Recirculating Aquaculture System (RAS)
The main goal of RAS is to maintain high water quality optimized for specific fish type to achieve excellent health and growth rates.
To maintain high water quality, the levels of certain substances must be controlled. These substances include Oxygen, Ammonia, Nitrite, Nitrates, carbon dioxide, hydrogen sulfide, salinity, waste solids.
Majority of these toxic substances are the product of decay from the solid wastes. This is the reason why solid waste must all be removed as much as possible. A good mechanical filter can remove these wastes.
After removing solid wastes, we use biofilter to process the ammonia and nitrites and convert it to nitrates which is far less toxic. Carbon dioxides are then removed by a degasser. Aeration adds oxygen to the system which is greatly needed by the fish and the biofilters.
The water is then sterilized to remove pathogens in the water. The sterilization process employs Ozone, and UV systems to destroy these bacteria. The water is now fully cleaned and recirculated back to the fish tank.
Main Components of RAS:
There are two types of Filters. Mechanical Filters and Biological Filters
There are two types of Mechanical Filters. Settleable solids filters and Suspended solids filter.
Suspended solids are tiny particles that do not easily settle by gravity and easily pass-through screen; these must be removed by special means. For this we use Suspended Solids Filter, which are protein Skimmer or Foam fractionator or foam filters or brush filters. These filters operate by attracting these tiny particles into the media or to the foam for easy removal.
Settleable solids are big particles that can be settled by gravity or trapped by a screen. For this we deploy Settleable Solids Filter, which are radial filter and drum filter. Radial filters operate using gravity to pull down solids for easy removal. Drum filters operate by screening out particles out of water.
These are media filters which culture beneficial bacteria process toxic substances in water. These bacteria need a lot of air to grow. These media are mostly plastic that lets the bacteria attach to it and grow. The more surface area the more bacteria that can attach to it the more ammonia that can be removed.
Fish and beneficial bacteria need lots of oxygen to grow. Substantial fish in water will start to deplete the available dissolved oxygen in water. Without dissolved oxygen in water fish starts to die. This is the reason oxygen must be continuously pumped into the water to keep the dissolved oxygen at a level optimum for beneficial bacteria and fish health and survival. Stocking density is directly influenced by capability of aeration systems.
This is a required component to ensure the pathogens or non-beneficial bacteria is controlled to an acceptable level. There are two types of sterilization processes. The Ozone method and the UV method. Ozone gas that is dissolved into the water is more potent than UV. Ozone is used where UV is insufficient enough to bring down pathogen bacterial count.