Floating wetland islands as a method of nitrogen mass reduction: results of a 1 year test.

Floating wetland islands (FWIs) were tested in Pasco County, Florida, as a method of reducing total nitrogen (TN) in reclaimed water during reservoir storage. The Pasco County Master Reuse System (PCMRS) is a regional reclaimed-water transmission and distribution system providing wastewater effluent disposal for the county. Total daily mass loading from reclaimed water is limited by nitrogen content in the PCMRS watershed. To test TN reduction efficacy, 20 FWIs were constructed, installed, and monitored in a lined pond receiving PCMRS reclaimed water. In total, 149 m2 of FWIs were installed, distributed as a connected network covering 1,122 m2, or 7% of pond area. Pond hydraulic residence time averaged 15.7 days. Treatment performance was assessed during three consecutive periods: establishment (first 6 months of grow-in), performance (8 months immediately following grow-in), and control (3 months after the FWIs were removed from the pond). The FWIs enhanced pond nitrogen removal capacity by 32%. The primary effect of the FWIs was to decrease organic nitrogen in the pond outflow. By evaluating the difference between the performance and control periods, an incremental TN removal rate for the FWIs was calculated to be 4.2 kg N/m2 FWI per year.