Anammox

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Anammox

Anammox, an abbreviation for anaerobic ammonium oxidation, is a stage in the nitrogen cycle

Nitrogen cycle

The nitrogen cycle is the biogeochemical cycle that describes the transformations of nitrogen and nitrogen-containing compounds in nature. It is a cycle which includes Gas components....
. In this biological process, nitrite

Nitrite

The nitrite ion is NO2-. The anion is bent, being isoelectronic with ozone. More generally, a nitrite compound is either a Salt or an ester of nitrous acid....
and ammonium

Ammonium

The ammonium cation is a positively electric charge polyatomic ion of the chemical formula NH4+. It has a formula weight of 18.05 and is formed by protonation of ammonia ....
are converted directly into dinitrogen gas. This process contributes up to 50% of the dinitrogen gas produced in the oceans. It is thus a major sink for fixed nitrogen and so limits oceanic primary productivity. The overall catabolic reaction is:

NH₄⁺ + NO₂^- ? N₂ + 2H₂O.

The bacteria that perform the anammox process belong to the bacterial phylum planctomycetes

Planctomycetes

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Encyclopedia

Anammox, an abbreviation for anaerobic ammonium oxidation, is a stage in the nitrogen cycle

Nitrogen cycle

Nitrite

The nitrite ion is NO2-. The anion is bent, being isoelectronic with ozone. More generally, a nitrite compound is either a Salt or an ester of nitrous acid....
and ammonium

Ammonium

Planctomycetes

Planctomycetes are a phylum of aquatic bacteria and are found in field samples of brackish water, and Marine and fresh water water samples. They reproduce by budding....
, of which Planctomyces and Pirellula are the best known genera. Currently four genera of anammox bacteria have been (provisionally) defined: Brocadia
Brocadia anammoxidans

"Candidatus Brocadia anammoxidans" is a bacterial member of the order Planctomycetes and therefore lacks peptidoglycan in its cell wall, has a compartmentalized cytoplasm....
, Kuenenia, Anammoxoglobus (all fresh water species), and Scalindua (marine species). The anammox bacteria are characterized by several striking properties: they all possess one anammoxosome, a membrane bound compartment inside the cytoplasm

Cytoplasm

The cytoplasm is the part of a Cell that is enclosed within the plasma membrane. In eukaryote cells the cytoplasm contains organelles, such as mitochondrion, that are filled with liquid kept separate from the rest of the cytoplasm by biological membranes....
which is the locus of anammox catabolism. Further, the membranes of these bacteria mainly consist of ladderane

Ladderane

A ladderane is an organic molecule containing two or more fused rings of cyclobutane. The name is a portmanteau because the serial cyclobutane rings look like a ladder and are singly bonded like alkanes....
lipids so far unique in biology. Of special interest is the turnover of hydrazine

Hydrazine

Hydrazine is a chemical compound with the chemical formula N2H4. It is a colourless liquid with an ammonia-like odor and is derived from the same industrial chemistry processes that manufacture ammonia....
(normally used as a high-energy rocket fuel, and poisonous to most living organisms) as an intermediate. A final striking feature of the organism is the extremely slow growth rate. The doubling time

Doubling time

The doubling time is the period of time required for a quantity to double in size or value. It is applied to population growth, inflation, resource extraction, Consumption_ of goods, compound interest, the volume of Cancer, and many other things which tend to grow over time....
is nearly two weeks.

The application of the anammox process lies in the removal of nitrogen in wastewater treatment. Instead of the conventional nitrification

Nitrification

Nitrification is the biological redox 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....
-denitrification

Denitrification

Denitrification is a microbially facilitated process of dissimilatory nitrate reduction that may ultimately produce molecular nitrogen through a series of intermediate gaseous nitrogen oxide products....
process, only half of the nitrogen has to be oxidized partly to nitrite

Nitrite

The nitrite ion is NO2-. The anion is bent, being isoelectronic with ozone. More generally, a nitrite compound is either a Salt or an ester of nitrous acid....
. For the enrichment of the anammox organisms a biofilm system seems to be especially suited in which the necessary sludge age of more than 20 days can be ensured. Other possibilities are sequencing batch reactor

Sequencing batch reactor

Sequencing batch reactors or sequential batch reactors are industrial processing tanks for the treatment of wastewater. SBR reactors treat waste water such as sewage or output from anaerobic digesters or mechanical biological treatment facilities in batches....
s (SBR) or gas-lift-loop reactors using granular sludge. The cost reduction compared to conventional nitrogen removal is considerable; the technique, however, is still young. The first full scale sludge-water treatment plant using the biological process of anammox was built 2000 in Germany (Hattingen). As of 2006 there are three full scale processes in The Netherlands. One on a municipal wastewater treatment plant (in Rotterdam

Rotterdam

Rotterdam ; city and municipality in the Netherlands province of South Holland, situated in the west of the Netherlands. The municipality is the List of cities in the Netherlands with over 100,000 people in the country, with a population of 584,046 on 1 January 2007 and comprises the southern part of the Randstad, the List of metropolitan are...
), one on an industrial treatment plant (tannery) and one full scale application using SBR at the wastewater treatment plant Strass, Austria.