Manufacturing method for slow‑release sludge-based nutrient soil

Abstract

The present invention provides a manufacturing method for slow‑release sludge-based nutrient soil. The manufacturing method comprises: blending a first biochar, a compound microbial agent, and a first binder in a set ratio, and performing first-stage granulation to form first-stage slow-release nutrient soil particles; blending dewatered sludge and a slow‑release material in a set ratio, and blending same with the first-stage slow-release nutrient soil particles for second-stage granulation to form second-stage slow‑release nutrient soil particles; and blending a second biochar and a second binder in a set ratio, and blending same with the second-stage slow-release nutrient soil particles for third-stage granulation to form third-stage slow-release nutrient soil particles. The manufacturing method relates to using multi-stage granulation to prepare slow-release sludge-based nutrient soil, which can not only achieve slow release of organic matter, nutrients and salts, but also reduce the mobility of toxic and hazardous substances in dewatered sludge, thereby reducing the risk of soil and water pollution, improving the utilization rate of nutrients in the dewatered sludge, and reducing the environmental risks posed by the dewatered sludge.

Description

A method for preparing slow-release sludge-based nutrient soil Technical Field

[0001] This invention belongs to the field of nutrient soil production technology, and more specifically, relates to a method for producing slow-release sludge-based nutrient soil. Background Technology

[0002] Currently, Beijing's municipal sewage sludge is mainly treated using advanced anaerobic digestion technology and plate and frame filter press dewatering. The dewatered sludge cake is then crushed and transported to parks, woodlands, and other land use applications. During the advanced anaerobic digestion process, the sludge is sterilized, and the organic matter is decomposed into a stable state. The land use method for dewatered sludge is to directly mix the powdered sludge with the topsoil. This method has the problem of rapid release of organic matter, nutrients, and salts from the dewatered sludge, which can easily lead to soil compaction and nutrient loss, failing to fully realize the soil improvement effect of dewatered sludge. Therefore, it is necessary to process dewatered sludge into a slow-release sludge-based nutrient soil, allowing its nutrients to be slowly released and fully absorbed by plants, while also avoiding the problem of eutrophication caused by leaching into groundwater and other water bodies. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing slow-release sludge-based nutrient soil. This method solves the problem mentioned in the background art where, after dewatering and crushing, advanced anaerobic digested sludge is directly mixed with soil for land application, resulting in the rapid release of organic matter, nutrients, and salts. On the one hand, nutrients cannot be fully utilized, and on the other hand, it may cause environmental problems such as eutrophication of water bodies and soil compaction.

[0004] To achieve the above objectives, the present invention provides a method for preparing a slow-release sludge-based nutrient soil, the method comprising:

[0005] The first biochar, the composite microbial agent and the first binder are mixed in a set ratio and then subjected to first-stage granulation to form first-stage slow-release nutrient soil particles.

[0006] The dewatered sludge and slow-release material are mixed in a set ratio and then mixed with the first-stage slow-release nutrient soil particles for second-stage granulation to form the second-stage slow-release nutrient soil particles.

[0007] The second biochar and the second binder are mixed in a set ratio and then mixed with the second-stage slow-release nutrient soil particles for third-stage granulation to form the third-stage slow-release nutrient soil particles.

[0008] Preferably, the manufacturing method further includes:

[0009] The prepared third-stage slow-release nutrient soil particles are transported to a belt dryer for low-temperature drying to achieve the set moisture content.

[0010] Preferably, the step of mixing the first biochar, the composite microbial agent, and the first binder in a predetermined ratio, and then performing first-stage granulation to form first-stage slow-release nutrient soil particles includes:

[0011] The first biochar, compound microbial agent and first binder are mixed in a ratio of 100:1 to 3:15 to 30, and then transported to a round pot granulator for first-stage granulation. At the same time, water is sprayed to wet the soil so that the diameter of the first-stage slow-release nutrient soil particles is maintained at 9 to 11 mm.

[0012] Preferably, the step of mixing dewatered sludge and slow-release material in a set ratio, and then mixing it with first-stage slow-release nutrient soil particles for second-stage granulation to form second-stage slow-release nutrient soil particles includes:

[0013] Dewatered sludge and slow-release material are mixed at a ratio of 100:10-20, and then transported to a round pot granulator. At the same time, water is sprayed to wet the mixture. Based on the first-stage slow-release nutrient soil particles produced by the first-stage granulation, a second-stage granulation is carried out. The diameter of the first-stage slow-release nutrient soil particles will increase to form the second-stage slow-release nutrient soil particles, so that the diameter of the second-stage slow-release nutrient soil particles is maintained at 14-16 mm.

[0014] Preferably, the step of mixing the second biochar and the second binder in a set ratio, and then mixing them with the second-stage slow-release nutrient soil particles for third-stage granulation to form third-stage slow-release nutrient soil particles includes:

[0015] The second biochar and the second binder are mixed in a ratio of 100:15 to 30, and then transported to a round pot granulator. At the same time, water is sprayed to wet the mixture. Based on the second-stage slow-release nutrient soil particles produced by the second-stage granulation, the third-stage granulation is carried out. The diameter of the second-stage slow-release nutrient soil particles will increase to form the third-stage slow-release nutrient soil particles, so that the diameter of the third-stage slow-release nutrient soil particles is maintained at 18 to 22 mm.

[0016] Preferably, the step of transporting the prepared third-stage slow-release nutrient soil particles to a belt dryer for low-temperature drying to achieve a set moisture content includes:

[0017] The moisture content of the third-stage slow-release nutrient soil particles should be ≤20%.

[0018] Preferably, the step of mixing the first biochar, the composite microbial agent, and the first binder in a predetermined ratio, and performing first-stage granulation to form first-stage slow-release nutrient soil particles further includes:

[0019] The first type of biochar is sludge-based biochar.

[0020] Compound microbial agents include a variety of microorganisms;

[0021] The first adhesive is starch.

[0022] Preferably, the step of mixing dewatered sludge and slow-release material in a set ratio, and then mixing it with first-stage slow-release nutrient soil particles for second-stage granulation to form second-stage slow-release nutrient soil particles further includes:

[0023] Dewatered sludge is the sludge cake produced by plate and frame filter press after advanced anaerobic digestion sludge is crushed and screened.

[0024] The slow-release material is made by mixing potato starch and mineral binder in a 1:1 ratio.

[0025] Preferably, the step of mixing the second biochar and the second binder in a set ratio and then mixing them with the second-stage slow-release nutrient soil particles for third-stage granulation to form third-stage slow-release nutrient soil particles further includes:

[0026] The second type of biochar is sludge-based biochar, shell biochar, lignocellulosic biochar, or straw biochar;

[0027] The second adhesive is a polysaccharide.

[0028] Preferably, the second biochar is sludge-based biochar, shell biochar, lignocellulosic biochar, or straw biochar, including:

[0029] The particle diameter of the second biochar is selected to be ≤0.5mm.

[0030] This invention provides a method for preparing slow-release sludge-based nutrient soil, the beneficial effects of which are:

[0031] The manufacturing method first involves mixing first-stage biochar, composite microbial agents, and a first binder in a predetermined ratio to form first-stage slow-release nutrient soil particles. The first-stage biochar serves as the core of the slow-release sludge-based nutrient soil, providing a carrier for microorganisms and slowly releasing nutrients. During the slow-release process, a soil micro-ecology gradually forms, which is beneficial for soil improvement. Simultaneously, the composite microbial agents increase the abundance and diversity of beneficial microorganisms in the soil, improve the soil microbial community structure, and promote nutrient release and cycling. Then, dewatered sludge and the slow-release material are mixed in a predetermined ratio. The first-stage slow-release nutrient soil particles are then mixed with the second-stage slow-release nutrient soil particles, which contain organic matter, nutrients, and salts that are essential for soil. Next, the second biochar and the second binder are mixed in a set ratio and then combined with the second-stage slow-release nutrient soil particles to form the third-stage slow-release nutrient soil particles. The second biochar adsorbs and blocks organic matter, nutrients, and heavy metals released from the inner layer of dewatered sludge. Through encapsulation, adsorption, and complexation, it reduces the migration rate of organic matter, nutrients, and heavy metals in the inner layer of dewatered sludge, thereby achieving a slow-release effect.

[0032] This production method uses multi-stage granulation to prepare slow-release sludge-based nutrient soil, which can slowly release organic matter, nutrients and salts, effectively improving the soil and promoting plant growth. At the same time, it can reduce the migration of toxic and harmful substances in dewatered sludge, reduce the risk of pollution to soil and water bodies, improve the utilization rate of nutrients in dewatered sludge, and reduce the environmental risks posed by dewatered sludge.

[0033] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0034] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0035] Figure 1 shows a flowchart of a method for preparing a slow-release sludge-based nutrient soil according to an embodiment of the present invention. Detailed Implementation

[0036] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0037] As shown in Figure 1, the present invention provides a method for preparing a slow-release sludge-based nutrient soil, the method comprising:

[0038] The first biochar, the composite microbial agent and the first binder are mixed in a set ratio and then subjected to first-stage granulation to form first-stage slow-release nutrient soil particles.

[0039] The dewatered sludge and slow-release material are mixed in a set ratio and then mixed with the first-stage slow-release nutrient soil particles for second-stage granulation to form the second-stage slow-release nutrient soil particles.

[0040] The second biochar and the second binder are mixed in a set ratio and then mixed with the second-stage slow-release nutrient soil particles for third-stage granulation to form the third-stage slow-release nutrient soil particles.

[0041] Specifically, to address the problem of excessively rapid release of organic matter, nutrients, and salts when advanced anaerobic digestion sludge is directly mixed with soil after dewatering and crushing for land application, which leads to insufficient nutrient utilization and potential environmental problems such as eutrophication and soil compaction, this application provides a method for preparing slow-release sludge-based nutrient soil. This method first mixes a first-stage biochar, a composite microbial agent, and a first binder in a predetermined ratio to form first-stage slow-release nutrient soil particles. The first-stage biochar serves as the core of the slow-release sludge-based nutrient soil, providing a carrier for microorganisms and slowly releasing nutrients. During the slow-release process, a soil micro-ecology gradually forms, which is beneficial for soil improvement. Simultaneously, the composite microbial agent... To increase the abundance and diversity of beneficial microorganisms in the soil, improve the soil microbial community structure, and promote nutrient release and cycling; then, dewatered sludge and slow-release materials are mixed in a set ratio and mixed with the first-stage slow-release nutrient soil particles to form the second-stage slow-release nutrient soil particles, in which the dewatered sludge is rich in organic matter, nutrients, salts and other substances needed by the soil; then, the second biochar and the second binder are mixed in a set ratio and mixed with the second-stage slow-release nutrient soil particles to form the third-stage slow-release nutrient soil particles, in which the second biochar has an adsorption and blocking effect on organic matter, nutrients, heavy metals and other substances released by the inner layer of dewatered sludge, and reduces the migration rate of organic matter, nutrients, heavy metals and other substances in the inner layer of dewatered sludge through encapsulation, adsorption and complexation, thereby achieving a slow-release effect.

[0042] The biochar produced in this method has a high specific surface area, well-developed pore structure, and abundant functional groups. It has been widely studied and applied in soil remediation and improvement. The addition of biochar can regulate the soil pore structure, improve soil permeability and water retention capacity, improve soil aggregate structure, provide habitats for microorganisms, provide nutrients and carbon sources, promote the growth and reproduction of microorganisms and plants, and also adsorb toxic and harmful substances and reduce their migration rate. However, the preparation cost of biochar is relatively high. It is more economical to mix dewatered sludge with biochar in a certain proportion to prepare slow-release sludge-based nutrient soil. This application adopts a multi-stage granulation method and uses biochar and other materials to support and encapsulate dewatered sludge to produce slow-release sludge-based nutrient soil with multi-stage slow release of nutrients, thereby maximizing the utility of dewatered sludge land use and minimizing environmental risks.

[0043] Preferably, the manufacturing method further includes:

[0044] The prepared third-stage slow-release nutrient soil particles are transported to a belt dryer for low-temperature drying to achieve the set moisture content.

[0045] Specifically, the moisture content of the third-stage slow-release nutrient soil particles should be ≤20%.

[0046] Preferably, mixing the first biochar, the composite microbial agent, and the first binder in a predetermined ratio, and then performing first-stage granulation to form first-stage slow-release nutrient soil particles includes:

[0047] The first biochar, compound microbial agent and first binder are mixed in a ratio of 100:1 to 3:15 to 30, and then transported to a round pot granulator for first-stage granulation. At the same time, water is sprayed to wet the soil so that the diameter of the first-stage slow-release nutrient soil particles is maintained at 9 to 11 mm.

[0048] The first type of biochar is sludge-based biochar.

[0049] Compound microbial agents include a variety of microorganisms;

[0050] The first adhesive is starch.

[0051] Specifically, sludge-based biochar, compound microbial agents, and starch are mixed in a ratio of 100:1 to 3:15 to 30. The mixed material is then transported to a round pot granulator for the first stage of granulation. At the same time, water is sprayed to wet the material. The diameter of the first-stage slow-release nutrient soil particles is maintained at about 9 to 11 mm.

[0052] Sludge-based biochar is produced by the pyrolysis of sludge at a temperature of 600–800℃ and a time of 30–60 minutes. The sludge carbon produced after pyrolysis is screened and granulated with a diameter of 0.5–1 mm. This granules serve as the core of the slow-release sludge-based nutrient soil, providing a carrier for microorganisms and slowly releasing nutrients. During the slow-release process of the sludge-based nutrient soil, a soil micro-ecology is gradually formed, which is beneficial for soil improvement.

[0053] The compound microbial agent contains a variety of microorganisms, including Bacillus subtilis, Bacillus licheniformis, Aspergillus niger, and yeast, which helps to increase the abundance and diversity of beneficial microorganisms in the soil, improve the structure of the soil microbial community, and promote the release and cycling of nutrients.

[0054] The starch used can be tuber starch with high viscosity, such as cassava starch or potato starch. Starch is a type of natural organic polymer compound with good viscosity and binding properties. It is a type of biodegradable and environmentally friendly binder.

[0055] Preferably, mixing dewatered sludge and slow-release material in a set ratio, and then mixing with first-stage slow-release nutrient soil particles for second-stage granulation to form second-stage slow-release nutrient soil particles includes:

[0056] Dewatered sludge and slow-release material are mixed at a ratio of 100:10-20, and then transported to a round pot granulator. At the same time, water is sprayed to wet the mixture. Based on the first-stage slow-release nutrient soil particles produced by the first-stage granulation, the second-stage granulation is carried out. The diameter of the first-stage slow-release nutrient soil particles will increase to form the second-stage slow-release nutrient soil particles, so that the diameter of the second-stage slow-release nutrient soil particles is maintained at 14-16 mm.

[0057] Dewatered sludge is the sludge cake produced by plate and frame filter press after advanced anaerobic digestion sludge is crushed and screened.

[0058] The slow-release material is made by mixing potato starch and mineral binder in a 1:1 ratio.

[0059] Specifically, dewatered sludge and slow-release material are mixed at a ratio of 100:10-20, and then transported to a round pot granulator. At the same time, water is sprayed to wet the material. Based on the first-stage slow-release nutrient soil particles produced by the first-stage granulation, a second-stage granulation is carried out to increase the diameter of the first-stage slow-release nutrient soil particles to 14-16 mm, forming the second-stage slow-release nutrient soil particles.

[0060] The dewatered sludge is the sludge cake produced after plate and frame filter press of advanced anaerobic digestion sludge. It is obtained after crushing and screening. The sludge cake is 10-20 mm thick, with a moisture content of 50%-60%, an organic matter content of 40-50% (dry basis), and total nutrients [total nitrogen (as N) + total phosphorus (as P2O5) + total potassium (as K2O)] ≥ 6%. The sludge cake is transported to a crusher for crushing and screening to keep the sludge particle diameter ≤ 2 mm after crushing. The hot water hydrolysis treatment unit in the advanced anaerobic digestion process has a good inactivation effect on pathogens and roundworm eggs in the sludge. The anaerobic digestion treatment unit can stabilize the organic matter in the sludge.

[0061] The slow-release material is made by mixing potato starch and mineral binder in a 1:1 ratio. The mineral binder can be attapulgite, vermiculite, bentonite, diatomaceous earth, kaolin, montmorillonite, etc. The mineral binder has the characteristics of high temperature stability and water resistance, which can provide higher particle stability.

[0062] Preferably, mixing the second biochar and the second binder in a set ratio and mixing them with the second-stage slow-release nutrient soil particles for third-stage granulation to form third-stage slow-release nutrient soil particles includes: mixing the second biochar and the second binder in a ratio of 100:15 to 30, then transporting the mixture to a round pot granulator while simultaneously spraying water to wet it; and performing third-stage granulation based on the second-stage slow-release nutrient soil particles produced by the second-stage granulation, so that the diameter of the second-stage slow-release nutrient soil particles will increase to form third-stage slow-release nutrient soil particles, and keeping the diameter of the third-stage slow-release nutrient soil particles at 18 to 22 mm.

[0063] The second type of biochar is sludge-based biochar, shell biochar, lignocellulosic biochar, or straw biochar;

[0064] The second adhesive is a polysaccharide.

[0065] Specifically, the second biochar and the second binder are mixed in a ratio of 100:15 to 30 and transported to a round pot granulator. At the same time, water is sprayed to wet the material. Based on the second-stage granulation, the second-stage slow-release nutrient soil particles are subjected to third-stage granulation, so that the diameter of the second-stage slow-release nutrient soil particles increases to 18 to 22 mm, forming the third-stage slow-release nutrient soil particles.

[0066] The second type of biochar is sludge-based biochar, shell biochar, wood-based biochar, straw-based biochar, etc. with a particle diameter of ≤0.5mm. Smaller particles of biochar have a larger specific surface area, which can adsorb and block organic matter, nutrients, heavy metals and other substances released by the inner dewatered sludge.

[0067] The second binder consists of natural polysaccharides such as chitosan, pectin, sodium alginate, carboxymethyl cellulose, and starch. These substances have good biodegradability, are abundant in source, and are inexpensive. Through encapsulation, adsorption, and complexation, they reduce the migration rate of organic matter, nutrients, and heavy metals in the inner layer of dewatered sludge, thereby achieving a slow-release effect.

[0068] Example 1

[0069] Sludge-based biochar, compound microbial agent, and cassava starch are mixed in a ratio of 100:2:20. The mixed material is transported to a round pot granulator for the first stage of granulation. At the same time, water is sprayed to wet the material. The diameter of the first-stage slow-release nutrient soil particles is about 11mm.

[0070] Next, the dewatered sludge, cassava starch, and attapulgite soil are mixed in a ratio of 100:10:5 and transported to a round pot granulator. At the same time, water is sprayed to wet the material. Based on the first-stage slow-release nutrient soil particles produced by the first-stage granulation, the second-stage granulation is carried out. The diameter of the first-stage slow-release nutrient soil particles increases to about 16mm, forming the second-stage slow-release nutrient soil particles.

[0071] The sludge-based biochar and pectin are then mixed in a ratio of 100:25 and transported to a circular pot granulator. At the same time, water is sprayed to wet the material. Based on the second-stage slow-release nutrient soil particles produced by the second-stage granulation, the third-stage granulation is carried out. The diameter of the second-stage slow-release nutrient soil particles increases to about 19mm, forming the third-stage slow-release nutrient soil particles.

[0072] Finally, the prepared third-stage slow-release nutrient soil particles are transported to a belt dryer for drying, and the moisture content is reduced to below 20%, resulting in slow-release sludge-based organic nutrient soil #1.

[0073] Example 2

[0074] Sludge-based biochar, compound microbial agent, and cassava starch are mixed in a ratio of 100:1.5:22. The mixed material is transported to a round pot granulator for the first stage of granulation. At the same time, water is sprayed to wet the material. The diameter of the first-stage slow-release nutrient soil particles is about 10mm.

[0075] Next, the dewatered sludge, cassava starch, and attapulgite soil are mixed in a ratio of 100:10:10 and transported to a round pot granulator. At the same time, water is sprayed to wet the material. Based on the first-stage slow-release nutrient soil particles produced by the first-stage granulation, the second-stage granulation is carried out. The diameter of the first-stage slow-release nutrient soil particles increases to about 15mm, forming the second-stage slow-release nutrient soil particles.

[0076] The sludge-based biochar and pectin are then mixed in a ratio of 100:20 and transported to a circular pot granulator. At the same time, water is sprayed to wet the material. Based on the second-stage slow-release nutrient soil particles produced by the second-stage granulation, the third-stage granulation is carried out. The diameter of the second-stage slow-release nutrient soil particles increases to about 20mm, forming the third-stage slow-release nutrient soil particles.

[0077] Finally, the prepared slow-release nutrient soil particles are transported to a belt dryer for drying, and the moisture content is reduced to below 20%, resulting in slow-release sludge-based organic nutrient soil #2.

[0078] Example 3

[0079] Sludge-based biochar, compound microbial agent, and cassava starch are mixed in a ratio of 100:2:25. The mixed material is then transported to a round pot granulator for the first stage of granulation. At the same time, water is sprayed to wet the material. The resulting first-stage slow-release nutrient soil particles have a diameter of approximately 9 mm.

[0080] Next, the dewatered sludge, cassava starch, and attapulgite soil are mixed in a ratio of 100:12:5 and transported to a round pot granulator. At the same time, water is sprayed to wet the material. Based on the first-stage slow-release nutrient soil particles produced by the first-stage granulation, the second-stage granulation is carried out. The diameter of the first-stage slow-release nutrient soil particles increases to about 14mm, forming the second-stage slow-release nutrient soil particles.

[0081] The sludge-based biochar and pectin are then mixed in a ratio of 100:15 and transported to a circular pot granulator. At the same time, water is sprayed to wet the material. Based on the second-stage slow-release nutrient soil particles produced by the second-stage granulation, the third-stage granulation is carried out. The diameter of the second-stage slow-release nutrient soil particles increases to about 18mm, forming the third-stage slow-release nutrient soil particles.

[0082] Finally, the prepared slow-release nutrient soil particles are transported to a belt dryer for drying, and the moisture content is reduced to below 20%, resulting in slow-release sludge-based organic nutrient soil #3.

[0083] In summary, the nutrient release rates of dewatered sludge and slow-release sludge-based organic nutrient soils #1, #2, and #3 were determined according to GB / T23348-2009 (Slow-Release Fertilizers). The results are shown in the table below. The nutrient release rate of the slow-release sludge-based organic nutrient soils was significantly lower than that of the dewatered sludge.

[0084] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing a slow-release sludge-based nutrient soil, characterized in that, The production method includes: The first biochar, the composite microbial agent and the first binder are mixed in a set ratio and then subjected to first-stage granulation to form first-stage slow-release nutrient soil particles. The dewatered sludge and slow-release material are mixed in a set ratio and then mixed with the first-stage slow-release nutrient soil particles for second-stage granulation to form the second-stage slow-release nutrient soil particles. The second biochar and the second binder are mixed in a set ratio and then mixed with the second-stage slow-release nutrient soil particles for third-stage granulation to form the third-stage slow-release nutrient soil particles.

2. The method for preparing a slow-release sludge-based nutrient soil according to claim 1, characterized in that, The production method also includes: The prepared third-stage slow-release nutrient soil particles are transported to a belt dryer for low-temperature drying to achieve the set moisture content.

3. The method for preparing a slow-release sludge-based nutrient soil according to claim 1, characterized in that, The process of mixing the first biochar, the composite microbial agent, and the first binder in a predetermined ratio, and then performing first-stage granulation to form first-stage slow-release nutrient soil particles includes: The first biochar, compound microbial agent and first binder are mixed in a ratio of 100:1 to 3:15 to 30, and then transported to a round pot granulator for first-stage granulation. At the same time, water is sprayed to wet the soil so that the diameter of the first-stage slow-release nutrient soil particles is maintained at 9 to 11 mm.

4. The method for preparing a slow-release sludge-based nutrient soil according to claim 1, characterized in that, The step of mixing dewatered sludge and slow-release material in a set ratio, and then mixing it with first-stage slow-release nutrient soil particles for second-stage granulation to form second-stage slow-release nutrient soil particles includes: Dewatered sludge and slow-release material are mixed at a ratio of 100:10-20, and then transported to a round pot granulator. At the same time, water is sprayed to wet the mixture. Based on the first-stage slow-release nutrient soil particles produced by the first-stage granulation, a second-stage granulation is carried out. The diameter of the first-stage slow-release nutrient soil particles will increase to form the second-stage slow-release nutrient soil particles, so that the diameter of the second-stage slow-release nutrient soil particles is maintained at 14-16 mm.

5. The method for preparing a slow-release sludge-based nutrient soil according to claim 1, characterized in that, The step of mixing the second biochar and the second binder in a set ratio, and then mixing them with the second-stage slow-release nutrient soil particles for third-stage granulation to form the third-stage slow-release nutrient soil particles includes: The second biochar and the second binder are mixed in a ratio of 100:15 to 30, and then transported to a round pot granulator. At the same time, water is sprayed to wet the mixture. Based on the second-stage slow-release nutrient soil particles produced by the second-stage granulation, the third-stage granulation is carried out. The diameter of the second-stage slow-release nutrient soil particles will increase to form the third-stage slow-release nutrient soil particles, so that the diameter of the third-stage slow-release nutrient soil particles is maintained at 18 to 22 mm.

6. The method for preparing a slow-release sludge-based nutrient soil according to claim 2, characterized in that, The process of transporting the prepared third-stage slow-release nutrient soil particles to a belt dryer for low-temperature drying to achieve a set moisture content includes: The moisture content of the third-stage slow-release nutrient soil particles should be ≤20%.

7. The method for preparing a slow-release sludge-based nutrient soil according to claim 1, characterized in that, The process of mixing the first biochar, the composite microbial agent, and the first binder in a predetermined ratio, and then performing first-stage granulation to form first-stage slow-release nutrient soil particles further includes: The first type of biochar is sludge-based biochar. Compound microbial agents include a variety of microorganisms; The first adhesive is starch.

8. The method for preparing a slow-release sludge-based nutrient soil according to claim 1, characterized in that, The process of mixing dewatered sludge and slow-release materials in a set ratio, and then mixing them with first-stage slow-release nutrient soil particles for second-stage granulation to form second-stage slow-release nutrient soil particles further includes: Dewatered sludge is the sludge cake produced by plate and frame filter press after advanced anaerobic digestion sludge is crushed and screened. The slow-release material is made by mixing potato starch and mineral binder in a 1:1 ratio.

9. The method for preparing a slow-release sludge-based nutrient soil according to claim 1, characterized in that, The step of mixing the second biochar and the second binder in a set ratio, and then mixing them with the second-stage slow-release nutrient soil particles for third-stage granulation to form the third-stage slow-release nutrient soil particles further includes: The second type of biochar is sludge-based biochar, shell biochar, lignocellulosic biochar, or straw biochar; The second adhesive is a polysaccharide.

10. The method for preparing a slow-release sludge-based nutrient soil according to claim 9, characterized in that, The second type of biochar is sludge-based biochar, shell biochar, lignocellulosic biochar, or straw biochar, including: The particle diameter of the second biochar is selected to be ≤0.5mm.

Images