Phosphorus retention by the Everglades Nutrient Removal: An Everglades stormwater treatment area

The Everglades Nutrient Removal (ENR) Project was constructed to reduce total phosphorus (TP) levels in stormwater runoff water from the Everglades Agricultural Area (EAA). The ENR Project operates as a once-through treatment system and has the capacity to process about one-third of the annual runoff that would otherwise be pumped directly into Water Conservation Area 1 (WCA-1). Water is first pumped from the Inflow Pump Station into a holding cell (buffer cell) and then distributed via gravity flow to two independent, parallel treatment trains separated by a transverse levee (Treatment Cells 1 --> 3 and 2 --> 4). Treatment Cells 1 and 2 are intended to remove the bulk of the nutrient load that enters the ENR Project, while Treatment Cells 3 and 4 are intended to accomplish the final polishing of the water to lower nutrient concentrations. Besides providing the South Florida Water Management District (SFWMD) with practical experience in the construction, operation, and maintenance of a large-scale treatment wetland, the primary performance objective of the ENR Project is to reduce the influent TP mass by up to 75%. A secondary performance objective is to achieve a long-term annual flow-weighted mean TP concentration of no greater than 50 mu g PL(-1) at the outlet. Monitoring was conducted to document TP levels in the ENR Project for one year during construction phase (February 1993 to February 1994) and during the first 29 months of operation (from August 1994 to December 1996). The nutrient removal efficiency during operation was calculated in terms of decreases in both TP loads and concentrations. Monthly TP load removal ranged from 65 to 91% and averaged 80% for the entire period of record. Total P concentrations of influent water ranged from 66 to 201 mu g P L(-1), while outlet concentrations ranged from 10 to 39 mu g P L(-1). Analysis of TP mass and concentration reductions indicated that the ENR Project had exceeded its performance objectives during the first 29 months of operation.