Mechanical filters (MFs) play a vital role in recirculating aquaculture systems (RASs) by removing the solids that are suspended in the water as it moves through the system.  Concentrating these solids in the MF makes it easy to remove them from the system completely by automated and manual flushing, and this in turn enables the RAS to operate more efficiently.  These solids are typically fish faeces but also include some bacterial wastes, and are thus mostly generated in the fish tanks.  As the water in a RAS is pumped continuously into the fish tanks, it overflows, carrying the solid wastes with it.  Faeces are light and therefore easily carried by the flowing water as it exits the fish tank, but they also break up easily.  As larger particles are easier for the MF to remove them from the water, we allow the water to gravity feed from the fish tanks to the MF, as pumping at this stage breaks up the particles, reducing their size and making it more difficult for the MF to remove them.  
 
There are many MF types that are suitable for use in RASs. I have placed some of the most commonly used options into three broad categories in the table below according to the manner in which they operate:
 

The settlement type rely on the particles being heavier than water, and thus settling via gravity.  Both types are made without moving parts and are very reliable in their action, but only remove really large particles (typically >100?m) and have an issue with resuspension of solids if not cleaned frequently (twice daily).  As such these filters are useful but only as pre-filters to reduce the work load of the primary MF, which is then selected from one of the other two categories.

Screening type filters come in various forms but drum filters are the most effective of these as they have a large surface area, enabling them to handle large water flow volumes, and are self cleaning.  Drum filters can be scaled to filter water down to about 40?m with tilapia and 60?m with catfish, the difference being due to the bacterial growth which quickly blocks the screens in a catfish RAS.  These filters are extremely expensive, notoriously fickle and require specialist maintenance, and as such not my recommendation for use in Africa.
 
I believe that the MF filter based on a stationary bed of floating media is the best solution for RAS mechanical filtration in the African context.  These filters are effective, efficient, not massively expensive to install or manage, and very simply in their mode of operation.  Water enters a void space below a 50cm bed of floating media, and the large particles settle out in this void space.  The water rises slowly through the media and particles are trapped within the media bed and clean water overflows through the top of the media.  When the filter requires cleaning the flow is redirected through the other MFs (we install several in parallel for this purpose).  Water is drained from the chamber being cleaned whilst the media is vigorously stirred, allowing the trapped particles to be released and removed to waste.
 
Scaling the size of a MF in based on water flow rate and there needs to be 1m2 of floating bed surface area for every 12m3/hr of water flow.  This ratio allows for very clean water to be achieved, making these filters super efficient and allowing the rest of the RAS to function optimally.
 
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Training Material
We have also loaded our training material to the online shop for self study purposes.  In this way you can purchase the chapters you want to increase your knowledge in specific areas.
  
2nd hand fish farming equipment for sale
We are selling a selection of fish farming and aquaponics equipment, some of which is listed below.  Interested parties can email me for more information - first come first serve.
 
fibreglass tank 1.4m diameter x 1.2m deep @ R867 each
blower 0.75kW @ R3 668
dutch buckets with 20mm fittings @ R39.20
For a full list see our online shop.
 
All prices are pre-Vat and ex-Grahamstown.
  

Aquaculture Farm for Sale 
The Aquaculture Academy, Grahamstown is for sale.  The farm of 4.4ha has excellent quality water and has permits to farm trout, tilapia and catfish.  Currently we also farm cucumbers and other crops organically on the effluent water from the fish.  There are several bee hives, hand tame chickens and many pecan nut saplings.
 
The farm has a 5-bedroom main dwelling, a bed sitter and a large lecture facility / office complex.
 
The excellent schooling in Grahamstown is a huge drawcard as this farm affords an opportunity to live the lifestyle whilst your children obtain top schooling 1.3km from the farm.
 
Interested parties are invited to contact me on 083 4060 208.
 
Aquaculture Courses
The following Courses are scheduled to be held in Pretoria in 2021:
 
Commercial Aquaponics 8 & 9 February 2021
 
Fish Farm Management 10 to 12 February 2021
 
Practical Aquaculture Course 22-26 March 2021
 
Grab this opportunity to learn the practical aspects of fish farming; the doing rather than just the theory.  
 
To obtain further information email us on info@aquaafrica.co.za.

Aquaculture Products for Sale
 
We offer a wide range of products to the Aquaculture Industry.  These products can be viewed and purchased from our secure online store at Aquaculture Store.
 
We are currently offering the following special whilst stocks last:
 
Aeration Diffusers: we have several sizes of Aero Tube diffusers available - check on online shop for further information.
 
If you need anything that is not listed, drop me an email and I will attempt to source it for you.