Composite magnetic biological filler with gradient magnetic response and surface microstructure and preparation method thereof

Abstract

The invention provides a composite magnetic biological filler with gradient magnetic response and a surface microstructure, which comprises a core layer, a transition layer and a surface functional layer, the mass concentration of neodymium iron boron magnetic powder of the core layer is sequentially reduced, and a preparation method of the composite magnetic biological filler comprises the following steps: putting raw materials of polyethylene and neodymium iron boron magnetic powder of the core layer into a hopper of a double-screw extruder; putting raw materials of polyethylene, neodymium iron boron magnetic powder and hydroxyapatite of a transition layer into a hopper of another twin-screw extruder, putting raw materials of polyethylene, neodymium iron boron magnetic powder, hydroxyapatite and an antioxidant of a surface functional layer into a hopper of a third twin-screw extruder, and injecting a photosensitizer into a second area of the third hopper for melting; conveying each layer of molten melt into a die head through a metering gear pump, extruding to obtain a composite blank, performing ultraviolet radiation, rolling on the surface of the blank to form a microstructure, and finally magnetizing to obtain the composite magnetic biological filler. According to the invention, the magnetic response performance, the biocompatibility and the hydrophilicity are integrated into a whole, and the method can be used for treating water pollution.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental engineering, and particularly relates to a composite magnetic biological filler with gradient magnetic response and surface microstructure and a preparation method thereof. BACKGROUND

[0002] Mobile bed biological membrane reactor (MBBR) is widely used in the field of wastewater treatment due to its high biomass, small footprint, strong impact load resistance and other advantages, and the performance of the suspended biological filler as its core component directly determines the system's biofilm formation speed, biological membrane activity and final treatment efficiency. The modification of traditional biological fillers is mostly focused on the improvement of a single performance, such as giving magnetism by blending magnetic powder to strengthen mass transfer, or improving biological affinity by coating hydroxyapatite on the surface, but the existing technology has obvious limitations: uniform blending of high content of magnetic powder will lead to hydrophobic surface of the filler, uncontrollable roughness, and may also have a magnetic stress effect on microorganisms; the modified layer formed by the post-processing process has weak adhesion with the substrate, and is easy to wear and fall off during long-term use.

[0003] In summary, there is currently a lack of a new type of composite filler in the industry that starts from the design of the filler body structure, organically combines strong magnetic response, biological affinity and stable functional layer, and the existing technology either sacrifices biological compatibility for magnetism, or the modified layer has a short service life, or the function design is single, which cannot meet the needs of efficient, stable and intelligent MBBR process. Therefore, developing a new type of composite filler that can synergistically optimize the magnetic properties, surface properties and structural stability, and promote the rapid, stable and efficient attachment and growth of microorganisms, has become a technical problem to be solved in the field. SUMMARY

[0004] In view of the problems existing in the prior art, the present application provides a composite magnetic biological filler with gradient magnetic response and surface microstructure and a preparation method thereof.

[0005] The present application adopts the following technical solutions: (1) The present application provides a composite magnetic biological filler with gradient magnetic response and surface microstructure, which comprises a core layer, a transition layer and a surface functional layer distributed in sequence; the core layer is a mixture comprising polyethylene and neodymium-iron-boron magnetic powder; the transition layer is a mixture comprising polyethylene, neodymium-iron-boron magnetic powder and hydroxyapatite; the surface functional layer is a mixture comprising polyethylene, neodymium-iron-boron magnetic powder, hydroxyapatite and an antioxidant, and the outer surface of the surface functional layer is provided with a microstructure, and the surface functional layer is grafted with a hydrophilic polymer; the mass concentration of neodymium-iron-boron magnetic powder in the core layer, the transition layer and the surface functional layer decreases in sequence.

[0006] Further, in the core layer, the mass concentration of the neodymium-iron-boron magnetic powder is 3-8%; in the transition layer, the mass concentration of the neodymium-iron-boron magnetic powder is 1-3%, and the mass concentration of the hydroxyapatite is 1-3%; in the surface functional layer, the mass concentration of the neodymium-iron-boron magnetic powder is less than 0.5%, and the mass concentration of the hydroxyapatite is 2-5%.

[0007] The application also provides a preparation method of the composite magnetic biological filler with gradient magnetic response and surface microstructure. S1, the raw material polyethylene and the neodymium-iron-boron magnetic powder of the core layer are premixed and then placed into the hopper of a parallel double-screw extruder, the raw material polyethylene, the neodymium-iron-boron magnetic powder and the hydroxyapatite of the transition layer are premixed and then placed into the hopper of another parallel double-screw extruder, and the raw material polyethylene, the neodymium-iron-boron magnetic powder, the hydroxyapatite and the antioxidant of the surface functional layer are premixed and then placed into the hopper of a third parallel double-screw extruder, and a photosensitizer is injected into the second zone below the hopper of the third parallel double-screw extruder for melt blending; S2, the melt of each layer after melt blending is injected into a special die with a coaxial annular flow channel through a metering gear pump, and is synchronously extruded to obtain a composite embryo; S3, the composite embryo is placed into an ultraviolet irradiation curing chamber, and microgrooves are formed on the surface of the embryo by rolling a embossing roller to form a microstructure; S4, the composite embryo after curing, shaping and having a microstructure is cut into particles, and then is placed into a magnetizing device for magnetization to obtain a composite magnetic biological filler.

[0008] Further, in the step S1, the mass of the photosensitizer is 0.5% of the total mass of the surface functional layer; the photosensitizer comprises hydroxyethyl acrylate, acrylamide, maleic anhydride and a photoinitiator, and the mass ratio of the hydroxyethyl acrylate, the acrylamide, the maleic anhydride and the photoinitiator is 10:60:25:5.

[0009] Further, in the step S1, the mass of the antioxidant is 0.05% of the total mass of the surface functional layer.

[0010] Further, in the step S1, the temperature of the first zone of the three parallel double-screw extruders is 165℃, the temperature of the second zone is 175℃, the temperature of the third zone is 180℃, and the temperature of the die head is 185℃.

[0011] Further, in the step S2, the temperature of the die head is 180℃.

[0012] Further, in the step S3, the main wavelength of the ultraviolet irradiation source in the ultraviolet irradiation curing chamber is 365nm, and the power is 120W / cm. The irradiation intensity is not less than 800mJ / cm 2 .

[0013] Further, in the step S4, firstly, deep magnetization is carried out in a pulse magnetic field of 2.5-3.5T, and then the filler is treated in a rotating weak magnetic field of 0.1-0.3T for 1-3 minutes, so that the filler obtains an anisotropic magnetic moment.

[0014] Further, in the step S4, the magnetizing process is as follows: the filler is placed in the center of the coil of a pulse magnetizer, a pulse magnetic field with a peak strength of 3.0T and a pulse width of 10ms is applied, and the treatment time is 10ms; the filler magnetized by the pulse is transferred to a uniform weak magnetic field with a field strength of 0.20T, a rotating platform is started, and the filler is rotated in the uniform weak magnetic field at a rotating speed of 15rpm for 3 minutes; after the magnetic field is turned off, the magnetizing is completed.

[0015] (Three) The application also provides the use of the composite magnetic biological filler with gradient magnetic response and surface microstructure in water treatment, which can be used for sewage treatment or aquaculture tail water treatment.

[0016] The application has the following beneficial effects: (1) The method of the application integrates strong magnetic response performance, biological affinity, stable hydrophilic surface and reliable mechanical stability by the three-layer structure design of the core layer, the transition layer and the surface functional layer. Meanwhile, the application also provides a preparation method of the filler, which realizes one-time forming of the gradient structure and the surface micro-nano structure by coaxial co-extrusion and ultraviolet synchronous curing process, so as to ensure firm combination and stable performance of the functional layers.

[0017] (2) The gradient composite magnetic biological filler of the application solves the inherent contradiction between high magnetism and excellent biological interface, the inner layer drives the directional migration and enrichment of microorganisms by strong magnetism, the outer layer meets the needs of microorganism colonization by low magnetic disturbance and high affinity interface, and the two work together to improve the biofilm formation speed and significantly enhance the activity of the biofilm; by means of ultraviolet synchronous curing technology, the hydrophilic polymer network and the substrate form stable chemical bonding, and the micro-groove structure formed by physical etching makes the combination strength and durability of the functional layers far exceed those of the traditional coating process, so as to effectively avoid the problem of wear and tear in long-term use; at the same time, the filler is magnetized to accurately respond to a complex external magnetic field, which provides material support for the dynamic regulation of the MBBR process, and has the properties of filler magnetism, biocompatibility, structural stability and process adaptability, and is practical. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the contact angle of the composite magnetic biological filler prepared in Example 1 and the ordinary filler. DETAILED DESCRIPTION

[0019] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application and the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0020] Embodiment 1 The present embodiment provides a composite magnetic biological filler with gradient magnetic response and surface microstructure, comprising: a core layer, a transition layer and a surface functional layer distributed in sequence, wherein: (1) The core layer comprises high-density polyethylene (HDPE) 94.0% and neodymium-iron-boron magnetic powder 6%.

[0021] (2) The transition layer comprises high-density polyethylene 96.5%, neodymium-iron-boron magnetic powder 1.5%, hydroxyapatite (HAp, nanorod, particle size 50-100 nm, length 200-500 nm) 2.0%.

[0022] (3) The surface functional layer comprises high-density polyethylene 95.0%, neodymium-iron-boron magnetic powder with a mass concentration of 0.5%, hydroxyapatite 3.95%, photosensitizer 0.5%, and antioxidant (BASF) 0.05%. The photosensitizer comprises hydroxyethyl acrylate, acrylamide, maleic anhydride and photoinitiator (Irgacure 184), and the mass ratio of hydroxyethyl acrylate, acrylamide, maleic anhydride and photoinitiator is 10:60:25:5.

[0023] The preparation method of the composite magnetic biological filler with gradient magnetic response and surface microstructure described above is as follows: Step 1, the raw material polyethylene and neodymium-iron-boron magnetic powder of the core layer are premixed for 5 minutes and then placed into the hopper of a parallel double-screw extruder, the raw material polyethylene, neodymium-iron-boron magnetic powder and hydroxyapatite of the transition layer are premixed for 5 minutes and then placed into the hopper of another parallel double-screw extruder, and the raw material polyethylene, neodymium-iron-boron magnetic powder, hydroxyapatite and antioxidant of the surface functional layer are premixed for 5 minutes and then placed into the hopper of a third parallel double-screw extruder, the temperature of each zone of the three double-screw extruders is set as: zone 1 165℃, zone 2 175℃, zone 3 180℃, and the die head 185℃. The photosensitizer is injected through a lateral liquid injection pump below the second zone of the hopper of the third parallel double-screw extruder for melt blending. The melt of each layer after melt blending enters the corresponding metering gear pump to accurately control the output flow (the flow ratio of the core layer: transition layer: surface layer ≈4:2.5:3.5).

[0024] Step 2: The melt after molten blending is injected into a specially designed coaxial three-layer annular distribution die head. The die head has three independent coaxial annular flow channels with adjustable flow channel gaps. The die head temperature is 180℃. The final extruded composite preform diameter is 10.0±0.2mm.

[0025] Step 3: Place the composite preform into a UV curing chamber. A row of medium-pressure mercury lamps (main wavelength 365nm, power 120W / cm) is arranged vertically along the preform's direction of travel within the chamber. UV light triggers in-situ free radical polymerization of the photosensitive monomers in the surface layer melt. The monomer radicals initiate acrylamide-maleic anhydride copolymerization, forming a hydrophilic network that is covalently grafted onto the HEA and HDPE molecular chains.

[0026] While being irradiated with ultraviolet light, the surface of the preform is rolled with an embossing roller (roller temperature 80℃) to form a continuous array of grooves with a depth of 5±1μm, a width of 15±2μm, and axial parallel distribution, thus forming a microstructure. Step 4: The solidified and microstructured continuous preform is fed into a pelletizer and cut into short columnar fillers with a length of 10.0±0.5mm. The cut fillers are then placed in a magnetizing device for two-stage magnetization.

[0027] The magnetization process is as follows: the packing material is placed in the center of the pulse magnetizer coil, and a pulsed magnetic field with a peak intensity of 3.0T and a pulse width of 10ms is applied for a processing time of 10ms; the pulse-magnetized packing material is transferred to a uniform weak magnetic field with a field strength of 0.20T, and the rotating platform is started to make the packing material rotate at a speed of 15rpm for 3 minutes in the uniform weak magnetic field; after the magnetic field is turned off, the magnetization is completed, and the composite magnetic biological packing material is obtained.

[0028] Performance characterization and testing 1. SEM The composite magnetic biofiller prepared in Example 1 was subjected to brittle fracture in liquid nitrogen. The cross-section was then sputter-coated with gold and observed using a scanning electron microscope. The results clearly showed a three-layer structure with tight interfacial bonding and no visible delamination or gaps. Top-view SEM images showed that a regular microgroove structure completely covered the filler surface.

[0029] 2. Hydrophilic Figure 1 In the diagram, 'a' is a contact angle view of a common packing material (polyethylene), with a contact angle range of 110.45 ± 0.25°. 'b' is a contact angle view of the composite magnetic biological packing material prepared in this embodiment, with a contact angle range of 97.1 ± 0.6°. A smaller contact angle indicates better hydrophilicity. The composite magnetic biological packing material prepared in this embodiment exhibits significantly higher hydrophilicity than the common packing material, improving its biocompatibility and promoting the attachment and growth of microorganisms.

[0030] 3. Surface electrical properties Using a solid surface Zeta potential analyzer, under conditions of 0.001 mol / L KCl background electrolyte and pH=7.0, the surface Zeta potential of the composite magnetic biological packing material prepared in this embodiment was +1.5 mV, while that of the polyethylene packing material was -60.3 mV. The surface positive charge was significantly enhanced, indicating a reversal of its surface charge characteristics, transforming it into a positively charged material. Since the surface of microorganisms in general wastewater is negatively charged, the positively charged magnetic packing material exhibits better biocompatibility, thereby promoting the attachment and growth of microorganisms on the packing surface.

[0031] 4. Magnetic properties The composite magnetic biological filler prepared in this embodiment was magnetized, and the filler was measured using a vibrating sample magnetometer. The results showed that the saturation magnetic intensity of the composite magnetic biological filler prepared in this embodiment was 2.2 emu / mg, and the remanence at T2% was 0.3 emu / mg. This confirms the anisotropy generated by multi-stage magnetization.

[0032] 5. Mechanical strength The results, obtained using an electronic universal testing machine, are shown in Tables 1 and 2. The results indicate that the radial compressive strength (yield point) of the composite magnetic biofiller prepared in this embodiment is 9.96 ± 0.3 MPa, and the axial tensile breaking strength is 8.99 ± 0.2 MPa. Although slightly lower than that of polyethylene fillers (~12.35 MPa and ~11.35 MPa), it fully meets the conventional requirements for the mechanical strength of fillers in the MBBR process (typically requiring >5 MPa).

[0033] Table 1: Packing Compressive Strength Parameters

[0034] Table 2: Tensile Strength Parameters of Fillers

[0035] 6. Small-scale experiment Two identical laboratory-scale MBBR reactors (effective volume 5L) were established, each filled with 30% of the following: R1 - commercial K3 polyethylene packing (blank control) and R2 - the TG packing of this invention.

[0036] Simulated domestic sewage (COD≈400mg / L, NH4+) was prepared by inoculating with activated sludge from the same source and adding glucose, ammonium chloride, and potassium dihydrogen phosphate. + Intermittent aeration was performed with N≈30mg / L to allow biofilm formation. The amount of wet biofilm on the packing material was determined by periodic sampling and weighing.

[0037] On day 7 of biofilm formation, the biofilm density per unit packing material in the R2 (TG) reactor reached 1.2 mg / cm³. 3R1 was only 0.5 mg / cm³. 3 This indicates that the biofilm formation rate of TG packing material is significantly higher.

[0038] After the biofilm matures, switch to continuous flow mode to treat simulated urban wastewater (COD≈500mg / L, NH4+). + -N≈40mg / L, pH=7.5, DO=4-5mg / L). Average data over two weeks of stable operation showed: COD removal rates: R2 (TG) was 91.5%, and R1 was 84.7%.

[0039] Ammonia nitrogen removal rates: R2 (TG) was 95.3%, and R1 was 87.5%.

[0040] After 10 days of operation, reactor R2, with TG magnetic packing, outperformed the control group in ammonia nitrogen removal, and the removal efficiency stabilized after 8 days. In contrast, reactor R1, with commercial packing, showed poor removal performance throughout the entire operation period.

[0041] By day 26 of the experiment, the average influent ammonia nitrogen concentration was 42.5 mg / L. At this time, the average effluent ammonia nitrogen concentrations of reactors R1 and R2 were 25.26 mg / L and 22.04 mg / L, respectively, corresponding to average removal rates of 40.56% and 48.14%. This shows that reactor R2 achieved the highest ammonia nitrogen removal rate, which was 7.58% higher than that of R1. This result indicates that, compared to the blank packing material, the magnetic packing material with a magnetic field of this invention is more conducive to the attachment and growth of microorganisms, thereby shortening the reactor start-up period.

[0042] Taking into account the experimental results of COD removal rate and ammonia nitrogen removal rate, it can be concluded that although magnetic packing sacrifices some mechanical strength, magnetic modification, a functional modification technology, can effectively shorten the start-up time of MBBR reactor and enhance the pollutant removal capacity of MBBR process, providing research evidence for packing modification in the field of biological treatment.

[0043] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A composite magnetic biofiller with gradient magnetic response and surface microstructure, characterized in that, The composite magnetic biofiller comprises a core layer, a transition layer, and a surface functional layer distributed sequentially. The core layer is a mixture of polyethylene and neodymium iron boron magnetic powder; The transition layer is a mixture comprising polyethylene, neodymium iron boron magnetic powder and hydroxyapatite; The surface functional layer is a mixture of polyethylene, neodymium iron boron magnetic powder, hydroxyapatite and antioxidant, and the outer surface of the surface functional layer is provided with microstructures and the surface functional layer is grafted with hydrophilic polymers. The mass concentration of NdFeB magnetic powder in the core layer, transition layer and surface functional layer decreases sequentially.

2. The composite magnetic biofiller with gradient magnetic response and surface microstructure according to claim 1, characterized in that, In the core layer, the mass concentration of neodymium iron boron magnetic powder is 3-8%; In the transition layer, the mass concentration of neodymium iron boron magnetic powder is 1-3%, and the mass concentration of hydroxyapatite is 1-3%. In the surface functional layer, the mass concentration of neodymium iron boron magnetic powder is less than 0.5%, and the mass concentration of hydroxyapatite is 2-5%.

3. The method for preparing the composite magnetic biofiller with gradient magnetic response and surface microstructure as described in claim 1, characterized in that, Includes the following steps: S1. The raw material polyethylene of the core layer is premixed with NdFeB magnetic powder and placed into the hopper of a parallel twin-screw extruder. The raw material polyethylene of the transition layer, NdFeB magnetic powder and hydroxyapatite are premixed and placed into the hopper of another parallel twin-screw extruder. The raw material polyethylene of the surface functional layer, NdFeB magnetic powder, hydroxyapatite and antioxidant are premixed and placed into the hopper of a third parallel twin-screw extruder. A photosensitizer is injected into the second zone below the hopper of the third parallel twin-screw extruder for melt blending. S2. The melt layers after molten blending are conveyed to the die head and extruded through a metering gear pump to obtain a composite preform; S3. Place the composite preform into an ultraviolet irradiation curing chamber and simultaneously roll the surface of the preform with an embossing roller to form a microstructure. S4. The solidified and microstructured composite embryo is granulated and then placed in a magnetizing device for magnetization to obtain a composite magnetic biological filler.

4. The method for preparing the composite magnetic biofiller with gradient magnetic response and surface microstructure according to claim 3, characterized in that, In step S1, the mass of the photosensitizer is 0.5% of the total mass of the surface functional layer; The photosensitizer includes hydroxyethyl acrylate, acrylamide, maleic anhydride, and a photoinitiator, with a mass ratio of hydroxyethyl acrylate, acrylamide, maleic anhydride, and photoinitiator of 10:60:25:

5.

5. The method for preparing the composite magnetic biofiller with gradient magnetic response and surface microstructure according to claim 3, characterized in that, In step S1, the mass of the antioxidant is 0.05% of the total mass of the surface functional layer.

6. The method for preparing the composite magnetic biofiller with gradient magnetic response and surface microstructure according to claim 3, characterized in that, In step S1, the temperature of the first zone of the three parallel twin-screw extruders is 165°C, the temperature of the second zone is 175°C, the temperature of the third zone is 180°C, and the temperature of the die head is 185°C.

7. The method for preparing the composite magnetic biofiller with gradient magnetic response and surface microstructure according to claim 3, characterized in that, In step S2, the temperature of the die head is 180℃.

8. The method for preparing the composite magnetic biofiller with gradient magnetic response and surface microstructure according to claim 1, characterized in that, In step S3, the dominant wavelength of the ultraviolet irradiation source in the ultraviolet irradiation curing chamber is 365 nm, and the power is 120 W / cm. The irradiation intensity is not less than 800 mJ / cm. 2 .

9. The method for preparing the composite magnetic biofiller with gradient magnetic response and surface microstructure according to claim 1, characterized in that, In step S4, the magnetization process is as follows: first, deep magnetization is carried out in a pulsed magnetic field of 2.5-3.5T, and then the filler is treated in a rotating weak magnetic field of 0.1-0.3T for 1-3 minutes to obtain anisotropic magnetic moments.

10. The application of the composite magnetic biological packing material with gradient magnetic response and surface microstructure as described in claim 1 in water treatment.

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