Glossary of Constructed Wetlands Terminology

Absorb (absorption)

The passing of nutrient material into the body of a plant or animal.

Acidogenic leachate

A leachate which is converted by anaerobic microbial activity to carbon dioxide and organic fatty acids.

Activated sludge

A method of biological wastewater treatment involving aeration with flocculating microbial biomass.


The collection of nutrient material on the surface of the plant or animal.


Requiring atmospheric oxygen.


One of many-celled microscopic aquatic plants.


The first stage of nitrogen transformation by reduction to ammoniacal nitrogen.


A condition in which no oxygen is available as free oxygen, nitrite or nitrate.


Deficient in dissolved oxygen (not containing dissolved oxygen but where reduction of nitrate or nitrite may occur).

Aspect ratio

Length to width ratio.


Able to derive energy from inorganic reactions, e.g. nitrifying bacteria.


The inclined sides of a constructed wetland from the surface of the bed to the level of the surrounding soil.

Biochemical oxygen demand(BOD)

The amount of dissolved oxygen consumed by the degradation of organic matter by bacteria in water in the dark, usually over a period of 5 days at 20°C.


The microscopic growth of organisms which forms as a slime over stones, plants or some other support usually in aquatic environments.

Biological filter

A bed of inert material; sewage trickles through the media and is treated through the action of bacteria and other microorganisms; also known as a conventional,trickling or percolating filter.


The mass of animals and plants within a habitat measured at a given time.


Community of living organisms.


Blocking or clogging with small particles or debris.


Scatter freely.


Fall of water by gravity from a high to low level.

Chemical oxygen demand (COD)

The amount of oxygen consumed by chemical oxidation.

Consent Standard

Licence to discharge wastewater at or better than a standard set by a regulatory authority; UK Water Companies usually have to comply with BOD/SS/amm-N standards, and possibly with additional phosphorus, total nitrogen and bacteria standards.

Constructed wetland

Artificial wetland engineered to achieve biological and physicochemical improvement in the environment.

Conventional filter

See biological filter.


The reduction of nitrite and nitrate to nitrogen gas by bacteria under anoxic conditions.

Discharge consent

Consent issued by the Environment Agency under Schedule 10 of Water Resources act 1991.

Emergent macrophytes

Aquatic plants rooted in the support medium with much of their green parts above the surface of the water.


Enrichment of the aquatic environment with nutrients resulting in increased primary production.


Loss of water vapour from the leaves of green plants during photosynthesis.


Capable of living aerobically or anaerobically.


Vertical distance between the maximum water level in a container and the top of the side walls of the container.

Grey water

Water from sinks, baths, showers and kitchens.

Heavy metals

Metalliferous elements and their derivatives including zinc, lead, copper, iron, mercury, cadmium, cobalt, manganese and nickel.

Hydraulic conductivity

The ability to support medium to conduct fluid through the interstices between particles which make up the medium.


The cultivation of plants in a liquid film of nutrients.

Indicator bacteria

Micro-organisms used to indicate the presence of faecal contamination.


Animal without a backbone.

Ionic exchange

Movement of chemical ions between sites.


A layer of dead vegetation which serves as an important site for micro-organisms.


Green plants.


Visible with the naked eye.


Evil-smelling, nauseous (offensive to smell).


A mixture of clay and carbonate of lime.


Soil, gravel or other material used in a constructed wetland in which to grow plants and support micro-organisms; also known as support matrix.

Methanogenic leachate

A leachate which is converted by anaerobic methanogenic bacteria to produce methane.


An organism that is not visible with the naked eye.


The oxidation of ammoniacal nitrogen to nitrite and nitrate by autotrophic bacteria under aerobic conditions.

Nitrogen fixation

Conversion of nitrogen gas into nitrogenous compounds.


A substance that supports growth.

Organic loading

The strength of wastewater measured by its amount of organic matter able to be consumed by biochemical processes.


A disease-producing organism.

Percolating filter

See biological filter.


Allowing movement of liquids and gases.


Scale based on hydrogen ion concentration and ranging from highly acid (0) to highly alkaline (14)


Process by which the energy of sunlight is trapped by green pigment in plants, and is used to build up plant tissue from carbon dioxide and water.

Plug flow

Theoretical movement of fluid particles which pass through a compartment without dispersion and are discharged in the same sequence and at the same concentration in which they entered.


An integrated culture of aquatic animals and plants that co-exist so that their combined effect is to improve water quality.

Population equivalent

Amount of degradable matter (expressed in terms of BOD or of other significant properties) or volume of wastewater produced per capita (1 pe < 150 l.d-1 < 0.15m3.d-1).


The process by which chemicals move out of solution to be deposited in soild form; also rain, snow , sleet or hail.

Primary production

Incorporation of carbon dioxide into organic matter by photosynthetic organisms or autotrophic bacteria.

Primary treatment

Physical separation of solids, usually by settlement, before secondary biological sewage treatment.


The rate of production of biomass.


To knead into an impervious layer.


Below ground stem of macrophytes.

Root zone

The area around the growing tips of the roots of a plant.

Roughing filter

A biological filter which is operated at a high loading rate to achieve partial pre-treatment of wastewater.

Screening zone

A zone which provides a screen to protect reeds from storms of wind and rain.

Secondary treatment

First biological stage of treatment for sewage.

Sewer dikes

Trenches or ditches into which sewage flows and infiltrates into the surrounding soil for purification by micro-organisms growing in the soil.


Substances acted upon by an enzyme or a surface upon which a micro-organism lives and from which it may derive nutrients.

Support medium

Soil, gravel or other material used as the support matrix within the constructed wetland.

Suspended solids (SS)

Dry weight per volume of matter in a sample retained by a filter.

Tertiary treatment

Treatment following the biological stage of treatment for sewage, which may incorporate removal of nitrate and removal of surplus suspended solids.

Total solids (TS)

Material remaining in a sample when all the water has been evaporated.

Trickling filter

See Biological filter.