Constructed Wetland Septic Systems

What are constructed wetland systems?

Constructed wetlands replicate natural processes occurring in natural wetlands. The difference between a conventional septic system and constructed wetland is the addition of the constructed wetland either in addition to a drain field or instead of a drain field. The septic tank is the same and wastewater moves from the septic tank via the outlet pipe into the wetland cell. A wetland cell is a man-made system not only relies on gravel, sand and soil and the microbes contained to filter pathogens and nutrients, it also uses aquatic plant life.

The wastewater effluent travels by pipe from the outlet pipe through perforated pipes distributing the domestic wastewater. An impermeable liner, gravel and sand fill, as well as the required wetland plants, must be able to survive in a perpetually saturated setting.

A constructed wetland system is usually gravity fed, but it can also be fed by a pump via the distribution box. After domestic wastewater has been treated in the constructed wetland it will exit the natural wetlands and trickle into the leach field for final treatment and removal of pathogens and nutrients by the soil before reaching groundwater.

The main types of constructed wetlands

There are many different types of constructed wetland system, below you will find the most popular. The choice of constructed wetland will be determined by the space available, amount of effluent or stormwater runoff

• Subsurface flow constructed wetlands - these can be either with vertical flow constructed wetlands (the wastewater effluent moves from top to bottom, moving through the planted layer, down through the wetland cell and out into the leach field) or with horizontal flow constructed wetlands (the effluent moves e.g. from left to right, parallel to the surface). These are popular as they do not require much space.
• Surface flow constructed wetlands - this wetland has horizontal flow. A horizontal flow constructed wetland has the water enter at one end and exit horizontally at the other end. Surface flow constructed wetland can often attract mosquitos that bread in the surface water.
• Floating treatment wetland with only free-floating macrophytes, floating-leaved macrophytes (aquatic plants).

Plant species and aquatic plants used

The wide availability, capacity to develop at various water depths, simplicity of transport and transplantation, and broad tolerance of water composition make cattails (Typha latifolia) popular in the construction of wetlands in the United States. Common Reed (Phragmites australis) is also a common wetland plant species in both blackwater treatment and greywater treatment systems for wastewater purification.

Frequently asked questions

Vertical or horizontal flow constructed wetlands?

This will depend on space, vertically constructed wetlands need less space. Horizontal flow wetlands are popular in municipal and industrial wastewater purification to polish or finish off the treatment process on a mass scale.

Is wildlife safe in constructed wetlands?

Often a wildlife habitat will establish itself within the wetlands. They do not assist to treat wastewater, but they do assist the wetland plants in their natural wildlife habitat.

Surface flow constructed wetlands or subsurface flow?

A big benefit for subsurface flow wetlands is the reduction in mosquitos. Surface flow wetlands are also known as free water surface wetlands and the water sitting often attracts mosquitos.

Have there been any advances in wetland wastewater treatment?

Constructed wetland technology has not progressed in recent decades. The main reason for this is constructed wetlands use natural processes and therefore do not rely on constructed wetland technology to improve. When you rely on nature, it is hard to improve on this process.