A subsurface flow constructed wetland consist of a trench lined with clay or other impermeable layer. The trench is filled with gravel or sand which is covered with vegetation. Water that flows through the filter bed is filtrated mechanically and treated by microbiological processes.
Subsurface flow constructed wetlands are mainly used as natural treatment systems to improve water quality. A subsurface flow constructed wetland usually consist of an excavated trench lined with impermeable layer of plastic membrane or clay, filled with porous media such as stones, gravel or coarse sand, and covered with planted or natural vegetation. The water distribution through the media can be vertical or horizontal ensuring that the water level remain below the surface of the filter bed. Due to physical processes the water is filtrated mechanically, while microbiological activity in the filter media leads to removal of nutrients, BOD5 and total suspended solids.
Localisation and implementation
Subsurface flow constructed wetlands can be adapted to remove pollution from domestic wastewater, storm water, contaminated industrial wastewaters, and agricultural runoff. The dimensions of constructed wetlands should be calculated based on the amount and quality of the inflowing water. The water can be distributed through the system without electricity in a proper slope of the area.
Effects, duration and maintenance
The subsurface flow constructed wetland has a potential to significantly remove nitrogen and phosphorous compounds as well as to decrease concentrations of total suspended solids and biochemical oxygen demand in the water.
The constructed wetland as a treatment system has low implementation and maintenance costs. During exploitation it is required to remove the vegetation once per year and periodically monitor the water distribution system. In case of any evidences of clogging in the water distribution system the porous media need to be replaced.
Subsurface constructed wetlands - extended description
Subsurface constructed wetlands - links to resources
Author and contact:
Linda Grinberga, Latvia University of Life Science and Technologies (LLU), Latvia. e-mail