Cycle nitrogen

The cycle of the nitrogen is, a biogeochemical Cycle which describes the succession of the modifications undergone by the various forms of the Azote (Diazote, Nitrate, Nitrite, Ammoniac, nitrogenizes organic (Protéine S)).

General information

The atmosphere is the independent source of nitrogen, in the form of Diazote, since it contains 78% in volume of them. The nitrogen, made up essential with many biological processes, finds inter alia in the amino-acid constituting the Protéine S, and in the nitrogenized bases present in DNA. Processes are necessary to transform atmospheric nitrogen into an assimilable form by the organizations.

The atmospheric nitrogen is fixed by Bactérie S present in the ground, such as Azobacter vinelandii , thanks to an enzyme, the nitrogénase . This one which produces Ammoniac starting from atmospheric nitrogen and of the Hydrogène of water. Some of these bacteria, like Rhizobium , live in Symbiose with Plante S, producing ammonia and drawing Glucide S of the plant in the rhizosphère. The ammonia can also come from the decomposition of organizations died by bacteria Saprophyte S in the form of Ion S Ammonium.

In the well oxygenated grounds, but also into oxygenated aquatic environment, bacteria transform ammonia into Nitrite, then in Nitrate S, during the process of Nitrification. One can break up this transformation into nitritation and nitratation.

The vegetable absorb thanks to their root S the Ion S Nitrate and, to a lesser extent, the Ammonium present in the ground, and incorporate them in the amino-acids and proteins. The plants thus constitute the primary source of assimilable nitrogen by the animal .

Into medium Anoxique, (ground or aquatic environment not oxygenated) of the bacteria known as denitrifying transforms nitrates into gas Diazote, it is the Dénitrification.

Ammonification

It is the production of ammonium or ammonia because of a biological activity, to leave either organic matter in decomposition, or by the nitrate reduction.

Starting from the organic matter

The purpose of the ammonification starting from the organic matter is to produce a source of nitrogen directly usable by the organizations for their own synthesis.

Realized only by one bacterial biomass:

Bacteria gram- ( Entérobactérie, Pseudomonacea …)
Bacteria Gram-plus ( Bacillus …)
Bacteria Gram-plus ( Entérocoques …)
Mushrooms

Starting from nitrates

It has as goals:

to produce energy by reduction of ammonium nitrates.
to produce the assimilable nitrogen shape. It is denitrification assimilatrice or the ammonification assimilatrice.

Application in treatment of waste water

The purification plants have in particular as function to degrade molecular and ammoniacal the nitrate nitrogen shapes, then if required to cause a detnitrification (or denitratation) in order to reduce the concentration of this element in rejected water.

Application in aquariophilie

In an aquarium, the dejections of fish and not consumed food are the primary sources of the ammonia, which is extremely toxic. The cycle of nitrogen in aquariophilie represents the transformations which this ammonia will undergo to be transformed finally into nitrates definitely less toxic. Indeed a first population of bacteria (called nitrosomonas) will still degrade it out of nitrites, themselves very toxic. A second population of bacteria (called nitrobacter) then will appear, which it will transform nitrites into nitrates, whose rate is generally acceptable in fresh water aquariophilie up to 50 mg/l. On the other hand, the “hard “corals do not support rates higher than 1-2 mg/l.

These populations of bacteria will appear gradually as from the moment when the aquarium is started: it is necessary to count approximately 3 weeks before being able to introduce first fish. Indeed at the end of a few days one will see appearing a nitrite peak, due to the first population of bacteria; it should be waited until the nitrites are completely undetectable to be able to put fish in the aquarium, because they are very toxic products.

The bacteria degrading ammonia and nitrites are present in water, the ground of the aquarium, and filters it when one has one. If a red fish can apparently live without the presence of a pump, for the sea water or tropical fresh water aquariophilie, a water pump equipped with a filter is essential: indeed the useful bacteria are aerobic, i.e. they need oxygen to live. The circulation of water thus allows on the one hand simply that water charged out of nitrites and ammonia is put in contact with the bacteria, and on the other hand that those receive oxygen necessary.

As from the moment when the cycle of nitrogen settled, one says that the aquarium is balanced: that thus means that there are more presence of ammonia or nitrites. This balance depends on the presence of the bacteria in the aquarium: one thus should never change the totality of the water of the aquarium of only one blow under penalty of being likely to unbalance it completely; in this case it would have again to be waited until the bacteria reform themselves… In the same way one never should clean the filter masses with detergents, only with the water of the same temperature as the tank (directly with the water drained by ex); they should not either be cleaned at the same time as one changes water, for the same reasons.

In an aquarium intended for the maintenance and the reproduction of the corals, it is essential to maintain the nitrate rate in lower part of 1-2 mg/l. For that, the only technique is: (1) to maintain very a weak density of fish settlement (“1 cm of fish “for 10 liters is 5 fish of 10 cm for an aquarium of 500 liters) and (2) to eliminate thanks to a scummer organic waste before those do not return in the cycle of nitrogen. One will finally help of alive stones , structures adapted particularly well to lodging of anaerobic populations of bacteria, which will convert nitrates (NO3) into gas nitrogen (N2) which then will escape from the system. It is said whereas the cycle of nitrogen was buckled. This is particularly true in the récifaux vats.

See too

biological Fixing of the nitrogen

Bonds external

Cycle of the nitrogen Diagram of the cycle of nitrogen out of aquarium

Simple: Nitrogen cycles

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