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Biological Filtration

Biological filtration refers to filtration methods that utilise living organisms to neutralise or remove undesirable substances from a process liquid.  It is the removal of waste metabolites that would otherwise accumulate from keeping, feeding and growing aquatic animals in a closed recirculating system that is considered here. After oxygen, it is the accumulation of ammonia - the waste metabolite from protein digestion - that is probably the most limiting factor affecting the successful operation of closed recirculation systems. The removal of ammonia (NH3) by oxidation to nitrite (NO2) and finally nitrate (NO3) is carried out primarily by the bacteria Nitrosomonas sp. and Nitrobacter sp. respectively. This process is called NITRIFICATION. Un-ionised ammonia and nitrite are both toxic to fish at relatively low concentrations whereas nitrate, the end product of nitrification, is relatively nontoxic at even quite high concentrations. The rate of nitrification is proportional to temperature, proceeding particularly slowly below 10°C, and is optimal around 30°C. However, the metabolic rate of aquatic animals is also proportionately lower at reduced temperatures and it is perfectly feasible to consider recirculation at cooler temperatures. 

The particular size and type of filtration equipment for a given application will depend on a number of factors including, but not limited to, the type of livestock being held, the total stocking density, the amount of food that is added to the system and the temperature of the water. Please contact us if you would like to discuss your requirements in more detail, or complete our online enquiry form, and a member of our team will be in touch.

Biological Filtration Technical Information

Fluidised Sand Bed Filters Technical Fact

TMC Fluid Sand Filters incorporate a unique anti-siphon device which guarantees that in the event of a power/flow interruption, no media will back-siphon into the supply pipework.
If this were to occur, the Fluid Sand Filter would have to be completely stripped down and re-commissioned, usually resulting in the sand’s biofilm becoming unviable

TMC Fluidised Sand Bed Filters are designed to operate with 50-100% expansion of the sand bed (approx. 75% of the total filter column height).  Flow rates specified are designed to be a maximum of 180m3/hr per m2 of cross-sectional filter area.

The maximum livestock mass of the TMC Commercial Fluid Sand Towers has been calculated based on a feed rate of 3% body weight per day, feed with a protein content of 50% and at warm water temperatures. Most commercial facilities operate at high stocking densities and want to achieve high growth rates, resulting in an increased demand on the bio-filtration. To compensate for this, the maximum livestock mass has been reduced. 

Trickle Bio-Tower Technical Fact

All materials used in the production of TMC’s Re-gas/Biotowers are from virgin nontoxic plastics. It is critical that any products used in the construction of Re-gas/Bio-towers are nontoxic. Aside from the fact that they need to sustain populations of aerobic bacteria, the high surface areas associated with these filters means that there will be significant leaching of any toxic substances should they be present. Please refer to the pricing tables for materials of construction of each of the units. 

All units utilise our TMC Bio-Rings with an approximate surface area of 210m2/m3, and a biological capacity of a minimum of 140g of TAN processed per m3 of media per 24 hours. Flow rates specified are designed to be 30m3/hr per m2 of cross-sectional filter area.


Fluidised Sand Bed Filters