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Sizing an aeration system for
aquaculture
Aeration homepage |
| Quick guide for aeration in tanks and raceways |
Below a temperature of 20 deg C, 2 x 3m diffuser and an air flowrate of
20 cubm/hr will provide all of the oxygen required by 1000 kg of
salmonids, assuming the average weight of the fish is above 50g. If
the water temperatures are above 20 deg C then additional aeration may be
required.
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| Quick guide for fish transportation |
For fish transportation best results are achieved using both air and oxygen in the same tank. The air diffuser should be similar in
length to the length of the tank. Example, tank length 1.5m, diffuser length 1.3m. A diffuser of this length is sized to pass 4 cubic metres of
air per hour. However this would be too much air for the tank. It is recommended that the air flowrate should be 1/2 to a 1/4 of the diffusers
designed flow rate.
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Efficiency & sizing of system |
The efficiency of an aeration system is related to a number of key environmental parameters. If you wish
Dryden Aquaculture to determine your farms aeration requirements some basic information is required of your facility, please answer as many of the questions
given below;
- Provide a schematic plan of your farms showing tank spacing
- Dimensions of tanks
- Water depth
- Species of fish/crustacean
- Water flowrate through the tanks
- Type of enclosure, e.g. earth pond/concrete/fibreglass
- Maximum stocking density
- Maximum size of the fish
- Maximum water temperature
- Details on water quality
- Soft or hard freshwater, or sea-water
- Source of water e.g., spring/borehole/river/lake
- Detailed water analysis of water if available
- Salinity of the water
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| Number of air diffusers |
As a rule of thumb guide 2 of our 10cu.m/hr diffusers for every 1000kg
of fish/shrimps if the water temperatures are less than 20 degrees
centigrade. At temperatures between 20 and 30 degrees centigrade the number of diffusers is increase to between 3 and 4 diffusers
of the same size. The number of diffusers calculated on this basis will provide 100% of the oxygen requirements of the stock. If the water flowrate is
turned off the diffusers will be able to maintain the dissolved oxygen levels at approximately 70% saturation. If you half the number of diffusers, the
oxygen levels will be maintained at 50% to 60% saturation.
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| Air Flowrate |
Determine the number of diffusers (x ) and multiply the number of diffusers by 9 to calculate the total air flowrate.
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| Air ring main |
An air ring main is installed around the fish farm, this air ring main can be fabricated from metal or plastic pipe. Dryden Aqua can supply the
pipework, or you may obtain it from a local supplier. The size of the air ring main is based on the length of the air ring main and the amount of air
required for the system. The table below gives a guideline for sizing the main pipe work.
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Air Flowrate
Size of pipe
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cubm/hr
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50 to 100
63mm
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100 to 200
90mm
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200 to 600
125mm
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600 to 1000
150mm
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| Sub-Air ring main |
The main air ring main should be of the size given in the above table. If there are ponds or tanks inside this air ring main, then the ring man
should be cross linked with smaller diameter pipework. The number of diffusers should be counted, air flowrate determined, and then the size of the pipe
is based on the air flowrate according to the above table.
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| Air hose connections |
Hose 1/2" PVC braided hose is connected to the air ring main, the other end of the hose is connected to the air diffuser. The maximum permissible
length of hose can be up to 10m, any longer than this length and you should increase the size of hose to 3/4".
A saddle clamp is fitted around the air ring main, or sub air ring main, the saddle has a 1/2" female threaded connection into which is screwed a
hose tail. The hose is push fitted onto this tail and secured with a screw clip. A hose tail is fitted to the diffuser as standard, the hose is push
fitted onto this tail and secured with a screw clip. The diffuser is then placed into the fish tank, or thrown into the pond. The diffuser has its own
internal ballast therefore no additional weight or ballast will be required.
Once you have calculated the number of diffusers, air hose requirements and size of air ring main; please advise Dryden Aqua and we will provide you
with a quotation for the equipment. As an indication the cost is usually in the order of £20 per diffuser for all of the fittings.
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| Air Blower |
Once you know the number of diffusers and the air flow requirements of the system, the air blower(s) can be sized. If the air flowrate is above 50
cubm/hr then a roots type air blower should be employed. The sizing of the air blower is also based on the back-pressure. If the water depth is not more
than 2 metres then the running pressure for the blower will be approximately 0.5 bar. In order to give a degree of margin the air blower should be sized
with the pressure relief valves set at 0.8 bar.
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