Kitchen biogas residue micro-plastic deep separation method based on in-situ biological membrane stripping and hydrophobic magnetic induction

Abstract

The invention belongs to the technical field of solid waste treatment and resource utilization, and relates to a kitchen biogas residue micro-plastic deep separation method based on in-situ biological membrane stripping and hydrophobic magnetic induction. Comprising the following steps: adding an EPS deconstruction compound enzyme preparation and a cationic chelating agent into kitchen biogas residues subjected to anaerobic digestion, and carrying out ultrasonic treatment to strip a biological membrane on the surface of micro-plastic so as to obtain biogas residue slurry; the EPS deconstruction compound enzyme preparation is prepared from protease, alpha-amylase and cellulase; fully mixing super-hydrophobic magnetic nanoparticles with the biogas residue slurry, and then carrying out magnetic separation; the super-hydrophobic magnetic nanoparticles are magnetic nanoparticles of which the surfaces are modified with hydrophobic groups. According to the method provided by the invention, through a chemical-physical synergistic effect, efficient stripping of a biological membrane on the surface of the micro-plastic is realized, the micro-plastic is accurately captured in a targeted manner by utilizing a hydrophobic magnetic effect, meanwhile, the dehydration performance of the biogas residues is improved, and synergistic interaction of removal of the micro-plastic and recycling of the biogas residues is realized.

Description

Technical Field

[0001] This invention belongs to the field of solid waste treatment and resource utilization technology, and relates to a method for deep separation of microplastics from kitchen waste biogas residue based on in-situ biofilm stripping and hydrophobic magnetic induction. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] With the widespread adoption of co-anaerobic digestion technology for food waste and organic solid waste, the yield of anaerobic digestion residue has been increasing year by year. Residue is rich in nutrients such as nitrogen, phosphorus, potassium, and organic matter, and land application (returning it to the field) is its most economical and mainstream resource utilization method. However, because food waste inevitably contains plastic packaging, disposable lunch boxes, and other plastic waste, these plastics are broken down into microplastics with particle sizes of less than 5mm or even less than 1mm during the crushing and mixing processes of anaerobic digestion, and remain in the residue for a long time.

[0004] Microplastics are difficult to degrade and easily migrate. If returned to the field with biogas residue, they can damage soil structure, affect crop growth, and even enter the human body through the food chain, harming the ecological environment and human health. Therefore, removing microplastics from biogas residue is a prerequisite for its safe resource utilization. However, existing biogas residue microplastic treatment technologies have many significant shortcomings and are difficult to meet practical application needs:

[0005] (1) Physical screening failure: Existing physical screening equipment such as vibrating screens and drum screens are mainly for impurities with a particle size greater than 2mm. They have a very poor interception effect on microplastics with a particle size less than 2mm, and the removal rate is usually less than 30%. (2) Difficulty in density sorting: During anaerobic digestion, microorganisms secrete a large amount of extracellular polymers (EPS). These EPS tightly wrap the surface of microplastics, changing the surface properties of microplastics from "hydrophobic" to "hydrophilic". At the same time, the bioflocculation of EPS increases the apparent density of microplastics, resulting in a high overlap between their settling coefficient and the organic sludge particles in the biogas residue. Traditional air flotation and sedimentation methods cannot achieve effective separation. (3) Serious loss of resources: If the air flotation method is forcibly used to separate microplastics, it will inevitably take away a large amount of light organic matter (such as humus) from the biogas residue, resulting in a significant reduction in the fertilizer efficiency of the biogas residue and loss of its resource value; (4) Risk of secondary pollution: Some technologies use strong acids and strong alkalis to degrade microplastics. Although they can achieve a certain removal effect, they will destroy the nutrients in the biogas residue and the acid and alkali waste liquid produced will easily cause secondary pollution.

[0006] In summary, existing technologies cannot achieve efficient and precise removal of microplastics with small particle sizes from biogas residue, and may lead to resource loss or secondary pollution. Therefore, there is an urgent need to develop a technical solution that can accurately identify microplastics, efficiently separate microplastics from high-viscosity, complex biogas residue systems, and also facilitate the resource utilization of biogas residue. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for deep separation of microplastics from kitchen waste biogas residue based on in-situ biofilm stripping and hydrophobic magnetic induction. The method provided by the present invention achieves efficient stripping of biofilms on the surface of microplastics through chemical-physical synergy, accurately targets and captures microplastics using hydrophobic magnetic effects, and improves the dewatering performance of biogas residue, thereby achieving synergistic effects of microplastic removal and biogas residue resource utilization.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A method for deep separation of microplastics from kitchen waste biogas residue based on in-situ biofilm exfoliation and hydrophobic magnetic induction includes the following steps: EPS deconstruction complex enzyme preparation and cationic chelating agent are added to the anaerobic digested food waste residue, and ultrasonic treatment is performed to remove the biofilm on the surface of microplastics, thereby obtaining a waste residue slurry; the EPS deconstruction complex enzyme preparation is composed of protease, α-amylase and cellulase. The superhydrophobic magnetic nanoparticles are thoroughly mixed with the biogas residue slurry and then magnetically separated; the superhydrophobic magnetic nanoparticles are magnetic nanoparticles with hydrophobic groups modified on their surface.

[0009] EPS is a core component of the biofilm on the surface of microplastics, mainly composed of proteins, polysaccharides, cellulose, etc., and depends on calcium. 2+ Mg 2+The divalent cations maintain the stable structure of EPS. This invention uses an EPS deconstruction complex enzyme preparation composed of protease, α-amylase, and cellulase to degrade the protein and polysaccharide backbone of the biofilm. A cationic chelating agent captures the divalent cations that maintain the EPS structure, thus disrupting the stable structure of EPS. Simultaneously, the cavitation effect of ultrasonic treatment generates localized high temperature, high pressure, and strong shear force, further accelerating the rupture and peeling of the biofilm. Ultimately, the hydrophilic biofilm on the microplastic surface is forcibly peeled off, restoring the original hydrophobic surface properties of the microplastic. After the above treatment, only the microplastic in the biogas residue system regains its hydrophobicity, while organic sludge particles and nutrients remain hydrophilic components. To address this, based on the principle of similar compatibility and the principle of minimizing surface energy, this invention uses superhydrophobic magnetic nanoparticles to thoroughly mix the treated biogas residue slurry. During mixing, the superhydrophobic magnetic nanoparticles specifically adsorb and aggregate on the microplastic surface, forming a stable "microplastic-magnetic seed" composite. The hydrophilic organic sludge particles and nutrients do not interact with the hydrophobic magnetic seeds and remain dispersed in the slurry. Then, the "microplastic-magnetic seed" composite is separated from the slurry through magnetic separation, thereby achieving deep separation of microplastics from kitchen waste biogas residue.

[0010] Addressing the common problem of existing technologies neglecting the core obstacle of microplastic surface biofilms (EPS) to separation efficiency, resulting in low separation efficiency, this invention breaks away from the traditional passive separation approaches such as "physical sieving" and "density sorting." It pioneers an active separation logic of "in-situ biofilm peeling-hydrophobic magnetic targeting capture," precisely identifying the core contradiction of "biofilm encapsulation leading to the hydrophilicity of microplastics." Through chemical-physical synergy, it actively peels off the biofilm, restoring the inherent hydrophobicity of microplastics. Then, it utilizes the "like dissolves like" principle to achieve precise differentiation between microplastics and biogas residue components. This fundamentally solves the technical challenge of separating microplastics with small particle sizes and constructs a complete technical chain of "problem targeting - principle innovation - solution implementation."

[0011] The beneficial effects of this invention are as follows: (1) Precise and targeted separation with high microplastic removal rate: This invention restores the hydrophobicity of microplastics through "biofilm stripping" and uses the specific adsorption of "hydrophobic magnetic seeds" to achieve targeted capture of microplastics, fundamentally solving the problem of the difficulty in separating microplastics from biogas residue components. The microplastic removal rate can reach more than 95%. At the same time, the hydrophobic magnetic seeds only bind to microplastics and do not adsorb organic sludge, nutrients, etc. in biogas residue, thus avoiding the loss of biogas residue fertilizer effect and ensuring its resource value.

[0012] (2) Synergistically improve the dewatering performance of biogas residue and reduce disposal costs: The method of the present invention can effectively reduce the content of "bound water" in biogas residue by destroying EPS (EPS is the main carrier of bound water). After mechanical dewatering (such as plate and frame filter press), the moisture content of the filter cake of the clean biogas residue treated by the present invention can be reduced from more than 80% in traditional treatment methods to less than 60%, which greatly reduces the volume and weight of the filter cake and reduces the cost of subsequent transportation, landfill or incineration.

[0013] (3) Environmentally friendly and free from secondary pollution: The EPS deconstruction complex enzyme preparation used in this invention is biodegradable, the cationic chelating agent and organic solvent are easy to handle, and the magnetic seeds can be recycled and reused (recovery rate ≥90%). The entire process has no toxic or harmful waste liquid or waste residue discharge, which meets the requirements of green environmental protection.

[0014] (4) The process is simple and easy to promote industrially: The method provided by this invention can use mature chemical equipment (homogenization tank, stirred reaction vessel, high gradient magnetic separator, magnetic separator, etc.), the process parameters are easy to control, the operation is simple, and it can be directly connected to the existing biogas residue treatment production line without large-scale transformation. The industrial promotion prospects are broad. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0016] Figure 1 This is a process flow diagram of an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the biofilm peeling and hydrophobic magnetic seed adsorption mechanism on the microplastic surface in this invention.

[0018] Figure 3 The images show SEM images of untreated kitchen waste biogas residue microplastics and SEM images of microplastics after pretreatment in step S1, as shown in Example 1 of this invention. Detailed Implementation

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] Given that existing technologies cannot effectively remove microplastics with small particle sizes encapsulated by biofilms in biogas residue, which can easily lead to resource loss or secondary pollution, this invention proposes a method for deep separation of microplastics in kitchen waste biogas residue based on in-situ biofilm stripping and hydrophobic magnetic induction to solve the above technical problems.

[0022] A typical embodiment of the present invention provides a method for deep separation of microplastics from kitchen waste biogas residue based on in-situ biofilm exfoliation and hydrophobic magnetic induction, comprising the following steps: EPS deconstruction complex enzyme preparation and cationic chelating agent are added to the anaerobic digested food waste residue, and ultrasonic treatment is performed to remove the biofilm on the surface of microplastics, thereby obtaining a waste residue slurry; the EPS deconstruction complex enzyme preparation is composed of protease, α-amylase and cellulase. The superhydrophobic magnetic nanoparticles are thoroughly mixed with the biogas residue slurry and then magnetically separated; the superhydrophobic magnetic nanoparticles are magnetic nanoparticles with hydrophobic groups modified on their surface.

[0023] This invention utilizes a combination of EPS deconstruction complex enzyme preparation and cationic chelating agent with low-frequency ultrasonic stripping to remove biofilm and restore the hydrophobicity of microplastics. Microplastics are specifically captured by superhydrophobic magnetic nanoparticles, and solid-liquid separation is achieved through high-gradient magnetic separation. The magnetic seeds are recyclable, resulting in no secondary pollution. This invention achieves a microplastic removal rate of over 95% and can reduce the moisture content of the filter cake after mechanical dewatering of biogas residue from 80% to below 60%, combining the advantages of precise separation, synergistic effect, and environmental friendliness.

[0024] In some embodiments, before adding the EPS deconstruction complex enzyme preparation and the cationic chelating agent, the moisture content of the anaerobic digested food waste residue is adjusted to 90%~95%. Under these conditions, it is more conducive to the peeling off of the biofilm on the microplastic surface.

[0025] In the EPS deconstruction complex enzyme preparation, protease is responsible for degrading proteins in EPS, α-amylase degrades polysaccharides, and cellulase degrades cellulose. The three work synergistically to achieve efficient EPS deconstruction. In some embodiments, the mass ratio of protease, α-amylase, and cellulase is (2~4):(1~2):1. Under this condition, the deconstruction effect on EPS is better.

[0026] In some embodiments, the amount of EPS deconstruction complex enzyme preparation added is 0.1% to 0.5% of the dry weight of kitchen waste biogas residue. This dosage ensures the biofilm stripping effect while avoiding cost waste caused by excessive enzyme.

[0027] In some embodiments, the cationic chelating agent is selected from aminocarboxylate or hydroxycarboxylate chelating agents. Specifically, the cationic chelating agent is disodium ethylenediaminetetraacetate (EDTA-2Na) or sodium citrate. Studies have shown that when the cationic chelating agent is EDTA-2Na or sodium citrate, especially when the concentration in the slurry is 0.01~0.05 mol / L, it can efficiently capture Ca from EPS. 2+ Mg 2+ It disrupts the cross-linking structure of EPS without damaging the nutrients in biogas residue.

[0028] In some embodiments, the concentration of the cationic chelating agent in the slurry is 0.01~0.05 mol / L.

[0029] In some embodiments, the ultrasonic treatment conditions for peeling off the biofilm on the microplastic surface are: frequency of 20~40kHz, power of 100~300W, and time of 20~60 min.

[0030] In some embodiments, the water contact angle of the superhydrophobic magnetic nanoparticles is greater than 110°.

[0031] In some embodiments, the average particle size of the superhydrophobic magnetic nanoparticles is 50~200 nm.

[0032] In some embodiments, the superhydrophobic magnetic nanoparticles are obtained by modifying the surface of magnetic nanoparticles with γ-methacryloyloxypropyltrimethoxysilane or stearic acid. This ensures that they possess excellent hydrophobicity and magnetic responsiveness.

[0033] In some embodiments, the amount of superhydrophobic magnetic nanoparticles added is 0.3% to 1.0% of the dry weight of kitchen waste biogas residue. This condition enables sufficient capture of microplastics.

[0034] After the superhydrophobic magnetic nanoparticles are thoroughly mixed with the biogas residue slurry, the magnetic particles can be attached to the surface of the microplastics by utilizing hydrophobic interactions to form a "microplastic-magnetic seed" composite. Through magnetic separation, the "microplastic-magnetic seed" composite can be trapped under the action of a magnetic field, thereby achieving the separation of the microplastics from the biogas residue slurry. In some embodiments, the magnetic field strength is 0.5~1.5 T during magnetic separation.

[0035] In some embodiments, a high-gradient magnetic separator is used for magnetic separation, with a slurry flow rate of 0.5~2.0 m / h. This condition, combined with a magnetic field strength of 0.5~1.5 T, enables efficient retention of the "microplastic-magnetic seed" composite and rapid separation of clean biogas residue.

[0036] In some embodiments, the magnetically separated composite is subjected to desorption treatment to break the bond between the superhydrophobic magnetic nanoparticles and the microplastics. Specifically, the desorption treatment process involves adding an organic solvent to the composite and performing desorption at 25–40°C under ultrasonic-assisted conditions. More specifically, the organic solvent is selected from ethanol or acetone.

[0037] The preferred steps of the method described in this invention are as follows: Figure 1 As shown, its principle is as follows Figure 2 As shown, specifically: Step S1: Pretreatment of biogas residue homogenization and biofilm stripping The anaerobic digested food waste residue is sent to a homogenizing tank, and the moisture content of the residue is adjusted to 90%-95%. Then, EPS deconstruction compound enzyme preparation and cationic chelating agent are added to the homogenizing tank. The low-frequency ultrasonic generator is turned on, and the reaction is stirred for 20-60 minutes under a low-frequency ultrasonic field (ultrasonic frequency of 20-40 kHz and power of 100-300 W) to achieve the peeling of the biofilm on the surface of microplastics.

[0038] The core principle of this step is that EPS is the core component of the biofilm on the surface of microplastics, mainly composed of proteins, polysaccharides, cellulose, etc., and depends on Ca²⁺. + Mg² + The divalent cations maintain the stable structure of the EPS. This invention uses an EPS deconstruction complex enzyme preparation to degrade the protein and polysaccharide backbone of the biofilm. A cationic chelating agent captures the divalent cations that maintain the EPS structure, thereby disrupting the stable structure of the EPS. At the same time, the cavitation effect of low-frequency ultrasound generates local high temperature, high pressure and strong shear force, which further accelerates the rupture and peeling of the biofilm. Ultimately, the hydrophilic biofilm on the surface of the microplastic is forcibly peeled off, restoring the original hydrophobic surface properties of the microplastic.

[0039] Step S2: Hydrophobic magnetic seed targeted aggregation induction The biogas residue slurry pretreated in step S1 is fed into a stirred reactor, and superhydrophobic magnetic nanoparticles (magnetic seeds) are added to it. The mixture is stirred rapidly at a speed of 300~500 r / min for 10~30 min to allow the magnetic seeds and microplastics to fully interact.

[0040] The core principle of this step is as follows: After treatment in step S1, only the microplastics in the biogas residue system regain hydrophobicity, while the organic sludge particles and nutrients remain hydrophilic components. Based on the principle of similar compatibility and the principle of minimizing surface energy, the superhydrophobic magnetic nanoparticles will specifically adsorb and aggregate on the surface of the microplastics, forming a stable "microplastic-magnetic seed" composite; while the hydrophilic organic sludge particles, nutrients, and other components do not interact with the hydrophobic magnetic seeds and remain dispersed in the slurry.

[0041] Step S3: High-gradient magnetic separation The mixed slurry obtained in step S2 is pumped into a high gradient magnetic separator (HGMS), and the slurry flow rate is adjusted to 0.5~2.0 m / h. Under the action of a strong magnetic field of 0.5~1.5 T, the "microplastic-magnetic seed" composite is trapped by the magnetic medium in the magnetic separator; while the clean biogas residue slurry (containing organic sludge, nutrients, etc.) that is not combined with magnetic seeds passes through the magnetic field and enters the subsequent deep dewatering section.

[0042] Step S4: Magnetic Seed Recovery and Microplastic Disposal The "microplastic-magnetic seed" composite retained by the high-gradient magnetic separator is sent to a desorption tank. An organic solvent is added to the desorption tank, the temperature is adjusted to 25-40 °C, and an ultrasonic generator (e.g., 40 kHz, 200 W) is turned on for ultrasonic desorption for 15-30 min to destroy the hydrophobic adsorption between the magnetic seed and the microplastic. The desorbed mixture is then sent to a magnetic separator, where the magnetic seed is magnetically separated and recovered. After cleaning and drying, it is regenerated and reused. The desorbed microplastic is sent to a heat treatment device (such as an incinerator) for harmless treatment after solid-liquid separation, or sent to a designated landfill for safe landfilling.

[0043] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0044] The raw materials and equipment used in the embodiments of this invention are all conventional commercial products, and the testing methods used are all national or industry standard methods.

[0045] The food waste biogas residue used in this embodiment of the invention all came from a certain food waste co-anaerobic digestion treatment plant, and the basic characteristics of the biogas residue are shown in Table 1; the protease (enzyme activity 10000 U / g), α-amylase (enzyme activity 8000 U / g), and cellulase (enzyme activity 5000 U / g) in the EPS deconstruction complex enzyme preparation were all purchased from a certain biotechnology company; the superhydrophobic magnetic nanoparticles were all self-made, and the preparation method was as follows: using Fe3O4 nanoparticles as the core, grafting KH-570 or stearic acid through the sol-gel method, and then washing and drying them; the high gradient magnetic separator (HGMS) model was SLon-100, and the magnetic field strength was adjustable; the microplastic detection was carried out by Fourier transform infrared spectroscopy (FTIR) combined with microscopic counting method, and the moisture content of the filter cake was detected by gravimetric method (GB / T 24121-2009).

[0046] Table 1 Basic characteristics of food waste biogas residue Moisture content (%) Organic matter content (%) on a dry basis Dry basis nitrogen content (%) Phosphorus content (%) on dry basis Initial microplastic content (cells / g dry basis) Main particle size range of microplastics (μm) Basic biogas residue 92.5 68.3 3.2 1.8 1256 10-1000 1. The preparation process of KH-570 modified superhydrophobic magnetic nanoparticles with an average particle size of 50 nm and a water contact angle of 115° is as follows: Weigh 10 g of Fe3O4 nanoparticles with an average particle size of 50 nm and disperse them in 300 mL of a mixed solvent of anhydrous ethanol and deionized water (volume ratio 4:1). Disperse the nanoparticles under ultrasonic power of 200 W for 30 min to form a uniform magnetic suspension. Adjust the pH of the suspension to 4.0-5.0 with acetic acid. Under mechanical stirring (300-500 r / min), slowly add 6 g of silane coupling agent KH-570 (γ-methacryloyloxypropyltrimethoxysilane), wherein the mass ratio of KH-570 to Fe3O4 nanoparticles is 0.5:1. After the addition is complete, heat the reaction system to 60-70 °C and reflux the reaction mixture for 6 minutes. h, hydrophobic groups were grafted onto the surface of Fe3O4 using the hydrolysis-condensation reaction of KH-570; after the reaction, the product was magnetically separated using a magnet, and washed 3-5 times alternately with anhydrous ethanol and deionized water to remove unreacted silane coupling agent. Finally, the product was dried in a vacuum drying oven at 60℃ for 12 h to obtain the superhydrophobic magnetic nanoparticles.

[0047] 2. The preparation process of KH-570 modified superhydrophobic magnetic nanoparticles with an average particle size of 100 nm and a water contact angle of 120° is as follows: 10 g of Fe3O4 nanoparticles with an average particle size of 100 nm were weighed and dispersed in a mixed solvent of anhydrous ethanol and deionized water (volume ratio 4:1) for 200 mL. The dispersion was ultrasonically controlled for 30 min to form a homogeneous magnetic fluid. The pH of the system was adjusted to 4.0–5.0 using acetic acid. Under constant temperature water bath conditions of 60 °C and mechanical stirring (400 r / min), 6 g of silane coupling agent KH-570 was slowly added dropwise, maintaining a KH-570 to Fe3O4 mass ratio of 0.6:1. After the addition was complete, the reaction system was heated to 70 °C and continuously refluxed with stirring for 8 h. The hydrolysis and condensation reaction of the silane coupling agent formed a dense hydrophobic coating layer on the surface of the magnetic particles. After the reaction, the product was separated by an external magnetic field and washed at least three times alternately with anhydrous ethanol and deionized water. Finally, it was dried in a vacuum drying oven at 60 °C for 12 h to obtain a product with an average particle size of 100 nm. Superhydrophobic magnetic nanoparticles with a wavelength of nm and a water contact angle of 120°.

[0048] 3. The preparation process of KH-570 modified superhydrophobic magnetic nanoparticles with an average particle size of 200 nm and a water contact angle of 125° is as follows: 10 g of Fe3O4 nanoparticles with an average particle size of 200 nm were weighed and dispersed in a mixed solvent of 300 mL of anhydrous ethanol and deionized water (volume ratio 4:1). The dispersion was ultrasonically dispersed for 40 min to ensure uniform suspension of larger particles. The pH of the system was adjusted to 4.0-5.0 with acetic acid. Under constant temperature water bath at 65℃ and mechanical stirring (500 r / min), 8 g of silane coupling agent KH-570 was slowly added dropwise (controlling the mass ratio of KH-570 to Fe3O4 to be 0.8:1). After the addition was complete, the reaction system was heated to 75℃ and continuously refluxed and stirred for 10 h to promote deep condensation and dense coating of hydrophobic groups on the surface of magnetic particles. After the reaction was completed, the product was separated by an external magnetic field and washed 3-5 times alternately with anhydrous ethanol and deionized water. Finally, it was dried in a vacuum drying oven at 60℃ for 12 h to obtain superhydrophobic magnetic nanoparticles with an average particle size of 200 nm and a water contact angle of 125°.

[0049] 4. The preparation process of stearic acid-modified superhydrophobic magnetic nanoparticles with an average particle size of 100 nm and a water contact angle of 118° is as follows: 10 g of Fe3O4 nanoparticles with an average particle size of 100 nm were weighed and dispersed in 300 mL of anhydrous ethanol. The dispersion was ultrasonically dispersed for 30 min to form a uniform magnetic suspension. 5 g of stearic acid was weighed and added to the suspension, controlling the mass ratio of stearic acid to Fe3O4 to be 0.5:1. The reaction system was heated to 75 °C (slightly higher than the melting point of stearic acid) and reacted at a constant temperature for 6 h under mechanical stirring (400 r / min). The carboxyl groups of stearic acid molecules chemically bonded (coordination or esterification) with the hydroxyl groups on the surface of the magnetic particles, thereby introducing hydrophobic long carbon chains on the particle surface. After the reaction, the product was separated by an external magnetic field and washed 3-5 times with anhydrous ethanol to completely remove unreacted stearic acid. Finally, the product was dried in a vacuum drying oven at 60 °C for 12 h to obtain superhydrophobic magnetic nanoparticles with an average particle size of 100 nm and a water contact angle of 118°.

[0050] Example 1 1. The experimental objective of this embodiment is to verify the biofilm stripping effect of EPS deconstruction complex enzyme preparation (ratio 2:1:1, dosage 0.1% dry basis) + EDTA-2Na (0.01 mol / L) + low-frequency ultrasound synergistic effect, and the targeted separation effect of KH-570 modified Fe3O4 magnetic seeds (50 nm, dosage 0.3% dry basis).

[0051] 2. Material characteristics: The biogas residue used is the basic biogas residue in Table 1; the EPS deconstruction compound enzyme preparation ratio is protease: α-amylase: cellulase = 2:1:1, with a total addition of 0.1% dry basis; the chelating agent is EDTA-2Na, with a concentration of 0.01 mol / L; the superhydrophobic magnetic nanoparticles are KH-570 modified Fe3O4, with an average particle size of 50 nm, a water contact angle of 115°, and an addition of 0.3% dry basis.

[0052] 3. Experimental Procedure: S1: Take 10 kg of basic biogas residue (0.75 kg dry weight) and place it in a homogenizing tank. Add deionized water to adjust the moisture content to 90%. Add 0.75 g (0.1% × 0.75 kg) of EPS deconstruction complex enzyme preparation and EDTA-2Na solution (0.01 mol / L). Turn on the low-frequency ultrasonic generator (20 kHz, 100 W) and stir for 60 min. The microplastics before and after this step are as follows: Figure 3 As shown.

[0053] S2: The pretreated biogas residue slurry is fed into a stirred reactor, and 2.25 g (0.3% × 0.75 kg) of KH-570 modified Fe3O4 magnetic seeds are added. The mixture is stirred at 300 r / min for 30 min.

[0054] S3: Pump the mixed slurry into a high gradient magnetic separator, adjust the magnetic field strength to 0.5 T and the slurry flow rate to 0.5 m / h, and perform magnetic separation.

[0055] S4: Collect the retentate from the magnetic separator, add ethanol (organic solvent), adjust the temperature to 25 ℃, turn on the ultrasonic generator (40 kHz, 200 W) for ultrasonic desorption for 30 min, and then send it to the magnetic separator to recover the magnetic seeds and detect the magnetic seed recovery rate; after solid-liquid separation, the microplastic content of the desorbed microplastics is detected.

[0056] 4. Experimental results: Microplastic removal rate was 95.2%, the moisture content of the filter cake after cleaning biogas residue plate and frame filter press was 59.8%, and the magnetic seed recovery rate was 90.5%.

[0057] Example 2 1. The experimental objective of this embodiment is to verify the biofilm stripping effect of EPS deconstruction complex enzyme preparation (ratio 2:1:1, dosage 0.3% dry basis) + sodium citrate (0.03 mol / L) + low-frequency ultrasound synergistic effect, as well as the targeted separation effect of KH-570 modified Fe3O4 magnetic seeds (100 nm, dosage 0.6% dry basis).

[0058] 2. Material characteristics: The biogas residue used is the basic biogas residue in Table 1; the EPS deconstruction compound enzyme preparation ratio is protease: α-amylase: cellulase = 2:1:1, with a total addition of 0.3% dry basis; the chelating agent is sodium citrate, with a concentration of 0.03 mol / L; the superhydrophobic magnetic nanoparticles are KH-570 modified Fe3O4, with an average particle size of 100 nm, a water contact angle of 120°, and an addition of 0.6% dry basis.

[0059] 3. Experimental Procedure: S1: Take 10 kg of basic biogas residue (0.75 kg dry weight) and put it into the homogenization tank. Add deionized water to adjust the moisture content to 92%. Add 2.25 g (0.3% × 0.75 kg) of EPS deconstruction complex enzyme preparation and sodium citrate solution (0.03 mol / L). Turn on the low-frequency ultrasonic generator (30 kHz, 200 W) and stir for 40 min.

[0060] S2: The pretreated biogas residue slurry is fed into a stirred reactor, and 4.5 g (0.6% × 0.75 kg) of KH-570 modified Fe3O4 magnetic seeds are added. The mixture is stirred at 400 r / min for 20 min.

[0061] S3: Pump the mixed slurry into a high gradient magnetic separator, adjust the magnetic field strength to 1.0 T and the slurry flow rate to 1.0 m / h, and perform magnetic separation.

[0062] S4: Collect the retentate from the magnetic separator, add acetone (organic solvent), adjust the temperature to 30 ℃, turn on the ultrasonic generator (40 kHz, 200 W) for ultrasonic desorption for 25 min, and then send it to the magnetic separator to recover the magnetic seeds; after solid-liquid separation, the content of microplastics is detected.

[0063] 4. Experimental results: Microplastic removal rate was 97.8%, the moisture content of the filter cake after cleaning biogas residue plate and frame filter press was 56.3%, and the magnetic seed recovery rate was 93.2%.

[0064] Example 3 1. The experimental objective of this embodiment is to verify the biofilm stripping effect of EPS deconstruction complex enzyme preparation (ratio 2:1:1, dosage 0.5% dry basis) + EDTA-2Na (0.05 mol / L) + low-frequency ultrasound synergistic effect, and the targeted separation effect of KH-570 modified Fe3O4 magnetic seeds (200 nm, dosage 1.0% dry basis).

[0065] 2. Material characteristics: The biogas residue used is the basic biogas residue in Table 1; the EPS deconstruction compound enzyme preparation ratio is protease: α-amylase: cellulase = 2:1:1, with a total addition of 0.5% dry basis; the chelating agent is EDTA-2Na, with a concentration of 0.05 mol / L; the superhydrophobic magnetic nanoparticles are KH-570 modified Fe3O4, with an average particle size of 200 nm, a water contact angle of 125°, and an addition of 1.0% dry basis.

[0066] 3. Experimental Procedure: S1: Take 10 kg of basic biogas residue (0.75 kg dry weight) and put it into the homogenization tank. Add deionized water to adjust the moisture content to 95%. Add 3.75 g (0.5% × 0.75 kg) of EPS deconstruction complex enzyme preparation and EDTA-2Na solution (0.05 mol / L). Turn on the low-frequency ultrasonic generator (40 kHz, 300 W) and stir for 20 min.

[0067] S2: The pretreated biogas residue slurry is fed into a stirred reactor, and 7.5 g (1.0% × 0.75 kg) of KH-570 modified Fe3O4 magnetic seeds are added. The mixture is stirred at 500 r / min for 10 min.

[0068] S3: Pump the mixed slurry into a high gradient magnetic separator, adjust the magnetic field strength to 1.5 T and the slurry flow rate to 2.0 m / h, and perform magnetic separation.

[0069] S4: Collect the retentate from the magnetic separator, add ethanol (organic solvent), adjust the temperature to 40 ℃, turn on the ultrasonic generator (40 kHz, 200 W) for ultrasonic desorption for 15 min, and then send it to the magnetic separator to recover the magnetic seeds; after solid-liquid separation, the content of microplastics is detected.

[0070] 4. Experimental results: Microplastic removal rate was 98.5%, the moisture content of the filter cake after cleaning biogas residue plate and frame filter press was 53.1%, and the magnetic seed recovery rate was 95.8%.

[0071] Example 4 1. The experimental objective of this embodiment is to verify the biofilm stripping effect of EPS deconstruction complex enzyme preparation (ratio 3:1.5:1, dosage 0.3% dry basis) + EDTA-2Na (0.03 mol / L) + low-frequency ultrasound synergistic effect, as well as the targeted separation effect of stearic acid modified Fe3O4 magnetic seeds (100 nm, dosage 0.6% dry basis).

[0072] 2. Material characteristics: The biogas residue used is the basic biogas residue in Table 1; the EPS deconstruction compound enzyme preparation ratio is protease: α-amylase: cellulase = 3:1.5:1, with a total addition of 0.3% dry basis; the chelating agent is EDTA-2Na, with a concentration of 0.03 mol / L; the superhydrophobic magnetic nanoparticles are stearic acid modified Fe3O4, with an average particle size of 100 nm, a water contact angle of 118°, and an addition of 0.6% dry basis.

[0073] 3. Experimental Procedure: S1: Take 10 kg of basic biogas residue (0.75 kg dry weight) and put it into the homogenization tank. Add deionized water to adjust the moisture content to 92%. Add 2.25 g (0.3% × 0.75 kg) of EPS deconstruction complex enzyme preparation and EDTA-2Na solution (0.03 mol / L). Turn on the low-frequency ultrasonic generator (30 kHz, 200 W) and stir for 40 min.

[0074] S2: The pretreated biogas residue slurry is fed into a stirred reactor, and 4.5 g (0.6% × 0.75 kg) of stearic acid modified Fe3O4 magnetic seeds are added. The mixture is stirred at 400 r / min for 20 min.

[0075] S3: Pump the mixed slurry into a high gradient magnetic separator, adjust the magnetic field strength to 1.0 T and the slurry flow rate to 1.0 m / h, and perform magnetic separation.

[0076] S4: Collect the retentate from the magnetic separator, add acetone (organic solvent), adjust the temperature to 30 ℃, turn on the ultrasonic generator (40 kHz, 200 W) for ultrasonic desorption for 25 min, and then send it to the magnetic separator to recover the magnetic seeds. After solid-liquid separation, the microplastic content of the desorbed microplastics is detected.

[0077] 4. Experimental results: Microplastic removal rate was 97.5%, the moisture content of the filter cake after cleaning biogas residue plate and frame filter press was 55.7%, and the magnetic seed recovery rate was 92.8%.

[0078] Example 5 1. The experimental objective of this embodiment is to verify the biofilm stripping effect of EPS deconstruction complex enzyme preparation (ratio 4:2:1, dosage 0.3% dry basis) + EDTA-2Na (0.03 mol / L) + low-frequency ultrasound synergistic effect, and the targeted separation effect of KH-570 modified Fe3O4 magnetic seeds (100 nm, dosage 0.6% dry basis).

[0079] 2. Material characteristics: The biogas residue used is the basic biogas residue in Table 1; the EPS deconstruction compound enzyme preparation ratio is protease: α-amylase: cellulase = 4:2:1, with a total addition of 0.3% dry basis; the chelating agent is EDTA-2Na, with a concentration of 0.03 mol / L; the superhydrophobic magnetic nanoparticles are KH-570 modified Fe3O4, with an average particle size of 100 nm, a water contact angle of 120°, and an addition of 0.6% dry basis.

[0080] 3. Experimental Procedure: S1: Take 10 kg of basic biogas residue (0.75 kg dry weight) and put it into a homogenizing tank. Add deionized water to adjust the moisture content to 92%. Add 2.25 g (0.3% × 0.75 kg) of EPS deconstruction complex enzyme preparation and EDTA-2Na solution (0.03 mol / L). Turn on the low-frequency ultrasonic generator (30 kHz, 200 W) and stir the reaction for 40 min. S2: The pretreated biogas residue slurry is fed into a stirred reactor, and 4.5 g (0.6% × 0.75 kg) of KH-570 modified Fe3O4 magnetic seeds are added. The mixture is stirred at 400 r / min for 20 min.

[0081] S3: Pump the mixed slurry into a high gradient magnetic separator, adjust the magnetic field strength to 1.0 T and the slurry flow rate to 1.0 m / h, and perform magnetic separation.

[0082] S4: Collect the retentate from the magnetic separator, add ethanol (organic solvent), adjust the temperature to 30 ℃, turn on the ultrasonic generator (40 kHz, 200 W) for ultrasonic desorption for 25 min, and then send it to the magnetic separator to recover the magnetic seeds; after solid-liquid separation, the content of microplastics is detected.

[0083] 4. Experimental results: Microplastic removal rate was 98.2%, the moisture content of the filter cake after cleaning biogas residue plate and frame filter press was 54.2%, and the magnetic seed recovery rate was 94.5%.

[0084] Example 6 1. The purpose of this experiment is to verify the biofilm stripping effect of EPS deconstruction complex enzyme preparation (ratio 2:1:1, dosage 0.3% dry basis) + sodium citrate (0.03 mol / L) + low-frequency ultrasound in a low moisture content (90%) biogas residue system, as well as the targeted separation effect of KH-570 modified Fe3O4 magnetic seeds (100 nm, dosage 0.6% dry basis).

[0085] 2. Material characteristics: The biogas residue used is the basic biogas residue in Table 1, with a moisture content of 90% after adjustment; the EPS deconstruction complex enzyme preparation has a ratio of protease: α-amylase: cellulase = 2:1:1, with a total addition of 0.3% dry basis; the chelating agent is sodium citrate, with a concentration of 0.03 mol / L; the superhydrophobic magnetic nanoparticles are KH-570 modified Fe3O4, with an average particle size of 100 nm, a water contact angle of 120°, and an addition of 0.6% dry basis.

[0086] 3. Experimental Procedure: S1: Take 10 kg of basic biogas residue (0.75 kg dry weight) and put it into the homogenization tank. Add a small amount of deionized water to adjust the moisture content to 90%. Add 2.25 g (0.3% × 0.75 kg) of EPS deconstruction complex enzyme preparation and sodium citrate solution (0.03 mol / L). Turn on the low-frequency ultrasonic generator (30 kHz, 200 W) and stir for 40 min.

[0087] S2: The pretreated biogas residue slurry is fed into a stirred reactor, and 4.5 g (0.6% × 0.75 kg) of KH-570 modified Fe3O4 magnetic seeds are added. The mixture is stirred at 400 r / min for 20 min.

[0088] S3: Pump the mixed slurry into a high gradient magnetic separator, adjust the magnetic field strength to 1.0 T and the slurry flow rate to 1.0 m / h, and perform magnetic separation.

[0089] S4: Collect the retentate from the magnetic separator, add acetone (organic solvent), adjust the temperature to 30 ℃, turn on the ultrasonic generator (40 kHz, 200 W) for ultrasonic desorption for 25 min, and then send it to the magnetic separator to recover the magnetic seeds; after solid-liquid separation, the content of microplastics is detected.

[0090] 4. Experimental results: Microplastic removal rate was 97.3%, the moisture content of the filter cake after cleaning biogas residue plate and frame filter press was 57.1%, and the magnetic seed recovery rate was 93.0%.

[0091] Example 7 1. The experimental objective of this embodiment is to verify the biofilm stripping effect of EPS deconstruction complex enzyme preparation (ratio 2:1:1, dosage 0.3% dry basis) + EDTA-2Na (0.03 mol / L) + low-frequency ultrasound in a biogas residue system with high moisture content (95%), as well as the targeted separation effect of KH-570 modified Fe3O4 magnetic seeds (100 nm, dosage 0.6% dry basis).

[0092] 2. Material characteristics: The biogas residue used is the basic biogas residue in Table 1, with a moisture content of 95% after adjustment; the EPS deconstruction complex enzyme preparation has a ratio of protease: α-amylase: cellulase = 2:1:1, with a total addition of 0.3% dry basis; the chelating agent is EDTA-2Na, with a concentration of 0.03 mol / L; the superhydrophobic magnetic nanoparticles are KH-570 modified Fe3O4, with an average particle size of 100 nm, a water contact angle of 120°, and an addition of 0.6% dry basis.

[0093] 3. Experimental Procedure: S1: Take 10 kg of basic biogas residue (0.75 kg dry weight) and put it into the homogenization tank. Add deionized water to adjust the moisture content to 95%. Add 2.25 g (0.3% × 0.75 kg) of EPS deconstruction complex enzyme preparation and EDTA-2Na solution (0.03 mol / L). Turn on the low-frequency ultrasonic generator (30 kHz, 200 W) and stir the reaction for 40 min.

[0094] S2: The pretreated biogas residue slurry is fed into a stirred reactor, and 4.5 g (0.6% × 0.75 kg) of KH-570 modified Fe3O4 magnetic seeds are added. The mixture is stirred at 400 r / min for 20 min.

[0095] S3: Pump the mixed slurry into a high gradient magnetic separator, adjust the magnetic field strength to 1.0 T and the slurry flow rate to 1.0 m / h, and perform magnetic separation.

[0096] S4: Collect the retentate from the magnetic separator, add ethanol (organic solvent), adjust the temperature to 30 ℃, turn on the ultrasonic generator (40 kHz, 200 W) for ultrasonic desorption for 25 min, and then send it to the magnetic separator to recover the magnetic seeds; after solid-liquid separation, the content of microplastics is detected.

[0097] 4. Experimental results: Microplastic removal rate was 97.6%, the moisture content of the filter cake after cleaning biogas residue plate and frame filter press was 55.9%, and the magnetic seed recovery rate was 92.9%.

[0098] Example 8 1. The purpose of this experiment is to verify the separation effect after the magnetic seeds are recycled three times, as well as the biodegradability (environmental friendliness) of the enzyme preparation.

[0099] 2. Material characteristics: The biogas residue used is the basic biogas residue in Table 1; the EPS deconstruction complex enzyme preparation ratio is protease: α-amylase: cellulase = 2:1:1, with a total addition of 0.3% dry basis; the chelating agent is EDTA-2Na, with a concentration of 0.03 mol / L; the superhydrophobic magnetic nanoparticles are KH-570 modified Fe3O4 magnetic seeds recovered and regenerated in Example 2 (recycled 3 times), with an average particle size of 100 nm, a water contact angle of 119°, and an addition of 0.6% dry basis.

[0100] 3. Experimental Procedure: S1: Take 10 kg of basic biogas residue (0.75 kg dry weight) and put it into a homogenizing tank. Add deionized water to adjust the moisture content to 92%. Add 2.25 g (0.3% × 0.75 kg) of EPS deconstruction complex enzyme preparation and EDTA-2Na solution (0.03 mol / L). Turn on the low-frequency ultrasonic generator (30 kHz, 200 W) and stir for 40 min. After the reaction is completed, detect the enzyme activity residue in the biogas residue slurry (to verify biodegradability).

[0101] S2: The pretreated biogas residue slurry is fed into a stirred reactor, and 4.5 g (0.6% × 0.75 kg) of KH-570 modified Fe3O4 magnetic seeds that have been recycled 3 times are added. The mixture is stirred at 400 r / min for 20 min.

[0102] S3: Pump the mixed slurry into a high gradient magnetic separator, adjust the magnetic field strength to 1.0 T and the slurry flow rate to 1.0 m / h, and perform magnetic separation.

[0103] S4: Collect the retentate from the magnetic separator, add acetone (organic solvent), adjust the temperature to 30 ℃, turn on the ultrasonic generator (40 kHz, 200 W) for ultrasonic desorption for 25 min, and then send it to the magnetic separator to recover the magnetic seeds; after solid-liquid separation, the content of microplastics is detected.

[0104] 4. Experimental results: Microplastic removal rate was 96.9%, the moisture content of the filter cake after cleaning biogas residue plate and frame filtration was 56.8%, and the magnetic seed recovery rate was 92.5%; the enzyme activity residue in the biogas residue slurry was only 8.3% of the initial value, indicating that the enzyme preparation can be rapidly biodegraded without secondary pollution.

[0105] The statistical results of each embodiment are shown in Table 2.

[0106] Table 2 Comparison of the effects of each embodiment Example Microplastic removal rate (%) Moisture content of filter cake (%) Magnetic seed recovery rate (%) Remark 1 95.2 59.8 90.5 Enzyme dosage 0.1%, magnetic seed 50 nm 2 97.8 56.3 93.2 Sodium citrate, magnetic seeds 100 nm 3 98.5 53.1 95.8 Enzyme dosage 0.5%, magnetic field 1.5 T 4 97.5 55.7 92.8 Stearic acid modified magnetic seeds 5 98.2 54.2 94.5 Enzyme ratio 4:2:1 6 97.3 57.1 93.0 The biogas residue has a moisture content of 90%. 7 97.6 55.9 92.8 8 96.9 56.8 92.5 Table 2 shows that: 1. All embodiments exhibit high microplastic removal and magnetic seed recovery rates, while maintaining low filter cake moisture content. This demonstrates that the method of the present invention can accurately, efficiently, and purposefully capture microplastics, while simultaneously improving the dewatering performance of biogas residue and increasing the recycling rate of magnetic seeds.

[0107] 2. Parameter optimization of the EPS deconstruction complex enzyme preparation affects the effectiveness of the method of this invention. In Example 5, the enzyme ratio was 4:2:1, and its microplastic removal rate was 98.2%, significantly higher than the microplastic removal rate (97.8%) of Example 2 with an enzyme ratio of 2:1:1. In Example 3, the removal rate reached 98.5% with an addition of 0.5%, significantly higher than the 95.2% achieved with an addition of 0.1% in Example 1. This indicates that the dosage can be dynamically adjusted based on the EPS content in the biogas residue; for biogas residue with high EPS content, the dosage can be appropriately increased.

[0108] 3. Optimization of parameters for biofilm removal assistance affects the effectiveness of the method of the present invention. In Example 3, biofilm removal was more thorough when using 40 kHz and 300 W, with a removal rate of up to 98.5%; at the same time, the removal rate (98.5%) of Example 3 using 0.05 mol / L EDTA-2Na was higher than that of Example 2 using 0.03 mol / L sodium citrate (97.8%).

[0109] 4. Optimization of the parameters of the superhydrophobic magnetic seeds affects the effectiveness of the method of this invention. Example 2 (KH-570 modified) achieved a removal rate of 97.8%, higher than the 97.5% of Example 4 (stearic acid modified). The removal rates of Examples 2 (100 nm) and 3 (200 nm) were both higher than those of Example 1 (50 nm), indicating that excessively small particle sizes tend to agglomerate, while excessively large particle sizes reduce the specific surface area, affecting adsorption efficiency. Example 3 achieved a removal rate of 98.5% with an addition of 1.0% of the superhydrophobic magnetic seeds; therefore, an appropriate amount of superhydrophobic magnetic seeds can ensure sufficient contact between the magnetic seeds and the microplastics.

[0110] 5. Optimization of the parameters of the magnetic separation process affects the effectiveness of the method of the present invention. In Example 3, the removal rate was 98.5% when using 1.5 T and 2.0 m / h, and in Example 2, it was 97.8% when using 1.0 T and 1.0 m / h. High flow rates (such as >2.0 m / h) require matching with higher magnetic field strength to avoid the "microplastic-magnetic seed" composite being not fully retained.

[0111] 6. The parameter combination in Example 3 (0.5% enzyme addition, 40 kHz / 300 W ultrasound, 1.5 T magnetic field) is one of the optimal cases, indicating that multi-parameter synergistic optimization can further increase the effectiveness of the method of the present invention.

[0112] Comparative Example 1 1. The purpose of this comparative experiment is to verify the separation effect of the physical sieving method (background art defect 1) on microplastics in biogas residue in the prior art, and to serve as the baseline comparison of this invention.

[0113] 2. Material characteristics: The biogas residue used is completely consistent with the basic biogas residue in Table 1; an existing vibrating screen is used (screen mesh size 0.15 mm, corresponding to 150 μm, which is the fine screen mesh size commonly used in existing technology).

[0114] 3. Experimental procedure (excluding the core steps of this invention): Take 10 kg of basic biogas residue (0.75 kg dry weight) and put it into a homogenization tank. Adjust the moisture content to 92% and directly pump it into a vibrating screen for screening. Collect the clean biogas residue under the screen and test the microplastic content, filter cake moisture content and nitrogen and phosphorus nutrient retention rate.

[0115] 4. Experimental results: Microplastic removal rate 28.6% (only a small amount of microplastics with a particle size >150 μm can be retained), filter cake moisture content 82.3% (no EPS destruction step, high bound water content), nitrogen retention rate 94.5%, phosphorus retention rate 93.8% (no chemical action during sieving, no loss of nutrients but extremely poor separation effect).

[0116] Comparative Example 2 1. The purpose of this comparative experiment is to verify the effect of using only hydrophobic magnetic seed magnetic separation when the "biofilm stripping pretreatment" step is missing, highlighting the necessity of biofilm stripping.

[0117] 2. Material characteristics: The biogas residue used is the same as the basic biogas residue in Table 1; the superhydrophobic magnetic seed parameters are exactly the same as those in Example 2 (KH-570 modified Fe3O4, 100 nm, dosage 0.6% dry basis).

[0118] 3. Experimental procedure (step S1 is missing): S1 is omitted (no EPS deconstruction complex enzyme preparation or chelating agent is added, and no ultrasonic treatment is performed); 10 kg of basic biogas residue was directly adjusted to 92% moisture content and sent to a stirred reactor, 4.5 g of superhydrophobic magnetic seeds were added, and the mixture was stirred at 400 r / min for 20 min; subsequent steps S3-S4 are the same as in Example 2.

[0119] 4. Experimental results: Microplastic removal rate was 52.3% (the biofilm on the surface of microplastics was not peeled off, the hydrophobicity was not restored, and the magnetic seed adsorption was insufficient), filter cake moisture content was 79.5% (no EPS damage, no improvement in dehydration performance), and magnetic seed recovery rate was 93.0% (the performance of the magnetic seed itself was not affected, only the adsorption target was insufficient).

[0120] Comparative Example 3 1. The purpose of this comparative experiment is to verify the separation effect of replacing the "superhydrophobic magnetic seeds" of this invention with "ordinary magnetic particles (non-hydrophobic)" and to highlight the core value of the targeting of hydrophobic magnetic seeds.

[0121] 2. Material characteristics: The biogas residue used is the same as the basic biogas residue in Table 1; the biofilm stripping pretreatment parameters are the same as those in Example 2 (enzyme ratio 2:1:1, dosage 0.3% dry basis, sodium citrate 0.03 mol / L, 30 kHz / 200 W sonication for 40 min); the magnetic seed is replaced with unmodified ordinary Fe3O4 magnetic seed (100 nm, water contact angle 35°, hydrophilic, dosage 0.6% dry basis).

[0122] 3. Experimental procedure (key material replacement): Step S1 is completely consistent with Example 2; Step S2 involves adding 4.5 g of ordinary hydrophilic Fe3O4 magnetic seeds, and subsequent steps S3-S4 are consistent with Example 2.

[0123] 4. Experimental Results: Microplastic removal rate was 48.7% (ordinary magnetic seeds lack hydrophobic targeting and simultaneously adsorb hydrophilic organic sludge from the biogas residue, leading to insufficient microplastic capture due to competitive adsorption), filter cake moisture content was 57.2% (S1 step was normal, and dewatering performance was improved), nitrogen retention rate was 85.3%, phosphorus retention rate was 83.6% (ordinary magnetic seeds adsorb organic sludge, resulting in nutrient loss), and magnetic seed recovery rate was 92.7%.

[0124] Comparative Example 4 1. The purpose of this comparative experiment is to verify the effect of using only single enzymatic hydrolysis for biofilm removal when the synergistic effect of "chelating agent + ultrasound" is missing, highlighting the necessity of the multi-technology synergy in step S1 of this invention.

[0125] 2. Material characteristics: The biogas residue used is the same as the basic biogas residue in Table 1; only EPS deconstruction compound enzyme preparation is added (same as in Example 2: ratio 2:1:1, dosage 0.3% dry basis), no chelating agent is added, and no ultrasonic treatment is performed; the hydrophobic magnetic seed parameters are the same as in Example 2.

[0126] 3. Experimental procedure (S1 step missing): S1: The moisture content of the biogas residue was adjusted to 92%, and only 2.25 g of enzyme preparation was added. The reaction was stirred for 40 min (no chelating agent, no ultrasound); the subsequent S2-S4 steps were the same as in Example 2.

[0127] 4. Experimental results: Microplastic removal rate was 69.5% (single enzymatic hydrolysis could not destroy the cross-linked structure of EPS, the biofilm was not completely peeled off, and the hydrophobicity of microplastics was not fully restored), filter cake moisture content was 71.8% (EPS was not completely destroyed, and the removal of bound water was limited), and magnetic seed recovery rate was 93.1%.

[0128] Table 3 shows the comparisons between Examples 1, 3, and 5 and Comparative Examples 1 to 4.

[0129] Table 3. Comprehensive Comparison of Effects between Examples and Comparative Examples Microplastic removal rate (%) Moisture content of filter cake (%) Nitrogen retention rate (%) Phosphorus retention rate (%) Key differences (compared to this invention) Example 1 95.2 59.8 96.2 95.5 The complete process of this invention uses low enzyme dosage. Example 3 98.5 53.1 97.8 96.9 The complete process and optimal parameter combination of this invention Example 5 98.2 54.2 97.5 96.3 The complete process of this invention optimizes the enzyme ratio. Comparative Example 1 28.6 82.3 94.5 93.8 Without any of the core steps of this invention, existing technology Comparative Example 2 52.3 79.5 95.1 94.3 Step S1 is missing; only the magnetic separation core is retained. Comparative Example 3 48.7 57.2 85.3 83.6 Replace the superhydrophobic magnetic seeds of this invention with ordinary magnetic seeds. Comparative Example 4 69.5 71.8 96.0 95.2 S1 step missing chelating agent + ultrasound synergistic effect Table 3 shows that, firstly, Comparative Example 1 is existing technology, lacking any of the core steps of this invention. Its microplastic removal rate is only 28.6%, and the filter cake moisture content is as high as 82.3%, indicating that existing technology cannot effectively remove the tiny microplastic particles encapsulated by the biofilm in biogas residue, and also suffers from poor dewatering performance. Comparisons 2-4 with the Examples show that when pretreatment for biofilm stripping is lacking, or when magnetic capture is performed using ordinary magnetic seeds, or when only EPS deconstruction complex enzyme preparation is used for biofilm stripping pretreatment, microplastics cannot be effectively removed. The microplastic removal rate is below 70%, even below 50%, and the dewatering efficiency is low, resulting in a high filter cake moisture content. Furthermore, the comparison between the Comparative Examples and the Examples also shows that the method of this invention can avoid the loss of biogas residue fertilizer efficiency, ensuring its resource value.

[0130] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for deep separation of microplastics from kitchen waste biogas residue based on in-situ biofilm exfoliation and hydrophobic magnetic induction, characterized in that, Includes the following steps: EPS deconstruction complex enzyme preparation and cationic chelating agent are added to the anaerobic digested food waste residue, and ultrasonic treatment is carried out to remove the biofilm on the surface of microplastics and obtain digestate slurry. The EPS deconstruction complex enzyme preparation is composed of protease, α-amylase and cellulase; The superhydrophobic magnetic nanoparticles are thoroughly mixed with the biogas residue slurry and then magnetically separated; the superhydrophobic magnetic nanoparticles are magnetic nanoparticles with hydrophobic groups modified on their surface.

2. The method as described in claim 1, characterized in that, in Before adding EPS decomposition complex enzyme preparation and cationic chelating agent, the moisture content of the anaerobic digested kitchen waste residue should be adjusted to 90%~95%.

3. The method as described in claim 1, characterized in that, The mass ratio of protease, α-amylase and cellulase is (2~4):(1~2):1; Alternatively, the amount of EPS decomposition compound enzyme preparation added is 0.1% to 0.5% of the dry basis mass of kitchen waste biogas residue.

4. The method as described in claim 1, characterized in that, The cationic chelating agent is selected from aminocarboxylic acid salts or hydroxycarboxylic acid salts; preferably, the cationic chelating agent is disodium ethylenediaminetetraacetate or sodium citrate. Alternatively, the concentration of the cationic chelating agent in the slurry is 0.01~0.05 mol / L.

5. The method as described in claim 1, characterized in that, The ultrasonic treatment conditions for peeling off the biofilm from the microplastic surface are: frequency of 20~40 kHz, power of 100~300 W, and time of 20~60 min.

6. The method as described in claim 1, characterized in that, The water contact angle of the superhydrophobic magnetic nanoparticles is greater than 110°; Alternatively, the average particle size of the superhydrophobic magnetic nanoparticles is 50~200 nm; Alternatively, the superhydrophobic magnetic nanoparticles are obtained by modifying the surface of magnetic nanoparticles with γ-methacryloyloxypropyltrimethoxysilane or stearic acid; Alternatively, the amount of superhydrophobic magnetic nanoparticles added is 0.3% to 1.0% of the dry weight of kitchen waste biogas residue.

7. The method as described in claim 1, characterized in that, During magnetic separation, the magnetic field strength is 0.5~1.5 T; Alternatively, a high-gradient magnetic separator can be used for magnetic separation, with a slurry flow rate of 0.5~2.0 m / h.

8. The method as described in claim 1, characterized in that, The composite after magnetic separation is subjected to desorption treatment to break the bond between the superhydrophobic magnetic nanoparticles and the microplastics.

9. The method of claim 8, characterized in that, The desorption process is as follows: an organic solvent is added to the composite, and desorption is carried out at 25~40℃ under ultrasonic-assisted conditions.

10. The method of claim 9, characterized in that, The organic solvent is selected from ethanol or acetone.

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