A method for denitrification and dephosphorization of mariculture tail water

Abstract

The application provides a seawater breeding tail water denitrification and dephosphorization method, and relates to the technical field of seawater breeding tail water treatment. The seawater breeding tail water is efficiently purified through a three-stage treatment process of pre-enrichment conditioning, magnetic-assisted fluidized bed denitrification and anaerobic-aerobic alternate dephosphorization by using a magnetic micro-electrolysis carrier. The carrier has a gradient-pore-size core layer and a phosphatized modified magnetic protective shell layer double-layer structure. The core layer has a micro-electrolysis function and can continuously release ferrous ions to strengthen denitrification and dephosphorization. The magnetic shell layer has phosphorus absorption and easy separation characteristics. Under the assistance of a magnetic field, the carrier is gathered to form a high-concentration reaction zone, thereby improving the treatment efficiency. The carrier can be recycled and reused through magnetic separation, and has the advantages of high treatment efficiency, low operation cost, simple operation and the like.

Description

Technical Field

[0001] This invention relates to the field of marine aquaculture wastewater treatment technology, and in particular to a method for removing nitrogen and phosphorus from marine aquaculture wastewater. Background Technology

[0002] With the rapid development of mariculture, environmental pollution caused by aquaculture wastewater discharge has become increasingly prominent. Mariculture wastewater contains high concentrations of nitrogen, phosphorus nutrients, and organic matter; direct discharge can lead to eutrophication and frequent red tides in marine areas. Currently used biological methods for treating mariculture wastewater suffer from difficulties in screening salt-tolerant bacteria, low treatment efficiency, and large land area requirements. While chemical methods offer better treatment results, they are costly and prone to secondary pollution. Micro-electrolysis technology can effectively enhance nitrogen and phosphorus removal, but traditional micro-electrolysis packing materials are prone to passivation and failure in high-salt environments and are difficult to recycle and regenerate.

[0003] Therefore, it is of great significance to develop a nitrogen and phosphorus removal technology that is suitable for high-salinity seawater aquaculture wastewater, has high treatment efficiency, and can be operated sustainably. Summary of the Invention

[0004] The first aspect of this invention is to provide a biocoupler for denitrification and phosphorus removal in marine aquaculture tailwater. The carrier is spherical and includes, from the outside to the inside, a protective shell layer with a thickness of 0.3 to 0.5 mm and a micro-electrolysis core layer with a diameter of 2.1 to 2.9 mm. The core layer has a gradient pore size structure, with the pore size gradually increasing from the inside to the outside: the pore size in the inner layer is 15~40 μm, accounting for 20~30% of the total pore volume; the pore size in the middle layer is 50~120 μm, accounting for 40~50% of the total pore volume; and the pore size in the outer layer is 150~300 μm, accounting for 25~35% of the total pore volume.

[0005] Preferably, the magnetic protective shell comprises, by weight: Phosphorylated magnetite nanoparticles, with a particle size of 20-50 nm, were prepared by the following method: Fe3O4 nanoparticles were dispersed in an ethanol-water mixed solution, triethanolamine was added as a stabilizer, and phosphoric acid solution was added dropwise at 60-70℃ for 4-6 h to form Fe-OP chemical bonds on the magnetite surface. The phosphorylated magnetite had an adsorption capacity of 32-38 mg / g for phosphate and maintained superparamagnetism with a coercivity of <5 Oe. 16-18 parts of polyvinyl alcohol, with a degree of polymerization of 1750±50; 6-8 parts of nano-silica with a particle size of 10-20 nm; 2.5 to 3.5 parts of dimethyl diallyl ammonium chloride monomer.

[0006] Preferably, the micro-electrolysis core layer comprises, by weight: 48-52 parts of zero-valent iron powder, 24-28 parts of activated carbon powder, 12-15 parts of nano-magnetite, and 8-10 parts of copper powder. The zero-valent iron, copper powder, and activated carbon constitute a galvanic cell system, wherein iron acts as the anode to provide electrons, copper acts as the cathode to accept electrons, and activated carbon acts as a conductive medium to transfer electrons and provide a large specific surface area. The nano-magnetite enhances the magnetic response performance of the carrier on the one hand, and acts as a catalyst to promote the micro-electrolysis reaction on the other hand.

[0007] Preferably, the method for preparing the carrier includes the following steps: S1. Weigh out 1 / 3 of the zero-valent iron powder, activated carbon powder, nano magnetite, and copper powder according to the formula ratio, mix them evenly, add 20~35 μm calcium carbonate powder, and stir evenly; dissolve the bentonite-based binder in water to prepare an 8% solution, and slowly add it to the above mixture while stirring, controlling the moisture content of the mixture to be 19%~21%, so that it forms a plastic mud-like material; shape the mud into an inner core sphere with a diameter of 2.1~2.3 mm through a base, and air dry at room temperature to form a semi-dry state with certain strength but not completely hardened; Then, weigh out 1 / 3 of the zero-valent iron powder, activated carbon powder, nano-magnetite, and copper powder according to the formula ratio, mix them evenly, add 60~100 μm ammonium carbonate particles, and stir evenly; dissolve the bentonite-based binder in water to prepare a 6% solution (the concentration should be slightly lower to facilitate coating), and prepare coating slurry A with a solid content of 15%~18%; spray or dip coating slurry A onto the semi-dry inner core sphere to achieve a middle layer thickness of 0.15~0.25 mm, and dry it to a moisture content of 10% after coating; Then, weigh out 1 / 3 of the zero-valent iron powder, activated carbon powder, nano magnetite, and copper powder according to the formula ratio, mix them evenly, add 120~250 μm polyethylene glycol 2000 particles, and stir evenly; dissolve the bentonite-based binder in water to prepare a 6% solution, and prepare coating slurry B with a solid content of 15%~18%; place the carrier with the middle layer again in the fluidized bed coating equipment, and evenly spray or dip the outer layer slurry. By controlling the coating time, the outer layer thickness reaches 0.15~0.25 mm, and finally the total diameter of the core layer reaches 2.5~3.0 mm; The three-layer coated carrier was air-dried at room temperature until the moisture content was less than 5%. Then, the temperature was increased to 120°C at a rate of 5°C / min and held for 1 h to completely remove residual moisture. Next, the temperature was increased to 280°C at a rate of 3°C / min and held for 1.5 h to partially carbonize the adhesive and decompose the ammonium carbonate. Finally, the temperature was increased to 420°C at a rate of 2°C / min and held for 2 h to completely decompose the pore-forming agent and sinter the carrier. The carrier was then allowed to cool naturally to room temperature and soaked in 0.08 mol / L hydrochloric acid solution for 30 min to remove the surface oxide layer. Then, the carrier was rinsed with deionized water until the pH value was 6.5~7.0. Finally, the carrier was dried under nitrogen protection for later use. S2. Prepare the shell coating mixture by adding phosphorylated nano-Fe3O4, polyvinyl alcohol, nano-SiO2, and dimethyl diallyl ammonium chloride monomer to deionized water and ultrasonically dispersing it. The solid content of the mixture is controlled at 15%~18%. The carrier obtained in S1 is placed in a fluidized bed spray coating system after surface activation treatment. The shell coating mixture is uniformly sprayed onto the surface of the carrier. The spraying rate and drying temperature are controlled to allow the shell layer to accumulate gradually, forming a uniform shell layer with a thickness of 0.3~0.5 mm. During the coating process, 4% calcium chloride atomized liquid is sprayed intermittently for layered cross-linking and curing. The total coating time is 90~120 min. After coating, the carrier is soaked in 4% calcium chloride solution for 60 min for final curing to form a stable three-dimensional network structure. The surface activation treatment method is as follows: The support is immersed in a hydrogen peroxide solution with pH=10 for 25-35 min to form hydroxyl (-OH) active sites on the surface; the support is immersed in an ethanol solution containing 2% KH-550 and treated at 55-65℃ for 1.5-2.5 h to allow the -Si(OC2H5)3 end of the silane molecule to react with the surface hydroxyl groups, leaving -NH2 groups; the support is rinsed with anhydrous ethanol and dried at 80℃ for 1 h. S3. Rinse the carrier surface thoroughly with sterile artificial seawater to remove residual calcium chloride and uncured components, then dry.

[0008] The second aspect of this invention is to provide a method for denitrification and phosphorus removal from marine aquaculture tailwater, comprising three stages: pre-enrichment and conditioning, magnetically assisted fluidized bed denitrification, and alternating anaerobic and aerobic phosphorus removal.

[0009] The first stage is the pre-enrichment and conditioning stage (hydraulic retention time is 2-4 h): The aforementioned carrier is added to the pretreatment tank at a filling ratio of 10%-15%, along with a water conditioner. This conditioner is a mixture of sodium bicarbonate (alkalinity adjuster) and disodium hydrogen phosphate (pH buffer), mixed at a mass ratio of 3:1. The dosage is determined based on the alkalinity of the influent, generally 50-100 mg / L, to adjust the influent pH to 7.8-8.2. A permanent magnet grid with a magnetic field strength of 0.25-0.35 T is installed at the bottom of the pretreatment tank. The grid consists of neodymium iron boron permanent magnets spaced at intervals of 5... The carrier is arranged in a cm grid pattern. Under the influence of a magnetic field, the carrier aggregates towards the grid area, forming a local high-concentration carrier zone, which improves the contact efficiency between the carrier and the wastewater. The zero-valent iron in the core layer of the carrier begins to react with dissolved oxygen and water molecules in the water in a galvanic cell reaction. The iron acts as the anode and is oxidized to release ferrous ions. The released ferrous ions combine with phosphate ions in the water under weakly alkaline conditions, forming a magnetic ferrous phosphate-magnetite composite precipitate on the phosphorylated Fe3O4 surface of the carrier shell. The positively charged surface of the carrier shell adsorbs negatively charged suspended solids and organic colloids in the water, improving the turbidity of the water.

[0010] The second stage is the magnetically assisted fluidized bed denitrification stage (hydraulic retention time of 8-12 h): Pretreated wastewater is introduced into the fluidized bed reactor with a carrier filling ratio of 20%-30%. The reactor is divided into two functional zones: a pre-nitrification zone and a post-denitrification zone. The pre-nitrification zone accounts for 35%-40% of the total reactor length, and the post-denitrification zone accounts for 60%-65%. In the denitrification zone, carbon sources are supplemented according to the influent C / N ratio to maintain it at 4-6. An electromagnet array with a magnetic field strength of 0.12-0.18 T is installed outside the nitrification zone, and the dissolved oxygen concentration in the nitrification zone is controlled to be 3.5-4.5 T through aeration. mg / L, and add aerobic nitrifying bacteria agent, which is a mixed agent of Nitrosomonas and Nitrobacterium, mixed at an effective viable count of 1:1, at a dosage of 0.5‰~1‰ of water (mass-volume ratio, based on the mass of the agent / volume of water, g / L). The main function of the nitrification zone is to oxidize ammonia nitrogen in wastewater to nitrate nitrogen, providing substrate for subsequent denitrification. An electromagnet array with a magnetic field strength of 0.05~0.08 T is set outside the denitrification zone, and the dissolved oxygen concentration in the denitrification zone is maintained at 0.2~0.5 by controlling the aeration rate. Under anoxic conditions of mg / L, heterotrophic denitrifying bacteria are added to the denitrification zone. These bacteria are a mixture of *Paracoccus denitrifyingus* and *Thiobacillus denitrifyingus*, mixed at a viable ratio of 2:1, with a dosage of 1‰~2‰ of the water (mass-volume ratio, calculated as bacteria mass / water volume, g / L). The carrier circulates with the water flow in the fluidized bed. Under the influence of the magnetic field, the movement trajectory of the carrier changes, increasing the opportunities for collision and contact between carriers and between the carrier and wastewater. The core layer of the carrier continuously releases ferrous ions. This autotrophic denitrification process can reduce the organic carbon source requirement by 40%~50%. The microcurrent generated by the micro-electrolysis core layer, under the synergistic effect of the external magnetic field, accelerates the denitrification rate. The nitrifying bacteria agent is a mixed agent of salt-tolerant Nitrosomonas and Nitrobacterium, which maintains more than 70% activity at a salinity of 25‰ to 35‰ after being acclimated to a salinity gradient. The denitrifying bacteria agent is a marine-derived strain or a strain acclimated to high salinity.

[0011] The third stage is the alternating anaerobic and aerobic phosphorus removal stage: the denitrification effluent enters the phosphorus removal reactor with a carrier filling ratio of 15% to 20%; the phosphorus removal reactor adopts a sequencing batch operation mode, alternating between the two processes of anaerobic phosphorus release and aerobic phosphorus uptake. During the anaerobic phosphorus release stage, the dissolved oxygen concentration is <0.3 mg / L, and the anaerobic time is 2-3 h. Adding an polyphosphate-accumulating bacteria (a mixture of sodium acetate and glucose at a mass ratio of 1:1) increases the influent COD concentration by 80-120 mg / L. Under anaerobic conditions, polyphosphate-accumulating bacteria decompose polyphosphates within themselves to release energy, while simultaneously absorbing external carbon sources to synthesize polyhydroxy fatty acids for energy storage. Phosphorus is released into the water in the form of orthophosphate. During the aerobic phosphorus uptake stage, aeration is used to achieve a dissolved oxygen concentration of 2.5-3.5 mg / L, and the aerobic time is 2.5-3.5 h. Under aerobic conditions, polyphosphate-accumulating bacteria oxidize and decompose the polyhydroxy fatty acids stored within themselves to obtain energy, and excessively absorb phosphates from the water to synthesize polyphosphates for storage within the bacteria, thus achieving biological phosphorus removal. Meanwhile, the ferrous ions released by the carrier core layer in the previous stage are oxidized to ferric ions. The ferric ions combine with phosphate ions in the water to form ferric phosphate precipitate, thus achieving chemical phosphorus removal. The effluent after phosphorus removal enters the sedimentation tank for sludge-water separation. The supernatant meets the discharge standards or is reused. The precipitated sludge and carrier mixture enter the magnetic separation device for separation.

[0012] Preferably, after 50 to 80 days of continuous use, the nitrogen and phosphorus removal efficiency of the carrier gradually decreases due to the consumption of zero-valent iron in the micro-electrolysis core layer and the decline in bacterial activity. When the total nitrogen removal rate is <75% or the total phosphorus removal rate is <85%, the carrier is regenerated.

[0013] The carrier regeneration method is as follows: Take out the carrier, rinse it with clean water to remove the sludge and biofilm attached to the surface, and then soak it in a 0.1 mol / L hydrochloric acid solution for 4-6 h to remove the inorganic precipitates and oxide layer on the carrier surface. Then rinse the carrier repeatedly with clean water until neutral, and soak the carrier in a 0.03 mol / L hydrogen peroxide solution for 2-3 h to further remove organic pollutants in the carrier pores. Rinse the carrier again with clean water until neutral.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows: The carrier of this invention adopts a gradient pore size design with differentiated pore size distribution in the inner and outer layers, which not only ensures space for microbial attachment and growth but also improves mass transfer efficiency. The phosphorylation-modified magnetic shell has a high adsorption capacity for phosphorus and facilitates magnetic separation and recovery. Thirdly, the micro-electrolysis core layer continuously releases ferrous ions, synergistically achieving autotrophic denitrification and chemical phosphorus removal, reducing carbon source requirements by 40% to 50%. The magnetic field assists in improving the carrier aggregation and collision efficiency, enhancing the treatment effect. The carrier can be regenerated through acid washing and oxidation treatment, with a long service life and low operating cost.

[0015] This invention achieves a total nitrogen removal rate of 82%~88% and a total phosphorus removal rate of 88%~93%, with stable and compliant effluent quality. It is suitable for treating marine aquaculture tailwater and other high-salinity wastewater. Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Unless otherwise specified, all experiments were repeated three times, and the results are expressed as mean ± standard deviation. All raw materials were commercially available.

[0017] Example 1 I. Preparation of the carrier 1. Preparation of phosphorylated nanomagnetite 20 g of Fe3O4 nanoparticles (30 nm in diameter) were dispersed in 500 mL of an ethanol-water mixture (volume ratio 3:1). 15 mL of triethanolamine was added as a stabilizer, and 30 mL of 85% phosphoric acid solution was slowly added dropwise at 65 °C for 5 h to form Fe-OP chemical bonds on the magnetite surface. After the reaction, the surface was washed 5 times alternately with deionized water and ethanol, and then dried under vacuum at 60 °C for 12 h to obtain phosphorylated magnetite nanoparticles with an adsorption capacity of 35 mg / g for phosphate and a coercivity of 3.2 Oe. 2. Preparation of the micro-electrolysis core layer S1-1: Weigh out 8 g of zero-valent iron powder (200 mesh) and activated carbon powder (specific surface area 1200 m²) according to the formula. 2 4 g of ( / g) nano magnetite, 2 g of copper powder (300 mesh), and 1.33 g of copper powder were mixed evenly. 1.2 g of 28 μm calcium carbonate powder was added and stirred evenly. Bentonite-based binder (montmorillonite content ≥85%) was dissolved in water to prepare an 8% solution, which was slowly added to the above mixture to form a plastic mud-like material. Granulation was performed to obtain inner core spheres with a diameter of 2.2 mm, and the mixture was air-dried at room temperature for 24 h. S1-2: Weigh out 8 g of zero-valent iron powder, 4 g of activated carbon powder, 2 g of nano-magnetite, and 1.33 g of copper powder according to the formula, mix them evenly, add 1.5 g of 80 μm ammonium carbonate particles, and stir evenly; dissolve the bentonite-based binder in water to prepare a 6% solution, and make coating slurry A with a solid content of 16%; place the semi-dry inner core sphere in a fluidized bed coating device, spray coating slurry A evenly, control the thickness to 0.20 mm, and dry until the moisture content is 10%; S1-3: Weigh out 8 g of zero-valent iron powder, 4 g of activated carbon powder, 2 g of nano magnetite, and 1.34 g of copper powder according to the formula, mix them evenly, add 2.0 g of 180 μm polyethylene glycol 2000 particles, and stir evenly; dissolve the bentonite-based adhesive in water to prepare a 6% solution, and make coating slurry B with a solid content of 16%; place the carrier with the middle layer again in the fluidized bed coating equipment, and spray the outer layer slurry evenly, controlling the outer layer thickness to be 0.20 mm, so that the total diameter of the core layer reaches 2.6 mm; S1-4: The three-layer coated carrier is air-dried at room temperature until the moisture content is <5%; then the temperature is increased to 120℃ at a rate of 5℃ / min and held for 1 h, then increased to 280℃ at a rate of 3℃ / min and held for 1.5 h, and finally increased to 420℃ at a rate of 2℃ / min and held for 2 h; after naturally cooling to room temperature, it is soaked in 0.08 mol / L hydrochloric acid solution for 30 min, rinsed with deionized water until pH 6.8, and dried under nitrogen protection for later use; 3. Preparation of the magnetic protective shell S2: Prepare the shell coating mixture by adding 40 g of phosphorylated nano-Fe3O4, 17 g of polyvinyl alcohol (degree of polymerization 1750), 7 g of nano-SiO2 (particle size 15 nm), and 3 g of dimethyl diallyl ammonium chloride monomer to 350 mL of deionized water and ultrasonically dispersing for 30 min. Place the core layer carrier in a fluidized bed spray coating system and uniformly spray the shell mixture onto the surface of the surface-activated carrier. Control the spraying rate at 2 mL / min and the drying temperature at 50℃ to form a uniform shell layer with a thickness of 0.4 mm. The surface activation treatment method is as follows: immerse the carrier in a hydrogen peroxide solution with pH=10 for 30 min to form hydroxyl (-OH) active sites on the surface; immerse the carrier in an ethanol solution containing 2% KH-550 and treat at 60℃ for 2 h; rinse with anhydrous ethanol and dry at 80℃ for 1 h; during the coating process, spray 4% calcium chloride atomized liquid every 15 min for layered cross-linking and curing, with a total coating time of 100 minutes. min; after coating, soak the carrier in 4% calcium chloride solution for 60 min for final curing; S3: rinse the surface of the carrier thoroughly with sterile artificial seawater and dry at 50℃ for 12 h to obtain the finished carrier.

[0018] II. Treatment of Seawater Aquaculture Wastewater Influent water quality: salinity 30‰, total nitrogen 100 mg / L, ammonia nitrogen 75 mg / L, total phosphorus 10 mg / L, COD 250 mg / L, pH 7.5, temperature 25℃; Phase 1: Pre-enrichment and conditioning. 60 L of carrier material was added to the pretreatment tank (effective volume 500 L), with a carrier filling ratio of 12%. 75 mg / L of water conditioner (a mixture of sodium bicarbonate and disodium hydrogen phosphate at a mass ratio of 3:1) was added to adjust the influent pH to 8.0. A permanent magnet grid with a magnetic field strength of 0.30 T was installed at the bottom of the pretreatment tank. The grid consisted of neodymium iron boron permanent magnets arranged at 5 cm intervals. The hydraulic retention time was 3 hours. The second stage: Magnetic-assisted fluidized bed denitrification. Pretreated wastewater is introduced into a fluidized bed reactor (effective volume 1000 L), with a carrier filling ratio of 25%. The reactor is divided into a pre-nitrification zone (40% of the length) and a post-denitrification zone (60% of the length). Nitrification zone: An external electromagnet array with a magnetic field strength of 0.15 T is installed, aeration controls the dissolved oxygen concentration to 4.0 mg / L, and 0.8‰ of nitrifying bacteria (a 1:1 mixture of Nitrosomonas and Nitrifying Bacillus) is added. Denitrification zone: An external electromagnet array with a magnetic field strength of 0.06 T is installed, controlling the dissolved oxygen concentration to 0.5 mg / L, with an influent C / N ratio of 5. 1.5‰ of denitrifying bacteria (a 2:1 mixture of Paracoccus denitrifying and Thiobacillus denitrifying) is added; hydraulic retention time is 10 hours. The third stage: Anaerobic and aerobic alternating phosphorus removal and denitrification effluent enters the phosphorus removal reactor (effective volume 600 L), with a carrier filling ratio of 18%; a sequencing batch reactor (SBR) operation mode is adopted; anaerobic phosphorus release stage: dissolved oxygen <0.3 mg / L, anaerobic time 2.5 h, with the addition of an synergist (sodium acetate and glucose mixed at a mass ratio of 1:1) to increase the influent COD concentration by 100 mg / L; aerobic phosphorus uptake stage: dissolved oxygen 3.0 mg / L, aerobic time 3.0 h; total hydraulic retention time 18.5 h.

[0019] Example 2 The difference from Example 1 is that: the thickness of the magnetic protective shell is 0.3 mm, the diameter of the micro-electrolysis core layer is 2.1 mm; the inner layer is 15-40 μm (accounting for 26% of the total pore volume), the middle layer is 50-120 μm (accounting for 44% of the total pore volume), and the outer layer is 150-300 μm (accounting for 30% of the total pore volume); the content of phosphorylated nano Fe3O4 is 38 parts, polyvinyl alcohol is 16 parts, nano SiO2 is 8 parts, and dimethyl diallyl ammonium chloride monomer is 3.5 parts.

[0020] Example 3 The difference from Example 1 is as follows: the thickness of the magnetic protective shell is 0.5 mm, the diameter of the micro-electrolysis core layer is 2.9 mm; the pore size of the inner region is 35 μm (accounting for 25% of the total pore volume), the pore size of the middle region is 100 μm (accounting for 45% of the total pore volume), and the pore size of the outer region is 250 μm (accounting for 30% of the total pore volume); the content of phosphorylated nano Fe3O4 is 42 parts, polyvinyl alcohol is 18 parts, nano SiO2 is 6 parts, and dimethyl diallyl ammonium chloride monomer is 2.5 parts; the magnetic field strength in the pre-enrichment conditioning stage is 0.35 T, the magnetic field strength in the nitration zone is 0.18 T, and the magnetic field strength in the denitration zone is 0.08 T.

[0021] Example 4 The difference from Example 1 is as follows: the carrier filling ratio is adjusted to: 10% for the pre-enrichment stage, 20% for the fluidized bed denitrification stage, and 15% for the phosphorus removal stage; the length of the nitrification zone accounts for 35% of the total reactor length, and the length of the denitrification zone accounts for 65%; the water conditioner dosage is 50 mg / L, and the influent pH is adjusted to 7.8; the total hydraulic retention time is 14.5 h (2 h for pre-enrichment, 8 h for denitrification, and 4.5 h for phosphorus removal, of which 2 h is anaerobic and 2.5 h is aerobic).

[0022] Example 5 The difference from Example 1 is as follows: the carrier filling ratio is adjusted to: 15% for the pre-enrichment stage, 30% for the fluidized bed denitrification stage, and 20% for the phosphorus removal stage; the dosage of nitrifying bacteria is 1‰, and the dosage of denitrifying bacteria is 2‰; the dosage of water conditioner is 100 mg / L, and the pH of the influent is adjusted to 8.2; the total hydraulic retention time is 20.5 h (4 h for pre-enrichment, 12 h for denitrification, and 4.5 h for phosphorus removal, of which 2 h is anaerobic and 2.5 h is aerobic).

[0023] Comparative Example 1 The difference from Example 1 is that: a gradient aperture structure is not used, the core layer aperture is uniformly 80-100 μm, and other conditions are the same.

[0024] Comparative Example 2 The difference from Example 1 is that the magnetic protective shell does not use phosphorylated modified nano-magnetite, but directly uses unmodified ordinary Fe3O4, while other conditions are the same.

[0025] Comparative Example 3 The difference from Example 1 is that no magnetic field auxiliary system is set up (the pretreatment tank is not equipped with a permanent magnet grid, and the fluidized bed reactor is not equipped with an electromagnet array), while other conditions are the same.

[0026] Comparative Example 4 The difference from Example 1 is that the micro-electrolysis core layer does not use a layered preparation process, but rather all raw materials are mixed at once and formed as a whole. The core layer has no gradient pore structure, while other conditions are the same.

[0027] Comparative Example 5 The difference from Example 1 is that only a two-stage treatment process (fluidized bed denitrification and phosphorus removal stage) is used, omitting the pre-enrichment and conditioning stage, while other conditions are the same.

[0028] The material properties obtained from each embodiment and comparative example were tested using conventional methods, and the results are shown in Tables 1-3.

[0029] Table 1 Comparison of processing effects of different embodiments and comparative examples

[0030] Note: Different letters in the same column indicate significant differences (P<0.05), while the same letter indicates no significant differences (P≥0.05).

[0031] Table 2. Treatment effect of the carrier under different salinity conditions

[0032] Note: The influent contained 100 mg / L total nitrogen, 10 mg / L total phosphorus, and 250 mg / L COD, using the process conditions of Example 1.

[0033] The treatment effects of Examples 2-5 under the same salinity gradient conditions showed the same trend as that of Example 1. That is, as the salinity increased from 25‰ to 35‰, the total nitrogen removal rate, total phosphorus removal rate and COD removal rate all showed a gradual decreasing trend, but the decrease was small. The removal rates of each example under different salinity conditions did not differ by more than 3%, indicating that the carrier and process of the present invention have stable treatment effects in the salinity range of 25‰ to 35‰.

[0034] Table 3 Evaluation of Carrier Regeneration Effect

[0035] Note: The carrier in Example 1 was regenerated after 60 days of continuous use.

[0036] The carriers prepared in Examples 2-5 were subjected to the same regeneration treatment and evaluation. The results showed that the regeneration effect of the carriers in each example was basically the same as that in Example 1, and the trends of activity recovery rate and carrier loss rate were the same. After four regenerations, the activity recovery rate of the carriers in Examples 2-5 was maintained in the range of 72% to 75%, and the carrier loss rate was controlled in the range of 10% to 13%, indicating that within the carrier structure and composition range defined in the claims of this invention, the carriers all have good regeneration performance and service life.

[0037] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for removing nitrogen and phosphorus from marine aquaculture wastewater, characterized in that, It includes three stages: pre-enrichment conditioning, magnetically assisted fluidized bed denitrification, and alternating anaerobic and aerobic phosphorus removal. Pre-enrichment and conditioning stage: A carrier with a magnetic protective shell and a micro-electrolysis core layer is added to the pretreatment tank. At the same time, a water quality conditioner is added to adjust the pH of the influent to weak alkalinity and a magnetic field is set in the pretreatment tank. Magnetic-assisted fluidized bed denitrification stage: Pretreated wastewater is introduced into a fluidized bed reactor, which is divided into a pre-nitrification zone and a post-denitrification zone. A magnetic field is set outside the nitrification zone to control the nitrification zone to aerobic conditions through aeration, and nitrifying bacteria are added to oxidize ammonia nitrogen in the wastewater into nitrate nitrogen. A magnetic field is set outside the denitrification zone to control the denitrification zone to anoxic conditions, and denitrifying bacteria are added. Anaerobic-aerobic alternating phosphorus removal stage: Denitrification effluent enters the phosphorus removal reactor and adopts a sequencing batch reactor operation mode, alternating between anaerobic phosphorus release and aerobic phosphorus uptake; Add a carbon source enhancer during the anaerobic phosphorus release stage; The effluent after phosphorus removal treatment enters a sedimentation tank for sludge-water separation. The precipitated sludge and carrier mixture are separated by a magnetic separation device. The core layer of the carrier has a gradient pore size structure, with the pore size gradually increasing from the inside to the outside: the pore size in the inner layer is 15~40μm, accounting for 20~30% of the total pore volume; the pore size in the middle layer is 50~120 μm, accounting for 40~50% of the total pore volume; and the pore size in the outer layer is 150~300 μm, accounting for 25~35% of the total pore volume.

2. The method for denitrification and phosphorus removal from marine aquaculture wastewater according to claim 1, characterized in that: During the pre-enrichment and conditioning stage, the carrier filling ratio is 10%~15%, and the water conditioner is a mixture of sodium bicarbonate and disodium hydrogen phosphate at a mass ratio of 3:1, with a dosage of 50~100 mg / L, to adjust the pH of the influent to 7.8~8.2; the magnetic field strength at the bottom of the pretreatment tank is 0.25~0.35 T; and the hydraulic retention time is 2~4 h.

3. The method for denitrification and phosphorus removal from marine aquaculture wastewater according to claim 1, characterized in that: In the magnetically assisted fluidized bed denitrification stage, the carrier filling ratio is 20%~30%; the length of the front nitrification zone accounts for 35%~40% of the total reactor length, and the length of the rear denitrification zone accounts for 60%~65% of the total reactor length; the magnetic field strength outside the nitrification zone is 0.12~0.18 T, and the dissolved oxygen concentration is 3.5~4.5 mg / L; the magnetic field strength outside the denitrification zone is 0.05~0.08 T, the dissolved oxygen concentration is 0.2~0.5 mg / L, the influent C / N ratio is 4~6, and the hydraulic retention time is 8~12 h.

4. The method for denitrification and phosphorus removal from marine aquaculture wastewater according to claim 1, characterized in that, The nitrifying bacteria agent is a mixed agent of Nitrosomonas and Nitrobacterium, and the dosage is 0.5‰ to 1‰ of water; the denitrifying bacteria agent is a mixed agent of Paracoccus denitrifying and Thiobacillus denitrifying, and the dosage is 1‰ to 2‰ of water.

5. The method for denitrification and phosphorus removal from marine aquaculture wastewater according to claim 1, characterized in that: In the alternating anaerobic and aerobic phosphorus removal stage, the carrier filling ratio is 15%~20%; in the anaerobic phosphorus release stage, the dissolved oxygen concentration drops to below 0.3 mg / L, the anaerobic time is 2~3 h, and the added carbon source enhancer is a mixture of sodium acetate and glucose at a mass ratio of 1:1, the dosage of which increases the influent COD concentration by 80~120 mg / L; in the aerobic phosphorus uptake stage, the dissolved oxygen concentration is 2.5~3.5 mg / L, and the aerobic time is 2.5~3.5 h.

6. The method for denitrification and phosphorus removal from marine aquaculture wastewater according to claim 1, characterized in that, The method for preparing the carrier includes the following steps: The micro-electrolysis core layer adopts a layered preparation process, in which zero-valent iron powder, activated carbon powder, nano magnetite and copper powder are fed in three batches, and then mixed with pore-forming agents of different particle sizes. After mixing, they are coated and formed layer by layer, and then sintered to form a core layer with a gradient pore size structure. After surface activation treatment, the core layer is coated with a shell mixture containing phosphorylated nano Fe3O4, polyvinyl alcohol, nano SiO2 and dimethyl diallyl ammonium chloride monomer, and then cross-linked and cured with calcium chloride solution to form a magnetic protective shell.

7. The method for denitrification and phosphorus removal from marine aquaculture wastewater according to claim 6, characterized in that, The surface activation treatment method is as follows: the core layer carrier is immersed in a hydrogen peroxide solution with pH=10 for 25~35 min to form hydroxyl active sites on the surface; the carrier is immersed in an ethanol solution containing 2% KH-550 and treated at 55~65℃ for 1.5~2.5 h to allow silane molecules to react with surface hydroxyl groups and leave amino groups; the carrier is rinsed with anhydrous ethanol and then dried.

8. The method for denitrification and phosphorus removal from marine aquaculture wastewater according to claim 1, characterized in that, The carrier is regenerated after 50-80 days of continuous use. The regeneration method is as follows: take out the carrier and rinse it with water, soak it in 0.1 mol / L hydrochloric acid solution for 4-6 h to remove inorganic precipitates and oxide layers on the surface, rinse it with water until the pH value is 6.5-7.5, soak it in 0.03 mol / L hydrogen peroxide solution for 2-3 h to remove organic pollutants, and rinse it again with water until neutral.

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