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

Abstract

The invention belongs to the technical field of phosphorus-containing wastewater treatment and recycling, and relates to a flowing electrode capacitive deionization system and method for selective enrichment of phosphorus in phosphorus-containing wastewater. According to the structure, a first collector plate, a first anion exchange membrane, a cation exchange membrane, a second anion exchange membrane and a second collector plate are sequentially arranged in parallel from left to right; the ion exchange membranes divide 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 flowing electrode chamber, the cathode flowing electrode chamber and the electrode liquid storage chamber circularly flows; the technical problems of low phosphorus enrichment multiple, poor selectivity, large acid and alkali consumption, high treatment cost and easy scaling are solved, and the method has good application prospects in the aspects of phosphorus-containing wastewater treatment and phosphorus recovery.

Description

Technical Field

[0001] The present invention belongs to the technical field of phosphorus-containing wastewater treatment and resource utilization, and particularly relates to a flow electrode capacitive deionization system and method for selective enrichment of phosphorus in phosphorus-containing wastewater. Background Art

[0002] Phosphorus is an essential element required by all life forms on earth and is also a non-renewable resource. Currently, humanity is generally facing the contradiction between phosphorus deficiency and phosphorus pollution. On the one hand, at the current consumption rate, 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 water body phosphorus pollution and eutrophication. Removing and recovering 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 speaking, 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 effective struvite precipitation; when recovering vivianite, when the phosphorus concentration increases from 50 mg / L to 400 mg / L, the phosphorus recovery rate can increase 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 recovery efficiency of phosphorus recovery products.

[0003] Common methods for enriching phosphorus in wastewater include ion exchange, physical adsorption and membrane enrichment technology. In the ion exchange and physical adsorption process, phosphate is captured on ion exchange resins or adsorbents, and then eluted to obtain a higher concentration of phosphorus solution. A variety of ion exchange resin materials and adsorbent materials have been developed for the selective enrichment of phosphorus. For example, the invention patent "A resin for removing phosphorus from water, preparation method and application thereof" (authorization announcement number CN112591851B) uses a weak acid cationic resin to load lanthanum, and achieves selective removal and enrichment of phosphorus through the high selectivity of lanthanum oxygen bonds for 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-modify regenerated cellulose hydrogel with a low-melting-point acid anhydride, and then in-situ generates nano rare earth hydroxides in its porous structure to synthesize a loaded hydrogel material with selective adsorption capacity for phosphorus. The invention patent "A method for preparing a highly unsaturated coordination system trivalent cerium phosphorus removal adsorbent" (authorization announcement number CN111203190B) discloses a trivalent cerium phosphorus removal adsorbent with a uniform MOF structure synthesized using trimesic acid and trivalent cerium ions. Although these synthetic materials have excellent phosphorus adsorption performance, they still face challenges such as limited phosphorus adsorption capacity, high acid and alkali consumption during material generation, and performance degradation after multiple cycles, which limits their widespread application. Membrane technologies such as nanofiltration and reverse osmosis are also used for phosphorus enrichment and recovery, and the phosphate retention rate can reach 80-99%. However, membrane enrichment technology is limited by the osmotic pressure difference, and the phosphate enrichment multiple is low. For example, the invention patent "A method for removing COD and recycling resources from high-phosphorus and high-COD production wastewater in the new energy industry" (application announcement number CN117964132A) only concentrates phosphorus by 6 times through a series of processes such as wastewater extraction, acid-base adjustment, aeration and reverse osmosis concentration. In addition, current membrane technology cannot selectively separate phosphates in the presence of competing anions. Therefore, in order to solve the shortcomings of existing phosphorus enrichment technology, it is urgent to develop a new phosphorus enrichment and recovery technology.

[0004] Flowing electrode capacitive deionization technology (FCDI) is a desalination technology developed based on the principle of supercapacitors. It has received widespread attention in recent years and has shown certain potential in phosphorus enrichment. The invention patent "A nitrogen and phosphorus synchronous recovery device in wastewater and its recovery method and application" (application publication number CN113184952A) adds a nitrogen recovery chamber and a phosphorus recovery chamber to the traditional flowing electrode capacitive deionization device. The positively charged nitrogen and negatively charged phosphorus in the wastewater enter the nitrogen recovery chamber and the phosphorus recovery chamber through the cation and anion exchange membranes respectively under the action of the electric field, and are finally recovered in the form of concentrated ammonia water and phosphoric acid. However, during the operation of the device, sodium hydroxide and hydrochloric acid need to be added to the nitrogen and phosphorus recovery chambers to balance the charge migration. The addition of strong acid and strong base will not only shorten the service life of the device, but also produce a large amount of high-salt wastewater. The invention patent "A flowing electrode capacitor deionization system and method for recovering phosphorus from leachate of phosphogypsum storage yard and simultaneously desalting brine" (authorization announcement number CN116102133B) proposes a dual-module flowing electrode capacitor deionization system. The system connects the flowing electrode liquid chambers of two three-chamber flowing electrode capacitor deionization devices in series, which can achieve efficient phosphorus removal of the device and avoid the simultaneous enrichment and precipitation of calcium, magnesium ions and phosphate and sulfate ions in the flowing electrode chambers. However, this structure requires the simultaneous treatment of brine as a counter-ion supplement when treating phosphorus-containing wastewater, resulting in doubling of the treatment energy consumption.

[0005] Traditional electric drive and membrane enrichment methods will simultaneously enrich anions and cations. As the enrichment concentration continues to increase, phosphate ions and sulfate ions are very likely to form precipitation with common cations such as calcium and magnesium in wastewater, which reduces the stability of the device operation and affects the purity of the final phosphorus recovery product. In summary, the existing phosphorus-containing wastewater treatment and concentration methods have problems such as low phosphorus enrichment multiples, poor enrichment selectivity, large acid and alkali consumption, and high treatment costs. Mobile electrode capacitive deionization technology has high application potential in the field of resource recovery, but the phosphorus recovery process of existing related research is complicated and still cannot achieve selective enrichment of phosphorus. Since phosphorus-containing wastewater often contains a variety of anions, developing a phosphorus-containing wastewater treatment and phosphorus selective enrichment method with low cost, low energy consumption, high enrichment selectivity, and good stability has important application value and environmental benefits. Summary of the invention

[0006] In view of the defects of the prior art, the present invention provides a mobile electrode capacitive deionization system and method for the selective enrichment of phosphorus in phosphorus-containing wastewater, which aims to solve the technical problems of low phosphorus enrichment multiple, poor enrichment selectivity, large acid and alkali consumption, high treatment cost and easy scaling in the existing phosphorus-containing wastewater treatment and phosphorus concentration technologies.

[0007] According to the first aspect of the present invention, there is provided a flow electrode capacitive deionization system for the selective enrichment of phosphorus in phosphorus-containing wastewater. Its structure is that a first current collector plate, a first anion exchange membrane, a cation exchange membrane, a second anion exchange membrane, and a second current collector plate are arranged in parallel from left to right; the area between the first current collector plate and the first anion exchange membrane is the anode flow electrode chamber; the area between the first anion exchange membrane and the cation exchange membrane is the first solution chamber; the area between the cation exchange membrane and the second anion exchange membrane is the second solution chamber; the area between the second anion exchange membrane and the second current collector plate is the cathode flow electrode chamber; the liquid outlet of the anode flow electrode chamber is connected to the liquid inlet of the cathode flow electrode chamber through a first pipeline; the liquid outlet of the cathode flow electrode chamber is connected to the liquid inlet of the anode flow electrode chamber through a second pipeline; an electrode liquid storage chamber is connected to the first pipeline; a circulation pump is connected to the first pipeline and / or the second pipeline; the first solution chamber is connected to a phosphorus-containing wastewater pool; the second solution chamber is connected to a brine pool.

[0008] Preferably, the first current collector plate is connected to the positive electrode of the power supply; the second current collector plate is connected to the negative electrode 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 a 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 liquid in the electrode liquid 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 salts), 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 to 100 g / L; the mass of the conductive agent is 5 to 10 wt% of the mass of the initial electrode liquid; the pH of the initial electrode liquid is 7.5 to 10.5.

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

[0016] Preferably, the phosphorus-containing wastewater in the phosphorus-containing wastewater tank 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 elements is below 1000 mg / L, and the phosphorus element content is 5-500 mg / L.

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

[0018] (1) Transport the phosphorus-containing wastewater in the phosphorus-containing wastewater tank to the first solution chamber; transport the brine in the brine tank 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 pipeline. The electrode liquid in the cathode flow electrode chamber enters the anode flow electrode chamber through the second pipeline, and the electrode liquid in the anode flow electrode chamber enters the electrode liquid storage chamber again through the first pipeline, 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 supply to operate the first current collector plate and the second current collector plate under the condition of being energized;

[0021] (4) After the phosphorus in the electrode liquid in the electrode liquid storage chamber reaches a predetermined concentration, recover the phosphorus in the electrode liquid.

[0022] Preferably, in step (1), the specific liquid inlet mode for transporting the phosphorus-containing wastewater in 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 is specifically to transport the phosphorus-containing wastewater from the phosphorus-containing wastewater tank to the first solution chamber by a water pump, and discharge it after single deionization treatment; the circulating water inlet is specifically to transport the phosphorus-containing wastewater from the phosphorus-containing wastewater tank to the first solution chamber by a water pump, return it to the phosphorus-containing wastewater tank after deionization treatment, and then circulate into the first solution chamber for treatment;

[0023] Preferably, in step (1), the specific liquid inlet mode for transporting the brine in the brine tank to the second solution chamber is selected from single-pass water inlet or circulating water inlet; the single-pass water inlet is specifically to transport the brine from the brine tank to the second solution chamber by a water pump, and discharge it after single ion enrichment; the circulating water inlet is specifically to transport the brine from the brine tank to the second solution chamber by a water pump, return it to the brine tank after ion enrichment, and then circulate into the second solution chamber for treatment.

[0024] Preferably, after step (4), it further includes passing the electrode liquid in the electrode liquid storage chamber through solid-liquid separation and then into the precipitation chamber to achieve phosphorus recovery;

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

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

[0027] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0028] (1) By introducing a first solution chamber into the flow-through electrode capacitive deionization system in the present invention, the anions in the first solution chamber enter the anode flow-through electrode chamber under the action of an electric field, and the cations in the first solution chamber enter the second solution chamber under the action of an electric field. Therefore, the phosphorus-containing wastewater in the first solution chamber is treated into fresh water that can be recycled; by introducing a second solution chamber into the flow-through electrode capacitive deionization system in the present invention, the slow transmembrane migration rate of phosphorus compared with other anions is utilized to inhibit the continuous migration of phosphorus entering the flow-through electrode liquid into the second solution chamber, realizing the selective interception and enrichment of phosphorus in the cathode flow-through electrode chamber; on the other hand, the enrichment of other cations in the second solution chamber can be realized by introducing the second solution chamber, and the separate enrichment of phosphorus and cations can effectively reduce the scaling behavior of metal ions such as calcium and magnesium in the flow-through electrode liquid chamber and the solution chamber. Therefore, the flow-through electrode capacitive deionization system and method of the present invention, as a low-energy-consuming wastewater treatment technology, have good application prospects in both phosphorus-containing wastewater treatment and phosphorus recovery.

[0029] (2) The present invention limits the content of phosphorus element in the phosphorus-containing wastewater to 5-500 mg / L, and the concentration of the electrolyte in the initial electrode liquid to 10-100 g / L. The purpose is that in 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-through electrode chamber and then pass through the cathode flow-through electrode chamber through circulation. Since the concentration of the electrolyte in the electrode liquid is relatively high at 10-100 g / L, by pre-introducing a high-concentration competitive anion in the flow-through electrode liquid, the proportion of phosphorus in the anions migrating into the second solution chamber is further reduced, realizing the high-selectivity interception and enrichment of phosphorus in the electrode liquid.

[0030] (3) The present invention defines the salt concentration in the brine to be 0.5 - 3 g / L, aiming to reduce the internal resistance of the system in the initial stage of the device operation. The brine is introduced into the second solution chamber. Brine with a certain concentration can prevent the internal resistance of the device from being too large in the initial stage of operation. Excessive internal resistance of the device will lead to a low desalination rate of the device; too high a salt concentration in the brine will inhibit the entry of cations in the first solution chamber and anions in the cathode flow electrode chamber into the second solution chamber due to excessive osmotic pressure, thereby reducing the operation efficiency of the device.

[0031] (4) The present invention defines the thickness of the second anion exchange membrane to be 1 - 2 times that of the first anion exchange membrane, so as to further reduce the selectivity of the anion exchange membrane to phosphorus, thereby reducing the transfer of phosphate ions in the cathode flow electrode chamber to the second solution chamber and improving the enrichment ability of phosphorus in the flow electrode liquid; the present invention defines the flow rate V1 of the phosphorus-containing wastewater transported to the first solution chamber to be 1 - 10 times that of the flow rate V2 of the brine in the brine tank transported to the second solution chamber, aiming to improve the water recovery rate of the device.

[0032] (5) Phosphorus in the flow electrode liquid of the present invention is recovered by the ferrous sulfate or ferrous chloride precipitation method. Cl in ferrous sulfate or ferrous chloride - and SO4 2- displaces phosphorus in the solution, and anions available for competing with phosphorus in the solution are replenished. There is no need to additionally supplement a large amount of electrolytes in the electrode liquid. The solution after phosphorus recovery can be mixed with the separated conductive agent material again and can continue to be used as the electrode liquid for circulation.

[0033] (6) The present invention adopts a flow electrode capacitive deionization system and the corresponding operation method, which can achieve efficient removal of ions in the phosphorus-containing wastewater and simultaneously achieve selective enrichment of phosphorus elements therein, greatly reducing the use of chemical reagents such as acids and alkalis and the operation cost. The phosphorus removal rate and recovery efficiency are greater than 90%, the phosphorus enrichment multiple reaches 5 - 100 times, and the separated phosphorus-rich solution can be used to prepare high-value phosphorus recovery products such as high-purity vivianite, having significant economic and environmental benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 FIG. is a schematic diagram of a flow electrode capacitive deionization system provided by Embodiment 1 of the present invention;

[0035] Figure 2 FIG. is an XRD pattern of vivianite prepared by the method for treating phosphorus-containing wastewater and selectively enriching and recovering phosphorus based on the flow electrode capacitive deionization technology provided by Embodiment 2 of the present invention.

[0036] Figure 3 FIG. is an SEM image of vivianite prepared by the method for treating phosphorus-containing wastewater and selectively enriching and recovering phosphorus based on the flow electrode capacitive deionization technology provided by Embodiment 2 of the present invention.

[0037] Among them, 1 is the first current collector plate; 2 is the anodic flow electrode chamber; 3 is the first anion exchange membrane; 4 is the first solution chamber; 5 is the cation exchange membrane; 6 is the second solution chamber; 7 is the second anion exchange membrane; 8 is the cathodic flow electrode chamber; 9 is the electrode liquid storage chamber; 10 is the circulation pump; 11 is the second current collector plate; 12 is the first pipeline; 13 is the phosphorus-containing wastewater tank; 14 is the brine tank; 15 is the second pipeline; 16 is the precipitation chamber. Specific embodiments

[0038] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present 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 only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] In view of the deficiencies of the prior art, the present invention provides a flow electrode capacitive deionization system and method for selectively enriching phosphorus in phosphorus-containing wastewater. The flow electrode capacitive deionization system includes a first current collector plate 1, a second current collector plate 11, an anodic flow 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 cathodic flow electrode chamber 8, an electrode liquid storage chamber 9, and a circulation pump 10. Among them, the anodic flow electrode chamber 2, the cathodic flow electrode chamber 8, and the electrode liquid storage chamber 9 are connected in a circulating manner to form an independent circulating circuit for the flow electrode liquid.

[0040] The method and principle of the present invention are as follows: After applying a certain voltage to the first current collector plate 1 and the second current collector plate 11 at both ends of the flow electrode capacitive deionization device, the flow electrodes in the anodic flow electrode chamber 2 and the cathodic flow electrode chamber 8 will be positively charged and negatively charged respectively after directly or indirectly contacting the first current collector plate 1 and the second current collector plate 11. When the phosphorus-containing wastewater enters the first solution chamber 4, under the action of the electric field, cations in the solution (such as Na + , K + , Ca 2+ , Mg 2+ , NH4 + , etc.) migrate through the cation exchange membrane 5 to the second solution chamber 6; at the same time, phosphate ions (such as H2PO4 - , HPO4 2- , PO4 3- ) and other anions (such as F - , Cl - , SO4 2- , NO3 -) migrate to the anode flow electrode chamber 2 through the first anion exchange membrane 3, and then these anions circulate along the electrode liquid circulation loop to the electrode liquid storage chamber 9 and the cathode flow electrode chamber 8. Since the voltage of the cathode flow electrode chamber 8 is negative, under the action of charge repulsion, phosphate ions and other anions will migrate towards the second solution chamber 6. However, the transmembrane migration rate of phosphate ions is slower than that of other anions, and the electrode liquid contains a large amount of electrolytes such as sodium sulfate or sodium chloride. The high-concentration anions in the electrolyte and other anions circulating to the cathode flow electrode chamber 8 will compete with the phosphate ions for permeating through the second anion exchange membrane 7. In addition, the second anion exchange membrane 7 is an enhanced or thickened anion exchange membrane, which further hinders the permeation of phosphate. Therefore, phosphate will gradually accumulate in the electrode liquid. After the operation is completed, the electrode liquid storage chamber 9 contains part of the initial electrolyte, a small amount of anions migrated from the first solution chamber 4, and most of the phosphate migrated from the first solution chamber 4 that is intercepted. Since the flowing electrode liquid does not contain easily precipitated cations such as Ca 2+ and Mg 2+ , the cations are all enriched in the second solution chamber 6. Therefore, scaling is not likely to occur in both the anode flow electrode chamber 2 and the cathode flow electrode chamber 8; the phosphate concentration in the second solution chamber 6 is relatively low, and it is not likely to form precipitates with the enriched Ca 2+ and Mg 2+ and other cations to cause membrane scaling. When the phosphorus in the electrode liquid storage chamber 9 is enriched to a certain extent, the flowing electrode liquid in the electrode liquid storage chamber 9 is subjected to solid-liquid separation by operations such as suction filtration or microfiltration. After separating the solid conductive agent, a phosphorus-rich clarified solution is obtained. After adding ferrous salt to the solution, vivianite (iron phosphate, Fe3(PO4)2·8H2O) can be generated through the reaction shown in formula (1) (where n can be 1, 2, 3):

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

[0042] And other anions present in the solution are retained in the solution because they cannot react with ferrous ions to form precipitates, ensuring the high purity of the product. Since the ferrous in the solution is added in the form of ferrous sulfate or ferrous chloride, Cl - or SO4 2- consumed by migration before in the flowing electrode liquid is also supplemented when adding ferrous. Mixing the solution after recovering phosphate with the solid conductive material during the solid-liquid separation of the electrode liquid can be reused as the flowing electrode liquid again.

[0043] Example 1

[0044] A flow electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater used in this example is shown in the schematic diagram as Figure 1 shown. Its structure is arranged in parallel from left to right as a first current collector plate 1, a first anion exchange membrane 3, a cation exchange membrane 5, a second anion exchange membrane 7, and a second current collector plate 11 in sequence;

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

[0046] The liquid outlet of the anode flow electrode chamber 2 is connected to the liquid inlet of the cathode flow electrode chamber 8 through a first pipeline 12; the liquid outlet of the cathode flow electrode chamber 8 is connected to the liquid inlet of the anode flow electrode chamber 2 through a second pipeline 15; an electrode liquid storage chamber 9 and a circulation pump 10 are connected to the first pipeline 12; the first solution chamber 4 is connected to a phosphorus-containing wastewater pool 13; the second solution chamber 6 is connected to a brine pool 14. The electrode liquid storage chamber 9 is connected to a precipitation chamber 16; the first current collector plate 1 is connected to the positive pole of a power supply; the second current collector plate 11 is connected to the negative pole of the power supply, and the thickness of the second anion exchange membrane 7 is 2 times the thickness of the first anion exchange membrane 3

[0047] Example 2

[0048] Figure 1 This is the process flow diagram of the flow electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater of the present invention. In this example, a flow electrode capacitive deionization system in Example 1 is used to achieve desalination of phosphorus-containing wastewater and simultaneous phosphorus enrichment. The specific process is as follows:

[0049] Configure simulated phosphorus-containing wastewater by adding 1.94 g of sodium dihydrogen phosphate to 1 L of water to prepare simulated phosphorus-containing wastewater (total phosphorus 500 mg / L). At a flow rate of 10 mL / min, the simulated phosphorus-containing wastewater is pumped into the first solution chamber 4 in a circulating water inlet manner, so that it circulates in the phosphorus-containing wastewater tank 13 and the first solution chamber 4; at a flow rate of 2.5 mL / min, brine (NaCl content is 1500 mg / L) is pumped into the second solution chamber 6 in a one-way water inlet manner through a water pump; at a flow rate of 10 mL / min, the flow electrode in the flow electrode storage chamber 9 is sequentially pumped into the cathode flow electrode chamber 8 and the anode flow electrode chamber 2 through a circulating pump, and makes it circulate in the above three chambers; after the water outlet in the first solution chamber 4 is stable, power on, control the voltage between the first current collector plate 1 and the second current collector plate 11 to be 1.2 V, and continuously operate the device until the conductivity of the phosphorus-containing wastewater tank drops below 100 μS / cm.

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

[0051] After the operation and treatment are completed, measure the remaining phosphorus content in the phosphorus-containing wastewater tank 13, and calculate that the remaining phosphorus concentration and removal rate in the phosphorus-containing wastewater tank 13 are: 5.2 mg / L, 98.96%, and the phosphorus concentration multiple in the flow electrode liquid is 8.4 times. A phosphorus-rich supernatant with pH = 7.5 is obtained from the slurry in the flow electrode storage chamber 9 by suction filtration, and its composition is: total phosphorus 3906 mg / L, Cl - 872 mg / L, Na + 3517 mg / L.

[0052] The ferrous chloride solution and the phosphorus-rich supernatant are transported to the precipitation chamber 16 for crystallization reaction according to the total Fe / P molar ratio of 1.5. Use 0.05 mol / L hydrochloric acid and 0.05 mol / L sodium hydroxide to control the solution pH = 7.5. After stirring the reaction for 0.5 h, continue to stand and precipitate for 2.5 h. After the precipitation is completed, filter to obtain a solid sample. The XRD pattern of the solid sample obtained from Example 2 is as Figure 2 shown, and all its characteristic diffraction peaks are consistent with vivianite (chemical formula Fe3(PO4)2·8H2O); the SEM image of the solid sample is as Figure 3 shown, and it presents a petal shape, which is consistent with the surface morphology structure of vivianite reported in the existing literature; through chemical purity calculation, the purity of vivianite in the obtained solid sample reaches 98.5%.

[0053] Example 3

[0054] This example uses a flow-electrode capacitive deionization system for the selective enrichment of phosphorus in phosphorus-containing wastewater in Example 1. Compared with Example 2, the main difference is that the addition amount of electrolyte sodium chloride in the electrode liquid storage chamber 9 is 10 g.

[0055] After the operation and treatment are completed, the remaining phosphorus content in the phosphorus-containing wastewater pool is measured, and the remaining concentration and removal rate of phosphorus in the phosphorus-containing wastewater pool are calculated as: 4.8 mg / L and 99.04% respectively, and the phosphorus concentration multiple in the flow electrode liquid is 9.8 times. A phosphorus-rich supernatant with pH = 7.5 is obtained from the slurry in the electrode liquid storage chamber 9 by suction filtration, and its composition is: total phosphorus 4579 mg / L, Cl - 51040 mg / L, Na + 36650 mg / L.

[0056] The ferrous chloride solution and the phosphorus-rich supernatant are transported to the precipitation chamber 16 for crystallization reaction according to the molar ratio of total Fe / P of 1.5. 0.05 mol / L hydrochloric acid and 0.05 mol / L sodium hydroxide are used to control the solution pH = 7.5. After stirring and reacting for 0.5 h, it is left to stand and precipitate for another 2.5 h. After the precipitation is completed, the solid sample is obtained by filtration. The obtained solid sample is characterized by XRD and shown to be vivianite with a purity of 98.7%.

[0057] Example 4

[0058] This example uses a phosphorus-containing wastewater treatment and phosphorus selective enrichment system based on flow-electrode capacitive deionization technology in Example 1. Compared with Example 3, the main difference is that the phosphorus-containing wastewater is actual wastewater (the supernatant of the sludge thickening tank from Tangxunhu Wastewater Treatment Plant), and the actual wastewater is passed through a filtration device to remove suspended solids (total phosphorus 42.3 mg / L, SO4 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 + 35.6 mg / L). The addition amount of sodium chloride in the electrode liquid storage chamber 9 is 3 g, and the phosphorus-containing wastewater is transported into the first solution chamber 4 by a water pump in a one-way inlet mode at a flow rate of 10 mL / min, and the brine (NaCl content is 1500 mg / L) is transported into the second solution chamber 6 by a water pump at a flow rate of 1.0 mL / min for one-way inlet, and it runs continuously for 20 h.

[0059] During the operation, the content of each ion in the effluent of the first solution chamber 4 is measured, and the removal rate of each ion in the phosphorus-containing wastewater is calculated as: total phosphorus 90.3%, SO42- 92.6%, Cl - 94.3, NO3 - 46.7%, Ca 2+ 81.5%, Mg 2+ 76.1%, NH4 + 83.1%. The phosphorus concentration multiple in the flowing electrode solution is 99.2 times. Through suction filtration, a phosphorus-rich supernatant with pH = 7.5 is obtained from the slurry in the electrode solution storage chamber 9, and its composition is: total phosphorus 3862 mg / L, SO4 2- 810 mg / L, Cl - 11200 mg / L, NO3 - 58 mg / L, Na + 11060 mg / L.

[0060] The ferrous chloride solution is transported to the precipitation chamber 16 for crystallization reaction with the phosphorus-rich supernatant at a total Fe / P molar ratio of 1.5. The pH of the solution is controlled at 7.5 using 0.05 mol / L hydrochloric acid and 0.05 mol / L sodium hydroxide. After stirring the reaction for 0.5 h, it is left to stand and precipitate for another 2.5 h. After the precipitation is completed, the solid sample is obtained by filtration. The obtained solid sample is characterized by XRD and shown to be vivianite, with a purity reaching 98.3%.

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

[0062] In summary, the present invention provides a flowing electrode capacitive deionization system and method for treating phosphorus-containing wastewater and simultaneously recovering phosphorus therein. By adopting the flowing electrode capacitive deionization system and the corresponding operation method, it is possible to simultaneously achieve the rapid removal of ions in the phosphorus-containing wastewater and the efficient and selective enrichment of phosphorus elements therein, greatly reducing the use of chemical reagents such as acids and alkalis and the operating cost. Moreover, the phosphorus removal rate, enrichment multiple, and recovery efficiency are high. The separated phosphorus-rich solution can be used to prepare high-value phosphorus recovery products such as high-purity vivianite, which has significant economic and environmental benefits. The present invention is of great significance for environmental protection and the recovery of phosphorus resources in phosphorus-containing wastewater.

[0063] It is easy for those skilled in the art to understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A mobile electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater, characterized in that: The structure comprises a first current collecting plate (1), a first anion exchange membrane (3), a cation exchange membrane (5), a second anion exchange membrane (7) and a second current collecting plate (11) which are sequentially arranged in parallel from left to right; The area between the first current collecting plate (1) and the first anion exchange membrane (3) is the anode flow electrode chamber (2); the area between the first anion exchange membrane (3) and the cation exchange membrane (5) is the first solution chamber (4); the area between the cation exchange membrane (5) and the second anion exchange membrane (7) is the second solution chamber (6); and the area between the second anion exchange membrane (7) and the second current collecting plate (11) is the cathode flow electrode chamber (8); The liquid outlet of the anode flow electrode chamber (2) is connected to the liquid inlet of the cathode flow electrode chamber (8) through a first pipe (12); the liquid outlet of the cathode flow electrode chamber (8) is connected to the liquid inlet of the anode flow electrode chamber (2) through a second pipe (15); the first pipe (12) is connected to an electrode liquid storage chamber (9); the first pipe (12) and / or the second pipe (15) are connected to a circulation pump (10); the first solution chamber (4) is connected to a phosphorus-containing wastewater pool (13); and the second solution chamber (6) is connected to a salt water pool (14).

2. A mobile electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater according to claim 1, characterized in that: The first current collecting plate (1) is connected to the positive electrode of a power source; the second current collecting plate (11) is connected to the negative electrode of a power source; and the thickness of the second anion exchange membrane (7) is 1 to 2 times the thickness of the first anion exchange membrane (3).

3. A mobile 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; preferably, the ferrous salt is ferrous sulfate or ferrous chloride.

4. A mobile electrode capacitive deionization system for selective enrichment of phosphorus in phosphorus-containing wastewater according to claim 1, characterized in that: The initial electrode solution in the electrode solution storage chamber (9) comprises a conductive agent, an electrolyte and a solvent; Preferably, the conductive agent is selected from one or more of activated carbon, conductive carbon black, carbon nanotubes, or redox active substances; preferably, the redox active substances are selected from ferrocyanide, ferrocene, viologen compounds (1,1'-dialkyl-4,4'-bipyridylium salts), 2,2,6,6-tetramethylpiperidinium oxide or their derivatives; preferably, the electrolyte is selected from one or two of sodium chloride and sodium sulfate; preferably, the solvent is water; The concentration of the electrolyte is 10-100 g / L; the mass of the conductive agent accounts for 5-10 wt% of the mass of the initial electrode liquid; and the pH of the initial electrode liquid is 7.5-10.

5.

5. The mobile 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 both of sodium sulfate and sodium chloride; the salt concentration in the brine is 0.5-3 g / L.

6. A mobile 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 matter is 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 selectively enriching phosphorus in phosphorus-containing wastewater using a mobile electrode capacitive deionization system according to any one of claims 1 to 6, characterized in that: The steps include: (1) transporting the phosphorus-containing wastewater in the phosphorus-containing wastewater pool to the first solution chamber; transporting the brine in the brine pool to the second solution chamber; (2) Turn on the circulation pump to 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, and 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 supply so that the first current collecting plate and the second current collecting plate operate under power-on conditions; (4) When the phosphorus in the electrode solution in the electrode solution storage chamber reaches a predetermined concentration, the phosphorus in the electrode solution is recovered.

8. The method for selectively enriching phosphorus in phosphorus-containing wastewater according to claim 7, characterized in that: In step (1), the specific liquid inlet method for conveying the phosphorus-containing wastewater in the phosphorus-containing wastewater pool to the first solution chamber is selected from single-pass water inlet or circulating water inlet; the single-pass water inlet is specifically to convey the phosphorus-containing wastewater from the phosphorus-containing wastewater pool to the first solution chamber via a water pump, and discharge it after a single deionization treatment; the circulating water inlet is specifically to convey the phosphorus-containing wastewater from the phosphorus-containing wastewater pool to the first solution chamber via a water pump, and return it to the phosphorus-containing wastewater pool after deionization treatment, and then circulate it into the first solution chamber for treatment; In step (1), the specific liquid inlet method for conveying 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 is specifically that the brine is conveyed from the brine pool to the second solution chamber by a water pump and discharged after a single ion enrichment; the circulating water inlet is specifically that the brine is conveyed from the brine pool to the second solution chamber by a water pump, and after ion enrichment, it returns to the brine pool and then circulates into the second solution chamber for treatment.

9. The method for selectively enriching phosphorus in phosphorus-containing wastewater according to claim 7, characterized in that: After step (4), the method further includes passing the electrode liquid in the electrode liquid storage chamber into a precipitation chamber after solid-liquid separation to achieve phosphorus recovery; The solid-phase conductive agent obtained after the solid-liquid separation and the solution after phosphorus is recovered in the precipitation chamber are mixed and then continuously introduced into the electrode liquid storage chamber for cyclic use.

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

Images