Directional crystallization recovery device and method for coupling dynamic pulsed electric field with local pH oscillation

Abstract

The invention discloses a directional crystallization recovery device and method by coupling a dynamic pulsed electric field with local pH oscillation, and relates to the technical field of environmental engineering. The device comprises an electrochemical reactor, a pulse power supply system and a control system, an anode region and a cathode region which are separated by a microporous diaphragm are arranged in the reactor, the anode is a titanium-based IrO2-Ta2O5 coating electrode, and the cathode is a porous carbon felt loaded calcium silicate composite electrode. According to the method, high-frequency square waves are applied through a pulsed power supply, organic phosphorus is degraded in an anode region, local pH oscillation is induced in a cathode region, calcium silicate is promoted to be dissolved to release Ca < 2 + >, and the Ca < 2 + > and phosphate are directionally crystallized on the surface of a carbon felt to form high-purity hydroxyapatite. The method can realize the phosphorus recovery rate of more than 99%, the product purity of more than 95%, effectively inhibits electrode passivation, adapts to complex wastewater treatment, and has the advantages of high efficiency, energy conservation and high additional value of recovered products.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental engineering, and more particularly to a directional crystallization recovery device and method coupled with dynamic pulse electric field and local pH oscillation. BACKGROUND

[0002] With the acceleration of global population growth, industrialization and the intensification of agricultural production, the demand for phosphorus resources continues to increase. However, as a non-renewable resource, phosphorus resources are limited in reserves and face the risk of depletion. At the same time, the discharge of phosphorus-containing wastewater generated by human activities is also increasing, leading to the increasingly serious problem of water eutrophication, which seriously threatens the ecological environment and human health. Therefore, it is of great strategic significance and economic value to develop efficient, economic and environmentally friendly phosphorus recovery technologies to realize the recycling of phosphorus resources.

[0003] Traditional phosphorus recovery technologies mainly include chemical precipitation, biological phosphorus removal, adsorption and membrane separation methods. Chemical precipitation (such as struvite precipitation) involves adding calcium salts, magnesium salts, etc. to wastewater to make phosphate combine with metal ions to form precipitates. However, this method has the disadvantages of high reagent consumption, high sludge production, low purity of precipitates and susceptibility to interference from other coexisting ions, especially when dealing with high-concentration or complex-component wastewater, the crystallization efficiency and product purity often cannot meet the requirements. Biological phosphorus removal utilizes microorganisms to absorb and release phosphorus under anaerobic-aerobic alternating conditions to achieve biological enrichment of phosphorus, but this method has high requirements for water quality and complex operating conditions, and the form of phosphorus recovery is usually phosphorus-rich sludge, which has high subsequent treatment cost. Adsorption method uses adsorbents to adsorb phosphate in wastewater, but the regeneration of adsorbents and secondary pollution problems remain to be solved. Membrane separation technology can effectively intercept phosphate, but the problem of membrane fouling is serious and the operating cost is high.

[0004] In recent years, electrochemical method as a new phosphorus recovery technology has attracted widespread attention due to its advantages of no or small amount of chemical reagent addition, simple operation, small occupation area, etc. Electrochemical phosphorus recovery usually generates hydroxyl ions (OH - ) by electrolysis of water or direct electrolytic oxidation, increases the local pH value, and promotes the formation of phosphate crystals with metal ions (such as Ca 2+ , Mg 2+ ) in the solution on the electrode surface or in the solution. However, existing electrochemical phosphorus recovery technologies still face many challenges: First, in the electrolysis process, the anode surface is prone to passivation, forming an oxide layer or adsorbing organic matter, leading to a decrease in electrode activity, a decrease in current efficiency, and an increase in energy consumption, which seriously affects the electrode life and system stability. For example, when treating wastewater containing organophosphorus or high-concentration inorganic phosphorus, the anode may undergo adsorption and polymerization of organic matter or deposition of metal oxides, thereby accelerating passivation. The traditional direct current electrolysis mode is particularly prone to causing continuous oxidation reactions on the electrode surface, exacerbating passivation.

[0005] Second, in the process of electrochemical phosphorus recovery, the crystallization process of phosphate is affected by various factors, including pH, metal ion concentration, temperature, mass transfer rate, etc. The existing technology often has difficulty in accurately regulating the local microenvironment, resulting in low crystallization efficiency or the formation of amorphous precipitates, which reduces the purity of the recovered product. Especially for complex wastewater with high salinity or containing multiple coexisting ions, impurity ions are prone to co-precipitation with phosphate, further reducing the purity of the crystallization product.

[0006] Third, some electrochemical phosphorus recovery technologies require high voltage or current density to achieve effective phosphorus recovery, resulting in high energy consumption, increasing operating costs, and limiting their large-scale application. Electrode passivation also increases the internal resistance of the system, increasing energy consumption.

[0007] Therefore, it is necessary to propose a dynamic pulsed electric field coupled with local pH oscillation directional crystallization recovery device and method to solve the above problems. SUMMARY

[0008] The purpose of the present application is to solve the problems of electrode passivation, low crystallization efficiency, and high energy consumption in existing electrochemical phosphorus recovery technologies.

[0009] The present application specifically adopts the following technical solutions to achieve the above purposes: The dynamic pulsed electric field coupled with local pH oscillation directional crystallization recovery device comprises: An electrochemical reactor, the reactor is internally provided with an anode and a cathode, and is separated into an anode zone and a cathode zone by a microporous diaphragm; The anode is a titanium-based IrO2-Ta2O5 coated electrode, which is used to oxidatively degrade organophosphorus or phosphate in wastewater under the action of a pulsed electric field; The cathode is a porous carbon felt loaded calcium silicate composite electrode, and the calcium silicate serves as a Ca 2+ source and a pH buffer, and the porous carbon felt provides nucleation sites for phosphate crystallization; A pulse power system is electrically connected to the anode and the cathode, used to apply a high-frequency pulsed square wave to realize a dynamic pulsed electric field and drive the cathode to generate OH - , inducing local pH oscillation; The control system comprises an online pH sensor and a programmable logic controller for real-time monitoring of the pH value of the cathode region and adjusting the parameters of the pulse power supply system through feedback to maintain the dynamic oscillation of the local pH value of the cathode region.

[0010] Further, the anode adopts a rectangular flat plate shape with a size of 5 cm x 5 cm and a thickness of 1.0 mm to 1.5 mm. The IrO2-Ta2O5 coating is prepared by a thermal decomposition method, wherein the iridium source is chloroiridic acid, the tantalum source is pentachloride or ethanolic tantalum, the molar ratio of Ir:Ta is 7:3, the solvent is n-butanol / ethylene glycol mixed solvent, and citric acid or acetylacetone is added to inhibit the aggregation of the precursor, while 3% of Sb2O3 or SnO2 is introduced to expand the crack width and increase the active surface area.

[0011] Further, the cathode is a structure of a carbon felt sleeve wrapped around a titanium plate with a size ranging from 10 mm x 10 mm x 1 mm to 100 mm x 100 mm x 1 mm; the calcium silicate is loaded onto the porous carbon felt by an in-situ synthesis method, specifically by immersing the carbon felt in a sodium silicate solution with a concentration of 30%-40% and a calcium carbonate solution, reacting at 80-90°C for 40-60 minutes to generate calcium silicate, and then drying at 115-125°C for standby.

[0012] Further, the loading capacity of the calcium silicate is 0.3-0.5 g-CaSiO3 / g-carbon felt, and the ideal particle size range is D50≤1 µm, and the ideal specific surface area is ≥20 m 2 / g.

[0013] Further, 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%-85%.

[0014] Further, the pulse power supply system outputs a high-frequency pulse square wave with a working voltage of 5V to 20V, a pulse frequency of 500Hz to 5kHz, and a pulse duty cycle of 30% to 50%.

[0015] Further, the control system monitors the pH value of the cathode region in real time through the online pH sensor and transmits the data to the PLC, which dynamically adjusts the voltage, frequency, and duty cycle of the pulse power supply system according to the preset program and real-time pH value to maintain the local pH of the cathode region oscillating between 8.5 and 10.5.

[0016] The directional crystallization recovery method of dynamic pulse electric field coupled with local pH oscillation comprises the directional crystallization recovery device of dynamic pulse electric field coupled with local pH oscillation as described above, and comprises the following steps: a) wastewater pretreatment: adjust the pH value of phosphorus-containing wastewater to 6.0-7.0, and add trace calcium silicate, the concentration is 0.5mM to 2mM; b) pulse electrolysis and directional crystallization: the pretreated wastewater is introduced into the electrochemical reactor, and high-frequency pulse square wave is applied to the anode and cathode through the pulse power system, so that the oxidation degradation of organic phosphine occurs in the anode area, and under the condition of local pH oscillation, calcium silicate is dissolved in the cathode area Ca 2+ , and high-purity hydroxyapatite crystals are formed on the carbon felt surface with phosphate; c) product separation: the carbon felt loaded with HAP crystals is taken out from the electrochemical reactor, and high-purity HAP product is recovered by washing and centrifugal separation, and the treated effluent is discharged.

[0017] Further, the pH value in step a) is adjusted by using sodium hydroxide or hydrochloric acid.

[0018] Further, in step b), the pulse electrolysis process is carried out under the conditions of working voltage 5V to 20V, pulse frequency 500Hz to 5kHz, pulse duty cycle 30% to 50%, and the local pH in the cathode area is dynamically oscillated between 8.5 to 10.5 by the control system.

[0019] Compared with the prior art, the beneficial effects of the present application are: 1、The present application can realize the phosphorus recovery efficiency of more than 99%, which is much higher than the 70%-85% of the traditional electrochemical method, greatly improving the utilization rate of phosphorus resources. For example, in three embodiments, the phosphorus recovery efficiency is stable at more than 98.8%.

[0020] 2、The present application, by the synergistic effect of dynamic pH regulation and calcium silicate, can realize the directional crystallization of phosphorus with high purity, and the product hydroxyapatite HAP purity can reach more than 95%, which is much higher than the 80%-90% of the traditional electrolysis method, avoiding the generation of amorphous precipitate and improving the added value of the recovered product.

[0021] 3、The present application has good adaptability to complex wastewater, including wastewater containing organic phosphine, high-iron phosphorus slag, high-ammonia nitrogen and other components, can realize the synchronous degradation of organic phosphine and the recovery of phosphorus, solve the problem that the traditional method is difficult to handle, and show strong industrialization potential. BRIEF DESCRIPTION OF DRAWINGS

[0022] Fig. 1 is a schematic diagram of the directional crystallization recovery device of the present application.

[0023] Fig. 2 is a total flow chart of the phosphorus directional crystallization recovery method in the present application.

[0024] Reference signs: 110, anode; 120, cathode; 130, microporous diaphragm; 140, water inlet; 150, water outlet; 170, pH sensor; 200, pulse power supply system; 300, control system. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] Please refer to Figs. 1-2 The present application proposes a directional crystallization recovery device and method based on dynamic pulse electric field coupling local pH oscillation. The present application combines pulse electric field technology, local pH precise control and multifunctional calcium silicate composite material to overcome many bottlenecks in traditional electrochemical phosphorus recovery technology.

[0027] Firstly, the core of the device of the present application is an electrochemical reactor.

[0028] The main body of the electrochemical reactor can adopt a rectangular or cylindrical structure, and its volume can be flexibly designed between several liters and several hundred liters according to the processing scale and application scenarios. For example, for laboratory scale, a 5-50L rectangular reactor can be used; for industrial applications, it can be expanded to several hundred 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 is provided with a water inlet 140, a water outlet 150, and a fixing structure for installing an anode 110, a cathode 120 and a microporous diaphragm 130.

[0029] Anode 110: The present application uses a titanium-based IrO2-Ta2O5 coated electrode as the anode 110, which mainly functions to oxidize and degrade organic phosphine compounds in wastewater and promote the formation of inorganic phosphate during electrolysis. At the same time, the IrO2-Ta2O5 coating has excellent corrosion resistance and electrocatalytic activity, which can effectively inhibit electrode passivation and prolong electrode life.

[0030] The anode 110 is preferably a rectangular flat plate with a standard size of 5cm x 5cm and a thickness ranging from 1.0mm to 1.5mm. It is beneficial to the assembly of the electrode and the uniform distribution of current. For larger scale reactors, the anode 110 can adopt a wave plate or a mesh structure to increase the effective electrode area while maintaining good fluid mass transfer.

[0031] To prepare the IrO2-Ta2O5 coating, a thermal decomposition method is used, and the specific steps are as follows: The precursor solution is prepared by selecting H2IrCl6 as the iridium source, which provides the Ir element, and TaCl5 or ethanol tantalum as the tantalum source, which provides the Ta element. The molar ratio of Ir to Ta is controlled at 7:3.

[0032] Solvent: A mixture of n-butanol and ethylene glycol is used, with n-butanol 200 mL + ethylene glycol 100 mL (i.e. 2:1), which has good solubility and moderate evaporation rate, helping to form a uniform coating.

[0033] Additives: A small amount of citric acid or acetylacetone is added as a complexing agent. For example, assuming the total metal amount is 0.1 mol, the amount of citric acid or acetylacetone used is about 0.005-0.015 mol, corresponding to a mass of about 0.96-2.88 g of citric acid or 0.5-1.5 g of acetylacetone, which effectively inhibits precursor aggregation and ensures the stability of the coating precursor solution.

[0034] Lattice defect regulation: 3% of Sb2O3 or SnO2 is introduced to form lattice defects during sintering, expanding the crack width to 5-10 µm, thereby significantly increasing the active surface area of the electrode, improving the electrocatalytic performance and prolonging the electrode life.

[0035] Coating: The titanium substrate that has been pretreated by methods such as sandblasting and pickling is immersed in the prepared precursor solution and coated by methods such as brushing and spraying. The coating process is repeated multiple times to achieve the desired coating thickness.

[0036] Low-temperature drying: After each coating, low-temperature drying is performed at a temperature range of 120-160°C for several minutes to tens of minutes to gently remove the solvent, avoiding the formation of bubbles or cracks in the coating due to rapid solvent boiling, and ensuring the uniformity and density of the coating.

[0037] High-temperature oxidation: The dried electrode is subjected to high-temperature oxidation in an air atmosphere at 450-550°C 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.

[0038] Stress relief: To further reduce internal stress cracks in the coating and promote crystal growth, the temperature is finally raised to 550°C to 560°C and maintained for 5-10 minutes to optimize the coating structure.

[0039] 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 IrO2-Ta2O5 solid solution.

[0040] The cathode 120 of the present application adopts a porous carbon felt loaded calcium silicate CaSiO3 composite electrode as the cathode 120. The cathode 120, as the interface of the electrolytic reaction, integrates the Ca 2+ source and pH buffering function, while providing a large number of sites for the nucleation of HAP crystals.

[0041] Carrier and catalyst: The carrier is selected as porous carbon felt, which has high porosity, large specific surface area and good electrical conductivity, can provide stable support structure for the electrolytic reaction, and at the same time provide abundant sites for the subsequent nucleation and growth of hydroxyapatite HAP.

[0042] Calcium silicate as a stable Ca 2+ source, can slowly dissolve and release Ca 2+ ions to provide calcium ions for the formation of HAP. Secondly, CaSiO3 has good pH buffering capacity, which helps to stabilize the local pH of the cathode region, so that it remains at 8.5-10.5 during dynamic oscillation, avoiding too high or too low pH, thereby reducing the need for additional acid and alkali reagents. In addition, the surface properties of CaSiO3 also help the heterogeneous nucleation of HAP crystals.

[0043] The carrier carbon felt of the cathode 120 is sewn into a "pocket" shape to firmly wrap a titanium plate as a current collector and structural support. The specific size can be adjusted according to the reactor scale and processing capacity, for example, from 10mm x 10mm x 1mm for laboratory scale to 100mm x 100mm x 1mm for industrial scale. The close combination of titanium plate and carbon felt ensures good electrical contact, while the "pocket" structure makes the carbon felt easy to disassemble and clean, facilitating the recovery of HAP crystals and the regeneration of the cathode 120.

[0044] Loading method of CaSiO3: in-situ synthesis method is adopted to load calcium silicate on the porous carbon felt, ensuring the close combination of CaSiO3 and carbon felt fibers. The specific steps are as follows: immersion: immerse the pretreated carbon felt in the mixed solution of sodium silicate Na2SiO3 and calcium carbonate CaCO3 prepared in advance. The concentration of the solution is in the range of 30% to 40% to ensure sufficient reactant concentration.

[0045] The reaction is carried out at a temperature of 80-90°C for 40-60 minutes. Under this condition, the silicate reacts with calcium ions in-situ to generate nanoscale or submicron calcium silicate precipitates, which are firmly bonded to the surface of the carbon felt fibers.

[0046] After the reaction is completed, the carbon felt loaded with calcium silicate is taken out and dried at a temperature of 115-125°C to remove moisture and solidify the calcium silicate coating, forming a stable composite cathode 120.

[0047] The ideal loading amount of calcium silicate is 0.3-0.5 g-CaSiO3 / g-carbon felt, which can ensure sufficient Ca 2+ supply and pH buffering capacity without excessively increasing the mass and resistance of the cathode 120. The ideal particle size range of calcium silicate is sub-micron to nanometer (D50≤1 µm) to provide greater specific surface area and higher reactivity. The ideal specific surface area should be greater than or equal to 20 m 2 / g. The porosity of the carbon felt itself is not strictly limited, and commercially available carbon felt with high porosity and good electrical conductivity can be generally selected.

[0048] Anode and cathode connection and spacing The positive electrode of the power supply is connected to the anode 110, and the negative electrode is connected to the cathode 120. The power supply device is equipped with metal clamps, and the anode 110 and the cathode 120 are reliably connected to the power supply through copper wires. This connection 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.

[0049] The spacing between the cathode 120 and the anode 110 is controlled between 1.5 mm and 25 mm. Smaller spacing can reduce cell voltage and reduce energy consumption; but too small spacing may cause mass transfer limitation or short circuit risk. The actual selection needs to be optimized according to the properties of the wastewater, current density, and reactor design.

[0050] In order to realize the "zoning design" of the cathode zone and the anode 110 zone and maintain the local pH oscillation, the present application sets a microporous diaphragm 130 between the cathode zone and the anode 110 zone. The diaphragm is preferably made of polytetrafluoroethylene (PTFE) material. PTFE has excellent chemical stability, corrosion resistance, mechanical strength and biological inertia, and can stably operate in complex electrochemical environment for a long time.

[0051] The thickness of the diaphragm is usually 0.08 mm to 0.3 mm, the pore size is 0.2 µm to 100 µm, and the porosity is 65%-85%. It allows the effective migration of water molecules and part of ions (such as PO4 3- ), while effectively blocking the diffusion of macromolecular organic matter, colloidal particles or specific metal ions (such as Fe 3+ ) from the anode 110 zone to the cathode zone, avoiding their co-precipitation in the cathode zone and ensuring product purity.

[0052] The microporous diaphragm 130 is fixed between the anode 110 and the cathode 120 inside the reactor, forming independent anode 110 zone and cathode zone.

[0053] The present application adopts pulse power system 200 as the power system to realize the application of dynamic pulse electric field. The power system outputs high-frequency pulse square wave. Compared with traditional direct current electrolysis, pulse electrolysis can effectively inhibit electrode passivation and reduce energy consumption.

[0054] Working voltage: 5V to 20V.

[0055] Pulse frequency: 500Hz to 5kHz. High-frequency pulses help maintain electrode surface activity and promote mass transfer.

[0056] Pulse duty cycle: 30% to 50%. The adjustment of the duty cycle affects the time ratio of pulse "on" and "off", and in turn affects the average current density and the amplitude of local pH oscillation.

[0057] In addition to high-frequency pulse square wave, other pulse waveforms such as rectangular wave, trapezoidal wave or triangular wave can also be used in theory. However, square wave is preferred by the present application due to its simplicity, ease of control and good performance in inhibiting passivation and promoting crystallization.

[0058] In actual operation, by optimizing the working voltage, pulse frequency and duty cycle, the best parameter combination can be found to achieve the highest phosphorus recovery efficiency, the lowest energy consumption and the longest electrode life. For example, the combination of high frequency (>1kHz) and moderate duty cycle 30-50% has been proven to be significantly effective in inhibiting passivation.

[0059] To realize the dynamic regulation of local pH in the cathode zone, the present application is equipped with a control system 300. The system mainly includes an online pH sensor 170, a programmable logic controller (PLC) and a connection interface with the pulse power system 200. Optionally, an oxidation-reduction potential (ORP) sensor can also be integrated to more comprehensively monitor the internal environment of the reactor. The online pH sensor 170 monitors the pH value of the cathode zone in real time and transmits the data to the PLC. The PLC dynamically adjusts the parameters of the pulse power source according to the preset target pH oscillation range (8.5-10.5) and real-time monitoring data.

[0060] During the "on" period of pulse electrolysis, OH - is generated on the surface of the cathode 120, causing the local pH to rise. During the "off" period (or low current density period) of the pulse, the generation of OH - stops or significantly decreases, at which time the pH value of the cathode zone will decrease due to the buffering effect (dissolution of CaSiO3), ion migration and the reaction with H +The reaction naturally falls back to the original state after the pulse is over. The control system 300 captures the pH change, dynamically adjusts the pulse parameters according to the preset oscillation mode, and thus realizes the accurate and dynamic oscillation of the local pH between 8.5 and 10.5. The alkaline environment required for HAP crystallization is ensured, and the co-precipitation of impurities during the pH drop is effectively avoided.

[0061] II. Process flow The present application provides a phosphorus directional crystallization recovery method based on dynamic pulse electric field coupling local pH oscillation. The detailed process flow includes three main steps: pretreatment, pulse electrolysis and directional crystallization, and product separation.

[0062] Step a, wastewater pretreatment, the wastewater containing organic phosphorus, orthophosphate and other impurities is preliminarily adjusted to meet the requirements of the subsequent electrolysis and crystallization process.

[0063] First, using common acid-base adjuster such as sodium hydroxide (NaOH) or hydrochloric acid (HCl), the overall pH value of the wastewater to be treated is adjusted to 6.0-7.0. This pH range helps to start the subsequent electrochemical reaction and avoids non-target precipitation in the initial stage.

[0064] A small amount of calcium silicate (CaSiO3) is added to the pretreated wastewater, and the concentration is usually controlled at 0.5 mM to 2 mM. The CaSiO3 added in this stage mainly serves as the initial Ca 2+ source and as a pH buffer to help maintain the pH stability of the cathode area throughout the process.

[0065] The present application is suitable for treating various complex wastewater, including but not limited to high-concentration organic phosphorus pesticide wastewater, municipal sludge anaerobic fermentation liquid and phosphorus iron residue leaching liquid. Typical influent characteristics may include: Total phosphorus concentration: 800 mg / L (as P, high-concentration wastewater), to 120 mg / L (low-concentration).

[0066] Organic matter content: COD can reach 12,000 mg / L, such as methanol equivalent, or contains organic phosphorus, such as glyphosate, HEDP, ATMP, DTPMP, etc., with a concentration range from hundreds to tens of thousands of mg / L. Organic phosphorus is not a single substance, but a general term for a variety of compounds, with a wide range of molecular formulas and initial total phosphorus concentrations, for example: glyphosate (C3H8NO5P), HEDP (C2H8O7P2Na2), ATMP (C3H 12 N2O9P3Na4), DTPMP (C9H 28 N3O 15 P5Na7) and the like.

[0067] Other ion composition: chloride ion (Cl -) up to 8000 mg / L, as hydrochloric acid equivalent, sulfate (SO4 2- ) 1500 mg / L, as sulfuric acid equivalent, ammonia nitrogen <10 mg / L, as ammonium chloride equivalent, total dissolved solids about 15,000 mg / L. Iron ion (Fe 3+ ) up to 500 mg / L, for phosphorus iron residue. Detailed analysis of the influent helps to adjust the subsequent electrolysis parameters and CaSiO3 dosage according to the water quality characteristics.

[0068] The pretreated wastewater is introduced into the electrochemical reactor of the present application. Under the action of dynamic pulse electric field, strong oxidation reaction occurs at the anode 110. The organic phosphine compounds in the wastewater are efficiently oxidized and degraded, and finally converted into phosphate. At the same time, water oxidation reaction occurs, producing oxygen. The pulse electric field mode can effectively inhibit the formation or adsorption of the passivation layer on the surface of the anode 110, maintain the electrode activity, and prolong the service life. In the cathode region separated by the microporous diaphragm 130, water reduction produces hydroxyl ions and hydrogen gas, resulting in a local increase in pH in the cathode region. The calcium silicate loaded on the surface of the cathode 120 slowly dissolves in the local alkaline environment, releasing Ca 2+ ions, providing sufficient calcium source for HAP crystallization.

[0069] By controlling the system 300 to dynamically adjust the parameters of the pulse power supply, the local pH value in the cathode region is periodically oscillated between 8.5 and 10.5. During the pulse "on" period, OH - is generated, resulting in an increase in pH; during the pulse "off" period, the generation of OH - is reduced, and the pH naturally falls due to the buffering effect of CaSiO3, ion migration and 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 continuous high pH conditions, ensuring the purity of the product.

[0070] Phosphate (PO4 3- ) and calcium silicate released Ca 2+ enrich on the surface of carbon felt, and under the induction of local pH oscillation, form high-purity hydroxyapatite (HAP) crystals with carbon felt fibers as nucleation sites. This ensures the stability of the crystal form and high purity of the product.

[0071] Operating parameters: the pulse electrolysis process is carried out under the following conditions: Operating voltage: 5V to 20V.

[0072] Pulse frequency: 500Hz to 5kHz.

[0073] Pulse duty cycle: 30% to 50%.

[0074] Temperature: Depending on the wastewater properties and microbial activity requirements, it is usually between 25-50°C to promote reaction rate and crystallization process.

[0075] Hydraulic retention time: Depending on the treatment capacity and phosphorus concentration, it can be adjusted from tens of minutes to several hours.

[0076] Step c, after the completion of the electrolytic crystallization, the solid-liquid mixture in the reactor is discharged from the discharge port. The carbon felt loaded with HAP crystals can be easily detached from the cathode 120 structure.

[0077] Detachment requires first physical cleaning to remove loose crystalline material attached to the surface of the carbon felt. The HAP crystals that have fallen off the carbon felt or formed in the solution are separated from the water phase through a centrifugal separation unit, obtaining a high-purity HAP product. To achieve the recycling of the carbon felt, it can be subjected to a regeneration process: using a sodium hydroxide or potassium hydroxide solution to perform an alkaline wash of the carbon felt to remove surface-adsorbed oil and some organic matter. Rinsing with clean water removes residual alkali. An acid wash using a dilute hydrochloric acid or nitric acid solution removes possible metal impurities or residual amorphous precipitates present on the surface of the carbon felt. Again, rinsing with clean water, possibly combined with ultrasonic agitation to improve cleaning, ensures the complete removal of the acid and impurities. Finally, a final rinse with deionized water ensures the purity of the carbon felt. After sufficient drying, the carbon felt can be reloaded with calcium silicate and used in the next cycle.

[0078] The effluent after HAP separation has a significantly reduced phosphorus concentration and can be directly discharged according to local discharge standards or further treated, such as membrane filtration, activated carbon adsorption, and then reused. The effluent water quality or other indicators such as COD, TOC, SS, etc. are also improved. The recovered high-purity HAP product can be used as a high-value-added phosphorus fertilizer, industrial raw material, or functional material, achieving the resource utilization of phosphorus resources. Specific embodiments

[0079] In order to better understand the present application, the following specific embodiments will be described in detail. These examples are only used to illustrate the present application and should not be interpreted as limiting the scope of the present application.

[0080] Example 1: Treatment of high-concentration organic phosphorus pesticide wastewater (glyphosate production wastewater) This example aims to verify the effectiveness of the present application in treating high-concentration organic phosphorus wastewater, especially its ability to degrade organic phosphorus and efficiently recover phosphorus.

[0081] The wastewater to be treated is high-concentration organic phosphorus pesticide wastewater generated during the production of glyphosate. Glyphosate concentration: about 200 mg / L. Initial total phosphorus (as P): about 35 mg / L. Initial pH: about 6.0. Chloride ion (Cl -Concentration: about 3000 mg / L. Other organic and inorganic salt content is high, with certain corrosive.

[0082] This wastewater contains high concentrations of organophosphorus compounds, which pose a challenge to traditional phosphorus recovery technologies and can lead to electrode passivation and low recovery efficiency.

[0083] The electrochemical reaction device designed by the present application is specifically configured as follows: Reactor: 50L in volume, rectangular structure, 304 stainless steel, good corrosion resistance.

[0084] Anode 110: Ti / IrO2-Ta2O5 wave plate electrode, effective area 0.5m 2 . Improve reaction efficiency. The coating is prepared according to the thermal decomposition method described in the present application, which ensures its catalytic activity and stability.

[0085] Cathode 120: porous carbon felt loaded CaSiO3 composite electrode, loading amount 0.2g-CaSiO3 / g-carbon felt. The carbon felt is sewn into a "pocket" shape to wrap the titanium plate, the size is 10cm×10cm×1cm, a total of 10 pieces. CaSiO3 is loaded by in-situ synthesis method to ensure its uniformity and stability.

[0086] Inter-electrode distance: the distance between anode and cathode 110 is 3cm.

[0087] Microporous diaphragm 130: PTFE material, thickness 0.2mm, pore size 0.45µm, porosity 75%, used to separate the cathode area and anode 110 area.

[0088] Process operating conditions Pretreatment: First, adjust the pH of glyphosate production wastewater to 6.5 with sodium hydroxide, then add a small amount of CaSiO3, concentration 1.0mM, stir evenly.

[0089] Pulse electrolysis: Working voltage: 10V (constant voltage mode).

[0090] Current density: 50mA / cm 2 (peak).

[0091] Pulse frequency: 1.5kHz.

[0092] Duty cycle: 50%.

[0093] Temperature: 30±2℃.

[0094] Hydraulic retention time (HRT): 40 minutes.

[0095] Cathode zone pH oscillation range: 8.8-10.5. The pH in the cathode zone is maintained within the set oscillation range by real-time monitoring and dynamic adjustment of the pulse power parameters through the online pH sensor 170 and the PLC control system 300.

[0096] Ca 2+ Dosage: In this example, in addition to the CaSiO3 added in the pretreatment stage, 0.5 mM of Ca 2+ is additionally added during the electrolysis process to ensure sufficient calcium source required for HAP crystallization, provided by dissolved CaSiO3 and a small amount of supplementary calcium salt.

[0097] Results and performance After continuous operation, the following excellent results were achieved in this example: Glyphosate degradation rate: ≥99.5%. This indicates that the device has high degradation capacity for organic phosphorus compounds.

[0098] Phosphorus recovery rate: 99.2%. This is much higher than the 70%-85% recovery rate of traditional electrolysis methods, demonstrating the significant advantage of the present invention in phosphorus recovery.

[0099] HAP crystal purity: 96.5%. The recovered product is high-purity hydroxyapatite with high crystalline purity, having high resource utilization value.

[0100] Energy consumption: 18.5 kWh / kg P. This is much lower than traditional electrolysis methods, significantly reducing operating costs.

[0101] Electrode life: Anode 110 shows good stability, with no obvious signs of passivation after more than 600 hours of continuous operation, significantly extending the electrode life.

[0102] This example fully demonstrates the advantages of the present invention in treating high-concentration organic phosphorus wastewater, including high efficiency, low energy consumption, high purity, and long life.

[0103] Example Two: Treatment of Municipal Sludge Anaerobic Fermentation Liquid (High Ammonia Nitrogen and Phosphorus Wastewater) This example aims to evaluate the performance of the present invention in treating municipal sludge anaerobic fermentation liquid containing high ammonia nitrogen and phosphorus, with particular attention to phosphorus recovery efficiency, ammonia nitrogen retention, and energy consumption.

[0104] The wastewater to be treated is municipal sludge anaerobic fermentation liquid, characterized by high ammonia nitrogen, high phosphorus, and containing a certain amount of suspended solids (SS) and organic matter. Total phosphorus: about 120 mg / L. Ammonia nitrogen: about 800 mg / L. Initial pH: about 7.2. Suspended solids (SS): about 500 mg / L. Other organic matter and inorganic salts.

[0105] The wastewater, if directly discharged, will cause serious environmental pollution, and the valuable phosphorus resource contained therein needs to be recovered.

[0106] Device parameters The electrochemical reaction device designed according to the present application is configured as follows: Reactor: The volume is 200L, the square structure is adopted, the material is cPVC, and good corrosion resistance is achieved.

[0107] Anode 110: Ti / IrO2-Ta2O5 mesh electrode, effective area is 2.0m 2 The mesh design further increases the effective surface area of the electrode and improves the current efficiency. The coating preparation method is the same as that in Example One.

[0108] Cathode 120: Porous carbon felt loaded CaSiO3 composite electrode, loading amount is 0.3g-CaSiO3 / g-carbon felt. The size of the carbon felt is 20cm×20cm×1cm, and there are a total of 20 pieces.

[0109] Inter-electrode distance: The distance between the anode and the cathode 110 is 4cm.

[0110] Microporous diaphragm 130: PP material, thickness is 1.0mm, pore size is 1.0µm, porosity is 70%, used to separate the cathode area and the anode 110 area.

[0111] Process operating conditions Pretreatment: The municipal sludge anaerobic fermentation liquid is adjusted to pH 6.8 with a small amount of dilute hydrochloric acid, and then a trace amount of CaSiO3 is added, the concentration is 0.5mM, and stirring is uniform.

[0112] Pulse electrolysis: Working voltage: 12V (constant voltage mode).

[0113] Current density: 30mA / cm 2 (peak value).

[0114] Pulse frequency: 1.0kHz.

[0115] Duty cycle: 40%.

[0116] Temperature: 35℃.

[0117] Hydraulic retention time: 60 minutes.

[0118] Cathode area pH oscillation range: 8.5-10.2.

[0119] Ca 2+ Dosage: 0mM. This example completely relies on the dissolution of CaSiO3 loaded on the cathode 120 to provide Ca 2+Without additional calcium salt, the synergistic strengthening effect of CaSiO3 is verified.

[0120] Results and performance Phosphorus recovery rate: 98.8%. High-efficiency phosphorus recovery is achieved.

[0121] Product: mainly HAP, with a small amount of struvite (MgNH4PO4·6H2O). This is because the anaerobic fermentation liquid contains a certain amount of magnesium ions and ammonia nitrogen, and under local alkaline conditions, part of the phosphate will react with magnesium ions and ammonia nitrogen to form struvite. However, HAP is still the main product.

[0122] Ammonia nitrogen retention rate: ≥95%. Due to the control of pH oscillation in the cathode zone, the loss of ammonia nitrogen caused by continuous high pH is avoided, and good retention of ammonia nitrogen is achieved.

[0123] Energy consumption: 15.8 kWh / kg P. The energy consumption is very excellent, further confirming the energy-saving advantage of the present application.

[0124] This example shows that when treating high ammonia nitrogen phosphorus wastewater, the present application not only can efficiently recover phosphorus, but also can effectively retain ammonia nitrogen, reduce blow-off loss, while maintaining low energy consumption and high purity product.

[0125] These two examples fully demonstrate that the present application technology can maintain high phosphorus recovery rate and high product purity under different water quality conditions. By flexibly adjusting the pulse parameters and reaction conditions, it can adapt to different wastewaters from high organic matter to high impurities, showing strong adaptability and industrialization potential. Compared with traditional electrochemical phosphorus recovery technology, the present application has made significant improvements in phosphorus recovery efficiency, energy consumption, crystallization purity and electrode life, etc., providing a new solution for green and efficient recovery of phosphorus resources.

[0126] The above is only a preferred embodiment of the present application, and does not limit the present application. The patent protection scope of the present application is subject to the claims, and any equivalent structural changes made by using the content of the present application should also be included in the protection scope of the present application.

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, 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 by an in-situ synthesis method, specifically by immersing the porous carbon felt in a 30%-40% sodium silicate and calcium carbonate solution, reacting at 80-90℃ for 40-60 minutes to generate calcium silicate, and then drying it 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 an ideal particle size range of D50≤1µm and an ideal 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 at a concentration of 0.5 mM to 2 mM; 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 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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