CN118236929A

CN118236929A - Calcium phosphate-based hydrogel and preparation method and application thereof

Info

Publication number: CN118236929A
Application number: CN202410407909.2A
Authority: CN
Inventors: 唐睿; 李博博; 周振; 吴钧; 周传庭; 王雨; 安莹; 胡真虎; 朱鸿华; 熊万熹
Original assignee: Shanghai Electric Power University
Current assignee: Shanghai Electric Power University
Priority date: 2024-04-07
Filing date: 2024-04-07
Publication date: 2024-06-25

Abstract

The invention relates to the field of sewage treatment, and discloses calcium phosphate-based hydrogel and a preparation method and application thereof. The method comprises the following steps: (1) In the presence of water, dissolving a gel forming agent and a microparticle affinity agent to obtain a mixed solution; (2) Carrying out contact reaction on the mixed solution and an anaerobic ammonia oxidation sludge solution to obtain a sludge gel solution; (3) Dripping the sludge gel solution into a calcium-based cross-linking agent solution for cross-linking reaction to obtain gel-embedded sludge; (4) And (3) carrying out phosphorylation treatment on the gel-embedded sludge by using a potassium phosphate solution to obtain the phosphorylated calcium-based hydrogel. The calcium phosphate-based hydrogel prepared by the method can provide a mass transfer channel for a substrate of anammox bacteria, enhances the mass transfer capacity and mechanical strength of the hydrogel, and reduces the release of later macromolecular organic matters, thereby reducing the influence on the activity of autotrophic anammox bacteria.

Description

Calcium phosphate-based hydrogel and preparation method and application thereof

Technical Field

The invention relates to the field of sewage treatment, in particular to calcium phosphate-based hydrogel and a preparation method and application thereof.

Background

With the continuous increase of sewage discharge of urban domestic sewage, cultivation wastewater, medical wastewater, landfill leachate and the like, the problem of nitrogen pollution in water bodies is particularly serious. The pollution of nitrogen is extremely harmful, and can promote the eutrophication of water, so that the aquatic ecological system is disordered or even crashed, and the nitrogen can induce human methemoglobin after entering drinking water, thereby directly endangering human health. Therefore, the denitrification of the sewage is of great importance in the sewage treatment process, and is also a difficulty in pollution emission reduction work.

Traditional denitrification mainly depends on a nitrification-denitrification process in a microbial treatment method, and the process depends on perfect cooperation of Ammonia Oxidizing Bacteria (AOB), nitrite Oxidizing Bacteria (NOB) and denitrifying bacteria (DNB), and is the denitrification process adopted by most sewage plants at present. Although the traditional denitrification process has obtained more mature management experience and plays a great role in the nitrogen emission of sewage, the traditional digestion-denitrification process still has a plurality of defects along with the urgent demands of energy conservation, emission reduction, pollution reduction and carbon reduction in the world. This requires that new denitrification processes more conforming to the concept of sustainable development be developed and applied.

Compared with the traditional nitrification-denitrification process, the anaerobic ammonia oxidation process can reduce the aeration by 60%, does not need to additionally add an organic carbon source, has the advantages of high nitrogen removal load, low operation cost, small occupied area, less residual sludge and the like, and is an effective way for treating high-nitrogen wastewater. Therefore, the anaerobic ammonia oxidation process is an efficient denitrification technology with wide application prospect.

However, anaerobic ammonia oxidation bacteria have many defects, such as slow growth, long generation period, easy environmental influence and the like, and the anaerobic ammonia oxidation bacteria easily form a granular state in the growth process, so that air bags are easily formed in the anaerobic ammonia oxidation bacteria, mature anaerobic ammonia oxidation particles float on the upper part of a reactor and are finally flushed out of the reactor, so that the problem of easy loss of organisms is solved, and high-efficiency denitrification cannot be realized. In addition, in the short-cut nitrification-anaerobic ammonia oxidation integrated (PN/A) process, the ammonia oxidation process dominated by Ammonia Oxidizing Bacteria (AOB) is difficult to accurately control aeration, so that Dissolved Oxygen (DO) affects the activity of the anaerobic ammonia oxidizing bacteria, and the development of PN/A in practical engineering application is limited.

In view of the above problems, it has been studied in recent years that embedding microorganisms in hydrogels by immobilization technology can limit oxygen transfer, create good conditions for anaerobic ammoxidation, and thus achieve good treatment effects in PN/A. However, with the continuous and intensive research of the technology of fixing anammox bacteria by using hydrogels, the defects of the hydrogels themselves are found to limit the engineering application of the immobilization method, such as poor mass transfer performance, low mechanical strength and easy collapse of the hydrogels, and the phenomenon of slow release of organic matters in the application.

Therefore, the problems of poor mass transfer performance, low mechanical strength and easy collapse and slow release of organic matters in application of the hydrogel are solved, and the hydrogel is a precondition for promoting engineering application of an anaerobic ammonia oxidation process.

Disclosure of Invention

The invention aims to solve the problems of poor mass transfer performance, low mechanical strength and easy collapse of hydrogel and slow release of organic matters in application in the prior art.

To achieve the above object, a first aspect of the present invention provides a method for preparing a phosphorylated calcium-based hydrogel, the method comprising:

(1) In the presence of water, dissolving a gel forming agent and a microparticle affinity agent to obtain a mixed solution;

(2) Carrying out contact reaction on the mixed solution and an anaerobic ammonia oxidation sludge solution to obtain a sludge gel solution;

(3) Dripping the sludge gel solution into a calcium-based cross-linking agent solution for cross-linking reaction to obtain gel-embedded sludge;

(4) Carrying out phosphorylation treatment on the gel-embedded sludge by using a potassium phosphate solution to obtain a calcium phosphate-based hydrogel;

wherein the gel forming agent is at least one selected from polyvinyl alcohol, polyacrylamide, polyethylene glycol and polyurethane;

The microparticle affinity agent is at least one selected from carboxymethyl cellulose, alginate, gelatin, agar, carrageenan, ceramic, coral sand, vesuvianite, biochemical cotton, activated carbon and SiO ₂.

In a second aspect the present invention provides a calcium phosphate based hydrogel prepared by the method of the first aspect.

In a third aspect, the present invention provides the use of a calcium phosphate-based hydrogel according to the second aspect in sewage treatment.

Compared with the prior art, the method provided by the invention has at least the following beneficial effects:

(1) The method provided by the invention has the advantages of simple process steps, convenient operation and easy popularization, and the calcium-based hydrogel material has a higher pore structure by carrying out phosphorylation treatment on the calcium-based hydrogel, so that the mass transfer capacity of the gel balls can be enhanced, and the high-efficiency transmission of anaerobic ammonia oxidizing bacteria substrates is facilitated;

(2) According to the method provided by the invention, through the calcium-based hydrogel subjected to phosphorylation treatment, more inorganic calcium phosphate is formed on the surface of the calcium-based hydrogel, so that the mechanical strength of the hydrogel can be improved;

(3) The method provided by the invention can also reduce the release of later-stage organic matters, thereby avoiding the influence on anaerobic ammonia oxidizing bacteria in a PN/N integrated process;

(4) The invention is not only suitable for embedding microorganisms in the sewage treatment industry, but also suitable for embedding functional microorganisms or biological enzymes related to the industries such as food, biochemical industry and the like.

Drawings

FIG. 1 is a flow chart of a preferred embodiment of the present invention;

FIG. 2 is a physical view of a calcium phosphate-based hydrogel prepared in accordance with a preferred embodiment of the present invention;

FIG. 3 is a graph of mass transfer rate for calcium phosphate-based hydrogels prepared according to a preferred embodiment of the present invention;

FIG. 4 is a graph showing the results of mechanical strength testing of calcium phosphate-based hydrogels prepared according to the preferred embodiments of the present invention;

FIG. 5 is a graph showing the results of the organic matter release test of calcium phosphate-based hydrogels prepared according to the preferred embodiment of the present invention.

Detailed Description

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

The technical principle of the invention comprises:

In the calcium phosphate-based hydrogel provided by the invention, macromolecular organic matters are crosslinked with a crosslinking agent to form an organic calcium structure, and as the solubility product (Ksp) of calcium phosphate is smaller, phosphate can replace macromolecular organic matters in the hydrogel during the phosphorylation treatment. In addition, the calcium-based hydrogel subjected to phosphorylation forms inorganic calcium phosphate with larger strength, so that the hydrogel has larger pore structure and mechanical strength, and the influence on anaerobic ammonia oxidizing bacteria embedded in the hydrogel in the later period can be avoided after macromolecular organic matters are replaced.

As previously described, a first aspect of the present invention provides a method of preparing a phosphorylated calcium-based hydrogel, the method comprising:

The potassium phosphate solution in the invention is K ₃PO₄ solution.

According to a preferred embodiment, in step (1), the gel former is polyvinyl alcohol.

More preferably, in step (1), the weight average molecular weight of the polyvinyl alcohol is 89000 to 98000. It is found that in the preferred case, the polymer chains can be connected with each other through physical action (such as hydrogen bond, ionic bond or Van der Waals force) and chemical bond formation to form a three-dimensional network structure, so that the mechanical strength of the calcium phosphate-based hydrogel prepared by the method provided by the invention is better.

According to a preferred embodiment, in step (1), the particulate affinity agent is sodium alginate.

Preferably, in step (1), the temperature of dissolution is 30-100 ℃.

Preferably, in step (1), the dissolving is performed using at least one of stirring, shaking, ultrasonic, homogenizing, and vortexing.

Preferably, in step (1), the amount of the gel-forming agent is controlled so that the content of the gel-forming agent in the mixed liquid is 5 to 50wt%.

Preferably, in step (1), the amount of the particulate affinity agent is controlled so that the content of the particulate affinity agent in the mixed liquid is 0.5 to 20wt%. It was found that in this preferred case, the hydrogel is favored to adsorb small-molecule inorganic substances in the wastewater.

Preferably, the method of the present invention further comprises: in step (2), the mixed liquor is sterilized before the mixed liquor is contacted and reacted with the anaerobic ammonium oxidation sludge solution.

More preferably, the sterilization is carried out at a temperature of 100-500 ℃ and a pressure of 60-360 kPa using high temperature and high pressure.

The high-temperature and high-pressure sterilization apparatus according to the present invention is not limited to the above-mentioned apparatus and equipment, and may be carried out using an apparatus and equipment commonly used in the art, and may be carried out using, for example, a steam separator, a high-pressure reaction tube, a high-temperature and high-pressure sterilization pot, a reaction pot, an electric steam generator, a decomposition pot, a vulcanizing pot, a decomposition tower, a polymerization pot, an autoclave, an ultra-high pressure pot, a shift furnace, a digester, a steam ball, an autoclave, or a gas producer.

Preferably, in step (2), the anaerobic ammonium oxidation sludge solution has a sludge concentration of 1-50g VSS/L. It was found that anaerobic ammonium oxidation bacteria are better able to grow in a concentrated manner in this preferred case.

Preferably, in step (2), the conditions of the contact reaction at least satisfy: the temperature is 5-80 ℃ and the time is 0.5-6h.

Preferably, in the step (2), the volume ratio of the mixed solution to the anaerobic ammonia oxidation sludge solution is 1:0.5-2.

Preferably, in the step (3), the calcium-based crosslinking agent solution is selected from at least one of a calcium hydroxide solution, a calcium chloride saturated boric acid solution, a calcium bromide solution, a calcium iodide solution, a calcium chlorate solution, a calcium perchlorate solution, a calcium permanganate solution, a calcium dihydrogen phosphate solution, a calcium gluconate solution, a calcium nitrate solution, a calcium hydrogen sulfate solution, a calcium hydrogen sulfite solution, and a calcium hypochlorite solution.

According to a preferred embodiment, in step (3), the concentration of the calcium-based crosslinker solution is between 0.5 and 30 wt.%.

Preferably, in step (3), the dropping speed of the sludge gel solution is 0.05 to 5 mL/s per 1L of the calcium-based crosslinking agent solution.

Preferably, in the step (3), the dropping is performed by at least one of peristaltic pump, diaphragm pump, centrifugal pump and manual dropping.

Preferably, in step (3), the cross-linking reaction is performed in a hydrogel-specific drip apparatus to control the morphology of the resulting gel-embedded sludge, such as a particulate drip pump.

Preferably, in step (3), the conditions of the crosslinking reaction at least satisfy: the temperature is between-2 ℃ and 50 ℃ and the time is between 1 and 36 hours.

Preferably, in step (4), the concentration of the potassium phosphate solution is 5-500 mg P/L.

Preferably, in step (4), the phosphorylation treatment is performed under stirring conditions, and at least: the rotation speed is 10-200rpm, the temperature is-5 ℃ to 40 ℃ and the time is 0.5-50h.

Preferably, in the step (4), the dosage volume ratio of the potassium phosphate solution to the gel-embedded sludge is 2-20:1.

As previously described, the second aspect of the present invention provides a calcium phosphate-based hydrogel prepared by the method of the first aspect.

As previously mentioned, a third aspect of the present invention provides the use of a calcium phosphate-based hydrogel according to the second aspect of the present invention in sewage treatment.

The present invention will be described in detail by way of examples, and unless otherwise specified, all materials used are commercially available.

Gel forming agent:

Gel forming agent I: is polyvinyl alcohol with a weight average molecular weight of 92000, and is purchased from Shanghai Ala Biochemical technology Co., ltd, and has a brand name of P434371;

gel forming agent II: the polyvinyl alcohol has a weight average molecular weight of 10000 and is purchased from Shanghai Ala Biochemical technology Co., ltd, and the brand name is P434372;

Microparticle affinity agent: sodium alginate, available from national pharmaceutical group chemical reagent Co., ltd, trade name 30164424.

Anaerobic ammoxidation sludge solution:

Anaerobic ammoxidation sludge solution I: granular sludge in the mature period in UASB-like reactor with sludge concentration of 10g VSS/L;

Anaerobic ammoxidation sludge solution II: granular sludge in mature period in UASB system reactor with sludge concentration of 0.5g VSS/L;

calcium-based crosslinker solution: a saturated boric acid solution of calcium chloride at a concentration of 4 wt%.

Potassium phosphate solution:

Potassium phosphate solution I: the concentration is 15 mg P/L;

Potassium phosphate solution II: the concentration was 2 mg P/L.

Example 1

This example is for illustrating the method for preparing a phosphorylated calcium-based hydrogel according to the present invention, and is performed according to the procedure shown in fig. 1, which includes the steps of:

(1) Dissolving a gel forming agent (gel forming agent I) and a particle affinity agent in water at a speed of 600rpm by adopting a heat-collecting magnetic stirrer at 95 ℃ for 120min to obtain a mixed solution, wherein the dosage of the gel forming agent and the particle affinity agent is controlled so that the content of the gel forming agent is 25wt% and the content of the particle affinity agent is 5wt% in the mixed solution;

(2) Sterilizing the mixed solution at the temperature of 121 ℃ and the pressure of 120kPa for 20min to obtain a sterilized mixed solution, and then carrying out contact reaction with an anaerobic ammonia oxidation sludge solution (anaerobic ammonia oxidation sludge solution I) for 2h at the temperature of 35 ℃ to obtain a sludge gel solution; wherein, the dosage volume ratio of the mixed solution to the anaerobic ammonia oxidation sludge solution is 1:1, a step of;

(3) At the temperature of 4 ℃, dropwise adding the sludge gel solution into a calcium-based cross-linking agent solution by adopting a particle dropwise adding pump to carry out cross-linking reaction for 24 hours to obtain calcium-based hydrogel, then flushing with clear water for three times until no foam is generated, and then storing in a refrigerator at the temperature of 4 ℃ to obtain gel-embedded sludge; wherein the dropping speed of the sludge gel solution is 1 mL/s for every 1L of the calcium-based crosslinking agent solution;

(4) The gel-embedded sludge was subjected to a phosphorylation treatment in a potassium phosphate solution (potassium phosphate solution I) using a magnetic stirrer at 25 ℃ and a rotational speed of 80rpm for 6 hours, wherein the volume ratio of the potassium phosphate solution to the gel-embedded sludge was 10:1, finally obtaining the calcium phosphorylate hydrogel, which is named as P1;

Fig. 2 is a physical diagram of P1, in which it can be seen that the calcium phosphate-based hydrogel has a regular morphology and a good mechanical strength.

Example 2

This example was conducted in a similar manner to example 1 except that in step (1), the gel-forming agent used was gel-forming agent II;

Finally, the phosphorylated calcium-based hydrogel is obtained and is named as P2.

Example 3

This example was conducted in a similar manner to example 1 except that in step (2), the anaerobic ammonium oxidation sludge solution used was anaerobic ammonium oxidation sludge solution II;

finally, the phosphorylated calcium-based hydrogel is obtained and is named as P3.

Example 4

This example was conducted in a similar manner to example 1 except that in step (4), the potassium phosphate solution used was potassium phosphate solution II;

finally, the phosphorylated calcium-based hydrogel is obtained and is named as P4.

Comparative example 1

This comparative example was carried out in a similar manner to example 1, except that in step (1), the dissolution was carried out using lignin of equal mass instead of the particulate affinity agent;

The final calcium phosphorylate hydrogel was designated DP1.

Comparative example 2

This comparative example was conducted in a similar manner to example 1 except that in step (4), the phosphorylation treatment was not conducted, and the operation of step (4) includes:

(4) Treating the gel-embedded sludge obtained in step (3) in physiological saline (NaCl concentration of 0.9 wt%) using a magnetic stirrer at 25 ℃ and a rotational speed of 80rpm for 6 hours, wherein the ratio of the amount of physiological saline to the gel-embedded sludge is 10 by volume: 1, a step of;

Finally, a calcium-based hydrogel was obtained, designated DP2.

Test example 1

Mass transfer experiments were performed on the phosphorylated calcium-based hydrogels and calcium-based hydrogels prepared in the examples section above, including:

The calcium phosphate-based hydrogel and the calcium-based hydrogel prepared in the above examples are respectively washed with clear water for 10min each time until the cleaning solution is free from foam and becomes clear, 30 particles are respectively put into 100mL of nitrous solution with the concentration of 10 mg/L for mass transfer experiments, 0min, 5min, 15min, 30min, 1h, 2h and 4h are respectively sampled, a 0.22 μm filter membrane is used for filtration, the nitrous concentration in the samples taken at the above time points is measured by an N- (1-naphthyl) -ethylenediamine photometry in national standard, and the mass transfer rate k is obtained by fitting the results of the samples by a quasi-first-order kinetic equation (the formula is shown as follows), and the results are shown in FIG. 3.

Wherein y is the adsorption amount of the adsorption substance in the time (x), and the unit is gram (g);

x is the time elapsed during the adsorption process in minutes (min);

a is equilibrium adsorption quantity, and the unit is gram (g);

e is a natural constant.

Test example 2

The phosphorylated calcium-based hydrogels and calcium-based hydrogels prepared in the examples section above were subjected to mechanical strength test experiments comprising:

Washing the calcium phosphate-based hydrogel and the calcium phosphate-based hydrogel prepared in the above examples respectively with clear water for 10min each time until the cleaning solution is free from foam and becomes clear, respectively taking 100 particles (total particle number) into 100 mL pure water, carrying out mechanical strength experiments in a constant-temperature shaking table at 25 ℃ and 120 rpm, checking the breaking degree of gel particles in each bottle when t ₁ time points (12 h) and t ₂ time points (36 h) are passed, breaking according to the fact that each gel has a falling off or breaks, and calculating the breaking rate (100% of broken particle number/total particle number) of the hydrogel in each bottle, so as to represent the mechanical strength of the hydrogel, wherein the smaller the breaking rate is, the greater the mechanical strength of the hydrogel is; also, the larger the crushing ratio is, the smaller the mechanical strength thereof is. The crushing rate of each hydrogel was obtained, and the results are shown in FIG. 4.

Test example 3

Testing the comparison of late release organics for different phosphorylated and calcium-based hydrogels prepared in the examples section above, comprising:

Washing the calcium phosphate-based hydrogel and the calcium-based hydrogel prepared in the above example part respectively with clear water for 10min each time until the cleaning solution is free from foam and becomes clear, putting 50 particles into 100mL of pure water respectively, carrying out experiments in a constant-temperature shaking table at 25 ℃ and 120rpm, respectively sampling and measuring the COD content in a system of each bottle after passing through a time point t ₃ (12 h) and a time point t ₄ (48 h), measuring the COD of water samples taken at the time points t ₃ and t ₄ by a national standard water quality chemical oxygen demand dichromate method, and further comparing the conditions of releasing macromolecular organic matters in the later stages of the hydrogels subjected to different treatments: the smaller the COD concentration is, the less macromolecular organic matters are released; also, the greater the COD concentration, the more macromolecular organic it releases. The test results are shown in FIG. 5.

The results show that the calcium phosphate-based hydrogel prepared by the method provided by the invention is a porous hydrogel embedding material, provides a mass transfer channel for substrates of anaerobic ammonia oxidation bacteria, enhances the mass transfer capacity of the hydrogel, enhances the mechanical strength of the hydrogel, and reduces the release of later-stage macromolecular organic matters, thereby reducing the influence on the activity of autotrophic anaerobic ammonia oxidation bacteria and providing support for promoting the engineering application of anaerobic ammonia oxidation technology.

The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, a number of simple variants of the technical solution of the invention are possible, including combinations of the individual technical features in any other suitable way, which simple variants and combinations should likewise be regarded as being disclosed by the invention, all falling within the scope of protection of the invention.

Claims

1. A method of preparing a phosphorylated calcium-based hydrogel, the method comprising:

2. The method according to claim 1 or 2, wherein in step (4), the concentration of the potassium phosphate solution is 5-500 mg P/L.

3. The method according to claim 1 or 2, wherein in step (1), the amount of the gel-forming agent is controlled so that the content of the gel-forming agent in the mixed liquid is 5 to 50wt%.

4. The method according to claim 1 or 2, wherein in step (1), the amount of the particulate affinity agent is controlled so that the content of the particulate affinity agent in the mixed liquor is 0.5 to 20wt%.

5. The method according to claim 1 or 2, wherein in step (2), the anaerobic ammonium oxidation sludge solution has a sludge concentration of 1 to 50g VSS/L.

6. The process according to claim 1 or 2, characterized in that in step (2) the conditions of the contact reaction at least satisfy: the temperature is 5-80 ℃ and the time is 0.5-6h.

7. The method according to claim 1 or2, wherein in step (2), the ratio of the mixed liquor to the anaerobic ammonium oxidation sludge solution is 1:0.5-2.

8. The method according to claim 1 or 2, wherein in step (3), the concentration of the calcium-based crosslinker solution is 0.5-30wt%.

9. A calcium-phosphate-based hydrogel prepared by the method of any one of claims 1-8.

10. Use of the calcium phosphate-based hydrogel of claim 9 in sewage treatment.