What Is Constructed Wetland? What Is The Function Of A Man Made Wetland?
What Is Constructed Wetland?
A constructed wetland is a man-made wetland that helps purify sewage, greywater, stormwater runoff, or industrial wastewater.
It can also be used for restoring land after mining or as a replacement for natural areas that have been lost to development.
It works by using the natural processes of plants, soil, and living organisms to treat wastewater.
The design of the wetland must be tailored to the specific type of wastewater. Both centralized and decentralized wastewater systems can use constructed wetlands.
Pre-treatment is necessary when wastewater contains high levels of suspended solids or organic matter (as indicated by BOD and COD).
What Is The Function Of A Man Made Wetland?
Constructed wetlands are a solution for treating raw sewage, stormwater, agricultural and industrial waste.
They imitate natural wetlands to manage stormwater, decrease nutrient levels, and provide habitat for wildlife.
Wetlands can be used for wastewater or greywater treatment and are often recommended as a “best management practice” by regulatory agencies for controlling urban runoff.
Why Constructed Wetlands Used For Wastewater Treatment?
Constructed wastewater wetlands offer numerous ecological advantages, primarily filtering and eliminating pollutants, pathogens, and nutrients from sewage.
Municipal wastewater includes toxic substances that can harm aquatic life, but effective wastewater wetlands can decrease this risk and enhance downstream water quality.
Additionally, these wetlands can store carbon and provide habitats, diversity, and flood control.
However, it is important to properly dispose of the plants if they contain adsorbed contaminants such as heavy metals, as removal depends on adsorption or degradation through microbes or light.
What Is A Vertical Flow Constructed Wetland?
A vertical flow constructed wetland is a type of filter bed that uses plants to treat wastewater. The wastewater is introduced on top of the bed and flows vertically through the filter matrix to the bottom where it’s collected.
Unlike horizontal wetlands, vertical flow wetlands create aerobic conditions. They can be built as a shallow excavation or above ground structure and require a minimum surface area of 1-3m2 per person equivalent.
A layer of gravel, sand, and plants (such as reeds, cattails, or Echinochloa pyramidalis) make up the filter bed, which must have an impermeable liner and effluent collection system.
To prevent clogging, the influent should be pre-treated before entering the wetland. The wetland’s design depends on hydraulic and organic loads.
Vertical flow wetlands have the ability to nitrify but limited denitrification, so they may be combined with a Free-Water Surface or Horizontal Flow Wetland for a complete treatment process.
What Are The Three Main Types Of Constructed Wetlands?
Different types of constructed wetlands:
- Surface flow: resembles natural swamps, where plants are rooted in sand/gravel. They are used for treating runoff from roads with unpredictable flow rates, without requiring anaerobic pre-treatment. Design depends on space, temperature, and load.
- Horizontal subsurface flow: mainly used for aerobic post-treatment of domestic wastewater, requiring anaerobic pre-treatment.
Gravel layer prevents odor, and wastewater is treated as it passes through the matrix. A reliable and low-cost solution.
- Vertical flow: uses intermitting pumping of pre-treated wastewater to trickling down, effectively forcing aeration.
20 times more aeration capacity, no short circuits, and nitrate removal under anoxic conditions. Design parameters include aquifer level and matrix depth.
