Constructed wetlands represent artificial wetlands with the main objective to harvest, treat and store storm-/grey water runoff in urban areas. Processes/services of natural wetlands are adapted to constructed wetlands focusing on water purification and (underground) storage. Hydrological processes of natural wetlands are simulated in constructed wetlands. Wetlands are complex systems: The established vegetation, the soil and microbiological activity play an important role for the filter performance of constructed wetlands. (salt) Marshes, swamps, peat bogs, coral reefs, mangroves or lagoons represent different types of wetlands. Constructed wetlands are basins (shallow) that are filled with substrate. The substrate type is variable but usually CWs are filled with sand or gravel. The substrate layer is planted with vegetation/aquatic plants. Constructed wetlands have an inlet (pipe) for storm water runoff. The water flows horizontal through the wetland while it is naturally filtered and cleaned. The main processes in a constructed wet roof are: settling of particles, filtration, chemical transformation, adsorption+ ion exchange e.g. on plants and substrates, uptake/breakdown/transformation of pollutants and nutrients by microorganisms and plants. The storm water runoff can flow over or through the substrate layer. The constructed wetland is equipped with an outlet (pipe, weir) for a controlled water discharge. The purified water flows into another pond where it is stored. The treated storm water can be used for different purposes (e.g. for irrigation within the city in green areas). According to the type of constructed wetlands wastewater flows 1) horizontal over the ground surface or 2) horizontal under the ground surface through the substrate layer or 3) vertical through the constructed wetland hybrid systems.
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