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Biological Filters are the heart of a life support system for closed aquatic culture systems.

There are many types of biological filters available that Pure Aquatics have experience in using, deigning, building and implementing.

Pure Aquatics both manufacture and import a variety of biological filters and filter media suitable for a wide variety of biological loads and applications.

MBBR Filters – Moving bed biological reactors

Moving bed biological reactors (MBBR’S) have become the standard in biological filtration in recirculating aquaculture systems and for good reason.

They are robust, easy to build, inexpensive to operate, require low pumping heads and they control biofilm thickness, ensuring optimum biological performance.

They also simultaneously oxygenate the filter and strip a percentage of CO2 for the system.

Through extensive and ongoing research, experience and development, Pure Aquatics have optimised our MBBR design for high removal, high oxygenation, superior mixing and easy maintenance.

Trickle Filters/degassing unit

Trickle filters were a very widely used biological filter in the past and still have their place in aquaculture today.

Trickle filters are flexible, they have a wide hydraulic loading range, oxygenate and degass the water as a function of their opperation, and have a very high ammonia and nitrite consumption rate per m2. Just like all filters, the higher the ammonia and nitrite levels the more the biological filter removes (however effluent concentrations go up), however trickle filters really excel at high ammonia concentrations.

The 0ne thing they do not do is self clean, and clogging can be an issue. Ways to negate this is to filter the water to a fine degree, and/or increase the void space of the media, which also decreases surface area.

They can also be more expensive to operate due to having to pump to elevated heights for operation.

Employed as degassing units under gravity or on low head pumping loops they are very effective, especially for high density culture systems.

Trickle filters are worth considering for biological filters in certain applications and should not be discounted.

Fluid Bed Filters

Fluid bed filters, also called fluid sand filters, fluidised bed filters or fluidised sand filters, pack a huge surface area into a compact area.

Depending on sand choice, surface areas can range from 8000m2/m3 up to and sometimes exceeding 20,000m2/m3.

They operate well in RAS systems but require the water to be quite clean prior to entering the filter due to their susceptibility to blocking or producing thick bio films that result in excess sand loss.

Fluid bed filters lose sand over time as the sand is colonised by bacteria and becomes lighter and floats out of the system.this can be managed by siphoning the top layer, increasing velocity at the top of the vessel etc but is generally a higher maintenance filter than an MBBR.

They may have a high surface area, but removal rates are generally lower per m2 as a fluid bed is a very abrasive environment, ammonia removal per footprint however, is still at the higher end. Pumping and energy requirements is higher compared to some other biological filter options, but they do have their place in biological filtration.