Rerating capacity of a constructed wetland treatment system

The 482-hectare (ha) City of Orlando (Florida) Easterly Wetlands (OEW) was designed to reduce nutrient concentrations in 0.90 m3/s of wastewater from the Iron Bridge Regional Water Reclamation Facility. Design influent nutrient concentrations were 6 mg/L total nitrogen (TN) and 0.75 mg/L total phosphorus (TP). Actual TN and TP concentrations have been less than design, averaging 2.6 mg/L and 0.29 mg/L, respectively from January 1988 through December 1999. If influent concentrations remain at these levels, the OEW may have the potential to treat significantly higher flows since less than 20% of the total area was utilized for nutrient reduction. To test this theory, a capacity study was performed for approximately nine months in 1997 and 1998. Simulated flows of approximately 1.26 m3/s, 1.66 m3/s, and 1.93 m3/s were tested. It was found that approximately 15% of the area was utilized for nutrient reduction during the 1.26 m3/s simulation, 35% in the 1.66 m3/s, and 1.93 m3/s simulations. Based on these testing results, an application was submitted to the state in early 2000 to increase the permitted capacity to 1.57 m3/s.