A constructed or an artificial wetland is a type of organic wastewater treatment system, which mimics and enhances the functions of naturally occurring wetlands in the purification of water. The system makes use of water, aquatic plants such as reeds and duckweed, naturally existing microorganisms, as well as a filter bed which is often formed of sand, silt, or gravel.

These can be used for secondary and tertiary wastewater treatment. There are many alternative designs, such as vertical wetlands, which need less space but more power to perform tasks like pumping or syphoning, than horizontal wetlands, which can rely on terrain and gravity instead.

Let us learn about the constructed wetland technology in sewage treatment plants, with its process flow-chart and working function in detail.

What is Constructed Wetland Technology in STP Plant?

It is an artificial shallow basin which is filled with the substrate, mostly dirt or gravel. It is home to the species which can withstand saturated conditions. Following that, water is introduced into the system from one end and flows over the top (surface flow), or through the substrate (subsurface flow), before being discharged from other end which is at a lower position through a weir.

What is the basic idea behind a constructed wetland system?

The basic idea is that the combination of substrates, microbes, and plant functions as a filter and purification system.  

1: In order to allow for the sedimentation of solids, water is first slowed when it enters the wetland.

2: Plant roots and the substrate of the constructed wetland filter out bigger wastewater particles, as water moves over it.

3: The bacteria and plants then naturally break down and absorb the pollutants, and nutrients present in the wastewater, eliminating them from the water.

4: The pathogens present in wastewater will also be killed by UV radiation, antibiotics secreted by plants, and the retention duration in the wetland, which varies based on the design and desired quality level.

5: Water can be safely discharged into surface waterways or used for a variety of purposes, after being treated in a constructed wetland for sewage treatment plants.

What are the various components or elements of a constructed wetland?

A constructed wetland is a system made up of various components that work together. Correctly designed and constructed basin that can contain water, a substrate that offers filtration pathways, habitat/growth media for the required organisms, as well as communities of microorganisms and aquatic invertebrates that typically emerge spontaneously, are all components of engineered or constructed wetland systems.

Typically, a constructed wetland for STPs consists of three main elements:

A: An impermeable layer exists in a constructed wetland (generally clay).

B: In addition, it has a layer of gravel that serves as the substrate, necessary for giving the root zone support and nutrients.

C: Additionally, it features a zone of above-surface vegetation.

Groundwater can be forced to flow through the wetland by pumping it or naturally by gravity. Plants and other natural bacteria work inside the anaerobic cells to degrade the pollutants. Through continued exposure to the plants and the passage of water between cell compartments, the aerobic cell conducts the work of further enhancing the water quality.

In the constructed wetlands primarily to remove metals, the use of straw, manure, or compost with little to no soil substrate has been useful. However, in wetlands created to clean water contaminated by explosives, a procedure known as phytoremediation uses certain plant species, to speed up the deterioration.

Working of constructed wetlands for the treatment of sewage

Numerous connected strategies can be used to enhance the water quality in a constructed wetland system. The mechanisms include:

· the settling of suspended particles,

· filtration,

· chemical precipitation,

· chemical transformation,

· adsorption and ion exchange on the surfaces of plants, substrate, sediment, and litter,

· breakdown as well as the transformation of pollutants by microorganisms and the plants uptake, and

· transformation of nutrients by microorganisms and plants along with predation and natural die-off.

The removal can be done chemically through adsorption (ionic and covalent), oxidation, reduction, and UV degradation; biologically through microbiological degradation through catabolism and anabolism, and through plant uptake and storage; and physically by the filtration and settlement processes that filters some materials, while degrading others.

Flow chart for sewage treatment in constructed wetlands

Benefits of constructed wetlands for wastewater management

As wetlands age, the pace at which contaminants are removed may slow down. To manage wastewater and runoff, however, manmade or constructed wetlands are a practical and affordable option for a number of reasons.

· These have the potential to be more cost-effective and less expensive to construct than other forms of treatment.

· The fact that on-site labour is only needed occasionally rather than continuously, for operation and maintenance.

· The constructed wetlands also accommodate flow variations, sustainably facilitate water recycling and reuse, offer good habitat for a variety of wetland creatures, and can be designed to blend in with the surrounding environment. 

· In addition to improving water quality, it can offer wildlife habitat that promotes tourism and other recreational activities, and aesthetic enrichment of open spaces.

The public favours constructed wetlands as ecologically sensitive treatment methods, because of all the aforementioned economic, ecological, and aesthetic advantages.

Key characteristics of constructed wetland wastewater treatment systems

· Cost-effective in terms of construction, maintenance, and operation

· Utilizes technology that is easy to comprehend

· It is used to treat wastewater from human waste, agricultural runoff, storm water, and some metals or pollutants from mining and industry

· Low energy requirements are necessary for operations

· Provides a habitat for plants and animals, which helps to protect the environment.

Construction of constructed wetland systems for wastewater treatment

In order to prevent harm to natural wetlands and other aquatic resources, constructed wetlands are typically built on uplands and outside floodplains or flood ways.

Excavation, backfilling, grading, diking, and the installation of water control structures are routinely used, to create wetlands and to create the proper hydraulic flow patterns. An impervious, compacted clay liner is typically built, and the original soil is then spread over the liner, if the location has very permeable soils. Then, wetland vegetation is either planted or given time to grow organically.

Conclusion

In fact, even though constructed wetlands have been used commercially to manage and degrade municipal and industrial wastewater, care must be taken in how these systems handle unusual wastes, such as explosives and those that contain resistant genes.

For the control of such acute strains, there needs to be a significant shift towards a more localised management of the water cycle, and more effective monitoring strategies based on a small number of indicators that would facilitate, the assessment of the anthropogenic impact on the water.

Learn more about our options for treating sewage with the use of constructed wetlands

Wastewater is harmful to the environment and to people's health. To prevent wastewater pollution, poisonous and dangerous substances that are released into the water must be eliminated.

We provide various wastewater treatment solutions for treating sewage. We also provide outstanding wastewater solutions for any sector with high-quality, dependable products and a knowledgeable engineering group. To find out more about our alternatives for treating sewage, get in touch with us. Call us at +91 9650608473 or email at enquiry@netsolwater.com for further information.