Biotechnology and Bioinformatics (1+1)

6.2.4.8. Submerged filters

Submerged filters are excellent choices for small systems because they are very versatile. They can be located in a separate tank or in the culture tank. They can be horizontal flow, up flow or down flow. They can be aerated or not.

· The most important consideration for the design is the even distribution of water to the packing.

· It is very common for submerged filters to be designed as large, flat and thin sections of packing with water direction being up flow or down flow.

· There is typically no provision for distributing the water to all areas of the media.

· The length of the water path through the media is very short and the resistance to flow is very low.

· This is a recipe for disaster. The water flow will short circuit though a small section of the media and the rest of the biofilter will become anaerobic.

· Ideally the flow path through a submerged filter should be as long as possible. A long thin raceway is the best. This type of biofilter is known as a long path, plug flow submerged filter.

· Another possible alternative is the use of aeration to induce a circulating flow around a tank.

· The goal should always be to provide sufficient velocity through the media to insure a fresh supply of oxygen and nutrients to the bugs on the surface of the media.