Nucleation granulation method for synthesizing compound fertilizer by utilizing nitrogen and phosphorus in sludge water and humus and application of nucleation granulation method

Abstract

The invention relates to a nucleation granulation method for synthesizing a compound fertilizer by utilizing nitrogen and phosphorus in sludge water and humus and application of the nucleation granulation method. The nucleation granulation method comprises the following steps: adding a seed crystal into a nucleation granulation reactor; introducing the to-be-treated sludge water into the nucleation granulation reactor, and adjusting the pH value of the to-be-treated sludge water to be alkaline; nitrogen, phosphorus and humus in the sludge water to be treated are enriched on the surfaces of the seed crystals to form compound fertilizer granules. The seed crystal is added, the pH value of the sludge water to be treated is adjusted, the nucleation energy barrier is effectively reduced, nitrogen, phosphorus and humus in the sludge water are induced to be enriched on the surface of the seed crystal, and finally the slow-release compound fertilizer granulation body with the diameter being 2 mm is formed. The prepared compound fertilizer granules have the characteristics of high purity, uniform size, regular shape and the like, no sludge is generated in the whole process, secondary pollution is avoided, and efficient resource utilization of nitrogen, phosphorus and humus is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, in particular to a nucleus crystal granulation method for synthesizing compound fertilizer by utilizing nitrogen, phosphorus and humus in sludge water and an application thereof. Background Art

[0002] During urban sewage treatment, sludge water, a byproduct of the process, is difficult to treat due to its high concentrations of harmful substances such as nitrogen, phosphorus, humus, organic matter, heavy metal ions, and pathogenic microorganisms. Phosphorus, as an essential element for life, plays an indispensable role in agriculture, industry, and other fields. However, if pollutants such as nitrogen, phosphorus, and humus accumulate in sludge water and are not properly treated, they can lead to eutrophication of the receiving water, causing a series of environmental problems such as excessive algal growth, hypoxia, and deterioration of water quality.

[0003] Currently, most treatment strategies for sludge dewatering wastewater involve returning it to the front end of the biological treatment process for secondary treatment. However, when the nitrogen and phosphorus content in the sludge dewatering wastewater exceeds the biological treatment system's processing capacity, it places an additional burden on the biological treatment system. Excessive nitrogen and phosphorus may not only interfere with the normal growth and activity of microorganisms in the biological treatment system, causing increased sludge volume and imbalanced microbial community structure, thereby affecting the stability and treatment effectiveness of the biological treatment system. At the same time, excessive nitrogen and phosphorus may also inhibit the microorganisms' ability to degrade other pollutants, such as organic matter, thereby reducing the overall efficiency of the biological treatment system.

[0004] Although traditional urban sewage treatment processes can achieve standard discharge of pollutants, they often ignore the recovery and utilization of resources such as nitrogen, phosphorus and humus, resulting in waste of resources.

[0005] Therefore, the efficient recovery and utilization of nitrogen, phosphorus and humus in sludge water has become the focus of research and has important environmental and economic significance. Summary of the Invention

[0006] In order to solve at least one of the above technical problems, the present invention provides a nucleus crystal granulation method for synthesizing compound fertilizer using nitrogen, phosphorus and humus in sludge water and its application.

[0007] As one aspect, the present invention provides a nucleus crystallization granulation method for synthesizing compound fertilizer using nitrogen, phosphorus and humus in sludge water. The nucleus crystallization granulation method comprises: adding crystal seeds into a nucleus crystallization granulation reactor; passing the sludge water to be treated into the nucleus crystallization granulation reactor, and adjusting the pH of the sludge water to be treated to be alkaline; the nitrogen, phosphorus and humus in the sludge water to be treated are enriched on the surface of the crystal seeds to form compound fertilizer granulations; wherein, by adjusting the pH value of the sludge water to be treated, the reaction conditions of the nitrogen, phosphorus and humus in the sludge water to be treated on the surface of the crystal seeds are changed, and the compound fertilizer granulations are obtained under the synergistic action of multiple mechanisms of chemical, shear and functional group strengthening.

[0008] In some embodiments of the present invention, the seed crystal is a group-modified natural ore obtained by a method combining calcination and chemical impregnation, and the specific steps include: washing the natural ore to remove surface impurities, and then drying it at a temperature of 100-150°C for 2-4 hours to remove excess water to obtain a pretreated natural ore; placing the pretreated natural ore in a high-temperature furnace and calcining it at a temperature range of 800-1200°C for 2-6 hours to remove part of the crystal water by high-temperature calcination, thereby increasing the crystallinity and specific surface area of ​​the natural ore, and naturally cooling it to room temperature after the calcination to obtain a calcined natural ore; impregnating the calcined natural ore in The precursor mass concentration is 5-20% in a precursor solution for 30 minutes to 2 hours, so that the calcined natural ore fully contacts and absorbs the precursor in the precursor solution to obtain an impregnated natural ore; the impregnated natural ore is washed with deionized water 3-5 times, and then dried again at a temperature of 100-120°C for 2-4 hours to remove residual water and solvent to obtain a precursor-modified natural ore; under the protection of an inert atmosphere, the precursor-modified natural ore is heated to 200-300°C for a curing treatment of 2-8 hours to obtain a group-modified natural ore; wherein the precursor is a compound containing a group, and the group can enhance the adsorption performance and reaction activity of the natural ore.

[0009] In some embodiments of the present invention, the natural ore includes one or more of magnesite, quartz sand, and serpentine.

[0010] In some embodiments of the present invention, the group includes one or more of an amino group, a carboxyl group, a quaternary ammonium salt group, and an amide group.

[0011] In some embodiments of the present invention, the pH value ranges from 8.5 to 9.5.

[0012] In some embodiments of the present invention, in the step of adjusting the pH of the sludge water to be treated to be alkaline, a chemical is used to adjust the pH value; wherein the chemical includes one or more of hydrochloric acid, sodium hydroxide, and magnesium hydroxide, and the volume ratio of the water intake of the sludge water to be treated to the chemical intake is (400-600):1.

[0013] In some embodiments of the present invention, the dosage of the seed crystals is 20% to 30% of the volume of the nuclear crystallization granulation reactor.

[0014] In some embodiments of the present invention, the compound fertilizer granules include the following effective components (in mass percentage): 15-25% nitrogen (calculated as nitrogen element); 5-10% phosphorus (calculated as phosphorus pentoxide); 10-20% humus (calculated as organic matter); and 3-7% other trace elements and minerals.

[0015] As another aspect, the present invention provides a compound fertilizer granulation body synthesized by utilizing nitrogen, phosphorus and humus in sludge water obtained by the above-mentioned core crystal granulation method.

[0016] The technical solution provided by the embodiment of the present invention has the following advantages:

[0017] 1. The present invention realizes the efficient synthesis of nitrogen, phosphorus and humus to form compound fertilizer granules, effectively recovers and reuses resources such as phosphorus, provides high-quality fertilizers for agriculture, and promotes resource recycling and sustainable agricultural development.

[0018] 2. The present invention significantly reduces the amount of reagents used in the synthesis process, greatly reduces the risk of secondary environmental pollution, exhibits environmental protection and energy-saving characteristics, and significantly reduces processing costs.

[0019] 3. The present invention does not generate sludge and does not require additional sludge treatment steps, which simplifies the operation process, reduces treatment costs, and makes sludge water treatment more efficient and convenient.

[0020] 4. The present invention occupies a small area, has a high degree of automation, and combines low operating costs to significantly improve economic and social benefits, while synergistically improving the comprehensive effect of sewage treatment. DETAILED DESCRIPTION

[0021] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0023] According to an embodiment of one aspect of the present invention, a nucleus crystallization granulation method for synthesizing compound fertilizer using nitrogen, phosphorus and humus in sludge water is provided, and the nucleus crystallization granulation method comprises: adding crystal seeds into a nucleus crystallization granulation reactor; passing the sludge water to be treated into the nucleus crystallization granulation reactor, and adjusting the pH of the sludge water to be treated to be alkaline; the nitrogen, phosphorus and humus in the sludge water to be treated are enriched on the surface of the crystal seeds to form compound fertilizer granulations; wherein, by adjusting the pH value of the sludge water to be treated, the reaction conditions of the nitrogen, phosphorus and humus in the sludge water to be treated on the surface of the crystal seeds are changed, and the compound fertilizer granulations are obtained under the synergistic action of multiple mechanisms of chemical, shear and functional group strengthening.

[0024] The embodiment of the present invention discloses a method for synthesizing compound fertilizer from nitrogen, phosphorus, and humus in sludge water by adding seed crystals to the sludge water, using the seed crystals as collision active centers during the reaction process. By adjusting the pH of the sludge water with a reagent, the adhesion of nitrogen, phosphorus, and humus to the seed crystal surface is improved. Through multiple synergistic effects such as chemical, shear, and functional group strengthening, nitrogen, phosphorus, and humus in the sludge water are efficiently and rapidly enriched on the seed crystal surface, ultimately forming a slow-release compound fertilizer granule. This method not only solves the problem of poor biodegradability of sludge water, but also achieves efficient resource utilization of nitrogen, phosphorus, and humus, reduces operating costs, and provides high-quality compound fertilizer products, offering a new solution for agricultural production and environmental protection.

[0025] In some embodiments of the present invention, a method for synthesizing compound fertilizer using nitrogen, phosphorus and humus in sludge water comprises the following steps:

[0026] (1) adding seed crystals into a nuclear crystal granulation reactor containing sludge to be treated;

[0027] (2) The sludge water to be treated is passed into the nucleus crystallization granulation reactor, and the reagent solution is added to the sludge water to be treated, and the pH value of the sludge water to be treated is adjusted to the alkaline range;

[0028] (3) Nitrogen, phosphorus and humus in the sludge water to be treated are enriched on the surface of the seed crystals to form compound fertilizer granules.

[0029] In some embodiments of the present invention, in step (1), under the condition that the volume of the entire nuclear crystallization granulation reactor is fully filled, the amount of seed crystal added is in the range of 20% to 30% of the volume of the nuclear crystallization granulation reactor to ensure that the fluidization state of the seed crystal can reach the best. For example, the filling volume of the seed crystal can be 21%, 22%, 24%, 26%, 29%, etc.

[0030] In some embodiments of the present invention, in step (1), the seed crystal is based on natural ore and is treated by a specific surface modification method to introduce groups that enhance adsorption and reactivity to optimize its role in the compound fertilizer synthesis process. The groups include one or more of amino, carboxyl, quaternary ammonium salt, and amide groups, which can electrostatically attract negatively charged nitrogen, phosphorus, and humus molecules to enhance the reactivity of the seed crystal.

[0031] In some embodiments of the present invention, in step (1), the seed crystal is a group-modified natural ore, and the group-modified natural ore is prepared by a surface modification method combining calcination and chemical impregnation.

[0032] In some embodiments of the present invention, in step (1), the seed crystal is a group-modified natural ore obtained by a method combining calcination and chemical impregnation, which specifically includes the following steps:

[0033] a) washing the selected natural ore to remove surface impurities, and then drying the ore at a temperature of 100 to 150° C. (e.g., 109° C., 113° C., 127° C., 136° C., 141° C., 149° C., etc.) for 2 to 4 hours (e.g., 2.1 hours, 2.8 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.7 hours, 3.9 hours, etc.) to ensure that excess moisture is removed, thereby obtaining a pretreated natural ore;

[0034] b) placing the pretreated natural ore obtained in step a) in a high-temperature furnace and calcining it at a temperature range of 800 to 1200° C. (for example, 809° C., 913° C., 1027° C., 1086° C., 1121° C., 1189° C., etc.) for 2 to 6 hours (for example, 2.1 hours, 3.8 hours, 4.2 hours, 4.4 hours, 5.6 hours, 5.7 hours, 5.9 hours, etc.), removing part of the crystal water by high-temperature calcination, thereby increasing the crystallinity and specific surface area of ​​the natural ore, and naturally cooling it to room temperature after the calcination to obtain a calcined natural ore;

[0035] c) preparing a precursor solution, wherein the concentration of the precursor in the precursor solution is controlled to be 5-20% (for example, 5.6%, 6.3%, 7.9%, 10.8%, 13.7%, 15.9%, 17.8%, 19.6%, etc.); completely immersing the calcined natural ore in the solution, and maintaining the solution by mechanical stirring or ultrasonic treatment for 30 minutes to 2 hours (for example, 0.5 hours, 0.6 hours, 0.8 hours, 1.3 hours, 1.6 hours, 1.9 hours, etc.) to ensure that the calcined ore fully contacts and absorbs the precursor substances in the precursor solution;

[0036] d) After the impregnation is completed, the natural ore obtained in step c) is taken out and washed with deionized water for 3 to 5 times until the washing liquid is clear, and the excess precursors and by-products attached to the surface are removed;

[0037] e) drying the natural ore washed in step d) again at a temperature of 100-120° C. (e.g., 101° C., 103° C., 106° C., 108° C., 113° C., 118° C., etc.) for 2-4 hours (e.g., 2.5 hours, 2.6 hours, 3.1 hours, 3.3 hours, 3.6 hours, 3.9 hours, etc.) to remove residual water and solvent, thereby obtaining a precursor-modified natural ore;

[0038] f) heating the precursor-modified natural ore obtained in step e) to 200-300° C. (for example, 201° C., 213° C., 236° C., 258° C., 273° C., 298° C., etc.) under an inert atmosphere (for example, nitrogen) for curing for 2-8 hours (for example, 2.5 hours, 3.6 hours, 4.1 hours, 5.3 hours, 6.6 hours, 7.9 hours, etc.) to convert the precursor substance into the desired group on the surface or inside the ore; obtaining the group-modified natural ore; finally, screening and grading the group-modified natural ore to screen out seed crystals with uniform particle size and stable performance.

[0039] In some embodiments of the present invention, in step (2), in the nuclear crystallization granulation reactor, the ratio of the water volume of the sludge water to be treated to the drug volume of the drug solution is (400-600):1, for example, it can be 423:1, 467:1, 503:1, 537:1, 572:1, 596:1, etc.

[0040] In some embodiments of the present invention, in step (2), the reagent in the reagent solution for adjusting the pH of the sludge water to be treated includes one or more of hydrochloric acid, sodium hydroxide, and magnesium hydroxide.

[0041] In some embodiments of the present invention, in step (2), the pH of the sludge water to be treated is adjusted to be controlled within the range of 8.5 to 9.5, for example, 8.6, 8.7, 8.9, 9.1, 9.3, 9.4, etc.

[0042] In some embodiments of the present invention, in step (3), the mass percentage of the effective ingredients in the compound fertilizer granules is 15-25% nitrogen (calculated as nitrogen element), for example, it can be 16.3%, 17.8%, 21.1%, 22.8%, 23.9%, 24.3%, etc.; 5-10% phosphorus (calculated as phosphorus pentoxide), for example, it can be 11.8%, 12.4%, 14.6%, 16.3%, 18.7%, 19.4%, etc.; 10-20% humus (calculated as organic matter), for example, the humus content can be 12.6%, 13.9%, 16.8%, 17.3%, 18.3%, 19.6%, etc.; 3-7% other trace elements and minerals, for example, it can be 3.2%, 4.1%, 4.9%, 5.6%, 6.1%, 6.9%, etc.

[0043] The scheme of the present invention is further illustrated by the following examples.

[0044] Example 1

[0045] The test water of this embodiment was taken from sludge dewatering wastewater of a certain city sewage treatment plant, wherein the COD concentration was 803.8 mg / L, the ammonia nitrogen concentration was 347.3 mg / L, and the total phosphorus concentration was 2.6 mg / L.

[0046] The following experimental steps were used to process it:

[0047] (1) adding seed crystals into a nuclear crystal granulation reactor containing sludge to be treated; wherein the amount of seed crystals added is 20% of the volume of the nuclear crystal granulation reactor;

[0048] (2) The sludge water to be treated is passed into the nucleus crystallization granulation reactor, and the reagent sodium hydroxide solution is added into the nucleus crystallization granulation reactor at the same time, and the pH value of the sludge water to be treated is adjusted to 8.5; wherein, the ratio of the inlet volume of the sludge water to be treated to the inlet volume of the reagent solution is 400:1;

[0049] (3) Nitrogen, phosphorus and humus in the sludge water to be treated are enriched on the surface of the seed crystals to form compound fertilizer granules;

[0050] (4) The COD concentration, ammonia nitrogen concentration and total phosphorus concentration of the effluent treated by steps (1), (2) and (3) were measured. The test results are shown in Table 1.

[0051] Example 2

[0052] The test water of this embodiment was taken from sludge dewatering wastewater of a certain city sewage treatment plant, wherein the COD concentration was 803.8 mg / L, the ammonia nitrogen concentration was 347.3 mg / L, and the total phosphorus concentration was 2.6 mg / L.

[0053] The following experimental steps were used to process it:

[0054] (1) adding seed crystals into a nuclear crystal granulation reactor containing sludge to be treated; wherein the amount of seed crystals added is 25% of the volume of the nuclear crystal granulation reactor;

[0055] (2) The sludge water to be treated is passed into the nuclear crystal granulation reactor, and the magnesium hydroxide solution is added into the nuclear crystal granulation reactor at the same time, and the pH value of the sludge water to be treated is adjusted to 9.0; wherein, the ratio of the inlet volume of the sludge water to be treated to the inlet volume of the drug solution is 500:1

[0056] (3) Nitrogen, phosphorus and humus in the sludge water to be treated are enriched on the surface of the seed crystals to form compound fertilizer granules;

[0057] (4) The COD concentration, ammonia nitrogen concentration and total phosphorus concentration of the effluent treated by steps (1), (2) and (3) were measured. The test results are shown in Table 1.

[0058] Example 3

[0059] The test water of this embodiment was taken from sludge dewatering wastewater of a certain city sewage treatment plant, wherein the COD concentration was 803.8 mg / L, the ammonia nitrogen concentration was 347.3 mg / L, and the total phosphorus concentration was 2.6 mg / L.

[0060] The following experimental steps were used to process it:

[0061] (1) adding seed crystals into a nuclear crystal granulation reactor containing sludge to be treated; wherein the amount of seed crystals added is 30% of the volume of the nuclear crystal granulation reactor;

[0062] (2) The sludge water to be treated is passed into the nucleus crystallization granulation reactor, and the reagent sodium hydroxide solution is added into the nucleus crystallization granulation reactor at the same time, and the pH value of the sludge water to be treated is adjusted to 9.5; wherein, the ratio of the inlet volume of the sludge water to be treated to the inlet volume of the reagent solution is 600:1;

[0063] (3) Nitrogen, phosphorus and humus in the sludge water to be treated are enriched on the surface of the seed crystals to form compound fertilizer granules;

[0064] (4) The COD concentration, ammonia nitrogen concentration and total phosphorus concentration of the effluent treated by steps (1), (2) and (3) were measured. The test results are shown in Table 1.

[0065] Table 1 Parameter test results of sludge effluent after treatment in Examples 1 to 3

[0066] COD concentration / (mg / L) Ammonia nitrogen concentration / (mg / L) Total phosphorus concentration / (mg / L) Example 1 387.3 20 0.8 Example 2 344.9 16 0.4 Example 3 329.1 13 0.5

[0067] The present invention discloses a method for synthesizing compound fertilizer from nitrogen, phosphorus, and humus in sludge water, and its application. By adding seed crystals and adjusting the pH of the sludge water to be treated, and by combining the volume ratio of the reagent solution to the sludge water to be treated, the nucleation energy barrier is effectively reduced, and nitrogen, phosphorus, and humus in the sludge water are induced to accumulate on the surface of the seed crystals, ultimately forming slow-release compound fertilizer granules with a diameter of 2 mm. The prepared slow-release compound fertilizer granules have the characteristics of high purity, uniform size, and regular shape. No sludge is generated during the entire process, thus avoiding secondary pollution.

[0068] The core crystal granulation method and its application for synthesizing compound fertilizer from nitrogen, phosphorus, and humus in sewage sludge water, provided in embodiments of the present invention, achieves efficient extraction and synthesis of nitrogen, phosphorus, and humus from sewage sludge water, effectively resolving the high load on the biological treatment section caused by nitrogen, phosphorus, and humus in sewage sludge water. It also achieves efficient recovery and utilization of nitrogen, phosphorus, and humus in sewage sludge water, converting them into a compound fertilizer product with practical application value. This method not only helps reduce the risk of eutrophication of water bodies and achieves effective recovery and utilization of nitrogen and phosphorus resources, but also provides a high-quality fertilizer source for agricultural production, reducing the burden on the biological treatment system, and has important environmental and economic significance.

[0069] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0070] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments described herein, but is to be construed in the widest possible manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for synthesizing compound fertilizer by using nitrogen, phosphorus and humus in sludge water, characterized in that: The nucleus crystal granulation method comprises: adding seed crystals into a nuclear crystal granulation reactor; The sludge water to be treated is passed into the nuclear crystal granulation reactor, and the pH of the sludge water to be treated is adjusted to be alkaline; The nitrogen, phosphorus and humus in the sludge water to be treated are enriched on the surface of the seed crystals to form compound fertilizer granules; Among them, by adjusting the pH value of the sludge water to be treated, the reaction conditions of nitrogen, phosphorus and humus in the sludge water to be treated on the surface of the seed crystal are changed, and the compound fertilizer granules are obtained under the synergistic action of multiple mechanisms of chemical, shear and functional group strengthening.

2. The method for nucleation granulation according to claim 1, characterized in that: The seed crystal is a group-modified natural ore obtained by a method combining calcination and chemical impregnation, and the specific steps include: The natural ore is cleaned to remove surface impurities, and then dried at a temperature of 100 to 150° C. for 2 to 4 hours to remove excess water to obtain a pretreated natural ore; The pretreated natural ore is placed in a high-temperature furnace and calcined at a temperature range of 800 to 1200° C. for 2 to 6 hours, wherein a portion of crystal water is removed by high-temperature calcination to increase the crystallinity and specific surface area of ​​the natural ore, and the calcined natural ore is naturally cooled to room temperature after the calcination is completed to obtain a calcined natural ore; The calcined natural ore is immersed in a precursor solution with a precursor mass concentration of 5 to 20% for 30 minutes to 2 hours, so that the calcined natural ore fully contacts and absorbs the precursor in the precursor solution to obtain an immersed natural ore; The impregnated natural ore is washed with deionized water for 3 to 5 times, and then dried again at a temperature of 100 to 120° C. for 2 to 4 hours to remove residual water and solvent to obtain a precursor-modified natural ore; Under the protection of an inert atmosphere, the precursor-modified natural ore is heated to 200-300° C. for curing for 2-8 hours to obtain a group-modified natural ore; Wherein, the precursor is a compound containing the group, and the group can enhance the adsorption performance and reaction activity of natural ore.

3. The method for nucleation granulation according to claim 2, characterized in that: The natural ore includes one or more of magnesite, quartz sand and serpentine.

4. The method for nucleation granulation according to claim 2 or 3, characterized in that: The group includes one or more of an amino group, a carboxyl group, a quaternary ammonium salt group, and an amide group.

5. The method for nucleation granulation according to any one of claims 1 to 4, characterized in that: The pH value ranges from 8.5 to 9.

5.

6. The method for nucleation granulation according to any one of claims 1 to 5, characterized in that: In the step of adjusting the pH of the sludge water to be treated to be alkaline, a reagent is used to adjust the pH value; Wherein, the reagent includes one or more of hydrochloric acid, sodium hydroxide, and magnesium hydroxide, and the volume ratio of the water amount of the sludge water to be treated to the amount of the reagent is (400-600):

1.

7. The method for nucleation granulation according to any one of claims 1 to 6, characterized in that: The dosage of the seed crystal is 20% to 30% of the volume of the nuclear crystal granulation reactor.

8. The method for nucleation granulation according to any one of claims 1 to 7, characterized in that: The compound fertilizer granules include the following effective components (by mass percentage): 15-25% nitrogen (calculated as elemental nitrogen); 5-10% phosphorus (calculated as phosphorus pentoxide); 10-20% humus (based on organic matter); 3-7% other trace elements and minerals.

9. A compound fertilizer granulate synthesized by utilizing nitrogen, phosphorus and humus in sludge water obtained by the core crystal granulation method as claimed in any one of claims 1 to 8.