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Schematic design of constructed wetlands for sewage treatment.

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Schematic design of constructed wetlands for sewage treatment.

to supply nutrients to aquatic plants and animals. As most ecology students learn, wetlands are the most productive ecosystems in the world, straddling the intersection of land and water. They are also nature's filters, helping to remove sediments and heavy metals, as well as oil and grease, from stormwater and transforming sewage nutrients into life-giving carbon, nitrogen, phosphorus and trace minerals. Properly designed, constructed wetlands can provide wildlife habitat and open space for green building projects, as well as a place for school tours and outdoor environmental education.

Constructed wetlands can have either surface or subsurface flows. Surface flows resemble marshes, while subsurface flows support a wide variety of plants by supplying them with nutrients. Plantings of reed beds are popular in European constructed wetlands, and plants such as cattails, sedges and bulrushes are used worldwide.162 As of 2004 more than 5,000 constructed wetlands had been built in Europe, and more than 1,000 were in operation in the US.163

Constructed wetlands may be cheaper to build than traditional sewage and stormwater treatment plants, have lower operating and maintenance costs and can handle widely varying volumes of wastewater. For example, the Tres Rios constructed wetlands is a 7-mile, 480-acre riparian corridor in the southwestern part of Phoenix, at the conjunction of the Salt and Gila rivers. As a wildlife sanctuary and place of repose in an increasingly dense urban area, Tres Rios not only treats sewage from the 91st Avenue treatment plant, but provides many public-use benefits for the Phoenix metropolitan area.164

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