A gravity type particle filter and a filtering method

Abstract

The application discloses a gravity type particle filter and a filtering method, and belongs to the field of water treatment. The gravity type particle filter comprises a pool body, a graded sand and gravel layer, a graded filter material layer, a supporting layer and a well shaft. The graded sand and gravel layer, the graded filter material layer and the supporting layer are sequentially arranged in the pool body from top to bottom. The lower part of the supporting layer is provided with a water passage. The inner bottom wall of the pool body is provided with the well shaft. The top end of the well shaft is located above the top end of the pool body. The well shaft is communicated with the water passage. The thickness of the graded filter material layer is 2-12 times of the thickness of the graded sand and gravel layer. The gravity type particle filter and the filtering method have the advantages that the dense physical interception of the 10-40 cm upper graded sand and gravel layer and the large-thickness biochemical purification design of the 80-120 cm lower porous graded filter material layer form a synergistic filtering structure with thin upper layer and thick lower layer. The deep filter material is prevented from being blocked. The dual water purification effects of solid suspended substance interception and soluble pollutant degradation are realized. Large-flux operation is realized.

Description

Technical Field

[0001] This invention belongs to the field of water treatment, and particularly relates to a gravity particulate filter and filtration method. Background Technology

[0002] To ensure the sustainable development of aquaculture, countries and regions are actively developing aquaculture models that can effectively control water quality, leading to the continuous development of recirculating aquaculture systems (RAS) technology. The main process of RAS is: culture pond → microfiltration unit → protein skimmer → biological treatment tank → degassing tower → ultraviolet / ozone disinfection → culture pond. The microfiltration unit is an indispensable piece of equipment in this process.

[0003] Microfilters primarily utilize screens with varying pore sizes to filter aquaculture water to different degrees, achieving solid-liquid separation. Their main function is to remove suspended solids such as feces and uneaten feed from the aquaculture water, considered the "first line of defense" for maintaining stable water quality in aquaculture systems. However, the actual flow rate of microfilters is usually lower than their design capacity, requiring an additional 30%-50% of the processing capacity. This necessitates selecting larger microfilter models, increasing construction and operating costs. Furthermore, microfilters suffer from problems such as nozzle clogging, difficult maintenance, and bearing deformation. Their unstable flow rate prevents significant changes in the process of industrialized recirculating aquaculture systems.

[0004] Therefore, in order to solve the problem of solid-liquid separation in the process of factory-scale recirculating aquaculture and to transform the process system of factory-scale recirculating aquaculture, there is an urgent need for a gravity particulate filter and filtration method that can achieve solid-liquid separation between the suspended solids in the aquaculture water and the aquaculture water, can meet the requirements of high-throughput operation, and also has a biochemical function. Summary of the Invention

[0005] The purpose of this invention is to provide a gravity-type particulate filter and filtration method to overcome at least one of the above-mentioned defects in the prior art.

[0006] To achieve this objective, the present invention adopts the following technical solution: The present invention provides a gravity particulate filter, comprising a pool body, a graded sand and gravel layer, a graded filter media layer, a support layer, and a well cylinder. The pool body is provided with the graded sand and gravel layer, the graded filter media layer, and the support layer in sequence from top to bottom. The lower part of the support layer has a water passage. The well cylinder is provided on the bottom wall of the pool body. The top of the well cylinder is located above the top of the pool body and is connected to the water passage. The thickness of the graded filter media layer is 2-12 times the thickness of the graded sand and gravel layer.

[0007] Preferably, the thickness of the graded sand and gravel layer is 10-40cm, and the thickness of the graded filter media layer is 80-120cm.

[0008] Preferably, the graded sand and gravel layer includes, from top to bottom, a first sand layer, a second sand layer, a third sand layer, and a crushed stone layer, with the sand particle size of the first sand layer, the second sand layer, and the third sand layer increasing sequentially, and the stone particle size of the crushed stone layer being larger than that of the sand particle size of the third sand layer.

[0009] Preferably, the graded filter media layer includes, from bottom to top, a drainage layer, a first filter layer, and a second filter layer. The drainage layer, the first filter layer, and the second filter layer are all filled with porous filter media, and the particle size of the porous filter media in the drainage layer, the first filter layer, and the second filter layer decreases sequentially.

[0010] Preferably, the porous filter media is calcium-based, with a porosity > 50% and a bulk density of 0.3-0.8 g / cm³. 3 Specific surface area > 15m² 2 / g.

[0011] Preferably, it also includes a level gauge, a controller, a circulating water pump, an outlet pipe, a backwash water pump, and a backwash water pipe. The level gauge and the circulating water pump are installed in the lower part of the well. The outlet end of the circulating water pump is connected to the outlet pipe, and the outlet end of the outlet pipe extends to the outside of the well. The inlet end of the backwash water pump is connected to the backwash water pipe, and the outlet end of the backwash water pipe extends into the well. The level gauge is electrically connected to the controller, and the controller is electrically connected to the circulating water pump and the backwash water pump.

[0012] Preferably, it also includes a blower and a backwash pipe, the outlet of the blower is connected to the backwash pipe, the outlet of the backwash pipe is located below the support layer, and the blower is electrically connected to the controller.

[0013] The present invention also provides a filtration method using the above-mentioned gravity particle filter, comprising the following steps: continuously feeding aquaculture water into the upper part of the pool, and under the action of gravity, the aquaculture water passes through a graded sand and gravel layer and a graded filter media layer in sequence, and then enters the well through the water passage and is discharged.

[0014] Preferably, when the liquid level inside the wellbore is detected to have dropped to a preset threshold, a backflushing operation is performed to restore the throughput of the gravity particulate filter.

[0015] Preferably, backwashing is water washing and / or air washing.

[0016] Preferably, the filtration rate of the gravity particulate filter is 6-15 m / h.

[0017] Preferably, the supply of aquaculture water to the upper part of the pool is intermittently stopped according to a preset cycle.

[0018] The beneficial effects of this invention are as follows: 1. Through the dense physical interception of the upper 10-40cm graded sand and gravel layer and the thick biochemical purification design of the lower 80-120cm porous graded filter media layer, a synergistic filtration structure with a thin upper layer and a thick lower layer is formed. This not only avoids clogging of the deep filter media, but also achieves the dual water purification effect of solid suspended solids interception and dissolved pollutant degradation, enabling high-throughput operation.

[0019] 2. During the backwashing process, the biofilm in the lower graded filter media layer will detach. Due to the obstruction of the upper dense graded sand and gravel layer, the detached biofilm cannot pass through the graded sand and gravel layer. Instead, it will follow the water flow into the well shaft and be discharged into the aquaculture pond through the circulating water pump, providing natural biological feed for aquatic products, promoting intestinal development of aquatic products, improving the immunity of aquatic products, and making the product color more natural and healthier.

[0020] 3. Through its unique shallow and dense upper structure and deep and loose lower structure, the air bladders are mainly formed below the graded sand and gravel layer. By intermittently stopping the supply of aquaculture water to the upper part of the pond at specific cycles, deaeration is achieved, reducing the consumption of alkalinity during the circulating aquaculture process and improving the water purification capacity of the purification system. No additional deaeration equipment is required.

[0021] 4. Due to the gradation and shallow characteristics of the sand and gravel layers, backwashing fluidization is easy to achieve and sewage discharge is efficient and thorough.

[0022] 5. Through the optimization of the gradation of the filter media layer, the air-water distribution is more uniform and the backwashing efficiency is significantly improved.

[0023] 6. The backwash air and water volume is reduced by more than 1 / 5 compared with traditional filter beds, significantly reducing operating energy consumption and costs.

[0024] 7. Gravity particle filters can be installed independently or integrated with the aquaculture system, depending on local conditions. The size of the gravity particle filter can be adjusted according to the actual scale and conditions of aquaculture.

[0025] 8. Calcium-based filter media is selected. With its high porosity, large specific surface area, alkalinity and light weight, it can quickly form a biofilm and efficiently degrade ammonia nitrogen and nitrite, stabilize the pH of the water body, keep the graded filter media layer loose and not prone to caking, and achieve mild fluidization cleaning with a small amount of air and water. Together with the upper sand and gravel layer, it can significantly reduce the air and water consumption of backwashing.

[0026] 9. Backwashing is precisely triggered by liquid level, avoiding the lag of manual judgment.

[0027] 10. Construct an air-water combined backwashing system, in which airflow and water flow work together to achieve efficient desorption and discharge of pollutants from the filter layer, resulting in more thorough cleaning, faster flux recovery, uniform air-water distribution, and lower energy consumption, greatly simplifying operation and maintenance. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the gravity particulate filter of the present invention.

[0029] Figure 2 This is a control block diagram of the present invention.

[0030] The labels in the attached diagram are as follows: 1-Pool body, 2-Graded sand and gravel layer, 3-Graded filter media layer, 4-Support layer, 5-Well shaft, 6-Water passage, 21-First sand layer, 22-Second sand layer, 23-Third sand layer, 24-Gravel layer, 31-Drainage layer, 32-First filter layer, 33-Second filter layer, 7-Level gauge, 8-Controller, 9-Circulating water pump, 10-Outlet pipe, 11-Backwash water pump, 12-Backwash water pipe, 13-Fan, 14-Backwash air pipe. Detailed Implementation

[0031] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0032] Contents not described in detail in this specification are prior art known to those skilled in the art. In the description of this invention, it should be understood that terms such as "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, terms such as "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0033] like Figures 1 to 2 As shown, the gravity particle filter provided in this embodiment includes a pool body 1, a graded sand and gravel layer 2, a graded filter media layer 3, a support layer 4, and a well shaft 5. The graded sand and gravel layer 2, the graded filter media layer 3, and the support layer 4 are arranged sequentially from top to bottom inside the pool body 1. The lower part of the support layer 4 has a water passage channel 6. The well shaft 5 is arranged on the bottom wall of the pool body 1. The top of the well shaft 5 is located above the top of the pool body 1. The well shaft 5 is connected to the water passage channel 6. The thickness of the graded filter media layer 3 is 2-12 times the thickness of the graded sand and gravel layer 2.

[0034] The graded sand and gravel layer 2 has a thickness of 10-40 cm, and the graded filter media layer 3 has a thickness of 80-120 cm. The graded sand and gravel layer 2 comprises, from top to bottom, a first sand layer 21, a second sand layer 22, a third sand layer 23, and a crushed stone layer 24. The particle size of the sand in the first sand layer 21, second sand layer 22, and third sand layer 23 increases sequentially, while the particle size of the gravel in the crushed stone layer 24 is larger than that of the sand in the third sand layer 23. The graded filter media layer 3 comprises, from bottom to top, a drainage layer 31, a first filter layer 32, and a second filter layer 33. All three layers are filled with porous filter media, and the particle size of the porous filter media decreases sequentially.

[0035] By employing a layering ratio of thinner top and thicker bottom, a highly efficient synergy between physical interception and biological purification is achieved. The upper 10-40cm graded sand and gravel layer 2, with its continuous gradation of finer particles at the top and coarser particles at the bottom, forms a dense interception layer. This effectively traps fish feces, uneaten feed, and other suspended solids, preventing them from entering the lower graded filter media layer 3 at the source. This protects the filter media structure in the core area of ​​biological purification and reduces the risk of clogging in the deeper filter media. The lower 80-120cm graded filter media layer 3 features a thick design, combined with the porous structure of the filter media, providing ample space for microbial biofilm formation. It also increases the air-water contact area, enhances contact reaction efficiency, and strengthens the biochemical degradation of dissolved pollutants such as ammonia nitrogen and nitrite, achieving dual water purification through physical interception and biological purification.

[0036] The graded design enables efficient and low-consumption backwashing, significantly reducing operating costs. The upper graded sand and gravel layer 2 adopts a continuous gradation of fine at the top and coarse at the bottom, with a thickness of only 10-40cm. During backwashing, only a small amount of air and water is needed to quickly fluidize the graded sand and gravel layer 2. The trapped solid suspended matter is loosened and detached with the fluidized sand and gravel, and is finally efficiently discharged by the backwash water flow. This avoids the high water and air consumption problems of traditional filter backwashing. Thus, through the gradation and shallow characteristics of the sand and gravel layer, backwashing fluidization is easily achieved and sewage discharge is efficient and thorough. The lower filter media layer adopts a coarse-to-fine gradation. The large-particle filter media in the drainage layer 31 can cut and disperse backwash bubbles, achieving uniform distribution of air and water within the graded filter media layer 3. This avoids excessive localized impact that could damage the filter media structure, and allows for the cleaning of both the graded sand and gravel layer 2 and the graded filter media layer 3, as well as overall flux recovery, with less air and water. Thus, through the optimized gradation of the graded filter media layer 3, the air and water distribution is more uniform, and the backwashing efficiency is significantly improved. The backwash air and water volume is reduced by more than 1 / 5 compared to traditional filters, significantly reducing operating energy consumption and costs.

[0037] Through an integrated structural design combining a thin, dense sand and gravel interception layer with a thick, porous filter media purification layer, a single gravity particulate filter can simultaneously achieve the dual functions of physical interception of suspended solids and biochemical degradation of pollutants. This eliminates the need for multiple additional sets of equipment, saving space in the aquaculture system, simplifying equipment operation and maintenance, and making it more suitable for practical aquaculture applications. The gravity particulate filter in this embodiment has a high filtration rate and high load capacity; a minimum of 10m³ filter is required for a 100m³ aquaculture pond. 2 Gravity particle filters can achieve high-flow circulation once per hour, enhancing pollutant metabolism, rapidly purifying aquaculture pond water quality, and maintaining a stable aquatic environment. Gravity particle filters can be installed independently or integrated with the aquaculture system, adapting to local conditions. The size of the gravity particle filter can be adjusted according to the actual scale and conditions of aquaculture.

[0038] The porous filter media is calcium-based, with a porosity > 50% and a bulk density of 0.3-0.8 g / cm³. 3 Because calcium-based filter media has a porosity > 50% and a specific surface area > 15m², 2 With a high specific surface area, it provides ample attachment sites for functional microorganisms such as ammonia-oxidizing bacteria. Combined with its rapid biofilm formation (initial biofilm formation time < 5 days), it can quickly form a dense and stable biofilm, accelerating the biochemical degradation of dissolved pollutants such as ammonia nitrogen and nitrite in aquaculture water, achieving highly efficient water purification. The calcium-based filter media is alkaline, simultaneously replenishing alkalinity to the recirculating aquaculture system during the biochemical purification process, effectively buffering pH fluctuations in the water and preventing acidification from affecting the survival of aquaculture organisms and microbial activity, thus maintaining the acid-base balance of the aquaculture system. With a bulk density of 0.3-0.8 g / cm³ and high porosity, the graded filter media layer 3 maintains a loose state over the long term, preventing flux reduction caused by caking. During backwashing, a small amount of air and water can achieve slight fluidization of the graded filter media layer 3, efficiently desorbing aging biofilm and tiny impurities, restoring the biochemical purification channels, and preventing disorder and loss of the porous filter media, thus extending the service life of the porous filter media. Combined with the fluidized discharge of the upper graded sand and gravel layer 2, it achieves a low consumption advantage of reducing backwash air and water volume by more than 1 / 5 compared to traditional filter beds. During the backwashing process, the biofilm in the lower graded filter media layer 3 will detach. Due to the obstruction of the upper dense graded sand and gravel layer 2, the detached biofilm cannot pass through the graded sand and gravel layer 2. Instead, it will follow the water flow into the well shaft 5 and be discharged into the aquaculture pond through the circulating water pump 9, providing natural biological feed for aquatic products, promoting intestinal development of aquatic products, improving the immunity of aquatic products, and making the product color more natural and healthier.

[0039] The system also includes a level gauge 7, a controller 8, a circulating water pump 9, an outlet pipe 10, a backwash water pump 11, and a backwash water pipe 12. The level gauge 7 and the circulating water pump 9 are installed in the lower part of the well shaft 5. The outlet end of the circulating water pump 9 is connected to the outlet pipe 10, and the outlet end of the outlet pipe 10 extends to the outside of the well shaft 5. The inlet end of the backwash water pump 11 is connected to the backwash water pipe 12, and the outlet end of the backwash water pipe 12 extends into the well shaft 5. The level gauge 7 is electrically connected to the controller 8, and the controller 8 is electrically connected to the circulating water pump 9 and the backwash water pump 11.

[0040] During normal operation, the circulating water pump 9 pumps the purified aquaculture water in the well 5 back to the aquaculture pond through the outlet pipe 10, achieving closed-loop water circulation. When the graded sand and gravel layer 2 is not blocked, the system's inflow and outflow remain dynamically balanced, and the liquid level in the well 5 remains stable within a preset range. No manual operation is required throughout the process, meeting the high-efficiency operation requirements of factory-style aquaculture. The level gauge 7 monitors the liquid level changes in the well 5 in real time, directly reflecting the degree of solid suspension interception and accumulation by the graded sand and gravel layer 2. As the interception increases, the water resistance of the graded sand and gravel layer 2 increases, the outflow decreases, and the liquid level in the well 5 drops synchronously. When the liquid level drops to a preset threshold, the controller 8 automatically triggers a backwash operation, eliminating the need for manual judgment and ensuring precise and controllable backwash timing. By implementing an electrical linkage design between the level gauge 7, controller 8, and two water pumps, a fully automated control closed loop is constructed, encompassing status monitoring, signal transmission, and command execution. This avoids the lag and errors inherent in manual operation, enables unmanned continuous operation of the filter, significantly reduces maintenance costs, and extends the service life of the graded sand and gravel layer 2 and the graded filter media layer 3 through timely backwashing, ensuring the long-term stable operation of the aquaculture system. The backwashing cycle can also be adjusted according to actual operating conditions.

[0041] It also includes a fan 13 and a backwash pipe 14. The air outlet of the fan 13 is connected to the backwash pipe 14. The air outlet of the backwash pipe 14 is located below the support layer 4. The fan 13 is electrically connected to the controller 8.

[0042] A combined water and air backwashing system is constructed using blower 13 and backwashing air pipe 14. The backwashing airflow is precisely applied to the filter layers (graded sand and gravel layer 2 and graded filter media layer 3) from inside the well shaft 5. The air bubbles agitate the pollutants (suspended solids, aging biofilm) in the graded sand and gravel layer 2 and graded filter media layer 3, making it easier to desorb pollutants. Combined with the upward water flow from backwashing water pipe 12, synergistic cleaning of air desorption and water discharge is achieved. Compared with water washing alone, the filter layer is cleaned more thoroughly, and the flux recovery speed is improved. The airflow can cut and disperse the air bubbles in the backwashing water flow, allowing air and water to be evenly distributed within the filter layer, avoiding cleaning dead zones caused by insufficient local flushing force, and reducing the risk of local compaction of the filter layer during backwashing, thus ensuring the stability of the filter layer structure. The turbulent effect of airflow reduces backwash water consumption and backwashing time. Combined with the lightweight and high porosity characteristics of the graded filter media layer 3, only a small amount of air and water is needed to achieve efficient cleaning of the graded sand and gravel layer 2 and the graded filter media layer 3. The total energy consumption (water and electricity consumption) of backwashing is further reduced compared to single water washing, maintaining the core advantage of reducing backwash air and water consumption by more than 1 / 5 compared to traditional filters. The blower 13 is electrically connected to the controller 8 and can be started and stopped synchronously with the backwash water pump 11 to achieve automated control of air and water combined backwashing. There is no need for manual operation of the air circuit, further simplifying the operation and maintenance process.

[0043] This invention also provides a filtration method using the aforementioned gravity-type particulate filter, comprising the following steps: continuously feeding aquaculture water into the upper part of the tank 1; under gravity, the aquaculture water sequentially passes through a graded sand and gravel layer 2 and a graded filter media layer 3, then enters the well cylinder 5 through the water passage 6, and is subsequently discharged. When the liquid level inside the well cylinder 5 is detected to have dropped to a preset threshold, a backwashing operation is performed to restore the throughput of the gravity-type particulate filter. The backwashing includes water washing and / or air washing. The filtration rate of the gravity-type particulate filter is 6-15 m / h, with a large adjustment range, allowing for adjustment according to actual aquaculture needs to meet high-throughput operation. In this embodiment, the gravity-type particulate filter is built into the aquaculture tank, where the water level is higher than the top of the gravity-type particulate filter but lower than the top of the well cylinder 5.

[0044] Normal filtration process: The aquaculture water is fed into the upper part of the tank 1 and flows from top to bottom through the graded sand and gravel layer 2 and the graded filter media layer 3 under the action of gravity. The graded sand and gravel layer 2, with its continuous gradation of finer particles at the top and coarser particles at the bottom, physically intercepts fish feces, uneaten feed, and other suspended solids. The graded filter media layer 3, relying on its high porosity and large specific surface area, enriches microorganisms such as ammonia-oxidizing bacteria to form a biofilm, which biochemically degrades dissolved pollutants such as ammonia nitrogen and nitrite. The filtered purified water is collected in the well 5 through the water passage 6 at the bottom of the support layer 4, and then pumped back to the aquaculture tank by the circulating water pump 9 through the outlet pipe 10, completing the closed-loop circulation of the water.

[0045] Backwashing Triggering and Execution: During normal operation, the inflow and outflow of water are dynamically balanced, and the liquid level in well 5 remains stable. As the amount of solid suspended matter intercepted by the graded sand and gravel layer 2 increases, the water resistance increases, the outflow decreases, and the liquid level in well 5 gradually drops. When the level gauge 7 detects that the liquid level has dropped to the preset threshold, the controller 8 automatically starts the backwash water pump 11 (water washing) and / or the blower 13 (air washing): the backwash water flow diffuses upward from the support layer 4, and the backwash airflow acts synchronously on the filter layer. The two work together to achieve fluidization of the graded sand and gravel layer 2 and slight fluidization of the graded filter media layer 3, efficiently desorbing and discharging solid suspended matter, quickly restoring the system throughput. The discharged solid suspended matter can be discharged by retrieval or other means.

[0046] Filtration rate adjustment and adaptation: During the filtration process, the filtration rate can be flexibly adjusted between 6-15m / h according to the actual needs such as the scale of aquaculture and the water pollution load. This ensures efficient and high-flow operation when the pollution is low, and can also improve the filtration and purification effect by reducing the filtration rate when the pollution is high.

[0047] Intermittent water inflow cessation: Following a preset cycle, the supply of aquaculture water to the upper part of the tank is intermittently stopped. Specifically: When the circulating water pump 9 pumps the purified aquaculture water from the well 5 back to the aquaculture tank through the outlet pipe 10, water from the aquaculture tank simultaneously enters the upper part of the tank 1, thus establishing a circulating water balance. By intermittently shutting off the circulating water pump 9 for a period of time, during which time the aquaculture water no longer flows into the tank 1, natural deaeration can be achieved.

[0048] The gravity particulate filter of this invention achieves degassing through its unique shallow and dense upper structure (graded sand and gravel layer 2) and deep and loose lower structure (lower graded filter media layer 3). Due to processes such as carbon dioxide produced by biofilm metabolism and air introduced by the circulating water pump 9, gases are carried into the tank 1, forming air pockets. This process leads to a reduction in the water flow area, decreased purification efficiency, and alkalinity loss due to carbon dioxide accumulation. The special upper and lower structure of the gravity particulate filter allows the air pockets to form primarily below the graded sand and gravel layer 2. By intermittently stopping the supply of aquaculture water to the upper part of the tank 1 at specific periods, the water pressure disappears after the water inflow stops, and the air pockets naturally float to the surface and are discharged, achieving degassing. This reduces alkalinity consumption during the circulating aquaculture process, improves the water purification capacity of the purification system, and eliminates the need for additional degassing equipment.

[0049] The gravity particle filter of this embodiment was applied to recirculating aquaculture, eliminating the need for the original microfilter and shortening the process flow. Practical verification has shown that the gravity particle filter performs exceptionally well in aquaculture. The influent was from the fishpond, and the effluent was from the gravity particle filter. Operating data is shown in Table 1 below.

[0050] Table 1. Operating Data of Gravity Particulate Filter Based on testing and analysis during actual aquaculture processes, gravity-type particulate filters can effectively purify water quality, significantly reducing ammonia nitrogen and nitrite levels in both influent and effluent. They achieve solid-liquid separation in the aquaculture water, with an average suspended solids concentration in backwash wastewater exceeding 500 mg / L. The average daily wastewater discharge is approximately 3-10%, and the discharged effluent can be used for agricultural irrigation, thus realizing the recycling of water resources. Here, SS refers to suspended solids.

[0051] This invention combines gravity-driven co-current filtration with both physical interception and biochemical degradation, efficiently removing suspended solids while simultaneously degrading harmful dissolved pollutants, resulting in purification effects far exceeding those of single filtration methods. A wide filtration rate adjustment range of 6-15 m / h adapts to the throughput requirements of various aquaculture scenarios, meeting the core demands of high-throughput operation in factory-scale recirculating aquaculture systems. Precise liquid level-triggered backwashing avoids the lag of manual judgment. The optional combined backwashing mode of water and air washing, combined with the lightweight and high-porosity characteristics of the thin-graded sand and gravel layer 2 and the graded filter media layer 3, requires only a small amount of air and water to achieve thorough cleaning, significantly reducing backwashing energy and water consumption. The backwashing process is automated, requiring no manual intervention. The filtration process requires no complex manual control, only periodic replenishment of a small amount of surface sand and gravel. Intelligent closed-loop control enables unmanned continuous operation, reducing maintenance workload and human error. The graded design and reasonable gradation of the graded filter media layer 3 prevents caking and loss of porous filter media, extending the service life of the graded filter media layer 3 and ensuring long-term stable operation of the aquaculture system. The method is simple and can be flexibly adapted to existing aquaculture systems (set up separately or in combination). It does not require additional water quality conditioning or bacterial cultivation equipment, which saves space and reduces construction and operating costs. It is especially suitable for the high efficiency, energy saving and stability requirements of factory-style recirculating aquaculture.

[0052] The control method of the present invention is automatic control through controller 8. The control circuit of controller 8 can be implemented by simple programming by those skilled in the art. The power supply is also common knowledge in the art. Furthermore, the present invention is mainly used to protect mechanical devices, so the control method and circuit connection will not be explained in detail.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gravity-type particulate filter, characterized in that: It includes the pool body, graded sand and gravel layer, graded filter media layer, support layer, and well shaft; The interior of the pool is provided with a graded sand and gravel layer, a graded filter media layer, and a support layer from top to bottom; The lower part of the support layer has a water passage; The bottom wall of the pool is provided with a well cylinder, and the top of the well cylinder is located above the top of the pool body; The well shaft is connected to the water passage; The thickness of the graded filter media layer is 2-12 times the thickness of the graded sand and gravel layer.

2. The gravity particulate filter according to claim 1, characterized in that: The thickness of the graded sand and gravel layer is 10-40cm, and the thickness of the graded filter media layer is 80-120cm.

3. The gravity particulate filter according to claim 1, characterized in that: The graded sand and gravel layer includes, from top to bottom, a first sand layer, a second sand layer, a third sand layer, and a crushed stone layer; The particle size of the sand in the first, second, and third sand layers increases sequentially. The gravel particle size of the crushed stone layer is larger than that of the sand particle size of the third sand layer.

4. The gravity particulate filter according to claim 1, characterized in that: The graded filter media layer includes, from bottom to top, a drainage layer, a first filter layer, and a second filter layer; The drainage layer, the first filter layer, and the second filter layer are all filled with porous filter media; The particle size of the porous filter media in the drainage layer, the first filter layer, and the second filter layer decreases sequentially.

5. The gravity particulate filter according to claim 4, characterized in that: The porous filter media is calcium-based, with a porosity > 50% and a bulk density of 0.3-0.8 g / cm³. 3 Specific surface area > 15m² 2 / g.

6. The gravity particulate filter according to claim 1, characterized in that: It also includes a level gauge, controller, circulating water pump, outlet pipe, backwash water pump, and backwash water pipe; A level gauge and a circulating water pump are installed in the lower part of the wellbore. The outlet end of the circulating water pump is connected to an outlet pipe, and the outlet end of the outlet pipe extends to the outside of the well shaft. The inlet of the backwash water pump is connected to a backwash water pipe, and the outlet of the backwash water pipe extends into the well shaft. The level gauge is electrically connected to the controller, and the controller is electrically connected to the circulating water pump and the backwash water pump.

7. The gravity particulate filter according to claim 6, characterized in that: It also includes the blower and backflushing air pipe; The air outlet of the fan is connected to a backwash pipe, and the air outlet of the backwash pipe is located below the support layer. The fan is electrically connected to the controller.

8. A filtration method, characterized in that, Filtration using the gravity particle filter according to any one of claims 1-7 includes the following steps: The aquaculture water is continuously fed into the upper part of the pool. Under the action of gravity, the aquaculture water passes through the graded sand and gravel layer and the graded filter media layer in sequence, and then enters the well through the water passage and is discharged.

9. The filtration method according to claim 8, characterized in that: When the liquid level inside the wellbore is detected to have dropped to a preset threshold, a backflushing operation is performed to restore the flow rate of the gravity particulate filter.

10. The filtration method according to claim 8, characterized in that: According to the preset cycle, the supply of aquaculture water to the upper part of the pool is intermittently stopped.

Images