An electrochemical and biochemical remediation method for riverbed sediments containing heavy metals

Abstract

This invention discloses an electrochemical and biochemical remediation method for river sediment containing heavy metals, comprising the following steps: (1) pumping the river sediment containing heavy metals to a first module, adding aerobic bacteria and acidophilic bacteria to the first module, and performing aerobic aeration in the first module; (2) pumping the sediment treated in step (1) to a second module, adding organic acid to the second module; (3) pumping the sediment treated in step (2) to a third module, wherein the relative groove areas of adjacent filter plates of the vertical filter press in the third module form a closed filter chamber; a first composite diaphragm filter cloth and a second composite diaphragm filter cloth are respectively provided on the upper and lower sides of the closed filter chamber; the first composite diaphragm filter cloth and the second composite diaphragm filter cloth remove heavy metals from the sediment in each closed filter chamber. This invention provides an electrochemical and biochemical remediation method for river sediment containing heavy metals, which efficiently removes heavy metals from the sediment, so that the sediment can be utilized as a resource.

Description

Technical Field

[0001] This invention relates to the field of heavy metal treatment technology, and in particular to an electrochemical and biochemical remediation method for riverbed sediment containing heavy metals. Background Technology

[0002] Currently, river sediment containing heavy metals is mainly dewatered by gravity before being transported to appropriate treatment terminals for processing, including stabilization / solidification, chemical leaching, oxidation-reduction, and resource utilization.

[0003] Existing technologies for treating heavy metals in sediment mainly have the following problems: (1) Difficulty in efficient removal and stabilization of heavy metals: Heavy metals in sediment have complex forms and are not easy to be extracted efficiently. Existing technologies such as stabilization / solidification, chemical rinsing, oxidation-reduction, and microbial leaching have unstable treatment effects and are difficult to remove all types of heavy metals efficiently at the same time.

[0004] (2) Low dehydration and volume reduction efficiency and risk of secondary pollution: The dredged sediment usually has a very high water content (up to 80% or more). Traditional natural drying is slow and requires a large area. Mechanical dehydration (such as plate and frame filter press) requires the addition of flocculants. The effluent from the filter press may contain a high content of pollutants, which can easily cause secondary pollution.

[0005] (3) The long-term stability of solidification and stabilization technology is questionable: Cement and other solidification technologies can effectively reduce the risk of short-term leaching of heavy metals, but the solidified body is in a natural environment (such as wet and dry alternation, freeze and thaw, carbon dioxide erosion, acid precipitation) for a long time, which may pose a risk of long-term slow release of heavy metals. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide an electrochemical and biochemical remediation method for river sediment containing heavy metals.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: An electrochemical-biochemical synergistic remediation method for riverbed sediments containing heavy metals includes the following steps: (1) Pump the riverbed sediment containing heavy metals to the first module, add aerobic bacteria and acidophilic bacteria to the first module, and carry out aerobic aeration and fully stir the sediment in the first module; (2) Pump the sediment treated in step (1) to the second module, and add organic acid with heavy metal complexing function to the second module; (3) The bottom sludge treated in step (2) is pumped to the third module. After the adjacent filter plates of the vertical filter press in the third module are closed, the relative groove areas of the adjacent filter plates form a sealed filter chamber. The upper and lower sides of the sealed filter chamber are respectively provided with a first composite diaphragm filter cloth and a second composite diaphragm filter cloth. The first composite diaphragm filter cloth includes, from top to bottom, a first diaphragm filter cloth layer, a biochar-supported nano-zero ferric iron layer, an anode conductive layer, a biochar-supported nano-zero ferric iron layer, and a first diaphragm filter cloth layer. The second composite diaphragm filter cloth includes, from top to bottom, a second diaphragm filter cloth layer, a cathode layer, a cathode liquid collection tank layer, and a second diaphragm filter cloth layer. The first composite diaphragm filter cloth and the second composite diaphragm filter cloth remove heavy metals from the bottom sludge in each sealed filter chamber. (4) Pump the mud cake that has been processed and dehydrated in step (3) to the mud improvement module.

[0008] In one embodiment, in step (2), the organic acid is citric acid, the pH is maintained at 2.0-4.0, and the bottom mud is stirred for 30-45 minutes.

[0009] In one embodiment, in step (3), multiple filter plates of the vertical filter press are horizontally stacked on the frame, and the multiple filter plates are driven to close together by the pressing device; The bottom sludge to be filtered is introduced into each sealed filter chamber through the feed pipe. The filtrate of the bottom sludge passes through the first composite diaphragm filter cloth and the second composite diaphragm filter cloth and is discharged through the liquid passage holes around the filter plate. The sludge cake remains in the sealed filter chamber. The first composite diaphragm filter cloth removes heavy metals from the sludge cake and filtrate after filtration in each sealed filter chamber. The second diaphragm filter cloth removes heavy metals from the sludge cake and filtrate after filtration in each sealed filter chamber.

[0010] In one embodiment, in step (3), the anode layer is a RuO2 / TiO2 composite nano-conductive layer; the voltage gradient of the third module is 1.5V / cm, the pH value of the anode area is 2.0-4.0, the biochar-supported nano-zero-valent iron layer accounts for 0.5-2wt% of the total mass of the first composite membrane filter cloth, and the processing time of the third module is 60-72h.

[0011] In one embodiment, in step (3), the cathode layer is a graphite conductive mesh layer.

[0012] In one embodiment, in step (4), in the mud improvement module, the mud cake is crushed and stirred, and mud stabilizer, mud conditioner and mud structure improver are added to the crushed mud during the stirring process.

[0013] In one embodiment, in step (4), a crusher is used to crush the mud; a twin-shaft mixer is used to mix the crushed mud.

[0014] In one embodiment, in step (4), the mud stabilizer is biochar.

[0015] In one embodiment, in step (4), the mud conditioner is organic matter.

[0016] In one embodiment, in step (4), the mud structure modifier is vermiculite.

[0017] Compared with existing technologies, the beneficial effects of this invention are: (1) The present invention provides an electrochemical and biochemical remediation method for river sediment containing heavy metals, which achieves a removal rate of more than 90% for each heavy metal, with a minimum As removal rate of 90% and a maximum Cr and Pb removal rate of more than 95%, demonstrating the significant advantages of electrochemical and biochemical remediation technology in the field of treatment of river sediment containing heavy metals.

[0018] (2) The vertical plate and frame filter press in the third module of the present invention, combined with electrodialysis, can achieve efficient dewatering. The moisture content of the treated mud cake can be reduced to below 50%. The mechanism of achieving the dewatering effect is as follows: On the one hand, conventional mechanical filter press removes free water by mechanical pressure; on the other hand, electrodialysis causes negatively charged bottom mud particles to migrate to the anode under the drive of the electric field, and pore water migrates to the cathode and is discharged. Thus, under the dual action of mechanical pressure and electric field force, the bound water is efficiently removed, and the dewatering efficiency is greatly improved. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the first module provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the structure of the second module provided in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the structure of multiple filter plates, a first composite diaphragm filter cloth, and a second composite diaphragm filter cloth in the vertical filter press provided in Embodiment 1 of the present invention. Figure 4 This is a schematic diagram of the structure of the first composite membrane filter cloth provided in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the structure of the second composite membrane filter cloth provided in Embodiment 1 of the present invention.

[0020] In the diagram: 1. First module; 2. Aeration pipe; 3. Aerobic bacteria inlet; 4. Acidophilic bacteria inlet; 5. Second module; 6. Dosing pump; 7. Sludge pump; 8. Electric lifting mixer; 9. Filter plate; 10. First composite diaphragm filter cloth; 101. First diaphragm filter cloth layer; 102. Biochar-supported nano-zero-valent iron layer; 103. RuO2 / TiO2 composite nano-conductive layer; 104. Biochar-supported nano-zero-valent iron layer; 11. Second composite diaphragm filter cloth; 111. Second diaphragm filter cloth layer; 112. Graphite conductive mesh layer; 113. Cathode liquid collection tank layer; 12. Sealed filter chamber. Detailed Implementation

[0021] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0022] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0023] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. The main heavy metal pollutants in the sediment are Cu, Zn, Cr, Pb, Cd, and As, and their initial total concentrations are shown in Table 2. Example

[0024] like Figure 1-5 As shown, riverbed sediment contaminated with heavy metals was used as the test material. The initial water content of the sediment was about 83%, and the initial pH was 3.5-4.0.

[0025] An electrochemical-biochemical synergistic remediation method for riverbed sediments containing heavy metals includes the following steps: The riverbed sediment containing heavy metals is pumped to the first module 1. Aerobic bacteria and acidophilic bacteria are added to the first module 1 through aerobic bacteria inlet 3 and acidophilic bacteria inlet 4, respectively. Aerobic aeration is carried out in the first module 1 for 48 hours by inserting an aeration pipe 2 into the first module 1.

[0026] Heavy metals in sediment are usually not in the form of free ions, but are encapsulated or bound in organic matter (especially hydrophilic biopolymers) and mineral particles. This bound state is very stable, and direct removal using physicochemical methods (such as acid leaching and flocculation) is inefficient and costly.

[0027] Module 1 activates and transfers heavy metals from the solid phase to the liquid phase through microbial-mediated bioleaching.

[0028] Aerobic bacteria degrade hydrophilic organic biopolymers (such as proteins and polysaccharides) that encapsulate heavy metals in the sediment, providing favorable conditions for the removal of heavy metals from the sediment.

[0029] Acidophilic bacteria are responsible for producing strong acid (sulfuric acid), lowering the pH of the system, and directly releasing heavy metals fixed by sulfides through oxidation.

[0030] Aerobic aeration provides oxygen to the first module, providing the necessary electron acceptors for the metabolic activities of aerobic bacteria and acidophilic thiobacilli; it also thoroughly mixes the sediment to ensure that the sediment, inoculants, and air are in full contact, ensuring uniform reaction, preventing anaerobic conditions at the bottom, and playing a mass transfer role, promoting the diffusion of metabolic products (such as acids) and contact with the substrate.

[0031] The bottom sludge treated in step (1) is pumped to the second module 5 through the sludge pump 7. Citric acid is added to the second module 5 using the dosing pump 6 to keep the pH of the second module 5 at 3.0. The bottom sludge is then stirred for 30 minutes by the electric lifting mixer 8 in the second module 5 to ensure uniform mixing.

[0032] Citric acid is mainly used to condition and enhance the physical structure of mud, and its main functions are as follows.

[0033] Complexing and stabilizing heavy metals: Citric acid is a weak organic acid and a strong complexing agent; it can react with dissolved heavy metal ions (such as Fe) 3+ Al 3+ Cu 2+ (etc.) to form stable water-soluble complexes, preventing heavy metals from redeposition or hydrolysis during subsequent dehydration.

[0034] During the subsequent filtration process, as water is squeezed out, the concentration of metal ions and pH in the filtrate may change locally, which can easily lead to the formation of hydroxide precipitates. These precipitates can clog the pores of the filter cloth. However, after being complexed with citric acid, the metal ions remain in a dissolved state and flow out smoothly with the filtrate, thus protecting the permeability of the filter cloth.

[0035] Improving sludge particle structure: Citric acid can change the surface charge and hydrophilicity of sludge colloidal particles, destroy the stable colloidal structure, and cause fine particles to flocculate into larger flocs, releasing more bound water, thus making it easier to remove water during filter press and forming drier and stronger sludge cakes.

[0036] Assisted acidification and buffering: Supplement the acidic environment, maintain the low pH value of the system, is milder than pure inorganic acid, and has a certain buffering capacity, ensuring that the heavy metal ions leachate remain in a soluble state before entering the filter press, and avoid precipitation caused by pH rise.

[0037] The sludge processed in step (2) is pumped to the third module. Multiple filter plates 9 of the vertical filter press are stacked horizontally on the frame and driven by the pressing device to close them together. After the adjacent filter plates 9 of the vertical filter press in the third module are closed, the relative groove areas of the adjacent filter plates 9 form a sealed filter chamber 12. The upper and lower sides of the sealed filter chamber 12 are respectively provided with a first composite diaphragm filter cloth 10 and a second composite diaphragm filter cloth 11. The first composite diaphragm filter cloth 10 includes, from top to bottom, a first diaphragm filter cloth layer 101, a biochar-supported nano zero-valent iron layer 102, a RuO2 / TiO2 composite nano conductive layer 103, a biochar-supported nano zero-valent iron layer 104, and a first diaphragm filter cloth layer 101. The second composite diaphragm filter cloth 11 includes, from top to bottom, a second diaphragm filter cloth layer 111, a graphite conductive mesh layer 112, a cathodic liquid collection tank layer 113, and a second diaphragm filter cloth layer 111.

[0038] Biochar-supported nano-zero-valent iron layer 102 uses biochar (straw / bamboo charcoal / wood chip pyrolysis, etc.) as a carrier, with 5-20 nm of zero-valent iron (Fe) uniformly loaded on its surface. 0 The carbon-based composite repair material consists of particles; the surface of the biochar-supported nano-zero-valent iron layer 102 generally has an inert oxide layer (Fe2O3 / Fe3O4). The biochar-supported nano-zero-valent iron layer 102 can be commercially available or prepared in the laboratory. The RuO2 / TiO2 composite nano-conductive layer 103 is a mixed metal oxide (MMO) conductive coating composed of nano-ruthenium dioxide (RuO2) and nano-titanium dioxide (TiO2), coated on a titanium substrate, commonly known as ruthenium titanium coating / DSA anode coating. The RuO2 / TiO2 composite nano-conductive layer 103 can be commercially available or prepared in the laboratory.

[0039] The bottom sludge to be filtered is introduced into each sealed filter chamber 12 through a feed pipe. The filtrate from the bottom sludge passes through the first composite diaphragm filter cloth 10 and the second composite diaphragm filter cloth 11, and is discharged through the liquid passage holes around the filter plate. The sludge cake remains in the sealed filter chamber. The first composite diaphragm filter cloth 10 removes heavy metals from both the sludge cake and the filtrate after filtration in each sealed filter chamber, and the second composite diaphragm filter cloth 12 removes heavy metals from both the sludge cake and the filtrate after filtration in each sealed filter chamber. The processing time for the third module is 72 hours.

[0040] The first composite membrane filter cloth 10 serves as the anode layer. The RuO2 / TiO2 composite nano-conductive layer 103 is energized. The voltage gradient of the third module is controlled at 1.5V / cm to ensure smooth migration of heavy metal ions while reducing oxygen evolution side reactions. The biochar-supported nano-zero-valent iron layer 102 accounts for 1.0wt% of the total mass of the first composite membrane filter cloth 10 to prevent excessive pore blockage. The pH value of the anode layer is controlled at 3.0 to enhance Fe... 0 To prevent precipitation and dissolution.

[0041] The mechanism of heavy metal removal by the anodic layer is as follows.

[0042] First, the RuO2 / TiO2 composite nano-conductive layer 103 and the biochar-supported nano-zero-valent iron layer 102 work together to remove heavy metal pollutants in the sediment. The core principle is that the anodic electrochemical action activates the activity of the biochar-supported nano-zero-valent iron layer, and the migration path of heavy metals is controlled by the electric field, ultimately achieving efficient and targeted removal. The mechanism of action is as follows.

[0043] The surface oxide layer of the biochar-supported nano-zero-valent iron layer 102 is activated by an electric field: the active oxygen species (such as ·OH, H2O2) generated after the RuO2 / TiO2 composite nano-conductive layer 103 is energized can etch the inert oxide layer (Fe2O3 / Fe3O4) on the surface of the biochar-supported nano-zero-valent iron layer 102, exposing the Fe core of the biochar-supported nano-zero-valent iron layer 102. 0 This enhances its reducing activity. Simultaneously, maintaining the pH of the anode layer at 2-4 promotes the dissolution of iron oxides and accelerates the reduction of Fe. 0 Release electrons: Fe 0 →Fe 2+ +2 e − These electrons are used directly to reduce high-valence heavy metals, such as Cr. 6+ Reduced to Cr 3+ As 5+ Restore to As 3+ .

[0044] Electromigration-driven enrichment of heavy metals into biochar-supported nano-zero-valent iron 102 layers: The positive voltage applied at the anode attracts negatively charged heavy metal complexes (such as CdCl4). 2- (etc.), while the cathode attracts cationic heavy metals (such as Cu). 2+ Ni 2+ Through directional electromigration, heavy metals are forcibly transported to the enrichment region of the biochar-supported nano-zero-valent iron layer (usually located in the middle of the electrode or near the anode), significantly improving contact efficiency.

[0045] Anodic Fenton reaction enhances redox coupling: Anodic reaction generates H2O2. 2H₂O→H₂O₂+2H + +2e - ; Fe dissolved from biochar-supported nano-zero-valent iron layer 102 2+ The Fenton reaction occurs: Fe 2+ +H₂O₂→Fe 3+ +·OH+OH − ; •OH can degrade organic matter that is complexed with heavy metals, such as humic acid, releasing free heavy metal ions, making them more easily captured by the biochar-supported nano-zero-valent iron layer; The ·OH generated by the Fenton reaction can degrade organic matter complexed with heavy metals, thereby releasing the heavy metals into free heavy metal ions. Simultaneously, Fe... 3+ Hydrolysis generates Fe(OH)3 colloid, which is then used to fix heavy metals through co-precipitation.

[0046] Secondly, regarding the heavy metal removal mechanism of the anode layer, the heavy metal removal mechanism of the RuO2 / TiO2 composite nano-conductive layer 103 is as follows.

[0047] In the entire anode layer, the RuO2 / TiO2 composite nano-conductive layer 103 and the biochar-supported nano-zero-valent iron functional layer 102 do not work independently, but rather enhance each other through multiple interactions.

[0048] Functional sequence: The RuO2 / TiO2 composite nano-conductive layer 103 first generates ·OH and HOCl, which oxidize and dissociate the organic chelated heavy metals into free ions. At the same time, it destroys EPS to reduce dehydration resistance, creating favorable conditions for the reduction / adsorption fixation of the biochar-supported nano-zero-valent iron layer 102 located below.

[0049] Electrochemical activation of Fe 0 The high potential and reactive oxygen species generated by the RuO2 / TiO2 composite nano-conductive layer 103 can erode the Fe in the biochar-supported nano-zero-valent iron functional layer 102 from the anodic direction. 0 The passivated oxide layer (Fe2O3 / Fe3O4) of the particles exposes the 102 core Fe of the biochar-supported nano-zero-valent iron functional layer. 0 This significantly improves the reduction activity and electron utilization of the biochar-supported nano-zero-valent iron functional layer 102. 0 Releasing electrons to reduce high-valence heavy metals: Fe 0 +M n+ →Fe 2+ +M 0 ↓; Fe 3+ Mediated redox synergy: Fe 0 Fe produced by oxidation 2+ / Fe 3+ The ions react with the anolyte H₂O₂ to form ·OH, further enhancing the oxidizing power; Fe 3+ The hydrolysis product Fe(OH)3 exhibits excellent flocculation and capture ability for heavy metal ions, forming a secondary fixed layer; Fe 2+ It can also be oxidized again to Fe by the high potential and active chlorine in the anodic region. 3 +This forms a redox cycle of iron ions.

[0050] Enhanced electron conduction: The biochar layer itself is conductive. When inserted between RuO2 / TiO2 and the sediment, it can form a three-dimensional conductive network, expand the range of electric field action, and promote the transport of electrons from the anode to more distant areas.

[0051] Dual stabilization and anchoring: High-valence heavy metal ions oxidized by the RuO2 / TiO2 composite nano-conductive layer 103 migrate to the biochar-supported nano-zero-valent iron functional layer 102 and are then reduced to zero-valent metals or form stable iron alloy precipitates. This achieves a dual stabilization path of first oxidation, dissolution and release, and then reduction, adsorption and fixation, which is more thorough than the single reduction method.

[0052] The second composite membrane filter cloth 11 is the cathode layer, and the cathode layer serves as the electron (e) layer. - The provider of the cathode layer, whose main function is to process and collect heavy metal ions from the anode, has the following mechanism for removing heavy metals.

[0053] Electroreduction deposition (main mechanism): Under energized conditions, the cathode (graphite conductive mesh layer 112) surface is negatively charged, attracting positively charged metal cations (such as Cu). 2+ Cd 2+ Zn 2+ These ions gain electrons at the cathode and are reduced to zero-valent metal atoms.

[0054] M 2+ +2e - →M 0 (e.g., Cu) 2+ +2e - →Cu); Heavy metals are electroplated onto a graphite conductive mesh in the form of elemental metals, achieving complete separation and direct recovery from the liquid phase to the solid phase.

[0055] Catholyte collection and pH adjustment: A water reduction reaction also occurs at the cathode: 2H₂O + 2e⁻ - →H₂↑+2OH - ; The generated hydrogen gas is safely discharged or utilized through an exhaust valve; hydroxide ions (OH-) are produced. ⁻ This process can locally increase the pH value in the cathode area, which is conducive to the formation of hydroxides by certain heavy metals (such as amphoteric Zn and Pb), which precipitate on the graphite conductive mesh and are thus removed from the sediment. Heavy metal hydroxides form scale on the graphite conductive mesh layer 112, and this portion of the liquid containing the precipitate is collected and discharged through the catholyte collection tank layer 113, maintaining stable system operation. Table 1 shows the main removal mechanisms of different heavy metals in the sediment in the synergistic system.

[0056] Table 1: Main removal mechanisms of different heavy metals in sediment in the synergistic system

[0057] (4) Pump the mud cake that has been processed and dehydrated in step (3) to the mud improvement module.

[0058] In the mud improvement module, the mud cake is crushed and stirred. During the stirring process, mud stabilizer, mud conditioner and mud structure improver are added to the crushed mud.

[0059] Dehydrated mud cakes are usually large, hard, and have a dense internal structure. Breaking up the large mud cakes with a crusher makes them uniform in size, laying the foundation for subsequent uniform mixing; increasing the specific surface area allows the stabilizers and conditioners added later to come into more full and effective contact with the mud and act; improving physical properties makes the final product loose in texture, avoids clumping, and meets the physical requirements of soil or substrate.

[0060] After crushing, the mud is mixed by a twin-shaft mixer. During the mixing process, mud stabilizer biochar, mud conditioner organic matter (which can be humus), and mud structure improver vermiculite are added.

[0061] The porous structure and surface functional groups of biochar can physically adsorb and chemically complex residual or incompletely removed trace heavy metals or organic pollutants, immobilizing them and reducing their bioavailability and mobility; its huge specific surface area can adsorb water and nutrients, release them slowly, and at the same time provide a habitat for beneficial microorganisms.

[0062] Clay conditioners provide nitrogen, phosphorus, potassium, and various trace elements to clay, significantly improving the porosity, air permeability, and water retention of clay products. They can also stabilize the pH value of the products and mitigate the impact of changes in the external environment.

[0063] Vermiculite is lightweight and porous, which can effectively reduce the overall bulk density of the product, making it more loose and meeting the requirements of potting substrate or landscaping soil. Its unique layered structure can absorb a large amount of water while maintaining sufficient porosity, thus resolving the water-air imbalance. At the same time, it has a certain cation exchange capacity, which helps retain fertilizer.

[0064] In this embodiment, after the sediment has undergone four processing steps, samples were taken to determine the residual total concentration of various heavy metals in the dewatered sediment cake, and the removal rate of each heavy metal ion was calculated. The removal rate was calculated using the following formula.

[0065] Removal rate = (initial concentration − residual concentration) / initial concentration × 100%.

[0066] The removal effects of various heavy metals in the sediment treated by the remediation method of this embodiment are shown in Table 2.

[0067] Table 2: Removal effect of various heavy metals in the sediment of Example 1 Cu(Ⅱ) 1200 ≤80 ≥93.3% Zn(Ⅱ) 1500 ≤105 ≥93.0% Cr(Ⅵ / Ⅲ) 800 ≤40 ≥95.0% Pb(Ⅱ) 600 ≤30 ≥95.0% Cd(Ⅱ) 200 ≤12 ≥94.0% As(V / III) 150 ≤15 ≥90.0% As can be seen from the data in Table 2, the removal rate of the six typical heavy metals using the remediation method in this embodiment reached over 90%, with Cr and Pb achieving a removal rate of over 95%, thus realizing efficient and synergistic removal.

[0068] Comparative Example 1 The electrochemical-biochemical remediation method for heavy metal-containing riverbed sediments in this comparative example is the same as that in Example 1, except that in step (3), the first composite membrane filter cloth includes, from top to bottom, a first membrane filter cloth layer, a Ti / MO layer, and a Ti / MO layer. x Coated electrode plate, first diaphragm filter cloth layer.

[0069] Comparative Example 2 The electrochemical-biochemical remediation method for heavy metal-containing riverbed sediments in this comparative example is the same as that in Example 1, except that in step (3), the first composite membrane filter cloth includes, from top to bottom, a first membrane filter cloth layer, a Ti / MO layer, and a Ti / MO layer. x Coated electrode plate, RuO2 / TiO2 composite nano-conductive layer, Ti / MO x Coated electrode plate, first diaphragm filter cloth layer.

[0070] Comparative Example 3 The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments in this comparative example is the same as that in Example 1, except that in step (3), the first composite membrane filter cloth includes, from top to bottom, a first membrane filter cloth layer, a biochar-supported nano-zero-valent iron layer, and a Ti / MO layer. x Coated electrode plate, biochar-supported nano-zero-valent iron layer, and first diaphragm filter cloth layer.

[0071] Comparative Example 4 The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments in this comparative example refers to Example 1. The only difference between Example 1 and Example 1 is that in step (3), the second composite membrane filter cloth includes, from top to bottom, a second membrane filter cloth layer, a stainless steel mesh, a cathodic liquid collection tank layer, and a second membrane filter cloth layer.

[0072] In Comparative Examples 1-4, after the sediment underwent four treatment steps, samples were taken to determine the residual total concentration of various heavy metals in the dewatered sediment cake, and the removal rate of each heavy metal ion was calculated. The formula for calculating the removal rate is as follows.

[0073] Removal rate = (initial concentration − residual concentration) / initial concentration × 100%.

[0074] The removal effects of various heavy metals in the sediment treated by the remediation methods in Comparative Examples 1-4 are shown in Table 3.

[0075] Table 3: Heavy metal removal efficiency of sediments from Example 1 and Comparative Examples 1-4 As shown in Table 3, the data results of Comparative Example 1 indicate that in Comparative Example 3, only Ti / MO is retained in the anode layer. x The coated electrode plate had the biochar-supported nano-zero-valent iron layer and the RuO2 / TiO2 composite nano-conductive layer removed. Comparative Example 1 showed significantly lower removal rates for heavy metals compared to Example 1, with an average removal rate of less than 42% for the six heavy metals, and an As removal rate of only about 30%. This clearly demonstrates that relying solely on the electromigration effect of the conventional anodic electric field and direct anodic oxidation is insufficient for the efficient removal of various forms of heavy metals from sediment. This also conversely proves that there is an indispensable synergistic effect between the electrocatalytic oxidation function (generating ·OH and HOCl, degrading organic complexes) of the RuO2 / TiO2 composite nano-conductive layer in the anode layer of Example 1 and the reduction / adsorption fixation function of the biochar-supported nano-zero-valent iron layer; whereas Comparative Example 1, lacking both, experienced a precipitous drop in heavy metal removal efficiency.

[0076] The data results of Comparative Example 2 show that: Comparative Example 2 retained the RuO2 / TiO2 composite nano-conductive layer but removed the biochar-supported nano-zero-valent iron layer, resulting in a 15-25% decrease in the removal rate of each heavy metal compared to Example 1. The removal effect of Comparative Example 2 is significantly higher than that of Comparative Example 1, indicating that the RuO2 / TiO2 composite nano-conductive layer itself has strong electrocatalytic oxidation ability, effectively degrading the organic matter coating layer and converting heavy metals into more migratory forms with higher valence states. However, due to the lack of the reduction, adsorption, and fixation function of the biochar-supported nano-zero-valent iron layer, the heavy metal removal rate is still significantly lower than that of this invention. This fully demonstrates that while the RuO2 / TiO2 composite nano-conductive layer alone can achieve oxidation, dissolution, and release, it lacks the subsequent reduction, adsorption, and fixation steps, failing to achieve the synergistic effect of the dual-pathway oxidation followed by reduction as described in this invention.

[0077] Comparative Example 3 results show that: Comparative Example 3 retained the biochar-supported nano-zero-valent iron layer but replaced the RuO2 / TiO2 composite nano-conductive layer with a conventional Ti / MO layer. x The removal rate of heavy metals on the coated electrode plate decreased further compared to Comparative Example 2, and decreased by 23-30% compared to Example 1. While the removal effect of Comparative Example 3 was higher than that of Comparative Example 1, it was far lower than that of Example 1. This indicates that conventional Ti / MO... x The anode is insufficient in activating the biochar-supported nano-zero-valent iron layer and generating active species: on the one hand, the lack of high potential and active oxygen species generated by the RuO2 / TiO2 composite nano-conductive layer makes it difficult to effectively etch the passivation layer on the surface of the biochar-supported nano-zero-valent iron layer, leading to Fe... 0The reduction activity is reduced; on the other hand, the selectivity of the chlorine evolution reaction (CER) of conventional anodes is much lower than that of RuO2 electrodes. In the absence of active chlorine oxidizing and degrading organic complexes, a large amount of heavy metals are still encapsulated by organic matter and are difficult to be captured by the carbon-supported nano-zero-valent iron layer. Therefore, although the carbon-supported nano-zero-valent iron layer alone has a certain reduction and adsorption capacity, its effect is greatly reduced if the pretreatment and activation steps of the RuO2 / TiO2 composite nano-conductive layer are lacking.

[0078] The data results of Comparative Example 4 show that, in Comparative Example 4, the conductive material of the cathode layer was replaced with a conventional stainless steel mesh, while the anode layer and filter press area remained the same as in this invention. The removal rates of various heavy metals decreased by 18-25% compared to Example 1. The removal effect of Comparative Example 4 was better than Comparative Examples 2 and 3, but significantly lower than Example 1. This is because, although the conductivity of the stainless steel mesh meets basic requirements, its surface is prone to the precipitation of metal hydroxides and scaling during the electrochemical process, leading to a gradual decrease in the effective conductive area and thus weakening the efficiency of cathode electroreduction deposition. Furthermore, the chemical inertness of stainless steel mesh is significantly lower than that of graphite, and corrosion may occur in alternating acidic / alkaline polar environments, affecting long-term operational stability. In contrast, the graphite conductive mesh of this invention has excellent conductivity, excellent chemical stability, and corrosion resistance, and can stably provide electrons to reduce heavy metal ions, ensuring the continuous and efficient operation of the electroreduction deposition function.

[0079] Based on the experimental results in Table 3 above, the following key conclusions can be drawn: The synergistic effect of the anode layer is the core technical advantage of this invention: by comparing the removal rate data of Comparative Examples 1, 2, and 3 with that of Example 1, it is fully demonstrated that there is indeed a significant synergistic effect between the RuO2 / TiO2 composite nano-conductive layer and the biochar-supported nano-zero-valent iron layer in the anode layer. Together, they constitute a complete dual heavy metal stabilization pathway of first oxidation, dissolution and release, and then reduction, adsorption and fixation.

[0080] The synergistic mechanism between the RuO2 / TiO2 composite conductive nanolayer and the biochar-supported zero-valent iron nanolayer was verified: the RuO2 / TiO2 composite conductive nanolayer generates active chlorine species HOCl / OCl through the chlorine evolution reaction (CER). - It efficiently degrades organic matter complexed with heavy metals, releasing organically encapsulated heavy metals into free ions; simultaneously, the high potential and reactive oxygen species generated can activate Fe in the biochar-supported nano-zero-valent iron layer. 0 The passivated oxide layer on the particles significantly enhances the reduction activity of the biochar-supported nano-zero-valent iron layer. The biochar-supported nano-zero-valent iron layer then captures free heavy metal ions, reducing them through reduction (e.g., Crr). 6+ Reduced to Cr 3+It is stabilized and fixed through adsorption / coprecipitation. Both are indispensable.

[0081] The graphite conductive mesh in the cathode layer makes a significant contribution: comparing the removal rate difference between Comparative Example 4 and Example 1, it is demonstrated that the conductive stability and chemical inertness of the graphite conductive mesh are superior to those of the stainless steel mesh, and it can provide a more continuous and efficient electroreduction deposition function.

[0082] Based on the above data, Example 1 achieved a removal rate of over 90% for all heavy metals, with the lowest As removal rate reaching 90% and the highest Cr and Pb removal rates exceeding 95%, significantly outperforming Comparative Examples 1-4 (whose average removal rates ranged from 35% to 78%). This demonstrates the significant advantages of electrochemical synergistic biochemical remediation technology in the treatment of heavy metal-containing riverbed sediments.

[0083] The vertical plate and frame filter press in the third module of this embodiment 1, combined with electrodialysis, can achieve efficient dewatering. The moisture content of the treated mud cake can be reduced to below 50%. The mechanism of dewatering is as follows: on the one hand, conventional mechanical filter press removes free water by mechanical pressure; on the other hand, electrodialysis causes negatively charged bottom mud particles to migrate towards the anode under the drive of the electric field, and pore water migrates towards the cathode and is discharged. Thus, under the dual action of mechanical pressure and electric field force, bound water is efficiently removed, and the dewatering efficiency is greatly improved.

[0084] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for electrochemical and biochemical remediation of riverbed sediment containing heavy metals, characterized in that, Includes the following steps: (1) Pump the riverbed sediment containing heavy metals to the first module, add aerobic bacteria and acidophilic bacteria to the first module, and carry out aerobic aeration and fully stir the sediment in the first module; (2) Pump the sediment treated in step (1) to the second module, and add organic acid with heavy metal complexing function to the second module; (3) The bottom sludge treated in step (2) is pumped to the third module. After the adjacent filter plates of the vertical filter press in the third module are closed, the relative groove areas of the adjacent filter plates form a sealed filter chamber. The upper and lower sides of the sealed filter chamber are respectively provided with a first composite diaphragm filter cloth and a second composite diaphragm filter cloth. The first composite diaphragm filter cloth includes, from top to bottom, a first diaphragm filter cloth layer, a biochar-supported nano-zero ferric iron layer, an anode conductive layer, a biochar-supported nano-zero ferric iron layer, and a first diaphragm filter cloth layer. The second composite diaphragm filter cloth includes, from top to bottom, a second diaphragm filter cloth layer, a cathode layer, a cathode liquid collection tank layer, and a second diaphragm filter cloth layer. The first composite diaphragm filter cloth and the second composite diaphragm filter cloth remove heavy metals from the bottom sludge in each sealed filter chamber. The mud cake that has been processed and dehydrated in step (3) is pumped to the mud improvement module.

2. The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments according to claim 1, characterized in that, In step (2), the organic acid is citric acid, the pH is maintained at 2.0-4.0, and the bottom mud is stirred for 30-45 minutes.

3. The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments according to claim 1, characterized in that, In step (3), the multiple filter plates of the vertical filter press are stacked horizontally on the frame, and the multiple filter plates are driven to close together by the pressing device; The bottom sludge to be filtered is introduced into each sealed filter chamber through the feed pipe. The filtrate of the bottom sludge passes through the first composite diaphragm filter cloth and the second composite diaphragm filter cloth and is discharged through the liquid passage holes around the filter plate. The sludge cake remains in the sealed filter chamber. The first composite diaphragm filter cloth removes heavy metals from the sludge cake and filtrate after filtration in each sealed filter chamber. The second diaphragm filter cloth removes heavy metals from the sludge cake and filtrate after filtration in each sealed filter chamber.

4. The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments according to claim 1, characterized in that, In step (3), the anode layer is a RuO2 / TiO2 composite nano-conductive layer; the voltage gradient of the third module is 1.5V / cm, the pH value of the anode area is 2.0-4.0, the biochar-loaded nano-zero-valent iron layer accounts for 0.5-2wt% of the total mass of the first composite membrane filter cloth, and the processing time of the third module is 60-72h.

5. The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments according to claim 1, characterized in that, In step (3), the cathode layer is a graphite conductive mesh layer.

6. The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments according to claim 1, characterized in that, In step (4), in the mud improvement module, the mud cake is crushed and stirred, and mud stabilizer, mud conditioner and mud structure improver are added to the crushed mud during the stirring process.

7. The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments according to claim 6, characterized in that, In step (4), a crusher is used for crushing; a twin-shaft mixer is used to mix the crushed mud.

8. The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments according to claim 6, characterized in that, In step (4), the mud stabilizer is biochar.

9. The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments according to claim 6, characterized in that, In step (4), the mud conditioner is organic matter.

10. The electrochemical and biochemical remediation method for heavy metal-containing riverbed sediments according to claim 6, characterized in that, In step (4), the mud structure modifier is vermiculite.

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