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Constructed wetlands make use of the natural purification processes of vegetation, soils and microbes to remove contaminants from discharge. Uses of constructed wetlands for water purification include applications in industrial wastewater and municipal wastewater and storm water treatment. This relatively low-cost technology improves water security and access, making it important for climate change adaptation. Additionally, green spaces created by wetlands produce habitats for wildlife and may improve recreational value.
There are two main types of constructed wetlands: subsurface flow and surface flow. Both are constructed on top of an impermeable basin that is placed in the ground. Subsurface flow wetlands filter and purify water under the surface of the soil, and are therefore filled with porous soils and sand. Water is either purified vertically through the soil and collected in pipes in the underlying basin, or goes through the soil layer in a more diagonal direction due to a slant, after which it is also collected in pipes and sent to an external reservoir. Surface flow wetlands consist of more impervious, silty soils that keep water above the soil. The water moves slowly in a horizontal pattern through the vegetation and top soil, removing sediment and contaminants before it is collected in pipes at the wetland’s end.