Apparatus and method for directional crystallization recovery by dynamic pulsed electric field coupled with local pH oscillation

Abstract

The application discloses a kind of dynamic pulse electric field coupling local pH oscillation directional crystallization recovery device and method, it is related to environmental engineering technical field.The device includes electrochemical reactor, pulse power system and control system;Anode area and cathode area separated by microporous diaphragm are equipped in reactor, anode is titanium-based IrO2-Ta2O5 Coating electrode, and cathode is porous carbon felt loaded calcium silicate composite electrode.The method is by pulse power supply high-frequency square wave, degrades organic phosphorus in anode area, induces local pH oscillation in cathode area, and promotes calcium silicate dissolution Ca 2+ Phosphate directional crystallization on carbon felt surface forms high-purity hydroxyapatite.The application can realize phosphorus recovery rate more than 99%, product purity is more than 95%, effectively inhibit electrode passivation, adapt to complex wastewater treatment, with the advantages of high efficiency, energy saving, recovery product additional value is high.

Description

Technical Field

[0001] This invention relates to the field of environmental engineering technology, and more specifically to a directional crystallization recovery device and method for dynamic pulsed electric field coupled local pH oscillation. Background Technology

[0002] Traditional phosphorus recovery technologies mainly include chemical precipitation, biological phosphorus removal, adsorption, and membrane separation. Chemical precipitation (such as struvite precipitation) involves adding calcium and magnesium salts to wastewater, causing phosphates to combine with metal ions to form precipitates. However, this method suffers from drawbacks such as high reagent consumption, high sludge production, low precipitate purity, and susceptibility to interference from other coexisting ions. Especially when treating wastewater with high concentrations or complex compositions, its crystallization efficiency and product purity often fail to meet requirements. Biological phosphorus removal utilizes microorganisms to absorb and release phosphorus under alternating anaerobic and aerobic conditions, achieving phosphorus bioaccumulation. However, this method has high water quality requirements, complex operating conditions, and the recovered phosphorus is usually in the form of phosphorus-rich sludge, resulting in high subsequent treatment costs. Adsorption uses adsorbents to adsorb phosphates from wastewater, but the regeneration and secondary pollution problems of adsorbents remain unresolved. While membrane separation technology can effectively retain phosphates, membrane fouling is a serious problem, leading to high operating costs.

[0003] In recent years, electrochemical methods have gained widespread attention as an emerging phosphorus recovery technology due to their advantages such as requiring little or no chemical additives, simple operation, and small footprint. Electrochemical phosphorus recovery typically involves the electrolysis of water to generate hydroxide ions (OH-). - Alternatively, direct electrolytic oxidation can raise the local pH value, promoting the reaction of phosphates with metal ions (such as Ca) in the solution. 2+ Mg 2+ Phosphate crystals form on the electrode surface or in the solution. However, existing electrochemical phosphorus recovery technologies still face many challenges: First, during electrolysis, the anode surface is prone to passivation, forming an oxide layer or adsorbing organic matter, leading to decreased electrode activity, reduced current efficiency, and increased energy consumption, severely impacting electrode lifespan and system stability. For example, when treating wastewater containing organophosphorus compounds or high concentrations of inorganic phosphorus, the anode may experience adsorption and polymerization of organic matter or deposition of metal oxides, thus accelerating passivation. Traditional DC electrolysis is particularly prone to causing continuous oxidation reactions on the electrode surface, exacerbating passivation.

[0004] Secondly, in the electrochemical phosphorus recovery process, the crystallization of phosphates is affected by various factors, including pH value, metal ion concentration, temperature, and mass transfer rate. Existing technologies often struggle to precisely control the local microenvironment, leading to low crystallization efficiency or the formation of amorphous precipitates, thus reducing the purity of the recovered product. This is particularly true for complex wastewater with high salinity or containing multiple coexisting ions, where impurity ions easily co-precipitate with phosphates, further reducing the purity of the crystallized product.

[0005] Third, some electrochemical phosphorus recovery technologies require high voltage or current densities to achieve effective phosphorus recovery, resulting in significant energy consumption, increased operating costs, and limited large-scale application. Electrode passivation also further increases system internal resistance and energy consumption.

[0006] Therefore, it is necessary to propose a directional crystallization and recovery device and method with dynamic pulsed electric field coupling and local pH oscillation to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to solve the problems of electrode passivation, low crystallization efficiency, and high energy consumption in existing electrochemical phosphorus recovery technologies.

[0008] To achieve the above objectives, the present invention specifically adopts the following technical solution: A directional crystallization and recovery device with dynamic pulsed electric field coupling and local pH oscillation includes: An electrochemical reactor, wherein the reactor is provided with an anode and a cathode, and is separated into an anode region and a cathode region by a microporous membrane; The anode is a titanium-based IrO2-Ta2O5 coated electrode, used to oxidize and degrade organophosphorus or phosphate in wastewater under the action of a pulsed electric field; The cathode is a porous carbon felt-supported calcium silicate composite electrode, wherein the calcium silicate serves as Ca. 2+ The porous carbon felt acts as a source and pH buffer, providing nucleation sites for phosphate crystallization. A pulsed power supply system, electrically connected to the anode and cathode, is used to apply a high-frequency pulsed square wave to achieve a dynamic pulsed electric field and drive the cathode to generate OH. - Inducing local pH oscillations; The control system, including an online pH sensor and a programmable logic controller, is used to monitor the pH value of the cathode area in real time and adjust the parameters of the pulse power supply system through feedback to maintain the dynamic oscillation of the local pH value in the cathode area.

[0009] Furthermore, the anode is a rectangular plate with dimensions of 5cm × 5cm and a thickness of 1.0mm to 1.5mm; The IrO2-Ta2O5 coating is prepared by thermal decomposition, wherein the iridium source is chloroiridic acid, the tantalum source is tantalum pentachloride or tantalum ethoxide, the Ir:Ta molar ratio is 7:3, the solvent is a mixed solvent of n-butanol / ethylene glycol, and citric acid or acetylacetone is added to inhibit precursor aggregation, while 3% Sb2O3 or SnO2 is introduced to expand the crack width and increase the active surface area.

[0010] Furthermore, the cathode is a structure in which carbon felt is sewn into a bib-like shape to wrap the titanium plate, with a size ranging from 10mm×10mm×1mm to 100mm×100mm×1mm; the calcium silicate is loaded onto the porous carbon felt through an in-situ synthesis method, specifically by immersing the carbon felt in a 30%-40% sodium silicate and calcium carbonate solution, reacting it at 80-90℃ for 40-60 minutes to generate calcium silicate, and then drying it at 115-125℃ for later use.

[0011] Furthermore, the calcium silicate loading is 0.3-0.5 g-CaSiO3 / g-carbon felt, with an ideal particle size range of D50 ≤ 1 µm and an ideal specific surface area ≥ 20 m². 2 / g.

[0012] Furthermore, the microporous membrane is made of polytetrafluoroethylene material with a thickness of 0.08 mm to 0.3 mm, a pore size of 0.2 µm to 100 µm, and a porosity of 65% to 85%.

[0013] Furthermore, the pulse power supply system outputs a high-frequency pulse square wave with an operating voltage of 5V to 20V, a pulse frequency of 500Hz to 5kHz, and a pulse duty cycle of 30% to 50%.

[0014] Furthermore, the control system monitors the pH value of the cathode area in real time through the online pH sensor and transmits the data to the PLC. The PLC dynamically adjusts the voltage, frequency and duty cycle of the pulse power supply system according to the preset program and the real-time pH value to maintain the local pH of the cathode area oscillating between 8.5 and 10.5.

[0015] A method for directional crystallization and recovery based on dynamic pulsed electric field coupled local pH oscillation, comprising the aforementioned directional crystallization and recovery apparatus for dynamic pulsed electric field coupled local pH oscillation, includes the following steps: a) Wastewater pretreatment: Adjust the pH of the phosphorus-containing wastewater to 6.0-7.0, and add trace amounts of calcium silicate until the calcium silicate concentration in the wastewater is 0.5mM to 2mM; b) Pulse Electrolysis and Directional Crystallization: Pretreated wastewater is introduced into an electrochemical reactor. High-frequency pulsed square waves are applied to the anode and cathode through a pulsed power supply system, causing oxidative degradation of organophosphorus compounds in the anode region and calcium silicate dissolution and release of Ca in the cathode region under localized pH oscillation conditions. 2+And together with phosphate, they form high-purity hydroxyapatite crystals on the surface of the carbon felt; c) Product separation: The carbon felt loaded with HAP crystals is removed from the electrochemical reactor, and high-purity HAP products are recovered by washing and centrifugation, and the effluent is treated to meet the standards.

[0016] Furthermore, sodium hydroxide or hydrochloric acid is used to adjust the pH value in step a).

[0017] Furthermore, in step b), the pulse electrolysis process is carried out under the conditions of working voltage of 5V to 20V, pulse frequency of 500Hz to 5kHz, and pulse duty cycle of 30% to 50%, and the local pH of the cathode area is dynamically oscillating between 8.5 and 10.5 by the control system.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention can achieve a phosphorus recovery efficiency of over 99%, far exceeding the 70%-85% of traditional electrochemical methods, thus greatly improving the utilization rate of phosphorus resources. For example, in the three embodiments, the phosphorus recovery efficiency was consistently above 98.8%.

[0019] 2. This invention, through dynamic pH control and the synergistic effect of calcium silicate, can achieve high-purity directional crystallization of phosphorus. The product, hydroxyapatite (HAP), has a purity of over 95%, far exceeding the 80%-90% of traditional electrolysis methods. This avoids the formation of amorphous precipitates and increases the added value of the recovered products.

[0020] 3. This invention has good adaptability to complex wastewater, including wastewater containing multiple components such as organophosphorus, high iron phosphorus slag, and high ammonia nitrogen. It can achieve simultaneous degradation of organophosphorus and recovery of phosphorus, solving the problem that traditional methods are difficult to handle, and showing strong industrialization potential. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the directional crystallization recovery device of the present invention.

[0022] Figure 2 This is a flowchart of the phosphorus-directed crystallization recovery method in this invention.

[0023] Reference numerals: 110, anode; 120, cathode; 130, microporous diaphragm; 140, inlet; 150, outlet; 170, pH sensor; 200, pulse power supply system; 300, control system. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] Please see Figures 1 to 2 This invention proposes a directional crystallization recovery device and method based on dynamic pulsed electric field coupling with local pH oscillation. This invention combines pulsed electric field technology, precise local pH control, and multifunctional calcium silicate composite materials to overcome many bottlenecks in traditional electrochemical phosphorus recovery technologies.

[0026] I. The core of the device of this invention is an electrochemical reactor.

[0027] The main body of this electrochemical reactor can be rectangular or cylindrical, and its volume can be flexibly designed from several liters to hundreds of liters depending on the processing scale and application scenario. For example, a rectangular reactor of 5-50L can be used for laboratory scale; for industrial applications, it can be expanded to hundreds of liters. The reactor body is usually made of corrosion-resistant materials, such as polyvinyl chloride (cPVC), polypropylene (PP), stainless steel, etc., especially in non-corrosive or weakly corrosive environments. The reactor interior is equipped with an inlet 140, an outlet 150, and a fixing structure for mounting the anode 110, cathode 120, and microporous diaphragm 130.

[0028] Anode 110: This invention uses a titanium-based IrO2-Ta2O5 coated electrode as anode 110. Its main function is to oxidize and degrade organophosphorus compounds in wastewater during electrolysis and promote the formation of inorganic phosphates. Simultaneously, the IrO2-Ta2O5 coating exhibits excellent corrosion resistance and electrocatalytic activity, effectively inhibiting electrode passivation and extending electrode life.

[0029] The anode 110 is preferably a rectangular plate with a standard size of 5cm × 5cm and a thickness ranging from 1.0mm to 1.5mm. This facilitates electrode assembly and uniform current distribution. For larger-scale reactors, the anode 110 can employ a corrugated plate or mesh structure to increase the effective electrode area while maintaining good fluid mass transfer.

[0030] The IrO2-Ta2O5 coating was prepared by thermal decomposition, and the specific steps are as follows: The precursor solution was prepared using the following methods: Iridium source: H₂IrCl₆ (chloroiridium acid) to provide Ir; Tantalum source: TaCl₅ (tantalum pentachloride) or tantalum ethoxide to provide Ta. The molar ratio of Ir to Ta was controlled at 7:3.

[0031] Solvent: A mixed solvent of n-butanol and ethylene glycol is used, 200 mL of n-butanol + 100 mL of ethylene glycol (i.e., 2:1), which has good solubility and moderate evaporation rate, and helps to form a uniform coating.

[0032] Additives: Add a small amount of citric acid or acetylacetone as a complexing agent. Taking Ir:Ta=7:3 as an example (assuming the total metal content is 0.1mol), the amount of citric acid or acetylacetone is about 0.005~0.015mol, which corresponds to a mass of about 0.96~2.88g of citric acid or 0.5~1.5g of acetylacetone. This effectively inhibits precursor aggregation and ensures the stability of the coating precursor solution.

[0033] Lattice defect control: Introducing 3% Sb2O3 or SnO2 to form lattice defects during sintering, expanding the crack width to 5-10µm, thereby significantly increasing the active surface area of ​​the electrode, improving electrocatalytic performance and extending electrode life.

[0034] Coating: The titanium substrate, which has undergone pretreatment such as sandblasting and pickling, is immersed in the prepared precursor solution and coated by brushing, spraying, or other methods. The coating process is repeated multiple times to achieve the desired coating thickness.

[0035] Low-temperature drying: After each coating, perform low-temperature drying within the temperature range of 120-160℃ for several minutes to tens of minutes to gently remove the solvent and avoid blistering or cracking of the coating due to rapid boiling of the solvent, ensuring that the coating is uniform and dense.

[0036] High-temperature oxidation: The dried electrode is subjected to high-temperature oxidation in air at 450-550℃ for 10-30 minutes. This step promotes the decomposition of the precursor and the formation of an IrO2-Ta2O5 solid solution. IrO2 provides the main electrocatalytic activity, while Ta2O5 enhances the mechanical strength and stability of the coating.

[0037] Stress relief: In order to further reduce internal stress cracks in the coating and promote crystal growth, the temperature was finally raised from 550℃ to 560℃ and held for 5-10 minutes to optimize the coating structure.

[0038] During high-temperature oxidation, the following main chemical reactions occur: 2H2IrCl6+O2→2IrO2+6HCl↑+Cl2↑ 4TaCl5 + 5O2 → 2Ta2O5 + 10Cl2↑ The reaction ensures the formation of the IrO2-Ta2O5 solid solution.

[0039] The cathode 120 of this invention uses a porous carbon felt-supported calcium silicate (CaSiO3) composite electrode as the cathode 120. This cathode 120 serves as the interface for the electrolytic reaction, integrating Ca... 2+ It provides both source and pH buffering functions, while also offering numerous nucleation sites for HAP crystals.

[0040] Support and catalyst: The carrier is a porous carbon felt, which has high porosity, large specific surface area and good conductivity, providing a stable support structure for the electrolytic reaction, and providing abundant sites for the subsequent nucleation and growth of hydroxyapatite (HAP).

[0041] Calcium silicate is a stable form of Ca 2+ Source, capable of slowly dissolving and releasing Ca 2+ Firstly, CaSiO3 provides calcium ions for HAP formation. Secondly, CaSiO3 has good pH buffering capacity, which helps stabilize the local pH in the cathode area, keeping it between 8.5 and 10.5 during dynamic oscillations, avoiding excessively high or low pH levels, thus reducing the need for external acid or alkali reagents. Furthermore, the surface properties of CaSiO3 also contribute to the heterogeneous nucleation of HAP crystals.

[0042] The carbon felt carrier of cathode 120 is sewn into a "bib" shape to firmly wrap a titanium plate as a current collector and structural support. The specific design can be adjusted according to the reactor size and throughput, for example, from 10mm × 10mm × 1mm in a laboratory setting to 100mm × 100mm × 1mm in an industrial setting. The tight bond between the titanium plate and the carbon felt ensures good electrical contact, while the "bib"-like structure makes the carbon felt easy to disassemble and clean, facilitating the recovery of HAP crystals and the regeneration of cathode 120.

[0043] Loading method for CaSiO3: Calcium silicate is loaded onto porous carbon felt using an in-situ synthesis method, ensuring a tight bond between CaSiO3 and the carbon felt fibers. Specific steps are as follows: Impregnation: The pretreated carbon felt is impregnated in a pre-prepared mixed solution of sodium silicate (Na2SiO3) and calcium carbonate (CaCO3). The solution concentration ranges from 30% to 40% to ensure sufficient reactant concentration.

[0044] The reaction is carried out at a temperature of 80-90℃ for 40-60 minutes. Under these conditions, silicates react in situ with calcium ions to form nano- or submicron-sized calcium silicate precipitates, which are firmly bonded to the fiber surface of the carbon felt.

[0045] After the reaction is complete, the carbon felt loaded with calcium silicate is removed and dried at 115-125℃ to remove moisture and cure the calcium silicate coating, forming a stable composite cathode 120.

[0046] The ideal loading of calcium silicate is 0.3-0.5 g-CaSiO3 / g-carbon felt, which ensures sufficient Ca content. 2+ It provides both supply and pH buffering capacity without excessively increasing the mass and resistance of cathode 120. The ideal particle size range for calcium silicate is submicron to nanometer (D50 ≤ 1µm) to provide a larger specific surface area and higher reactivity. The ideal specific surface area should be greater than or equal to 20 m². 2 / g. There are no strict limitations on the porosity of carbon felt itself; commercially available carbon felt with high porosity and good electrical conductivity is usually sufficient.

[0047] Anode and cathode 110 connection and spacing The positive terminal of the power supply is connected to the anode 110, and the negative terminal is connected to the cathode 120. The power supply unit is equipped with metal clips that reliably connect the anode 110 and cathode 120 to the power supply via copper wires. This connection method ensures that the current can be stably and efficiently transmitted to the electrodes. The electrodes are fixed inside the reactor by insulating supports or clamps to ensure their stable position and prevent short circuits.

[0048] The spacing between the cathode 120 and the anode 110 should be controlled between 1.5 mm and 25 mm. A smaller spacing can reduce cell voltage and energy consumption; however, too small a spacing may lead to mass transfer limitations or short-circuit risks. The actual selection needs to be optimized based on the wastewater properties, current density, and reactor design.

[0049] To achieve a "zonal design" between the cathode and anode 110 regions and maintain local pH oscillations, this invention incorporates a microporous membrane 130 between the cathode and anode 110 regions. The membrane is preferably made of polytetrafluoroethylene (PTFE). PTFE possesses excellent chemical stability, corrosion resistance, mechanical strength, and bioinertness, enabling it to operate stably for extended periods in complex electrochemical environments.

[0050] The membrane thickness is typically 0.08 mm to 0.3 mm, with a pore size of 0.2 µm to 100 µm and a porosity of 65%-85%. It allows water molecules and some ions (such as PO42-) to pass through. 3- It effectively prevents the migration of large organic molecules, colloidal particles, or specific metal ions (such as Fe). 3+ It diffuses from the anode 110 region to the cathode region, avoiding co-precipitation in the cathode region and ensuring product purity.

[0051] The microporous membrane 130 is fixed inside the reactor between the anode 110 and the cathode 120, forming independent anode 110 region and cathode region.

[0052] This invention employs a pulsed power supply system 200 as the power supply system to apply a dynamic pulsed electric field. This power supply system outputs a high-frequency pulsed square wave, which, compared to traditional DC electrolysis, effectively suppresses electrode passivation and reduces energy consumption.

[0053] Operating voltage: 5V to 20V.

[0054] Pulse frequency: 500Hz to 5kHz. High-frequency pulses help maintain electrode surface activity and promote mass transfer.

[0055] Pulse duty cycle: 30% to 50%. Adjusting the duty cycle affects the ratio of pulse "on" to "off" time, which in turn affects the average current density and the amplitude of local pH oscillations.

[0056] Besides high-frequency pulsed square waves, other pulse waveforms such as rectangular waves, trapezoidal waves, or triangular waves can theoretically be used. However, square waves are preferred in this invention due to their simplicity, ease of control, and good performance in suppressing passivation and promoting crystallization.

[0057] In practice, by optimizing the operating voltage, pulse frequency, and duty cycle, the optimal combination of parameters can be found to achieve the highest phosphorus recovery efficiency, lowest energy consumption, and longest electrode life. For example, the combination of high frequency (>1kHz) and a moderate duty cycle of 30-50% has proven to be effective in suppressing passivation.

[0058] To achieve dynamic control of the local pH in the cathode area, this invention is equipped with a control system 300. This system mainly includes an online pH sensor 170, a programmable logic controller (PLC), and a connection interface with the pulse power supply system 200. Optionally, an oxidation-reduction potential (ORP) sensor can also be integrated for more comprehensive monitoring of the reactor's internal environment. The online pH sensor 170 monitors the pH value in the cathode area in real time and transmits the data to the PLC. Based on a preset target pH oscillation range (8.5-10.5) and real-time monitoring data, the PLC dynamically adjusts the parameters of the pulse power supply using an algorithm.

[0059] During the "on" period of pulse electrolysis, OH- is generated on the surface of cathode 120. - This leads to a local pH increase. During the "off" phase of the pulse (or the low current density phase), OH... - The generation of [a substance] ceases or decreases significantly. At this time, the pH value in the cathode region will decrease due to buffering (dissolution of CaSiO3), ion migration, and interaction with H+ in the solution. + The pH naturally decreases due to the reaction. The control system 300 captures pH changes and dynamically adjusts pulse parameters according to the preset oscillation mode, thereby achieving precise and dynamic oscillation of the local pH between 8.5 and 10.5. This ensures the alkaline environment required for HAP crystallization while effectively preventing the co-precipitation of impurities during the pH decrease period.

[0060] II. Process Flow This invention provides a method for phosphorus directional crystallization recovery based on dynamic pulsed electric field coupling and local pH oscillation. The detailed process flow includes three main steps: pretreatment, pulsed electrolysis and directional crystallization, and product separation.

[0061] Step a, wastewater pretreatment, involves pre-adjusting the wastewater containing organophosphorus, orthophosphate, and other impurities to meet the requirements of subsequent electrolysis and crystallization processes.

[0062] First, use common acid-base adjusters such as sodium hydroxide (NaOH) or hydrochloric acid (HCl) to adjust the overall pH of the wastewater to be treated to 6.0-7.0. This pH range helps to initiate the subsequent electrochemical reaction and avoids non-target precipitation in the initial stage.

[0063] A trace amount of calcium silicate (CaSiO3) is added to the pretreated wastewater, with the concentration typically controlled between 0.5 mM and 2 mM. The CaSiO3 added at this stage primarily serves as the initial Ca... 2+ It is a source and acts as a pH buffer throughout the process, helping to maintain pH stability in the cathode area.

[0064] This invention is applicable to the treatment of various complex wastewaters, including but not limited to high-concentration organophosphorus pesticide wastewater, municipal sludge anaerobic fermentation broth, and phosphate-iron waste residue acid leaching solution. Typical influent characteristics may include: Total phosphorus concentration: 800 mg / L (as P, high concentration wastewater), up to 120 mg / L (medium to low concentration).

[0065] Organic matter content: COD can reach 12,000 mg / L, such as methanol equivalent, or contain organophosphorus compounds such as glyphosate, HEDP, ATMP, and DTPMP, with concentrations ranging from hundreds to tens of thousands of mg / L. Organophosphorus compounds are not single substances, but a collective term for various compounds with extremely wide ranges of molecular formulas and initial total phosphorus concentrations. Examples include glyphosate (C3H8NO5P), HEDP (C2H8O7P2Na2), and ATMP (C3H... 12 N2O9P3Na4), DTPMP (C9H) 28 N3O 15 P5Na7, etc.

[0066] Other ionic components: Chloride ions (Cl...) - The concentration can be as high as 8000 mg / L, such as the equivalent of hydrochloric acid, or sulfate (SO4). 2- 1500 mg / L, equivalent to sulfuric acid; ammonia nitrogen <10 mg / L, equivalent to ammonium chloride; total dissolved solids approximately 15,000 mg / L. Iron ions (Fe...) 3+The concentration can reach 500 mg / L, specifically for phosphorus-iron waste residue. Detailed analysis of the influent helps adjust subsequent electrolysis parameters and CaSiO3 dosage based on water quality characteristics.

[0067] Pretreated wastewater is introduced into the electrochemical reactor of this invention. Under the action of a dynamic pulsed electric field, a strong oxidation reaction occurs at the anode 110. Organophosphorus compounds in the wastewater are efficiently oxidized and degraded, ultimately converting into phosphates. Simultaneously, a water oxidation reaction occurs, producing oxygen. The pulsed electric field mode effectively inhibits the formation or adsorption of a passivation layer on the surface of the anode 110, maintaining electrode activity and extending its service life. In the cathode region separated by the microporous membrane 130, water reduction produces hydroxide ions and hydrogen gas, leading to a local pH increase in the cathode region. Calcium silicate loaded on the surface of the cathode 120 slowly dissolves in the local alkaline environment, releasing Ca2+. 2+ Ions provide an ample calcium source for HAP crystallization.

[0068] The parameters of the pulse power supply are dynamically adjusted by the control system 300 to cause the local pH value in the cathode area to oscillate periodically between 8.5 and 10.5. During the pulse "on" period, OH... - The formation leads to an increase in pH; during the pulse "off" period, OH... - As production decreases, the pH naturally drops due to the buffering effect of CaSiO3, ion migration, and the consumption of H+ in the solution. This effectively promotes the directional crystallization of HAP while avoiding the co-precipitation of impurities such as metal hydroxides under continuously high pH conditions, thus ensuring product purity.

[0069] Phosphate (PO4) 3- ) and the Ca released by calcium silicate 2+ High-purity hydroxyapatite (HAP) crystals are formed by enriching on the surface of carbon felt and using carbon felt fibers as nucleation sites under the induction of local pH oscillations. This ensures the crystal stability and high purity of the product.

[0070] Operating parameters: The pulse electrolysis process is carried out under the following conditions: Operating voltage: 5V to 20V.

[0071] Pulse frequency: 500Hz to 5kHz.

[0072] Pulse duty cycle: 30% to 50%.

[0073] Temperature: Depending on the wastewater properties and microbial activity requirements, it is usually between 25-50℃ to promote the reaction rate and crystallization process.

[0074] Hydraulic retention time: can be adjusted from tens of minutes to several hours depending on the treatment volume and phosphorus concentration.

[0075] Step c, after the product separation and electrolytic crystallization are completed, the solid-liquid mixture in the reactor is discharged from the outlet. The carbon felt loaded with HAP crystals can be easily removed from the cathode 120 structure.

[0076] Disassembly first requires physical cleaning to remove loose crystals adhering to the carbon felt surface. A centrifugal separation unit separates the HAP crystals that have detached from the carbon felt or formed in the solution from the aqueous phase, obtaining a high-purity HAP product. To achieve carbon felt recycling, it can be regenerated: the carbon felt is alkaline-washed with sodium hydroxide or potassium hydroxide solution to remove adsorbed oil and some organic matter. It is then rinsed with water to remove residual alkali. Acid washing is performed using dilute hydrochloric acid or dilute nitric acid solution to remove any metallic impurities or residual amorphous precipitates that may be present on the carbon felt surface. A second rinse with water, possibly combined with ultrasonic vibration to enhance cleaning effectiveness and ensure thorough removal of acid and impurities, is then performed. Finally, a final rinse with deionized water is conducted to ensure the purity of the carbon felt. After thorough drying, the carbon felt can be reloaded with calcium silicate and used in the next cycle.

[0077] The effluent after HAP separation has a significantly reduced phosphorus concentration and can be discharged directly according to local emission standards, or further treated, such as by membrane filtration or activated carbon adsorption, before reuse. Other water quality indicators, such as COD, TOC, and SS, are also improved. The recovered high-purity HAP product can be used as a high-value-added phosphate fertilizer, industrial raw material, or functional material, realizing the resource utilization of phosphorus resources. Specific Implementation

[0078] To better understand the present invention, detailed descriptions are provided below with reference to specific embodiments. These embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0079] Example 1: Treatment of high-concentration organophosphorus pesticide wastewater (glyphosate production wastewater) This embodiment aims to verify the effectiveness of the present invention in treating high-concentration organophosphorus wastewater, particularly its ability to degrade organophosphorus and efficiently recover phosphorus.

[0080] The wastewater to be treated is high-concentration organophosphorus pesticide wastewater generated during the glyphosate production process. Glyphosate concentration: approximately 200 mg / L. Initial total phosphorus (as P): approximately 35 mg / L. Initial pH: approximately 6.0. Chloride ion concentration (Cl...) - Concentration: Approximately 3000 mg / L. It contains high levels of other organic matter and inorganic salts, and is somewhat corrosive.

[0081] This wastewater contains high concentrations of organophosphorus compounds, posing a challenge to traditional phosphorus recovery technologies and easily leading to electrode passivation and low recovery efficiency.

[0082] The electrochemical reaction device designed using this invention has the following specific configuration: Reactor: 50L in volume, rectangular structure, made of 304 stainless steel, with good corrosion resistance.

[0083] Anode 110: Ti / IrO2-Ta2O5 corrugated plate electrode, with an effective area of ​​0.5m². 2 To improve reaction efficiency, the coating preparation is strictly carried out according to the thermal decomposition method described in this invention to ensure its catalytic activity and stability.

[0084] Cathode 120: A porous carbon felt-supported CaSiO3 composite electrode with a loading of 0.2 g-CaSiO3 / g-carbon felt. The carbon felt is sewn into a "bib" shape to wrap around a titanium plate, with dimensions of 10 cm × 10 cm × 1 cm, for a total of 10 pieces. The CaSiO3 is loaded using an in-situ synthesis method to ensure its uniformity and stability.

[0085] The distance between the anode and cathode (110) is 3cm.

[0086] Microporous diaphragm 130: made of PTFE, with a thickness of 0.2 mm, a pore size of 0.45 µm, and a porosity of 75%, used to separate the cathode region and the anode 110 region.

[0087] Process operating conditions Pretreatment: First, adjust the pH of the glyphosate production wastewater to 6.5 with sodium hydroxide, then add a trace amount of CaSiO3 at a concentration of 1.0 mM and stir evenly.

[0088] Pulse electrolysis: Operating voltage: 10V (constant voltage mode).

[0089] Current density: 50 mA / cm 2 (Peak).

[0090] Pulse frequency: 1.5kHz.

[0091] Duty cycle: 50%.

[0092] Temperature: 30±2℃.

[0093] Hydraulic retention time (HRT): 40 minutes.

[0094] The pH oscillation range in the cathode area is 8.8-10.5. The online pH sensor 170 and PLC control system 300 monitor and dynamically adjust the pulse power supply parameters in real time to maintain the pH oscillation in the cathode area within the set range.

[0095] Ca 2+Dosage: In this embodiment, in addition to the CaSiO3 added during the pretreatment stage, an additional 0.5 mM Ca is added during the electrolysis process. 2+ The calcium source is provided by dissolved CaSiO3 and a small amount of supplemental calcium salt to ensure sufficient calcium for HAP crystallization.

[0096] Results and effectiveness After continuous operation, this embodiment achieved the following excellent results: Glyphosate degradation rate: ≥99.5%. This indicates that the device of the present invention has a high efficiency in degrading organophosphorus compounds.

[0097] Phosphorus recovery rate: 99.2%. This is far higher than the 70%-85% recovery rate of traditional electrolysis methods, demonstrating the significant advantages of this invention in phosphorus recovery.

[0098] HAP crystal purity: 96.5%. The recovered product is high-purity hydroxyapatite with high crystal purity and high resource utilization value.

[0099] Energy consumption: 18.5 kWh / kg P. This is far lower than that of traditional electrolysis, significantly reducing operating costs.

[0100] Electrode life: Anode 110 exhibits good stability, with no obvious signs of passivation after more than 600 hours of continuous operation, and the electrode life is significantly extended.

[0101] This embodiment fully demonstrates that the present invention has the advantages of high efficiency, low energy consumption, high purity and long life in treating high-concentration organophosphorus wastewater.

[0102] Example 2: Treatment of anaerobic fermentation broth from municipal sludge (high ammonia nitrogen and phosphorus wastewater) This embodiment aims to evaluate the performance of the present invention in treating anaerobic fermentation broth from municipal sludge containing high levels of ammonia nitrogen and phosphorus, with particular attention to phosphorus recovery efficiency, ammonia nitrogen retention, and energy consumption.

[0103] The wastewater to be treated is anaerobic fermentation broth from municipal sludge, characterized by high ammonia nitrogen, high phosphorus, and a certain amount of suspended solids (SS) and organic matter. Total phosphorus: approximately 120 mg / L. Ammonia nitrogen: approximately 800 mg / L. Initial pH: approximately 7.2. Suspended solids (SS): approximately 500 mg / L. Other organic matter and inorganic salts are also present.

[0104] Direct discharge of this wastewater would cause serious environmental pollution, and it contains valuable phosphorus resources that need to be recycled.

[0105] Device parameters The electrochemical reaction device designed using this invention has the following specific configuration: Reactor: 200L in volume, with a square structure, made of cPVC, which has good corrosion resistance.

[0106] Anode 110: Ti / IrO2-Ta2O5 mesh electrode, with an effective area of ​​2.0 m². 2 The mesh design further increases the effective surface area of ​​the electrodes, improving current efficiency. The coating preparation method is the same as in Example 1.

[0107] Cathode 120: A porous carbon felt-supported CaSiO3 composite electrode with a loading of 0.3 g-CaSiO3 / g-carbon felt. The carbon felt dimensions are 20 cm × 20 cm × 1 cm, and there are a total of 20 pieces.

[0108] The distance between the anode and cathode is 4cm.

[0109] Microporous diaphragm 130: made of PP material, with a thickness of 1.0 mm, a pore size of 1.0 µm, and a porosity of 70%, used to separate the cathode region and the anode region 110.

[0110] Process operating conditions Pretreatment: Adjust the pH of the municipal sludge anaerobic fermentation liquid to 6.8 with a small amount of dilute hydrochloric acid, then add a trace amount of CaSiO3 at a concentration of 0.5mM and stir evenly.

[0111] Pulse electrolysis: Operating voltage: 12V (constant voltage mode).

[0112] Current density: 30 mA / cm 2 (Peak).

[0113] Pulse frequency: 1.0kHz.

[0114] Duty cycle: 40%.

[0115] Temperature: 35℃.

[0116] Hydraulic residence time: 60 minutes.

[0117] pH oscillation range in the cathode region: 8.5-10.2.

[0118] Ca 2+ Dosage: 0 mM. In this embodiment, Ca is entirely provided by the dissolution of CaSiO3 loaded on cathode 120. 2+ No additional calcium salt was required to verify the synergistic strengthening effect of CaSiO3.

[0119] Results and effectiveness Phosphorus recovery rate: 98.8%. High-efficiency phosphorus recovery has been achieved.

[0120] Products: Primarily HAP, with a small amount of struvite (MgNH4PO4·6H2O). This is because the anaerobic fermentation broth contains a certain amount of magnesium ions and ammonia nitrogen; under locally alkaline conditions, some phosphates react with magnesium ions and ammonia nitrogen to form struvite. However, HAP remains the main product.

[0121] Ammonia nitrogen retention rate: ≥95%. Due to the control of pH oscillation in the cathode area, ammonia nitrogen stripping loss caused by continuous high pH is avoided, thus achieving good retention of ammonia nitrogen.

[0122] Energy consumption: 15.8 kWh / kg P. This excellent energy efficiency further confirms the energy-saving advantages of this invention.

[0123] This embodiment demonstrates that when treating wastewater with high ammonia nitrogen and phosphorus content, the present invention can not only efficiently recover phosphorus but also effectively retain ammonia nitrogen, reduce stripping losses, and maintain low energy consumption and high-purity products.

[0124] These two examples fully demonstrate that the technology of this invention can maintain high phosphorus recovery rate and high product purity under different water quality conditions. By flexibly adjusting pulse parameters and reaction conditions, it can be adapted to different wastewaters ranging from high organic matter to high impurities, demonstrating strong adaptability and industrialization potential. Compared with traditional electrochemical phosphorus recovery technology, this invention has achieved significant improvements in phosphorus recovery efficiency, energy consumption, crystallization purity, and electrode lifespan, providing a new solution for the green and efficient recovery of phosphorus resources.

[0125] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the content of the present invention's specification shall also be included within the scope of protection of the present invention.

Claims

1. A directional crystallization and recovery device using dynamic pulsed electric field coupled with localized pH oscillation, characterized in that, include: An electrochemical reactor, wherein the reactor is provided with an anode and a cathode, and is separated into an anode region and a cathode region by a microporous membrane; The anode is a titanium-based IrO2-Ta2O5 coated electrode, used to oxidize and degrade organophosphorus or phosphate in wastewater under the action of a pulsed electric field; The cathode is a porous carbon felt-supported calcium silicate composite electrode, wherein the calcium silicate serves as Ca. 2+ The porous carbon felt acts as a source and pH buffer, providing nucleation sites for phosphate crystallization. A pulsed power supply system, electrically connected to the anode and cathode, is used to apply a high-frequency pulsed square wave to achieve a dynamic pulsed electric field and drive the cathode to generate OH. - Inducing local pH oscillations; The control system, including an online pH sensor and a programmable logic controller (PLC), is used to monitor the pH value of the cathode area in real time and adjust the parameters of the pulse power supply system through feedback to maintain the dynamic oscillation of the local pH value in the cathode area.

2. The directional crystallization and recovery device with dynamic pulsed electric field coupling and local pH oscillation according to claim 1, characterized in that, The anode is a rectangular plate with dimensions of 5cm × 5cm and a thickness of 1.0mm to 1.5mm; The IrO2-Ta2O5 coating is prepared by thermal decomposition, wherein the iridium source is chloroiridic acid, the tantalum source is tantalum pentachloride or tantalum ethoxide, the Ir:Ta molar ratio is 7:3, the solvent is a mixed solvent of n-butanol / ethylene glycol, and citric acid or acetylacetone is added to inhibit precursor aggregation, while 3% Sb2O3 or SnO2 is introduced to expand the crack width.

3. The directional crystallization and recovery device for dynamic pulsed electric field coupling and local pH oscillation according to claim 1, characterized in that, The cathode is a structure in which carbon felt is sewn into a bib-like shape to wrap a titanium plate, with a size ranging from 10mm×10mm×1mm to 100mm×100mm×1mm; the calcium silicate is loaded onto the porous carbon felt through an in-situ synthesis method. Specifically, the porous carbon felt is immersed in a mixed solution of sodium silicate and calcium carbonate, the concentration of which is 30%-40%, and reacted at 80-90℃ for 40-60 minutes to generate calcium silicate, which is then dried at 115-125℃ for later use.

4. The directional crystallization and recovery device with dynamic pulsed electric field coupling and local pH oscillation according to claim 3, characterized in that, The calcium silicate loading is 0.3~0.5 g-CaSiO3 / g-carbon felt, with a particle size range of D50≤1µm and a specific surface area ≥20m². 2 / g.

5. The directional crystallization and recovery device for dynamic pulsed electric field coupling and local pH oscillation according to claim 1, characterized in that, The microporous membrane is made of polytetrafluoroethylene material with a thickness of 0.08 mm to 0.3 mm, a pore size of 0.2 µm to 100 µm, and a porosity of 65% to 85%.

6. The directional crystallization and recovery device for dynamic pulsed electric field coupling and local pH oscillation according to claim 1, characterized in that, The pulse power supply system outputs a high-frequency pulse square wave with an operating voltage of 5V to 20V, a pulse frequency of 500Hz to 5kHz, and a pulse duty cycle of 30% to 50%.

7. The directional crystallization and recovery device for dynamic pulsed electric field coupling and local pH oscillation according to claim 1, characterized in that, The control system monitors the pH value of the cathode area in real time through the online pH sensor and transmits the data to the PLC. The PLC dynamically adjusts the voltage, frequency and duty cycle of the pulse power supply system according to the preset program and the real-time pH value to maintain the local pH of the cathode area oscillating between 8.5 and 10.

5.

8. A method for directional crystallization and recovery of localized pH oscillations coupled by a dynamic pulsed electric field, comprising the directional crystallization and recovery apparatus for dynamic pulsed electric field coupled with localized pH oscillations as described in any one of claims 1-7, characterized in that, Includes the following steps: a) Wastewater pretreatment: Adjust the pH of the phosphorus-containing wastewater to 6.0-7.0, and add trace amounts of calcium silicate until the calcium silicate concentration in the wastewater is 0.5mM to 2mM; b) Pulse Electrolysis and Directional Crystallization: Pretreated wastewater is introduced into an electrochemical reactor. High-frequency pulsed square waves are applied to the anode and cathode through a pulsed power supply system, causing oxidative degradation of organophosphorus compounds in the anode region and calcium silicate dissolution and release of Ca in the cathode region under localized pH oscillation conditions. 2+ And together with phosphate, high-purity hydroxyapatite crystals are formed on the surface of porous carbon felt; c) Product separation: The carbon felt loaded with HAP crystals is removed from the electrochemical reactor, and high-purity HAP products are recovered by washing and centrifugation, and the effluent is treated to meet the standards.

9. The method for directional crystallization and recovery based on dynamic pulsed electric field coupled local pH oscillation according to claim 8, characterized in that, In step a), sodium hydroxide or hydrochloric acid is used to adjust the pH value.

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