Fe3O4-coated NH2-Zn-MOFs adsorption method and device for recovering phosphorus from biogas slurry pretreated by persulfate

Abstract

The invention relates to a Fe3O4 (at) NH2-Zn-MOFs adsorption method and device for recovering phosphorus from biogas slurry pretreated by persulfate, and the method comprises the following steps: fixing a Fe3O4 (at) NH2-Zn-MOFs composite material on an aerogel adsorption column to obtain a Fe3O4 (at) NH2-Zn-MOFs aerogel adsorption column; the method comprises the following steps: transferring PO4 < 3-> in biogas slurry to a Fe3O4 (at) NH2-Zn-MOFs aerogel adsorption column by utilizing a Fe3O4 (at) NH2-Zn-MOFs adsorption device through an adsorption process, and eluting PO4 < 3-> adsorbed in the Fe3O4 (at) NH2-Zn-MOFs aerogel adsorption column by utilizing an acid solution, so as to obtain a high-concentration phosphate leaching solution; and adjusting the pH value and supplementing Fe < 3 + >, and recovering high-purity FePO4 crystals from the high-concentration phosphate leachate. Compared with the prior art, the method has the advantage that the high-purity FePO4 crystals can be recycled from the high-concentration phosphate leachate. In addition, adsorption and desorption crystallization can be synchronously carried out through valve regulation and control, so that the overall recovery efficiency of phosphorus is improved.

Description

Technical Field

[0001] This invention relates to the field of biogas slurry treatment and resource regeneration technology, and in particular to a Fe3O4@NH2-Zn-MOFs adsorption method and apparatus for recovering phosphorus from biogas slurry pretreated with persulfate. Background Technology

[0002] In recent years, the number and scale of wastewater treatment plants have been continuously expanding. During the wastewater treatment process, a large amount of sludge is generated. Sludge contains a large amount of organic matter, nitrogen, phosphorus, and other nutrients. Improper treatment not only wastes resources but also causes serious environmental pollution. Phosphorus resources are particularly precious and have become a significant issue facing China and the world.

[0003] Phosphorus is an essential element for the growth of living organisms and is widely used in agriculture, chemical industry, food, and other fields. However, the Earth's phosphorus resources are limited and unevenly distributed. China has large reserves of phosphate rock, but the grade is low, and the environmental pollution caused by mining and utilization is serious. In addition, the large-scale mining and use of phosphorus resources has led to a continuous decline in the grade of phosphate rock and an accelerated rate of resource depletion. Therefore, finding an efficient and environmentally friendly method for the recovery and utilization of phosphorus resources has become an urgent task.

[0004] Sludge is rich in phosphorus; statistics show that over 90% of phosphorus is transferred to sludge during wastewater treatment. Anaerobic digestion, as a mature sludge treatment technology, has advantages such as low energy consumption and high treatment efficiency, and has become one of the main methods for sludge treatment. However, during anaerobic digestion, phosphorus in sludge is mainly released into the biogas slurry in dissolved form. Therefore, how to efficiently separate and recover phosphorus from biogas slurry has become a research hotspot in the field of sludge treatment. In addition, in recent years, persulfate-based anaerobic digestion technology has attracted much attention in the field of environmental engineering. This technology utilizes the strong oxidizing properties of persulfate to effectively improve sludge treatment and increase anaerobic digestion efficiency, showing great potential in promoting sludge reduction and resource utilization.

[0005] Currently, researchers have conducted extensive studies on phosphorus recovery from biogas slurry, primarily employing methods such as chemical precipitation, adsorption-desorption, membrane separation, and ion exchange. Among these, chemical precipitation is simple to operate but consumes large amounts of reagents, produces significant amounts of sludge, and has a low phosphorus recovery rate. Membrane separation offers good recovery, but membrane materials are expensive, prone to fouling, and have high operation and maintenance costs. Ion exchange has a high phosphorus recovery rate, but ion exchange resin regeneration is difficult, resulting in high operating costs. Adsorption-desorption, as a novel phosphorus recovery technology, offers advantages such as ease of operation, large adsorption capacity, and low operating costs, and is gradually attracting researchers' attention. The adsorbent is crucial in adsorption-desorption methods, with activated carbon, biomass materials, and mineral materials being among the most studied adsorbents. These adsorbents exhibit high adsorption capacity for phosphorus in biogas slurry and demonstrate good stability and reusability. However, achieving more efficient adsorption remains a critical technical challenge. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a Fe3O4@NH2-Zn-MOFs adsorption method and apparatus for recovering phosphorus from biogas slurry pretreated with persulfate. First, an Fe3O4@NH2-Zn-MOFs aerogel adsorption column is prepared, and then PO4 in the biogas slurry is adsorbed using an adsorption process. 3- The PO4 adsorbed in the Fe3O4@NH2-Zn-MOFs aerogel adsorption column was then eluted with an acidic solution. 3- Then adjust the pH and supplement Fe. 3+ This allows for the recovery of high-purity FePO4 crystals from high-concentration phosphate leachate. Furthermore, valve control enables adsorption and desorption crystallization to proceed simultaneously.

[0007] The objective of this invention can be achieved through the following technical solutions: The first objective of this invention is to provide a Fe3O4@NH2-Zn-MOFs adsorption method for recovering phosphorus from persulfate pretreated biogas slurry, the method comprising the following steps: (1) Solid-liquid separation was performed on the biogas slurry after persulfate pretreatment to obtain solid biogas residue and biogas slurry after solid-liquid separation; (2) The solid biogas residue is fed into the anaerobic digestion reactor, and the biogas liquid after solid-liquid separation is put into the Fe3O4@NH2-Zn-MOFs aerogel adsorption column for adsorption to obtain the material after adsorption saturation. (3) The material after adsorption saturation is desorbed and regenerated and then reused to obtain the desorbed liquid; (4) The desorption solution enters the crystallizer for crystallization and recovery, and FePO4 crystals are recovered.

[0008] Furthermore, steps (2), (3), and (4) specifically include the following processes: Fe3O4@NH2-Zn-MOFs composite material was fixed on an aerogel adsorption column to obtain Fe3O4@NH2-Zn-MOFs aerogel adsorption column; Using a Fe3O4@NH2-Zn-MOFs adsorption device, PO4 in the solid-liquid separated biogas slurry is removed through an adsorption process. 3- The PO4 adsorbed in the Fe3O4@NH2-Zn-MOFs aerogel adsorption column was transferred to the Fe3O4@NH2-Zn-MOFs aerogel adsorption column and eluted with an acidic solution. 3- A high-concentration phosphate leachate was obtained, which is the desorption solution. Adjusting the pH of high-concentration phosphate leachate and supplementing Fe 3+ High-purity FePO4 crystals were recovered from the high-concentration phosphate leachate.

[0009] Furthermore, the preparation process of the Fe3O4@NH2-Zn-MOFs composite material includes the following steps: NH2-Zn-MOFs composite materials were prepared by introducing amino-modified MOFs materials and using a solvothermal method. Based on the obtained NH2-Zn-MOFs composite material, a magnetic adsorbent Fe3O4@NH2-Zn-MOFs composite material was prepared by the intercalation method.

[0010] Furthermore, the process of preparing NH2-Zn-MOF composite materials by introducing amino-modified MOF materials and using a solvothermal method includes the following steps: Zinc salt solution and aminocarboxylic acid ligand solution were mixed, and then o-phenylenediamine solution was added to carry out the first reaction. After the reaction, the mixture was washed and dried to obtain NH2-Zn-MOFs composite material. Based on the obtained NH2-Zn-MOFs composite material, the process of preparing magnetic adsorbent Fe3O4@NH2-Zn-MOFs composite material by intercalation method includes the following steps: The prepared NH2-Zn-MOFs composite material was dispersed in water with dissolved oxygen removed, ammonia was added, and under stirring and nitrogen protection, ferric salts and ferrous salts were added to carry out a second reaction. After the reaction, the mixture was purified, washed, and dried to obtain the Fe3O4@NH2-Zn-MOFs composite material.

[0011] Furthermore, the zinc salt in the zinc salt solution is zinc nitrate hexahydrate; the zinc salt solution is a solution obtained by dissolving the zinc salt in water.

[0012] Further, the aminocarboxylic acid ligand in the aminocarboxylic acid ligand solution is 5-aminoisophthalic acid; the aminocarboxylic acid ligand solution is a solution obtained by dissolving the aminocarboxylic acid ligand in a mixed solution of ethanol and N,N-dimethylformamide.

[0013] Furthermore, the o-phenylenediamine solution is a solution obtained by dissolving o-phenylenediamine in a mixed solution of ethanol and N,N-dimethylformamide.

[0014] Furthermore, the conditions for the first reaction are as follows: it is carried out in a sealed reaction vessel and heated to 80~120℃ and maintained for 30~42 hours.

[0015] Furthermore, the preparation process of the water with dissolved oxygen removed includes the following steps: taking deionized water, pretreating it with nitrogen gas, and obtaining the water with dissolved oxygen removed.

[0016] Furthermore, the trivalent iron salt is ferric chloride hexahydrate.

[0017] Furthermore, the ferrous salt is ferrous chloride tetrahydrate.

[0018] Furthermore, the conditions for the second reaction are: stirring the reaction in a water bath at 55~75℃ for 1~3 hours.

[0019] Furthermore, the process of immobilizing the Fe3O4@NH2-Zn-MOFs composite material on an aerogel adsorption column to obtain the Fe3O4@NH2-Zn-MOFs aerogel adsorption column includes the following steps: Chitosan was dissolved in formic acid to obtain a chitosan solution; The Fe3O4@NH2-Zn-MOFs composite material was added to the obtained chitosan solution to obtain a mixed emulsion; Glutaraldehyde was added to the resulting mixed emulsion to carry out a cross-linking reaction, resulting in Fe3O4@NH2-Zn-MOFs hydrogel; The obtained Fe3O4@NH2-Zn-MOFs hydrogel was soaked in formic acid aqueous solution for 1-5 h, freeze-dried under vacuum for 36-72 h, and then washed to obtain Fe3O4@NH2-Zn-MOFs aerogel adsorption column.

[0020] The second objective of this invention is to provide a Fe3O4@NH2-Zn-MOFs adsorption device for realizing the Fe3O4@NH2-Zn-MOFs adsorption method for recovering phosphorus from biogas slurry pretreated with persulfate. The Fe3O4@NH2-Zn-MOFs adsorption device includes a first aerogel adsorption column, a second aerogel adsorption column, and a crystallizer. The first and second aerogel adsorption columns are respectively connected to the crystallizer via pipes. Both the first and second aerogel adsorption columns are Fe3O4@NH2-Zn-MOFs aerogel adsorption columns.

[0021] Furthermore, the Fe3O4@NH2-Zn-MOFs adsorption device also includes an anaerobic digestion reactor; the first aerogel adsorption column and the second aerogel adsorption column are respectively connected to the anaerobic digestion reactor through pipelines.

[0022] Furthermore, a second valve is provided on the pipe between the outlet of the first aerogel adsorption column and the inlet of the anaerobic digester.

[0023] Furthermore, a fourth valve is provided on the pipe between the outlet of the second aerogel adsorption column and the inlet of the anaerobic digester.

[0024] Furthermore, a first valve is provided on the pipe between the second valve and the inlet of the anaerobic digester, and on the pipe between the fourth valve and the inlet of the anaerobic digester.

[0025] Furthermore, a third valve is provided on the pipe between the inlet of the first aerogel adsorption column and the outlet of the anaerobic digester.

[0026] Furthermore, a fifth valve is provided on the pipe between the inlet of the second aerogel adsorption column and the outlet of the anaerobic digester.

[0027] Furthermore, a sixth valve is provided on the pipe between the inlet of the first aerogel adsorption column and the outlet of the crystallizer.

[0028] Furthermore, an eighth valve is provided on the pipe between the inlet of the second aerogel adsorption column and the outlet of the crystallizer.

[0029] Furthermore, a seventh valve is provided on the pipe between the outlet of the first aerogel adsorption column and the inlet of the crystallizer.

[0030] Furthermore, a ninth valve is provided on the pipe between the outlet of the second aerogel adsorption column and the inlet of the crystallizer.

[0031] Furthermore, during the initial feeding, the first valve is closed, the second and third valves are open, and the remaining valves (the fourth, fifth, sixth, seventh, eighth, and ninth valves) are closed. The biogas slurry pretreated with persulfate enters the anaerobic digester through the first aerogel adsorption column. The Fe3O4@NH2-Zn-MOFs in the first aerogel adsorption column activate the persulfate through the interaction between Fe(II)-O-Zn(II). After feeding is completed, the first valve is opened, and the biogas slurry after solid-liquid separation circulates through the first aerogel adsorption column while undergoing anaerobic digestion, activating persulfate and adsorbing PO4. 3- .

[0032] Furthermore, when the first aerogel adsorption column is saturated, the second and third valves are closed, and the fourth and fifth valves are opened, allowing the biogas slurry after solid-liquid separation to enter the second aerogel adsorption column for adsorption; the sixth and seventh valves are opened, and an acidic solution (such as sulfuric acid) is added to the first aerogel adsorption column for elution, and the high-concentration phosphate leachate eluted is crystallized in the crystallizer.

[0033] Furthermore, when the second aerogel adsorption column is saturated, the fourth, fifth, sixth, and seventh valves are closed, while the second, third, eighth, and ninth valves are opened. The first aerogel adsorption column is used for adsorption, and the second aerogel adsorption column is used for elution. These are used alternately to simultaneously carry out adsorption and crystallization.

[0034] The technical concept of this invention is as follows: Biocompatible zinc-organic frameworks possess high specific surface area and porous structures, providing numerous active sites that can effectively bind to phosphorus molecules, thereby achieving efficient adsorption. Therefore, this invention proposes a Fe3O4@NH2-Zn-MOFs adsorption process for recovering phosphorus from biogas slurry, recovering high-purity battery-grade FePO4 from complex biogas slurry. The purity of the high-purity battery-grade FePO4 can reach 90-98%.

[0035] The method of the present invention specifically includes the following steps: 1. An amino-modified MOF material was introduced, and an NH₂-Zn-MOF composite material was prepared using a solvothermal method. Zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) was accurately weighed and dissolved in deionized water. Separately, 5-aminoisophthalic acid was weighed and dissolved in a 7:3 volume ratio of ethanol and N,N-dimethylformamide (DMF). The mixture was stirred for 30–60 minutes until the solution changed from colorless to pale yellow, yielding mixed solution A. Then, o-phenylenediamine was weighed and dissolved in a 7:3 volume ratio of ethanol and DMF. This was added to mixed solution A, and the mixture was stirred for 20 minutes until a pale yellow suspension formed. This suspension was sealed in a 100 mL reactor and heated to 80–120 °C for 30–42 hours. After cooling to room temperature, the mixture was washed three times with DMF and ethanol, and then dried overnight in a vacuum drying oven at 50–70 °C to obtain a pale yellow powder, NH₂-Zn-MOFs. Amino functional groups can provide additional adsorption sites, which can interact with phosphorus compounds through electrostatic interactions, coordination interactions, or the formation of hydrogen bonds, thus helping to improve the material's ability to adsorb phosphorus.

[0036] 2. Magnetic adsorbent Fe3O4@NH2-Zn-MOFs was prepared using an intercalation method. Deionized water was pretreated with nitrogen for 20-40 minutes to remove dissolved oxygen. Then, NH2-Zn-MOFs powder was weighed and added to the pretreated water, followed by ultrasonic treatment for 10-30 minutes to ensure thorough dispersion. Next, 25-35% ammonia solution was slowly added, and FeCl3·6H2O and FeCl2·4H2O were added sequentially under continuous mechanical stirring and nitrogen protection. The mixed solution was stirred in a water bath at 55-75℃ for 1-3 hours to promote the formation of Fe3O4 nanoparticles on the surface of NH2-Zn-MOFs. After the reaction was complete, the Fe3O4@NH2-Zn-MOFs composite material was purified by separation using an external magnetic field and washed multiple times with deionized water until the pH of the washing solution reached neutral. Finally, the product was dried overnight in a vacuum drying oven at 60 °C to obtain black powder Fe3O4@NH2-Zn-MOFs.

[0037] 3. Preparation of Fe3O4@NH2-Zn-MOFs aerogel adsorption column. Chitosan CS was dissolved in (1% v / v) formic acid aqueous solution to obtain a 1% (w / v) CS solution. Fe3O4@NH2-Zn-MOFs powder was added to the 1% (w / v) CS solution (Fe3O4@NH2-Zn-MOFs:CS = 1:1 (w / w)) and dispersed into an emulsion to obtain a mixed emulsion. Then, 2% (w / w) glutaraldehyde (mixed emulsion:glutaraldehyde = 1:4 (v / v)) was added to participate in the crosslinking reaction (the crosslinking reaction was carried out at 25-30℃ for 2-4 h, with thorough stirring to ensure complete condensation reaction between chitosan and glutaraldehyde). The Fe3O4@NH2-Zn-MOFs hydrogel prepared by the above process was immersed in (1% v / v) formic acid aqueous solution for 1-5 h and then freeze-dried under vacuum for 36-72 h. Then, the column was washed with deionized water to obtain Fe3O4@NH2-Zn-MOFs aerogel adsorption column.

[0038] 4. Construct a Fe3O4@NH2-Zn-MOFs adsorption device (Fe3O4@NH2-Zn-MOFs adsorption unit) for phosphorus recovery from persulfate pretreated biogas slurry. The adsorption process device consists of three parts: a first aerogel adsorption column, a second aerogel adsorption column, and a crystallizer. During initial feeding, the first valve is closed, the second and third valves are open, and the remaining valves are closed. The biogas slurry after solid-liquid separation passes through the first aerogel adsorption column. The Fe3O4@NH2-Zn-MOFs in the first aerogel adsorption column, through the interaction between Fe(II)-O-Zn(II), makes it easier for Fe(II) in the Fe3O4@NH2-Zn-MOFs to lose electrons, thereby activating the persulfate, increasing the ability to generate ROS, and enhancing phosphorus release. After feeding, the first valve is opened, allowing the material to circulate through the first aerogel adsorption column while undergoing anaerobic digestion, activating the persulfate and adsorbing PO4. 3- When adsorption approaches saturation, the second and third valves close, while the fourth and fifth valves open, allowing the biogas slurry to enter the second aerogel adsorption column for adsorption. Simultaneously, the sixth and seventh valves open, adding sulfuric acid to the first aerogel adsorption column for elution. The resulting high-concentration phosphate leachate crystallizes in the crystallization section. This crystallization is controlled by adjusting the pH and supplementing Fe. 3+ FePO4 crystals are recovered from high-concentration phosphate leachate. When the second aerogel adsorption column is near saturation, the fourth, fifth, sixth, and seventh valves are closed, while the second, third, eighth, and ninth valves are opened. The first aerogel adsorption column is used for adsorption, and the second aerogel adsorption column is used for elution. This alternating use allows for simultaneous adsorption and crystallization, improving the overall recovery efficiency.

[0039] Furthermore, the pH value can be precisely adjusted by adding NaOH solution or dilute hydrochloric acid to maintain the system at pH 6.0-7.5.

[0040] Furthermore, when Fe in the system 3+ When the concentration decreases, it is restored by adding ferric sulfate (Fe2(SO4)3) solution to ensure the supply of metal ions required for the subsequent FePO4 crystallization reaction.

[0041] Compared with the prior art, the present invention has the following beneficial effects: 1. The Fe3O4@NH2-Zn-MOFs adsorption method for recovering phosphorus from persulfate-pretreated biogas slurry provided by this invention is a Fe3O4@NH2-Zn-MOFs adsorption process for recovering phosphorus from persulfate-pretreated biogas slurry. The MOFs material Fe3O4@NH2-Zn-MOFs introduced with amino functional groups provides additional adsorption sites for the adsorbent, significantly improving the material's adsorption capacity for phosphorus. The biogas slurry is discharged after anaerobic digestion of sludge pretreated with persulfate. The interaction between persulfate and Fe3O4 makes it easier for Fe(II) in Fe3O4@NH2-Zn-MOFs to lose electrons, activating the persulfate and generating more reactive oxygen species (ROS), further enhancing phosphorus release and thus improving the adsorption and recovery rate of phosphorus by the adsorbent. This can be achieved by adjusting the pH value and supplementing Fe. 3+ High-purity FePO4 crystals can be recovered from high-concentration phosphate leachate, enabling the effective utilization of phosphorus resources.

[0042] 2. The Fe3O4@NH2-Zn-MOFs adsorption method and apparatus for recovering phosphorus from biogas slurry pretreated with persulfate provided by the present invention can simultaneously perform phosphorus adsorption and desorption crystallization by valve regulation, thereby improving the overall recovery efficiency, reducing equipment investment and operating costs, and facilitating the large-scale and industrialized recovery of phosphorus resources. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the Fe3O4@NH2-Zn-MOFs adsorption device provided by the present invention.

[0044] Explanation of the labels in the diagram: 1. First aerogel adsorption column; 2. Second aerogel adsorption column; 3. Crystallizer; 4. Anaerobic digestion reactor; 5-1. First valve; 5-2. Second valve; 5-3. Third valve; 5-4. Fourth valve; 5-5. Fifth valve; 5-6. Sixth valve; 5-7. Seventh valve; 5-8. Eighth valve; 5-9. Ninth valve. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0046] Any preparation methods, materials, structures, or composition ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0047] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0048] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0049] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0050] This invention discloses a Fe3O4@NH2-Zn-MOFs adsorption process for recovering phosphorus from biogas slurry pretreated with persulfate. First, Fe3O4@NH2-Zn-MOFs powder is prepared, and amino groups are introduced to modify the MOFs material, providing additional adsorption sites and improving the material's phosphorus adsorption capacity. Fe3O4 can activate persulfate (PS), increasing its ability to generate ROS and enhancing phosphorus release. The Fe3O4@NH2-Zn-MOFs powder is then immobilized on an aerogel adsorption column, and PO4 in the biogas slurry is adsorbed using the adsorption process. 3-The PO4 adsorbed in the Fe3O4@NH2-Zn-MOFs aerogel adsorption column was then eluted with an acidic solution. 3- Then adjust the pH and supplement Fe. 3+ This allows for the recovery of high-purity FePO4 crystals from high-concentration phosphate leachate. Furthermore, valve control enables simultaneous adsorption and desorption crystallization, thereby improving the overall phosphorus recovery efficiency.

[0051] This invention provides a Fe3O4@NH2-Zn-MOFs adsorption method for recovering phosphorus from persulfate pretreated biogas slurry, the method comprising the following steps: Fe3O4@NH2-Zn-MOFs composite material was fixed on an aerogel adsorption column to obtain Fe3O4@NH2-Zn-MOFs aerogel adsorption column; Using a Fe3O4@NH2-Zn-MOFs adsorption device, PO4 in biogas slurry is removed through an adsorption process. 3- The PO4 adsorbed in the Fe3O4@NH2-Zn-MOFs aerogel adsorption column was transferred to the Fe3O4@NH2-Zn-MOFs aerogel adsorption column and eluted with an acidic solution. 3- A high-concentration phosphate leachate was obtained; Adjusting pH and supplementing Fe 3+ FePO4 crystals were recovered from the high-concentration phosphate leachate.

[0052] In some embodiments of the present invention, the preparation process of the Fe3O4@NH2-Zn-MOFs composite material includes the following steps: NH2-Zn-MOFs composite materials were prepared by introducing amino-modified MOFs materials and using a solvothermal method. Based on the obtained NH2-Zn-MOFs composite material, Fe3O4@NH2-Zn-MOFs composite material was prepared by the intercalation method.

[0053] In the following embodiments, the biogas slurry originates from the effluent of an anaerobic digester at a wastewater treatment plant in Xi'an, and enters the pretreatment unit after solid-liquid separation. In the pretreatment unit, a persulfate (PS) oxidation system is used, achieved by adding persulfate (such as Na2S2O8 used in this invention) and reacting it with Fe... 2+ SO4· is generated under ultraviolet (UV) light or heating conditions (UV light is used in this invention) for activation. - This process achieves chain breaking of macromolecular organic matter and release of some phosphorus forms, resulting in persulfate pretreated biogas slurry, which provides a higher proportion of dissolved phosphorus for subsequent adsorption reactions.

[0054] Example 1 This embodiment provides a Fe3O4@NH2-Zn-MOFs adsorption method for recovering phosphorus from persulfate pretreated biogas slurry, comprising the following steps: Accurately weigh 0.375 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and dissolve it in 15 mL of deionized water. Separately weigh 0.215 g of 5-aminoisophthalic acid and dissolve it in 15 mL of a 7:3 mixture of ethanol and N,N-dimethylformamide (DMF). Mix the two solutions and stir for 45 minutes. The solution changes from colorless to pale yellow, yielding mixed solution A. Add o-phenylenediamine: Weigh 0.128 g of o-phenylenediamine and dissolve it in 15 mL of a 7:3 mixture of ethanol and DMF. Add this to mixed solution A and stir for 20 minutes. The solution becomes a pale yellow suspension, yielding mixed solution B. Seal mixed solution B in a 100 mL reactor and heat to 100°C for 36 hours. After cooling to room temperature, wash three times with DMF and ethanol respectively, and dry overnight in a vacuum drying oven at 60°C to obtain pale yellow powder NH2-Zn-MOFs.

[0055] Take 200 mL of deionized water and pretreat it with nitrogen for 30 minutes to remove dissolved oxygen, obtaining pretreated water. Weigh 1.0 g of NH2-Zn-MOFs powder and add it to the pretreated water, then sonicate for 15 minutes to ensure sufficient dispersion. Slowly add 15 mL of 28% ammonia solution, and under continuous mechanical stirring and nitrogen protection, add 0.6 g of FeCl3·6H2O and 0.2 g of FeCl2·4H2O sequentially. Stir the mixture in a 65℃ water bath for 2 hours to promote the formation of Fe3O4 nanoparticles on the surface of NH2-Zn-MOFs. Separation and washing: After the reaction, separate and purify the Fe3O4@NH2-Zn-MOFs composite material using an external magnetic field, and wash it several times with deionized water until the pH of the washing solution reaches neutral. Dry the product overnight in a vacuum drying oven at 60℃ to obtain black powder Fe3O4@NH2-Zn-MOFs.

[0056] Chitosan (CS) was dissolved in a 1% (v / v) formic acid aqueous solution to obtain a 1% (w / v) CS solution. Fe3O4@NH2-Zn-MOFs powder was added to the 1% (w / v) CS solution (Fe3O4@NH2-Zn-MOFs:CS = 1:1 (w / w)) and dispersed into an emulsion to obtain a mixed emulsion. 2% (w / w) glutaraldehyde (mixed emulsion:glutaraldehyde = 1:4 (v / v)) was added to participate in the crosslinking reaction (the crosslinking reaction was carried out at 25℃ for 3 h, with thorough stirring to ensure complete condensation between chitosan and glutaraldehyde). The Fe3O4@NH2-Zn-MOFs hydrogel prepared by the above process was immersed in a 1% (v / v) formic acid aqueous solution for 2 hours and then freeze-dried under vacuum for 48 hours. After washing with deionized water, a Fe3O4@NH2-Zn-MOFs aerogel adsorption column was obtained.

[0057] like Figure 1 As shown, the Fe3O4@NH2-Zn-MOFs adsorption device consists of three parts: a first aerogel adsorption column 1, a second aerogel adsorption column 2, and a crystallizer 3. The device achieves simultaneous adsorption, desorption, and crystallization through valve regulation.

[0058] The first aerogel adsorption column 1 and the second aerogel adsorption column 2 are respectively connected to the crystallizer 3 through pipes; the first aerogel adsorption column 1 and the second aerogel adsorption column 2 are both Fe3O4@NH2-Zn-MOFs aerogel adsorption columns.

[0059] The Fe3O4@NH2-Zn-MOFs adsorption device also includes an anaerobic digestion reactor 4; the first aerogel adsorption column 1 and the second aerogel adsorption column 2 are respectively connected to the anaerobic digestion reactor 4 through pipelines.

[0060] A second valve 5-2 is provided on the pipeline between the outlet of the first aerogel adsorption column 1 and the inlet of the anaerobic digestion reactor 4.

[0061] A fourth valve 5-4 is provided on the pipeline between the outlet of the second aerogel adsorption column 2 and the inlet of the anaerobic digester 4.

[0062] A first valve 5-1 is provided on the pipeline between the second valve 5-2 and the inlet of the anaerobic digester 4, and on the pipeline between the fourth valve 5-4 and the inlet of the anaerobic digester 4.

[0063] A third valve 5-3 is provided on the pipeline between the inlet of the first aerogel adsorption column 1 and the outlet of the anaerobic digestion reactor 4.

[0064] A fifth valve 5-5 is installed on the pipe between the inlet of the second aerogel adsorption column 2 and the outlet of the anaerobic digester 4.

[0065] A sixth valve 5-6 is provided on the pipe between the inlet of the first aerogel adsorption column 1 and the outlet of the crystallizer 3.

[0066] An eighth valve 5-8 is provided on the pipe between the inlet of the second aerogel adsorption column 2 and the outlet of the crystallizer 3.

[0067] A seventh valve 5-7 is provided on the pipe between the outlet of the first aerogel adsorption column 1 and the inlet of the crystallizer 3.

[0068] A ninth valve 5-9 is provided on the pipe between the outlet of the second aerogel adsorption column 2 and the inlet of the crystallizer 3.

[0069] The biogas slurry after persulfate pretreatment is subjected to solid-liquid separation to obtain solid biogas residue and solid-liquid separated biogas slurry. The solid biogas residue is sent to anaerobic digester 4, while the solid-liquid separated biogas slurry enters the first aerogel adsorption column 1 for adsorption.

[0070] Initial feed: Valve 5-1 is closed, valves 5-2 and 5-3 are open, and the remaining valves are closed. The persulfate-pretreated biogas slurry passes through the first aerogel adsorption column 1. The Fe3O4@NH2-Zn-MOFs in the first aerogel adsorption column 1 activate the persulfate PS through the interaction between Fe(II)-O-Zn(II), increasing the ability to generate ROS and enhancing phosphorus release. Circulating adsorption: After feeding, valve 5-1 is opened. The biogas slurry after solid-liquid separation circulates through the first aerogel adsorption column 1 while undergoing anaerobic digestion, activating the persulfate PS and adsorbing PO4. 3- Adsorption saturation treatment: When the first aerogel adsorption column 1 is close to saturation, the second valve 5-2 and the third valve 5-3 are closed, and the fourth valve 5-4 and the fifth valve 5-5 are opened. The biogas slurry after solid-liquid separation enters the second aerogel adsorption column 2 for adsorption. Elution and crystallization: The sixth valve 5-6 and the seventh valve 5-7 are opened, and sulfuric acid is added to the first aerogel adsorption column 1 for elution. The high-concentration phosphate leachate eluted from the column crystallizes in the crystallization section. The pH value is adjusted and Fe is added. 3+ FePO4 crystals are recovered from high-concentration phosphate leachate. Alternating use: When the second aerogel adsorption column 2 is near saturation, the fourth valve 5-4, fifth valve 5-5, sixth valve 5-6, and seventh valve 5-7 are closed, while the second valve 5-2, third valve 5-3, eighth valve 5-8, and ninth valve 5-9 are opened. The first aerogel adsorption column 1 is used for adsorption, and the second aerogel adsorption column 2 is used for elution. This alternating use allows for simultaneous adsorption and crystallization, improving overall recovery efficiency. The recovered high-purity FePO4 can reach 90% purity.

[0071] The pH value can be precisely adjusted by adding NaOH solution or dilute hydrochloric acid (HCl) to maintain the system at pH 6.0-7.5.

[0072] When Fe in the system 3+ When the concentration decreases, it is restored by adding ferric sulfate (Fe2(SO4)3) solution to ensure the supply of metal ions required for the subsequent FePO4 crystallization reaction.

[0073] The Fe3O4@NH2-Zn-MOFs used in this process introduce amino functional groups, providing additional adsorption sites and significantly improving the material's phosphorus adsorption capacity. Fe3O4 interacts with persulfate, activating it and generating more reactive oxygen species (ROS), further enhancing phosphorus release. Valve control allows for simultaneous adsorption and desorption crystallization, improving overall recovery efficiency and reducing equipment investment and operating costs. Adjusting the pH and supplementing Fe... 3+ High-purity FePO4 crystals can be recovered from high-concentration phosphate leachate, thus achieving effective utilization of phosphorus resources.

[0074] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A Fe304@NH2-Zn-MOFs adsorption method for recovering phosphorus from a pretreated biogas slurry with persulfate, characterized in that, The method comprises the following steps: (1) performing solid-liquid separation on the biogas slurry pretreated by the persulfate to obtain a solid-liquid separated biogas slurry; (2) the solid-liquid separated biogas slurry enters a Fe3O4@NH2-Zn-MOFs aerogel adsorption column for adsorption to obtain a saturated adsorption material; (3) the saturated adsorption material is reused after desorption and regeneration to obtain a desorption liquid; (4) the desorption liquid is crystallized and recovered to recover FePO4 crystals.

2. The Fe304@NH2-Zn-MOFs adsorption method for recovering phosphorus from the biogas slurry pretreated by persulfate according to claim 1, characterized in that, Steps (2), (3) and (4) specifically comprise the following processes: The Fe3O4@NH2-Zn-MOFs composite material is fixed on the aerogel adsorption column to obtain a Fe3O4@NH2-Zn-MOFs aerogel adsorption column; PO4 in the biogas slurry separated by the adsorption device of Fe3O4@NH2-Zn-MOFs is eluted by an acid solution 3- is transferred to the Fe3O4@NH2-Zn-MOFs aerogel adsorption column, and PO4 adsorbed in the Fe3O4@NH2-Zn-MOFs aerogel adsorption column is eluted by an acid solution 3- to obtain a phosphate leaching solution, i.e., the desorption solution Adjusting pH and replenishing Fe 3+ recovering FePO4 crystals from the phosphate leach solution.

3. The Fe304@NH2-Zn-MOFs adsorption method for recovering phosphorus from the biogas slurry pretreated by persulfate according to claim 2, characterized in that, The preparation process of the Fe3O4@NH2-Zn-MOFs composite material comprises the following steps: The MOFs material is modified by introducing an amino group, and an NH2-Zn-MOFs composite material is prepared by a solvothermal method; Based on the prepared NH2-Zn-MOFs composite material, a Fe3O4@NH2-Zn-MOFs composite material is prepared by an embedding method.

4. The Fe304@NH2-Zn-MOFs adsorption method for recovering phosphorus from the biogas slurry pretreated by persulfate according to claim 3, characterized in that, The process of preparing the NH2-Zn-MOFs composite material by introducing an amino group to modify the MOFs material and using a solvothermal method comprises the following steps: The zinc salt solution and the amino carboxylic acid ligand solution are mixed, and then the o-phenylenediamine solution is added to perform a first reaction, and then the NH2-Zn-MOFs composite material is obtained by washing and drying after the reaction; Based on the prepared NH2-Zn-MOFs composite material, a Fe3O4@NH2-Zn-MOFs composite material is prepared by an embedding method, which comprises the following steps: The prepared NH2-Zn-MOFs composite material is dispersed in water from which dissolved oxygen is removed, ammonia water is added, and under stirring and nitrogen protection, ferric salt and ferrous salt are added to perform a second reaction, and then the Fe3O4@NH2-Zn-MOFs composite material is obtained by purification, washing and drying after the reaction; The zinc salt in the zinc salt solution is zinc nitrate hexahydrate; The zinc salt solution is a solution obtained by dissolving a zinc salt in water; The amino carboxylic acid ligand in the amino carboxylic acid ligand solution is 5-aminoisophthalic acid; The amino carboxylic acid ligand solution is a solution obtained by dissolving an amino carboxylic acid ligand in a mixed solution of ethanol and N,N-dimethylformamide; The o-phenylenediamine solution is a solution obtained by dissolving o-phenylenediamine in a mixed solution of ethanol and N,N-dimethylformamide; The first reaction is performed in a sealed reaction kettle, heated to 80-120°C and kept for 30-42 hours; The preparation process of the water from which dissolved oxygen is removed comprises the following steps: taking deionized water, pretreating with nitrogen to obtain the water from which dissolved oxygen is removed; The ferric salt is ferric chloride hexahydrate The ferrous salt is ferrous chloride tetrahydrate; The second reaction is performed under stirring at 55-75°C water bath for 1-3 hours.

5. The Fe304@NH2-Zn-MOFs adsorption method for recovering phosphorus from the biogas slurry pretreated by persulfate according to claim 2, characterized in that, The process of fixing the Fe3O4@NH2-Zn-MOFs composite material on the aerogel adsorption column to obtain a Fe3O4@NH2-Zn-MOFs aerogel adsorption column comprises the following steps: Dissolve chitosan in formic acid to obtain a chitosan solution; Add the Fe3O4@NH2-Zn-MOFs composite material to the obtained chitosan solution to obtain a mixed emulsion; Add glutaraldehyde to the obtained mixed emulsion to perform a crosslinking reaction, thereby obtaining Fe3O4@NH2-Zn-MOFs hydrogel; Soak the obtained Fe3O4@NH2-Zn-MOFs hydrogel in an aqueous formic acid solution for 1-5 hours, vacuum freeze dry for 36-72 hours, and then wash to obtain a Fe3O4@NH2-Zn-MOFs aerogel adsorption column.

6. A Fe304@NH2-Zn-MOFs adsorption device for realizing the Fe304@NH2-Zn-MOFs adsorption method for recovering phosphorus from the persulfate pretreated biogas slurry according to any one of claims 1-5, characterized in that, The Fe3O4@NH2-Zn-MOFs adsorption device comprises a first aerogel adsorption column (1), a second aerogel adsorption column (2), and a crystallizer (3); The first aerogel adsorption column (1) and the second aerogel adsorption column (2) are respectively connected to the crystallizer (3) through pipelines; The first aerogel adsorption column (1) and the second aerogel adsorption column (2) are both Fe3O4@NH2-Zn-MOFs aerogel adsorption columns. 7.The Fe3O4@NH2-Zn-MOFs adsorption device of claim 6, wherein, The Fe3O4@NH2-Zn-MOFs adsorption device further comprises an anaerobic digestion reactor (4); The first aerogel adsorption column (1) and the second aerogel adsorption column (2) are respectively connected to the anaerobic digestion reactor (4) through pipelines. 8.The Fe3O4@NH2-Zn-MOFs adsorption device of claim 7, wherein, A second valve (5-2) is arranged on the pipeline between the outlet of the first aerogel adsorption column (1) and the inlet of the anaerobic digestion reactor (4); A fourth valve (5-4) is arranged on the pipeline between the outlet of the second aerogel adsorption column (2) and the inlet of the anaerobic digestion reactor (4); A first valve (5-1) is arranged on the pipeline between the second valve (5-2) and the inlet of the anaerobic digestion reactor (4) and on the pipeline between the fourth valve (5-4) and the inlet of the anaerobic digestion reactor (4); A third valve (5-3) is arranged on the pipeline between the inlet of the first aerogel adsorption column (1) and the outlet of the anaerobic digestion reactor (4); A fifth valve (5-5) is arranged on the pipeline between the inlet of the second aerogel adsorption column (2) and the outlet of the anaerobic digestion reactor (4); A sixth valve (5-6) is arranged on the pipeline between the inlet of the first aerogel adsorption column (1) and the outlet of the crystallizer (3); An eighth valve (5-8) is arranged on the pipeline between the inlet of the second aerogel adsorption column (2) and the outlet of the crystallizer (3); A seventh valve (5-7) is arranged on the pipeline between the outlet of the first aerogel adsorption column (1) and the inlet of the crystallizer (3); A ninth valve (5-9) is arranged on the pipeline between the outlet of the second aerogel adsorption column (2) and the inlet of the crystallizer (3). 9.The Fe3O4@NH2-Zn-MOFs adsorption device of claim 8, wherein, When the initial feed, the first valve (5-1) is closed, the second valve (5-2), the third valve (5-3) is opened, the fourth valve (5-4), the fifth valve (5-5), the sixth valve (5-6), the seventh valve (5-7), the eighth valve (5-8), the ninth valve (5-9) is in a closed state, the pretreated biogas slurry is passed through the first aerogel adsorption column (1), and the Fe3O4@NH2-Zn-MOFs in the first aerogel adsorption column (1) activates the persulfate through the interaction between Fe(II)-O-Zn(II); After the feeding is completed, the first valve (5-1) is opened, and the biogas liquid after solid-liquid separation is circulated through the first aerogel adsorption column (1) while being subjected to anaerobic digestion, and the activated persulfate simultaneously adsorbs PO4 3- ; When the first aerogel adsorption column (1) is saturated, the second valve (5-2) and the third valve (5-3) are closed, the fourth valve (5-4) and the fifth valve (5-5) are opened, and the solid-liquid separated biogas slurry enters the second aerogel adsorption column (2) for adsorption; the sixth valve (5-6) and the seventh valve (5-7) are opened, and an acidic solution is added to the first aerogel adsorption column (1) for elution, and the eluted phosphate leaching solution is crystallized in the crystallizer (3). 10.The Fe3O4@NH2-Zn-MOFs adsorption device of claim 9, wherein, When the second aerogel adsorption column (2) is saturated, the fourth valve (5-4), the fifth valve (5-5), the sixth valve (5-6), and the seventh valve (5-7) are closed, the second valve (5-2), the third valve (5-3), the eighth valve (5-8), and the ninth valve (5-9) are opened, the first aerogel adsorption column (1) is used for adsorption, and the second aerogel adsorption column (2) is eluted, which are used alternately and simultaneously for adsorption and crystallization.

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