Preparation method and application of nano zero-valent iron biochemical modifier

Abstract

This invention relates to the field of water treatment technology, specifically to a method for preparing and applying a nano-zero-valent iron biochemical modifier. This invention prepares nano-zero-valent iron through a physical method, then disperses it with glycerol, performs primary coating with sodium carboxymethyl cellulose, and performs secondary coating with polydimethylallyl ammonium chloride. This solves the problems of agglomeration, oxidation, and storage of nano-zero-valent iron. It is then applied to biological denitrification and phosphorus removal in wastewater, enhancing denitrification in a low C / N ratio environment, reducing the dosage of phosphorus removal agents, achieving effective denitrification and phosphorus removal, and reducing the total salt content and sludge volume in municipal wastewater effluent.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a method for preparing and applying a nano-zero-valent iron biochemical modifier. Background Technology

[0002] my country's municipal wastewater discharge standards have evolved from comprehensive standards to specialized standards, and from single indicators to multi-faceted management, showing three major trends: stricter standards, expanded indicators, and more refined supervision. The effluent discharge exhibits increasingly stringent discharge requirements. Currently, many local standards require wastewater treatment plants to meet Class IV or near-Class IV surface water standards. Due to the generally low COD and high total nitrogen in municipal wastewater treatment plants, a large amount of carbon source needs to be added during the denitrification process of their biological systems to ensure the effective removal of nitrate nitrogen. When the total nitrogen is too high, it will also lead to persistently high total nitrogen in the system, resulting in effluent exceeding the standards.

[0003] As a novel environmental functional material, nano-zero valent iron (nZVI) has the characteristics of small particle size, large specific surface area and strong reducing power. nZVI can provide electron donors and drive autotrophic denitrification, achieving efficient denitrification without or with little addition of organic carbon sources, and greatly improving the denitrification efficiency of low carbon-nitrogen ratio.

[0004] Existing technological shortcomings and difficulties: 1. Municipal wastewater generally has a low carbon-to-nitrogen ratio (C / N<5), requiring the addition of carbon sources (methanol, sodium acetate, etc.) to improve denitrification capacity. However, the increased salinity of the treated water causes secondary pollution, and the addition of carbon sources further increases the load on the system's COD removal.

[0005] 2. Municipal wastewater treatment plants are designed to produce effluent according to Class A or Class B standards, but it is difficult to meet the standards for total nitrogen and total phosphorus after upgrading.

[0006] 3. Commercially available nano-zero valent iron (nZVI) products are expensive, prone to aggregation and oxidation, and have low activity, making them unsuitable for wastewater treatment applications that require low costs.

[0007] 4. The preparation of nano-zero-valent iron generates production wastewater, causing secondary pollution. For example, the nano-zero-valent iron in patent ZL202211017674.3 (authorization announcement number: CN115490322B), entitled "A method for simultaneous denitrification and phosphorus removal by bio-denitrification based on carbon-coated nano-zero-valent iron materials," is prepared by adding glucose to Fe(NO3)3•9H2O and then reacting it hydrothermally to prepare carbon-supported Fe3O4, followed by high-temperature calcination and reduction with hydrogen to obtain carbon-coated Fe. 0The calcination process consumes a large amount of heat energy, and the hydrothermal reaction produces a large amount of production wastewater. For example, the patent ZL 201911334348.3 (authorization announcement number: CN112058194B), entitled "Liquid phase pulse discharge plasma treatment reaction device and treatment method", involves nano-zero valent iron. It uses a nanosecond pulse power supply to generate active species such as OH and H2 through pulse discharge to reduce Fe²⁺ / Fe³⁺ in the liquid to nano-zero valent iron. It requires an ultra-high voltage of 10-100kV, the reaction liquid is acidic, and the production process will also produce saline wastewater, causing secondary pollution. Its discharge power is 50-500W, which cannot meet the needs of large-volume municipal sewage. Summary of the Invention

[0008] The problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing and applying a nano-zero valent iron biochemical modifier.

[0009] This invention is achieved through the following technical solution: A method for preparing a nano-zero-valent iron biochemical modifier includes a liquid-phase pulsed discharge reactor. The reactor includes a reaction chamber with an outlet on the upper side wall and an inlet on the bottom surface. The inlet connects to a linear water inlet within the reaction chamber. Electrodes are positioned on both sides of the inlet, with a central discharge region between the electrodes. The side of the electrodes facing the central discharge region is sloped. The electrodes are connected to terminals on the outside. The terminals on both sides are connected to the positive and negative terminals of a microsecond-level pulse power supply via pulse output cables. The method for preparing the nano-zero-valent iron biochemical modifier includes the following steps: Step S1: Reduced iron particles with a diameter of 3-6 mm are placed between the two electrodes in the reaction chamber of the liquid-phase pulse discharge reactor. A microsecond-level pulse power supply is activated, and deoxygenated water enters the reaction chamber through the inlet and water inlet, impacting the reduced iron particles. The water flow velocity is 1-1.5 m / s. The reduced iron particles in the central discharge region vaporize and condense into sheet-like nano-zero-valent iron particles with a diameter of 10-100 nm. The nano-zero-valent iron flows out with the deoxygenated water through the outlet into a cyclone precipitator. The supernatant is recycled. Cyclone precipitation yields Fe with a nano-zero-valent iron mass percentage of 10-15%. 0 -H2O solid-liquid mixture.

[0010] Step S2: Take the Fe obtained in step S1 0A solid-liquid mixture of H2O is stirred with glycerol in a mixing tank to obtain mixture A, wherein the glycerol purity is 95% and the mass percentage of glycerol in mixture A is 3%; then, low-viscosity sodium carboxymethyl cellulose is added and stirred to obtain mixture B, wherein the mass percentage of sodium carboxymethyl cellulose in mixture B is 10%; then, polydimethylallyl ammonium chloride is added and mixed evenly to obtain a nano-zero-valent iron biochemical modifier, wherein the mass percentage of nano-zero-valent iron in the nano-zero-valent iron biochemical modifier is 8-10%, and the mass percentage of polydimethylallyl ammonium chloride in the nano-zero-valent iron biochemical modifier is 10-15%.

[0011] As a preferred option: The width of the above-mentioned water inlet hole is 1mm.

[0012] In step S1, the peak voltage of the microsecond-level pulse power supply is 1-2kV, the frequency is 1KHz, the pulse width is 10µS, the discharge energy is 5-30J, and the discharge power is 5-30kW.

[0013] In step S2, glycerol is added and mixed at a speed of 500-800 r / min for 20 min.

[0014] In step S2, low-viscosity sodium carboxymethyl cellulose is added and stirred for 30 minutes.

[0015] In step S2, the low-viscosity sodium carboxymethyl cellulose is obtained by mixing solid sodium carboxymethyl cellulose with deoxygenated water at a mass ratio of 1:10, pre-dissolving, and then stirring until homogeneous.

[0016] In step S2, the raw material mass fraction of polydimethylallyl ammonium chloride is 20%.

[0017] This invention also includes an application of the nano-zero-valent iron biochemical modifier prepared according to the method of this invention, wherein the prepared nano-zero-valent iron biochemical modifier is used in biological denitrification and phosphorus removal of wastewater, and the application includes the following steps: Dilute the nZVI biochemical modifier 10 times with clean water and add the diluted nZVI biochemical modifier to the anoxic tank at a dosage of 10-20 mg / L. The water in the anoxic tank then enters the aerobic tank for biochemical reaction. The effluent standard is total nitrogen ≤10 mg / L and total phosphorus ≤0.3 mg / L.

[0018] The nano-zero-valent iron biochemical modifier prepared in this invention, when applied in the process of biological wastewater treatment as a microbial modifier for denitrification and dephosphorization, can improve the efficiency of biological denitrification and dephosphorization of municipal or industrial wastewater. The beneficial effects of this invention are as follows: 1. The nZVI of this invention is prepared by a purely physical process of reducing iron particles in the liquid phase through vaporization-condensation. The deoxygenated water is recycled and ultimately enters the product. The preparation process generates no wastewater or waste residue and has zero emissions. The prepared nZVI biochemical modifier has a neutral pH, does not affect the acidity or alkalinity of wastewater, does not increase the salinity of wastewater, and the product is iron hydroxide / iron phosphate. No toxic or harmful substances are generated and there is no secondary pollution.

[0019] 2. nZVI was prepared by physical method, with simultaneous glycerol dispersion. CMC-Na improved the biocompatibility and stability of nZVI and formed a primary coating. PDMDAAC was used for coating to maximize the activity of nZVI and solve the problems of nZVI aggregation, oxidation and storage.

[0020] 3. The nZVI preparation method has a high yield and can be mass-produced. The yield of nZVI per unit of equipment is 6 kg / h (Fe). 0 It can produce 1.5 tons / day of nZVI biochemical modifier, which can meet the needs of municipal sewage treatment plants with a capacity of 100,000 to 150,000 tons.

[0021] 4. Low cost: The power consumption to prepare 1 kg of nZVI is 3.5 kWh, the proportion of surface modification materials is low, and nZVI is the main cost.

[0022] 5. Due to its timely coating and low surface oxidation rate, nZVI exhibits high activity after entering wastewater, requiring a dosage as low as 10-20 mg / L (corresponding to Fe) for nitrogen removal enhancement. 0 The dosage is 1-2 mg / L, while the dosage of similar products (ZL202211017674.3) is 50-200 mg / L.

[0023] 6. nZVI enhances the denitrification ability of denitrifying bacteria and can partially or completely replace external carbon sources, generally saving 40-50% of external carbon sources.

[0024] 7. The Fe released during the denitrification of nZVI biochemical modifier 2+ With PO4 in wastewater 3- Ferrous phosphate is generated and eventually oxidized into ferric phosphate, which precipitates into the sludge. This can reduce the dosage of PAC / PFC by 30-50% (related to the phosphorus content in the wastewater), achieving simultaneous nitrogen and phosphorus removal.

[0025] 8. When the nZVI biochemical modifier prepared by this invention is used in wastewater treatment, the reduction in the amount of carbon source and PAC added leads to a decrease in the salinity of the effluent (nZVI is eventually converted into Fe(OH)3 / FePO4 and will not remain in the water body). The nZVI biochemical modifier improves the efficiency of denitrification / nitrification bacteria, and the organic matter in the sludge per unit mass is reduced, which is manifested as a reduction in sludge volume, thereby reducing the total salt content and sludge volume of municipal wastewater effluent. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the liquid phase discharge preparation device of the present invention; Figure 2 The image shows a scanning electron microscope (SEM) image of the prepared nano-zero-valent iron.

[0027] In the diagram, 1 is the liquid outlet; 2 is the reduced iron particles; 3 is the electrode; 4 is the terminal block; 5 is the water inlet; 6 is the liquid inlet; 7 is the microsecond-level pulse power supply; 8 is the pulse output cable; and 9 is the insulating ceramic plate. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0029] This invention includes a method for preparing a nano-zero-valent iron biochemical modifier, comprising the following steps: Step S1: Preparation of nano-zero valent iron This invention uses a physical method to prepare nano-zero valent iron (nZVI). The equipment used includes a liquid-phase pulsed discharge reactor, which includes a reaction chamber. An outlet 1 is provided on the upper side wall of the reaction chamber, and an inlet 6 is provided on the bottom surface of the reaction chamber. The inlet 6 is connected to a water inlet 5 inside the reaction chamber. Electrodes 3 are provided on both sides of the inlet 6, and a horizontal insulating ceramic plate 9 is connected between the two electrodes 3. The water inlet 5 is located in the middle of the insulating ceramic plate 9. The area between the two electrodes 3 is the intermediate discharge area. The electrodes 3 are made of iron or stainless steel, and the electrodes 3 are connected to terminals 4. The terminals 4 on both sides are connected to the positive and negative terminals of a microsecond-level pulse power supply 7 through pulse output cables 8.

[0030] This invention features a low-loss electrode design for the liquid-phase pulse discharge reactor: if a gap occurs between electrode 3 and reduced iron particles 2, a discharge reaction will occur, leading to electrode 3 wear. In this invention, the contact surface between electrode 3 and reduced iron particles 2 is designed as an inclined plane. Under the action of gravity, the reduced iron particles 2 and electrode 3 are tightly attached, making it difficult for a discharge reaction to occur. As the reduced iron particles 2 are consumed during discharge, they will move obliquely downward along the inclined plane of electrode 3 towards the central discharge area. This ensures that after the reduced iron particles 2 are added once, the load rate of the liquid-phase pulse discharge reactor is >75% within 30 minutes. The liquid-phase pulse discharge reactor was continuously discharged for 600 hours at the pilot site, and slight discharge traces were observed on electrode 3.

[0031] This invention also incorporates a high-load-rate design for the liquid-phase pulse discharge reactor: the water inlet 5 within the reaction chamber is designed as a linear hole, i.e., a narrow slit is opened on the insulating ceramic plate 9. The water inlet 5 is a narrow slit design, preferably with a width of 1 mm, and its length is equal to the width of the reaction chamber. When deoxygenated water enters the reaction chamber, it forms a water curtain, impacting the reduced iron particles 2 between the two electrodes 3, disrupting the short circuit between the two electrodes 3. Subsequently, under the action of a high-voltage pulse power supply, discharge occurs. The discharge area radiates outwards from the water inlet 5 as the center. Under this water inlet mode, the load rate (power utilization rate) of the liquid-phase pulse discharge reactor is >85%.

[0032] In this invention, the material can be added directly from the top of the reaction chamber to the liquid phase pulse discharge reactor, with reduced iron particles 2 added every 30 minutes. Alternatively, the existing feeding device can be linked with the power load rate, and the existing feeding device can be automatically started, stopped, or adjusted according to the change in the power load rate to achieve automatic feeding on demand.

[0033] In the preparation of nano-zero-valent iron using liquid-phase discharge, deoxygenated water was selected as the liquid phase. A microsecond-level pulsed power supply with a peak voltage of 1-2 kV, a frequency of 1 kHz, a pulse width of 10 μS, a discharge energy of 5-30 J, and a discharge power of 5-30 kW was used. Reduced iron particles 2 with a diameter of 3-6 mm are placed on an insulating ceramic plate 9 between two electrodes 3 in the reaction chamber. Deoxygenated water enters the reaction chamber through the bottom inlet 6 and then through the linear water inlet 5 to impact the reduced iron particles 2. The water flow velocity is 1-1.5 m / s. Due to the change in resistance between the reduced iron particles 2, plasma discharge occurs between the particles under high voltage. The reduced iron particles 2 are uniformly discharged in the liquid phase between the two electrodes. The surface of the reduced iron particles 2 in the middle discharge area is instantly vaporized under the action of plasma and then rapidly condensed into sheet-like nano-zero valent iron particles by the liquid. The prepared nZVI particles have a diameter of 10-100 nm. They flow out with the deoxygenated water through the outlet 1. Then the deoxygenated water carries the nZVI into a hydrocyclone precipitator for enrichment. The supernatant is recycled. The hydrocyclone precipitator yields nZVI (Fe2+). 0 Fe with a mass percentage of 10-15% 0 -H2O solid-liquid mixture.

[0034] Plasma liquid-phase discharge occurs between reduced iron particles 2. These particles are stacked in the reaction chamber. When no deoxygenated water is introduced between the two electrodes 3, they are in a short-circuit state. When deoxygenated water enters the reaction chamber, it impacts the reduced iron particles 2, creating tiny gaps between them. Under a 1-2 kV pulse voltage, plasma discharge is generated. The kinetic energy generated by the discharge vibrates more reduced iron particles 2. With an electrical output of 5-30 kW, 50-70% of the reduced iron particles 2 in the reaction chamber have Fe on their surface. 0 The local high temperature generated by the discharge vaporizes the substance, which is then condensed into solid nZVI by the deoxygenated water and carried out of the reaction chamber from the outlet 1 along with the flow of the deoxygenated water.

[0035] Step S2: Preparation of nano-zero valent iron biochemical modifier nZVI dispersion and coating: The Fe prepared in step S1 0 - Add glycerol to the H2O solid-liquid mixture in a mixing tank, mix and stir for 20 minutes to obtain mixture A; wherein, industrial grade glycerol with a purity of 95% is used, the mass percentage of glycerol in mixture A is 3%, and the stirring speed is 500-800 r / min to prevent nZVI agglomeration; Then, low-viscosity sodium carboxymethyl cellulose (CMC-Na) was added and stirred for 30 minutes to obtain mixture B. Low-viscosity sodium carboxymethyl cellulose (CMC-Na) improves the biocompatibility and stability of nZVI and forms a primary coating. The mass percentage of sodium carboxymethyl cellulose (CMC-Na) in mixture B is 10%. The added low-viscosity sodium carboxymethyl cellulose (CMC-Na) is obtained by mixing solid CMC-Na with deoxygenated water at a mass ratio of 1:10, pre-dissolving and then stirring evenly at a stirring speed of 100-200 r / min. Then, polydimethylallyl ammonium chloride (PDMDAAC) is added and mixed evenly to increase the nZVI coating density, thus obtaining a nano-zero-valent iron biochemical modifier (nZVI biochemical modifier). The obtained nZVI biochemical modifier is nZVI(Fe 0 The nZVI biochemical modifier is a uniform black viscous liquid with a mass percentage of 8-10% and a neutral pH value between 6 and 8. The mass percentage of PDMDAAC in the final nZVI biochemical modifier is 10-15%, and the mass fraction of the raw material PDMDAAC added at the beginning is 20%.

[0036] As mentioned above, glycerol's dispersibility is manifested in the formation of a monomolecular organic film on the surface of nZVI through hydroxyl hydrogen bonding, generating steric repulsion between nZVI particles, reducing the surface energy of nZVI particles, and making the dispersion system more stable. CMC-Na is a strong anionic stabilizer. It is adsorbed on the surface of nZVI and improves the suspension stability of nZVI in water through electrostatic repulsion and steric hindrance effects. The organic protective film formed by CMC-Na on the surface of nZVI slows down the oxidation rate of nZVI. CMC-Na can be completely degraded in the biochemical system. Coating the surface of nZVI reduces the physical toxicity caused by direct contact between nZVI and denitrifying bacteria cell membranes, and has good biocompatibility. PDMDAAC is a strong cationic functional agent. PDMDAAC and CMC-Na form anionic and cationic composite coating. On the one hand, it balances the strong negative charge of CMC-Na, optimizes the interfacial charge, and enhances the affinity of nZVI for negatively charged pollutants (nitrates, phosphates). On the other hand, the coating layer generated by the interaction of anionic and cationic adsorption is more dense, providing longer-lasting antioxidant protection for nZVI.

[0037] This embodiment applies the above-prepared nZVI biochemical modifier to an application test, including stability test and microbial activity test.

[0038] 1) Stability test: The nZVI biochemical modifier was left to stand at room temperature in a closed state for 90 days to observe its stability. No agglomeration or stratification was observed, and the Fe content in the product was detected. 0 The content reduction rate is <1%, which meets the production operation requirements. The nZVI biochemical modifier that has been left to stand in a closed state for 90 days was used for denitrification test. Compared with the newly prepared nZVI biochemical modifier of the present invention, which was directly used for denitrification test, it does not require an increase in the amount of nZVI biochemical modifier and the two can achieve the same effect. The results show that the nZVI biochemical modifier prepared by the present invention has good stability.

[0039] 2) Microbial activity test: In the operation test of the nZVI biochemical modifier in the municipal wastewater treatment plant, the dosage concentration was 10 mg / L, the tank temperature was 14℃, the nitrate nitrogen at the end of the anoxic tank was 3-5 mg / L, the carbon source was reduced by 10% every 48 hours, and the carbon source was reduced by 50%. Under normal system operation, the nitrate nitrogen at the end of the anoxic tank was <5 mg / L, the total nitrogen in the aerobic effluent was <10 mg / L, the total phosphorus was <0.3 mg / L, and the dosage of phosphorus removal agent (PAC) was reduced by 20%, indicating that it has a significant promoting effect on nitrogen and phosphorus removal in denitrification.

[0040] This invention also includes the application of the above-prepared nano-zero-valent iron biochemical modifier in biological nitrogen and phosphorus removal from wastewater, comprising the following steps: 1) Pretreatment: Dilute the above-prepared nZVI biochemical modifier with water 10 times.

[0041] 2) Addition of nZVI biochemical modifier: Add the pretreated and diluted nZVI biochemical modifier to the anoxic tank at a dosage of 10-20 mg / L.

[0042] 3) Biochemical reaction: Water from the anoxic tank enters the aerobic tank. The nZVI biochemical modifier adsorbs sludge as an electron donor, providing electrons to the denitrifying bacteria. This promotes the reduction of NO3-N / NO2-N to N2 by the denitrifying bacteria, and the oxidized Fe... 2+ With PO4 3- Ferrous phosphate is generated and completely converted into ferric phosphate precipitate in the aerobic tank.

[0043] 4) Effluent standards: Total nitrogen ≤10mg / L, total phosphorus ≤0.3mg / L.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can still be made to the technical solutions described in the above embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a nano-zero-valent iron biochemical modifier, characterized in that: The reactor includes a liquid phase pulse discharge reactor, which includes a reaction chamber. An outlet (1) is provided on the upper side wall of the reaction chamber, and an inlet (6) is provided on the bottom surface of the reaction chamber. The inlet (6) is connected to a linear water inlet (5) in the reaction chamber. Electrodes (3) are provided on both sides of the inlet (6). A horizontal insulating ceramic plate (9) is connected between the two electrodes (3). The water inlet (5) is located in the middle of the insulating ceramic plate 9. The area between the electrodes (3) is the intermediate discharge area. The side of the electrode (3) facing the intermediate discharge area is an inclined surface. The electrode (3) is connected to a terminal (4) to the outside. The two terminals (4) are connected to the positive and negative poles of a microsecond-level pulse power supply (7) through a pulse output cable (8). The preparation method of nano-zero valent iron biochemical modifier includes the following steps: Step S1: Place reduced iron particles (2) with a particle size of 3-6 mm between the two electrodes (3) in the reaction chamber of the liquid phase pulse discharge reactor, turn on the microsecond-level pulse power supply (7), and deoxygenated water enters the reaction chamber through the liquid inlet (6) and water inlet (5) to impact the reduced iron particles (2). The water flow velocity is 1-1.5 m / s. The reduced iron particles (2) in the middle discharge area are vaporized and condensed into sheet-like nano-zero valent iron particles with a particle size of 10-100 nm. The nano-zero valent iron flows out with the deoxygenated water through the liquid outlet (1) into the cyclone precipitator. The supernatant is recycled. The cyclone precipitator yields Fe with a nano-zero valent iron mass percentage of 10-15%. 0 -H2O solid-liquid mixture; Step S2: Take the Fe obtained in step S1 0 A solid-liquid mixture of H2O is stirred with glycerol in a mixing tank to obtain mixture A, wherein the glycerol purity is 95% and the mass percentage of glycerol in mixture A is 3%; then, low-viscosity sodium carboxymethyl cellulose is added and stirred to obtain mixture B, wherein the mass percentage of sodium carboxymethyl cellulose in mixture B is 10%; then, polydimethylallyl ammonium chloride is added and mixed evenly to obtain a nano-zero-valent iron biochemical modifier, wherein the mass percentage of nano-zero-valent iron in the nano-zero-valent iron biochemical modifier is 8-10%, and the mass percentage of polydimethylallyl ammonium chloride in the nano-zero-valent iron biochemical modifier is 10-15%.

2. The preparation method of the nano-zero-valent iron biochemical modifier according to claim 1, characterized in that: The width of the water inlet hole (5) is 1 mm.

3. The preparation method of the nano-zero-valent iron biochemical modifier according to claim 1, characterized in that: In step S1, the microsecond-level pulse power supply (7) has a peak voltage of 1-2kV, a frequency of 1KHz, a pulse width of 10uS, a discharge energy of 5-30J, and a discharge power of 5-30kw.

4. The preparation method of the nano-zero-valent iron biochemical modifier according to claim 1, characterized in that: In step S2, glycerol is added and mixed at a speed of 500-800 r / min for 20 min.

5. The preparation method of the nano-zero-valent iron biochemical modifier according to claim 1, characterized in that: In step S2, low-viscosity sodium carboxymethyl cellulose is added and stirred for 30 minutes.

6. The preparation method of the nano-zero-valent iron biochemical modifier according to claim 1, characterized in that: In step S2, the low-viscosity sodium carboxymethyl cellulose is obtained by mixing solid sodium carboxymethyl cellulose with deoxygenated water at a mass ratio of 1:10, pre-dissolving, and then stirring until homogeneous.

7. The preparation method of the nano-zero-valent iron biochemical modifier according to claim 1, characterized in that: In step S2, the raw material mass fraction of polydimethylallyl ammonium chloride is 20%.

8. The method for preparing the nano-zero-valent iron biochemical modifier according to any one of claims 1-7, characterized in that: The nano-zero-valent iron biochemical modifier prepared by the method is used in biological denitrification and phosphorus removal of wastewater.

9. The preparation method of the nano-zero-valent iron biochemical modifier according to claim 8, characterized in that: The nano-zero-valent iron biochemical modifier used in biological nitrogen and phosphorus removal from wastewater includes the following steps: diluting the nZVI biochemical modifier 10 times with clean water, adding the diluted nZVI biochemical modifier to the anoxic tank at a dosage of 10-20 mg / L, and then allowing the water in the anoxic tank to enter the aerobic tank for biochemical reaction. The effluent standard is total nitrogen ≤10 mg / L and total phosphorus ≤0.3 mg / L.

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