Solar interface evaporator for recovering ammonia nitrogen and preparation method thereof

Abstract

The application provides a solar interface evaporator for recycling ammonia nitrogen and a preparation method thereof, and belongs to the technical field of water treatment. The solar interface evaporator is composed of a substrate, a photo-thermal conversion layer and a precipitation crystallization layer. The photo-thermal conversion layer is located on the upper surface of the substrate, and the precipitation crystallization layer is located on the side surface of the substrate. The prepared solar interface evaporator is optimized in structure, and ion state ammonium is converted into solid deposit magnesium ammonium phosphate through a chemical precipitation reaction, so that the generation and escape of free state ammonia are reduced, and the ammonia nitrogen is recycled in the form of slow-release fertilizer. The solar interface evaporator utilizes the high concentration of Mg 2+ , and only needs to introduce phosphate in the evaporator. When the ammonia nitrogen is recycled to generate magnesium ammonium phosphate, the addition amount of magnesium salt can be reduced.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a solar-powered interfacial evaporator for recovering ammonia nitrogen and its preparation method. Background Technology

[0002] With global population growth, the food production industry is developing rapidly, and the scale of mariculture is constantly expanding. The accumulation of uneaten feed, excrement, and biological metabolism during mariculture leads to a surge in ammonia nitrogen levels in mariculture wastewater, exacerbating eutrophication and further polluting water bodies. To maintain the ecological health of aquaculture waters and the sustainable development of the industry, wastewater treatment is essential. Treatment technologies for mariculture wastewater mainly include physical, chemical, and biological methods. Physical methods remove suspended particulate matter through filtration and adsorption; chemical methods remove toxic substances through flocculation and oxidation disinfection; and biological methods treat wastewater through the natural purification capabilities of microorganisms and plants. Due to the complex composition and high treatment difficulty of mariculture wastewater, existing traditional treatment processes cannot meet the requirements, exhibiting unstable treatment effects and difficulty in achieving a balance between resource utilization and advanced treatment. Solar interfacial distillation technology, which utilizes solar energy to heat and evaporate the interfacial solution using photothermal materials, is considered a green and environmentally friendly wastewater regeneration method. This technology combines thermally driven separation with membrane filtration characteristics, effectively removing salt, macromolecular pollutants, and non-volatile substances. Current solar interfacial distillation technology primarily aims to improve freshwater production and resource recovery by optimizing evaporator design. However, ammonia nitrogen in marine aquaculture wastewater mainly exists in the form of ionic ammonium (NH4+). + Ammonium nitrogen exists in two forms: ionic ammonium and free ammonia (NH3). During distillation, ionic ammonium decomposes into free ammonia upon heating. Free ammonia is highly toxic and easily volatilizes and escapes upon heating at the evaporation interface, increasing the difficulty of recovery and reducing resource recovery efficiency. Therefore, it is necessary to propose a new method for the resource-efficient recovery of ammonia nitrogen from marine aquaculture tailwater. Summary of the Invention

[0003] The purpose of this invention is to provide a solar interface evaporator for recovering ammonia nitrogen and its preparation method, so as to solve the problem of low ammonia nitrogen recovery efficiency caused by the easy volatilization and escape of free ammonia in marine aquaculture tailwater when heated in the prior art.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] The present invention provides a solar interface evaporator for recovering ammonia nitrogen. The solar interface evaporator is composed of a substrate, a photothermal conversion layer and a precipitation crystallization layer, wherein the photothermal conversion layer is located on the upper surface of the substrate and the precipitation crystallization layer is located on the side of the substrate.

[0006] Preferably, the substrate is made of wood pulp sponge or polyurethane sponge; the substrate is columnar; and the raw materials for the photothermal conversion layer are sodium alginate, photothermal materials, and calcium chloride.

[0007] Preferably, the raw materials for the precipitated crystallization layer are sodium alginate, phosphate and calcium chloride.

[0008] The present invention also provides a method for preparing the above-described solar interface evaporator for recovering ammonia nitrogen, comprising the following steps:

[0009] S1: A mixed dispersion of sodium alginate and photothermal material A is coated on the upper surface of the substrate, and then a calcium chloride solution is sprayed on to obtain a substrate with a coating.

[0010] S2: A mixed dispersion of sodium alginate and phosphate B is coated onto the side of a substrate with a coating, and then a calcium chloride solution is sprayed on it before a cross-linking reaction is carried out to obtain a solar interface evaporator.

[0011] Preferably, in step S1, the mass concentration of sodium alginate in the mixed dispersion A is 3-5%.

[0012] Preferably, in step S1, the photothermal material is a carbon material; and the mass content of the photothermal material in the mixed dispersion A is 3-5%.

[0013] Preferably, in step S1, the molar ratio of calcium ions in the sodium alginate and calcium chloride solution is 1:1 to 5.

[0014] Preferably, in step S2, the mass concentration of sodium alginate in the mixed dispersion B is 3-5%; the phosphate comprises one or more of sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate; and the mass concentration of phosphate in the mixed dispersion B is 1-5%.

[0015] Preferably, in step S2, the molar ratio of calcium ions in the sodium alginate and calcium chloride solution is 1:1 to 5.

[0016] Preferably, the crosslinking reaction is carried out at a temperature of 4–20°C for 10–20 hours.

[0017] The reaction principle of the solar interface evaporator of this invention: ionic ammonium reacts with magnesium ions (Mg). 2+ ), phosphate (PO4) 3- The reaction produces slow-release fertilizer magnesium ammonium phosphate (commonly known as struvite, Mg(NH4)PO4·6H2O) precipitate, which reduces the generation of free ammonia and realizes the resource recovery of ammonia nitrogen, thereby improving the recovery efficiency.

[0018] NH4 + +Mg 2+ +PO43- +6H₂O→NH₄MgPO₄·6H₂O↓

[0019] The beneficial effects of this invention are:

[0020] The solar interface evaporator prepared in this invention uses a chemical precipitation reaction to convert ionic ammonium into solid deposit magnesium ammonium phosphate through structural optimization design. This reduces the generation and escape of free ammonia while recovering ammonia nitrogen in the form of slow-release fertilizer.

[0021] The solar interface evaporator prepared in this invention utilizes the high concentration of Mg in the wastewater from seawater aquaculture. 2+ Only phosphate ions need to be introduced into the evaporator, which can reduce the amount of magnesium salt added when generating magnesium ammonium phosphate from ammonia nitrogen through resource recovery.

[0022] In this invention, the substrate material for the solar interface evaporator is preferably wood pulp sponge, the photothermal material is biomass carbon, and the hydrogel is sodium alginate gel—all environmentally friendly materials. After wastewater treatment, the evaporator, rich in magnesium ammonium phosphate slow-release fertilizer, can be used as a culture medium for plant cultivation, achieving resource recycling and reuse. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the solar interface evaporator of the present invention;

[0024] Figure 2 The surface wettability test results are for the solar interface evaporator of Example 1;

[0025] Figure 3 This is a test diagram of the photothermal conversion capacity of the solar interface evaporator in Example 1;

[0026] Figure 4 The graph shows the evaporation capacity test of the solar interface evaporator of Example 1 under different conditions. Detailed Implementation

[0027] The present invention provides a solar interface evaporator for recovering ammonia nitrogen. The solar interface evaporator is composed of a substrate, a photothermal conversion layer and a precipitation crystallization layer, wherein the photothermal conversion layer is located on the upper surface of the substrate and the precipitation crystallization layer is located on the side of the substrate.

[0028] In this invention, the substrate is made of wood pulp sponge or polyurethane sponge; the substrate is columnar; and the raw materials for the photothermal conversion layer are sodium alginate, photothermal materials, and calcium chloride.

[0029] The substrate of this invention has an interwoven porous structure. The lower surface of the solar interface evaporator is not modified in any way, maintaining the hydrophilic surface and porous structure for water transport. Both the photothermal conversion layer and the precipitation crystallization layer are hydrophilic surfaces.

[0030] In this invention, the raw materials for the precipitated crystallization layer are sodium alginate, phosphate and calcium chloride.

[0031] The present invention also provides a method for preparing the above-described solar interface evaporator for recovering ammonia nitrogen, comprising the following steps:

[0032] S1: A mixed dispersion of sodium alginate and photothermal material A is coated on the upper surface of the substrate, and then a calcium chloride solution is sprayed on to obtain a substrate with a coating.

[0033] S2: A mixed dispersion of sodium alginate and phosphate B is coated onto the side of a substrate with a coating, and then a calcium chloride solution is sprayed on it before a cross-linking reaction is carried out to obtain a solar interface evaporator.

[0034] In this invention, in step S1, the mass concentration of sodium alginate in the mixed dispersion A is 3-5%, specifically 3%, 4%, or 5%.

[0035] In this invention, in step S1, the photothermal material is a carbon material; the mass content of the photothermal material in the mixed dispersion A is 3-5%, specifically 3%, 4%, or 5%.

[0036] In this invention, the carbon material is preferably bamboo charcoal, coconut shell carbon powder, or carbon nanotubes.

[0037] In this invention, in step S1, the molar ratio of calcium ions in the sodium alginate and calcium chloride solution is 1:1 to 5, preferably 1:1.

[0038] In this invention, in step S2, the mass concentration of sodium alginate in the mixed dispersion B is 3-5%; the phosphate includes one or more of sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate; the mass concentration of phosphate in the mixed dispersion B is 1-5%, specifically 1%, 2%, 3%, 4%, or 5%.

[0039] In this invention, in step S2, the molar ratio of calcium ions in the sodium alginate and calcium chloride solution is 1:1 to 5, preferably 1:1.

[0040] In this invention, the mass concentration of the calcium chloride solution is 5-10%, preferably 8% or 10%.

[0041] In this invention, the volume ratio of the mixed dispersion A to the mixed dispersion B is 2-3:4-5. The purpose is to control the gel layer thickness in step S1 to be lower than the gel layer thickness in step S2.

[0042] In this invention, the phosphate ion content in the phosphate is preferably the same as that in the NH4+ solution. +Mg 2+ The molar ratio should be 1:1:1 when adding the ingredients.

[0043] In this invention, the temperature of the crosslinking reaction is 4 to 20°C, specifically 4°C, 5°C, 8°C, 10°C, 15°C, or 20°C; the time is 10 to 20 hours, specifically 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, or 20 hours.

[0044] In this invention, sodium alginate-calcium ion gel is used to achieve ion crosslinking and immobilization. During operation, the temperature of the distillation membrane surface in the solar interface evaporator for recovering ammonia nitrogen is ≤50℃.

[0045] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0046] Example 1

[0047] A cylindrical wood pulp sponge matrix (20 mm in diameter and 10 mm in height) was washed with deionized water and dried for later use. 0.3 g of sodium alginate was dispersed in 10 mL of deionized water, stirred thoroughly, and then 0.3 g of 300-mesh bamboo charcoal was added. The mixture was then ultrasonically treated to obtain a mixed dispersion A. 0.3 g of sodium alginate was also dispersed in 10 mL of deionized water, stirred thoroughly, and then 0.2 g of disodium hydrogen phosphate was added. The mixture was then ultrasonically treated to obtain a mixed dispersion B. 6 mL of mixed dispersion A was coated onto the upper surface of the cylindrical wood pulp sponge matrix, followed by a 1 mL spray of a 10% calcium chloride solution. Then, 10 mL of mixed dispersion B was coated onto the side surface of the cylindrical wood pulp sponge matrix, followed by a 2 mL spray of an 8% calcium chloride solution. The matrix was then subjected to a cross-linking reaction at 20°C for 10 hours to obtain a solar interface evaporator.

[0048] Example 2

[0049] A cylindrical polyurethane sponge matrix (20 mm in diameter and 5 mm in height) was washed with deionized water and dried for later use. 0.5 g of sodium alginate was dispersed in 10 mL of deionized water, stirred thoroughly, and then 0.4 g of 325-mesh coconut shell carbon powder was added. The mixture was then ultrasonically treated to obtain dispersion A. 0.5 g of sodium alginate was also dispersed in 10 mL of deionized water, stirred thoroughly, and then 0.1 g of sodium phosphate was added. The mixture was then ultrasonically treated to obtain dispersion B. 2.5 mL of dispersion A was coated onto the upper surface of the cylindrical wood pulp sponge matrix, followed by a 0.7 mL spray of a 10% calcium chloride solution. Then, 5 mL of dispersion B was coated onto the side surface of the cylindrical wood pulp sponge matrix, followed by a 1.75 mL spray of an 8% calcium chloride solution. The matrix was then subjected to a crosslinking reaction at 10°C for 10 hours to obtain a solar interface evaporator.

[0050] Example 3

[0051] A cylindrical wood pulp sponge matrix (20 mm in diameter and 5 mm in height) was washed with deionized water and dried for later use. 0.4 g of sodium alginate was dispersed in 10 mL of deionized water, stirred thoroughly, and then 0.5 g of carbon nanotubes were added. The mixture was then sonicated to obtain dispersion A. 0.4 g of sodium alginate was also dispersed in 10 mL of deionized water, stirred thoroughly, and then 0.1 g of disodium hydrogen phosphate was added. The mixture was then sonicated to obtain dispersion B. 2.5 mL of dispersion A was coated onto the upper surface of the cylindrical wood pulp sponge matrix, followed by a spray of 0.7 mL of an 8% calcium chloride solution. Then, 4 mL of dispersion B was coated onto the side surface of the cylindrical wood pulp sponge matrix, followed by a spray of 1 mL of an 8% calcium chloride solution. The matrix was then subjected to a cross-linking reaction at 4°C for 15 h to obtain a solar interfacial evaporator.

[0052] Comparative Example 1

[0053] A cylindrical wood pulp sponge matrix (20 mm in diameter and 10 mm in height) was washed with deionized water and dried for later use. 0.3 g of sodium alginate was dispersed in 10 mL of deionized water, stirred thoroughly, and then 0.3 g of 300-mesh bamboo charcoal was added. The mixture was then ultrasonically treated to obtain a mixed dispersion A. 6 mL of mixed dispersion A was coated onto the upper surface of the cylindrical wood pulp sponge matrix, followed by spraying with 1 mL of a 10% calcium chloride solution. The matrix was then subjected to a cross-linking reaction at 20°C for 10 h to obtain a solar interface evaporator.

[0054] The solar interface evaporators prepared in Example 1 and Comparative Example 1 were respectively tested under a solar intensity (1 kWm). -2 Under irradiation, its evaporation efficiency and effect on treating simulated marine aquaculture wastewater were tested. The simulated marine aquaculture wastewater contained 300L of seawater taken from the waters near Heishijiao, Dalian, and other added components. The amounts of the other added components were: 13.2g NH4Cl, 33.5g NaHCO3, 0.35g MgSO4·7H2O, 1.52g Na2HPO4, and 17.0g sodium acetate trihydrate.

[0055] The surface wettability of the solar interface evaporator in Example 1 was tested, and the results are as follows: Figure 2 As shown, the water contact angle is 38.9°, and the water droplet almost disappears after 3 seconds, indicating that the photothermal conversion layer has excellent hydrophilicity. The photothermal conversion capability of the solar interface evaporator in Example 1 is as follows: Figure 3 As shown, under strong sunlight, the temperature of the wetted evaporating surface gradually increased from 25°C to 42°C within 30 minutes, demonstrating excellent photothermal conversion capability. The evaporation results of Example 1 are as follows... Figure 4As shown, in a dark environment, the natural evaporation efficiency is 0.25 kg m -2 h -1 Under intense sunlight, the evaporation efficiency of pure water is 1.36 kg m³. -2 h -1 The evaporation efficiency was 1.32 kg m when treating a 3.5% NaCl solution. -2 h -1 The evaporation efficiency was 1.21 kg m when treating a 10.0% NaCl solution. -2 h -1 .

[0056] Example 1 and its effect on the treatment of ammonia nitrogen in simulated seawater aquaculture wastewater show that, under a certain solar intensity, the evaporation efficiency is 1.30 kg m³. -2 h -1 Adding 0.1% phenolphthalein indicator to the condensate generated in Example 1 and Comparative Example 1 respectively, it was found that the color of the condensate in Example 1 did not change, indicating that no molecular ammonia was generated during the evaporation process and dissolved in the condensate to form free ammonium (i.e., In contrast, the condensate in Comparative Example 1 turned pale red, further confirming that the precipitated crystallization layer can effectively inhibit the decomposition of ionic ammonium into free ammonia (i.e., ).

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A solar interface evaporator for recovering ammonia nitrogen, characterized in that, The solar interface evaporator consists of a substrate, a photothermal conversion layer, and a precipitation crystallization layer, wherein the photothermal conversion layer is located on the upper surface of the substrate and the precipitation crystallization layer is located on the side of the substrate. The substrate is made of wood pulp sponge or polyurethane sponge; the substrate is columnar. The raw materials for the photothermal conversion layer are sodium alginate, photothermal materials, and calcium chloride. The raw materials for the precipitated crystallization layer are sodium alginate, phosphate and calcium chloride; The method for preparing the solar interface evaporator includes the following steps: S1: A mixed dispersion of sodium alginate and photothermal material A is coated on the upper surface of the substrate, and then a calcium chloride solution is sprayed on to obtain a substrate with a coating. S2: A mixed dispersion of sodium alginate and phosphate B is coated onto the side of a substrate with a coating, and then a calcium chloride solution is sprayed on it before a cross-linking reaction is carried out to obtain a solar interface evaporator.

2. The method for preparing the solar interface evaporator for recovering ammonia nitrogen according to claim 1, characterized in that, Includes the following steps: S1: A mixed dispersion of sodium alginate and photothermal material A is coated on the upper surface of the substrate, and then a calcium chloride solution is sprayed on to obtain a substrate with a coating. S2: A mixed dispersion of sodium alginate and phosphate B is coated onto the side of a substrate with a coating, and then a calcium chloride solution is sprayed on it before a cross-linking reaction is carried out to obtain a solar interface evaporator.

3. The method for preparing a solar interface evaporator for recovering ammonia nitrogen according to claim 2, characterized in that, In step S1, the mass concentration of sodium alginate in the mixed dispersion A is 3-5%.

4. The method for preparing a solar interface evaporator for recovering ammonia nitrogen according to claim 2 or 3, characterized in that, In step S1, the photothermal material is a carbon material; the mass content of the photothermal material in the mixed dispersion A is 3-5%.

5. The method for preparing a solar interface evaporator for recovering ammonia nitrogen according to claim 4, characterized in that, In step S1, the molar ratio of calcium ions in the sodium alginate and calcium chloride solution is 1:1 to 5.

6. The method for preparing a solar interface evaporator for recovering ammonia nitrogen according to claim 3 or 5, characterized in that, In step S2, the mass concentration of sodium alginate in the mixed dispersion B is 3-5%; the phosphate contains one or more of sodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate; and the mass concentration of phosphate in the mixed dispersion B is 1-5%.

7. The method for preparing a solar interface evaporator for recovering ammonia nitrogen according to claim 6, characterized in that, In step S2, the molar ratio of calcium ions in the sodium alginate and calcium chloride solution is 1:1 to 5.

8. The method for preparing a solar interface evaporator for recovering ammonia nitrogen according to claim 5 or 7, characterized in that, The cross-linking reaction is carried out at a temperature of 4–20°C for 10–20 hours.

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