Constructed wetlandsDecember 19, 2009
Ecological way to manage wastewater
|While natural wetlands should never receive wastewater from urban runoff, constructed wetlands can pick the city’s storm water runoff and waste water and biologically treat it to acceptable standards|
EYE-CAPTURING: Constructed wetlands to treat wastewater.
Wetlands are areas like swamps and marshes typically subject to soil saturation and flooding during parts or whole of the year.
They have a unique variety of flora and fauna which can withstand the occasional full submergence as well as full dry conditions and are often referred to as the nurseries of life.
Wetlands have long been recognised as potential zones capable of handling various pollutants and being capable of absorbing or transforming them.
Many of the ‘tank’ ecosystem of south India are wetlands in the sense that they can be submerged during parts of the year and be dry during other times.
With tanks in urban areas losing their original purpose of providing agricultural water, their conversion to constructed wetlands has the potential to treat urban wastewater in a decentralised fashion, absorb and mitigate the impact of urban floods as well as provide a bio-diversity spot for flora and fauna.
Constructed wetlands are artificially built wetlands designed to mimic the natural wetlands. Wetlands are different from pools or lakes primarily with more vegetation coverage and less water at shallow depths.
It is possible to design and classify the constructed wetlands as fully submerged wetland where the water is in contact with air and a subsurface horizontal flow constructed wetland where the water flows in a stone or brick bat medium and is not in contact with the air.
Constructed wetlands are typically shallow structures which are kept to depths of 1 meter or less. The bottom of the wetland is usually lined to prevent water from percolating down into the aquifer.
Constructed wetlands have shown tremendous potential of assisting in the biological digestion of human wastewater flows. The plant species can be of the variety that float on the surface, are completely submerged or are rooted at the bottom of the wetland.
Each plant species has a different role to play in the wetland by itself and also as host to other organisms such as bacteria.
In the home: A small constructed wetland can come up at the household level itself. Many sites and homes in the city’s periphery come up in places where there is no underground drainage facility. Here a modified septic tank called a baffled reactor can be built.
The wastewater from the home both from the kitchen and the bathroom is allowed to predigest in the baffled reactor and then allowed to flow into a constructed wetland.
This further treats the waste water as also allows a uniquely bio-diverse area spring up close to the home.
Bringing in a landscape feature
The Rajans have a house far away from the city and many homes in the layout had to take recourse to a septic tank and a leaching system for taking care of their waste water.
The Rajans chose to go for a baffle reactor and a constructed wetland instead and have therefore not only been able to treat wastewater well but also obtain a beautiful landscape feature on their plot
In layouts and apartments: Constructed wetlands can be designed to handle large volumes of wastewater and storm water emerging from these developments. Again a certain form of pre-treatment or pre-digestion of waste water is needed before the constructed wetlands take over and treat the water further.
By integrating it with parks and open spaces, walkways can be created with a palate of plants to enhance the visual appeal of the landscape while providing the functionality of treating wastewater.
At the city level: Constructed wetlands have treated wastewater flowing in canals in the city of Fuzhou,China.
Formerly a stinking 80 km network of flowing wastewater is now a lush green walkway around the city with no smell an with a clarity level in the canals which is much higher. The system was designed by John Todd and Ocean Arks international.
While natural wetlands should never receive wastewater from urban runoff, constructed wetlands can pick the city’s storm water runoff and waste water and biologically treat it to acceptable standards reducing turbidity levels, reducing bacteria , removing nutrients and increasing oxygen level of water while enhancing bio diversity.
Water wisdom calls for using nature and its bio-diversity as an ally in maintaining and enhancing the quality of life in our cities and homes.