Tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system and method

Abstract

The invention discloses a tea garden sloping field surface runoff nitrogen and phosphorus multi-stage treatment and recovery system and method, and the system comprises a tea garden sloping field and a drainage ditch arranged in the tea garden sloping field, and further comprises a multi-stage permeable reactive barrier and a multi-stage soil seepage ditch which are arranged in the tea garden sloping field, the multi-stage permeable reactive barrier comprises at least three stages of permeable reactive barriers which are arranged in parallel at intervals; the multiple stages of soil seepage ditches are arranged close to the last-stage permeable reactive barrier and comprise water collecting ditches which are arranged in parallel in the direction perpendicular to the sloping field, M-shaped soil bricks are arranged in the water collecting ditches, pebbles are filled in the water collecting ditches, and the upper portions of the water collecting ditches are filled with vegetation belts; and the surface runoff passing through the multi-stage permeable reactive barrier enters the multi-stage soil seepage ditch and overflows to the drainage ditch of the tea garden slope through the multi-stage soil seepage ditch. By coupling the multi-stage permeable reactive barrier and the multi-stage soil seepage ditch technology, nitrogen and phosphorus pollution driven by runoff of the southwest tea garden is effectively prevented and controlled, and nitrogen and phosphorus are effectively recovered.

Description

Technical Field

[0001] The invention belongs to the technical field of nitrogen and phosphorus pollution treatment, and specifically relates to a multi-stage treatment and recovery system and method for nitrogen and phosphorus in surface runoff from a slope of a tea garden. Background Art

[0002] Non-point source pollution from farmland has become an important cause of excessive nitrogen and phosphorus and eutrophication in my country's surface water. Source control and process blocking are effective ways to control non-point source pollution from farmland. The Southwest Tea Area is located in southwest China, including Yunnan, Guizhou, Sichuan and southeastern Tibet. It is the oldest tea area in China. It has rich tea tree varieties and produces black tea, green tea, Tuo tea, compressed tea and Pu'er tea. It is a major base for the development of large-leaf black broken tea in China. The region has the characteristics of abundant rainfall, large slope in the tea area and large runoff coefficient. Tea trees like fertilizer. Generally, tea gardens are produced with 15-30 kg of nitrogen fertilizer per mu and 4-6 kg of phosphorus fertilizer per mu. Excessive fertilizer nitrogen and phosphorus enter natural water bodies with surface runoff. However, as crop nutrients, nitrogen and phosphorus cannot fully solve the problem of excessive fertilizer application at the source by only treating them as pollutants. Therefore, effective nitrogen and phosphorus coordinated pollution control and recovery, reducing nitrogen and phosphorus pollution in surface runoff, and effectively recovering some nitrogen and phosphorus to feed back farmland nutrition are technical problems that need to be solved urgently. Summary of the invention

[0003] The purpose of the present invention is to solve the above-mentioned problems and provide a tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system and method, by coupling a multi-stage permeable reaction wall with a multi-stage soil seepage ditch technology, using slope runoff, biochar adsorption, wall-ditch composite slope hydrological process regulation, microbial agent nutrient conversion and other processes, effectively block and control the nitrogen and phosphorus pollution driven by the runoff of southwestern tea gardens and effectively recover nitrogen and phosphorus, and reuse them in the tea garden soil, replenish the tea garden soil nutrients, improve the soil physical and chemical properties, and achieve the purpose of integrated treatment of nitrogen and phosphorus pollution control and recovery and reuse.

[0004] To achieve the above-mentioned purpose, the present invention provides a tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, comprising a tea garden slope and a drainage ditch arranged on the tea garden slope, and also comprising a multi-stage permeable reaction wall and a multi-stage soil seepage ditch arranged on the tea garden slope, wherein the multi-stage permeable reaction wall comprises at least three stages of permeable reaction walls arranged in parallel and at intervals; the multi-stage soil seepage ditch is arranged adjacent to the last stage permeable reaction wall, and comprises a water collection ditch perpendicular to the slope direction, wherein M-shaped soil bricks are arranged in the water collection ditch and filled with pebbles, and the upper part of the water collection ditch is filled with a vegetation belt; the surface runoff passing through the multi-stage permeable reaction wall enters the multi-stage soil seepage ditch, and then overflows to the drainage ditch of the tea garden slope through the multi-stage soil seepage ditch.

[0005] In the above tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, the permeable reaction wall includes a permeable reaction wall body and a biochar filler filled in the permeable reaction wall body; the soil bricks include a soil brick body and a biochar filler filled in the soil brick body; the proportion of the biochar filler in the permeable reaction wall is 5% to 10%, and the proportion of the biochar filler in the soil bricks is 15% to 20%. The biochar fillers in the permeable reaction wall and the soil bricks can adsorb nitrogen and phosphorus in the surface runoff.

[0006] Furthermore, the biochar filler is prepared by low-temperature cross-linking reaction using biochar, lithium slag, sodium alginate-cassava starch and a cross-linking agent as raw materials, and the biochar is biochar loaded with microbial agents.

[0007] The biochar filler provided by the present invention comprises lithium slag in the raw material mainly containing alkali metal oxides (such as Li 2 O、Na 2 O.K 2 O), the acidic substances (such as sulfuric acid) remaining in the slag by the acid method, lithium slag can be used as aggregate to fill the pores of biochar, improve the overall rigidity of the material, and neutralize the alkalinity of biochar, adjust the pH of the material to 5.5-7.5, form insoluble iron phosphate and aluminum phosphate compounds on its surface, and are beneficial to the biological nitrogen fixation of microbial agents and the stability of ammonium nitrogen. The mixture of biochar and lithium slag solves the problem of poor physical performance of pure biochar, improves the density of the mixture, and reduces the problem of biochar moving upward in the soil with the sedimentation of soil particles for a long time; secondly, it improves the strength and mechanical properties of the mixture and delays the agglomeration with the soil structure; in addition, short-term lithium slag adjusts the surface pH of biochar and improves the fixation of nitrogen and phosphorus on its surface; long-term lithium slag can be released with water and interact with soil organic matter to adjust the physical structure of the soil.

[0008] Furthermore, the biochar filler in the present invention is preferably prepared by the following method, which specifically comprises the following steps:

[0009] S1. Mixing the biochar loaded with microbial agents and lithium slag in a ratio of 1:1.5-2 to obtain a premix;

[0010] S2, adding sodium alginate and cassava starch to the soil leachate to obtain a pre-mixed solution, wherein the mass fraction of sodium alginate is 2-5%, and the mass fraction of cassava starch is 20-30%;

[0011] S3, adding the prepared mixture into the prepared mixed liquid at a solid-liquid ratio of 1g:10-20mL, stirring and mixing until it is uniform and viscous to obtain a mixed liquid;

[0012] S4. Inject the mixed liquid into a mold, add a cross-linking agent into the mold, and cross-link for 8 to 12 hours at 3 to 5° C. to prepare a colloid plate, and obtain the biochar filler after washing.

[0013] In the above tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, in step S3, a hemp net is also added to the mold, and the hemp net is a net woven from hemp fibers.

[0014] In the above-mentioned tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, the wall height below the soil of the permeable reaction wall is not less than 40 cm. The wall above the soil is the main part of intercepting slope runoff. Affected by the runoff coefficient, slope, and rainfall, the wall height above the soil is designed using the following formula:

[0015]

[0016] Where: H n H is the height of the wall above the soil, the maximum value does not exceed 5cm, n-1 =0.6H n ;

[0017] C is the slope runoff coefficient, ranging from 0 to 1, dimensionless;

[0018] H is the local average rainfall depth, in mm;

[0019] θ is the slope of the slope, in degrees.

[0020] The average particle size of lithium slag is preferably in the range of 80 to 120 mesh. Biochar and lithium slag are mixed in a ratio of 1:1.5 to 2. Too high a content of lithium slag will cause an excessively high content of S elements, accelerate soil acidification, and affect plant growth. Soil leachate can provide a native soil environment (including nutrients, trace elements, and indigenous microorganisms) for microbial agents, which can further train microorganisms and improve the activity and efficacy of microbial agents in applied soil. Soil leachate can be obtained by conventional methods in the art. The present invention selects 5 kg of surface soil from the technical application site, naturally air-dries, grinds through a 2 mm sieve, and continuously stirs with 50 L of tap water for 12 hours, naturally settles, and extracts the supernatant to obtain soil leachate. Furthermore, the cross-linking agent can be a conventional cross-linking agent in the art. In the present invention, the cross-linking agent is preferably 10 g· / L of CaCl 2 Solution.

[0021] The above-mentioned tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, the preparation method of biochar loaded with microbial agents can be prepared by conventional methods in the field. In the present invention, the microbial agent is adsorbed on the surface of biochar by the equilibrium adsorption method. Phosphate-solubilizing bacteria are used to form a microbial composite agent in a ratio of 1:5 to 2:1 (biomass ratio), and LB culture medium is used to load it on the surface of biochar at a liquid-solid ratio of 20ml:1g. After constant temperature shaking at 25℃ for 24h, solid-liquid separation is performed after high-speed centrifugation to separate the biochar loaded with microbial agents.

[0022] In the above tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, the distance between adjacent permeable reaction walls is no more than 10 cm, the wall thickness is no more than 20 cm, and the wall bulk density above the soil is no less than 1.8 g / cm 3 The bulk density of the wall below the soil is not higher than 2g / cm 3 .

[0023] In the above-mentioned tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, the soil bricks arranged in the water collection ditch are at least two layers, and the two adjacent layers of soil bricks are staggered.

[0024] In the above-mentioned tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, the soil bricks are no more than 6 cm in height, no more than 12 cm in width, the tooth height is no more than 4 cm, and the tooth width is not less than 2 cm.

[0025] In the above-mentioned tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, the pebbles are filled in the spaces between the teeth of the soil bricks and the remaining spaces in the grooves, the median particle size of the pebbles filled in the teeth is not greater than 2 mm, and the pebbles filled in the remaining parts are greater than 2 mm.

[0026] The present invention also provides a method for multi-stage treatment and recovery of nitrogen and phosphorus in surface runoff from a tea garden slope, comprising the following steps:

[0027] S1. During the winter period from December to February of the following year, the above-mentioned tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system is deployed on the tea garden slope;

[0028] S2. Generally, no maintenance is required during the spring, summer and autumn seasons from March to November of the following year. After heavy rainfall, the silt intercepted by the vegetation belt on the multi-level soil seepage ditch is removed to keep the runoff water seepage smooth;

[0029] S3. In the winter from December to February of the following year, the M-shaped soil bricks in the multi-level soil seepage ditch are dug out, and after screening, the soil bricks that have recovered nitrogen and phosphorus from surface runoff for one year are returned to the tea garden to supplement soil fertility, and the multi-level soil seepage ditch is rebuilt;

[0030] S4. Reconstruct the multi-level permeable reaction wall every three years and reuse the wall material in the tea garden soil.

[0031] In the above step S3, the soil may clump, and after screening, it can be dispersed into small particles, which is helpful for nutrient release.

[0032] The tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system and method provided by the present invention have the following beneficial effects:

[0033] 1. The present invention realizes nitrogen and phosphorus pollution control and recycling through the coupling design of permeable reaction wall and multi-stage soil seepage ditch, and through slope runoff, biochar adsorption, wall-ditch composite slope hydrological process regulation, microbial agent nutrient conversion, etc. The permeable reaction wall and soil bricks reused in the tea garden soil can supplement the soil nutrients in the tea garden, improve the soil physical and chemical properties, and be conducive to sustainable ecological development.

[0034] 2. The present invention improves the biochar filler and loads the microbial agent on the surface of the biochar, which can effectively improve the recovery efficiency of the biochar for runoff nitrogen and phosphorus; lithium slag is used as an aggregate to fill the pores of the biochar, improve the overall rigidity of the material, and neutralize the alkalinity of the biochar, forming insoluble iron phosphate and aluminum phosphate compounds on its surface, and is beneficial to the biological nitrogen fixation of the microbial agent and the stability of ammonium nitrogen. The mixture of the two solves the problem of poor physical performance of pure biochar, improves the density of the mixture, and reduces the problem of biochar moving upward in the soil for a long time as soil particles settle; secondly, it improves the strength and mechanical properties of the mixture and delays the agglomeration with the soil structure; in addition, short-term lithium slag adjusts the surface pH of the biochar and improves the fixation of nitrogen and phosphorus on its surface; long-term lithium slag can be released with water and interact with soil organic matter to adjust the physical structure of the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the structure of the multi-stage treatment and recovery system for nitrogen and phosphorus in the surface runoff of a tea garden slope according to the present invention;

[0036] Figure 2 It is a schematic diagram of the arrangement of soil bricks in the multi-stage soil seepage ditch of the present invention;

[0037] Figure 3 is the average recovery rate of TN and TP in the experimental example;

[0038] Figure 4 This is a diagram comparing the recovery effects of nitrogen and phosphorus in surface runoff in the experimental example.

[0039] Explanation of the accompanying drawings: 1. Tea garden slope; 2. Drainage ditch; 3. Multi-level permeable reaction wall; 4. Multi-level soil seepage ditch. DETAILED DESCRIPTION

[0040] The technical solutions of the embodiments of the present invention are clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the present invention.

[0041] Example 1

[0042] This embodiment provides a tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, such as Figure 1 As shown, it includes a tea garden slope 1, a drainage ditch 2 set on the tea garden slope 1, and a multi-level permeable reaction wall 3 and a multi-level soil seepage ditch 4 set on the tea garden slope 1. The drainage ditch 2 set on the tea garden slope 1 is the original soil drainage ditch of the tea garden. The surface runoff through the multi-level permeable reaction wall 3 enters the multi-level soil seepage ditch 4, and the water overflows from the multi-level soil seepage ditch 4 to the original soil drainage ditch.

[0043] The multi-stage permeable reaction wall 3 includes three stages of permeable reaction walls arranged in parallel and at intervals. The height of the permeable reaction wall below the soil is not less than 40 cm, and the height of the wall above the soil is designed using the following formula:

[0044]

[0045] Where: H n H is the height of the wall above the soil, the maximum value does not exceed 5cm, n-1 =0.6H n ;

[0046] C is the slope runoff coefficient, ranging from 0 to 1, dimensionless;

[0047] H is the local average rainfall depth, in mm;

[0048] θ is the slope of the slope, in degrees.

[0049] The distance between adjacent permeable reaction walls shall not exceed 10 cm, the wall thickness shall not exceed 20 cm, and the bulk density of the wall above the soil shall not be less than 1.8 g / cm 3 The bulk density of the wall below the soil is not higher than 2g / cm 3 .

[0050] The multi-stage soil seepage ditch 4 is arranged next to the last permeable reaction wall, including a water collection ditch perpendicular to the slope direction. The bottom and both sides of the ditch are compacted, and M-shaped soil bricks are arranged in the water collection ditch and filled with pebbles to facilitate water flow. The upper part of the water collection ditch is filled with a vegetation belt. Figure 2As shown, there are two layers of soil bricks in the water collection ditch, and the two adjacent layers of soil bricks are staggered. The height of the soil brick does not exceed 6cm, the width does not exceed 12cm, the tooth height does not exceed 4cm, and the tooth width is not less than 2cm. Pebbles are filled in the teeth of the soil bricks and the rest of the space in the ditch. The median particle size of the pebbles filled in the teeth is not greater than 2mm, and the pebbles filled in the rest are larger than 2mm.

[0051] The permeable reaction wall includes a permeable reaction wall body and a biochar filler filled in the permeable reaction wall body. The soil brick includes a soil brick body and a biochar filler filled in the soil brick body. The proportion of the biochar filler in the permeable reaction wall is 5% to 10%, and the proportion of the biochar filler in the soil brick is 15% to 20%. The biochar filler in the permeable reaction wall and the soil brick can adsorb nitrogen and phosphorus in surface runoff.

[0052] Biochar filler is made of biochar, lithium slag, sodium alginate-cassava starch and cross-linking agent as raw materials, and is prepared by low-temperature cross-linking reaction. Biochar must meet the requirements of the "Biochar" (NY / T 3672-2020) standard, and the median particle size is not less than 18 mesh, preferably 30-40 mesh, and the specific surface area is not less than 100m 2 / g, biochar can be produced by pruning tea gardens, and the biochar produced by high temperature (>650℃) pyrolysis has a lignin content of not less than 20%.

[0053] In order to improve the recovery efficiency of runoff nitrogen and phosphorus by biochar, microbial agents are loaded on its surface. Therefore, the biochar is biochar loaded with microbial agents. The microbial agents are adsorbed on the surface of biochar by the equilibrium adsorption method. Phosphate-solubilizing bacteria are used to form a microbial composite agent at a ratio of 1:5 to 2:1 (biomass ratio). LB culture medium is used to load the biochar surface at a liquid-solid ratio of 20ml:1g. After constant temperature shaking at 25℃ for 24h, the solid-liquid separation is carried out after high-speed centrifugation to separate the biochar loaded with microbial agents.

[0054] The biochar filling process specifically includes the following steps:

[0055] S1, mixing the biochar loaded with microbial agents and 100-mesh lithium slag in a ratio of 1:1.5 to obtain a pre-mixture;

[0056] S2, adding sodium alginate and cassava starch to the soil leachate to obtain a pre-mixed solution, wherein the mass fraction of sodium alginate is 2% and the mass fraction of cassava starch is 20%;

[0057] S3, adding the prepared mixture into the prepared mixed liquid at a solid-liquid ratio of 1g:20mL, stirring and mixing until the mixture is uniform and viscous, to obtain a mixed liquid;

[0058] S4. Pour the mixed liquid into a mold equipped with a hemp mesh, and add 10 g· / L CaCl 2 The solution is used as a cross-linking agent and cross-linked at 3 to 5° C. for 8 to 12 hours to prepare a colloidal plate, which is then washed to obtain a biochar filler.

[0059] The hemp net is made of natural hemp fiber, with a unit mesh size of 1cm*1cm.

[0060] The soil extract was prepared by the following steps: 5 kg of surface soil from the technical application site was selected, naturally air-dried, ground through a 2 mm sieve, and continuously stirred with 50 L of tap water for 12 h, allowed to settle naturally, and the supernatant was extracted and passed through a 0.45 um membrane to obtain the soil extract.

[0061] Since the rainy season on the slopes of southwest China is from July to September and tea picking begins in March and April, the construction of the above-mentioned tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system project should be carried out in the winter between December and February of the following year.

[0062] Example 2

[0063] This embodiment provides a method for multi-stage treatment and recovery of nitrogen and phosphorus in surface runoff from a tea garden slope, comprising the following steps:

[0064] S1. During the winter period from December to February of the following year, the above-mentioned tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system is deployed on the tea garden slope 1;

[0065] S2. Generally, no maintenance is required during the spring, summer and autumn seasons from March to November of the following year. After heavy rainfall, the silt intercepted by the vegetation belt on the multi-level soil seepage ditch 4 is removed to keep the runoff water seepage smooth;

[0066] S3. In the winter of December to February of the following year, the M-shaped soil bricks in the multi-level soil seepage ditch 4 are dug out, and after screening, the soil bricks that have recovered nitrogen and phosphorus from the surface runoff for one year are returned to the tea garden to supplement soil fertility, and the multi-level soil seepage ditch 4 is reconstructed;

[0067] S4. Reconstruct the multi-level permeable reaction wall 3 every three years, and reuse the wall for tea garden soil.

[0068] Experimental example

[0069] 1. Experiment on the effects of biochar and microbial agents on nitrogen and phosphorus recovery

[0070] A 25cm*10cm*85cm in length, width and height percolation device was constructed to simulate the recovery efficiency of nitrogen and phosphorus in water by materials, and the pure soil, soil with biochar (mass fraction of 5%) and soil with biochar loaded with microbial agents (mass fraction of 5%) were compared. The influent flow rate was 10cm / d, TP was 5-6mg / L, and TN was 40-45mg / L. The startup period was 10d, and it was continuously operated for 30d after 10d. The average recovery rates of TN and TP at 30d were as follows: Figure 3 shown.

[0071] For pure soil, the recovery rates of total nitrogen and total phosphorus in the effluent increased to 68.19% and 92.70% respectively after adding biochar, which shows that biochar can effectively improve the recovery of total nitrogen and total phosphorus in water. After loading biochar with microbial agents, the recovery rates of total nitrogen and total phosphorus in the effluent further increased to 76.07% and 96.30%, indicating that the composite material of microbial agents and biochar can enhance the effect of biochar, and biochar as a carrier can also improve biological activity.

[0072] 2. Effect of multi-stage combined recycling technology

[0073] By constructing a slope with a slope of 5°, a length of 25 cm, a width of 10 cm, and a runoff of 10 mm / d, we constructed traditional permeable reaction walls, reaction walls + seepage ditches, and multi-stage reaction walls + multi-stage seepage ditches (multi-stage recovery technology). The results are as follows: Figure 4 shown.

[0074] The results show that the traditional permeable reaction wall has a certain recovery effect on nitrogen and phosphorus in runoff. Since the total phosphorus in the runoff is mostly in particulate form, the recovery rate of total nitrogen is slightly lower than that of total phosphorus. However, the total nitrogen recovery rate has been significantly improved after the combination process, and after the multi-stage combination process, the total nitrogen recovery rate has increased from 72.50% to 92.51%, and the total phosphorus has also increased to 99.45%, indicating that the multi-stage combination recovery process has a good strengthening effect compared with the traditional permeable reaction wall.

[0075] Those skilled in the art will appreciate that the embodiments herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system, comprising a tea garden slope (1) and a drainage ditch (2) arranged on the tea garden slope (1), characterized in that: The invention also comprises a multi-stage permeable reaction wall (3) and a multi-stage soil seepage ditch (4) arranged on the tea garden slope (1), wherein the multi-stage permeable reaction wall (3) comprises at least three stages of permeable reaction walls arranged in parallel and at intervals; the multi-stage soil seepage ditch (4) is arranged adjacent to the last stage permeable reaction wall, and comprises a water collection ditch perpendicular to the slope direction, wherein M-shaped soil bricks are arranged in the water collection ditch and filled with pebbles, and the upper part of the water collection ditch is filled with a vegetation belt; surface runoff passing through the multi-stage permeable reaction wall (3) enters the multi-stage soil seepage ditch (4), and then overflows through the multi-stage soil seepage ditch (4) to the drainage ditch (2) of the tea garden slope (1).

2. The tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system according to claim 1 is characterized by: The permeable reaction wall comprises a permeable reaction wall body and a biochar filler filled in the permeable reaction wall body, wherein the proportion of the biochar filler in the permeable reaction wall is 5% to 10%; the soil brick comprises a soil brick body and a biochar filler filled in the soil brick body, wherein the proportion of the biochar filler in the soil brick is 15% to 20%.

3. The tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system according to claim 2 is characterized by: The biochar filler is prepared by using biochar, lithium slag, sodium alginate-cassava starch and a cross-linking agent as raw materials through a low-temperature cross-linking reaction. The biochar is biochar loaded with microbial agents.

4. The tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system according to claim 3 is characterized by: The preparation method of the biochar filler comprises the following steps: S1. Mixing the biochar loaded with microbial agents and lithium slag in a ratio of 1:1.5-2 to obtain a premix; S2, adding sodium alginate and cassava starch to the soil leachate to obtain a pre-mixed solution, wherein the mass fraction of sodium alginate is 2-5%, and the mass fraction of cassava starch is 20-30%; S3, adding the prepared mixture into the prepared mixed liquid at a solid-liquid ratio of 1g:10-20mL, stirring and mixing until it is uniform and viscous to obtain a mixed liquid; S4. Inject the mixed liquid into a mold, add a cross-linking agent into the mold, and cross-link for 8 to 12 hours at 3 to 5° C. to prepare a colloid plate, and obtain the biochar filler after washing.

5. The tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system according to claim 4 is characterized by: In the step S3, a hemp net is also added into the mold, and the hemp net is a net woven from hemp fibers.

6. The tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system according to claim 1 is characterized by: The height of the permeable reaction wall below the soil is not less than 40 cm, and the height of the wall above the soil is designed using the following formula: Where: H n H is the height of the wall above the soil, the maximum value does not exceed 5cm, n-1 =0.6 H n ; C is the slope runoff coefficient, ranging from 0 to 1, dimensionless; H is the local average rainfall depth, in mm; θ is the slope of the slope, in degrees.

7. The tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system according to claim 1 is characterized by: The distance between adjacent permeable reaction walls is no more than 10 cm, the wall thickness is no more than 20 cm, and the bulk density of the wall above the soil is no less than 1.8 g / cm 3 The bulk density of the wall below the soil is not higher than 2g / cm 3 .

8. The tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system according to any one of claims 1 to 7, characterized in that: There are at least two layers of soil bricks arranged in the drainage ditch, and the two adjacent layers of soil bricks are arranged alternately; the height of the soil bricks does not exceed 6 cm, the width does not exceed 12 cm, the tooth height does not exceed 4 cm, and the tooth width is not less than 2 cm.

9. The tea garden slope surface runoff nitrogen and phosphorus multi-stage treatment and recovery system according to any one of claims 1 to 7, characterized in that: The pebbles are filled in the spaces between the teeth of the soil bricks and the remaining spaces in the grooves. The median particle size of the pebbles filled in the teeth is no more than 2 mm, and the median particle size of the pebbles filled in the remaining spaces is larger than 2 mm.

10. A multi-stage treatment and recovery method for nitrogen and phosphorus in surface runoff from a tea garden slope, characterized in that: The following steps are involved: S1. During the winter period from December to February of the following year, a tea garden slope (1) is provided with a multi-stage treatment and recovery system for nitrogen and phosphorus in surface runoff from a tea garden slope as claimed in any one of claims 1 to 9; S2. Generally, no maintenance is required during the spring, summer and autumn seasons from March to November of the following year. After heavy rainfall, the silt intercepted by the vegetation belt on the multi-level soil seepage ditch (4) is removed to keep the runoff water seepage smooth; S3. In the winter of December to February of the following year, the M-shaped soil bricks in the multi-level soil seepage ditch (4) are dug out, screened, and the soil bricks that have recovered nitrogen and phosphorus from the surface runoff for one year are returned to the tea garden to supplement soil fertility, and the multi-level soil seepage ditch (4) is reconstructed; S4. Reconstruct the multi-level permeable reaction wall (3) every three years, and reuse the wall for tea garden soil.

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