Long-Term Performance of a Constructed Wetland for Metal Removal

Constructed wetlands have the ability to economically remove pollutants from water and retain them in sediment. This paper describes the long-term performance of a constructed wetland for metal removal, including the efficiency of metal removal, and the retention of metals in the wetland sediment. It is based on four years of data collected from the A-01 wetland treatment system, a surface flow wetland planted with Schoenoplectus californicus (giant bulrush). The system is designed to remove Cu and other metals from the A-01 National Pollution Discharge Elimination System (NPDES) outfall effluent at the Savannah River Site near Aiken, SC. Copper, Zn, and Pb concentrations in water were usually reduced 60 to 80% during passage through the A-01 treatment system. Most of the metal removed by the wetland cells was accumulated in the two top layers of the substrate; i.e., the floc and organic layers. This gradient was strongly correlated with percent organic matter, pH, and the concentration of all metals. These results showed that most metals in the A-01 wetland sediments behaved similarly: their concentrations decreased as sediment depth increased.