Constructed wetlands
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Constructed wetlands are artificial wastewater treatment systems consisting of shallow ponds or channels which have been planted with aquatic plants and which rely upon natural microbial, biological, physical and chemical processes to treat wastewater. They have impervious clay or synthetic liners and engineered structures to control the flow direction, liquid detention time and water level. Depending on the type of system, they contain an inert porous media such as rock, gravel or sand. Historically, constructed wetlands were already used since centuries to treat a variety of wastewaters such as municipal wastewater, urban runoff, agricultural drainage, etc. However, this lesson focuses mainly on the treatment of municipal wastewater or its separated flows such as greywater. The constructed wetlands according to this application are considered as a mayor treatment step, which usually need a pre-treatment and, depending on the reuse purpose, a post treatment.
This system can be divided into two types, on the one hand is free-water surface type (FWS) in which the water level is over the surface, and on the other hand is subsurface type (SF), in which the water level is maintained below the surface. The latter one can be further categorized into two types based on the pattern of flow, one with horizontal subsurface (HSF) and one with vertical subsurface flow (VSF). The SF type can also be called “reed bed�.
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