Authored by Dr. Sudarsan J S
Humans have exploited natural resources since the early eras of civilization to ensure comfort and wellbeing. Among these, a natural resource key to survival is water.
Even as water makes up a large part of Earth’s surface, nearly 70%, we’re struggling to meet the demand for potable water. Statistics point out that water scarcity is affecting 40% of the world’s population. Now, researchers and scientists are looking at novel ways to treat wastewater and make it fit for consumption.
In these methods, wastewater from various sources is treated and reused. And one method of wastewater treatment is ‘constructed wetlands’. In his research study, ‘Artificial Constructed Wetlands: A Novel Idea for Wastewater Treatment to Attain Sustainable Environment’, Dr. Sudarsan J.S. sheds more light on this method.
What are Constructed Wetlands?
“It’s a designed and man-made complex of saturated substrates, emergent and submergent vegetation, animal life and water that simulates natural wetlands for human use and benefits.” – Hammer (1989)
Let’s try and break down this scientific statement further.
Constructed wetlands are artificial wastewater treatment systems. They consist of shallow ponds or channels having aquatic plants. These wetlands rely on natural microbial, biological, physical and chemical processes to treat wastewater.
Waterproof clay, or synthetic liners, and engineered structures control the flow direction, captivity of liquid time and water level. Depending on the type of system, they may contain rock, gravel or sand.
Wetlands are transitional environments, between land and water ecosystems, where the land may be covered constantly or repeatedly with shallow water.
To sum it up, The Wire rightly puts across this comparison between forests and wetlands – “Just as forests are called the ‘lungs of the earth’, wetlands are the kidneys that regulate water and filter waste from the landscape.”
The Case for Constructed Wetlands
Here are some benefits of using constructed wetlands for wastewater treatment:
1. Quality
The purpose of constructed wetlands is to make wastewater fit for use again. By intercepting and treating effluents, it removes pollutants and improves the quality of water.
2. Stability
Constructed wetlands usually consist of reeds planted in gravel or sand. It makes them more stable, since they’re engineered using natural processes such as vegetation, soil, and associated microbial groups.
3. Reliability
They have been previously used to treat various types of wastewaters including urban, municipal, industrial, agricultural and acid mine drainage.
4. Low-cost
Wetlands provide a much more cost-effective option than constructing water treatment plants. Plants generally need more investment and maintenance. Constructed wetlands, on the other hand, use a combination of natural and man-made solutions reducing cost of operation.
5. Flood reduction
Wetlands also have other uses such as reducing floods. They regulate the flow of water as it travels from the aquatic to land ecosystem.
6. Habitat Promotion
Constructed wetlands could also contribute to enhancing the habitat for threatened or endangered species of aquatic animals.
Type of Constructed Wetland used
Constructed wetlands use two types of flow – horizontal and vertical. In his study, Dr. Sudarsan J.S. discusses horizontal-flow wetlands.
Horizontal-flow wetlands, further, may be of two types:
- Free-water surface-flow (FWF)
- Subsurface water-flow (SSF)
In FWF, as the name suggests, the effluent flows freely above the sand or gravel bed in which reeds are planted. Plus, there may be patches of open water. Effluents are treated by plant stems and leaves, which are densely planted.
However, dense planting can limit oxygen distribution into the water. Therefore, FWF wetlands are generally less effective than SSF wetlands (in which effluent is treated by the roots). In SSF, the effluent passes through the sand or gravel bed.
How do Constructed Wetlands treat Wastewater?
A constructed wetland uses natural geochemical and biological processes to treat metals, organics, and other pollutants in water.
1. Layers
It has three primary components –
- The watertight layer (generally clay) prevents penetration of wastes into the lower water storage area.
- The gravel layer provides nutrients and support for the root zone. It’s where the water flows, and breaking down of pollutants takes place.
- The above ground vegetation layer contains plant material.
2. Systems
Both systems with and without oxygen, exist within the wetland and can be divided into separate cells. Groundwater is either pumped or allowed to flow naturally through the wetland.
The ‘without oxygen’ system uses plants with natural microbes to degrade the contaminant. The ‘with oxygen’ system further improves water quality through continued exposure to plants and movement of water between compartments. Straw, manure or compost is used, with little or no soil, for the removal of metals.
For wetlands constructed to treat explosives-contaminated water, certain plant species are used for degradation.
3. Technology
The process filters some materials and degrades others. Technology is used to incorporate principal components of wetland ecosystems, that promote degradation, by controlling contaminants using plants.
4. Removal mechanism
Removal mechanisms can act uniquely, sequentially, or simultaneously on each contaminant group or species.
Major physical removal mechanisms in wetlands include settling, sedimentation, and volatilization. Settling as a result of gravity is responsible for most of the removal of suspended solids.
A Summary of Dr. Sudarsan J S’s Study
Vegetation
Typha latifolia, a local wetland species, was used in the study. The plants were collected from a nearby lake and planted in the wetland unit. They increased the residence time of water and sedimentation of suspended particles.
They also added oxygen and were used to remove suspended solids, nutrients, heavy metals, toxic organic compounds and bacteria from acid mine drainage, agricultural landfill and urban stormwater runoff.
Basis of the Model
The constructed wetland’s prototype model was based on the U.S. Environmental Protection Agency’s (USEPA) design criteria. The same was modified for Indian conditions.
The samples were analysed for the contaminants – pH, BOD, COD, Total Solids (TS), Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Total Volatile Solids (TVS), Available Nitrogen (AN) and Phosphorous (P) as per the American Public Health Association (APHA) guidelines.
From the above results, the percentage reduction is more than 70% after the treatment.
Results
Constructed wetlands have been used extensively to treat several types of wastewaters and runoff.
The dairy wastewater tested in this study contained high levels of BOD, COD, total solids, total dissolved solids, total suspended solids, nitrogen and phosphorus. The results indicate treatment efficiency significantly improved within 3 days of Hydraulic Retention Time (HRT). HRT should be given special attention in the design of future full-scale facilities.
We also learn that wetland plant species and soil play a significant role in the treatment of wastewater.
This shows that the lab scale model of constructed wetland is working effectively to treat the dairy wastewater and the principle of RRR (Reduce, Recycle and Reuse) is implemented successfully.
Overall, this nature-based, low-cost wastewater treatment technology will save ecosystems effectively.
Conclusion
There’s a growing need to protect our planet’s resources for future generations. Water, one of the very basic resources for survival, is threatened by pollution and wastage without having proper systems in place to renew it.
Constructed wetlands can prove beneficial in helping treat wastewater, making it potable again. They’re not just effective but also low-cost, and work in partnership with nature.
For more in-depth information, you can read Dr. Sudarsan J.S.’s research study and refer to the sources below.
References:
- EPA Manual, July 1993, “Subsurface flow constructed wetlands for wastewater”
- “Dairy wastewater generation and characteristics”, http://www.ctahr.hawaii.edu/wwm/waste.asp
- Gottschall, N, C. Boutin, 2007, The role of plants in removal of nutrients at a constructed wetland treating agricultural dairy wastewater. Ecol. Eng. ONTARIO
- Reed, S. C., Wastewater engineering – Treatment and Reuse, 2003 McGraw Hill
- Kickuth. R, 1977, Degradation and incorporation of nutrients from rural wastewater by plant rhizosphere under liminic condition
- U.S EPA 1988 Design Manual – Constructed wetlands and aquatic plant system for municipal wastewater treatment, EPA625/11-88/022
- Reed, S. C. 1992, Constructed wetland characterization – Green leaves and Hammond L.A for U.S EPA RREL, Cincinnati, OH.
- APHA manual 2005, 21st edition – Standard Methods for the Examination of Water and Wastewater, Centennial edition, APHA.
- Munoz P, Drizo A, Hession W.C. 2006 – Flow Patterns of Dairy Wastewater Constructed wetland in a Cold Climate, Water Research 40(3209-3218)
- Garg S.K. 2004, Water Supply and Waste Water Engineering Vol. I & II, Khanna Publications, New Delhi.
Credits
Author
Dr. Sudarsan J.S. is an Environmental Engineering professional currently working at NICMAR as Asst. Professor. He’s also skilled in sustainability, waste and team management. The education management industry has been his workplace for over a decade, complete with a Doctorate & Masters in Environmental Engineering plus PGDIS in Industrial Safety Technology. This article is written with insights from his research study on constructed wetlands, with his express permission.
Editor
Ayesha comes with 5+ years of experience in the online marketing industry. She’s a freelance writer & editor, working with B2B clients in SaaS, Sustainability & Education sectors. Previously a social media manager for notable brands, now she loves writing long-form and website content. When she’s not being a wordsmith, she’s reading thrillers, watching MCU films, and cooking up new dishes. Connect with her on LinkedIn to keep up with her.