A flow electrode slurry, a preparation method thereof and an ammonium ion enrichment recovery method

Abstract

This application discloses a flow electrode slurry and its preparation method, as well as a method for enriching and recovering ammonium ions, relating to the field of flow electrode preparation technology. The slurry includes biochar and a supporting electrolyte solution. The biochar is obtained by cultivating aquatic plants in ammonia-nitrogen-containing wastewater to obtain biomass and then pyrolyzing the biomass. The surface of the biochar contains nitrogen- and / or oxygen-containing functional groups. The solid content of the flow electrode slurry is 1-10 wt%. This application effectively recovers NH4+ from ammonia-nitrogen-containing wastewater. + Selective recycling.

Description

Technical Field

[0001] This application relates to the field of flow electrode preparation technology, and in particular to a flow electrode slurry and its preparation method, and a method for enriching and recovering ammonium ions. Background Technology

[0002] The harmless treatment and resource utilization of ammonia-nitrogen-containing wastewater (such as biogas slurry, livestock and poultry breeding wastewater, and landfill leachate) is an important issue in the current environmental field. Taking biogas slurry as an example, as a byproduct of anaerobic digestion, it contains a high concentration of ammonium ions (NH4+). + Direct discharge of ammonia nitrogen wastewater not only causes serious environmental problems such as eutrophication but also wastes nitrogen resources that could be used as fertilizer. Therefore, the efficient separation and recovery of ammonium ions from ammonia nitrogen wastewater, turning waste into treasure, has dual significance for environmental protection and resource recycling.

[0003] Currently, methods for removing or recovering ammonia nitrogen from wastewater mainly include air stripping, chemical precipitation, ion exchange, biological denitrification, and electrochemical methods (such as capacitive deionization). However, these methods generally have limitations in removing NH4+. + A common drawback is low selectivity. For example, traditional capacitive deionization technology often uses fixed electrodes, which lack specificity for ion adsorption; while mobile electrode capacitive deionization can achieve continuous operation, commonly used commercial activated carbon mobile electrode materials have limited surface functional groups, particularly in Na+. + K + Under the competition of coexisting cations, for NH4 + The insufficient preferential adsorption capacity leads to a high content of impurity ions in the recovered product.

[0004] The above content is only used to help understand the technical solution of this application and does not represent an admission that the above content is prior art. Summary of the Invention

[0005] The main objective of this application is to provide a flow electrode slurry and its preparation method, as well as a method for enriching and recovering ammonium ions, to effectively recover NH4+ from ammonia-containing wastewater. + Selective recycling.

[0006] To achieve the above objectives, this application proposes a flow electrode slurry, the flow electrode slurry comprising: Biochar and supporting electrolyte solution, wherein the biochar is obtained by culturing aquatic plants in ammonia nitrogen-containing wastewater to obtain biomass and then pyrolyzing the biomass, the surface of the biochar contains nitrogen-containing and / or oxygen-containing functional groups, and the solid content of the flowing electrode slurry is 1~10 wt%.

[0007] In one embodiment, the ammonia-nitrogen-containing wastewater includes at least one of anaerobic digestion liquid, livestock and poultry breeding wastewater, landfill leachate, fermentation wastewater, and ammonium-containing agricultural tailwater.

[0008] In one embodiment, the aquatic plant includes at least one of water hyacinth, duckweed, reeds, and algae.

[0009] In one embodiment, the supporting electrolyte solution includes at least one of Na2SO4 solution, K2SO4 solution, NaCl solution, and KCl solution.

[0010] To achieve the above objectives, this application proposes a method for preparing a flow electrode slurry. The method comprises the following steps: Provide aquatic plants; The aquatic plants were cultured in wastewater containing ammonia nitrogen for 3-14 days to obtain biomass; The biomass is pyrolyzed to obtain biochar; The biochar was mixed with a supporting electrolyte solution to obtain a flow electrode slurry.

[0011] In one embodiment, the ammonium ion concentration of the ammonia nitrogen-containing wastewater is less than or equal to 1500 mg / L.

[0012] In one embodiment, the pyrolysis conditions include: a pyrolysis temperature of 500~900℃, a holding time of 0.5~4 h, and a heating rate of 2~20℃ / min.

[0013] In one embodiment, after the step of pyrolyzing the biomass to obtain biochar, the method further includes: The biochar is modified by at least one of heteroatom doping, metal oxide loading, physical activation, chemical activation, and surface oxidation modification.

[0014] Furthermore, to achieve the above objectives, this application proposes a method for enriching and recovering ammonium ions, comprising the following steps: The flow electrode slurry is placed in a flow electrode capacitor deionization device, and the liquid to be recovered is introduced into the processing liquid channel of the flow electrode capacitor deionization device for adsorption. The flow electrode slurry is the flow electrode slurry as described in any one of claims 1 to 4, or is prepared by the method as described in any one of claims 5 to 8. The ammonium ion concentration of the liquid to be recovered is 100~2000 mg / L. The adsorbed liquid to be recovered is passed out through the treatment liquid channel, and an acidic desorption solution is introduced for desorption. An ammonium ion enrichment solution is obtained by performing multiple cycles of adsorption and desorption, wherein the acidic desorption solution is replaced every 2 to 4 cycles.

[0015] In one embodiment, the conditions for the multiple cycles of adsorption and desorption include at least one of the following: The volume of the flowing electrode slurry is 40~150 mL / side, and the flow rate of the flowing electrode slurry is 1~20 mL / min; The volume of the liquid to be recovered is 100~1000 mL, and the flow rate of the liquid to be recovered is 1~20 mL / min; The adsorption voltage is +0.6 to +1.4 V, and the adsorption time is 20 to 120 min. The desorption voltage is -0.3 to -1.2 V, and the desorption time is 10 to 90 min.

[0016] One or more technical solutions proposed in this application have at least the following technical effects: A flowing electrode slurry is provided, comprising: biochar and a supporting electrolyte solution, wherein the biochar is obtained by cultivating aquatic plants in ammonia-nitrogen-containing wastewater to obtain biomass and then pyrolyzing the biomass; the surface of the biochar contains nitrogen- and / or oxygen-containing functional groups, which can react with ammonium ions (NH4+) in the wastewater. + The formation of hydrogen bonds or electrostatic interactions, along with the defective structure and suitable pore size distribution of biochar, enhances its resistance to NH4+. + Size matching and interfacial affinity. When this biochar is used in a flow electrode, its surface properties endow the electrode material with affinity for NH4. + The biochar exhibits superior recognition and adsorption capabilities. Furthermore, the addition of a supporting electrolyte solution effectively enhances the conductivity of the flow electrode slurry, reduces internal electrode resistance, and promotes rapid ion migration under the influence of an electric field, thereby ensuring the efficient and stable operation of the entire electrochemical enrichment process. Through the synergistic effect of the selective interface provided by the biochar and the favorable electrochemical environment provided by the supporting electrolyte solution, this flow electrode slurry, when applied to a membrane flow electrode capacitive deionization system, can achieve highly efficient and selective enrichment and recovery of ammonium ions in complex wastewater matrices. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of the method for preparing the flow electrode slurry according to an embodiment of this application; Figure 2 This is a schematic diagram illustrating a method for preparing the flow electrode slurry according to an embodiment of this application. Figure 3 This is a schematic diagram illustrating a scenario of the ammonium ion enrichment and recovery method according to an embodiment of this application. Figure 4 This is a desorption It curve diagram of the ammonium ion enrichment and recovery method in the embodiments of this application; Figure 5 The results of 15 adsorption and desorption cycles of the flowing electrode slurry in the embodiments of this application. Figure 1 ; Figure 6 The results of 15 adsorption and desorption cycles of the flowing electrode slurry in the embodiments of this application. Figure 2 ; Figure 7 The results of 15 adsorption and desorption cycles of the flowing electrode slurry in the embodiments of this application. Figure 3 ; Figure 8 This is a graph showing the sweep rate capacitance analysis results of the flowing electrode slurry in an embodiment of this application; Figure 9 This is a graph showing the XPS analysis results of the flow electrode slurry in an embodiment of this application; Figure 10 This is a graph showing the FTIR analysis results of the flowing electrode slurry in an embodiment of this application; Figure 11 The results of 36 adsorption and desorption cycles of the flowing electrode slurry in the embodiments of this application. Figure 1 ; Figure 12 The results of 36 adsorption and desorption cycles of the flowing electrode slurry in the embodiments of this application. Figure 2 ; Figure 13 The results of 36 adsorption and desorption cycles of the flowing electrode slurry in the embodiments of this application. Figure 3 .

[0020] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0022] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the flow electrode slurry and its preparation method, as well as the ammonium ion enrichment and recovery method of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0023] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0024] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0025] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0026] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0027] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0028] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0029] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the technical solution of this application is further described below in conjunction with the accompanying drawings and embodiments. However, this application is not limited to the listed embodiments, but should also include any other well-known modifications within the scope of the claims made in this application.

[0030] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0031] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0032] Current methods for ammonia nitrogen removal or recovery mainly include stripping absorption, chemical precipitation, ion exchange, adsorption, biological denitrification, electrochemical separation, and capacitive deionization. Among these, stripping absorption requires pH adjustment, aeration, or heating, resulting in high energy and chemical consumption, and limited adaptability to low-to-medium concentrations or complex water bodies. Chemical precipitation or ion exchange methods may generate secondary solid waste or regenerated liquid, and their selectivity and regeneration stability are affected by coexisting ions. Ordinary activated carbon or conventional porous carbon materials primarily rely on electro-bilayer adsorption, which is less effective for ammonium ions (NH4+). + The interface affinity of ) is limited, in Na + When coexisting cations are present, non-selectivity is easily exhibited; traditional capacitive deionization electrodes are mostly fixed electrodes, which are prone to problems such as insufficient electrode regeneration, limited flux, salt accumulation, and reduced electrode life during long-term operation; in membrane flow electrode capacitive deionization (mFCDI) technology, commercial activated carbon is often used as the flow electrode, which is difficult to balance the resource utilization of waste biomass, the selectivity of complex matrices in wastewater, and high concentrations of NH4. + Product liquid output.

[0033] This application provides a solution for a flowing electrode slurry, comprising: biochar and a supporting electrolyte solution, wherein the biochar is obtained by cultivating aquatic plants in ammonia-nitrogen-containing wastewater to obtain biomass and then pyrolyzing the biomass; the surface of the biochar contains nitrogen- and / or oxygen-containing functional groups, which can react with ammonium ions (NH4+) in the wastewater. + The formation of hydrogen bonds or electrostatic interactions, along with the defective structure and suitable pore size distribution of biochar, enhances its resistance to NH4+. + Size matching and interfacial affinity. When this biochar is used in a flow electrode, its surface properties endow the electrode material with affinity for NH4. + The biochar exhibits superior recognition and adsorption capabilities. Furthermore, the addition of a supporting electrolyte solution effectively enhances the conductivity of the flow electrode slurry, reduces internal electrode resistance, and promotes rapid ion migration under the influence of an electric field, thereby ensuring the efficient and stable operation of the entire electrochemical enrichment process. Through the synergistic effect of the selective interface provided by the biochar and the favorable electrochemical environment provided by the supporting electrolyte solution, this flow electrode slurry, when applied to a membrane flow electrode capacitive deionization system, can achieve highly efficient and selective enrichment and recovery of ammonium ions in complex wastewater matrices.

[0034] Based on this, the first aspect of the present application provides a flowable electrode slurry, comprising: Biochar and supporting electrolyte solution, wherein the biochar is obtained by culturing aquatic plants in ammonia nitrogen-containing wastewater to obtain biomass and then pyrolyzing the biomass, the surface of the biochar contains nitrogen-containing and / or oxygen-containing functional groups, and the solid content of the flow electrode slurry is 1~10 wt%.

[0035] During the aforementioned cultivation process, aquatic plants absorb nutrients such as nitrogen from wastewater, enriching their biomass with nitrogen- and oxygen-containing functional group precursors. Upon pyrolysis of this biomass, these functional groups are retained or transformed, forming abundant nitrogen-containing (e.g., pyridine nitrogen, pyrrole nitrogen, graphitic nitrogen) and oxygen-containing (e.g., carboxyl, hydroxyl, carbonyl) polar groups on the biochar surface. These functional groups can react with the target ion—ammonium ions (NH4+). + This allows for the formation of hydrogen bonds or enhanced electrostatic interactions. Simultaneously, the biochar possesses a defect structure and suitable pore size distribution determined by the pyrolysis process, which further enhances its ability to bind to NH4+ with smaller hydration radii. + Size-matching effect and interfacial affinity. When this specific biochar is used in a flow electrode, its unique surface chemistry endows the electrode material with NH4+. + The biochar provides a selective interface and a favorable electrochemical environment, enabling the biochar slurry to effectively improve conductivity, reduce internal resistance, and promote rapid ion migration under an electric field, thus ensuring efficient and stable operation of the entire electrochemical enrichment process. Through the synergistic effect of the selective interface provided by the biochar and the favorable electrochemical environment provided by the supporting electrolyte solution, this biochar slurry, when applied to a membrane flow electrode capacitive deionization (mFCDI) device, can effectively capture ions in the presence of Na+. + K + In complex wastewater matrices containing multiple coexisting ions, NH4+ can be controlled. + The efficient and selective enrichment and recovery of NH4 overcomes the current limitations of NH4. + NH4 recycling method + The defect of insufficient selectivity.

[0036] Controlling the solid content within the range of 1–10 wt% balances the electroadsorption capacity of the flowing electrode and the hydrodynamic properties of the slurry. If the solid content is too low (below 1 wt%), there is insufficient effective electrode material in the slurry, leading to a decrease in the system's adsorption capacity per unit volume and reduced processing efficiency. If the solid content is too high (above 10 wt%), the slurry viscosity increases sharply, its fluidity deteriorates, and it is prone to sedimentation or blockage in pipelines and channels, increasing the load on the circulating pump and the instability of system operation. It may even increase the risk of electrical short circuits due to excessively close particle contact.

[0037] Optionally, the solid content of the flowing electrode slurry can be: 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, etc.

[0038] In one feasible embodiment, the ammonia nitrogen-containing wastewater includes at least one of anaerobic digestion liquid, livestock and poultry breeding wastewater, landfill leachate, fermentation wastewater, and ammonium-containing agricultural tailwater.

[0039] Anaerobic digestion fluids (such as biogas slurry) typically contain high concentrations of NH4. + The wastewater also contains Na + K + Ca 2+ The presence of multiple coexisting ions and organic compounds is a key indicator for testing NH4+. + Selective ideal substrates. Livestock and poultry farming wastewater has a composition similar to biogas slurry, with high nitrogen and phosphorus content. Landfill leachate is a highly complex, high-concentration organic wastewater with extremely high ammonia nitrogen concentration. Fermentation wastewater (such as kitchen waste fermentation liquid) is also rich in ammonium ions. Ammonium-containing agricultural wastewater mainly originates from farmland runoff, with relatively low ammonia nitrogen concentration but large volume. All of the above wastewater types share a common characteristic: they contain NH4+. + And interfering ions, using them as a medium for cultivating aquatic plants such as water hyacinth, can achieve primary water purification through plant absorption, and also allow the plants to naturally adapt to and accumulate NH4+ during their growth. + Interacting functional groups enable the final biochar to react with NH4+. + It has stronger recognition capabilities.

[0040] It should be noted that the wastewater source in this application is not limited to this. Any ammonia nitrogen-containing wastewater that can support the growth of aquatic plants and enrich them with relevant functional groups can be used. The embodiments of this application do not limit this.

[0041] In one feasible embodiment, the aquatic plants include at least one of water hyacinth, duckweed, reeds, and algae.

[0042] Water hyacinth (Eichhornia crassipes) is a typical large aquatic plant characterized by its large biomass, rapid growth rate, strong adaptability to the environment, and outstanding nitrogen and phosphorus absorption capacity. Duckweed is small, reproduces rapidly, is rich in protein, and its surface also has abundant functional groups. Reeds are common emergent plants with well-developed root systems and high biomass yield; their stems easily form porous carbon structures after pyrolysis. Algae (such as Chlorella and Spirulina) have extremely high nitrogen affinity and surface active sites. All of these aquatic plants share a common characteristic: when growing in nitrogen-rich environments, they accumulate nitrogen-containing compounds (such as proteins and amino acids) and form oxygen-containing functional groups, which are essential for producing high NH4+. + Ideal precursors for selective biochar. Using them as raw materials can achieve high-value utilization of waste biomass (such as waste generated from water hyacinth control) and obtain flow electrode materials with performance far exceeding that of ordinary commercial activated carbon.

[0043] In one feasible embodiment, the supporting electrolyte solution includes at least one of Na2SO4 solution, K2SO4 solution, NaCl solution, and KCl solution.

[0044] The main function of the supporting electrolyte is to increase the ionic strength of the flowing electrode slurry, reduce the solution resistance, and thus improve charge transport efficiency, allowing the electric field energy to act more effectively on the migration of charged ions. Its concentration can be 10–100 mM. Na₂SO₄ is an inert electrolyte, and its anion SO₄²⁻ 2- It is less prone to redox side reactions at the electrodes, ensuring the electrochemical stability of the system. K2SO4 has similar properties to Na2SO4. NaCl and KCl have higher ionic conductivity and lower cost, but their Cl- content is lower. - Ions may undergo side reactions at certain high potentials, so the potential window must be considered during use. The most suitable type and concentration of supporting electrolyte can be selected based on the operating voltage of the actual flow electrode capacitive deionization device, the characteristics of the biochar material, and cost considerations. The selection of the supporting electrolyte needs to be coordinated with the biochar material to jointly construct a low-internal-resistance, high-stability flow electrode system, which is the foundation for achieving continuous and efficient electroadsorption / desorption.

[0045] For example, a 30 mM Na2SO4 solution is used as the supporting electrolyte solution.

[0046] In this embodiment, a flow electrode slurry is provided, comprising: biochar and a supporting electrolyte solution, wherein the biochar is obtained by cultivating aquatic plants in ammonia-nitrogen-containing wastewater to obtain biomass and then pyrolyzing the biomass; the surface of the biochar contains nitrogen- and / or oxygen-containing functional groups, which can react with ammonium ions (NH4+) in the wastewater. + The formation of hydrogen bonds or electrostatic interactions, along with the defective structure and suitable pore size distribution of biochar, enhances its resistance to NH4+. + Size matching and interfacial affinity. When this biochar is used in a flow electrode, its surface properties endow the electrode material with affinity for NH4. + The biochar exhibits superior recognition and adsorption capabilities. Furthermore, the addition of a supporting electrolyte solution effectively enhances the conductivity of the flow electrode slurry, reduces internal electrode resistance, and promotes rapid ion migration under the influence of an electric field, thereby ensuring the efficient and stable operation of the entire electrochemical enrichment process. Through the synergistic effect of the selective interface provided by the biochar and the favorable electrochemical environment provided by the supporting electrolyte solution, this flow electrode slurry, when applied to a membrane flow electrode capacitive deionization system, can achieve highly efficient and selective enrichment and recovery of ammonium ions in complex wastewater matrices.

[0047] A second aspect of this application provides a method for preparing a flow electrode slurry. This method is used to prepare the flow electrode slurry as described above. (Refer to...) Figure 1 This includes the following steps: Step S10: Provide aquatic plants; Step S20: The aquatic plant is placed in wastewater containing ammonia nitrogen and cultured for 3-14 days to obtain biomass; Cultivating aquatic plants in wastewater containing ammonia nitrogen aims to utilize the plants' natural absorption and metabolism during growth to enrich their bodies with nutrients such as nitrogen from the wastewater. This process not only provides some primary purification of the wastewater, but more importantly, it allows for the pre-formation of NH4+ in the plant biomass. + Nitrogen- and oxygen-containing functional group precursors with close interactions lay the material foundation for the subsequent preparation of highly selective biochar. If the cultivation time is too short (less than 3 days), the aquatic plants will not absorb nitrogen sufficiently, resulting in limited biomass growth and insufficient enrichment of functional groups within the plants, ultimately affecting the selective adsorption performance of the biochar. If the cultivation time is too long (more than 14 days), the plants may enter a period of growth decline, and some of the absorbed nitrogen may be released back into the water, leading to a decrease in biomass quality. Furthermore, the excessively long process cycle is not conducive to practical application.

[0048] In one feasible embodiment, after the culture is completed, the culture medium is allowed to stand for 30-60 minutes and then filtered through a 0.22-1.0 μm microporous membrane. The resulting culture supernatant contains residual NH4. + And Na + K + The coexisting ions have stable composition and are derived from the same source as the biochar material. They can be directly used as the feed liquid for the subsequent flow electrode capacitive deionization device, achieving a high degree of matching between the culture wastewater and the treatment object. This is beneficial for the subsequent flow electrode capacitive deionization device to maintain selectivity under low background salinity.

[0049] It should be noted that NH4 is subsequently recovered from the negative electrode using a flow electrode capacitor deionization device. + In this case, the above-mentioned culture supernatant can be selected as the feed liquid of the device, or pretreated wastewater containing ammonia nitrogen can be selected as the feed liquid, as long as it meets the water quality requirements of the flow electrode capacitor deionization device. This application embodiment does not limit this.

[0050] Optionally, the cultivation time can be: 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days, 10 days, 11 days, 12 days, 13 days, 14 days, etc.

[0051] Step S30: The biomass is pyrolyzed to obtain biochar; After cultivation and harvesting, biomass needs to be washed to remove surface deposits, dried to reduce moisture content, and pulverized to increase heating uniformity before being placed in an inert atmosphere (such as nitrogen or argon) or under oxygen-limited conditions for pyrolysis. Pyrolysis, conducted in an anaerobic or low-oxygen environment, involves the high-temperature degradation of biomass macromolecular structures (such as cellulose, hemicellulose, and lignin), causing cracking, rearrangement, and carbonization, ultimately forming a carbon-rich solid product—biochar—with a well-developed porous structure, high specific surface area, and specific surface chemical properties. This process effectively retains and transforms precursor functional groups accumulated by the plant during cultivation, forming nitrogen-containing (such as pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen) and oxygen-containing (such as carboxyl, hydroxyl, and carbonyl groups) groups on the biochar surface that interact with NH4+. + It has polar sites with affinity, and at the same time constructs microporous and mesoporous structures that are conducive to ion transport and storage.

[0052] It should be noted that, in order to adapt to the stable circulation of the flowing electrode slurry, the biochar can be further subjected to grinding, sieving, acid washing or water washing, drying and other steps to control particle size, ash content, pore structure and surface functional groups. The embodiments of this application do not limit this.

[0053] Step S40: Mix the biochar with the supporting electrolyte solution to obtain a flow electrode slurry.

[0054] The purpose of mixing is to uniformly disperse solid biochar particles in a liquid supporting electrolyte solution, forming a flowable suspension, i.e., a flowing electrode slurry. To ensure the slurry's flowability and electrical contact stability, the mixing process can employ various methods, such as magnetic stirring, mechanical stirring, ultrasonic dispersion, or pre-circulation dispersion using a circulating pump. These methods effectively break up the agglomeration of biochar particles, enabling them to achieve a uniform and stable dispersion in the solution.

[0055] In one feasible embodiment, the ammonium ion concentration of the ammonia nitrogen-containing wastewater is less than or equal to 1500 mg / L.

[0056] NH4 in raw ammonia nitrogen-containing wastewater (such as biogas slurry) + The concentration may be very high, and direct use in cultivating aquatic plants could cause stress effects and affect plant growth. Therefore, it usually needs to be diluted, with a dilution ratio of 2 to 100 times, to reduce the NH4 content in the wastewater used for cultivation. + The concentration is at a level suitable for plant growth. When dilution is insufficient (e.g., undiluted raw biogas slurry, initial NH4+...), the concentration is low. + At a concentration of approximately 3271 mg / L, excessively high ammonia nitrogen concentrations can inhibit or even toxicize aquatic plants. Within 7 days of cultivation, NH4+... + Although the net absorption reached approximately 446 mg, obvious plant mortality occurred; when excessive dilution occurred (e.g., biogas slurry diluted more than 100 times, initial NH4+...) +When the concentration was approximately 37 mg / L, the ammonia nitrogen matrix concentration was too low, and the net absorption after 7 days of culture was only about 33 mg, which had no obvious application value.

[0057] In one feasible embodiment, the pyrolysis conditions include: pyrolysis temperature of 500~900 ℃, holding time of 0.5~4 h, and heating rate of 2~20 ℃ / min.

[0058] Pyrolysis temperature is a crucial parameter affecting the physicochemical properties of biochar. If the temperature is too low (below 500 ℃), biomass carbonization is incomplete, resulting in insufficient specific surface area and pore volume development, and a large amount of tar-like substances clogging the pores. If the temperature is too high (above 900 ℃), although the degree of graphitization may increase, a large number of oxygen- and nitrogen-containing active functional groups on the surface will decompose and disappear, thus reducing the resistance to NH4+. + The chemical affinity and selectivity decrease. The holding time (i.e., the duration of maintaining the peak pyrolysis temperature) is set to 0.5–4 hours. If the time is too short, the pyrolysis reaction will be incomplete; if the time is too long, energy consumption will increase and may lead to pore structure collapse. The heating rate is set to 2–20 °C / min. If the heating rate is too slow (less than 2 °C / min), the pyrolysis process will become extremely lengthy, resulting in a decrease in throughput per unit time, a significant increase in energy consumption, poor economic efficiency, and shrinkage and densification of the carbon skeleton, leading to a decrease in specific surface area and pore volume, and a reduction in surface active sites. If the heating rate is too fast (greater than 20 °C / min), a huge instantaneous temperature difference and thermal stress will be generated between the inside and surface of the biomass particles, causing particle breakage or the formation of irregular macropores. At the same time, micropore development is restricted, the uniformity of the pore structure deteriorates, and volatiles are released rapidly, resulting in excessive destruction of nitrogen- and oxygen-containing functional groups, which affects NH4+. + Selectivity is reduced, and there are security risks.

[0059] Optionally, the pyrolysis temperature can be: 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, etc.

[0060] Optionally, the heat preservation time can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc.

[0061] Optionally, the heating rate can be: 2 ℃ / min, 4 ℃ / min, 6 ℃ / min, 8 ℃ / min, 10 ℃ / min, 12 ℃ / min, 14 ℃ / min, 16 ℃ / min, 18 ℃ / min, 20 ℃ / min, etc.

[0062] For example, refer to Figure 2The cultivation was carried out in a transparent plexiglass container (e.g., 20×20×10 cm, working volume 3 L). Fresh water hyacinth plants were selected (fresh weight not less than about 25 g / plant, 2 large plants + 2 small plants). Before cultivation, the plant surface was washed with ultrapure water and ethanol, and then pre-acclimatized in tap water for 2-3 days. The temperature was controlled at 20-32 ℃, with natural or artificial lighting, a light-dark ratio of about 12 h:12 h (light intensity controlled within the range of 5000-15000 lx), and a relative humidity of 60-90%. The original biogas slurry was diluted 5 times, and the acclimatized water hyacinth was placed in the diluted biogas slurry for 7 days to investigate plant adaptability and NH4+. + Removal effect. After cultivation, water hyacinth biomass was harvested as a precursor for subsequent biochar production; the supernatant was collected after the culture medium was allowed to stand for 30 min, and filtered through a 0.45 μm filter membrane before being used as the feed liquid for the mFCDI device. The results showed that after 7 days of cultivation, NH4+ removal efficiency was significantly reduced. + The concentration decreased from approximately 652 mg / L to approximately 436 mg / L. Subsequently, the water hyacinth obtained from this culture was used to prepare biochar, and the supernatant from the culture was used as the feed liquid for the mFCDI unit. The NH4+ concentration in this representative feed liquid was... + Na + K + The concentrations were 436.35 mg / L, 116.36 mg / L, and 8.55 mg / L, respectively. The cultured water hyacinth biomass was washed, dried, and pulverized, then pyrolyzed under an inert atmosphere or limited oxygen conditions. The pyrolysis temperature was 700 ℃; the holding time was 1–2 h; and the heating rate was 2–20 ℃ / min. The pyrolysis products were cooled, ground, and sieved to obtain water hyacinth biochar. The water hyacinth biochar was mixed with a 30 mM Na₂SO₄ supported electrolyte solution to form a flowing electrode slurry with a solid content of 4 wt%. This slurry will be used for subsequent enrichment and recovery in the mFCDI unit to obtain NH₄-rich material. + The regenerated liquid.

[0063] In one feasible embodiment, after step S30, which involves pyrolyzing biomass to obtain biochar, the method further includes: Step S31 involves modifying the biochar by at least one of heteroatom doping, metal oxide loading, physical activation, chemical activation, or surface oxidation modification.

[0064] To further enhance the NH4+ ionization of biochar + Depending on the adsorption capacity and selectivity, or to adapt to wastewater systems with different compositions, biochar can be further modified. Heteroatom doping: By introducing heteroatoms such as nitrogen (N), sulfur (S), and phosphorus (P) (precursors such as urea, melamine, thiourea, and phytic acid), the electronic structure and surface polarity of carbon materials can be modulated, enhancing their affinity for NH4+.+ The interaction between metals and metal oxides: Supports such as MgO, MnO2, ZnO, and ZnAl-LDH can utilize the interaction between the metal centers and NH4+. + Specific coordination or ion exchange interactions between them. Physical activation: High-temperature treatment under a CO2 or water vapor atmosphere can further etch the carbon framework, increasing the micropore ratio and specific surface area. Chemical activation: Pyrolysis of biomass mixed with activators such as KOH, ZnCl2, and H3PO4 can generate more abundant ultrapores, greatly increasing the specific surface area (e.g., up to 2000 μm). 2 / g or more). Surface oxidation modification: Treating biochar with oxidants such as H2O2, HNO3, and O3 can increase the density of oxygen-containing functional groups such as –COOH, –OH, and C=O on its surface, thereby further enhancing its resistance to NH4+. + Prioritizes interface affinity and hydrophilicity.

[0065] Optionally, the above-mentioned modification methods can be used alone or in combination to synergistically optimize the physical structure and surface chemical properties of biochar and meet the performance requirements of different application scenarios. This application embodiment does not limit this.

[0066] Compared with the prior art, the beneficial effects of the method for preparing the flow electrode slurry provided in this application are the same as those of the flow electrode slurry provided in the above embodiments, and will not be repeated here.

[0067] The third aspect of this application provides a method for enriching and recovering ammonium ions, including the following steps: Step A10: Place the flowing electrode slurry in the flowing electrode capacitor deionization device, and pass the liquid to be recovered into the processing liquid channel in the flowing electrode capacitor deionization device for adsorption. The flowing electrode slurry is the flowing electrode slurry as described above, or is prepared by the method described above. The ammonium ion concentration of the liquid to be recovered is 100~2000 mg / L. Step A20: Pass the adsorbed liquid to be recovered out through the treatment liquid channel and pass in the acidic desorption liquid for desorption. Optionally, the flow electrode capacitor deionization device can be a three-channel membrane flow electrode capacitor deionization device (i.e., mFCDI device), or a multi-channel flow electrode capacitor deionization device, a stacked flow electrode capacitor deionization device, a continuous flow electrode capacitor deionization device, or a modular flow electrode capacitor deionization device. The embodiments of this application do not limit this.

[0068] In one feasible embodiment, reference Figure 2 and Figure 3 The mFCDI device has a three-channel structure, with the middle channel being the treatment liquid channel (the liquid to be recovered is introduced during adsorption, and the liquid to be recovered is rich in NH4).+ And Na exists + The device contains impurity ions, and the flow electrode channels (through which the flow electrode slurry is introduced) are located on both sides. The treatment solution and the flow electrode are separated by a cation exchange membrane (CEM) and an anion exchange membrane (AEM). The membrane stack structure of the device consists of multiple stacked components, including: (a) end plates: located on the outermost side of the membrane stack, serving to fix and support; (b) current collectors: in contact with the flow electrode slurry, used for conducting current; (c) anion exchange membrane (AEM): separating the anode flow electrode channel from the treatment solution channel, allowing only anions to pass through; (d) treatment solution chamber partition: forming the middle treatment solution channel for the flow of feed liquid; (e) cation exchange membrane (CEM): separating the cathode flow electrode channel from the treatment solution channel, allowing only cations (such as NH4+) to pass through. + (f) Sealing gaskets: placed between components to seal and prevent leakage. During operation, peristaltic pumps drive fluid flow in each circuit: the feed liquid is pumped into the intermediate treatment liquid channel, and the flowing electrode slurry on both sides is also driven by pumps, circulating between the external storage tank and the electrode channel. During the adsorption stage, a voltage is applied between the two collector plates, with a negative potential on the cathode side and a positive potential on the anode side; NH4 in the feed liquid... + Under the influence of an electric field, cations pass through the cation exchange membrane (CEM) into the flow electrode channel on the cathode side, where they are captured by adsorbents such as biochar in the flow electrode slurry. The treated solution flows out from the treated liquid channel, becoming the treated effluent, which will be recycled as dilution water. The acidic desorption solution is used to receive NH4 released from the flow electrode during the desorption stage. + It is usually dilute sulfuric acid, hydrochloric acid, nitric acid or citric acid, etc., with a concentration of 10~100 mM.

[0069] The liquid to be recovered includes the supernatant obtained after the aforementioned cultivation of aquatic plants. Since the roots of the aquatic plants act as a natural biosorbent and biofilter, they can simultaneously remove some organic matter, suspended solids, and some high-valence metal ions (Mg²⁺) from the ammonia-nitrogen-containing wastewater. 2+ Ca 2+ This reduces organic fouling of the ion exchange membrane and electrode scaling in the flow electrode capacitive deionization (FED) device. Simultaneously, testing showed that the conductivity of the culture supernatant decreased from 3.48 mS / cm to 2.86 mS / cm, which is more conducive to maintaining the selectivity of the FED device under low background salinity. In addition, the liquid to be recovered also includes pretreated ammonia-nitrogen-containing wastewater, which, after sedimentation, membrane filtration, and pH adjustment if necessary, meets the influent water quality requirements of the FED device. Its NH4... + The concentration range was controlled between 100 and 2000 mg / L to ensure sufficient ionic strength and migration flux without causing excessively rapid electrode saturation or accelerated membrane fouling due to excessively high concentrations. If the NH4+ in the culture supernatant...+ At concentrations below 100 mg / L, the driving force and efficiency of mFCDI treatment will decrease significantly; if the concentration is above 2000 mg / L, the high osmotic pressure and ionic strength will have an adverse effect on the long-term stability of the flow electrode and ion exchange membrane.

[0070] Optionally, the concentration of ammonium ions in the liquid to be recovered can be: 100 mg / L, 300 mg / L, 500 mg / L, 700 mg / L, 1000 mg / L, 1300 mg / L, 1500 mg / L, 1700 mg / L, 2000 mg / L, etc.

[0071] For example, a 30 mM H2SO4 solution was selected as the acidic desorption solution.

[0072] Step A30 involves performing multiple cycles of adsorption and desorption to obtain an ammonium ion enrichment solution, wherein the acidic desorption solution is replaced every 2 to 4 cycles.

[0073] The role of the adsorption stage is to apply a positive voltage between the two flow electrodes (i.e., the anode is connected to one flow electrode and the cathode is connected to the other flow electrode), and the positively charged NH4+... + Na + K + Under the drive of an electric field, cations migrate from the treatment liquid channel through the cation exchange membrane to the cathode-side flow electrode and are stored in the interfacial double layer or pores of the biochar of the flow electrode, thereby achieving the separation of target ions from the treatment liquid. The desorption stage serves to release the captured cations from the biochar surface and pores through reverse voltage or electrode polarity switching (applying a negative voltage), allowing them to re-enter the flow electrode slurry and further penetrate the cation exchange membrane into the acidic desorption liquid channel, thus achieving the separation of NH4+. + Concentration and recovery. A single batch of desorbed solution can be used continuously for multiple desorption cycles to improve NH4 concentration. + Enrichment concentration; however, as the concentration of NH4 in the desorption solution increases... + Na + As plasma gradually accumulates, the desorption current and desorption energy consumption increase, and the Na in the product solution... + Impurities may also increase. In a specific verification, desorption tests were performed five consecutive times without changing the desorption solution, and the desorption current-time (It) curves were recorded. The results are as follows: Figure 4 As shown, the current area of ​​the first to third desorption processes gradually increases (indicating that NH4+) + The amount of desorption is accumulating, but the current response of the 4th to 5th desorption is significantly more severe and fluctuates more, indicating that continued reuse of the desorption solution will cause intensified polarization, increased mass transfer resistance, or impurity ions (such as Na+). + Significant accumulation of ).

[0074] For example, the desorption solution is replaced every 3 cycles, which can be applied to the enrichment solution NH4. + Achieving the optimal balance between concentration, product liquid purity, and desorption energy consumption avoids complicating the product liquid composition and causing operational instability due to excessive reuse.

[0075] It should be noted that the refresh strategy for the treated solution (i.e., the liquid to be recovered) in the flowing electrode capacitive deionization unit is independent of the desorption liquid reuse strategy and can be flexibly selected according to actual operating conditions. The refresh of the treated solution includes at least one of the following: Batch circulation mode: A single batch of treated solution (e.g., 300 mL) is circulated and adsorbed in a closed loop until NH4... + The entire solution is replaced when the concentration drops to a set threshold (e.g., ≤50 mg / L or below 20% of the initial concentration); Semi-continuous mode: The entire treatment solution is replaced every N adsorption-desorption cycles (e.g., every 3 cycles, matching the frequency of desorption solution replacement); Continuous unidirectional flow mode: The treatment solution flows continuously through the treatment solution channel in a unidirectional manner (flow rate 1~20 mL / min, preferably 5 mL / min), without circulation, and the effluent contains NH4. + Once the standards are met, the waste can be discharged directly or transferred to subsequent units.

[0076] For example, a semi-continuous mode is used in 36 adsorption and desorption cycles, in which the treatment solution and desorption solution are replaced synchronously every 3 adsorption and desorption cycles. This mode is simple to operate and has stable performance.

[0077] Optionally, the number of cycles based on which each replacement of the acidic desorption solution is based can be 2, 3, 4, etc.

[0078] It should be noted that the switching from adsorption to desorption can be timed, meaning the programmable power supply / controller automatically switches according to a preset duration (e.g., adsorption 60 min – desorption 45 min – brief open-circuit flushing 30 s – enter the next cycle), or it can be triggered, such as current threshold triggering (switching to the desorption stage when the current in the adsorption stage drops to 20-40% of the initial current) or effluent concentration threshold triggering (switching to the desorption stage when the effluent NH4 concentration drops to 20-40% of the initial current). + Switching is triggered when the concentration drops to a set threshold or when the charge threshold is triggered (switching occurs when the accumulated charge reaches the charge corresponding to the theoretical adsorption capacity of the electrode). This application does not limit this aspect.

[0079] In one feasible embodiment, the conditions for multiple cycles of adsorption and desorption include at least one of the following: The volume of the flowing electrode slurry is 40~150 mL / side, and the flow rate of the flowing electrode slurry is 1~20 mL / min; The volume of the flowing electrode slurry determines the total amount of active material that can participate in electroadsorption within a single flowing electrode channel. A volume that is too small (less than 40 mL / side) will result in insufficient effective electrode material, limited adsorption capacity, and reduced NH4 in the treated solution. + Insufficient removal of NH4+ leads to poor slurry circulation stability and a tendency to settle due to localized oversaturation. Excessive volume (greater than 150 mL / side) increases system circulation resistance and pump energy consumption. Furthermore, excessively thick electrode channels can cause uneven electric field distribution, resulting in high utilization rates for particles near the membrane and low utilization rates for particles further away, thus reducing overall efficiency. In addition, slurry flow rate affects the contact frequency and mass transfer efficiency between electrode particles and the ion exchange membrane. Too low a flow rate (less than 1 mL / min) results in slow slurry turnover, severe concentration polarization at the membrane interface, and a decreased adsorption rate; too high a flow rate (greater than 20 mL / min) leads to insufficient residence time of the slurry in the channel, causing some NH4+ to be lost. + They are carried out before they can be captured, and the high shear force may exacerbate the wear of the membrane by the particles.

[0080] The volume of the liquid to be recovered is 100~1000 mL, and the flow rate of the liquid to be recovered is 1~20 mL / min; The volume of the liquid to be recovered determines the amount of wastewater that can be treated in a single batch. A volume that is too small (less than 100 mL) is not conducive to practical engineering applications, and frequent sample changes also increase operational complexity; a volume that is too large (greater than 1000 mL) will significantly prolong the processing time per batch, and with the increase of NH4... + NH4 is continuously adsorbed, leaving residual NH4 in the treatment solution. + As the concentration decreases, the driving force for subsequent adsorption decreases, leading to an increase in energy consumption per unit area. Furthermore, the flow rate of the treatment solution affects the concentration of NH4+. + Mass transfer rate and residence time at the membrane surface. If the flow rate is too low (less than 1 mL / min), the boundary layer thickens, limiting ion transport and resulting in low adsorption efficiency; if the flow rate is too high (greater than 20 mL / min), NH4+... + If the contact time with the membrane is too short, the membrane will not have enough time to migrate before being carried away, resulting in a decrease in the removal rate.

[0081] The adsorption voltage is +0.6 to +1.4 V, and the adsorption time is 20 to 120 min. If the adsorption voltage is too low (less than +0.6 V), the electric field strength is insufficient to effectively overcome the migration resistance of ions in the solution and membrane. +Both the adsorption rate and adsorption capacity decreased significantly. If the adsorption voltage is too high (greater than +1.4 V), it will trigger side reactions of water electrolysis (hydrogen evolution and oxygen evolution), leading to a decrease in current efficiency and a sharp increase in energy consumption. It may also cause oxidative corrosion of the biochar electrode material or degradation of the ion exchange membrane. Furthermore, the adsorption time determines the degree of ion enrichment in each cycle. If the time is too short (less than 20 min), adsorption will not reach equilibrium, resulting in low utilization of the electrode material and increased NH4+ in the treated solution. + The removal rate is not high. If the time is too long (greater than 120 min), the adsorption rate will approach zero in the later stage. Continuing to extend the adsorption time will only increase the cycle time, reduce the processing throughput per unit time, and may cause slight desorption of adsorbed ions or further occupation of active sites by competing ions.

[0082] The desorption voltage is -0.3 to -1.2 V, and the desorption time is 10 to 90 min.

[0083] During the desorption phase, a reverse voltage is applied, causing the captured cations to release from the electrode surface. If the desorption voltage is too low (e.g., above -0.2 V), the driving force is insufficient, and NH4+ ions will not be released. + Incomplete release leads to low desorption efficiency and residual NH4. + Occupying active sites affects the capacity of the next adsorption cycle. Excessive desorption voltage (above -1.2 V) can also trigger water electrolysis, generating numerous bubbles that interfere with the flow of the desorption solution. Furthermore, excessively high reverse potentials may compromise the structural stability of the biochar. In addition, the desorption time needs to be sufficient for most of the adsorbed NH4 to dissipate. + Migration occurs into the acidic desorption solution. If the time is too short (less than 10 min), desorption is incomplete, and the cumulative effect leads to capacity decay over long periods. If the time is too long (greater than 90 min), the current is almost zero in the later stages of desorption; further extending the time does not increase the amount of desorption, but only prolongs the cycle time and reduces overall efficiency.

[0084] Optionally, the volume of the flowing electrode slurry can be: 40 mL / side, 50 mL / side, 60 mL / side, 70 mL / side, 80 mL / side, 90 mL / side, 100 mL / side, 110 mL / side, 120 mL / side, 130 mL / side, 140 mL / side, 150 mL / side, etc.

[0085] Optionally, the flow rate of the flowing electrode slurry can be: 1 mL / min, 3 mL / min, 5 mL / min, 7 mL / min, 9 mL / min, 11 mL / min, 13 mL / min, 15 mL / min, 17 mL / min, 20 mL / min, etc.

[0086] Optionally, the volume of the liquid to be recovered can be: 100 mL, 200 mL, 300 mL, 400 mL, 500 mL, 600 mL, 700 mL, 800 mL, 900 mL, 1000 mL, etc.

[0087] Optionally, the flow rate of the liquid to be recovered can be: 1 mL / min, 3 mL / min, 5 mL / min, 7 mL / min, 9 mL / min, 11 mL / min, 13 mL / min, 15 mL / min, 17 mL / min, 20 mL / min, etc.

[0088] Optionally, the adsorption voltage can be: +0.6 V, +0.7 V, +0.8 V, +0.9 V, +1 V, +1.1 V, +1.2 V, +1.3 V, +1.4 V, etc.

[0089] Optionally, the adsorption time can be: 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, etc.

[0090] Optionally, the desorption voltage can be: -0.3 V, -0.4 V, -0.5 V, -0.6 V, -0.7 V, -0.8 V, -0.9 V, -1 V, -1.1 V, -1.2 V, etc.

[0091] Optionally, the desorption time can be: 10 min, 20 min, 30 min, 40 min, 45 min, 50 min, 60 min, 70 min, 80 min, 90 min, etc.

[0092] For example, in 36 adsorption and desorption cycles, the adsorption voltage was +1.0 V, the adsorption time was 60 min, the desorption voltage was -0.6 V, the desorption time was 45 min, and the desorption solution was 50 mL of 30 mM H2SO4.

[0093] To enable those skilled in the art to clearly understand the details and operations of the above embodiments of this application, and to demonstrate the significant improvement in the performance of the flowing electrode slurry of the embodiments of this application, the above technical solutions are illustrated below through multiple embodiments and comparative examples.

[0094] Example 1 The original biogas slurry was diluted 5 times, and water hyacinth was cultured in the diluted slurry for 7 days. After cultivation, the water hyacinth biomass was harvested as a precursor for subsequent biochar. The cultured water hyacinth biomass was washed, dried, and pulverized, and then pyrolyzed under vacuum at a temperature of 700 °C for 1 h at a heating rate of 2 °C / min. The pyrolysis products were cooled, ground, and sieved to obtain water hyacinth biochar (D-V700). D-V700 was mixed with a 30 mM Na2SO4 supported electrolyte solution to form a flowing electrode slurry with a solid content of 4 wt%.

[0095] Example 2 The original biogas slurry was diluted 5 times, and water hyacinth was cultured in the diluted slurry for 7 days. After cultivation, the water hyacinth biomass was harvested as a precursor for subsequent biochar. The cultured water hyacinth biomass was washed, dried, and pulverized, and then pyrolyzed under a N2 atmosphere at a temperature of 700 ℃ for 1 h at a heating rate of 2 ℃ / min. The pyrolysis product was cooled, ground, and sieved to obtain water hyacinth biochar (D-N700). D-N700 was mixed with a 30 mM Na2SO4 supported electrolyte solution to form a flowing electrode slurry with a solid content of 4 wt%.

[0096] Comparative Example 1 Water hyacinth was cultured in clean water for 7 days. After cultivation, the water hyacinth biomass was harvested as a precursor for subsequent biochar production. The cultured water hyacinth biomass was washed, dried, and pulverized, then pyrolyzed under vacuum at a temperature of 700 °C for 1 h at a heating rate of 2 °C / min. The pyrolysis product was cooled, ground, and sieved to obtain water hyacinth biochar (W-V700). W-V700 was mixed with a 30 mM Na₂SO₄ supported electrolyte solution to form a flowing electrode slurry with a solid content of 4 wt%.

[0097] Comparative Example 2 Commercial activated carbon (AC) was mixed with a 30 mM Na2SO4-supported electrolyte solution to form a flow electrode slurry with a solid content of 4 wt%.

[0098] Raman spectral data of Examples 1-2 and Comparative Examples 1-2 were compared, and the results are shown in Table 1 below: Table 1

[0099] As can be seen, Example 1 (D-V700) I D / I G The value was highest in group four, followed by Example 2 (D-N700), both of which were significantly higher than Comparative Example 1 (W-V700) and Comparative Example 2 (AC). D / I G The ratio reflects the defect density of carbon materials. The higher the ratio, the more abundant the edge sites, heteroatom defects, and micropore defects in the material. (This can be related to NH4+.) + Electroadsorption provides more active sites. AC's I D / I G With a defect density of only 0.56, it lacks sufficient ion adsorption sites, making efficient ammonia nitrogen capture difficult. In contrast, the high Ig value of D-N700 and D-V700... D / I G The value indicates that the preparation process of the flow electrode slurry successfully introduced a large number of active defect sites, which can significantly improve the resistance to NH4. + The adsorption capacity and selectivity of D-V700 and D-N700 are compared. Therefore, D-V700 exhibits significant advantages in defect structure, with D-V700 having the optimal defect density and theoretically the best fit for NH4. + The recovered electroadsorption properties.

[0100] The various indicators of Example 1 and Comparative Examples 1-2 were tested, and the results are shown in Table 2 below: Table 2

[0101] It is evident that, under the same 700 ℃ vacuum pyrolysis conditions, the key indicators such as BET specific surface area, N / O content, and specific capacitance of D-V700 obtained from biogas slurry cultivation are significantly higher than those of W-V700 obtained from water cultivation and commercial activated carbon AC. This demonstrates that nutrients such as nitrogen and organic matter in the biogas slurry are enriched by water hyacinth and then transformed into more concentrated nitrogen- and oxygen-containing active sites through pyrolysis. Under the operating conditions of the mFCDI device, D-V700 exhibits higher NH4 content compared to AC. + Adsorption / desorption capacity and NH4 + / Na + Selectivity was demonstrated, confirming the effectiveness of the D-V700-prepared flow electrode slurry for enriching and recovering NH4. + Its advantages.

[0102] Under the same operating conditions of the mFCDI device, the flowing electrode slurries of Example 1 (D-V700) and Comparative Example 2 (AC) were subjected to 15 adsorption and desorption cycles. The results are as follows: Figure 5 , Figure 6 , Figure 7 As shown (where D-V700 SEC) ads This represents the unit NH4 of D-V700 during the adsorption stage. + Reduced energy consumption, D-V700 SEC total This represents the unit NH4 of D-V700 during the entire adsorption and desorption process. + Total energy consumption for recovery, AC SECads This represents the unit NH4 of D-V700 during the adsorption stage. + Remove energy consumption and ACSEC total The unit NH4 represents AC during the entire adsorption and desorption process. + (Total energy consumption for recovery), compared to D-V700, AC NH4 + The adsorption and desorption capacities are low, the selectivity coefficient is less than 1, and the unit NH4 + Removal amount, energy consumption, and unit NH4 + The high total energy consumption for recovery indicates that ordinary AC has limited effectiveness against NH4 in real complex matrices. + The lack of priority confirms the inadequacy of the flow electrode slurry in the embodiments of this application for NH4. + High selectivity.

[0103] Scan rate capacitance analysis, X-ray photoelectron spectroscopy (XPS) analysis, and Fourier transform infrared spectroscopy (FTIR) analysis were performed on Example 1 (D-V700). The results of the scan rate capacitance analysis are as follows: Figure 8 As shown, the contribution of surface capacitance increases significantly with increasing scan rate, exhibiting obvious pseudocapacitive characteristics at higher scan rates, indicating that D-V700 has rapid interfacial charge storage behavior. This is closely related to its abundant nitrogen- and oxygen-containing functional groups—these functional groups can undergo rapid and reversible redox reactions during charge and discharge, thus providing NH4+ for NH4+ storage. + Provides additional chemical affinity sites, significantly enhancing the affinity for NH4. + Priority capture capability. XPS analysis results are as follows: Figure 9 As shown, adsorbed NH4 + Subsequently, the peak positions and intensities of the O 1s spectra attributed to carboxyl (-COOH), hydroxyl (-OH), and carbonyl (C=O) groups shifted or decreased, indicating that the oxygen-containing functional groups interacted with NH4+. + Hydrogen bonds or electrostatic interactions are formed between them. In the N 1s spectrum, the characteristic peaks of pyridine nitrogen (N-6), pyrrole nitrogen (N-5), and graphitic nitrogen (NQ) show significant shifts or changes in peak area, indicating that nitrogen-containing sites are also directly involved in NH4+. + The adsorption occurred. In the C 1s spectrum, the relative content of CO / C=O related components decreased after adsorption, further confirming the participation of oxygen-containing functional groups. The FTIR analysis results are as follows: Figure 10 As shown, adsorbed NH4 + Then, it was attributed to OH (approximately 3400 cm). -1 ) and NH (approximately 3200 cm -1 The stretching vibration peak of C=O (approximately 1700 cm⁻¹) broadens significantly or redshifts, indicating an enhanced hydrogen bond network. -1 ) and CO (approximately 1100-1200 cm) -1The decrease or shift in peak intensity of NH4 indicates that oxygen-containing groups such as carboxyl and hydroxyl groups interact with NH4+. + Coordination or ion exchange occurred. Furthermore, at approximately 1400 cm⁻¹... -1 Nearby, substances belonging to NH4 were found. + The characteristic peaks of the bending vibration directly prove that ammonium ions were successfully captured and stably exist on the biochar surface. These results together reveal the effect of D-V700 on NH4+. + Its high selectivity stems from its unique surface chemistry—the abundant nitrogen- and oxygen-containing functional groups introduced through biogas slurry cultivation, which enable it to interact with NH4+. + It forms multiple interactions such as hydrogen bonds, electrostatics, and coordination, while its pseudocapacitive behavior further enhances interfacial affinity.

[0104] Furthermore, the flowing electrode slurry of Example 1 (D-V700) was subjected to 36 adsorption and desorption cycles in an mFCDI apparatus. The results are as follows: Figure 11 , Figure 12 , Figure 13 As shown, the adsorption and desorption capacities, selectivity coefficient, and total unit energy consumption are not significantly different from the data from 15 cycles, indicating that the flow electrode slurry provided in this embodiment has strong chemical stability and exhibits good performance in the enrichment and recovery process for NH4. + It exhibits high selectivity. The concentration of its enrichment solution and enrichment factor were measured, and the results are shown in Table 3 below, further confirming the high selectivity of the flowing electrode slurry for NH4 in this embodiment. + High selectivity.

[0105] Table 3

[0106] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the patent protection scope of this application.

Claims

1. A flowable electrode slurry, characterized in that, The flowing electrode slurry includes: Biochar and supporting electrolyte solution, wherein the biochar is obtained by culturing aquatic plants in ammonia nitrogen-containing wastewater to obtain biomass and then pyrolyzing the biomass, the surface of the biochar contains nitrogen-containing and / or oxygen-containing functional groups, and the solid content of the flowing electrode slurry is 1~10 wt%.

2. The flow electrode slurry as described in claim 1, characterized in that, The ammonia-nitrogen-containing wastewater includes at least one of the following: anaerobic digestion liquid, livestock and poultry breeding wastewater, landfill leachate, fermentation waste liquid, and ammonia-containing agricultural tailwater.

3. The flow electrode slurry as described in claim 1, characterized in that, The aquatic plants include at least one of water hyacinth, duckweed, reeds, and algae.

4. The flowing electrode slurry as described in claim 1, characterized in that, The supporting electrolyte solution includes at least one of Na2SO4 solution, K2SO4 solution, NaCl solution, and KCl solution.

5. A method for preparing a flowing electrode slurry, characterized in that, The method is used to prepare a flow electrode slurry as described in any one of claims 1 to 4, and the method includes the following steps: Provide aquatic plants; The aquatic plants were cultured in wastewater containing ammonia nitrogen for 3-14 days to obtain biomass; The biomass is pyrolyzed to obtain biochar; The biochar was mixed with a supporting electrolyte solution to obtain a flow electrode slurry.

6. The method as described in claim 5, characterized in that, The concentration of ammonium ions in the ammonia nitrogen-containing wastewater is less than or equal to 1500 mg / L.

7. The method as described in claim 5, characterized in that, The pyrolysis conditions include: pyrolysis temperature of 500~900℃, holding time of 0.5~4 h, and heating rate of 2~20℃ / min.

8. The method as described in claim 5, characterized in that, After the step of pyrolyzing the biomass to obtain biochar, the method further includes: The biochar is modified by at least one of heteroatom doping, metal oxide loading, physical activation, chemical activation, and surface oxidation modification.

9. A method for enriching and recovering ammonium ions, characterized in that, Includes the following steps: The flow electrode slurry is placed in a flow electrode capacitor deionization device, and the liquid to be recovered is introduced into the processing liquid channel of the flow electrode capacitor deionization device for adsorption. The flow electrode slurry is the flow electrode slurry as described in any one of claims 1 to 4, or is prepared by the method as described in any one of claims 5 to 8. The ammonium ion concentration of the liquid to be recovered is 100~2000 mg / L. The adsorbed liquid to be recovered is passed out through the treatment liquid channel, and an acidic desorption solution is introduced for desorption. An ammonium ion enrichment solution is obtained by performing multiple cycles of adsorption and desorption, wherein the acidic desorption solution is replaced every 2 to 4 cycles.

10. The method as described in claim 9, characterized in that, The conditions for the multiple cycles of adsorption and desorption include at least one of the following: The volume of the flowing electrode slurry is 40~150 mL / side, and the flow rate of the flowing electrode slurry is 1~20 mL / min; The volume of the liquid to be recovered is 100~1000 mL, and the flow rate of the liquid to be recovered is 1~20 mL / min; The adsorption voltage is +0.6 to +1.4 V, and the adsorption time is 20 to 120 min. The desorption voltage is -0.3 to -1.2 V, and the desorption time is 10 to 90 min.

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