One-hour sludge drying agent and application thereof in sludge drying and nutrient soil

Abstract

The invention belongs to the technical field of environment, and relates to a one-hour sludge drying agent and application thereof in sludge drying and nutrient soil. The drying agent comprises the following components in percentage by weight: 50-60% of calcium oxide, 5-10% of sodium hydroxide and 5-10% of aluminum powder. The application of the drying agent in sludge drying comprises the following steps: adding dry biomass into sludge with the water content of 70-80wt%, uniformly stirring, then adding the drying agent, uniformly stirring, and standing for 1 hour, so that the water content of the sludge is reduced to 33wt% or below, the heavy metal is passivated by 97-99%, and the harmful bacteria are killed by 100% to obtain dry sludge; according to the application of the drying agent in nutrient soil, dry sludge obtained through drying of the drying agent and urea are subjected to mechanical granulation together to prepare nutrient soil particles with a slow release function. According to the invention, the sludge treatment efficiency is obviously improved, the treatment time and cost are reduced, and the resource utilization of the sludge is realized.

Description

Technical Field

[0001] The invention belongs to the field of environmental technology and relates to a 1-hour sludge drying agent and application thereof in sludge drying and nutrient soil. Background Art

[0002] At present, the mainstream method of treating sludge at home and abroad is mechanical extrusion followed by incineration or landfill. However, due to the complex structural characteristics of sludge, it is difficult to reduce the moisture content to below 60wt% through mechanical dehydration, which not only increases the energy loss of subsequent treatment, but also causes environmental pollution. To solve this problem, researchers have tried to add conditioners (such as calcium oxide, biomass powder, slag, etc.) to the sludge to enhance its dehydration, but this type of technology still needs to be combined with a filter press for dehydration, which not only increases the complexity of the operation, but also the entire dehydration process is usually longer.

[0003] In order to solve the above problems, some new sludge dehydration technologies have been proposed to improve the sludge treatment efficiency. For example, patent application CN112159073A discloses an inorganic mineral composite dehydrating agent prepared by cement, aluminate cement, alkaline earth metal oxides, artificial volcanic ash, gypsum and limestone, but it still needs to be dried or squeezed for dehydration, which takes a long time. Patent application CN113860701A discloses a sludge dehydrating agent. Although it has self-heating properties and can reach a temperature of 40-50°C after 3-4 hours, its dehydration efficiency is still low, resulting in a long overall drying process. Patent application CN113860700A discloses a method of mixing biomass ash and sludge in combination with sun exposure, but the drying time still takes one week and the efficiency is relatively low.

[0004] In summary, although there are a variety of sludge dewatering methods in the prior art, they generally have the problem of being time-consuming. Summary of the invention

[0005] The purpose of the present invention is to solve the problems existing in the prior art and to provide a 1-hour sludge drying agent and its application in sludge drying and nutrient soil.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A one-hour sludge drying agent comprises, by weight percentage, 50-60% calcium oxide, 5-10% sodium hydroxide and 5-10% aluminum powder.

[0008] The one-hour sludge drying agent of the present invention can realize the 1-hour drying of sludge without heating, mainly because: ① calcium oxide plays a role of skeleton and preheating in the sludge; ② sodium hydroxide and aluminum powder produce a huge amount of heat, so that the sludge is heated to 100°C in 1 minute; ③ oxygen, sodium hydroxide and aluminum powder in the air are combined to generate free radicals, which can decompose sludge particles, destroy the water-locking structure of the sludge, and make the sludge hydrophobic, and at the same time convert bound water into free water that is easy to remove, and the free water is quickly heated to 100°C, becomes water vapor, and quickly escapes in the channel formed by calcium oxide, so that the moisture content of the sludge is reduced to below 33wt% after 1 hour.

[0009] As the preferred technical solution:

[0010] The one-hour sludge drying agent as described above, by weight percentage, also includes 5-10% zero-valent nano-iron, 5-10% heat preservation agent (diatomaceous earth, kaolin or other natural clay), and 5-10% porous biochar; wherein the effects of zero-valent nano-iron include: reducing the valence state of heavy metals, adsorbing heavy metals, increasing the iron content of sludge and thereby improving the nutrients of the nutrient soil made from the sludge; the effects of the heat preservation agent include: acting as a skeleton, diluting water, hindering heat loss, and adsorbing heavy metals; the effects of the porous biochar include: acting as a skeleton, adsorbing heavy metals, and improving the nutrients of the nutrient soil made from the sludge.

[0011] As described above, in a 1-hour sludge drying agent, the average particle size of the porous biochar is 100-200 mesh. Controlling the particle size of the porous biochar is beneficial to reducing the degree of shrinkage during soil drying, improving soil structure, and improving soil water retention capacity.

[0012] The preparation steps of the porous biochar as a 1-hour sludge drying agent as described above are as follows:

[0013] (a) washing the straw (rice, corn) for 3-5 times, drying it at 105-125°C for 10-12 hours, and crushing it to obtain straw powder;

[0014] (b) mixing the straw powder and potassium hydroxide powder uniformly, wherein the mass of the potassium hydroxide is 5-10% of the mass of the straw powder, and carbonizing the mixture in a muffle furnace at 900-1000° C. for 10-12 h under a nitrogen atmosphere;

[0015] (c) Cooling the carbonized product, mixing the carbonized product with a 1-2 mol / L aqueous solution of hydrochloric acid, stirring for 10-15 h, filtering, washing with water until neutral, drying at 105-125° C. for 12-15 h, grinding and sieving to obtain porous biochar.

[0016] As described above, the one-hour sludge drying agent has an average particle size of zero-valent nano-iron of 30-70nm. The present invention sets the particle size of zero-valent nano-iron to 30-70nm based on its high efficiency and wide applicability in environmental remediation and pollution control. This particle size range can maximize its reaction activity, maintain good dispersibility, and expand its application field, thereby playing a greater role in practical applications.

[0017] As described above, the preparation process of the one-hour sludge drying agent, zero-valent nano-iron, is as follows: ferrous sulfate heptahydrate and sodium borohydride in a molar ratio of 2:1-1.2 are added to deionized water, and nitrogen is continuously introduced. After stirring for 5-8 hours, the product is recovered with a magnet, and rinsed with deionized water for 3-5 times, vacuum dried, and ground to obtain zero-valent nano-iron.

[0018] The present invention also provides a sludge drying method, which comprises adding dry biomass (mushroom residue, sawdust, furfural residue, etc.) to sludge with a moisture content of 70-80wt% (obtained by plate and frame filter pressing) and stirring evenly, then adding a drying agent and stirring evenly, and then standing for 1 hour, so that the moisture content of the sludge is reduced to below 33wt%, heavy metals are passivated by 97-99%, harmful bacteria are killed by 100%, and dry sludge is obtained, wherein the drying agent is a 1-hour sludge drying agent as described in any of the above items.

[0019] As the preferred technical solution:

[0020] In the sludge drying method as described above, the mass of the dry biomass is 10-20% of the mass of the sludge, and the mass of the drying agent is 10-30% of the mass of the sludge.

[0021] The present invention also provides a dry sludge, which is prepared by using a sludge drying method as described in any one of the above items.

[0022] The present invention also provides an application of the dry sludge as described above, wherein urea is added to the dry sludge, and nutrient soil particles with a slow-release function are obtained through mechanical granulation, wherein the mass of urea is 60-70% of the mass of the dry sludge.

[0023] Beneficial effects:

[0024] (1) The present invention significantly improves the efficiency of sludge treatment, reduces treatment time and cost, and can quickly dry the sludge to a moisture content of less than 33wt% within 1 hour.

[0025] (2) The present invention utilizes the heat generated by the internal reaction of the desiccant to achieve sludge temperature increase and water evaporation, thereby reducing energy consumption and carbon emissions, and conforming to the concept of green environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1is the sludge in Example 1 ( Figure 1 a) and dry sludge ( Figure 1 (b) Physical picture;

[0027] Figure 2 is the temperature rise curve of the sludge in the drying process in Example 1;

[0028] Figure 3 The change in the number of Escherichia coli in the sludge in Example 1 before and after drying;

[0029] Figure 4 It is the 1-20 day urea release rate of the nutrient soil particles with slow-release function in Example 1. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0031] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0032] Heavy metal passivation rate: Determined in accordance with “Determination of the total amount of 19 metal elements in soil and sediments by inductively coupled plasma mass spectrometry” (HJ 1315-2023).

[0033] Killing rate of harmful bacteria: Determined in accordance with the "Standard Test Method for Urban Sludge" (CJ / T 221-2023) and "Agricultural Sludge Pollutant Control Standard" (GB 4284-2018).

[0034] Urea release rate: Spread 40g of washed quartz sand (particle size 2.5-5mm) evenly on the culture dish, take 10g of nutrient soil particles with slow-release function and put them in the culture dish, spray 5ml of water regularly every day. For 20 consecutive days, take out 2g of quartz sand from the culture dish every day and mix it with 5ml of deionized water, and analyze the urea content in the mixed solution by ultraviolet spectrophotometer.

[0035] Example 1

[0036] A method for preparing nutrient soil particles with a slow-release function, the specific steps are as follows:

[0037] (1) Preparation of raw materials;

[0038] Straw: rice straw;

[0039] Potassium hydroxide;

[0040] Hydrochloric acid aqueous solution: concentration is 1 mol / L;

[0041] Ferrous sulfate heptahydrate;

[0042] Sodium borohydride;

[0043] Deionized water;

[0044] Calcium oxide;

[0045] Sodium hydroxide;

[0046] Aluminum powder;

[0047] Insulation agent: diatomaceous earth;

[0048] Sludge: moisture content is 70wt%, as shown in the figure Figure 1 As shown in a;

[0049] Dry biomass: dried mushroom residue;

[0050] Urea;

[0051] (2) Preparation of porous biochar and zero-valent nano-iron respectively;

[0052] The preparation steps of porous biochar are as follows:

[0053] (a) washing the straw with water for 5 times, drying it at 105°C for 10 h, and crushing it to obtain straw powder;

[0054] (b) mixing straw powder and potassium hydroxide in a mass ratio of 10:1 uniformly, and carbonizing at 900°C for 10 h in a nitrogen atmosphere to obtain a carbonized product;

[0055] (c) cooling the carbonized product, mixing the carbonized product with a hydrochloric acid aqueous solution at a mass ratio of 1:10, stirring for 11 hours, filtering, washing with water until neutral, drying at 105° C. for 12 hours, grinding and sieving to obtain porous biochar with an average particle size of 100 mesh;

[0056] The preparation steps of zero-valent nano-iron are as follows: adding ferrous sulfate heptahydrate and sodium borohydride in a molar ratio of 2:1 into deionized water, and continuously introducing nitrogen gas, stirring for 5 hours, recovering the product with a magnet, and washing it with deionized water for 3 times, vacuum drying, and grinding to obtain zero-valent nano-iron with an average particle size of 30 nm;

[0057] (3) Preparation of 1-hour sludge drying agent;

[0058] In terms of weight percentage, the 1-hour sludge drying agent is composed of 60% calcium oxide, 10% sodium hydroxide, 10% aluminum powder, 5% zero-valent nano-iron, 5% heat preservation agent and 10% porous biochar;

[0059] (4) Preparation of dry sludge;

[0060] Add dry biomass to the sludge and stir evenly, then add a 1-hour sludge drying agent and stir evenly, and then let it stand for 1 hour, so that the moisture content of the sludge is reduced to 33wt%, the heavy metal is passivated by 99%, and the harmful bacteria are killed by 100%, and dry sludge is obtained; wherein the mass of the dry biomass is 10% of the mass of the sludge, and the mass of the 1-hour sludge drying agent is 10% of the mass of the sludge;

[0061] The actual picture of dry sludge is as follows Figure 1 As shown in b, the temperature rise curve of sludge during the drying process is as follows Figure 2 As shown in Figure 2, the number of E. coli in the sludge before and after drying changes as shown in Figure 2. Figure 3 As shown;

[0062] (5) Preparation of nutrient soil particles with slow-release function;

[0063] Urea is added to the dry sludge and granulated mechanically to obtain nutrient soil particles with a slow-release function; wherein the mass of urea is 60% of the mass of the dry sludge.

[0064] The 1-20-day urea release rate of the finally obtained nutrient soil particles with slow-release function is as follows: Figure 4 shown.

[0065] Example 2

[0066] A method for preparing nutrient soil particles with a slow-release function, the specific steps are as follows:

[0067] (1) Preparation of raw materials;

[0068] Straw: rice straw;

[0069] Potassium hydroxide;

[0070] Hydrochloric acid aqueous solution: concentration is 1.5 mol / L;

[0071] Ferrous sulfate heptahydrate;

[0072] Sodium borohydride;

[0073] Deionized water;

[0074] Calcium oxide;

[0075] Sodium hydroxide;

[0076] Aluminum powder;

[0077] Insulation agent: kaolin;

[0078] Sludge: moisture content is 75wt%;

[0079] Dry biomass: dry sawdust;

[0080] Urea;

[0081] (2) Preparation of porous biochar and zero-valent nano-iron respectively;

[0082] The preparation steps of porous biochar are as follows:

[0083] (a) The straw was washed three times with water, dried at 110°C for 11 h, and crushed to obtain straw powder;

[0084] (b) mixing straw powder and potassium hydroxide in a mass ratio of 15:1 uniformly, and carbonizing at 950°C for 11 h in a nitrogen atmosphere to obtain a carbonized product;

[0085] (c) cooling the carbonized product, mixing the carbonized product with a hydrochloric acid aqueous solution at a mass ratio of 1:10, stirring for 12 h, filtering, washing with water until neutral, drying at 110° C. for 13 h, grinding and sieving to obtain porous biochar with an average particle size of 120 mesh;

[0086] The preparation steps of zero-valent nano-iron are as follows: adding ferrous sulfate heptahydrate and sodium borohydride in a molar ratio of 2:1.15 into deionized water, and continuously introducing nitrogen gas, stirring for 6 hours, recovering the product with a magnet, and washing it with deionized water for 4 times, vacuum drying, and grinding to obtain zero-valent nano-iron with an average particle size of 50 nm;

[0087] (3) Preparation of 1-hour sludge drying agent;

[0088] In terms of weight percentage, the 1-hour sludge drying agent is composed of 55% calcium oxide, 5% sodium hydroxide, 10% aluminum powder, 10% zero-valent nano-iron, 10% heat preservation agent and 10% porous biochar;

[0089] (4) Preparation of dry sludge;

[0090] Add dry biomass to the sludge and stir evenly, then add a 1-hour sludge drying agent and stir evenly, and then let it stand for 1 hour, so that the moisture content of the sludge is reduced to 29wt%, the heavy metal is passivated by 98%, and the harmful bacteria are killed by 100%, and dry sludge is obtained; wherein the mass of the dry biomass is 15% of the mass of the sludge, and the mass of the 1-hour sludge drying agent is 15% of the mass of the sludge;

[0091] (5) Preparation of nutrient soil particles with slow-release function;

[0092] Urea is added to the dry sludge and granulated mechanically to obtain nutrient soil particles with a slow-release function; wherein the mass of urea is 65% of the mass of the dry sludge.

[0093] The 20-day urea release rate of the finally prepared nutrient soil particles with slow-release function was 92%.

[0094] Example 3

[0095] A method for preparing nutrient soil particles with a sustained-release function is basically the same as Example 2, except that: in step (3), the weight percentage of sodium hydroxide is 10%, and the weight percentage of zero-valent nano-iron is 5%; in step (4), after standing for 1 hour, the moisture content of the sludge is reduced to 30wt%, the heavy metal is passivated by 99%, and the harmful bacteria are killed by 100%.

[0096] The 1-20 day urea release rate of the finally obtained nutrient soil particles with slow-release function is shown in Table 1:

[0097] Table 1 Time (days) Urea release rate (%) Time (days) Urea release rate (%) 1 20 11 65 2 26 12 68 3 32 13 73 4 35 14 78 5 43 15 82 6 46 16 85 7 51 17 86 8 54 18 85 9 57 19 87 10 64 20 89

[0098] Example 4

[0099] A method for preparing nutrient soil particles with a sustained-release function is basically the same as in Example 2, except that: the zero-valent nano-iron and porous biochar in step (3) are replaced by an equal mass of a heat preservation agent (the same as in Example 3); after standing for 1 hour in step (4), the moisture content of the sludge is reduced to 30wt%, the heavy metals are passivated by 98%, and the harmful bacteria are killed by 100%.

[0100] The 20-day urea release rate of the finally prepared nutrient soil particles with slow-release function was 89%.

[0101] Example 5

[0102] A method for preparing nutrient soil particles with a slow-release function, the specific steps are as follows:

[0103] (1) Preparation of raw materials;

[0104] Straw: corn stover;

[0105] Potassium hydroxide;

[0106] Hydrochloric acid aqueous solution: concentration is 2 mol / L;

[0107] Ferrous sulfate heptahydrate;

[0108] Sodium borohydride;

[0109] Deionized water;

[0110] Calcium oxide;

[0111] Sodium hydroxide;

[0112] Aluminum powder;

[0113] Insulation agent: kaolin;

[0114] Sludge: moisture content is 80wt%;

[0115] Dry biomass: dry furfural residue;

[0116] Urea;

[0117] (2) Preparation of porous biochar and zero-valent nano-iron respectively;

[0118] The preparation steps of porous biochar are as follows:

[0119] (a) washing the straw with water for 5 times, drying it at 125°C for 12 h, and crushing it to obtain straw powder;

[0120] (b) mixing straw powder and potassium hydroxide at a mass ratio of 20:1 uniformly, and carbonizing at 1000°C for 12 h in a nitrogen atmosphere to obtain a carbonized product;

[0121] (c) cooling the carbonized product, mixing the carbonized product with a hydrochloric acid aqueous solution at a mass ratio of 1:10, stirring for 13 h, filtering, washing with water until neutral, drying at 125° C. for 14 h, grinding and sieving to obtain porous biochar with an average particle size of 170 mesh;

[0122] The preparation steps of zero-valent nano-iron are as follows: adding ferrous sulfate heptahydrate and sodium borohydride in a molar ratio of 2:1.2 into deionized water, and continuously introducing nitrogen gas, stirring for 7 hours, recovering the product with a magnet, and washing it with deionized water for 5 times, vacuum drying, and grinding to obtain zero-valent nano-iron with an average particle size of 60 nm;

[0123] (3) Preparation of 1-hour sludge drying agent;

[0124] In terms of weight percentage, the 1-hour sludge drying agent is composed of 50% calcium oxide, 10% sodium hydroxide, 10% aluminum powder, 10% zero-valent nano-iron, 10% heat preservation agent and 10% porous biochar;

[0125] (4) Preparation of dry sludge;

[0126] Add dry biomass to the sludge and stir evenly, then add 1-hour sludge drying agent and stir evenly, and then let it stand for 1 hour, so that the moisture content of the sludge is reduced to 25wt%, the heavy metal is passivated by 97%, and the harmful bacteria are killed by 100%, and dry sludge is obtained; wherein the mass of the dry biomass is 20% of the mass of the sludge, and the mass of the 1-hour sludge drying agent is 20% of the mass of the sludge;

[0127] (5) Preparation of nutrient soil particles with slow-release function;

[0128] Urea is added to the dry sludge and granulated mechanically to obtain nutrient soil particles with a slow-release function; wherein the mass of urea is 70% of the mass of the dry sludge.

[0129] The 20-day urea release rate of the finally prepared nutrient soil particles with slow-release function was 94%.

[0130] Example 6

[0131] A method for preparing nutrient soil particles with a slow-release function, the specific steps are as follows:

[0132] (1) Preparation of raw materials;

[0133] Straw: corn stover;

[0134] Potassium hydroxide;

[0135] Hydrochloric acid aqueous solution: concentration is 2 mol / L;

[0136] Ferrous sulfate heptahydrate;

[0137] Sodium borohydride;

[0138] Deionized water;

[0139] Calcium oxide;

[0140] Sodium hydroxide;

[0141] Aluminum powder;

[0142] Insulation agent: diatomaceous earth;

[0143] Sludge: moisture content is 70wt%;

[0144] Dry biomass: dried mushroom residue;

[0145] Urea;

[0146] (2) Preparation of porous biochar and zero-valent nano-iron respectively;

[0147] The preparation steps of porous biochar are as follows:

[0148] (a) washing the straw with water for 4 times, drying it at 105°C for 10 h, and crushing it to obtain straw powder;

[0149] (b) mixing straw powder and potassium hydroxide at a mass ratio of 20:1 uniformly, and carbonizing at 900°C for 10 h in a nitrogen atmosphere to obtain a carbonized product;

[0150] (c) cooling the carbonized product, mixing the carbonized product with a hydrochloric acid aqueous solution at a mass ratio of 1:10, stirring for 15 h, filtering, washing with water until neutral, drying at 120° C. for 15 h, grinding and sieving to obtain porous biochar with an average particle size of 200 mesh;

[0151] The preparation steps of zero-valent nano-iron are as follows: adding ferrous sulfate heptahydrate and sodium borohydride in a molar ratio of 2:1.2 into deionized water, and continuously introducing nitrogen gas, stirring for 8 hours, recovering the product with a magnet, and washing it with deionized water for 3 times, vacuum drying, and grinding to obtain zero-valent nano-iron with an average particle size of 70 nm;

[0152] (3) Preparation of 1-hour sludge drying agent;

[0153] In terms of weight percentage, the 1-hour sludge drying agent is composed of 60% calcium oxide, 10% sodium hydroxide, 5% aluminum powder, 10% zero-valent nano-iron, 10% heat preservation agent and 5% porous biochar;

[0154] (4) Preparation of dry sludge;

[0155] Add dry biomass to the sludge and stir evenly, then add 1-hour sludge drying agent and stir evenly, and then let it stand for 1 hour, so that the moisture content of the sludge is reduced to 30wt%, the heavy metal is passivated by 98%, and the harmful bacteria are killed by 100%, and dry sludge is obtained; wherein the mass of the dry biomass is 20% of the mass of the sludge, and the mass of the 1-hour sludge drying agent is 30% of the mass of the sludge;

[0156] (5) Preparation of nutrient soil particles with slow-release function;

[0157] Urea is added to the dry sludge and granulated mechanically to obtain nutrient soil particles with a slow-release function; wherein the mass of urea is 70% of the mass of the dry sludge.

[0158] The 20-day urea release rate of the finally prepared nutrient soil particles with slow-release function was 96%.

Claims

1. A 1-hour sludge drying agent, characterized in that: Calculated by weight percentage, it includes 50-60% calcium oxide, 5-10% sodium hydroxide, and 5-10% aluminum powder.

2. A 1-hour-level sludge drying agent according to claim 1, characterized in that: Calculated by weight percentage, it also includes 5-10% zero-valent nano-iron, 5-10% heat preservation agent, and 5-10% porous biochar.

3. A 1-hour-level sludge drying agent according to claim 2, characterized in that, The average particle size of porous biochar is 100-200 mesh.

4. A 1-hour-level sludge drying agent according to claim 3, characterized in that: The preparation steps of porous biochar are as follows: (a) washing the straw, drying it and crushing it to obtain straw powder; (b) mixing the straw powder and potassium hydroxide uniformly, wherein the mass of the potassium hydroxide is 5-10% of the mass of the straw powder, and carbonizing at 900-1000° C. for 10-12 h in a nitrogen atmosphere; (c) Cooling the carbonized product, mixing the carbonized product with a 1-2 mol / L hydrochloric acid aqueous solution, stirring, filtering, washing with water until neutral, drying, grinding and sieving, thereby obtaining porous biochar.

5. A 1-hour-level sludge drying agent according to claim 2, characterized in that: The average particle size of zero-valent nano-iron is 30-70nm.

6. A 1-hour-level sludge drying agent according to claim 5, characterized in that: The preparation process of zero-valent nano-iron is as follows: add ferrous sulfate heptahydrate and sodium borohydride in a molar ratio of 2:1-1.2 into deionized water, and continuously introduce nitrogen. After stirring for 5-8 hours, the product is recovered with a magnet, rinsed with deionized water, vacuum dried, and ground to obtain zero-valent nano-iron.

7. A sludge drying method, characterized in that: Add dry biomass to sludge with a moisture content of 70-80wt% and stir evenly, then add a drying agent and stir evenly, and then let it stand for 1 hour, so that the moisture content of the sludge is reduced to below 33wt%, heavy metals are passivated by 97-99%, and harmful bacteria are killed by 100%, thereby obtaining dry sludge, wherein the drying agent is a 1-hour sludge drying agent as described in any one of claims 1 to 6.

8. A sludge drying method according to claim 7, characterized in that: The mass of the dry biomass is 10-20% of the mass of the sludge, and the mass of the drying agent is 10-30% of the mass of the sludge.

9. A dry sludge, characterized in that: The sludge is prepared by the sludge drying method as described in claim 7 or 8.

10. An application based on the dry sludge according to claim 9, characterized in that: Urea is added to the dry sludge and granulated mechanically to obtain nutrient soil particles with a slow-release function, wherein the mass of urea is 60-70% of the mass of the dry sludge.

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