In 2012, the Florida Department of Environmental Protection requested that Bonita Springs work to reduce the total maximum daily load of nitrogen in its waterways to .74mg/L under what is referred to as the “Everglades West Coast Basin Management Action Plan”. This tasked the city of Bonita Springs to reduce the amount of nitrogen along the Imperial River to more closely reflect those of pre-development and agriculture levels. The FDEP has projected a target reduction amount of 60,000lbs by the year 2027, of which Bonita Springs is required to remove 9303lbs. The city has already successfully removed around 3301lbs of nitrogen from the waterways through various removal methods and has been developing a sustainable long-term solution for the remaining 6000lbs of nitrogen.
Under the guidance of city council, construction began on phase 1 of its bioreactor project located in downtown Bonita Springs. The goal for phase one of this project was to capture nitrogen removal ratings data as a baseline for FDEP to review and approve a removal efficiency rating for the bioreactor systems to facilitate the achievement of clean water statewide.
What is a Bioreactor?
Bioreactors use an anaerobic (oxygen-starved) environment to leverage naturally occurring denitrification bacteria to remove nitrogen in the water. They work by running water through pipes into basins filled with carbon-based filtering materials (ie: wood chips) that are used to collect the nitrogen and expel a more natural quality of water into local waterways. The woodchips act as a carbon source for anaerobic bacteria to colonize. The bacteria, in turn, strip nitrogen entrained in the stormwater runoff and convert it into nitrogen gas. This technology is proving to be highly effective at nitrogen removal, while at the same time being very cost-effective. Over the last 20 years state and local governments across the United States have experimented with bioreactors as a cost-effective way to naturally denitrify bodies of water that contain excessive nitrogen pollution and restore the quality of water.
The Big Ideas
The bioreactor property serves dual purposes. To remove nitrogen and as a space that is a heavily used parking area with 101 parking stalls available. Over sixty special events are held in downtown Bonita at Riverside Park each year. Among them, the city hosts events like July 4th and Holiday in the Park and event patrons use this lot for easy access to the events.
The Felts Avenue Bio-Reactor Project utilizes a bio-retention process for nitrogen removal from stormwater runoff. The bio-reactor concept is a low-impact development technique that requires very little “above ground” disturbance. It involves constructing sub-surface retention beds of woodchips, or burying pipes filled with woodchips, to create an anaerobic (oxygen-starved) nitrogen removing environment.
In addition, its underground footprint allows for above-ground use of the landscape that is not necessarily stormwater treatment-related. The Felts Avenue project capitalizes on this key feature by incorporating an at-grade 101-stall parking facility above the bioreactor's water treatment cells. If the project had utilized a traditional dry retention pond to treat the incoming stormwater, the area that would have been available for parking would have only yielded 28 spaces, as opposed to the 101.
Bonita Springs Results
Professional Geologist Greg Rawls recently reported that phase 1 of the City of Bonita Springs bioreactor project had been able to effectively remove between 77- 98% of nitrate, a key species of nitrogen closely associated with manmade fertilizer, from the water filtered through the system. “I think what we’ve created, is what’s going to be considered the new gold standard for nitrogen removal,” stated Professional Geologist Greg Rawls. He attributes the increased effectiveness of the Bonita Springs Bioreactor to Florida’s warmer groundwater temperatures that facilitate the anaerobic bacterial activity that systems like this run on. “We’re blowing away the removal efficiencies and rates with this system,” he stated during the conclusion of his presentation at last Wednesday’s Council Meeting. This is great news as the city considers moving forward with the next phase of this project to meet and exceed the upcoming 5-year requirement for the BMAP. The ease of scalability, effectiveness and efficiency in terms of land usage and cost that phase 1 of this project demonstrated serves as a solid framework for the City Council to review further applications of the system citywide.
