A flow electrode capacitive deionization system and method for selective enrichment of phosphorus in phosphorus-containing wastewater

Abstract

The application belongs to the technical field of phosphorus-containing wastewater treatment and resource utilization, and relates to a flow electrode capacitive deionization system and method for selective enrichment of phosphorus in phosphorus-containing wastewater. The structure is that a first current collecting plate, a first anion exchange membrane, a cation exchange membrane, a second anion exchange membrane and a second current collecting plate are sequentially and parallelly arranged from left to right; each ion exchange membrane separates the system into an anode flow electrode chamber, a first solution chamber, a second solution chamber and a cathode flow electrode chamber; electrode liquid in the anode flow electrode chamber, the cathode flow electrode chamber and an electrode liquid storage chamber circulates and flows; the technical problem of low phosphorus enrichment multiple, poor selectivity, large acid and alkali consumption, high treatment cost and easy scaling is solved, and the application has good application prospect in phosphorus-containing wastewater treatment and phosphorus recovery.

Description

Technical Field

[0001] This invention belongs to the field of phosphorus-containing wastewater treatment and resource utilization technology, specifically relating to a flow electrode capacitive deionization system and method for selective enrichment of phosphorus in phosphorus-containing wastewater. Background Technology

[0002] Phosphorus is an essential element for all life forms on Earth and is a non-renewable resource. Currently, humanity faces a widespread contradiction between phosphorus deficiency and phosphorus pollution. On the one hand, at the current rate of consumption, the world's primary phosphate rock resources are expected to be depleted within the next 50-100 years. On the other hand, phosphorus is discharged into natural water bodies, leading to phosphorus pollution and eutrophication. Removing and recycling phosphorus from wastewater is an effective method to alleviate the phosphorus crisis and prevent phosphorus pollution in water. Phosphorus can be effectively recovered from wastewater through precipitation and crystallization processes, but the purity of the recovered product is directly affected by the phosphate concentration in the wastewater; generally, the higher the phosphorus concentration, the higher the purity of the recovered product. For example, a phosphate concentration higher than 100 mg / L is considered a necessary condition for the effective precipitation of struvite; when recovering lapis lazuli, increasing the phosphorus concentration from 50 mg / L to 400 mg / L can increase the phosphorus recovery rate from 28.2% to 97.2%. Therefore, it is necessary to increase the phosphorus concentration in the solution through enrichment technology to facilitate phosphorus recovery and improve the purity and efficiency of the recovered product.

[0003] Common methods for phosphorus enrichment in wastewater include ion exchange, physical adsorption, and membrane enrichment technologies. In ion exchange and physical adsorption processes, phosphates are captured on ion exchange resins or adsorbents and then eluted to obtain a higher concentration of phosphorus solution. Various ion exchange resins and adsorbents have been developed for the selective enrichment of phosphorus. For example, the invention patent "A resin for phosphorus removal from water, preparation method and application" (authorization announcement number CN112591851B) uses a weak acid cation resin loaded with lanthanum, and achieves selective removal and enrichment of phosphorus through the high selectivity of lanthanum oxygen bond to phosphate. The invention patent "A method for preparing a modified cellulose-based phosphorus removal adsorbent" (authorization announcement number CN110947371B) uses an in-situ solvent replacement method to graft and modify regenerated cellulose hydrogel with low melting point acid anhydride, and then generates nano-rare earth hydroxide in situ in its porous structure, synthesizing a loaded hydrogel material with selective phosphorus adsorption capacity. The invention patent "A method for preparing a highly unsaturated coordination system trivalent cerium phosphorus removal adsorbent" (authorization announcement number CN111203190B) discloses a method for synthesizing a trivalent cerium phosphorus removal adsorbent with a uniform MOF structure using trimesic acid and trivalent cerium ions. While these synthetic materials possess excellent phosphorus adsorption properties, they still face challenges such as limited phosphorus adsorption capacity, high acid and alkali consumption during material production, and performance degradation after multiple cycles, thus restricting their widespread application. Membrane technologies, such as nanofiltration and reverse osmosis, are also used for phosphorus enrichment and recovery, achieving phosphate rejection rates of 80-99%. However, membrane enrichment technologies are limited by osmotic pressure differences, resulting in lower phosphate enrichment ratios. For example, the invention patent "A Method for COD Removal and Resource Recovery from High-Phosphorus, High-COD Production Wastewater in the New Energy Industry" (application announcement number CN117964132A) only concentrated phosphorus by 6 times through a series of processes including extraction, acid-base adjustment, aeration, and reverse osmosis concentration. Furthermore, current membrane technologies cannot selectively separate phosphates in the presence of competing anions. Therefore, to address the shortcomings of existing phosphorus enrichment technologies, there is an urgent need to develop a new phosphorus enrichment and recovery technology.

[0004] Flow electrode capacitive deionization (FCDI) is a desalination technology developed based on the principle of supercapacitors. It has received widespread attention in recent years and has shown potential in phosphorus enrichment. The invention patent "A Simultaneous Nitrogen and Phosphorus Recovery Device and its Recovery Method and Application in Wastewater" (Application Publication No. CN113184952A) adds nitrogen and phosphorus recovery chambers to a traditional FCDI device. Positively charged nitrogen and negatively charged phosphorus in the wastewater pass through cation and anion exchange membranes respectively into the nitrogen and phosphorus recovery chambers under the influence of an electric field, and are ultimately recovered as concentrated ammonia and phosphoric acid, respectively. However, during the operation of this device, sodium hydroxide and hydrochloric acid need to be added to the nitrogen and phosphorus recovery chambers to balance charge migration. The addition of strong acids and alkalis not only shortens the lifespan of the device but also generates a large amount of high-salinity wastewater. The invention patent "A Flow Electrode Capacitive Deionization System and Method for Recovering Phosphorus from Leachate from Phosphogypsum Stockpile and Simultaneously Desalinating with Brine" (Authorization Announcement No. CN116102133B) proposes a dual-module flow electrode capacitive deionization system. This system connects the flow electrode liquid chambers of two three-chamber flow electrode capacitive deionization devices in series, which can achieve efficient phosphorus removal and avoid the simultaneous enrichment and precipitation of calcium, magnesium and other ions with phosphate and sulfate ions in the flow electrode chamber. However, this structure requires simultaneous treatment of brine as a counterion supplement when treating phosphorus-containing wastewater, resulting in a doubling of treatment energy consumption.

[0005] Traditional electro-driven and membrane enrichment methods simultaneously enrich cations and anions. However, as the enrichment concentration increases, phosphate and sulfate ions readily precipitate with common cations in wastewater, such as calcium and magnesium, leading to decreased operational stability and affecting the purity of the final phosphorus recovery product. In summary, existing methods for treating and concentrating phosphorus-containing wastewater suffer from low phosphorus enrichment ratios, poor selectivity, high acid and alkali consumption, and high treatment costs. While flow electrode capacitive deionization technology holds significant potential in resource recovery, current phosphorus recovery processes are complex and still cannot achieve selective phosphorus enrichment. Since phosphorus-containing wastewater often contains multiple anions, developing a low-cost, low-energy-consumption, highly selective, and stable method for treating phosphorus-containing wastewater and selectively enriching phosphorus has significant application value and environmental benefits. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a flow electrode capacitive deionization system and method for selective enrichment of phosphorus in phosphorus-containing wastewater. The purpose is to solve the technical problems of low phosphorus enrichment ratio, poor enrichment selectivity, high acid and alkali consumption, high treatment cost, and easy scaling in existing phosphorus-containing wastewater treatment and phosphorus concentration technologies.

[0007] According to a first aspect of the present invention, a flow electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater is provided. The system comprises, from left to right, a first current collector, a first anion exchange membrane, a cation exchange membrane, a second anion exchange membrane, and a second current collector arranged in parallel. The region between the first current collector and the first anion exchange membrane is an anode flow electrode chamber; the region between the first anion exchange membrane and the cation exchange membrane is a first solution chamber; the region between the cation exchange membrane and the second anion exchange membrane is a second solution chamber; the region between the second anion exchange membrane and the second current collector is a cathode flow electrode chamber; the outlet of the anode flow electrode chamber is connected to the inlet of the cathode flow electrode chamber via a first pipe; the outlet of the cathode flow electrode chamber is connected to the inlet of the anode flow electrode chamber via a second pipe; an electrode solution storage chamber is connected to the first pipe; a circulation pump is connected to the first pipe and / or the second pipe; the first solution chamber is connected to a phosphorus-containing wastewater tank; and the second solution chamber is connected to a brine tank.

[0008] Preferably, the first current collector is connected to the positive terminal of the power supply; the second current collector is connected to the negative terminal of the power supply, and the thickness of the second anion exchange membrane is 1 to 2 times the thickness of the first anion exchange membrane.

[0009] Preferably, the electrode liquid storage chamber is connected to the precipitation chamber; the precipitant in the precipitation chamber is a ferrous salt; preferably, the ferrous salt is ferrous sulfate or ferrous chloride.

[0010] Preferably, the initial electrode solution in the electrode solution storage chamber includes a conductive agent, an electrolyte, and a solvent;

[0011] Preferably, the conductive agent is selected from one or more of activated carbon, conductive carbon black, carbon nanotubes, or redox active substances;

[0012] Preferably, the redox active substance is selected from ferricyanide, ferrocene, viologen compounds (1,1'-dialkyl-4,4'-bipyridinium salt), 2,2,6,6-tetramethylpiperidine oxide, or their derivatives; preferably, the electrolyte is selected from one or two of sodium chloride and sodium sulfate.

[0013] Preferably, the solvent is water;

[0014] Preferably, the concentration of the electrolyte is 10-100 g / L; the mass of the conductive agent is 5-10 wt% of the mass of the initial electrode solution; and the pH of the initial electrode solution is 7.5-10.5.

[0015] Preferably, the brine in the brine pool is selected from one or two of sodium sulfate and sodium chloride; the salt concentration in the brine is 0.5 to 3 g / L.

[0016] Preferably, the phosphorus-containing wastewater in the phosphorus-containing wastewater pond is a solution after solid-liquid separation, wherein the total suspended solids are below 0.5 mg / L, the total content of calcium and magnesium is below 1000 mg / L, and the phosphorus content is 5-500 mg / L.

[0017] According to another aspect of the present invention, a method for selective enrichment of phosphorus in phosphorus-containing wastewater using the aforementioned flow electrode capacitive deionization system is provided, comprising the following steps:

[0018] (1) The phosphorus-containing wastewater in the phosphorus-containing wastewater tank is transported to the first solution chamber; the brine in the brine tank is transported to the second solution chamber;

[0019] (2) Turn on the circulation pump and pump the initial electrode liquid in the electrode liquid storage chamber to the cathode flow electrode chamber through the first pipe. The electrode liquid in the cathode flow electrode chamber enters the anode flow electrode chamber through the second pipe. The electrode liquid in the anode flow electrode chamber enters the electrode liquid storage chamber through the first pipe, so that the electrode liquid forms a circulation loop in the cathode flow electrode chamber, the anode flow electrode chamber and the electrode liquid storage chamber.

[0020] (3) Turn on the power so that the first current collector and the second current collector are powered on;

[0021] (4) When the phosphorus in the electrode solution in the electrode solution storage chamber reaches the predetermined concentration, the phosphorus in the electrode solution is recovered.

[0022] Preferably, in step (1), the specific method of conveying the phosphorus-containing wastewater from the phosphorus-containing wastewater tank to the first solution chamber is selected from single-pass water inlet or circulating water inlet; the single-pass water inlet specifically refers to conveying the phosphorus-containing wastewater from the phosphorus-containing wastewater tank to the first solution chamber by a water pump, and discharging it after a single deionization treatment; the circulating water inlet specifically refers to conveying the phosphorus-containing wastewater from the phosphorus-containing wastewater tank to the first solution chamber by a water pump, returning it to the phosphorus-containing wastewater tank after deionization treatment, and then circulating it into the first solution chamber for treatment;

[0023] Preferably, in step (1), the specific liquid inlet method for transporting the brine in the brine pool to the second solution chamber is selected from single-pass water inlet or circulating water inlet; the single-pass water inlet specifically refers to the brine being transported from the brine pool to the second solution chamber by a water pump, and discharged after a single ion enrichment; the circulating water inlet specifically refers to the brine being transported from the brine pool to the second solution chamber by a water pump, and after ion enrichment, returned to the brine pool and then circulated into the second solution chamber for treatment.

[0024] Preferably, after step (4), the electrode liquid in the electrode liquid storage chamber is passed into the precipitation chamber after solid-liquid separation to achieve phosphorus recovery;

[0025] Preferably, the solid conductive agent obtained after solid-liquid separation and the solution after phosphorus recovery in the precipitation chamber are mixed and then continuously fed into the electrode liquid storage chamber for recycling.

[0026] Preferably, in step (1), the flow rate of phosphorus-containing wastewater from the phosphorus-containing wastewater tank to the first solution chamber is V1; the flow rate of brine from the brine tank to the second solution chamber is V2; wherein V1 and V2 satisfy V1:V2 = 1 to 10.

[0027] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0028] (1) This invention introduces a first solution chamber into the flowing electrode capacitive deionization system. Anions in the first solution chamber enter the anode flowing electrode chamber under the influence of an electric field, while cations in the first solution chamber enter the second solution chamber under the same electric field. Therefore, the phosphorus-containing wastewater in the first solution chamber becomes recyclable freshwater after treatment. This invention, by introducing a second solution chamber into the flowing electrode capacitive deionization system, utilizes the characteristic that phosphorus migrates across the membrane more slowly than other anions to inhibit the continued migration of phosphorus into the second solution chamber from the flowing electrode solution, achieving selective retention and enrichment of phosphorus in the cathode flowing electrode chamber. Furthermore, the introduction of the second solution chamber allows for the enrichment of other cations within it. The separate enrichment of phosphorus and cations effectively reduces the scaling behavior of metal ions such as calcium and magnesium in the flowing electrode solution chamber and the solution chamber. Therefore, the flowing electrode capacitive deionization system and method of this invention, as a low-energy wastewater treatment technology, has promising application prospects in the treatment and recovery of phosphorus-containing wastewater.

[0029] (2) The present invention limits the phosphorus content in phosphorus-containing wastewater to 5-500 mg / L and the electrolyte concentration in the initial electrode solution to 10-100 g / L. The purpose is that during the continuous treatment process of the low-concentration phosphorus-containing wastewater entering the first solution chamber, both anions and phosphate ions in the solution will enter the anode flow electrode chamber and then circulate through the cathode flow electrode chamber. Since the electrolyte concentration in the electrode solution is relatively high at 10-100 g / L, by introducing a high concentration of competing anions in the flow electrode solution in advance, the proportion of phosphorus in the anions migrating to the second solution chamber is further reduced, thereby achieving high selective retention and enrichment of phosphorus in the electrode solution.

[0030] (3) The present invention limits the salt concentration in the brine to 0.5-3 g / L in order to reduce the internal resistance of the system in the early stage of device operation. The brine is introduced into the second solution chamber. A certain concentration of brine can prevent the internal resistance of the device from being too high in the early stage of device operation. If the internal resistance of the device is too high, the desalination rate of the device will be low. If the salt concentration of the brine is too high, the osmotic pressure will inhibit the entry of cations in the first solution chamber and anions in the cathode flow electrode chamber into the second solution chamber, thereby reducing the operating efficiency of the device.

[0031] (4) The present invention limits the thickness of the second anion exchange membrane to 1 to 2 times the thickness of the first anion exchange membrane in order to further reduce the selectivity of the anion exchange membrane for phosphorus, thereby reducing the transfer of phosphate ions from the cathode flow electrode chamber to the second solution chamber and improving the enrichment capacity of phosphorus in the flow electrode liquid; the present invention limits the flow rate V1 of phosphorus-containing wastewater to the first solution chamber to 1 to 10 times the flow rate V2 of brine from the brine pool to the second solution chamber, in order to improve the water recovery rate of the device.

[0032] (5) Phosphorus in the flowing electrode solution of this invention is recovered by precipitation with ferrous sulfate or ferrous chloride. The ferrous sulfate or ferrous chloride contains Cl... - and SO4 2- The phosphorus in the solution was replaced, and the anions that could compete with phosphorus were replenished. No additional large amount of electrolyte was needed in the electrode solution. The solution after phosphorus recovery could be reused as an electrode solution after being mixed with the separated conductive agent material again.

[0033] (6) The present invention uses a flow electrode capacitive deionization system and corresponding operating method to achieve efficient removal of ions from phosphorus-containing wastewater and selective enrichment of phosphorus elements, which greatly reduces the use of chemical reagents such as acids and alkalis and operating costs. The phosphorus removal rate and recovery efficiency are greater than 90%, and the phosphorus enrichment multiple is 5 to 100 times. The separated phosphorus-rich solution can be used to prepare high-purity blue iron ore and other high-value phosphorus recovery products, which have significant economic and environmental benefits. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a flow electrode capacitor deionization system provided in Embodiment 1 of the present invention;

[0035] Figure 2 The image shows the XRD pattern of lapis lazuli prepared by the method for treating phosphorus-containing wastewater and selectively enriching and recovering phosphorus based on flow electrode capacitive deionization technology provided in Embodiment 2 of the present invention.

[0036] Figure 3 The image shows a SEM image of lapis lazuli prepared by the method for treating phosphorus-containing wastewater and selectively enriching and recovering phosphorus based on flow electrode capacitive deionization technology provided in Embodiment 2 of the present invention.

[0037] The components are as follows: 1. First collector plate; 2. Anode flow electrode chamber; 3. First anion exchange membrane; 4. First solution chamber; 5. Cation exchange membrane; 6. Second solution chamber; 7. Second anion exchange membrane; 8. Cathode flow electrode chamber; 9. Electrode solution storage chamber; 10. Circulation pump; 11. Second collector plate; 12. First pipeline; 13. Phosphorus-containing wastewater tank; 14. Brine tank; 15. Second pipeline; 16. Sedimentation chamber. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] This invention addresses the shortcomings of existing technologies by providing a flowing electrode capacitive deionization system and method for the selective enrichment of phosphorus in phosphorus-containing wastewater. The flowing electrode capacitive deionization system includes a first current collector 1, a second current collector 11, an anode flowing electrode chamber 2, a first anion exchange membrane 3, a first solution chamber 4, a cation exchange membrane 5, a second solution chamber 6, a second anion exchange membrane 7, a cathode flowing electrode chamber 8, an electrode solution storage chamber 9, and a circulation pump 10. The anode flowing electrode chamber 2, the cathode flowing electrode chamber 8, and the electrode solution storage chamber 9 are cyclically connected, forming an independent flowing electrode solution circulation loop.

[0040] The method and principle of this invention are as follows: After applying a certain voltage to the first current collector 1 and the second current collector 11 at both ends of the flowing electrode capacitor deionization device, the flowing electrodes in the anode flowing electrode chamber 2 and the cathode flowing electrode chamber 8 will become positively and negatively charged respectively after directly and indirectly contacting the first current collector 1 and the second current collector 11. When phosphorus-containing wastewater enters the first solution chamber 4, under the action of the electric field, the cations in the solution (such as Na+) will... + K + Ca 2+ Mg 2+ NH4 + Phosphate ions (such as H2PO4) migrate through cation exchange membrane 5 to the second solution chamber 6; simultaneously, phosphate ions in the solution (such as H2PO4) migrate through cation exchange membrane 5 to the second solution chamber 6. - HPO4 2- PO4 3- ) and other anions (such as F) - Cl - SO4 2- NO3 -Phosphate ions migrate through the first anion exchange membrane 3 to the anode flow electrode chamber 2. These anions then circulate along the electrode solution loop to the electrode solution storage chamber 9 and the cathode flow electrode chamber 8. Since the voltage in the cathode flow electrode chamber 8 is negative, phosphate ions and other anions migrate towards the second solution chamber 6 due to charge repulsion. However, the transmembrane migration rate of phosphate ions is slower than that of other anions. Furthermore, the electrode solution contains a large amount of sodium sulfate or sodium chloride electrolyte. The high concentration of anions in the electrolyte, along with other anions circulating to the cathode flow electrode chamber 8, competes with phosphate ions for passage through the second anion exchange membrane 7. Additionally, the second anion exchange membrane 7, being an enhanced or thickened type, further hinders phosphate permeation, leading to a gradual accumulation of phosphate in the electrode solution. After operation, the electrode solution storage chamber 9 contains some of the initial electrolyte, a small amount of anions migrated from the first solution chamber 4, and most of the phosphate that migrated from the first solution chamber 4. Since the flow electrode solution does not contain Ca... 2+ Mg 2+ Easily precipitable cations are concentrated in the second solution chamber 6, thus preventing scaling in both the anolyte flow electrode chamber 2 and the cathode flow electrode chamber 8. The lower phosphate concentration in the second solution chamber 6 also makes it less prone to reacting with the concentrated Ca2+. 2+ Mg 2+ The formation of cations leads to precipitate formation and membrane scaling. When phosphorus accumulates to a certain level in the electrode solution storage chamber 9, the flowing electrode solution in the electrode solution storage chamber 9 is separated into solid and liquid phases using vacuum filtration or microfiltration. After separating the solid conductive agent, a phosphorus-rich clear solution is obtained. After adding ferrous salt to the solution, the reaction shown in formula (1) (where n can be 1, 2, or 3) generates lapis lazuli (ferrous phosphate, Fe3(PO4)2·8H2O).

[0041] 3Fe 2+ +2H 3-n PO4 n- +8H2O=Fe3(PO4)2·8H2O↓+(6-2n)H + (1)

[0042] Other anions present in the solution cannot undergo precipitation reactions with ferrous ions and are thus retained in the solution, ensuring the high purity of the product. Since the ferrous ions in the solution are added in the form of ferrous sulfate or ferrous chloride, the addition of ferrous ions also replenishes the Cl- ions previously consumed by the migration in the flowing electrode solution. - or SO4 2- The solution after phosphate recovery can be mixed again with the solid conductive material from the solid-liquid separation of the electrode liquid and reused as a flowing electrode liquid.

[0043] Example 1

[0044] This example uses a flow electrode capacitive deionization system for the selective enrichment of phosphorus in phosphorus-containing wastewater, as shown in the schematic diagram below. Figure 1 As shown, its structure consists of a first current collector 1, a first anion exchange membrane 3, a cation exchange membrane 5, a second anion exchange membrane 7, and a second current collector 11 arranged in parallel from left to right.

[0045] The region between the first current collector 1 and the first anion exchange membrane 3 is the anode flow electrode chamber 2; the region between the first anion exchange membrane 3 and the cation exchange membrane 5 is the first solution chamber 4; the region between the cation exchange membrane 5 and the second anion exchange membrane 7 is the second solution chamber 6; and the region between the second anion exchange membrane 7 and the second current collector 11 is the cathode flow electrode chamber 8.

[0046] The outlet of the anode flowing electrode chamber 2 is connected to the inlet of the cathode flowing electrode chamber 8 via a first pipe 12; the outlet of the cathode flowing electrode chamber 8 is connected to the inlet of the anode flowing electrode chamber 2 via a second pipe 15; an electrode liquid storage chamber 9 and a circulation pump 10 are connected to the first pipe 12; the first solution chamber 4 is connected to a phosphorus-containing wastewater tank 13; the second solution chamber 6 is connected to a brine tank 14. The electrode liquid storage chamber 9 is connected to a sedimentation chamber 16; the first current collector 1 is connected to the positive terminal of the power supply; the second current collector 11 is connected to the negative terminal of the power supply; the thickness of the second anion exchange membrane 7 is twice the thickness of the first anion exchange membrane 3.

[0047] Example 2

[0048] Figure 1 This is a process flow diagram of the mobile electrode capacitive deionization system for selective phosphorus enrichment in phosphorus-containing wastewater according to the present invention. This embodiment uses a mobile electrode capacitive deionization system from Example 1 to achieve desalination and simultaneous phosphorus enrichment of phosphorus-containing wastewater. The specific process is as follows:

[0049] To prepare simulated phosphorus-containing wastewater, 1.94 g of sodium dihydrogen phosphate was added to 1 L of water to prepare simulated phosphorus-containing wastewater (total phosphorus 500 mg / L). The simulated phosphorus-containing wastewater was pumped into the first solution chamber 4 at a flow rate of 10 mL / min, circulating within the phosphorus-containing wastewater tank 13 and the first solution chamber 4. Meanwhile, brine (NaCl content 1500 mg / L) was pumped into the second solution chamber 6 at a flow rate of 2.5 mL / min, using a single-pass pump. At a flow rate of 10 mL / min, the flowing electrodes in the electrode solution storage chamber 9 were sequentially pumped into the cathode flowing electrode chamber 8 and the anode flowing electrode chamber 2, circulating within these three chambers. Once the effluent from the first solution chamber 4 stabilized, power was applied, controlling the voltage between the first collector plate 1 and the second collector plate 11 to 1.2 V, and the device was continuously operated until the conductivity of the phosphorus-containing wastewater tank dropped below 100 μS / cm.

[0050] The electrode solution storage chamber 9 contains 113g of flowing electrode solution; the flowing electrode solution is a suspension of activated carbon, conductive carbon black, sodium chloride, and water; the suspension contains 9g of activated carbon, 1g of conductive carbon black, 1g of sodium chloride, and 100g of water. The thicknesses of the first anion exchange membrane 3 and the second anion exchange membrane 7 are 50μm and 100μm, respectively.

[0051] After the treatment process was completed, the residual phosphorus content in phosphorus-containing wastewater tank 13 was measured. The calculated residual phosphorus concentration and removal rate in phosphorus-containing wastewater tank 13 were 5.2 mg / L and 98.96%, respectively, with a phosphorus concentration factor of 8.4 times in the flowing electrode solution. A phosphorus-rich supernatant with pH = 7.5 was obtained from the slurry in electrode solution storage chamber 9 by filtration. Its composition was: total phosphorus 3906 mg / L, Cl... - 872 mg / L, Na + 3517 mg / L.

[0052] Ferrous chloride solution was mixed with phosphorus-rich supernatant at a total Fe / P molar ratio of 1.5 and transferred to precipitation chamber 16 for crystallization. The pH of the solution was controlled at 7.5 using 0.05 mol / L hydrochloric acid and 0.05 mol / L sodium hydroxide. After stirring for 0.5 h, the mixture was allowed to stand for 2.5 h to precipitate. After precipitation, the solid sample was obtained by filtration. The XRD pattern of the solid sample obtained in Example 2 is shown below. Figure 2 As shown, all its characteristic diffraction peaks are consistent with those of vivianite (chemical formula Fe3(PO4)2·8H2O); the SEM image of the solid sample is shown below. Figure 3 As shown, it exhibits a petal-like shape, which is consistent with the surface morphology and structure of vivianite reported in existing literature; the purity of vivianite in the obtained solid sample reached 98.5% after chemical purity calculation.

[0053] Example 3

[0054] This embodiment uses a flow electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater as described in Example 1. The main difference from Example 2 is that the amount of sodium chloride electrolyte added to the electrode liquid storage chamber 9 is 10g.

[0055] After the treatment process was completed, the residual phosphorus content in the phosphorus-containing wastewater tank was measured. The calculated residual phosphorus concentration and removal rate in the wastewater tank were 4.8 mg / L and 99.04%, respectively, with a phosphorus concentration factor of 9.8 times in the flowing electrode solution. A phosphorus-rich supernatant with pH = 7.5 was obtained from the slurry in electrode solution storage chamber 9 by filtration. Its composition was: total phosphorus 4579 mg / L, Cl... - 51040mg / L, Na + 36650mg / L.

[0056] Ferrous chloride solution was mixed with phosphorus-rich supernatant at a total Fe / P molar ratio of 1.5 and transferred to precipitation chamber 16 for crystallization. The pH of the solution was controlled at 7.5 using 0.05 mol / L hydrochloric acid and 0.05 mol / L sodium hydroxide. After stirring for 0.5 h, the mixture was allowed to stand for 2.5 h to precipitate. After precipitation, the solid sample was obtained by filtration. XRD characterization of the solid sample showed that it was vivianite with a purity of 98.7%.

[0057] Example 4

[0058] This embodiment employs a phosphorus-containing wastewater treatment and phosphorus selective enrichment system based on flowing electrode capacitive deionization technology, as described in Embodiment 1. The main difference from Embodiment 3 is that the phosphorus-containing wastewater is actual wastewater (originating from the supernatant of the sludge thickening tank at the Tangxun Lake wastewater treatment plant), and the actual wastewater is filtered to remove suspended solids (total phosphorus 42.3 mg / L, SO42). 2- 63.2 mg / L, Cl - 89.7 mg / L, NO3 - 3.0 mg / L, Ca 2+ 50.7 mg / L, Mg 2+ 15.5 mg / L, total iron 0.16 mg / L, NH4 + The sodium chloride content in electrode solution storage chamber 9 is 3g (35.6mg / L). The phosphorus-containing wastewater is pumped to the first solution chamber 4 at a single-pass inlet rate of 10mL / min. The brine (NaCl content is 1500mg / L) is pumped to the second solution chamber 6 at a single-pass inlet rate of 1.0mL / min and runs continuously for 20h.

[0059] During operation, the content of various ions in the effluent from the first solution chamber 4 was measured, and the removal rates of various ions in the phosphorus-containing wastewater were calculated as follows: total phosphorus 90.3%, SO42- ...2- 92.6%, Cl - 94.3, NO3 - 46.7%, Ca 2+ 81.5%, Mg 2+ 76.1%, NH4 + The phosphorus concentration in the flowing electrode solution was 83.1%, with a concentration factor of 99.2 times. A phosphorus-rich supernatant with pH = 7.5 was obtained from the slurry in electrode solution storage chamber 9 by vacuum filtration. Its composition was: total phosphorus 3862 mg / L, SO42- 2- 810 mg / L, Cl - 11200mg / L, NO3 - 58mg / L, Na + 11060mg / L.

[0060] Ferrous chloride solution was mixed with phosphorus-rich supernatant at a total Fe / P molar ratio of 1.5 and transported to precipitation chamber 16 for crystallization. The pH of the solution was controlled at 7.5 using 0.05 mol / L hydrochloric acid and 0.05 mol / L sodium hydroxide. After stirring for 0.5 h, the mixture was allowed to stand for 2.5 h to precipitate. After precipitation, the solid sample was obtained by filtration. XRD characterization of the solid sample showed that it was vivianite with a purity of 98.3%.

[0061] The results show that, after the above process, the phosphorus concentration in the electrode solution can reach 5 to 100 times the initial phosphorus concentration in the first solution chamber 4. The phosphorus enriched in the electrode solution has high purity after being recovered by the blue iron ore method, and has extremely high application value. At the same time, the flow electrode capacitor deionization system with the addition of a concentration chamber has also significantly improved in terms of stability, desalination rate and charge efficiency compared with the ordinary three-chamber system.

[0062] In summary, this invention provides a flow electrode capacitive deionization system and method for treating and simultaneously recovering phosphorus from phosphorus-containing wastewater. By employing the flow electrode capacitive deionization system and corresponding operating method, it is possible to simultaneously achieve rapid removal of ions from phosphorus-containing wastewater and efficient selective enrichment of phosphorus, significantly reducing the use of chemical reagents such as acids and alkalis and the operating costs. Moreover, it achieves high phosphorus removal rate, enrichment factor, and recovery efficiency. The separated phosphorus-rich solution can be used to prepare high-purity blue iron ore and other high-value phosphorus recovery products, which has significant economic and environmental benefits. This invention is of great significance for environmental protection and the recovery of phosphorus resources from phosphorus-containing wastewater.

[0063] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A flowing electrode capacitive deionization system for the selective enrichment of phosphorus in phosphorus-containing wastewater, characterized in that, Its structure consists of a first current collector (1), a first anion exchange membrane (3), a cation exchange membrane (5), a second anion exchange membrane (7), and a second current collector (11) arranged in parallel from left to right. The region between the first current collector (1) and the first anion exchange membrane (3) is the anode flow electrode chamber (2); the region between the first anion exchange membrane (3) and the cation exchange membrane (5) is the first solution chamber (4); the region between the cation exchange membrane (5) and the second anion exchange membrane (7) is the second solution chamber (6); and the region between the second anion exchange membrane (7) and the second current collector (11) is the cathode flow electrode chamber (8). The outlet of the anode flowing electrode chamber (2) is connected to the inlet of the cathode flowing electrode chamber (8) via a first pipe (12); the outlet of the cathode flowing electrode chamber (8) is connected to the inlet of the anode flowing electrode chamber (2) via a second pipe (15); an electrode liquid storage chamber (9) is connected to the first pipe (12); a circulation pump (10) is connected to the first pipe (12) and / or the second pipe (15); the circulation pump (10) on the first pipe (12) is used to circulate the initial electrode liquid in the electrode liquid storage chamber (9) through... The solution is pumped through the first pipeline to the cathode flow electrode chamber (8); the first solution chamber (4) is connected to the phosphorus-containing wastewater tank (13); the second solution chamber (6) is connected to the brine tank (14); the thickness of the second anion exchange membrane (7) is 1 to 2 times the thickness of the first anion exchange membrane (3); the second anion exchange membrane (7) is an enhanced or thickened anion exchange membrane used to block the permeation of phosphate; the initial electrode solution in the electrode solution storage chamber (9) includes a conductive agent, an electrolyte and a solvent; the concentration of the electrolyte is 10 to 100 g / L.

2. The flowing electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater according to claim 1, characterized in that, The first current collector (1) is connected to the positive terminal of the power supply; the second current collector (11) is connected to the negative terminal of the power supply.

3. The flowing electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater according to claim 1, characterized in that, The electrode liquid storage chamber (9) is connected to the precipitation chamber (16); the precipitant in the precipitation chamber (16) is a ferrous salt; the ferrous salt is ferrous sulfate or ferrous chloride.

4. A flow electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater according to claim 1, characterized in that, The conductive agent is selected from one or more of activated carbon, conductive carbon black, carbon nanotubes, or redox active substances; the redox active substance is selected from one or more of ferricyanide, ferrocene, viologen compounds, 2,2,6,6-tetramethylpiperidine oxide, or their derivatives; the electrolyte is selected from one or two of sodium chloride and sodium sulfate; the solvent is water; the viologen compound is 1,1'-dialkyl-4,4'-bipyridinium salt; The conductive agent accounts for 5-10 wt% of the initial electrode solution; the pH of the initial electrode solution is 7.5-10.

5.

5. A flowing electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater according to claim 1, characterized in that, The brine in the brine pool is selected from one or two of sodium sulfate and sodium chloride; the salt concentration in the brine is 0.5~3 g / L.

6. A flowing electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater according to claim 1, characterized in that, The phosphorus-containing wastewater in the phosphorus-containing wastewater pool (13) is a solution after solid-liquid separation, wherein the total suspended solids are below 0.5 mg / L, the total content of calcium and magnesium is below 1000 mg / L, and the phosphorus content is 5~500 mg / L.

7. A method for selective enrichment of phosphorus in phosphorus-containing wastewater using a flow electrode capacitive deionization system according to any one of claims 1-6, characterized in that, Includes the following steps: (1) The phosphorus-containing wastewater in the phosphorus-containing wastewater tank is transported to the first solution chamber; the brine in the brine tank is transported to the second solution chamber; (2) Turn on the circulation pump and pump the initial electrode liquid in the electrode liquid storage chamber to the cathode flow electrode chamber through the first pipe. The electrode liquid in the cathode flow electrode chamber enters the anode flow electrode chamber through the second pipe. The electrode liquid in the anode flow electrode chamber enters the electrode liquid storage chamber through the first pipe, so that the electrode liquid forms a circulation loop in the cathode flow electrode chamber, the anode flow electrode chamber and the electrode liquid storage chamber. (3) Turn on the power so that the first current collector and the second current collector are running under energized conditions; (4) When the phosphorus in the electrode solution in the electrode solution storage chamber reaches the predetermined concentration, the phosphorus in the electrode solution is recovered.

8. The method for selective enrichment of phosphorus in phosphorus-containing wastewater according to claim 7, characterized in that, In step (1), the specific method of conveying the phosphorus-containing wastewater from the phosphorus-containing wastewater tank to the first solution chamber is selected from single-pass water inlet or circulating water inlet; the single-pass water inlet specifically refers to conveying the phosphorus-containing wastewater from the phosphorus-containing wastewater tank to the first solution chamber by a water pump, and then discharging it after a single deionization treatment; the circulating water inlet specifically refers to conveying the phosphorus-containing wastewater from the phosphorus-containing wastewater tank to the first solution chamber by a water pump, and then returning it to the phosphorus-containing wastewater tank after deionization treatment and then circulating it into the first solution chamber for treatment; In step (1), the specific liquid inlet method for transporting the brine in the brine pool to the second solution chamber is selected from single-pass water inlet or circulating water inlet; the single-pass water inlet specifically refers to the brine being transported from the brine pool to the second solution chamber by a water pump, and discharged after a single ion enrichment; the circulating water inlet specifically refers to the brine being transported from the brine pool to the second solution chamber by a water pump, and returned to the brine pool after ion enrichment and then circulated into the second solution chamber for treatment.

9. The method for selective enrichment of phosphorus in phosphorus-containing wastewater according to claim 7, characterized in that, After step (4), the electrode liquid in the electrode liquid storage chamber is passed into the precipitation chamber after solid-liquid separation to achieve phosphorus recovery; The solid conductive agent obtained after solid-liquid separation, and the solution after phosphorus recovery in the precipitation chamber are mixed and then continuously fed into the electrode liquid storage chamber for recycling.

10. The method for selective enrichment of phosphorus in phosphorus-containing wastewater according to claim 7, characterized in that, In step (1), the flow rate of phosphorus-containing wastewater from the phosphorus-containing wastewater tank to the first solution chamber is V1; the flow rate of brine from the brine tank to the second solution chamber is V2; where V1 and V2 satisfy V1:V2=1~10.

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