The supply of oxygen is one of the most vital processes in a RAS. Oxygen supply comes either as purchase of bulk liquid oxygen or an own supply of generated oxygen. In both cases, it is relatively costly. It therefore has to be provided to the fish in the most safe and cost-effective way.
There is normally distinguished between:
- Pressure oxygen vessels, often as oxygen cones (OC’s)
- Low head oxygenation (LHO’s)
- Deep shaft
The OC concept has been widely used in European RAS. OC’s have high capacity and are very responsive in oxygen regulation. Because of the very high dissolution of up to 800%, or even higher, one only needs to oxygenate on a partial water flow. This high capacity and responsiveness comes at a cost however, the high energy requirements for pumping under high a pressure and also the relatively high capital costs.
LHO’s are systems that operate under modest pressure mixing water and oxygen in various vessels where it is possible to achieve oxygen saturation rates of 180-200 % on the full flow.
Deep shaft can be used if one has the necessary ground depth, 7-10 meters, available. Deep shaft at > 7 m will be able to achieve saturation rates of up to 300%.
If ground criteria allow, IAA use deep shaft principles. If ground criteria do not allow deep shaft, we use LHO’s supplemented with pressure oxygen cones for peak loads.