Method for increasing phosphorite phosphorus content in biochar

Abstract

The invention discloses a method for increasing apatite phosphorus content in biochar, which comprises the following steps: mixing sludge, biomass, biochar and calcium oxide to prepare a mixed material, biologically drying the mixed material for less than or equal to 12 days, adding magnesium chloride after 25 hours in the biologically drying process, pyrolyzing the obtained biologically dried product to obtain the phosphorite phosphorus content in the biochar. The preparation of the biochar is completed. According to the method disclosed by the invention, under the combined action of calcium oxide and magnesium chloride, a biological drying product with low water content and high apatite phosphorus content can be formed through biological drying treatment; the content of phosphorite phosphorus in the biochar can be remarkably increased under the condition of low pyrolysis energy consumption through simple pyrolysis treatment, the biochar with the high phosphorite phosphorus content is obtained, and the method has the advantages of being simple in process, convenient to operate, low in cost, high in drying efficiency, small in pollution gas emission amount, low in energy consumption, environmentally friendly and the like; and the method has important promotion significance for realizing resource utilization of the sludge-based biochar.

Description

Technical Field

[0001] The invention belongs to the field of organic solid waste disposal and resource utilization, and relates to a method for preparing biochar by utilizing dried sludge, and specifically to a method for increasing the apatite phosphorus content in the biochar. Background Art

[0003] As a porous carbon material, biochar has a high specific surface area and abundant surface functional groups. It can not only effectively adsorb heavy metals and organic pollutants in the soil, but also improve soil structure and soil fertility. Therefore, it has broad application prospects in agriculture and environmental remediation. In addition, apatite phosphorus (AP) in biochar is an important phosphorus source with the characteristics of slow release and long-term effect. It can effectively improve the utilization efficiency of soil phosphorus and reduce phosphorus loss and environmental pollution. Compared with traditional chemical phosphate fertilizers, apatite phosphorus in biochar has lower environmental risks and higher ecological benefits. However, the existing technology of preparing biochar by pyrolysis of sludge still has some shortcomings: first, since the sludge contains a large amount of water, the energy consumption in the pyrolysis process of the sludge is high, and the equipment investment cost is large, which limits its large-scale industrial application. Further, the sludge biological drying technology with low cost, environmental friendliness and great resource potential is widely used to reduce the water content of sludge, but the existing conventional sludge biological drying technology still has the following shortcomings: the activity of microorganisms is greatly affected by environmental conditions, the treatment cycle is long, the operating conditions are strict, and odor and greenhouse gases will be generated. At the same time, there are also defects such as low sludge drying efficiency, high and difficult to control pollutant gas emissions, which limits the wide application of sludge in the preparation of biochar. In particular, during the biological drying process of sludge, a large amount of apatite phosphorus is dissolved into the water phase and taken away with the evaporation of water, resulting in a significant decrease in the content of apatite phosphorus in the dried sludge, and ultimately it is difficult to prepare biochar with a high content of apatite phosphorus. Secondly, the stability and biosafety of sludge pyrolysis products still need further research to ensure their safe use in agriculture and environmental remediation. In addition, the existing technology still has some shortcomings in phosphorus control. For example, the release rate and utilization efficiency of phosphorus in biochar are affected by many factors, including the structural characteristics of biochar, soil conditions and microbial activity. The complex interaction of these factors makes it difficult to accurately regulate the controlled release effect of phosphorus. In addition, the existing biochar preparation processes mainly include carbonization, hydrothermal carbonization, gasification, microwave pyrolysis, etc. The following methods need to be further optimized: (a) The pore structure of biochar is low due to the high moisture content of sludge; (b) The high energy consumption during the pyrolysis process due to the high moisture content of sludge makes it difficult to quickly digest a large amount of sludge; (c) The various components in the sludge are easy to react during the pyrolysis process to form new pollutants, resulting in serious secondary pollution problems. At the same time, the preparation process and application method of biochar also need to be further optimized to improve the fixation and release efficiency of phosphorus and achieve efficient utilization of phosphorus resources.For example, in the existing process of preparing biochar from sludge, the sludge is first dried, and then the dried sludge is mixed with calcium oxide and calcium chloride, and placed in a microwave pyrolysis furnace for rapid pyrolysis and carbonization to prepare phosphorus-rich biochar. However, the apatite inorganic phosphorus content in the prepared phosphorus-rich biochar is only 6.44 mg / g at most. Obviously, this method is difficult to effectively increase the apatite phosphorus content, and the apatite phosphorus content in the prepared biochar is still low, making it difficult to achieve efficient utilization of biochar. Therefore, obtaining a sludge drying method with simple process, convenient operation, low processing cost, high drying efficiency, low pollution gas emission, environmental friendliness, and stable phosphorus source is of great significance to improving the AP content of sludge-based biochar and realizing the resource utilization of sludge-based biochar. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for increasing the apatite phosphorus content in biochar with simple process, convenient operation, low cost, high drying efficiency, low pollutant gas emissions, low energy consumption and environmental friendliness in view of the shortcomings of the prior art.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for increasing the apatite phosphorus content in biochar comprises the following steps:

[0007] S1. Mix sludge A, biomass A, biochar A and calcium oxide to obtain a mixed material A;

[0008] S2, bio-drying the mixed material A obtained in step S1, during which magnesium chloride is added to the mixed material A after 25 hours of bio-drying, and the bio-drying time is controlled to be ≤12 days to obtain a bio-drying product;

[0009] S3. Pyrolyzing the bio-dried product obtained in step S2 to complete the preparation of biochar.

[0010] The above method is further improved, in step S2, the biological drying time is 6 days to 11 days.

[0011] The above method is further improved, in step S2, the biological drying process also includes the following treatment: aerating and turning the mixed material A, aerating the mixed material A on day 0, the number of aeration treatments is 3 times, the aeration volume is controlled to be 0.4L / min kg during the aeration treatment, the aeration time of a single aeration treatment is 30min, and the compost is turned once on days 1, 3, 5, 8, 11, 15 and 21.

[0012] The above method is further improved in that in step S2, during the biological drying process, magnesium chloride is added to the mixed material A during the period of 25h to 50h.

[0013] The above method is further improved in that in step S1, the amount of calcium oxide added is 1% to 4% of the dry weight of the mixed material A.

[0014] The above method is further improved in that in step S2, the amount of magnesium chloride added is 1% to 4% of the dry weight of the mixed material A.

[0015] The above method is further improved in that in step S1, the amount of calcium oxide added is 2% to 3% of the dry weight of the mixed material A.

[0016] The above method is further improved, in step S2, the amount of magnesium chloride added is 2% to 3% of the dry weight of the mixed material A; and the magnesium chloride is anhydrous magnesium chloride.

[0017] The above method is further improved in that step S1 further comprises adding domesticated sludge; the amount of the domesticated sludge added is 20% to 25% of the weight of the sludge A.

[0018] The above method is further improved, wherein the domesticated sludge is prepared by domesticating sludge B, biomass B, and biochar B, comprising the following steps:

[0019] (1) mixing sludge B, biomass B, and biochar B to obtain a mixed material B;

[0020] (2) The mixed material B is subjected to acclimation treatment to obtain acclimated sludge.

[0021] The above method is further improved, in step (1), the biomass B is at least one of wheat straw, camellia oleifera cake, camellia oleifera shell, and reed; the amount of biomass B added is 35% to 40% of the weight of the sludge B; the wheat straw is in powder form with a particle size of 4 mm to 5 mm; the camellia oleifera cake is in powder form with a particle size of 20 mesh to 50 mesh; the biochar B is at least one of bamboo charcoal, stalk biochar, peanut shell biochar, sludge biochar, and manure biochar; the amount of biochar B added is 5% of the total dry weight of the sludge B and biomass B; the particle size of the biochar B is 60 mesh to 80 mesh.

[0022] The above method is further improved, in step (2), the acclimation treatment is carried out under aerobic conditions; during the acclimation treatment, the compost is turned at 0, 1, 3, 5, 8, 11, 15 and 21; the acclimation treatment time is 21 days; after the acclimation treatment is completed, the following treatment is also included: placing the material obtained after the acclimation treatment in a bacterial culture room at 60°C for 24 hours.

[0023] The above method is further improved in that in step S1, the moisture content of the mixed material A is 55% to 60%.

[0024] The above method is further improved, wherein the biomass A is at least one of wheat straw, camellia oleifera cake, camellia oleifera shell, and reed; the amount of biomass A added is 35% to 40% of the weight of the sludge A; the wheat straw is in powder form with a particle size of 4 mm to 5 mm; the camellia oleifera cake is in powder form with a particle size of 20 mesh to 50 mesh; the biochar A is at least one of bamboo charcoal, stalk biochar, peanut shell biochar, sludge biochar, and manure biochar; the amount of biochar A added is 5% of the total dry weight of the domesticated sludge, sludge A, and biomass A; the biochar A is in powder form with a particle size of 60 mesh to 80 mesh.

[0025] The above method is further improved, in step S3, the heating rate in the pyrolysis process is 3°C / min, and the heating time is 157min; the pyrolysis is carried out at 500°C; and the pyrolysis time is 120min.

[0026] The above method is further improved in that in step S3, the pyrolysis process also includes introducing nitrogen into the pyrolysis system, and the flow rate of the nitrogen is 200 mL / min.

[0027] Compared with the prior art, the advantages of the present invention are:

[0028] (1) In view of the defects of existing sludge-based biochar, such as high raw material moisture content, high pyrolysis energy consumption, low apatite phosphorus content and difficulty in increasing, the present invention provides a method for increasing the apatite phosphorus content in biochar. Calcium oxide and magnesium chloride are added successively during the biological drying process. Under the joint action of calcium oxide and magnesium chloride, on the one hand, the moisture in the sludge can be efficiently removed and the production of greenhouse gases can be significantly reduced. While effectively reducing greenhouse gas emissions, it also effectively reduces the energy consumption in the subsequent pyrolysis process, making the pyrolysis process more efficient and able to convert biomass in the sludge into biochar faster. On the other hand, phosphorus (including apatite phosphorus) can be retained in the biological drying product to the greatest extent. Specifically, adding calcium oxide first can increase the pH value of the pile in the early stage of biological drying and provide abundant calcium ions, wherein the increase in calcium ion content Adding magnesium chloride will accelerate the formation of insoluble calcium phosphate in the pile, reduce the solubility of apatite phosphorus, and thus increase the phosphorus content in the pile. Further, adding magnesium chloride in the middle stage of biological drying will bring new stress to the microorganisms in the pile, reduce the activity of phosphorus-dissolving microorganisms such as Streptomyces, Bacillus and Pseudomonas, so that the dissolution of insoluble calcium phosphate can be propagated. At the same time, the added magnesium chloride will also provide magnesium ions to the pile, and magnesium ions also contribute to the fixation of phosphorus and the mineralization of biomass, so that a large amount of phosphorus (including apatite phosphorus) can be effectively fixed in the biological drying product. More importantly, in order to avoid the dissolution of insoluble calcium phosphate by phosphorus-dissolving microorganisms, the present invention further optimizes the time of biological drying. By controlling the time of biological drying to ≤12 days, phosphorus (including apatite phosphorus) can be retained in the biological drying product to the greatest extent. On this basis, the biological drying product is pyrolyzed to convert the biological drying product into biochar and retain the apatite phosphorus in the biochar, thereby significantly increasing the content of apatite phosphorus in the biochar. In addition, in the present invention, after the sludge is treated by biological drying, the moisture content is significantly reduced and the texture is looser, so that the sludge can be effectively prevented from adhering and coking during the pyrolysis process, which is beneficial to reduce the wear of the equipment and reduce the maintenance cost and use cost of the equipment; not only that, after the sludge is treated by biological drying, the ash content in the biochar can be reduced, and its calorific value and adsorption performance can be improved. Therefore, the biochar generated by the pyrolysis treatment of the biologically dried sludge has higher purity and better physical and chemical properties, such as better stability of the biochar, which can solve the stability and safety problems of the pyrolysis products. It is worth mentioning that in the process of biological drying, the sludge can remove some volatile organic compounds and heavy metals, thereby reducing the release of these harmful substances during the pyrolysis process and reducing the risk of secondary pollution. Moreover, the dried sludge can generate biochar with different pore sizes and surface functional groups during the pyrolysis process. These characteristics make biochar have a wider application potential in adsorption, catalysis and soil improvement, and can promote the slow release effect of phosphorus and help to improve the activity of microorganisms in the soil.In the method of the present invention, under the joint action of calcium oxide and magnesium chloride, a bio-dried product with low water content and high apatite phosphorus content can be formed through biological drying treatment, and then through simple pyrolysis treatment, the apatite phosphorus content in the biochar can be significantly increased under low pyrolysis energy consumption conditions and biochar with high apatite phosphorus content can be obtained. The method has the advantages of simple process, convenient operation, low cost, high drying efficiency, low pollutant gas emissions, low energy consumption, and environmental friendliness, and is of great significance for promoting the resource utilization of sludge-based biochar.

[0029] (2) In view of the problems of low drying efficiency and large emission of polluting gases in the existing sludge biological drying methods, in the method of the present invention, calcium oxide and magnesium chloride are added successively during the biological drying process. Under the joint action of calcium oxide and magnesium chloride, the moisture in the sludge can be efficiently removed, and the emission of greenhouse gases can be significantly reduced. The details are as follows: (a) The calcium oxide added first accelerates the evaporation of water through an exothermic reaction, and the magnesium chloride added later further reduces the moisture in the sludge through hygroscopic action. In addition, magnesium chloride, as a strong hygroscopic agent, can absorb free moisture in the sludge, and combined with the dehydrating effect of calcium oxide, significantly improves the efficiency of the sludge. The dehydration efficiency of sludge is improved. Moreover, the addition of magnesium chloride can also change the surface tension of sludge, reduce the adhesion between water molecules and sludge particles, and make it easier to separate water from sludge. Therefore, under the synergistic effect of calcium oxide and magnesium chloride, the dehydration speed of sludge is accelerated, thereby shortening the entire drying cycle and improving the drying efficiency. In particular, the water content of sludge treated with calcium oxide and magnesium chloride is greatly reduced, which is more suitable for resource utilization, such as fertilizer, soil conditioner or building material. In addition, this treatment method can also reduce microbial activity and reduce the risk of transmission of pathogens and harmful substances. (b) In terms of affecting the internal environment of sludge, adding calcium oxide first can increase the pH value of sludge, help inhibit microbial activity, and reduce the decomposition of organic matter, while the subsequent addition of magnesium chloride helps to form a stable sludge structure, regulate the osmotic pressure of sludge and promote the degradation of organic matter. Moreover, calcium oxide can neutralize acidic substances in sludge and reduce the generation of odorous gases, while the hygroscopic effect of magnesium chloride helps to control the humidity of sludge and further reduce odor. (c) By adding calcium oxide and magnesium chloride successively, the growth conditions and treatment environment of microorganisms can be controlled to ensure the stability and safety of the treatment process and provide favorable conditions for the growth environment of microorganisms. Specifically, on the one hand, calcium oxide, as an alkaline substance, can neutralize the acidic substances in the sludge and increase the pH value of the sludge. The adjustment of this pH value helps to create an environment suitable for the growth and metabolism of microorganisms. In addition, the chemical reaction of calcium oxide and magnesium chloride can generate calcium hydroxide and calcium chloride. These compounds can provide certain microorganisms with the necessary calcium and magnesium nutrients and promote their growth and metabolic activities. On the other hand, adding calcium oxide first can increase the temperature of the sludge, provide a suitable growth environment for certain thermophilic microorganisms, and accelerate the metabolic rate of microorganisms. The magnesium chloride added later can reduce the moisture content of the sludge due to its hygroscopic effect, reduce the inhibitory effect of moisture on microbial metabolism, and thus promote the metabolic activities of microorganisms.(d) In terms of the physical and chemical properties of sludge, the addition of calcium oxide and magnesium chloride can improve the physical structure of sludge, increase porosity, provide more oxygen, and reduce certain substances in sludge that inhibit the growth of microorganisms, such as heavy metals and toxic organic compounds, thereby improving the activity of microorganisms and enhancing the tolerance of microorganisms to environmental changes. In addition, the addition of calcium oxide and magnesium chloride can change the chemical environment of sludge, which may promote the formation and stability of different microbial communities and increase the diversity of microbial communities. (e) The addition of calcium oxide and magnesium chloride successively can not only ensure efficient water removal, but also reduce the energy loss in the biological drying process. Specifically: Under normal circumstances, biological drying requires a large amount of energy to achieve the drying and processing of materials. In the present invention, after the addition of calcium oxide and magnesium chloride successively, the situation has undergone a positive change. Calcium oxide has a strong water absorption capacity. It can react chemically with the water in the material to generate calcium hydroxide and release heat. This part of heat can accelerate the evaporation of water and reduce the energy required for external heating. At the same time, calcium hydroxide can adjust the pH of the material, optimize the living environment of microorganisms, promote the metabolic activity of microorganisms, and improve Drying efficiency. Further, the magnesium chloride added later can form crystalline hydrates under certain conditions, absorb moisture in the material, and thus reduce the moisture content. In addition, magnesium chloride can also affect the cell osmotic pressure of microorganisms, regulate the metabolic process of microorganisms, and enhance the ability of microorganisms to decompose organic matter to generate heat, which helps to reduce the input of external energy. It can be seen that under the joint action of the unique chemical properties of calcium oxide and magnesium chloride, the chemical reactions in the biological drying process can be effectively promoted, thereby reducing dependence on external energy, not only reducing energy input, but also optimizing the energy utilization efficiency of the entire biological drying process, so that the original high energy consumption process has been significantly improved. (f) By adding calcium oxide and magnesium chloride in sequence, greenhouse gas emissions during the biological drying of sludge can be reduced. Specifically, calcium oxide will form calcium hydroxide after dissolving in water, which can increase the pH value of the system. This alkaline environment helps to inhibit the growth of anaerobic microorganisms and reduce the production of greenhouse gases such as methane. In addition, calcium oxide reacts with water to form calcium hydroxide, which further reacts with carbon dioxide to form calcium carbonate, thereby reducing the concentration of carbon dioxide in the atmosphere. More importantly, magnesium chloride can act as a catalyst to promote the decomposition and conversion of organic matter and reduce the emission of greenhouse gases (such as methane and carbon dioxide) produced under anaerobic conditions. Moreover, after adding calcium oxide and magnesium chloride, the dried biomass can be used as a fertilizer to improve the quality of sludge, reduce the release of volatile organic matter, and increase the carbon storage capacity of sludge, thereby indirectly reducing greenhouse gas emissions.Therefore, in the method of the present invention, by successively adding calcium oxide and magnesium chloride during the biological drying process, the moisture in the sludge can be efficiently removed under the joint action of calcium oxide and magnesium chloride, and the emission of greenhouse gases can be significantly reduced. It has the advantages of low drying cost, high drying efficiency, less polluting gas, and environmental friendliness. It can not only effectively solve the problem of greenhouse gas emission reduction in the sludge biological drying process, but also is conducive to achieving rapid sludge reduction, high use value, and good application prospects.

[0030] (3) In the present invention, by optimizing the addition amount of calcium oxide to 1% to 4% of the dry weight of the mixture A, especially when the addition amount of calcium oxide is 2% to 3% of the dry weight of the mixture A, not only can the pH value of the pile (mixed material A) be adjusted to a suitable range, but also the composition and richness of the microorganisms in the pile can be optimized, so that the moisture in the pile can be removed more quickly and efficiently. When the dosage of calcium oxide is too low, it is not conducive to the regulation of the pH value of the pile, and it is difficult to obtain a suitable pH. When the dosage of calcium oxide is too high, it will seriously stress the microbial community structure, making it difficult to use microbial heat to improve the drying effect. In addition, in the present invention, by optimizing the addition amount of magnesium chloride to 1% to 4% of the dry weight of the mixture A, especially when the addition amount of magnesium chloride is 2% to 3% of the dry weight of the mixture A, the mineralization rate of organic matter in the pile can be effectively promoted, and a weakly acidic pH value can be provided for the pile microorganisms.

[0031] (4) In the present invention, the biological drying system also includes: adding domesticated sludge, wherein the domesticated sludge is prepared by domesticating sludge, biomass, and biochar. By adding domesticated sludge, efficient inoculation of microorganisms in sludge biological drying can be achieved, which is not only beneficial to improving the quality of sludge, but also can significantly improve the efficiency and effect of sludge treatment. In addition, the sludge biological drying technology of adding domesticated products in the present invention also has the following advantages: it can accelerate the decomposition of organic matter and improve sludge stability; reduce odor and reduce greenhouse gas emissions; improve resource utilization potential and reduce the use of chemical additives; enhance sludge biological activity and increase calorific value; promote harmless treatment and improve treatment flexibility; reduce energy consumption and promote ecological circulation; improve safety. These advantages show that adding domesticated sludge has important application value and prospects in the process of sludge biological drying. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0033] Figure 1 This is a process flow chart for reducing sludge moisture content and greenhouse gas emissions during biological drying in Example 1 of the present invention.

[0034] Figure 2 This is a diagram showing changes in system temperature during the biodrying process of Example 1 of the present invention and Comparative Examples 1-4.

[0035] Figure 3 This is a diagram showing changes in the moisture content of the system during the biological drying process of Example 1 of the present invention and Comparative Examples 1-4.

[0036] Figure 4 This is a diagram showing changes in greenhouse gas potential values ​​of the system during the biological drying process of Example 1 of the present invention and Comparative Examples 1-4.

[0037] Figure 5 This is a graph showing changes in apatite phosphorus content in sludge-based biochar prepared in Example 1 and Comparative Examples 1-4 of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0039] The materials and instruments used in the following examples are all commercially available.

[0040] Embodiment 1:

[0041] A method for reducing the moisture content of sludge and greenhouse gas emissions during biological drying, the process flow chart of which is as follows Figure 1 As shown, the following steps are included:

[0042] (1) preparing domesticated sludge, which is obtained by domesticating sludge B, biomass B, and biochar B, specifically:

[0043] (1.1) Bamboo charcoal, wheat straw and camellia oleifera cake are dried, crushed and sieved respectively to obtain bamboo charcoal powder with a particle size of 60 to 80 mesh, wheat straw with a particle size of 4 to 5 mm and camellia oleifera cake powder with a particle size of 20 to 50 mesh.

[0044] (1.2) According to the addition amount of wheat straw and camellia oleifera cake being 20% ​​and 16.67% of the sludge weight, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, 94.6g of bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly to obtain a mixed material B.

[0045] (1.2) The mixed material B is subjected to a 21-day acclimation treatment. During the acclimation treatment, the compost is turned on days 0, 1, 3, 5, 8, 11, 15 and 21. After 21 days of acclimation, the material is placed in a bacterial culture room at 60°C for 24 hours to obtain an acclimation product, namely, acclimated sludge.

[0046] (2) According to the addition amount of domesticated sludge, wheat straw and camellia oleifera cake being 21%, 20% and 16.67% of the weight of the sludge, 630g of domesticated sludge, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total weight of the semi-mixed material, bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly, and the moisture content of the material was adjusted to 55% to obtain a mixed material A; according to the addition amount of calcium oxide being 2.5% of the dry weight of the mixed material A, calcium oxide was added to the mixed material A for biological drying treatment, wherein the biological drying treatment time was 11 days and 21 days; at the same time, during the biological drying process, anhydrous magnesium chloride was added to the mixed material A at 48h (the second day), wherein the addition amount of anhydrous magnesium chloride was 2.5% of the dry weight of the mixed material A.

[0047] The biological drying process of step (2) also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, aerating the mixed material A three times, controlling the aeration volume (air) to be 0.4 L / min kg during the aeration process, and turning the compost once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying of the sludge and obtain a biological drying product.

[0048] (3) pyrolyzing the bio-dried product obtained after biological treatment for 11 days and 21 days in step (2), specifically:

[0049] (3.1) After the bio-drying is completed, the bio-drying product is crushed and sieved to 100-150 mesh to obtain the bio-drying product powder.

[0050] (3.2) The powder of the biological drying product is placed in a quartz boat, weighed, and placed in a tube furnace for pyrolysis treatment. The heating rate of the pyrolysis process is 3°C / min, the heating time is 157min, the temperature is raised to 500°C, and pyrolysis is carried out at 500°C for 120min. Metal plugs are plugged at both ends of the tube furnace to prevent the sample from leaking out and to prevent the outside air from entering the tube furnace. At the same time, nitrogen is introduced into the tube furnace during the pyrolysis process to allow the gas generated during the pyrolysis process to be discharged and to fill the tube furnace with nitrogen. The flow rate of nitrogen is 200mL / min. After the pyrolysis is completed, it is cooled, taken out and weighed to obtain sludge-based biochar.

[0051] Comparative Example 1:

[0052] A biological drying method for sludge is basically the same as Example 1, except that in Comparative Example 1, calcium oxide and magnesium chloride are not added.

[0053] In Comparative Example 1, the biological drying method of sludge comprises the following steps:

[0054] (1) preparing domesticated sludge, which is obtained by domesticating sludge B, biomass B, and biochar B, specifically:

[0055] (1.1) Bamboo charcoal, wheat straw and camellia oleifera cake are dried, crushed and sieved respectively to obtain bamboo charcoal powder with a particle size of 60 to 80 mesh, wheat straw with a particle size of 4 to 5 mm and camellia oleifera cake powder with a particle size of 20 to 50 mesh.

[0056] (1.2) According to the addition amount of wheat straw and camellia oleifera cake being 20% ​​and 16.67% of the sludge weight, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, 94.6g of bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly to obtain a mixed material B.

[0057] (1.2) The mixed material B is subjected to a 21-day acclimation treatment. During the acclimation treatment, the compost is turned on days 0, 1, 3, 5, 8, 11, 15 and 21. After 21 days of acclimation, the material is placed in a bacterial culture room at 60°C for 24 hours to obtain an acclimation product, namely, acclimated sludge.

[0058] (2) According to the addition amount of domesticated sludge, wheat straw and camellia oleifera cake being 21%, 20% and 16.67% of the sludge weight, 630g of domesticated sludge, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed uniformly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total weight of the semi-mixed material, bamboo charcoal was added to the semi-mixed material, and the mixture was mixed uniformly, and the moisture content of the material was adjusted to 55% to obtain a mixed material A; the mixed material A was subjected to biological drying treatment for 11 days and 21 days.

[0059] The biological drying process of step (2) also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, aerating the mixed material A three times, controlling the aeration volume to be 0.4 L / min kg during the aeration process, and turning the compost once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying of the sludge.

[0060] (3) pyrolyzing the bio-dried product obtained after biological treatment for 11 days and 21 days in step (2), specifically:

[0061] (3.1) After the bio-drying is completed, the bio-drying product is crushed and sieved to 100-150 mesh to obtain the bio-drying product powder.

[0062] (3.2) The powder of the biological drying product is placed in a quartz boat, weighed, and placed in a tube furnace for pyrolysis treatment. The heating rate of the pyrolysis process is 3°C / min, the heating time is 157min, the temperature is raised to 500°C, and pyrolysis is carried out at 500°C for 120min. Metal plugs are plugged at both ends of the tube furnace to prevent the sample from leaking out and to prevent the outside air from entering the tube furnace. At the same time, nitrogen is introduced into the tube furnace during the pyrolysis process to discharge the gas generated during the pyrolysis process and to fill the tube furnace with nitrogen. The flow rate of nitrogen is 200mL / min. After the pyrolysis is completed, it is cooled, taken out and weighed to obtain sludge-based biochar.

[0063] Comparative Example 2:

[0064] A biological drying method for sludge is basically the same as Example 1, except that in Comparative Example 2, calcium oxide is not added, and magnesium chloride is directly added to the mixed material A.

[0065] In Comparative Example 2, the biological drying method of sludge comprises the following steps:

[0066] (1) preparing domesticated sludge, which is obtained by domesticating sludge B, biomass B, and biochar B, specifically:

[0067] (1.1) Bamboo charcoal, wheat straw and camellia oleifera cake are dried, crushed and sieved respectively to obtain bamboo charcoal powder with a particle size of 60 to 80 mesh, wheat straw with a particle size of 4 to 5 mm and camellia oleifera cake powder with a particle size of 20 to 50 mesh.

[0068] (1.2) According to the addition amount of wheat straw and camellia oleifera cake being 20% ​​and 16.67% of the sludge weight, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, 94.6g of bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly to obtain a mixed material B.

[0069] (1.2) The mixed material B is subjected to a 21-day acclimation treatment. During the acclimation treatment, the compost is turned on days 0, 1, 3, 5, 8, 11, 15 and 21. After 21 days of acclimation, the material is placed in a bacterial culture room at 60°C for 24 hours to obtain an acclimation product, namely, acclimated sludge.

[0070] (2) According to the addition amount of domesticated sludge, wheat straw and camellia oleifera cake being 21%, 20% and 16.67% of the weight of the sludge, 630g of domesticated sludge, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total weight of the semi-mixed material, bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly, and the moisture content of the material was adjusted to 55% to obtain a mixed material A; according to the addition amount of anhydrous magnesium chloride being 5% of the dry weight of the mixed material A, anhydrous magnesium chloride was added to the mixed material A for biological drying treatment for 11 days and 21 days.

[0071] The biological drying process of step (2) also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, aerating the mixed material A three times, controlling the aeration volume to be 0.4 L / min kg during the aeration process, and turning the compost once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying of the sludge.

[0072] (3) pyrolyzing the bio-dried product obtained after biological treatment for 11 days and 21 days in step (2), specifically:

[0073] (3.1) After the bio-drying is completed, the bio-drying product is crushed and sieved to 100-150 mesh to obtain the bio-drying product powder.

[0074] (3.2) The powder of the biological drying product is placed in a quartz boat, weighed, and placed in a tube furnace for pyrolysis treatment. The heating rate of the pyrolysis process is 3°C / min, the heating time is 157min, the temperature is raised to 500°C, and pyrolysis is carried out at 500°C for 120min. Metal plugs are plugged at both ends of the tube furnace to prevent the sample from leaking out and to prevent the outside air from entering the tube furnace. At the same time, nitrogen is introduced into the tube furnace during the pyrolysis process to allow the gas generated during the pyrolysis process to be discharged and to fill the tube furnace with nitrogen. The flow rate of nitrogen is 200mL / min. After the pyrolysis is completed, it is cooled, taken out and weighed to obtain sludge-based biochar.

[0075] Comparative Example 3:

[0076] A biological drying method for sludge is basically the same as Example 1, except that in Comparative Example 3, magnesium chloride is not added.

[0077] The biological drying method of sludge used in Comparative Example 3 comprises the following steps:

[0078] (1) preparing domesticated sludge, which is obtained by domesticating sludge B, biomass B, and biochar B, specifically:

[0079] (1.1) Bamboo charcoal, wheat straw and camellia oleifera cake are dried, crushed and sieved respectively to obtain bamboo charcoal powder with a particle size of 60 to 80 mesh, wheat straw with a particle size of 4 to 5 mm and camellia oleifera cake powder with a particle size of 20 to 50 mesh.

[0080] (1.2) According to the addition amount of wheat straw and camellia oleifera cake being 20% ​​and 16.67% of the sludge weight, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, 94.6g of bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly to obtain a mixed material B.

[0081] (1.2) The mixed material B is subjected to a 21-day acclimation treatment. During the acclimation treatment, the compost is turned on days 0, 1, 3, 5, 8, 11, 15 and 21. After 21 days of acclimation, the material is placed in a bacterial culture room at 60°C for 24 hours to obtain an acclimation product, namely, acclimated sludge.

[0082] (2) According to the addition amount of domesticated sludge, wheat straw and camellia oleifera cake being 21%, 20% and 16.67% of the sludge weight, 630g of domesticated sludge, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total weight of the semi-mixed material, bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly, and the moisture content of the material was adjusted to 55% to obtain a mixed material A; according to the addition amount of calcium oxide being 5% of the dry weight of the mixed material A, calcium oxide was added to the mixed material A for biological drying treatment for 11 days and 21 days.

[0083] The biological drying process of step (2) also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, aerating the mixed material A three times, controlling the aeration volume to be 0.4 L / min kg during the aeration process, and turning the compost once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying of the sludge.

[0084] (3) pyrolyzing the bio-dried product obtained after biological treatment for 11 days and 21 days in step (2), specifically:

[0085] (3.1) After the bio-drying is completed, the bio-drying product is crushed and sieved to 100-150 mesh to obtain the bio-drying product powder.

[0086] (3.2) The powder of the biological drying product is placed in a quartz boat, weighed, and placed in a tube furnace for pyrolysis treatment. The heating rate of the pyrolysis process is 3°C / min, the heating time is 157min, the temperature is raised to 500°C, and pyrolysis is carried out at 500°C for 120min. Metal plugs are plugged at both ends of the tube furnace to prevent the sample from leaking out and to prevent the outside air from entering the tube furnace. At the same time, nitrogen is introduced into the tube furnace during the pyrolysis process to discharge the gas generated during the pyrolysis process and to fill the tube furnace with nitrogen. The flow rate of nitrogen is 200mL / min. After the pyrolysis is completed, it is cooled, taken out and weighed to obtain sludge-based biochar.

[0087] Comparative Example 4:

[0088] A biological drying method for sludge is basically the same as Example 1, except that in Comparative Example 4, the order of adding calcium oxide and magnesium chloride is reversed.

[0089] The biological drying method of sludge used in Comparative Example 3 comprises the following steps:

[0090] (1) preparing domesticated sludge, which is obtained by domesticating sludge B, biomass B, and biochar B, specifically:

[0091] (1.1) Bamboo charcoal, wheat straw and camellia oleifera cake are dried, crushed and sieved respectively to obtain bamboo charcoal powder with a particle size of 60 to 80 mesh, wheat straw with a particle size of 4 to 5 mm and camellia oleifera cake powder with a particle size of 20 to 50 mesh.

[0092] (1.2) According to the addition amount of wheat straw and camellia oleifera cake being 20% ​​and 16.67% of the sludge weight, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total dry weight of the semi-mixed material, 94.6g of bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly to obtain a mixed material B.

[0093] (1.2) The mixed material B is subjected to a 21-day acclimation treatment. During the acclimation treatment, the compost is turned on days 0, 1, 3, 5, 8, 11, 15 and 21. After 21 days of acclimation, the material is placed in a bacterial culture room at 60°C for 24 hours to obtain an acclimation product, namely, acclimated sludge.

[0094] (2) According to the addition amount of domesticated sludge, wheat straw and camellia oleifera cake being 21%, 20% and 16.67% of the weight of the sludge, 630g of domesticated sludge, 600g of wheat straw and 500g of camellia oleifera cake were added to 3000g of original sludge (with a moisture content of 80%), and the mixture was mixed evenly to obtain a semi-mixed material; according to the addition amount of biochar being 5% of the total weight of the semi-mixed material, bamboo charcoal was added to the semi-mixed material, and the mixture was mixed evenly, and the moisture content of the material was adjusted to 55% to obtain a mixed material A; according to the addition amount of anhydrous magnesium chloride being 2.5% of the dry weight of the mixed material A, anhydrous magnesium chloride was added to the mixed material A for biological drying treatment for 11 days and 21 days. During the biological drying process, calcium oxide was added to the mixed material A at 48h (the second day), wherein the addition amount of calcium oxide was 2.5% of the dry weight of the mixed material A.

[0095] The biological drying process of step (2) also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, aerating the mixed material A three times, controlling the aeration volume to be 0.4 L / min kg during the aeration process, and turning the compost once on days 1, 3, 5, 8, 11, 15 and 21 to complete the biological drying of the sludge.

[0096] (3) pyrolyzing the bio-dried product obtained after biological treatment for 11 days and 21 days in step (2), specifically:

[0097] (3.1) After the bio-drying is completed, the bio-drying product is crushed and sieved to 100-150 mesh to obtain the bio-drying product powder.

[0098] (3.2) The powder of the biological drying product is placed in a quartz boat, weighed, and placed in a tube furnace for pyrolysis treatment. The heating rate of the pyrolysis process is 3°C / min, the heating time is 157min, the temperature is raised to 500°C, and pyrolysis is carried out at 500°C for 120min. Metal plugs are plugged at both ends of the tube furnace to prevent the sample from leaking out and to prevent the outside air from entering the tube furnace. At the same time, nitrogen is introduced into the tube furnace during the pyrolysis process to allow the gas generated during the pyrolysis process to be discharged and to fill the tube furnace with nitrogen. The flow rate of nitrogen is 200mL / min. After the pyrolysis is completed, it is cooled, taken out and weighed to obtain sludge-based biochar.

[0099] During the biological drying process of Example 1 and Comparative Examples 1-4, the temperature, moisture content and greenhouse gas potential (GWP) in the system were monitored in real time. The results are as follows: Figures 2 to 4 At the same time, the changes in apatite phosphorus content in sludge-based biochar were tested, and the results were as follows Figure 5 shown.

[0100] Depend on Figure 2 It can be seen that in Comparative Example 1, when calcium oxide and magnesium chloride were not added, no stress was exerted on the pile, and the temperature of the biological drying system could rise to 59.0°C at the highest, but there was still a defect of low biological drying temperature. In Comparative Example 2, when magnesium chloride was added alone, no stress was exerted on the pile, and the temperature of the biological drying system could rise to 59.6°C at the highest, but there was still a defect of low biological drying temperature. In Comparative Example 3, when calcium oxide is added alone, the temperature of the bio-drying system can rise to a maximum of 51.2°C on the 2nd to 3rd day, and there are defects of slow heating rate and low bio-drying temperature. The reasons are: on the one hand, although calcium oxide has an exothermic effect after absorbing water, this effect has an immediate effect, so the temperature will drop quickly, and in a larger bio-drying system, this heat is relatively small; on the other hand, calcium oxide has a bactericidal effect and will destroy the community structure of microorganisms in the pile, and the temperature of the pile is mainly generated by the metabolism of microorganisms, so adding calcium oxide in the early stage of bio-drying is not conducive to the heating of the pile. In particular, the calcium oxide added in Comparative Example 3 is 5% of the dry weight of the mixed material. Excessive calcium oxide has a stronger stress effect on the pile, which is not conducive to improving the metabolic rate of alkaliphilic thermophilic microorganisms, so the heating is slower and the maximum temperature is lower. In comparative example 4, magnesium chloride is added first, and then calcium oxide is added. On the 1st to 2nd day, the temperature of the biological drying system can rise to a maximum of 53.7°C. There are defects of slow heating rate and low biological drying temperature. The reason is that the calcium oxide is added at the heating stage of the biological drying system. The calcium oxide added at this time will destroy the bacterial community structure and inhibit the heating process of the pile body because calcium oxide itself has a bactericidal effect. At the same time, although the pile body will restore part of the bacterial community after adding calcium oxide, this time point has missed the optimal heating period of the biological drying system. Therefore, the order of adding magnesium chloride first and then calcium oxide is not conducive to improving the drying effect. Completely different from them, in Example 1, calcium oxide is added first and then magnesium chloride, and the biological drying temperature can rise to a maximum of 63.28°C within the 1st to 2nd day. In addition, in the existing conventional sludge biological drying method, it takes at least 2 to 4 days to heat up to the highest temperature, that is, the system temperature can be raised to the highest after 2 to 4 days of biological drying, and there is also a defect of slow heating rate. It can be seen that compared with the conventional sludge biological drying method, the present invention successively adds calcium oxide and magnesium chloride in the biological drying system. Under the joint action of calcium oxide and magnesium chloride, it is beneficial to quickly increase the temperature of the sludge, thereby facilitating the effective removal of water in the sludge.

[0101] Depend on Figure 3It can be seen that in Comparative Example 1, when calcium oxide and magnesium chloride are not added, the final moisture content of bio-drying can reach 15.94%; in Comparative Example 2, when magnesium chloride is added alone, the final moisture content of bio-drying can reach 22.13%; in Comparative Example 3, when calcium oxide is added alone, the final moisture content of bio-drying can reach 25.27%; in Comparative Example 4, magnesium chloride is added first, and then calcium oxide is added. After 11 days of bio-drying, the moisture content of bio-drying is as high as 15% or more, and after 21 days of bio-drying, the final moisture content of bio-drying can reach 11.65%. Completely different from them, in Example 1, calcium oxide is added first, and then magnesium chloride is added. After 8 days of bio-drying, the moisture content of bio-drying can be reduced to 10%, and after 11 days of bio-drying, the moisture content of bio-drying can be kept within 10%, and the final moisture content of bio-drying can reach 7.76%. In addition, in the conventional sludge biological drying method, the moisture content of the biological drying can only be reduced to 26.9% after 11 days of biological drying. By comparison, compared with the conventional sludge biological drying method, the present invention adds calcium oxide and magnesium chloride in the biological drying system in sequence, and under the joint action of calcium oxide and magnesium chloride, the moisture in the sludge can be efficiently removed, thereby significantly reducing the moisture content of the sludge during the biological drying process.

[0102] Depend on Figure 4 It can be seen that in Comparative Example 1, when calcium oxide and magnesium chloride are not added, the greenhouse gas potential caused by greenhouse gas emissions during the biological drying process is 354.29 g / m 2 In Comparative Example 2, the greenhouse gas potential caused by the emission of greenhouse gases during the biological drying process when magnesium chloride was added alone was 186.22 g / m 2 In Comparative Example 3, when calcium oxide was added alone, the greenhouse gas potential caused by greenhouse gas emissions during the biological drying process was 340.14 g / m 2 In comparative example 4, magnesium chloride was added first and then calcium oxide. The greenhouse gas potential caused by greenhouse gas emissions during the biological drying process was 186.70 g / m 2 In contrast, in Example 1, calcium oxide was added first and then magnesium chloride. The greenhouse gas potential caused by greenhouse gas emissions during the biological drying process was 104.24 g / m 2. The emission of greenhouse gases in biological systems is mainly the result of microbial activities, and in the operation of reducing greenhouse gas emissions, the order of adding additives mainly reduces greenhouse gas emissions from two directions. The first aspect is to rely on the inherent chemical properties of calcium oxide. Since the emission of greenhouse gases has already begun in the initial stage of biological drying, adding calcium oxide first can reduce carbon dioxide emissions throughout the entire biological drying cycle, while in Example 4, calcium oxide is added on the second day, and it is difficult to rely on calcium oxide to absorb a large amount of carbon dioxide emitted during the heating and high temperature stages, so the overall emission reduction effect is weaker than Example 1. The second aspect is achieved by relying on the microbial community structure in the pile. By optimizing the order of adding calcium oxide and magnesium chloride, their stress effects on bacteria can be utilized to construct a suitable microbial community structure, thereby effectively improving the carbon dioxide emission reduction effect. Specifically, in Example 1, calcium oxide is added first, which can promote the growth and reproduction of thermophilic microorganisms, which is beneficial to improving the drying effect, while inhibiting the growth and reproduction of anaerobic microorganisms, which is beneficial to reducing the water production of greenhouse gases such as methane. By comparison, it can be seen that compared with the conventional sludge biological drying method, in the present invention, calcium oxide and magnesium chloride are added successively in the biological drying system. Under the joint action of calcium oxide and magnesium chloride, the emission of greenhouse gases in the biological drying process can be significantly reduced.

[0103] Depend on Figure 5 It can be seen that in Comparative Example 1, when the product after 11 days of biological drying was subjected to pyrolysis treatment, the maximum apatite phosphorus content in the prepared sludge-based biochar was 20.33 mg / g. In Comparative Example 2, when the product after 11 days of biological drying was subjected to pyrolysis treatment, the maximum apatite phosphorus content in the prepared sludge-based biochar was 20.52 mg / g. In Comparative Example 3, when the product after 11 days of biological drying was subjected to pyrolysis treatment, the maximum apatite phosphorus content in the prepared sludge-based biochar was 21.73 mg / g. In Comparative Example 4, when the product after 11 days of biological drying was subjected to pyrolysis treatment, the maximum apatite phosphorus content in the prepared sludge-based biochar was 21.53 mg / g. Compared with Comparative Example 1, the apatite phosphorus content in the biochar in the dried sludge pyrolysis system of Comparative Example 4 was only increased by 8.69%. Different from them, in Example 1, when the product after 11 days of biological drying was pyrolyzed, the apatite phosphorus content in the prepared sludge-based biochar was as high as 23.70 mg / g. Compared with Comparative Example 1, the apatite phosphorus content of the biochar in the dried sludge pyrolysis system of Example 1 increased by 16.57%. Figure 5It can be seen that when the product after 21 days of biological drying is subjected to pyrolysis treatment, the apatite phosphorus content in the prepared sludge-based biochar is significantly reduced. This may be due to the long drying time, the competition between nutrients such as carbon, nitrogen, and phosphorus in the sludge, which promotes the release of apatite phosphorus, and due to the continuous microbial activity, more non-apatite inorganic phosphorus is biologically utilized, that is, the phosphorus content in the prepared biological drying product is significantly reduced, and finally the apatite phosphorus content in the prepared sludge-based biochar is significantly reduced. It can be seen that in the present invention, when the product with a biological drying time of less than 12 days is used as a raw material for preparing sludge-based biochar, the apatite phosphorus content in the biochar can be significantly increased.

[0104] It can be seen from the above results that compared with conventional sludge biological drying, in the method of the present invention, under the joint action of calcium oxide and magnesium chloride, a biological drying product with low water content and high apatite phosphorus content can be formed through biological drying treatment, and then through simple pyrolysis treatment, the apatite phosphorus content in the biochar can be significantly increased under low pyrolysis energy consumption conditions and biochar with high apatite phosphorus content can be obtained. It has the advantages of simple process, convenient operation, low cost, high drying efficiency, low pollution gas emissions, low energy consumption, and environmental friendliness, which is of great significance for realizing the resource utilization of sludge-based biochar.

[0105] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for increasing the apatite phosphorus content in biochar, characterized in that: The following steps are involved: S1. Mix sludge A, biomass A, biochar A and calcium oxide to obtain a mixed material A; S2, bio-drying the mixed material A obtained in step S1, during which magnesium chloride is added to the mixed material A after 25 hours of bio-drying, and the bio-drying time is controlled to be ≤12 days to obtain a bio-drying product; S3. Pyrolyzing the bio-dried product obtained in step S2 to complete the preparation of biochar.

2. The method according to claim 1, characterized in that In step S2, the biological drying time is 6 to 11 days.

3. The method according to claim 2, characterized in that In step S2, the biological drying process also includes the following treatments: aerating and turning the mixed material A, aerating the mixed material A on day 0, the number of aeration treatments is 3 times, the aeration volume is controlled at 0.4 L / min kg during the aeration treatment, the aeration time of a single aeration treatment is 30 min, and the compost is turned once on days 1, 3, 5, 8, 11, 15 and 21.

4. The method according to claim 2, characterized in that In step S2, during the biological drying process, magnesium chloride is added to the mixed material A during the period of 25 hours to 50 hours.

5. The method according to claim 4, characterized in that In step S1, the amount of calcium oxide added is 1% to 4% of the dry weight of the mixed material A; In step S2, the amount of magnesium chloride added is 1% to 4% of the dry weight of the mixed material A.

6. The method according to claim 5, characterized in that In step S1, the amount of calcium oxide added is 2% to 3% of the dry weight of the mixed material A; In step S2, the amount of magnesium chloride added is 2% to 3% of the dry weight of the mixed material A; and the magnesium chloride is anhydrous magnesium chloride.

7. The method according to any one of claims 1 to 6, characterized in that: Step S1 further includes adding domesticated sludge; the amount of the domesticated sludge added is 20% to 25% of the weight of the sludge A; the domesticated sludge is prepared by domesticating sludge B, biomass B, and biochar B, and includes the following steps: (1) Mixing sludge B, biomass B, and biochar B to obtain a mixed material B; the biomass B is at least one of wheat straw, camellia oleifera cake, camellia oleifera shell, and reed; the amount of biomass B added is 35% to 40% of the weight of the sludge B; the wheat straw is in powder form with a particle size of 4 mm to 5 mm; the camellia oleifera cake is in powder form with a particle size of 20 mesh to 50 mesh; the biochar B is at least one of bamboo charcoal, stalk biochar, peanut shell biochar, sludge biochar, and manure biochar; the amount of biochar B added is 5% of the total dry weight of the sludge B and biomass B; the particle size of the biochar B is 60 mesh to 80 mesh; (2) The mixed material B is subjected to acclimation treatment to obtain acclimated sludge; the acclimation treatment is carried out under aerobic conditions; during the acclimation treatment, the compost is turned over at 0, 1, 3, 5, 8, 11, 15 and 21 days; the acclimation treatment lasts for 21 days; after the acclimation treatment is completed, the following treatment is also included: the material obtained after the acclimation treatment is placed in a bacterial culture room at 60° C. for 24 hours.

8. The method according to claim 7, characterized in that In step S1, the moisture content of the mixed material A is 55% to 60%; the biomass A is at least one of wheat straw, camellia oleifera cake, camellia oleifera shell, and reed; the addition amount of the biomass A is 35% to 40% of the weight of the sludge A; the wheat straw is in powder form with a particle size of 4 mm to 5 mm; the camellia oleifera cake is in powder form with a particle size of 20 mesh to 50 mesh; the biochar A is at least one of bamboo charcoal, stalk biochar, peanut shell biochar, sludge biochar, and manure biochar; the addition amount of the biochar A is 5% of the total dry weight of the domesticated sludge, sludge A, and biomass A; the biochar A is in powder form with a particle size of 60 mesh to 80 mesh.

9. The method according to any one of claims 1 to 6, characterized in that: In step S3, the heating rate during the pyrolysis process is 3°C / min, and the heating time is 157min; the pyrolysis is carried out at 500°C; and the pyrolysis time is 120min.

10. The method according to claim 9, characterized in that In step S3, the pyrolysis process further includes introducing nitrogen into the pyrolysis system, and the flow rate of the nitrogen is 200 mL / min.

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