The Recirculating Aquaculture System (RAS for short) is an industrial aquaculture model that enables the recycling of aquaculture water within the system through a series of water treatment technologies, including physical filtration, biological filtration, oxygenation, and disinfection. Its core principle is to simulate the material circulation process of the natural ecosystem. In a relatively closed environment, organic wastes such as uneaten feed and feces generated during the aquaculture process are converted into harmless substances, while the water quality is maintained stable, providing a suitable growth environment for aquatic products.

Physical Filtration Unit: This is the first line of defense in the RAS system, which is used to remove solid particles in the water, such as uneaten feed, feces, and so on. Mechanical filtration equipment is usually adopted, such as drum filter, microstrainers, sand filters, etc. Drum filter can filter out larger particulate impurities, with a filtration precision generally around several tens of micrometers, which can effectively prevent these impurities from damaging subsequent equipment and polluting the water quality.

Biological Filtration Unit: This is a crucial part of the system. It mainly uses microorganisms to decompose harmful substances in the water, such as ammonia nitrogen and nitrite. The biological filter is a common biological filtration device, and its interior is filled with biological filter media, such as ceramic rings, biochemical balls, etc. These filter media provide attachment and growth sites for beneficial microorganisms like nitrifying bacteria.

Oxygenation Unit: To ensure sufficient oxygen supply for aquatic products, the RAS system is equipped with oxygenation devices. Commonly used ones include microporous aerators and pure oxygen aeration devices. Microporous aerators can evenly disperse air into the water, increasing the dissolved oxygen content in the water; pure oxygen aeration devices can more efficiently raise the dissolved oxygen level in the water.

Disinfection Unit: It is used to kill pathogens such as harmful bacteria, viruses, and parasites in the water, ensuring a healthy aquaculture environment. Ultraviolet disinfection devices and ozone generators are commonly used disinfection equipment.

• Efficient Water Use: The RAS system recycles water, significantly reducing water consumption. It usually saves more than 90% of water compared to traditional aquaculture.
• Environmentally Friendly: Due to the strict treatment and recycling of water, the RAS system can effectively reduce wastewater discharge.
• High-density Cultivation: The RAS system can achieve high-density cultivation in a limited space, remarkably increasing the yield per unit area.
• Controllable Growth Environment: The RAS system can precisely control key water quality parameters such as water temperature, dissolved oxygen, and pH value.
• Reduced Disease Transmission Risk: Since the water is strictly filtered and disinfected, the RAS system can effectively reduce the risk of pathogen transmission.
• Space-saving: The RAS system usually uses indoor facilities and occupies a small area, which is especially suitable for areas with limited land resources.
• Economic Benefits: The RAS system can significantly improve aquaculture efficiency and product quality, thus bringing higher economic returns.

Urban Aquaculture: In urban environments, land resources are scarce and expensive. The advantage of the Recirculating Aquaculture System (RAS) in efficiently using space stands out. It can establish high-density aquaculture facilities in relatively small indoor spaces.

High-Value Aquatic Product Cultivation: For high-market-value aquatic products such as grouper, rainbow trout, and prawns, the RAS system can provide precise environmental control, meeting their strict requirements for water quality, temperature, light, and other growth conditions.

Seedling Breeding: Seedling breeding requires extremely high environmental stability. The RAS system can precisely control key factors such as water quality and temperature, providing a good growth environment for seedlings.

Aquatic Science Research and Teaching: In the fields of scientific research and teaching, the RAS system provides a controllable experimental and teaching environment. Researchers can easily set different aquaculture conditions to observe the growth and physiological changes of aquatic products.