In the factory-based recirculating water aquaculture system, the purification efficiency of water quality directly determines the aquaculture density, disease prevention and control, and economic benefits.
In this sophisticated water circulation system, there is an "invisible guardian" that works silently all the time, and that is - the biological filler.
In the circulating water system, pollutants such as fish excrement and leftover feed will accumulate rapidly, leading to excessive ammonia nitrogen and nitrite, which threatens the survival of farmed organisms.
The function of biological fillers is to provide stable habitats for beneficial microorganisms such as nitrifying bacteria and denitrifying bacteria.
The core indicator of biological fillers is specific surface area
The specific surface area of biological fillers determines the attachment space for microorganisms. For instance, the specific surface area of traditional ceramic rings is approximately 200m²/m³, while that of the new type of biological gel can reach 20,000 m²/m³, which is equivalent to building a "skyscraper" for microorganisms. Microorganisms form biofilms on the surface of the packing material, converting pollutants into harmless substances by decomposing ammonia nitrogen and organic matter.
The two major camps of biological carriers: fixed beds vs. mobile beds
In the biological treatment unit of recirculating aquaculture, the installation methods of biological fillers are divided into two major categories: fixed beds and moving beds.
Fixed-bed biological carriers: The fillers are fixed on the support or the tank body, and the water flows through the gaps of the fillers. Microorganisms grow on the static surface. Common ones include ceramic ring brush fillers, etc.
The fixed-bed biological carrier has stable microbial attachment, and the biofilm is not easy to fall off, making it suitable for slow-growing nitrifying bacteria. However, the accumulation of suspended solids is prone to clogging, requiring regular backwashing. Moreover, it has weak shock resistance, and fluctuations in water quality may cause a large amount of biofilm to fall off.
2. Moving bed biological carrier: Utilizing a new type of suspended filler (polyethylene filler), the filler is suspended in water and flows freely through aeration or stirring, allowing microorganisms to grow in a dynamic environment.
The application of the new type of suspended packing is the technical core of this process. The packing is made of specially treated polypropylene material, which has a large specific surface area, and its surface is conducive to the growth of biofilms. Moreover, the ingenious structural design ensures that the packing does not clage or clog during use.
It is convenient to maintain and the packing can be replenished or replaced without halting production. It is suitable for high-density aquaculture or scenarios with large fluctuations in water quality.
How to choose?
High-density aquaculture/Marine aquaculture: Mobile beds are preferred as they have strong shock resistance and are suitable for complex water qualities.
Low-cost/low-density breeding: Fixed-bed fillers (such as ceramic rings) offer better cost performance.
What factors should be considered when selecting biological fillers?
Look at the specific surface area: A larger specific surface area means more microbial attachment sites, which can enhance the efficiency of water purification.
Look at the material: The material is directly related to the safety of the farmed organisms. It is necessary to choose safe, reliable and highly pure materials, and avoid fillers containing harmful substances such as heavy metals.
Look at the appearance and structure: A good shape design can provide more protected specific surface area, creating favorable conditions for the growth of biofilms.