In-depth Demand Report | Disassembling Recirculating Fish Farming Systems

Recirculating Aquaculture System (RAS) Process Design Principles
Unlike traditional flow-through aquaculture, Recirculating Aquaculture System (RAS) achieves water reuse through advanced treatment technologies and equipment. All components must operate in a scientifically sequenced workflow to ensure efficacy. Key design principles include:
1. Sequential Treatment: Solids → Liquids → Gases
Failure to remove solid suspended particles first will compromise subsequent steps. For instance, biofilter media coated with particles hinder nitrifying bacteria from converting ammonia nitrogen, degrading water quality. Excess organic matter from particles may also overload biofilters.
Treatment Sequence:
1. Solid Particle Removal
2. Dissolved Contaminant Removal
3. CO₂ Stripping
4. Disinfection
5. Oxygenation & Temperature Control
2. Solid Waste Treatment by Particle Size
In the Recirculating Aquaculture System (RAS) system, solid particulate matter mainly comes from the feces of aquaculture organisms and feed that has not been consumed. The treatment of solid waste can adopt different treatment methods according to the particle size, from large to small.

Particle size of solid particles
Treatment Method
Equipment
Sedimentable particles larger than 100 microns (mainly residual feces)
Sedimentation
Vertical Flow Sedimentation Tank
Suspended solid particles between 30-100 microns
Filtration
Microscreen Filter
Suspended solid particles smaller than 30 microns
Foam Fractionation
Protein Skimmer

For larger particles with a particle size of over 100 microns (mainly fish manure and residual bait), these particles are sedimentable. To avoid increasing the load on subsequent processes after they break in the system, a precipitation process can be adopted. Vertical flow settler is a device that uses gravity separation to remove sedimentable particles. Through the vertical flow sedimentation process, 60% -70% of solid particles are removed.

After pre-treatment by a vertical flow settler, most of the sedimentable particles have been removed, and the remaining majority are for suspended solid particles between 30-100 microns. This part of the particles can be physically filtered through a microfilter.

After being filtered by a microfilter, the remaining particles are small suspended particles below 30 microns and some soluble organic matter. The particles in this part are mainly separated by foam through protein separator. Foam separation is a common method, which can remove micro suspended particles, soluble organic matter, and has certain functions of increasing oxygen and removing carbon dioxide.

3. Sequential Filtration Before Disinfection
3.1 Impact of Suspended Solids on UV Disinfection
Suspended particles in water can scatter and absorb ultraviolet radiation. This absorption and scattering effect can lead to the consumption of ultraviolet energy during propagation, further reducing the intensity and bactericidal effect of ultraviolet radiation. A study has found a correlation between suspended solids content and the survival of fecal coliforms in wastewater exposed to ultraviolet radiation. Bacteria with surface attached particles are protected by suspended particles, therefore, ultraviolet disinfection can only reduce the survival capacity by 3-4 log10 units.

Suspended particulate matter can limit the penetration depth of ultraviolet rays in water. In clear water, ultraviolet rays can penetrate the water relatively deeply and disinfect water at different depths. However, when there are suspended particles in the water, the penetration ability of ultraviolet rays will be hindered.

Taking a Recirculating Aquaculture System (RAS) pond as an example, in the absence of suspended particulate matter, ultraviolet radiation may be effective in disinfecting water bodies up to a depth of 0.5-1 meters. But if the concentration of suspended particles in the water is high, ultraviolet rays may only penetrate depths of 0.2-0.3 meters, making it difficult for deeper water bodies to be fully disinfected, forming disinfection blind spots. This can lead to the continued growth and reproduction of microorganisms in these insufficiently disinfected areas, affecting the water quality of the entire Recirculating Aquaculture System (RAS) system.

In the absence of suspended particulate matter interference, a certain level of ultraviolet radiation dose (such as 10-20mJ/cm ²) can effectively kill it. But if there are a large number of suspended particles in the water, the ultraviolet intensity may only be 50% -70% of the original. To achieve the same disinfection effect, it is necessary to extend the ultraviolet irradiation time or increase the power of the ultraviolet lamp. Otherwise, some microorganisms may not be completely killed, resulting in incomplete disinfection and increasing the risk of infection by aquaculture organisms.
3.2 Impact of Suspended Solids on Ozone Disinfection
Suspended particulate matter will adsorb ozone in water. Due to the large specific surface area of suspended particles, ozone molecules are easily attached to their surfaces. For example, suspended particles such as feed residues, fecal particles, and microbial aggregates have many active sites on their surfaces that can physically adsorb ozone. This makes it difficult for ozone to effectively come into contact with pathogens (such as bacteria, viruses, fungi, etc.) in water after binding with suspended particulate matter, thereby reducing disinfection efficiency. It's like the disinfection "bullet" (ozone) being intercepted by the "obstacle" (suspended particles) in the middle.

The organic components in suspended particulate matter compete with pathogens for ozone. Many suspended particles contain organic matter, such as incompletely digested proteins, sugars, etc. These organic compounds, like pathogens, can undergo oxidation reactions with ozone. When there are too many suspended particles in water, ozone will preferentially react with these organic substances, consuming a large amount of ozone and reducing the amount of ozone used for disinfecting pathogens. For example, in a Recirculating Aquaculture System (RAS) system containing high concentrations of suspended particulate matter, ozone may first devote most of its energy to oxidizing organic matter on the surface of the particles, while only a small amount of ozone can be used to kill harmful microorganisms in the water.
3.3 Benefits of Filtration Before Disinfection
After physical filtration (removal of suspended solids), biological filtration (removal of soluble harmful substances), and gas filtration (removal of carbon dioxide), the aquaculture water has become very clear. At this time, whether using ultraviolet disinfection or ozone disinfection, the effect will be very good.
4. Water Circulation Parameter Design
The core of Recirculating Aquaculture System (RAS) is the water cycle. So how to make water circulate? The circulation pump is the core, and its function is like the human heart. The biological filter is the highest point of the entire circulation system, where water flows into various aquaculture ponds through natural atmospheric pressure and then into the pump pool. The circulating pump then pumps water from the pump pool into the biofilter, thereby achieving water circulation.

The circulation pump is so important, so it must be designed with one main and one backup. When the main water pump malfunctions, the backup water pump can be started in a timely manner to prevent breeding accidents.
Circulation Rate Design
The circulation rate of Recirculating Aquaculture System (RAS) is very important. An appropriate circulation rate can ensure uniform water quality in the aquaculture pond. Through circulation, dissolved oxygen, nutrients, and temperature can be evenly distributed throughout the entire water body, avoiding local water quality deterioration. The most important thing is to promote the removal of suspended particulate matter through the circulation of water. The flow of circulating water can bring suspended particles to the filtration equipment for treatment. Adequate circulation rate can improve the removal efficiency of suspended particulate matter and prevent its excessive accumulation in aquaculture ponds. Therefore, the speed of circulation determines the level of suspended particulate matter.

The calculation of circulation rate first requires determining the feeding amount based on the maximum biological carrying capacity, and then calculating the amount of suspended particulate matter produced per hour based on the feeding amount. Then, based on the target value of TSS designed for pond circulating water and the processing capacity of each equipment, calculate the circulation rate.

In summary, the calculation of cycle rate is relatively complex. Based on empirical values, it can be simply used as a reference value to cycle every 1 hours. Taking the cultivation of sea bass in a 1000 cubic meter circulating water body as an example, the cycle frequency is set to a 2-hour cycle. Therefore, the hourly cycle rate is 1000/2=500 tons/hour.
Variable Flow Design
Circulating pump is the equipment with the highest energy consumption in circulating water aquaculture. If the circulation pump is kept in a high-speed circulation state, it will quickly remove waste from the aquaculture water from the aquaculture tank, but the energy consumption is too high. If the circulation pump is kept running at low speed, although the energy consumption is low, the removal rate of waste from the aquaculture tank in the aquaculture water is slow. By installing frequency converters and intelligent control terminals, the variable flow technology can automatically adjust the parameters of the circulating water cycle according to different breeding stages and water quality parameters based on algorithms, achieving variable flow circulation.
Reference Diagram

Reference Process ParametersMaximum number of cycles for the circulating water system24 cycles/day
Breeding density
Seawater (e.g., Grouper): ≥50 kg/m³
Freshwater (e.g., Bass): ≥50 kg/m³
Utilization rate of aquaculture water in the circulating water system
≥90%
Water exchange rate
≤10%
UV sterilization rate
≥99.9%

How to solve the problem of sewage filtration in fish ponds
One of the several issues that people in the aquaculture industry are more worried about during the breeding process is the sewage filtration of fish ponds. After all, breeding is related to water. The quality of the water body determines whether the breeding can be successful. Traditional fish ponds are In the natural environment, dirt can settle at the bottom of the pond and be naturally resolved, absorbed and transformed, but in artificial ponds it must be resolved through artificial means.

Outdoor galvanized sheet canvas fish pond
There are many methods and modes of fish pond filtration. For example, equipment filtration is a water circulation mode that uses a microfiltration machine to separate and precipitate fish excrement and bait residues, purify the water and put it back into use again. There is also biological filtration, which is common. There is an aquaponics system model, which uses vegetables floating on the water to absorb fish excrement as nutrients and make soilless vegetables. It not only grows vegetables but also purifies the water. It can also precipitate and filter out larger impurities. , and finally clean the water body through a microbial pool to the point where fish can be raised again. It is also a water-saving circulating aquaculture model, which is more ecological and environmentally friendly and has less impact on the environment.

Large canvas fish pond breeding base
The new aquaculture equipment galvanized sheet canvas fish pond is simple to install and build, has a long service life, the material is environmentally friendly and does not pollute the fish, and the requirements for the terrain are relatively flexible. Wolize Company believes that intensive management can carry out high-density aquaculture with higher benefits. , is now a popular choice for many people in the aquaculture industry. Galvanized sheet canvas fish pond farming has filtration and sewage problems. Many farmers also choose to adopt the filtration mode of aquaponics. The "double harvest of fish and vegetables" has higher environmental benefits.

Fish farming canvas pond
Filtration of Canvas Fish Ponds When installing fish ponds, many farmers will choose to make the bottom of the fish pond into the shape of a pot bottom and then equip it with a fish toilet. The advantage of the pot bottom shape is that dirt will gather on the fish toilet along the slope and then be discharged, so The working principle of the fish toilet is sedimentation. Is the fish toilet easy to use? The fish toilet collects feces very conveniently and quickly, and can be said to be easy to use. The installation location of the fish toilet can also be determined according to the planning of the breeding base and the direction of the pipeline, which is also relatively flexible.

Fish farming in canvas fish ponds can be done indoors or outdoors. The advantage of canvas fish pond farming is that it can control the water level and temperature, which cannot be achieved by traditional soil pond farming. How big is the canvas fish pond for aquaculture fish pond? This depends on the species of fish that the farmers choose to breed and the scale of farming. Larger fish use larger ponds. Of course, large-scale farms also have larger breeding ponds. Generally, fish species are selected with a diameter of more than six meters and a height of about 1.45 meters. The round galvanized sheet canvas pond can also be used for grass carp farming. The canvas fish pond is easy to feed and manage, and can clearly record the breeding data, which is conducive to improving the breeding experience.


Fish farming in canvas fish ponds is a modern and popular fish farming model. So how effective is it?
Under conventional culture in the canvas pond, according to the size of the fish species and the density of growth, generally one cubic water body can produce about 50 kg of adult fish. Of course, not every kind of fish can produce so much in the canvas pond. The selected fish species should be able to resist stress and low oxygen to resist high density. The gradual rise of canvas pond farming has enabled many people without ponds to find a good way to develop aquaculture, but there are still many risks in canvas fish pond farming that deserve our attention.
Let me briefly introduce, especially the last one, please keep in mind.
1. The stability of the water body in the canvas pool is low, and the frequency of water intake and drainage increases in the case of high-density farming, resulting in high stress on the water body and easy injury to the fish. It is recommended to choose fish bodies with strong vitality and emergency resistance. Water changes can be done slowly in and out at regular intervals.
2. The water body in the canvas pool itself has insufficient oxygen capacity, so it is recommended to install oxygen increasing equipment.
3. In order to save space, the water level of the canvas pool is increased and the density is doubled. The density is too high, which will affect the health of the fish. Adequate water level placement, appropriate density is recommended.

If you want to make a lot of money in aquaculture, you need to pay attention to these items in daily management:

1. Insist on patrolling the pond at least twice a day. The purpose is to check the feeding situation of the fish, the water quality of the pond, and the weather conditions of the day. The feedback from the pond patrol can be used as the basis for feeding and medication in the next few days.
2. Take a sample every 10-15 days, check the growth of the fish, check whether there are any abnormalities on the surface, gills, and internal organs of the fish, if there is any abnormality, find out the cause of the problem in time, and prescribe the right medicine, usually in the early stage of the disease , works best and costs less.
3. For qualified farms, it is necessary to insist on regular water quality testing, at least once every 10 days to test the water quality of all ponds. The testing content includes: PH value, ammonia nitrogen, nitrite, water hardness, pond algae phase, if it is shrimp. Crab, but also to detect Vibrio. If there is an abnormality in the index, the cause must be found out in time and corresponding treatment should be taken.
4. Make a feeding and medication plan every 10-15 days. The feeding plan is calculated based on the amount of sample in the pond, the cumulative amount of feed fed, and the conversion rate to calculate the approximate number of fish in the fish pond, and then arrange according to a certain feeding rate. The medication plan is arranged according to the feedback of daily proofing, and the disinfection is carried out every 2 months. The specific day can be flexibly grasped according to the actual situation.
5. Fish out sick fish and dead fish in time, and remove them frequently to prevent the dead fish from corrupting and polluting water quality.

In addition, in high-density farming operations, the incidence of fish diseases and insect pests is often high, and there are often a large amount of pesticide and other chemical residues in the harvested fish, which will deteriorate the water quality. In the future of aquaculture, natural farming will inevitably be carried out in a low-density farming environment, and the use and pollution of pesticides will be avoided as much as possible.