Lanthanum-containing phosphorus locking agent as well as preparation method and application thereof

Abstract

The invention discloses a lanthanum-containing phosphorus locking agent as well as a preparation method and application thereof, and belongs to the technical field of black and odorous water body treatment. The technical key points are as follows: the mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel bead is characterized in that the bead has a core-shell structure: the core structure is mesoporous lanthanum oxide, and mesopores with the pore diameter of 3-6 nm are formed in the mesoporous lanthanum oxide; the shell structure is sodium alginate / chitosan gel; the functional microorganisms and the mesoporous lanthanum oxide are wrapped in the shell structure; the surface of the shell structure is also provided with a through hole, and the aperture of the through hole is 50-200 nm.

Description

Technical Field

[0001] The present invention relates to the technical field of black and odorous water treatment, and more specifically, to a lanthanum-containing phosphorus-locking agent, a preparation method and application thereof. Background Art

[0002] Phosphorus is a significant pollutant in black and odorous water bodies. Due to the low dissolved oxygen concentration in black and odorous water bodies, phosphorus bound to iron oxides in sediments is released into the water, leading to elevated phosphorus concentrations. This phosphorus stimulates algae growth in the water. The decomposition of the dead algae consumes significant amounts of dissolved oxygen and forms black and odorous substances such as methane, hydrogen sulfide, and ammonia, further exacerbating the water's black and odorous nature. Therefore, phosphorus control is a crucial task in the treatment of black and odorous water bodies.

[0003] The addition of phosphorus-locking agents has been widely recognized as a method of controlling phosphorus in water bodies in recent years. 3+ , Ca 2+ or La 3+ Can be used with PO4 3- It can form precipitates or complexes, thereby effectively reducing the phosphorus concentration in the water. At the same time, the phosphorus lock agent can form a passivation layer at the sediment-water interface to hinder the release of phosphorus in the sediment to the overlying water.

[0004] Among the various phosphorus-locking agents, lanthanum-containing phosphorus-locking agents have shown the most superior effect. 3+ Can be used with PO4 3- It forms a very stable precipitate, and the effect is not affected by the external environment (PH and DO, etc.).

[0005] like: Reference 1: AU8938198A, which developed Phoslock lanthanum-containing phosphorus-locking agent (LMB). The principle of its phosphorus removal is that lanthanum metal forms an insoluble lanthanum-phosphate complex with free phosphate in water, and then locks the phosphate in bentonite.

[0006] Reference 2: "Tian Liming. Preparation of a lanthanum-loaded volcanic ash phosphorus-locking agent and its inhibitory effect on phosphorus release from Jiuli Lake sediment [D] China University of Mining and Technology, 2023" developed a lanthanum-loaded NaOH-La-modified volcanic ash phosphorus-locking agent. Scanning electron microscopy (SEM) analysis revealed that acidification treatment increased the surface roughness and porosity of the volcanic ash, increasing its specific surface area. Lanthanum was uniformly distributed on the surface of the modified volcanic ash.

[0007] Document 3: CN116177723A, which discloses a slow-release heavy metal removal / phosphorus locking biological filter material, its preparation method and application. It is a clay mineral with montmorillonite as the main component, and the cations in the calcium-based bentonite are mainly calcium ions, which can also form calcium phosphate precipitates with phosphates and have a certain adsorption and slow-release effect on lanthanum chloride heptahydrate, thereby extending the slow-release period of lanthanum chloride heptahydrate.

[0008] Document 4: CN112237897B, which discloses a layered bimetallic-based nano-lanthanum material, a preparation method and application thereof, which has better phosphorus removal effect.

[0009] Therefore, the main research and development direction of existing lanthanum-containing phosphorus-binding agents is to improve the phosphorus removal effect. However, when using lanthanum-containing phosphorus-binding agents to treat black and odorous water bodies, the following issues need to be considered: (1) The high concentration of organic matter in black and odorous water bodies will compete for the effective adsorption sites on the surface of the phosphorus-locking agent, resulting in a significant decrease in the phosphorus control performance of the lanthanum-containing phosphorus-locking agent.

[0010] (2) In order to remove organic pollutants and odorous substances from black and odorous water bodies, microorganisms need to be used to biodegrade these substances. However, microbial agents are often lost under the action of water flow, and there are also problems such as low viable bacterial counts and poor bacterial stability, which affect the remediation effect of black and odorous water bodies. Therefore, how to fix microorganisms is also a technical issue. Summary of the Invention

[0011] The purpose of this application is to provide a lanthanum-containing phosphorus-locking agent to address the deficiencies of the above-mentioned prior art.

[0012] Another object of the present application is to provide a method for preparing a lanthanum-containing phosphorus-locking agent.

[0013] Another object of the present application is to provide a lanthanum-containing phosphorus-locking agent for use in the treatment of black and odorous water bodies.

[0014] The technical solution of this application is as follows: A lanthanum-containing phosphorus-locking agent, which is a mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel ball, wherein the ball has a "core-shell" structure: The core structure is mesoporous lanthanum oxide, and mesopores with a pore size of 3 to 6 nm are formed inside the mesoporous lanthanum oxide; Wherein, the shell structure is sodium alginate / chitosan gel; Wherein, the functional microorganism and the mesoporous lanthanum oxide are both encapsulated in the shell structure; The surface of the shell structure also has through holes, and the pore diameter of the through holes is 50-200 nm.

[0015] Furthermore, the sodium alginate / chitosan gel is a polymer network; the polymer network is formed by chitosan and sodium alginate under the action of CaCl2.

[0016] Furthermore, the diameter of the mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel beads is between 1 mm and 2 mm.

[0017] Furthermore, the functional microorganism is between the mesoporous lanthanum oxide and the sodium alginate / chitosan gel.

[0018] Furthermore, in a dry state, the specific surface area of the lanthanum-containing phosphorus-locking agent is 100 to 200 m 2 / g.

[0019] Furthermore, the lanthanum-containing phosphorus-locking agent has an adsorption capacity of 8 to 25 mg / g of phosphorus, calculated as phosphorus element; the organic matter degradation capacity is characterized by the COD removal rate during the water purification process. For water bodies with COD less than 100 mg / L, the COD removal rate can reach 60 to 85%.

[0020] A method for preparing a lanthanum-containing phosphorus-locking agent comprises the following steps: S100, preparing mesoporous lanthanum oxide; S100 includes sub-steps S101 to S103; S101, use 1% volume fraction hydrochloric acid to prepare La with a concentration of 0.5~2 mol / L 3+ An aqueous solution in which cetyltrimethylammonium bromide (CTAB) is dissolved as a template. The concentration of CTAB is close to its solubility, which is 13 g / L. S102, use 0.5~6 mol / L NaOH solution, KOH solution or ammonia water to titrate La at a rate of 0.1~0.5 mL / min 3+ -CTAB solution, finally raise the pH of the mixture to 6-8, and continue stirring for more than 4 hours; S103, after centrifuging the mixed solution, transferring the solid to a Soxhlet extractor, reacting the solid with a 9:1 or 8:2 ethanol-water mixture (i.e., a ratio of ethanol to water of 9:1 or 8:2) for 4-8 hours to remove the template; and drying to obtain mesoporous lanthanum oxide; S200, preparing mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel beads, which includes sub-steps S201 to S203; S201, prepare a sodium alginate aqueous solution with a concentration of 2-20 g / L (i.e., 2-20 g of sodium alginate per liter of solution); add the mesoporous lanthanum oxide obtained in S100 thereto and mix, so that the mass concentration of the mesoporous lanthanum oxide is 5-10 g per liter of solution; then, add the functional bacteria solution, stir evenly, and obtain suspension A; S202, preparing a chitosan solution with a mass concentration of 5-15 g / L (i.e., 5-15 g of chitosan per liter of solution), and adding CaCl2 to a concentration of 2-20 g / L (i.e., 2-20 g of CaCl2 per liter of solution) to form solution B; S203, using a peristaltic pump, while maintaining stirring, add suspension A dropwise to solution B at a rate of 0.5-1.5 mL / min; the volume ratio of solution A to solution B is 1:1; S204, in 4 o C for 24 h to form a sodium alginate / chitosan gel object with a semi-interpenetrating structure, in which the mesoporous lanthanum oxide and functional microorganisms are encapsulated.

[0021] Furthermore, La used in S101 3+ The salt is any one or more of LaCl3 and LaNO3.

[0022] Furthermore, the drying method of the mesoporous lanthanum oxide product in S103 is drying or freeze-drying, wherein the drying temperature is 45~65 o C.

[0023] Furthermore, the suspension A and solution B during the titration process should be kept stirred, and the stirring methods include mechanical stirring and magnetic stirring. The stirring rate should ensure that the mesoporous lanthanum oxide does not precipitate, but it should not be too fast to affect the stability of the hydrogel particles in solution B and the immobilization of microorganisms. It should be controlled between 100 and 300 r / min.

[0024] Furthermore, the functional microbial solution used is a commercial composite bacterial solution, specifically including Bacillus, photosynthetic bacteria, lactic acid bacteria and nitrifying bacteria, but not limited to the above bacteria. The functions of the embedded microorganisms include producing oxygen, degrading organic matter and removing ammonia nitrogen. The composite bacterial solution used was measured by spectrophotometry before use. 600 The cell concentration is calculated based on the absorbance at λ = 600 nm, which should be greater than 1 × 10 6 When preparing suspension A, the amount of bacterial solution added is 0.5~10 g / L.

[0025] An application of the aforementioned lanthanum-containing phosphorus-locking agent in the treatment of black and odorous water bodies.

[0026] The beneficial effects of this application are: First, the present application provides a lanthanum-containing phosphorus-binding agent that also has the function of degrading black and odorous substances. The mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel beads obtained in the present application have a "core-shell" structure and are a lanthanum-containing phosphorus-binding agent that also has the function of degrading black and odorous substances.

[0027] Mesoporous lanthanum oxide is the core of the material. Incorporating the pore-forming agent CTAB, the lanthanum oxide forms mesopores with pore sizes ranging from 3 to 6 nm. This pore size allows only phosphate ions (approximately 0.5 nm in diameter) to diffuse in, while blocking organic matter such as humus and microbial extracellular polymers (ECPs) in the water. This ensures that the phosphorus-binding sites on the inner surface of the lanthanum oxide particles are not occupied by organic matter in the water, preserving their phosphorus-binding capacity even in high-organic-matter, black and odorous water environments.

[0028] The alginate / chitosan hydrogel particles, which encapsulate functional microorganisms, serve as the "shell" of the material. The microorganisms immobilized within the hydrogel effectively remove black and odorous substances from the aqueous environment, while also minimizing their adverse effects on phosphorus control within the mesoporous lanthanum oxide. The alginate / chitosan hydrogel (i.e., polymer network) exhibits a semi-interpenetrating structure and is relatively stable. The pore size of the "shell" ranges from 50 to 200 nm, facilitating microbial attachment while not hindering the entry of phosphate into the mesoporous lanthanum oxide "core."

[0029] By organically combining lanthanum-containing phosphorus-locking agents and immobilized microbial technology to form a "core-shell" structure, the removal of organic pollutants in black and odorous water bodies is achieved, and their adverse effects on the function of lanthanum-containing phosphorus-locking agents are controlled to the greatest extent.

[0030] Second, the lanthanum-containing phosphorus-locking agent developed in this application has the following three effects when applied to the treatment of black and odorous water bodies: (1) Good ability to eliminate black and odor: Black and odorous substances in water can be degraded by functional microorganisms immobilized in the sodium alginate / chitosan "shell"; (2) Super strong phosphorus fixation ability: Phosphate in water can freely diffuse through the sodium alginate / chitosan "shell" to the surface of lanthanum oxide, and then enter the interior of lanthanum oxide through the mesopores to form lanthanum phosphate spectrum with lanthanum atoms, permanently fixing phosphorus and eliminating the risk of algae outbreaks.

[0031] (3) The elimination of black and odorous substances and the ability to fix phosphorus are coordinated with each other: the sodium alginate / chitosan "shell" layer eliminates black and odorous substances and prevents them from competing for the phosphorus fixation sites on the surface of lanthanum oxide, while not hindering the passage of phosphate; the mesoporous lanthanum oxide "core" can stably fix phosphorus, and the microorganisms and metabolites in the "shell" cannot enter the mesopores, and the two functions do not interfere with each other.

[0032] Third, the difficulty of the preparation method of the present application is: (1) How to ensure that mesoporous lanthanum oxide has mesopores with a pore size of 3-6 nm? First, the pore-forming agent CTAB is added during the synthesis of lanthanum oxide. After synthesis, the CTAB is extracted with ethanol through a Soxhlet extractor, and the CTAB vacancies form mesopores. Second, the CTAB concentration is 13g / L, which ensures that the pore size of the mesoporous lanthanum oxide is 3-6nm.

[0033] (2) How to ensure that the surface of the shell structure also has through-pores with a pore size of 50-200 nm? The key factor affecting this problem is the concentration of sodium alginate and chitosan solutions: the lower the concentration, the looser the cross-linked network; conversely, the denser it is.

[0034] In addition, the CaCl2 concentration, cross-linking time and cross-linking temperature were also considered accordingly to ensure that the pore size of the cross-linked network meets the requirements.

[0035] That is, "the concentration of sodium alginate is 2-20 g / L; the concentration of chitosan in the chitosan solution is 5-15 g / L", "the concentration of CaCl2 is 2-20 g / L", "the volume ratio of solution A to solution B is 1:1", "at 4 o C for 24 hours to form sodium alginate / chitosan gel beads with a semi-interpenetrating structure", which is essentially the same as "the surface of the shell structure also has through holes with a pore size of 50-200 nm". The above preparation method ensures that "the surface of the shell structure also has through holes with a pore size of 50-200 nm". BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be further described in detail below with reference to the embodiments in the accompanying drawings, but this does not constitute any limitation to the present invention.

[0037] Figure 1 This is a process flow chart of the lanthanum-containing phosphorus-locking agent of this application.

[0038] Figure 2 This is an actual product picture of the lanthanum-containing phosphorus-locking agent of this application. DETAILED DESCRIPTION

[0039] The present invention is described in detail below with reference to specific embodiments.

[0040] Example 1 (1) Material synthesis First, mesoporous lanthanum oxide is prepared.

[0041] Prepare a 1 mol / L LaCl3 aqueous solution and add CTAB to make the concentration reach 13 g / L; use 6 mol / L ammonia water to titrate LaCl3 at a rate of 0.1 mL / min. 3+-CTAB mixture to finally raise its pH to 7.5±0.5, and continue stirring for more than 4 hours; then centrifuge and transfer the solid to a Soxhlet extractor, react with a 9:1 ethanol-water mixture for 8 hours, and then dry to obtain mesoporous lanthanum oxide.

[0042] Then, mesoporous lanthanum oxide-functional bacteria-sodium alginate / chitosan hydrogel beads were prepared.

[0043] A 10 g / L sodium alginate aqueous solution was prepared, to which mesoporous lanthanum oxide was added to form a 10 g / L suspension, and then 5% volume fraction of Bacillus and photosynthetic bacteria functional bacteria solution were added and stirred to obtain suspension A; a 5 g / L chitosan solution was prepared, and CaCl2 was added to make its concentration reach 15 g / L to form solution B, and suspension A was added dropwise to solution B at a rate of 1 mL / min. o The obtained mesoporous lanthanum oxide-functional bacteria-sodium alginate / chitosan hydrogel beads were approximately spherical with a particle size of 1-2 mm.

[0044] (2) Effect of black and odorous water treatment This material was used to treat a black and smelly water body in Minhang District, Shanghai. Due to long-term agricultural non-point source pollution, the water quality of this water body has seriously deteriorated. The dissolved oxygen is only 0.5 mg / L, the bottom mud is black, and the COD, total phosphorus, and ammonia nitrogen concentrations are 41.6, 19.9, and 0.74 mg·L, respectively. -1 The water surface is covered with Spirogyra. 2 After the addition of the materials, the dissolved oxygen concentration in the water continued to rise, remaining at 1.5 mg / L after 35 days. After 162 days, the COD, total phosphorus, and ammonia nitrogen concentrations reached 18.05, 0.15, and 0.24 mg / L, respectively. During this process, due to the significant reduction in phosphorus concentration in the lake, the Spirodendrum spp. on the surface gradually turned yellow and died, the turbid water became clear, and the odor essentially disappeared.

[0045] Example 2 (1) Material synthesis First, mesoporous lanthanum oxide is prepared.

[0046] Prepare a 0.5 mol / L LaCl3 aqueous solution and add CTAB to make it 13 g / L. Use 2 mol / L NaOH to titrate LaCl3 at a rate of 0.1 mL / min. 3+ -CTAB mixed solution to finally raise its pH to 6.5±0.5, and continue stirring for more than 4 hours; then centrifuge and transfer the solid to a Soxhlet extractor, react with an 8:2 ethanol-water mixture for 6 hours, and then dry to obtain mesoporous lanthanum oxide.

[0047] Then, mesoporous lanthanum oxide-functional bacteria-sodium alginate / chitosan hydrogel beads were prepared.

[0048] A 10 g / L sodium alginate aqueous solution was prepared, to which mesoporous lanthanum oxide was added to form a suspension with a concentration of 8 g / L, and then 5% by volume of nitrifying bacteria, photosynthetic bacteria and lactic acid bacteria functional bacteria were added and stirred to obtain suspension A. A 5 g / L chitosan solution was prepared, and CaCl2 was added to make its concentration reach 15 g / L to form solution B. Suspension A was added dropwise to solution B at a rate of 1 mL / min. o The obtained mesoporous lanthanum oxide-functional bacteria-sodium alginate / chitosan hydrogel beads were approximately spherical with a particle size of 0.8-1.5 mm.

[0049] (2) Effect of black and odorous water treatment This material was used to treat a black and odorous water body in Xi'an, Shaanxi Province. The water body, located in the slow-flowing area of a river, had become completely turbid due to the long-term discharge of wastewater from a municipal sewage plant and the burden of non-point sources from surrounding cities. The benthic flora and fauna were completely extinct. The COD, total phosphorus, and ammonia nitrogen concentrations in the water were 91.2, 3.95, and 7.84 mg·L, respectively. -1 . According to 2.5kg / m 2 Fifty-two days after the addition of the materials, COD, total phosphorus, and ammonia nitrogen concentrations dropped to 13.05, 0.25, and 0.24 mg / L, respectively. Black algae, aquatic plants, reappeared in the lake, and the odor essentially disappeared. Monitoring continued for 208 days, with no algae remaining in the water, demonstrating the long-term cleanliness of the black and odorous waters.

[0050] The above embodiments are preferred implementation modes of the present application and are only used to facilitate the explanation of the present application. They are not intended to limit the present application in any form. Any person with ordinary knowledge in the relevant technical field, if they do not depart from the scope of the technical features proposed in the present application, can make equivalent embodiments by making partial changes or modifications to the technical content disclosed in the present application, and they do not depart from the technical features of the present application. They are still within the scope of the technical features of the present application.

Claims

1. A lanthanum-containing phosphorus-locking agent, which is a mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel bead, characterized in that: The pellets have a "core-shell" structure: The core structure is mesoporous lanthanum oxide, and mesopores with a pore size of 3 to 6 nm are formed inside the mesoporous lanthanum oxide; Wherein, the shell structure is sodium alginate / chitosan gel; Wherein, the functional microorganism and the mesoporous lanthanum oxide are both encapsulated in the shell structure; The surface of the shell structure also has through holes, and the pore diameter of the through holes is 50-200 nm.

2. The lanthanum-containing phosphorus-locking agent according to claim 1, wherein The sodium alginate / chitosan gel is a polymer network; the polymer network is formed by chitosan and sodium alginate under the action of CaCl2.

3. The lanthanum-containing phosphorus-locking agent according to claim 1, wherein The diameter of the mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel beads is between 1 mm and 2 mm.

4. The lanthanum-containing phosphorus-locking agent according to claim 1, wherein The functional microorganism is between the mesoporous lanthanum oxide and the sodium alginate / chitosan gel.

5. The lanthanum-containing phosphorus-locking agent according to claim 1, wherein In a dry state, the specific surface area of the lanthanum-containing phosphorus-locking agent is 100-200 m 2 / g.

6. The lanthanum-containing phosphorus-locking agent according to claim 1, wherein Calculated in terms of phosphorus element, the phosphorus adsorption capacity of the lanthanum-containing phosphorus-locking agent is 8-25 mg / g; the organic matter degradation ability is characterized by the COD removal rate during the water purification process. For water bodies with COD less than 100 mg / L, the COD removal rate can reach 60-85%.

7. A method for preparing a lanthanum-containing phosphorus-locking agent, characterized in that: The following steps are involved: S100, preparing mesoporous lanthanum oxide, which includes sub-steps S101 to S103; S101, use 1% volume fraction hydrochloric acid to prepare La with a concentration of 0.5~2 mol / L 3+ Aqueous solution, in which CTAB was dissolved as a template, the concentration of CTAB was 13 g / L; S102, titrating the solution obtained in step S101 with a 0.5-6 mol / L NaOH solution, KOH solution, or aqueous ammonia at a rate of 0.1-0.5 mL / min until the pH of the mixed solution is finally raised to 6-8, and continuing stirring for more than 4 hours; S103, after centrifuging the mixed solution, the solid is transferred to a Soxhlet extractor and reacted with a 9:1 or 8:2 ethanol-water mixture for 4-8 hours to remove the template, and dried to obtain mesoporous lanthanum oxide. S200, preparing mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel beads, which includes sub-steps S201 to S203; S201, preparing a sodium alginate aqueous solution, wherein the sodium alginate concentration in the sodium alginate aqueous solution is 2-20 g / L; adding the mesoporous lanthanum oxide obtained in S100 thereto and mixing, wherein each liter of the solution contains 5-10 g of mesoporous lanthanum oxide; then, adding a functional bacterial solution, stirring uniformly, to obtain a suspension A; when preparing the suspension A, the functional bacterial solution is added at a concentration of 0.5-10 g / L; S202, preparing a chitosan solution, wherein the concentration of chitosan in the chitosan solution is 5-15 g / L, and adding CaCl2, wherein the concentration of CaCl2 is 2-20 g / L, to form solution B; S203, using a peristaltic pump, while maintaining stirring, add suspension A dropwise to solution B at a rate of 0.5-1.5 mL / min; the volume ratio of solution A to solution B is 1:1; S204, in 4 o C for 24 h to form a sodium alginate / chitosan gel object with a semi-interpenetrating structure, in which the mesoporous lanthanum oxide and functional microorganisms are encapsulated.

8. The method for preparing a lanthanum-containing phosphorus-locking agent according to claim 7, wherein: The OD of the functional bacterial solution used was measured by spectrophotometry before use. 600 The cell concentration should be no less than 1×10 6 cell / ml.

9. The method for preparing a lanthanum-containing phosphorus-locking agent according to claim 8, wherein: La used in S101 3+ The salt is any one or more of LaCl3 and LaNO3.

10. Use of the lanthanum-containing phosphorus-locking agent according to any one of claims 1 to 6 in the treatment of black and odorous water bodies.

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