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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Constructed wetland | 2/5 | https://en.wikipedia.org/wiki/Constructed_wetland | reference | science, encyclopedia | 2026-05-05T07:17:43.561117+00:00 | kb-cron |
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. Nitrification is strictly an aerobic process in which the end product is nitrate (NO−3). The process of nitrification oxidizes ammonium (from the wastewater) to nitrite (NO−2), and then nitrite is oxidized to nitrate (NO−3).
==== Denitrification ====
Denitrification is the biochemical reduction of oxidized nitrogen anions, nitrate and nitrite to produce the gaseous products nitric oxide (NO), nitrous oxide (N2O) and nitrogen gas (N2), with concomitant oxidation of organic matter. The end product, N2, and to a lesser extent the intermediary by product, N2O, 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, including cyanide and nitrate.
=== Phosphorus removal === Phosphorus 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. In freshwater aquatic ecosystems, 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 in water receiving heavy discharges of phosphorus-rich wastes. Because phosphorus does not have an atmospheric component, unlike nitrogen, the phosphorus cycle 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 of insoluble phosphates with ferric iron, calcium, and aluminium 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. 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 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.
=== 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 and other sources (e.g., leachate or FDG washwater at coal-fired power plants), 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 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, 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: