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4.2.5 Constructed wetlands

Constructed wetlands are in-between lagoons (4.2.3) and land based treatment systems (4.2.4). A constructed wetland consists of a gravel bed in which wetland species, such as reeds, are planted (Figure 2.31). Wastewater (usually after settling of solids) passes through the gravel bed, and organic substances are degraded by bacteria attached to the surfaces of the bed and plant roots. The removal of BOD and SS in beds with and without plants does not appear to differ by very much. Wetland plants take up nutrients (nitrogen and phosphorus) when water residence time is long. Long-term nutrient removal requires harvesting of the plants. Constructed wetlands need to be designed to minimise problems with insects (mosquitoes and midges).

 

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