Microbial load metal-doped porous biochar electrode material, preparation method thereof and application thereof in desalination of saline-alkali soil

Abstract

The application relates to the technical field of saline-alkali soil remediation, and particularly discloses a kind of microbial loading metal-doped porous biochar electrode materials and a preparation method and application thereof.The electrode material is composed of iron-calcium-magnesium ternary doped porous biochar matrix and loaded salt-tolerant alkali-producing microorganisms.The preparation method comprises the following steps: after biomass is immersed in an iron-calcium-magnesium mixed salt solution, pyrolysis is carried out to obtain doped biochar powder, the doped biochar powder is mixed with a NaCl pore-forming agent and a binder to form a shape, a through porous structure is formed through salt washing and pore-forming, and then the microorganisms are loaded through vacuum immersion and immobilization.The material realizes the combined action of electrochemical driving, metal doping and biological synergy, effectively solves the problems of low desalination efficiency, short-lasting effect and poor ecological compatibility of saline-alkali soil, and has the advantages of high efficiency, long-lasting and ecological friendliness.

Description

Technical Field

[0001] This invention relates to the field of saline-alkali soil remediation technology, and in particular to a microbial-loaded metal-doped porous biochar electrode material, its preparation method, and its application in saline-alkali soil desalination. Background Technology

[0002] The Hetao Irrigation District in Inner Mongolia is an important grain production base in China, but soil salinization is a prominent problem due to factors such as drought, high evaporation, high groundwater levels, and improper irrigation. The soil in this region contains high levels of Na... + Cl - The accumulation of saline ions leads to soil compaction, poor permeability, and decreased fertility, severely restricting crop growth and sustainable agricultural development. Currently, the restoration of saline-alkali land in the Hetao Irrigation District mainly relies on traditional methods such as physical, chemical, and biological approaches.

[0003] Physical methods (such as irrigation to leach salt and deep plowing) can reduce surface soil salinity in the short term, but they consume a lot of water and can easily lead to salt migration to deeper layers or a rise in the groundwater level, causing secondary salinization and are not sustainable. Chemical methods (such as applying gypsum, phosphogypsum, and other soil conditioners) replace sodium through ion exchange. + However, soil conditioners are consumed in large quantities and are costly; long-term use may damage soil structure or introduce new chemicals. Biological methods (such as planting salt-tolerant plants and applying microbial agents) are eco-friendly, but the remediation cycle is long and the effects are slow. Furthermore, under high salt stress, the activity and colonization capacity of microorganisms are limited, resulting in limited desalination efficiency.

[0004] In recent years, electrochemical remediation technology has attracted attention due to its advantages such as high efficiency, controllability, and environmental friendliness. However, this technology is mostly used for the remediation of water pollution and soil organic pollution, with almost no reports on its application in desalination of saline-alkali soils. Furthermore, traditional inert electrodes (such as graphite and titanium-based electrodes) used for organic pollution removal only act as electronic conductors, with limited desalination capacity, and are prone to polarization and efficiency decline during long-term operation. Although research on porous carbon materials loaded with metal oxides has been reported, these often have limited functionality and do not consider the mechanism of action in the complex environment of saline-alkali lands. For example, purely metal-doped electrodes may lack biological activity, and desalination products are easily desorbed. Therefore, there is an urgent need to develop novel electrode materials that combine efficient electron transport, abundant desalination active sites, and biosynergistic enhancement functions to solve the problems of low efficiency, high cost, short-lasting effects, and insufficient ecological compatibility in existing saline-alkali land desalination technologies. This is also a key technological challenge for improving the efficiency of electrochemical remediation of saline-alkali lands and achieving long-term ecological governance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a microbial-loaded metal-doped porous biochar electrode material, its preparation method, and its application in desalination of saline-alkali soils.

[0006] Specifically, the first aspect of the present invention provides a microbial-loaded metal-doped porous biochar electrode material, comprising: a metal-doped porous biochar matrix having a porous structure and salt-tolerant alkali-producing microorganisms loaded in the matrix; wherein the metal-doped porous biochar matrix is ​​an iron-calcium-magnesium ternary doped biochar.

[0007] As a further explanation of the present invention, in the iron-calcium-magnesium ternary doped biochar, the molar ratio of iron, calcium and magnesium elements is 5:(1-3):(1-3).

[0008] As a further explanation of the present invention, the porous structure is formed by the dissolution of a pore-forming agent, wherein the pore-forming agent is NaCl particles.

[0009] As a further explanation of the present invention, the salt-tolerant alkali-producing microorganism is at least one of Bacillus licheniformis, Bacillus pasteurellii, Paracoccus denitrificans, or Pseudomonas.

[0010] A second aspect of the present invention provides a method for preparing the microbial-loaded metal-doped porous biochar electrode material as described above, comprising the following steps: Step 1: Mix iron-calcium-magnesium ternary doped biochar powder, pore-forming agent and binder to form a slurry, and then shape it to obtain an electrode material preform; Step 2: The electrode material preform is subjected to salt washing and pore-forming to dissolve the pore-forming agent and form a wetted electrode material matrix with a through-porous structure; Step 3: The inoculum containing salt-tolerant alkali-producing microorganisms is loaded into the pores of the wet electrode material matrix by vacuum impregnation, followed by microbial immobilization and low-temperature drying to obtain the electrode material.

[0011] As a further illustration of the present invention, in step 1, the iron-calcium-magnesium ternary doped biochar powder is prepared through the following steps: Implanting biomass raw materials in a solution containing Fe 3+ Ca 2+ Mg 2+ In the mixed salt solution, the total metal ion concentration of the mixed salt solution is 1-2 M, Fe 3+ :Ca 2+ :Mg 2+ The molar ratio is 5:(1-3):(1-3); After impregnation, the powder is pyrolyzed at 600℃-800℃ for 1-3 hours under inert gas protection, and then ground and sieved to obtain the iron-calcium-magnesium ternary doped biochar powder.

[0012] As a further explanation of the present invention, in step 1, the pore-forming agent is NaCl particles; the mass ratio of the iron-calcium-magnesium ternary doped biochar to the pore-forming agent is (70-90):(30-10); the binder is at least one of sodium carboxymethyl cellulose, sodium alginate or polyvinyl alcohol, and the amount used is 5-10% of the dry weight of the electrode material.

[0013] As a further explanation of the present invention, in step 2, the process of washing salt and creating holes is as follows: immerse the electrode material blank in water and let it stand for 5-7 hours, changing the water 2-4 times during the period.

[0014] As a further explanation of the present invention, in step 3, the vacuum impregnation method involves immersing the wetted electrode material substrate in an inoculation solution under a negative pressure of -0.10 to -0.05 MPa for 15-30 minutes; wherein the cell density of salt-tolerant alkali-producing microorganisms in the inoculation solution is ≥1.0 × 10^8 CFU / mL; The microbial immobilization involves immersing the substrate loaded with microorganisms in an immobilization carrier solution with a concentration of 1%-5% for 5-10 minutes. The immobilization carrier is at least one of chitosan, sodium alginate, polyvinyl alcohol, or gelatin.

[0015] A third aspect of this invention provides the application of the microbially loaded metal-doped porous biochar electrode material as described above in the desalination treatment of saline-alkali soil, characterized in that the electrode material is implanted as a cathode into the saline-alkali soil, an electric current is applied to form an electric field, and the electric field is used to drive the Na+ in the soil... + Na migrates to the cathode and is achieved through ion exchange and synergistic effects of microbial metabolism in the electrode material. + Adsorption, fixation and transformation.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: 1. This invention constructs a highly efficient conductive network through iron doping, and combined with an external electric field, achieves Na… + Rapid directional migration and enrichment; synergistic effect of calcium and magnesium active sites and microbial metabolic alkalization significantly enhances Na+. + The improved fixation and precipitation efficiency solves the problem of limited desalination capacity of traditional electrodes.

[0017] 2. This invention colonizes salt-tolerant alkali-producing microorganisms within the electrode pores, continuously metabolizing and producing alkali, secreting EPS, and generating CO2. This not only synergizes with the electrochemical process to maintain a high pH environment but also achieves biological fixation of salts through the formation of biofilms and carbonate precipitation, overcoming the shortcomings of traditional technologies such as unsustainable effects and easy desorption of products.

[0018] 3. The electrode provided by this invention uses agricultural waste as a carbon source and the loaded microorganisms originate from the soil environment. The overall material is environmentally friendly. The introduction of microorganisms enhances the self-protection function and ecological restoration function of the electrode, and realizes the transformation from simple physical and chemical desalination to integrated desalination-remediation treatment.

[0019] 4. This invention creatively couples electrochemical driving, ternary metal doping and microbial remediation into one, breaking through the limitations of single-function materials. Through multi-mechanism synergy, it solves key technical bottlenecks such as low efficiency, high cost and insufficient ecological compatibility in complex saline-alkali land environments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the electrochemical reaction apparatus used in the experiments of this invention.

[0021] Figure 2 (a) and Figure 2 (b) are SEM images and physical images of the microbial-loaded metal-doped porous biochar electrode material obtained in Example 1.

[0022] Figure 3 The total charge measurement results for each experimental group.

[0023] Figure 4 The results show the final pH values ​​of the cathode chambers for each experimental group.

[0024] Figure 5 The decrease in electrical conductivity (EC) and sodium adsorption ratio (SAR) of soil extracts for each experimental group was calculated.

[0025] Figure 6 The change in cathode electrode mass (Δm) for each experimental group. Detailed Implementation

[0026] 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.

[0027] In recent years, electrochemical remediation technology has attracted attention due to its advantages such as high efficiency, controllability, and environmental friendliness. However, this technology is mostly used for the remediation of water pollution and soil organic pollution, with almost no reports on its application in desalination of saline-alkali soils. Furthermore, traditional inert electrodes (such as graphite and titanium-based electrodes) used for organic pollution removal only act as electronic conductors, with limited desalination capacity, and are prone to polarization and efficiency decline during long-term operation. Although research on porous carbon materials loaded with metal oxides has been reported, these often have limited functionality or do not consider the mechanism of action in the complex environment of saline-alkali land. For example, purely metal-doped electrodes may lack biological activity, and desalination products are easily desorbed. Therefore, there is an urgent need to develop novel electrode materials that combine efficient electron transport, abundant desalination active sites, and biosynergistic enhancement functions to solve the problems of low efficiency, high cost, short-lasting effects, and insufficient ecological compatibility of existing saline-alkali land desalination technologies. This is also a key technological challenge for improving the efficiency of electrochemical remediation of saline-alkali land and achieving long-term ecological governance.

[0028] To address the aforementioned technical problems, this invention proposes a microbial-supported metal-doped porous biochar electrode material, comprising a porous metal-doped porous biochar matrix and salt-tolerant, alkali-producing microorganisms supported within the matrix; wherein the metal-doped porous biochar matrix is ​​an iron-calcium-magnesium ternary doped biochar. Firstly, iron doping constructs a conductive network, improving electron transfer efficiency and providing a foundation for electrochemical driving, ensuring rapid cathode reactions. Secondly, calcium and magnesium doping provides desalination active sites, immobilizing Na through ion exchange or precipitation. + When an external electric field is applied, it drives the directional migration of ions, providing the power for the entire system and causing salt to accumulate at the electrode; the cathode reaction produces OH-. - This activates calcium and magnesium oxides and creates an alkaline environment. Finally, salt-tolerant alkali-producing microorganisms can metabolize and produce alkali, which interacts with electrochemical OH groups. - It synergistically raises pH and promotes calcium-magnesium reactions; and its secreted EPS adsorbs Na. + It decomposes carbon sources to produce CO2, which forms carbonate precipitates with calcium and magnesium, ultimately achieving efficient and long-lasting desalination and ecological restoration of saline-alkali soils.

[0029] The preparation method of the microbial-loaded metal-doped porous biochar electrode material provided by the present invention includes the following steps: Step 1: Mix metal-doped porous biochar powder with pore-forming agent and binder to form electrode slurry and preliminarily shape electrode material preform.

[0030] Specifically, the metal-doped porous biochar powder mentioned in step 1 is an iron-calcium-magnesium ternary doped biochar powder, which is obtained by impregnating a biomass precursor with loaded iron-calcium-magnesium active components and then pyrolyzing and carbonizing it.

[0031] More specifically, the preparation process of the iron-calcium-magnesium ternary doped biochar powder is as follows: Step 11: Mix the biomass raw materials with Fe 3+ Ca 2+ Mg 2+ The mixed salt solution was impregnated at a mass ratio of 1:(2-3), wherein the total metal ion concentration in the mixed salt solution was 1-2 M, and Fe 3+ :Ca 2+ :Mg 2+ The molar ratio is 5:(1-3):(1-3).

[0032] Among them, the preferred biomass raw materials are agricultural waste, such as straw powder, corn cob powder, rice husks and sawdust.

[0033] During pyrolysis, iron is reduced to zero-valent iron or iron oxide nanoparticles. These particles possess excellent conductivity and can form a continuous conductive network within the biochar, significantly enhancing the electrode's electron transport capability. Meanwhile, calcium and magnesium oxides or hydroxides serve as excellent desalination active sites, capable of removing salt ions from water through ion exchange, surface complexation, or electrostatic adsorption. Excessive iron content can lead to biochar pore blockage, while insufficient iron content may result in inadequate conductivity. The presence of iron may promote the dispersion of calcium and magnesium, forming a richer pore structure and surface defects. To achieve the optimal balance between conductivity, desalination activity, and structural stability of the electrode material, Fe... 3+ :Ca 2+ :Mg 2+ The molar ratio is set to 5:(1-3):(1-3), preferably 5:3:2.

[0034] Step 12: Pyrolyze the impregnated biomass by heating it to 600℃-800℃ and holding it there for 1-3 hours under an inert gas atmosphere.

[0035] Step 13: Grind and sieve the pyrolysis product to obtain the iron-calcium-magnesium ternary doped biochar powder.

[0036] The iron-calcium-magnesium ternary doped biochar powder obtained through the above steps contains zero-valent iron or iron oxide nanoparticles for forming a conductive network, as well as calcium oxide or magnesium oxide that can form desalination active sites and a rich porous structure.

[0037] Specifically, in step 1, the mass ratio of the metal-doped porous biochar powder to the pore-forming agent is (70-90):(30-10); the pore-forming agent is NaCl particles. The amount of binder is 5-10% of the dry weight of the obtained electrode material, specifically any one of sodium carboxymethyl cellulose, sodium alginate, and polyvinyl alcohol.

[0038] Specifically, the initial forming of the electrode material blank can be achieved by filling the slurry into the mold, compacting it, and smoothing it.

[0039] Step 2: The electrode material preform is subjected to salt washing and pore-forming to form a wetted electrode material matrix with a through-porous structure.

[0040] Step 2 creates a macroporous network inside the electrode, which provides more exposure of active sites. The macroporous network is also conducive to electrolyte penetration and ion transport, reduces concentration polarization, and can accommodate microbial cells, allowing them to attach and grow, as well as allow the diffusion of nutrients and metabolites.

[0041] Specifically, the process of washing salt to create pores is as follows: the electrode material preform is immersed in water and left to stand to dissolve the NaCl pore-creating agent. The water is changed 2-4 times during this period, and the total standing time is 5-7 hours.

[0042] Step 3: Using a vacuum impregnation method, the inoculum containing salt-tolerant alkali-producing microorganisms is loaded into the pores of the wet electrode material matrix, and then the microorganisms are immobilized and dried at low temperature to obtain the final electrode material.

[0043] Step 3 utilizes vacuum negative pressure to forcibly draw the microbial suspension into the porous structure inside the electrode, achieving a uniform and high-density loading of microorganisms within the electrode. Salt-tolerant alkali-producing microorganisms can withstand high-salt environments and survive and reproduce in saline-alkali soils. These microorganisms possess alkali-producing characteristics, generating NH3 and organic bases during metabolism, further increasing the pH, thereby reacting with OH- produced electrochemically. - Synergistically, it enhances the desalination effect of calcium and magnesium oxides; in addition, extracellular polymeric substances (EPS) secreted by microorganisms can adsorb Na+. + They form biofilms, which protect the electrode materials and themselves. These microorganisms can also decompose organic matter to produce CO2, which forms carbonate precipitates with calcium and magnesium ions, further fixing the salt content.

[0044] Specifically, the salt-tolerant and alkali-producing microorganisms can be selected from Bacillus licheniformis, Bacillus pasteurellii, Paracoccus denitrificationis, or related Pseudomonas species, etc., with Bacillus licheniformis being the preferred Gram-positive bacterium widely present in soil. It has strong salt tolerance and alkali-producing ability, can form spores, has strong stress resistance, and is easy to survive and colonize in soil.

[0045] Specifically, in step 3, the vacuum impregnation method is as follows: the wetted electrode substrate is placed in a vacuum environment, the inoculation solution is poured in to completely immerse the electrode, and the negative pressure is maintained at -0.10 to -0.05 MPa for 15-30 minutes, and then the vacuum is slowly released; wherein, in order to ensure that microorganisms are efficiently loaded into the electrode pores, the cell density of the inoculation solution is preferably ≥10^8 CFU / mL.

[0046] Specifically, in step 3, the microbial immobilization process is as follows: the wetted electrode material substrate loaded with microorganisms is immersed in a solution containing an immobilization carrier for 5-10 minutes to form a biocompatible protective film on the electrode surface and in the pores; wherein, the immobilization carrier can be chitosan, sodium alginate, polyvinyl alcohol, gelatin, etc.; the concentration of the solution containing the immobilization carrier is 1%-5%, preferably a 2% chitosan-ethanol solution.

[0047] Specifically, in step 3, the drying process after microbial immobilization is as follows: the immobilized electrode material is placed in a constant temperature incubator at 30-35℃ and dried at low temperature for 24-36 hours until constant weight is achieved; preferably, after drying, it is sealed and stored in a refrigerator at 4℃.

[0048] The microbial-loaded metal-doped porous biochar electrode material obtained by the above preparation method provided by this invention can be applied in the desalination process of saline-alkali soil to achieve efficient desalination. Specifically, the electrode material can be implanted into the saline-alkali soil, and a weak direct current can be applied to form an electric field to drive Na+. + They migrate toward the cathode and are adsorbed and collected.

[0049] In summary, the microbial-loaded metal-doped porous biochar electrode material prepared by the above-mentioned method provided by this invention, when applied to the desalination treatment of saline-alkali soil, utilizes the synergistic effect of electrochemical driving, ternary metal doping, and salt-tolerant alkali-producing microorganisms to achieve efficient and sustained desalination and ecological restoration of saline-alkali soil. Specifically: when this electrode material is used as an electrode for the desalination treatment of saline-alkali soil, an external voltage first drives the Na+ in the soil... + Migrating towards the cathode, while a reduction reaction occurs at the cathode to generate OH. - Iron-doped substrates can efficiently transfer electrons and maintain the cathode reaction rate, while OH... - This activates CaO / MgO, which then reacts with Na that migrates to the cathode. + An ion exchange occurs, transferring Na + Fixed as insoluble matter or released through displacement, Bacillus licheniformis ultimately utilizes the carbon source within the electrode pores for metabolism, producing alkali to raise the environmental pH, and secreting EPS to capture Na+. + It also generates CO2, which promotes carbonate precipitation.

[0050] The preparation method provided by the present invention will be specifically described below through examples and comparative examples.

[0051] The microbial strains used in the following examples and comparative examples are all Bacillus licheniformis, strain number CGMCC1.3649, purchased from the China General Microbiological Culture Collection Center.

[0052] Prepare Bacillus licheniformis inoculum solution from the purchased lyophilized Bacillus licheniformis powder according to the following steps: Step 1: Revive the lyophilized powder: Add about 1 mL of LB liquid medium to Bacillus licheniformis lyophilized powder, gently blow and aspirate to dissolve it completely, and prepare a bacterial suspension.

[0053] Step 2: Activation culture: Transfer the obtained bacterial suspension to an Erlenmeyer flask containing 10 mL of LB liquid medium; place it in a constant temperature shaker and culture at 35°C and 180 rpm for 24 hours until the culture medium becomes turbid, at which point the bacteria are in the logarithmic growth phase.

[0054] Step 3: Expanding the culture: Transfer the above activated bacterial solution to fresh LB liquid medium at an inoculation rate of 3%, and continue to culture under the same conditions with shaking until the late logarithmic phase (about 18 hours); collect the bacterial cells by centrifugation and discard the supernatant; wash once with sterile physiological saline, centrifuge again, and finally resuspend with sterile physiological saline to adjust the cell concentration to about 1.0 × 10^8 CFU / mL.

[0055] Furthermore, to provide the initial metabolic substrate for microorganisms within the electrode, approximately 0.5% of sodium alginate-encapsulated starch microspheres were added to the bacterial suspension.

[0056] Example 1 This embodiment provides a method for preparing a microbially loaded metal-doped porous biochar electrode material, which includes the following steps: Step 1: Preparation of iron-calcium-magnesium ternary doped biochar powder: Precursor treatment: The straw powder was washed with deionized water until neutral and then dried at 80°C to obtain straw powder.

[0057] Preparation of mixed salt solution: Dissolve FeCl3·6H2O, CaCl2·6H2O, and MgCl2·6H2O in deionized water to prepare a mixed solution with a total metal ion concentration of 1.5 M, wherein Fe... 3+ :Ca 2+ :Mg 2+ The molar ratio is controlled at 5:3:2.

[0058] Impregnation: Mix the dried straw powder with the above mixed salt solution at a mass ratio of 1:2.5, and then continuously stir and impregnate for 12 hours to ensure full impregnation.

[0059] Drying and pyrolysis: The impregnated mixture was dried in an oven at 80°C for 24 hours. The dried blocks were then ground and placed in a tube furnace for pyrolysis under a high-purity nitrogen protective atmosphere, with the temperature increased to 700°C at a rate of 5°C / min and held for 1.5 hours.

[0060] Grinding: After the pyrolysis is completed and the mixture is allowed to cool naturally, the resulting black solid is ground and passed through a 200-mesh sieve to obtain iron-calcium-magnesium ternary doped biochar powder.

[0061] Step 2: Preparation of porous electrode material wet preform: Electrode slurry preparation: Weigh the above-mentioned iron-calcium-magnesium ternary doped biochar powder and NaCl particles with a particle size of 180-250 μm at a mass ratio of 4:1 and mix them. Then, slowly add 4 wt% sodium carboxymethyl cellulose aqueous solution while stirring until a uniform, viscous paste-like slurry is formed. The sodium carboxymethyl cellulose solid accounts for approximately 8% of the total dry weight of the electrode material.

[0062] Preliminary molding: The slurry is filled into the polytetrafluoroethylene electrode mold, and gently compacted with a pressure bar to remove air bubbles. The surface is then smoothed to obtain a wet electrode material preform.

[0063] Pore ​​formation: Immerse the wet electrode material blank along with the mold in deionized water and let it stand for 6 hours, changing the water 3-4 times during this period, to completely dissolve the NaCl pore-forming agent and form a macroporous network inside the electrode.

[0064] Step 3: Microbial loading and immobilization: Vacuum impregnation loading: Transfer the porous electrode material wet preform obtained in step 2 to a vacuum dryer, pour in sufficient amount of the above Bacillus licheniformis inoculation solution to ensure complete immersion of the electrode, turn on the vacuum pump, maintain a negative pressure of -0.08 MPa for 20 minutes, and then slowly release the vacuum.

[0065] Immobilization: Take out the wet embryo of electrode material loaded with Bacillus licheniformis and immerse it in 2% chitosan (dissolved in 1% acetic acid solution) for 5 minutes to form a thin biocompatible protective film.

[0066] Low-temperature drying and storage: The immobilized electrode material wet embryos were placed in a constant temperature incubator at 33℃ and dried at low temperature for 36 hours until constant weight. The dried electrode material was then stored in a sealed container at 4℃ for later use.

[0067] The SEM and physical images of the microbial-loaded metal-doped porous biochar electrode material obtained in this embodiment are shown below. Figure 2 As shown in (a) and (b), from Figure 2 (a) shows that the obtained biochar electrode material has a loose and porous structure and no obvious agglomeration of dopants, indicating that the metal is uniformly doped in the biochar.

[0068] Comparative Example 1 Comparative Example 1 provides a method for preparing a microbial-loaded metal-doped porous biochar electrode material. The only difference between this method and Example 1 is that in step 1, FeCl3·6H2O used in the preparation of the mixed salt solution is omitted, and the microbial-loaded metal-doped porous biochar electrode material doped with only calcium and magnesium is finally obtained.

[0069] Comparative Example 2 Comparative Example 2 provides a method for preparing a microbial-loaded metal-doped porous biochar electrode material. The only difference between this method and Example 1 is that, in step 1, CaCl2·6H2O and MgCl2·6H2O used in the preparation of the mixed salt solution are omitted, and a microbial-loaded metal-doped porous biochar electrode material doped only with metallic iron is finally obtained.

[0070] Comparative Example 3 Comparative Example 3 provides a method for preparing a metal-doped porous biochar electrode material, which differs from Example 1 only in that: the microbial loading and immobilization in step 3 are omitted, and the final result is a metal-doped porous biochar electrode material without microbial loading.

[0071] The following electrochemical experiments were designed to verify the specific effects of the microbial-loaded metal-doped porous biochar electrode material provided by this invention on the desalination treatment of saline-alkali soil.

[0072] I. Design of Electrochemical Reaction Device: like Figure 1 As shown, a reactor for electrochemical reactions is made of plexiglass. The reactor body is divided into three chambers: an anode chamber containing a high-purity graphite plate electrode; a soil chamber filled with simulated saline-alkali soil; and a cathode chamber containing electrodes prepared in the above-described embodiments or comparative examples. The soil chamber and the two electrode chambers are separated by a plexiglass baffle with uniformly spaced small holes. Glass fiber filter paper is lined on both sides of the baffle to prevent the migration of soil particles and electrode materials. A DC regulated power supply is used, and a digital multimeter is connected in series in the circuit to monitor the current. Small holes are provided above the cathode and anode chambers for replenishing electrolyte, measuring pH / conductivity, and taking samples.

[0073] II. Experimental Procedure: 2.1 Experimental Groups: The following experimental groups were set up according to different electrodes: G1 (blank control group): The cathode uses the same high-purity graphite plate electrode as the anode, and an electric field is applied simultaneously.

[0074] G2 (Control Group 1): The cathode was a biochar electrode loaded with microorganisms but without Fe doping (the electrode prepared in Comparative Example 1), denoted as CaMg-BC-M electrode, and an electric field was applied simultaneously.

[0075] G3 (Control Group 2): The cathode was a biochar electrode loaded with microorganisms but not doped with CaMg (the electrode prepared in Comparative Example 2), denoted as Fe-BC-M electrode, and an electric field was applied simultaneously.

[0076] G4 (Control Group 3): The cathode was a biochar electrode without microorganisms (the electrode prepared in Comparative Example 3), denoted as FeCaMg-BC electrode, and an electric field was applied simultaneously.

[0077] G5 (Control Group 4): The cathode uses a complete microbial preloaded FeCaMg-BC electrode (the electrode prepared in Example 1), denoted as FeCaMg-BC-M electrode, but no electric field is applied.

[0078] G6 (Complete Experimental Group): The cathode uses a complete microbial preloaded FeCaMg-BC electrode (the electrode prepared in Example 1), denoted as FeCaMg-BC-M electrode, and an electric field is applied simultaneously.

[0079] 2.2 Filling with saline-alkali soil: The saline-alkali soil was layered into the soil chamber, each layer gently compacted to ensure uniform density, with a filling density controlled at 1.3 g / cm³. A 0.1 mol / L NaCl electrolyte was injected into the anode chamber, and a nutrient solution containing 0.1 mol / L NaCl + 0.1 g / L glucose electrolyte was injected into the cathode chamber, with the liquid level flush with the soil surface. Electrodes were installed, the circuit was connected but the power was not turned on, and the mixture was allowed to stand at room temperature for 24 hours to allow for preliminary equilibrium of moisture and ion distribution between the soil and the electrolyte. (The saline-alkali soil used in the experiment was collected from a typical salinized area in the Hetao Irrigation District of Inner Mongolia. The top 20 cm soil was taken, naturally air-dried, and then plant debris and stones were removed before sieving through a 2 mm sieve. The basic soil properties were as follows: pH 8.5, electrical conductivity (EC, 1:5 soil-to-water ratio) 2.5 mS / cm, and the main anion was Cl₂.) - and SO4 2- The sodium adsorption ratio (SAR) is 15 (mmol / L)^(1 / 2).

[0080] 2.3 Experiment Implementation: Except for control group 4, all other experimental groups were powered by DC power and subjected to the same constant voltage (3V). The experiment was conducted at room temperature for a total duration of 7 days. During the experiment, electrolyte needed to be replenished to the anode and cathode chambers periodically to maintain the relative stability of the ionic strength of the system.

[0081] 2.4 Experimental Indicators and Detection Methods: Total charge: The total amount of electricity passing through the circuit during the 7-day total operating time is directly read by a multimeter connected in series in the circuit.

[0082] Cathode chamber endpoint pH value: This is the pH value of the electrolyte in the cathode chamber measured at the end of the experiment (day 7).

[0083] Soil extract electrical conductivity (EC): Take 3-5g of soil sample from the middle of the soil chamber, add deionized water at a mass ratio of 1:5 (soil:water), shake for 30 minutes, let stand for 30 minutes, and then filter. Measure the EC value of the filtrate using a conductivity meter. Soil EC decrease (%): The percentage decrease in EC value measured on day 7 compared to the initial value on day 0 (before the start of the experiment).

[0084] Sodium adsorption ratio (SAR) of soil extract: Take 3-5g of soil sample from the middle of the soil chamber, add deionized water at a soil:water mass ratio of 1:5, shake for 30 minutes, let stand for 30 minutes, and then filter. Determine the Na content in the filtrate using ion chromatography. + Ca 2+ Mg 2+ Concentration (unit: mmol / L). Calculation: SAR = [Na + ] / √(([Ca 2+ ]+[Mg 2+ ]) / 2). Soil SAR decrease (%): The percentage decrease in SAR value measured on day 7 compared to the initial value on day 0 (before the start of the experiment).

[0085] Cathode electrode mass change (Δm): After the experiment, carefully remove the cathode electrode, gently rinse the surface with deionized water to remove adhering soil and soluble salts, dry it at 60℃ to constant weight, and weigh it using an analytical balance. Calculation: Compare the dry weight of the electrode with the electrode treated in the same way before the experiment to calculate the increase in mass.

[0086] III. Experimental Results Figures 3-6 The results of various indicator tests are as follows, Figure 3 The total charge measurement results for each experimental group; Figure 4 The results of the final pH value detection in the cathode chamber of each experimental group; Figure 5 The decrease in electrical conductivity (EC) and sodium adsorption ratio (SAR) of soil extracts for each experimental group; Figure 6 The change in cathode electrode mass (Δm) for each experimental group.

[0087] As can be seen from the figure, all indicators of G5 (no electric field) are close to the natural state, indicating that the electrochemical migration and reaction efficiency driven by the electric field is extremely low. The charge (Q) of G2 (Fe-deficient) is much lower than that of G6 and G3, indicating a lack of conductive network, hindered electron transport, and low electrochemical driving efficiency. Despite the presence of calcium, magnesium, and microorganisms, insufficient electric field power results in limited EC and SAR removal rates. Although G3 (Ca / Mg-deficient) has the highest pH (relying solely on electrochemical and biological alkalization), it has the lowest SAR reduction and very little electrode weight gain. This indicates that this group can only temporarily transfer Na through migration and adsorption. + However, these substances could not be permanently fixed through ion exchange / precipitation, resulting in incomplete desalination and no improvement in soil structure. The EC and SAR removal rates and electrode weight gain of G4 (lacking microorganisms) were significantly lower than those of G6, indicating that the lack of bioaugmentation led to a slower pH increase and lower calcium and magnesium activation efficiency. Simultaneously, the lack of EPS-assisted adsorption and CO2-promoted carbonate precipitation resulted in Na+... + Fixed capacity and efficiency decreased. G6 achieved optimal performance in terms of charge, EC reduction, SAR reduction, and electrode weight gain. This indicates that the conductive network formed by iron ensures high current. High current and microorganisms jointly drive the pH to rise rapidly to the ideal range. High pH fully activates the calcium and magnesium active sites, while calcium and magnesium efficiently fix Na+. + and release Ca 2+ / Mg 2+ The reduction of SAR, coupled with the further enhancement of this process by microbial metabolites, creates a highly efficient synergistic desalination cycle.

[0088] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0089] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A microbially supported metal-doped porous biochar electrode material, characterized in that, include: A metal-doped porous biochar matrix with a porous structure and salt-tolerant alkali-producing microorganisms loaded in the matrix; wherein the metal-doped porous biochar matrix is ​​an iron-calcium-magnesium ternary doped biochar.

2. The microbial-loaded metal-doped porous biochar electrode material according to claim 1, characterized in that, In the iron-calcium-magnesium ternary doped biochar, the molar ratio of iron, calcium and magnesium is 5:(1-3):(1-3).

3. The microbial-loaded metal-doped porous biochar electrode material according to claim 1, characterized in that, The porous structure is formed by the dissolution of a pore-forming agent, which is NaCl particles.

4. The microbial-loaded metal-doped porous biochar electrode material according to claim 1, characterized in that, The salt-tolerant alkali-producing microorganism is at least one of Bacillus licheniformis, Bacillus pasteurellis, Paracoccus denitrificans, or Pseudomonas.

5. A method for preparing microbial-loaded metal-doped porous biochar electrode material as described in any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Mix iron-calcium-magnesium ternary doped biochar powder, pore-forming agent and binder to form a slurry, and then shape it to obtain an electrode material preform; Step 2: The electrode material preform is subjected to salt washing and pore-forming to dissolve the pore-forming agent and form a wetted electrode material matrix with a through-porous structure; Step 3: The inoculum containing salt-tolerant alkali-producing microorganisms is loaded into the pores of the wet electrode material matrix by vacuum impregnation, followed by microbial immobilization and low-temperature drying to obtain the electrode material.

6. The method according to claim 5, characterized in that, In step 1, the iron-calcium-magnesium ternary doped biochar powder is prepared through the following steps: Biomass raw materials are impregnated with Fe. 3+ Ca 2+ Mg 2+ In the mixed salt solution, the total metal ion concentration of the mixed salt solution is 1-2 M, Fe 3+ :Ca 2+ :Mg 2+ The molar ratio is 5:(1-3):(1-3); After impregnation, the powder is pyrolyzed at 600℃-800℃ for 1-3 hours under inert gas protection, and then ground and sieved to obtain the iron-calcium-magnesium ternary doped biochar powder.

7. The method according to claim 5, characterized in that, In step 1, the pore-forming agent is NaCl particles; the mass ratio of the iron-calcium-magnesium ternary doped biochar to the pore-forming agent is (70-90):(30-10); the binder is at least one of sodium carboxymethyl cellulose, sodium alginate, or polyvinyl alcohol, and the amount used is 5-10% of the dry weight of the electrode material.

8. The method according to claim 5, characterized in that, In step 2, the process of washing salt and creating holes is as follows: immerse the electrode material blank in water and let it stand for 5-7 hours, changing the water 2-4 times during this period.

9. The method according to claim 5, characterized in that, In step 3, the vacuum impregnation method involves immersing the wetted electrode material substrate in an inoculation solution under a negative pressure of -0.10 to -0.05 MPa for 15-30 minutes; wherein the cell density of salt-tolerant alkali-producing microorganisms in the inoculation solution is ≥1.0 × 10^8 CFU / mL; The microbial immobilization involves immersing the substrate loaded with microorganisms in an immobilization carrier solution with a concentration of 1%-5% for 5-10 minutes. The immobilization carrier is at least one of chitosan, sodium alginate, polyvinyl alcohol, or gelatin.

10. The application of a microbial-loaded metal-doped porous biochar electrode material as described in any one of claims 1-4 in the desalination treatment of saline-alkali soil, characterized in that, The electrode material was implanted as a cathode into saline-alkali soil, and an electric field was formed by applying a current. This electric field was then used to drive the Na+ in the soil... + Na migrates to the cathode and is achieved through ion exchange and synergistic effects of microbial metabolism in the electrode material. + Adsorption, fixation and transformation.

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