Method and system for recovering phosphorus in phosphorus-containing wastewater

Abstract

The invention discloses a method and system for recovering phosphorus in phosphorus-containing wastewater, and the method comprises the following steps: (1) adjusting the pH value of the phosphorus-containing wastewater to 8.0-9.0, and then adding ammonium salt, magnesium salt and polyaluminum chloride into the phosphorus-containing wastewater to obtain a magnesium ammonium phosphate precipitate; (2) adding a sodium hydroxide solution into the magnesium ammonium phosphate precipitate to carry out an aluminum ion dissolution reaction, and after the reaction is finished, separating and purifying a reaction product to obtain a high-purity magnesium ammonium phosphate crystal and a sodium metaaluminate solution; and (3) introducing CO2 gas into the sodium metaaluminate solution, neutralizing and regenerating the sodium metaaluminate solution into polyaluminum chloride, and reusing the polyaluminum chloride. According to the method, the operation steps are flexibly adjusted according to different phosphorus concentrations in the phosphorus-containing wastewater, so that the phosphorus removal efficiency is improved, struvite crystals are purified, resource utilization is facilitated, meanwhile, the flocculant polyaluminum chloride can be recycled, and the treatment cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of wastewater phosphorus recovery technology. Specifically, this invention relates to a method and system for recovering phosphorus from phosphorus-containing wastewater. Background Technology

[0002] Phosphorus is a key element for maintaining ecosystems and industrial production, and it is also a non-renewable and scarce resource. However, the direct discharge of large amounts of phosphorus-containing wastewater without effective treatment has led to increasingly prominent eutrophication problems in water bodies, causing environmental issues such as cyanobacterial blooms and water quality deterioration. On the other hand, global phosphate rock resources are facing the risk of depletion, and the recycling of phosphorus resources has become a research hotspot in the fields of environment and resources.

[0003] Currently, the main method for phosphorus recovery from water is chemical precipitation, among which struvite (magnesium ammonium phosphate, MgNH4PO4·6H2O) precipitation has attracted widespread attention because it can simultaneously remove phosphorus and recover high-value phosphorus. However, traditional struvite precipitation has the following problems: 1) The generated struvite particles are small (0.5-20μm), with poor settling performance, which easily leads to excessive phosphorus concentration in the effluent; 2) A large amount of coagulant needs to be added to promote sedimentation, resulting in high reagent costs; 3) The settled sludge contains a large number of impurities, making it difficult to directly utilize resources and resulting in high disposal costs. Therefore, developing a high-efficiency, low-cost phosphorus recovery technology that can achieve resource recycling is of great significance. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method and system for recovering phosphorus from phosphorus-containing wastewater. This method flexibly adjusts the operating steps according to different phosphorus concentrations in the wastewater, thereby improving phosphorus removal efficiency. It also purifies struvite crystals for resource utilization and enables the recovery of the flocculant polyaluminum chloride, significantly reducing treatment costs and solving problems such as slow struvite crystal settling rate, poor reagent utilization, and difficulty in sludge resource utilization.

[0005] The first aspect of this invention provides a method for recovering phosphorus from phosphorus-containing wastewater, comprising the following steps: (1) Adjust the pH of the phosphorus-containing wastewater to 8.0-9.0, and then add ammonium salt, magnesium salt and polyaluminum chloride to the phosphorus-containing wastewater to obtain magnesium ammonium phosphate precipitate; (2) Add sodium hydroxide solution to the magnesium ammonium phosphate precipitate to carry out aluminum ion dissolution reaction. After the reaction is completed, the reaction product is separated and purified to obtain high-purity magnesium ammonium phosphate crystals and sodium aluminate solution. (3) CO2 gas is introduced into the sodium aluminate solution to neutralize and regenerate it into polyaluminum chloride for reuse.

[0006] In some embodiments, in step (1), when the phosphorus-containing wastewater is high-phosphorus wastewater with a phosphorus concentration ≥30mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 8.0-9.0, and then add ammonium salt and magnesium salt to the phosphorus-containing wastewater and stir to react, generating magnesium ammonium phosphate precipitate; then mix the magnesium ammonium phosphate precipitate with polyaluminum chloride to enhance flocculation and promote the sedimentation of the magnesium ammonium phosphate precipitate; And / or, when the phosphorus-containing wastewater is low-phosphorus wastewater with a phosphorus concentration of <30mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 8.0-9.0, and then add polyaluminum chloride to the phosphorus-containing wastewater for pre-flocculation to generate aluminum hydroxide flocs; then mix the aluminum hydroxide flocs with ammonium salt and magnesium salt to induce crystallization reaction to generate magnesium ammonium phosphate precipitate.

[0007] In some embodiments, in step (1), the ammonium salt is ammonium chloride or ammonium sulfate, and the magnesium salt is magnesium chloride or magnesium sulfate; And / or, the NH4 in the ammonium salt + With the Mg in the magnesium salt 2+ PO4 in the phosphorus-containing wastewater 3- The molar ratio is (1.0-1.3):(1.0-1.3):1.

[0008] In some embodiments, in step (1), the dosage of polyaluminum chloride is 10-50 mg / L.

[0009] In some embodiments, when the phosphorus-containing wastewater is high-phosphorus wastewater with a phosphorus concentration ≥30mg / L, the stirring speed of the stirring reaction in step (1) is 100-300rpm; And / or, when the phosphorus-containing wastewater is low-phosphorus wastewater with a phosphorus concentration of <30mg / L, the time for the induced crystallization reaction in step (1) is ≥25 minutes, and the particle size of the aluminum hydroxide flocs is >100μm.

[0010] In some embodiments, in step (2), the concentration of the sodium hydroxide solution is 4-6 mol / L; And / or, the reaction time for the aluminum ion dissolution reaction is 30-60 minutes; And / or, the purity of the high-purity magnesium ammonium phosphate crystals is ≥92%.

[0011] In some embodiments, in step (3), the amount of CO2 gas introduced is such that the pH of the sodium aluminate solution is 5.0-6.0; And / or, the regeneration rate of the polyaluminum chloride is >80%.

[0012] A second aspect of the present invention also provides a system for recovering phosphorus from phosphorus-containing wastewater. The system is used to implement the method described in the first aspect and includes a reaction unit, a strong alkali regeneration unit, and a polyaluminum chloride regeneration unit connected in sequence; wherein the reaction unit includes a crystallization tank and a coagulation tank.

[0013] In some embodiments, when the phosphorus-containing wastewater is high-phosphorus wastewater with a phosphorus concentration ≥30mg / L, the crystallization tank is connected in sequence to the coagulation tank, the strong alkali regeneration unit, and the polyaluminum chloride regeneration unit; And / or, when the phosphorus-containing wastewater is low-phosphorus wastewater with a phosphorus concentration of <30mg / L, the coagulation tank is connected in sequence to the crystallization tank, the strong alkali regeneration unit, and the polyaluminum chloride regeneration unit.

[0014] In some embodiments, the crystallization tank is equipped with a pH probe and a stirrer; And / or, the bottom of the coagulation tank is provided with an inclined plate sedimentation zone with a surface load ≤0.8m. 3 / m 2 h; And / or, the strong alkali regeneration unit includes an alkali-resistant reactor and a centrifuge, wherein the alkali-resistant reactor is made of 316L stainless steel and has an alkali concentration ≥6mol / L; And / or, the polyaluminum chloride regeneration unit includes a carbonization tower and an online pH controller.

[0015] The advantages and beneficial effects of the embodiments of the present invention are as follows: (1) High phosphorus removal rate: In the embodiments of the present invention, the sedimentation of high phosphorus wastewater is accelerated by the flocculation effect of PAC. PAC flocculation shortens the sedimentation time of struvite from >60min to 15-30min; for low phosphorus wastewater, PAC forms flocs to induce crystallization, and the crystallization efficiency is increased by 50%.

[0016] (2) Resource recycling and cost saving: The embodiments of the present invention reduce the amount of agent used by recycling and reusing PAC, thereby reducing costs. At the same time, the crystal purity of the treated struvite is ≥92%, which meets the fertilizer standard and can be sold as a slow-release fertilizer or chemical raw material.

[0017] (3) Wide range of applications: The system for recovering phosphorus from phosphorus-containing wastewater in this embodiment of the invention can flexibly change the influent sequence for wastewater with different phosphorus contents, so that the system can be applied to the treatment of high and low concentration phosphorus-containing wastewater at the same time, such as municipal sewage, aquaculture wastewater and other scenarios, with a wider range of applications. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the system for recovering phosphorus from phosphorus-containing wastewater according to Embodiment 1 of the present invention.

[0019] Figure 2 This is a schematic diagram of the system for recovering phosphorus from phosphorus-containing wastewater according to Embodiment 2 of the present invention.

[0020] Figure labels: 1-Crystallization tank, 101-pH probe, 102-Agitator, 2-Coagulation tank, 3-Alkali-resistant reactor, 4-Centrifuge, 5-Carbonization tower, 6-pH online controller. Detailed Implementation

[0021] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] In this invention, when a value is described as a range, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as specific numerical values ​​falling within that range, regardless of whether specific numerical values ​​or specific subranges are explicitly specified.

[0023] In this invention, the terms “comprising” and “including” and their various variations mean that other elements or wholes may be included but are not specifically described.

[0024] In this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0025] The first aspect of this invention provides a method for recovering phosphorus from phosphorus-containing wastewater, comprising the following steps: (1) Adjust the pH of the phosphorus-containing wastewater to 8.0-9.0, and then add ammonium salt, magnesium salt and polyaluminum chloride to the phosphorus-containing wastewater to obtain magnesium ammonium phosphate precipitate; (2) Add sodium hydroxide solution to the magnesium ammonium phosphate precipitate to carry out aluminum ion dissolution reaction. After the reaction is completed, the reaction product is separated and purified to obtain high-purity magnesium ammonium phosphate crystals and sodium aluminate solution. (3) CO2 gas is introduced into the sodium aluminate solution to neutralize and regenerate it into polyaluminum chloride for reuse.

[0026] In some embodiments, in step (1), when the phosphorus-containing wastewater is high-phosphorus wastewater with a phosphorus concentration ≥30mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 8.0-9.0, and then add ammonium salt and magnesium salt to the phosphorus-containing wastewater and stir to react, generating magnesium ammonium phosphate precipitate; then mix the magnesium ammonium phosphate precipitate with polyaluminum chloride to enhance flocculation and promote the sedimentation of the magnesium ammonium phosphate precipitate; And / or, when the phosphorus-containing wastewater is low-phosphorus wastewater with a phosphorus concentration of <30mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 8.0-9.0, and then add polyaluminum chloride to the phosphorus-containing wastewater for pre-flocculation to generate aluminum hydroxide flocs; then mix the aluminum hydroxide flocs with ammonium salt and magnesium salt to induce crystallization reaction to generate magnesium ammonium phosphate precipitate.

[0027] The principle of this invention is as follows: Struvite, scientifically known as magnesium ammonium phosphate (MgNH4PO4·6H2O), abbreviated as MAP, is a white powdery inorganic crystalline mineral with a relative density of 1.71. In wastewater treatment, the struvite precipitation method involves adding magnesium ions to wastewater containing phosphates and ammonia nitrogen, reacting to form insoluble struvite precipitate, thus achieving nitrogen and phosphorus removal from the wastewater. Compared to the traditional activated sludge process, this method can reduce sludge volume by approximately 49% and is of great significance for the recovery of ammonia nitrogen resources.

[0028] In aqueous solution, the formation process of struvite can be described by the following three chemical equations:

[0029] The formation of struvite is greatly affected by the pH value of the aqueous solution. When the Mg content in the solution increases... 2+ NH4 + PO4 3- When the activity product is greater than the solubility product of struvite (the solubility product constant of struvite, Ksp, is 3.89 × 10⁻⁶), -10 -7.08×10 -14 ( ), which will spontaneously precipitate to form guano.

[0030] In wastewater with high phosphorus content, the high concentration of phosphate leads to rapid crystallization upon the addition of magnesium and ammonium salts, resulting in a large number of small struvite particles. These small struvite particles are difficult to settle and separate. Therefore, the recovery method in this invention utilizes the coagulation effect of polyaluminum chloride (PAC) to transform the small struvite particles into flocs larger than 100 μm (aggregates formed by the coagulation of tiny struvite particles under PAC). This ensures complete struvite sedimentation, thereby achieving a high phosphorus removal rate.

[0031] In wastewater with low phosphorus content, the concentration of phosphate is too low to reach the Ksp required for struvite precipitation, resulting in insufficient crystallization kinetics and a very slow crystallization process. Therefore, polyaluminum chloride (PAC) is used to regulate the crystallization mode from homogeneous crystallization (which occurs in high-phosphorus wastewater) to heterogeneous crystallization (i.e., seed-induced crystallization) that can occur even under low supersaturation. The role of PAC in this process is to hydrolyze into flocs larger than 100 μm (mainly composed of aluminum hydroxide). These flocs act as seed crystals for struvite crystallization, providing a reaction site for subsequent struvite crystallization and adsorbing and enriching phosphate ions. This allows for the subsequent addition of ammonium and magnesium salts, resulting in Mg2+ crystallization. 2+ NH4 + and PO4 3- The three substances can induce crystallization on the surface of the floc, and then the floc will quickly settle down along with the struvite aggregates that have crystallized on the surface, thereby achieving phosphorus removal.

[0032] The precipitated sludge obtained after treatment with ammonium salts, magnesium salts, and polyaluminum chloride in step (1) is further treated with a high-concentration sodium hydroxide solution: the aluminum salts in the sludge react with sodium hydroxide to generate sodium aluminate. The sodium aluminate solution can be adjusted by pH to convert aluminum ions into a reusable aluminum salt solution (AlCl3), which can be reused as a raw material for PAC preparation. At the same time, the struvite in the sludge does not react due to its strong alkali resistance, while the attached aluminum salts are dissolved by the sodium hydroxide solution, improving the purity of the struvite product. The separated struvite has a purity of ≥92% and can be used as a slow-release fertilizer or chemical raw material (such as for the preparation of phosphoric acid).

[0033] In some embodiments, in step (1), the ammonium salt is ammonium chloride or ammonium sulfate, and the magnesium salt is magnesium chloride or magnesium sulfate; And / or, the NH4 in the ammonium salt + With the Mg in the magnesium salt 2+ PO4 in the phosphorus-containing wastewater 3- The molar ratio is (1.0-1.3):(1.0-1.3):1.

[0034] In some embodiments, in step (1), the dosage of polyaluminum chloride is 10-50 mg / L.

[0035] In some embodiments, when the phosphorus-containing wastewater is high-phosphorus wastewater with a phosphorus concentration ≥30mg / L, the stirring speed of the stirring reaction in step (1) is 100-300rpm; And / or, when the phosphorus-containing wastewater is low-phosphorus wastewater with a phosphorus concentration of <30mg / L, the time for the induced crystallization reaction in step (1) is ≥25 minutes, and the particle size of the aluminum hydroxide flocs is >100μm.

[0036] In some embodiments, in step (2), the concentration of the sodium hydroxide solution is 4-6 mol / L; And / or, the reaction time for the aluminum ion dissolution reaction is 30-60 minutes; And / or, the purity of the high-purity magnesium ammonium phosphate crystals is ≥92%, which can be directly used as a slow-release fertilizer (compliant with GB / T34763-2017 standard).

[0037] In some embodiments, in step (3), the amount of CO2 gas introduced is such that the pH of the sodium aluminate solution is 5.0-6.0, so that the aluminum component in the sodium aluminate solution is converted into a reusable PAC solution, thereby realizing the recycling of resources; And / or, the regeneration rate of the polyaluminum chloride is >80%.

[0038] A second aspect of the present invention also provides a system for recovering phosphorus from phosphorus-containing wastewater. The system is used to implement the method described in the first aspect and includes a reaction unit, a strong alkali regeneration unit, and a polyaluminum chloride regeneration unit connected in sequence. The reaction unit includes a crystallization tank 1 and a coagulation tank 2.

[0039] In some embodiments, when the phosphorus-containing wastewater is high-phosphorus wastewater with a phosphorus concentration ≥30mg / L, the crystallization tank 1 is connected in sequence to the coagulation tank 2, the strong alkali regeneration unit, and the polyaluminum chloride regeneration unit; And / or, when the phosphorus-containing wastewater is low-phosphorus wastewater with a phosphorus concentration of <30mg / L, the coagulation tank 2 is sequentially connected to the crystallization tank 1, the strong alkali regeneration unit, and the polyaluminum chloride regeneration unit.

[0040] In some embodiments, the crystallization tank 1 is equipped with a pH probe 101 and a stirrer 102; And / or, the bottom of the coagulation tank 2 is provided with an inclined plate sedimentation zone with a surface load ≤ 0.8m. 3 / m 2 h; And / or, the strong alkali regeneration unit includes an alkali-resistant reactor 3 and a centrifuge 4, wherein the alkali-resistant reactor 3 is made of 316L stainless steel and has an alkali concentration ≥6mol / L; And / or, the polyaluminum chloride regeneration unit includes a carbonization tower 5 and an online pH controller 6.

[0041] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Unless otherwise stated, all raw materials used in the embodiments are conventional commercially available products, or can be prepared by known methods; experimental methods not specified in the embodiments are conventional methods and conditions well known in the art.

[0042] Example 1 The following is in conjunction with the appendix Figure 1 This embodiment describes in detail the method for recovering phosphorus from high-phosphorus wastewater.

[0043] This embodiment provides a method for recovering phosphorus from high-phosphorus wastewater (total phosphorus concentration of 65 mg / L) from a pig farm, including the following steps: (1) After adjusting the pH of the high-phosphorus wastewater to 8.5, place it in crystallization tank 1, and then follow the NH4... + :Mg 2+ :PO4 3- Magnesium chloride and ammonium chloride were added to crystallization tank 1 in a molar ratio of 1.1:1.1:1, and stirred at 200 rpm for 15 minutes to generate struvite microcrystals. Then, it was transferred to coagulation tank 2, and 30 mg / L of polyaluminum chloride (PAC) was added. The mixture was stirred slowly at 50 rpm for 10 minutes to promote struvite floc formation. The total phosphorus concentration of the supernatant was tested and found to be reduced to 0.8 mg / L, meeting the discharge standard. The struvite precipitate was collected in the bottom sedimentation zone. (2) The struvite precipitate obtained in step (1) is transported to the alkali-resistant reactor 3, and 5 mol / L NaOH solution is added to carry out the aluminum ion dissolution reaction. After the reaction is carried out for 40 minutes, the reaction product is separated and purified by centrifuge 4 to obtain struvite product with a purity of 94% and sodium aluminate solution. (3) The sodium aluminate solution was transported to carbonization tower 5 and CO2 gas was introduced to adjust the pH of the sodium aluminate solution to 5.8, neutralizing and regenerating it into PAC. The PAC reuse rate reached 83%, and the overall reagent cost per ton of water was reduced by 38%. During the experiment, the phosphorus concentration in the effluent was 0.8 mg / L, and the cost per ton of water was reduced by 35%.

[0044] Example 2 The following is in conjunction with the appendix Figure 2 This embodiment describes in detail the method for recovering phosphorus from low-phosphorus wastewater.

[0045] This embodiment provides a method for recovering phosphorus from low-phosphorus wastewater (total phosphorus concentration of 1.5 mg / L) effluent from the secondary sedimentation tank of a municipal wastewater treatment plant, comprising the following steps: (1) After adjusting the pH of the low-phosphorus wastewater to 8.5, place it in coagulation tank 2, then add 40 mg / L of PAC to coagulation tank 2 and stir rapidly to form aluminum hydroxide flocs; then transfer the resulting mixture to crystallization tank 1 and follow the NH4+ formula. + :Mg 2 + :PO4 3- Magnesium chloride and ammonium sulfate were added to crystallization tank 1 in a molar ratio of 1.05:1.05:1, and NH4+ was induced at a rotation speed of 40 rpm.+ and Mg 2+ Heterogeneous nucleation and crystallization occurred on the surface of aluminum hydroxide flocs for 25 minutes, forming a dense struvite coating layer and settling. The supernatant was tested and found to have a total phosphorus concentration of 0.2 mg / L and an aluminum residue of less than 0.2 mg / L, meeting the national emission standards. The struvite precipitate was collected in the bottom sedimentation zone. (2) The struvite precipitate obtained in step (1) is transported to the alkali-resistant reactor 3, and 5 mol / L NaOH solution is added to carry out the aluminum ion dissolution reaction. After the reaction is carried out for 40 minutes, the reaction product is separated and purified by centrifuge 4 to obtain struvite product with a purity of 93% and sodium aluminate solution. (3) The sodium aluminate solution is transported to carbonization tower 5 and CO2 gas is introduced to adjust the pH of the sodium aluminate solution to 5.8, neutralize and regenerate it into PAC. The PAC recycling rate reaches 81%, realizing efficient resource recovery under low phosphorus concentration conditions.

[0046] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0047] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0048] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0049] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for recovering phosphorus from phosphorus-containing wastewater, characterized in that, Includes the following steps: (1) Adjust the pH of the phosphorus-containing wastewater to 8.0-9.0, and then add ammonium salt, magnesium salt and polyaluminum chloride to the phosphorus-containing wastewater to obtain magnesium ammonium phosphate precipitate; (2) Add sodium hydroxide solution to the magnesium ammonium phosphate precipitate to carry out aluminum ion dissolution reaction. After the reaction is completed, the reaction product is separated and purified to obtain high-purity magnesium ammonium phosphate crystals and sodium aluminate solution. (3) CO2 gas is introduced into the sodium aluminate solution to neutralize and regenerate it into polyaluminum chloride for reuse.

2. The method for recovering phosphorus from phosphorus-containing wastewater according to claim 1, characterized in that, In step (1), when the phosphorus-containing wastewater is high-phosphorus wastewater with a phosphorus concentration ≥30mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 8.0-9.0, and then add ammonium salt and magnesium salt to the phosphorus-containing wastewater and stir to react, generating magnesium ammonium phosphate precipitate; then mix the magnesium ammonium phosphate precipitate with polyaluminum chloride to enhance flocculation and promote the sedimentation of the magnesium ammonium phosphate precipitate; And / or, when the phosphorus-containing wastewater is low-phosphorus wastewater with a phosphorus concentration of <30mg / L, the specific process of step (1) is as follows: adjust the pH of the phosphorus-containing wastewater to 8.0-9.0, and then add polyaluminum chloride to the phosphorus-containing wastewater for pre-flocculation to generate aluminum hydroxide flocs; then mix the aluminum hydroxide flocs with ammonium salt and magnesium salt to induce crystallization reaction to generate magnesium ammonium phosphate precipitate.

3. The method for recovering phosphorus from phosphorus-containing wastewater according to claim 1 or 2, characterized in that, In step (1), the ammonium salt is ammonium chloride or ammonium sulfate, and the magnesium salt is magnesium chloride or magnesium sulfate; And / or, the NH4 in the ammonium salt + With the Mg in the magnesium salt 2+ PO4 in the phosphorus-containing wastewater 3- The molar ratio is (1.0-1.3):(1.0-1.3):

1.

4. The method for recovering phosphorus from phosphorus-containing wastewater according to claim 1 or 2, characterized in that, In step (1), the dosage of polyaluminum chloride is 10-50 mg / L.

5. The method for recovering phosphorus from phosphorus-containing wastewater according to claim 2, characterized in that, When the phosphorus-containing wastewater is high-phosphorus wastewater with a phosphorus concentration ≥30mg / L, the stirring speed of the stirring reaction in step (1) is 100-300rpm; And / or, when the phosphorus-containing wastewater is low-phosphorus wastewater with a phosphorus concentration of <30mg / L, the time for the induced crystallization reaction in step (1) is ≥25 minutes, and the particle size of the aluminum hydroxide flocs is >100μm.

6. The method for recovering phosphorus from phosphorus-containing wastewater according to claim 1, characterized in that, In step (2), the concentration of the sodium hydroxide solution is 4-6 mol / L; And / or, the reaction time for the aluminum ion dissolution reaction is 30-60 minutes; And / or, the purity of the high-purity magnesium ammonium phosphate crystals is ≥92%.

7. The method for recovering phosphorus from phosphorus-containing wastewater according to claim 1, characterized in that, In step (3), the amount of CO2 gas introduced is such that the pH of the sodium aluminate solution is 5.0-6.0; And / or, the regeneration rate of the polyaluminum chloride is >80%.

8. A system for recovering phosphorus from phosphorus-containing wastewater, characterized in that, The system is used to implement the method according to any one of claims 1-7, comprising a reaction unit, a strong alkali regeneration unit, and a polyaluminum chloride regeneration unit connected in sequence; wherein the reaction unit comprises a crystallization tank and a coagulation tank.

9. The system for recovering phosphorus from phosphorus-containing wastewater according to claim 8, characterized in that, When the phosphorus-containing wastewater is high-phosphorus wastewater with a phosphorus concentration ≥30mg / L, the crystallization tank is connected in sequence to the coagulation tank, the strong alkali regeneration unit, and the polyaluminum chloride regeneration unit; And / or, when the phosphorus-containing wastewater is low-phosphorus wastewater with a phosphorus concentration of <30mg / L, the coagulation tank is connected in sequence to the crystallization tank, the strong alkali regeneration unit, and the polyaluminum chloride regeneration unit.

10. The system for recovering phosphorus from phosphorus-containing wastewater according to claim 8, characterized in that, The crystallization tank is equipped with a pH probe and a stirrer; And / or, the bottom of the coagulation tank is provided with an inclined plate sedimentation zone with a surface load ≤0.8m. 3 / m 2 h; And / or, the strong alkali regeneration unit includes an alkali-resistant reactor and a centrifuge, wherein the alkali-resistant reactor is made of 316L stainless steel and has an alkali concentration ≥6mol / L; And / or, the polyaluminum chloride regeneration unit includes a carbonization tower and an online pH controller.

Images