Constructed wetland - AbsoluteAstronomy.com

A constructed wetland or wetpark is an artificial wetland

Wetland

A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....

, marsh

Marsh

In geography, a marsh, or morass, is a type of wetland that is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, other herbaceous plants, and moss....

or swamp

Swamp

A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...

created as a new or restored habitat

Habitat

* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...

for native and migratory wildlife

Wildlife

Wildlife includes all non-domesticated plants, animals and other organisms. Domesticating wild plant and animal species for human benefit has occurred many times all over the planet, and has a major impact on the environment, both positive and negative....

, for anthropogenic discharge such as wastewater

Wastewater

Wastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...

, stormwater

Stormwater

Stormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...

runoff, or sewage treatment

Sewage treatment

Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...

, for land reclamation after mining

Mining

Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

, refineries

Refinery

A refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value.-Types of refineries:Different types of refineries are as follows:...

, or other ecological disturbances such as required mitigation

Flood mitigation

Flood mitigation involves managing the effects of flooding, such as redirecting flood run-off, rather than trying to prevent it altogether. It is management of people, through measures such as evacuation and dry/wet proofing properties for example....

for natural wetlands lost to a development.

Natural wetland

Wetland

s act as a biofilter

Biofilter

Biofiltration is a pollution control technique using living material to capture and biologically degrade process pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, and microbiotic oxidation of contaminants in air...

, removing sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

s and pollutant

Pollutant

A pollutant is a waste material that pollutes air, water or soil, and is the cause of pollution.Three factors determine the severity of a pollutant: its chemical nature, its concentration and its persistence. Some pollutants are biodegradable and therefore will not persist in the environment in the...

s such as heavy metals from the water, and constructed wetlands can be designed to emulate these features.

Biofiltration

Vegetation in a wetland provides a substrate (roots, stems, and leaves) upon which microorganism

Microorganism

A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...

s can grow as they break down organic materials. This community of microorganisms is known as the periphyton

Periphyton

Periphyton are a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that are attached to submerged surfaces in most aquatic ecosystems. It serves as an important food source for invertebrates, tadpoles, and some fish. It can also absorb contaminants; removing them from...

. The periphyton and natural chemical processes are responsible for approximately 90 percent of pollutant

Pollutant

removal and waste breakdown. The plants remove about seven to ten percent of pollutants, and act as a carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

source for the microbes when they decay. Different species of aquatic plant

Aquatic plant

Aquatic plants are plants that have adapted to living in aquatic environments. They are also referred to as hydrophytes or aquatic macrophytes. These plants require special adaptations for living submerged in water, or at the water's surface. Aquatic plants can only grow in water or in soil that is...

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. |-
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| Newly planted Constructed Wetland.
| Same Constructed Wetland, two years later.
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Natural wetlands

Ramsar Classification System for Wetland Type
Ramsar Classification System for Wetland Type
The Ramsar Classification System for Wetland Type is a wetland classification developed within the Ramsar Convention on Wetlands intended as a means for fast identification of the main types of wetlands for the purposes of the Convention....

- Ramsar Convention
Ramsar Convention
The Ramsar Convention is an international treaty for the conservation and sustainable utilization of wetlands, i.e., to stem the progressive encroachment on and loss of wetlands now and in the future, recognizing the fundamental ecological functions of wetlands and their economic, cultural,...

Subsurface-flow wetlands

Subsurface-flow wetlands can be further classified as horizontal flow and vertical flow constructed wetlands. Subsurface-flow wetlands move effluent (household wastewater, agricultural or mining runoff, tannery

Tanning

Tanning is the making of leather from the skins of animals which does not easily decompose. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name . Coloring may occur during tanning...

or meat

Meat

Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...

processing wastes, or storm drain

Storm drain

A storm drain, storm sewer , stormwater drain or drainage well system or simply a drain or drain system is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems...

s, or other water to be cleansed) through a gravel

Gravel

Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

(generally limestone or volcanic rock lavastone

Lava filter

A lava filter is a biological filter that uses lavastone pebbles as support material on which microorganisms can grow in a thin biofilm. This community of microorganisms, known as the periphyton break down the odor components in the air, such as hydrogen sulfide. The biodegradation processes that...

or sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

medium on which plants are rooted. In subsurface-flow systems, the effluent may move either horizontally, parallel to the surface, or vertically, from the planted layer down through the substrate and out. Subsurface horizontal-flow wetlands are less hospitable to mosquito

Mosquito

Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...

es, (as there is no water exposed to the surface) whose populations can be a problem in surface-flow constructed wetlands. Carnivorous plant

Carnivorous plant

Carnivorous plants are plants that derive some or most of their nutrients from trapping and consuming animals or protozoans, typically insects and other arthropods. Carnivorous plants appear adapted to grow in places where the soil is thin or poor in nutrients, especially nitrogen, such as acidic...

s have been used to address this problem. Subsurface-flow systems have the advantage of requiring less land area for water treatment, but are not generally as suitable for wildlife habitat as are surface-flow constructed wetlands.

Surface-flow wetlands

Surface-flow wetlands move effluent above the soil in a planted marsh or swamp, and thus can be supported by a wider variety of soil types including bay mud

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 estuaries, which are normally in temperate regions that have experienced cyclical glacial cycles...

and other silt

Silt

Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...

y clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

s.

Plantings of reedbeds are popular in European constructed wetlands, and plants such as cattails (Typha
Typha
Typha is a genus of about eleven species of monocotyledonous flowering plants in the family Typhaceae. The genus has a largely Northern Hemisphere distribution, but is essentially cosmopolitan, being found in a variety of wetland habitats...

spp.), sedges

Cyperaceae

Cyperaceae are a family of monocotyledonous graminoid flowering plants known as sedges, which superficially resemble grasses or rushes. The family is large, with some 5,500 species described in about 109 genera. These species are widely distributed, with the centers of diversity for the group...

, Water Hyacinth (Eichhornia crassipes
Eichhornia crassipes
Eichhornia crassipes, commonly known as Common Water Hyacinth, is an aquatic plant native to the Amazon basin, and is often considered a highly problematic invasive species outside its native range.-Ecology:...

) and Pontederia
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...

spp. are used worldwide (although Typha and Phragmites are highly invasive). Recent research in use of constructed wetlands for subarctic regions has shown that buckbeans (Menyanthes trifoliata
Menyanthes
Menyanthes is a monotypic genus of flowering plant in the family Menyanthaceae containing the single species Menyanthes trifoliata...

) and pendant grass (Arctophila fulva
Arctophila
Arctophila is a genus of grass in the Poaceae family.- External links :*...

) are also useful for metals uptake.

Tidal Flow wetlands

Tidal Flow wetlands are the latest evolution of wetland technology, used to treat domestic, agricultural & industrial wastewater, including heavy load. In this system, organic carbon is primarily oxidized with nitrate, which is produced through a series of flood and drain cycles, from one side of the wetland to the other. This process holds a number of benefits over traditional subsurface & surface-flow wetlands including, reduced land requirements and increased de-nitrification capabilities for the treatment of heavy load.

General contaminants removal

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 within a constructed wetland occurs as it passes through the wetland medium and the plant rhizosphere

Rhizosphere (ecology)

The rhizosphere is the narrow region of soil that is directly influenced by root secretions and associated soil microorganisms. Soil which is not part of the rhizosphere is known as bulk soil. The rhizosphere contains many bacteria that feed on sloughed-off plant cells, termed rhizodeposition, and...

. A thin film around each root hair is aerobic

Aerobic

Aerobic is a word that means "requiring air", where "air" usually means oxygen.Aerobic may also refer to:* Aerobic exercise, prolonged exercise of moderate intensity* Aerobics, a form of aerobic exercise...

due to the leakage of oxygen from the rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s, root

Root

In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

s, and rootlets. Aerobic

Aerobic organism

An aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment.Faculitative anaerobes grow and survive in an oxygenated environment and so do aerotolerant anaerobes.-Glucose:...

and anaerobic

Anaerobic organism

An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present...

micro-organisms facilitate decomposition of organic matter. Microbial nitrification

Nitrification

Nitrification is the biological oxidation of ammonia with oxygen into nitrite followed by the oxidation of these nitrites into nitrates. Degradation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil...

and subsequent denitrification

Denitrification

Denitrification is a microbially facilitated process of nitrate reduction that may ultimately produce molecular nitrogen through a series of intermediate gaseous nitrogen oxide products....

releases nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

as gas to the atmosphere

Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

. Phosphorus

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

is coprecipitated

Coprecipitation

In chemistry, coprecipitation or co-precipitation is the carrying down by a precipitate of substances normally soluble under the conditions employed...

with iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, and calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

compounds located in the root-bed medium. Suspended solids

Suspended solids

Suspended solids refers to small solid particles which remain in suspension in water as a colloid or due to the motion of the water. It is used as one indicator of water quality....

filter out as they settle in the water column in surface flow wetlands or are physically filtered out by the medium within subsurface flow wetland cells. Harmful bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

and virus

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

es are reduced by filtration and adsorption by biofilm

Biofilm

A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...

s on the rock media in subsurface flow and vertical flow systems.

Nitrogen removal

The dominant forms of nitrogen in wetlands that are of importance to wastewater treatment

Wastewater Treatment

Wastewater treatment may refer to:* Sewage treatment* Industrial wastewater treatment...

include organic nitrogen, ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

, ammonium

Ammonium

The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...

, nitrate

Nitrate

The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...

, nitrite

Nitrite

The nitrite ion has the chemical formula NO2−. The anion is symmetric with equal N-O bond lengths and a O-N-O bond angle of ca. 120°. On protonation the unstable weak acid nitrous acid is produced. Nitrite can be oxidised or reduced, with product somewhat dependent on the oxidizing/reducing agent...

, and nitrogen gases. Inorganic forms are essential to plant growth in aquatic systems but if scarce can limit or control plant productivity. Total Nitrogen refers to all nitrogen species. 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

Methemoglobinemia is a disorder characterized by the presence of a higher than normal level of methemoglobin in the blood. Methemoglobin is an oxidized form of hemoglobin that has an increased affinity for oxygen, resulting in a reduced ability to release oxygen to tissues. The oxygen–hemoglobin...

in infants, which decreases the blood's oxygen transport ability. The UK has experienced a significant increase in nitrate concentration in groundwater

Groundwater

Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

and rivers.

Organic nitrogen

Mitsch & Gosselink define nitrogen mineralisation as "the biological transformation of organically combined nitrogen to ammonium nitrogen during organic matter degradation". This can be both an aerobic and anaerobic process and is often referred to as ammonification. Mineralisation of organically combined nitrogen releases inorganic nitrogen as nitrates, nitrites, ammonia and ammonium, making it available for plants, fungi and bacteria. Mineralisation rates may be affected by oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

levels in a wetland.

and ammonium

The formation of ammonia occurs via the mineralisation or ammonification of organic matter under either anaerobic or aerobic conditions. The ammonium ion

Ion

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

is the primary form of mineralized nitrogen in most flooded wetland soils. This ion forms when ammonia combines with water as follows:

+ +

Upon formation, several pathways are available to the ammonium ion. It can be absorbed by plants and algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

and converted back into organic matter, or the ammonium ion can be electrostatically held on negatively charged surfaces of soil particles. At this point, the ammonium ion can be prevented from further oxidation because of the anaerobic nature of wetland soils. Under these conditions the ammonium ion is stable and it is in this form that nitrogen predominates in anaerobic sediments typical of wetlands.

Most wetland soils have a thin aerobic layer at the surface. As an ammonium ion from the anaerobic sediments diffuses upward into this layer it converts to nitrite or nitrified. An increase in the thickness of this aerobic layer results in an increase in nitrification. This diffusion of the ammonium ion sets up a concentration gradient across the aerobic-anaerobic soil layers resulting in further nitrification reactions.

Nitrification

Nitrification

is the biological conversion of organic and inorganic nitrogenous compounds from a reduced state to a more oxidized state. Nitrification is strictly an aerobic process in which the end product is nitrate ; this process is limited when anaerobic conditions prevail. Nitrification will occur readily down to 0.3 ppm dissolved oxygen. The process of nitrification (1) oxidizes ammonium (from the sediment) to nitrite , and then (2) nitrite is oxidized to nitrate . The overall nitrification reactions are as follows:

(1) 2 + 3 4 + 2 + 2

(2) 2 + 2
(Davies & Hart, 1990)

Two different bacteria are required to complete this oxidation of ammonium to nitrate. Nitrosomonas
Nitrosomonas
Nitrosomonas is a genus comprising rod shaped chemoautotrophic bacteria.This rare bacteria oxidizes ammonia into nitrite as a metabolic process. Nitrosomonas are useful in treatment of industrial and sewage waste and in the process of bioremediation. They are important in the nitrogen cycle by...

sp. oxidizes ammonium to nitrite via reaction (1), and Nitrobacter
Nitrobacter
Nitrobacter is genus of mostly rod-shaped, gram-negative, and chemoautotrophic bacteria.Nitrobacter plays an important role in the nitrogen cycle by oxidizing nitrite into nitrate in soil...

sp. oxidizes nitrite to nitrate via reaction (2).

Denitrification
Denitrification
Denitrification is a microbially facilitated process of nitrate reduction that may ultimately produce molecular nitrogen through a series of intermediate gaseous nitrogen oxide products....

is the biochemical reduction of oxidized nitrogen anions, nitrate and nitrite to produce the gaseous products nitric oxide (NO), nitrous oxide and nitrogen gas , with concomitant oxidation of organic matter. The general sequence is as follows:

NO

The end products, and are gases that re-enter the atmosphere. Denitrification occurs intensely in anaerobic environments but also in aerobic conditions. Oxygen deficiency causes certain bacteria to use nitrate in place of oxygen as an electron acceptor

Electron acceptor

An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process....

for the reduction of organic matter. Denitrification is restricted to a narrow zone in the sediment immediately below the aerobic-anaerobic soil interface. Denitrification is considered to be the predominant microbial process that modifies the chemical composition of nitrogen in a wetland system and the major process whereby elemental nitrogen returns to the atmosphere. To summarize, the nitrogen cycle

Nitrogen cycle

The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. This transformation can be carried out by both biological and non-biological processes. Important processes in the nitrogen cycle include fixation, mineralization, nitrification, and denitrification...

is completed as follows: ammonia in water, at or near neutral pH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

is converted to ammonium ions; the aerobic bacterium Nitrosomonas sp. oxidizes ammonium to nitrite; Nitrobacter sp. then converts nitrite to nitrate. Under anaerobic conditions, nitrate is reduced to relatively harmless nitrogen gas that enters the atmosphere.

Domestic sewage - ammonia

In a review of 19 surface flow wetlands it was found that nearly all reduced total nitrogen. A review of both surface flow and subsurface flow wetlands concluded that effluent nitrate concentration is dependent on maintaining anoxic conditions within the wetland so that denitrification can occur and that subsurface flow wetlands were superior to surface flow wetlands for nitrate removal. The 20 surface flow wetlands reviewed reported effluent nitrate levels below 5 mg/L; the 12 subsurface flow wetlands reviewed reported effluent nitrate ranging from <1 to < 10 mg/L. Results obtained from the Niagara-On-The-Lake vertical flow systems show a significant reduction in both total nitrogen and ammonia (> 97%) when primary treated effluent was applied at a rate of 60L/m²/day. Calculations showed that over 50% of the total nitrogen going into the system was converted to nitrogen gas. Effective removal of nitrate from the sewage lagoon influent was dependent on medium type used within the vertical cell as well as water table level within the cell.

Mine water - ammonia

Constructed wetlands have been used to remove ammonia from mine drainage. In Ontario

Ontario

Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....

, Canada, drainage from the polishing pond at the Campbell Mine flows by gravity through a 9.3 hectare surface flow constructed wetland during the ice-free season. Ammonia is removed by approximately 95% on inflows of up to 15000 cubic metres (529,720 cu ft)/day during the summer months, while removal rates decrease to 50-70% removal during cold months. This ammonia was oxidized to nitrate, which was immediately and quantitatively removed in the wetland. Surprisingly, and contrary to Reed (see above), anoxic conditions were not necessary for nitrate removal, which occurred as readily on leaf and detritus biofilm as it did in sediments. Other contaminants, including copper, are also removed in the wetland, such that the final discharge is fully detoxified. Campbell became one of the first gold mines in Ontario to produce a completely non-toxic discharge, as determined by acute and chronic toxicity tests. At the Ranger Uranium Mine, in Australia, ammonia is removed in "enhanced" natural wetlands (rather than fully engineered constructed wetlands), along with manganese, uranium and other metals.

Other mines use natural or constructed wetlands to remove nitrogenous compounds from contaminated mine water, including cyanide (at the Jolu and Star Lake Mines, using natural muskeg and wetlands) and nitrate (demonstrated at the Quinsam Coal Mine). Wetlands were also proposed to remove nitrogenous compounds (present as blasting residues) from diamond mines in Northern Canada. However, land application is equally effective and is easier to implement than a constructed wetland.

Phosphorus removal

Phosphorus

occurs naturally in both organic and inorganic forms. The analytical measure of biologically available orthophosphates

Phosphate

A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...

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.

In freshwater aquatic ecosystem

Aquatic ecosystem

An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems....

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

in water receiving heavy discharges of phosphorus-rich wastes. Because phosphorus does not have an atmospheric component, unlike nitrogen, the phosphorus cycle

Phosphorus cycle

The phosphorus cycle is the biogeochemical cycle that describes 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 movement of phosphorus, because phosphorus and...

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
Precipitation (chemistry)
Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...

of insoluble phosphates with ferric
Ferric
Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron or Fe2+...

iron, calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

, and aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

found in wetland soils.

Biomass plants incorporation - phosphorus

Higher plants in wetland systems may be viewed as transient nutrient storage compartments absorbing nutrients during the growing season and releasing them at senescence. Generally, plants in nutrient-rich habitats accumulate more nutrients than those in nutrient-poor habitats, a phenomenon referred to as luxury uptake of nutrients. 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. Vascular plants may account for only a small amount of phosphorus uptake with only 5 to 20% of the nutrients detained in a natural wetland being stored in harvestable plant material. Bernard and Solsky also reported relatively low phosphorus retention, estimating that a sedge (Carex
Carex
Carex is a genus of plants in the family Cyperaceae, commonly known as sedges. Other members of the Cyperaceae family are also called sedges, however those of genus Carex may be called "true" sedges, and it is the most species-rich genus in the family. The study of Carex is known as...

sp.) wetland retained 1.9 g of phosphorus per square meter of wetland. Bulrushes (Scirpus
Scirpus
The plant genus Scirpus consists of a large number of aquatic, grass-like species in the family Cyperaceae , many with the common names club-rush or bulrush . Other common names are deergrass or grassweed.The genus has a cosmopolitan distribution, and grows in wetlands and moist soil...

sp.) in a constructed wetland system receiving secondarily treated domestic wastes contained 40.5% of the total phosphorus influent. The remaining 59.0% was found to be stored in the gravel substratum. Phosphorus removal in a surface flow wetland treatment system planted with one of Scirpus sp., Phragmites
Phragmites
Phragmites, the Common reed, is a large perennial grass found in wetlands throughout temperate and tropical regions of the world. Phragmites australis is sometimes regarded as the sole species of the genus Phragmites, though some botanists divide Phragmites australis into three or four species...

sp. or Typha
Typha
Typha is a genus of about eleven species of monocotyledonous flowering plants in the family Typhaceae. The genus has a largely Northern Hemisphere distribution, but is essentially cosmopolitan, being found in a variety of wetland habitats...

sp. was investigated by Finlayson and Chick (1983).

Phosphorus removal of 60%, 28%, and 46% were found for Scirpus sp., Phragmites sp. and Typha sp. respectively. This may prove to be a low estimate. Vascular plants are a major phosphorus storage compartment accounting for 67.3% of the influent phosphorus. Plant adsorption may reach 80% phosphorus removal.

Only a small proportion (<20%) of phosphate removal by constructed wetlands can be attributed to nutritional uptake by bacteria, fungi and algae. The lack of seasonal fluctuation in phosphorus removal rates suggests that the primary mechanism is bacterial and alga fixation. However, this mechanism may be temporary, because the microbial pool is small and quickly becomes saturated at which point the soil medium takes over as the major contributor to phosphate removal.

Plants create a unique environment at the biofilm's attachment surface. Certain plants transport oxygen which is released at the biofilm/root interface, perhaps adding oxygen to the wetland system. Plants also increase soil or other root-bed medium hydraulic conductivity. As roots and rhizomes 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.

Whether or not wetland systems act as a phosphorus sink or source seems to depend on system characteristics such as sediment and hydrology. There seems to be a net movement of phosphorus into the sediment in many lakes. In Lake Erie as much as 80% of the total phosphorus is removed from the waters by natural processes and is presumably stored in the sediment. Marsh sediments high in organic matter act as sinks. Phosphorus release from a marsh exhibits a cyclical pattern. Much of the spring phosphorus release comes from high phosphorus concentrations locked up in the winter ice covering the marsh; in summer the marsh acts as a phosphorus sponge. Phosphorus is exported from the system following dieback of vascular plants. Phosphorus concentrations in water are reduced during the growing season due to plant uptake but decomposition and subsequent mineralisation of organic matter releases phosphorus over the winter and accounts for the higher winter phosphorus concentrations in the marsh.

Retention by soils or root-bed media - phosphorus

Two types of phosphate retention mechanisms may occur in soils or root-bed media: chemical adsorption onto the medium and physical precipitation of the phosphate ion. Both result from the attraction between phosphate ion and ions of Al, Fe or Ca and terminates with formation of various iron phosphates (Fe-P), aluminum phosphates (Al-P) or calcium phosphates (Ca-P).

Oxidation-reduction potential (ORP, formally reported as ) of soil or water is a measure of its ability to reduce

Redox

Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

or oxidize

Redox

Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

chemical substances and may range between -350 and +600 millivolts (mV). Though redox potential does not affect phosphorus' oxidation state, redox potential is indirectly important because of its effect on iron solubility (through reduction of ferric oxides). Severely reduced conditions in the sediments may result in phosphorus release, Typical wetland soils may have an of -200 mV. Under these reduced conditions (Ferric

Ferric

Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron or Fe2+...

iron) in insoluble ferric oxides may be reduced to soluble (Ferrous

Ferrous

Ferrous , in chemistry, indicates a divalent iron compound , as opposed to ferric, which indicates a trivalent iron compound ....

iron). Any phosphate ion bound to the ferric oxide may be released back into solution as it dissolves However, the diffusing in the water column may be re-oxidized to and re-precipitated as an iron oxide when it encounters oxygenated surface water. This precipitation reaction may remove phosphate from the water column and deposit it back on the surface of sediments . Thus, there can be a dynamic uptake and release of phosphorus in sediments that is governed by the amount of oxygen in the water column. A well documented occurrence in the hypolimnion

Hypolimnion

The hypolimnion is the dense, bottom layer of water in a thermally-stratified lake. It is the layer that lies below the thermocline.Typically the hypolimnion is the coldest layer of a lake in summer, and the warmest layer during winter...

of lakes is the release of soluble phosphorus when conditions become anaerobic. This phenomenon also occurs in natural wetlands. Oxygen concentrations of less than 2.0 mg/l result in the release of phosphorus from sediments.

Domestic sewage - phosphorus

Adsorption to binding sites within sediments was the major phosphorus removal mechanism in the surface flow constructed wetland system at Port Perry, Ontario

Port Perry, Ontario

Port Perry is a community located in Scugog Township, Durham Region, Ontario, Canada. The town is located east of Uxbridge and southwest of Peterborough. Many residents commute to Toronto on a daily basis. Port Perry's municipal website reported a population of just over 9,500 in 2010.Port Perry...

Release of phosphorus from the sediments occurred when anaerobic conditions prevailed. The lowest wetland effluent phosphorus levels occurred when oxygen levels of the overlying water column were above 1.0 mg / L. Removal efficiencies for total phosphorus were 54-59% with mean effluent levels of 0.38 mg P/L. Wetland effluent phosphorus concentration was higher than influent levels during the winter months.

The phosphorus removed in a VF wetland in Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

over a short term was stored in the following wetland components in order of decreasing importance: substratum> macrophyte >biofilm, but over the long term phosphorus storage was located in macrophyte> substratum>biofilm components. Medium iron-oxide adsorption provides additional removal for some years.

A comparison of phosphorus removal efficiency of two large-scale, surface flow wetland systems in Australia which had a gravel substratum to laboratory phosphorus adsorption indicated that for the first two months of wetland operation, the mean phosphorus removal efficiency of system 1 and 2 was 38% and 22%, respectively. Over the first year a decline in removal efficiencies occurred. During the second year of operation more phosphorus came out than was put in. This release was attributed to the saturation of phosphorus binding sites. Close agreement was found between the phosphorus adsorption capacity of the gravel as determined in the laboratory and the adsorption capacity recorded in the field.

The phosphorus adsorption capacity of a subsurface flow constructed wetland system containing a predominantly quartz gravel in the laboratory using the Langmuir adsorption isotherm was 25 mg P/g gravel. Close agreement between calculated and realized phosphorus adsorption was found. The poor adsorption capacity of the quartz gravel implied that plant uptake and subsequent harvesting were the major phosphorus removal mechanism.

Metals removal

Constructed wetlands have been used extensively for the removal of dissolved metals and metalloids. Although these contaminants are prevalent in mine drainage, they are also found in stormwater, landfill leachate

Leachate

Leachate is any liquid that, in passing through matter, extracts solutes, suspended solids or any other component of the material through which it has passed....

and other sources (e.g., leachate or FDG washwater at coal-fired power plants

Fossil fuel power plant

A fossil-fuel power station is a power station that burns fossil fuels such as coal, natural gas or petroleum to produce electricity. Central station fossil-fuel power plants are designed on a large scale for continuous operation...

), for which treatment wetlands have been constructed for mines, and other applications.

Mine water - Acid drainage removal

A seminal publication was a 1994 report from the US Bureau of Mines described the design of wetlands for treatment of acid mine drainage from coal mines. This report replaced the existing trial-and-error process with a strong scientific approach. This legitimized this technology and was followed in treating other contaminated waters.

General application

The three types, using reed beds (constructed wetlands but using principally reed plants), are used. All these systems are used commercially, usually together with septic tanks as primary treatment, Imhoff tanks or screeners in order to separate the solids from the liquid effluent). Some designs however are being used to act as primary treatment as well. An other way is the combination Constructed wetland- Composting toilet

Composting toilet

A composting toilet is a dry toilet that using a predominantly aerobic processing system that treats excreta, typically with no water or small volumes of flush water, via composting or managed aerobic decomposition...

.

System types are:

Surface flow (SF) Constructed Wetland (or reed bed)
Sub Surface Flow (SSF) Constructed Wetland (or reed bed)
Vertical Flow (VF) Constructed Wetland (or reed bed)

All three types are placed in a basin with a substrate. For most undertakings the bottom is lined with either a geomembrane (kind of rubber / plastic), 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 - generally limestone or pumice/volcanic rock, depending on local availability or sand

Sand

or a mixture of various sizes of media (for vertical flow constructed wetlands).

Design characteristics - commercial systems

Surface flow Constructed Wetlands - characterized by the horizontal flow of wastewater across the roots of the plants. They are being phased out due to the large land-area requirements to purify water—20 square metres (215.3 sq ft) per person—and the increased smell and poor purification in winter..

Subsurface flow Constructed Wetlands - the flow of wastewater occurs between the roots of the plants and there is no water surfacing (kept below gravel). As a result the system is more efficient, doesn't attract mosquitoes, is less odorous and less sensitive to winter conditions. Also, less area is needed to purify water—5 –. A downside to the system are the intakes, which can clog easily, although some larger sized gravel will often bypass this problem . . For large applications, they are often used in combination with vertical flow constructed wetlands. In warm climate, for organic loaded sewage, they require about 3.5m2/150 Liter for black and grey water combined, with an average water level of 0.50 meters. In cold climate they will require the double size (7 m2/150L). For black water treatment only, they will require 2 m2/50 Liter in warm weather.

Vertical flow Constructed Wetlands - these are similar to subsurface flow constructed wetlands but the flow of water is vertical instead of horizontal and the water goes through a mix of media (generally 4 different granulometries), it requires less space than SF but is dependent on an external energy source. Intake of oxygen into the water is better (thus bacteria activity increased), and pumping is pulsed to reduce obstructions within the intakes. The increased efficiency requires only 3 square metres (32.3 sq ft) of space per person.

Plants and other organisms - commercial systems

Plants

Although the majority of constructed wetland designers have long relied principally on Typhas and Phragmites, both species are extremely invasive, although effective. The field is currently evolving however towards greater biodiversity. Other designers (see http://www.wastewatergardens.net) use up to 200 different species, all climates included.
In North America, cattails (Typha latifolia
Typha latifolia
Typha latifolia is a perennial herbaceous plant in the genus Typha. It is found as a native plant species in North and South America, Europe, Eurasia, and Africa...

) 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) are common (both in blackwater treatment but also in greywater treatment systems to purify wastewater). In self-purifying water reservoir

Reservoir

A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...

s (used to purify rainwater) however, certain other plants are used as well. These reservoirs firstly need to be dimensioned to be filled with 1/4 of lavastone and water-purifying plants to purify a certain water quantity.

They include a wide variety of plants, depending on the local climate

Climate

Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

and location. Plants are usually indigenous

Indigenous (ecology)

In biogeography, a species is defined as native to a given region or ecosystem if its presence in that region is the result of only natural processes, with no human intervention. Every natural organism has its own natural range of distribution in which it is regarded as native...

in that location for ecological

Ecology

Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

reasons and optimum workings. Plants that supply oxygen

Oxygen

and shade

Shade

Shade is the blocking of sunlight by any object, and also the shadow created by that object. Shade also consists of the colors grey, black, white, etc...

are also added in to complete the ecosystem

Ecosystem

An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

The plants used (placed on an area 1/4 of the water mass) are divided in 4 separate water depth-zones:

0–20 cm; Yellow Iris (Iris pseudacorus
Iris pseudacorus
Iris pseudacorus is a species of Iris, native to Europe, western Asia and northwest Africa. Common names include yellow iris and yellow flag...

), Simplestem Bur-reed (Sparganium erectum
Sparganium
Sparganium is a genus of flowering plants, containing about 20 species in temperate regions of both the Northern and Southern Hemispheres. It was previously placed alone in the family Sparganiaceae...

), ... may be placed here (temperate climates)
40–60 cm; Water Soldier (Stratiotes aloides
Stratiotes aloides
-Origins:found in Europe and NW AsiaIn Britain it was once common in East Anglia and still is in many places, particularly wet ditches and healthy ponds.-Description:A rosette of serrated leaves.White flowers are produced in the Summer....

), European Frogbit (Hydrocharis morsus-ranae
Hydrocharis morsus-ranae
Hydrocharis morsus-ranae, Frogbit, is a flowering plant belonging to the genus Hydrocharis in the family Hydrocharitaceae. In North America, it is referred to as Common Frogbit or European Frogbit to distinguish it from the related American Frogbit .It is a small floating plant resembling a small...

), ... may be placed here (temperate climates)
60–120 cm; European White Waterlily (Nymphaea alba
Nymphaea alba
Nymphaea alba, also known as the European White Waterlily, White Lotus, or Nenuphar, is an aquatic flowering plant of the family Nymphaeaceae....

), ... my be placed here (temperate climates)
Below 120 cm; Eurasian Water-milfoil (Myriophyllum spicatum
Myriophyllum spicatum
Myriophyllum spicatum is a species of Myriophyllum native to Europe, Asia, and north Africa. It is a submerged aquatic plant, and grows in still or slow-moving water.-Description:...

), may be placed here (temperate climates)

The plants are usually grown on Coco Peat

Coco Peat

Coco peat , also known as coir pith, coir fibre pith, coir dust, or simply coir, is made from coconut husks, which are byproducts of other industries that use coconuts...

. At the time of implantation to water-purifying ponds, de-nutrified soil is used to prevent unwanted algae

Algae

and other organism

Organism

In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

s from taking over.

Fish and bacteria

Finally, locally grown bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

and non-predatory fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

are added to eliminate or reduce pests, such as mosquito

Mosquito

Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...

s. The bacteria are usually grown locally by submerging straw

Straw

Straw is an agricultural by-product, the dry stalks of cereal plants, after the grain and chaff have been removed. Straw makes up about half of the yield of cereal crops such as barley, oats, rice, rye and wheat. It has many uses, including fuel, livestock bedding and fodder, thatching and...

to support bacteria arriving from the surroundings.

Three types of (non-predatory) fish are chosen to ensure that the fish can coexist: 1. surface; 2. middle-ground swimmers, and 3. bottom.

Examples of three types (for temperate climates) are:

Surface swimming fish: Common dace
Common dace
The common dace , also known as the dace or the Eurasian dace, is a fresh- or brackish-water fish belonging to the family Cyprinidae. It is an inhabitant of the rivers and streams of Europe north of the Alps as well as in Asia. It is most abundant in France and Germany, and has also spread to...

(Leuciscus leuciscus), Ide (Leuciscus idus), common rudd (Scardinius erythrophthalmus), ...
Middle-swimmers: Common roach (Rutilus rutilus), ...
Bottom-swimming fish: Tench
Tench
The tench or doctor fish is a freshwater and brackish water fish of the cyprinid family found throughout Eurasia from Western Europe including the British Isles east into Asia as far as the Ob and Yenisei Rivers. It is also found in Lake Baikal...

(Tinca tinca), ...

Hybrid systems

Hybrid systems for example aerate the water after it exits the final reedbed using cascades such as Flowforms before holding the water in a shallow pond. Also, primary treatments as septic tanks, and different types of pumps as grinder pump

Grinder pump

A grinder pump is a waste management device. Waste from water-using household appliances flows through the home’s pipes into the grinder pump’s holding tank. Once the waste inside the tank reaches a specific level, the pump will turn on, grind the waste into a fine slurry, and pump it to the...

s may also be added.

External links

American Society of Professional Wetland Engineers website - a wetland restoration for habitat and treatment 'wiki'
On-line constructed wetlands workshop moderated by Greg Gearheart and Bob Gearheart
Robert A. Gearheart
Robert A. Gearheart is an emeritus professor of Environmental Engineering at Humboldt State University, in Arcata, California.Dr...

.
U.S.EPA: Constructed Wetlands resources website - United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
Google Books: "Creating Freshwater Wetlands" - by Donald A. Hammer
Constructed wetlands in Lake Macquarie, Australia
Federal Park Wetlands, Australia
Whites Creek Wetland, Australia
Wetpark: Water treatment systems website
WATER REPORT: Compost Toilets and Constructed Wetlands

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Biofiltration

Natural wetlands

Subsurface-flow wetlands

Surface-flow wetlands

Tidal Flow wetlands

General contaminants removal

Nitrogen removal

Organic nitrogen

and ammonium

Domestic sewage - ammonia

Mine water - ammonia

Phosphorus removal

Biomass plants incorporation - phosphorus

Retention by soils or root-bed media - phosphorus

Domestic sewage - phosphorus

Metals removal

Mine water - Acid drainage removal

General application

Design characteristics - commercial systems

Plants and other organisms - commercial systems

Plants

Fish and bacteria

Hybrid systems

See also

Literature citations

External links