A method for remediation of garden contaminated soil

Abstract

This invention discloses a method for remediating contaminated soil in gardens, belonging to the field of garden soil remediation technology. The method involves adjusting the soil pH to activate the soil contaminated with heavy metals, then applying a remediation agent to fix the heavy metal ions in the soil, and then sowing and inoculating hyperaccumulating plants inoculated with arbuscular mycorrhizal fungi. By applying the remediation agent to fix the heavy metal ions in the soil, the hyperaccumulating plants can germinate and grow well without being stressed by heavy metal ions, thereby absorbing and accumulating more heavy metal ions in the soil. The inoculated arbuscular mycorrhizal fungi can, on the one hand, secrete organic acids to activate and release the heavy metal ions fixed by the remediation agent, allowing them to be gradually absorbed and accumulated by the plants; on the other hand, they can increase the plant's absorption efficiency of heavy metal ions. Through the combined effect of these steps, the hyperaccumulating plants can grow well in the heavy metal contaminated soil, thereby effectively absorbing and removing heavy metal ions from the soil and efficiently remediating heavy metal contaminated garden soil.

Description

Technical Field

[0001] This invention relates to the field of garden soil remediation technology, and in particular to a method for remediating contaminated garden soil. Background Technology

[0002] Gardens are beautiful natural environments and recreational areas created within a specific region using engineering techniques and artistic methods. This involves modifying the terrain, or further constructing hills, stacking rocks, managing water features, planting trees and flowers, building structures, and arranging pathways. With national development, increased urbanization, and the promotion of green living concepts, urban garden landscapes are becoming increasingly common. Currently, gardens primarily focus on planting vegetation, and soil is the foundation for the growth of this vegetation.

[0003] Pollution from factory emissions, excessive use of fertilizers and pesticides, and improper irrigation have damaged soil structure and physicochemical properties, leading to problems such as excessive heavy metals, poor aeration, and reduced water retention. These issues severely affect the survival rate and growth of landscaping plants, with excessive heavy metal ions having a particularly significant impact. Currently, soil remediation methods commonly use topsoil replacement and remediation agents. However, topsoil replacement involves large-scale construction, high investment costs, damages soil structure, and raises concerns about waste soil treatment. While remediation agents are simple to apply, their effects are often limited, and excessive application can damage the soil. Furthermore, remediation agents cannot completely remove heavy metal ions from the soil, potentially causing secondary pollution. Phytoremediation, which involves planting plants to absorb and accumulate heavy metal ions in the soil, offers economic, ecological, and environmental advantages. However, conventional methods can lead to heavy metal stress affecting plant growth and reducing biomass, resulting in poor remediation effects and long remediation times.

[0004] Therefore, there is a need to find a method for remediating contaminated garden soil, and to address the problem that when using conventional methods to remediate heavy metal-contaminated garden soil, plants are easily subjected to heavy metal stress, which affects plant growth and leads to poor remediation effect and long remediation time. Summary of the Invention

[0005] Therefore, the purpose of this invention is to provide a method for remediating garden soil contaminated with heavy metals, which solves the problem that when using conventional methods to remediate garden soil contaminated with heavy metals, plants are easily subjected to heavy metal stress, affecting plant growth and resulting in poor remediation effect and long remediation time.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] A method for remediating contaminated soil in gardens, the method comprising the following steps:

[0008] (1) After removing weeds and impurities from the soil, till the soil and adjust the soil pH to 4.5-5.5. Let it stand for 5-10 days.

[0009] (2) On a sunny morning between 9 and 10 a.m., apply 0.1-0.3 kg / m 2 Spray the repair agent onto the soil in the specified amount. After spraying for 4 hours, till the soil to a depth of 20-30cm. After tilling, spray the repair agent a second time in the same amount. Adjust the soil pH to 6-7 3-6 days after applying the repair agent.

[0010] (3) After germination, the hyperaccumulated plant seeds are added to the substrate inoculated with arbuscular mycorrhizal fungi, mixed evenly, and then sown.

[0011] (4) After the planted hyperaccumulating plants mature, remove them by the roots and then repeat the planting of hyperaccumulating plants in step (3) until the content of heavy metal ions in the soil meets the standard of the "Soil Environmental Quality Agricultural Land Soil Risk Control Standard (Trial)" (GB15618-2018). After obtaining the restored garden soil, garden plants can be planted in accordance with conventional methods.

[0012] This invention selects vetiver / centipede grass, a plant with good absorption and enrichment effects on various heavy metal ions, for sowing. During its growth, the plant absorbs and enriches heavy metal ions in the soil. Then, the mature vetiver / centipede grass that has absorbed and enriched heavy metal ions is uprooted, thereby completely removing heavy metal ions from the soil and carrying out green and efficient remediation of heavy metal-contaminated garden soil.

[0013] Furthermore, the repair agent in step (2) includes the following raw materials:

[0014] Chitosan, 50wt% isopropanol aqueous solution, 1,2-epoxybutane, nano-silica, L-asparagine, dithiothreitol.

[0015] Furthermore, the preparation method of the repair agent is as follows:

[0016] A: Add chitosan to 50wt% isopropanol aqueous solution and stir to disperse. After standing for 2-6 hours, add 1,2-epoxybutane and stir to react at room temperature for 1 hour. Then raise the temperature to 60-70℃ and continue to react for 20-40 minutes. After the reaction is completed, filter to remove the filtrate and then dry at 45℃ to obtain modified chitosan.

[0017] B: Add nano-silica to water and stir to disperse. Heat to 60-80℃ and keep warm for 1-2 hours. Then add dithiothreitol and react at a constant temperature for 30-60 minutes. After that, cool to 40-50℃ and add L-asparagine and react for 1-2 hours. After the reaction is complete, filter to remove the filtrate and place at 4℃ overnight to obtain pretreated nano-silica.

[0018] C: Add water to the modified chitosan to prepare a 2wt% modified chitosan solution, immediately add pretreated nano-silica and mix evenly, then let stand at 4℃ for 12-24h to obtain the repair agent.

[0019] This invention remediates heavy metal-contaminated soil by planting hyperaccumulating plants. However, under the stress of heavy metal ions, the germination and growth of hyperaccumulating plants are significantly inhibited, reducing the remediation effect. Therefore, this invention prepares a remediation agent to treat the soil to adsorb and fix heavy metal ions in the soil, thereby eliminating the stress of heavy metal ions on hyperaccumulating plants and ensuring their good germination and growth. At the same time, arbuscular mycorrhizal fungi are inoculated when the hyperaccumulating plants are sown. The physiological metabolic activities of arbuscular mycorrhizal fungi release organic acids, which gradually activate the heavy metal ions adsorbed and fixed by the remediation agent, causing them to be gradually released and absorbed and enriched by the plants. This also increases the amount of heavy metal ions absorbed and enriched by the plants. Through the combined action of the remediation agent, hyperaccumulating plants, and arbuscular mycorrhizal fungi, the good growth of hyperaccumulating plants and their efficient absorption and enrichment of heavy metal ions are ensured, achieving rapid and efficient remediation of heavy metal-contaminated soil.

[0020] Furthermore, in step A, the mass ratio of chitosan, 50wt% isopropanol aqueous solution, and 1,2-epoxybutane is (0.5-1):(5-10):(0.2-0.5).

[0021] Furthermore, in step B, the mass ratio of nano-silica, dithiothreitol, and L-asparagine is (2-4):(0.2-0.5):(0.1-0.2).

[0022] Furthermore, in step C, the mass ratio of 2wt% modified chitosan solution to pretreated nano-silica is (5-10):(2-4).

[0023] Furthermore, the hyperaccumulating plant in the step is either vetiver or centipede grass.

[0024] Furthermore, the specific steps for germinating hyperaccumulated plant seeds in step (3) are as follows:

[0025] The seeds of the hyperaccumulating plant were soaked in 75% ethanol solution for 30 seconds and then disinfected in 0.1% mercuric chloride solution for 5-8 minutes. They were then rinsed 5 times with sterile water to obtain disinfected seeds. The disinfected seeds were soaked in clean water for 12-24 hours to obtain pretreated seeds. The pretreated seeds were placed in a petri dish with two layers of filter paper, the filter paper was moistened with water, and then the dish was placed in an incubator for germination treatment at 25°C in the dark until the seeds showed signs of germination to obtain germinated hyperaccumulating plant seeds.

[0026] Furthermore, the specific operation of inoculating the substrate with arbuscular mycorrhizal fungi in step (3) is as follows:

[0027] A substrate is prepared by mixing peat moss and coconut coir in a volume ratio of 1:2. Arbuscular mycorrhizal fungi are then added to the substrate in a mass ratio of substrate to arbuscular mycorrhizal fungi of 50:1 to obtain the substrate inoculated with arbuscular mycorrhizal fungi.

[0028] Furthermore, the arbuscular mycorrhizal fungus is *Glomus mosie*.

[0029] Beneficial effects:

[0030] 1. This invention uses plants that have a good absorption and enrichment effect on various heavy metal ions to absorb and enrich heavy metal ions in garden soil. Then, the plants that have absorbed and enriched heavy metal ions are removed by the roots, thereby completely removing excess heavy metal ions from the soil, improving soil properties, and achieving green and efficient remediation of heavy metal polluted garden soil.

[0031] 2. Before planting hyperaccumulating plants, this invention first activates the heavy metal-contaminated soil, then applies a remediation agent to fix and repair heavy metal ions in the soil, thereby eliminating the stress of heavy metal ions on plant germination and growth, promoting better plant growth to repair the soil; and during plant planting, arbuscular mycorrhizal fungi are inoculated, and the arbuscular mycorrhizal fungi secrete organic acids that gradually release the heavy metal ions fixed by the remediation agent, which are then absorbed and enriched by the plants, while increasing the amount of heavy metal ions absorbed and enriched by the plants. The combined effect of these steps effectively improves the remediation effect of heavy metal-contaminated garden soil. Detailed Implementation

[0032] The present invention will be described in detail below with reference to specific embodiments:

[0033] Example 1: Preparation of Repair Agent

[0034] A: Add 0.6 kg of chitosan to 6 kg of 50 wt% isopropanol aqueous solution and stir to disperse. After standing for 4 h, add 0.3 kg of 1,2-epoxybutane. Stir and react at room temperature for 1 h, then heat to 65 °C and continue to react for 30 min. After the reaction is complete, filter to remove the filtrate, and then dry at 45 °C to obtain modified chitosan.

[0035] B: Add 3 kg of nano silica to 15 kg of water and stir to disperse. Heat to 70°C and keep warm for 1.5 h. Then add 0.3 kg of dithiothreitol and react at a constant temperature for 40 min. After that, cool to 45°C and add 0.15 kg of L-asparagine and react for 1.5 h. After the reaction is complete, filter to remove the filtrate and place at 4°C overnight to obtain pretreated nano silica.

[0036] C: Prepare a 7kg 2wt% modified chitosan solution by adding water to the modified chitosan. Immediately add 3kg of pretreated nano-silica and mix evenly. Let stand at 4℃ for 18h to obtain the repair agent.

[0037] Example 2: Preparation of Repair Agent II

[0038] A: Add 0.5 kg of chitosan to 5 kg of 50 wt% isopropanol aqueous solution and stir to disperse. After standing for 2 hours, add 0.2 kg of 1,2-epoxybutane. Stir and react at room temperature for 1 hour, then heat to 60°C and continue to react for 20 minutes. After the reaction is complete, filter to remove the filtrate, and then dry at 45°C to obtain modified chitosan.

[0039] B: Add 2 kg of nano silica to 10 kg of water and stir to disperse. Heat to 60°C and keep warm for 1 hour. Then add 0.2 kg of dithiothreitol and react at a constant temperature for 30 minutes. After that, cool to 40°C and add 0.1 kg of L-asparagine and react for 1 hour. After the reaction is complete, filter to remove the filtrate and place at 4°C overnight to obtain pretreated nano silica.

[0040] C: Prepare a 2wt% modified chitosan solution by adding water to 5kg of modified chitosan, immediately add 2kg of pretreated nano-silica, mix evenly, and let stand at 4℃ for 16h to obtain the repair agent.

[0041] Example 3: Preparation of Repair Agent

[0042] A: Add 1 kg of chitosan to 10 kg of 50 wt% isopropanol aqueous solution and stir to disperse. After standing for 6 h, add 0.5 kg of 1,2-epoxybutane. Stir and react at room temperature for 1 h, then heat to 70 °C and continue to react for 40 min. After the reaction is complete, filter to remove the filtrate, and then dry at 45 °C to obtain modified chitosan.

[0043] B: Add 4 kg of nano silica to 20 kg of water and stir to disperse. Heat to 80°C and keep warm for 1 hour. Then add 0.5 kg of dithiothreitol and react at a constant temperature for 60 minutes. After that, cool down to 40°C and add 0.2 kg of L-asparagine and react for 2 hours. After the reaction is complete, filter to remove the filtrate and place at 4°C overnight to obtain pretreated nano silica.

[0044] C: Prepare a 2wt% modified chitosan solution by adding water to 10kg of modified chitosan, immediately add 4kg of pretreated nano-silica, mix evenly, and let stand at 4℃ for 24h to obtain the repair agent.

[0045] Comparative Example 1: Preparation of Repair Agent

[0046] Compared with Example 1, the only difference is that in Comparative Example 1, chitosan is not modified in step A during the preparation of the repair agent, while chitosan solution can be prepared directly in step C.

[0047] Comparative Example 2: Preparation of Repair Agent

[0048] Compared with Example 1, the only difference is that dithiothreitol was not added in step B of the preparation of the repair agent in Comparative Example 2, as detailed below:

[0049] A: Same as Example 1;

[0050] B: Add 3 kg of nano silica to 15 kg of water and stir to disperse. Heat to 70°C and keep warm for 1.5 h. Then cool down to 45°C and add 0.15 kg of L-asparagine to react for 1.5 h. After the reaction is complete, filter to remove the filtrate and place at 4°C overnight to obtain pretreated nano silica.

[0051] C: Same as in Example 1.

[0052] Comparative Example 3: Preparation of Repair Agent

[0053] Compared with Example 1, the only difference is that L-asparagine was not added in step B of the preparation of the repair agent in Comparative Example 3, as detailed below:

[0054] A: Same as Example 1;

[0055] B: Add 3 kg of nano silica to 15 kg of water and stir to disperse. Heat to 70°C and keep warm for 1.5 h. Then add 0.3 kg of dithiothreitol and react at a constant temperature for 40 min. After the reaction is complete, filter to remove the filtrate and place at 4°C overnight to obtain pretreated nano silica.

[0056] C: Same as in Example 1.

[0057] Comparative Example 4: Preparation of Repair Agent

[0058] Compared with Example 1, the only difference is that step B was missing in the preparation of the repair agent in Comparative Example 4, i.e., no pretreatment of nano-silica was performed, and conventional nano-silica was used instead, as detailed below:

[0059] A: Same as Example 1;

[0060] B: Prepare a 7kg 2wt% modified chitosan solution by adding water to the modified chitosan, immediately add 3kg nano silica and mix evenly, then let stand at 4℃ for 18h to obtain the repair agent.

[0061] Comparative Example 5: Preparation of Repair Agent

[0062] Compared with Example 1, the only difference is that in Comparative Example 5, cold treatment was not performed in step B during the preparation of the repair agent, as detailed below:

[0063] A: Same as Example 1;

[0064] B: Add 3 kg of nano silica to 15 kg of water and stir to disperse. Heat to 70°C and keep warm for 1.5 h. Then add 0.3 kg of dithiothreitol and react at a constant temperature for 40 min. After that, cool down to 45°C and add 0.15 kg of L-asparagine and react for 1.5 h. After the reaction is complete, filter to remove the filtrate to obtain pretreated nano silica.

[0065] Comparative Example 6: Preparation of Repair Agent

[0066] Compared with Example 1, the only difference is that steps A and B were omitted in the preparation of the repair agent in Comparative Example 6. The repair agent was prepared directly using conventional chitosan and conventional nano-silica, as detailed below:

[0067] A 2wt% chitosan solution was prepared by adding water to 7 kg of chitosan. Immediately after that, 3 kg of nano-silica was added and mixed evenly. The solution was then left to stand at 4°C for 18 hours to obtain the repair agent.

[0068] Example 4: Garden Soil Remediation

[0069] (1) After removing weeds and impurities from the soil, till the soil to a depth of about 35cm. After tilling, adjust the soil pH to 5 and let it stand for 8 days.

[0070] (2) At 9:00 AM on a sunny day, according to 0.2 kg / m 2 The amount of the remediation agent prepared in Example 3 was sprayed into the soil. After spraying for 4 hours, the soil was tilled to a depth of about 25 cm. After tilling, the same amount of remediation agent was sprayed a second time. Four days after the remediation agent was applied, the soil pH was adjusted to 6.5.

[0071] (3) Soak vetiver seeds in 75% ethanol solution for 30 seconds, then disinfect them in 0.1% mercuric chloride solution for 6 minutes, and then wash them 5 times with sterile water to obtain disinfected seeds; soak the disinfected seeds in clean water for 18 hours to obtain pretreated seeds; place the pretreated seeds in a petri dish lined with two layers of filter paper, sprinkle water to moisten the filter paper, and place it in an incubator for germination treatment at 25℃ in the dark until the seeds show white sprouts to obtain germinated vetiver seeds; mix peat moss and coconut coir in a volume ratio of 1:2 to obtain a substrate, put the substrate in an autoclave and sterilize it at 121℃ for 15 minutes, then add *Gnaphalium moss* in a mass ratio of substrate: *Gnaphalium moss* = 50:1 and mix evenly to obtain a substrate for inoculating arbuscular mycorrhizal fungi; then mix the germinated plant seeds: substrate inoculated with arbuscular mycorrhizal fungi in a mass ratio of 1:40 and then apply the mixture at 0.5 kg / m³. 2 Spread the seeds in sufficient quantities;

[0072] (4) After the planted vetiver grass matures, it should be pulled up by the roots. Then, the vetiver grass should be planted again in step (3) until the content of heavy metal ions in the soil meets the standard of the "Soil Environmental Quality Agricultural Land Soil Risk Control Standard (Trial)" (GB15618-2018). After the restoration of the garden soil is obtained, garden plants can be planted in accordance with conventional methods.

[0073] Experiment: Garden Soil Remediation Experiment

[0074] 1. Experimental preparation: The remediation agents prepared in Example 1 and Comparative Examples 1-6 were used to conduct garden soil remediation experiments. The experiments were conducted at the Rose Garden Experimental Base on TEDA Street, Binhai New Area, Tianjin. A block area was designated as the experimental area. Before the experiment, the initial contents of cadmium, copper, and lead in the soil of the experimental area were measured. Then, the experimental area was divided into 12 small areas, each with an area of ​​3×3m, corresponding to experimental group 1, control groups 1-10, and blank control group, respectively.

[0075] 2. Experimental Methods:

[0076] Experimental Group 1: The repair agent prepared in Example 1 and the repair method in Example 4 were used;

[0077] Control groups 1-6: The repair agents of comparative examples 1-6 and the repair method of example 4 were used respectively;

[0078] Control group 7: The remediation agent of Example 1 was used. In the soil remediation, the soil pH was not adjusted in step (1), and the remaining steps were carried out according to the method of Example 4.

[0079] Control group 8: The remediation agent of Example 1 was used. When carrying out soil remediation, Moses Glomerula was not inoculated in the substrate. The substrate and the germinated seeds were directly mixed and sown. The remaining steps were carried out according to the method of Example 4.

[0080] Control group 9: No remediation agent was applied to the soil of control group 9, but water was applied instead. The remaining steps were carried out according to the method in Example 4.

[0081] Control group 10: When the soil remediation was carried out in control group 10, the soil pH was not adjusted after the remediation agent was applied in step (2), and the remaining steps were carried out according to the method of Example 4.

[0082] Blank control group: The blank control group was directly sown with pre-germinated seeds after soil cleaning and tilling, as detailed below:

[0083] (1) After removing weeds and impurities from the soil, till the soil to a depth of about 35cm and let it stand for 8 days.

[0084] (2) Vetiver seeds were soaked in 75% ethanol solution for 30 seconds and then disinfected in 0.1% mercuric chloride solution for 6 minutes. They were then rinsed 5 times with sterile water to obtain disinfected seeds. The disinfected seeds were soaked in clean water for 18 hours to obtain pretreated seeds. The pretreated seeds were placed in a petri dish lined with two layers of filter paper, the filter paper was moistened with water, and the dish was placed in an incubator at 25°C in the dark for germination treatment until the seeds showed white sprouts. Peat moss and coconut coir were mixed in a volume ratio of 1:2 to obtain a substrate. The substrate was sterilized in an autoclave at 121°C for 15 minutes. The pretreated seeds were then mixed with the substrate at a mass ratio of 1:40 and then applied at a concentration of 0.5 kg / m³. 2 The amount is sown.

[0085] (3) Results detection: Five months after sowing, the vetiver grass in each group was uprooted, the soil around the roots was removed, and the weight of the vetiver grass in each group was weighed. The cadmium, copper, and lead content in the soil was measured again. The data are shown in Table 1.

[0086] Table 1

[0087]

[0088]

[0089] Based on the data analysis in Table 1, we can conclude that:

[0090] (1) After planting vetiver grass in the heavy metal contaminated soil in Experimental Group 1, the vetiver grass grew well and had a high biomass. The cadmium, copper and lead content in the soil had been significantly reduced. This indicates that the method of the present invention can remove heavy metal ions in the soil relatively quickly and effectively, and has a good effect on the remediation of heavy metal contaminated garden soil, thus providing a better environment for the growth of garden plants.

[0091] (2) In control group 1, the remediation agent did not treat the chitosan. The prepared remediation agent had strong permeability and penetrated downwards, which reduced the fixation effect of the remediation agent on heavy metal ions in the soil. The migration of heavy metal ions in the soil led to a decrease in the amount absorbed and accumulated by plants. In contrast, in experimental group 1, the chitosan solution prepared by modifying the chitosan in the remediation agent gelled due to temperature changes after entering the soil, which enhanced the fixation effect on heavy metal ions and inhibited the migration of heavy metal ions. As a result, the amount absorbed and accumulated by plants increased, and the remediation effect was relatively better.

[0092] (3) In the preparation of the repair agents in control groups 2 and 3, dithiothreitol and L-asparagine were not added respectively. As a result, the adsorption activity of the adsorption active sites of nano silica in the repair agents of control groups 3 and 4 was consistent for heavy metal ions in the soil. After the arbuscular mycorrhizal fungi secreted organic acids, the adsorbed heavy metal ions were released in large quantities at the same time, which caused stress to the plants, reduced the plant biomass and reduced the repair effect. In experimental group 1, dithiothreitol and L-asparagine were used to modify nano silica, respectively, and groups with different binding abilities to heavy metal ions were introduced. Then, under the competitive binding of the secreted organic acids, the bound and fixed heavy metal ions were released one after another, eliminating the stress of heavy metal ions and improving the absorption and enrichment of plants.

[0093] (4) In the control group 8, no arbuscular mycorrhizal fungi were inoculated during soil remediation, and the plant failed to secrete organic acids to activate the fixed heavy metal ions. The amount absorbed and accumulated by the plants was small, and a large amount of heavy metal ions were released after the remediation agent degraded in the later stage. Therefore, the content of heavy metal ions in the soil did not decrease significantly.

[0094] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Technical aspects, shapes, and structures not described in detail in this invention are all well-known technologies.

Claims

1. A method for remediating contaminated soil in gardens, characterized in that, The method includes the following steps: Step (1) After removing weeds and impurities from the soil, till the soil and adjust the soil pH to 4.5-5.

5. Let it stand for 5-10 days. Step (2) On a sunny morning between 9 and 10 a.m., apply 0.1-0.3 kg / m 2 Spray the repair agent onto the soil in the specified amount. After spraying for 4 hours, till the soil to a depth of 20-30cm. After tilling, spray the repair agent a second time in the same amount. Adjust the soil pH to 6-7 3-6 days after applying the repair agent. Step (3) After germination, the hyperaccumulated plant seeds are added to the substrate inoculated with arbuscular mycorrhizal fungi, mixed evenly, and then sown. After the hyperaccumulating plants planted in step (4) mature, they are pulled up by the roots. Then, the hyperaccumulating plants are planted again in the same way as in step (3) until the heavy metal ion content in the soil meets the national standard and the garden soil is restored. The repair agent in step (2) includes the following raw materials: Chitosan, 50wt% isopropanol aqueous solution, 1,2-epoxybutane, nano-silica, L-asparagine, dithiothreitol; The preparation method of the repair agent is as follows: Step A: Add chitosan to 50wt% isopropanol aqueous solution and stir to disperse. After standing for 2-6 hours, add 1,2-epoxybutane and stir to react at room temperature for 1 hour. Then raise the temperature to 60-70℃ and continue to react for 20-40 minutes. After the reaction is completed, filter to remove the filtrate and then dry at 45℃ to obtain modified chitosan. Step B: Add nano-silica to water and stir to disperse. Heat to 60-80℃ and keep warm for 1-2 hours. Then add dithiothreitol and react at a constant temperature for 30-60 minutes. After that, cool to 40-50℃ and add L-asparagine and react for 1-2 hours. After the reaction is complete, filter to remove the filtrate and place at 4℃ overnight to obtain pretreated nano-silica. Step C: Add water to the modified chitosan to make a 2wt% modified chitosan solution, add pretreated nano-silica and mix evenly, then let stand at 4℃ for 12-24 hours to obtain the repair agent.

2. The method for remediating contaminated soil in gardens according to claim 1, characterized in that, In step A, the mass ratio of chitosan, 50wt% isopropanol aqueous solution, and 1,2-epoxybutane is (0.5-1):(5-10):(0.2-0.5).

3. The method for remediating contaminated soil in gardens according to claim 2, characterized in that, In step B, the mass ratio of nano-silica, dithiothreitol, and L-asparagine is (2-4):(0.2-0.5):(0.1-0.2).

4. The method for remediating contaminated soil in gardens according to claim 3, characterized in that, In step C, the mass ratio of 2wt% modified chitosan solution to pretreated nano-silica is (5-10):(2-4).

5. A method for remediating contaminated soil in gardens according to claim 4, characterized in that, The hyperaccumulating plant is either vetiver or centipede grass.

6. A method for remediating contaminated soil in gardens according to claim 5, characterized in that, The specific steps for germinating hyperaccumulating plant seeds in step (3) are as follows: The seeds of hyperaccumulating plants were soaked in 75% ethanol solution for 30 seconds and then disinfected in 0.1% mercuric chloride solution for 5-8 minutes. They were then rinsed 5 times with sterile water to obtain disinfected seeds. The disinfected seeds were then soaked in clean water for 12-24 hours to obtain pretreated seeds. Pretreated seeds were placed in a petri dish lined with two layers of filter paper. The filter paper was moistened with water and then placed in an incubator for germination treatment at 25°C in the dark until the seeds showed signs of sprouting, thus obtaining hyperaccumulated plant seeds after germination.

7. A method for remediating contaminated soil in gardens according to claim 6, characterized in that, The specific steps for inoculating the substrate with arbuscular mycorrhizal fungi in step (3) are as follows: A substrate is prepared by mixing peat moss and coconut coir in a volume ratio of 1:

2. Arbuscular mycorrhizal fungi are then added to the substrate in a mass ratio of substrate to arbuscular mycorrhizal fungi of 50:1 to obtain the substrate inoculated with arbuscular mycorrhizal fungi.

8. A method for remediating contaminated soil in gardens according to claim 7, characterized in that, The arbuscular mycorrhizal fungus is *Glomus mosie*.

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