A double-migration electric field electrocoagulation three-electrode system and method for phosphorus removal of tail water

Abstract

The present application relates to the technical field of electrochemical water treatment, and discloses a double-migration electric field electrocoagulation three-electrode system and method for phosphorus removal of tail water, a plurality of parallelly arranged electrode arrays are arranged in an electrocoagulation reaction module, each electrode array comprises sequentially arranged first inert electrodes, a sacrificial metal electrode and second inert electrodes, the first inert electrodes and the second inert electrodes are respectively located on the two sides of the sacrificial metal electrode, and a symmetric electrode group with the sacrificial metal electrode as a symmetric center is formed; a power supply module is electrically connected with the electrode arrays and is used for applying a periodically changing electric field to the electrode arrays; the present application adopts a sandwich type symmetric electrode configuration of double-side inert electrodes-middle sacrificial metal electrode, a periodically changing electric field in four stages is executed in a time sequence cycle, and the double problems of low-concentration mass transfer dead zone and electrode passivation are solved, so that a deep phosphorus removal electrocoagulation technology is realized, which realizes double-side alternating migration mass transfer intensification, effectively inhibits electrode passivation, and realizes full-process low-energy-consumption operation.

Description

Technical Field

[0001] This invention relates to the field of electrochemical water treatment technology, and in particular to a dual-migratory electric field electrocoagulation three-electrode system and method for phosphorus removal from wastewater. Background Technology

[0002] The large-scale development of aquaculture has led to a continuous increase in the discharge of phosphorus-containing wastewater. The total phosphorus concentration in this wastewater is typically low (0.5–5 mg / L), but discharge standards are becoming increasingly stringent, with some regions requiring total phosphorus levels in the effluent to be below 0.5 mg / L or even 0.4 mg / L. Among traditional phosphorus removal methods, chemical flocculation requires large amounts of reagents and produces high sludge yields; adsorption methods are expensive and difficult to regenerate; and membrane filtration involves large equipment investments and severe membrane fouling. None of these methods can simultaneously meet the requirements of deep removal of low-concentration phosphorus and low-cost operation.

[0003] Electrocoagulation technology has attracted much attention due to its advantages such as eliminating the need for chemical flocculants, producing less sludge, and being easy to operate. However, traditional two-electrode electrocoagulation systems powered by constant DC power suffer from two structural defects when treating low-concentration phosphorus-containing water: First, under low-concentration conditions, the diffusion mass transfer kinetics of phosphate ions are extremely weak, resulting in insufficient flux of ions reaching the electrode surface, leading to low flocculant utilization and slow reaction rates. Second, prolonged DC operation causes the formation of a dense oxide film (passivation layer) on the anode surface, while concentration polarization occurs on the cathode side, resulting in a continuous increase in cell voltage and a continuous decrease in current efficiency. These two defects make it difficult for traditional electrocoagulation to remove phosphorus concentrations to below 0.1 mg / L, and the overall energy consumption is relatively high.

[0004] To alleviate electrode passivation, periodic polarity reversal electrocoagulation technology has been proposed (e.g., CN1418175A), which strips the surface passivation layer by periodically exchanging the polarity of the anode and cathode. However, this technology only solves the electrode passivation problem and does not address the fundamental bottleneck of the low-concentration mass transfer dead zone. Ion mass transfer still relies on natural diffusion, and the treatment time and electrode area still need to be greatly extended when treating low-concentration water.

[0005] Tian et al. (Water Research, 2018, 138: 129-136) constructed a migration electric field assisted air cathode electrocoagulation system (MEAEC), employing a three-electrode configuration of Ti inert electrode, Fe sacrificial anode, and activated carbon air cathode, achieving low-energy phosphorus removal through two-stage cyclic operation. However, this system has the following shortcomings: First, the migration electric field is unidirectional and one-sided, resulting in limited mass transfer enhancement; second, the air cathode preparation process is complex and requires exposure to air for self-breathing oxygen supply, limiting the sealing design and engineering application of the housing; third, the system only has a two-stage cycle and lacks dynamic alternating control of the migration field direction.

[0006] CN202210459828A discloses a three-electrode electrocoagulation system with a carbon-based adsorption electrode, consisting of a carbon-based adsorption electrode, an iron sacrificial anode, and an inert metal plate. It achieves phosphorus removal through a two-stage cyclic operation of a migration adsorption stage and an electrocoagulation stage. However, the migration adsorption stage of this system inevitably involves a cathode hydrogen evolution reaction, with most of the cathode current consumed in hydrogen production rather than ion migration and enrichment, fundamentally limiting energy utilization efficiency. Furthermore, the carbon-based adsorption electrode suffers from structural stability issues during long-term operation, and the two-stage equal-duration design lacks temporal optimization.

[0007] In summary, existing electrocoagulation phosphorus removal technologies still face the following core problems that have not been solved simultaneously when treating water bodies with low phosphorus concentrations: (1) the problem of mass transfer dead zones at low concentrations—existing technologies have failed to achieve bilateral, efficient, and low-energy-consumption ion migration and mass transfer enhancement; (2) the persistent problems of electrode passivation and concentration polarization; and (3) the energy waste caused by side reactions of electrochemically desorbed gas. Therefore, it is urgent to develop a deep phosphorus removal electrocoagulation technology that can achieve bilateral alternating migration and mass transfer enhancement under low concentration conditions, effectively suppress electrode passivation, and operate with low energy consumption throughout the process. Summary of the Invention

[0008] The purpose of this invention is to provide a dual-migration electric field electrocoagulation three-electrode system and method for phosphorus removal from wastewater. It aims to solve or improve at least one of the above-mentioned technical problems. It adopts a sandwich-type symmetrical electrode configuration with double-sided inert electrodes and a middle sacrificial metal electrode. By performing four-stage cyclic electric field transformations in a time sequence, it solves the dual problems of low-concentration mass transfer dead zone and electrode passivation. It realizes a deep phosphorus removal electrocoagulation technology with enhanced dual-sided alternating migration mass transfer, effective suppression of electrode passivation, and low energy consumption throughout the process, thus achieving deep treatment of low-concentration phosphorus-containing wastewater.

[0009] To achieve the above objectives, the present invention provides a dual-migration electric field electrocoagulation three-electrode system for phosphorus removal from wastewater, comprising: An electrocoagulation reaction module is provided with multiple sets of parallel electrode arrays. Each set of electrode arrays includes a first inert electrode, a sacrificial metal electrode, and a second inert electrode arranged in sequence. The first inert electrode and the second inert electrode are located on both sides of the sacrificial metal electrode, forming a symmetrical electrode group with the sacrificial metal electrode as the center of symmetry. A power supply module, electrically connected to the electrode array, is used to apply a periodically changing electric field to the electrode array; The periodically transformed electric field is configured to execute the following four stages in a time-sequential cycle: Phase 1: Connect the first inert electrode to the positive terminal of the power supply, connect the second inert electrode to the negative terminal of the power supply, disconnect the sacrificial metal electrode, run for a first set time, establish a transverse electric field between the first inert electrode and the second inert electrode, drive the negatively charged target ions in the liquid phase to migrate directionally towards the first inert electrode, and form a double-layer capacitor on the surface of the first inert electrode. Phase Two: Connect the first inert electrode to the negative terminal of the power supply, connect the sacrificial metal electrode to the positive terminal of the power supply, disconnect the second inert electrode, run for a second set time, the sacrificial metal electrode undergoes an anodic dissolution reaction to release metal cations, which react with the enriched target ions to form an insoluble precipitate, and at the same time the first inert electrode releases the ions enriched by the double layer capacitor formed in Phase One to the area near the sacrificial metal electrode in a capacitor discharge mode. Phase 3: Connect the second inert electrode to the positive terminal of the power supply, connect the first inert electrode to the negative terminal of the power supply, disconnect the sacrificial metal electrode, run for a third set time, drive the residual target ions in the liquid phase to migrate in the opposite direction to the other side of the sacrificial metal electrode for enrichment, and form a double-layer capacitor on the surface of the second inert electrode. Phase 4: Connect the second inert electrode to the negative terminal of the power supply and connect the sacrificial metal electrode to the positive terminal of the power supply. Disconnect the first inert electrode and run for a fourth set time. The sacrificial metal electrode anolyses and reacts with the enriched target ions to form an insoluble precipitate. At the same time, the second inert electrode releases the ions enriched by the double-layer capacitor formed in Phase 3 to the area near the sacrificial metal electrode in a capacitor discharge mode.

[0010] Optionally, the first inert electrode and the second inert electrode are each independently selected from one of titanium, titanium alloy, titanium-based coated electrode, graphite, conductive ceramic or stainless steel; the titanium-based coated electrode includes Ti / IrO electrode, Ti / RuO electrode, Ti / Pt electrode or Ti / Ru / Ir electrode.

[0011] Optionally, the sacrificial metal electrode is selected from iron, aluminum, magnesium, zinc or their alloys; the sacrificial metal electrode has a plate-like, mesh-like, foam-like or porous structure.

[0012] Optionally, the distance between the sacrificial metal electrode and the first inert electrode and the distance between the sacrificial metal electrode and the second inert electrode are each independently 0.5 to 5 cm; the first set time, the second set time, the third set time and the fourth set time are each independently 5 to 60 s.

[0013] Optionally, the operating voltages of Stage 1 and Stage 3 are each independently 0.3 to 5V, which are lower than the water electrolysis voltage under actual operating conditions, so that no significant water electrolysis side reactions occur in Stage 1 and Stage 3.

[0014] Optionally, the operating voltages of stage two and stage four are each independently 0.5 to 20V.

[0015] Optionally, the periodic electric field is repeated to circulate and treat the wastewater until the concentration of the target pollutant ions in the wastewater reaches the discharge standard. The target pollutant ions are at least one of phosphate, fluoride, arsenate, or chromate. The system is used to treat low-concentration phosphorus-containing wastewater, which is municipal sewage effluent or aquaculture effluent.

[0016] Optionally, the electrode array is configured with 1 to 50 groups, and the groups of electrode arrays are connected in parallel; the electrocoagulation reaction module includes a housing, and electrode slots are correspondingly provided on both side walls of the housing. The electrode array is modularly installed and disassembled by inserting into the electrode slots; the housing is also provided with an inlet and an outlet, which are located at both ends of the multiple groups of electrode arrays, and the water inlet and outlet are arranged in a bottom-inlet and top-outlet manner; the electrocoagulation reaction modules can be stacked to form a larger combined system.

[0017] Optionally, the power supply module further includes a reverse voltage recoil unit, which is configured to periodically or under a preset trigger condition switch the system to recoil mode for a set recoil time; the preset trigger condition is that the tank voltage rises to twice its initial value; in the recoil mode, the first inert electrode and the second inert electrode are both connected to the positive terminal of the power supply or alternately connected to the positive terminal of the power supply, and the sacrificial metal electrode is connected to the negative terminal of the power supply to apply a recoil voltage; the recoil voltage is 0.5 to 10V, and the recoil time is 30 to 600s.

[0018] This invention also provides a three-electrode method for phosphorus removal from wastewater using a dual-migration electric field electrocoagulation system, comprising the following steps: S1: Connect the first inert electrode to the positive electrode, the second inert electrode to the negative electrode, disconnect the sacrificial metal electrode, run for a first set time, drive the negatively charged target ions in the liquid phase to migrate in a directional manner toward the first inert electrode, and form a double-layer capacitor on the surface of the first inert electrode. S2: Connect the first inert electrode to the negative electrode, connect the sacrificial metal electrode to the positive electrode, disconnect the second inert electrode, run for a second set time, the sacrificial metal electrode anolyses and releases metal cations, which react with the enriched target ions to form an insoluble precipitate, and at the same time the first inert electrode releases the ions enriched in its double layer capacitance to the area near the sacrificial metal electrode in a capacitor discharge mode. S3: Connect the second inert electrode to the positive electrode and the first inert electrode to the negative electrode. Disconnect the sacrificial metal electrode and run for a third set time to drive the residual target ions in the liquid phase to migrate in the opposite direction to the other side of the sacrificial metal electrode for enrichment, and form a double-layer capacitor on the surface of the second inert electrode. S4: Connect the second inert electrode to the negative electrode and the sacrificial metal electrode to the positive electrode. Disconnect the first inert electrode and run for a fourth set time. The sacrificial metal electrode dissolves at the anode and reacts with the enriched target ions to form an insoluble precipitate. At the same time, the second inert electrode releases the ions enriched by the double layer capacitor formed in S3 to the area near the sacrificial metal electrode in a capacitor discharge mode. Steps S1 to S4 are executed repeatedly until the effluent quality reaches the target value, thus achieving deep wastewater treatment.

[0019] The present invention discloses the following technical effects: This invention constructs a dynamic lateral migration electric field between the dual inert electrodes and the sacrificial metal electrode by sequentially executing four stages of polarity switching. This electric field can directionally accelerate the migration and enrichment of dilute phosphate ions towards the sacrificial anode region, effectively overcoming the mass transfer bottleneck caused by the slow natural diffusion of ions in low-concentration water. After treatment by this system, the phosphorus concentration in the effluent can be reduced from approximately 1 mg / L to below 0.1 mg / L in a short time, achieving deep treatment of low-concentration phosphorus-containing wastewater.

[0020] This invention employs a three-electrode configuration consisting of two inert electrodes and a sacrificial metal electrode, combined with a periodically changing electric field operation mode. The periodic polarity reversal continuously breaks the concentration polarization on the electrode surface, fundamentally alleviating the problem of electrode passivation in traditional electrocoagulation and improving the stability of the system. Simultaneously, through the synergistic mechanism of electric field migration enrichment and in-situ electrocoagulation, the probability of collision and binding between phosphate ions and iron-based flocculants is greatly increased.

[0021] The periodic electric field of this invention significantly accelerates ion mass transfer efficiency and reduces the ineffective energy consumption for overcoming solution resistance and concentration polarization, enabling the system to operate efficiently at extremely low operating voltages and greatly reducing operational energy consumption. Simultaneously, the use of high-mechanical-strength, corrosion-resistant titanium plates as peripheral electrodes effectively avoids electrode wear in complex tailwater environments, ensuring the long-term, stable operation of the system. Attached Figure Description

[0022] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a front sectional view of the overall structure of the present invention; Figure 2 This is a top view of the overall structure of the present invention; Figure 3 This is a side sectional view of the overall structure of the present invention; Figure 4 This is a schematic diagram of the electrode array structure of the present invention; Figure 5 This is a schematic diagram of the four stages of the periodic transformation electric field of the present invention; Figure 6 The graph shows the phosphorus removal effect under different migration and flocculation voltages in Embodiment 1 of the present invention. Figure 7 This is a diagram showing the operating consumption and cost under different migration and flocculation voltages in Embodiment 1 of the present invention; Figure 8 The graph shows the phosphorus removal effect under different migration and flocculation voltages in Embodiment 2 of the present invention. Figure 9 This is a diagram showing the operating consumption and cost under different migration and flocculation voltages in Embodiment 2 of the present invention; Figure 10 The graph shows the phosphorus removal effect under different migration and flocculation voltages in Embodiment 3 of the present invention. Figure 11 This is a diagram showing the operating consumption and cost under different migration and flocculation voltages in Embodiment 3 of the present invention; Figure 12 The graph shows the phosphorus removal effect under different migration and flocculation voltages in Embodiment 4 of the present invention. Figure 13 This is a diagram showing the operating consumption and cost under different migration and flocculation voltages in Embodiment 4 of the present invention.

[0023] In the diagram: 1. First inert electrode; 2. Second inert electrode; 3. Sacrificial metal electrode; 4. Housing; 5. Electrode slot; 6. Inlet; 7. Outlet. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Reference Figures 1 to 13 This invention provides a dual-migration electric field electrocoagulation three-electrode system for phosphorus removal in wastewater, comprising: The electrocoagulation reaction module is provided with multiple sets of parallel electrode arrays. Each set of electrode arrays includes a first inert electrode 1, a sacrificial metal electrode 3 and a second inert electrode 2 arranged in sequence. The first inert electrode 1 and the second inert electrode 2 are located on both sides of the sacrificial metal electrode 3, forming a symmetrical electrode group with the sacrificial metal electrode 3 as the center of symmetry. The power supply module is electrically connected to the electrode array and is used to apply a periodically changing electric field to the electrode array. The periodically changing electric field is configured to execute the following four stages in a time-sequential cycle: Phase 1: Connect the first inert electrode 1 to the positive terminal of the power supply, connect the second inert electrode 2 to the negative terminal of the power supply, disconnect the sacrificial metal electrode 3, run for a first set time, establish a transverse electric field between the first inert electrode 1 and the second inert electrode 2, drive the negatively charged target ions in the liquid phase to migrate in a directional manner toward the first inert electrode 1, and form a double-layer capacitor on the surface of the first inert electrode 1. Phase 2: Connect the first inert electrode 1 to the negative terminal of the power supply, connect the sacrificial metal electrode 3 to the positive terminal of the power supply, disconnect the second inert electrode 2, run for the second set time, the sacrificial metal electrode 3 undergoes an anodic dissolution reaction to release metal cations, which react with the enriched target ions to form an insoluble precipitate, while the first inert electrode 1 releases the ions enriched by the double layer capacitor formed in Phase 1 to the area near the sacrificial metal electrode 3 in a capacitor discharge mode. Phase 3: Connect the second inert electrode 2 to the positive terminal of the power supply, connect the first inert electrode 1 to the negative terminal of the power supply, disconnect the sacrificial metal electrode 3, run for a third set time, drive the residual target ions in the liquid phase to migrate in the opposite direction to the other side of the sacrificial metal electrode 3 for enrichment, and form a double-layer capacitor on the surface of the second inert electrode 2. Phase 4: Connect the second inert electrode 2 to the negative terminal of the power supply, connect the sacrificial metal electrode 3 to the positive terminal of the power supply, disconnect the first inert electrode 1, run for the fourth set time, the sacrificial metal electrode 3 anolytes and reacts with the enriched target ions to form an insoluble precipitate, and at the same time, the second inert electrode 2 releases the ions enriched by the double layer capacitor formed in Phase 3 to the area near the sacrificial metal electrode 3 in a capacitor discharge mode.

[0027] The above-mentioned four-stage periodic transformation electric field simultaneously realizes a triple cooperative mechanism in this system: Firstly, the dual-sided alternating migration and enrichment mechanism. Stages one and three drive phosphate ions to migrate towards the central sacrificial metal electrode from the left and right sides respectively, alternately replenishing the target ions to the reaction region from both sides. This fundamentally overcomes the mass transfer dead zone problem caused by ion-dependent natural diffusion in low-concentration water bodies and significantly increases the effective ion flux on the surface of the sacrificial metal electrode.

[0028] Secondly, the inert electrode double-layer capacitor charging and discharging mechanism. In stages one and three, the applied electric field creates a double-layer capacitor on the surface of the inert electrode, pre-enriching some anions capacitively near the electrode surface. In stages two and four, the inert electrode switches to a negative electrode and releases the enriched anions near the sacrificial metal electrode in a capacitor discharge mode. This charging and discharging process involves only the charging and discharging of the double layer and does not rely on Faraday electrolysis, thus avoiding hydrogen evolution side reactions. The energy utilization efficiency is far higher than that of ion migration mechanisms driven by electrolysis current.

[0029] Third, the dynamic depassivation and deconcentration polarization mechanism. The rapid polarity switching on the order of seconds continuously refreshes the double layer structure and ion concentration distribution on the electrode surface, effectively breaking the gradually accumulating concentration polarization layer, preventing the formation of a dense passivation film on the surface of the sacrificial metal electrode, and maintaining high reactivity.

[0030] In this embodiment, the first inert electrode 1 and the second inert electrode 2 are each independently selected from one of titanium, titanium alloy, titanium-based coated electrode, graphite, conductive ceramic, or stainless steel; the titanium-based coated electrode includes Ti / IrO electrode, Ti / RuO electrode, Ti / Pt electrode, or Ti / Ru / Ir electrode. Furthermore, the first inert electrode 1 and the second inert electrode 2 can be made of pure titanium plate or titanium alloy plate to balance conductivity, mechanical strength, corrosion resistance, and economy. Furthermore, the first inert electrode 1 and the second inert electrode 2 should be made of the same material to ensure the stability of the system operation. Furthermore, when the wastewater or effluent to be treated contains a high chloride ion content (>200 mg / L), titanium-based and titanium-based coated electrodes should be preferred to enhance the corrosion resistance of the inert electrodes.

[0031] In this embodiment, the sacrificial metal electrode 3 is selected from iron, aluminum, magnesium, zinc, or their alloys; the sacrificial metal electrode 3 has a plate-like, mesh-like, foam-like, or porous structure to increase the effective reaction area. Preferably, a 60-100 mesh iron mesh is used, with a filling density of 10-100 m² / m³.

[0032] In this embodiment, the distance between the sacrificial metal electrode 3 and the first inert electrode 1, and the distance between the sacrificial metal electrode 3 and the second inert electrode 2, are each independently 0.5 to 5 cm. If the distance is too large, it will increase the ohmic resistance of the solution and the ion migration path, resulting in increased energy consumption; if the distance is too small, it will restrict the flow of fluid and increase the risk of short circuit. The first setting time, the second setting time, the third setting time, and the fourth setting time are each independently 5 to 60 seconds. The setting time for each stage can be the same, or different durations can be set according to the size of the electrode plate, the influent water quality conditions, and the treatment target. If the setting time is too short, it may lead to insufficient ion migration; if the setting time is too long, it may lead to the re-accumulation of concentration polarization, saturation of the double layer capacitance, and an extension of the treatment cycle.

[0033] In this embodiment, the operating voltages of stage one and stage three are each independently 0.3 to 5V, which are lower than the water electrolysis voltage under actual operating conditions, so that no significant water electrolysis side reactions occur in stage one and stage three.

[0034] In this embodiment, the operating voltages of stage two and stage four are each independently 0.5 to 20V.

[0035] In this embodiment, the electric field is repeatedly and periodically changed to circulate and treat the wastewater until the concentration of the target pollutant ions in the wastewater reaches the discharge standard. The target pollutant ions are at least one of phosphate, fluoride, arsenate or chromate. The system is used to treat low-concentration phosphorus-containing wastewater, which is municipal sewage effluent or aquaculture effluent.

[0036] In this embodiment, the electrode array is set to 1 to 50 groups, and the groups of electrode arrays are connected in parallel; the electrocoagulation reaction module includes a box 3, and electrode slots 5 are provided on both sides of the box 4. The electrode array is modularly installed and disassembled by inserting into the electrode slots 5; the box 4 is also provided with an inlet 6 and an outlet 7, which are located at both ends of multiple groups of electrode arrays, and the water inlet and outlet are in the bottom and outlet manner; the electrocoagulation reaction modules can be stacked to form a larger combined system.

[0037] By setting electrode slots 5, plug-and-play modular installation and disassembly of the electrodes are achieved. This greatly facilitates daily maintenance, replacement, or cleaning of the electrodes, reduces the difficulty of system operation and maintenance, and allows for flexible adjustment of the number or type of electrode array according to changes in water quality. Furthermore, placing the inlet 6 and outlet 7 at both ends of the electrode array ensures that the treated wastewater must pass through the entire electrode area when flowing through the tank 4, guaranteeing the uniformity of hydraulic residence time and the sufficiency of the electric field effect. The inlet 6 and outlet 7 are arranged in a bottom-in, top-out manner to enhance the hydraulic propulsion effect by utilizing the density difference of the water flow and gravity, avoiding short-circuiting and dead zones. This also aligns with the natural upward floating direction of bubbles generated during electrocoagulation, promoting solid-liquid separation. This design utilizes the density difference of water and gravity to achieve better hydraulic propulsion and effectively avoid short-circuiting and dead zones. More importantly, the bottom-in, top-out water flow direction is consistent with the natural upward floating direction of bubbles such as hydrogen and oxygen generated during electrocoagulation, helping the bubbles carry flocs to the water surface, achieving solid-liquid separation. Meanwhile, this fluid dynamics design enhances the turbulence of water between electrodes, further improving mass transfer efficiency and enabling the system to better adapt to large hydraulic shock loads.

[0038] In this embodiment, the depth of the electrode slot 5 is 0.1cm. The depth of the electrode slot 5 is 0.1cm, which can provide sufficient mechanical clamping force to ensure that the electrode remains vertically stable under long-term water flow impact and prevent short circuits. It also avoids the loss of the effective working area of ​​the electrode due to the electrode slot 5 being too deep, thus ensuring the effective coverage of the electric field and the material utilization rate.

[0039] In this embodiment, the housing 4 is made of a corrosion-resistant insulating material, selected from acrylic, polypropylene, polyvinyl chloride, or polytetrafluoroethylene. Acrylic has excellent processability, good transparency, and sufficient mechanical strength. Assembling the housing 4 using acrylic sheets facilitates rapid construction and modification of the housing 4 in laboratory or pilot-scale operations. Its transparency allows operators to directly observe the water flow, floc formation, and sedimentation within the housing 4, facilitating real-time monitoring of the process operation and fault diagnosis.

[0040] In this embodiment, the power supply module further includes a reverse voltage recoil unit, which is configured to periodically or under a preset trigger condition to switch the system to recoil mode for a set recoil time; the preset trigger condition is that the tank voltage rises to twice the initial value; in recoil mode, the first inert electrode 1 and the second inert electrode 2 are both connected to the positive terminal of the power supply or alternately connected to the positive terminal of the power supply, and the sacrificial metal electrode 3 is connected to the negative terminal of the power supply to apply a recoil voltage; the recoil voltage is 0.5 to 10V, and the recoil time is 30 to 600s.

[0041] After long-term operation of the system, the surface of the sacrificial metal electrode 3 may become roughened, develop local pits, or undergo uneven corrosion due to continuous anodic leaching, leading to uneven electric field distribution and decreased flocculation efficiency. Simultaneously, the long-term accumulation and precipitation of hardness ions and precipitated anions in the solution on the inert electrode surface can also affect the charging and discharging efficiency of the electric double-layer capacitor.

[0042] The reverse voltage backflush produces the following effects: a cathodic reduction reaction occurs on the surface of the sacrificial metal electrode 3, which reduces and repairs the locally over-oxidized areas on the surface, restoring surface uniformity; when the inert electrode is used as the anode, all residual anions are released, and an oxygen evolution reaction occurs on its surface to generate microbubbles. The physical shearing and peeling action of the bubbles removes the hardness salts and organic contaminants deposited on the surface of the inert electrode, restoring the double-layer capacitance performance; when the sacrificial metal electrode 3 is used as the cathode, the hydrogen bubbles generated also have a physical cleaning effect on its surface.

[0043] In this embodiment, the power supply module also includes a real-time current / voltage acquisition module, which is used to record the current-time curve and / or voltage-time curve during each stage of operation. By analyzing the charging current curve of stage one and / or stage three, the module monitors the health status of the electric double layer capacitance of the inert electrode (a continuous decrease in the peak charging current may indicate the accumulation of deposits on the surface of the inert electrode or the decay of the electric double layer capacitance, at which point the backflush regeneration program can be automatically triggered), and / or by analyzing the changing trend of the operating current in stage two and / or stage four, the module assesses the passivation degree and consumption status of the sacrificial metal electrode, and issues an early warning prompt to replace the electrode when necessary.

[0044] In this embodiment, the power supply module also includes an online water quality monitoring sensor and a feedback control system. The online water quality monitoring sensor is used to measure the phosphorus concentration, pH value, conductivity and / or turbidity of the influent and effluent in real time or intermittently. The feedback control system automatically adjusts one or more of the following operating parameters according to the measured water quality parameters: operating voltage of each stage, set time of each stage, total processing time and / or number of cycle cycles.

[0045] Operating voltage at each stage: When the influent phosphorus concentration is high, the flocculation voltage of stage two / four should be appropriately increased to increase the dissolution rate of the sacrificial metal electrode; when the influent conductivity is low, the migration voltage of stage one / three should be appropriately increased to compensate for the ohmic voltage drop of the solution, but preferably not exceeding the electrolysis voltage of water, or the migration time should be controlled so that water electrolysis has not yet occurred.

[0046] Setting time for each stage: When the influent phosphorus concentration is high, the flocculation time of stage two / four should be appropriately extended; when the influent conductivity is high (high ionic strength), the migration time of stage one / three can be appropriately shortened, because high ionic strength is beneficial to reducing the ohmic resistance of the solution, as well as double layer compression and capacitance formation.

[0047] Total treatment time and / or number of cycles: The decision to terminate treatment or add additional cycles is made in real time based on the comparison between the phosphorus concentration in the effluent monitored online and the target value.

[0048] The present invention also provides a three-electrode method for phosphorus removal from wastewater using a dual-migration electric field electrocoagulation system, characterized by using the system of any one of claims 1 to 9, comprising the following steps: S1: Connect the first inert electrode 1 to the positive electrode, the second inert electrode 2 to the negative electrode, disconnect the sacrificial metal electrode 3, run for a first set time, drive the negatively charged target ions in the liquid phase to migrate in a directional manner toward the first inert electrode 1, and form a double-layer capacitor on the surface of the first inert electrode 1. S2: Connect the first inert electrode 1 to the negative electrode, connect the sacrificial metal electrode 3 to the positive electrode, disconnect the second inert electrode 2, run for the second set time, the sacrificial metal electrode 3 anolyses and releases metal cations, which react with the enriched target ions to form an insoluble precipitate. At the same time, the first inert electrode 1 releases the ions enriched in its double layer capacitor to the area near the sacrificial metal electrode 3 in a capacitor discharge mode. S3: Connect the second inert electrode 2 to the positive electrode, connect the first inert electrode 1 to the negative electrode, disconnect the sacrificial metal electrode 3, run for a third set time, drive the residual target ions in the liquid phase to migrate in the opposite direction to the other side of the sacrificial metal electrode 3 for enrichment, and form a double-layer capacitor on the surface of the second inert electrode 2. S4: Connect the second inert electrode 2 to the negative electrode and the sacrificial metal electrode 3 to the positive electrode. Disconnect the first inert electrode 1 and run for the fourth set time. The sacrificial metal electrode 3 dissolves at the anode and reacts with the enriched target ions to form an insoluble precipitate. At the same time, the second inert electrode 2 releases the ions enriched by the double layer capacitor formed in S3 to the area near the sacrificial metal electrode 3 in a capacitor discharge mode. Steps S1 to S4 are executed repeatedly until the effluent quality reaches the target value, thus achieving deep wastewater treatment.

[0049] Example 1: Parameter optimization for electrocoagulation by migrating electric fields (0.5V vs. 1V) Electrode array structure: The first inert electrode 1 and the second inert electrode 2 are titanium sheet electrodes with an area of ​​3×5=15cm², a thickness of 1mm, and a filling density of about 50m² / m³; the sacrificial metal electrode 3 is an iron mesh electrode with an area of ​​3×5=15cm², a thickness of 1mm, and a filling density of about 18m² / m³.

[0050] Chamber 4 Structure: Chamber 4 has an effective volume of 45 mL and internal dimensions of length × width × height = 3 × 3 × 5 cm. The electrode assembly is fixed by slits etched into the inner wall of chamber 4, and the change in reaction volume caused by the slits is negligible.

[0051] Operation: Group 1 (G1): Ti-1 (first inert electrode 1) — Fe — Ti-2 (second inert electrode 2), migration voltage 1.0V, flocculation voltage 1.0V. First stage: Apply a voltage of 1.0V between electrodes Ti-1 and Ti-2 for 10s; Second stage: Apply a voltage of 1.0V between electrode Ti-1 and the iron mesh for 10s; Third stage: Apply a voltage of -1.0V between electrodes Ti-1 and Ti-2 for 10s; Fourth stage: Apply a voltage of 1.0V between electrode Ti-2 and the iron mesh for 10s.

[0052] Group 2 (G2): Ti-1 (first inert electrode 1) — Fe — Ti-2 (second inert electrode 2), migration voltage 0.7V, flocculation voltage 0.5V. First stage: Apply a voltage of 0.7V between electrodes Ti-1 and Ti-2 for 10s; Second stage: Apply a voltage of 0.5V between electrode Ti-1 and the iron mesh for 10s; Third stage: Apply a voltage of -0.7V between electrodes Ti-1 and Ti-2 for 10s; Fourth stage: Apply a voltage of 0.5V between electrode Ti-2 and the iron mesh for 10s.

[0053] Wastewater settings: Actual tilapia wastewater, particulate matter content 20 mg / L, active phosphorus content approximately 1.0 mg / L.

[0054] Cost accounting: Electricity price 0.8 yuan / kWh, iron electrode price 6000 yuan / ton.

[0055] Experimental results: such as Figure 6 As shown (G1-10C represents group 1 running for 10 cycles; G1-6C represents group 1 running for 6 cycles; G2-10C represents group 2 running for 10 cycles), both electromigration 0.7V + flocculation 0.5V and electromigration 1V + electroflocculation 1V can be used in electroflocculation systems with migratory electric fields. The energy consumption and iron-phosphorus ratio of the electromigration 1V + electroflocculation 1V operating group are slightly higher than those of the electromigration 0.7V + electroflocculation 0.5V operating group. Figure 7 As shown, the core factor affecting cost is the utilization efficiency of iron, which accounts for 80% to 90% of the final cost calculation. The Fe / P ratio of the electromigration 1V + electrocoagulation 1V operating group is higher, which means that more iron is consumed to remove the same amount of active phosphorus.

[0056] Example 2: Parameter optimization for electrocoagulation by migrating electric fields (1V vs. 3V) Box 4 structure: Same as in Example 1.

[0057] Operation: Group 1 (G1): Ti-1 (first inert electrode 1) — Fe — Ti-2 (second inert electrode 2), migration voltage 1.0V, flocculation voltage 1.0V (operating parameters are the same as those of Group 1 in Example 1).

[0058] Group 2 (G2): Ti-1 (first inert electrode) — Fe — Ti-2 (second inert electrode 2), migration voltage 1.0V, flocculation voltage 3.0V. First stage: Apply a voltage of 1.0V between electrodes Ti-1 and Ti-2 for 10s; Second stage: Apply a voltage of 3.0V between electrode Ti-1 and the iron mesh for 10s; Third stage: Apply a voltage of -1.0V between electrodes Ti-1 and Ti-2 for 10s; Fourth stage: Apply a voltage of 3.0V between electrode Ti-2 and the iron mesh for 10s.

[0059] Tailwater setup and cost accounting: Same as Example 1.

[0060] Experimental results: such as Figure 8 As shown (G1-10C indicates group 1 running for 10 cycles; G2-10C indicates group 2 running for 10 cycles), both electromigration 1V + flocculation 1V and electromigration 1V + electroflocculation 3V can be used in electroflocculation systems with migratory electric fields. Figure 9 As shown, the electromigration 1V + electrocoagulation 3V system achieves the same phosphorus removal effect in 120s as the 1V flocculation voltage system in 400s, with similar iron / phosphorus ratios. This indicates that the electromigration 1V + electrocoagulation 3V system has higher phosphorus removal efficiency, but its operating energy consumption is also higher than that of the electromigration 1.0V + electrocoagulation 3.0V system. Since the iron-phosphorus ratios of the two systems are similar, the electromigration 1V + electrocoagulation 3V system parameters should be prioritized when phosphorus removal efficiency is the primary consideration.

[0061] Example 3: Electrocoagulation by Migrating Electric Field Compared with Traditional Reverse Electrocoagulation Electrode array structure: Same as in Example 1.

[0062] Traditional inverted electrode electrocoagulation system structure: symmetrical arrangement of double iron mesh electrodes, area 3×5=15cm², thickness 1mm, electrode spacing 1cm, filling density approximately 50m² / m³.

[0063] Box 4 structure: Same as in Example 1.

[0064] Operation: Group 1 (G1): Ti-1 (first inert electrode 1) — Fe — Ti-2 (second inert electrode 2), migration voltage 1.0V, flocculation voltage 3.0V. First stage: Apply a voltage of 1.0V between electrodes Ti-1 and Ti-2 for 10s; Second stage: Apply a voltage of 3.0V between electrode Ti-1 and the iron mesh for 10s; Third stage: Apply a voltage of -1.0V between electrodes Ti-1 and Ti-2 for 10s; Fourth stage: Apply a voltage of 3.0V between electrode Ti-2 and the iron mesh for 10s.

[0065] Group 2 (G2): Fe-1—Fe-2 (3V constant voltage). First stage: Apply voltage 3.0V to Fe-1 for 10s; Second stage: Rest stage for 10s; Third stage: Apply voltage 3.0V to Fe-1 for 10s; Fourth stage: Rest stage for 10s.

[0066] Wastewater settings: Actual tilapia wastewater, particulate matter content 20mg / L, active phosphorus content approximately 4mg / L.

[0067] Cost accounting: Same as in Example 1.

[0068] Experimental results: such as Figure 10 As shown (G1-10C represents group 1 running for 10 cycles; G2-10C represents group 2 running for 10 cycles), the electroflocculation system with a migration electric field of 1V electromigration + 3V flocculation exhibits higher phosphorus removal efficiency and a lower iron-phosphorus ratio within the same flocculation time compared to the traditional reverse-polarity electroflocculation system. Figure 11 As shown, its energy consumption is also lower than that of traditional reverse-polar electrocoagulation, indicating that electrocoagulation with a migration electric field of 1V+flocculation3V has significant advantages when treating effluent and should be given priority.

[0069] Example 4: Single-sided CDI + air cathode electrocoagulation compared with migratory electric field electrocoagulation Electrode array structure: Same as in Example 1.

[0070] The structure of the single-sided CDI + iron electrode + air cathode electrocoagulation system is as follows: One side of the sacrificial metal electrode 3 is the CDI electrode, and the other side is the air cathode. The two electrodes are symmetrically arranged on both sides of the sacrificial metal electrode 3. The CDI electrode has an area of ​​3×5=15cm² and a thickness of about 0.3cm; the air cathode has an area of ​​3×5=15cm² and a thickness of about 1.3cm, with a packing density of about 50m² / m³; the flocculation electrode is an iron mesh electrode with an area of ​​3×5=15cm², a thickness of 1mm, and a packing density of about 18m² / m³.

[0071] Box 4 structure: Same as in Example 1.

[0072] Operation: Group 1 (G1): Ti-1 (first inert electrode 1) — Fe — Ti-2 (second inert electrode 2), migration voltage 0.7V, flocculation voltage 0.5V. First stage: Apply a voltage of 0.7V between electrodes Ti-1 and Ti-2 for 6s; Second stage: Apply a voltage of 0.5V between electrode Ti-1 and the iron mesh for 6s; Third stage: Apply a voltage of -0.7V between electrodes Ti-1 and Ti-2 for 6s; Fourth stage: Apply a voltage of 0.5V between electrode Ti-2 and the iron mesh for 6s.

[0073] Group 2 (G2): CDI (film capacitor electrode) — Fe — AC (air cathode), migration voltage 0.7V, flocculation voltage 0.5V. First stage: Apply a voltage of 0.7V between CDI and AC for 6s; Second stage: Apply a voltage of 0.5V between CDI and iron mesh for 6s; Third stage: Apply a voltage of -0.7V between CDI and AC for 6s; Fourth stage: Apply a voltage of 0.5V between CDI and iron mesh for 6s.

[0074] Wastewater treatment: The synthetic wastewater is prepared by dissolving NaH2PO4 in deionized water to make the initial PO4 concentration 1.0 mg / L, and then adding seven competing ions (Cl⁻, SO4²⁻, HCO3⁻, CO3²⁻, NO3⁻, Ca²⁺ and Mg²⁺) at a concentration of 1 mg / L.

[0075] Cost accounting: Same as in Example 1.

[0076] Experimental results: such as Figure 12 As shown (G1-2.5C represents group 1 running for 2.5 cycles; G2-2.5C represents group 2 running for 2.5 cycles), the electroflocculation system with an electromigration electric field of 1V + flocculation of 3V has a similar phosphorus removal effect to the single-sided CDI electroflocculation system within the same flocculation time. However, as... Figure 13 As shown, the energy consumption and Fe / P ratio of electrocoagulation by the migrating electric field are lower, and the overall cost is much lower than that of single-sided CDI electrocoagulation.

[0077] This invention treats effluent with an initial total phosphorus concentration of approximately 1–1.5 mg / L. Under low voltage (1.0V) and a 400s operating time, the total phosphorus in the effluent can be reduced to below 0.1 mg / L, achieving a removal rate of >90%, reaching an ultra-deep phosphorus removal level. Traditional two-electrode electrocoagulation and periodic polarity reversal electrocoagulation cannot achieve this depth under the same voltage and time.

[0078] This invention utilizes a four-stage periodic electric field transformation to alternately change the polarity of the two inert electrodes, driving the directional migration and enrichment of phosphate ions from both sides of the sacrificial metal electrode 3. This completely overcomes the mass transfer bottleneck of ion-dependent natural diffusion in low-concentration water. The alternating migration on both sides increases the flux of ions reaching the surface of the sacrificial electrode by several times compared to the traditional single-sided diffusion mode. The collision and combination probability of flocculant (Fe²⁺) and target ions (PO₄³⁻) is significantly improved, the Fe / P consumption ratio is reduced, and iron electrode consumption is saved while achieving the same phosphorus removal effect.

[0079] In stages one and three of this invention, a migration electric field lower than the water electrolysis voltage (<1.23V) is applied between the two inert electrodes, or the voltage is applied for a short time. This allows the electrical energy to be primarily used to establish the double-layer capacitance and drive ion electromigration, without significant side reactions in water electrolysis. In stages two and four, the inert electrodes operate in capacitor discharge mode, releasing the pre-enriched anions in the double layer, again without producing hydrogen evolution. Throughout the four stages of the system, there is almost no hydrogen evolution, and nearly 100% of the electrical energy is used for the "useful work" of ion migration and flocculation. The energy utilization efficiency is far higher than that of existing two-electrode and three-electrode systems, where hydrogen evolution is inevitable during the migration stage.

[0080] This invention utilizes a second-level rapid polarity switching mechanism to continuously refresh the double-layer structure and ion concentration distribution on the electrode surface, effectively suppressing the accumulation of concentration polarization layers and the formation of passivation films on the sacrificial metal electrode surface. Compared to the periodic polarity reversal (reversal cycle 10-15 min) of traditional two-electrode electrocoagulation, the second-level switching of this invention essentially prevents the initial formation of the passivation layer, rather than performing peeling and repair after passivation has already occurred, thus maintaining sustained high reactivity.

[0081] This invention uses only inert electrodes (such as Ti) and sacrificial metal electrodes (such as Fe), eliminating the need for air cathodes, carbon-based adsorption electrodes, or other functionalized electrode materials. Compared to existing MEAEC systems, it eliminates the need for the multi-layered rolled air cathode fabrication process involving activated carbon catalyst layer-stainless steel mesh-gas diffusion layer, and also eliminates the need for electrodes to be exposed to air for self-oxygenation. Compared to carbon-based three-electrode systems, it eliminates the complex electrode fabrication process involving biomass carbonization, pore formation, and molding. The electrode materials are simple and readily available, the system structure is concise, and manufacturing costs and maintenance difficulties are significantly reduced.

[0082] The reverse voltage backflush regeneration method provided by this invention can periodically restore the activity of the electrode surface, extend the service life of the electrode, ensure the long-term stable operation of the system, and further reduce the operation and maintenance costs.

[0083] This invention can be configured with online water quality monitoring and real-time electrochemical signal acquisition modules to achieve adaptive parameter adjustment based on influent water quality and operational status diagnosis based on electrochemical signals, thereby improving the system's automation level and operational reliability.

[0084] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0085] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A three-electrode system for phosphorus removal from wastewater using a dual-migratory electric field electrocoagulation method, characterized in that, include: An electrocoagulation reaction module is provided with multiple sets of parallel electrode arrays. Each set of electrode arrays includes a first inert electrode (1), a sacrificial metal electrode (3), and a second inert electrode (2) arranged in sequence. The first inert electrode (1) and the second inert electrode (2) are located on both sides of the sacrificial metal electrode (3), forming a symmetrical electrode group with the sacrificial metal electrode (3) as the center of symmetry. A power supply module, electrically connected to the electrode array, is used to apply a periodically changing electric field to the electrode array; The periodically transformed electric field is configured to execute the following four stages in a time-sequential cycle: Phase 1: Connect the first inert electrode (1) to the positive terminal of the power supply, connect the second inert electrode (2) to the negative terminal of the power supply, disconnect the sacrificial metal electrode (3), run for a first set time, establish a transverse electric field between the first inert electrode (1) and the second inert electrode (2), drive the negatively charged target ions in the liquid phase to migrate in a directional manner toward the first inert electrode (1), and form a double-layer capacitor on the surface of the first inert electrode (1); Phase 2: Connect the first inert electrode (1) to the negative terminal of the power supply, connect the sacrificial metal electrode (3) to the positive terminal of the power supply, disconnect the second inert electrode (2), run for a second set time, the sacrificial metal electrode (3) undergoes an anodic dissolution reaction to release metal cations, which react with the enriched target ions to generate an insoluble precipitate, while the first inert electrode (1) releases the ions enriched by the double layer capacitor formed in Phase 1 to the area near the sacrificial metal electrode (3) in a capacitor discharge mode; Phase 3: Connect the second inert electrode (2) to the positive terminal of the power supply, connect the first inert electrode (1) to the negative terminal of the power supply, disconnect the sacrificial metal electrode (3), run for a third set time, drive the residual target ions in the liquid phase to migrate in the opposite direction to the other side of the sacrificial metal electrode (3) for enrichment, and form a double-layer capacitor on the surface of the second inert electrode (2). Phase 4: Connect the second inert electrode (2) to the negative terminal of the power supply, connect the sacrificial metal electrode (3) to the positive terminal of the power supply, disconnect the first inert electrode (1), run for a fourth set time, the sacrificial metal electrode (3) dissolves at the anode and reacts with the enriched target ions to generate an insoluble precipitate, and at the same time the second inert electrode (2) releases the ions enriched by the double layer capacitor formed in Phase 3 to the area near the sacrificial metal electrode (3) in a capacitor discharge mode.

2. The dual-migration electric field electrocoagulation three-electrode system for phosphorus removal in effluent according to claim 1, characterized in that, The first inert electrode (1) and the second inert electrode (2) are each independently selected from one of titanium, titanium alloy, titanium-based coated electrode, graphite, conductive ceramic or stainless steel; the titanium-based coated electrode includes Ti / IrO electrode, Ti / RuO electrode, Ti / Pt electrode or Ti / Ru / Ir electrode.

3. The dual-migration electric field electrocoagulation three-electrode system for phosphorus removal in effluent according to claim 1, characterized in that, The sacrificial metal electrode (3) is selected from iron, aluminum, magnesium, zinc or their alloys; the sacrificial metal electrode (3) is plate-shaped, mesh-shaped, foam-shaped or porous.

4. The dual-migration electric field electrocoagulation three-electrode system for phosphorus removal in effluent according to claim 1, characterized in that, The distance between the sacrificial metal electrode (3) and the first inert electrode (1) and the distance between the sacrificial metal electrode (3) and the second inert electrode (2) are each independently 0.5 to 5 cm; the first set time, the second set time, the third set time and the fourth set time are each independently 5 to 60 s.

5. A dual-migration electric field electrocoagulation three-electrode system for phosphorus removal in effluent according to claim 1, characterized in that, The operating voltages of Stage 1 and Stage 3 are each independently 0.3–5V, which are lower than the water electrolysis voltage under actual operating conditions, so that no significant water electrolysis side reactions occur in Stage 1 and Stage 3.

6. The dual-migration electric field electrocoagulation three-electrode system for phosphorus removal in effluent according to claim 1, characterized in that, The operating voltages of Phase Two and Phase Four are each independently 0.5–20V.

7. A dual-migration electric field electrocoagulation three-electrode system for phosphorus removal in effluent according to claim 1, characterized in that, The system repeats the periodic electric field transformation to circulate and treat wastewater until the concentration of the target pollutant ions in the wastewater reaches the discharge standard. The target pollutant ions are at least one of phosphate, fluoride, arsenate, or chromate. The system is used to treat low-concentration phosphorus-containing wastewater, which is municipal sewage effluent or aquaculture effluent.

8. A dual-migration electric field electrocoagulation three-electrode system for phosphorus removal in effluent according to claim 1, characterized in that, The electrode array is configured as 1 to 50 groups, and the groups of electrode arrays are connected in parallel; the electrocoagulation reaction module includes a box (3), and the two side walls of the box (4) are provided with electrode slots (5). The electrode array is modularly installed and disassembled by inserting into the electrode slots (5); the box (4) is also provided with an inlet (6) and an outlet (7). The inlet (6) and the outlet (7) are located at the two ends of the multiple groups of electrode arrays, and the water inlet and outlet are in the bottom and outlet manner; the electrocoagulation reaction modules can be stacked twice to form a larger combined system.

9. A dual-migration electric field electrocoagulation three-electrode system for phosphorus removal in effluent according to claim 1, characterized in that, The power supply module further includes a reverse voltage backflush unit, which is configured to periodically or under a preset trigger condition to switch the system to backflush mode for a set backflush time; the preset trigger condition is that the tank voltage rises to twice the initial value; in the backflush mode, the first inert electrode (1) and the second inert electrode (2) are both connected to the positive terminal of the power supply or are alternately connected to the positive terminal of the power supply, and the sacrificial metal electrode (3) is connected to the negative terminal of the power supply to apply a backflush voltage; the backflush voltage is 0.5 to 10V, and the backflush time is 30 to 600s.

10. A three-electrode method for phosphorus removal from wastewater using a dual-migration electric field electrocoagulation system, characterized in that... Using the system according to any one of claims 1 to 9 includes the following steps: S1: Connect the first inert electrode (1) to the positive electrode, the second inert electrode (2) to the negative electrode, disconnect the sacrificial metal electrode (3), run for a first set time, drive the negatively charged target ions in the liquid phase to migrate in the direction of the first inert electrode (1), and form a double-layer capacitor on the surface of the first inert electrode (1). S2: Connect the first inert electrode (1) to the negative electrode, connect the sacrificial metal electrode (3) to the positive electrode, disconnect the second inert electrode (2), run for a second set time, the sacrificial metal electrode (3) anolyses and releases metal cations, which react with the enriched target ions to generate an insoluble precipitate, while the first inert electrode (1) releases the ions enriched in its double layer capacitor to the area near the sacrificial metal electrode (3) in a capacitor discharge mode. S3: Connect the second inert electrode (2) to the positive electrode, connect the first inert electrode (1) to the negative electrode, disconnect the sacrificial metal electrode (3), run for a third set time, drive the residual target ions in the liquid phase to migrate in the opposite direction to the other side of the sacrificial metal electrode (3) for enrichment, and form a double layer capacitor on the surface of the second inert electrode (2). S4: Connect the second inert electrode (2) to the negative electrode and the sacrificial metal electrode (3) to the positive electrode. Disconnect the first inert electrode (1) and run for a fourth set time. The sacrificial metal electrode (3) dissolves at the anode and reacts with the enriched target ions to generate an insoluble precipitate. At the same time, the second inert electrode (2) releases the ions enriched by the double layer capacitor formed in S3 to the area near the sacrificial metal electrode (3) in a capacitor discharge mode. Steps S1 to S4 are executed repeatedly until the effluent quality reaches the target value, thus achieving deep wastewater treatment.

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