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The bacterium Nitrosomonas oxydizes Ammonia to Nitrite, the bacterium Nitrobacter the Nitrite to
Nitrate.
Am Oxygen ----- > N Oxygen -----> Nitrate
(Nitrosomonas) (Nitrobacter)
In most aquaria, nitrate is the endproduct of bacterial metabolism and accumulates in the water.
Only higher water plants and algaes are able to remove this nitrate from aquarium water.
What is the effect of nitrate in the aquarium?
-
Overfertilization/etrophication: The aquarium is overfertilized, the algae growth increases and
cannot be controlled anymore.
-
Toxic effects to the animals: Many invertebrate animals in sea water tanks are very sensitive to
higher nitrate levels.
3.
Working principle of the Nitratereductor
In the AB Aqua Medic Nitratereductor the water is treated anaerobically. In the absence of oxygen,
many bacteria are able to use nitrate as a substitute for oxygen for their metabolism.
2 Nitrate ----> nitrogen gas + 3 oxygen
2 NO3 ----> N2 + 3 O2
Oxygen is used for metabolism, the nitrogen is excreted into the water. Nitrogen gas is a natural
compound of water and totally harmless.
It is, however, necessary to increase the metabolism of bacteria so that they can reduce enough
nitrate. For this reason, the nitrate removing bacteria have to be fed with organic substances. The
tablet food Denimar
contains organic substances that can be used completely by the bacteria. The
only waste product is CO
2
.
The flow rate through the Nitratereductor is very slow. This is the main difference to other
aquarium filters where the water is often treated once per hour or even more often. The water in
the
Nitratereductor
should have a retention time of 2 - 4 hours. It is, however, sufficient to treat it
once per week. If the filter is adjusted correctly, the water leaves the filter nearly free of nitrite and
nitrate.
4.
Description of the
Nitratereductor
The AB Aqua Medic Nitratereductor
consists of a reaction vessel (1) of 2.3 l volume. To provide
surface material for bacteria the filter is filled with AB Aqua Medic Deniballs. They create an ideal
microclimate for denitrification. To avoid dead zones, the water is recirculated internally in the
Nitratereductor. A recirculation pump is placed in the top.
In denitrifying filters, especially in units where the water has to pass through a long way, it can
occur that there is no even flow in the filter. Zones with a very low redox potential are created
where hydrogensulfide is produced (the filter starts to smell badly). On the other side, zones with a
rather high flow may arise where nitrate is reduced only to nitrite. In each case, the conditions
vary in the different zones of the filter and it is nearly impossible to find its right working point.
These unpleasant effects are avoided by the construction of the AB Aqua Medic Nitratereductor.
The recirculation ensures a complete mixing and the same redox potential level in the whole filter.
Zones with a very low redox potential and the production of hydrogen sulfide are avoided. The
redox potential can be used for controlling the filter. The effectivity and the reliability of the filter
can be increased .
