Constructed Wetlands:
All wastewater treatment systems rely on bacteria to breakdown effluent in the water. Constructed wetlands function by providing a unique ecology- through plant material and other physical medium- which the bacteria inhabits. Constructed Wetlands can be used to treat a wide array of wastewater sources: from stormwater runoff to municipal wastewater/sewage, agricultural runoff, livestock waste, and industrial waste.
There are 2 general types of constructed wetlands: free water surface & subsurface flow. As you can imagine, wastewater flows over emergent vegetation with the water surface exposed in the former, while the water flows beneath a planted aggregate (gravel, etc.) bed in the latter.

The following is how some sites have been using these technologies, from the book Living Systems: Innovative Materials and Technologies for Landscape Architecture by Liat Margolis and Alexander Robinson (which is pretty interesting).
1. Stormwater Garden
Blackstone Power Plant Renovation (Harvard University, Cambridge MA)
Landworks Studio, Inc.
The designers envisioned the stormwater garden as a sculptural expression of water movement across the landscape, where ‘landforms of positive and negative relief’ orchestrate water flow from high points to low point of collection and conveyance.
Project consists of two separate courtyards, Common Courtyard and Albro Courtyard, to emphasize positive relief (landforms) and negative relief (bioswales), respectively. Albro Courtyard contains a 30×100’ linear cell set 3’ below grade which retains 1’-1.25’ surface runoff for 72 hours. The cell is layered with 3” of mulch atop 4’ of soil atop 1’ of sand.

2. Networked Sidewalk Stormwater System
SW 12th Avenue Green Street Project, (Portland, OR)
Portland Bureau of Environmental Services
Distributing hydrological performance through a network, the project compresses the stormwater planters in size and finds more room for pedestrians, on-street parking, landscaping, street lighting, and signage.
The project consists of a series of four 4×17’ planters set 9” below grade surrounded by a 4” curb. The system was sized to handle 60% of SW 12 street run-off (180,000 gal annually). The planters were filled with native soils amended with an equal mix of sand, compost, and screened loam. Native Grooved Rush and Tupelo were planted for their water absorption and drought resistance. The project won an ASLA General Design Award of Honor in 2006.


3. Cleansing Biotopes
DaimlerChrystler Plaza, (Berlin, Germany)
Atelier Dreiseitl
The cleansing biotopes are a form of constructed wetlands that are particularly effective for stormwater treatment. This effectiveness stems from their fast water circulation and highly efficient metabolism of excess nutrients.
In order to treat run-off from surrounding roofs, the design collects stormwater in an open-air water feature. The cistern holds 35,000 cf and is circulated through a sequence of biotopes within three days. The biotopes are planted in a relatively shallow sand-mineral mix that is non-organic, low-nutrient, and highly-porous. The filter substrate consist of three layers- 90% sand, 5% mineral additives, and 5% lava rock.


4. On-Site Sewage Treatment System
Sidwell Friends School, (Washington, DC)
Andropogon Associates + Kieran Timberlake Associates + Natural Systems International
The multiple mechanisms are integrated into both the landscape and architecture, and leveraged into a system that enhances the character and operation of both.
The terraced wetlands serves as a site for wastewater treatment, an outdoor courtyard, classroom, and diverse habitat. Sewage from the building undergoes primary treatment underground and then circulates through a series of reed beds n the courtyard. A trickle and sand filter provide further treatment. The treated water is then used back in the building to serve flush toilets. The system receives 3,000 gal/day and takes four to six days to circulate the wastewater before discharge.



