Because of the efficient treatment processes of wetlands, engineered treatment wetlands are increasingly being used to treat stormwater and wastewater, and especially combined sewer overflows (CSO). Constructed treatment wetlands are low-cost, require minimal maintenance, can be implemented in a decentralized fashion, and contribute to ecosystem preservation. All of these reasons have brought treatment wetlands to the forefront for consideration by communities working to reduce CSOs and improve water quality, especially in small cities with limited resources. Goals of this study were to compare the removal of stormwater pollutants including total suspended solids (TSS), biochemical oxygen demand (BOD), and nutrients (nitrogen and phosphorus) through subsurface flow (SSF) and free-water surface (FWS) wetland configurations. Additionally, each wetland system was composed of multiple basins optimized to remove certain stormwater contaminants. Stormwater, pond and synthetic waters were used to test the efficiency of contaminant removal. Over the course of two years, undergraduate students built wetlands and performed experiments to investigate contaminate removal efficiency. Overall, we found that both wetlands were effective in removing TSS, BOD and nitrate. BOD removal (up to 47%) occurred in the basins with highest organic content, and TSS (up to 82%), nitrate (58-88%) and nitrite (up to 50%) removal occurred in the basins with the highest sand content. The FWS configuration was advantageous for nitrate and nitrite removal, but was not significantly more effective than the SSF. We did not observe significant phosphate removal. Follow up studies will consider additional wetland configurations and operational methods.
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