Preparation method and application of magnetically responsive bimetallic conductive microspheres

Abstract

This invention relates to the field of food waste treatment, specifically to a method for preparing and applying magnetically responsive bimetallic conductive microspheres. The method includes: 1) drying and pulverizing agricultural waste, food waste sludge, or residual sludge, and then mixing it with iron salts, cobalt salts, and nitrogen-containing ligands to obtain a bimetallic loaded precursor; 2) subjecting the precursor to oxygen-limited thermal conversion under a nitrogen, argon, or nitrogen-hydrogen mixed atmosphere to obtain Fe-Co bimetallic nitrogen-doped porous carbon material; 3) mixing the porous carbon material with graphene oxide dispersion, sodium alginate solution, and buffering functional components to form a composite suspension; 4) adding the composite suspension dropwise to an ion-containing crosslinking curing liquid to form composite gel microspheres; and 5) drying the composite gel microspheres and subjecting them to low-temperature reduction heat treatment to obtain magnetically responsive bimetallic conductive microspheres. This method is suitable for wet, semi-dry, and high-solid-state anaerobic digestion systems, and is applicable to the anaerobic resource recovery of high-load food waste.

Description

Technical Field

[0001] This invention relates to the field of food waste treatment, specifically to a method for preparing and applying magnetically responsive bimetallic conductive microspheres. Background Technology

[0002] Food waste is characterized by high moisture content, high organic matter content, easy putrefaction, easy acidification, and complex salt and oil composition. Its main organic components include carbohydrates, proteins, and fats, possessing a high theoretical methanogenic potential and making it an important substrate for anaerobic digestion and resource recovery. However, in actual engineering operations, the anaerobic digestion of food waste often faces the problem of a mismatch between rapid hydrolysis and acidification and the methanogenic process. A large amount of soluble organic matter is converted into volatile fatty acids in a short period, leading to a rapid drop in pH, inhibiting the activity of methanogenic bacteria, and subsequently resulting in acid accumulation and system instability.

[0003] Furthermore, proteins and nitrogenous organic matter in food waste release ammonia nitrogen during anaerobic degradation. Under medium-high temperature, high pH, ​​or high load operating conditions, some ammonium nitrogen is converted into free ammonia, which inhibits the cell membrane, enzyme system, and electron transport processes of methanogens. Acidification inhibition and ammonia inhibition often overlap, making it difficult to achieve long-term stable operation of high-load anaerobic digestion of food waste.

[0004] To alleviate the above problems, existing technologies typically employ methods such as adding alkali, diluting the feed, reducing the organic load, extending the hydraulic retention time, adding trace elements, or adding biochar. However, adding alkali can easily increase reagent costs and effluent salt load; reducing the load will decrease the reactor volumetric gas production rate; although ordinary biochar or activated carbon can provide certain attachment sites and conductivity, it is prone to agglomeration, sedimentation, or loss with sludge discharge in high solids systems, making it difficult to form a stable bulk electron transport network.

[0005] In recent years, direct interspecies electron transfer has been considered an important pathway to enhance anaerobic methanogenesis. Electron transfer among acid-producing bacteria, syntrophic oxidizing bacteria, and methanogens can be promoted through conductive materials, electrodes, or bioelectrochemical methods, reducing dependence on hydrogen diffusion mass transfer. However, existing electrically assisted anaerobic systems suffer from problems such as the electric field's effect being limited to the electrode surface, insufficient bulk enhancement, easy electrode scaling and passivation, and difficulty in recovering conductive additives. Especially in high-solids food waste systems, traditional electrode enhancement methods struggle to uniformly apply energy across the entire reactor volume, resulting in significant localized enhancement but limited overall efficiency. Summary of the Invention

[0006] In view of the problems of acidification, ammonia inhibition, low electron transfer efficiency, electrode passivation and loss of conductive materials in the existing technology for treating food waste, the purpose of this invention is to provide an anaerobic resource recovery system for food waste based on reconfigurable electron channels of magnetically responsive bimetallic conductive microspheres, which can form a sustainable, controllable and recyclable electron transfer network in the bulk phase of the reactor.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing magnetically responsive bimetallic conductive microspheres, comprising the following steps: Step 1: After drying and pulverizing agricultural waste, kitchen waste sludge or residual sludge, mix it with iron salt, cobalt salt and nitrogen-containing ligand to obtain a bimetallic supported precursor; Step 2: The bimetallic supported precursor is subjected to oxygen-limited thermal conversion in a nitrogen, argon or nitrogen-hydrogen mixed atmosphere to obtain Fe-Co bimetallic nitrogen-doped porous carbon material; Step 3: Mix the Fe-Co bimetallic nitrogen-doped porous carbon material with graphene oxide dispersion, sodium alginate solution and buffering components to form a composite suspension; Step 4: Add the composite suspension dropwise into a cross-linking curing liquid containing calcium ions, magnesium ions, or iron ions to form composite gel microspheres; Step 5: After drying, the composite gel microspheres are subjected to low-temperature reduction heat treatment at 250 to 450 °C to obtain magnetically responsive bimetallic conductive microspheres.

[0008] In the above-mentioned method for preparing magnetically responsive bimetallic conductive microspheres, the iron salt is one or more of ferric chloride, ferric nitrate, ferrous sulfate, or ferric acetylacetonate; the cobalt salt is one or more of cobalt chloride, cobalt nitrate, cobalt acetate, or cobalt acetylacetonate; and the nitrogen-containing ligand is one or more of urea, melamine, chitosan, dopamine, ethylenediaminetetraacetic acid, or imidazole compounds.

[0009] The above-described method for preparing magnetically responsive bimetallic conductive microspheres, wherein the magnetically responsive bimetallic conductive microspheres comprise, from the inside out: Fe-Co bimetallic nitrogen-doped porous carbon core: formed through oxygen-limited thermal conversion. Fe is used to construct magnetic response components, iron-based electron transfer sites and iron-sulfur protein-related trace element supply. Co is used to supplement the trace elements required by cobalamin-related enzyme systems, promote methyl transfer and methanogenesis metabolism. Fe and Co form Fe-Nx, Co-Nx and Fe-Co composite active sites in the nitrogen-containing carbon skeleton. Reduced graphene oxide conductive interface layer: used to connect the porous carbon core and the outer biofilm, reduce the electron transfer impedance inside and between microspheres, and the sheet structure increases the surface roughness of microspheres, providing an interface for anaerobic microorganisms to attach; The outer layer, containing carboxyl, hydroxyl, and phosphate groups, forms a buffering function: the outer biofilm is formed by cross-linking alginate, carboxylated polysaccharides, phytates, phosphates, or weakly basic mineral components. It has the ability to adsorb ammonium nitrogen, buffer pH, and complex metal ions, thus buffering the local acidification environment and reducing the instantaneous impact of free ammonia on methanogens.

[0010] In the above-mentioned method for preparing magnetically responsive bimetallic conductive microspheres, the molar ratio of Fe to Co in the Fe-Co bimetallic nitrogen-doped porous carbon core is 2:1-8:1, the particle size of the magnetically responsive bimetallic conductive microspheres is 0.3-3.0 mm, the saturation magnetization is 8-45 emu / g, and the volume resistivity is less than 100 Ω·cm.

[0011] An anaerobic resource recovery system for food waste based on magnetically responsive bimetallic conductive microspheres includes: Food waste pretreatment unit: used to remove impurities, crush, slurry and extract oil from food waste, so that food waste is formed into a homogeneous substrate suitable for anaerobic digestion; Anaerobic resource recovery reactor: It is equipped with multiple sets of staggered inert mesh anodes and inert mesh cathodes, and disperses magnetically responsive bimetallic conductive microspheres obtained by the preparation method of magnetically responsive bimetallic conductive microspheres as described above, for use in the anaerobic hydrolysis, acidification, acetic acid production and methanogenesis processes of kitchen waste. Periodic polarity reversal micro electric field unit: connected to the inert mesh anode and inert mesh cathode, it consists of a DC low-voltage power supply, a polarity reversal controller, a current density regulator and a mesh electrode array. It is used to control the interfacial polarization of magnetically responsive bimetallic conductive microspheres in the anaerobic resource recovery reactor under the action of a low-voltage micro electric field. The microspheres are arranged in a short-range orientation, forming a conductive chain structure dispersed in the reactor bulk phase. The magnetically responsive conductive microsphere recycling unit consists of an external magnetic trap, a return pipeline, and a regeneration device. The external magnetic trap is installed at one or more locations on the discharge pipeline, the circulation pipeline, or the outer wall of the reactor. It is used to intercept the magnetically responsive bimetallic conductive microspheres in the effluent and return them to the anaerobic resource recovery reactor. Process feedback control unit: including pH, ORP, conductivity, biogas flow rate, methane content and VFA concentration detection modules, dynamically adjusts micro electric field voltage, polarity reversal period, magnetic response bimetallic conductive microsphere reflux ratio and stirring intensity according to the reaction state.

[0012] In the aforementioned anaerobic resource recovery system for kitchen waste based on magnetically responsive bimetallic conductive microspheres, the inert mesh anode is a titanium-based iridium-tantalum oxide coated electrode, a titanium-based ruthenium-iridium oxide coated electrode, or a graphite felt electrode, and the inert mesh cathode is a stainless steel mesh, carbon felt, graphite plate, or titanium mesh. The distance between the inert mesh anode and the inert mesh cathode is 2 to 15 cm.

[0013] In the aforementioned anaerobic resource recovery system for food waste based on magnetically responsive bimetallic conductive microspheres, the periodic polarity reversal micro-electric field unit applies a voltage of 0.3 to 1.2 V and a current density of 0.02 to 1.50 A / m. 2 The polarity reversal cycle is 6 to 72 hours, and a power-off buffer phase of 0.5 to 10 minutes is set before each polarity reversal.

[0014] A method for anaerobic resource recovery of food waste based on the anaerobic resource recovery system for food waste as described in any of the above claims includes the following steps: Step 1: After removing impurities, crushing, slurrying and oil extraction from the kitchen waste, adjust the total solids content to 6% to 15% to obtain the kitchen waste fermentation substrate; Step 2: Pump the fermentation substrate of the kitchen waste into the anaerobic resource recovery reactor and inoculate it with anaerobic granular sludge, digested sludge or methanogenic enrichment sludge; Step 3: Add magnetically responsive bimetallic conductive microspheres to the anaerobic resource recovery reactor at a dosage of 1 to 8 g / L; Step 4: Activate the periodic polarity reversal micro-electric field unit, apply a low-voltage micro-electric field of 0.3 to 1.2 V, and perform polarity reversal according to a period of 6 to 72 h; Step 5: During the anaerobic fermentation process, the magnetically responsive bimetallic conductive microspheres form a reconstructed three-dimensional conductive chain structure under the action of a micro-electric field, which promotes direct interspecies electron transfer among acid-producing bacteria, syntrophic oxidizing bacteria and methanogenic bacteria, and enables volatile fatty acids to be rapidly converted into methane. Step 6: Before the fermentation broth is discharged, the magnetically responsive bimetallic conductive microspheres are retained by the magnetically responsive conductive microsphere recycling unit and returned to the anaerobic resource recovery reactor.

[0015] In the aforementioned anaerobic resource recovery method for kitchen waste, when the pH in the anaerobic resource recovery reactor is below 6.8 or the concentration of volatile fatty acids is above 2000 mg / L, the process feedback control unit increases the micro-electric field voltage to 0.8 to 1.2 V and shortens the polarity reversal cycle to 6 to 24 h; when the methane production rate is stable and the pH is maintained at 7.0 to 7.8, the micro-electric field voltage is reduced to 0.3 to 0.8 V to reduce energy consumption and maintain stable methane production.

[0016] In the above-mentioned anaerobic resource utilization method for kitchen waste, the magnetically responsive bimetallic conductive microspheres are regenerated after being recycled for 5 to 20 cycles by a combination of one or more of the following methods: weak acid washing, low-intensity ultrasonic cleaning, nitrogen purging, or low-temperature reduction treatment.

[0017] The beneficial effects of the preparation method and application of the magnetically responsive bimetallic conductive microspheres of this invention are as follows: By using magnetically responsive bimetallic conductive microspheres, it is possible to simultaneously solve the problems of rapid accumulation of VFA and sudden drop in pH during high-load anaerobic digestion of kitchen waste, the problem of inhibition of ammonia nitrogen and free ammonia during the degradation of high-protein kitchen waste, the problems of easy aggregation, sedimentation and difficulty in recycling of ordinary conductive materials, the problem of limited electric field range, electrode passivation and scaling in electrically assisted anaerobic systems, and the problem of low methanation rate caused by insufficient electron transfer efficiency between acid-producing bacteria and methanogenic bacteria.

[0018] By forming reconfigurable conductive chains in the reactor bulk phase using magnetically responsive bimetallic conductive microspheres, the local enhancement of the electrode surface is transformed into bulk enhancement of the entire reactor, which improves the electron transfer efficiency among acid-producing bacteria, syntrophic oxidizing bacteria and methanogenic bacteria, and constructs a bulk reconfigurable electron transfer network.

[0019] The buffered outer layer of the magnetically responsive bimetallic conductive microspheres can adsorb some ammonium nitrogen and buffer local pH fluctuations; the Fe-Co bimetallic nitrogen-doped porous carbon core can slowly release trace elements required for anaerobic metabolism and promote the maintenance of key methanogenic enzyme systems; the conductive interface layer can promote the rapid conversion of VFA into methane, reduce the risk of acidification from the source, and simultaneously alleviate acidification and ammonia inhibition.

[0020] The magnetically responsive bimetallic conductive microspheres have magnetic response characteristics. They can be intercepted and recycled by an external magnetic trap, and can be reused after regeneration, thereby reducing material operating costs, preventing the loss of conductive materials, and realizing recycling.

[0021] Periodic polarity reversal alters the direction of ion migration on the electrode surface, reducing calcium and magnesium deposition and electrode passivation caused by unidirectional polarization. Simultaneously, the conductive microspheres share some of the electron transfer function, reducing the localized load on the electrode surface and lowering the risk of electrode scaling and passivation.

[0022] It can adapt to the background of high TS, high VFA impact and high ammonia nitrogen in food waste, and is suitable for wet, semi-dry and high solid anaerobic digestion systems, and is suitable for anaerobic resource recovery of high-load food waste. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the anaerobic resource recovery system for kitchen waste in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the fabrication process of magnetically responsive bimetallic conductive microspheres in an embodiment of the present invention. Figure 3 This is a flowchart illustrating the recycling and regeneration process of magnetically responsive bimetallic conductive microspheres in an embodiment of the present invention. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described below in conjunction with specific embodiments and accompanying drawings.

[0025] Example 1 This embodiment describes a method for preparing magnetically responsive bimetallic conductive microspheres. The resulting Fe-Co bimetallic conductive microspheres possess magnetic responsiveness, conductivity, microbial adhesion ability, and trace element slow-release function, providing functional materials for the subsequent construction of a three-dimensional bulk electron transport network in a food waste anaerobic system. Figure 2 As shown, it includes the following steps.

[0026] Step 1: After drying and pulverizing agricultural waste, kitchen waste sludge or residual sludge, mix it with iron salt, cobalt salt and nitrogen-containing ligand to obtain a bimetallic supported precursor.

[0027] The iron salt is one or more of ferric chloride, ferric nitrate, ferrous sulfate or ferric acetylacetonate; the cobalt salt is one or more of cobalt chloride, cobalt nitrate, cobalt acetate or cobalt acetylacetonate; and the nitrogen-containing ligand is one or more of urea, melamine, chitosan, dopamine, ethylenediaminetetraacetic acid or imidazole compounds.

[0028] Step 2: The bimetallic supported precursor is subjected to oxygen-limited thermal conversion in a nitrogen, argon, or nitrogen-hydrogen mixed atmosphere to obtain Fe-Co bimetallic nitrogen-doped porous carbon material.

[0029] Step 3: Mix the Fe-Co bimetallic nitrogen-doped porous carbon material with graphene oxide dispersion, sodium alginate solution and buffering components to form a composite suspension.

[0030] Step 4: Add the composite suspension dropwise into a cross-linking curing liquid containing calcium ions, magnesium ions, or iron ions to form composite gel microspheres.

[0031] Step 5: After drying, the composite gel microspheres are subjected to low-temperature reduction heat treatment at 250 to 450 °C to obtain magnetically responsive bimetallic conductive microspheres.

[0032] Specifically, 100 g of dried kitchen waste biogas residue or straw powder was added to a mixed solution of FeCl3·6H2O and CoCl2·6H2O, with the molar ratio of Fe to Co set to 2:1, 4:1, and 8:1, respectively. Urea was added as a nitrogen source, and the mixture was stirred for 6 hours, then sonicated for 30 minutes, and subsequently dried at 80 °C.

[0033] The dried precursor was placed in a tube furnace and heated to 750 °C at a rate of 5 °C / min under a nitrogen atmosphere, and held for 3 h to obtain Fe-Co bimetallic nitrogen-doped porous carbon material.

[0034] The obtained material was added to a graphene oxide dispersion and ultrasonically dispersed for 30 min. Then, sodium alginate, carboxymethyl cellulose, and sodium phytate were added to form a homogeneous composite suspension. The suspension was then dropped into a CaCl2-MgCl2 composite crosslinking solution using a pelletizing device to form gel microspheres. After freeze-drying, the gel microspheres were subjected to a low-temperature reduction treatment at 350 °C for 2 h under a nitrogen-hydrogen mixed atmosphere to obtain magnetically responsive bimetallic conductive microspheres.

[0035] The magnetically responsive bimetallic conductive microspheres are black, nearly spherical particles with a particle size of 0.3–3.0 mm, concentrated in the range of 0.8–1.5 mm. They have a saturation magnetization of 8–45 emu / g and a volume resistivity of less than 100 Ω·cm.

[0036] The magnetically responsive bimetallic conductive microspheres consist of, from the inside out: an Fe-Co bimetallic nitrogen-doped porous carbon core, a reduced graphene oxide conductive interface layer, and a buffering outer layer containing carboxyl, hydroxyl, and phosphate groups.

[0037] Fe-Co bimetallic nitrogen-doped porous carbon core: formed through oxygen-limited thermal conversion. Fe is used to construct magnetically responsive components, iron-based electron transfer sites, and supply trace elements related to iron-sulfur proteins. Co is used to supplement the trace elements required by cobalamin-related enzyme systems, promote methyl transfer and methanogenesis metabolism. Fe and Co form Fe-Nx, Co-Nx, and Fe-Co complex active sites in the nitrogen-containing carbon skeleton.

[0038] In the Fe-Co bimetallic nitrogen-doped porous carbon core, the molar ratio of Fe to Co is 2:1-8:1. When the Fe:Co ratio is 4:1, the microspheres have high magnetization, low resistivity and good metal leaching safety, making them suitable as the preferred material in this embodiment.

[0039] Reduced graphene oxide conductive interface layer: used to connect the porous carbon core to the outer biofilm, reduce the electron transfer impedance inside and between microspheres, and the sheet structure increases the surface roughness of the microspheres, providing an interface for the attachment of anaerobic microorganisms.

[0040] The outer layer, containing carboxyl, hydroxyl, and phosphate groups, forms a buffering function: the outer biofilm is formed by cross-linking alginate, carboxylated polysaccharides, phytates, phosphates, or weakly basic mineral components. It has the ability to adsorb ammonium nitrogen, buffer pH, and complex metal ions, thus buffering the local acidification environment and reducing the instantaneous impact of free ammonia on methanogens.

[0041] The specific preparation conditions and main properties are shown in Table 1.

[0042] Table 1. Preparation conditions and main properties of magnetically responsive bimetallic conductive microspheres .

[0043] As shown in Table 1, when the Fe:Co ratio is 4:1 and the pyrolysis temperature is 750 °C, the material exhibits a relatively balanced specific surface area, electrical conductivity, magnetic responsiveness, and metal release safety. Therefore, in subsequent embodiments, MBC-2 is preferably used as the magnetically responsive bimetallic conductive microsphere.

[0044] Example 2 This embodiment constructs an anaerobic resource recovery system for kitchen waste that can realize magnetically responsive conductive microsphere dispersion, micro-electric field induction, polarity reversal, magnetic recovery, and process feedback control, thus verifying the engineering feasibility of this technical solution.

[0045] like Figure 1 As shown, an anaerobic resource recovery system for kitchen waste based on magnetically responsive bimetallic conductive microspheres includes: Food waste pretreatment unit: used to remove impurities, crush, slurry and extract oil from food waste, so that food waste is formed into a homogeneous substrate suitable for anaerobic digestion.

[0046] Anaerobic resource recovery reactor: It is equipped with multiple sets of staggered inert mesh anodes and inert mesh cathodes, and dispersed inside are magnetically responsive bimetallic conductive microspheres obtained by the preparation method of magnetically responsive bimetallic conductive microspheres in Example 1, which are used for the anaerobic hydrolysis, acidification, acetic acid production and methanogenesis processes of kitchen waste.

[0047] The inert mesh anode is a titanium-based iridium-tantalum oxide coated electrode, a titanium-based ruthenium-iridium oxide coated electrode, or a graphite felt electrode, and the inert mesh cathode is a stainless steel mesh, carbon felt, graphite plate, or titanium mesh. The distance between the inert mesh anode and the inert mesh cathode is 2 to 15 cm.

[0048] Periodic polarity reversal micro-electric field unit: connected to the inert mesh anode and inert mesh cathode, it consists of a DC low-voltage power supply, a polarity reversal controller, a current density regulator and a mesh electrode array. It is used to control the interfacial polarization of magnetically responsive bimetallic conductive microspheres in the anaerobic resource recovery reactor under the action of a low-voltage micro-electric field. The microspheres are arranged in a short-range orientation, forming a conductive chain structure dispersed in the reactor bulk phase.

[0049] The periodic polarity reversal micro-electric field unit applies a voltage ranging from 0.3 to 1.2 V and a current density ranging from 0.02 to 1.50 A / m. 2 The polarity reversal cycle is 6 to 72 hours, and a power-off buffer phase of 0.5 to 10 minutes is set before each polarity reversal.

[0050] The magnetically responsive conductive microsphere recycling unit consists of an external magnetic trap, a return pipeline, and a regeneration device. The external magnetic trap is installed at one or more locations on the discharge pipeline, the circulation pipeline, or the outer wall of the reactor. It is used to intercept the magnetically responsive bimetallic conductive microspheres in the effluent and return them to the anaerobic resource recovery reactor.

[0051] Process feedback control unit: including pH, ORP, conductivity, biogas flow rate, methane content and VFA concentration detection modules, dynamically adjusts micro electric field voltage, polarity reversal period, magnetic response bimetallic conductive microsphere reflux ratio and stirring intensity according to the reaction state.

[0052] Specifically, a continuous stirred anaerobic reactor with an effective volume of 10 L is used as the main body. The reactor is equipped with 4 sets of titanium-based iridium-tantalum oxide-coated mesh anodes and 4 sets of stainless steel mesh cathodes, with the anodes and cathodes arranged alternately and the electrode spacing being 6 cm.

[0053] The reactor is connected to an external low-voltage DC power supply and a polarity reversal controller, with a voltage adjustment range of 0.3–1.2 V and a polarity reversal cycle adjustment range of 6–72 h. An annular permanent magnet trap is installed at the reactor outlet to trap the magnetically responsive bimetallic conductive microspheres flowing out with the effluent and return them to the reactor through a reflux pipeline.

[0054] The reactor is equipped with modules for detecting pH, ORP, conductivity, temperature, biogas flow rate, and methane content. Food waste is fed into the reactor after being cleaned, crushed, oil extracted, and slurry prepared.

[0055] The main structure and operating parameters of the anaerobic resource recovery system for kitchen waste are shown in Table 2.

[0056] Table 2. Main Structure and Operating Parameters of the Anaerobic Resource Utilization System for Food Waste .

[0057] The anaerobic resource recovery system for food waste can stably complete the processes of food waste feeding, anaerobic fermentation, micro-electric field control, magnetic trapping of microspheres, and reflux. Under the combined action of stirring and micro-electric field, the magnetically responsive conductive microspheres can be stably dispersed in the reactor bulk phase without significant agglomeration or large-scale loss.

[0058] The results show that the system has a clear structure and controllable parameters, and can meet the operational requirements of material dispersion, electric field enhancement and material recycling in the high solids anaerobic digestion process of kitchen waste.

[0059] Example 3 An anaerobic resource recovery method for food waste based on an anaerobic resource recovery system is applicable to wet or medium-to-high solids content anaerobic digestion systems for food waste. The method includes the following steps: the total solids content of the food waste fermentation substrate is 6% to 15%, preferably 8% to 12%; the reaction temperature is 35±2 ℃ or 55±2 ℃; the organic loading rate is 2 to 12 g VS / L·d; and the hydraulic retention time is 8 to 30 d. Step 1: After removing impurities, crushing, slurrying and oil extraction from the kitchen waste, adjust the total solids content to 6% to 15% to obtain the kitchen waste fermentation substrate.

[0060] Step 2: Pump the fermentation substrate of the kitchen waste into the anaerobic resource recovery reactor and inoculate it with anaerobic granular sludge, digested sludge or methanogenic enrichment sludge.

[0061] Step 3: Add magnetically responsive bimetallic conductive microspheres to the anaerobic resource recovery reactor at a dosage of 1 to 8 g / L.

[0062] Step 4: Start the periodic polarity reversal micro electric field unit, apply a low voltage micro electric field of 0.3 to 1.2 V, and perform polarity reversal according to a period of 6 to 72 h.

[0063] Step 5: During anaerobic fermentation, the magnetically responsive bimetallic conductive microspheres form a reconstructed three-dimensional conductive chain structure under the action of a micro-electric field, which promotes direct interspecies electron transfer among acid-producing bacteria, symbiotic oxidizing bacteria and methanogenic bacteria, and enables volatile fatty acids to be rapidly converted into methane.

[0064] Step 6: Before the fermentation broth is discharged, the magnetically responsive bimetallic conductive microspheres are retained in the magnetically responsive conductive microsphere recycling unit and returned to the anaerobic resource recovery reactor. After 5 to 20 cycles of recycling, the magnetically responsive bimetallic conductive microspheres are regenerated through one or more of the following methods: weak acid washing, low-intensity ultrasonic cleaning, nitrogen purging, or low-temperature reduction treatment. Figure 3 As shown.

[0065] When the pH in the anaerobic resource recovery reactor is below 6.8 or the concentration of volatile fatty acids is above 2000 mg / L, the process feedback control unit increases the micro-electric field voltage to 0.8 to 1.2 V and shortens the polarity reversal cycle to 6 to 24 h. When the methane production rate is stable and the pH is maintained at 7.0 to 7.8, the micro-electric field voltage is reduced to 0.3 to 0.8 V to reduce energy consumption and maintain stable methane production.

[0066] Example 4 This embodiment mainly involves adjusting various constraints in the anaerobic resource recovery method for kitchen waste based on the anaerobic resource recovery system described in Embodiment 3 to obtain the best treatment effect.

[0067] I. Optimize the dosage of magnetically responsive bimetallic conductive microspheres.

[0068] This method is used to determine the appropriate dosage of magnetically responsive bimetallic conductive microspheres in the anaerobic digestion of food waste, avoiding insufficient dosage which leads to insignificant enhancement of electron transfer, or excessive dosage which leads to increased system viscosity, limited mass transfer, and increased risk of metal release.

[0069] Specifically, the kitchen waste after oil extraction was used as the substrate, the total saturation (TS) was adjusted to 10%, and mesophilic anaerobic digestion sludge was inoculated. The reaction temperature was controlled at 35±1 ℃, and the inoculation ratio, calculated as substrate VS:inoculation sludge VS = 1:1.

[0070] The dosage of magnetically responsive bimetallic conductive microspheres was set at 0, 1, 3, 5, and 8 g / L, without applying a micro-electric field, to investigate the effect of microsphere addition alone on the anaerobic digestion performance of food waste. The operation period was 30 days, and pH, VFA, methane yield, ammonia nitrogen, and microsphere recovery rate were measured.

[0071] Experimental results show that microsphere addition can reduce VFA accumulation and increase methane yield. The enhancement effect is significantly improved when the dosage increases from 1 g / L to 3 g / L; the improvement decreases when the dosage increases further to 5 g / L; and when the dosage reaches 8 g / L, the system viscosity increases, local mass transfer is limited, and the methane yield no longer increases significantly. Therefore, the preferred dosage is 3–5 g / L, as shown in Table 3.

[0072] Table 3. Effects of magnetically responsive bimetallic conductive microsphere dosage on anaerobic digestion of food waste. .

[0073] The results showed that 3 g / L magnetically responsive bimetallic conductive microspheres could significantly improve the stability of anaerobic digestion and methane generation in food waste, making it the preferred dosage that balances performance enhancement, material cost, and recycling efficiency.

[0074] II. Optimize the parameters of the periodic polarity reversal micro-electric field.

[0075] This study aims to determine the effects of low-voltage micro-electric fields and polarity reversal cycles on the formation of phase electron channels, suppression of electrode passivation, and methane generation in magnetically responsive conductive microspheres, and to screen suitable electric field operating parameters.

[0076] Specifically, 3 g / L of magnetically responsive bimetallic conductive microspheres were added to the anaerobic resource recovery reactor, with a total saturation (TS) of 10% for food waste, and the reactor was operated at a mesophilic temperature of 35±1 ℃. Different electric field operation modes were set up. No electric field is applied; A constant micro-electric field of 0.4 V is applied; A constant micro electric field of 0.8 V is applied; A micro electric field of 0.8 V was applied and its polarity was reversed every 12 hours; A micro-electric field of 0.8 V is applied and its polarity is reversed every 24 hours; A micro electric field of 1.2 V was applied and its polarity was reversed every 24 hours.

[0077] After 30 days of operation, methane yield, VFA concentration, energy consumption per unit VS, electrode deposits, and charge transfer impedance were measured.

[0078] Experimental results show that a low-voltage micro-electric field can further enhance the effect of magnetically responsive conductive microspheres. Compared with a constant electric field, periodic polarity reversal can reduce electrode deposition and charge transfer impedance. Among them, under the polarity reversal conditions of 0.8 V and 24 h, the methane yield is higher, the electrode passivation is less severe, and the energy consumption is relatively lower, as shown in Table 4.

[0079] Table 4. Effects of micro-electric field operation mode on anaerobic digestion performance and electrode passivation .

[0080] The results show that 0.8 V and 24 h polarity reversal can achieve good VFA control, methane generation and anti-passivation effects with low energy consumption, which is the preferred micro-electric field operation mode of this invention.

[0081] III. Comparison of the synergistic enhancement effects between the anaerobic resource recovery system for kitchen waste and the comparative system.

[0082] This demonstrates that the anaerobic resource recovery system for kitchen waste described in this technical solution is not a simple combination of adding ordinary conductive materials, ordinary electric-assisted anaerobic treatment, or recycling magnetic materials, but rather a system that generates a synergistic enhancement effect through magnetically responsive bimetallic conductive microspheres and a periodically polarity-reversed micro-electric field.

[0083] Specifically, using the same food waste substrate, a total sulfide (TS) content of 10%, a reaction temperature of 35±1 ℃, and an operating cycle of 60 days, the following treatment groups were set up.

[0084] CK group: No conductive material, no electric field.

[0085] Group BC: 3 g / L of ordinary biochar was added, and no electric field was applied.

[0086] Group E: Only a constant micro-electric field of 0.8 V is applied, without microspheres.

[0087] Group M: 3 g / L of magnetically responsive bimetallic conductive microspheres were added, with no electric field.

[0088] ME group: 3 g / L of magnetically responsive bimetallic conductive microspheres were added, and a constant micro-electric field of 0.8 V was applied.

[0089] M-PRE group: 3 g / L of magnetically responsive bimetallic conductive microspheres were added, and a periodic polarity reversal micro-electric field of 0.8 V for 24 h was applied.

[0090] The experimental results show that the CK group exhibited significant VFA accumulation and pH decrease in the early stages of operation; the ordinary biochar group, although having some buffering and adhesion effects, had limited stability in the later stages; the electric field-only group showed electrode passivation and reduced gas production; the combination of magnetically responsive microspheres and a constant electric field could improve methane yield, but electrode deposition was still significant; the M-PRE group of this invention showed the lowest VFA accumulation, the highest methane yield, and the best operational stability. (See Table 5.)

[0091] Table 5. Comparison of anaerobic resource utilization effects of the system of the present invention with different comparative examples. .

[0092] The results show that the M-PRE group of this invention has an approximately 129.8% higher methane yield than the CK group, an approximately 67.1% higher yield than the ordinary biochar group, and an approximately 46.6% higher yield than the single electric field group. This indicates a significant synergistic effect between the magnetically responsive bimetallic conductive microspheres and the periodic polarity reversal micro-electric field.

[0093] IV. Anti-acidification operation under high load impact.

[0094] This was used to verify the acidification resistance of the technical solution under high-load feeding of food waste and VFA impact conditions, and to prove that it is applicable to the anaerobic resource recovery process of food waste with large feeding fluctuations in actual engineering.

[0095] Specifically, an anaerobic resource recovery system for kitchen waste is adopted, with 3 g / L of magnetically responsive bimetallic conductive microspheres added, a low-voltage micro-electric field of 0.8 V applied, and a polarity reversal cycle of 24 h.

[0096] The anaerobic resource recovery reactor was first operated stably for 10 days at an OLR of 3 g VS / L·d, and then the OLR was gradually increased to 6, 9, and 12 g VS / L·d, with each stage lasting 10 days. The control group used a conventional anaerobic reactor without the addition of microspheres or the application of a micro-electric field.

[0097] pH, VFA, methane formation rate, and system recovery time were measured at each stage.

[0098] The experimental results showed that the control group exhibited significant VFA accumulation, a pH drop below 6.0, and a significantly reduced methane formation rate after the OLR was increased to 9 g VS / L·d. When the OLR was increased to 12 g VS / L·d, the control group showed acidification instability.

[0099] The anaerobic resource recovery system for food waste in this technical solution can still maintain a pH above 7.0 and a VFA concentration below 2000 mg / L when the OLR is 9 g VS / L·d. When the OLR is briefly increased to 12 g VS / L·d, although the VFA increases, it recovers to a stable level within 5 days, and the methane generation rate does not show a continuous decline.

[0100] The results show that the anaerobic resource recovery system for food waste in this technical solution can accelerate the conversion of VFA to methane through a reconfigurable three-dimensional conductive channel, and significantly improve the resistance of the anaerobic system for food waste to high load shocks.

[0101] V. Recovery, regeneration and recycling of magnetically responsive bimetallic conductive microspheres.

[0102] This study aims to verify the magnetic recovery capability, regeneration effect, and recycling stability of magnetically responsive bimetallic conductive microspheres during long-term operation, and to solve the problem of easy loss and difficult recycling of ordinary conductive materials in anaerobic systems.

[0103] Specifically, during continuous operation, the effluent enters an external magnetic collector, where the magnetically responsive bimetallic conductive microspheres are trapped and then returned to the reactor. Every 10 days of operation, a portion of the microspheres are removed for regeneration.

[0104] The regeneration steps are as follows: first, wash with a weakly acidic buffer solution of pH 6.0 for 5 min to remove inorganic deposits on the surface; then, perform low-intensity ultrasonic treatment for 2 min to peel off excessively thick or aged biofilms; finally, purge with nitrogen and return to the reactor.

[0105] Five consecutive cycles were run, each lasting 10 days, and the magnetic recovery rate, volume resistivity retention rate, methane yield retention rate, and Fe / Co leaching concentration were measured.

[0106] Experimental results show that the magnetically responsive bimetallic conductive microspheres maintained high recovery rates and conductivity across multiple cycles. After moderate regeneration, the surface deposits of the microspheres decreased, the resistivity recovered somewhat, and the methane yield remained at a high level. The Fe and Co leaching concentrations were low and did not significantly inhibit the anaerobic system. (See Table 6.)

[0107] Table 6. Recycling, regeneration, and electron transfer performance of magnetically responsive bimetallic conductive microspheres .

[0108] The results show that the magnetically responsive bimetallic conductive microspheres of the present invention can be effectively recycled and reused, and the regeneration treatment can restore some of their conductive activity and anaerobic enhancement effect.

[0109] VI. Verification of the enhanced mechanism of direct interspecific electron transport.

[0110] The main mechanism used to verify this technical solution for improving the anaerobic methanogenesis performance of food waste is not simply adsorption, pH buffering, or trace element supplementation, but rather the promotion of direct interspecies electron transfer by constructing reconfigurable three-dimensional electron channels.

[0111] Specifically, in the comparative experiment on the synergistic enhancement effect of the anaerobic resource utilization system for kitchen waste and the control group, anaerobic sludge samples from the CK group, M group, ME group and M-PRE group were analyzed for electrochemical impedance, cyclic voltammetry, key enzyme activity, functional genes and microbial community.

[0112] The detection indicators include: charge transfer impedance, redox peak current, coenzyme F420 activity, relative abundance of mcrA gene, relative abundance of Geobacter, relative abundance of Methanosarcina, and the protein / polysaccharide ratio in extracellular polymeric substances.

[0113] Simultaneously, the biofilm structure on the surface of the magnetically responsive bimetallic conductive microspheres was observed, and the adhesion of microorganisms to the surface of the microspheres and the formation of conductive interfaces were analyzed.

[0114] The experimental results showed that, compared with the CK group, the M-PRE group had significantly lower charge transfer impedance, enhanced redox peak current, increased relative abundance of the mcrA gene, and significant enrichment of functional microorganisms related to direct interspecific electron transport, such as Geobacter and Methanosarcina.

[0115] Scanning electron microscopy revealed a continuous and dense biofilm on the surface of the M-PRE microspheres, with microbial cells in close contact with the conductive microsphere surface, exhibiting obvious interfacial adhesion and bridging structures. Electrochemical tests showed that the periodic polarity reversal micro-electric field could maintain the activity of the conductive interface of the microspheres and reduce the charge transfer resistance of the system.

[0116] This demonstrates that the anaerobic resource recovery system for food waste constructs a bulk reconfigurable electron transport network through a synergistic process of "magnetically responsive bimetallic conductive microspheres—micro-electric field-induced polarization—polarity reversal reconstruction—functional microbial enrichment," thereby promoting rapid methanation of VFA and achieving stable enhancement of the anaerobic resource recovery process for food waste.

[0117] The above experiments show that magnetically responsive bimetallic conductive microspheres can be stably prepared and have high specific surface area, good magnetic responsiveness, and low resistivity.

[0118] When the microsphere dosage is 3–5 g / L, it can significantly reduce VFA accumulation and increase methane yield at a lower material cost.

[0119] A 0.8 V, 24 h periodic polarity reversal micro electric field can effectively induce the formation of bulk reconfigurable electron channels in conductive microspheres and reduce the risk of electrode passivation.

[0120] Compared with conventional biochar, single electric field, and single magnetic response microsphere treatment, the anaerobic resource recovery system for food waste exhibits higher methane yield, lower VFA accumulation, and stronger acidification resistance.

[0121] Magnetic-responsive bimetallic conductive microspheres can be recycled and regenerated through an external magnetic trap, avoiding the problems of ordinary conductive materials being difficult to recycle and easily lost.

[0122] The enhanced effect of the anaerobic resource utilization system for food waste is closely related to the enhanced direct interspecies electron transfer, demonstrating a clear technical logic chain of "material structure - electric field regulation - microbial electron transfer - methane generation".

[0123] VII. Verify the necessity of the three-layer structure of the magnetically responsive bimetallic conductive microspheres.

[0124] This study verifies the synergistic necessity of the Fe-Co bimetallic nitrogen-doped porous carbon core, the reduced graphene oxide conductive interface layer, and the carboxyl / phosphate-containing buffer outer layer in the magnetically responsive bimetallic conductive microspheres of this invention. It proves that the material of this invention is not a simple replacement of ordinary magnetic particles, single-metal conductive materials, or conventional coated microspheres, but rather achieves a comprehensive enhancement effect of bulk electron transfer, acid resistance, ammonia nitrogen buffering, biofilm adhesion, and material recycling through the synergistic structure of "magnetically responsive core - conductive interface layer - buffer bio-affinity outer layer".

[0125] Specifically, the anaerobic resource recovery system for food waste described in this technical solution uses an anaerobic resource recovery reactor with an effective volume of 10L. Food waste, after impurity removal, crushing, oil extraction, and slurry preparation, is used as the fermentation substrate, with a total saturation (TS) adjustment of 10%. Mesophilic anaerobic digested sludge is used as the inoculation sludge, with a substrate VS:inoculation sludge VS ratio of 1:1. The reaction temperature is controlled at 35±1 ℃, the stirring rate is 120 rpm, the dosage of magnetically responsive conductive material is 3 g / L, the micro-electric field voltage is 0.8 V, the polarity reversal cycle is 24 h, and the system operates continuously for 30 days.

[0126] To compare the contribution of different structural units to the enhancement of anaerobic digestion, the following treatment groups were set up: CK group: No conductive material is added, and no micro-electric field is applied.

[0127] Group C-1: Fe monometallic nitrogen-doped porous carbon microspheres were added, coated with a reduced graphene oxide layer and a buffering outer layer.

[0128] Group C-2: Co monometallic nitrogen-doped porous carbon microspheres were added, coated with a reduced graphene oxide layer and a buffering outer layer.

[0129] Group C-3: Fe-Co bimetallic nitrogen-doped porous carbon microspheres and a buffer outer layer were added, but the reduced graphene oxide conductive interface layer was not set.

[0130] Group C-4: Fe-Co bimetallic nitrogen-doped porous carbon core and reduced graphene oxide conductive interface layer are added, but no outer layer containing carboxyl / phosphate buffer function is set.

[0131] Group C-5: Fe-Co bimetallic nitrogen-doped porous carbon core, reduced graphene oxide conductive interface layer and inert alginate outer layer are added, but the outer layer does not contain carboxyl / phosphate functional components.

[0132] MBC group: Add the complete three-layer structure magnetically responsive bimetallic conductive microspheres of this invention, namely Fe-Co bimetallic nitrogen-doped porous carbon core, reduced graphene oxide conductive interface layer, and carboxyl / phosphate buffer outer layer.

[0133] During operation, the highest VFA concentration, lowest pH, cumulative methane yield, methane content, charge transfer impedance, microsphere magnetic recovery rate, ammonium nitrogen adsorption capacity, and surface biofilm adhesion were measured. After operation, microsphere samples were taken for scanning electron microscopy observation, and electrochemical impedance spectroscopy was used to evaluate the electron transport capacity of the material surface.

[0134] Experimental results show that materials with different structural deficiencies all exhibited certain anaerobic digestion enhancement effects, but their effects were significantly lower than those of the intact three-layer magnetically responsive bimetallic conductive microspheres. Fe monometallic microspheres possessed good magnetic responsiveness and certain conductivity, but lacked Co-related active sites, resulting in insufficient promotion of methanogenesis metabolism. Co monometallic microspheres could provide some trace element effects, but their magnetic responsiveness and structural stability were weak, leading to decreased material recovery efficiency. The absence of the reduced graphene oxide conductive interface layer increased the electron transfer impedance between microspheres and reduced the bulk conductive bridging ability. The lack of a buffering outer layer exacerbated pH fluctuations and reduced ammonia nitrogen buffering and biofilm adhesion. While the inert outer layer could maintain the microsphere morphology, its lack of functional groups such as carboxyl and phosphate groups limited its promotion of ammonium nitrogen adsorption, pH buffering, and microbial adhesion.

[0135] The complete three-layer MBC group exhibited the lowest VFA accumulation, highest pH stability, highest methane yield, lowest charge transfer impedance, and highest material recovery rate, indicating a significant synergistic effect among the Fe-Co bimetallic nitrogen-doped porous carbon core, the reduced graphene oxide conductive interface layer, and the carboxyl / phosphate-containing buffer outer layer, as shown in Table 7.

[0136] Table 7. Effect of the absence of the three-layer structure in magnetically responsive bimetallic conductive microspheres on the enhanced effect of anaerobic digestion. .

[0137] As shown in Table 7, the cumulative methane yield of the complete three-layer MBC group reached 478 mL / g VS, significantly higher than that of the groups lacking any of the structures. Compared with the C-3 group lacking the rGO conductive interface layer, the charge transfer impedance of the MBC group decreased from 73 Ω to 42 Ω, indicating that the reduced graphene oxide conductive interface layer can effectively reduce the electron transfer resistance between microspheres and between microspheres and the biofilm. Compared with the C-4 group lacking the buffering outer layer, the minimum pH of the MBC group increased from 6.4 to 7.1, and the maximum VFA concentration decreased from 2450 mg / L to 1180 mg / L, indicating that the carboxyl / phosphate buffering outer layer can alleviate local acidification and improve the system's shock resistance.

[0138] Although Fe monometallic group C-1 exhibits a high magnetic recovery rate, its methane yield is lower than that of the MBC group, indicating that the Co active site promotes methanogenesis. Co monometallic group C-2 shows lower methane yield and magnetic recovery rate than the MBC group, suggesting that the Fe component not only provides magnetic response and recovery capability but also participates in the construction of iron-based electron transport active sites. While group C-5, with its inert outer layer, has a lower charge transfer impedance, its VFA control and pH stability are weaker than those of the MBC group, indicating that the outer functional groups are not simply spherical structures but participate in ammonium nitrogen adsorption, pH buffering, and microbial attachment processes.

[0139] The above results demonstrate that the three-layer structure of the magnetically responsive bimetallic conductive microspheres used in this technical solution has a clear division of labor and synergistic effect: the Fe-Co bimetallic nitrogen-doped porous carbon core mainly provides magnetic responsiveness, bimetallic active sites, and the basis for electron transport; the reduced graphene oxide conductive interface layer mainly reduces electron transport impedance and enhances conductive bridging between microspheres; and the carboxyl / phosphate buffer outer layer mainly improves pH stability, ammonium nitrogen adsorption capacity, and microbial adhesion capacity. The combined effect of these three elements enables the material to form a stable, reconfigurable, and recyclable bulk electron transport network in a periodically polarity-reversing micro-electric field, thereby significantly improving the anaerobic resource recovery efficiency of food waste.

[0140] The above embodiments are merely illustrative of the structural concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing magnetically responsive bimetallic conductive microspheres, characterized in that, Includes the following steps: Step 1: After drying and pulverizing agricultural waste, kitchen waste sludge or residual sludge, mix it with iron salt, cobalt salt and nitrogen-containing ligand to obtain a bimetallic supported precursor; Step 2: The bimetallic supported precursor is subjected to oxygen-limited thermal conversion in a nitrogen, argon or nitrogen-hydrogen mixed atmosphere to obtain Fe-Co bimetallic nitrogen-doped porous carbon material; Step 3: Mix the Fe-Co bimetallic nitrogen-doped porous carbon material with graphene oxide dispersion, sodium alginate solution and buffering components to form a composite suspension; Step 4: Add the composite suspension dropwise into a cross-linking curing liquid containing calcium ions, magnesium ions, or iron ions to form composite gel microspheres; Step 5: After drying, the composite gel microspheres are subjected to low-temperature reduction heat treatment at 250 to 450 °C to obtain magnetically responsive bimetallic conductive microspheres.

2. The method for preparing magnetically responsive bimetallic conductive microspheres according to claim 1, characterized in that, The iron salt is one or more of ferric chloride, ferric nitrate, ferrous sulfate, or ferric acetylacetonate; the cobalt salt is one or more of cobalt chloride, cobalt nitrate, cobalt acetate, or cobalt acetylacetonate; and the nitrogen-containing ligand is one or more of urea, melamine, chitosan, dopamine, ethylenediaminetetraacetic acid, or imidazole compounds.

3. The method for preparing magnetically responsive bimetallic conductive microspheres according to claim 2, characterized in that, The magnetically responsive bimetallic conductive microsphere comprises, from the inside out: Fe-Co bimetallic nitrogen-doped porous carbon core: formed through oxygen-limited thermal conversion. Fe is used to construct magnetic response components, iron-based electron transfer sites and iron-sulfur protein-related trace element supply. Co is used to supplement the trace elements required by cobalamin-related enzyme systems, promote methyl transfer and methanogenesis metabolism. Fe and Co form Fe-Nx, Co-Nx and Fe-Co composite active sites in the nitrogen-containing carbon skeleton. Reduced graphene oxide conductive interface layer: used to connect the porous carbon core and the outer biofilm, reduce the electron transfer impedance inside and between microspheres, and the sheet structure increases the surface roughness of microspheres, providing an interface for anaerobic microorganisms to attach; The outer layer, containing carboxyl, hydroxyl, and phosphate groups, forms a buffering function: the outer biofilm is formed by cross-linking alginate, carboxylated polysaccharides, phytates, phosphates, or weakly basic mineral components. It has the ability to adsorb ammonium nitrogen, buffer pH, and complex metal ions, thus buffering the local acidification environment and reducing the instantaneous impact of free ammonia on methanogens.

4. The method for preparing magnetically responsive bimetallic conductive microspheres according to claim 3, characterized in that, In the Fe-Co bimetallic nitrogen-doped porous carbon core, the molar ratio of Fe to Co is 2:1-8:1, the particle size of the magnetically responsive bimetallic conductive microspheres is 0.3-3.0 mm, the saturation magnetization is 8-45 emu / g, and the volume resistivity is less than 100 Ω·cm.

5. A system for the anaerobic resource recovery of kitchen waste based on magnetically responsive bimetallic conductive microspheres, characterized in that, include: Food waste pretreatment unit: used to remove impurities, crush, slurry and extract oil from food waste, so that food waste is formed into a homogeneous substrate suitable for anaerobic digestion; Anaerobic resource recovery reactor: It is equipped with multiple sets of staggered inert mesh anodes and inert mesh cathodes, and disperses magnetically responsive bimetallic conductive microspheres obtained by the preparation method of magnetically responsive bimetallic conductive microspheres as described in any one of claims 1-4, for use in the anaerobic hydrolysis, acidification, acetic acid production and methanogenesis processes of kitchen waste. Periodic polarity reversal micro electric field unit: connected to the inert mesh anode and inert mesh cathode, it consists of a DC low-voltage power supply, a polarity reversal controller, a current density regulator and a mesh electrode array. It is used to control the interfacial polarization of magnetically responsive bimetallic conductive microspheres in the anaerobic resource recovery reactor under the action of a low-voltage micro electric field. The microspheres are arranged in a short-range orientation, forming a conductive chain structure dispersed in the reactor bulk phase. The magnetically responsive conductive microsphere recycling unit consists of an external magnetic trap, a return pipeline, and a regeneration device. The external magnetic trap is installed at one or more locations on the discharge pipeline, the circulation pipeline, or the outer wall of the reactor. It is used to intercept the magnetically responsive bimetallic conductive microspheres in the effluent and return them to the anaerobic resource recovery reactor. Process feedback control unit: including pH, ORP, conductivity, biogas flow rate, methane content and VFA concentration detection modules, dynamically adjusts micro electric field voltage, polarity reversal period, magnetic response bimetallic conductive microsphere reflux ratio and stirring intensity according to the reaction state.

6. The anaerobic resource recovery system for kitchen waste based on magnetically responsive bimetallic conductive microspheres according to claim 5, characterized in that: The inert mesh anode is a titanium-based iridium-tantalum oxide coated electrode, a titanium-based ruthenium-iridium oxide coated electrode, or a graphite felt electrode, and the inert mesh cathode is a stainless steel mesh, carbon felt, graphite plate, or titanium mesh. The distance between the inert mesh anode and the inert mesh cathode is 2 to 15 cm.

7. The anaerobic resource recovery system for kitchen waste based on magnetically responsive bimetallic conductive microspheres according to claim 6, characterized in that: The periodic polarity reversal micro-electric field unit applies a voltage of 0.3 to 1.2 V and a current density of 0.02 to 1.50 A / m. 2 The polarity reversal cycle is 6 to 72 hours, and a power-off buffer phase of 0.5 to 10 minutes is set before each polarity reversal.

8. A method for anaerobic resource recovery of food waste based on the anaerobic resource recovery system for food waste as described in any one of claims 5-7, characterized in that, Includes the following steps: Step 1: After removing impurities, crushing, slurrying and oil extraction from the kitchen waste, adjust the total solids content to 6% to 15% to obtain the kitchen waste fermentation substrate; Step 2: Pump the fermentation substrate of the kitchen waste into the anaerobic resource recovery reactor and inoculate it with anaerobic granular sludge, digested sludge or methanogenic enrichment sludge; Step 3: Add magnetically responsive bimetallic conductive microspheres to the anaerobic resource recovery reactor at a dosage of 1 to 8 g / L; Step 4: Activate the periodic polarity reversal micro-electric field unit, apply a low-voltage micro-electric field of 0.3 to 1.2 V, and perform polarity reversal according to a period of 6 to 72 h; Step 5: During the anaerobic fermentation process, the magnetically responsive bimetallic conductive microspheres form a reconstructed three-dimensional conductive chain structure under the action of a micro-electric field, which promotes direct interspecies electron transfer among acid-producing bacteria, syntrophic oxidizing bacteria and methanogenic bacteria, and enables volatile fatty acids to be rapidly converted into methane. Step 6: Before the fermentation broth is discharged, the magnetically responsive bimetallic conductive microspheres are retained by the magnetically responsive conductive microsphere recycling unit and returned to the anaerobic resource recovery reactor.

9. The anaerobic resource utilization method for kitchen waste according to claim 8, characterized in that: When the pH in the anaerobic resource recovery reactor is below 6.8 or the concentration of volatile fatty acids is above 2000 mg / L, the process feedback control unit increases the micro-electric field voltage to 0.8 to 1.2 V and shortens the polarity reversal cycle to 6 to 24 h. When the methane production rate is stable and the pH is maintained at 7.0 to 7.8, the micro-electric field voltage is reduced to 0.3 to 0.8 V to reduce energy consumption and maintain stable methane production.

10. The anaerobic resource utilization method for kitchen waste according to claim 8, characterized in that: After 5 to 20 cycles of use, the magnetically responsive bimetallic conductive microspheres are regenerated by a combination of one or more of the following methods: weak acid washing, low-intensity ultrasonic cleaning, nitrogen purging, or low-temperature reduction treatment.

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