Floating Wetland Systems for Nutrient Removal in Stormwater Ponds
Final report by UCF Stormwater Management Academy on the ability of floating treatment wetlands (FWT) to increase nutrient removal effectiveness in wet detention systems. FTW nutrient removal was measured in microcosms, macrocosms, and two wet detention systems. Planting media for the FWT also were evaluated. All media used to support the plants were acceptable, but expanded clay and tire crumb media was most cost effective, plants were sustained, and plant growth was superior to the use of other media. The plants that should be used to sustain removal were recommended with a diversity of plants recommended. The plants should also be replaced at least once a year. For Florida conditions, the replacement was recommended in the fall when runoff into the wet ponds is reduced significantly relative to the summer rainy season. The removal of plants was also supported by the finding that toxins were produced when the FTW was not removed late in the year and when runoff was relatively low. This is due to the fact the FTW was more efficient in removing nutrients than the algal masses. Thus some of the algal masses died and their toxins were released. The FTW pond area coverage recommended was 5% but when additional nutrient loads were added to the wet detention pond (as an example, from a fountain) a 10% area coverage was recommended. The additional credit for concentration reduction from the deployment of a FTW in a wet detention pond was recommended as 12%. The credit assumes plant selection, area coverage, pond location, and maintenance recommendations are followed.
Wet detention ponds are frequently used in stormwater management systems as part of a treatment train for attenuation of flow and removal of pollutants. Wet detention ponds designed and operated according to commonly used standards and specifications remove nutrients but the removal of nitrogen has remained low, about 30-40% concentration reduction on a yearly basis. A Floating Treatment Wetland (FTW) composed of selected plants suspended in a wet detention pond was proposed in this research to improve the removal of nutrients before discharge from a pond.