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Applications in Aquaculture

• inlet water from marine farms and hatcheries
• inlet water for freshwater farms and hatcheries
• marine and freshwater hatchery recycle systems
• effluent treatment system for critical applications where biological discharge has to be minimised or eliminated
• Bore hole water filtration for iron and manganese removal

Mechanical filtration systems have been used in aquaculture for many years.  The majority of the systems are based on static or moving screens and will remove particles from the water down to a limit of 20 microns, but more realistically the systems are best suited for solids filtration above 50 microns.  Static and moving screen technology is therefore applied to grow-out aquaculture applications and for effluent treatment.

If there are any particle smaller than 50 microns in the water,  the effectiveness of UVc and ozone  will be greatly diminished, fungi spores, parasites  and bacteria flora could also be present in the water at high concentration. The biofilters in the system will likely trap a proportion of the solids,  but the biofilter can also generate a bacterial floc.  In system critical applications such as hatcheries it is therefore desirable to achieve the best quality water for the juvenile stock,  be it in freshwater or marine systems.  Cartridge filters are occasionally used for these applications,  however due to the high loading the cartridge elements will not last,  so media filtration such as sand filters are used. 

Sand filters can give very good results in low density systems such as aquariums,  when operated at low flowrates ranging from 5 to 15 cubm/hr per square metre of filter bed surface area,  you can expect to remove around 90% of all the particles in the water down to around 10 microns.  This can make a huge improvement to the quality and clarity of the water. Removal of the fine solids will also reduce the load on the ozonation system making it easier to maintain the redox potential.  The size of the ozonation system can also be reduced, by at least 80% over system without media filtration.  However as soon as there is an serious loading on a sand filter,  biofouling of the sand takes over and the filter becomes blocked,  or serious channelling develops after a few weeks.  It can therefore become a time consuming a laborious problem to maintain sand filters.  In order to alleviate these problems,  Dryden Aqua have developed a new filtration media called AFM� or Active Filter Media.

At Dryden Aqua we have great deal of experience with ozonation, catalytic oxidation and zeolite ion exchange filtration systems.  It was considered that it may be possible to design a filtration media that was more than just a simple mechanic system like a sand filter.  

AFM� filtration media has been used in aquaculture since 1997,  the filtration media has been gaining acceptance as a superior filtration media,  and it probably accounts for a very high percentage of all filtration systems in Northern Europe. AFM� is used extensively with Atlantic salmon hatcheries and also with all of the main Halibut hatcheries in Europe.

AFM� is also used extensively in the Middle East, and Australia for a diverse range of aquaculture species, including shrimps and grouper.

Operating Parameters

In all cases the slower the water is passed trough the AFM� the better the performance of the filtration media. For Aquaculture applications, we recommend a flowrate between 5 and 15 cubic metres of water per hour per square meter of filter bed surface area. This water flowrate will give a good performance with grade 1 AFM� .  You would expect to remove a high percentage of the particles in the water down to around 5 microns.

For optimum performance an removal down to approximately 1 micron,  the flowrate should not exceed 5 cubm/hr. Grade 0 AFM� may also be used at these flowrates to achieve optimum solids removal.

Back-flush Frequency

The back-flush frequency will depend on the quality of the water entering the AFM� filter,  normally the filter should be back-flushed 2 times each day.  The back-flush flowrate must be at least 30 cubm/hr per square meter of filter bed surface area, back-flush duration is normally only about 2 minutes.