RAS means Recirculated Aquaculture Systems
RAS technology is the safest technology for farming of fish. And now production costs are often equivalent to the cost of farming fish in open systems.
A RAS systems consists in general of a set of fish tank structures, connected to a water treatment system, where the water is cleaned before the water is returned back to the fish tanks. There will still be discharge water from the facility, but typically well less than 1% of the internal flow.
The internal water treatment system consists normally of a mechanical filtration where particles bigger than 40-60 micron is filtered from the production water. Then the water is treated through a serie of biofilters, where disolved organic products are removed by bacteria, futher ammnoia is converted into Nitrate, which only in very high concentrations are harmfull to the fish.
One of the key compenents in the RAS system, and in reality the most critical is the CO2 stripper.
Especially in seawater many systems have failed due to the application of a poor CO2 stripping devise, only suitable for freshwater.
Some UV treatment of the water will take place as well, but as the bacteria produced in the biofilters are critical for maintaining a healthy abcterial balance in the fish tanks, normally only a side flow will be UV treated.
Finally oxygenation of the water and use of supersaturated water is a key tool in RAS operation.
The key water chemisty parameters in a RAS system, will depend on fish specie and f Fresh or seawater, but should normally in general be in the folllowing range, for obtaining good growth performance:
Oxygen : 90% saturation
CO2 levels : below 15 mg/l
NH3(N) : below 0,02 mg/l
Dr. Bent Urup and Aqua-Partners ApS have been managing the design of more than 50 individual RAS systems, for the following species:
Tuna, Seriola, Sole, Turbot, Halibut, cod, Salmon, trout, Eel, pearch, barramundi.
The key to a success in RAS farming can only be based on a deep respect to the requirement of the individual specie in a farming situation, and solid knowledge and practical experience of fish husbandry.