Eutrophication of US surface waters is a growing problem due to nitrogen and phosphorus runoff in stormwater. In natural ecosystems, wetlands can absorb and remove a variety of water pollutants, including nutrients. Wetlands also provide flood control and wildlife habitat. Mimicking natural systems, constructed treatment wetlands can remove stormwater pollutants, are economic to build and maintain, provide a bionetwork for a wide range of plants and animals, and can be used for educational purposes.
While constructed treatment wetlands can remove stormwater pollutants such as total suspended solids, organic carbon, and nitrates, a significant reduction in phosphate concentrations has not been observed using plant and soil media alone. Calcium carbonate was shown to reduce phosphate concentrations when added to soil media, but its effectiveness has not been tested in a wetland system. To further remove these pollutants, longer detention times were expected to decrease pollutant concentrations.
The ability of constructed treatment wetlands to remove phosphate from artificial stormwater was tested using two laboratory-scale, constructed treatment wetlands composed of three basins each. Water quality parameters including pH, turbidity, nitrate, and phosphate were monitored at each basin outlet. The final wetland basins were amended with two sizes of calcium carbonate in the form of limestone: 1.18-9.5mm pebbles removed 4-7% of phosphate, and fines removed a 20 – 22.5% of phosphate. The addition of recycle lines doubled the detention time of the wetlands systems from 3.46 ± 0.21 hr to 7.33 ± 0.18 hr, however, the recycle lines did not improve the removal of phosphate, nitrate, or turbidity, and worsened overall water quality.
To further optimize phosphate removal, follow up studies should include testing the removal efficiency of different concentrations of limestone fines in the soil.
Edwards, Katlyn, "Investigating the Removal of Stormwater Pollutants in Small-Scale, Constructed Treatment Wetlands" (2019). Rose-Hulman Summer Undergraduate Research Fellowships. 2.