Method and system for recycling phosphorus in wastewater with eggshells as calcium source

Abstract

The invention belongs to the technical field of wastewater treatment, and particularly discloses a method and system for recycling phosphorus in wastewater with eggshells as a calcium source. The method comprises two stages: in the first stage, the phosphorus-containing wastewater and a dilute sulfuric acid solution are mixed to obtain a mixed solution A, and the pH value of the mixed solution A is 3.0-5.0; enabling the pretreated eggshells to react with the mixed solution A to generate hydroxyl calcium phosphate precipitate, and entering a second stage after the stage runs for several days; in the second stage, the phosphorus-containing wastewater reacts with a mixed solution of calcium salt and calcium hydroxide, a mixed solution B is obtained, and the pH of the mixed solution B is 8.0-9.0; mixing and reacting the eggshell system treated in the first stage with a mixed solution B, and generating an insoluble substance hydroxyl calcium phosphate precipitate from Ca < 2 + >, hydroxyl ions and phosphate ions in water; and the concentration of phosphorus ions in the effluent is reduced to 0.5-5.5 mg / L. The problems of high cost, complex process and the like in the prior art are solved.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically discloses a method and system for recovering phosphorus from wastewater using eggshells as a calcium source. Background Technology

[0002] Phosphorus, as an essential element for life, plays an irreplaceable role in agricultural ecosystems and biogeochemical cycles. However, environmental problems caused by excessive phosphorus emissions have posed a potential threat to ecological security and sustainable development, urgently requiring attention. Domestic sewage, agricultural runoff, aquaculture wastewater, and industrial wastewater contain large amounts of phosphorus. After entering water bodies, phosphorus can cause algal blooms, deplete oxygen in the water, damage aquatic ecosystems, and threaten drinking water safety.

[0003] Currently, the main methods for phosphorus recovery include: chemical precipitation, biological treatment, physical adsorption, membrane separation, and crystallization. Chemical precipitation involves adding calcium, iron, or aluminum salts to form phosphate precipitates; it is simple to operate but the product has low added value. Biological treatment utilizes polyphosphate-accumulating bacteria to enrich phosphorus in sludge; it has low operating costs but requires secondary treatment for subsequent extraction. Physical adsorption and membrane separation are suitable for low-concentration phosphorus wastewater, but they face bottlenecks in material regeneration and energy consumption.

[0004] Crystallization recovers high-purity phosphorus-containing minerals by controlling pH and reagent dosage, offering both economic and environmental benefits. For example, struvite crystallization involves adjusting pH and introducing magnesium and ammonia nitrogen, causing phosphate to combine with magnesium and ammonium ions to form white crystalline precipitates, the product of which can be directly used as a slow-release fertilizer; lapis lazuli crystallization utilizes the reaction of iron ions with phosphate under acidic to neutral conditions to generate lapis lazuli crystals, the product of which can be used as an industrial raw material; calcium phosphate crystallization (Ca5(PO4)3(OH)) involves adding calcium salts to precipitate phosphorus in a neutral to alkaline environment, the product of which can be used in agriculture or as an industrial raw material.

[0005] Patent publication number CN 102190343A discloses a method for adsorbing phosphorus from wastewater using eggshells. The method involves pre-treating eggshells (chicken, duck, or goose eggshells) by removing the inner membrane, grinding them to 300 mesh to obtain eggshell powder, and then placing the powder in phosphorus-containing wastewater with a pH of 7-10. The mixture is reacted for 8-12 hours at a rotation speed of 50-200 r / min to complete the phosphorus adsorption and removal process.

[0006] Patent publication number CN 102380350 A discloses a method for removing and recovering phosphates from wastewater using a hydroxyapatite-modified eggshell adsorbent material. The method involves repeatedly washing and grinding eggshells after removing the inner membrane, obtaining eggshell powder (200 mesh), which is then placed in a solution of soluble calcium salt Ca(NO3)2 and soluble phosphate (NH4)2HPO4 and stirred. Simultaneously, alkali (NH3·OH) is added to precisely adjust the pH to 9, resulting in an eggshell-modified adsorbent material. This material is then reacted in phosphorus-containing water to effectively remove phosphorus from wastewater.

[0007] Both of the above phosphorus removal methods have certain drawbacks. The reaction adsorption takes too long, the amount of eggshells added is large, and the added state is all eggshell powder. In the subsequent solid-liquid separation, additional coagulant / dehydrating agent needs to be added, which increases the processing cost and complicates the reaction product disposal process, resulting in a double consumption of manpower and material resources. In the second method, the pH needs to be precisely controlled, which increases the complexity of the process operation. If the control is not proper, it will directly lead to a reduction in phosphorus removal efficiency. Summary of the Invention

[0008] The purpose of this invention is to provide a method and system for recovering phosphorus from wastewater using eggshells as a calcium source, which solves the problems of high cost and complex process in existing technologies.

[0009] This invention is achieved through the following technical solution: A method for recovering phosphorus from wastewater using eggshells as a calcium source includes two stages: First stage: Mix phosphorus-containing wastewater with dilute sulfuric acid solution to obtain mixed solution A, the pH of which is 3.0~5.0; The pretreated eggshells are reacted with mixed solution A to generate calcium hydroxyphosphate precipitate. After running for several days in this stage, the second stage begins. The second stage involves reacting phosphorus-containing wastewater with a mixed solution of calcium salts and calcium hydroxide to obtain mixed solution B, which has a pH of 8.0 to 9.0. The eggshell system, after the first stage of treatment, is mixed with mixed solution B for reaction. Ca 2+ Hydroxide ions react with phosphate ions in water to form insoluble calcium hydroxyphosphate precipitate, reducing the phosphate ion concentration in the effluent to 0.5–5.5 mg / L.

[0010] Furthermore, in the first stage, the pre-treated eggshells are obtained by washing, drying, and screening the waste eggshells.

[0011] Furthermore, in the first stage, when the pretreated eggshells react with mixed solution A, the pH of the reaction system is 6.0~8.0, and the hydraulic retention time is 30~40 minutes; The first phase of operation will last 50-60 days.

[0012] Furthermore, in the second stage, when the eggshell system after the first stage treatment is completed is mixed with mixed solution B, the pH of the reaction system is 7.0~8.0, and the hydraulic retention time is 30~40 minutes.

[0013] Furthermore, in the second stage, the calcium-to-phosphorus ratio is 5:1 to 8:1.

[0014] Furthermore, the pre-treated eggshell particle size is 0.58–0.85 mm or 0.85–1.7 mm.

[0015] The present invention also discloses a phosphorus recovery system for wastewater using eggshells as a calcium source, comprising an inlet tank, a sulfuric acid dosing tank, a calcium salt dosing tank, a static mixer, a mixing tank, a porous distribution plate, a fixed bed reactor, and an effluent tank. The sulfuric acid dosing tank, calcium salt dosing tank, and inlet tank are all connected to the static mixer, and the static mixer is connected to the mixing tank. The fixed-bed reactor comprises a calcium carbonate dissolution reaction zone, a calcium phosphate main precipitation reaction zone, and a reaction protection zone connected in sequence. The sulfuric acid dosing tank contains dilute sulfuric acid solution, and the calcium salt dosing tank contains a mixed solution of calcium salt and calcium hydroxide. Flow meters are installed on the pipelines connecting the inlet tank to the static mixer; sulfuric acid metering pumps are installed on the pipelines connecting the sulfuric acid dosing tank to the static mixer; calcium salt metering pumps are installed on the pipelines connecting the calcium salt dosing tank to the static mixer. An online influent detection device is installed in the influent tank to measure pH, total phosphorus, and dissolved phosphorus; an automatic control system is installed in the mixing tank to control the influent flow meter, sulfuric acid metering pump, and calcium salt metering pump. An automatic effluent detection device is installed at the outlet of the reaction protection zone to measure pH, total phosphorus, and dissolved phosphorus.

[0016] Furthermore, the mixing tank is connected to the fixed-bed reactor via a porous distribution plate; the porous distribution plate is installed at the reactor inlet, and an inlet pump is installed on the pipeline connecting the mixing tank and the porous distribution plate.

[0017] Furthermore, the reaction protection zone is equipped with a reactor outlet and a flushing outlet. The reactor outlet is connected to the effluent pool, and the flushing outlet is connected to the flushing wastewater collection pool.

[0018] Furthermore, it also includes a cleaning water tank, a drying oven, and standard screening equipment; After being washed in a washing tank, the waste eggshells are dried in an oven and then sent to a standard screening device to obtain pre-treated waste eggshells.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a method for phosphorus recovery from wastewater using eggshells as a calcium source. In the first stage, a control system precisely controls the dosage of sulfuric acid, ensuring thorough mixing of the sulfuric acid with the phosphorus-containing wastewater and maintaining a solution pH of 3.0–5.0 to ensure acidic conditions. In the second stage, a control system precisely controls the dosage of calcium salt, ensuring thorough mixing of the calcium salt with the phosphorus-containing wastewater and maintaining a solution pH of 8.0–9.0. To achieve phosphorus removal, the waste eggshells in the first stage serve as a calcium source, releasing a large amount of calcium under acidic conditions. 2+ It reacts with phosphate and hydroxide ions in water to form insoluble calcium hydroxyphosphate precipitate; the second stage adds calcium salt to provide Ca. 2+ It reacts with hydroxide ions and phosphate ions in water to form insoluble calcium hydroxyphosphate precipitate, reducing the phosphorus ion concentration in the effluent to 0.5-5.5 mg / L, with a soluble phosphorus removal rate of over 85%.

[0020] This invention not only boasts a simple process and high automation, but also utilizes discarded eggshells as a calcium source to promote the precipitation of hydroxyapatite, saving on traditional reagent dosages and achieving highly efficient and environmentally friendly phosphorus removal. The main component of the precipitate and recovered materials is hydroxyapatite, which can be used as agricultural slow-release fertilizer, industrial raw material, or directly for water environment remediation. The recovered particulate matter consists of hydroxyapatite particles with eggshell cores, which can also be used as agricultural slow-release fertilizer, industrial raw material, or directly for water environment remediation, representing a green and sustainable phosphorus recovery technology system. Utilizing eggshells as a calcium source to generate hydroxyapatite from phosphorus in wastewater can reduce the effluent phosphorus ion concentration to 0.5-5.5 mg / L, achieving green, environmentally friendly, and highly efficient phosphorus removal.

[0021] Furthermore, this invention incorporates recycled waste eggshells, providing a natural calcium source and completing the precipitation and separation system within the same reactor. This results in strong operability, low reagent costs, and reduced pollution.

[0022] This invention discloses a phosphorus recovery system for wastewater using eggshells as a calcium source, comprising an inlet tank, a flow meter, a sulfuric acid dosing tank, a calcium salt dosing tank, a sulfuric acid metering pump, a calcium salt metering pump, a static mixer, a mixing tank, an inlet pump, and a fixed-bed reactor. The dosage of dilute sulfuric acid / calcium salt and reaction conditions are controlled by an online detection and automatic control system. During operation, the reactor is flushed periodically. After sedimentation of the flushing wastewater, the supernatant is discharged. The precipitate (hydroxyphosphate) can be recycled for use as agricultural slow-release fertilizer, industrial raw material, or directly for water environment remediation. In the treatment process, the inlet tank, mixing tank, fixed-bed reactor, effluent tank, and flushing wastewater collection tank are connected sequentially in the direction of water inflow. A static mixer is installed in the direction of water inflow, connected to the inlet flow meter and the sulfuric acid and calcium salt dosing devices. The inlet water flow meter controls the inlet water volume, and the sulfuric acid / calcium salt metering pump controls the dosage of dilute sulfuric acid / calcium salt. The sulfuric acid / calcium salt enters the static mixer along with the wastewater, then flows into the mixing tank, fixed-bed reactor, effluent tank, and flushing wastewater collection tank. This ensures that the reagents are fully and evenly mixed, and also ensures that the pH of the solution in the first stage mixing tank is 3.0~5.0 and the pH of the solution in the second stage mixing tank is 8.0~9.0.

[0023] Furthermore, a porous distribution plate is installed at the inlet end of the fixed bed reactor to uniformly disperse the flow rate of phosphorus-containing wastewater entering the fixed bed reactor. Sedimentation and crystallization reactions occur in the reactor. The sedimentation reaction occurs in the pores of the eggshell, and the crystallization reaction occurs on the surface of the eggshell. The sediment is intercepted by the eggshell particles, and the effluent flows out of the fixed bed reactor outlet to the effluent pool. Attached Figure Description

[0024] Figure 1 The XRD patterns of the eggshells before and after the reaction are shown. Figure 2 This is a schematic diagram of the phosphorus recovery system in wastewater using eggshells as a calcium source according to the present invention. The components include: 1. Inlet tank; 2-1. First pipeline; 2-2. Second pipeline; 2-3. Third pipeline; 3. Flow meter; 4-1. Sulfuric acid metering pump; 4-2. Calcium salt metering pump; 5. Sulfuric acid dosing tank; 6. Calcium salt dosing tank; 7. Static mixer. 8-1. Inlet water online detection device; 8-2. Automatic control system; 8-3. Outlet water automatic detection device; 9. Fixed-bed reactor; 9-1. Calcium carbonate dissolution reaction zone; 9-2. Calcium phosphate main precipitation reaction zone; 9-3. Reaction protection zone; 10. Reactor inlet; 11-1. Reactor outlet; 11-2. Rinse outlet; 12. Porous distribution plate; 13. Mixing tank; 14. Effluent tank; 15. Rinse wastewater collection tank; 16. Inlet pump; 17. Waste eggshells; 18. Washing water tank; 19. Drying oven; 20. Standard screening equipment. Detailed Implementation To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0025] The components described and illustrated in the accompanying drawings and embodiments of this invention can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the invention provided in the following drawings is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the accompanying drawings and embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0026] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, element, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to the process, element, method, article, or apparatus.

[0027] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0028] like Figure 2 As shown, the present invention provides a phosphorus recovery system for wastewater using eggshells as a calcium source, comprising an inlet tank 1, a flow meter 3, a sulfuric acid dosing tank 5, a calcium salt dosing tank 6, a sulfuric acid metering pump 4-1, a calcium salt metering pump 4-2, a static mixer 7, a mixing tank 13, an inlet pump 16, and a fixed-bed reactor 9.

[0029] After being washed in the washing water tank 18, the waste eggshells are dried in the drying oven 19 and then enter the standard screening equipment 20 to obtain pre-treated waste eggshells 17. In an embodiment of the present invention, the eggshell is a recycled waste eggshell with a particle size of 0.58-0.85 mm or 0.85-1.7 mm.

[0030] Sulfuric acid dosing tank 5 stores dilute sulfuric acid solution, and calcium salt dosing tank 6 stores a mixed solution of calcium salt and calcium hydroxide.

[0031] An online influent monitoring device 8-1 is installed in the influent tank 1 to measure pH, total phosphorus (TP), and dissolved phosphorus (DP).

[0032] The mixing tank 13 is equipped with an automatic control system 8-2, which is used to control the influent flow meter 3, the sulfuric acid metering pump 4-1 and the calcium salt metering pump 4-2.

[0033] An automatic effluent detection device 8-3 is installed at the outlet of the reaction protection zone 9-3 to measure pH, total phosphorus (TP), and dissolved phosphorus (DP).

[0034] The inlet tank 1 is connected to the static mixer 7 via the first pipe 2-1, and a flow meter 3 is installed on the first pipe 2-1. The sulfuric acid dosing tank 5 is connected to the static mixer 7 via the second pipeline 2-2, and the second pipeline 2-2 is equipped with a sulfuric acid metering pump 4-1; the calcium salt dosing tank 6 is connected to the static mixer 7 via the third pipeline 2-3, and the third pipeline 2-3 is equipped with a calcium salt metering pump 4-2.

[0035] The inlet tank 1 is connected to the mixing tank 13 by a pipeline, the mixing tank 13 is connected to the fixed bed reactor 9 by a pipeline, the fixed bed reactor 9 is connected to the outlet tank 14 by a pipeline and to the flushing inlet pump 16, and the fixed bed reactor 9 is connected to the flushing wastewater collection tank 15 by a pipeline.

[0036] The sulfuric acid dosing tank 5 is connected to the sulfuric acid metering pump 4-1 via a pipeline; the calcium salt dosing tank 6 is connected to the calcium salt metering pump 4-2 via a pipeline; the inlet flow meter 3 is connected to the static mixer 7 via a pipeline; the metering pump 4-1, the calcium salt metering pump 4-2, and the static mixer 7 are connected to the static mixer 7 via a pipeline; the static mixer 7 is connected to the mixing tank 13 via a pipeline; the mixing tank 14 is connected to the inlet pump 16 via a pipeline; the inlet pump 16 is connected to the fixed bed reactor 9 via a pipeline; the fixed bed reactor 9 is connected to the effluent tank 14 via a pipeline; the effluent tank 5 is connected to the flushing pump 16 via a pipeline; the flushing pump 16 is connected to the fixed bed reactor 9 via a pipeline; and the fixed bed reactor 9 is connected to the flushing wastewater collection tank 15 via a pipeline.

[0037] The automatic control system 8-2 is connected to the inlet pool 1 via the inlet flow meter 3. The automatic control device 8-2 is connected to the sulfuric acid dosing tank 5 via the sulfuric acid metering pump 4-1. The automatic control device 8-2 is connected to the calcium salt dosing tank 6 via the calcium salt metering pump 4-2.

[0038] In an embodiment of the present invention, an inlet is provided at the bottom of one side of the water inlet tank 1, and an outlet is provided on the other side; the outlet is connected to a static mixer 7 via a flow meter 3; the static mixer 7 is connected to a sulfuric acid dosing tank 5 via a sulfuric acid metering pump 4-1, and the static mixer 7 is connected to a calcium salt dosing tank 6 via a calcium salt metering pump 4-2.

[0039] In an embodiment of the present invention, the mixing tank 13 is provided with an inlet on one side and an outlet on the other side; the inlet of the mixing tank 17 is connected to the static mixer 7; the outlet of the mixing tank 13 is connected to the inlet pump 16, and the inlet pump 16 is connected to the fixed bed reactor 9.

[0040] In an embodiment of the present invention, a porous distribution plate 12 is provided at the inlet end of the fixed bed reactor 9 to uniformly disperse the flow rate of phosphorus-containing wastewater entering the fixed bed reactor 9. Precipitation and crystallization reactions occur in the fixed bed reactor 9. The precipitation reaction occurs in the eggshell pores, and the crystallization reaction occurs on the eggshell surface. The precipitate is intercepted by the eggshell particles, and the effluent flows out through the outlet of the fixed bed reactor 9 to the effluent pool 14.

[0041] In an embodiment of the present invention, both the inlet pool 1 and the mixing pool 13 are connected to the automatic control system 8-2 by an online detection device 8-1, and the automatic control system 8-2 is controlled by a computer.

[0042] In an embodiment of the present invention, the pH of the first stage in the mixing tank 13 is 3.0~5.0, the stirring speed is 20 r / min, and the stirring time is 5 min per hour; the pH of the second stage is 8.0~9.0, the stirring speed is 20 r / min, and the stirring time is 5 min per hour.

[0043] In the first stage, the pH of the fixed-bed reactor 9 is 6.0-8.0 and the hydraulic retention time is 30-40 minutes; in the second stage, the pH of the fixed-bed reactor 9 is 7.0-8.0 and the hydraulic retention time is 30-40 minutes.

[0044] In this embodiment of the invention, the pH-adjusting agent is a dilute sulfuric acid solution. The sulfuric acid dosing tank 5, the calcium salt dosing tank 6, and the mixing tank 13 are all equipped with stirring paddles.

[0045] This invention provides a method and system for graded treatment and phosphorus recovery of phosphorus wastewater based on eggshell-derived calcium sources. The method involves adding eggshells of different particle sizes and a mixed solution of calcium chloride and calcium hydroxide into the phosphorus removal system in stages. Specifically, in the process of treating phosphorus-containing wastewater, the first stage involves filling the fixed-bed reactor 9 with waste eggshells; the second stage involves adding a mixed solution of calcium chloride and calcium hydroxide.

[0046] In the first stage of an embodiment of the present invention, a dilute sulfuric acid solution with a concentration of 0.5 mM to 50 mM is added to the wastewater at a volume ratio of 1:100 with the original water, so that the pH of the solution in the mixing tank 13 is 3.0 to 5.0.

[0047] In the second stage of an embodiment of the present invention, a mixed solution of calcium salt and calcium hydroxide is added to the wastewater to ensure a precise calcium-to-phosphorus ratio of 5:1 to 8:1, so that the pH of the mixed solution is 8.0 to 9.0.

[0048] The reaction mechanism in the first stage is as follows: calcium ions dissolve from the eggshell, and phosphate ions in the wastewater react with calcium ions and hydroxide ions to form hydroxycalcium phosphate precipitate.

[0049] The XRD patterns of the eggshells used in this invention and the eggshell samples after phosphorus recovery are shown below. Figure 1 As shown, the main component of eggshells is calcium carbonate, and the main components of eggshells after phosphorus recovery are calcium carbonate and hydroxyapatite.

[0050] Example The supernatant from the sludge thickening tank of a wastewater treatment plant in a certain city was selected as the treatment target. The first stage wastewater entered the influent tank 1, and dilute sulfuric acid solution was added to the sulfuric acid dosing tank 5. The sulfuric acid metering pump 4-1 and flow meter 3 were turned on. The online detection device 8-1 fed back to the sulfuric acid metering pump 4-1 and flow meter 3 through the automatic control system 8-2, effectively controlling the dilute sulfuric acid solution and wastewater to enter the static mixer 7 at a ratio of 1:100 for mixing, and then enter the mixing tank 13 to be fully and evenly mixed again at a speed of 20 r / min, so that the pH in the tank is between 3.0 and 5.0. Pre-treated waste eggshells 17 are filled into the fixed-bed reactor 9. Water in the mixing tank 13 enters from the reactor inlet 10, flows through the porous distribution plate 12 to disperse the flow, and reacts with the waste eggshells 17 in the fixed-bed reactor 9 to generate hydroxyapatite precipitate.

[0051] The initial pH of the reaction system in the fixed-bed reactor 9 was 8.2. As the reactor operated, the pH of the reaction system gradually decreased. By the 56th day, the pH of the reaction system had dropped to 6.0, after which the reactor entered the second stage.

[0052] In the second stage, wastewater enters the influent tank 1. Calcium salt solution is added to the calcium salt dosing tank 6. The calcium salt metering pump 4-2 and flow meter 3 are turned on. The online monitoring device 8-1, through the automatic control system 8-2, feeds back to the calcium salt metering pump 4-2 and flow meter 3, ensuring a precise calcium-to-phosphorus dosing ratio of 5:1 to 8:1. The solution then enters the static mixer 7 for mixing and enters the mixing tank 13, where it is thoroughly and evenly mixed again at a speed of 20 r / min, maintaining a pH between 8.0 and 9.0. Water in the mixing tank 13 enters from the reactor inlet 10 and flows through the porous distribution plate 12 to disperse the flow. 2+ Hydroxide ions react with phosphate ions in water to form an insoluble precipitate of calcium hydroxyphosphate.

[0053] The reactor is flushed once every 24 hours of operation, with a flushing expansion rate of 20% and a flushing time of 5 to 10 minutes.

[0054] When the eggshell particle size increases from 0.58–0.85 mm or 0.85–1.7 mm to >5 mm, the eggshell particles are removed and replaced with new eggshell particles with a size of 0.58–0.85 mm or 0.85–1.7 mm, and the reactor re-enters the first stage of operation.

[0055] Following the same method described above, the trends in pH, dissolved phosphorus concentration, total phosphorus concentration, and turbidity concentration of the effluent during the first and second stages of operation of the fixed-bed reactor 9 are shown in Tables 1 and 2.

[0056] Table 1. pH value, dissolved phosphorus concentration, total phosphorus concentration, and turbidity of the effluent during the first stage of operation of fixed-bed reactor 9.

[0057] Table 2. pH, dissolved phosphorus concentration, total phosphorus concentration, and turbidity of the effluent during the second stage of operation of fixed-bed reactor 9.

[0058] Comparative Example Five water samples were used in the laboratory to simulate phosphorus-containing wastewater in a reactor experiment to investigate the effects of coexisting substances at different concentrations on phosphorus removal, as well as the interference mechanisms and effects of these substances on phosphorus removal efficiency. Water sample 1: tap water + NaH₂PO₄ + ammonia nitrogen; Water sample 2: tap water + NaH₂PO₄ + glucose; Water sample 3: tap water + NaH₂PO₄ + bovine serum albumin; Water sample 4: tap water + NaH₂PO₄ + fulvic acid. Specific data are shown in Table 3. Phosphorus concentration was measured after three hours of operation under each condition.

[0059] Table 3. TP / DP concentrations at different water sample concentrations for different water sample groups.

[0060] It can be seen that within the concentration range of 0-100 mg / L of the coexisting substances, the concentration of soluble phosphorus in each group did not fluctuate significantly, indicating that these coexisting substances have little effect on the direct solubility of soluble phosphorus.

[0061] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for recovering phosphorus from wastewater using eggshells as a calcium source, characterized in that, It includes two stages: First stage: Mix phosphorus-containing wastewater with dilute sulfuric acid solution to obtain mixed solution A, the pH of which is 3.0~5.0; The pretreated eggshells are reacted with mixed solution A to generate calcium hydroxyphosphate precipitate. After running for several days in this stage, the second stage begins. The second stage involves reacting phosphorus-containing wastewater with a mixed solution of calcium salts and calcium hydroxide to obtain mixed solution B, which has a pH of 8.0 to 9.

0. The eggshell system, after the first stage of treatment, is mixed with mixed solution B for reaction. Ca 2+ Hydroxide ions react with phosphate ions in water to form insoluble calcium hydroxyphosphate precipitate, reducing the phosphate ion concentration in the effluent to 0.5–5.5 mg / L.

2. The method for recovering phosphorus from wastewater using eggshells as a calcium source according to claim 1, characterized in that, In the first stage, the pre-treated eggshells are obtained by washing, drying and screening the waste eggshells.

3. The method for recovering phosphorus from wastewater using eggshells as a calcium source according to claim 1, characterized in that, In the first stage, when the pretreated eggshells react with mixed solution A, the pH of the reaction system is 6.0~8.0, and the hydraulic retention time is 30~40 minutes; The first phase of operation will last 50 to 60 days.

4. The method for recovering phosphorus from wastewater using eggshells as a calcium source according to claim 1, characterized in that, In the second stage, when the eggshell system after the first stage treatment is completed is mixed with mixed solution B, the pH of the reaction system is 7.0~8.0, and the hydraulic retention time is 30~40 minutes.

5. The method for recovering phosphorus from wastewater using eggshells as a calcium source according to claim 1, characterized in that, In the second stage, the calcium-to-phosphorus ratio is 5:1 to 8:

1.

6. The method for recovering phosphorus from wastewater using eggshells as a calcium source according to claim 1, characterized in that, The pre-treated eggshells have a particle size of 0.58–0.85 mm or 0.85–1.7 mm.

7. A phosphorus recovery system for wastewater using eggshells as a calcium source, implementing the recovery method according to any one of claims 1-6, characterized in that, It includes an inlet tank (1), a sulfuric acid dosing tank (5), a calcium salt dosing tank (6), a static mixer (7), a mixing tank (13), a porous distribution plate (12), a fixed bed reactor (9), and an outlet tank (14). The sulfuric acid dosing tank (5), the calcium salt dosing tank (6), and the inlet tank (1) are all connected to the static mixer (7), and the static mixer (7) is connected to the mixing tank (13); The fixed-bed reactor (9) includes a calcium carbonate dissolution reaction zone (9-1), a calcium phosphate main precipitation reaction zone (9-2), and a reaction protection zone (9-3) connected in sequence. The sulfuric acid dosing tank (5) stores a dilute sulfuric acid solution, and the calcium salt dosing tank (6) stores a mixed solution of calcium salt and calcium hydroxide. A flow meter (3) is installed on the pipeline connecting the inlet tank (1) to the static mixer (7); a sulfuric acid metering pump (4-1) is installed on the pipeline connecting the sulfuric acid dosing tank (5) to the static mixer (7); a calcium salt metering pump (4-2) is installed on the pipeline connecting the calcium salt dosing tank (6) to the static mixer (7). An online water detection device (8-1) is installed in the water inlet tank (1) to measure pH, total phosphorus and dissolved phosphorus; an automatic control system (8-2) is installed in the mixing tank (13) to control the water inlet flow meter (3), sulfuric acid metering pump (4-1) and calcium salt metering pump (4-2). An automatic effluent detection device (8-3) is installed at the outlet of the reaction protection zone (9-3) to measure pH, total phosphorus, and dissolved phosphorus.

8. A phosphorus recovery system for wastewater using eggshells as a calcium source according to claim 7, characterized in that, The mixing tank (13) is connected to the fixed bed reactor (9) via a porous distribution plate (12); the porous distribution plate (12) is set at the reactor inlet (10), and an inlet pump (16) is installed on the pipeline connecting the mixing tank (13) and the porous distribution plate (12).

9. A phosphorus recovery system for wastewater using eggshells as a calcium source according to claim 7, characterized in that, The reaction protection zone (9-3) is equipped with a reactor outlet (11-1) and a flushing outlet (11-2). The reactor outlet (11-1) is connected to the effluent pool (14), and the flushing outlet (11-2) is connected to the flushing wastewater collection pool (15).

10. A phosphorus recovery system for wastewater using eggshells as a calcium source according to claim 7, characterized in that, It also includes a cleaning water tank (18), an oven (19), and a standard screening device (20); After being washed in a washing water tank (18), the waste eggshells are dried in an oven (19) and then sent to a standard screening device (20) to obtain pre-treated waste eggshells (17).

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