquatic vegetation – cattail, hydrilla, southern naiad, chara, bullrush, fire flag,” stated Graham.

“We intend to rely on 20 years of knowledge from STA operations as well as extensive plant and soil monitoring to adaptively manage the operations to increase the longevity of each of the planned STA cells. During the design process, we will develop an operations and maintenance plan which will include activities needed to maximize the effectiveness of the facility.”

A small portion of the property includes historic wetland areas, he added. A determination of the quantity of existing wetlands will be performed early in the design process.

The ranchland, totaling 3,350 acres, is currently being used for cattle grazing. If EIP is successful in negotiating a contract with the SFWMD to construct the project, they will develop a plan to transition the property and prepare for construction.

“The final layout will be determined during the design process. To maximize Phosphorous reduction and allow for operation flexibility we anticipate at least 4 STA cells,” said Graham.

It has not yet been determined if a primarily water storage component will be included in the project or if the water storage will only occur within the STA cells. The layout of the facility will be determined early in the design process for the facility.

Soil analysis and preliminary geotechnical evaluation of the site have been performed. Significant additional geotechnical evaluation will be performed to inform the design of the facility, he added.

While the information discussed at the SFWMD meeting indicated the project will reduce phosphorus in the water by 13-15 metric tons per year, Graham said if the site is configured to maximize phosphorous reduction, preliminary modeling indicates the site could reduce phosphorus by approximately 26 metric tons per year.

“There are many opportunities to increase the efficacy of the project without expanding the proposed project,” he added. The anticipated phosphorous reduction will be dependent on the chosen configuration of the project, number of STA cells, size of water attenuation feature and inclusion of hybrid technology.

The project will also help remove nitrogen from the water. Additional modeling needs to be performed to quantify benefits, Grahman stated.

According to Grahman, EIP will continue to pay property taxes as assessed. The contract is expected to include the option to transfer the successfully constructed facility to the SFWMD after five years of operations.

“EIP started to engage in the water quality space as a result of Governor DeSantis’s executive prioritizing and commitment of funding to the Everglades and state water quality,” explained Graham. “We first submitted this project concept to the Florida Department of Environmental Protection and then to SFWMD in late 2019 and early 2020 when they released RFI’s for the Lake Okeechobee Basin Managment Action Plan update and the Northern Everglades and Estuaries Protection Program.

“As follow up to those submittals we have had informal conversations with DEP and SWFMD staff regarding the project,” he continued.

“All of the preliminary site analysis, site configuration, nutrient modeling has been performed solely by EIP. We anticipate there will be modifications to our assumptions and therefore configuration and operation of the facility once we begin working with the district in the design process.”

The average annual phosphorus load from lower Kissimmee Basin is 94.3 metric tons of phosphorus, based on 2005-2018 data.

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