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• (Excerpt from Lloyd Rozema's Master's thesis):

Physical, chemical, and biological processes combine in wetlands to remove contaminants from wastewater. According to the Canadian Wildlife Service, an understanding of these processes is fundamental not only to designing wetland systems but to understanding the fate of chemicals once they have entered the wetland (Wren, 1997). Theoretically, treatment of wastewater within a constructed wetland occurs as it passes through the wetland medium and the plant rhizosphere. A thin aerobic film around each root hair is aerobic due to the leakage of oxygen from the rhizomes, roots, and rootlets (Hammer, 1989). Decomposition of organic matter is facilitated by aerobic and anaerobic micro-organisms present. Microbial nitrification and subsequent denitrification releases nitrogen as gas to the atmosphere. Phosphorus is co-precipitated with iron, aluminum, and calcium compounds located in the root-bed medium (Brix and Schierup, 1989; Davies and Hart, 1990; Fried and Dean,1955; Patrick and Reddy, 1976; Sah and Mikkelson, 1986). Suspended solids are filtered out as they settle in the water column in FWS wetlands or are physically filtered out by the medium within the SF or VF wetland cells. Harmful bacteria and viruses are reduced by filtration and adsorption by biological films on the sand media in SF and VF systems. Figure 1 provides a graphical representation of these processes.

Figure 1. Graphical representation of the treatment processes that
occur within a AQUA Wetland System.