Closed Loop Systems
I have chosen this type of system because it can elaborate on the requirements of any fish
farms, and display the concept of their operations. The opening page of this site shows a
graphic diagram of a closed loop system. The principle parts of such a system are the fish
tank, biological filters, and aerator.
Fish tanks have two main shapes. They can be either round or rectangular. Each one having
there supporters, some believe that circular tank can supply better oxygen-rich water and
exchange water better. Whereas rectangular shapes are to fish out the tanks. In circular tanks,
the flow of water is introduced on the top outer walls, and moves in a circular down and
inward motion. Whereas with rectangular tanks, water is introduced at one end, and is
removed at the other.
Biological filters serve to eliminate dissolved toxins, suspended solids, and bacteria. Solid
waste filters are the first in the process of filtration. To remove solid waste, various types of
sand or sedimentation ponds are used, and are cleaned regularly.
The best system that I support to remove dissolved waste are fluidized bed. In a tube
shaped filters with suspended sand, and a controlled upward flow of water in the tube,
bacteria attached to the suspended grains of sand convert contaminates like ammonia to
nitrites and then nitrates. At the upper end of the tube, where oxygen concentration are very
low, Nitrates are converted to nitrogen gas. Algae based filters are other types used to
remove toxins, and many municipal water treatment systems treat water in this way (they are
called lagoons). Algae filters are much more sensitive.
In the last filtration process, Ozone or ultraviolet light filters can be used, but are expensive
and dangerous to the fish if they are not operated properly. These filters serve to remove
unwanted bacteria that accumulate with time, and reduces the chance of disease in the system.
These filters are not displayed on the diagram.
The last step that the treated water has to encounter before returning to the fish tank is
aeration. The idea here is to provide the pumped water with as much oxygen as possible.
Aeration also servers as an gas exchanger. Gases like carbon dioxide and nitrogen are
removed. Aerator can have many forms, the main feature is to expose water with as much
surface area as possible in the surrounding air. This is achieved usually through a tower.
Water passes down the tower, and come in contact with many surfaces(perforated plates,
crushed stone). The aerator can also serve to cool or warm up the water.
As compared to cage farming or land based farms. Electrical cost are probable the most
with closed loop system, but not necessarily. In any land-based method, electrical costs of
lighting, aeration, or pumping are high. The cheapest type of farming is cage farming, but has
a higher risk attach to it on account of external factors.
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