
A constructed wetland is an artificial
wetland
A wetland is a distinct semi-aquatic ecosystem whose groundcovers are flooded or saturated in water, either permanently, for years or decades, or only seasonally. Flooding results in oxygen-poor ( anoxic) processes taking place, especially ...
to treat
sewage
Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewerage, sewer system. Sewage consists of wastewater discharged fro ...
,
greywater
Greywater (or grey water, sullage, also spelled gray water in the United States) refers to domestic wastewater generated in households or office buildings from streams without fecal contamination, i.e., all streams except for the wastewater fro ...
,
stormwater
Stormwater, also written storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed lan ...
runoff or
industrial wastewater
Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reused or released to a s ...
. It may also be designed for land reclamation after
mining
Mining is the Resource extraction, extraction of valuable geological materials and minerals from the surface of the Earth. Mining is required to obtain most materials that cannot be grown through agriculture, agricultural processes, or feasib ...
, or as a
mitigation
Mitigation is the reduction of something harmful that has occurred or the reduction of its harmful effects. It may refer to measures taken to reduce the harmful effects of hazards that remain ''in potentia'', or to manage harmful incidents that ...
step for natural areas lost to
land development
Land development is the alteration of landscape in any number of ways, such as:
* Changing landforms from a natural or semi-natural state for a purpose such as agriculture or House, housing
* subdivision (land), Subdividing real estate into Lot ( ...
. Constructed wetlands are engineered systems that use the natural functions of
vegetation
Vegetation is an assemblage of plants and the ground cover they provide. It is a general term, without specific reference to particular Taxon, taxa, life forms, structure, Spatial ecology, spatial extent, or any other specific Botany, botanic ...
,
soil
Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...
, and organisms to provide
secondary treatment
Secondary treatment (mostly biological wastewater treatment) is the removal of Biodegradation, biodegradable organic matter (in solution or suspension) from sewage or similar kinds of wastewater. The aim is to achieve a certain degree of effluent ...
to
wastewater
Wastewater (or waste water) is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of do ...
. The design of the constructed wetland has to be adjusted according to the type of wastewater to be treated. Constructed wetlands have been used in both centralized and
decentralized wastewater system
Decentralized wastewater systems (also referred to as decentralized wastewater treatment systems) convey, treat and dispose or reuse wastewater from small and low-density communities, buildings and dwellings in remote areas, individual public or ...
s. Primary treatment is recommended when there is a large amount of suspended solids or soluble organic matter (measured as
biochemical oxygen demand
Biochemical oxygen demand (also known as BOD or biological oxygen demand) is an analytical parameter representing the amount of dissolved oxygen (DO) consumed by aerobic bacteria growing on the organic material present in a water sample at a s ...
and
chemical oxygen demand
In environmental chemistry, the chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution, wh ...
).
Similar to natural wetlands, constructed wetlands also act as a
biofilter
Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, a ...
and/or can remove a range of
pollutant
A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effect, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...
s (such as organic matter,
nutrients
A nutrient is a substance used by an organism to survive, grow and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
,
pathogen
In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...
s,
heavy metals
upright=1.2, Crystals of lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead
Heavy metals is a controversial and ambiguous term for metallic elements with relatively h ...
) from the water. Constructed wetlands are designed to remove water pollutants such as suspended solids, organic matter and nutrients (nitrogen and phosphorus).
All types of pathogens (i.e., bacteria, viruses,
protozoa
Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...
ns and
helminths
Parasitic worms, also known as helminths, are a polyphyletic group of large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other par ...
) are expected to be removed to some extent in a constructed wetland. Subsurface wetlands provide greater pathogen removal than surface wetlands.
There are two main types of constructed wetlands: subsurface flow and surface flow. The planted vegetation plays an important role in contaminant removal. The filter bed, consisting usually of
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...
and
gravel
Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone.
Gr ...
, has an equally important role to play.
Some constructed wetlands may also serve as a
habitat
In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
for native and migratory
wildlife
Wildlife refers to domestication, undomesticated animals and uncultivated plant species which can exist in their natural habitat, but has come to include all organisms that grow or live wilderness, wild in an area without being species, introdu ...
, although that is not their main purpose. Subsurface flow constructed wetlands are designed to have either horizontal flow or vertical flow of water through the gravel and sand bed. Vertical flow systems have a smaller space requirement than horizontal flow systems.
Terminology
Many terms are used to denote constructed wetlands, such as
reed bed
A reedbed or reed bed is a natural habitat found in floodplains, waterlogged depressions and
estuaries. Reedbeds are part of a succession from young reeds colonising open water or wet ground through a gradation of increasingly dry ground. As ...
s, soil infiltration beds, treatment wetlands, engineered wetlands, man-made or artificial wetlands.
[Hoffmann, H., Platzer, C., von Münch, E., Winker, M. (2011)]
Technology review of constructed wetlands – Subsurface flow constructed wetlands for greywater and domestic wastewater treatment
Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH, Eschborn, Germany A
biofilter
Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, a ...
has some similarities with a constructed wetland, but is usually without plants.
The term of constructed wetlands can also be used to describe restored and recultivated land that was destroyed in the past through draining and converting into farmland, or mining.
Overview
A constructed wetland is an engineered sequence of water bodies designed to treat
wastewater
Wastewater (or waste water) is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of do ...
or
storm water runoff.
Vegetation in a wetland provides a substrate (roots, stems, and leaves) upon which
microorganism
A microorganism, or microbe, is an organism of microscopic scale, microscopic size, which may exist in its unicellular organism, single-celled form or as a Colony (biology)#Microbial colonies, colony of cells. The possible existence of unseen ...
s can grow as they break down organic materials. This community of microorganisms is known as the
periphyton
Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. The related term Aufwuchs ( German "surface growth" or "overgrowth", ) refers to the ...
. The periphyton and natural chemical processes are responsible for approximately 90 percent of
pollutant
A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effect, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...
removal and waste breakdown. The plants remove about seven to ten percent of pollutants, and act as a
carbon
Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...
source for the microbes when they decay. Different species of
aquatic plant
Aquatic plants, also referred to as hydrophytes, are vascular plants and Non-vascular plant, non-vascular plants that have adapted to live in aquatic ecosystem, aquatic environments (marine ecosystem, saltwater or freshwater ecosystem, freshwater ...
s have different rates of heavy metal uptake, a consideration for plant selection in a constructed wetland used for water treatment. Constructed wetlands are of two basic types: subsurface flow and surface flow wetlands.
Constructed wetlands are one example of
nature-based solutions
Nature-based solutions (or nature-based systems, and abbreviated as NBS or NbS) describe the development and sustainable use, use of nature (biodiversity) and natural processes to address diverse social issue, socio-environmental issues. These is ...
and of
phytoremediation
Phytoremediation technologies use living plants to clean up soil, air and water contaminated with hazardous contaminants. It is defined as "the use of green plants and the associated microorganisms, along with proper soil amendments and agronom ...
.
Constructed wetland systems are highly controlled environments that intend to mimic the occurrences of soil, flora, and microorganisms in natural wetlands to aid in treating wastewater. They are constructed with flow regimes, micro-biotic composition, and suitable plants in order to produce the most efficient treatment process.
Uses
Constructed wetlands can be used to treat raw sewage, storm water, agricultural and
industrial effluent
Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reused or released to a ...
. Constructed wetlands mimic the functions of natural wetlands to capture stormwater, reduce nutrient loads, and create diverse wildlife habitat. Constructed wetlands are used for
wastewater treatment
Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on ...
or for
greywater
Greywater (or grey water, sullage, also spelled gray water in the United States) refers to domestic wastewater generated in households or office buildings from streams without fecal contamination, i.e., all streams except for the wastewater fro ...
treatment.
Many regulatory agencies list treatment wetlands as one of their recommended "
best management practices" for controlling
urban runoff
Urban runoff is surface runoff of rainwater, landscape irrigation, and car washing created by urbanization. Impervious surfaces (roads, parking lots and sidewalks) are constructed during land development. During rain, storms, and other Precipitati ...
.
Removal of contaminants
Physical, chemical, and biological processes combine in wetlands to remove contaminants from wastewater. An understanding of these processes is fundamental not only to designing wetland systems but to understanding the fate of chemicals once they enter the wetland. Theoretically,
wastewater treatment
Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on ...
within a constructed wetland occurs as it passes through the wetland medium and the plant
rhizosphere
The rhizosphere is the narrow region of soil or Substrate (biology), substrate that is directly influenced by root secretions and associated soil microorganisms known as the root microbiome. Pore space in soil, Soil pores in the rhizosphere can ...
. A thin film around each root hair is
aerobic
Aerobic means "requiring air," in which "air" usually means oxygen.
Aerobic may also refer to
* Aerobic exercise, prolonged exercise of moderate intensity
* Aerobics, a form of aerobic exercise
* Aerobic respiration, the aerobic process of cellu ...
due to the leakage of oxygen from the
rhizome
In botany and dendrology, a rhizome ( ) is a modified subterranean plant stem that sends out roots and Shoot (botany), shoots from its Node (botany), nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from ...
s,
root
In vascular plants, the roots are the plant organ, organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often bel ...
s, and rootlets.
Aerobic
Aerobic means "requiring air," in which "air" usually means oxygen.
Aerobic may also refer to
* Aerobic exercise, prolonged exercise of moderate intensity
* Aerobics, a form of aerobic exercise
* Aerobic respiration, the aerobic process of cellu ...
and
anaerobic
Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to:
*Adhesive#Anaerobic, Anaerobic ad ...
micro-organisms facilitate decomposition of organic matter. Microbial
nitrification
''Nitrification'' is the biological oxidation of ammonia to nitrate via the intermediary nitrite. Nitrification is an important step in the nitrogen cycle in soil. The process of complete nitrification may occur through separate organisms or ent ...
and subsequent
denitrification
Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitr ...
releases
nitrogen
Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
as gas to the
atmosphere
An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
.
Phosphorus
Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...
is
coprecipitated with
iron
Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...
,
aluminium
Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
, and
calcium
Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
compounds located in the root-bed medium.
[Brix, H., Schierup, H. (1989): Danish experience with sewage treatment in constructed wetlands. In: Hammer, D.A., ed. (1989): Constructed wetlands for wastewater treatment. Lewis publishers, Chelsea, Michigan, pp. 565–573] Suspended solids
Suspended solids refers to small solid particles which remain in suspension in water as a colloid or due to motion of the water. Suspended solids can be removed by sedimentation if their size or density is comparatively large, or by filtration ...
filter out as they settle in the water column in surface flow wetlands or are physically filtered out by the medium within subsurface flow wetlands. Harmful
bacteria
Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
,
fungi
A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
, and
virus
A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...
es are reduced by filtration and adsorption by
biofilm
A biofilm is a Syntrophy, syntrophic Microbial consortium, community of microorganisms in which cell (biology), cells cell adhesion, stick to each other and often also to a surface. These adherent cells become embedded within a slimy ext ...
s on the gravel or sand media in subsurface flow and vertical flow systems.
Nitrogen removal
The dominant forms of nitrogen in wetlands that are of importance to
wastewater
Wastewater (or waste water) is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of do ...
treatment include
organic nitrogen
Nitrogen is a chemical element; it has symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in ...
,
ammonia
Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
,
ammonium
Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...
,
nitrate
Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...
and
nitrite
The nitrite polyatomic ion, ion has the chemical formula . Nitrite (mostly sodium nitrite) is widely used throughout chemical and pharmaceutical industries. The nitrite anion is a pervasive intermediate in the nitrogen cycle in nature. The name ...
. Total nitrogen refers to all nitrogen
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
. Wastewater nitrogen removal is important because of ammonia's toxicity to fish if discharged into watercourses. Excessive nitrates in drinking water is thought to cause
methemoglobinemia
Methemoglobinemia, or methaemoglobinaemia, is a condition of elevated methemoglobin in the blood. Symptoms may include headache, dizziness, shortness of breath, nausea, poor muscle coordination, and blue-colored skin (cyanosis). Complications ma ...
in infants, which decreases the blood's oxygen transport ability. Moreover, excess input of N from point and non-point sources to surface water promotes eutrophication in rivers, lakes, estuaries, and coastal oceans which causes several problems in aquatic ecosystems e.g. toxic algal blooms, oxygen depletion in water, fish mortality, loss of aquatic biodiversity.
Ammonia removal occurs in constructed wetlands – if they are designed to achieve biological nutrient removal – in a similar ways as in
sewage treatment
Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water p ...
plants, except that no external, energy-intensive addition of air (oxygen) is needed.
It is a two-step process, consisting of
nitrification
''Nitrification'' is the biological oxidation of ammonia to nitrate via the intermediary nitrite. Nitrification is an important step in the nitrogen cycle in soil. The process of complete nitrification may occur through separate organisms or ent ...
followed by
denitrification
Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitr ...
. The
nitrogen cycle
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmosphere, atmospheric, terrestrial ecosystem, terrestrial, and marine ecosystems. The conversion of nitrogen can ...
is completed as follows: ammonia in the wastewater is converted to ammonium ions; the aerobic bacterium ''
Nitrosomonas
''Nitrosomonas'' is a genus of Gram-negative bacteria belonging to the class Betaproteobacteria. It is one of the five genera of ammonia-oxidizing bacteria and, as an obligate chemolithoautotroph, uses ammonia (NH3) as an energy source and c ...
'' sp. oxidizes ammonium to nitrite; the bacterium ''
Nitrobacter
''Nitrobacter'' is a genus comprising rod-shaped, gram-negative, and chemoautotrophic bacteria. The name ''Nitrobacter'' derives from the Latin neuter gender noun ''nitrum, nitri'', alkalis; the Ancient Greek noun βακτηρία, βακτηρ� ...
'' sp. then converts nitrite to nitrate. Under anaerobic conditions, nitrate is reduced to relatively harmless nitrogen gas that enters the atmosphere.
Nitrification
Nitrification is the biological conversion of organic and inorganic nitrogenous compounds from a reduced state to a more oxidized state, based on the action of two different bacteria types.
[Wetzel, R.G. (1983): Limnology. Orlando, Florida: Saunders college publishing.] Nitrification is strictly an aerobic process in which the end product is nitrate (). The process of nitrification oxidizes ammonium (from the wastewater) to nitrite (), and then nitrite is oxidized to nitrate ().
Denitrification
Denitrification is the biochemical reduction of oxidized nitrogen anions, nitrate and nitrite to produce the gaseous products nitric oxide (NO),
nitrous oxide
Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or factitious air, among others, is a chemical compound, an Nitrogen oxide, oxide of nitrogen with the Chemical formula, formula . At room te ...
() and nitrogen gas (), with concomitant oxidation of organic matter.
The end product, , and to a lesser extent the intermediary by product, , are gases that re-enter the atmosphere.
Ammonia removal from mine water
Constructed wetlands have been used to remove ammonia and other nitrogenous compounds from contaminated
mine water
Pit water, mine water or mining water is water that collects in a mining, mine and which has to be brought to the surface by water management methods in order to enable the mine to continue working.
Origin
Although all water that enters pit work ...
, including cyanide and nitrate.
Phosphorus removal
Phosphorus
Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...
occurs naturally in both organic and inorganic forms. The analytical measure of biologically available
orthophosphates is referred to as soluble reactive phosphorus (SR-P). Dissolved organic phosphorus and insoluble forms of organic and inorganic phosphorus are generally not biologically available until transformed into soluble inorganic forms.
[Mitsch, J.W., Gosselink, J.G. (1986): Wetlands. New York: Van Nostrand Reinhold Company, p. 536]
In freshwater
aquatic ecosystem
An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environ ...
s phosphorus is typically the major limiting nutrient. Under undisturbed natural conditions, phosphorus is in short supply. The natural scarcity of phosphorus is demonstrated by the explosive growth of
algae
Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
in water receiving heavy discharges of phosphorus-rich wastes. Because phosphorus does not have an atmospheric component, unlike nitrogen, the
phosphorus cycle
The phosphorus cycle is the biogeochemical cycle that involves the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the moveme ...
can be characterized as closed. The removal and storage of phosphorus from wastewater can only occur within the constructed wetland itself. Phosphorus may be sequestered within a wetland system by:
# The binding of phosphorus in organic matter as a result of incorporation into living biomass,
#
Precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
of insoluble phosphates with
ferric
In chemistry, iron(III) or ''ferric'' refers to the chemical element, element iron in its +3 oxidation number, oxidation state. ''Ferric chloride'' is an alternative name for iron(III) chloride (). The adjective ''ferrous'' is used instead for i ...
iron,
calcium
Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
, and
aluminium
Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
found in wetland soils.
Biomass plants incorporation
Aquatic vegetation may play an important role in phosphorus removal and, if harvested, extend the life of a system by postponing phosphorus saturation of the sediments.
[Guntensbergen, G.R., Stearns, F., Kadlec, J.A. (1989): Wetland vegetation. In Hammer, D.A., ed. (1989): Constructed wetlands for wastewater treatment. Lewis publishers, Chelsea, Michigan, pp. 73–88] Plants create a unique environment at the biofilm's attachment surface. Certain plants transport oxygen which is released at the biofilm/root interface, adding oxygen to the wetland system. Plants also increase soil or other root-bed medium hydraulic conductivity. As roots and
rhizome
In botany and dendrology, a rhizome ( ) is a modified subterranean plant stem that sends out roots and Shoot (botany), shoots from its Node (botany), nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from ...
s grow they are thought to disturb and loosen the medium, increasing its porosity, which may allow more effective fluid movement in the rhizosphere. When roots decay they leave behind ports and channels known as macropores which are effective in channeling water through the soil.
Metals removal
Constructed wetlands have been used extensively for the removal of dissolved metals and
metalloids
A metalloid is a chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. The word metalloid comes from the Latin ''metallum'' ("metal") and the Greek ''oeides'' ("resembling ...
. Although these contaminants are prevalent in mine drainage, they are also found in
stormwater
Stormwater, also written storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed lan ...
,
landfill leachate
A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed.
Leachate is a widely used term in the environmental sciences whe ...
and other sources (e.g., leachate or FDG washwater at
coal-fired power plants
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is a type of ...
), for which treatment wetlands have been constructed for mines.
Mine water—Acid drainage removal
Constructed wetlands can also be used for treatment of
acid mine drainage
Acid mine drainage, acid and metalliferous drainage (AMD), or acid rock drainage (ARD) is the outflow of acidic water from metal mines and coal mines.
Acid rock drainage occurs naturally within some environments as part of the rock weatherin ...
from coal mines.
Pathogen removal
Constructed wetlands are not designed for pathogen removal, but have been designed to remove other water quality constituents such as suspended solids, organic matter (biochemical oxygen demand and chemical oxygen demand) and nutrients (nitrogen and phosphorus).
All types of pathogens are expected to be removed in a constructed wetland; however, greater pathogen removal is expected to occur in a subsurface wetland. In a free water surface flow wetland one can expect 1 to 2
log10 reduction of pathogens; however, bacteria and virus removal may be less than 1 log10 reduction in systems that are heavily planted with vegetation.
This is because constructed wetlands typically include vegetation which assists in removing other pollutants such as nitrogen and phosphorus. Therefore, the importance of sunlight exposure in removing viruses and bacteria is minimized in these systems.
Removal in a properly designed and operated free water surface flow wetland is reported to be less than 1 to 2 log10 for bacteria, less than 1 to 2 log10 for viruses, 1 to 2 log10 for protozoa, and 1 to 2 log10 for helminths.
In subsurface flow wetlands, the expected removal of pathogens is reported to be 1 to 3 log10 for bacteria, 1 to 2 log10 for viruses, 2 log10 for protozoa, and 2 log10 for helminths.
The log10 removal efficiencies reported here can also be understood in terms of the common way of reporting removal efficiencies as percentages: 1 log10 removal is equivalent to a removal efficiency of 90%; 2 log10 = 99%; 3 log10 = 99.9%; 4 log10 = 99.99% and so on.
Types and design considerations

Constructed wetland systems can be surface flow systems with only free-floating
macrophytes
Aquatic plants, also referred to as hydrophytes, are vascular plants and non-vascular plants that have adapted to live in aquatic environments ( saltwater or freshwater). In lakes, rivers and wetlands, aquatic vegetations provide cover for aquat ...
, floating-leaved macrophytes, or submerged macrophytes; however, typical free water surface systems are usually constructed with emergent macrophytes. Subsurface flow-constructed wetlands with a vertical or a horizontal flow regime are also common and can be integrated into urban areas as they require relatively little space.
The main three broad types of constructed wetlands include:
* Subsurface flow constructed wetland – this wetland can be either with vertical flow (the effluent moves vertically, from the planted layer down through the substrate and out) or with horizontal flow (the effluent moves horizontally, parallel to the surface)
* Surface flow constructed wetland (this wetland has horizontal flow)
* Floating treatment wetland
The former types are placed in a basin with a substrate to provide a surface area upon which large amounts of waste degrading biofilms form, while the latter relies on a flooded treatment basin upon which aquatic plants are held in flotation till they develop a thick mat of roots and rhizomes upon which biofilms form. In most cases, the bottom is lined with either a polymer
geomembrane
A geomembrane is very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (liquid or gas) migration in a human-made project, structure, or system. Geomembranes are m ...
, concrete or clay (when there is appropriate clay type) in order to protect the water table and surrounding grounds. The substrate can be either
gravel
Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone.
Gr ...
—generally limestone or pumice/volcanic rock, depending on local availability,
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...
or a mixture of various sizes of media (for vertical flow constructed wetlands).
Constructed wetlands can be used after a
septic tank
A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatment ...
for primary treatment (or other types of systems) in order to separate the solids from the liquid effluent. Some constructed wetland designs however do not use upfront primary treatment.
Subsurface flow

In subsurface flow constructed wetlands the flow of wastewater occurs between the roots of the plants and there is no water surfacing (it is kept below gravel). As a result, the system is more efficient, does not attract mosquitoes, is less odorous and less sensitive to winter conditions. Also, less area is needed to purify water. A downside to the system are the intakes, which can clog or
bioclog easily, although some larger sized gravel will often solve this problem.
Subsurface flow wetlands can be further classified as horizontal flow or vertical flow constructed wetlands. In the vertical flow constructed wetland, the effluent moves vertically from the planted layer down through the substrate and out (requiring air pumps to aerate the bed). In the horizontal flow constructed wetland the effluent moves horizontally via gravity, parallel to the surface, with no surface water thus avoiding mosquito breeding. Vertical flow constructed wetlands are considered to be more efficient with less area required compared to horizontal flow constructed wetlands. However, they need to be interval-loaded and their design requires more know-how while horizontal flow constructed wetlands can receive wastewater continuously and are easier to build.
Due to the increased efficiency a vertical flow subsurface constructed wetland requires only about of space per
person equivalent, down to 1.5 square metres in hot climates.
The "French System" combines primary and secondary treatment of raw wastewater. The effluent passes various filter beds whose grain size is getting progressively smaller (from gravel to sand).
Applications
Subsurface flow wetlands can treat a variety of different wastewaters, such as household wastewater, agricultural, paper mill wastewater, mining
runoff,
tannery
Tanning, or hide tanning, is the process of treating skins and hides of animals to produce leather. A tannery is the place where the skins are processed.
Historically, vegetable based tanning used tannin, an acidic chemical compound derived fr ...
or
meat
Meat is animal Tissue (biology), tissue, often muscle, that is eaten as food. Humans have hunted and farmed other animals for meat since prehistory. The Neolithic Revolution allowed the domestication of vertebrates, including chickens, sheep, ...
processing wastes,
storm water
Stormwater, also written storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed lan ...
.
The quality of the effluent is determined by the design and should be customized for the intended reuse application (like irrigation or toilet flushing) or the disposal method.
Design considerations
Depending on the type of constructed wetlands, the wastewater passes through a gravel and more rarely
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...
medium on which plants are rooted.
A
gravel
Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone.
Gr ...
medium (generally limestone or volcanic rock
lavastone) can be used as well (the use of lavastone will allow for a surface reduction of about 20% over limestone) is mainly deployed in horizontal flow systems though it does not work as efficiently as sand (but sand will clog more readily).
Constructed subsurface flow wetlands are meant as
secondary treatment
Secondary treatment (mostly biological wastewater treatment) is the removal of Biodegradation, biodegradable organic matter (in solution or suspension) from sewage or similar kinds of wastewater. The aim is to achieve a certain degree of effluent ...
systems which means that the effluent needs to first pass a primary treatment which effectively removes solids. Such a primary treatment can consist of sand and grit removal, grease trap,
compost
Compost is a mixture of ingredients used as plant fertilizer and to improve soil's physical, chemical, and biological properties. It is commonly prepared by Decomposition, decomposing plant and food waste, recycling organic materials, and man ...
filter,
septic tank
A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatment ...
,
Imhoff tank
The Imhoff tank, named for German engineer Karl Imhoff (1876–1965), is a chamber suitable for the reception and processing of sewage. It may be used for the clarification of sewage by simple settling and sedimentation, along with anaerobic dig ...
, anaerobic baffled reactor or
upflow anaerobic sludge blanket (UASB) reactor.
The following treatment is based on different biological and physical processes like filtration, adsorption or nitrification. Most important is the biological filtration through a biofilm of
aerobic
Aerobic means "requiring air," in which "air" usually means oxygen.
Aerobic may also refer to
* Aerobic exercise, prolonged exercise of moderate intensity
* Aerobics, a form of aerobic exercise
* Aerobic respiration, the aerobic process of cellu ...
or
facultative bacteria
A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...
. Coarse sand in the filter bed provides a surfaces for microbial growth and supports the adsorption and filtration processes. For those microorganisms the oxygen supply needs to be sufficient.
Especially in warm and dry climates the effects of evapotranspiration and precipitation are significant. In cases of water loss, a vertical flow constructed wetland is preferable to a horizontal because of an unsaturated upper layer and a shorter retention time, although vertical flow systems are more dependent on an external energy source. Evapotranspiration (as is rainfall) is taken into account in designing a horizontal flow system.
The effluent can have a yellowish or brownish colour if
domestic wastewater
Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from residen ...
or
blackwater is treated. Treated
greywater
Greywater (or grey water, sullage, also spelled gray water in the United States) refers to domestic wastewater generated in households or office buildings from streams without fecal contamination, i.e., all streams except for the wastewater fro ...
usually does not tend to have a colour. Concerning pathogen levels, treated greywater meets the standards of pathogen levels for safe discharge to surface water.
[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
Creative Commons Attribution-ShareAlike 3.0 Unported
license. Treated domestic wastewater might need a tertiary treatment, depending on the intended reuse application.
Plantings of
reedbed
A reedbed or reed bed is a natural habitat found in floodplains, waterlogged depressions and
estuaries. Reedbeds are part of a succession from young reeds colonising open water or wet ground through a gradation of increasingly dry ground. As ...
s are popular in European constructed subsurface flow wetlands, although at least twenty other plant species are usable. Many fast growing timer plants can be used, as well for example as ''Musa'' spp., ''Juncus'' spp., cattails (''
Typha
''Typha'' is a genus of about 30 species of monocotyledonous flowering plants in the family Typhaceae. These plants have a variety of common names, in British English as bulrushStreeter D, Hart-Davies C, Hardcastle A, Cole F, Harper L. 2009. ' ...
'' spp.) and
sedges
The Cyperaceae () are a family of graminoid (grass-like), monocotyledonous flowering plants known as sedges. The family is large; botanists have described some 5,500 known species in about 90 generathe largest being the "true sedges" (genu ...
.
Operation and maintenance
Overloading peaks should not cause performance problems while continuous overloading lead to a loss of treatment capacity through too much suspended solids, sludge or fats.
Subsurface flow wetlands require the following maintenance tasks: regular checking of the pretreatment process, of pumps when they are used, of influent loads and distribution on the filter bed.
Comparisons with other types
Subsurface wetlands are less hospitable to
mosquito
Mosquitoes, the Culicidae, are a Family (biology), family of small Diptera, flies consisting of 3,600 species. The word ''mosquito'' (formed by ''Musca (fly), mosca'' and diminutive ''-ito'') is Spanish and Portuguese for ''little fly''. Mos ...
es compared to surface flow wetlands, as there is no water exposed to the surface. Mosquitos can be a problem in surface flow constructed wetlands. Subsurface flow systems have the advantage of requiring less land area for water treatment than surface flow. However, surface flow wetlands can be more suitable for wildlife habitat.
For urban applications the area requirement of a subsurface flow constructed wetland might be a limiting factor compared to conventional municipal
wastewater treatment plants
Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on ...
. High rate aerobic treatment processes like
activated sludge
The activated sludge process is a type of biological wastewater treatment process for treating sewage or Industrial wastewater treatment, industrial wastewaters using aeration and a biological floc (biofilm), floc composed of bacteria and protozoa ...
plants, trickling filters, rotating discs, submerged aerated filters or
membrane bioreactor
Membrane bioreactors are combinations of membrane processes like microfiltration or ultrafiltration with a biological wastewater treatment process, the activated sludge process. These technologies are now widely used for municipal and industri ...
plants require less space. The advantage of subsurface flow constructed wetlands compared to those technologies is their operational robustness which is particularly important in developing countries. The fact that constructed wetlands do not produce secondary sludge (
sewage sludge
Sewage sludge is the residual, semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater. The term "septage" also refers to sludge from simple wastewater treatment but is connected to si ...
) is another advantage as there is no need for
sewage sludge treatment
Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge treatment is focused on reducing sludge weight and volume to reduce transportation and disposal costs, and on redu ...
.
However, primary sludge from primary settling tanks does get produced and needs to be removed and treated.
Costs
The costs of subsurface flow constructed wetlands mainly depend on the costs of sand with which the bed has to be filled.
Another factor is the cost of land.
Surface flow

Surface flow wetlands, also known as free water surface constructed wetlands, can be used for tertiary treatment or polishing of effluent from
wastewater treatment
Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on ...
plants. They are also suitable to treat stormwater drainage.
Surface flow constructed wetlands always have horizontal flow of wastewater across the roots of the plants, rather than vertical flow. They require a relatively large area to purify water compared to subsurface flow constructed wetlands and may have increased smell and lower performance in winter.
Surface flow wetlands have a similar appearance to ponds for wastewater treatment (such as "
waste stabilization pond
Waste stabilization ponds (WSPs or stabilization ponds or waste stabilization lagoons) are ponds designed and built for wastewater treatment to reduce the organic content and remove pathogens from wastewater. They are man-made depressions confine ...
s") but are in the technical literature not classified as ponds.
Pathogens are destroyed by natural decay, predation from higher organisms, sedimentation and UV irradiation since the water is exposed to direct sunlight.
The soil layer below the water is anaerobic but the roots of the plants release oxygen around them, this allows complex biological and chemical reactions.
Surface flow wetlands can be supported by a wide variety of soil types including
bay mud
Bay mud consists of thick deposits of soft, unconsolidated silty clay, which is saturated with water; these soil layers are situated at the bottom of certain estuary, estuaries, which are normally in temperate regions that have experienced cyclic ...
and other
silt
Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...
y
clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
s.
Plants such as water hyacinth (''
Eichhornia crassipes
''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth, is an aquatic plant native to South America, naturalized throughout the world, and often invasive outside its native range.[Pontederia
''Pontederia'' is a genus of tristylous aquatic plants, members of which are commonly known as pickerel weeds. ''Pontederia'' is endemic to the Americas, distributed from Canada to Argentina, where it is found in shallow water or on mud. The genu ...]
'' spp. are used worldwide (although ''Typha'' and ''Phragmites'' are highly invasive).
However, surface flow constructed wetlands may encourage mosquito breeding. They may also have high algae production that lowers the effluent quality and due to open water surface mosquitos and odours, it is more difficult to integrate them in an urban neighbourhood.
File:Newly planted constructed wetland.jpg, Newly planted constructed wetland
File:Mature Constructed Wetland.jpg, Same constructed wetland, two years later
Hybrid systems
A combination of different types of constructed wetlands is possible to use the specific advantages of each system.
Integrated constructed wetland
An integrated constructed wetland is an unlined free surface flow constructed wetland with emergent vegetated areas and local soil material. Its objectives is not only to treat wastewater from farmyards and other wastewater sources, but also to integrate the wetland infrastructure into the landscape and enhancing its
biological diversity
Biodiversity is the variability of life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and phylogenetic diversity. Diversity is not distributed evenly on Eart ...
.
[Scholz M., Sadowski A. J., Harrington R. and Carroll P. (2007b), Integrated Constructed Wetlands Assessment and Design for Phosphate Removal. ''Biosystems Engineering'', 97 (3), 415–423.]
Integrated constructed wetland facilitates may be more robust treatment systems compared to other constructed wetlands.
[Mustafa A., Scholz M., Harrington R. and Carrol P. (2009) Long-term Performance of a Representative Integrated Constructed Wetland Treating Farmyard Runoff. ''Ecological Engineering'', 35 (5), 779–790.][Scholz M., Harrington R., Carroll P. and Mustafa A. (2007a), The Integrated Constructed Wetlands (ICW) Concept. ''Wetlands'', 27 (2), 337–354.][ This is due to the greater biological complexity and generally relatively larger land area use and associated longer hydraulic ]residence time
The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body). The residence time of a set of parcels is quantified in terms of the frequency distribu ...
of integrated constructed wetland compared to conventional constructed wetlands.[Carty A., Scholz M., Heal K., Gouriveau F. and Mustafa A. (2008), The Universal Design, Operation and Maintenance Guidelines for Farm Constructed Wetlands (FCW) in ]Temperate Climates
In geography, the temperate climates of Earth occur in the middle latitudes (approximately 23.5° to 66.5° N/S of the Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ra ...
. ''Bioresource Technology'', 99 (15), 6780–6792.
Integrated constructed wetlands are used in Ireland
Ireland (, ; ; Ulster Scots dialect, Ulster-Scots: ) is an island in the North Atlantic Ocean, in Northwestern Europe. Geopolitically, the island is divided between the Republic of Ireland (officially Names of the Irish state, named Irelan ...
, the UK and the United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
since about 2007. Farm constructed wetlands, which are a subtype of integrated constructed wetlands, are promoted by the Scottish Environment Protection Agency
The Scottish Environment Protection Agency (SEPA; ) is Scotland's Environmental regulation, environmental regulator and national flood forecasting, flood warning and strategic flood risk management authority.[Northern Ireland
Northern Ireland ( ; ) is a Countries of the United Kingdom, part of the United Kingdom in the north-east of the island of Ireland. It has been #Descriptions, variously described as a country, province or region. Northern Ireland shares Repub ...]
Environment Agency
The Environment Agency (EA) is a non-departmental public body, established in 1996 and sponsored by the United Kingdom government's Department for Environment, Food and Rural Affairs, with responsibilities relating to the protection and enha ...
since 2008.[
]
Other design aspects
The design of a constructed wetland can greatly effect the surrounding environment. A wide range of skills and knowledge is needed in the construction and can easily be detrimental to the site if not done correctly. A long list of professions ranging from civil engineers to hydrologists
Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and drainage basin sustainability. A practitioner of hydrology is called a hydro ...
to wildlife biologists to landscape architect
A landscape architect is a person who is educated in the field of landscape architecture. The practice of landscape architecture includes: site analysis, site inventory, site planning, land planning, planting design, grading, storm water manage ...
s are needed in this design process. The landscape architect can utilize a wide range of skills to help accomplish the task of constructing a wetland that may not be thought of by other professions. Ecological landscape architects are also qualified to create wetland restoration designs in coordination with wetland scientists that increase the community value and appreciation of a project through well designed access, interpretation, and views of the project. Landscape architecture has a long history of engagement with the aesthetic dimension of wetlands. Landscape architects also guide through the laws and regulations associated with constructing a wetland.
Plants and other organisms
Plants
''Typhas'' and ''Phragmites'' are the main species used in constructed wetland due to their effectiveness, even though they can be invasive outside their native range.
In North America, cattails (''Typha latifolia
''Typha latifolia'' is a perennial herbaceous wetland plant in the genus ''Typha''. It is known in English as bulrushStreeter D, Hart-Davies C, Hardcastle A, Cole F, Harper L. 2009. ''Collins Flower Guide''. Harper Collins (sometimes as common b ...
'') are common in constructed wetlands because of their widespread abundance, ability to grow at different water depths, ease of transport and transplantation, and broad tolerance of water composition (including pH, salinity, dissolved oxygen and contaminant concentrations). Elsewhere, Common Reed (''Phragmites australis
''Phragmites australis'', known as the common reed, is a species of flowering plant in the grass family Poaceae. It is a wetland grass that can grow up to tall and has a cosmopolitan distribution worldwide.
Description
''Phragmites australis' ...
'') are common (both in blackwater treatment but also in greywater treatment
Greywater (or grey water, sullage, also spelled gray water in the United States) refers to domestic wastewater generated in households or office buildings from streams without fecal contamination, i.e., all streams except for the wastewater fro ...
systems to purify wastewater).
Plants are usually indigenous
Indigenous may refer to:
*Indigenous peoples
*Indigenous (ecology)
In biogeography, a native species is indigenous to a given region or ecosystem if its presence in that region is the result of only local natural evolution (though often populari ...
in that location for ecological
Ecology () is the natural science of the relationships among living organisms and their environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere levels. Ecology overlaps with the closely re ...
reasons and optimum workings.
File:Newly planted constructed wetland - details (3110372910).jpg, Newly planted constructed wetland for blackwater treatment (Lima, Peru)
File:Constructed wetland (5547294390).jpg, The large roots of this uprooted plant growing in a constructed wetlands indicate a healthy plant (Lima, Peru)
File:Flowform.jpg, A hybrid system using Flowforms in a treatment pond, in Norway
Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...
.
Animals
Locally grown non-predator
Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...
y fish
A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
can be added to surface flow constructed wetlands to eliminate or reduce pests, such as mosquito
Mosquitoes, the Culicidae, are a Family (biology), family of small Diptera, flies consisting of 3,600 species. The word ''mosquito'' (formed by ''Musca (fly), mosca'' and diminutive ''-ito'') is Spanish and Portuguese for ''little fly''. Mos ...
s.
Stormwater
Stormwater, also written storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. Stormwater can soak into the soil ( infiltrate) and become groundwater, be stored on depressed lan ...
wetlands provide habitat for amphibians but the pollutants they accumulate can affect the survival of larval stages, potentially making them function as "ecological trap
Ecological traps are scenarios in which rapid environmental change leads organisms to prefer to settle in poor-quality habitats.
The concept stems from the idea that organisms that are actively selecting habitat must rely on environmental cues to h ...
s".
Costs
Since constructed wetlands are self-sustaining their lifetime costs are significantly lower than those of conventional treatment systems. Often their capital costs are also lower compared to conventional treatment systems. They do take up significant space, and are therefore not preferred where real estate costs are high.
History
Primary clarifier effluent was discharged directly to natural wetland
A wetland is a distinct semi-aquatic ecosystem whose groundcovers are flooded or saturated in water, either permanently, for years or decades, or only seasonally. Flooding results in oxygen-poor ( anoxic) processes taking place, especially ...
s for decades before environmental regulations discouraged the practice. Subsurface flow constructed wetlands with sand filter beds have their origin in China and are now used in Asia in small cities.
Examples
Austria
The total number of constructed wetlands in Austria
Austria, formally the Republic of Austria, is a landlocked country in Central Europe, lying in the Eastern Alps. It is a federation of nine Federal states of Austria, states, of which the capital Vienna is the List of largest cities in Aust ...
is 5,450 (in 2015). Due to legal requirements (nitrification), only vertical flow constructed wetlands are implemented in Austria as they achieve better nitrification
''Nitrification'' is the biological oxidation of ammonia to nitrate via the intermediary nitrite. Nitrification is an important step in the nitrogen cycle in soil. The process of complete nitrification may occur through separate organisms or ent ...
performance than horizontal flow constructed wetlands. Only about 100 of these constructed wetlands have a design size of 50 population equivalent Population equivalent (PE) or unit per capita loading, or equivalent person (EP), is a parameter for characterizing industrial wastewaters. It essentially compares the polluting potential of an industry (in terms of biodegradable organic matter) wi ...
s or more. The remaining 5,350 treatment plants are smaller than that.
Canada
As part of the remediation efforts to remove contamination from CFB Goose Bay
Canadian Forces Base Goose Bay , commonly referred to as CFB Goose Bay, is a Canadian Forces Base located in the municipality of Happy Valley-Goose Bay in the province of Newfoundland and Labrador. It is operated as an air force base by ...
, one of the waste dumps was transformed into an engineered wetland.
See also
* Decentralized wastewater system
Decentralized wastewater systems (also referred to as decentralized wastewater treatment systems) convey, treat and dispose or reuse wastewater from small and low-density communities, buildings and dwellings in remote areas, individual public or ...
* Ecological engineering
Ecological engineering uses ecology and engineering to predict, design, construct or restore, and manage ecosystems that integrate " human society with its natural environment for the benefit of both".W.J. Mitsch & S.E. Jorgensen (1989), "Introdu ...
*Ecological sanitation
Ecological sanitation, commonly abbreviated as ecosan (also spelled eco-san or EcoSan), is an approach to sanitation provision which aims to safely reuse excreta in agriculture. It is an approach, rather than a technology or a device which is ch ...
* Floodplain restoration
Floodplain restoration is the process of fully or partially restoring a river's floodplain to its original conditions before having been affected by the construction of levees (dikes) and the draining of wetlands and marshes.
The objectives of ...
* Integrated constructed wetland
A constructed wetland is an artificial wetland to treat sewage, greywater, stormwater runoff or Industrial wastewater treatment, industrial wastewater. It may also be designed for land reclamation after mining, or as a Flood mitigation, mitigatio ...
* Passive treatment system A passive treatment system is a method for removing metals from acid mine drainage. There are several types of passive treatment systems, each of which may be used on their own or in combination to treat effluents. The type of system selected is dep ...
*Sanitation
Sanitation refers to public health conditions related to clean drinking water and treatment and disposal of human excreta and sewage. Preventing human contact with feces is part of sanitation, as is hand washing with soap. Sanitation systems ...
* Vegetative treatment system
* Water-sensitive urban design
Water-sensitive urban design (WSUD) is a land planning and engineering design approach which integrates the urban water cycle, including stormwater, groundwater, and wastewater management and water supply, into urban design to minimise environmen ...
* Wetland classification Classification of wetlands has been a problematical task, with the commonly accepted definition of what constitutes a wetland being among the major difficulties. A number of national wetland classifications exist. In the 1970s, the Ramsar Convention ...
* Wetlands Construídos (a company in Brazil)
References
External links
Constructed Wetlands – US Environmental Protection Agency
— Handbook, studies and related resources
Publications on constructed wetlands
in the library of the Sustainable Sanitation Alliance
The Sustainable Sanitation Alliance (SuSanA) is a loose network of organizations who are "working along the same lines towards achieving sustainable sanitation". It began its work in 2007, one year before the United Nations International Year o ...
{{DEFAULTSORT:Constructed Wetland
Artificial landforms
Environmental engineering
Environmental terminology
Sewerage infrastructure
Stormwater management
Sustainable design
Wetlands
Ecological restoration
Water and the environment
Chinese inventions