In-situ water quality purification device and method for a recirculating aquaculture system

Abstract

The application discloses the technical field of water treatment of aquaculture, and relates to an in-situ water purification device and method for a recirculating aquaculture system, which comprises a membrane aeration biofilm reactor unit arranged on a main circulating pipeline, and a membrane aeration biofilm assembly arranged in the membrane aeration biofilm reactor unit. The application uses the natural antibiotic residues caused by conventional disease prevention and treatment operations in the recirculating aquaculture system as a selective stress factor, does not need to add any chemical agent or antibiotic from outside, maintains the antibiotic residue concentration in a sub-therapeutic concentration window through an antibiotic stress regulation module, selectively inhibits the transition middle layer nitrite oxidizing bacteria, does not need to additionally add an antibiotic adding device during the operation of the device, avoids secondary pollution and additional operation cost caused by the introduction of the chemical agent, meets the development needs of green recirculating aquaculture, and reduces the operation complexity and maintenance difficulty of the system.

Description

Technical Field

[0001] This invention relates to the field of aquaculture water treatment technology, specifically to an in-situ water purification device and method for a recirculating aquaculture system. Background Technology

[0002] Recirculating aquaculture systems (RAS) have become the core model of modern aquaculture due to their high water utilization rate, high stocking density, and strong production controllability. However, with the increase in stocking density, RAS faces two irreconcilable technical contradictions, which are also long-standing pain points in the industry: First, RAS has an extremely low carbon-to-nitrogen ratio, making it difficult for conventional biological denitrification to efficiently remove nitrates, and the accumulated toxicity seriously threatens the safety of farmed organisms.

[0003] On the one hand, the influent to RAS (Respiratory Aquaculture System) is aquaculture wastewater, with pollutants mainly consisting of ammonia nitrogen and urea produced by fish metabolism, and the content of readily available organic carbon sources is generally low. The carbon-to-nitrogen ratio (C / N) of typical RAS aquaculture wastewater is only 0.5:1-3:1, far below the theoretical threshold of C / N ≥ 5:1 required for heterotrophic denitrification. Currently, RAS commonly uses moving bed biofilm reactors or rotating biological discs for aerobic nitrification, converting highly toxic ammonia nitrogen into less toxic nitrates. However, due to the scarcity of carbon sources for denitrification, nitrates cannot be effectively removed. In addition, RAS typically has a water recycling rate of over 90%, leading to the continuous accumulation of nitrates in the system. When the nitrate nitrogen concentration in the water exceeds 15 mg / L, Litopenaeus vannamei exhibits growth inhibition and abnormal molting; when it exceeds 25 mg / L, carnivorous fish such as turbot and grouper experience decreased immunity, gill tissue damage, and increased mortality. Most existing RAS systems can only control nitrate concentrations by changing 10%-20% of the water daily, which not only wastes water resources but also easily introduces foreign pathogens.

[0004] On the other hand, high-density regenerated aquaculture systems (RAS) have a higher incidence of diseases such as bacterial septicemia, enteritis, and gill rot. Farmers commonly use antibiotic-mixed feed or regular medicated baths for disease control. Antibiotics that are not metabolized by farmed organisms or adsorbed by uneaten feed enter the recirculating water, forming stable residues of 1-10 μg / L. Studies have confirmed that nitrite-oxidizing bacteria (NOB) are significantly more sensitive to tetracyclines and sulfonamides than ammonia-oxidizing bacteria (AOB) and denitrifying bacteria; low concentrations of antibiotics can specifically inhibit NOB activity, while AOB and denitrifying bacteria can maintain high activity. However, existing technologies define these antibiotic residues as "recalcitrant new pollutants" and have developed processes such as ozone oxidation, activated carbon adsorption, and membrane filtration to remove them. These methods not only increase energy consumption but also ignore their potential biological regulatory value.

[0005] However, existing MABR (membrane biofilm reactor) aquaculture water treatment solutions do not take into account the inherent antibiotic residue characteristics of RAS, and cannot achieve the spontaneous maintenance of short-cut nitrification and denitrification. They still require external carbon sources or complex regulation, which also increases the operating cost and complexity of aquaculture water treatment. Summary of the Invention

[0006] The purpose of this invention is to provide an in-situ water purification device and method for a recirculating aquaculture system, in order to solve the problems mentioned above, such as the inability to achieve spontaneous maintenance of short-cut nitrification and denitrification, the need for external carbon sources or complex regulation, and the increased operating costs and complexity of aquaculture water treatment.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides an in-situ water purification device for a recirculating aquaculture system, applied to the recirculating aquaculture system. The recirculating aquaculture system has a built-in ammonia nitrogen concentration probe, a nitrite nitrogen concentration probe, a nitrate nitrogen concentration probe, and a dissolved oxygen concentration probe. The inlet and outlet of the recirculating aquaculture system are connected to a main circulation pipeline. A rotary drum microfilter and an ultraviolet sterilizer are connected to the main circulation pipeline. The device includes: A membrane aeration biofilm reactor unit is installed on the main circulation pipeline. The membrane aeration biofilm reactor unit is equipped with a membrane aeration biofilm component inside. The surface of the membrane aeration biofilm component forms a layered biofilm distributed radially from the inside to the outside. The layered biofilm includes an aerobic inner layer, a transition middle layer, and an anoxic outer layer. The aerobic inner layer is enriched with ammonia-oxidizing bacteria, and the anoxic outer layer is enriched with denitrifying bacteria. An antibiotic stress regulation module includes an antibiotic residue monitoring unit, a stress intensity judgment unit, and a feedback regulation unit. The antibiotic residue monitoring unit is installed on a membrane aeration biofilm reactor unit and is used to monitor the antibiotic residue concentration in the circulating water in real time and output monitoring data. The stress intensity judgment unit has a preset sub-therapeutic concentration window threshold. The stress intensity judgment unit receives the monitoring data and compares the antibiotic residue concentration with the sub-therapeutic concentration window threshold to obtain stress intensity result data. The feedback regulation unit is communicatively connected to the water exchange valve of the recirculating aquaculture system and to the farmer's terminal, and is used to output a water exchange ratio adjustment signal or a medication prompt signal based on the stress intensity result data. An online monitoring and control module is installed on the main circulation pipeline. The online monitoring and control module is electrically connected to the ammonia nitrogen concentration probe, nitrite nitrogen concentration probe, nitrate nitrogen concentration probe and dissolved oxygen concentration probe. The online monitoring and control module is electrically connected to the membrane aeration biofilm reactor unit. The online monitoring and control module is communicatively connected to the circulating water valve of the recirculating aquaculture system. The online monitoring and control module is used to adjust the circulating water volume of the recirculating aquaculture system and the aeration volume of the membrane aeration biofilm reactor unit. The antibiotic stress regulation module maintains the residual antibiotic concentration in the circulating water within the sub-therapeutic concentration window threshold through a feedback regulation unit, thereby selectively inhibiting the activity of nitrite-oxidizing bacteria in the transition layer.

[0008] As a further embodiment of the present invention: the membrane aeration biofilm reactor unit includes a horizontal cylindrical tank, the bottom end of which is connected to an air compressor, the air compressor being electrically connected to an online monitoring and control module, the top end of which is provided with an exhaust port, the inlet end of which is connected to an inlet pipe, the outlet end of which is connected to an outlet pipe, the inlet pipe being connected to a rotary drum microfilter, the outlet pipe being connected to an ultraviolet sterilizer and an outlet return pipe, the return end of which is connected to the horizontal cylindrical tank, and both the inlet and outlet pipes being connected to an antibiotic residue monitoring unit; The horizontal cylindrical tank is vertically fixed with a membrane aeration biofilm assembly. The membrane aeration biofilm assembly is a hollow fiber membrane. The hollow fiber membrane adopts closed-end aeration to form a dissolved oxygen gradient that decreases from the inside to the outside within the hollow fiber membrane, forming an aerobic inner layer, a transitional middle layer, and an anoxic outer layer that are distributed radially from the inside to the outside.

[0009] As a further aspect of the present invention: the hollow fiber membrane is made of polyvinylidene fluoride or polydimethylsiloxane, and the membrane pore size of the hollow fiber membrane is 0.05μm-0.4μm.

[0010] As a further aspect of the present invention: the filling density of the membrane aeration biofilm module is 150m³. 2 / m 3 -300m 2 / m 3 The internal air pressure of the hollow fiber membrane is 10 kPa-100 kPa.

[0011] As a further aspect of the present invention: the antibiotic residue monitoring unit is an online antibiotic sensor based on the principle of enzyme-linked immunosorbent assay (ELISA), and the detection limit of the online antibiotic sensor is 0.1 μg / L.

[0012] As a further aspect of the present invention: the concentration threshold of the sub-therapeutic concentration window is 1 μg / L-10 μg / L.

[0013] Secondly, the present invention provides an in-situ water purification method for a recirculating aquaculture system, the method comprising the following steps: S1: Using activated sludge containing nitrifying and denitrifying bacteria as seed sludge and aquaculture wastewater as substrate, a layered biofilm is formed on the surface of the membrane aeration biofilm component until the ammonia nitrogen removal rate is greater than 90% and the nitrite nitrogen accumulation ratio is greater than 0.6. S2: The antibiotic stress regulation module maintains a sub-therapeutic concentration of antibiotics in the influent, so that the activity of nitrite oxidizing bacteria in the transition middle layer is selectively inhibited to a first preset value, while the activity of ammonia oxidizing bacteria in the aerobic inner layer is retained to a second preset value and the activity of denitrifying bacteria in the anoxic outer layer is retained to a third preset value. S3: Circulating water enters the membrane aeration biofilm reactor unit. Ammonia nitrogen is oxidized to nitrite nitrogen by ammonia-oxidizing bacteria in the aerobic inner layer. The nitrite nitrogen diffuses to the transition middle layer and the anoxic outer layer and is reduced to nitrogen gas by denitrifying bacteria. The treated effluent is disinfected by the ultraviolet sterilizer and then returned to the recirculating aquaculture system. S4: The online monitoring and control module dynamically adjusts the feedback control parameters of aeration pressure and antibiotic stress intensity in the membrane aeration biofilm component based on the ammonia nitrogen concentration, nitrite nitrogen concentration and nitrate nitrogen concentration in the circulating water, so as to maintain the short-cut nitrification and denitrification pathway stably.

[0014] As a further aspect of the present invention: in S1, the seed sludge is the return sludge from the aerobic tank of a municipal wastewater treatment plant, and the thickness of the layered biofilm is 300μm-400μm.

[0015] As a further aspect of the present invention: In S2, the concentration of the antibiotic is increased from 0.5 μg / L to the target concentration weekly, with an induction period of 2 to 8 weeks. The antibiotic is one or more of sulfonamides, tetracyclines, macrolides, and quinolones. The total antibiotic concentration in the circulating water is maintained at 1 μg / L to 10 μg / L, and the carbon-to-nitrogen ratio of the aquaculture wastewater is 0.5:1 to 3:1.

[0016] As a further aspect of the present invention: In S3, the hydraulic retention time of the membrane aeration biofilm reactor unit is 24h, the water temperature of the membrane aeration biofilm reactor unit is 20℃-30℃, and the reflux ratio of the circulating water is 95%.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes naturally occurring antibiotic residues in recirculating aquaculture systems, which are generated during routine disease control operations, as selective stress factors. Without the need for any external chemical agents or antibiotics, the antibiotic residue concentration is maintained within a sub-therapeutic concentration window through an antibiotic stress regulation module, thereby achieving selective inhibition of nitrite-oxidizing bacteria in the transitional middle layer. This eliminates the need for additional antibiotic dosing equipment during system operation, avoiding secondary pollution and additional operating costs caused by the introduction of chemical agents. It aligns with the development needs of green recirculating aquaculture and reduces the operational complexity and maintenance difficulty of the system.

[0018] 2. This invention achieves in-situ embedding of the denitrification unit by setting the membrane aeration biofilm reactor unit on the main circulation pipeline between the rotary drum microfilter and the ultraviolet sterilizer. This eliminates the need for an external large reactor or external effluent treatment facility, does not increase the additional floor space, and offers flexible installation options. It can be directly adapted to the upgrade and renovation needs of existing recirculating aquaculture systems, effectively solving the problems of large floor space and inability to be compactly integrated into the main circulation channel in traditional post-denitrification processes.

[0019] 3. This invention, through the synergistic cooperation of the antibiotic stress regulation module, the online monitoring and control module, and the membrane aeration biofilm reactor unit, preserves the activity of ammonia-oxidizing bacteria in the aerobic inner layer and the activity of denitrifying bacteria in the anoxic outer layer within the sub-therapeutic concentration window. At the same time, it selectively inhibits the NOB activity in the transition middle layer, achieving stable maintenance of the short-cut nitrification and denitrification pathway. Under the typical low C / N ratio conditions of recirculating aquaculture systems, it can efficiently remove total inorganic nitrogen without the need for external organic carbon sources, solving the common industry problem of denitrification carbon source scarcity and continuous nitrate accumulation caused by the low C / N ratio in traditional RAS systems.

[0020] 4. This invention uses an antibiotic residue monitoring unit to detect antibiotic concentrations in inlet and outlet pipes in real time. Combined with the sub-therapeutic concentration window threshold comparison of the stress intensity judgment unit and the linkage control of the water exchange valve and the farmer's terminal of the feedback control unit, it realizes intelligent closed-loop control of antibiotic stress intensity. It does not require changing the farmers' existing disease prevention and control habits. Only an antibiotic concentration monitoring link needs to be added. The "residual pollutants" that originally required cost removal can be transformed into denitrification control resources, which is highly accepted by farmers.

[0021] 5. This invention utilizes a hollow fiber membrane closed-end aeration method in its membrane aeration biofilm module. Oxygen diffuses from the inner cavity of the membrane to the outer liquid phase without bubbles, achieving an oxygen utilization rate of nearly 100%, significantly reducing aeration energy consumption compared to traditional aeration methods. Simultaneously, the online monitoring and control module dynamically adjusts the aeration rate and circulating water volume based on the concentrations of ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and dissolved oxygen, achieving precise oxygen supply and energy-saving operation. This significantly reduces the operating energy consumption and overall cost of water purification, enhancing the system's economic applicability and market promotion value. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the device connection structure of the present invention; Figure 2 This is a schematic diagram of the functional partitioning of the biomembrane in this invention; Figure 3 This is a diagram illustrating the operating performance of the device of the present invention, wherein, Figure 3 a is a schematic diagram of nitrate nitrogen concentration; Figure 3 b is a schematic diagram of ammonia nitrogen concentration; Figure 3 c is a schematic diagram of soluble COD concentration; Figure 3 d is a schematic diagram of antibiotic concentration in RAS.

[0023] In the diagram: 1. Recirculating aquaculture system; 2. Rotary drum microfilter; 3. Horizontal cylindrical tank; 4. Membrane aeration biofilm module; 41. Hollow fiber membrane; 5. Antibiotic stress control module; 6. Effluent return pipe; 7. Ultraviolet sterilizer; 8. Air compressor; 9. Main circulation pipeline; 10. Online monitoring and control module. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example: Please see Figure 1 This embodiment provides a specific structure of an in-situ water purification device for a recirculating aquaculture system and its application in freshwater RAS tilapia farming. The in-situ water purification device for a recirculating aquaculture system (RAS) is applied to a recirculating aquaculture system (RAS). The recirculating aquaculture system 1 is equipped with ammonia nitrogen concentration probe, nitrite nitrogen concentration probe, nitrate nitrogen concentration probe and dissolved oxygen concentration probe. The inlet and outlet of the recirculating aquaculture system 1 are connected to the main circulation pipeline 9. The main circulation pipeline 9 is connected to a rotary drum microfilter 2 and an ultraviolet sterilizer 7.

[0026] Among them, the recirculating aquaculture system 1 is a circular concrete-cast aquaculture pond with a diameter of 3.2m and an effective water depth of 1.2m, with a stocking density of 30kg / m³. 3 -50kg / m 3 Enrofloxacin and tetracycline are routinely mixed into the feed (0.5% of the feed weight, once a week) to prevent bacterial enteritis. Antibiotic residues naturally exist in the circulating water, with a stable concentration of 1μg / L-10μg / L, eliminating the need for additional antibiotics. The inlet is located on the upper part of the pool wall, and the outlet is located on the lower part. The rotary drum microfilter 2 uses an automatic backwashing rotary drum microfilter with a 60mm pore size and a processing capacity of 5m³. 3 Installed after the RAS (Recirculating Aquaculture System) outlet, it can intercept more than 90% of insoluble solids such as uneaten feed and feces in the aquaculture wastewater, reducing the suspended solids concentration in the effluent to below 10 mg / L, thus preventing the accumulation of insoluble solids or even pipe blockage in the horizontal cylindrical tank. A tubular UV sterilizer is selected, with a 30W UV lamp and an irradiation dose ≥30 mJ / cm². 2It can kill more than 99% of pathogens in the effluent, preventing the aquaculture water flowing back to RAS from carrying pathogens.

[0027] The device includes a membrane aeration biofilm reactor unit, an antibiotic stress regulation module 5, and an online monitoring and control module 10. The membrane aeration biofilm reactor unit is installed on the main circulation pipeline 9. Inside the unit is a membrane aeration biofilm module 4. The surface of the module 4 forms a layered biofilm distributed radially from the inside out. This layered biofilm includes an aerobic inner layer, a transitional middle layer, and an anoxic outer layer (e.g., an aerobic inner layer, a transitional middle layer, and an anoxic outer layer). Figure 2 As shown in the figure, the aerobic inner layer is enriched with ammonia-oxidizing bacteria, while the anaerobic outer layer is enriched with denitrifying bacteria. The membrane aeration biofilm reactor unit includes a horizontal cylindrical tank 3. This horizontal cylindrical tank (the core unit of the MABR treatment) 3 is a horizontal, sealed tank made of PE material, with a diameter of 1m and a length of 2m, and an effective volume of 1.5m³. 3 A 0.6m × 0.2m transparent acrylic observation window is provided on the side of the tank for observing the operating status of the internal membrane module; a sludge discharge port is provided at the bottom of the tank; the working pressure is atmospheric pressure; the bottom of the horizontal cylindrical tank 3 is connected to an air compressor 8, which is electrically connected to an online monitoring and control module 10; an exhaust port is provided at the top of the horizontal cylindrical tank 3; the water inlet end of the horizontal cylindrical tank 3 is connected to an inlet pipe; the water outlet end of the horizontal cylindrical tank 3 is connected to an outlet pipe; the water inlet pipe is connected to a rotary drum microfilter 2; and the water outlet pipe is connected to an ultraviolet sterilizer 7 and an outlet pipe. The return pipe 6 connects to the horizontal cylindrical tank 3 at its return end. Both the inlet and outlet pipes are connected to antibiotic residue monitoring units. The return pipe 6 uses a DN50 (nominal diameter 50 mm) UPVC (unplasticized polyvinyl chloride) pipe with a flow rate controlled at 0.2 m / s, guiding the MABR-treated water to the UV sterilizer 7, corresponding to a hydraulic retention time (HRT) of 24 h. The air compressor 8 is a silent oil-free air compressor with a rated pressure of 0.1 MPa and an air supply of 0.5 m³ / s. 3 / h, connected to the bottom air inlet of membrane aeration biofilm module 4 through DN25 (nominal diameter 25 mm) PU (polyurethane) pipe, to provide a stable oxygen source for membrane module, with an oxygen utilization rate of over 95%; The interior of the horizontal cylindrical tank 3 is vertically fixed with a membrane aeration biofilm component 4. The membrane aeration biofilm component 4 is a hollow fiber membrane 41. The hollow fiber membrane 41 adopts closed-end aeration to form a dissolved oxygen gradient that decreases from the inside to the outside within the hollow fiber membrane 41, forming an aerobic inner layer, a transition middle layer and an anoxic outer layer that are distributed radially from the inside to the outside. The membrane aeration biofilm module 4 uses a polyvinylidene fluoride (PVDF) hollow fiber membrane with a pore size of 0.22 μm, a single membrane filament diameter of 2.2 mm, and a length of 0.8 m. Each module contains approximately 5000 membrane filaments, and the effective area of ​​a single module is approximately 27.6 m². 2 Located 10 cm from the bottom of the tank, a closed-end aeration system is used, maintaining the internal pressure at 17 kPa ± 1 kPa. Oxygen diffuses bubble-free from the inner cavity of the membrane through the membrane wall to the liquid phase on the outer side, forming a dissolved oxygen gradient on the membrane surface that decreases from the inside to the outside: dissolved oxygen in the inner layer is 1.5 mg / L-2.5 mg / L, in the intermediate layer it is 0.3 mg / L-0.8 mg / L, and in the outermost layer it is less than 0.2 mg / L, providing a basis for the formation of a stratified biofilm. The packing density of the membrane aeration biofilm module is 150 m³ / s. 2 / m 3 -300m 2 / m 3 The antibiotic stress regulation module 5 includes an antibiotic residue monitoring unit, a stress intensity judgment unit, and a feedback regulation unit. The antibiotic residue monitoring unit is installed on the membrane aeration biofilm reactor unit and is used to monitor the antibiotic residue concentration in the circulating water in real time and output monitoring data. The stress intensity judgment unit has a preset sub-therapeutic concentration window threshold. The stress intensity judgment unit receives the monitoring data and compares the antibiotic residue concentration with the sub-therapeutic concentration window threshold to obtain the stress intensity result data. The feedback regulation unit is communicatively connected to the water exchange valve of the recirculating aquaculture system 1 and to the farmer's terminal. It is used to output a water exchange ratio adjustment signal or a medication prompt signal based on the stress intensity result data. The antibiotic stress regulation module does not have an external antibiotic dosing device. The online monitoring and control module 10 is installed on the main circulation pipeline 9. It is electrically connected to the ammonia nitrogen concentration probe, nitrite nitrogen concentration probe, nitrate nitrogen concentration probe, and dissolved oxygen concentration probe. The module is also electrically connected to the membrane aeration biofilm reactor unit and communicatively connected to the circulating water valve of the recirculating aquaculture system 1. The module is used to regulate the circulating water volume of the recirculating aquaculture system 1 and the aeration rate of the membrane aeration biofilm reactor unit. By transmitting control signals to the circulating water valve, the module controls the flow of water into the membrane aeration biofilm reactor. The total circulating water volume of the unit is controlled, and the control signal is transmitted to the air compressor 8 of the membrane aeration biofilm reactor unit. The aeration volume of the membrane aeration biofilm reactor unit is adjusted by adjusting the air output of the air compressor 8, so as to match the circulating water volume and the water quality pollutant degradation requirements, and ensure that the water quality parameters are stable within the suitable range for aquaculture. The entire device, through the synergistic effect of antibiotic residue monitoring and biological enhanced water purification, reduces the sub-therapeutic concentration antibiotic residue in the aquaculture water in situ without the addition of exogenous antibiotics, while maintaining the stability of conventional water quality indicators and reducing the energy and water resource consumption caused by water exchange. The antibiotic stress regulation module 5 maintains the residual antibiotic concentration in the circulating water within the sub-therapeutic concentration window threshold through the feedback regulation unit, so as to selectively inhibit the activity of nitrite oxidizing bacteria in the transition layer.

[0028] This invention utilizes naturally occurring antibiotic residues in recirculating aquaculture systems, resulting from routine disease control operations, as a selective stress factor. Without the need for any exogenous chemical agents or antibiotics, the antibiotic residue concentration is maintained within a sub-therapeutic concentration window through an antibiotic stress regulation module. This achieves selective inhibition of nitrite-oxidizing bacteria (NOB) in the transitional mid-layer, eliminating the need for additional antibiotic dosing equipment during operation. This avoids secondary pollution and additional operating costs associated with the introduction of chemical agents, aligning with the development needs of green recirculating aquaculture while reducing the system's operational complexity and maintenance difficulty.

[0029] This invention achieves in-situ embedding of the denitrification unit by placing the membrane aeration biofilm reactor unit on the main circulation pipeline between the rotary drum microfilter and the ultraviolet sterilizer. This eliminates the need for an external large reactor or external effluent treatment facility, thus avoiding additional floor space. The installation method is flexible and can be directly adapted to the upgrade and renovation needs of existing recirculating aquaculture systems. It effectively solves the problems of traditional post-denitrification processes having a large floor space and being unable to be compactly integrated into the main circulation channel.

[0030] This invention, through the synergistic cooperation of an antibiotic stress regulation module, an online monitoring and control module, and a membrane aeration biofilm reactor unit, preserves the activity of ammonia-oxidizing bacteria in the aerobic inner layer and denitrifying bacteria in the anoxic outer layer within a sub-therapeutic concentration window. Simultaneously, it selectively inhibits NOB activity in the transition middle layer, achieving stable maintenance of the short-cut nitrification-denitrification pathway. This reduces the electron donor requirement for denitrification by 40% compared to full nitrification-denitrification. Under the typical low C / N ratio (0.5-3:1) conditions of recirculating aquaculture systems, it efficiently removes total inorganic nitrogen without the need for external organic carbon sources. This solves the common industry problem of carbon source scarcity and continuous nitrate accumulation in traditional RAS systems due to low C / N ratios.

[0031] This invention uses an antibiotic residue monitoring unit to detect antibiotic concentrations in inlet and outlet pipes in real time. Combined with the sub-therapeutic concentration window threshold comparison of the stress intensity judgment unit and the linkage control of the water exchange valve and the farmer's terminal of the feedback control unit, it realizes intelligent closed-loop control of antibiotic stress intensity. It does not require changing the farmers' existing disease prevention and control habits. Only an antibiotic concentration monitoring link needs to be added. The "residual pollutants" that originally required cost removal can be transformed into denitrification control resources, which is highly accepted by farmers.

[0032] This invention utilizes a hollow fiber membrane closed-end aeration method in its membrane aeration biofilm module. Oxygen diffuses bubble-free from the inner cavity of the membrane to the outer liquid phase, achieving near 100% oxygen utilization and significantly reducing aeration energy consumption compared to traditional aeration methods. Simultaneously, the online monitoring and control module dynamically adjusts the aeration rate and circulating water volume based on the concentrations of ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, and dissolved oxygen, achieving precise oxygen supply and energy-saving operation. This significantly reduces the operating energy consumption and overall cost of water purification, enhancing the system's economic applicability and market promotion value.

[0033] In this embodiment, the hollow fiber membrane 41 is made of polyvinylidene fluoride or polydimethylsiloxane, and the membrane pore size of the hollow fiber membrane 41 is 0.05μm-0.4μm.

[0034] Specifically, the hollow fiber membrane 41 is made of polyvinylidene fluoride or polydimethylsiloxane. Compared with conventional polypropylene, these two materials have better chemical stability and biocompatibility. They can not only maintain structural stability in the circulating water environment for a long time, but also provide a more suitable interface for the attachment and growth of functional bacteria, which is conducive to the formation and stable maintenance of biofilm. The appropriate membrane pore size range can ensure that oxygen permeates evenly into the biofilm during aeration, and can also prevent impurities in the water from clogging the membrane pores, thus ensuring the long-term stable operation of membrane aeration.

[0035] In this embodiment, the filling density of the membrane aeration biofilm module 4 is 150m³. 2 / m 3 -300m 2 / m3 The internal air pressure of the hollow fiber membrane 41 is 10kPa-100kPa.

[0036] Specifically, the filling density of membrane aeration biofilm module 4 is 150m³. 2 / m 3 -300m 2 / m 3 , While ensuring sufficient hollow fiber membrane to provide attachment area for functional bacteria, ample water flow channels are reserved to avoid excessive water circulation resistance and to prevent excessive overlap of biofilms on different membrane fiber surfaces from affecting material transport. This balances the denitrification capacity and operational stability of the reactor. The internal pressure of the hollow fiber membrane 41 is controlled at 10kPa-100kPa, which ensures that oxygen can diffuse smoothly through the membrane wall into the biofilm to meet the respiratory and metabolic needs of different functional bacteria, while avoiding excessive pressure that would cause bubbles to overflow from the membrane wall, damaging the biofilm structure and wasting oxygen.

[0037] In this embodiment, the antibiotic residue monitoring unit is an online antibiotic sensor based on the principle of enzyme-linked immunosorbent assay (ELISA), and the detection limit of the online antibiotic sensor is 0.1 μg / L.

[0038] Specifically, the online antibiotic sensor can obtain the antibiotic residue concentration in the reactor effluent in real time, eliminating the need for manual sampling and laboratory testing, thus significantly shortening the testing cycle. The online antibiotic sensor has a detection limit of 0.1 μg / L, accurately detecting low concentrations of antibiotic residues and promptly monitoring the compliance of antibiotics in the effluent. When the antibiotic residue concentration is detected to exceed the preset threshold, the system adjustment mechanism is quickly triggered to adjust the reactor's operating parameters, ensuring that the effluent quality consistently meets standards.

[0039] In this embodiment, the sub-therapeutic concentration window threshold is 1 μg / L-10 μg / L.

[0040] Specifically, the sub-therapeutic concentration window threshold of 1μg / L-10μg / L is determined based on the common concentration range of antibiotics discharged from urban wastewater treatment plants and the risk of inducing microbial resistance. When the online antibiotic sensor detects that the residual concentration in the effluent is within this range, it indicates that the microorganisms in the reactor are already facing resistance selection pressure from sub-therapeutic concentration antibiotics. At this time, the bypass disinfection unit can be triggered to start, and the effluent can be deeply treated to prevent microorganisms carrying resistance genes from entering the natural environment with the effluent discharge, effectively blocking the environmental transmission path of antibiotic resistance.

[0041] A method for in-situ water purification in a recirculating aquaculture system 1, the method comprising the following steps: S1 (MABR Unit Biofilm Start-up Step): Using activated sludge containing nitrifying and denitrifying bacteria as seed sludge and aquaculture wastewater as substrate, a layered biofilm is formed on the surface of the membrane aeration biofilm component 4 until the ammonia nitrogen removal rate is greater than 90% and the nitrite nitrogen accumulation ratio is greater than 0.6. S2 (Antibiotic stress induction step): The antibiotic stress regulation module 5 maintains a sub-therapeutic concentration of antibiotics in the influent, so that the activity of nitrite oxidizing bacteria in the transition middle layer is selectively inhibited to the first preset value, while the activity of ammonia oxidizing bacteria in the aerobic inner layer is maintained to the second preset value and the activity of denitrifying bacteria in the anoxic outer layer is maintained to the third preset value. S3 (In-situ Operation Steps): Circulating water enters the membrane aeration biofilm reactor unit. Ammonia nitrogen is oxidized to nitrite nitrogen by ammonia-oxidizing bacteria in the aerobic inner layer. Nitrite nitrogen diffuses to the transition middle layer and the anoxic outer layer and is reduced to nitrogen gas by denitrifying bacteria. The treated effluent is disinfected by the ultraviolet sterilizer 7 and then returned to the recirculating aquaculture system 1. S4 (Coordinated Regulation Step): The online monitoring and control module 10 dynamically adjusts the feedback regulation parameters of the aeration pressure and antibiotic stress intensity in the membrane aeration biofilm component 4 based on the ammonia nitrogen concentration, nitrite nitrogen concentration and nitrate nitrogen concentration in the circulating water, so as to maintain the short-cut nitrification and denitrification pathway stably.

[0042] In this embodiment, in S1, the seed sludge is the return sludge from the aerobic tank of a municipal wastewater treatment plant, and the thickness of the layered biofilm is 300μm-400μm.

[0043] Specifically, S1: MABR unit biofilm formation start-up. Using sludge returned from the aerobic tank of a local municipal wastewater treatment plant as the inoculum, the sludge concentration (MLSS) in the horizontal cylindrical tank 3 was controlled at 3000±215 mg / L after inoculation. During the initial start-up phase, the influent was aquaculture wastewater from the recirculating aquaculture system 1. The air supply pressure of the air compressor 8 was controlled at 17±1 kPa, the HRT at 24 h, the water temperature at 25±2℃, and the dissolved oxygen at 2-3 mg / L. The biofilm formation start-up period was 6-8 weeks. When the ammonia nitrogen removal rate of the MABR effluent was consistently above 90% and the nitrite nitrogen accumulation ratio (nitrite nitrogen / nitrate nitrogen) ≥0.6, the biofilm formation was considered successful, at which point a stable biofilm with a thickness of approximately 300 μm had formed on the membrane surface.

[0044] S2: Community acclimatization under antibiotic stress. After successful biofilm formation, the biofilm was acclimatized using naturally occurring enrofloxacin residues (1 μg / L-10 μg / L) in the recirculating aquaculture system 1 for a period of 4 weeks. During the acclimatization period, samples were taken every 2 weeks to test the activity of functional bacteria in different areas of the biofilm. The results showed that the ammonia oxidation activity of the ammonia-oxidizing bacteria (AOB) in the inner membrane layer was 120.2±4.3 nmolN / (mgprotein·h), with a retention rate of 82.5±3.6% compared to the control group; the nitrite oxidation activity of the nitrite-oxidizing bacteria (NOB) in the intermediate layer was only 23.6±3.9 nmolN / (mgprotein·h), which was inhibited to 27.7±2.9% compared to the control group; and the denitrification activity of the denitrifying bacteria in the outermost layer was 94.3±5.1 nmolN / (mgprotein·h), with a retention rate of 87.3±2.7% compared to the control group. After acclimatization, the MABR unit achieved stable short-range nitrification and denitrification functions, and nitrite nitrogen was no longer further oxidized to nitrate nitrogen, but could directly diffuse to the outer layer and be reduced to nitrogen gas by the denitrifying bacteria.

[0045] S3: Steady-state operation and intelligent control. After acclimatization, the system enters the steady-state operation phase, controlling the HRT to 24h, the air compressor 8 supply pressure to 15±1kPa, and the water temperature to 20-30℃. The antibiotic stress control module 5 uploads concentration data to the central control system every 30 minutes: when the antibiotic concentration is detected to be below 1μg / L, the central control system sends a prompt to the farmer, suggesting that enrofloxacin be added to the feed once more (without changing the type of drug, and the amount added is still 0.5% of the feed weight). After 1-3 days, the concentration will rise back to the effective window, and the denitrification efficiency will remain stable. When the enrofloxacin concentration is detected to be above 10μg / L, the central control system prompts the farmer to increase the daily water change ratio from 5% to 10%. After 5 days, the concentration will fall back to the effective window, avoiding the simultaneous inhibition of AOB and denitrifying bacteria activity by high concentrations of antibiotics.

[0046] S4: During steady-state operation, the influent water quality of the MABR was: ammonia nitrogen 7.16±0.16 mg / L, nitrate nitrogen 29.46±1.54 mg / L, and the effluent water quality was: ammonia nitrogen <0.51 mg / L (average removal rate 96.53%), nitrate nitrogen <4.0 mg / L (average removal rate 92.16%), which fully met the water quality requirements for tilapia farming.

[0047] Example 1

[0048] In-situ treatment of freshwater RAS tilapia farming wastewater: Please see Figure 3 The experimental RAS aquaculture pond had a volume of 10m³. 3(Diameter 3.2m, effective water depth 1.3m), cultured species is Nile tilapia, initial weight (85±12)g / fish, stocking density 40kg / m³ 3 (Approximately 470 fish), daily feeding rate 2.5%-3.0% (dry matter basis), with backwashing of the rotary drum microfilter 1 hour after feeding. To prevent bacterial septicemia, enrofloxacin is added to the feed once a month at a rate of 0.5% of the feed weight. Enrofloxacin residues can be detected in the circulating water on the day of feeding and for 3-5 days thereafter. After long-term operation, the system reaches a steady-state residue concentration of 1.51±0.89 μg / L (e.g., ...). Figure 3 d) Other water quality indicators of RAS raw water (MABR unit influent) are shown in Table 1, and the detection methods of each water quality indicator and biofilm thickness are shown in Table 2.

[0049]

[0050] Table 1. Water Quality Indicators of RAS Raw Water (MABR Unit Influent)

[0051] Table 2. Methods for detecting water quality indicators and biofilm thickness. The MABR unit uses a PVDF hollow fiber membrane module with a single membrane fiber diameter of 2.2 μm and an effective membrane area of ​​approximately 27 m². 2 It is connected in series after the rotary drum microfilter and before the ultraviolet germicidal lamp; the antibiotic residue monitoring module uses an enzyme-linked immunosorbent assay (ELISA) sensor to monitor the concentration of enrofloxacin in real time.

[0052] Phase 1 (Biofilm Initiation): Inoculated sludge came from aerobic sludge from a municipal wastewater treatment plant. The sludge concentration (MLSS) was controlled at 3200±187 mg / L. The aeration pressure inside the hollow fiber membrane was controlled at 17 kPa, HRT=24h, and water temperature at 25±2℃. The influent was RAS raw water (antibiotics were not deliberately controlled, and fluctuated naturally from 1.2μg / L to 3.8μg / L with the feeding cycle). From the 4th week, light yellow slime was visible on the membrane surface, and the biofilm thickness measured by CLSM was 120~180μm. By the end of the 7th week, the biofilm thickness stabilized at 350±40μm, the ammonia nitrogen removal rate was >90%, and the nitrite nitrogen accumulation ratio (NO2) was [not specified]. - -N / NO3 - If -N)>0.65, the biofilm is considered mature.

[0053] Phase 2 (Antibiotic Stress Acclimation): After 7 weeks of acclimation, the biofilm thickness stabilized at 350 μm, and the ammonia nitrogen removal rate stabilized at over 90%. After biofilm maturation, acclimation continued for another 4 weeks using the inherent enrofloxacin residue in RAS (2.23±0.82 μg / L). At the end of week 11, samples were taken to measure the activity of different layers: Inner layer AOB: 128.5±9.3 nmolN / (mgprotein·h), which was 82.6±3.7% of the antibiotic-free control group (biofilm formation only, no stress); Middle layer NOB: 21.6±4.7 nmolN / (mgprotein·h), which was 26.1±3.6% of the antibiotic-free control group; Outer layer denitrification: 96.1±7.2 nmolN / (mgprotein·h), which was 88.5±4.2% of the antibiotic-free control group. This indicates that the inherent antibiotics in RAS have achieved community reconstruction through "selective inhibition of NOB, retention of AOB + denitrification".

[0054] Phase III Steady-State Operation Period: (Weeks 12-20, 8 weeks in total): HRT = 24h, aeration pressure approximately 17kPa, water temperature 25±2℃, RAS maintained at a residual concentration by mixing enrofloxacin with feed once a month (early weeks 12 and 16), with an average concentration of 1.51±0.89μg / L. Influent / effluent water quality during the steady-state period is detailed below. Figure 3 .

[0055] Data shows that, for example Figure 3 As shown in figure a, the MABR-coupled antibiotic sustained-release system constructed in this invention is effective against high concentrations of nitrate nitrogen (NO3). - The system exhibits excellent removal efficiency for NO3-N. Under simulated high-load RAS operation conditions, the influent nitrate nitrogen concentration remained consistently high at 30-35 mg / L with fluctuations of less than 8%; after system treatment, the effluent NO3-N concentration was significantly reduced. - -N concentration was rapidly reduced to below 5 mg / L, corresponding to NO3 - The average removal rate of NO3- was 92.16%. This result confirms the crucial role of selective antibiotic stress: subtherapeutic concentrations of antibiotics effectively inhibited the activity of nitrite-oxidizing bacteria (NOB) in the biofilm, blocking the entire nitrification pathway of "ammonia nitrogen-nitrite-nitrate," forcing nitrogen transformation to stop at the nitrite stage, thereby significantly reducing NO3-. - The accumulated level of -N reduces the load on the subsequent denitrification process.

[0056] Figure 3 b demonstrates the system's response to ammonia nitrogen (NH4). + The efficient conversion characteristics of NH4+ (-N) further validate the rationality of the layered biofilm structure. + -N concentration remained stable in the range of 7-8 mg / L, while NH4 in the effluent... +The NOB concentration approached 0 mg / L, with an average removal rate as high as 95.53%. This high efficiency is attributed to the unique oxygen gradient distribution of the MABR membrane module. Ammonia-oxidizing bacteria (AOBs) enriched in the aerobic inner layer of the membrane surface utilize oxygen permeating through the membrane to rapidly oxidize ammonia nitrogen to nitrite. Simultaneously, antibiotic stress further optimizes the bacterial community structure, inhibiting NOB while preserving the metabolic activity of AOBs, ensuring stable operation of short-cut nitrification, and providing sufficient electron acceptors (nitrite) for the denitrifying bacteria in the anoxic / anaerobic outer layer.

[0057] Combination Figure 3 Analysis of c and 3d shows that the system exhibits excellent carbon source utilization efficiency and intelligent regulation capability under low C / N ratio conditions. The influent soluble COD concentration is approximately 40 mg / L, while the effluent COD remains stable at 10-15 mg / L, indicating that the system achieves deep denitrification with only a small amount of endogenous carbon source. This is attributed to the theoretical advantage of short-cut denitrification saving approximately 40% of carbon source compared to full-process denitrification. The antibiotic concentration exhibits a dynamic characteristic of "initial pulse dosing followed by sustained release," with high initial concentrations rapidly screening for tolerant bacteria, followed by a stable sub-therapeutic level of 1-10 μg / L or higher, continuously exerting its ecological regulation function. In summary, the synergistic strategy of "MABR physical structure + antibiotic chemical stress" established in this invention successfully achieves NH4+ denitrification. + The short-cut nitrification-denitrification coupling from -N to N2 solves the problems of insufficient carbon source and nitrate accumulation in traditional RAS, demonstrating extremely high in-situ purification efficiency.

[0058] During the same period, the nitrate nitrogen in the control RAS (without MABR unit) continued to accumulate to 42.5±4.2 mg / L, approaching the nitrate tolerance limit of this type of fish. This led to chronic stress symptoms in tilapia, such as decreased feed intake and increased serum cortisol. This further verified the targeted solution of the nitrate toxicity problem under low carbon-to-nitrogen ratio of this technology. It achieves targeted regulation of biofilm functional areas without the need for exogenous carbon sources or antibiotics. It can be achieved solely by relying on the inherent antibiotic residues of RAS, which is fully compatible with the operational needs of actual recirculating aquaculture systems.

[0059] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An in-situ water purification device for a recirculating aquaculture system, applied to the recirculating aquaculture system, wherein the recirculating aquaculture system has built-in ammonia nitrogen concentration probes, nitrite nitrogen concentration probes, nitrate nitrogen concentration probes, and dissolved oxygen concentration probes; the inlet and outlet of the recirculating aquaculture system are connected to a main circulation pipeline; a rotary drum microfilter and an ultraviolet sterilizer are connected to the main circulation pipeline; characterized in that... include: A membrane aeration biofilm reactor unit is installed on the main circulation pipeline. The membrane aeration biofilm reactor unit is equipped with a membrane aeration biofilm component inside. The surface of the membrane aeration biofilm component forms a layered biofilm distributed radially from the inside to the outside. The layered biofilm includes an aerobic inner layer, a transition middle layer, and an anoxic outer layer. The aerobic inner layer is enriched with ammonia-oxidizing bacteria, and the anoxic outer layer is enriched with denitrifying bacteria. An antibiotic stress regulation module includes an antibiotic residue monitoring unit, a stress intensity judgment unit, and a feedback regulation unit. The antibiotic residue monitoring unit is installed on a membrane aeration biofilm reactor unit and is used to monitor the antibiotic residue concentration in the circulating water in real time and output monitoring data. The stress intensity judgment unit has a preset sub-therapeutic concentration window threshold. The stress intensity judgment unit receives the monitoring data and compares the antibiotic residue concentration with the sub-therapeutic concentration window threshold to obtain stress intensity result data. The feedback regulation unit is communicatively connected to the water exchange valve of the recirculating aquaculture system and to the farmer's terminal, and is used to output a water exchange ratio adjustment signal or a medication prompt signal based on the stress intensity result data. An online monitoring and control module is installed on the main circulation pipeline. The online monitoring and control module is electrically connected to the ammonia nitrogen concentration probe, nitrite nitrogen concentration probe, nitrate nitrogen concentration probe and dissolved oxygen concentration probe. The online monitoring and control module is electrically connected to the membrane aeration biofilm reactor unit. The online monitoring and control module is communicatively connected to the circulating water valve of the recirculating aquaculture system. The online monitoring and control module is used to adjust the circulating water volume of the recirculating aquaculture system and the aeration volume of the membrane aeration biofilm reactor unit. The antibiotic stress regulation module maintains the residual antibiotic concentration in the circulating water within the sub-therapeutic concentration window threshold through a feedback regulation unit, thereby selectively inhibiting the activity of nitrite-oxidizing bacteria in the transition layer.

2. The in-situ water purification device for a recirculating aquaculture system according to claim 1, characterized in that, The membrane aeration biofilm reactor unit includes a horizontal cylindrical tank. The bottom end of the horizontal cylindrical tank is connected to an air compressor, which is electrically connected to an online monitoring and control module. An exhaust port is provided at the top of the horizontal cylindrical tank. The water inlet end of the horizontal cylindrical tank is connected to an inlet pipe, and the water outlet end of the horizontal cylindrical tank is connected to an outlet pipe. The inlet pipe is connected to a rotary drum microfilter, and the outlet pipe is connected to an ultraviolet sterilizer and an outlet return pipe. The return end of the outlet return pipe is connected to the horizontal cylindrical tank. Both the inlet pipe and the outlet pipe are connected to an antibiotic residue monitoring unit. The horizontal cylindrical tank is vertically fixed with a membrane aeration biofilm assembly. The membrane aeration biofilm assembly is a hollow fiber membrane. The hollow fiber membrane adopts closed-end aeration to form a dissolved oxygen gradient that decreases from the inside to the outside within the hollow fiber membrane, forming an aerobic inner layer, a transitional middle layer, and an anoxic outer layer that are distributed radially from the inside to the outside.

3. The in-situ water purification device for a recirculating aquaculture system according to claim 2, characterized in that, The hollow fiber membrane is made of polyvinylidene fluoride or polydimethylsiloxane, and the membrane pore size is 0.05μm-0.4μm.

4. The in-situ water purification device for a recirculating aquaculture system according to claim 3, characterized in that, The packing density of the membrane aeration biofilm module is 150 m³. 2 / m 3 -300m 2 / m 3 The internal air pressure of the hollow fiber membrane is 10 kPa-100 kPa.

5. The in-situ water purification device for a recirculating aquaculture system according to claim 4, characterized in that, The antibiotic residue monitoring unit is an online antibiotic sensor based on the principle of enzyme-linked immunosorbent assay (ELISA), and the detection limit of the online antibiotic sensor is 0.1 μg / L.

6. The in-situ water purification device for a recirculating aquaculture system according to claim 5, characterized in that, The sub-therapeutic concentration window has a concentration threshold of 1 μg / L-10 μg / L.

7. A method for in-situ water purification in a recirculating aquaculture system, characterized in that, The method using the in-situ water purification device for a recirculating aquaculture system as described in any one of claims 1-6 includes the following steps: S1: Using activated sludge containing nitrifying and denitrifying bacteria as seed sludge and aquaculture wastewater as substrate, a layered biofilm is formed on the surface of the membrane aeration biofilm component until the ammonia nitrogen removal rate is greater than 90% and the nitrite nitrogen accumulation ratio is greater than 0.

6. S2: The antibiotic stress regulation module maintains a sub-therapeutic concentration of antibiotics in the influent, so that the activity of nitrite oxidizing bacteria in the transition middle layer is selectively inhibited to a first preset value, while the activity of ammonia oxidizing bacteria in the aerobic inner layer is retained to a second preset value and the activity of denitrifying bacteria in the anoxic outer layer is retained to a third preset value. S3: Circulating water enters the membrane aeration biofilm reactor unit. Ammonia nitrogen is oxidized to nitrite nitrogen by ammonia-oxidizing bacteria in the aerobic inner layer. The nitrite nitrogen diffuses to the transition middle layer and the anoxic outer layer and is reduced to nitrogen gas by denitrifying bacteria. The treated effluent is disinfected by the ultraviolet sterilizer and then returned to the recirculating aquaculture system. S4: The online monitoring and control module dynamically adjusts the feedback control parameters of aeration pressure and antibiotic stress intensity in the membrane aeration biofilm component based on the ammonia nitrogen concentration, nitrite nitrogen concentration and nitrate nitrogen concentration in the circulating water, so as to maintain the short-cut nitrification and denitrification pathway stably.

8. The in-situ water purification device for a recirculating aquaculture system according to claim 7, characterized in that, In S1, the seed sludge is the return sludge from the aerobic tank of a municipal wastewater treatment plant, and the thickness of the layered biofilm is 300μm-400μm.

9. The in-situ water purification device for a recirculating aquaculture system according to claim 8, characterized in that, In S2, the concentration of the antibiotic is increased from 0.5 μg / L to the target concentration weekly, with an induction period of 2-8 weeks. The antibiotic is one or more of sulfonamides, tetracyclines, macrolides, and quinolones. The total antibiotic concentration in the circulating water is maintained at 1 μg / L-10 μg / L, and the carbon-to-nitrogen ratio of the aquaculture wastewater is 0.5:1-3:

1.

10. The in-situ water purification device for a recirculating aquaculture system according to claim 9, characterized in that, In S3, the hydraulic retention time of the membrane aeration biofilm reactor unit is 24h, the water temperature of the membrane aeration biofilm reactor unit is 20℃-30℃, and the reflux ratio of the circulating water is 95%.

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