Preparation method and application of a composite soil conditioner that can enhance carbon sequestration effect

Abstract

This invention relates to the field of soil pollution remediation, and discloses a method for preparing and applying a composite soil conditioner that enhances carbon sequestration. The method for preparing the soil conditioner includes the following steps: Step A: Biochar preparation; Step B: Biochar microalgae particle preparation; Step C: Oyster shell powder preparation; Step D: Particle coating to obtain inner and outer layers of soil conditioner. The soil conditioner comprises two layers bonded together by auxiliary materials. The inner layer includes microalgae particles enriched and recovered from biochar, which can improve acidic soil for a longer period and provide organic matter, nitrogen, and phosphorus nutrients. The outer layer includes calcined oyster shell powder, which rapidly adjusts soil acidity and provides calcium salts. This composite soil conditioner, with the synergistic effect of multiple materials, can effectively improve acidic soil over a longer period by combining rapid and slow action, passivating heavy metals in the soil, providing organic matter, calcium, nitrogen, phosphorus, and other nutrients, improving the nutritional quality of vegetables, and enhancing soil carbon sequestration, thus exhibiting good comprehensive benefits.

Description

Technical Field

[0001] This invention relates to the field of soil pollution remediation, and more specifically, to a method for preparing and applying a composite soil conditioner that can enhance carbon sequestration. Background Technology

[0002] Climate change poses a severe threat and challenge to human survival and development. Soil carbon pools are the largest on land. Synergistic effects of soil environmental pollution control and soil carbon sequestration are more cost-effective than industrial carbon sequestration, and are a key strategy for addressing climate change worldwide, attracting widespread attention both domestically and internationally. Therefore, in the new era of "dual carbon" goals, the combined use of various solid waste resources with different carbon sequestration and soil conditioning characteristics to develop low-cost, high-efficiency, green, and low-carbon soil conditioners, synergistically enhancing soil environmental pollution control and soil solid waste management, is a crucial requirement for soil environmental governance technology. Microalgae are widely distributed in the natural environment, with diverse species, large quantities, and rapid growth. They can sequester carbon through photosynthesis and also play a role in controlling the absorption and accumulation of heavy metals in crops due to their ability to absorb and accumulate heavy metals. Aquaculture wastewater contains abundant algae and bacteria such as *Microcystis aeruginosa*, *Nostoc commune*, *Chlorella minutissima*, *Scenedesmus obliquus*, and *Chlamydomonsa reinhardtii*, as well as nitrogen and phosphorus nutrients, making it valuable for recycling. Waste wood mainly originates from construction sites, home renovations, discarded furniture, and timber processing plants, and its quantity is increasing year by year with economic development and rising living standards. Biochar, with its porosity and large surface area, decomposes slowly in soil, serving as both a carbon sequestration method and a high-quality soil conditioner. Heat-treating waste wood to produce biochar is beneficial for soil conditioning and carbon sequestration. Oyster shells amount to millions of tons in coastal areas of my country, typically piled up directly in streets and alleys or dumped into the sea, polluting the environment. Oyster shell powder, rich in calcium carbonate, can quickly condition acidic soils, solidify heavy metals in the soil, and provide calcium nutrition for crops. However, excessive application can lead to soil compaction.

[0003] In recent years, the technology of developing soil conditioners using microalgae, biochar, and oyster shell powder has developed rapidly. For example, patent number ZL202111085925.7, entitled "A microalgae ecological restoration agent for carbon fixation and control of arsenic pollution in paddy soil and its preparation method," describes the application of freeze-dried microalgae cultured in a phosphorus-free modified culture medium to paddy soil to control arsenic pollution and play a role in carbon fixation. However, its target is only arsenic, the number of metal elements described is limited, and it requires special environmental conditions for cultivation and transportation, resulting in high efficiency and cost. Patent application number 202310981314.3, entitled "A Soil Fertilizer Conditioner and Its Preparation Method", is prepared by leveraging the synergistic effects of various materials such as alkaline residue, calcium magnesium phosphate fertilizer, oyster shell, sepiolite, activator, rice husk, microbial agent, poultry and livestock manure, trace elements, paraffin oil, limonene, and urea. It can improve the pH and fertility of acidic soils and improve the yield and quality of crops. However, the technology involves a large number of materials, has little utilization of solid waste resources, and does not consider carbon sequestration effects. Patent application number 202410154192.5, entitled "A Soil Conditioner Based on Organic Acid-Activated Oyster Shells and Its Preparation Method," uses a combination of materials, including phosphate tailings powder and oxalic acid, roasted oyster shell powder and potassium alginate, and unroasted oyster shell powder, to form an inner, middle, and outer layer structure. While this effectively improves acidic soil, passivates various heavy metals, and provides potassium and phosphorus fertilizers to the soil with slow release, it does not consider the effects of varying soil acidification rates or carbon sequestration. Patent application number 202211693095.0, entitled "A Composite Soil Conditioner and Its Preparation Method," uses a compound of sulfur-containing amino acid-modified biochar and organic acid-metal complex-modified oyster shell powder. While this can passivate heavy metals in the soil for a relatively long time, the required processing steps are relatively complex and costly. It does not consider the long-term performance of different materials in the layered construction of the material and its carbon sequestration effect. Therefore, there is a need to develop more effective, simple, low-cost, and carbon-sequestrable soil conditioner preparation methods. Currently, microalgae, biochar, and oyster shell powder have different characteristics in carbon sequestration and soil pollution remediation. However, there are no reports on technologies that can combine them to develop new green and low-carbon soil conditioners that can both sequester carbon and control heavy metal pollution while improving crop quality. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a method for preparing a microalgae biochar oyster shell powder composite soil conditioner that can improve carbon sequestration effect. This method utilizes multiple solid wastes at low cost, combines the superior performance characteristics of different materials to construct a hierarchical structure, develops a new type of green and low-carbon soil conditioner and applies it, so as to achieve the purpose of sequestration, control of heavy metal pollution in soil and improvement of crop quality.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is:

[0006] A method for preparing a composite soil conditioner that can enhance carbon sequestration, comprising the following steps:

[0007] Step A: Biochar preparation;

[0008] Step B: Preparation of biochar microalgae particles;

[0009] Step C: Preparation of oyster shell powder;

[0010] Step D: Particle coating to obtain inner and outer layers of soil conditioner.

[0011] Preferably, the soil conditioner comprises, by weight, 20-30 parts waste wood biochar, 2-5 parts microalgae, and 68-75 parts oyster shell powder.

[0012] Preferably, the soil conditioner comprises two layers bonded together by auxiliary materials. The inner layer consists of microalgae particles enriched and recycled from aquaculture wastewater using biochar, and the outer layer consists of oyster shell powder that has been gently simmered at 850°C. The auxiliary material is a binder.

[0013] Preferably, in step A, the biochar preparation involves crushing waste wood into 2cm particles, adding them to a combustion furnace, maintaining an oxygen-deficient state by purging with nitrogen, pyrolyzing at 500°C for 2 hours, cooling to room temperature, and crushing them through a 60-mesh sieve to obtain biochar particles.

[0014] Preferably, in step B, the biochar particles prepared in step A are added to the aquaculture wastewater to precipitate and enrich the microalgae and their nitrogen and phosphorus nutrients. The water is then dried in an oven at 40°C to obtain biochar microalgae particles containing nitrogen and phosphorus nutrients.

[0015] Preferably, in step C, the oyster shell powder is prepared by washing the oyster shells, calcining them at a gentle temperature for 10 minutes, cooling them down, crushing them through a 60-mesh sieve, and obtaining oyster shell powder. The calcination temperature is 850°C.

[0016] Preferably, in step D, the biochar microalgae particles prepared in step B are placed on a disc granulator, the surface of the biochar microalgae particles is sprayed with a binder, and oyster shell powder is added to the rotating disc granulator so that the oyster shell powder is evenly coated on the surface of the biochar microalgae particles, thus obtaining an inner and outer layer soil conditioner.

[0017] Preferably, the binder is one or more of sodium carboxymethyl cellulose, calcium chloride, bentonite, and potassium alginate, with a solution concentration of 2.5 mol / L and a binder volume to oyster shell powder mass ratio of 16:1.

[0018] Application of a composite soil conditioner that can enhance carbon sequestration: The soil conditioner is applied to soil conditioning. Specific application method: The obtained microalgae oyster biochar composite soil conditioner is added to the soil for soil conditioning to inhibit the accumulation of heavy metals in crops, improve crop nutritional quality, and enhance soil carbon sequestration.

[0019] Preferably, depending on the type of soil crop and the soil pollution status, add 30-50 kg of soil conditioner per acre. The outer layer of oyster shell powder quickly conditions acidic soil, while the inner layer of microalgae biochar slowly improves acidic soil, passivates various heavy metals in the soil, and provides nutrients such as organic matter, calcium, nitrogen, and phosphorus, thereby improving the nutritional quality of vegetables and enhancing the soil carbon sequestration effect.

[0020] The advantages and beneficial effects of this invention are as follows:

[0021] 1. This method uses biochar prepared by thermal treatment of waste wood, microalgae recovered and enriched from aquaculture tailwater by coagulation and sedimentation, and various solid waste resources such as oyster shells from aquaculture. By utilizing the different material properties, a soil conditioner is constructed in a hierarchical manner. It can combine fast and slow treatments, prioritizing fast treatments and then slowing down the treatment of acidic soils, passivating various heavy metals in the soil, and providing nutrients such as organic matter, calcium, nitrogen, and phosphorus. Through algae growth and the action of biochar, the soil carbon sequestration effect and the nutritional quality of crops are improved.

[0022] 2. The composite soil conditioner of the present invention has been tested on different vegetable soils and edible parts, and the relevant experimental data have been measured. The results have confirmed the beneficial effects of the microalgae biochar oyster shell powder composite soil conditioner. It can significantly increase the soil organic matter content, enhance the carbon fixation effect, inhibit the absorption and accumulation of heavy metals in crops, and improve crop quality.

[0023] 3. The microalgae biochar and oyster shell powder composite soil conditioner screened in this invention is prepared by combining abundant solid waste resources for synergistic utilization. It is easy to obtain, store and process raw materials at low cost, and can be produced and promoted in large quantities. It has high comprehensive benefits such as carbon sequestration and environmental pollution control. Attached Figure Description

[0024] Figure 1 These are SEM images of the biochar microalgae particles, oyster shell powder, and microalgae biochar oyster shell powder from this invention.

[0025] Figure 2 These are XRD patterns of biochar, oyster shell powder, and microalgae biochar and oyster shell powder from this invention.

[0026] Figure 3 Appendix 1 shows the data from the greenhouse simulation experiment on soil conditioning in this invention;

[0027] Figure 4 Appendix 2 shows the field application data of soil conditioning in this invention. Detailed Implementation

[0028] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, features described in some examples may be combined in other examples.

[0029] Example 1

[0030] This embodiment proposes a method for preparing a composite soil conditioner that can enhance carbon sequestration, comprising the following steps:

[0031] Step A: Biochar preparation;

[0032] Waste wood was crushed into 2cm particles and added to a combustion furnace. Nitrogen gas was introduced to maintain an oxygen-deficient state. The mixture was pyrolyzed at 500℃ for 2 hours, cooled to room temperature, and then crushed through a 60-mesh sieve to obtain biochar particles.

[0033] Step B: Preparation of biochar microalgae particles;

[0034] The biochar particles prepared in step A are added to the aquaculture wastewater to precipitate and enrich the microalgae and their nitrogen and phosphorus nutrients. The water is then dried in an oven at 40°C to obtain biochar microalgae particles containing nitrogen and phosphorus nutrients.

[0035] Step C: Preparation of oyster shell powder;

[0036] The oyster shells were washed, gently roasted at a temperature of 850°C for 10 minutes, then cooled and crushed through a 60-mesh sieve to obtain oyster shell powder.

[0037] Step D: Particle coating to obtain inner and outer layers of soil conditioner.

[0038] The biochar microalgae particles prepared in step B are placed on a disc granulator. The surface of the biochar microalgae particles is sprayed with a binder. Oyster shell powder is added to the rotating disc granulator so that the oyster shell powder is evenly coated on the surface of the biochar microalgae particles, thus obtaining an inner and outer layer soil conditioner.

[0039] The binder is sodium carboxymethyl cellulose, with a solution concentration of 2.5 mol / L, and the binder volume to oyster shell powder mass ratio is 16:1.

[0040] in:

[0041] Soil conditioner, the ingredients are calculated by weight as follows: 20 parts waste wood biochar, 2 parts microalgae, and 75 parts oyster shell powder.

[0042] The soil conditioner consists of two layers, an inner and an outer layer, bound together by auxiliary materials. The inner layer comprises microalgae particles enriched and recycled from aquaculture wastewater using biochar, while the outer layer is oyster shell powder that has been gently simmered at 850°C. The auxiliary material is a binder.

[0043] Example 2

[0044] This embodiment proposes a method for preparing a composite soil conditioner that can enhance carbon sequestration, comprising the following steps:

[0045] Step A: Biochar preparation;

[0046] Waste wood was crushed into 2cm particles and added to a combustion furnace. Nitrogen gas was introduced to maintain an oxygen-deficient state. The mixture was pyrolyzed at 500℃ for 2 hours, cooled to room temperature, and then crushed through a 60-mesh sieve to obtain biochar particles.

[0047] Step B: Preparation of biochar microalgae particles;

[0048] The biochar particles prepared in step A are added to the aquaculture wastewater to precipitate and enrich the microalgae and their nitrogen and phosphorus nutrients. The water is then dried in an oven at 40°C to obtain biochar microalgae particles containing nitrogen and phosphorus nutrients.

[0049] Step C: Preparation of oyster shell powder;

[0050] The oyster shells were washed, gently roasted at a temperature of 850°C for 10 minutes, then cooled and crushed through a 60-mesh sieve to obtain oyster shell powder.

[0051] Step D: Particle coating to obtain inner and outer layers of soil conditioner.

[0052] The biochar microalgae particles prepared in step B are placed on a disc granulator. The surface of the biochar microalgae particles is sprayed with a binder. Oyster shell powder is added to the rotating disc granulator so that the oyster shell powder is evenly coated on the surface of the biochar microalgae particles, thus obtaining an inner and outer layer soil conditioner.

[0053] The binder is calcium chloride and bentonite, with a solution concentration of 2.5 mol / L and a binder volume to oyster shell powder mass ratio of 16:1.

[0054] in:

[0055] Soil conditioner, the ingredients by weight are 25 parts waste wood biochar, 3 parts microalgae, and 71 parts oyster shell powder.

[0056] The soil conditioner consists of two layers, an inner and an outer layer, bound together by auxiliary materials. The inner layer comprises microalgae particles enriched and recycled from aquaculture wastewater using biochar, while the outer layer is oyster shell powder that has been gently simmered at 850°C. The auxiliary material is a binder.

[0057] Example 3

[0058] This embodiment proposes a method for preparing a composite soil conditioner that can enhance carbon sequestration, comprising the following steps:

[0059] Step A: Biochar preparation;

[0060] Waste wood was crushed into 2cm particles and added to a combustion furnace. Nitrogen gas was introduced to maintain an oxygen-deficient state. The mixture was pyrolyzed at 500℃ for 2 hours, cooled to room temperature, and then crushed through a 60-mesh sieve to obtain biochar particles.

[0061] Step B: Preparation of biochar microalgae particles;

[0062] The biochar particles prepared in step A are added to the aquaculture wastewater to precipitate and enrich the microalgae and their nitrogen and phosphorus nutrients. The water is then dried in an oven at 40°C to obtain biochar microalgae particles containing nitrogen and phosphorus nutrients.

[0063] Step C: Preparation of oyster shell powder;

[0064] The oyster shells were washed, gently roasted at a temperature of 850°C for 10 minutes, then cooled and crushed through a 60-mesh sieve to obtain oyster shell powder.

[0065] Step D: Particle coating to obtain inner and outer layers of soil conditioner.

[0066] The biochar microalgae particles prepared in step B are placed on a disc granulator. The surface of the biochar microalgae particles is sprayed with a binder. Oyster shell powder is added to the rotating disc granulator so that the oyster shell powder is evenly coated on the surface of the biochar microalgae particles, thus obtaining an inner and outer layer soil conditioner.

[0067] The binder is sodium carboxymethyl cellulose, calcium chloride, bentonite, and potassium alginate, with a solution concentration of 2.5 mol / L and a binder volume to oyster shell powder mass ratio of 16:1.

[0068] in:

[0069] Soil conditioner, the ingredients by weight are 30 parts waste wood biochar, 5 parts microalgae, and 68 parts oyster shell powder.

[0070] The soil conditioner consists of two layers, an inner and an outer layer, bound together by auxiliary materials. The inner layer comprises microalgae particles enriched and recycled from aquaculture wastewater using biochar, while the outer layer is oyster shell powder that has been gently simmered at 850°C. The auxiliary material is a binder.

[0071] Example 4

[0072] This embodiment proposes the application of a composite soil conditioner that can enhance carbon sequestration.

[0073] The soil conditioner is applied to soil conditioning. The specific application method is as follows: the obtained microalgae oyster biochar composite soil conditioner is added to the soil to condition the soil, inhibit the accumulation of heavy metals in crops, improve the nutritional quality of crops, and enhance soil carbon sequestration.

[0074] Depending on the type of soil crop and the degree of soil pollution, add 30, 40, or 50 kg of soil conditioner per acre; in this example, 40 kg is preferred. The outer layer of oyster shell powder rapidly conditions acidic soil, while the inner layer of microalgae biochar slowly improves acidic soil, passivates various heavy metals in the soil, and provides nutrients such as organic matter, calcium, nitrogen, and phosphorus, thereby improving the nutritional quality of vegetables and enhancing the soil's carbon sequestration effect.

[0075] Example 5

[0076] In this embodiment, a microalgae-oyster biochar composite soil conditioner that can enhance carbon sequestration is prepared, specifically including the following steps:

[0077] Step A: After crushing the waste wood into 2cm particles, add them to the combustion furnace, purge with nitrogen to maintain an oxygen-deficient state, pyrolyze at 500℃ for 2 hours, cool to room temperature, crush through a 60-mesh sieve to obtain biochar particles.

[0078] Step B: Add 30 portions of the biochar granules prepared in Step A to the aquaculture wastewater, precipitate and enrich the microalgae and 2 portions of their nitrogen and phosphorus nutrients, and dry the water in a 40℃ oven to obtain biochar microalgae granules containing nitrogen and phosphorus nutrients, as shown in the attached figure. Figure 1 As shown.

[0079] Step C: Wash the oyster shells, gently roast them at a high temperature for 10 minutes, then cool them down, crush them through a 60-mesh sieve to obtain oyster shell powder. The roasting temperature is 850℃. (See attached...) Figure 1 As shown.

[0080] Step D: Obtain the inner and outer soil conditioners. Place the biochar microalgae particles prepared in Step B on a disc granulator. Spray the surface of the biochar microalgae particles with potassium alginate binder. Add 68 parts of oyster shell powder to the rotating disc granulator. The concentration of the potassium alginate binder solution is 2.5 mol / L, and the binder volume: oyster shell powder mass = 16:1, so that the oyster shell powder is evenly coated on the surface of the biochar microalgae particles, thus obtaining the inner and outer soil conditioners, as shown in the attached figure. Figure 1 As shown.

[0081] 60 kg of the obtained soil conditioner was evenly mixed with cadmium (2.84 mg / kg) and arsenic (68 mg / kg) contaminated soil and placed in a 25℃ natural light greenhouse for pot cultivation of carrots (Daucus carota var. sativa Hoffm). After a 60-day experiment and sampling analysis, the results showed that the extractable water content in the soil was significantly reduced, while the soil organic matter content was significantly increased. The cadmium and arsenic content in the edible parts of carrots decreased by 61 µg / kg and 242 µg / kg, respectively, while the soluble sugar, soluble protein, and vitamin C in the edible parts of carrots increased by 8 mg / g, 6 mg / g, and 0.5 mg / g, respectively. This demonstrated a good effect in carbon sequestration, heavy metal pollution control, and improvement of nutritional quality. The results are attached. Figure 3 As shown in Appendix 1.

[0082] Example 6

[0083] In this embodiment, a microalgae-oyster biochar composite soil conditioner that can enhance carbon sequestration is prepared, specifically including the following steps:

[0084] Step A: After crushing the waste wood into 2cm particles, add them to a combustion furnace, maintain an oxygen-deficient environment by purging with nitrogen, and pyrolyze at 500℃ for 2 hours. After cooling to room temperature, crush the particles through a 60-mesh sieve to obtain biochar particles. The XRD characterization of these particles is shown in the attached figure. Figure 2 As shown.

[0085] Step B: Add 28 portions of biochar granules prepared in Step A to the aquaculture wastewater, precipitate and enrich the microalgae and 3 portions of nitrogen and phosphorus nutrients therein, and dry the water in a 40℃ oven to obtain biochar microalgae granules containing nitrogen and phosphorus nutrients.

[0086] Step C: Wash the oyster shells, gently calcine them at a high temperature for 10 minutes, then cool them down, crush them through a 60-mesh sieve to obtain oyster shell powder. The calcination temperature was 850℃. Its XRD characterization is shown in the attached figure. Figure 2 As shown.

[0087] Step D: Obtain the inner and outer soil conditioners. Place the biochar microalgae particles prepared in Step B on a disc granulator. Spray the surface of the biochar microalgae particles with potassium alginate binder. Add 69 parts of oyster shell powder to the rotating disc granulator. The concentration of sodium carboxymethyl cellulose binder solution is 2.5 mol / L, and the binder volume: oyster shell powder mass = 16:1, so that the oyster shell powder is uniformly coated on the surface of the biochar microalgae particles, thus obtaining the inner and outer soil conditioners. The XRD characterization is shown in the attached figure. Figure 2 As shown.

[0088] 60 kg of the obtained microalgal biochar and oyster shell powder composite soil conditioner was uniformly mixed with cadmium (2.84 mg / kg) and arsenic (68 mg / kg) contaminated soil and placed in a 25℃ natural light greenhouse for pot cultivation. The planted crop was carrot (Daucus carota var. sativa Hoffm). After a 60-day experiment, the results showed that the extractable water content in the soil was significantly reduced, while the soil organic matter content was significantly increased. The cadmium and arsenic content in the edible part of the carrot decreased by 63 µg / kg and 245 µg / kg, respectively, while the soluble sugar, soluble protein, and vitamin C in the edible part of the carrot increased by 7 mg / g, 5 mg / g, and 0.6 mg / g, respectively. This demonstrated a good effect in carbon sequestration, heavy metal pollution control, and improvement of nutritional quality. The results are attached. Figure 3 As shown in Appendix 1.

[0089] Example 7

[0090] In this embodiment, a microalgae-oyster biochar composite soil conditioner that can enhance carbon sequestration is prepared, specifically including the following steps:

[0091] Step A: After crushing the waste wood into 2cm particles, add them to the combustion furnace, purge with nitrogen to maintain an oxygen-deficient state, pyrolyze at 500℃ for 2 hours, cool to room temperature, crush through a 60-mesh sieve to obtain biochar particles.

[0092] Step B: Add 26 portions of biochar granules prepared in Step A to the aquaculture wastewater, precipitate and enrich the microalgae and 3 portions of nitrogen and phosphorus nutrients therein, and dry the water in a 40℃ oven to obtain biochar microalgae granules containing nitrogen and phosphorus nutrients.

[0093] Step C: Wash the oyster shells, gently roast them for 10 minutes, then cool them down, crush them through a 60-mesh sieve to obtain oyster shell powder. The roasting temperature is 850℃.

[0094] Step D: Obtain the inner and outer soil conditioners. Place the biochar microalgae particles prepared in Step B on a disc granulator. Spray the surface of the biochar microalgae particles with calcium chloride binder. Add 71 parts of oyster shell powder to the rotating disc granulator. The concentration of potassium alginate binder solution is 2.5 mol / L, and the binder volume: oyster shell powder mass = 16:1, so that the oyster shell powder is evenly coated on the surface of the biochar microalgae particles, thus obtaining the inner and outer soil conditioners.

[0095] 60 kg of the obtained microalgal biochar and oyster shell powder composite soil conditioner was uniformly mixed with cadmium (2.84 mg / kg) and arsenic (68 mg / kg) contaminated soil and placed in a 25℃ natural light greenhouse for pot cultivation. The planted crop was green bell pepper (Capsicumannuum var. grossum). After 60 days of experimentation and analysis, the results showed that the extractable water content in the soil was significantly reduced, while the soil organic matter content was significantly increased. The cadmium and arsenic content in the edible part of the green bell pepper decreased by 69 µg / kg and 235 µg / kg, respectively, while the soluble sugar, soluble protein, and vitamin C in the edible part of the green bell pepper increased by 8 mg / g, 10 mg / g, and 2.0 mg / g, respectively. This demonstrated a good effect in carbon sequestration, heavy metal pollution control, and improvement of nutritional quality. The results are attached. Figure 3 As shown in Appendix 1.

[0096] Comparative Example 1

[0097] In this comparative example, a microalgae-oyster biochar composite soil conditioner that can enhance carbon sequestration was prepared, specifically including the following steps:

[0098] Step A: After crushing the waste wood into 2cm particles, add them to the combustion furnace, purge with nitrogen to maintain an oxygen-deficient state, pyrolyze at 500℃ for 2 hours, cool to room temperature, crush through a 60-mesh sieve to obtain biochar particles.

[0099] Step B: Add 24 portions of biochar granules prepared in Step A to the aquaculture wastewater, precipitate and enrich the microalgae and 4 portions of nitrogen and phosphorus nutrients therein, and dry the water in a 40℃ oven to obtain biochar microalgae granules containing nitrogen and phosphorus nutrients.

[0100] Step C: Wash the oyster shells, gently roast them for 10 minutes, then cool them down, crush them through a 60-mesh sieve to obtain oyster shell powder. The roasting temperature is 850℃.

[0101] Step D: Obtain the inner and outer soil conditioners. Place the biochar microalgae particles prepared in step B on a disc granulator, spray the surface of the biochar microalgae particles with bentonite binder, add 72 parts of oyster shell powder to the rotating disc granulator, the concentration of potassium alginate binder solution is 2.5 mol / L, and the binder volume: oyster shell powder mass = 16:1, so that the oyster shell powder is evenly coated on the surface of the biochar microalgae particles, thus obtaining the inner and outer soil conditioners.

[0102] 60 kg of the obtained microalgal biochar and oyster shell powder composite soil conditioner was uniformly mixed with cadmium (2.84 mg / kg) and arsenic (68 mg / kg) contaminated soil and placed in a 25℃ natural light greenhouse for pot cultivation. The planted crop was carrot (Daucus carota var. sativa Hoffm). After 60 days of experimentation and analysis, the results showed that the extractable water content in the soil was significantly reduced, while the soil organic matter content was significantly increased. The cadmium and arsenic content in the edible part of the carrot decreased by 67 µg / kg and 231 µg / kg, respectively, while the soluble sugar, soluble protein, and vitamin C in the edible part of the carrot increased by 10 mg / g, 8 mg / g, and 0.7 mg / g, respectively. This demonstrated a good effect in carbon sequestration, heavy metal pollution control, and improvement of nutritional quality. The results are attached. Figure 3 As shown in Appendix 1.

[0103] Comparative Example 2

[0104] In this comparative example, a microalgae-oyster biochar composite soil conditioner that can enhance carbon sequestration was prepared, specifically including the following steps:

[0105] Step A: After crushing the waste wood into 2cm particles, add them to the combustion furnace, purge with nitrogen to maintain an oxygen-deficient state, pyrolyze at 500℃ for 2 hours, cool to room temperature, crush through a 60-mesh sieve to obtain biochar particles.

[0106] Step B: Add 23 portions of biochar granules prepared in Step A to the aquaculture wastewater, precipitate and enrich the microalgae and 3 portions of nitrogen and phosphorus nutrients therein, and dry the water in a 40℃ oven to obtain biochar microalgae granules containing nitrogen and phosphorus nutrients.

[0107] Step C: Wash the oyster shells, gently roast them for 10 minutes, then cool them down, crush them through a 60-mesh sieve to obtain oyster shell powder. The roasting temperature is 850℃.

[0108] Step D: Obtain the inner and outer soil conditioners. Place the biochar microalgae particles prepared in step B on a disc granulator. Spray the surface of the biochar microalgae particles with potassium alginate binder. Add 74 parts of oyster shell powder to the rotating disc granulator. The concentration of the potassium alginate binder solution is 2.5 mol / L, and the binder volume: oyster shell powder mass = 16:1, so that the oyster shell powder is evenly coated on the surface of the biochar microalgae particles, thus obtaining the inner and outer soil conditioners.

[0109] 60 kg of the obtained microalgal biochar and oyster shell powder composite soil conditioner was uniformly mixed with cadmium (2.84 mg / kg) and arsenic (68 mg / kg) contaminated soil and placed in a 25℃ natural light greenhouse for pot cultivation. The planted crop was green bell pepper (Capsicumannuum var. grossum). After 60 days of experimentation and analysis, the results showed that the extractable water content in the soil was significantly reduced, while the soil organic matter content was significantly increased. The cadmium and arsenic content in the edible part of the green bell pepper decreased by 72 µg / kg and 232 µg / kg, respectively, while the soluble sugar, soluble protein, and vitamin C in the edible part of the green bell pepper increased by 6 mg / g, 8 mg / g, and 1.6 mg / g, respectively. This demonstrated a good effect in carbon sequestration, heavy metal pollution control, and improvement of nutritional quality. The results are attached. Figure 3 As shown in Appendix 1.

[0110] Application Case 1

[0111] The soil to be treated was selected from a carrot-growing field on the coast of Fujian Province. The main heavy metal pollutants in the soil were lead and cadmium. The compound soil conditioner from Case 6 was chosen. The experimental group was divided into a control group (no soil conditioner applied) and experimental group 1 (Case 6). Each group had an experimental area of ​​0.5 mu (approximately 0.067 hectares) and a planting density of 12,000 plants / mu (approximately 13,000 plants / mu). Before applying the soil conditioner, samples were collected from the experimental group. Samples were taken from 8-10 points in each group using the diagonal method, mixed thoroughly, and then the control group soil sample was obtained using the quartering method. After soil sampling, 80 kg of soil conditioner was evenly applied to the experimental area during tilling, according to the experimental design. Four months after routine field management, soil samples and edible parts of green peppers were collected again using the same method. The results are shown in the attached figure. Figure 4 As shown in Appendix Table 2, the results indicate that the application of the compound soil conditioner of the present invention can improve acidified soil, increase soil organic matter, inhibit the absorption and accumulation of heavy metals in soil pollution by crops, and improve the nutritional quality of crops.

[0112] Application Case 2

[0113] The soil to be treated was selected from a bell pepper plantation on the coast of Fujian Province. The main heavy metal pollutants in the soil were lead and cadmium. The compound soil conditioner from Case 7 was chosen. The experimental group was divided into a control group (no soil conditioner applied) and experimental group 2 (Case 7). Each group had an experimental area of ​​0.5 mu (approximately 0.067 hectares) and a planting density of 9000 plants / mu (approximately 667 hectares). Before applying the soil conditioner, samples were collected from the experimental group. Samples were collected from 8-10 points in each group using the diagonal method. After thorough mixing, the soil samples for the control group were obtained using the quartering method. After soil sampling, 80 kg of soil conditioner was evenly applied to the experimental area during tilling, according to the experimental design. Four months after routine field management, soil samples and edible bell pepper samples were collected again using the same method. The results are shown in the attached figure. Figure 4 As shown in Table 2, the results indicate that the application of the compound soil conditioner of the present invention can improve acidified soil, increase soil organic matter, inhibit the absorption and accumulation of heavy metals in soil pollution by crops, and improve the nutritional quality of crops.

[0114] The embodiments of this example have been described above. However, this example is not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms based on the guidance of this example, and all of them are within the protection scope of this example.

Claims

1. A method for preparing a composite soil conditioner that can enhance carbon sequestration, characterized in that, Includes the following steps: Step A: Biochar preparation; The biochar preparation involves crushing waste wood into 2cm particles, adding them to a combustion furnace, maintaining an oxygen-deficient state by purging with nitrogen, pyrolyzing at 500℃ for 2 hours, cooling to room temperature, and crushing them through a 60-mesh sieve to obtain biochar particles. Step B: Preparation of biochar microalgae particles; Step C: Preparation of oyster shell powder; Step D: Particle coating to obtain inner and outer layers of soil conditioner; The soil conditioner, by weight, comprises 20-30 parts waste wood biochar, 2-5 parts microalgae, and 68-75 parts oyster shell powder. The soil conditioner comprises two layers, an inner and an outer layer, bonded together by auxiliary materials. The inner layer consists of microalgae particles enriched and recycled from aquaculture wastewater using biochar, while the outer layer is oyster shell powder that has been gently calcined at 850°C. The auxiliary material is a binder.

2. The method for preparing a composite soil conditioner that can enhance carbon sequestration effect according to claim 1, characterized in that, In step B, the biochar particles prepared in step A are added to the aquaculture wastewater to precipitate and enrich the microalgae and their nitrogen and phosphorus nutrients. The water is then dried in an oven at 40°C to obtain biochar microalgae particles containing nitrogen and phosphorus nutrients.

3. The method for preparing a composite soil conditioner that can enhance carbon sequestration effect according to claim 1, characterized in that, In step C, the oyster shell powder is prepared by washing the oyster shells, calcining them at a gentle temperature for 10 minutes, cooling them down, crushing them through a 60-mesh sieve, and obtaining oyster shell powder. The calcination temperature is 850℃.

4. The method for preparing a composite soil conditioner that can enhance carbon sequestration effect according to claim 1, characterized in that, In step D, the biochar microalgae particles prepared in step B are placed on a disc granulator, and the surface of the biochar microalgae particles is sprayed with a binder. Oyster shell powder is added to the rotating disc granulator so that the oyster shell powder is evenly coated on the surface of the biochar microalgae particles, thus obtaining an inner and outer layer soil conditioner.

5. The method for preparing a composite soil conditioner that can enhance carbon sequestration effect according to claim 1, characterized in that, The binder is one or more of sodium carboxymethyl cellulose, calcium chloride, bentonite, and potassium alginate, with a solution concentration of 2.5 mol / L and a binder volume to oyster shell powder mass ratio of 16:

1.

6. The application of a composite soil conditioner that can enhance carbon sequestration, characterized in that, The soil conditioner prepared by the method described in claim 1, which can enhance carbon sequestration, is applied to soil conditioning. Specifically, the microalgae-oyster biochar composite soil conditioner is added to the soil to condition the soil, thereby inhibiting the accumulation of heavy metals in crops, improving the nutritional quality of crops, and enhancing soil carbon sequestration.

7. The application of the composite soil conditioner for improving carbon sequestration as described in claim 6, characterized in that, Depending on the type of soil crop and the soil pollution status, add 30-50 kg of soil conditioner per acre.

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