Looking at the New Industry Opportunities Behind Closed Recirculating Aquaculture System
Immutability, permanency and stability are three comments that closed recirculating aquaculture system has received from its buyers, which shows Shandong Wolize Biotechnology Co., Ltd.' s strong determination and perseverance of pursuing the highest standard of quality. The product is manufactured in a first-rate production line so that its materials and craftsmanship enjoy more durable quality than our competitors.
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We have professional staff forming an efficient service team. After confirming the receipt, customers can enjoy worry-free services in a fast manner at WOLIZE. Our after-sales team regularly participate in the service training conducted by industry experts. The staff usually show great passion and enthusiasm about these activities and are good at applying theoretical knowledge to practice - serving customers. Thanks to them, the goal of being a responsive enterprise has been achieved.
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Recirculating Aquaculture Disinfection System
In recirculating aquaculture systems, the hazards of bacteria and viruses cannot be underestimated. Bacteria consume a large amount of dissolved oxygen in water, leading to oxygen deficiency in farmed organisms, slow growth, and even death. Pathogenic bacteria such as Flavobacterium columnare and Aeromonas hydrophila can cause diseases like gill rot and septicemia in farmed organisms, leading to large-scale mortality and significant economic losses for aquaculturists. Viral infections are characterized by fast transmission and difficulty in control, which can infect a large number of farmed individuals in a short time, disrupt their physiological functions, and severely impact aquaculture efficiency.
Ultraviolet (UV) and ozone are highly effective in killing bacteria and viruses. UV radiation penetrates the cell membrane of microorganisms through strong radiative light waves, reaches the nucleus, and breaks the DNA double helix structure, preventing bacteria from reproducing and leading to their death. It is particularly effective against suspended bacterial microorganisms in water. Ozone, with strong oxidizing properties, reacts rapidly with bacteria and viruses, destroying their organelles, DNA, and RNA, and altering cell permeability, leading to cell lysis and death. It can kill a variety of microorganisms, including bacterial vegetative cells, spores, viruses, and fungi. Due to its good diffusibility, ozone can disinfect the entire aquaculture water without dead angles.
UV Sterilization
1. Classification by Installation Method
UV sterilization lamps can be classified into two types based on installation method: pipe-mounted and channel-mounted:
1. Pipe-mounted UV sterilization lamps are usually installed inside the water delivery pipelines of recirculating aquaculture systems. Water flows directly through the pipe section with the sterilization lamp, ensuring full contact between water and UV light, thus efficiently sterilizing the flowing water. Their advantages include a compact structure that integrates well with the pipeline system, making them suitable for water sterilization in scenarios with relatively low flow rates.
2. Channel-mounted UV sterilization lamps are generally installed above or on the sides of open water channels with a certain width and depth, irradiating and sterilizing the water flowing through the channel. They can cover a large area of water, making them suitable for handling large flow rates and open water bodies, ensuring that a large area of water is effectively irradiated by UV light to guarantee sterilization performance.
2. Classification by Voltage Intensity
UV sterilization lamps are divided into two types based on voltage intensity: low-pressure and medium-pressure:
Low-pressure (LP) UV sterilization lamps operate at relatively low voltages and typically generate single-wavelength UV light, mostly around 254 nanometers. This wavelength has a significant germicidal effect, low energy consumption, and good stability. However, their power is relatively limited, making them suitable for small-scale applications or places where extremely high sterilization intensity is not required.
Medium-pressure (MP) UV sterilization lamps operate at higher voltages, generating multi-wavelength UV light with a wider coverage and stronger germicidal capability. They have higher power, allowing rapid treatment of large-flow and highly polluted water bodies. However, they consume more energy and have higher equipment costs, making them commonly used in large-scale recirculating aquaculture systems with high requirements for sterilization efficiency and treatment capacity.
3. Principles and Influencing Factors of UV SterilizationUV light is a type of electromagnetic radiation, divided into multiple wavelength bands. The primary band used for sterilization is the UVC band (200-280 nanometers), with around 254 nanometers being the most effective wavelength for germicidal purposes. When recirculating water carrying microorganisms such as bacteria flows through the irradiation area of a UV sterilization lamp, the energy of UV photons is absorbed by the genetic material (such as DNA or RNA) inside the microbial cells. The chemical bonds in these genetic materials break after absorbing sufficient UV energy—for example, hydrogen bonds in the DNA double helix structure are destroyed—thereby disrupting genetic information processes such as replication and transcription. This prevents microorganisms like bacteria from reproducing, leading to their death and thus sterilizing and purifying the recirculating water, ensuring water quality safety and creating a healthy growth environment for farmed organisms.
The main factors influencing the effectiveness of UV sterilization in recirculating aquaculture are as follows:
1.UV Dosage
UV dosage, determined by UV intensity and irradiation time, is critical for sterilization effectiveness. Insufficient dosage cannot break the DNA or RNA structure of microorganisms like bacteria and viruses, leading to ineffective sterilization. Only when the specific dosage required by the target microorganisms is achieved can a good sterilization rate be ensured.
2.Water Turbidity
Suspended solids and organic particles in water increase turbidity. These impurities scatter and absorb UV light, preventing it from penetrating the water and reducing the actual UV exposure of microorganisms, thus decreasing sterilization efficiency. The higher the turbidity, the more UV light is attenuated, and the poorer the sterilization capability.
1. Water Flow Rate
Too fast a water flow rate shortens the residence time of microorganisms in the UV irradiation area, preventing them from receiving sufficient UV dosage and leading to incomplete sterilization. Too slow a flow rate, while ensuring irradiation time, may affect the overall efficiency of the recirculating water system.
2. Microbial Species
Different microorganisms have varying tolerances to UV light. For example, bacterial spores, due to their special structure, are more resistant to UV irradiation than ordinary bacterial cells. Viruses, lacking a cellular structure, also differ in their UV sensitivity from bacteria. Therefore, the types of microorganisms present affect sterilization efficacy.
3. Lamp Aging Degree
As usage time increases, the luminous efficiency of UV lamps gradually decreases, reducing the output UV intensity and the effective sterilization dosage provided. This leads to a decline in sterilization performance compared to when the lamps were newly installed.
In recirculating aquaculture systems, the hazards of bacteria and viruses cannot be underestimated. Bacteria consume a large amount of dissolved oxygen in water, leading to oxygen deficiency in farmed organisms, slow growth, and even death. Pathogenic bacteria such as Flavobacterium columnare and Aeromonas hydrophila can cause diseases like gill rot and septicemia in farmed organisms, leading to large-scale mortality and significant economic losses for aquaculturists. Viral infections are characterized by fast transmission and difficulty in control, which can infect a large number of farmed individuals in a short time, disrupt their physiological functions, and severely impact aquaculture efficiency.
Ultraviolet (UV) and ozone are highly effective in killing bacteria and viruses. UV radiation penetrates the cell membrane of microorganisms through strong radiative light waves, reaches the nucleus, and breaks the DNA double helix structure, preventing bacteria from reproducing and leading to their death. It is particularly effective against suspended bacterial microorganisms in water. Ozone, with strong oxidizing properties, reacts rapidly with bacteria and viruses, destroying their organelles, DNA, and RNA, and altering cell permeability, leading to cell lysis and death. It can kill a variety of microorganisms, including bacterial vegetative cells, spores, viruses, and fungi. Due to its good diffusibility, ozone can disinfect the entire aquaculture water without dead angles.
UV Sterilization
1. Classification by Installation Method
UV sterilization lamps can be classified into two types based on installation method: pipe-mounted and channel-mounted:
1. Pipe-mounted UV sterilization lamps are usually installed inside the water delivery pipelines of recirculating aquaculture systems. Water flows directly through the pipe section with the sterilization lamp, ensuring full contact between water and UV light, thus efficiently sterilizing the flowing water. Their advantages include a compact structure that integrates well with the pipeline system, making them suitable for water sterilization in scenarios with relatively low flow rates.
2. Channel-mounted UV sterilization lamps are generally installed above or on the sides of open water channels with a certain width and depth, irradiating and sterilizing the water flowing through the channel. They can cover a large area of water, making them suitable for handling large flow rates and open water bodies, ensuring that a large area of water is effectively irradiated by UV light to guarantee sterilization performance.
2. Classification by Voltage Intensity
UV sterilization lamps are divided into two types based on voltage intensity: low-pressure and medium-pressure:
Low-pressure (LP) UV sterilization lamps operate at relatively low voltages and typically generate single-wavelength UV light, mostly around 254 nanometers. This wavelength has a significant germicidal effect, low energy consumption, and good stability. However, their power is relatively limited, making them suitable for small-scale applications or places where extremely high sterilization intensity is not required.
Medium-pressure (MP) UV sterilization lamps operate at higher voltages, generating multi-wavelength UV light with a wider coverage and stronger germicidal capability. They have higher power, allowing rapid treatment of large-flow and highly polluted water bodies. However, they consume more energy and have higher equipment costs, making them commonly used in large-scale recirculating aquaculture systems with high requirements for sterilization efficiency and treatment capacity.
3. Principles and Influencing Factors of UV SterilizationUV light is a type of electromagnetic radiation, divided into multiple wavelength bands. The primary band used for sterilization is the UVC band (200-280 nanometers), with around 254 nanometers being the most effective wavelength for germicidal purposes. When recirculating water carrying microorganisms such as bacteria flows through the irradiation area of a UV sterilization lamp, the energy of UV photons is absorbed by the genetic material (such as DNA or RNA) inside the microbial cells. The chemical bonds in these genetic materials break after absorbing sufficient UV energy—for example, hydrogen bonds in the DNA double helix structure are destroyed—thereby disrupting genetic information processes such as replication and transcription. This prevents microorganisms like bacteria from reproducing, leading to their death and thus sterilizing and purifying the recirculating water, ensuring water quality safety and creating a healthy growth environment for farmed organisms.
The main factors influencing the effectiveness of UV sterilization in recirculating aquaculture are as follows:
1.UV Dosage
UV dosage, determined by UV intensity and irradiation time, is critical for sterilization effectiveness. Insufficient dosage cannot break the DNA or RNA structure of microorganisms like bacteria and viruses, leading to ineffective sterilization. Only when the specific dosage required by the target microorganisms is achieved can a good sterilization rate be ensured.
2.Water Turbidity
Suspended solids and organic particles in water increase turbidity. These impurities scatter and absorb UV light, preventing it from penetrating the water and reducing the actual UV exposure of microorganisms, thus decreasing sterilization efficiency. The higher the turbidity, the more UV light is attenuated, and the poorer the sterilization capability.
1. Water Flow Rate
Too fast a water flow rate shortens the residence time of microorganisms in the UV irradiation area, preventing them from receiving sufficient UV dosage and leading to incomplete sterilization. Too slow a flow rate, while ensuring irradiation time, may affect the overall efficiency of the recirculating water system.
2. Microbial Species
Different microorganisms have varying tolerances to UV light. For example, bacterial spores, due to their special structure, are more resistant to UV irradiation than ordinary bacterial cells. Viruses, lacking a cellular structure, also differ in their UV sensitivity from bacteria. Therefore, the types of microorganisms present affect sterilization efficacy.
3. Lamp Aging Degree
As usage time increases, the luminous efficiency of UV lamps gradually decreases, reducing the output UV intensity and the effective sterilization dosage provided. This leads to a decline in sterilization performance compared to when the lamps were newly installed.
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%
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%
The recirculating aquaculture system is a new type of aquaculture model, which uses a series of water treatment
units to process the wastewater generated in the aquaculture pond and then recycle it. The main principle of
RAS is to integrate advanced technologies in environmental engineering, civil engineering, modern biology,
electronic information and other disciplines to remove residual bait feces, ammonia nitrogen (TAN), nitrite nitrogen
(NO2--N ) and other harmful pollutants. For the purpose of purifying the breeding environment, the process of re-entering the purified water into the breeding pond by using physical filtration, biological filtration, removal of CO2,
disinfection, oxygenation, temperature adjustment and other treatments. It can not only solve the problem of low
utilization rate of water resources, but also provide a stable, reliable, comfortable and high-quality living environment
for breeding organisms, and provide favorable conditions for high-density farming.
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