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Biological Filters
All biological filters have in common the biological oxidation of wastes.
Submerged Filters
These are simple to consrtuct and are commonly used. They consist
of a shallow tank, box, or grow beds if you are into Aquaculture
and Hydroponics (Aquaponics) filled with filter media (gravel,
shell, limestone etc.) supported on a perfored filter plate. The
filter is all times flooded. To maintain oxidation througg out
the bed, water is pumped at a fairly hign rate of flow. Graval of
2 - 5mm in size is recommended.
Trickling Filters
These are able to cope with high populational loading but only
have a low input of water. The advantage of these filters is
their good oxogenation at ALL levels. The filter exists as a film
over the serface of the media, the intertices through the rest of
the bed containing air. The diffusion of oxygen into the water
occurs throught the whole filter bed.
If you are into Aquaculture and Hydroponics (Aquaponics) use the Submerged type of Filter to grow plants that like their roots wet. And use the Trickling type Filter for plants that like drained soil. In my greenhouse I also have pots and beds filled with potting soil that I fertilize with the stuff I get out of my settling filter and drip irrigate from the fish tank. (no retuen to the tank)