Wetland Filtration

Any area that is wet either due to a rainstorm or industrial/sewage discharge would not be considered a wetland. A Natural wetland is unique in that plants grow in it, animals live here, processes take place within that flooded water, and an ecosystem thrives. Wetland filtration, whether natural or manmade is a powerful water treatment solution.

Wetland Classification

  • Bog: or a bogland is characterized with the deposition of Peat (partially decayed organic matter or vegetation, covers large areas in the form of peatlands, mires, or moors) and Mosses (also called Bryophytes, are the small, usually one cell thick, flower-less plants, developed in the form of mats in damp shady places)
  • Fens: are pH neutral/alkaline, mineral-rich wetlands fed by either surface or groundwater. A fen is different from other wetlands because of its unique water chemistry, which maintains a stable water table year-round. Carnivorous plants (e.g., Butterworts “Pinguicula” use granular, sticky substances to entrap, lure the insects), Sedges, Brown Mosses are the dominant vegetation of Fen.
  • Swamps: are forested wetlands that are constantly flooded with nearby streaming water bodies and are dominated by water-loving trees, shrubs, bushes, herbaceous plants. The vegetation is so dense that when the water (maybe groundwater, precipitation, or tides) flows down through the roots, all the pollutants, nutrients (mainly P and N, either buried in the saturated soils or accumulated at the bottom of the swamp), and sediments are naturally filtered out.
  • Marsh: forms a transition between aquatic and terrestrial ecosystems as present at the edges of lakes or streams. Marshes are dominated by herbaceous vegetation (grasses, reeds, or rushes) and not woody plants. Papyrus (Cyperus papyrus), Cattail, Sawgrasses (Cladium spp.), and sedges are dominant among vegetation well-adapted for marshy wetlands.

Wetlands are an essential part of any ecosystem that offers habitats for many migrating birds, mammals (both small (minks, reptiles) and large (moose, etc.).), plants, and insects.

Wetlands are typically teeming with wildlife due to their diverse ecosystem and the fact that humans don’t usually frequent wetlands.

The Wetlands are the areas flooded with water, either permanently or temporarily that support aquatic plants and animal growth. Wetlands are beneficial for the area where they are present because they are involved in water purification, removal of nutrients from contaminated water, and water storage.

How do Natural Wetlands Work?

The water that enters any NW may be surface runoff from residential homes and lawns(fertilizers, pet waste, sewer, and septic), commercial hard surfaces (industrial waste, road salt, petroleum), agricultural land (livestock waste, chemical pesticides, and fertilizers) or direct sources such as streams, rainfall, and tides. All of which may contain large quantities of nutrients, suspended solids, chemicals, and pathogens.

Through the dense vegetation of NW, water moves slowly, settling down the sediments and suspended solids while the plants and microorganisms absorb nutrients. Gases like CO2 and other harmful gases are stored in sinks in wetlands. This is a wonderfully natural purification process that occurs in NW without us investing any energy and cost. We just need to stay out of their way.

Benefits and Uses of Natural Wetland Filtration

Flood Control and Water Storage

The continuous rains and snow-melting processes are the causes of floods. The wetlands (either Natural or Constructed) near the water-heads of rivers or streams play an important role in slowing down that water’s runoff and helping control damaging floods. The Natural Wetlands store back the water in its spongy sedimentation layers and release it during the drought periods. In this way, life in the wetlands survives during water scarcity periods due to stored water.

Heavy Metal’s Traps

The NaturalWetlands came into being through flooded water, rainwater, or runoff water. This water contains many nutrients (excessive Nitrogen, Carbon Dioxide, Phosphorus, and heavy metals). These nutrients get stored in the sediments or plant’s bodies and remain stored until plants die, are harvested by the animals, or microbial processes convert these elements into a gaseous form released into the atmosphere. If these natural nutrient absorbents would not be present, no one could be able to protect his/her land from that soil desolating water.

Water Purification

The animal and plant population in the wetlands helps absorb, utilize and decompose the water contaminants. Water-loving animals such as Oysters filter more than 200 Liters of water every day, searching for food. Water Hyacinths, Reed-grass, duckweed, and Cattail plants remove Iron, Copper, Mercury, and pathogens from the water and store them in their body or convert them into less toxic forms.

Check out our article on Phytoremediation.

A Balanced Ecosystem

They help bring a balance to the environment. The Natural Wetlands Control flood water by acting as a sponge to store excessive, un-wanted water and use it later during shortage periods. Loss of wetlands means the loss of many wetland animals and plant species and natural water filters, which causes an imbalance in the atmospheric conditions, flood peaks, and soil erosion.

Natural Predators

Wetlands not only filter nutrients from water but also reduce the mosquito population. It contains many insects, amphibians, and birds that act as natural predators for the mosquitos.

Biodiversity Nurturing

Aquatic plants and grasses of wetlands are part of large mammals’ diet, for example, cows, goats, deer, moose, etc. The birds dive into the shallow shorelines and capture small insects, which helps maintain a balance in the population of insects in the wetlands. Wetlands are the breeding grounds of many birds (Ducks, Geese, Cranes, Herons, Shorebirds, and Blackbirds, etc.); they are also excellent midday resting and hiding places for countless other creatures, both large and small.

Constructed Wetland Filtration System

We have constructed wetlands to act as Biofilters similar to that of Natural Wetlands to treat rainwater, groundwater, greywater, municipal water, and reclamation of mining-affected soils. Biological and Mechanical filters, Plants, and Sand/Gravel are collectively used in the backyards of houses and many industries to clean the water again and again, just like a natural wetland.

The big difference between a natural and a constructed wetland filtration system is that the NW are provided to us by nature and will not be found in cities or town centers, while CW can be created in small areas of the garden, back yard, landscapes, city lots, rooftops, commercial sites or just about anywhere. While the role of both is the same, i.e., the wastewater treatment and pollution control, we have the ability to greatly increase our water clarifying ability through the use of CW.

How Constructed Wetlands Work to Clean the Wastewater

A constructed wetland is a human-designed shallow wetland of varying sizes with different kinds of layering (sand, gravel, rocks) and wetland plant species growing in it. Wastewater flows from one end of CW or is pumped into the bottom, passes through the sub-surface/surface, and finally pours out at the other end, having been cleaned.

The system typically keeps the water just above the plant roots. The aquatic plant masses, especially the Reed-grass species, act as active reaction regions (with the help of microorganisms, complex physiochemical and biological reactions) and absorb N, P, pathogens, and other contaminants from the water.

Another advantage of constructed wetlands is that they allow for the settling out of sediment and sludge, which would otherwise end up in our pond and streams.

Components of Constructed Wetlands

There are many different styles and types of constructed wetlands. Different types have different applications, but many contain the same components.

  • A Geomembrane lining (synthetic polymer, very low permeability)
  • Concrete or clay lining (to protect the surrounding water table)
  • The substrate (gravel, rock, stone, sand) depending upon availability.
  • Water flow

Types of Constructed Wetlands

Surface Flow

As the name implies, the surface flow system is installed in the ground so that the water flows across the wetland’s surface. Surface flow wetlands are used to treat wastewater by settling down the particles, removing/destroying the pathogens, extracting nutrients using plants and other organisms living on the plants.

The UV irradiation kills pathogens, and sedimentation occurs as the wastewater flows slowly through the wetland. The below water soil layer is anaerobic while the plants’ roots provide oxygen, which allows the overall initiation of complex chemical and biological reactions to remove the nutrients.

Specifications of Surface Flow Wetland Filtration System:

  • A surface-flow system always has a Horizontal flow of water across the plant’s roots and never vertical.
  • It requires a large area for proper installment and functioning. These systems are also named “Waste Stabilization Ponds” because they work the same way as waste stabilization lagoons.
  • The treated water can be used for irrigation purposes or returned to the surface water.
  • The system is less efficient in the winter because of the decreased intensity of sunlight and temperature, both of which are important in the treatment processes.
  • The system is best suited for Tropical and Subtropical climates because of the constant availability of bright sunlight and high temperature but does provide value in almost any climate.
  • Due to the open water availability, the surface system may be used by aquatic animals.
  • The plants encouraged to grow in a surface flow filtration system are Pickerel-weed (Pontederia cordata), Common Water Hyacinth (Eichhornia crassipes), Broad-leaf Cattail (Typha latifolia), and Common Reed (Phragmites australis).

Subsurface Flow

The subsurface flow filtration system is installed similarly to the surface flow, but the water flows through the plants’ substrate and roots rather than across the surface.

Specifications of a subsurface flow system:

  • It is a more efficient system as the flow of water through the substrate and plant roots allows for more efficient water treatment than water flowing across the surface.
  • A subsurface flow may be horizontal or vertical. The vertical flow constructed wetland is the type most often used for treating pond water on backyard ponds and commercial and industrial retention ponds.
  • If used for wastewater treatment specifically, the subsurface system does the secondary wastewater treatment, i.e., the water has already passed through the primary treatment processes like a compost filter and settling area. After that, the working of the subsurface flow system starts.
  • The system does filtration, adsorption, and biodegradation. After passing through all the processing compartments, the treated wastewater will be safe enough for surface discharge or irrigation.
  • The plants encouraged to grow in a subsurface filtration system are:
    • Reed-grasses (the grasses build up reed-beds (considerable litter layer) that is helpful in pollutant removal from greywater)
    • Bul-Rush or Cattail (Scirpoides holoschoenus)
    • Soft Rush (Juncus effusus)
    • Musa spp.
    • Sedges (belongs to Carex, species-rich genus, similar to grasses).

Types of Filters in Constructed Wetlands:

Constructed wetland filters work as a natural filter to purify sewage, industrial, and runoff wastewater and cleaner water filtration such as pond or lake filtration. The system receives water and pushes it upward. The water passes through stones, gravel, and plant roots. These screens act as filters to remove nutrients, pollutants, etc. this is the most economical and ecologically beneficial method for the primary treatment of wastewater in small communities. There is no use of chemicals to clean the water; instead, the beneficial bacteria on the rocks, plant roots (Rhizofilteration: removal of contaminants from the water through a mass of roots) are the sources for pond water filtration.

Vertical up-flow constructed wetland filter:

Up-flow wetland filters are available in different shapes and sizes for small and medium to large scale pond installations. The working science behind all the up-flow filters is that the water is pumped into the bottom of the filter and then flows upward through certain filter media (will be different for different filters but mostly sand and gravel) to remove suspended solids. Then proceeds through the plant roots for further filtration through a combination of biological processes that remove the nutrients and pollutants. The water then flows back into the pond through a waterfall or stream, which provides more aeration and oxygenation of the water.

It is also suitable for the filtration of highly polluted water if designed for a longer percolation duration to increase the wastewater processing time.


  • A sedimentation tank (used for the settling of large solids to prevent clogging the filter)
  • A layered filter package (acts as a biochemical reactor).
    • Large to medium-sized stones at the bottom
    • Above it is a layer of smaller gravel
    • A layer of sand on top of the rock (in some applications)
    • Planted in the top layer are varieties of aquatic plants (microorganisms are present at the root of the plant, absorbing the nutrients from the water to grow).

Water from the sedimentation tank is pumped into the distribution tank. Then water moves through the reed plant’s roots to the bottom of the filter package. The bacteria present at the roots absorb the water’s nutrients, making it clean and clear.

This water cleaning system is available to install at a small scale for a garden, lawn, pond water treatment and large-scale sewage wastewater treatment, industrial water treatment, etc.

Horizontal flow constructed wetland filter:

It is the ideal filtration system for home gardening as it filters light to moderately polluted water. Almost 30 years ago, no one could think that they might need a filtration system to clean even their house water! Water pollution has been increased in the last few decades while the plants have stayed the same.

There are many varieties of wonderful plants that can help us to clean our water.


  • Water reservoir for settling (if filtering water with high levels of suspended solids)
  • Gravel and sand-filled basin
  • Reed grass or any other wetland species, e.g., Indian Lotus, Eel-grasses, Seagrasses, etc.

There is no need to pump the water as it flows with the force of gravity. The water from the tank flows towards the filters (gravel, sand, plant roots) horizontally. Significant removal of pathogens by aerobic decomposition, reduction of nutrient concentrations, reduced BOD of wastewater are the functional characteristics of a subsurface horizontal wetland filtration system.

Flow field filtration system:

The flow field is the preferable system that cleans large quantities of water compared with the above-described systems. A shallow trench (30-80 cm depth) is constructed, the water flows through this swale, the swamp vegetation planted in that trench cleans the running water through a number of chemical (either change the water nutrients concentrations to make them suitable for the soil) and biological processes (bacteria absorbs both the oxygen, Nitrogen and heavy metals from the wastewater).

The whole filtration system converts the unsuitable water into standard usable water. Again, the system can be installed for small and large-scale wastewater treatment and is often used to treat parking lot runoff.

The Benefits of constructed wetland’s filtration system

Nitrogen removal:

Nitrogen, in the form of Ammonia, Organic Nitrogen, Nitrate, Nitrite, and ammonium, is the chief element present in wastewater. Why is it important to remove Nitrogen when it is essential for plant growth? The answer is that not all the forms and excessive concentrations of Nitrogen are good for aquatic plants, animals, and soil. So it is important to either alter or remove excessive N before discharging the water.

  • Nitrification: Ammonia in the water is converted into Ammonium ions,
  • The Bacterium Nitrosomonas sp. aerobically convert Ammonium ion into Nitrite,
  • Nitrobacter sp. Changes the Nitrite into Nitrate,
  • Denitrification: Nitrate is then reduced (anaerobically) into harmless Nitrogen gas and released into the atmosphere.

Phosphorus removal:

Increased use of chemicals in the form of dyes, fertilizers, pesticides, LEDs, and safety matches, has also increased the P-pollution in water. Otherwise, P is in short supply under natural undisturbed conditions. It is not easy to remove P from water as it does not have an atmospheric component like Nitrogen.

The aquatic plants grown in wetlands absorb the P from water (it is an essential factor in any plant’s growth and development). The living biomass is then removed once their growth cycles are completed (have absorbed the maximum P they could) and replaced by new plants for the efficient removal of P. This is done for heavily contaminated water treatment. When treating pond water, simply removing the plants’ foliage and not allowing them to decompose back into the water will remove much of the phosphorous.

Pathogen removal:

Constructed wetland filters remove pathogens present in water. The sub-surface wetland removes the pathogens (Bacteria, Viruses, Protozoa, and Helminths) more efficiently than surface wetlands.

A sub-surface flow wetland removes:

  • 90-99.9% Bacteria
  • 90-99% Viruses
  • 90-99% Protozoa
  • 99% Helminths

A surface flow wetland efficiently removes:

  • 90-99% Bacteria
  • 90-92% Viruses
  • 90% Protozoa
  • 90-99%% Helminths

Source: Maiga, Y., von Sperling, M., Mihelcic, J. 2017. Constructed Wetlands. In: J.B. Rose and B. Jiménez-Cisneros, (eds) Global Water Pathogens Project. (C. Haas, J.R. Mihelcic and M.E. Verbyla) (eds) Part 4 Management Of Risk from Excreta and Wastewater) Michigan State University, E. Lansing, MI, UNESCO. Material was copied from this source, which is available under a Creative Commons Attribution-ShareAlike 3.0 Unported license.

Flood water retention:

When used for flood water retention, the wetland filters are installed in a retention area to allow for water accumulation, settling, and soaking back into the groundwater. They receive the water during surface runoff, storms, or floods. CW’s thick vegetation slows down the speed of flowing water, hence controlling the drastic effects of sudden, un-planned water deluge. Nowadays, CW’s are being established around industries and cities to protect the high-priced commodities from flood damages and clean the wastewater discharged by the industries.

An example of this is NIMR WATER TREATMENT PLANT, in Oman (consisted of 780hc of wetlands and large ponds) to clean the wastewater (115,000m3/day) discharged by the nearby oil industries.

Research-Based Accepted Facts About CW:

Construction of wetland filtration system for a small community:

In 2009, an experiment was conducted at the village of Ileydagi, Turkey, situated near Lake Egirdir, to check out the rate of removal of contaminants from the constructed wetland system. The system was further assisted with BSF (Buried Sand Filtration system) and BSSF-CW (Buried Sub-surface Flow Constructed Wetlands). After fourteen months of observation, it was concluded that the system removes:

  • 97% of BOD (Biological Oxygen Demand)
  • 85% of total Nitrogen
  • 69% of TP (total Phosphorus)

Whenever you go for an environment-friendly system to protect the soil, water, and air from further pollution, you have to engage the local people. Water pollution, lowering groundwater levels, and water shortage are the burning issues of every city, town, and country. We must all spread the word to make our friends and neighbors understand the wetlands’ benefits.

Sub-Surface Constructed Wetland for Single House Wastewater Treatment:

In Eastern Norway, subsurface, constructed wetland systems were separately installed in single houses to clean the sewage wastewater.

The system contains the following filters:

  • A septic tank: collecting and passing the wastewater to the bio-filter.
  • Aerobic Bio-filter: to remove organic waste and also for denitrification
  • Upflow saturated filter: remove P, microorganisms, and polishing the sewage water.
  • Upflow filter media: contains the finest sand at the top, coarsest in the middle, and gravel at the bottom (kept in fixed positions)

The system was installed for five years without any maintenance necessities. After three years of successful operation, the average values/day measured were:

  • N: 30%
  • P: 99.4%
  • SS: 70.8%
  • BOD: 97.8%
  • Zero Escherichia Coli/Coliphages

The treated water was tested to be beneficial for irrigation, soil, and the ecosystem as the excessive nutrients, organic matter, and pathogens have been removed.


As humans destroy more and more of the natural environment on this earth, we must be aware that the reduction of plant material covering this earth is not without consequences. Through the application of constructed wetland filters and re-constructing damaged or once filled wetlands, we can begin to turn the tide the other way. By coupling the efforts of wetland creation, permaculture, and the aggressive planting of trees and plants on every bare surface possible, we have a chance to save this earth and bring the earth’s natural ecosystem back into balance.

When it comes down to it, it’s not about hard-to-understand scientific principles or complex, hard-to-implement procedures; it’s really all about plants. We need more. Wouldn’t a healthy earth with a naturally balanced ecosystem be a lovely gift to leave your grandchildren?


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