Method for treating aquaculture tail water by magnetic bio-efficient flocculation coupled with bacteria-algae composite treatment

Abstract

The application discloses a kind of magnetic biological efficient flocculation coupling bacteria-algae composite processing aquaculture tail water method, belongs to the field of aquaculture tail water treatment.The steps are as follows: aquaculture tail water is collected into temporary storage pool by pipeline; tail water in temporary storage pool is lifted to magnetic biological efficient flocculation sedimentation tank / set by pump and is flocculated and deposited; after flocculation and deposition, tail water enters magnetic filler bacteria-algae composite pool for denitrification and phosphorus removal, part of sludge obtained by flocculation and deposition flows into sludge concentration tank by itself, and part of sludge is transported to water inlet by pipeline and mixed with incoming water; treated tail water in bacteria-algae composite pool is filtered into ecological phosphorus removal pool by modified oyster dam, and after effluent from ecological phosphorus removal pool is intercepted by modified fine oyster dam, residual suspended solids, various indexes meet discharge index requirements, and up to standard discharge or recycled for use in aquaculture farm for water replenishment.The application has the characteristics of small occupied area, high pollutant treatment efficiency, low system energy consumption and low carbon emission, and valuable materials in tail water can be recycled.

Description

Technical Field

[0001] This invention belongs to the field of marine aquaculture wastewater treatment, and specifically relates to a method for treating aquaculture wastewater using a magnetic biological high-efficiency flocculation coupled with bacterial and algal composite treatment. Background Technology

[0002] China is a major aquaculture country, ranking first in the world in aquaculture output. According to statistics, in 2021, the total output of aquatic products in China reached 66.9029 million tons. Of this, aquaculture output was 53.9441 million tons, and capture fishery output was 12.9589 million tons, with an aquaculture product to capture fishery product output ratio of 80.6:19.4. Marine product output was 33.8724 million tons, and freshwater product output was 33.0305 million tons, with a marine product to freshwater product output ratio of 50.6:49.4.

[0003] Marine aquaculture feed has a high protein content but low utilization rate, resulting in high emissions of nitrogen, phosphorus, and suspended solids. The fecal residue of farmed organisms introduces many pathogenic bacteria and viruses into the wastewater. Direct discharge of untreated wastewater leads to the imbalance of nearshore marine ecosystems, frequent red tides, disease outbreaks, and even poses a serious threat to the quality of the marine environment and the sustainable development of marine fishery resources. Therefore, the efficient treatment of marine aquaculture wastewater is urgently needed.

[0004] There are three main challenges in treating wastewater from marine aquaculture:

[0005] 1. High content of suspended solids: Taking the sea cucumber farming wastewater in Jinzhou City, Liaoning Province as a typical example, the suspended solids content of the wastewater is as high as 1000-2000 mg / L. The suspended solids are mainly composed of high-protein residual feed and animal excrement. If discharged directly without treatment, it will not only waste feed, but also release high concentrations of nitrogen and phosphorus, causing eutrophication of nearshore waters.

[0006] 2. Imbalance in C / N / P ratio: Since the main pollutants in aquaculture wastewater are high-protein residual feed and animal excrement, its CODcr is low, while total nitrogen and total phosphorus are high, resulting in an imbalance in the C / N / P ratio. Traditional biological processes are not suitable for direct use in aquaculture wastewater treatment.

[0007] 3. High salinity: The salinity of marine aquaculture tailwater is generally 25,000-35,000 mg / L. High salinity directly affects the efficiency of biological nitrogen and phosphorus removal processes. Nitrogen, phosphorus and other elements in aquaculture tailwater must be removed by using auxiliary biochemical processes.

[0008] Because marine aquaculture wastewater is characterized by large-scale discharge and significant fluctuations in water quality and quantity, current marine aquaculture wastewater treatment processes are mainly based on a process of "buffering water quality and quantity in a large regulating tank + coarse separation of suspended solids by microfiltration + separation of fine suspended solids by protein skimmer" followed by recycling. This process involves designing a very large regulating tank to buffer the highly volatile aquaculture wastewater discharge, and separating suspended solids in the wastewater through physical filtration and air flotation. The main disadvantages of this type of process are that it requires a large area (the regulating tank volume is about 20% of the aquaculture water volume), has low nitrogen and phosphorus removal efficiency (physical filtration has no effect on the removal of dissolved nitrogen and phosphorus), has high system energy consumption leading to high carbon emissions (the regulating tank lift pump, microfiltration machine, and protein skimmer all consume a lot of electricity), and cannot realize the resource utilization of valuable materials in the wastewater. Summary of the Invention

[0009] The purpose of this invention is to provide a method for treating aquaculture wastewater by magnetic biological high-efficiency flocculation coupled with bacteria and algae. By improving the water volume impact resistance of the process system to reduce the volume of the equalization tank, introducing a high-efficiency biochemical process to remove dissolved nitrogen and phosphorus elements in the wastewater, and using an aerobic composting process to realize the resource utilization of feed, the method ultimately ensures that the wastewater meets the discharge standards while realizing the resource utilization of the wastewater.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for treating aquaculture wastewater using a magnetic biological high-efficiency flocculation coupled with bacterial-algae composite treatment includes the following steps:

[0012] (1) The discharged seawater aquaculture wastewater is collected through pipelines and enters a temporary storage tank; the hydraulic retention time of the temporary storage tank is 2-4 hours;

[0013] (2) The effluent in the temporary storage tank enters the magnetic biological high-efficiency flocculation sedimentation tank / device for flocculation and sedimentation; the magnetic biological high-efficiency flocculation sedimentation tank / device is divided into a chemical dosing reaction zone, a flocculation sedimentation zone, a sludge return pump / external pump, a sludge collector and a matching chemical dosing device.

[0014] (3) After flocculation and sedimentation, the tailwater enters the magnetic packing algae and bacteria composite tank for nitrogen and phosphorus removal. Part of the sludge obtained from flocculation and sedimentation is transported to the inlet through pipeline and mixed with the incoming water. The ratio of sludge return flow to inlet flow in the sedimentation tank / device is 1:10-1:5.

[0015] (4) The wastewater from the bacterial-algae composite pond is filtered by a modified oyster dam and then enters the ecological phosphorus removal pond. The effluent from the ecological phosphorus removal pond is then filtered by a modified fine oyster dam to remove residual suspended solids before being discharged.

[0016] Preferably, in step (2), the magnetic biological high-efficiency flocculation sedimentation tank / device treats 1-50 m³ of water. 3 The treatment capacity is greater than 50m³ / h and can be achieved using one of the following materials: carbon steel corrosion-resistant, fiberglass, 2205, 2507, 904L, or titanium.3 When the flow rate is / h, a reinforced concrete structure pool is used.

[0017] Preferably, in step (2), the chemical reaction zones in the magnetic biological high-efficiency flocculation sedimentation tank / device are a primary reaction zone and a secondary reaction zone. Flocculant is added in the primary reaction zone, and flocculant and magnetic powder are added in the secondary reaction zone. The length-to-width ratio of the primary and secondary reaction zones is 1:1-1:2, and the hydraulic retention time is 5-15 min. The flocculant in the primary reaction zone is one of iron-based, aluminum-based, polyferric silicate, or polyaluminum silicate agents, and is continuously added at a dosage of 10-15 mg / L. The flocculant in the secondary reaction zone is anionic PAM, which is continuously added at a dosage of 1-3 mg / L. The magnetic powder in the secondary reaction zone is Fe3O4 powder, which is continuously added at a dosage of 1-50 ppm.

[0018] Preferably, in step (2), the flocculation sedimentation zone of the magnetic biological high-efficiency flocculation sedimentation tank / device is loaded with microbial flocs and is designed with biological sludge return; the length-to-width ratio of the sedimentation zone is 1:1-1:5, the surface loading is 0.5-2.5m / h, and the hydraulic retention time is 1-2h.

[0019] Preferably, in step (3), the bottom of the magnetic filler algae composite pond is filled with gravel matrix, and magnetic filler modules, microalgae and aeration devices are arranged intermittently in the pond. The modules are loaded with magnetic filler. The hydraulic retention time of the composite pond is 24-72h. The main component of the magnetic filler is Fe3O4-oyster shell, which is formed by grinding and crushing waste oyster shells, and then mixing them with Fe3O4 powder in a mass ratio of 1:1-1:2 to form balls.

[0020] Preferably, the microalgae are selected from either Chlorella vulgaris or Chlorella vulgaris, and the dosage is 30-50 g / h, with continuous addition for 7-15 days.

[0021] Preferably, in step (4), the modified oyster dam has a width of not less than 1.5m, a height of not less than 2m, and a length of not less than 5m. The foundation is made of reinforced concrete and the two sides are made of porous bricks. The oyster particles filled in the porous bricks of the modified oyster dam have a particle size of 2-4cm. The oyster particles in the modified fine oyster dam have a particle size of 1-2cm.

[0022] Preferably, in step (4), the ecological phosphorus removal pond is an earthen pond with zeolite and volcanic rock lining the bottom. The pond contains a reed island guide wall and a phosphorus removal ecological substrate. The dissolved oxygen in the pond is 0-0.4 mg / L. The hydraulic retention time of the ecological phosphorus removal pond is 24-72 h. The particle size of the zeolite and volcanic rock is 1 cm-5 cm, and the ratio is 1:1-1:5. The amount of phosphorus removal ecological substrate used is 5-100 m2. The surface of the phosphorus removal ecological substrate is coated with a phosphorus removal complexing agent EDTA.

[0023] Preferably, the amount of magnetic filler used is 1-20 m3.

[0024] In this invention, a level gauge is designed inside the temporary storage tank. The level gauge is interlocked with the booster pump. When the level is higher than the set high value, the pump starts; when the level is lower than the set low value, the pump stops. This level interlock solves the problem of unstable incoming water causing system shocks.

[0025] The effluent from the temporary storage tank is pumped to the magnetic biological high-efficiency flocculation sedimentation tank / device. There, it mixes with magnetic powder and microbial flocs. Utilizing the netting, sweeping, bridging, and adsorption effects of the magnetic powder and microbial flocs, suspended solids in the effluent aggregate into larger particles, gradually settling. The flocculation sedimentation zone is equipped with a collector where most suspended solids settle. Simultaneously, the suspended granular sludge, primarily composed of microbial flocs, exists in anaerobic-anoxic-aerobic zones from the inside out, depending on the varying conditions of contact and isolation with oxygen. Anaerobic polyphosphate-accumulating bacteria remove phosphorus, denitrifying bacteria remove nitrogen, and aerobic nitrifying bacteria assimilate, absorb, and degrade organic nitrogen, ammonia nitrogen, and organic phosphorus, ultimately removing most of the nitrogen and phosphorus from the effluent.

[0026] Part of the sludge in the receiver flows by gravity into the sludge thickening tank for concentration, while the rest is transported via pipeline to the inlet to mix with the incoming water. The sludge that has undergone gravity settling in the thickening tank is then pumped to a plate and frame filter press or screw press for dewatering until the moisture content is below 70%. Afterward, it is transferred to the feed recovery area to be added for aerobic composting, ultimately achieving the resource utilization of feed and excrement.

[0027] The effluent flows by gravity into a magnetic filler composite tank. The tank bottom is filled with gravel matrix, and magnetic filler modules and self-powered micro / nano aeration devices are interspersed throughout. The modules are loaded with magnetic filler microparticles and include reed / cattail ecological islands. Through the slow-release and electron-promoting effects of iron in the Fe3O4 magnetic filler, some reactive phosphate is physically removed, and the denitrification and phosphorus removal processes of microorganisms in the water are promoted. Microalgae (such as Chlorella and Elodea) are utilized to remove inorganic ions (e.g., NH4+) from the aquatic environment. + NO3 - NO2 - and H2PO4 - The microorganisms absorb nitrogen and phosphorus in wastewater, including organic pollutants such as urea (N and P). They decompose organic pollutants in the wastewater, releasing CO2 and producing organic acids, growth hormones, and inorganic salts. Microalgae absorb these substances through photosynthesis, consuming CO2 and releasing O2, thus increasing dissolved oxygen in the wastewater and promoting microbial metabolism. Simultaneously, the growth of reeds absorbs and assimilates nitrogen and phosphorus, consuming a considerable amount of these elements.

[0028] The main component of the magnetic filler is Fe3O4-oyster shell, which is formed by grinding and crushing waste oyster shells, then mixing them with Fe3O4 to form spheres. Fe3O4, as a magnetic material, contains both Fe(II) and Fe(III), and can slowly release Fe through hydrolysis. 2+ and Fe 3+ It directly participates in or promotes the denitrification and phosphorus removal reactions of microorganisms, and through its own electromagnetic properties, it can promote electron transfer between microorganisms, reduce energy consumption, and achieve a longer-term promoting effect on microbial growth.

[0029] Oyster shells in magnetic packing, with calcium carbonate as their effective component, possess a porous structure and strong adsorption capacity, creating favorable conditions for biofilm adhesion and formation. The Fe3O4-oyster shell packing constructs a stable iron slow-release system, achieving enhanced denitrification by Fe2+ and Fe3+ while simultaneously achieving phosphorus removal through a synergistic biological and chemical process. Chemical phosphorus removal effectively reduces iron concentration, avoiding secondary pollution caused by the addition of particles. Furthermore, iron is ubiquitous in the natural environment, has low toxicity, and is widely relied upon for cellular enzymatic reactions. Iron has multiple valence states, enabling it to continuously participate in redox reactions in the environment, transferring electrons and promoting biological metabolic reactions. In addition to participating in redox reactions, the iron(III) oxide powder itself is magnetic, and the local magnetic field can also promote biological metabolic reactions.

[0030] Self-powered nano-aeration equipment is a new type of high-efficiency aeration facility. Its solar power generation device converts solar energy into electrical energy. Utilizing its unique internal structure and gas-generating mechanism, it can produce bubbles in water with diameters ranging from tens of nanometers to several micrometers, while traditional microporous aeration bubbles have diameters between 0.5-5 mm. The huge specific surface area and the "diffuse" movement of nanobubbles in water significantly improve the utilization rate of oxygen from the air. Compared with conventional microporous aeration, nano-aeration technology has unparalleled power efficiency. According to experimental calculations, the oxygen transfer rate of nano-aeration can reach 20-25%, which is 5 times the oxygen utilization rate of conventional microporous aeration.

[0031] Meanwhile, reeds can absorb large amounts of nitrogen and phosphorus elements during their growth, thus achieving the ecological removal of nitrogen and phosphorus. The effluent from the magnetic packing tank is filtered through an oyster dam before entering the ecological phosphorus removal tank.

[0032] After the effluent passes through a modified oyster dam (oyster shells crushed to a particle size of 2cm-4cm) to remove residual suspended solids, it enters an ecological phosphorus removal pond. The bottom of the pond is lined with zeolite and volcanic rock, and the pond contains a reed island guide wall and a phosphorus removal ecological substrate. The dissolved oxygen in the pond is 0-0.4mg / L. At this time, denitrifying bacteria can use the organic matter in the water as an energy source and use nitrate nitrogen from the aerobic pond as an electron acceptor to reduce nitrate nitrogen to nitrogen gas, thereby ultimately achieving the removal of nitrogen from the water.

[0033] The phosphorus-removing ecological substrate possesses a high specific surface area and excellent adsorption performance, allowing it to float freely in water and form a three-dimensional structure of upper, middle, and lower layers, providing attachment and growth sites for microorganisms. Microorganisms accumulate on the surface of the ecological substrate, forming a biofilm. Simultaneously, due to the composite microenvironment of "aerobic-facultative-anaerobic" structure between the surface and interior of the biofilm, nitrification and denitrification processes can occur naturally, converting ionic nitrogen in the water into nitrogen gas that escapes from the system, reducing nitrogen levels in the water, inhibiting algal blooms, and reducing the release of endogenous pollutants. The installation and arrangement of the ecological substrate achieves microbial immobilization technology, preventing water flow from washing away effective microorganisms from the system, maintaining the number of effective microorganisms in the water, ensuring the stability and effectiveness of the microbial system, and contributing to water quality maintenance. Furthermore, the surface of the ecological substrate is coated with a highly efficient phosphorus-removing complexing agent, which specifically forms stable complexes with phosphorus, exhibiting strong phosphorus removal capabilities and high ecological safety.

[0034] After suspended solids are removed by filtering the effluent from the ecological phosphorus removal pond using modified ecological oyster dam (particle size 1cm-2cm), all indicators meet the requirements for aquaculture wastewater discharge and can be discharged in compliance with standards or recycled for aquaculture farm replenishment.

[0035] The working principle of this invention is:

[0036] The aquaculture wastewater first enters the magnetic biological high-efficiency flocculation sedimentation tank through the water inlet system. Most of the feed and animal excrement are removed through flocculation and sedimentation. The microbial flocs in the sedimentation tank remove nitrogen and phosphorus under anaerobic / anoxic / aerobic conditions, removing a portion of the dissolved nitrogen and phosphorus in the wastewater.

[0037] After the effluent enters the magnetic packing composite tank, the nitrogen and phosphorus in the effluent are removed by the assimilation and absorption of microorganisms, microalgae, and reeds through the slow release of iron, electron promotion, and complexation of active phosphate by the magnetic packing. At the same time, the effluent is aerated by a self-powered nano-aeration device, and the microalgae produce oxygen through photosynthesis. Aerobic bacteria convert organic nitrogen and ammonia nitrogen in the effluent into nitrate nitrogen. The nitrate nitrogen in the wastewater is then converted into nitrogen gas and removed through the action of denitrifying bacteria under anaerobic conditions.

[0038] The effluent is adsorbed and filtered by the oyster dam and then enters the ecological phosphorus removal pond. The zeolite, volcanic rock and ecological phosphorus removal substrate in the pond provide growth points for microorganisms to assimilate and absorb residual nitrogen and phosphorus nutrients. At the same time, the ecological phosphorus removal substrate is loaded with phosphorus removal complexing agent, which can specifically form a stable complex with phosphorus to ensure that the phosphorus content of the effluent meets the standards.

[0039] The effluent is adsorbed and filtered by a fine oyster dam before being discharged in compliance with standards.

[0040] This invention employs a process combining "magnetic biological flocculation sedimentation + magnetic packing composite tank + coarse oyster bar + ecological phosphorus removal tank + fine oyster bar" to maximize and efficiently treat aquaculture wastewater for resource utilization. With a smaller system footprint and lower energy consumption, it achieves compliant discharge of aquaculture wastewater and resource utilization of feed, among other benefits. The marine aquaculture wastewater treatment system built according to this process concept features a small footprint (reduced by approximately 50%-60% compared to conventional processes), high pollutant treatment efficiency (N and P treatment efficiency increased by approximately 80%-90%), low system energy consumption and low carbon emissions, and the ability to utilize valuable materials from the wastewater for resource recovery.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) To address the issues of high-protein feed residue and high excrement volume in marine aquaculture tailwater, a high-efficiency magnetic biological flocculation sedimentation process is adopted based on the different forms of feed and excrement in the tailwater. This process can remove feed and excrement through efficient flocculation sedimentation and also remove some N and P through microbial particle pre-degradation, reducing the load on subsequent treatment units. The recovered feed and animal excrement are dehydrated by a dewatering device, then disinfected and composted, ultimately realizing the resource utilization of waste.

[0043] (2) To address the imbalance of C / N / P ratio in aquaculture effluent, firstly, the nitrogen and phosphorus pollution caused by the slow release of residual feed and animal excrement is removed through the flocculation and sedimentation effect in the magnetic biological flocculation sedimentation process. Then, the total nitrogen is removed by the microbial particles in the magnetic biological flocculation sedimentation process and the microorganisms in the downstream tank, utilizing the action of nitrifying bacteria under aerobic conditions and denitrifying bacteria under hypoxic conditions. The total phosphorus is removed by the assimilation and absorption of polyphosphate-accumulating bacteria under anaerobic conditions. At the same time, the denitrification and phosphorus removal effects are enhanced by the use of phosphorus-removing ecological bases and magnetic fillers. The absorption of N and P by phosphorus-loving plants such as reeds is also utilized. Through the triple action of physical-plant-microbial, phosphorus removal is achieved.

[0044] (3) To address the problem of high energy consumption in traditional aerobic aeration, self-powered microporous aeration and microalgae oxygen production are adopted, eliminating the need for additional fans to consume electricity. Through microporous aeration and microalgae photosynthesis, oxygen is efficiently distributed and dissolved in water, ultimately ensuring the supply of oxygen required by aerobic microorganisms.

[0045] (4) Fine oyster shells are stacked to form an ecological filter dam, which not only has a physical interception function to remove suspended matter in the front pool, but also has the function of adsorbing and degrading organic matter due to its micropores that can carry microorganisms, thus helping to achieve high-efficiency removal of suspended matter, COD, N and P.

[0046] (5) A method for treating aquaculture wastewater by magnetic biological high-efficiency flocculation coupled with bacteria and algae, which has the characteristics of small footprint (about 40%-60% less than conventional biochemical systems), high pollutant treatment efficiency (suspended solids removal rate of over 95%, CODcr removal rate of over 90%, N and P removal rate of over 92%), low system energy consumption and low carbon emissions, and the ability to recycle valuable materials in the wastewater. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] A method for treating aquaculture wastewater using a magnetic biological high-efficiency flocculation coupled with bacterial-algae composite treatment includes the following steps:

[0050] (1) The discharged seawater aquaculture tailwater is collected by pipeline and flows into the temporary storage tank by gravity. Unlike the equalization tank in conventional processes, the hydraulic retention time of the temporary storage tank is 2-4 hours. As a result, the area occupied by the temporary storage tank will be more than 90% lower than that of the equalization tank with a retention time of 24-48 hours, which greatly reduces the system's land area.

[0051] The temporary storage tank is equipped with a level gauge, which is interlocked with the booster pump. When the level is higher than the set high value, the pump starts; when the level is lower than the set low value, the pump stops. This level interlock solves the problem of unstable incoming water causing system shocks.

[0052] The level gauge can be a float level gauge, ultrasonic level gauge or other instrument with level measurement function, and has signal transmission function to interlock with water pump;

[0053] The water pump is a submersible pump or a horizontal or vertical centrifugal pump. The pump body material must be resistant to seawater corrosion, such as 2205, 2507, or 904L.

[0054] (2) The tailwater in the temporary storage tank is pumped to the magnetic biological high-efficiency flocculation sedimentation tank / device.

[0055] The sedimentation tank / sedimentation unit is divided into a chemical dosing reaction zone, a flocculation sedimentation zone, a sludge return pump / external pump, a sludge collector, and a matching chemical dosing device. After the effluent is mixed with the returned sludge in the pipeline mixer, it enters the chemical dosing reaction zone. A small amount of flocculant is added in the primary reaction zone, and a small amount of magnetic powder and flocculant are added in the secondary reaction zone. The mixing of the chemicals and effluent is enhanced by the stirring action of the agitator. The uniformly mixed effluent enters the flocculation sedimentation zone, which contains magnetic powder and microbial floc particles. Inclined plates are installed, and biological sludge return is designed. Through the triple action of magnetic powder, flocculant, and microbial flocs, the settling rate of suspended solids in the water is enhanced.

[0056] The microbial flocs in the pool have different conditions of contact with and isolation from oxygen. The granular sludge is divided into anaerobic-anoxic-aerobic zones from the inside out. Anaerobic polyphosphate-accumulating bacteria remove phosphorus, denitrifying bacteria remove nitrogen, and aerobic nitrifying bacteria assimilate, absorb and degrade organic nitrogen, ammonia nitrogen and organic phosphorus, respectively, and finally remove most of the nitrogen and phosphorus from the effluent.

[0057] The settled suspended solids mainly consist of residual feed and excrement, which are collected by a sludge collector installed at the bottom. Some sludge is returned to the inlet to mix with the effluent, while some sludge flows by gravity into the sludge thickening tank. In the thickening tank, the sludge is separated from most of the water by gravity and then pumped to the sludge dewatering system to reduce the moisture content to 70%-80%. After that, it is transferred to the composting workshop, where lime is added for sterilization and sludge maturation. Then, aerobic bacteria are added, and through the degradation of microorganisms, the sludge is converted into organic fertilizer for sale, ultimately realizing the resource utilization of feed and excrement.

[0058] Among them, the high-efficiency sedimentation tank / device can treat water volumes of 1-500m³. 3 For water treatment capacities exceeding 500 m³ / h, an integrated system using corrosion-resistant carbon steel, fiberglass, 2205 / 2507 / 904L, or titanium materials is recommended. 3 When the flow rate is 1 / h, it is advisable to use a reinforced concrete structure tank to extend the service life of the equipment;

[0059] The length-to-width ratio of the primary and secondary reaction zones of the high-efficiency sedimentation tank / equipment is 1:1-1:2, and the designed retention time is 5-15 min, respectively.

[0060] The reagent added to the primary reaction zone of the high-efficiency sedimentation tank / equipment is one of the following: iron-based, aluminum-based, polyferric silicate-based, or polyaluminosilicate-based reagents.

[0061] The length-to-width ratio of the flocculation sedimentation zone in the high-efficiency sedimentation tank / equipment is 1:1-1:5, the designed surface loading rate is 0.5-2.5 m / h, and the hydraulic retention time is 1-2 h.

[0062] The inclined plates in the flocculation sedimentation zone of the high-efficiency sedimentation tank / equipment are made of PP, PE or other non-metallic materials and metal materials resistant to seawater chloride ion corrosion, such as 2205, 2507, 904L, and titanium.

[0063] The ratio of sludge return flow to influent flow in a high-efficiency sedimentation tank / equipment is 1:10-1:5.

[0064] The angle of the sludge collector should be 30-75°, and its volume should be 10%-30% of that of the high-efficiency sedimentation tank.

[0065] The sludge dewatering system of a high-efficiency sedimentation tank / equipment is one of the following: plate and frame filter press, screw press dewatering machine, or centrifugal dewatering machine;

[0066] (3) The effluent from the high-efficiency sedimentation tank overflows into the magnetic filler algae composite tank. The bottom of the tank is filled with gravel matrix, and magnetic filler modules are arranged intermittently in the tank. The modules are loaded with magnetic filler microparticles and are designed with reed / cattail ecological islands.

[0067] Through the slow-release and electron-promoting effects of iron in the magnetic filler Fe3O4, some reactive phosphate is physically removed, and the denitrification and phosphorus removal processes of microorganisms in the water are promoted. This utilizes the effects of microalgae on inorganic ions (such as NH4+) in the aquatic environment. + NO3 - NO2 - and H2PO4 - The microorganisms absorb nitrogen and phosphorus in wastewater, including organic pollutants such as urea (N and P). They decompose organic pollutants in the wastewater, releasing CO2 and producing organic acids, growth hormones, and inorganic salts. Microalgae absorb these substances through photosynthesis, consuming CO2 and releasing O2, thus increasing dissolved oxygen in the wastewater and promoting microbial metabolism. Simultaneously, the growth of reeds absorbs and assimilates nitrogen and phosphorus, consuming a considerable amount of these elements.

[0068] The main component of the magnetic filler is Fe3O4-oyster shell, which is formed by grinding and crushing waste oyster shells, then mixing them with Fe3O4 powder in a certain proportion and kneading them into balls. Fe3O4, as a magnetic material, contains both Fe(II) and Fe(III), and can slowly release Fe through hydrolysis. 2+ and Fe 3+ It directly participates in or promotes the denitrification and phosphorus removal reactions of microorganisms, and through its own electromagnetic properties, it can promote electron transfer between microorganisms, reduce energy consumption, and achieve a longer-term promoting effect on microbial growth.

[0069] Oyster shells in magnetic fillers, with calcium carbonate as their effective component, possess a porous structure and strong adsorption capacity, creating favorable conditions for biofilm adhesion and formation. The Fe3O4-oyster shell magnetic filler constructs a stable iron slow-release system, achieving Fe... 2+and Fe 3+ While enhancing nitrogen removal, it achieves a synergistic effect of biological and chemical phosphorus removal. Chemical phosphorus removal effectively reduces iron concentration and avoids secondary pollution caused by the addition of particles. Furthermore, iron is ubiquitous in the natural environment, has low toxicity, and is widely relied upon for cellular enzymatic reactions. Iron has multiple valence states, enabling it to continuously participate in redox reactions in the environment, transferring electrons and promoting biological metabolic reactions. In addition to participating in redox reactions, iron(III) oxide powder itself is magnetic, and the local magnetic field can also promote biological metabolic reactions.

[0070] Self-powered nano-aeration equipment is a new type of high-efficiency aeration facility. Its solar power generation device converts solar energy into electrical energy. Utilizing its unique internal structure and gas-generating mechanism, it can produce bubbles in water with diameters ranging from tens of nanometers to several micrometers, while traditional microporous aeration bubbles have diameters between 0.5-5 mm. The huge specific surface area and the "diffuse" movement of nanobubbles in water significantly improve the utilization rate of oxygen from the air. Compared with conventional microporous aeration, nano-aeration technology has unparalleled power efficiency. According to experimental calculations, the oxygen transfer rate of nano-aeration can reach 20-25%, which is 5 times the oxygen utilization rate of conventional microporous aeration.

[0071] Meanwhile, reeds can absorb large amounts of nitrogen and phosphorus elements during their growth, thus achieving the ecological removal of nitrogen and phosphorus. The effluent from the magnetic packing tank is filtered through an oyster dam before entering the ecological phosphorus removal tank.

[0072] The hydraulic retention time of the magnetic filler composite tank should be 24-72 hours, depending on the nitrogen and phosphorus content in the effluent.

[0073] Magnetic filler composite ponds should utilize existing aquaculture water bodies divided into ponds, newly built geotechnical ponds or reinforced concrete ponds, with gravel laid at the bottom, the gravel particles ranging from 1cm to 10cm.

[0074] Magnetic filler composite pond slope protection should be planted with local aquatic plants such as reeds and cattails to utilize the nitrogen and phosphorus absorption of plants to remove nitrogen and phosphorus;

[0075] In particular, the slope of the slope protection should be 1:3 to 1:1.3;

[0076] Microalgae are a type of autotrophic plant that is widely distributed on land and in the ocean, rich in nutrients, and has a high photosynthetic utilization rate; this invention patent preferably uses one of Chlorella vulgaris or Chlorella pulmonale.

[0077] Self-powered micro-nano aeration equipment is a common type of aeration equipment on the market, mainly used in the restoration and treatment of water bodies far from electrical connections.

[0078] The oyster dam is no less than 1.5m wide, no less than 2m high, and no less than 5m long. The foundation is made of reinforced concrete, and the two sides are made of perforated bricks.

[0079] Specifically, the oyster particles filled in the porous bricks of the oyster dam are 2-4 cm in diameter and are made from crushed oyster shells. The crushed oyster shells are then placed in a 20-mesh mesh bag and filled into the dam.

[0080] (4) The effluent after oyster dam filtration enters the ecological phosphorus removal pond. The bottom of the pond is covered with zeolite and volcanic rock. The pond contains a reed island guide wall and a phosphorus removal ecological substrate. The dissolved oxygen in the pond is 0-0.4 mg / L. At this time, denitrifying bacteria can use the organic matter in the water as an energy source and use the nitrate nitrogen from the aerobic pond as an electron acceptor to reduce the nitrate nitrogen to nitrogen gas, thereby ultimately achieving the removal of nitrogen from the water.

[0081] The phosphorus-removing ecological substrate possesses a high specific surface area and excellent adsorption performance, allowing it to float freely in water and form a three-dimensional structure of upper, middle, and lower layers, providing attachment and growth sites for microorganisms. Microorganisms accumulate on the surface of the ecological substrate, forming a biofilm. Simultaneously, due to the composite microenvironment of "aerobic-facultative-anaerobic" structure between the surface and interior of the biofilm, nitrification and denitrification processes can occur naturally, converting ionic nitrogen in the water into nitrogen gas that escapes from the system, reducing nitrogen levels in the water, inhibiting algal blooms, and reducing the release of endogenous pollutants. The installation and arrangement of the ecological substrate achieves microbial immobilization technology, preventing water flow from washing away effective microorganisms from the system, maintaining the number of effective microorganisms in the water, ensuring the stability and effectiveness of the microbial system, and contributing to water quality maintenance. Furthermore, the surface of the ecological substrate is coated with a highly efficient phosphorus-removing complexing agent, which specifically forms stable complexes with phosphorus, exhibiting strong phosphorus removal capabilities and high ecological safety.

[0082] After the effluent passes through the oyster dam (1mm-2mm particle size) to intercept residual suspended solids, all indicators meet the requirements for aquaculture wastewater discharge standards, and can be discharged in compliance with standards or recycled for replenishment of aquaculture farms.

[0083] The hydraulic retention time in an ecological phosphorus removal pond should be 24-72 hours, depending on the nitrogen and phosphorus content in the effluent.

[0084] Ecological phosphorus removal ponds should utilize existing aquaculture water bodies that have been divided into separate ponds, newly built geotechnical ponds, or reinforced concrete ponds, with the bottom of the ponds lined with zeolite and volcanic rock.

[0085] Zeolite and volcanic rock have a particle size of 1cm-5cm and a suitable ratio of 1:1-1:5. The microporous adsorption function of zeolite and volcanic rock is mainly utilized to provide attachment and growth sites for microorganisms.

[0086] The slope protection of the ecological phosphorus removal pond should be planted with local aquatic plants such as reeds and cattails to remove nitrogen and phosphorus by utilizing the nitrogen and phosphorus absorption of plants.

[0087] Specifically, the slope of the slope protection should preferably be 1:3 - 1:1.3;

[0088] The phosphorus removal ecological substrate is relatively common in the market and is often used in river restoration to enhance phosphorus removal. The typical specification parameters are shown in the following table:

[0089]

[0090] Example 1

[0091] The present invention was tested in a certain aquaculture enterprise in Linghai City, Jinzhou City. According to the seawater aquaculture tail water treatment process designed by the present invention, a sea cucumber seedling aquaculture tail water treatment system with a treatment capacity of 1 m 3 / h was constructed, adopting "magnetic biological high - efficiency flocculation sedimentation tank + magnetic filler composite pool + coarse oyster dam + ecological phosphorus removal pool + fine oyster dam". Due to the small treatment water volume, the system adopted an integrated device.

[0092] The inlet data of the seawater aquaculture tail water is shown in Table 2:

[0093] Table 2 Pollutant concentrations in seawater aquaculture tail water

[0094]

[0095] The volume of the temporary storage pool is 2 m3, and the hydraulic retention time is 2 h;

[0096] The magnetic biological high - efficiency sedimentation tank is made of fiberglass. The size of the first - stage dosing area is 0.25 m * 0.25 m * 2 m, the dosing agent is PAC, the dosing amount is 15 mg / L, and the hydraulic retention time is 7.5 minutes;

[0097] The size of the second - stage dosing area is 0.25 m * 0.25 m * 2 m, the magnetic powder dosing amount is 50 ppm; the dosing agent is anionic PAM, which is continuously dosed, the dosing amount is 3 mg / L, and the hydraulic retention time is 7.5 minutes;

[0098] The size of the sedimentation area is 1 m * 1 m * 2 m, the hydraulic retention time is 2 h, and the surface load is 1 m / h. The inclined plate material is PP.

[0099] The equipment size of the high - efficiency sedimentation tank is 1 m * 1.5 m * 3.2 m. Its supporting sludge dewatering device is a spiral press filter.

[0100] The magnetic filler bacteria - algae composite pool is separated from the idle pool of the aquaculture enterprise. The hydraulic retention time is 24 h, the amount of magnetic filler used is 1 m3, and the main component of the magnetic filler is Fe3O4 - oyster shell, which is formed by grinding and crushing waste oyster shells and then kneading them into balls with Fe3O4 powder in a mass ratio of 1:1.

[0101] The microalgae added is Chlorella vulgaris, with an initial addition rate of 50 g / h, and continuous addition starting from the water inlet.

[0102] One self-powered nano-aeration device with a power of 500W and an aeration rate of 300L / min.

[0103] The coarse oyster bark measures 5m x 1.5m x 2m, with oysters measuring 3cm-4cm in diameter.

[0104] The hydraulic retention time of the ecological phosphorus removal pond is 30 hours, and the amount of phosphorus removal ecological substrate used is 5 m2.

[0105] The oyster bark measures 5m x 1.5m x 2m, and the oysters have a diameter of 1cm-2cm.

[0106] After the equipment was installed, debugged, and the effluent met the standards, water samples were taken for testing after 3-5 days of operation. The effluent consistently met the Class I standard of Liaoning Province's marine aquaculture tailwater control standards. The effluent indicators are shown in Table 3.

[0107] Table 3 System Effluent Water Quality Indicators

[0108]

[0109] Example 2

[0110] This invention has been industrially applied in an aquaculture enterprise in Rizhao City. Based on the seawater aquaculture wastewater treatment process designed according to this invention, a treatment system with a capacity of 50m³ has been constructed. 3 The / h sea cucumber seedling aquaculture tailwater treatment system adopts the process of "magnetic biological high-efficiency flocculation sedimentation tank + magnetic filler composite tank + coarse oyster dam + ecological phosphorus removal tank + fine oyster dam". The system adopts a combination of equipment and geotechnical tanks. The magnetic biological high-efficiency flocculation sedimentation tank adopts fiberglass equipment (see details below), while the magnetic filler composite tank and ecological phosphorus removal tank adopt geotechnical tanks, utilizing the existing water tanks of the aquaculture enterprise.

[0111] The influent data for aquaculture wastewater from the enterprise are shown in Table 4:

[0112] Table 4 Concentration of pollutants in marine aquaculture wastewater

[0113]

[0114] The system's temporary storage tank has a volume of 100 m3 and a hydraulic retention time of 2 hours;

[0115] The magnetic biological high-efficiency sedimentation tank in the system is made of fiberglass. The size of the primary dosing area is 2.5m*2.5m*2m. The dosing agent is PAC, the dosage is 15mg / L, and the hydraulic retention time is 15 minutes.

[0116] The size of the secondary chemical dosing area is 2.5m * 2.5m * 2m, the magnetic powder dosage is 50 ppm; the chemical agent added is anionic PAM, the dosage is 1 mg / L, the hydraulic retention time is 15 minutes, and the dosing is continuous dosing, interlocked with the inlet water pump. When the inlet water pump stops running, the chemical dosing device stops running;

[0117] The size of the sedimentation area is 5m * 10m * 2m, the retention time is 2h, the surface loading is 1m / h, and the inclined plate material is PP.

[0118] The size of the high - efficiency sedimentation equipment is 127.5m * 5.0m * 3.2m. Its supporting sludge dewatering device is a spiral screw dehydrator made of 2205 material, and the scale of dry sludge treatment is 70 kg / h.

[0119] The magnetic filler bacteria - algae composite pool is separated from the idle pool of the aquaculture enterprise. The hydraulic retention time is 26h, the amount of magnetic filler used is 20m3. The main component of the magnetic filler is Fe3O4 - oyster shell, which is formed by grinding and pulverizing waste oyster shells and then kneading them into balls with Fe3O4 powder in a mass ratio of 1:2.

[0120] The micro - algae added is Chlorella vulgaris, the initial dosage is 50g / h, and the dosing is continuous for one week; there are 25 sets of self - powered nano - aeration devices, the power of each set is 500w, and the aeration volume is 300L / min.

[0121] The size of the coarse oyster dam is 5m * 1.5m * 2m, and the oyster particle size is 3cm - 4cm;

[0122] The hydraulic retention time of the ecological phosphorus removal pool is 33h, and the amount of ecological phosphorus removal base used is 100m2;

[0123] The size of the fine oyster dam is 5m * 1.5m * 2m, and the oyster particle size is 1cm - 2cm.

[0124] The system was debugged for 2 months and 15 days until the effluent was qualified. After running for 3 - 5 days, water samples were taken for detection, and the effluent stably reached the first - level standard of the seawater aquaculture tail water control standard in Liaoning Province. The effluent indicators are shown in Table 5:

[0125] Table 5 System effluent water quality indicators

[0126]

[0127] This invention presents a method for the efficient treatment of aquaculture wastewater using a magnetic biological flocculation coupled with bacterial and algal composite treatment. This method maximizes and efficiently utilizes the wastewater for resource recovery, achieving compliant discharge of wastewater and resource utilization of feed with a relatively small system footprint and low energy consumption. The seawater aquaculture wastewater treatment system constructed according to this process concept features a small footprint (reduced by approximately 50%-60% compared to conventional processes), high pollutant treatment efficiency (N and P treatment efficiency increased by approximately 80%-90%), low system energy consumption and low carbon emissions, valuable wastewater, and resource-recoverable materials.

[0128] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for treating aquaculture wastewater using a magnetic biological high-efficiency flocculation coupled with bacterial-algae composite treatment, characterized in that, Includes the following steps: (1) The discharged seawater aquaculture wastewater is collected through pipelines and enters a temporary storage tank; the hydraulic retention time of the temporary storage tank is 2-4 hours; (2) The effluent in the temporary storage tank enters the magnetic biological high-efficiency flocculation sedimentation tank for flocculation and sedimentation; the magnetic biological high-efficiency flocculation sedimentation tank is divided into a chemical dosing reaction zone, a flocculation sedimentation zone, a sludge return pump or external pump, a sludge collector and a supporting chemical dosing device. (3) After flocculation and sedimentation, the tailwater enters the magnetic packing algae and bacteria composite tank for nitrogen and phosphorus removal. Part of the sludge obtained from flocculation and sedimentation is transported to the inlet through pipeline and mixed with the incoming water. The ratio of sludge return flow to inlet flow in the magnetic biological high-efficiency flocculation sedimentation tank is 1:10-1:

5. (4) The effluent from the bacterial-algae composite pond is filtered by a modified oyster dam and then enters the ecological phosphorus removal pond. The effluent from the ecological phosphorus removal pond is then discharged after the residual suspended solids are intercepted by a modified fine oyster dam. In step (2), the chemical reaction zone in the magnetic biological high-efficiency flocculation sedimentation tank is divided into a primary reaction zone and a secondary reaction zone. Flocculant is added in the primary reaction zone, and flocculant and magnetic powder are added in the secondary reaction zone. The length-to-width ratio of the primary and secondary reaction zones is 1:1 to 1:2, and the hydraulic retention time is 5-15 min. The flocculant in the primary reaction zone is one of the following: iron-based, aluminum-based, polyferric silicate-based, or polyaluminum silicate-based agents. It is continuously added at a dosage of 10-15 mg / L. The flocculant in the secondary reaction zone is anionic PAM. It is continuously added at a dosage of 1-3 mg / L. The magnetic powder in the secondary reaction zone is Fe3O4 powder. It is continuously added at a dosage of 1-50 ppm. In step (3), the bottom of the magnetic filler algae composite pond is filled with gravel matrix, and magnetic filler modules, microalgae and aeration devices are arranged intermittently in the pond. The modules are loaded with magnetic filler. The hydraulic retention time of the composite pond is 24-72h. The main component of the magnetic filler is Fe3O4-oyster shell, which is formed by grinding and crushing waste oyster shells, and then mixing them with Fe3O4 powder in a mass ratio of 1:1-1:2 to form balls. In step (2), the flocculation sedimentation zone of the magnetic biological high-efficiency flocculation sedimentation tank contains microbial flocs and is designed with biological sludge return.

2. The method as described in claim 1, characterized in that, In step (2), the magnetic biological high-efficiency flocculation sedimentation tank treats 1-50 m³ of water. 3 The treatment capacity is greater than 50m³ / h and can be achieved using one of the following materials: carbon steel (corrosion resistant), fiberglass, 2205, 2507, 904L, or titanium. 3 When the flow rate is / h, a reinforced concrete structure pool is used.

3. The method as described in claim 1, characterized in that, The sedimentation zone has an aspect ratio of 1:1 to 1:5, a surface loading rate of 0.5 to 2.5 m / h, and a hydraulic retention time of 1 to 2 h.

4. The method as described in claim 1, characterized in that, The microalgae selected are either Chlorella vulgaris or Chlorella vulgaris, with an addition rate of 30-50 g / h, and continuous addition for 7-15 days.

5. The method as described in claim 1, characterized in that, In step (4), the modified oyster dam has a width of not less than 1.5m, a height of not less than 2m, and a length of not less than 5m. The foundation is made of reinforced concrete and the two sides are made of porous bricks. The oyster particles filled in the porous bricks of the modified oyster dam have a particle size of 2-4cm. The oyster particles in the modified fine oyster dam have a particle size of 1-2cm.

6. The method as described in claim 1, characterized in that, In step (4), the ecological phosphorus removal pond is an earthen pond with zeolite and volcanic rock lining the bottom. The pond contains a reed-covered flow-guiding wall and a phosphorus removal ecological substrate. The dissolved oxygen level in the pond is 0-0.4 mg / L. The hydraulic retention time of the ecological phosphorus removal pond is 24-72 hours. The zeolite and volcanic rock have a particle size of 1-5 cm and a ratio of 1:1-1:

5. The amount of phosphorus removal ecological substrate used is 5-100 mg / L. 2 .

7. The method as described in claim 1, characterized in that, The amount of magnetic filler used is 1-20m. 3 .

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