design to provide additional oxygen to the fish tank .
• Shutter board – To help distribute the weight ( 3.3 tons ) as well as to protect the suspended wooden floor in this case .
• Cement Blocks – To elevate DWC troughs and fish tank enabling gravity flow .
• Plumbing – Various PVC connectors and pipes connecting the various aquaponics components .
Information about the design : Water flow :
In a deep water culture ( DWC ) method , also known as the raft method or floating system , the nutrient rich water is circulated through long canals at a depth of about 25cm – 30cm while rafts ( usually polystyrene ) float on top . Plants are supported within holes in the rafts by net pots . The plant roots hang down in the nutrient-rich , oxygenated water , where they absorb large amounts of oxygen and nutrients which contribute to rapid growth conditions .
In the deep water culture unit described in this technology , water flows by gravity from the fish tank , through the mechanical ( radial ) filter into the combination biofilter / sump . From the biofilter , the water is pumped in two directions through a “ Y ” connector ( T-Junction ) and valves . 80 % of the water is pumped to the fish tank while the remaining water ( 20 %) is pumped into a circulating loop system which distributes the water evenly through the canals . By gravity , the water exiting the canals and returned to the biofilter / sump , where again it is pumped either into the fish tank or canals . The water that enters the fish tank causes the fish tank to overflow through the exit pipe and back into mechanical filters , thus completing the cycle .
However , when a low stocking density of fish ( i . e . 1 – 5 kg of fish per m 3 of fish tank ) is used , the DWC can be designed without using external filtration containers , mechanical or biological . In this system , water is pumped to the fish tank as well as the DWC canals . Water in the fish tanks , biofilter and canals is aerated using an air pump . The fish waste is broken down by nitrifying and mineralizing bacteria living in the biofilter , plant root surface and the canal walls . To avoid waste accumulation of solids at the bottom of the canals and biofilter , a radial filter is positioned where the water exits the fish tank .
Filtration :
Two types of filters need to be constructed for the system : first , a physical trap to catch the solid wastes ( radial filter ), and then a biological filter for nitrification . The designs described in this document use a mechanical swirl or radial filter to trap particulate wastes , with periodic draining of the captured solids . On exiting the radial filter , the water passes through a mesh screen ( Japanese matting ) to trap any remaining solids and then reaches the biofilter . The biofilter is well oxygenated with air stones and contains a biofiltration media , usually Bioballs ®, nylon netting or bottle caps , where the nitrifying bacteria transform the dissolved wastes . With insufficient filtration , the DWC units would clog , become anoxic and exhibit poor growing conditions for plants and fish alike .
The flow rate of the water entering each canal is relatively low . Generally , every canal has 1 – 4 hours of retention time . Retention time is a similar concept to turnover rate , and refers to the amount of time it takes to replace all the water in a container . For example , if the water volume of one trough is 300 litres and the flow rate of water entering the container is 150 litres / h , the retention time would be 2 hours ( 300 litres ÷ 150 litres / h ).
AgriKultuur | AgriCulture
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