Constructed wetland is a natural wastewater treatment system that uses natural geochemical and biological processes in a wetland ecosystem to treat the contaminants. The whole process is mediated by complex interactions between water, plants, soil/gravel media, microorganisms, and the atmosphere by using the power of nature and energy from the sun.
These artificial basins can be used to treat waste from sludge dewatering, landfill leachate, mine drainage, stormwater, industries, domestic or municipal purpose, and agricultural activities.
Constructed wetlands provide a sustainable way to treat polluted water with minimum operation and minimum cost. The structure and processes of constructed wetlands are briefly explained in this article.
How are Constructed Wetlands Built?
Constructed wetlands have three primary components:
- Impermeable layer of clay
- Substrate layer made of gravel
- Ground vegetation zone
The impermeable layer is usually made of clay that prevents the filtration of waste down into the lower aquifers.
The substrate layer provides nutrients and support for the root zone. This is the layer and the root zone where the water flows. The bioremediation and denitrification processes are performed in this layer. Above the substrate layer lies the ground vegetative layer that is either planted or allowed to establish naturally.
Constructed wetlands are constructed on uplands and outside floodplains without affecting other aquatic sources. The construction involves excavation, backfilling, grading, diking, and installation of water control structures to achieve the desired hydraulic flow patterns.
Constructed wetland is a cost-effective and technically feasible approach to treat wastewater that is not only less expensive to construct but also has low operational and maintenance expenses. Unlike other wastewater treatment methods, it is aesthetically pleasing and eliminates odors associated with wastewater.
Mechanism of Constructed Wetlands
As mentioned above, a constructed wetland is a composition of water, substrate, plants, invertebrates, and an array of microorganisms. The mechanisms followed in constructed wetlands to improve the quality of water can vary and are often interrelated. The common mechanisms include:
- The settlement of suspended matter
- The water coming in contact with substrate undergoes filtration, chemical precipitation, and chemical transformation by bioremediation and denitrification processes
- The water then undergoes absorption and ion exchange on the surface of vegetation, substrate, and sediment.
- The microorganism and plants break and transform the pollutants
- The microorganisms consume the nutrients
- The predation and natural die-off of the pathogens
Advantages of Constructed Wetlands
The advantages of constructed wetlands are:
- Less expensive compared to other wastewater treatment methods
- Low operational and maintenance costs
- Facilitate wastewater reuse and recycling
- Tolerate fluctuations in water flow
- Provide habitat for wetland organisms
- Can be constructed harmoniously into the landscape
- An environmentally-sensitive approach