Microalgae circulating sedimentation concentration and harvesting device and harvesting method thereof
By designing a microalgae circulating sedimentation and concentration device, the continuous sedimentation and concentration of algal cells is achieved by using a power pump to control the influent flow rate, and resources are recovered through a circulation system. This solves the problems of low efficiency and resource waste in existing technologies, and realizes efficient and low-cost microalgae concentration.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI OCEAN UNIV
- Filing Date
- 2026-03-18
- Publication Date
- 2026-05-29
AI Technical Summary
Existing microalgae concentration devices cannot operate continuously, and frequent replacement of filter membranes leads to low efficiency and high cost. Traditional sedimentation methods have low sedimentation efficiency and serious resource waste.
Design a microalgae circulating sedimentation and concentration device. Use a power pump to control the influent flow rate so that the algal cell settling velocity is greater than the liquid surface rising velocity, forming continuous concentration. Unused algal cells and nutrients are recovered through a circulation system to achieve cyclic concentration.
It enables continuous concentration of microalgae, reduces production costs, improves operational efficiency, effectively utilizes resources, and reduces resource waste.
Smart Images
Figure CN122104390A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of microalgae cultivation and concentration technology, specifically relating to a microalgae circulating sedimentation concentration harvesting device and its harvesting method. Background Technology
[0002] Microalgae are a class of prokaryotic or eukaryotic single-celled or multicellular photoautotrophic organisms widely distributed in various aquatic environments in nature. Microalgae can not only efficiently convert carbon sources into proteins, carbohydrates, and lipids, but also synthesize a variety of high-value-added bioactive components, such as phycobiliproteins, bioactive peptides, polyunsaturated fatty acids, natural pigments, and bioactive polysaccharides. These are widely used in ecological restoration, biofuel production, functional food production, and the healthcare and beauty industries.
[0003] Although microalgae have high utilization value, the concentration and harvesting process is one of the major bottlenecks restricting the application and rapid development of the microalgae industry. Microalgae concentration and harvesting methods generally include sedimentation, flocculation, centrifugation, and filtration. Existing microalgae concentration devices are mostly optimized for filtration. For example, CN222250700U and CN216023385U disclose novel microalgae concentration devices. The former improves the working efficiency of the concentration tank by optimizing the device structure; the latter improves the microalgae collection rate through multi-layer filtration and can classify and filter microalgae according to the size of individual cells. However, both require the algae to be collected only after the algae solution has been concentrated or the equipment has been shut down, making continuous operation impossible and requiring frequent filter membrane replacements. This reduces concentration efficiency and increases costs. Furthermore, the microalgae culture solution discharged during concentration cannot be reused, and the residual microalgae in the culture solution are wasted, indirectly increasing concentration costs.
[0004] Sedimentation is the simplest and lowest-cost method for concentrating and harvesting microalgae. This method relies on gravity to allow algal cells to settle naturally, thus concentrating the microalgae. However, traditional natural sedimentation has the following drawbacks: the sedimentation process is relatively long, and most microalgae settle inefficiently; a large number of microalgal cells remain suspended in the supernatant, resulting in significant microalgae loss. Compared to other concentration methods, traditional sedimentation offers no advantage, and existing microalgae concentration devices are rarely optimized for traditional sedimentation. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a microalgae circulating sedimentation concentration harvesting device and its harvesting method, aiming to achieve continuous circulating sedimentation concentration of microalgae with high concentration efficiency and low operating costs.
[0006] To achieve the above objectives, the present invention provides the following technical solution: A microalgae circulating sedimentation concentration harvesting device includes a light-shielding circulating sedimentation concentration tank. A liquid outlet pipe is connected to one side wall at the top of the circulating sedimentation concentration tank, and a liquid inlet pipe is connected to one side wall at the upper middle part of the circulating sedimentation concentration tank. The liquid inlet pipe is located below the liquid outlet pipe on the circulating sedimentation concentration tank. The inlet pipe is externally connected to a power pump, which continuously pumps algal solution into the circulating sedimentation and concentration tank. The liquid level in the circulating sedimentation and concentration tank begins to rise continuously, and the algal cells in the algal solution begin to settle downwards due to gravity. The power pump controls the inlet flow rate. If the settling speed of the algal cells is greater than the rising speed of the algal solution level, the algal cells will settle downwards and accumulate, forming concentrated algal solution. This concentrated algal solution eventually ends up in the lower part of the circulating sedimentation and concentration tank. The algal solution continuously enters the circulating sedimentation and concentration tank through the inlet pipe, thus forming continuous concentration.
[0007] Preferably, when the liquid level rise rate in the circulating sedimentation and concentration tank is V, and the settling rate of different microalgae under dark conditions is V... i To achieve the goal of continuous sedimentation and concentration of microalgae, the following conditions must be met: V0<πR 2 V i ; Where: V0 represents the flow rate of algal solution entering the circulating sedimentation and concentration tank, and R represents the inner radius of the tank.
[0008] Preferably, the inlet of the power pump is connected to an external algal culture device via a pipe, and the other end of the outlet pipe is also connected to the external algal culture device. The power of the power pump controls the inlet flow rate. The algal culture enters the circulating sedimentation and concentration tank after passing through the external algal culture device, the power pump, and the inlet pipe, and is then concentrated. The culture medium that still contains some algal cells after concentration is discharged from the outlet pipe and returned to the external algal culture device. It is then drawn back by the power pump and enters the circulating sedimentation and concentration tank again after passing through the external algal culture device, the power pump, and the inlet pipe for concentration to achieve a cyclic operation.
[0009] Preferably, one end of the outlet pipe is connected to the inner top of the external algal culture device, and the bottom of the inlet pipe is connected to the inner bottom of the external algal culture device.
[0010] Preferably, a liquid turbine flow meter is installed on the algal liquid inlet pipe, and the liquid turbine flow meter is located at the output end of the power pump.
[0011] Preferably, the circulating sedimentation concentration tank includes a lid, a body, and a bottom from top to bottom; the lid is directly placed on the body to cover the inside of the body, the body is fixed to the bottom, and the inside of the body is connected to the inside of the bottom.
[0012] Preferably, the barrel body is an acrylic cylindrical tube, the outer wall of which is wrapped with a black PE wrapping film, and the black PE wrapping film leaves a long strip-shaped window on the acrylic cylindrical tube; and the long strip-shaped transparent window extends from the top of the barrel body down to the bottom of the barrel body.
[0013] Preferably, the bottom of the tank is inserted into the four corner supports so that the circulating sedimentation and concentration tank is suspended in the air.
[0014] Preferably, the lid is a disc with a radius larger than the diameter of the barrel body, which is placed directly on the barrel body, and a sealing ring is provided at the contact point between the lid and the barrel body to seal the barrel body.
[0015] Preferably, the lid is also provided with an air outlet to balance the air pressure inside and outside the bucket; the upper end of the air outlet is connected to a flexible connector, which has a microporous filter membrane to filter out particles and microorganisms in the air and prevent contamination.
[0016] Preferably, the pore size of the microporous filter membrane is 0.22 μm.
[0017] Preferably, a second right-angle elbow is installed at the end of the liquid inlet pipe located inside the tank body. The end of the second right-angle elbow faces downward along the inside of the tank body to guide the algal cells to move downward.
[0018] Preferably, the bottom of the bucket is a hollow inverted cone, and the top of the cone bottom is connected to the bucket body, and the interior of the cone bottom is connected to the interior of the bucket body. The bottom of the bucket bottom is connected to a first sampling tube, the bottom of the first sampling tube is connected to a first right-angle elbow, one end of the first right-angle elbow is horizontally connected to a second sampling tube, and one end of the second sampling tube is connected to a sampling valve. The concentrated algae solution is collected periodically by opening the sampling valve.
[0019] A method for collecting and concentrating microalgae through a circulating sedimentation process, using the aforementioned apparatus, includes the following steps: S1. Determine the settling velocity V of microalgae requiring precipitation and concentration under dark conditions. i ; S2. After the microalgae cultivation in the external microalgae cultivation device is completed, turn on the power pump to continuously pump the algae solution into the circulating sedimentation and concentration tank through the inlet pipe; observe the flow rate of the liquid turbine flow meter and adjust the power of the power pump to make the flow rate V0 < πR. 2 V i The algal solution enters the circulating sedimentation and concentration tank to begin sedimentation and concentration, and the remaining culture solution is returned to the external microalgae culture device. S3. The algal solution returned to the external microalgae culture device is then circulated, precipitated, and concentrated through steps S1 and S2. S4. Periodically open the sampling valve to collect concentrated algal solution.
[0020] Preferably, after completing step S4 and the algal solution is completely concentrated, the power pump 5 is turned off, and the circulating sedimentation and concentration tank 6 is emptied and cleaned.
[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. Because the algal cells in the circulating sedimentation concentration tank of this invention settle at a rate greater than the rate at which the algal liquid surface rises, the algal cells will settle downwards and accumulate, forming a concentrated algal liquid, while the inlet pipe is always in the inlet state; thus, the algal liquid can be continuously concentrated, thereby reducing production costs and improving operating efficiency.
[0022] 2. Because the circulating sedimentation and concentration tank and the external microalgae cultivation device form a circulation system through the inlet and outlet pipes in this invention, many algal cells and unused nutrients such as nitrogen and phosphorus remain in the culture solution discharged from the outlet pipe during the operation of the device. Directly discarding these would result in resource waste. Therefore, the solution is directly returned to the microalgae cultivation device, where the remaining algal cells can continue to be cultivated, the nutrients can continue to be utilized, and feeding operations can be performed to accelerate the growth of algal cells in the microalgae cultivation device. Subsequently, the algal cells re-enter the circulating sedimentation and concentration tank for the next round of sedimentation and concentration. This cycle continues until the algal solution is concentrated and harvested, thus achieving the purpose of circulation. Attached Figure Description
[0023] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the three-dimensional structure of the circulating sedimentation and concentration tank in this invention; Figure 3 This is a schematic cross-sectional view of the three-dimensional structure of the circulating sedimentation concentration tank in this invention; Figure 4 This is a graph showing the sedimentation velocity of Chlorella cells under light-free conditions in this invention. Figure 5 This is a growth curve of Chlorella proteoglycans under different inoculation densities in this invention; In the diagram: 1. Microalgae cultivation device; 2. Culture medium outlet pipe; 3. Algal liquid inlet pipe; 4. Liquid turbine flow meter; 5. Power pump; 6. Circulating sedimentation and concentration tank; 7. Union joint; 8. Air outlet; 9. Tank lid; 10. Tank body; 11. Support; 12. Tank bottom; 13. First sampling tube; 14. First right-angle elbow; 15. Second sampling tube; 16. Sampling valve; 17. First right-angle elbow; 18. Strip window; 19. Sealing ring. Detailed Implementation
[0024] To make the technical means, creative features, objectives and effects of this invention easier to understand, the following embodiments are described in detail with reference to the accompanying drawings. It should be noted that the description of these embodiments is for the purpose of helping to understand this invention, but does not constitute a limitation of this invention.
[0025] like Figure 1-5 As shown, a microalgae circulating sedimentation concentration harvesting device includes a light-shielding circulating sedimentation concentration tank 6 (its interior is in darkness). An outlet pipe 2 is connected to one side wall of the top of the circulating sedimentation concentration tank 6, and an inlet pipe 3 is connected to one side wall of the circulating sedimentation concentration tank 6, with the inlet pipe 3 located below the outlet pipe 2 on the circulating sedimentation concentration tank 6. A power pump 5 is connected to the outside of the inlet pipe 3, and the power pump continuously pumps algal solution into the circulating sedimentation concentration tank. The inlet end of the power pump 5 is connected to an external algal solution cultivation device 1 via a pipe, and the other end of the outlet pipe 2 is also connected to an external algal solution cultivation device 1. The liquid culture device 1 is connected, and the power pump 5 controls the inlet water flow rate. The algal solution continuously enters the circulating sedimentation and concentration tank 6 through the external algal solution culture device 1, the power pump 5, and the inlet pipe 3 for concentration. The liquid level in the circulating sedimentation and concentration tank 6 begins to rise continuously. Due to gravity, the algal cells in the algal solution begin to settle downwards in the circulating sedimentation and concentration tank 6. The power pump controls the inlet water flow rate. If the settling velocity of the algal cells is greater than the rising velocity of the algal solution (it should be noted that the settling velocity Vi of different microalgae under dark conditions is determined by the following method: the experimental device is a self-made plexiglass cylindrical tube; the outer wall of the plexiglass cylindrical tube is made of 5... A 1 mm thick black PE wrapping film is used to block light. The plexiglass cylindrical tube is filled with the algal solution whose settling velocity needs to be measured. During settling, the algal cells will separate from the supernatant. The distance between the separation point and the surface of the algal solution, i.e., the settling distance, is measured every 1 hour. The experiment is set up in triplicate. Finally, a standard curve is plotted with settling time (h) as the x-axis and settling distance (cm) as the y-axis. The slope of the standard curve is the settling velocity Vi (cm / h). (Details follow...) Figure 4 As shown, algal cells will settle downwards and accumulate to form concentrated algal solution. This concentrated algal solution is located at the bottom of the circulating sedimentation and concentration tank 6. The culture medium that is still partially containing algal cells after concentration is discharged from the outlet pipe 2 and returned to the external algal culture device 1. It is then pumped by the power pump 5 and enters the circulating sedimentation and concentration tank 6 through the external algal culture device 1, the power pump 5, and the inlet pipe 3 for concentration to achieve a circulating operation.
[0026] When the rate of liquid level rise in the circulating sedimentation and concentration tank 6 is V, the settling velocity of different microalgae under dark conditions is V. i To achieve the goal of forming concentrated algal solution, the following conditions must be met: V0<πR 2 V i ; Where: V0 represents the flow rate of the algal solution entering the circulating sedimentation and concentration tank, and R represents the inner radius of the tank; specifically: the liquid level rise velocity V in the circulating sedimentation and concentration tank 6 is: V = V0 / πR 2 By controlling the flow rate V0, and thus controlling the liquid surface rise rate to be less than the algal cell settling rate V1, i.e., V0 / πR 2 <V1, thus deriving V0<πR 2 V1 is sufficient to concentrate the algal solution; therefore, to concentrate different microalgae using this device, it is only necessary to measure the settling velocity V of different microalgae under dark conditions. i Control the flow velocity V0 < πR 2 V i This allows for the concentrated harvesting of different microalgae.
[0027] During the operation of the device, the algal liquid discharged from the outlet pipe 2 still contains many algal cells and unused nutrients such as nitrogen and phosphorus. Directly discarding it would result in a waste of resources. Therefore, it is directly returned to the external algal liquid culture device 1. The remaining algal cells can continue to be cultured, and the nutrients can continue to be used. It can also be used for feeding operations to accelerate the growth of algal cells in the external algal liquid culture device 1. Subsequently, the algal cells re-enter the circulating sedimentation and concentration tank 6 for the next round of sedimentation and concentration. This cycle continues until the algal liquid concentration and harvesting are completed.
[0028] One end of the liquid outlet pipe 2 is connected to the inner top of the external algae culture device 1, and the bottom of the liquid inlet pipe 3 is connected to the inner bottom of the external algae culture device 1. Specifically, the barrel 10 is a hollow cylindrical barrel with a radius of R, open at both ends, with a circular opening on the side of the top end connected to the liquid outlet pipe 2, and a circular opening on the upper side of the middle part connected to the liquid inlet pipe 3.
[0029] A liquid turbine flow meter 4 is installed on the algae liquid discharge pipe. The liquid turbine flow meter 4 is located at the output end of the power pump 5. The liquid turbine flow meter 4 is used to display the flow rate V0 of the algae liquid entering the circulating sedimentation and concentration tank 6. The flow rate can be controlled by adjusting the power pump 5 according to the flow rate displayed on the dial of the liquid turbine flow meter 4.
[0030] The circulating sedimentation concentration tank 6 includes a lid 9, a body 10, and a bottom 12 from top to bottom; the lid 27 is directly placed on the body 10 to cover the inside of the body 10, the body 10 is fixed to the bottom 12, and the inside of the body 10 is connected to the inside of the bottom 12; specifically, the bottom of the body 10 and the top of the bottom 12 are connected by heat fusion.
[0031] The barrel 10 is an organic glass cylindrical tube, and the outer wall of the organic glass cylindrical tube is wrapped with a black PE wrapping film. The black PE wrapping film leaves a long strip-shaped viewing window 18 on the organic glass cylindrical tube; and the long strip-shaped transparent viewing window extends from the top of the barrel to the bottom of the barrel; the algal cell precipitation inside the barrel 10 can be observed through the strip-shaped viewing window 18.
[0032] The bottom 12 of the barrel is inserted into the four corner brackets 11 so that the circulating sedimentation concentration barrel 6 is suspended in the air; the lid 9 is a disc with a radius larger than the diameter of the barrel body 10, which is directly placed on the barrel body 10. A sealing ring 19 is provided at the contact point between the lid 9 and the barrel body 10 to seal the barrel body 10.
[0033] The lid 9 is also provided with an air outlet 8 to balance the air pressure inside and outside the tank; the upper end of the air outlet 8 is connected to a union 7 (the union 7 is a UPVC union, the model of which can be selected according to the size of the circulating sedimentation concentration tank 6, and the union 7 used in this embodiment is of the brand Muqiao and the size is DN15). The union 7 has a microporous filter membrane (pore size is 0.22μm) to filter out particles and microorganisms in the air and prevent contamination.
[0034] A second right-angle elbow 17 is installed at the end of the liquid inlet pipe 3 located inside the tank 10. The end of the second right-angle elbow 17 faces downward along the inside of the tank 10 to guide the algal cells to move downward.
[0035] The bottom of the bucket 12 is a hollow inverted cone, and the top of the cone bottom 12 is connected to the bucket body 10. The interior of the cone bottom 12 is connected to the interior of the bucket body 10. The bottom of the bucket bottom 12 is connected to a first sampling tube 13. The bottom of the first sampling tube 13 is connected to a first right-angle elbow 14. One end of the first right-angle elbow 14 is horizontally connected to a second sampling tube 15. One end of the second sampling tube 15 is connected to a sampling valve 16. The concentrated algal solution is collected periodically by opening the sampling valve 16.
[0036] A method for collecting and concentrating microalgae through a circulating sedimentation process, using the aforementioned apparatus, includes the following steps: S1. Determine the settling velocity V of microalgae requiring precipitation and concentration under dark conditions. i ; S2. After the microalgae cultivation in the external microalgae cultivation device 1 is completed, turn on the power pump 5, observe the flow rate of the liquid turbine flow meter 4, and adjust the power of the power pump 5 to make the flow rate V0 < πR. 2 V i The algal solution enters the circulating sedimentation and concentration tank 6 to begin sedimentation and concentration, and the remaining culture solution is returned to the external microalgae culture device 1. S3. The algal solution returned to the external microalgae culture device 1 is then circulated, precipitated, and concentrated through steps S1 and S2. S4. Periodically open sampling valve 14 to collect concentrated algal solution.
[0037] After completing step S4 and the algal solution is fully concentrated, turn off the power pump 5, empty and clean the circulating sedimentation concentration tank 6.
[0038] In a specific implementation example, the microalgae in step 1 is *Chlorella pyrenoidosa*, whose settling velocity under dark conditions is 24 cm / h. Figure 4 ); In a specific implementation example, the microalgae cultivation device 1 in step S2 is a photobioreactor system with a total reaction volume of 1800L. The culture medium is shrimp pond aquaculture wastewater, containing total nitrogen of 10-11 mg / L, ammonia nitrogen of 2.0-3.0 mg / L, nitrite of 0.4-0.5 mg / L, and total phosphorus of 1.6-1.8 mg / L. The optimal inoculation density of Chlorella is determined to be 1×10⁻⁶. 7 cells / mL, the optimal harvest time is day 6 of culture ( Figure 5 The circulating sedimentation and concentration tank 6 has a volume of 200L and a radius of 0.2m. Therefore, the flow rate of the algal solution entering the sedimentation tank should be V0 < πR. 2 V i ≈30 L / h. To ensure concentration efficiency, the flow rate V0 is maintained at 25-28 L / h.
[0039] The above embodiments are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Various modifications or variations that can be made by those skilled in the art without creative effort within the scope of the appended claims are still within the scope of protection of this patent.
Claims
1. A microalgae circulating sedimentation concentration harvesting device, characterized in that: The system includes a light-shielding circulating sedimentation and concentration tank, with an outlet pipe connected to one side wall of the top of the tank and an inlet pipe connected to one side wall of the tank, with the inlet pipe located below the outlet pipe on the circulating sedimentation and concentration tank. The inlet pipe is externally connected to a power pump for continuously pumping algal solution into the circulating sedimentation and concentration tank. As the liquid level slowly rises in the tank, algal cells gradually settle due to gravity. The inlet flow rate is controlled by the power pump. When the settling velocity of the algal cells exceeds the rising velocity of the liquid level in the tank, the algal cells will accumulate at the bottom, forming concentrated algal solution, which can be collected from the sampling tube as needed. Algal solution with low cell density in the upper outlet pipe returns to the algal culture device. In this way, the algal solution continuously enters the circulating sedimentation and concentration tank through the inlet pipe and returns to the algal culture device through the upper outlet pipe, thus achieving continuous concentration.
2. The microalgae circulating sedimentation concentration harvesting device according to claim 1, characterized in that: When the rate of liquid level rise in the circulating sedimentation and concentration tank is V, the settling velocity of different microalgae under dark conditions is V. i To achieve continuous precipitation and concentration of this microalgae, the following conditions must be met: V0<πR 2 V i ; Where: V0 represents the flow rate of the algal solution entering the circulating sedimentation and concentration tank, and R represents the inner radius of the tank.
3. The microalgae circulating sedimentation concentration harvesting device according to claim 2, characterized in that: The inlet of the power pump is connected to an external algal culture device via a pipe, and the other end of the outlet pipe is also connected to the external algal culture device. The power of the power pump controls the inlet flow rate. The algal culture enters the circulating sedimentation and concentration tank after passing through the external algal culture device, the power pump, and the inlet pipe, and is then concentrated. The culture medium that still contains some algal cells after concentration is discharged from the outlet pipe and returned to the external algal culture device. It is then drawn back by the power pump and enters the circulating sedimentation and concentration tank again after passing through the external algal culture device, the power pump, and the inlet pipe for concentration to achieve a cyclic operation.
4. The microalgae circulating sedimentation concentration harvesting device according to claim 3, characterized in that: The circulating sedimentation concentration tank includes a lid, a body, and a bottom from top to bottom; the lid is placed directly on the body to cover the inside of the body, the body is fixed to the bottom, and the inside of the body is connected to the inside of the bottom.
5. The microalgae circulating sedimentation concentration harvesting device according to claim 4, characterized in that: The barrel is a cylindrical tube made of plexiglass. The outer wall of the cylindrical tube is wrapped with a black PE wrapping film. The black PE wrapping film leaves a long strip-shaped window on the cylindrical tube. The long strip-shaped transparent window extends from the top of the barrel down to the bottom of the barrel.
6. The microalgae circulating sedimentation concentration harvesting device according to claim 5, characterized in that: A second right-angle elbow is installed at the end of the liquid inlet pipe located inside the tank. The end of the second right-angle elbow faces downward along the inside of the tank to guide the algal cells to move downward.
7. The microalgae circulating sedimentation concentration harvesting device according to claim 6, characterized in that: The bottom of the bucket is a hollow inverted cone, and the top of the cone bottom is connected to the bucket body, and the interior of the cone bottom is connected to the interior of the bucket body. The bottom of the bucket bottom is connected to a first sampling tube, the bottom of the first sampling tube is connected to a first right-angle elbow, one end of the first right-angle elbow is horizontally connected to a second sampling tube, and one end of the second sampling tube is connected to a sampling valve. The concentrated algae solution is collected periodically by opening the sampling valve.
8. A method for collecting and concentrating microalgae through a circulating sedimentation process, performed by the apparatus described in any one of claims 1-7, characterized in that: Includes the following steps: S1. Determine the settling velocity V of microalgae requiring precipitation and concentration under dark conditions. i ; S2. After the microalgae cultivation in the external microalgae cultivation device is completed, turn on the power pump to continuously pump the algae solution into the circulating sedimentation and concentration tank through the inlet pipe; observe the flow rate of the liquid turbine flow meter and adjust the power of the power pump to make the flow rate V0 < πR. 2 V i The algal solution enters the circulating sedimentation and concentration tank to begin sedimentation and concentration, and the remaining culture solution is returned to the external microalgae culture device. S3. The algal solution returned to the external microalgae culture device is then circulated, precipitated, and concentrated through steps S1 and S2. S4. Periodically open the sampling valve to collect concentrated algal solution.