Getting high Dissolved Oxygen in RAS aquaculture

AirOxi specializes in aquaculture aeration in all types of culture - Hatcheries, nurseries, biofloc (BFT) aeration, RAS, Growout ponds and IPRS (Raceway system). Whether for shrimp or fish you can depend on the wide range of AirOxi products for your high intensity fish farming or economical aeration for shrimp farming.

A lot of progressive farmers are now using RAS for fish aquaculture in tanks. Such intensive systems needs high level of oxygen. There are 3 ways to get high dissolved oxygen in RAS

1. Use high amount of air at the bio filter and in each tank using AirOxi tube and double stage turbine blower.

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Key features of this system is

• Low initial cost and low running cost
• High air flow – almost 2500 LPM
• The system has high amount of air flow so it is easy to divide the output air into various outlets and aerate multiple tanks with one blower
• Moderate SOTR (Standard Oxygen Transfer Rate) - Sufficient to maintain a DO level of 4 to 7 ppm
• 1 HP of blower with 25 mtrs of AirOxi tube can support 8 -10 tons of fish biomass in RAS with proper water exchange
• This system gives almost 4-6% dissolution at 4-5 feet depth of water

This system is ideal where there are a lot of small tanks and a central bio filter. All tanks and bio filters can be given aeration from a single blower.

However some farmers may want to maintain higher DO than the standard 4- 6 ppm range. Or the stocking density maybe higher, or the species of fish used in RAS culture maybe such that it needs more dissolved oxygen.

Or there maybe constraints of how much power is available at the site.

For such cases there are two very effective aeration solutions available.

1. One effective solution to get good dissolved oxygen with lower power is the Micro Bubble Generator. This 1 HP system mixes very fine bubbles of air with water and distributes them evenly at the discharge.

Because the bubbles are so fine it gives a high SOTR and one unit can support almost 4 tons of Fish biomass. The flow rate is only 3 to 5 LPM but because the bubbles stay in the water much longer, the dissolution of oxygen is higher – almost 15% at a depth of 4-5 feet of water

The micro bubble generator is very quiet machine and can be used on top of the tank as in the picture. This system is ideal for a layout where there are large tanks and each tank has high fish biomass, so each tank can be given proper aeration individually

1. Often an RAS system needs very high dissolved oxygen and yet is divided into small tanks and each tank is not big enough to have its own micro bubble generator.

So for such applications RAS aeration requirements, we can have a central oxygen concentrator with very fine bubble diffusers.

The smallest bubbles in diffusers are possible through ceramic plates or double walled diffusers

These can be combined with an oxygen concentrator to ensure very fine bubbles of 93% or almost pure oxygen dissolve in the RAS aquaculture system and give high dissolved oxygen

Such a concentrator can be kept centrally and the piping can be taken to each tank individually. At the tanks, the double walled diffuser or the ceramic plate can be used to ensure very fine bubbles diffuse the oxygen.

Such a system gives almost 25% dissolution at 4-5 feet depth of water