Production process method of low-salt sludge nutrient soil
By treating sludge with hot water hydrolysis-anaerobic digestion and drying-pyrolysis carbonization, sludge carbon is prepared as a conditioner, which solves the problems of increased salt content and electrical conductivity and nutrient loss in sludge nutrient soil during land application. This enables the production of low-salt slow-release sludge nutrient soil, improving soil fertility and environmental protection.
Patent Information
- Application Number
- CN202511209725.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-27
- Publication Date
- 2025-12-19
AI Technical Summary
The existing sludge nutrient soil has significantly increased salt content and electrical conductivity during land use, which is detrimental to the soil environment and plant growth. At the same time, organic matter and nutrients are rapidly lost, resulting in low nutrient utilization and groundwater pollution.
Sludge was treated by hot water hydrolysis-anaerobic digestion and drying-pyrolysis carbonization to prepare sludge carbon as a conditioner. It was combined with magnesium chloride and cationic polyacrylamide for conditioning. By constructing a framework and adsorbing extracellular polymers, the dewatering performance was improved, the salt content and conductivity were reduced, and the high specific surface area and pore structure of sludge carbon were used to adsorb nutrients and reduce loss.
It effectively reduces the salt content and electrical conductivity of sludge nutrient soil, improves soil fertility, reduces nutrient loss, enhances soil porosity and aeration, achieves slow release and fixation of nutrients, and protects the soil environment.
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Figure CN121159321A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of sludge treatment, and more particularly relates to a production process method of low-salt sludge nutrient soil. BACKGROUND
[0002] Domestic sludge is suitable for land use due to high organic matter content and high-temperature sterilization treatment by heat hydrolysis. However, the dewatering performance of anaerobic sludge after heat hydrolysis-anaerobic digestion is poor, and a large amount of inorganic conditioning agents need to be added before plate and frame filter pressing, which leads to a significant increase in the salt content and conductivity of sludge nutrient soil after plate and frame dewatering, and is not conducive to soil environment and plant growth after land use. At the same time, there are many small-molecule organic matters and water-soluble nutrient elements in anaerobic sludge, which will be quickly released and lost in large quantities after being applied to soil, especially in rainy weather, resulting in low nutrient utilization rate and groundwater pollution. SUMMARY
[0003] The purpose of the present application is to provide a production process method of low-salt sludge nutrient soil to solve the problems of the prior art, that is, the salt content and conductivity of the currently produced sludge nutrient soil will significantly increase, which is not conducive to soil environment and plant growth after land use, and the organic matter and nitrogen, phosphorus and other nutrients in the produced sludge nutrient soil will be quickly released and lost in large quantities, resulting in low nutrient utilization rate and groundwater pollution.
[0004] To achieve the above purpose, the present application provides a production process method of low-salt sludge nutrient soil, which comprises:
[0005] preliminarily dewatering domestic sludge to a target water content range to obtain preliminarily dewatered sludge;
[0006] performing heat hydrolysis-anaerobic digestion treatment on a part of the preliminarily dewatered sludge to obtain anaerobic sludge;
[0007] performing drying-thermal carbonization treatment on another part of the preliminarily dewatered sludge to obtain sludge carbon;
[0008] adding sludge carbon to the anaerobic sludge for conditioning to obtain conditioned sludge;
[0009] deeply dewatering the conditioned sludge to a target water content range to obtain sludge nutrient soil.
[0010] Preferably, the preliminary dewatering of domestic sludge to a target water content range comprises preliminarily centrifugal dewatering domestic sludge with a water content of 95% to 99% to a water content of 80% to 85% to obtain preliminarily dewatered sludge.
[0011] Preferably, the heat hydrolysis-anaerobic digestion of a portion of the primary dewatered sludge to obtain anaerobic digestion sludge comprises:
[0012] 50% to 80% of the primary dewatered sludge is subjected to heat hydrolysis at a temperature of 150°C to 180°C and a pressure of 6 bar to 7 bar for 30 min to 60 min to obtain heat hydrolysis sludge;
[0013] The heat hydrolysis sludge is subjected to anaerobic digestion at a temperature of 38°C to 45°C and a sludge retention time of 15 d to 30 d after multi-stage heat exchange cooling to obtain anaerobic digestion sludge.
[0014] Preferably, the heat hydrolysis-anaerobic digestion of a portion of the primary dewatered sludge to obtain anaerobic digestion sludge further comprises: the biogas produced in the anaerobic digestion process is purified and used for heat hydrolysis, drying-thermal decomposition carbonization.
[0015] Preferably, the drying-thermal decomposition carbonization of another portion of the primary dewatered sludge to obtain sludge carbon comprises:
[0016] 20% to 50% of the primary dewatered sludge is subjected to drying to reduce the moisture content of the sludge to 20% to 35% to obtain dried sludge;
[0017] The dried sludge is subjected to thermal decomposition carbonization at a temperature of 550°C to 800°C for 30 min to 90 min to obtain sludge carbon.
[0018] Preferably, the conditioning of the anaerobic digestion sludge by adding sludge carbon comprises: the anaerobic digestion sludge is stirred at 400 to 800 r / min for 10 min to 30 min to maintain a homogeneous state, and then an appropriate amount of magnesium chloride, sludge carbon, and cationic polyacrylamide are added in sequence to obtain conditioned sludge.
[0019] Preferably, the magnesium chloride is added in a molar ratio of Mg:P of 1.0 to 2.0, and the pH of the sludge is controlled at 8 to 9. If the pH of the sludge is insufficient, sodium hydroxide can be added to adjust the pH. The magnesium chloride is stirred at 400 r / min to 800 r / min for 20 min to 30 min during the addition.
[0020] Preferably, the sludge carbon is added in an amount of 20% to 70% of the anaerobic digestion sludge, and the sludge carbon is stirred at 400 to 800 r / min for 10 to 30 min during the addition.
[0021] Preferably, the cationic polyacrylamide is added in an amount of 0.5% to 5% of the anaerobic digestion sludge, and the cationic polyacrylamide is stirred at 200 to 400 r / min for 2 to 10 min during the addition.
[0022] Preferably, the deep dewatering of the conditioned sludge to a target moisture content range to obtain the organic nutrient soil comprises deep centrifugal dewatering of the conditioned sludge to a moisture content of 70-80%, dewatering filtrate is subjected to denitrification treatment by anaerobic ammonia oxidation technology, and the dewatered conditioned sludge is further subjected to drying treatment to reduce the moisture content of the conditioned sludge to below 60%, and the dried conditioned sludge is subjected to crushing, screening and granulation treatment to prepare the sludge nutrient soil.
[0023] The present application provides a kind of low salt sludge nutrient soil production process method, its beneficial effect lies in: the production process method based on existing hot hydrolysis-anaerobic digestion technology, a part of preliminary dewatering sludge is subjected to hot hydrolysis-anaerobic digestion treatment, another part of preliminary dewatering sludge is subjected to drying-carbonization treatment, the sludge carbon prepared is added to anaerobic digestion sludge as sludge conditioner, sludge dewatering performance is improved by the action of building skeleton, adsorbing extracellular polymer, replace part of inorganic conditioning agent, reduce the salt content and conductivity of sludge nutrient soil, while the high specific surface area and abundant pore of sludge carbon can adsorb moisture and nutrients, reduce nutrient loss, improve soil fertility.
[0024] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS
[0025] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which:
[0026] Figure 1 A flow chart of a low salt sludge nutrient soil production process method according to one embodiment of the present application is shown;
[0027] Figure 2 A schematic diagram of a low salt sludge nutrient soil production process method according to one embodiment of the present application is shown Figure 1 .
[0028] Figure 3 A schematic diagram of a low salt sludge nutrient soil production process method according to one embodiment of the present application is shown Figure 2 . DETAILED DESCRIPTION
[0029] Preferred embodiments of the present application will be described in more detail below. Although the following describes preferred embodiments of the present application, it is to be understood that the application can be carried out in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this application will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.
[0030] As shown in Figure 1 and Figure 2 The present application provides a production process for low-salt sludge nutrient soil, which comprises:
[0031] Preliminarily dewatering domestic sludge to a target water content range to obtain preliminarily dewatered sludge;
[0032] Performing thermal hydrolysis-anaerobic digestion treatment on a part of the preliminarily dewatered sludge to obtain anaerobically digested sludge;
[0033] Performing drying-pyrolytic carbonization treatment on another part of the preliminarily dewatered sludge to obtain sludge carbon;
[0034] Adding the sludge carbon to the anaerobically digested sludge for conditioning to obtain conditioned sludge;
[0035] Deeply dewatering the conditioned sludge to a target water content range to obtain sludge nutrient soil.
[0036] Specifically, to solve the problem that a large amount of inorganic agents need to be added to anaerobically digested sludge before plate-frame dewatering to improve its dewatering performance, which leads to a substantial increase in the salt content and conductivity of the produced sludge nutrient soil, destroys the ecological balance of the soil, and is not conducive to plant growth, and to solve the problem that the anaerobically digested sludge contains many small-molecule organic substances and easily released nutrient elements, which are easily lost in the soil and have low utilization rate, the present application provides a production process for low-salt sludge nutrient soil. The production process is based on the existing thermal hydrolysis-anaerobic digestion technology, a part of the preliminarily dewatered sludge is subjected to thermal hydrolysis-anaerobic digestion treatment, another part of the preliminarily dewatered sludge is subjected to drying-pyrolytic carbonization treatment, and the obtained sludge carbon is added to the anaerobically digested sludge as a sludge conditioner, which improves the dewatering performance of the sludge by building a skeleton and adsorbing extracellular polymers, replaces part of the inorganic conditioning agents, reduces the salt content and conductivity of the sludge nutrient soil, and at the same time, the high specific surface area and rich pores of the sludge carbon can adsorb water and nutrients, reduce nutrient loss, and improve soil fertility.
[0037] As shown in Figure 2 Preferably, another part of the preliminarily dewatered sludge is subjected to drying-pyrolytic carbonization treatment to obtain sludge carbon. This step can also be replaced by drying-pyrolytic carbonization treatment of part of the end dewatered sludge to obtain sludge carbon.
[0038] Preferably, the primary dewatering of the domestic sludge to a target moisture content range comprises: primary centrifugal dewatering of the domestic sludge with a moisture content of 95% to 99% to a moisture content of 80% to 85% to obtain primary dewatered sludge.
[0039] Specifically, the domestic sludge is at least one of bar screenings, primary sludge, and excess sludge generated in a sewage treatment process mainly using domestic sewage.
[0040] Preferably, the heat hydrolysis-anaerobic digestion of a portion of the primary dewatered sludge to obtain anaerobic digestion sludge comprises:
[0041] 50% to 80% of the primary dewatered sludge is subjected to heat hydrolysis at a temperature of 150°C to 180°C, a pressure of 6 bar to 7 bar, and a reaction time of 30 min to 60 min to obtain heat hydrolyzed sludge;
[0042] The heat hydrolyzed sludge is subjected to anaerobic digestion at a temperature of 38°C to 45°C and a sludge retention time of 15 d to 30 d after being cooled by multi-stage heat exchange to obtain anaerobic digestion sludge.
[0043] Preferably, the heat hydrolysis-anaerobic digestion of a portion of the primary dewatered sludge to obtain anaerobic digestion sludge further comprises: using biogas generated in the anaerobic digestion process after purification for heat hydrolysis, drying-thermal decomposition carbonization.
[0044] Specifically, the biogas generated in the anaerobic digestion process is purified by desulfurization and the like and used for heat hydrolysis, drying-thermal decomposition carbonization units. In order to improve the energy self-sufficiency rate in the process of treating domestic sludge, without affecting the subsequent sludge dewatering and sludge nutrient soil quality, the amount of sludge treated by heat hydrolysis-anaerobic digestion can be maximized, and the amount of sludge treated by drying-thermal decomposition carbonization can be minimized.
[0045] Preferably, the drying-thermal decomposition carbonization of another portion of the primary dewatered sludge to obtain sludge carbon comprises:
[0046] 20% to 50% of the primary dewatered sludge is subjected to drying to reduce the moisture content of the sludge to 20% to 35% to obtain dried sludge;
[0047] The dried sludge is subjected to thermal decomposition carbonization at a temperature of 550°C to 800°C and a reaction time of 30 min to 90 min to obtain sludge carbon.
[0048] Specifically, the dried sludge is transported to a carbonization furnace for thermal decomposition carbonization.
[0049] Preferably, the sludge carbon is added to the anaerobic digestion sludge for conditioning to obtain conditioned sludge, comprising: stirring the anaerobic digestion sludge at 400-800 r / min for 10-30 min to keep the sludge in a homogeneous state, and then adding appropriate amounts of magnesium chloride (MgCl2), sludge carbon and cationic polyacrylamide (CPAM) in sequence for conditioning to obtain conditioned sludge.
[0050] Specifically, the anaerobic digestion sludge is transported to a sludge conditioning tank for conditioning.
[0051] The magnesium chloride converts phosphorus elements in the anaerobic digestion sludge into magnesium ammonium phosphate crystals, which are retained in the sludge nutrient soil as slow-release phosphate fertilizer, improving the quality and slow-release performance of the sludge nutrient soil and solving the problem of excessive release of nutrients and salts in the process of sludge land use.
[0052] The cationic polyacrylamide (CPAM) is a commonly used high molecular weight organic flocculant that coagulates small sludge particles into large flocs through electric neutralization, adsorption and bridging, thereby achieving separation of sludge and water.
[0053] Preferably, the magnesium chloride is added in a Mg:P molar ratio of 1.0-2.0, and the pH value of the sludge is controlled at 8-9. If the pH value of the sludge is insufficient, sodium hydroxide can be added to adjust the pH value. The magnesium chloride is stirred at 400-800 r / min for 20-30 min during the addition.
[0054] Specifically, hexahydrated magnesium chloride (MgCl2·6H2O) can be used instead of magnesium chloride.
[0055] Preferably, the sludge carbon is added in an amount of 20%-70% of the anaerobic digestion sludge, and the sludge carbon is stirred at 400-800 r / min for 10-30 min during the addition.
[0056] Specifically, the sludge carbon is added in an amount of 20%-70% of the anaerobic digestion sludge (based on dry solids), and the sludge carbon is preferably made by drying and pyrolytic carbonization of another part of the primary dewatered sludge. Alternatively, other carbon-based materials such as coconut shell carbon, rice husk carbon and coal carbon can be used.
[0057] Preferably, the cationic polyacrylamide is added in an amount of 0.5%-5% of the anaerobic digestion sludge, and the cationic polyacrylamide is stirred at 200-400 r / min for 2-10 min during the addition.
[0058] Specifically, the cationic polyacrylamide is added in an amount of 0.5%-5% of the anaerobic digestion sludge (based on dry solids).
[0059] Preferably, the conditioned sludge is deep dewatered to a target moisture content range to obtain the organic nutrient soil. In this step, the plate and frame filter dewatering can be used to replace the centrifugal dewatering. The sludge carbon is added to the anaerobic digested sludge for conditioning to obtain the conditioned sludge. In this step, the aluminum / iron salt is added after the magnesium chloride is added during the conditioning, and the addition amount is 1-10% (based on the dry solid) of the anaerobic digested sludge, while stirring at 400-800 r / min for 30-60 min, and then the sludge carbon and the cationic polyacrylamide are sequentially added.
[0060] Specifically, the dewatering filtrate is transported to a treatment tank, and the anaerobic ammonia oxidation technology is used for denitrification treatment.
[0061] Preferably, the conditioned sludge is deep dewatered to a target moisture content range to obtain the organic nutrient soil. In this step, the plate and frame filter dewatering can be used to replace the centrifugal dewatering. The sludge carbon is added to the anaerobic digested sludge for conditioning to obtain the conditioned sludge. In this step, the aluminum / iron salt is added after the magnesium chloride is added during the conditioning, and the addition amount is 1-10% (based on the dry solid) of the anaerobic digested sludge, while stirring at 400-800 r / min for 30-60 min, and then the sludge carbon and the cationic polyacrylamide are sequentially added.
[0062] Preferably, the conditioned sludge is deep dewatered to a target moisture content range to obtain the organic nutrient soil. In this step, the plate and frame filter dewatering can be used to replace the centrifugal dewatering. The sludge carbon is added to the anaerobic digested sludge for conditioning to obtain the conditioned sludge. In this step, the aluminum / iron salt is added after the magnesium chloride is added during the conditioning, and the addition amount is 1-10% (based on the dry solid) of the anaerobic digested sludge, while stirring at 400-800 r / min for 30-60 min, and then the sludge carbon and the cationic polyacrylamide are sequentially added.
[0063] Example 1
[0064] 100 m 3 The domestic sludge with a moisture content of 97% and an organic matter content of 70% is transported to a centrifugal dewatering machine, so that the moisture content is reduced to 83%, and 17.6 t of the preliminary dewatered sludge is obtained.
[0065] The obtained 80% of the preliminary dewatered sludge (14.1 t) is subjected to a thermal hydrolysis-anaerobic digestion treatment, the thermal hydrolysis temperature is 165°C, the pressure is 6.5 bar, the reaction time is 30 min, the anaerobic digestion temperature is 42°C, and the reaction time is 18 d, so that 27 m 3 Anaerobic digested sludge (1.6 t DS).
[0066] The obtained 20% of the preliminary dewatered sludge (3.5 t) is subjected to a drying-carbonization treatment, the moisture content of the sludge after drying is 30%, the pyrolysis carbonization temperature is 600°C, and the reaction time is 30 min, so that 0.33 t of sludge carbon is obtained.
[0067] The obtained 27 m 3The anaerobic digested sludge is transported to a conditioning tank, stirred at 600 r / min for 20 min, 49 kg of magnesium chloride hexahydrate is added according to the Mg:P ratio of 1.3, stirred at 600 r / min for 30 min, 3.3 t of sludge carbon obtained is added, stirred at 600 r / min for 20 min, finally cationic polyacrylamide is added, the addition amount is 2.5% (calculated by dry solid) of the anaerobic digested sludge, stirred at 300 r / min for 5 min, to obtain conditioned sludge;
[0068] The conditioned sludge is transported to a centrifugal dewatering machine, so that the water content of the sludge is reduced to 80%, the phosphorus fixation rate in the dewatered conditioned sludge is about 80%, the dewatered filtrate is treated by anaerobic ammonia oxidation technology, the ammonia nitrogen removal rate is higher than 90%, the dewatered conditioned sludge is transported to a drying machine for drying, the water content of the dried conditioned sludge is 50%, and the dried conditioned sludge is subjected to crushing, screening and granulation treatment, to obtain low-salt slow-release sludge nutrient soil.
[0069] Example 2
[0070] 1000 m 3 The domestic sludge with a water content of 97% and an organic matter content of 65% is transported to a centrifugal dewatering machine, so that the water content is reduced to 83%, to obtain 176 t of primary dewatered sludge;
[0071] The 70% primary dewatered sludge (123 t) is subjected to hot hydrolysis-anaerobic digestion treatment, the hot hydrolysis temperature is 165°C, the pressure is 6.5 bar, the reaction time is 30 min, the anaerobic digestion temperature is 42°C, and the reaction time is 20 d, to obtain 250 m 3 Anaerobic digested sludge (15 t DS).
[0072] The 20% primary dewatered sludge (35 t) is subjected to drying-pyrolysis carbonization treatment, the water content of the sludge after drying is 30%, the pyrolysis carbonization temperature is 600°C, and the reaction time is 30 min, to obtain 3.3 t of sludge carbon.
[0073] The 250 m 3 The anaerobic digested sludge is transported to a conditioning tank, stirred at 600 r / min for 20 min, 49 kg of magnesium chloride hexahydrate is added according to the Mg:P ratio of 1.3, stirred at 600 r / min for 30 min, 3.3 t of sludge carbon obtained is added, stirred at 600 r / min for 20 min, finally cationic polyacrylamide is added, the addition amount is 2.5% (calculated by dry solid) of the anaerobic digested sludge, stirred at 300 r / min for 5 min, to obtain conditioned sludge;
[0074] The conditioned sludge is transported to a centrifugal dewatering machine to reduce the moisture content of the sludge to 80%, and the fixed rate of orthophosphorus in the dewatered conditioned sludge is about 85%. The dewatering filtrate is treated by anaerobic ammonia oxidation technology for denitrification, and the ammonia nitrogen removal rate is higher than 90%. The dewatered conditioned sludge is transported to a drying machine for drying. The moisture content of the dried conditioned sludge is 50%. The dried conditioned sludge is subjected to crushing, screening and granulation treatment to obtain the low-salt slow-release sludge nutrient soil.
[0075] In summary, in the production process of the low-salt sludge nutrient soil, the sludge pyrolysis carbonization technology can convert the sludge into stable sludge carbon, which has a high specific surface area, a developed pore structure and abundant functional groups, and can be applied to soil remediation and improvement. The porous structure of the sludge carbon can increase the soil porosity, improve the soil aeration and water permeability, and promote the development of plant root systems. The high specific surface area and abundant pores of the sludge carbon can adsorb water and nutrients, reduce nutrient loss, and improve soil fertility. The sludge carbon can also fix heavy metals in the soil through adsorption, precipitation and ion exchange mechanisms, reducing plant absorption. The sludge carbon can also be used as a sludge conditioner to improve the dewatering performance of the sludge by building a skeleton and adsorbing extracellular polymers. Due to the high cost of full-drying-pyrolysis of the sludge, part of the preliminary dewatered sludge can be subjected to drying-pyrolysis carbonization treatment, and the produced sludge carbon can be used as a sludge conditioner and added before the dewatering of the sludge treated by hot hydrolysis-anaerobic digestion, thereby reducing the use of inorganic conditioning agents and the salt content and conductivity of the sludge nutrient soil.
[0076] The sludge also contains a large amount of phosphorus elements, which are currently recovered by technologies such as magnesium ammonium phosphate (struvite) crystallization method using sludge dewatering filtrate or sludge incineration fly ash. Magnesium ammonium phosphate is a slow-release phosphorus fertilizer. In combination with the demand for sludge land use, the present application recovers phosphorus in situ by adding an appropriate amount of magnesium chloride, and fixes magnesium ammonium phosphate crystals in the sludge nutrient soil, which can convert the phosphorus elements in the sludge into a slow-release form, improve the quality of the sludge nutrient soil, and solve the problem of magnesium ammonium phosphate outlet.
[0077] The present application provides a production process of a low-salt slow-release sludge-based nutrient soil, which adds a sludge drying-pyrolysis carbonization process and a magnesium ammonium phosphate crystallization method based on the existing treatment process, solving the problems of rapid release of nutrients and salt, loss of organic matter, and increase of soil conductivity during sludge land use. The sludge nutrient soil prepared by the process contains a large amount of sludge carbon and magnesium ammonium phosphate, has the positive effects of slow-release of nutrient elements, low salt content, and improvement of soil porosity and aeration.
[0078] Having described various embodiments of the application, it is to be understood that the above description is meant to be illustrative only, and that many modifications and variations of the embodiments are possible without departing from the scope and spirit of the described embodiments. Many modifications and variations of the described embodiments are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims and their equivalents, the described embodiments can be practiced otherwise than as specifically described.
Claims
1. A process for the production of low-salt sludge nutrient soil, characterized by, The production process comprises: preliminary dewatering domestic sludge to a target moisture content range to obtain preliminary dewatered sludge; performing thermal hydrolysis-anaerobic digestion treatment on a part of the preliminary dewatered sludge to obtain anaerobic digestion sludge; performing drying-pyrolytic carbonization treatment on another part of the preliminary dewatered sludge to obtain sludge carbon; adding sludge carbon to the anaerobic digestion sludge for conditioning to obtain conditioned sludge; deep dewatering the conditioned sludge to a target moisture content range to obtain sludge nutrient soil.
2. A process for the production of low-salt sludge nutrient soil according to claim 1, characterized in that, The preliminary dewatering of the domestic sludge to the target moisture content range comprises: preliminarily centrifugal dewatering domestic sludge with a moisture content of 95%-99% to a moisture content of 80%-85% to obtain preliminary dewatered sludge.
3. The process as claimed in claim 1, wherein the process for production of low salt sludge nutrient soil is characterized by, The thermal hydrolysis-anaerobic digestion treatment on a part of the preliminary dewatered sludge to obtain anaerobic digestion sludge comprises: performing thermal hydrolysis treatment on 50%-80% of the obtained preliminary dewatered sludge, with a thermal hydrolysis reaction temperature of 150-180°C, a pressure of 6-7 bar, and a reaction time of 30-60 min, to obtain thermal hydrolysis sludge; performing anaerobic digestion treatment on the thermal hydrolysis sludge after multi-stage heat exchange cooling, with an anaerobic digestion reaction temperature of 38-45°C and a sludge retention time of 15-30 d, to obtain anaerobic digestion sludge.
4. A process for the production of low-salt sludge nutrient soil according to claim 3, characterized in that, The thermal hydrolysis-anaerobic digestion of a part of the preliminary dewatered sludge to obtain anaerobic digestion sludge also comprises: using biogas generated in the anaerobic digestion process after purification treatment for thermal hydrolysis and drying-pyrolytic carbonization.
5. The process as claimed in claim 1, wherein the process for production of low salt sludge nutrient soil is characterized by, The drying-pyrolytic carbonization treatment on another part of the preliminary dewatered sludge to obtain sludge carbon comprises: performing drying treatment on 20%-50% of the obtained preliminary dewatered sludge to reduce the moisture content of the sludge to 20%-35% to obtain dried sludge; performing pyrolytic carbonization treatment on the dried sludge, with a reaction temperature of 550-800°C and a reaction time of 30-90 min, to obtain sludge carbon.
6. The process as claimed in claim 1, wherein the process for production of low salt sludge nutrient soil is characterized by, The addition of sludge carbon to the anaerobic digestion sludge for conditioning to obtain conditioned sludge comprises: stirring the anaerobic digestion sludge at 400-800 r / min for 10-30 min to keep the sludge in a homogeneous state, and then adding appropriate amounts of magnesium chloride, sludge carbon, and cationic polyacrylamide in sequence for conditioning to obtain conditioned sludge.
7. A process for the production of low-salt sludge nutrient soil according to claim 6, characterized in that, The magnesium chloride is added in a Mg:P molar ratio of 1.0-2.0, while the pH value of the sludge is controlled at 8-9, and sodium hydroxide can be added to adjust the pH value if the pH value of the sludge is insufficient. The magnesium chloride is stirred at 400-800 r / min for 20-30 min during the addition.
8. A process for the production of low-salt sludge nutrient soil according to claim 6, characterized by, The addition amount of the sludge carbon is 20%-70% of the anaerobic digestion sludge, and the sludge carbon is stirred at 400-800 r / min for 10-30 min during the addition.
9. A process for the production of low-salt sludge nutrient soil according to claim 6, characterized by, The addition amount of the cationic polyacrylamide is 0.5%-5% of the anaerobic digestion sludge, and the cationic polyacrylamide is stirred at 200-400 r / min for 2-10 min during the addition.
10. The process as claimed in claim 1, wherein the process for production of low salt sludge nutrient soil is characterized by, The process of deeply dewatering the conditioned sludge to the target moisture content range to obtain organic nutrient soil includes: deeply centrifuging the conditioned sludge to dewater it to a moisture content of 70-80%; using anaerobic ammonia oxidation technology to denitrify the dewatered filtrate; further drying the dewatered conditioned sludge to reduce its moisture content to below 60%; and then crushing, screening, and granulating the dried conditioned sludge to produce sludge nutrient soil.