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Constructed wetlands can provide a solution for wastewater treatment

Constructed wetlands (CW) are emerging as affordable technologies for the treatment of wastewater in a decentralised framework. Constructed wetlands can be used to treat secondary or tertiary wastewater.

By Jyotsna Richhariya
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Constructed Wetland

Source: IAEA graphic based on Graphithèque/Adobe Stock

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Amidst the water stress concerns in major Indian cities, and towns, constructed wetlands (CW) are emerging as affordable technologies for the treatment of wastewater in a decentralised framework. Water stress has become a perennial concern, often insufficient to meet the growing demand for water by all economic sectors. With a growing population, the per capita availability of water has dropped from 1,816 cubic metres in 2001 to 1,545 cubic metres in 2011, according to Central Pollution Control Board data.

What are Constructed Wetlands?

Structure of Constructed wetlands (CW) . Source: US EPA

 constructed wetland is “an organic wastewater treatment system that mimics and improves the effectiveness of the processes that help to purify water similar to naturally occurring wetlands. The system uses water, aquatic plants (i.e.: reeds, duckweed), naturally occurring microorganisms and a filter bed (usually of sand, soils and/or gravel).”

Unlike conventional concrete tanks, these wetlands promote biodiversity by allowing a wide range of life forms, including microbes, aquatic plants, and even birds, to participate in the purifying process.

The concept of constructed wetlands was given by Kathe Seidel in the early 1950s. She studied the CW system for the treatment of different types of wastewater at the Max Planck Institute. The early systems developed by Seidel comprised a series of beds composed of sand and gravel with emergent vegetation (Typha, Scirpus, and Phragmites) and were named as hydro botanical systems.

Types of Constructed Wetlands

Constructed wetlands are often classified into two types: subsurface flow (SSF) and surface flow. SSF wetlands filter wastewater through gravel beds or porous medium, encouraging microbial activity that destroys organic materials. In contrast, SF wetlands are visually appealing above the water's surface, with softly flowing streams and rich flora.

While each design has unique advantages, both variations share a common goal: to transform pollutants into harmless molecules using natural processes.

Constructed wetlands can be used to treat secondary or tertiary wastewater. There are numerous designs available, including vertical wetlands, which require less acreage but require more energy for operations such as pumping or syphoning than horizontal wetlands, which can rely on gravity and terrain. The wide range of design, material, and technology possibilities allows the created wetland to be tailored to local conditions and available land. The price of land and materials determines costs, but where land is inexpensive and readily available, engineered wetlands are an extremely cost-effective technique of wastewater treatment.

Constructed Wetlands can also be classified according to their functions and aims in three main application areas :

  • Habitat creation: these systems are designed to provide a revitalised wildlife habitat and to enhance the pre-existing ecological benefits of the technology such as attracting animals such as birds and creating a green area while addressing the water/wastewater treatment and mitigation. In this category, four different types of CWs exist ponds, marshes, swamps and ephemeral wetlands. 

  • Flood control: these systems operate as runoff receivers during flood incidents and increase the stormwater storage capacity in urban areas. 

  • Wastewater treatment: systems designed and operated to receive and treat wastewater of different origin.

Constructed Wetlands for waste-water treatment in India

Some examples include the Asola Bhatti Wildlife Sanctuary in Delhi, which is located on the city's outskirts. A developed wetland system helps to cleanse sewage from adjacent settlements while also providing a habitat for varied flora and fauna, helping to regional biodiversity conservation.

Chennai, Tamil Nadu, Perungudi, and Kodungaiyur have built wetlands as part of their decentralised wastewater treatment approach. These wetlands successfully handle sewage from local communities, lessening the demand for centralised treatment facilities and dramatically lowering pollution levels.

The Kolkata East Wetlands in West Bengal, designated as a Ramsar site, feature a vast network of natural and constructed wetlands. These wetlands play a vital role in treating wastewater from Kolkata and its environs while also offering livelihood opportunities for local communities engaged in fishing and agriculture.

In Haryana, Palla village located along the Yamuna River hosts a constructed wetland system that treats wastewater from Delhi before its discharge into the river. This initiative helps enhance water quality in the Yamuna and mitigates pollution levels downstream, benefiting both human populations and aquatic ecosystems.

In Rajasthan, the Sariska Tiger Reserve has launched an innovative effort that uses artificial wetlands to filter wastewater from adjacent communities. This strategy not only addresses local people's sanitation needs, but also helps to maintain the reserve's natural integrity. Thereby, promoting wildlife habitat conservation.

Wastewater treatment system and pathways
Wastewater treatment systems and discharge pathways

Implementing Constructed Wetlands in India

In 2019, the Department of Biotechnology (DBT) and Central Pollution Control Board (CPCB) released a document on Constructed Wetlands (CWs) as an Alternative Technology for Sewage Management in India. The manual covers the various types of wetlands, their applications, and obstacles in treating sewage.

A plethora of new technological advancements. The guidebook provides detailed instructions for designing, constructing, operating, and maintaining engineered wetlands.

Under the National Water Mission of the Ministry of Jal Shakti, Department of Water Resources, River Development and Ganga Rejuvenation (DoWR, RD & GR) (strategy 1.4), two Programme (i) Developing Inventory of Wetland and (ii) National Plan for Conservation of Aquatic Ecosystem (NPCA) has been launched to create an inventory of wetlands including Ramsar Wetlands and to identify 115 wetlands in 24 states and 2 UTs for conservation and management respectively.

In India, the use of CWs for sewage treatment is limited due to factors such as lack of awareness, social acceptance, regulation and policy frameworks, and lack of guidelines for construction, operation, and maintenance. To promote the use of CWs for sewage treatment in India, it is necessary to raise awareness, involve local populations, develop supporting regulations, and provide clear guidelines. Implementing these initiatives will enable India to use CW technology for sustainable sewage treatment. Standardising CW systems is crucial for optimising their potential in sewage treatment, as part of NMCG's continuous work. 

Keep Reading

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