Preparation and efficient activation method of magnetic anaerobic ammonia oxidation immobilized particles

Abstract

The invention relates to a method for preparing and efficiently activating magnetic anaerobic ammonia oxidation immobilized particles, which comprises the following steps: by taking a cross-linked polymerization product of polyvinyl alcohol and sodium alginate as an embedding carrier and prepared magnetic mesoporous silica nanoparticles as a skeleton, embedding anaerobic ammonia oxidation bacterial sludge to prepare the magnetic anaerobic ammonia oxidation immobilized particles; the activation efficiency of the magnetic anaerobic ammonia oxidation immobilized particles is enhanced by applying a magnetic field with proper strength to the activation reactor. The magnetic mesoporous silicon oxide nanoparticles prepared from the modified Fe3O4 are rich in pore structure, the microorganism immobilization performance is enhanced, meanwhile, uniform mixing of the magnetic nanoparticles and bacterial sludge is facilitated, and the prepared immobilized particles are high in mechanical stability, high in substrate mass transfer capacity and high in biological stability. In the activation process of the immobilized particles, an external constant magnetic field is applied, a microbial population sensing system is enhanced, a metabolic network among microbial flora is enhanced, the activation efficiency of the magnetic anaerobic ammonia oxidation immobilized particles is improved, and a new strategy is provided for efficient operation of an anaerobic ammonia oxidation process.

Description

Technical Field

[0001] The invention relates to a preparation method and a high-efficiency activation method of magnetic anaerobic ammonium oxidation immobilized particles, belonging to the technical field of sewage treatment. Background Art

[0002] In recent years, the anaerobic ammonium oxidation process is considered to be one of the most promising processes in the field of sewage biological treatment due to its advantages such as low operating cost, simple operation and low carbon emissions. Autotrophic denitrification processes with anaerobic ammonium oxidation as the core, such as CANON, OLAND, DEMON, etc., have become important technologies for removing ammonia nitrogen from sewage. However, the biggest problem facing anaerobic ammonium oxidation is the low growth rate of anaerobic ammonium oxidizing bacteria and the long process startup cycle. Therefore, how to enhance the growth rate of anaerobic ammonium oxidizing bacteria, maintain the high density of anaerobic ammonium oxidizing bacteria in the reactor and prevent its loss are urgent problems to be solved in the promotion and application of anaerobic ammonium oxidation technology.

[0003] By using microbial immobilization technology, anaerobic ammonium oxidizing bacteria can be fixed in biological carriers, thereby effectively reducing the loss of functional bacteria, ensuring the biomass density in the reactor, and improving the anaerobic ammonium oxidizing activity. At the same time, immobilization technology can effectively improve the adaptability of microorganisms to adverse environments. Currently, the commonly used anaerobic ammonium oxidizing embedding material is a cross-linked polymer material of polyvinyl alcohol and sodium alginate, but the immobilized embedding particles produced generally have problems such as poor mechanical stability of the particles, weak mass transfer capacity, and low microbial activation efficiency.

[0004] Invention patent CN103408133B discloses an embedding and fixing method for anaerobic ammonium oxidation sludge, which improves the stability of immobilized beads by adding powdered activated carbon and magnetic powder to a mixed embedding agent of polyvinyl alcohol and sodium alginate, and improves the mechanical strength and mass transfer performance of the prepared anaerobic ammonium oxidation embedded beads. However, the activation efficiency of the immobilized anaerobic ammonium oxidation beads before sewage treatment is still low, and the growth rate of anaerobic ammonium oxidation bacteria is not enhanced.

[0005] Invention patent CN106517537B discloses a method for improving the activity of anaerobic ammonium oxidation embedded particles, by adding signal molecules AHLs to the mixing process of anaerobic ammonium oxidation sludge and polyvinyl alcohol-sodium alginate embedding agent to prepare anaerobic ammonium oxidation embedded particles, thereby improving the activity of anaerobic ammonium oxidation embedded particles, the preparation process is simple, and the operation is convenient. However, the addition of signal molecules will greatly increase the preparation cost of embedded particles, and as the signal molecules are consumed, the performance of embedded particles will gradually decrease. Summary of the invention

[0006] In view of the above problems existing in the prior art, the present invention provides a method for preparing and efficiently activating magnetic anaerobic ammonia oxidation immobilized particles, which solves the problems of poor mechanical stability, weak mass transfer capacity, and low activation efficiency of the immobilized particles in the prior art.

[0007] The technical solution provided by the present invention is as follows:

[0008] A method for preparing and efficiently activating magnetic anaerobic ammonium oxidation immobilized particles comprises the following steps:

[0009] (1) Preparation of magnetic mesoporous silica nanoparticles: Fe3O4 nanoparticles were dispersed in a 0.5 mol / L trisodium citrate solution and subjected to ultrasonic vibration for 20 minutes for modification, and then collected with a strong magnet and dried; the modified Fe3O4 particles were then dispersed in an ethanol / ammonia aqueous solution, and tetraethyl orthosilicate was slowly added dropwise while mechanically stirring. After stirring for 24 hours, the product was collected with a strong magnet and washed with anhydrous ethanol and deionized water and then dried; the product was then further dispersed in an ethanol / ammonia aqueous solution, hexadecyltrimethylammonium bromide was added and stirred for 2 hours, and tetraethyl orthosilicate was slowly added dropwise and stirred for 24 hours. The product was collected, washed three times with anhydrous ethanol and deionized water, respectively, and dried for use.

[0010] (2) Preparation of embedding agent: Add polyvinyl alcohol and sodium alginate into water, heat to dissolve and stir until mixed to obtain embedding agent.

[0011] (3) Mixing bacterial sludge and embedding agent: The magnetic mesoporous silica nanoparticles and the cultured anaerobic ammonia-oxidizing bacterial sludge are mixed uniformly in a certain proportion, and after the embedding agent is cooled to 35° C., the particles are added to the embedding agent and mixed uniformly to obtain a bacterial glue mixture.

[0012] (4) Preparation of magnetic anaerobic ammonium oxidizing immobilized particles: The bacterial gelatin mixture was slowly added dropwise to a saturated boric acid solution containing 4 wt % CaCl2, sealed and kept at 4°C to allow for full cross-linking. The cross-linked embedded particles were washed with deionized water to obtain magnetic anaerobic ammonium oxidizing immobilized particles.

[0013] (5) Activation of magnetic anaerobic ammonium oxidizer immobilized particles: A small sequencing batch reactor (SBR) is used to build an activation reactor. The magnetic anaerobic ammonium oxidizer immobilized particles are added to the activation reactor, and a constant static magnetic field is applied to the reactor. Wastewater containing ammonia nitrogen and nitrite nitrogen is introduced, and a certain hydraulic retention time is controlled to activate the immobilized particles.

[0014] Preferably, in step (1), the mass volume ratio of modified Fe3O4 to the twice added ethyl orthosilicate is 1:1 g / mL and 1:3 g / mL respectively, and the mass ratio of modified Fe3O4 to the added hexadecyltrimethylammonium bromide is 1:4.

[0015] Preferably according to the present invention, in step (1), the volume ratio of ethanol, ammonia water (25 wt%) and deionized water in the ethanol / ammonia water mixed solution is 6:0.4:4.

[0016] Preferably according to the present invention, in step (2), the mass percentage of polyvinyl alcohol in the embedding agent is 6-10%, and the mass percentage of sodium alginate is 2%.

[0017] Preferably, according to the present invention, in step (3), the mass volume ratio of the anaerobic ammonium oxidizing bacteria sludge to the embedding solution is 1:(5-8) g / mL, and the mass ratio of the magnetic mesoporous silica nanoparticles to the anaerobic ammonium oxidizing bacteria sludge is 1:(2-5).

[0018] Preferably, in step (4), the static cross-linking time is 12 hours, and the particle size of the magnetic immobilized particles formed by dropwise addition is 3-5 mm.

[0019] Preferably, according to the present invention, in step (5), the constant static magnetic field generating device of the activation reactor can be a parallelly placed permanent magnet, and the magnetic field strength at the center of the reactor is 40-100 mT.

[0020] Preferably, according to the present invention, in step (5), the constant static magnetic field generating device of the activation reactor can be composed of an electromagnetic coil wrapped around the reactor body and a DC power supply controller, and the magnetic field strength at the center of the reactor is controlled to be 40-100mT by controlling the DC power supply.

[0021] Preferably, according to the present invention, in step (5), the filling rate of the immobilized particles in the activation reactor is 40%-60%, the operating temperature is 30° C., and the hydraulic retention time is 12 hours.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention adopts a composite embedding material of polyvinyl alcohol-sodium alginate-magnetic mesoporous silica nanoparticles with an optimized ratio. The magnetic mesoporous silica nanoparticles have a rich pore structure and a large specific surface area, which can adsorb microorganisms in bacterial mud and improve the mechanical stability and substrate mass transfer capacity of the embedding particles. It can not only fix the microorganisms to prevent their loss, but also improve their living environment and have strong biological stability.

[0024] (2) The present invention fixes the anaerobic ammonia-oxidizing bacterial sludge in magnetic particles and uses an external magnetic field to activate it, thereby providing a stable micromagnetic field environment for the microorganisms. Under the action of the biomagnetic effect, the synthesis of microbial proteins is promoted, the enzyme activity is increased, and the microbial quorum sensing system is strengthened, which is beneficial to enhancing the activity of anaerobic ammonia-oxidizing bacteria and the metabolic network between the bacterial communities and improving the activation efficiency.

[0025] (3) The present invention uses modified Fe3O4 to prepare magnetic mesoporous silica nanoparticles, which have high biocompatibility, rich pore structure, and enhanced microbial fixation performance; the silica coating on the surface of nano-Fe3O4 can improve the stability of the magnetic material and prevent the agglomeration of the particles, which is beneficial to the preparation of immobilized particles and increases their service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Scanning electron microscopy and transmission electron microscopy images of prepared magnetic mesoporous silica nanoparticles

[0027] Figure 2 The magnetic anaerobic ammonium oxidation immobilized particles prepared in Example 1;

[0028] Figure 3 is a schematic diagram of an activation reactor;

[0029] Figure 4 The total nitrogen removal rate changes during the activation process of the examples and comparative examples;

[0030] Figure 5 The microbial community structure (genus level) of the examples and comparative examples after activation for 7 days.

[0031] Among them, 1. SBR reactor, 2. reactor water inlet, 3. reactor water outlet, 4. filled magnetic anaerobic ammonia oxidation immobilized particles, 5. artificial sewage, 6. permanent magnet, 7. electromagnetic coil, 8. DC power supply. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with embodiments and drawings, but the protection scope of the present invention is not limited to the described contents.

[0033] Example 1

[0034] A method for preparing and efficiently activating magnetic anaerobic ammonium oxidation immobilized particles specifically comprises the following steps:

[0035] (1) 1.5 g of Fe3O4 nanoparticles were dispersed in 100 mL of 0.5 mol / L trisodium citrate solution and ultrasonicated for 20 minutes. The modified Fe3O4 nanoparticles were collected by a strong magnet, washed with water for 3 times, dispersed in a mixed solution containing 60 mL of ethanol, 4 mL of ammonia (25 wt%) and 40 mL of deionized water and ultrasonicated for 30 minutes. Then, 1.5 mL of tetraethyl orthosilicate was slowly added dropwise while mechanically stirring. After the addition was completed, stirring was continued for 24 hours. The product was collected by a strong magnet and washed three times with anhydrous ethanol and deionized water. Then, the product was dispersed in an ethanol / ammonia mixed solution, 6 g of hexadecyltrimethylammonium bromide was added and mechanically stirred for 2 hours. Then, 4.5 mL of tetraethyl orthosilicate was slowly added dropwise. After stirring was continued for 24 hours, the product was collected by a strong magnet, washed three times with anhydrous ethanol and deionized water, respectively, and dried at 60°C to obtain magnetic mesoporous silica nanoparticles.

[0036] The prepared magnetic mesoporous silica nanoparticles were characterized by scanning electron microscopy and transmission electron microscopy. Figure 1 As shown in Figure 2, the prepared magnetic mesoporous silica nanoparticles have a diameter of about 100 nm, a rough surface, a typical core-shell structure, an average pore size of 8.9 nm, and a specific surface area of ​​276.8 m 2 / g, rich pores, strong adsorption and mass transfer capabilities.

[0037] (2) Add 6 g of polyvinyl alcohol and 2 g of sodium alginate to 100 mL of deionized water, heat to above 95°C and stir evenly to prepare an embedding agent; at the same time, weigh 37.5 g of boric acid and dissolve it in 100 mL of water to prepare a saturated boric acid solution, add 4 g of anhydrous CaCl2 and stir to fully dissolve it, prepare a cross-linking solution and place it at 4°C for use.

[0038] (3) After cooling the prepared embedding agent, place it in a 35°C water bath to keep it warm; take 20g of the enriched anaerobic ammonium-oxidizing granular sludge, grind it with a mortar, add 5g of magnetic mesoporous silica nanoparticles, mix well, and add it to 100mL of the embedding agent, stirring slowly to avoid generating bubbles.

[0039] (4) Use a peristaltic pump to drop the bacterial gelatin mixture into the cross-linking solution, and keep it at 4°C in a sealed container away from light for 12 hours to allow it to fully cross-link. Adjust the aperture of the needle to make the particle size of the particles formed by the dropwise addition 3-5 mm. Take out the prepared immobilized particles and wash them with deionized water for 3-5 times before use.

[0040] The prepared magnetic anaerobic ammonium oxidation immobilized particles are as follows Figure 2 As shown, it is a uniform spherical shape with a particle size of about 4 mm, and the bacterial mud and magnetic mesoporous silica nanoparticles are evenly distributed inside the particles.

[0041] (5) Add the magnetic anaerobic ammonium oxidation immobilized particles into a small SBR activation reactor with a volume of 1 L, and the immobilized particle filling ratio is 50%. Place two permanent magnets in parallel outside the SBR reactor, and adjust the distance between the permanent magnets so that the magnetic field strength at the center of the SBR reactor is 40 mT ( Figure 3 a). A peristaltic pump is used to introduce synthetic wastewater from the bottom of the reactor at one time, and the hydraulic retention time is controlled to be 12 hours. The operating temperature of the reactor is 30°C. The specific components of the synthetic wastewater are: ammonium sulfate ((NH4)2SO4): 472mg / L; sodium nitrite (NaNO2): 591mg / L; potassium bicarbonate (KHCO3): 500mg / L; potassium dihydrogen phosphate (KH2PO4): 25mg / L; magnesium sulfate (MgSO4): 98mg / L; calcium chloride (CaCl2): 23mg / L; trace elements: 1.25mL / L. The specific components of the trace elements are: ethylenediaminetetraacetic acid (EDTA): 20g / L; zinc sulfate (ZnSO4·7H2O): 0.43g / L; manganese chloride (MnCl2·4H2O): 0.99g / L; cobalt chloride (CoCl2·6H2O): 0.24g / L; nickel chloride (NiCl2·6H2O): 0.19g / L; copper sulfate (CuSO4·5H2O): 0.25g / L; sodium selenate (Na2SeO4·10H2O): 0.21g / L; sodium molybdate (Na2MoO4·2H2O): 0.22g / L; boric acid (H3BO4): 0.014g / L.

[0042] Embodiment 2:

[0043] Same as Example 1, except that in step (5), a magnetic field is generated outside the SBR reactor by means of a coil and a DC power supply ( Figure 3 b), by adjusting the current intensity, the magnetic field intensity at the center of the SBR reactor was made to be 40mT, 60mT, 80mT, and 100mT respectively.

[0044] Comparative Example 1:

[0045] The same as Example 1, except that in step (3), no magnetic nanoparticles are added to the embedding agent.

[0046] Comparative Example 2:

[0047] The same as Example 1, except that in step (3), 5 g of Fe3O4 nanoparticles are added to the embedding agent to replace the magnetic mesoporous silica nanoparticles.

[0048] Comparative Example 3:

[0049] The same as comparative example 2, except that in step (5), no magnetic field is applied during the activation process of the activation reactor.

[0050] The properties of the anaerobic ammonia oxidation granular immobilized particles prepared in Example 1, Comparative Example 1 and Comparative Example 2 were characterized, and the results are shown in Table 1. In Example 1 and Comparative Example 2, the mechanical strength and stability of the particles were improved due to the addition of magnetic particle materials, but in Example 1, the mass transfer performance was greatly improved due to the use of pore-rich magnetic mesoporous silica nanoparticles.

[0051] Example Average particle size Mechanical strength Expansion coefficient Mass transfer performance Example 1 4.0 0.86 1.03 Excellent Comparative Example 1 3.7 0.53 1.32 generally Comparative Example 2 3.9 0.82 1.07 generally

[0052] Note: The mass transfer performance test adopts the dye impregnation method, and the particles are taken and cut open at regular intervals to observe the dye impregnation rate.

[0053] The immobilized particles prepared in each embodiment and comparative example were activated, and the total nitrogen removal rate during the activation process was monitored. The results are as follows: Figure 4 As shown. After 7 days of activation, the total nitrogen removal rate of Example 1 and Example 2 can stably reach about 70%, and the magnetic field strength of 40-100mT has no obvious effect on the activation process. Under the action of the magnetic field, the denitrification efficiency of Comparative Example 1 is slowly improved, but after 15 days of activation, its total nitrogen removal rate reaches about 50%; due to the addition of magnetic powder, the denitrification efficiency of Comparative Example 2 is greatly improved under the action of the magnetic field, but the required activation time is longer than that of the embodiment; Comparative Example 3 does not apply a magnetic field during the activation process, and its denitrification efficiency is significantly affected. The microbial community structure after 7 days of activation in each embodiment and comparative example is analyzed, and the results are as follows Figure 5 As shown. Compared with the inoculated sludge, the abundance of the anaerobic ammonium oxidizing functional bacteria Candidatus Kuenenia in Example 1 and Example 2 was greatly improved after 7 days of activation. Compared with the comparative example, the immobilized particles prepared by the present invention have higher activity, and the activation method of the present invention significantly improves the activation efficiency of the anaerobic ammonium oxidizing immobilized particles.

[0054] The above is a schematic description of the invention and its implementation method, which is not restrictive. If a person skilled in the art is inspired by it and creatively designs a structure and embodiment similar to the technical solution without departing from the purpose of the invention, they should all fall within the scope of protection of this patent.

Claims

1. A method for preparing and efficiently activating magnetic anaerobic ammonium oxidation immobilized particles, comprising the following steps: (1) Preparation of magnetic mesoporous silica nanoparticles: Fe3O4 nanoparticles were dispersed in a 0.5 mol / L trisodium citrate solution and subjected to ultrasonic vibration for 20 minutes for modification, and then collected with a strong magnet and dried; the modified Fe3O4 particles were then dispersed in an ethanol / ammonia aqueous solution, and tetraethyl orthosilicate was slowly added dropwise while mechanically stirring. After stirring for 24 hours, the product was collected with a strong magnet and washed with anhydrous ethanol and deionized water and then dried; the product was then further dispersed in an ethanol / ammonia aqueous solution, hexadecyltrimethylammonium bromide was added and stirred for 2 hours, and tetraethyl orthosilicate was slowly added dropwise and stirred for 24 hours. The product was collected, washed three times with anhydrous ethanol and deionized water, respectively, and dried for use. (2) Preparation of embedding agent: Add polyvinyl alcohol and sodium alginate into water, heat to dissolve and stir until mixed to obtain embedding agent. (3) Mixing bacterial sludge and embedding agent: The magnetic mesoporous silica nanoparticles and the cultured anaerobic ammonia-oxidizing bacterial sludge are mixed uniformly in a certain proportion, and after the embedding agent is cooled to 35° C., the particles are added to the embedding agent and mixed uniformly to obtain a bacterial glue mixture. (4) Preparation of magnetic anaerobic ammonium oxidizing immobilized particles: The bacterial gelatin mixture was slowly added dropwise to a saturated boric acid solution containing 4 wt % CaCl2, sealed and kept at 4°C to allow for full cross-linking. The cross-linked embedded particles were washed with deionized water to obtain magnetic anaerobic ammonium oxidizing immobilized particles. (5) Activation of magnetic anaerobic ammonium oxidizer immobilized particles: Add the magnetic anaerobic ammonium oxidizer immobilized particles into a small sequencing batch reactor, apply a constant static magnetic field to the reactor, introduce wastewater containing ammonia nitrogen and nitrite nitrogen, and control a certain hydraulic retention time to activate the immobilized particles.

2. The method according to claim 1, characterized in that In step (1), the mass volume ratio of modified Fe3O4 to the twice added ethyl orthosilicate is 1:1 g / mL and 1:3 g / mL respectively, and the mass ratio of modified Fe3O4 to the added hexadecyltrimethylammonium bromide is 1:

4.

3. The method according to claim 1, characterized in that In step (1), the volume ratio of ethanol, ammonia water (25 wt%) and deionized water in the ethanol / ammonia water mixed solution is 6:0.4:

4.

4. The method according to claim 1, characterized in that: In step (2), the mass percentage of polyvinyl alcohol in the embedding agent is 6-10%, and the mass percentage of sodium alginate is 2%.

5. The method according to claim 1, characterized in that In step (3), the mass volume ratio of the anaerobic ammonium oxidizing bacteria sludge to the embedding solution is 1:(5-8) g / mL, and the mass ratio of the magnetic mesoporous silica nanoparticles to the anaerobic ammonium oxidizing bacteria sludge is 1:(2-5).

6. The method according to claim 1, characterized in that In step (4), the static cross-linking time is 12 hours, and the particle size of the magnetic immobilized particles formed by dropwise addition is 3-5 mm.

7. The method according to claim 1, characterized in that In step (5), the constant static magnetic field generating device of the activation reactor can be permanent magnets placed in parallel on both sides of the reactor, and the magnetic field strength at the center of the reactor is 40-100 mT.

8. The method according to claim 1, characterized in that In step (5), the constant static magnetic field generating device of the activation reactor can be composed of an electromagnetic coil wrapped around the reactor body and a DC power supply controller, and the magnetic field strength at the center of the reactor is controlled to be 40-100 mT by controlling the DC power supply.

9. The method according to claim 1, characterized in that: In step (5), the filling rate of immobilized particles in the activation reactor is 40%-60%, the operating temperature is 30° C., and the hydraulic retention time is 12 hours.

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