The Recirculating Aquaculture Systems principle is based on the re-use of water. Recirculating Aquaculture Systems rely on different water treatment techniques to maintain an optimal water quality for the fish. The interest in recirculation farms is still growing and the filtration techniques are constantly evolving.
The urge for RAS started when the demand for intensive aquaculture increased. RAS makes it possible to produce large amounts of fish with a small footprint and a minimal amount of water. Currently the water use of recirculating systems can be as low as 0.3 m3 water / kg feed resulting in an hourly degree of recirculation of >99%.
To be able to maintain proper water quality a cascade of water treatment steps need to be installed in the farm. System set-ups can change per species, but the main treatment processes consist of mechanical filtration, biological filtration, CO2 removal, O2 addition, recirculating pumps and some form of disinfection. In addition to this it is important to be able to control at least the pH and temperature of the water. Fish can be grown faster and with a better food conversion ratio compared to extensive fish farming because of this high amount of control over the water parameters. Furthermore, farming in a closed system on-land results in increased bio-security and a higher flexibility in site selection.