A device and method for treating seawater aquaculture tail water by coupling bacteria-algae granular sludge and pressure-driven ceramic membrane

Abstract

The application discloses a device and method for treating seawater breeding tail water by coupling bacteria-algae granular sludge and pressure-driven ceramic membrane, and the device comprises a water inlet mechanism, a flow stabilizing mechanism, a continuous flow ceramic membrane reactor, an illumination unit, an aeration mechanism and a pressure-driven water outlet mechanism; the continuous flow ceramic membrane reactor comprises a reactor body and a vertically arranged flat plate ceramic membrane assembly, and the aeration mechanism is arranged at the bottom of the reactor body; the bacteria-algae granular sludge system is inoculated and kept in the reactor body; the seawater breeding tail water continuously enters the continuous flow ceramic membrane reactor from the water inlet mechanism through the flow stabilizing mechanism, and the filtered water is continuously discharged from the flat plate ceramic membrane assembly under the action of a pressure difference. The application can realize the synchronous removal of nitrogen, phosphorus and organic matter under the conditions of continuous water inlet and constant flux water outlet, and can alleviate the ceramic membrane pollution through the bacteria-algae granular structure stability and the aeration granular scouring, and is suitable for treating seawater breeding tail water with high salinity, low carbon-nitrogen ratio and obvious water quality fluctuation.

Description

Technical Field

[0001] This invention relates to the field of water purification technology, specifically to a device and method for treating marine aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge. Background Technology

[0002] Intensive mariculture plays a vital role in ensuring aquatic product supply and promoting economic development in coastal areas. However, the wastewater generated during the aquaculture process also puts continuous pressure on nearshore aquatic environments. Uneaten feed, farmed animal excrement, microbial flocs, and resuspended bottom sediment lead to increased concentrations of nitrogen, phosphorus, organic matter, and suspended particulate matter in the wastewater. If the wastewater is discharged directly without effective treatment, it can easily cause eutrophication, algal blooms or red tides, oxygen depletion, bottom sediment deterioration, and degradation of the aquaculture ecosystem.

[0003] Marine aquaculture effluent differs from municipal sewage and general industrial wastewater. It is characterized by high salinity, high ionic strength, significant fluctuations in nitrogen and phosphorus concentrations with feeding and water exchange cycles, the coexistence of suspended particles and dissolved organic matter, and a relatively low availability of organic carbon. Traditional physicochemical treatment methods such as sedimentation, sand filtration, coagulation, and flotation mainly remove suspended particles and some colloids, but are insufficient for removing dissolved nitrogen and phosphorus. Although conventional activated sludge processes can degrade organic matter and convert nitrogen, microbial activity is easily inhibited under high salinity and low carbon source conditions, and sludge settling properties and system shock resistance are difficult to maintain in the long term.

[0004] Membrane bioreactors (MBRs) couple biological treatment with membrane separation, offering advantages such as stable effluent, strong biomass retention capacity, small footprint, and ease of reuse. Ceramic membranes possess advantages such as high mechanical strength, corrosion resistance, cleaning resistance, and long service life, exhibiting good engineering adaptability in seawater and high-salinity systems. However, membrane fouling remains the core issue limiting the long-term stable operation of MBRs. During operation, soluble microbial products, extracellular polymers, fine particles, colloidal substances, and inorganic salt fouling accumulate within the membrane pores and on the membrane surface, forming a gel layer or filter cake layer. This leads to increased filtration resistance, elevated transmembrane pressure differential, and increased cleaning frequency.

[0005] To address membrane fouling, existing technologies typically employ methods such as increasing aeration intensity, periodic backwashing, offline chemical cleaning, reducing membrane flux, or altering operating cycles. While these methods can delay membrane fouling to some extent, they are mostly passive controls at the operational level, leading to increased energy consumption, membrane module wear, increased cleaning agent consumption, and complex management. Furthermore, relying solely on physical or chemical cleaning is insufficient to reduce the generation and migration of membrane fouling precursors at the source.

[0006] Microalgae-microbe symbiotic granular sludge offers a novel technological approach for treating marine aquaculture wastewater. Microalgae release oxygen through photosynthesis and assimilate nutrients such as nitrogen and phosphorus in the water; bacteria degrade organic matter and provide carbon dioxide and inorganic nutrients for the microalgae. Granular sludge, as a carrier in the microalgae-microbe symbiotic system, possesses a larger particle size, better settling performance, higher biomass retention capacity, and potential microscale aerobic / anoxic zoning, which facilitates simultaneous organic matter degradation, nitrification, denitrification, nutrient assimilation, and solid-liquid separation.

[0007] The applicant found that existing research on granular sludge from bacteria and algae mainly focuses on the treatment of ordinary low-salinity wastewater or municipal sewage, with insufficient understanding of the coupling relationship between the formation of granular sludge from bacteria and algae in marine aquaculture effluent, particle structure stability, maintenance of microalgal activity, and mitigation of membrane fouling. Especially in pressure-driven continuous flow operation of ceramic membranes, there is a lack of complete device design and operation methods for utilizing granular sludge to reduce the migration of soluble pollutants to the membrane surface and improving the filter cake structure through particle movement near the membrane surface.

[0008] Therefore, the applicant proposed a pressure-driven ceramic membrane device coupled with bacteria and algae granular sludge, designed for the characteristics of marine aquaculture effluent, which enables stable removal of pollutants, stable maintenance of granular sludge, and effective mitigation of membrane fouling under conditions of continuous influent, constant flux effluent, and moderate aeration. Summary of the Invention

[0009] This invention aims to address the problems of insufficient nitrogen and phosphorus removal efficiency in conventional biological treatment of marine aquaculture wastewater, rapid membrane fouling in ordinary membrane bioreactors, significant increase in transmembrane pressure difference, frequent operation and cleaning, and insufficient sludge structural stability under high salinity conditions. It provides a device and method for treating marine aquaculture wastewater using a pressure-driven ceramic membrane coupled with bacterial and algal granular sludge. Without relying on complex external enhancement units, it utilizes the symbiotic metabolism of the bacterial and algal granular sludge, its granular structure, and the aeration-induced granular scouring effect to achieve source reduction and in-situ mitigation of membrane fouling during pressure-driven filtration of the ceramic membrane.

[0010] This invention is particularly suitable for marine aquaculture wastewater with high salinity, low carbon-to-nitrogen ratio, suspended particles and dissolved organic matter. It can also be used for the pretreatment of other high-salinity organic wastewater, drainage from recirculating aquaculture systems and reclaimed water from aquaculture with similar water quality characteristics.

[0011] The objective of this invention is achieved through the following technical solution: A device for treating mariculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge, comprising an inlet mechanism, a flow stabilizing mechanism, a continuous flow ceramic membrane reactor, a pressure-driven outlet mechanism, and a lighting unit and an aeration mechanism acting on the continuous flow ceramic membrane reactor, connected in sequence; the continuous flow ceramic membrane reactor includes a reactor body and a flat ceramic membrane assembly vertically arranged within the reactor body, with the aeration mechanism supplying aeration to the bottom of the reactor body; the reactor body is inoculated with and maintains an algae and granular sludge system; the mariculture wastewater continuously enters the continuous flow ceramic membrane reactor from the inlet mechanism via the flow stabilizing mechanism, and the algae and granular sludge are kept suspended under lighting and aeration conditions within the continuous flow ceramic membrane reactor, with pollutants removed through algae-microenvironment synergistic metabolism and particle microenvironment transformation; the filtered water is discharged through the flat ceramic membrane assembly under pressure difference, while sludge particles, microalgae, bacteria, and suspended particles are retained by the membrane assembly.

[0012] During operation, aeration maintains the suspension of the algae and bacteria particles and causes them to gently shear against the membrane surface. The algae and bacteria granular sludge system achieves simultaneous removal of nitrogen, phosphorus, and organic matter through microalgal nutrient assimilation, photosynthetic oxygen supply, bacterial organic matter degradation, transformation of the internal microenvironment of the granular sludge, and immobilization of structural extracellular polymers. Simultaneously, it reduces the migration of soluble microbial products and loosely bound extracellular polymers to the membrane surface, forming a looser, more permeable membrane cake layer, thereby reducing the rate of transmembrane pressure gradient growth and mitigating ceramic membrane fouling. This invention is suitable for the purification, reuse pretreatment, and advanced treatment of seawater aquaculture wastewater with high salinity, low C / N ratio, and significant water quality fluctuations.

[0013] Furthermore, the bacterial-algae granular sludge system comprises aerobic granular sludge and salt-tolerant seawater microalgae. The aerobic granular sludge provides a microbial carrier, granular framework, and organic matter degradation function, while the salt-tolerant seawater microalgae provides photosynthetic oxygen supply and nitrogen and phosphorus assimilation functions. Microalgal cells and their secretions serve as the biological core for bacterial attachment and aggregation, and the structural extracellular polymers jointly secreted by algae and bacteria enhance intercellular adhesion and granular framework strength. The mixed liquor suspended solids concentration of the aerobic granular sludge is 6500–8500 mg / L; the dosage concentration of the salt-tolerant seawater microalgae is 500–1000 mg / L.

[0014] The membrane fouling mitigation process includes three aspects: First, algal-microbe symbiosis improves the efficiency of nutrient assimilation and organic matter degradation, reducing the load of soluble pollutants entering the vicinity of the membrane surface; second, stabilizing algal-microbe particles fixes some extracellular polymers such as proteins and polysaccharides within the particle skeleton, reducing the migration of soluble microbial products and loosely bound extracellular polymers to the membrane surface; third, bottom aeration drives the particles to move near the membrane surface, forming a continuous and gentle shearing and scrubbing effect on deposited pollutants, keeping the filter cake layer loose and reducing the rate of increase in transmembrane pressure difference.

[0015] Specifically, the pressure-driven water outlet mechanism includes an outlet pipe, a peristaltic pump, and an outlet tank connected to the flat ceramic membrane module. The peristaltic pump is used to maintain constant flux filtration and discharge the filtered water from the inner cavity of the flat ceramic membrane module. A transmembrane pressure differential monitoring mechanism is also provided, which is connected to the outlet pipe and is used to record the change of transmembrane pressure differential over time and to determine the degree of membrane fouling.

[0016] Specifically, the flat ceramic membrane module is a sheet-like ceramic ultrafiltration membrane module, and the membrane material is alumina, zirconium oxide, silicon carbide or a composite ceramic material thereof, with a molecular weight cutoff of 100-500 kDa.

[0017] Specifically, the continuous flow ceramic membrane reactor is divided into an upper membrane separation zone and a lower aeration and mixing zone. The flat ceramic membrane module is arranged in the upper membrane separation zone, and the perforated aeration strip is arranged in the lower aeration and mixing zone and aerates towards the bottom of the flat ceramic membrane module to form gas-liquid disturbance and membrane shear from bottom to top.

[0018] Furthermore, the aeration mechanism includes an aeration pump, an air filter component, an air meter, an air volume regulating valve, and perforated aeration strips, with an aeration rate of 2.0–2.8 L / min, thereby creating an apparent upward flow velocity of 0.8–1.5 cm / s within the continuous flow ceramic membrane reactor.

[0019] Specifically, the water inlet mechanism includes a raw water tank and a water inlet pump. The raw water tank is connected to the water inlet pump via a delivery pipeline, and the outlet of the water inlet pump is connected to the flow stabilizing mechanism. The flow stabilizing mechanism is a flow stabilizing water storage tank or a constant liquid level water distribution tank.

[0020] To address the aforementioned technical problems, this invention also provides another technical solution: a method for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge. This method utilizes the aforementioned apparatus for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge. The method includes the following steps: S1, transporting seawater aquaculture wastewater from a raw water unit to a flow stabilization unit, and then continuously entering a continuous flow ceramic membrane reactor after flow stabilization; S2, inoculating the continuous flow ceramic membrane reactor with an algae and granular sludge system and activating the illumination unit and aeration unit to keep the algae and granular sludge system suspended and to carry out biotransformation of pollutants; S3, activating the pressure-driven effluent mechanism, and performing solid-liquid separation through a flat ceramic membrane module under pressure difference, allowing the filtered water to be continuously discharged.

[0021] Furthermore, step S4 is included to record the transmembrane pressure difference and evaluate the development of membrane fouling based on changes in the transmembrane pressure difference. When the transmembrane pressure difference reaches a preset maintenance threshold, the flat ceramic membrane module is rinsed with clean water, scrubbed with air and water, or cleaned offline. During normal operation, membrane fouling is mainly delayed by the stabilization of the bacterial and algae granular sludge system and the flushing of bottom aeration particles. In addition, during operation, the concentration of suspended solids in the mixed liquor, sludge volume index, average particle size, zeta potential, chlorophyll concentration, active algae concentration, adenosine triphosphate, soluble microbial products, extracellular polymers, and transmembrane pressure difference are detected to evaluate the stability of the bacterial and algae granular sludge system and the membrane fouling mitigation effect.

[0022] Specifically, before step S2, a mother reactor is set up to cultivate a bacterial and algal granular sludge system. Seawater salt-tolerant microalgae are added to the aerobic granular sludge and the system is run for 50–80 days. The water quality range of the seawater aquaculture effluent is pH 7.0–7.5, suspended solids 100–200 mg / L, chemical oxygen demand 80–130 mg / L, ammonia nitrogen 10–15 mg / L, total nitrogen 20–25 mg / L, and total phosphorus 1.5–3.0 mg / L. The continuous flow ceramic membrane reactor is operated at 15–30°C with a membrane flux of 10–90 LMH.

[0023] Specifically, the continuous flow ceramic membrane reactor operates at 20±2℃, with the membrane flux increasing progressively at 10, 30, 60, and 90 LMH. When the effective volume of the continuous flow ceramic membrane reactor is 1.836 L and the effective membrane area is 0.0064 m², the hydraulic retention times at membrane fluxes of 10, 30, 60, and 90 LMH are 28.69, 9.56, 4.78, and 3.19 h, respectively.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects: 1. Strong ability to remove pollutants simultaneously.

[0025] This invention couples microalgal nutrient assimilation, photosynthetic oxygen supply, bacterial organic matter degradation, and particle internal microenvironment transformation in the same continuous flow reactor, enabling simultaneous reduction of total nitrogen, total phosphorus, and chemical oxygen demand.

[0026] 2. Stable particle structure.

[0027] After the introduction of microalgae, the bacterial and algal granular sludge can gradually transform from small flocs into granules with clear boundaries and dense structure, resulting in a decrease in sludge volume index and an increase in average particle size. This indicates that the device of the present invention has better settling performance and biomass retention capacity.

[0028] 3. The rate of membrane fouling development has slowed down.

[0029] The bacterial and algal particle structure can reduce the release of fine particles and reduce the migration of soluble microbial products and loosely bound extracellular polymers to the membrane surface; at the same time, aeration causes the particles to physically scrub the membrane surface, making the filter cake layer more porous, thereby slowing down the rise of transmembrane pressure difference.

[0030] 4. Simple operation.

[0031] This invention employs continuous water inlet, constant flow water outlet, illumination, and bottom aeration to maintain stable operation without complex cycle switching, making it easy to couple or modify with existing ceramic membrane devices.

[0032] 5. Suitable for use with marine aquaculture wastewater.

[0033] This invention addresses aquaculture wastewater characterized by high salinity, high ionic strength, low carbon-to-nitrogen ratio, and significant water quality fluctuations. It establishes a dual-pathway technology system that combines "bacterial-algae symbiosis to enhance pollutant removal" with "particulate structure to alleviate membrane fouling." This system can be used for wastewater pretreatment to achieve discharge standards and reuse. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the device in this embodiment.

[0035] Figure 2 This is a schematic diagram of the continuous flow ceramic membrane reactor in this embodiment.

[0036] Figure 3 This is a schematic diagram of the structure of the flat ceramic membrane module in this embodiment.

[0037] Figure 4 This is a physical diagram and a three-dimensional structural diagram of the device in this embodiment.

[0038] Figure 5 This is a physical diagram and a three-dimensional corresponding structural schematic diagram of the device in another embodiment.

[0039] Figure 6 This is a schematic diagram illustrating the removal effects of nitrogen, phosphorus, and organic matter in an application example of this embodiment.

[0040] Figure 7 This is a schematic diagram illustrating the changes in sludge granulation, settling performance, and biological activity in the application example of this embodiment.

[0041] Figure 8 This is a schematic diagram illustrating the changes in EEM and polysaccharide proteins in an application example of this embodiment.

[0042] Figure 9 This is a schematic diagram of the transmembrane pressure difference change in an application example of this embodiment.

[0043] Figure 10 This is a schematic diagram illustrating the mechanism by which the bacterial and algae granular sludge enhances pollutant removal and mitigates membrane fouling according to the present invention.

[0044] In the picture: 1-Raw water tank; 2-Inlet pump; 3-Flow meter; 4-Steady flow storage tank; 5-Check valve; 6-Perforated aeration strip; 7-Air meter; 8-Air filter component; 9-Aeration pump; 10-Illumination unit; 11-Continuous flow ceramic membrane reactor; 12-Outlet water tank; 13-Transmembrane differential pressure recorder; 1310-TMP sensor; 14-Peristaltic pump; 15-Dissolved oxygen meter; 1110-Reactor body; 1120-Algae granular sludge system; 1130-Flat ceramic membrane module; 1133-Upper sealing component; 1134-Lower sealing component; 1135-Sheet ceramic membrane body. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be understood that the following embodiments are merely illustrative of the technical concept of the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, any conventional substitutions or proportional adjustments to the reactor size, membrane area, membrane material, microalgae species, aeration intensity, lighting method, water inlet method, and cleaning method without departing from the essence of the present invention should fall within the scope of protection of the present invention.

[0046] In this invention, "bacterial and algal granular sludge" refers to an algal-bacterial symbiotic granular system formed by introducing salt-tolerant seawater microalgae into granular sludge. It contains bacteria, microalgae, extracellular polymers, and a granular skeletal structure, exhibiting good settling performance and biomass retention capacity. "Pressure-driven ceramic membrane" refers to a filtration method where filtered water is discharged through a ceramic membrane module under the pressure difference across the membrane, preferably using a peristaltic pump to maintain a constant flux of effluent.

[0047] like Figures 1-4 As shown, the device for treating seawater aquaculture tailwater using a pressure-driven ceramic membrane coupled with algae granules and sludge in this embodiment includes an inlet mechanism, a flow stabilization mechanism, a continuous flow ceramic membrane reactor, a lighting unit, an aeration mechanism, and a pressure-driven outlet mechanism. The inlet mechanism, the flow stabilization mechanism, the continuous flow ceramic membrane reactor, and the pressure-driven outlet mechanism are connected in sequence, and the lighting unit and the aeration mechanism act on the continuous flow ceramic membrane reactor.

[0048] The water inlet mechanism includes a raw water tank 1, an inlet pump 2, and a flow meter 3. The raw water tank 1 is used to store simulated or actual seawater aquaculture tailwater. The tailwater in the raw water tank 1 is transported to the flow stabilization mechanism by the inlet pump 2. The flow meter 3 is installed on the conveying pipeline to observe and correct the inlet flow rate.

[0049] The flow stabilization mechanism is a flow stabilization storage tank or a constant-level distribution tank, used to reduce fluctuations in the influent flow rate and stably distribute water to the continuous flow ceramic membrane reactor. In this embodiment, the flow stabilization storage tank 4 is used. The flow stabilization storage tank 4 delivers the tailwater to the continuous flow ceramic membrane reactor 11. The flow stabilization storage tank 4 reduces influent fluctuations through a constant level or buffer volume, ensuring stable operation of the continuous flow ceramic membrane reactor 11 under continuous flow conditions. The flow stabilization mechanism also includes a check valve 5, which is installed on the delivery pipeline.

[0050] At least one continuous flow ceramic membrane reactor 11 may be installed, or two or more may be installed in parallel. When two parallel reactors are installed, one may serve as a bacterial-algae granular sludge reactor, and the other may serve as a control reactor for algae-free bacterial granular sludge, so as to compare the contribution of the bacterial-algae symbiotic system to pollutant removal and membrane fouling mitigation. In engineering applications, only the bacterial-algae granular sludge reactor may be retained, or multiple sets of parallel reactors may be used.

[0051] The illumination unit 10 is arranged outside or above the continuous flow ceramic membrane reactor 11 to maintain the growth of microalgae and photosynthetic oxygen supply in the microbial granular sludge system. The illumination mode is continuous illumination, intermittent illumination, or simulated natural illumination.

[0052] The aeration mechanism includes an aeration pump 9, an air filter component 8, an air volume meter 7, an air volume regulating valve (not shown), and perforated aeration strips 6. The aeration pump 9 is connected to the perforated aeration strips 6 via the air filter component 8, the air volume meter 7, and the air volume regulating valve. The perforated aeration strips 6 are placed inside the continuous flow ceramic membrane reactor 11 to provide aeration for the reactor. The air volume meter 7 displays the aeration volume, and the air volume regulating valve adjusts the aeration volume.

[0053] The pressure-driven effluent mechanism includes an effluent pipeline, a peristaltic pump 14, and an effluent tank 12. The continuous flow ceramic membrane reactor 11 is connected to the effluent pipeline, which is connected to the effluent tank 12 (or effluent collector) via the peristaltic pump 14. The peristaltic pump 14 acts as the pressure-driven effluent mechanism, driving the filtered water to ultimately flow into the effluent tank 12 (or effluent collector). The effluent pipeline is connected to a transmembrane differential pressure recorder 13, which records changes in the membrane module's operating resistance, facilitating the evaluation of membrane fouling development. The transmembrane differential pressure recorder 13 is equipped with a TMP sensor 1310.

[0054] like Figure 2 and Figure 3 As shown, the continuous flow ceramic membrane reactor 11 includes a reactor body 1110, a bacterial and algae granular sludge 1120 and a flat ceramic membrane module 1130, wherein the bacterial and algae granular sludge system 1120, the flat ceramic membrane module 1130 and the perforated aeration strip 6 are placed in the cavity of the reactor body 1110.

[0055] The reactor body 1110 is a container made of transparent or light-transmitting material to allow light to enter the interior of the reactor body 1110. A water inlet is provided at the bottom of the reactor body 1110, and the water supplied by the steady flow storage tank 4 enters the reactor body 1110 from the bottom and comes into full contact with the bacterial and algae granular sludge system 1120.

[0056] The flat-plate ceramic membrane module 1130 is vertically fixed in the middle of the cavity of the reactor body 1110. The flat-plate ceramic membrane module 1130 is provided with a membrane outlet at the top, which is connected to the peristaltic pump 14 through an outlet pipe. Both sides of the flat-plate ceramic membrane module 1130 are in contact with the mixed liquor. The filtered water enters the inner cavity of the membrane module under the action of pressure difference and is discharged.

[0057] The perforated aeration strip 6 is located below the flat ceramic membrane module 1130. The aeration pump 9 is connected to the perforated aeration strip 6 via the air filter component 8 and the air flow meter 7, so that when the bubbles rise, they pass over the surface of the flat ceramic membrane module 1130 and drive the granular sludge to move. In this preferred embodiment, the aeration holes of the perforated aeration strip 6 are evenly distributed along the width direction of the flat ceramic membrane module 1130, so that the bubbles rise evenly near the membrane surface of the flat ceramic membrane module 1130.

[0058] The flat-plate ceramic membrane module 1130 includes an upper sealing component 1133, a lower sealing component 1134, and a sheet-like ceramic membrane body 1135. The flat-plate ceramic membrane module is a sheet-like ceramic ultrafiltration membrane module, and the membrane material is alumina, zirconium oxide, silicon carbide, or a composite ceramic material thereof, with a molecular weight cutoff of 100–500 kDa. In this embodiment, a 300 kDa ultrafiltration membrane is preferred. The flat-plate ceramic membrane module 1130 can be fixed to the center of the reactor body 1110 by a support to avoid significant swaying under aeration disturbance, while ensuring that the bacterial and algal granular sludge system 1120 is uniformly distributed near the membrane surface.

[0059] The continuous flow ceramic membrane reactor can be divided into an upper membrane separation zone and a lower aeration and mixing zone. A flat-plate ceramic membrane module is arranged in the upper membrane separation zone, and perforated aeration strips are arranged in the lower aeration and mixing zone, aerating towards the bottom of the membrane module to create bottom-up gas-liquid disturbance and membrane surface shear. The aeration rate is 2.0–2.8 L / min, preferably 2.59 L / min, resulting in an apparent upflow velocity of 0.8–1.5 cm / s within the reactor, preferably 1.2 cm / s. Bottom aeration drives the movement of bacterial and algal granular sludge near the membrane surface, subjecting deposited pollutants to continuous and gentle hydraulic shear and particle scrubbing, thereby reducing the compaction of the filter cake layer and slowing the increase in transmembrane pressure difference.

[0060] In this embodiment, the continuous flow ceramic membrane reactor has dimensions of 51 cm × 6 cm × 6 cm, with a total volume of approximately 2.13 L. After deducting the reserved space at the top and the internal support structure, the effective volume is 1.836 L. The above dimensions are only a preferred embodiment for the laboratory unit. During engineering scale-up, the treatment capacity can be increased by increasing the number of reactors, increasing the membrane area, or using modular membrane modules.

[0061] Before starting the continuous flow ceramic membrane reactor in this embodiment, it is preferable to set up a mother reactor to cultivate and inoculate granular sludge. The cultivation method of the bacterial and algal granular sludge is as follows: aerobic granular sludge is added to the mother reactor, and seawater salt-tolerant microalgae are added. The seawater salt-tolerant microalgae are golden algae, diatoms, green algae, or a combination thereof, with golden algae being preferred. The addition concentration is 500-1000 mg / L, preferably 700 mg / L. The average particle size of the bacterial and algal granular sludge is 0.30-2.00 mm, preferably 0.45-0.70 mm.

[0062] The mother reactor operates under cyclical influent, aeration, settling, and effluent conditions for 50–80 days, preferably 70 days, to promote bridging and aggregation between microalgae, bacteria, and extracellular polymers. The purpose of this stage is not as a final effluent treatment process, but rather to obtain structurally stable, well-settling inoculum containing active microalgae.

[0063] After cultivation, the bacterial and algal granular sludge from the mother reactor is collected and inoculated into a continuous flow ceramic membrane reactor. During inoculation, the concentration of aerobic granular sludge in the continuous flow ceramic membrane reactor is controlled at 6500–8500 mg / L, preferably 7000 mg / L; the concentration of microalgae is controlled at 500–1000 mg / L, preferably 700 mg / L.

[0064] After inoculation with algae-bacterial granular sludge, acclimatization and start-up are carried out under light and aeration conditions. During start-up, the influent load and membrane flux can be gradually increased to allow the algae-bacterial granular sludge to adapt to the high salinity environment of seawater aquaculture effluent and the ceramic membrane filtration conditions. After start-up, the algae-bacterial granular sludge can maintain suspension, settling, and biological activity under continuous flow conditions. Through the combined effects of microalgal nutrient assimilation, bacterial organic matter degradation, internal microenvironment transformation, and extracellular polymer fixation within the granular skeleton, the algae-bacterial granular sludge reduces total nitrogen, total phosphorus, and chemical oxygen demand in the effluent.

[0065] like Figure 5 The diagram shown is a physical image and a three-dimensional corresponding structure of the device in another embodiment. The structure is basically the same as that of this embodiment, except that a dissolved oxygen meter 15 is also provided.

[0066] Application Examples This embodiment uses the tailwater quality of the Zhangzhou Wharf mariculture farm as a reference to prepare simulated mariculture tailwater in the laboratory to reduce the impact of fluctuations in actual tailwater with seasons, feeding cycles, and water exchange cycles on parallel experiments. The simulated tailwater includes organic carbon sources, nitrogen sources, phosphorus sources, inorganic salts, and suspended solids, and can reflect the characteristics of the coexistence of nitrogen, phosphorus, organic matter, and particulate matter in mariculture tailwater.

[0067] In this embodiment, two parallel reactors are set up: one as a bacterial-algae granular sludge reactor and the other as a control reactor for algae-free bacterial granular sludge, to compare the contribution of the bacterial-algae symbiotic system to pollutant removal and membrane fouling mitigation.

[0068] The preferred influent water quality range is: pH 7.0–7.5, suspended solids 100–200 mg / L, chemical oxygen demand 80–130 mg / L, ammonia nitrogen 10–15 mg / L, total nitrogen 20–25 mg / L, and total phosphorus 1.5–3.0 mg / L. In practical engineering applications, the above ranges can be adjusted adaptively according to the aquaculture species, stocking density, feeding intensity, and drainage system.

[0069] In this embodiment, the effective volume of the continuous flow ceramic membrane reactor is 1.836 L, the effective area of ​​the ceramic membrane is 0.0064 m², and the molecular weight cutoff is 300 kDa. The reactor temperature is controlled at 20 ± 2 °C, and a constant flux filtration method is used. The membrane flux can be increased stepwise by 10, 30, 60, and 90 LMH; the corresponding hydraulic retention times are 28.69, 9.56, 4.78, and 3.19 h, respectively.

[0070] The preferred aeration rate is 2.59 L / min, calculated from the apparent upflow velocity of 1.2 cm / s and the reactor cross-sectional area. Aeration not only provides mixing and oxygen supply but also creates disturbance in the granular sludge near the membrane surface, inhibiting filter cake compaction. The preferred aerobic granular sludge concentration is 7000 mg / L, and the preferred microalgae dosage concentration is 700 mg / L. Specific parameters are shown in Table 1.

[0071] reactor effective volume 1.0–3.0 L; preferably 1.836 L Scale up according to water treatment capacity Effective area of ​​ceramic membrane 0.003~0.020 m²; preferably 0.0064 m² sheet ceramic ultrafiltration membrane Molecular weight cutoff 100–500 kDa; preferably 300 kDa Adjustable according to water output requirements sludge concentration 6500–8500 mg / L; preferably 7000 mg / L Aerobic granular sludge Microalgae dosage 500–1000 mg / L; preferably 700 mg / L Salt-tolerant golden algae in seawater Aeration rate 2.0–2.8 L / min; preferably 2.59 L / min Corresponding to an upward flow velocity of approximately 1.2 cm / s Membrane flux 10–90 LMH Can be improved in stages Operating temperature 15~30℃; preferably 20±2℃ Adaptable to experimental and engineering operations Table 1 Influent flows from the raw water tank into the steady-flow storage tank via the influent pump, and then from the steady-flow storage tank into the continuous-flow ceramic membrane reactor. The steady-flow storage tank buffers instantaneous fluctuations in the influent, ensuring a continuous influent flow to the continuous-flow ceramic membrane reactor. Compared to periodic influent and effluent methods, continuous influent and effluent flow is more conducive to the long-term stable operation of the ceramic membrane system and better meets the requirements of engineered wastewater treatment. Water quality indicators are shown in Table 2.

[0072] pH - 7.0～7.5 Suspended matter SS mg / L 100～200 Chemical oxygen demand (COD) mg / L 80～130 <![CDATA[Ammonia nitrogen NH 4+ -N]]> mg / L 10～15 Total nitrogen (TN) mg / L 20～25 Total phosphorus TP mg / L 1.5～3.0 Table 2 The method for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge in this embodiment includes the following steps: S1. Add the effluent from seawater aquaculture to the raw water tank, start the inlet pump, and let the effluent enter the steady flow storage tank, and then continuously enter the continuous flow ceramic membrane reactor from the steady flow storage tank. S2. Inoculate the continuous flow ceramic membrane reactor with bacterial and algal granular sludge, start the lighting unit and aeration pump to keep the bacterial and algal granular sludge suspended, the microalgae maintain photosynthetic oxygen supply and nutrient assimilation, and the bacteria carry out organic matter degradation and nitrogen conversion. S3. Start the pressure-driven water outlet mechanism to allow the filtered water to enter the inner cavity of the flat ceramic membrane module through the membrane module and be discharged through the water outlet pipe. Maintain constant flux filtration by adjusting the speed of the peristaltic pump. S4. During operation, record the influent and effluent water quality, sludge properties, microalgae activity, soluble microbial products, extracellular polymers, and transmembrane pressure difference. When the transmembrane pressure difference reaches the preset threshold, perform maintenance and cleaning on the flat ceramic membrane module. Maintenance and cleaning include water rinsing, air-water scrubbing, or offline cleaning. During normal operation, membrane fouling is mainly delayed by the stability of the bacterial and algae granular sludge structure and the flushing of bottom aeration particles.

[0073] The continuous flow ceramic membrane reactor in this embodiment was operated at 20±2℃ using a constant flux filtration method. The membrane flux was gradually increased by 10, 30, 60, and 90 LMH to investigate the adaptability of the bacterial and algal granular sludge to pollutant removal and membrane fouling mitigation under different filtration intensities.

[0074] The hydraulic retention time is determined by the reactor's effective volume, membrane flux, and effective membrane area. When the effective volume is 1.836 L and the membrane area is 0.0064 m², the hydraulic retention times for 10, 30, 60, and 90 LMH are 28.69, 9.56, 4.78, and 3.19 h, respectively. These data can be used for preliminary calculations in laboratory operation and engineering scale-up.

[0075] The aeration rate is determined based on the apparent upflow velocity and the reactor cross-sectional area. With an apparent upflow velocity of 1.2 cm / s and a cross-sectional area of ​​36 cm², the aeration rate is 43.2 mL / s, or 2.59 L / min. This aeration rate effectively balances oxygen supply, mixing, particle suspension, and membrane shear.

[0076] In this embodiment, experimental data can be obtained through the following detection and evaluation methods: 1. During the operation of the continuous flow ceramic membrane reactor, influent and effluent samples should be collected periodically to test total nitrogen, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen, total phosphorus, and chemical oxygen demand (COD). Total nitrogen can be determined using alkaline potassium persulfate digestion-ultraviolet spectrophotometry; total phosphorus can be determined using persulfate digestion followed by ammonium molybdate spectrophotometry; ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen can be determined using their respective spectrophotometric methods; and COD can be determined using rapid digestion spectrophotometry.

[0077] 2. Sludge concentration and settling performance were characterized by mixed liquor suspended solids concentration, 5-minute sludge volume index, and 30-minute sludge volume index, respectively. The average sludge particle size was determined using a laser particle size analyzer, and particle morphology was observed using a stereomicroscope. Zeta potential was used to reflect particle surface electrical properties and aggregation stability.

[0078] 3. Microalgal growth and bioactivity can be characterized by chlorophyll concentration, active algal concentration, and adenosine triphosphate (ATP) content. Soluble microbial products and extracellular polymers can be fractionated for protein and polysaccharide content determination. Three-dimensional fluorescence spectroscopy can be used to analyze the fluorescent components of proteins, humic substances, and fulvic acids in the effluent and mixed solutions.

[0079] 4. Membrane fouling behavior is evaluated by the change in transmembrane pressure difference over time under constant flux conditions. After operation, the membrane fouling layer and granular sludge can be observed using scanning electron microscopy, bio-scanning electron microscopy, or confocal laser scanning microscopy to analyze the internal structure of the filter cake layer and algal particles on the membrane surface.

[0080] Using the above detection and evaluation methods, data results were obtained for two sets of reactors (a reactor with algal granular sludge and a control reactor without algal granular sludge), as follows: Figures 6-8 As shown, an analysis is performed, as follows: 1) Pollutant removal effect.

[0081] like Figure 6 As shown, during the stable operation phase, the total nitrogen in the influent was maintained at 20–25 mg / L. The total nitrogen in the effluent of the continuous flow ceramic membrane reactor using the algae-bacterial granular sludge system of this invention was maintained at 6.7–8.0 mg / L, with a total nitrogen removal rate of 63%–69%. In contrast, the total nitrogen in the effluent of the control reactor without algae-bacterial granular sludge was 11–13 mg / L, with a total nitrogen removal rate of 39%–44%. These results indicate that the algae-bacterial granular sludge system has a stronger nitrogen removal capacity after the introduction of microalgae.

[0082] Further analysis of inorganic nitrogen speciation revealed that ammonia nitrogen in both reactors was rapidly removed, while nitrite and nitrate nitrogen levels remained low. This indicates that the residual total nitrogen in the effluent did not primarily originate from incomplete nitrification or nitrate accumulation, but rather from dissolved or colloidal organic nitrogen. In this invention, microalgae assimilate inorganic nitrogen and convert it into nitrogen-containing substances such as intracellular proteins and pigments, while simultaneously providing oxygen for the bacteria, thereby improving nitrogen conversion and removal efficiency.

[0083] Both reactors demonstrated high phosphorus removal capabilities, with effluent total phosphorus levels generally below 0.1 mg / L; the granular sludge reactor with bacteria and algae produced even lower effluent total phosphorus levels with less fluctuation. Regarding chemical oxygen demand (COD), the granular sludge reactor with bacteria and algae reduced the influent COD from approximately 120–130 mg / L to 3–11 mg / L, achieving a removal rate of approximately 97.5%.

[0084] When the membrane flux increases from 10 LMH to 30 LMH, the total nitrogen removal rate may experience temporary fluctuations, mainly due to the shortened hydraulic retention time and reduced contact time between pollutants and biomass. As the granular sludge gradually adapts to the higher filtration intensity, the total nitrogen removal rate can recover to a higher level, indicating that the invention has a certain degree of operational flexibility.

[0085] 2) Evolution of granular sludge and maintenance of microalgae.

[0086] like Figure 7 As shown, during operation, the algae and bacteria granular sludge gradually transformed from small flocs into larger particles with clear boundaries and a more compact structure. In contrast, the particle formation process in the algae-free bacterial particle control system was relatively slow, resulting in smaller particles with a looser structure. This difference indicates that the presence of microalgae alters the sludge aggregation pattern, making the system more prone to forming stable algae-bacteria composite particles.

[0087] In the algae-bacterial granule sludge reactor, the 5-minute sludge volume index decreased from 92.85 mL / g to 63.15 mL / g, and the 30-minute sludge volume index decreased from 75.71 mL / g to 56.57 mL / g. In the control reactor without algae, the 5-minute and 30-minute sludge volume indices decreased from 128.57 mL / g to 88.89 mL / g and from 91.42 mL / g to 70.83 mL / g, respectively. The lower sludge volume index indicates that the algae-bacterial granules of this invention have better settling performance and a more mature granular structure.

[0088] The change in average particle size was consistent with the change in settling performance. The average particle size of the algae-bacterial granular sludge reactor increased from approximately 454 μm to approximately 627 μm, while the average particle size of the algae-free control reactor only increased from 119 μm to 349 μm. The larger particle size indicates that the fine flocs gradually transformed into larger particles, which also means that the system has a stronger ability to aggregate particles and maintain its structure.

[0089] Chlorophyll concentration, active algae concentration, and adenosine triphosphate (ATP) content indicate that microalgae can be effectively retained in a continuous flow ceramic membrane system, enhancing overall biological activity. The microalgal cells are encapsulated and retained by the granular framework, reducing loss with the effluent and promoting a mutually beneficial symbiotic relationship between microorganisms and algae.

[0090] 3) Membrane fouling mitigation effect.

[0091] like Figure 8 and Figure 9 As shown, during the operation of gradually increasing membrane flux, the transmembrane pressure difference of the algae-bacterial granular sludge reactor of this invention was consistently lower than that of the control reactor without algae. At the end of operation, the transmembrane pressure difference of the reactor of this invention was approximately 33.1 kPa, lower than the 42.2 kPa of the control reactor without algae, indicating that the algae-bacterial granular sludge has a significant mitigating effect on ceramic membrane fouling.

[0092] The transmembrane pressure differential growth rate further indicates that, at the 10, 30, and 60 LMH stages, the transmembrane pressure differential growth rates of the reactor of this invention are approximately 0.0284, 0.0808, and 0.2371 kPa / d, respectively, all lower than the growth rates of the corresponding stages in the algae-free control reactor. As the membrane flux increases, the driving force for filter cake compaction strengthens, but the structural stability of the algal and bacterial particles and the membrane surface scrubbing effect can still slow down the rapid increase in transmembrane pressure differential.

[0093] Analysis of soluble microbial products and extracellular polymers indicates that proteins and polysaccharides in the system of this invention are more involved in particle framework construction, rather than migrating to the membrane surface in a soluble or loosely bound state. Tightly bound extracellular polymers help maintain particle mechanical stability and reduce the release of small particles; as the levels of soluble microbial products and loosely bound extracellular polymers decrease, the tendency for membrane pore blockage and the formation of a gel layer on the membrane surface weakens.

[0094] Microscopic observation of the membrane surface reveals that the membrane fouling layer in the algae and bacteria granular sludge reactor is relatively loose with higher porosity, making it less likely for pollutants to deposit and form a dense resistance layer. In the algae-free control reactor, fine particles and sticky organic matter are more likely to accumulate on the membrane surface, forming a filter cake layer with higher resistance.

[0095] Therefore, the mechanism of action of this invention can be summarized by three pathways: "synergistic effect of bacteria and algae, stable particle structure, and scouring by aerated particles," as follows: Figure 10 As shown.

[0096] First, microalgae release oxygen and assimilate nitrogen and phosphorus through photosynthesis, while bacteria provide carbon dioxide and nutrients by degrading organic matter and converting nitrogen into microalgae, thus forming a mutually beneficial symbiotic relationship.

[0097] Secondly, the granular sludge from bacteria and algae has a large particle size and a relatively stable granular skeleton, which can maintain a high biomass within the reactor and create localized aerobic, anoxic, and anaerobic microenvironments. This microenvironment facilitates the synergistic occurrence of organic matter degradation, ammonia nitrogen oxidation, denitrification, and biological assimilation processes, thereby improving pollutant removal efficiency.

[0098] Furthermore, the granular sludge from bacteria and algae immobilizes some extracellular polymers as structural components, reducing the migration of soluble microbial products and loosely bound extracellular polymers to the membrane surface. Since these components are often important precursors to membrane pore blockage and gel layer formation, their reduced migration can alleviate membrane fouling at its source.

[0099] Finally, bottom aeration keeps the algae and bacteria particles in a fluidized or semi-fluidized state near the membrane surface. The particles and air bubbles work together on the membrane surface to strip away loose deposits, prevent the filter cake layer from compacting, and maintain a loose and porous structure of the fouling layer on the membrane surface.

[0100] Thus, the present invention achieves a lower transmembrane pressure difference and a longer stable operating cycle under pressure-driven ceramic membrane filtration conditions.

[0101] In engineering applications, single or multiple continuous-flow ceramic membrane reactors can be set up and operated in parallel according to the treatment volume. The raw water tank and steady-flow storage tank can be connected to an aquaculture wastewater collection pond or a circulating water system. The effluent can enter a reuse water tank, a subsequent disinfection unit, or a compliant discharge unit. When the influent nitrogen and phosphorus load increases, the treatment capacity can be enhanced by appropriately reducing the membrane flux, extending the hydraulic retention time, or increasing the concentration of algae and bacterial granular sludge. When the transmembrane pressure difference increases rapidly, the aeration rate can be appropriately increased or short-term air-water scrubbing can be performed to restore the loose structure of the membrane surface. During long-term operation, appropriate light should be maintained to ensure microalgae activity; if microalgae activity declines, the symbiotic state of bacteria and algae can be restored by supplementing salt-tolerant microalgae, adjusting the light intensity, or adjusting the hydraulic retention time.

[0102] The flat-panel ceramic membrane module in this invention can be used as a single sheet, multiple sheets, or modular combination, depending on the processing scale. Due to the high mechanical strength and cleaning resistance of the ceramic membrane, it is suitable for long-term operation under high salt and particulate disturbance conditions.

[0103] In summary, the device and method for treating marine aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and sludge provided by this invention can achieve simultaneous removal of nitrogen, phosphorus, and organic matter under continuous influent and constant flow effluent conditions, and alleviate ceramic membrane fouling through the stabilization of the algae and sludge structure and the flushing effect of aeration particles.

[0104] Compared with conventional bacterial granular sludge ceramic membrane systems, this invention exhibits advantages in total nitrogen removal, granule maturation, settling performance, and transmembrane pressure differential control, making it suitable for effluent purification in marine aquaculture, pretreatment for resource recovery and reuse, and green transformation of aquaculture. Any equivalent substitutions or conventional adjustments made to the device structure, operating parameters, microalgae species, and membrane module form based on the technical concept of this invention shall fall within the protection scope of this invention.

Claims

1. A device for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge, characterized in that, The system includes, in sequence, an inlet mechanism, a flow stabilizing mechanism, a continuous flow ceramic membrane reactor, a pressure-driven outlet mechanism, and a lighting unit and an aeration mechanism acting on the continuous flow ceramic membrane reactor. The continuous flow ceramic membrane reactor includes a reactor body and a flat ceramic membrane assembly vertically arranged within the reactor body. The aeration mechanism supplies aeration to the bottom of the reactor body. The reactor body is inoculated with and maintains a bacterial and algal granular sludge system. Seawater aquaculture tailwater continuously enters the continuous flow ceramic membrane reactor from the inlet mechanism through the flow stabilizing mechanism, and the filtered water is continuously discharged from the flat ceramic membrane assembly under pressure difference.

2. The device for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge as described in claim 1, characterized in that... The bacterial and algal granular sludge system includes aerobic granular sludge and salt-tolerant seawater microalgae; the suspended solids concentration of the aerobic granular sludge mixture is 6500–8500 mg / L; and the concentration of the salt-tolerant seawater microalgae is 500–1000 mg / L.

3. The device for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge as described in claim 1, characterized in that... The pressure-driven water outlet mechanism includes an outlet pipe, a peristaltic pump, and an outlet tank connected to the flat ceramic membrane module. The peristaltic pump is used to maintain constant flux filtration and discharge the filtered water from the inner cavity of the flat ceramic membrane module. A transmembrane pressure differential monitoring mechanism is also provided, which is connected to the outlet pipe and is used to record the change of transmembrane pressure differential over time and to determine the degree of membrane fouling.

4. The device for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae granules and sludge as described in claim 1, characterized in that... The continuous flow ceramic membrane reactor is divided into an upper membrane separation zone and a lower aeration and mixing zone. The flat ceramic membrane module is arranged in the upper membrane separation zone, and the perforated aeration strip is arranged in the lower aeration and mixing zone and aerates towards the bottom of the flat ceramic membrane module to form gas-liquid disturbance and membrane shear from bottom to top. The flat ceramic membrane module is a sheet-like ceramic ultrafiltration membrane module, and the membrane material is alumina, zirconium oxide, silicon carbide or their composite ceramic materials, with a molecular weight cutoff of 100-500 kDa.

5. The device for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae granules and sludge as described in claim 1, characterized in that... The aeration mechanism includes an aeration pump, an air filter component, an air meter, an air volume regulating valve, and perforated aeration strips. The aeration rate is 2.0 to 2.8 L / min, which creates an apparent upward flow velocity of 0.8 to 1.5 cm / s in the continuous flow ceramic membrane reactor.

6. The device for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae granules and sludge as described in claim 1, characterized in that... The water inlet mechanism includes a raw water tank and a water inlet pump. The raw water tank is connected to the water inlet pump via a delivery pipeline, and the outlet of the water inlet pump is connected to the flow stabilizing mechanism. The flow stabilizing mechanism is a flow stabilizing water storage tank or a constant liquid level water distribution tank.

7. A method for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with bacterial and algal granular sludge, characterized in that... The device for treating marine aquaculture wastewater using a pressure-driven ceramic membrane coupled with bacterial and algae granular sludge as described in any one of claims 1-6 includes the following steps: S1, the marine aquaculture wastewater is transported from the raw water unit to the flow stabilization unit, and after flow stabilization, it continuously enters the continuous flow ceramic membrane reactor; S2, the bacterial and algae granular sludge system is inoculated in the continuous flow ceramic membrane reactor, and the illumination unit and aeration unit are activated to keep the bacterial and algae granular sludge system suspended and to carry out biotransformation of pollutants; S3, the pressure-driven effluent unit is activated, and solid-liquid separation is carried out through the flat ceramic membrane module under the action of pressure difference, so that the filtered water is continuously discharged.

8. The method for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge as described in claim 7, characterized in that... The system also includes step S4, which records the transmembrane pressure difference and evaluates the development of membrane fouling based on changes in the transmembrane pressure difference. When the transmembrane pressure difference reaches a preset maintenance threshold, the flat ceramic membrane module is rinsed with clean water, scrubbed with air and water, or cleaned offline. During normal operation, membrane fouling is mainly delayed by the stabilization of the bacterial and algae granular sludge system and the flushing of bottom aeration particles. In addition, during operation, the concentration of suspended solids in the mixed liquor, sludge volume index, average particle size, zeta potential, chlorophyll concentration, active algae concentration, adenosine triphosphate, soluble microbial products, extracellular polymers, and transmembrane pressure difference are detected to evaluate the stability of the bacterial and algae granular sludge system and the membrane fouling mitigation effect.

9. The method for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge as described in claim 7, characterized in that... Before step S2, a mother reactor is set up to cultivate a bacterial and algal granular sludge system. Seawater salt-tolerant microalgae are added to the aerobic granular sludge and the system is run for 50–80 days. The water quality range of the seawater aquaculture effluent is pH 7.0–7.5, suspended solids 100–200 mg / L, chemical oxygen demand 80–130 mg / L, ammonia nitrogen 10–15 mg / L, total nitrogen 20–25 mg / L, and total phosphorus 1.5–3.0 mg / L. The continuous flow ceramic membrane reactor is operated at 15–30℃ with a membrane flux of 10–90 LMH.

10. The method for treating seawater aquaculture wastewater using a pressure-driven ceramic membrane coupled with algae and granular sludge as described in claim 9, characterized in that... The continuous flow ceramic membrane reactor operates at 20±2℃, with the membrane flux increasing progressively at 10, 30, 60, and 90 LMH. When the effective volume of the continuous flow ceramic membrane reactor is 1.836 L and the effective membrane area is 0.0064 m², the hydraulic retention times at membrane fluxes of 10, 30, 60, and 90 LMH are 28.69, 9.56, 4.78, and 3.19 h, respectively.

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