How Does The RAS System Work?

The Recirculating Aquaculture System (RAS) is often regarded as an advanced fish - farming system. It enables you to conduct high - density cultivation of various fish, shrimp, and shellfish indoors. This system can reduce the demand for fresh, clean water and maintain a healthy environment for aquatic organisms. This is because it purifies water through mechanical and biological filtration, reducing waste in the water. Water continuously circulates within the RAS system, and only a minimal amount of fresh water is needed to replenish losses. But do you know exactly how all this is achieved?

Today, we will discuss the specific working principles of the RAS system from aspects such as its composition, operation process, and usage advantages.

 

The RAS system is composed of a series of water - treatment units, including the following components:
• Growth tanks
• Mechanical filters (used to remove solid waste, such as feces)
• Biological filters (utilize bacteria to convert toxic ammonia into nitrate)
• Oxygenation systems (add dissolved oxygen)
• Water circulation pumps
These components work in concert within an almost closed - loop water - circulation system to maintain a healthy fish - farming environment. Due to the influence of factors such as seasons and temperature, we also add a heating system, ultraviolet sterilization, and pH control mechanisms to the system.

It mainly conducts cyclic treatment of the aquaculture water body through physical, biological filtration, and chemical methods. Its working process can be summarized as the following steps:

1. Physical Filtration: Wastewater from the aquaculture tank passes through a mechanical filter (such as a drum filter) to remove large - particle suspended matter like feces and uneaten bait (with a diameter > 30 microns).

2. Biological Filtration: The physically - treated water enters the bioreactor, where nitrifying bacteria convert toxic ammonia nitrogen (NH₃) into nitrite (NO₂⁻), and ultimately into less - toxic nitrate (NO₃⁻). Generally, a well - designed biofilter can achieve an ammonia - nitrogen conversion efficiency of over 95%.

3. Sterilization and Disinfection: At this point, the RAS system uses ultraviolet light (UV) or ozone (O₃) to sterilize the water body and kill pathogenic microorganisms.

4. Water Circulation, Temperature Adjustment, and Oxygenation: The treated water is adjusted by a heating/cooling device to reach the temperature most suitable for fish growth (salmon requires 8 - 14℃). In addition, pure oxygen needs to be injected into the water body to increase the dissolved oxygen (DO) to 8 - 12 mg/L, and finally, it is returned to the aquaculture tank.

 

The RAS can be used to farm almost any type of fish, whether they are freshwater fish, marine fish, or other aquatic animals. This mainly includes:
• Baramundi/ Asian Seabass/Bhetki
• Silver/Indian Pompano
• Tilapia
• Pearl spot/Karimeen
• Pangasius
• Rainbow Trout (especially in hilly/cold - water regions)
Among them, hybrid striped bass, channel catfish, and tilapia are the most common freshwater fish species in these intensive farming systems.

 

1. Water Conservation
In the traditional farming model, 15 - 20 tons of water are consumed to produce 1 kilogram of fish. However, the RAS system only requires 0.1 - 0.3 tons. This is because it needs very little water and continuously filters and reuses water within the system.

2. Environment - friendly
Through a closed - loop cycle, the RAS can avoid the eutrophication problem of lakes caused by the discharge of aquaculture wastewater. Otherwise, the toxins secreted by algae in the lake water will increase, leading to the death of aquatic animals. Moreover, indicators such as the water body's pH and hardness may also become abnormal.

3. Production Controllability
Combined with an automated feeding system, the RAS monitors water quality parameters (such as pH, dissolved oxygen, temperature) in real - time through a sensor network. This enables us to effectively reduce the feed conversion ratio (FCR) and increase the growth rate of fish.

Now we know how the RAS system works in water treatment. This mainly includes processes such as mechanical filtration, biological filtration, disinfection, water circulation, and oxygenation. According to the prediction of the Food and Agriculture Organization of the United Nations, by 2030, RAS will contribute 15% of the global aquaculture production and reduce the consumption of freshwater resources by approximately 12 billion cubic meters. If you want to know more, please feel free to contact AquaSust to obtain your exclusive aquaculture wastewater treatment solution.