Method for synchronously removing and recycling complex-state heavy metal wastewater based on multi-stage potential regulation and control

Abstract

The invention relates to the technical field of deep purification and resource recycling of heavy metal wastewater, and particularly discloses a synchronous removal and recycling method for complex-state heavy metal wastewater based on multi-stage potential regulation and control. According to the method, a dynamic electrochemical-biological confinement reaction field is formed on an anode-extracellular polymeric substance (EPS) interface, so that coordination and unification of electrochemical decomplexing, directional migration and in-situ deposition of complex-state metal are realized. The system adopts a multi-stage constant potential operation mode to drive complex dissociation and metal-phosphate co-deposition. The obtained sediment is of a flower-shaped hierarchical structure, the purity can reach 85% or above, and the removal rate of target metal exceeds 70%. The method is operated at normal temperature and normal pressure, does not need additional chemical oxidants, has the characteristics of greenness, controllability and recycling, and is suitable for advanced treatment and metal recovery of wastewater containing complex-state heavy metals in the industries of electroplating, circuit boards, metallurgy, chemical engineering and the like.

Description

Technical Field

[0001] This invention relates to the field of deep purification and resource recovery technology for heavy metal wastewater, specifically to a method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation. Background Technology

[0002] With the continuous development of industries such as metal surface treatment, electroplating, circuit board cleaning, precision manufacturing, and hydrometallurgy, various chelating agents are widely used in industrial production to achieve the stabilization, cleaning, and complexation masking of metal ions. These include ethylenediaminetetraacetic acid (EDTA), aminotriacetic acid (NTA), citric acid, tartaric acid, ammonia / amine compounds, aminocarboxylic acids, phosphonates, and their mixtures. Under typical water quality conditions, these chelating agents can form complexed heavy metals (M) with Cu, Ni, Co, Zn, Fe, Mn, Pb, Cd, and under certain conditions Cr (mainly Cr(III) complexes, but may also contain Cr(VI) requiring pre-reduction). Typical examples include EDTA-M, NTA-M, and citric acid-M. These complexes also possess high thermodynamic stability (stability constants generally exceeding 10). 6 Due to their coordination kinetic inertness, they exhibit significant water solubility and anti-precipitation properties, resulting in extremely high persistence and mobility in wastewater environments. These properties significantly reduce the removal efficiency of traditional physicochemical treatment processes such as precipitation, adsorption, and ion exchange. Further complicating matters, real-world industrial wastewater often contains multiple metals, multiple ligands, and interactions with organic matrices, making the deep removal of complexed heavy metals even more challenging.

[0003] Currently, the mainstream treatment strategies for complexed heavy metal wastewater mainly include advanced oxidation, chemical displacement / precipitation, membrane separation, and electrochemical methods. Advanced oxidation processes, represented by ozone, persulfate / persulfate, or UV / PMS systems, can break metal-ligand bonds through free radical or non-free radical pathways to disentangle the complex. However, these processes are usually accompanied by high energy consumption, large amounts of reagents, and the generation of complex byproducts. Under high concentrations or complex organic matrix conditions, they are prone to quenching of active species and reaction attenuation. Chemical displacement / precipitation methods often rely on the addition of iron salts, sulfides, or alkalis to release metal ions through competitive complexation or precipitation reactions. The resulting precipitates (such as hydroxides and sulfides) have loose structures, poor stability, and are prone to redissolution and secondary pollution, while lacking resource utilization value. Membrane separation technologies (such as nanofiltration and reverse osmosis) can effectively retain complexes and free metal ions, but they face problems such as high equipment investment, severe membrane fouling, and difficulty in disposing of concentrates. Electrochemical methods remove metal ions through electrocoagulation, electrodeposition, and other means, but they depend on electrode materials and operating potentials, and often exhibit insufficient selectivity and poor stability in multi-metal-multi-ligand systems.

[0004] To improve treatment efficiency, some studies have attempted to construct membrane-electrochemical combined processes (such as anodic oxidation-membrane enrichment) to enhance the decomposition of complexes and metal separation capabilities. However, such systems are complex in structure, consume a lot of energy, have high operating and maintenance costs, and are difficult to scale up. Furthermore, the microbial-induced endogenous phosphate mineralization technology proposed in recent years utilizes the release of phosphate ions from microbial metabolism to form metal phosphate deposits. While it has certain green advantages, the process relies on passive metabolic stress responses, lacking controllability and sustainability; the morphology and purity of the deposited products are also difficult to adjust, and the reaction cycle is long. Meanwhile, bioelectrochemical systems (BES), as an electrochemical-biological interface technology, have made progress in the degradation of organic matter and the removal of free metals. By driving the extracellular electron transfer (EET) process with an applied potential, it can regulate the direction of microbial metabolism and promote the reduction of metal ions. However, existing BES research mainly focuses on the oxidation of organic pollutants or the electrodeposition of free metals, and systematic research and feasible pathways are still lacking in the directional breakdown of complexed metals and the synergistic control of interfacial deposition.

[0005] In summary, the existing technologies generally have the following common problems: (1) The complex breaking process depends on external reagents or high-energy activation, resulting in poor system controllability; (2) The sediment phase is decoupled from the complex breaking process, making it difficult to achieve synchronous reaction; (3) The sediment products are mostly low-purity mixed sludge, lacking functional and resource value.

[0006] Therefore, there is an urgent need to develop an integrated technological approach that is green, low-energy, sustainably regulated, and has resource potential, capable of achieving the synergistic unification of directional complex breaking and confined deposition of complexed heavy metals under mild conditions. Summary of the Invention

[0007] The purpose of this invention is to provide a method for the simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation. By forming a dynamic electrochemical-biological confined reaction field at the anode-extracellular polymeric substance (EPS) interface, the electrochemical breakdown, directional migration, and in-situ deposition of complexed metals are synergistically unified, thereby achieving the integration of wastewater purification and metal phosphate resource recovery.

[0008] Existing bioelectrochemical systems (BES) mostly operate under constant potential, with the anode-biofilm interface only capable of electron transfer. This lack of precise control over the local electrochemical environment makes it difficult to form a structured interface with functional stratification and reaction confinement characteristics. Therefore, complexed metals often cannot effectively break down complexes and deposit directionally in such systems, limiting their resource utilization capabilities. This invention utilizes a multi-stage potential control strategy, leveraging the electron transfer activity of electroactive microorganisms and the chemical decomposition activity of complex-breaking bacterial communities, to actively induce the synergistic coupling of electron flow, ion flow, and chemical reactions within the anode-EPS interface. This forms a stable and tunable reaction field, achieving the integration and controllability of the complex-breaking, migration, and deposition process.

[0009] Specifically, this invention provides a method for the simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation, comprising the following steps:

[0010] S1: Construct a bioelectrochemical reactor, which includes an anode, a cathode, and a reference electrode, and operates under anaerobic conditions;

[0011] S2: Inject a basic culture medium containing carbon source and phosphate into the bioelectrochemical reactor, and inoculate it with a mixed bacterial solution containing electroactive bacteria and complex-breaking bacteria;

[0012] S3: Apply a multi-stage potential program to the anode of the bioelectrochemical reactor to form a dynamic electrochemical-biological confined reaction field at the anode-extracellular polymer interface; the multi-stage potential program includes at least two stages with different potentials, the potential range being between -0.4V and +0.4V relative to the reference electrode;

[0013] In steps S1-S3 above, a three-electrode bioelectrochemical reactor containing an anode, cathode, and reference electrode is constructed, and a constant potential is applied to drive the extracellular electron transfer (EET) process. A mixed bacterial solution containing electroactive bacteria and complex-breaking bacteria is inoculated into the bioelectrochemical system, using organic matter as a carbon source for energy. The system operates using a multi-stage constant potential control strategy, causing the anode-EPS interface to gradually evolve from an "attachment layer" to a "conductive layer" and a "reaction layer." Electroactive bacteria are enriched in the near-surface layer of the electrode, while complex-breaking bacteria are mainly distributed in the outer EPS region, forming a chemically reactive zone.

[0014] S4: Wastewater containing complexed heavy metals is introduced into the bioelectrochemical reactor and operated at a constant potential, so that the complexed heavy metals undergo electrochemical breakdown, directional migration and in-situ deposition within the confined reaction field to generate sediments;

[0015] In the dynamically confined reaction field constructed in S3, complexed heavy metal industrial wastewater is introduced into the reactor. During this stage, electroactive microorganisms maintain a stable anodic interface potential and electron flow supply. The degradation enzymes secreted by the complex-breaking bacteria, together with the EPS matrix containing carboxyl, amino, and hydroxyl groups, act on the complex, gradually weakening the metal-ligand bond and causing electron dissociation. The potential gradient and pH buffer structure synergistically promote the complex-breaking process of the complexed metal, releasing free metal ions (Mn2+, Mg ... + Under the influence of electric field and concentration gradient, the metal phosphates migrate directionally along the EPS microchannels and nucleate anisotropically with phosphates at the anode interface, forming flower-like or hierarchical petal-like metal phosphate deposits.

[0016] S5: After the reaction is completed, the deposits of the anode or EPS layer are scraped off, and after washing, drying or sieving, high-purity metal phosphates are obtained, realizing the simultaneous removal and resource recovery of complexed heavy metals in wastewater.

[0017] Furthermore, the aforementioned multi-stage potential procedure comprises three stages, as follows:

[0018] Low potential phase: The potential relative to the reference electrode is between -0.4V and -0.15V, lasting for 3-4 days;

[0019] Mid-potential phase: The potential relative to the reference electrode is between -0.1V and +0.1V, lasting for 2-3 days;

[0020] High potential phase: The potential relative to the reference electrode is between +0.15V and +0.4V, lasting for 2-3 days.

[0021] Preferably, in the above multi-stage potential program, each stage operates at a constant potential during operation;

[0022] Preferably, in step S4, the potential during constant potential operation is between -0.1V and +0.1V relative to the reference electrode, and the operation time is 2-3 days.

[0023] Preferably, the aforementioned electrochemical-biological confined reaction field has at least one of the following characteristics: an interfacial pH buffer layer with a ΔpH of 0.5 to 1.0, and a potential gradient of 40 to 60 mV formed on the anode surface. This dynamic electrochemical-biological confined reaction field can achieve the synergistic integration of electron flow, ion migration, and chemical reaction space.

[0024] Furthermore, the above-mentioned bioelectrochemical reactor is a three-electrode system, wherein the anode is selected from any one of graphite rod, carbon felt, carbon cloth and graphite brush, the cathode is selected from stainless steel mesh or graphite material, and the reference electrode is Ag / AgCl electrode or saturated calomel electrode.

[0025] Furthermore, in the above-mentioned mixed bacterial solution, the electroactive bacteria are selected from species of the genera *Geobacter* or *Shewanella*; the cytotoxic bacteria are selected from species of the genera *Chelativorans*, *Aminobacter*, or *Pseudomonas*.

[0026] Electroactive microorganisms achieve electron efflux through outer membrane cytochromes and conductive nanowires, establishing stable electron flux and potential gradients; complex-breaking bacteria secrete polysaccharide-protein complexes and chelate-degrading enzymes, providing reaction sites for complex adsorption, electron transfer, and metal-ligand bond breaking.

[0027] Furthermore, the above-mentioned basic culture medium contains sodium acetate and KH2PO4, wherein the concentration of sodium acetate is 0.5-1.5 g / L and the concentration of KH2PO4 is 0.1-0.3 g / L.

[0028] Furthermore, the aforementioned bioelectrochemical reactor operates under ambient temperature and pressure conditions, with the pH maintained between 6.5 and 7.5.

[0029] Furthermore, the above-mentioned deposits are metal phosphate or hydroxyphosphate nanoflowers, which have a petal-like hierarchical layered structure and a particle size of 0.5-3 μm.

[0030] Furthermore, the aforementioned complexed heavy metals include EDTA–M, NTA–M, or citric acid–M complexes, wherein M is Cu, Ni, Co, Zn, Fe, Mn, Pb, Cd, and Cr(III) under reducing conditions.

[0031] Preferably, the phosphorus source is endogenous phosphorus from wastewater, including orthophosphate, polyphosphate, bioavailable organic phosphorus compounds, and inorganic phosphorus released by microbial metabolism.

[0032] Preferably, the phase of the metal phosphate deposition product includes Cu3(PO4)2, Ni3(PO4)2, Zn3(PO4)2, Fe3(PO4)2·8H2O, Pb3(PO4)3, Cd3(PO4)2 or CrPO4·nH2O.

[0033] Preferably, the purity of the obtained metal phosphate deposit is greater than 85%, the target heavy metal removal rate is not less than 70%, and the total phosphorus removal rate is not less than 50%.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] (1) This invention constructs a dynamic reaction field through multi-stage potential induction to achieve triple synergistic regulation of electrons, ions and pH.

[0036] In traditional constant potential bioelectrochemical systems, the anode is at a single steady-state potential for a long time, and the interface only serves as an electron sink. The electron transfer process is limited by diffusion and occasional adsorption. The extracellular polymer (EPS) structure gradually becomes homogenized, the functional groups are randomly distributed, and the bacterial community lacks functional stratification, resulting in limited interfacial reactions and low mass transfer efficiency.

[0037] This invention employs a multi-stage constant potential sequence (e.g., -0.2→0.0→+0.2V vs Ag / AgCl) to induce self-organized evolution at the anode-EPS interface through time-series potential perturbation. The low-potential stage promotes the attachment of electroactive bacteria and the formation of a conductive network; the mid-potential stage enhances extracellular electron transport and promotes the expression of electron transport proteins such as heme cytochrome in the outer membrane; and the high-potential stage increases the electron affinity of the anode and induces redox rearrangement of functional groups such as carboxyl and hydroxyl groups in the EPS. The electrochemical effects at different stages collectively drive electron flux reconstruction, resulting in a gradient electron distribution at the interface. Simultaneously, alternating potentials induce localized oxidation at the anode and proton migration at the cathode, forming a stable pH buffer layer (ΔpH≈0.8) within the EPS, maintaining functional group dissociation equilibrium and promoting metal-phosphate binding. The dynamic changes in potential also exert selective pressure on the bacterial community, causing electroactive bacteria to aggregate to form a conductive inner layer, while complex-disrupting bacteria form a reaction zone on the outer layer. Ultimately, the anode-EPS interface self-organizes to form a dynamically confined reaction field with a stable potential gradient (40–60 mV) and pH distribution, enabling simultaneous and controllable electron flow, ion migration, and chemical reactions. Compared to the constant potential system, this interface transforms from a passive conductive layer into an active reaction field, providing a tunable microenvironment for subsequent complex disruption and deposition reactions.

[0038] (2) This invention achieves green dissociation and energy coupling conversion of complexes through the synergistic effect of electroactive bacteria and complex-breaking bacteria.

[0039] Complexed heavy metals (EDTA-M, NTA-M, etc.) possess extremely high stability constants and coordination inertness, requiring strong oxidants or high-temperature, high-alkali conditions for complex breakdown using traditional chemical methods. This invention utilizes the synergistic mechanism of electroactive bacteria and complex-breaking bacteria in a confined reaction field to achieve drug-free complex breakdown. Electroactive bacteria guide intracellular electrons to the anode via their outer membrane cytochrome network, maintaining a stable current and potential energy supply, providing the reduction potential for the complex breakdown reaction. The complex-breaking bacteria secrete chelate-degrading enzymes and a biopolymer EPS matrix rich in carboxyl and amine groups, directly acting on the metal-ligand bonds. The synergistic effect of electron flux and chemical degradation within the confined space allows for simultaneous regulation of the metal center's valence state and bond breaking. This "electro-biological dual-drive mechanism" significantly reduces the complex breakdown barrier, enabling the reaction to proceed under neutral and ambient temperature conditions without the need for external oxidants, avoiding secondary pollution, and achieving the coupling and conversion of energy and matter.

[0040] (3) The present invention realizes the directional migration and anisotropic nucleation of metal ions in a confined reaction field, thereby obtaining a deposition product with controllable morphology and purity.

[0041] In traditional precipitation systems, the binding of metal ions and phosphate ions relies on random diffusion, resulting in uneven and impurity-laden particles. This invention achieves precise control over ion migration direction and nucleation location through the coupled regulation of electric field, pH, and EPS structure. The electric field drives the directional migration of metal ions along the EPS microchannels, forming metal-rich regions; the negatively charged carboxyl and phosphate groups in the EPS act as soft templates, inducing anisotropic nucleation; electroactive bacteria maintain electron flow balance, inhibiting local supersaturation and heterogeneous deposition; and the pH buffer layer controls the local release of phosphate ions, allowing the crystallization process to proceed gradually. Finally, a hierarchical petal-like metal phosphate or hydroxyphosphate structure is obtained at the anode-EPS interface, with a particle size of 0.5–3 μm and a purity ≥85%. By adjusting the constant potential window (-0.2 to +0.2 V), predictable control of crystal hierarchy, density, and purity can be achieved.

[0042] (4) The present invention achieves the integration of complex breaking, migration and deposition processes and multi-metal adaptability, and has the functions of pollution purification and resource utilization.

[0043] The entire system continuously completes the three processes of complex breaking, migration, and deposition in a single reactor, avoiding the complex multi-stage process of "chemical complex breaking – precipitation – separation" in traditional processes. It operates under mild conditions, consumes little energy, and requires no chemical reagents. Because the confined reaction field has adjustable potential and pH distribution, metal-ligand pairs with different valence states and different complexing agent systems can automatically match the corresponding reaction energy levels. Therefore, this system is universally applicable to multi-metal complex wastewater containing Cu, Ni, Co, Zn, Fe, Pb, Cd, and Cr(III). It achieves simultaneous wastewater purification and metal phosphate resource recovery, providing an efficient pathway for the treatment of complexing agent-containing wastewater in industries such as electroplating, circuit boards, metallurgy, and chemicals. Attached Figure Description

[0044] Figure 1 The maximum current density (A), pH buffer layer (B), and potential gradient change (C) under multi-stage potential regulation and constant potential regulation.

[0045] Figure 2 SEM images generated under multi-stage potential control and constant potential control;

[0046] Figure 3 XRD patterns formed under multi-stage potential regulation and constant potential regulation;

[0047] Figure 4 This is a diagram of the microbial community formed under multi-stage potential regulation and constant potential regulation. Detailed Implementation

[0048] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0049] Example 1

[0050] This embodiment provides a method for the simultaneous removal and resource recovery of complexed heavy metal wastewater, including:

[0051] (1) A three-electrode bioelectrochemical reactor with an effective volume of 500 mL was constructed. The anode was made of carbon felt (3 cm × 5 cm), the cathode was made of stainless steel mesh, and the reference electrode was Ag / AgCl (saturated KCl). The system was operated under anaerobic conditions, with the temperature controlled at 30 ± 2 °C and the pH maintained at 7.0 ± 0.2.

[0052] (2) Sodium acetate (1.0 g·L⁻¹) is injected into the reactor. -1 ) and KH2PO4 (0.2 g·L -1 The basic culture medium was inoculated with 10 vol% activated sludge extract to provide electroactive microorganisms and complex-breaking bacteria.

[0053] The activated sludge leachate is derived from the sludge in the UASB reactor used to treat wastewater containing complexed heavy metals. The electroactive microorganisms contained in the leachate are Geobacter, and the complex-breaking microorganisms are Chelativorans and Aminobacter.

[0054] (3) A multi-stage potential program (-0.2V→0.0V→+0.2V vs Ag / AgCl, each stage lasting 3 days) was applied to the anode to induce the attachment of electroactive bacteria, the formation of a conductive network, and the rearrangement of EPS functional groups. After the operation was completed, a stable electrochemical-biological confined reaction field was formed.

[0055] (4) Subsequently, a solution containing 20 mg·L⁻¹ was introduced into the system. -1 Simulated wastewater containing EDTA–Cu (calculated as Cu) was kept at a constant potential of 0.0V and operated with Ag / AgCl for 2 days, resulting in the formation of a light blue deposit layer on the anode surface.

[0056] (5) After the reaction is completed, scrape off the deposits of the anode or EPS layer, and obtain high-purity metal phosphates after washing, drying or sieving.

[0057] Example 2

[0058] The difference between this embodiment and Embodiment 1 is that the bioelectrochemical reactor constructed in this embodiment has three electrodes: the anode is a graphite rod (3cm×5cm), the cathode is graphite, and the reference electrode is a calomel electrode.

[0059] Example 3

[0060] The difference between this embodiment and Embodiment 1 is that the bioelectrochemical reactor constructed in this embodiment has two electrodes: specifically, the anode is made of carbon cloth (3cm×5cm) and the cathode is made of stainless steel mesh.

[0061] Example 4

[0062] The difference between this embodiment and Embodiment 1 lies in the multi-stage potential procedure. This embodiment has two stages, specifically:

[0063] Low potential phase: -0.4V vs Ag / AgCl, lasting 4 days.

[0064] High potential phase: +0.4V vs Ag / AgCl, lasting for 3 days.

[0065] Example 5

[0066] The difference between this embodiment and Embodiment 1 lies in the multi-stage potential procedure. This embodiment has three stages, specifically:

[0067] Low potential phase: -0.3V vs Ag / AgCl, lasting 3 days.

[0068] Mid-potential phase: 0V vs Ag / AgCl, lasting 2 days.

[0069] High potential phase: +0.3V vs Ag / AgCl, lasting 2 days.

[0070] Example 6

[0071] The difference between this embodiment and Embodiment 1 lies in the multi-stage potential procedure. This embodiment has three stages, specifically:

[0072] Low potential phase: -0.15V vs Ag / AgCl, lasting 4 days.

[0073] Mid-potential phase: 0V vs Ag / AgCl, lasting 2 days.

[0074] High potential phase: +0.15V vs Ag / AgCl, lasting 2 days.

[0075] Example 7

[0076] The difference between this embodiment and Embodiment 1 lies in the wastewater introduced into the system and the constant potential in step (4). Specifically:

[0077] The wastewater is a simulated wastewater containing NTA–Ni at a concentration of 30 mg·L⁻¹. -1 (in Ni).

[0078] Maintain a constant potential of -0.1V vs Ag / AgCl for 3 days.

[0079] Example 8

[0080] The difference between this embodiment and Embodiment 1 lies in the wastewater introduced into the system and the constant potential in step (4). Specifically:

[0081] The wastewater is a simulated wastewater containing NTA–Cd at a concentration of 25 mg·L⁻¹. -1 (in Cd).

[0082] Maintain a constant potential of +0.1 V vs Ag / AgCl for 2 days.

[0083] Example 9

[0084] The difference between this embodiment and Embodiment 1 lies in the multi-stage potential program and the wastewater introduced. Specifically:

[0085] The simulated wastewater being treated contained three complex metals: Cu, Ni, and Zn (20 mg / L each). -1 EDTA is complexed at a 1:1 molar ratio.

[0086] The system was maintained under a multi-stage potential program (-0.2V→0.0V→+0.2V vs Ag / AgCl, each stage lasting 3 days).

[0087] The system current density remained stable at 0.9–1.1 mA·cm during operation. -2 The anode-EPS interface maintains a stable potential gradient and pH buffer structure, indicating that the confined reaction field can still maintain structural integrity and stable electron flux under multi-metal coexistence conditions.

[0088] The obtained sediments were observed by SEM to have a uniform flower-like hierarchical structure; X-ray diffraction (XRD) analysis showed that the product was a polymetallic phosphate mixed crystal phase with high crystallinity and low impurity content.

[0089] Comparative Example 1

[0090] The only difference between this comparative example and Example 1 is that the constant potential of 0.0 V vs Ag / AgCl applied to the anode in step (3) is the same as that of Example 1, and the operation time is the same. The other steps and process parameters are completely consistent with those of Example 1.

[0091] Performance testing

[0092] 1. Verify whether it is an electrochemical-biological confined reaction field.

[0093] For Example 1 and Comparative Example 1, a multi-stage potential program or a constant potential program was applied to the anode. After the operation was completed, the changes in anode current density, pH buffer layer, and potential gradient in the reaction system were measured.

[0094] The results are as follows Figure 1 As shown:

[0095] Figure A shows the maximum current density under multi-stage potential control and constant potential control. The maximum anode current density after multi-stage potential control is 5.5 A·m. -2 The maximum current density under constant potential control is only 3.5 A·m. -2 .

[0096] Figure B shows the pH buffer layer under multi-stage potential regulation and constant potential regulation. The pH microprobe detection shows that a buffer layer with ΔpH≈0.8 exists at the interface after multi-stage potential regulation, while no obvious pH gradient is formed under constant potential regulation.

[0097] Figure C shows the potential gradient changes under multi-stage potential control and constant potential control. The open-circuit potential distribution measurement shows that a potential gradient of about 50 mV is formed on the anode surface after multi-stage potential control, while no obvious potential distribution structure is formed under constant potential control.

[0098] This demonstrates that, in Example 1 of this application, a stable electrochemical-biological confined reaction field has been formed at the anode-EPS interface under multi-stage potential regulation; while in Comparative Example 1, which uses constant potential regulation, it is difficult to form an effective reaction field.

[0099] II. Investigate the effectiveness of heavy metal wastewater treatment.

[0100] (1) The waste liquids after the reaction of Example 1, Example 8 and Comparative Example 1 were analyzed by HPLC to calculate the removal rate of heavy metals and the degradation rate of EDTA.

[0101] The results are shown in Table 1:

[0102] Table 1

[0103] project Heavy metal removal rate (%) EDTA degradation rate (%) Example 1 80% 85% Example 8 Cu(82%)Ni(76%)Zn(70%) 65% Comparative Example 1 28% 30%

[0104] (2) The sediments were observed using SEM and X-ray diffraction, and the results are as follows: Figure 2 and Figure 3 As shown:

[0105] The light blue deposition layer formed on the anode surface in Example 1, as observed by SEM, exhibits a flower-like hierarchical structure. Figure 2 (A, B); XRD analysis showed that the main phase was Cu3(PO4)2, see Figure 3 (A).

[0106] In Comparative Example 1, SEM showed sparse, copper phosphate nanoflowers of varying sizes forming on the biofilm surface. Figure 2 (C); XRD analysis showed the presence of Cu elemental peaks, see [reference needed]. Figure 3 (B).

[0107] (3) Investigate the abundance of electroactive bacteria and cleavage-breaking bacteria.

[0108] Gene sequencing was used to investigate the abundance of electroactive bacteria and cleavage bacteria in the reaction systems of Example 1 and Comparative Example 1.

[0109] The results are as follows Figure 4 As shown:

[0110] In Example 1, the 16S rRNA sequencing results showed that the relative abundance of both electroactive bacteria and cleavage bacteria was significantly increased; while in Comparative Example 1, the 16S rRNA sequencing results showed that the relative abundance of both electroactive bacteria and cleavage bacteria was low.

[0111] In summary, the experimental data above demonstrate that a stable electrochemical-biological confined reaction field has been formed at the anode-EPS interface under multi-stage potential regulation. Furthermore, multi-stage potential regulation significantly enhances electron transport rate, EPS activity, and ion migration capacity, which are decisive conditions for the formation of the confined reaction field and the efficient removal of complexed heavy metals.

[0112] 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 method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation, characterized in that, It includes the following steps: S1: Construct a bioelectrochemical reactor, which includes an anode, a cathode, and a reference electrode, and operates under anaerobic conditions; S2: Inject a basic culture medium containing carbon source and phosphate into the bioelectrochemical reactor, and inoculate it with a mixed bacterial solution containing electroactive bacteria and complex-breaking bacteria; S3: Apply a multi-stage potential program to the anode of the bioelectrochemical reactor to form a dynamic electrochemical-biological confined reaction field at the anode-extracellular polymer interface; the multi-stage potential program includes at least two stages with different potentials, the potential range being between -0.4V and +0.4V relative to the reference electrode; S4: Wastewater containing complexed heavy metals is introduced into the bioelectrochemical reactor and operated at a constant potential, so that the complexed heavy metals undergo electrochemical breakdown, directional migration and in-situ deposition within the confined reaction field to generate sediments; S5: After the reaction is completed, the deposits of the anode or EPS layer are scraped off, and after washing, drying or sieving, high-purity metal phosphates are obtained, realizing the simultaneous removal and resource recovery of complexed heavy metals in wastewater.

2. The method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation according to claim 1, characterized in that, The multi-stage potential program includes three stages, in the following order: Low potential phase: The potential relative to the reference electrode is between -0.4V and -0.15V, lasting for 1-4 days; Mid-potential phase: The potential relative to the reference electrode is between -0.1V and +0.1V, lasting for 1-3 days; High potential phase: The potential relative to the reference electrode is between +0.15V and +0.4V, lasting for 1-3 days.

3. The method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation according to claim 2, characterized in that, In the multi-stage potential program, each stage operates at a constant potential during its execution. In step S4, the potential of the constant potential operation is between -0.1V and +0.1V relative to the reference electrode, and the operation time is 2-3 days.

4. The method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation according to claim 2, characterized in that, The electrochemical-biological confined reaction field has at least one of the following characteristics: the interface pH buffer layer ΔpH is 0.5~1.0, and the anode surface has a potential gradient of 40~60mV.

5. The method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation according to any one of claims 1-4, characterized in that, The bioelectrochemical reactor is a three-electrode system. The anode is selected from any one of graphite rod, carbon felt, carbon cloth and graphite brush. The cathode is selected from stainless steel mesh or graphite material. The reference electrode is an Ag / AgCl electrode or a saturated calomel electrode.

6. The method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation according to any one of claims 1-4, characterized in that, In the mixed bacterial solution, the electroactive bacteria are selected from species of the genera *Geobacter* or *Shewanella*; the cytotoxic bacteria are selected from species of the genera *Chelativorans*, *Aminobacter*, or *Pseudomonas*.

7. The method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation according to claim 1, characterized in that, The basic culture medium contains sodium acetate and KH2PO4, wherein the concentration of sodium acetate is 0.5-1.5 g / L and the concentration of KH2PO4 is 0.1-0.3 g / L.

8. The method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation according to claim 1, characterized in that, The bioelectrochemical reactor operates under normal temperature and pressure conditions, with the pH maintained between 6.5 and 7.

5.

9. The method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation according to claim 1, characterized in that, The deposits are metal phosphate or hydroxyphosphate nanoflowers, exhibiting a petal-like hierarchical layered structure with a particle size of 0.5-3 μm.

10. The method for simultaneous removal and resource recovery of complexed heavy metal wastewater based on multi-stage potential regulation according to claim 1, characterized in that, The complexed heavy metals include EDTA–M, NTA–M or citric acid–M complexes, wherein M is Cu, Ni, Co, Zn, Fe, Mn, Pb, Cd and Cr(III) under reducing conditions.

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