As explained in Article " Filtration: filters , all filters obey the same principle: the dirty water is taken from the tank, it passes through different filter materials properties and different roles, and finally it returns own in the tray.
The actual filtration work is performed by the filter media. Without them, the filter would only circulate water.
The different types of filtration: mechanical, biological and chemical
The filter media will retain waste ( mechanical filtration ), treat the water by bacteria (biological filtration ), and retain or distribute certain substances (chemical filtration ).
Each type of filter has its usefulness and is directed by appropriate filter media.
Multiplicity and the relative shares of filter media
A filter material can often be two or three actions (mechanical, biological and chemical).
is the dominating action which will be retained and which will be operated by appropriate positioning in the filter. The same filter material placed at various locations will not necessarily share the same casting.
Moreover, the casting choice of action will be made with respect to those of other filter media. Imagine the mass A good stock mechanical and biological, and mass B in good mechanical and biological action in very good: in this case the mass A will be dedicated to the mechanical action and mass B to the biological action. These reasons
(multiplicity and relativity of action) explain the apparent inconsistencies that imputes the neophyte: what is true in a case is not necessarily in another.
Mechanical filtration
Mechanical filtration is designed to retain particles or undissolved solids suspended in water.
It is performed by filter media acting as nets or porous materials. The particles are retained by two effects: either the particle is larger than the "mesh" of the filtering and is therefore blocked (or surface filtration media) or it is smaller than the "mesh" of mass filter but it will be blocked by getting lost in the maze formed by the filtering and impact against a surface encountered (effect depth or wall).
In practice, this second effect is most often at work.
particles are retained, they accumulate in the body and eventually the seal: the water does not pass (and it's even faster than the surface effect is at work). It needs to be cleaned regularly these media.
To avoid clogging too fast and too frequent cleanings, it is advisable to use in the direction of flow of water masses with "mesh" large, medium and fine: the maximum particle will be retained and clogging will be delayed.
The filter media used for mechanical filtration are: cotton, Perlon (such as cotton wool but with a synthetic material instead of cotton), mosses, some ceramics (to be first to hold the waste very large), etc..
Biological filtration
Biological filtration is designed to treat certain substances by bacteria. This is mainly to implement the nitrification of the nitrogen cycle that will convert the ammonia / ammonium to nitrite and nitrate.
This filtration will be done by filter media that will provide good support to the proliferation of bacterial colonies, while allowing water to circulate around and therefore the necessary oxygen.
This party does not dirty its operation: substances produced (nitrate) start with water. Instead, it should never have to clean this part, because cleaning will be disastrous for the bacterial colonies, which could cause an imbalance in the nitrogen cycle.
The water entering the biological part should be as clean as possible which is why it is always placed after the mechanical filtration.
The filter media used for biological filtration are: ceramics with high porosity, foams, very porous substrates such as pozzolan, etc.. In contrast, cotton and Perlon are low bacterial support.
Chemical filtration
Chemical filtration is intended to retain some dissolved substances in a material according to the physico-chemical properties. We also classify in this category of substances released by a material (eg peat humic acid release).
be found in this part of the coal (incorrectly said to be active), resins (anti-phosphate anti-nitrate, etc.) and many so-called miracle products. Their action decreases with time because they "meet" with the substances they hold.
Generally, these products must be used wisely and never for prolonged periods (except peat), because often there are long-term adverse effects.
Organization of filtration and filter media
In the classical case of compact filters internal or external and internal decantation, must establish the mechanical and biological filtration, and optionally, if necessary, chemical.
The order relative to the direction of flow of water (up and down have no meaning here) will be: mechanical filtration and biological filtration and finally, possibly, chemical filtration.
If the filter is small, we must focus on mechanical filtration while still trying to dedicate a game to biological filtration.
More on this organization in the article "Filtration: an example of organization of the filter" (forthcoming).
See also " Filtration: filters .
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