What are constructed wetlands?
Wetlands are areas of low flowing water that act as sponges to absorb incoming water and purify it before it flows into aquifers or local bodies of water. They also reduce storm surges along coastal areas, and provide wildlife habitat. They are natural treatment facilities that improve water quality through three primary mechanisms: settling of organic matter, filtration, and nutrient absorption.
Constructed wetlands, then, are engineered versions of natural wetlands. These systems use natural ecological processes to improve water quality just as a more conventional water treatment facility would, while also providing habitat for wildlife and adding natural beauty.
How do wetlands clean water?
When water flows into a wetland, it spreads out and flows through dense plant growth. The water slows down, allowing sediment to fall to the bottom to rest and provide points of attachment for plant growth. As the organic matter and sediments fall through the water some filtration occurs. This initial settling of organic matter and sediments is followed by more robust filtration by plants and microbes. Wetland plants do act as filters but the main mechanism behind water treatment is their microbial partners that feed off leftover pollutants. These microbes also work together with plants to facilitate nutrient absorption for plant growth and enhance water quality.
Why do we construct wetlands?
Human development, peat mining, and pollution have degraded and fragmented natural wetland habitats, reducing this once dominant form of natural water treatment across the globe. Integrating treatment wetlands as a natural system for treating wastewater is more cost-effective and more conducive to biologically productive systems than conventional treatment centers.
The Tres Rios Project in Phoenix, Arizona is one example of a constructed treatment wetland. In 1990, in order to meet recently updated DEQ standards, the local wastewater treatment plant needed to make improvements that were projected to cost around $635 million. Wetlands were proposed as a cost-effective means of polishing water while also providing quality ecosystem services. The 12-acre demonstration project was built in 1993 with support from the US Army Corp of Engineers for $3.5 million. The constructed wetland successfully receives about two million gallons of effluent per day within a 700 acre section of the Salt and Gila Rivers of southwestern Phoenix, improving water flow in addition to treating wastewater effluent.
Typically, constructing treatment wetlands requires a large amount of space separate from the local watershed. While constructed treatment wetlands are more cost-effective and better for the planet than traditional treatment facilities, they are still centralized infrastructure, requiring water to be transported from homes back to a central location for treatment.
The technology inspired by naturally occurring wetlands has developed rapidly over the last 70 years and continues to evolve. LeapFrog Design’s water reuse systems synthesize everything we’ve learned about large-scale constructed wetlands into small, modular wetlands for decentralized household water reuse.