A magnetite-loaded extracellular polymer material and its preparation method and application

Abstract

The present invention provides a magnetite-loaded extracellular polymer material, a preparation method thereof, and an application thereof. The preparation method comprises the following steps: mixing excess sludge with a sodium chloride solution and performing a heat treatment to dissociate the extracellular polymers in the excess sludge to obtain a mixed solution; centrifuging the mixed solution and filtering the supernatant through a filter membrane to obtain an extracellular polymer mixed solution; adding magnetite powder to the extracellular polymer mixed solution, stirring under ultrasonication until the powder is completely dissolved, adjusting the pH to neutral, and vacuum freeze-drying to obtain a first product; mixing the first product, sodium alginate, polyvinyl alcohol, and water, and then dripping a calcium chloride solution into the mixture for gelation to obtain hydrogel beads; and vacuum freeze-drying the hydrogel beads to obtain a magnetite-loaded extracellular polymer hydrogel material. The material can effectively and stably promote sludge granulation, effectively solve the problem of resource utilization of excess sludge, and help reduce production costs.

Description

Technical Field

[0001] The invention belongs to the technical field of water pollution control engineering, and particularly relates to an extracellular polymer material loaded with magnetite, a preparation method and an application thereof. Background Art

[0002] Compared to traditional activated sludge processes, aerobic granular sludge (AGS) technology has attracted research attention due to its advantages, including rapid settling rates and high biological activity. Aerobic granular sludge, with its high microbial biomass, nitrogen and phosphorus removal capabilities, and excellent sedimentation properties, holds great potential for application in industrial and municipal wastewater treatment. However, aerobic granular sludge technology also suffers from issues such as a long cycle time and poor long-term stability, making its widespread application in industrial projects more challenging.

[0003] Currently, the main approaches to addressing issues such as long formation cycles and poor long-term stability include promoting microbial aggregation to form granular sludge by adding divalent or trivalent metal ions, carriers, or flocculants. However, this approach introduces a large number of additional compounds, resulting in high costs and difficulties in sludge treatment and transportation. Currently, there is also a method of washing out poorly settling flocculent sludge by shortening the settling time. However, this method easily reduces the sludge concentration within the system to below 1000 mg / L, resulting in a high organic load and hindering the screening of slow-growing microorganisms such as glycogen-accumulating organisms (GAOs) and phosphate-accumulating organisms (PAOs). Therefore, promoting the granulation of aerobic sludge is a technical problem that needs to be urgently addressed in this field. Summary of the Invention

[0004] The present invention provides a method for preparing a magnetite-loaded extracellular polymer material, which can produce a magnetite-loaded extracellular polymer material with excellent performance. The material can effectively and stably promote the granulation of sludge, effectively solve the problem of resource utilization of excess sludge, and is conducive to reducing production costs.

[0005] The present invention also provides an extracellular polymer material loaded with magnetite, which can effectively and stably promote the granulation of sludge.

[0006] The present invention also provides an application method of an extracellular polymer material loaded with magnetite. Applying the extracellular polymer material loaded with magnetite in an aerobic granular sludge reactor helps to promote the formation of aerobic granular sludge and improve the stability and pollution removal efficiency of the system.

[0007] A first aspect of the present invention provides a method for preparing a magnetite-loaded extracellular polymeric material, comprising the following steps:

[0008] The excess sludge is mixed with a sodium chloride solution and subjected to a heating treatment to dissociate the extracellular polymers in the excess sludge to obtain a mixed solution; the mixed solution is centrifuged, and the supernatant is filtered through a filter membrane to obtain an extracellular polymer mixed solution;

[0009] FeCl3·6H2O was added to the extracellular polymer mixture, and the mixture was stirred under ultrasound until the powder was completely dissolved. The pH was adjusted to neutral, and the mixture was freeze-dried in vacuum to obtain the first product.

[0010] The first product, sodium alginate, polyvinyl alcohol and water are mixed, and then a calcium chloride solution is dropped into the mixture for gelation to obtain hydrogel beads; the hydrogel beads are vacuum freeze-dried to obtain an extracellular polymer hydrogel material loaded with magnetite.

[0011] The preparation method as described above, wherein the mass volume concentration of the sodium chloride solution is 0.8-1%;

[0012] The heating treatment temperature is 75~85℃ and the time is 25~30min.

[0013] In the preparation method as described above, the centrifugal treatment temperature is 0-4°C, the rotation speed is 4000-5000 rpm, and the time is 15-20 min.

[0014] In the preparation method as described above, the mass volume ratio of the FeCl3·6H2O and extracellular polymer mixture is 0.1-0.5%.

[0015] The preparation method as described above, wherein the process of mixing the first product, sodium alginate, polyvinyl alcohol and water comprises the following steps:

[0016] Dissolving sodium alginate and polyvinyl alcohol in water respectively to form a sodium alginate solution and a polyvinyl alcohol solution; then mixing the sodium alginate solution and the polyvinyl alcohol solution to obtain a mixed solution;

[0017] dispersing the first product in the mixed solution;

[0018] Wherein, the mass volume concentration of sodium alginate in the sodium alginate solution is 1-3%;

[0019] The mass volume concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 1-3%;

[0020] The mass volume concentration of the first product in the mixed solution is 0.1-0.3%.

[0021] The preparation method as described above, wherein the mass volume concentration of calcium chloride in the calcium chloride solution is 1-5%.

[0022] The preparation method as described above, wherein the vacuum freeze-drying temperature is -30 to -40°C and the time is 24 to 48 hours;

[0023] The particle size of the magnetite-loaded extracellular polymer hydrogel material is 3-5 mm.

[0024] The second aspect of the present invention provides an extracellular polymer material loaded with magnetite, which is prepared by the preparation method described in the first aspect.

[0025] A third aspect of the present invention provides an application method of an extracellular polymeric material loaded with magnetite, wherein the extracellular polymeric material loaded with magnetite is added to an aerobic granular sludge reactor;

[0026] The magnetite-loaded extracellular polymer material is prepared by the preparation method described in the first aspect or the magnetite-loaded extracellular polymer material described in the second aspect.

[0027] In the application method as described above, the dosage of the magnetite-loaded extracellular polymer material is 0.5-2 g / L.

[0028] The implementation of the present invention has at least the following beneficial effects:

[0029] The preparation method of the magnetite-loaded extracellular polymer material provided by the present invention is to prepare a hydrogel material by combining the extracellular polymer in the excess sludge with FeCl3·6H2O. Through the synergistic effect of the two, on the one hand, it can act as a reinforcing agent to promote and accelerate the aggregation of particulate matter in the sludge to achieve sludge granulation, which helps to improve system stability and pollution removal efficiency. On the other hand, it can effectively solve the resource recovery problem of the large amount of excess sludge generated by sewage treatment plants and achieve sludge reduction. Secondly, the excess sludge, magnetite and other materials used in the present invention are all non-toxic and harmless materials and will not cause secondary pollution. In addition, the above-mentioned preparation method is simple and easy to operate, which helps to reduce production costs.

[0030] The magnetite-loaded extracellular polymer material provided by the present invention can effectively and stably promote the granulation of sludge.

[0031] The application method of the magnetite-loaded extracellular polymer material provided by the present invention is to apply the magnetite-loaded extracellular polymer material to an aerobic granular sludge reactor, which helps to promote the formation of aerobic granular sludge and improve the stability and pollution removal efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of a method for preparing an extracellular polymer material loaded with magnetite in one embodiment of the present invention;

[0033] Figure 21 is a structural diagram of an SBR reactor in one embodiment of the present invention. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0035] like Figure 1 As shown, the first aspect of the present invention provides an extracellular polymer material loaded with magnetite, comprising the following steps: mixing excess sludge with a sodium chloride solution and performing a heat treatment to dissociate the extracellular polymer in the excess sludge to obtain a mixed solution; centrifuging the mixed solution and filtering the supernatant through a filter membrane to obtain an extracellular polymer mixed solution; adding FeCl3·6H2O to the extracellular polymer mixed solution, adjusting the pH to 7.5-8, stirring under ultrasonication until the powder is completely dissolved, adjusting the pH to neutral, and vacuum freeze-drying to obtain a first product; mixing the first product, sodium alginate, polyvinyl alcohol, and water, and then dropping a calcium chloride solution into the mixture for gelation to obtain hydrogel beads; and vacuum freeze-drying the hydrogel beads to obtain an extracellular polymer hydrogel material loaded with magnetite.

[0036] Excess sludge refers to the solid waste discharged from sedimentation tanks (or sedimentation areas). Excess sludge contains a portion of the microorganisms and metabolites found in activated sludge. Specifically, the excess sludge of the present invention can be obtained from the dewatering plant, aerobic tanks, or secondary sedimentation tanks of a sewage treatment plant. Sludge is classified as either flocculent sludge or granular sludge. Flocculent sludge refers to tiny particles suspended in water, exhibiting a flocculent or colloidal appearance. Granular sludge, also known as bottom sediment, refers to the granular sediment accumulated at the bottom of a water body or in sedimentation tanks.

[0037] Specifically, activated sludge refers to flocs containing various aerobic microbial communities that grow in aeration tanks. Since activated sludge contains a large number of microorganisms, in the secondary biochemical treatment of sewage, aeration is used to bring wastewater containing organic matter into contact with activated sludge containing a large number of microorganisms. The organic matter in the wastewater is decomposed and degraded during the growth and metabolism of the microorganisms. In this process, microorganisms continuously consume the organic matter in the wastewater, which is also accompanied by the aging and death of the microorganisms. When these dead microorganisms and other substances accumulate to a certain amount, they need to be removed by sedimentation or filtration to maintain the stable operation of the activated sludge system. The removed sludge is the residual activated sludge.

[0038] Excess sludge contains not only active microbial organisms but also a large amount of organic matter in the form of extracellular polymeric substances (EPS). EPS is a high-molecular organic substance or polymer released by microorganisms under specific conditions. It is usually attached to the cell wall surface of bacteria and its main components are proteins (PN), polysaccharides (PS), DNA, humic acid, and lipids.

[0039] In the present invention, before the excess sludge is mixed with the sodium chloride solution and subjected to heat treatment, the excess sludge is washed and centrifuged three times with the first sodium chloride solution to remove impurities on the surface of the excess sludge. The washed excess sludge is then dissolved in the second sodium chloride solution and subjected to heat treatment. During the heat treatment, extracellular polymeric substances in the excess sludge are dissociated, resulting in a mixed solution.

[0040] The mixed solution is centrifuged to remove impurities, and the supernatant is filtered through a filter membrane to obtain an extracellular polymeric substance mixed solution. In other words, the extracellular polymeric substance mixed solution contains a large amount of extracellular polymeric substance.

[0041] Vacuum freeze-drying involves freezing the mixture into a solid state and then dehydrating it at low temperature and pressure, utilizing the sublimation properties of water. Because vacuum freeze-drying occurs in a low-temperature, low-oxygen environment, most biological reactions are stagnant. Furthermore, the process is devoid of liquid water, allowing the water to sublime directly in a solid state, preserving the original structure and shape of the material to the greatest extent possible. The final product is magnetite-loaded extracellular polymeric substances (Fe3O4@EPS).

[0042] The first product, sodium alginate, polyvinyl alcohol, and water were mixed, and then a calcium chloride solution was added dropwise for gelation, resulting in hydrogel beads. The hydrogel beads were then freeze-dried in a vacuum to produce a magnetite-loaded extracellular polymer hydrogel material. The addition of sodium alginate, polyvinyl alcohol, and calcium chloride solution promoted gel coating on the surface of the Fe3O4@EPS, forming hydrogel particles of a specific size that facilitated both placement in an aerobic granular sludge reactor and collection for reuse.

[0043] According to the research of the present invention, the above-mentioned magnetite-loaded extracellular polymer material is applied to an aerobic granular sludge reactor, which can effectively and stably promote the granulation of sludge, improve the stability and pollution removal efficiency of the system, and help reduce production costs. This is because the extracellular polymers in the residual sludge are made into a hydrogel material with magnetite, and the extracellular polymers can be wrapped around the magnetite. At this time, under the joint action of the extracellular polymers and magnetite, it can be used as a matrix to maintain the structure of aerobic granular sludge and wrap the mixed microbial community to aggregate it together. On the one hand, the sticky nature of the extracellular polymer is conducive to the mutual agglomeration of microorganisms; on the other hand, magnetite can neutralize the negative charge on the surface of the extracellular polymer, not only can the extracellular polymer be wrapped around the magnetite, but the polysaccharide contained in the extracellular polymer is hydrophilic, which can further increase the positive charge content, and can neutralize the negative charge on the surface of most cells, thereby reducing the electrostatic repulsion between cells to achieve sludge granulation. Therefore, the present invention promotes sludge granulation through the synergistic effect of extracellular polymers and magnetite, which helps to improve system stability and pollution removal efficiency.

[0044] Furthermore, the present invention utilizes excess sludge as raw material, effectively reclaiming the large amount of excess sludge generated by sewage treatment plants and reducing sludge volume. Furthermore, the excess sludge and magnetite are non-toxic and harmless, preventing secondary pollution.

[0045] In some embodiments, the mass volume concentration of the sodium chloride solution is 0.8-1%, for example, 0.8%, 0.82%, 0.85%, 0.88%, 0.9%, 0.92%, 0.95%, 0.98%, 1% or a range consisting of any two thereof; the heating temperature is 75-85°C, for example, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C or a range consisting of any two thereof; the time is 25-30 min, for example, 25 min, 26 min, 27 min, 28 min, 29 min, 30 min or a range consisting of any two thereof.

[0046] In some embodiments, the centrifugation temperature is 0-4°C, for example, 0°C, 1°C, 2°C, 3°C, 4°C, or a range consisting of any two thereof; the rotation speed is 4000-5000 rpm, for example, 4000 rpm, 4100 rpm, 4200 rpm, 4300 rpm, 4400 rpm, 4500 rpm, 4600 rpm, 4700 rpm, 4800 rpm, 4900 rpm, 5000 rpm, or a range consisting of any two thereof; and the time is 15-20 min, for example, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, or a range consisting of any two thereof.

[0047] In some embodiments, the mass volume ratio of the FeCl3·6H2O to the extracellular polymer mixture is 0.1-0.5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or a range consisting of any two thereof.

[0048] In some embodiments, the process of mixing the first product, sodium alginate, polyvinyl alcohol and water includes the following steps: dissolving sodium alginate and polyvinyl alcohol in water to form a sodium alginate solution and a polyvinyl alcohol solution respectively; then mixing the sodium alginate solution and the polyvinyl alcohol solution to obtain a mixed solution; dispersing the first product in the mixed solution; wherein the mass volume concentration of sodium alginate in the sodium alginate solution is 1~3%, for example, 1%, 1.5%, 2%, 2.5%, 3% or a range consisting of any two thereof; the mass volume concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 1~3%, for example, 1%, 1.5%, 2%, 2.5%, 3% or a range consisting of any two thereof; the mass volume concentration of the first product in the mixed solution is 0.1~0.3%, for example, 0.1%, 0.15%, 0.2%, 0.25%, 0.3% or a range consisting of any two thereof.

[0049] In some embodiments, the mass volume concentration of calcium chloride in the calcium chloride solution is 1-5%, for example, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5% or any two thereof.

[0050] In some embodiments, the vacuum freeze-drying temperature is -30~-40°C, for example, -30°C, -32°C, -34°C, -36°C, -38°C, -40°C or a range consisting of any two thereof; the time is 24~48h, for example, 24h, 26h, 28h, 30h, 35h, 40h, 45h, 48h or a range consisting of any two thereof; the particle size of the extracellular polymer hydrogel material loaded with magnetite is 3~5mm, for example, 3mm, 3.2mm, 3.5mm, 3.8mm, 4mm, 4.2mm, 4.5mm, 4.8mm, 5mm or a range consisting of any two thereof.

[0051] The second aspect of the present invention provides an extracellular polymer material loaded with magnetite, which is prepared using the preparation method provided in the first aspect.

[0052] The third aspect of the present invention provides an application method of an extracellular polymer material loaded with magnetite, wherein the extracellular polymer material loaded with magnetite is added to an aerobic granular sludge reactor; the extracellular polymer material loaded with magnetite is prepared by the preparation method provided by the first aspect or the extracellular polymer material loaded with magnetite provided by the second aspect.

[0053] The present invention does not limit the specific type of the aerobic granular sludge reactor. For example, the aerobic granular sludge reactor may be a sequencing batch reactor (SBR reactor).

[0054] Specifically, the tank body of the above-mentioned aerobic granular sludge reactor is provided with a stirring unit and an aeration unit, and an aeration pipe is provided at the bottom. The tank body of the aerobic granular sludge reactor is provided with an inlet pipe and an outlet pipe. The outlet pipe can be arranged in the middle of the tank body, and an outlet valve is provided on the outlet pipe, and an inlet valve is provided on the inlet pipe. The stirring unit and the aeration unit are both provided with valves for controlling the switch.

[0055] The aerobic granular sludge reactor can operate in anaerobic, aerobic, or anoxic modes, with the anaerobic section providing only agitation at a speed of 200-250 rpm and an operating cycle of 4-6 hours. The volume of water discharged from the aerobic granular sludge reactor during each cycle accounts for 40-60% of the total reactor volume.

[0056] The aerobic granular sludge reactor contains wastewater to be treated and seed sludge. The seed sludge can be selected from activated sludge in the sewage plant's dewatering plant, secondary sedimentation tank, or aerobic tank. The activated sludge is flocculent. The seed sludge is retrieved and air-dried for one day before being added to the aerobic granular sludge reactor. The initial seed sludge concentration is controlled at 5000-6000 mg / L. The magnetite-loaded extracellular polymeric substance (ECP) material is added to the aerobic granular sludge reactor in a specific ratio. The particle size, settling properties, and pollutant removal efficiency of the activated sludge are observed throughout the process, and the effect of the magnetite-loaded ECP material on the aerobic sludge granulation process is monitored.

[0057] In some embodiments, the dosage of the magnetite-loaded extracellular polymer material is 0.5-2 g / L, for example, 0.5 g / L, 0.8 g / L, 1.0 g / L, 1.2 g / L, 1.4 g / L, 1.6 g / L, 1.8 g / L, 2 g / L or any two thereof.

[0058] The present invention will be further described below with reference to specific examples and comparative examples.

[0059] Example 1

[0060] 1. Preparation of magnetite-loaded extracellular polymeric materials

[0061] S1. Obtain excess sludge from the sludge discharged from the dewatering workshop, aerobic tank, or secondary sedimentation tank of the sewage treatment plant. Wash and centrifuge the excess sludge three times with a 0.9% sodium chloride solution to remove impurities on the surface of the excess sludge. Dissolve the washed excess sludge in a 0.9% sodium chloride solution and heat it in a water bath at 80°C for 30 minutes. After heating, cool the excess sludge mixture and centrifuge it at 4°C and 5000 rpm for 20 minutes. Remove the supernatant and filter the supernatant through a 0.45 μm filter membrane to obtain an extracellular polymer mixture.

[0062] S2. Dissolve 2.5 g of FeCl3·6H2O in 500 mL of extracellular polymer solution, with a mass volume ratio of FeCl3·6H2O to the extracellular polymer solution of 0.5%. Stir thoroughly under ultrasound until completely mixed, and adjust the pH to neutral. The resulting mixed solution is then poured into a stainless steel reaction vessel and incubated in a high-pressure reactor at 200°C for 24 hours. The polymerized black solid-liquid mixture is then centrifuged at 5000 rpm for 5 minutes and centrifuged alternately with deionized water and anhydrous ethanol three times. The resulting solid sediment is dried in a vacuum drying oven at 80°C for 24 hours and passed through a 100-mesh sieve to obtain the first Fe3O4@EPS product.

[0063] S3. Sodium alginate (SA) and polyvinyl alcohol (PVA) were dissolved in deionized water and magnetically stirred to obtain a sodium alginate solution and a polyvinyl alcohol solution, respectively. The mass volume concentration of sodium alginate in the sodium alginate solution was 2%, and the mass volume concentration of polyvinyl alcohol in the polyvinyl alcohol solution was 1%. The two solutions were mixed and stirred for 12 hours to obtain a mixed solution. A fixed amount of Fe3O4@EPS first product was dispersed in the mixed solution for 12 hours, reaching a mass volume concentration of 0.3%. The mixture was then dropwise added to a CaCl2 solution for gelation for 24 hours to obtain hydrogel beads. The calcium chloride concentration in the calcium chloride solution was 2%. The hydrogel beads were repeatedly rinsed and freeze-dried to obtain a magnetite-loaded extracellular polymeric substance material (Fe3O4@EPS composite hydrogel material). The vacuum freeze-drying temperature was -40°C for 24 hours, and the particle size of the magnetite-loaded extracellular polymeric substance hydrogel material was 4 mm.

[0064] 2. Application of magnetite-loaded extracellular polymeric materials

[0065] A columnar SBR reactor made of organic glass was used, with an inner diameter of 10 cm, a height of 32 cm, an effective volume of 2.3 L, and a height-to-diameter ratio of 3. Water was fed into the SBR reactor from the top, an aeration head was installed at the bottom to connect to an aeration pump for aeration, and a water outlet valve was installed in the middle of the reactor. The reactor operated in anaerobic / aerobic / anoxic modes, and a stirrer was used to provide stirring during the entire process of settling and before discharging the water. The stirring speed was about 250 rpm. The structural diagram of the SBR reactor is shown in the figure below. Figure 2 As shown;

[0066] The reactor operates for 6 hours, consisting of 2 minutes of water inlet, 120 minutes of anaerobic conditions, 90 minutes of aerobic conditions, 123-133 minutes of anoxic conditions, 5-15 minutes of settling time, and 10 minutes of water outlet. Four cycles are run daily, and the reactor's water inlet, stirring, aeration, water outlet, and lighting are all connected to microcomputer-controlled switches to maintain normal operation. The reactor's volume exchange ratio is 50%, and the hydraulic retention time is 12 hours.

[0067] Artificially simulate domestic sewage as the inlet of the SBR reactor, and the inlet COD, NH4 + -N and TP concentrations were controlled at 211±18.5, 22±1.2, and 3.21±0.17 mg / L, respectively. An appropriate amount of activated sludge was taken from the aerobic tank of the sewage treatment plant as inoculum sludge. The inoculum sludge was placed in the reactor to an initial sludge concentration of 5500 mg / L (MLSS) and a volume index of 104.34 mg / L. The settling time was gradually shortened to select granular sludge.

[0068] The Fe3O4@EPS composite hydrogel material was added to the influent at a dosage of 1 g / L, and the particle size of the granular sludge and the removal rate of carbon, nitrogen and phosphorus in the reactor were regularly measured.

[0069] The results showed that the average particle size of the sludge reached 570 μm at 30 days, the chemical oxygen demand (COD) removal rate was above 90%, the average total nitrogen (TIN) removal rate was 83.8%, and the total phosphorus (TP) removal rate was 85.1%.

[0070] Example 2

[0071] The preparation process is basically the same as that of Example 1, except that Fe3O4@EPS composite hydrogel material is added to the influent water at a dosage of 2 g / L, and other conditions remain unchanged.

[0072] The results showed that the average sludge particle size reached 620 μm at 30 days, the COD removal rate was above 90%, the average TIN removal rate was 85.4%, and the TP removal rate was 86.8%.

[0073] Example 3

[0074] The preparation process was basically the same as that of Example 2, except that 0.5 g of FeCl₃·6H₂O was dissolved in 500 mL of extracellular polymeric solution, and the mass volume ratio of FeCl₃·6H₂O to extracellular polymeric solution was 0.1%. Other conditions remained unchanged.

[0075] The results showed that the average sludge particle size reached 555 μm at 30 days, the COD removal rate was above 90%, the average TIN removal rate was 82.7%, and the TP removal rate was 83.1%.

[0076] Example 4

[0077] The preparation process was basically the same as that of Example 2, except that 1.5 g of FeCl₃·6H₂O was dissolved in 500 mL of extracellular polymeric solution, and the mass volume ratio of FeCl₃·6H₂O to extracellular polymeric solution was 0.3%. Other conditions remained unchanged.

[0078] The results showed that the average sludge particle size reached 595 μm at 30 days, the COD removal rate was above 90%, the average TIN removal rate was 83.5%, and the TP removal rate was 84.9%.

[0079] Comparative Example 1

[0080] 1. The preparation process of the hydrogel material is as follows: sodium alginate (SA) and polyvinyl alcohol (PVA) are respectively dissolved in deionized water, and sodium alginate solution and polyvinyl alcohol solution are respectively obtained by magnetic stirring, wherein the mass volume concentration of sodium alginate in the sodium alginate solution is 2%, and the mass volume concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 1%. The two solutions are mixed and stirred for 12 hours to obtain a mixed solution; then CaCl2 solution is dropped into the mixed solution for gelation treatment for 24 hours to obtain hydrogel beads; the hydrogel beads are repeatedly rinsed and dried by freeze-drying to obtain a hydrogel material, and the mass volume concentration of calcium chloride in the calcium chloride solution is 2%.

[0081] 2. The application process is basically the same as that in Example 1, except that the Fe3O4@EPS composite hydrogel material in Example 1 is replaced by the hydrogel material of this comparative example. Specifically, in this comparative example, the hydrogel material is added to the influent at a dosage of 2 g / L, and the particle size of the granular sludge and the carbon, nitrogen and phosphorus removal rate in the reactor are regularly measured.

[0082] The results showed that at 30 days, the average sludge particle size was 390 μm, the COD removal rate was above 90%, the average TIN removal rate was 79.4%, and the TP removal rate was 80.3%.

[0083] Comparative Example 2

[0084] Sodium alginate (SA) and polyvinyl alcohol (PVA) were dissolved in deionized water, respectively, and magnetic stirring was used to obtain sodium alginate solution and polyvinyl alcohol solution, respectively. The mass volume concentration of sodium alginate in the sodium alginate solution was 2%, and the mass volume concentration of polyvinyl alcohol in the polyvinyl alcohol solution was 1%. The two solutions were mixed and stirred for 12 hours to obtain a mixed solution. A quantitative FeCl3·6H2O sample was dispersed in the above mixed solution for 12 hours, and the mass volume concentration of FeCl3·6H2O in the mixed solution was 0.3%. Then, CaCl2 solution was added dropwise for gelation treatment for 24 hours to obtain hydrogel beads. The mass volume concentration of calcium chloride in the calcium chloride solution was 2%. The hydrogel beads were repeatedly rinsed and dried by freeze-drying to obtain Fe3O4 composite hydrogel material. The application process is basically the same as that in Example 1, except that the Fe3O4@EPS composite hydrogel material in Example 1 is replaced by the Fe3O4 composite hydrogel material in this comparative example. Specifically, in this comparative example, Fe3O4 composite hydrogel material is added to the influent at a dosage of 2 g / L, and the particle size of the granular sludge and the carbon, nitrogen and phosphorus removal rate in the reactor are regularly measured.

[0085] The results showed that at 30 days, the average sludge particle size was 540 μm, the COD removal rate was above 90%, the average TIN removal rate was 82.2%, and the TP removal rate was 82.7%.

[0086] Comparative Example 3

[0087] 500 mL of the extracellular polymer solution was incubated in an autoclave at 200°C for 24 hours. The solid-liquid mixture was then centrifuged at 5000 rpm for 5 minutes and centrifuged three times alternately with deionized water and anhydrous ethanol. The resulting solid sediment was dried in a vacuum oven at 80°C for 24 hours and passed through a 100-mesh sieve to obtain the EPS solid product.

[0088] Sodium alginate (SA) and polyvinyl alcohol (PVA) were dissolved in deionized water, respectively, and magnetic stirring was used to obtain sodium alginate solution and polyvinyl alcohol solution, respectively. The mass volume concentration of sodium alginate in the sodium alginate solution was 2%, and the mass volume concentration of polyvinyl alcohol in the polyvinyl alcohol solution was 1%. The two solutions were mixed and stirred for 12 hours to obtain a mixed solution. A certain amount of EPS solid product was dispersed in the above mixed solution for 12 hours, and the mass volume concentration of EPS in the mixed solution was 0.3%. Then, it was dropped into CaCl2 solution for gelation treatment for 24 hours to obtain hydrogel beads. The mass volume concentration of calcium chloride in the calcium chloride solution was 2%. The hydrogel beads were repeatedly rinsed and dried by freeze-drying to obtain an extracellular polymer composite hydrogel material. The application process is basically the same as that in Example 1, except that the Fe3O4@EPS composite hydrogel material in Example 1 is replaced by the extracellular polymer composite hydrogel material of this comparative example. Specifically, the extracellular polymer composite hydrogel material is added to the influent in this comparative example at a dosage of 2 g / L, and the particle size of the granular sludge and the carbon, nitrogen and phosphorus removal rate in the reactor are regularly measured.

[0089] The results showed that at 30 days, the average sludge particle size was 490 μm, the COD removal rate was above 90%, the average TIN removal rate was 81.5%, and the TP removal rate was 81.9%.

[0090] It can be seen that the Fe3O4@EPS composite hydrogel material of Examples 1-4 has a promoting effect on the enhanced aerobic granular sludge. After adding this material, the particle size of the aerobic granular sludge system is significantly increased and the pollutant removal rate is also improved.

[0091] The above describes in detail the preferred embodiments of the present invention and their experimental verification. It should be understood that a person skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solution that can be derived by a person skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art shall be within the scope of protection of the present invention.

Claims

1. A method for preparing an extracellular polymer material loaded with Fe3O4, characterized in that: The following steps are involved: The excess sludge is mixed with a sodium chloride solution and subjected to a heating treatment to dissociate the extracellular polymers in the excess sludge to obtain a mixed solution; the mixed solution is centrifuged, and the supernatant is filtered through a filter membrane to obtain an extracellular polymer mixed solution; FeCl3·6H2O was added to the extracellular polymer mixture, and the mixture was stirred under ultrasound until the powder was completely dissolved. The pH was adjusted to neutral, and the mixture was incubated at high temperature and high pressure, centrifuged, and freeze-dried in a vacuum to obtain the first product. The first product, sodium alginate, polyvinyl alcohol and water are mixed, and then a calcium chloride solution is dropped into the mixture for gelation to obtain hydrogel beads; the hydrogel beads are vacuum freeze-dried to obtain an extracellular polymer hydrogel material loaded with magnetite.

2. The preparation method according to claim 1, characterized in that The mass volume concentration of sodium chloride solution is 0.8~1%; The heating treatment temperature is 75~85℃ and the time is 25~30min.

3. The preparation method according to claim 1, characterized in that The temperature of the centrifugal treatment is 0~4°C, the speed is 4000~5000rpm, and the time is 15~20min.

4. The preparation method according to claim 1, characterized in that The mass volume ratio of the FeCl3·6H2O and extracellular polymer mixed solution is 0.1-0.5%.

5. The preparation method according to claim 1, characterized in that The process of mixing the first product, sodium alginate, polyvinyl alcohol and water comprises the following steps: Dissolving sodium alginate and polyvinyl alcohol in water respectively to form a sodium alginate solution and a polyvinyl alcohol solution; then mixing the sodium alginate solution and the polyvinyl alcohol solution to obtain a mixed solution; dispersing the first product in the mixed solution; Wherein, the mass volume concentration of sodium alginate in the sodium alginate solution is 1-3%; The mass volume concentration of polyvinyl alcohol in the polyvinyl alcohol solution is 1-3%; The mass volume concentration of the first product in the mixed solution is 0.1-0.3%.

6. The preparation method according to claim 1, characterized in that The mass volume concentration of calcium chloride in the calcium chloride solution is 1-5%.

7. The preparation method according to claim 1, characterized in that The vacuum freeze drying temperature is -30 to -40°C and the time is 24 to 48 hours; The particle size of the magnetite-loaded extracellular polymer hydrogel material is 3-5 mm.

8. An extracellular polymer material loaded with magnetite, characterized in that: The method is prepared according to any one of claims 1 to 7.

9. A method for applying a magnetite-loaded extracellular polymer material, characterized in that: adding the magnetite-loaded extracellular polymeric material into an aerobic granular sludge reactor; The magnetite-loaded extracellular polymer material is prepared by the preparation method according to any one of claims 1 to 7 or the magnetite-loaded extracellular polymer material according to claim 8.

10. The application method according to claim 9, characterized in that: The dosage of the magnetite-loaded extracellular polymer material is 0.5-2 g / L.

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