A multi-stage treatment and recovery system and method for nitrogen and phosphorus in tea garden slope surface runoff

Abstract

The application discloses a tea garden slope land surface runoff nitrogen and phosphorus multistage treatment and recovery system and method, which comprises a tea garden slope land and a drainage ditch arranged on the tea garden slope land, further comprises a multistage permeable reaction wall and a multistage soil seepage ditch arranged on the tea garden slope land, the multistage permeable reaction wall comprises at least three levels of permeable reaction walls arranged in parallel and at intervals, the multistage soil seepage ditch is arranged close to the last permeable reaction wall and comprises a water collecting ditch arranged in parallel with the slope land direction, M-shaped soil bricks are arranged in the water collecting ditch and filled with pebbles, and the upper part of the water collecting ditch is filled with a vegetation belt; the surface runoff of the multistage permeable reaction wall enters the multistage soil seepage ditch, and then overflows to the drainage ditch of the tea garden slope land through the multistage soil seepage ditch. The application is coupled with the multistage permeable reaction wall and the multistage soil seepage ditch technology, effectively controls and blocks the nitrogen and phosphorus pollution driven by the runoff of the southwest tea garden, and effectively recovers the nitrogen and phosphorus.

Description

Technical Field

[0001] This invention belongs to the field of nitrogen and phosphorus pollution treatment technology, specifically relating to a multi-stage treatment and recovery system and method for nitrogen and phosphorus in surface runoff on tea garden slopes. Background Technology

[0002] Non-point source pollution from farmland has become a significant cause of excessive nitrogen and phosphorus levels and eutrophication in my country's surface waters. Source control and process interruption are effective ways to manage farmland non-point source pollution. Excessive nitrogen and phosphorus from fertilizers enter natural water bodies via surface runoff. However, treating nitrogen and phosphorus merely as pollutants is insufficient to fully address the problem of excessive fertilizer application at the source, as nitrogen and phosphorus are essential nutrients for crops. Therefore, effectively controlling and recovering nitrogen and phosphorus in a coordinated manner, reducing nitrogen and phosphorus pollution in surface runoff while simultaneously recovering some nitrogen and phosphorus to nourish farmland, is a pressing technical challenge. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned problems and provide a multi-stage treatment and recovery system and method for nitrogen and phosphorus from surface runoff on tea garden slopes. By coupling multi-stage permeable reactive walls with multi-stage soil seepage trenches, and utilizing processes such as slope runoff, biochar adsorption, wall-ditch composite slope hydrological process regulation, and microbial inoculant nutrient conversion, the system effectively controls nitrogen and phosphorus pollution driven by runoff in southwestern tea gardens and effectively recovers nitrogen and phosphorus, which are then reused in the tea garden soil to replenish soil nutrients, improve soil physicochemical properties, and achieve the goal of integrated treatment of nitrogen and phosphorus pollution control and recycling.

[0004] To achieve the above objectives, the present invention provides a multi-stage nitrogen and phosphorus treatment and recovery system for surface runoff on tea garden slopes, including a tea garden slope and drainage ditches set on the tea garden slope, and also including multi-stage permeable reactive walls and multi-stage soil seepage ditches set on the tea garden slope. The multi-stage permeable reactive walls include at least three stages of permeable reactive walls set in parallel at intervals. The multi-stage soil seepage ditches are arranged adjacent to the last stage of permeable reactive walls and include a water collection ditch perpendicular to the slope direction. The water collection ditch is filled with M-shaped soil bricks and pebbles, and the upper part of the water collection ditch is filled with vegetation. Surface runoff passing through the multi-stage permeable reactive walls enters the multi-stage soil seepage ditches and then overflows into the drainage ditches on the tea garden slope.

[0005] The aforementioned multi-stage nitrogen and phosphorus treatment and recovery system for surface runoff in tea plantations on slopes comprises a permeable reactive wall consisting of a permeable reactive wall body and biochar filler material filling the permeable reactive wall body; and soil bricks consisting of soil brick bodies and biochar filler material filling the soil brick bodies; the proportion of biochar filler material in the permeable reactive wall is 5%–10%, and the proportion of biochar filler material in the soil bricks is 15%–20%. The biochar filler material in both the permeable reactive wall and the soil bricks can adsorb nitrogen and phosphorus from surface runoff.

[0006] Furthermore, the biochar filler is prepared by a 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 this invention uses lithium slag as raw material, which mainly contains alkali metal oxides (such as Li₂O, Na₂O, and K₂O) and residual acidic substances (such as sulfuric acid) in the slag produced by the acid process. The lithium slag can act as aggregate to fill the pores of the biochar, improving the overall rigidity of the material. It can also neutralize the alkalinity of the biochar, adjusting the pH of the material to 5.5–7.5, forming insoluble iron phosphate and aluminum phosphate compounds on its surface, which is beneficial to the biological nitrogen fixation and ammonium nitrogen stability of microbial agents. The mixture of biochar and lithium slag solves the problem of poor physical efficiency of pure biochar, increases the density of the mixture, and reduces the problem of biochar moving upwards with soil particles over a long period. Secondly, it improves the strength and mechanical properties of the mixture and delays agglomeration with the soil structure. Furthermore, in the short term, the lithium slag adjusts the surface pH of the biochar, improving the fixation of nitrogen and phosphorus on its surface; in the long term, the lithium slag can be released with water and interact with soil organic matter, regulating the soil physical structure.

[0008] Furthermore, the biochar packing material described in this invention is preferably prepared using the following method, specifically including the following steps:

[0009] S1. After mixing biochar loaded with microbial inoculant and lithium slag in a ratio of 1:1.5 to 2, a preliminary mixture is obtained;

[0010] S2. Sodium alginate and cassava starch are added to the soil leachate to obtain a preparative mixture, wherein the mass fraction of sodium alginate in the preparative mixture is 2-5% and the mass fraction of cassava starch is 20-30%.

[0011] S3. Add the prepared mixture to the prepared mixture at a solid-liquid ratio of 1g:10-20mL, stir and mix evenly until it becomes viscous to obtain a mixed liquid;

[0012] S4. Inject the mixed liquid into the mold, add a crosslinking agent to the mold, and crosslink at 3-5℃ for 8-12 hours to prepare a colloidal plate. After cleaning, the biochar filler is obtained.

[0013] In the above-mentioned multi-stage treatment and recovery system for nitrogen and phosphorus in surface runoff from tea garden slopes, step S3 involves adding a hemp net to the mold. The hemp net is a net woven from hemp fibers.

[0014] In the aforementioned multi-stage nitrogen and phosphorus treatment and recovery system for surface runoff on tea plantation slopes, the height of the permeable reactive wall below the soil is no less than 40cm. The wall above the soil is the main part for intercepting slope runoff. Affected by runoff coefficient, slope, and rainfall, the height of the wall above the soil is designed using the following formula:

[0015]

[0016] In the formula: H n The height of the wall above the soil, with a maximum value not exceeding 5cm, H n-1 =0.6H n ;

[0017] C is the slope runoff coefficient, which ranges from 0 to 1 and is dimensionless.

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

[0019] θ represents the slope, measured in degrees (°).

[0020] The preferred average particle size range for lithium slag is 80–120 mesh. Biochar and lithium slag are mixed in a ratio of 1:1.5–2. Excessive lithium slag content will result in excessive sulfur content, accelerating soil acidification and affecting plant growth. Soil leachate provides a native soil environment (including nutrients, trace elements, and indigenous microorganisms) for microbial agents, further training the microorganisms and improving the activity and efficacy of the microbial agents in the applied soil. Soil leachate can be obtained using conventional methods in the art. In this invention, 5 kg of topsoil from the application site is selected, naturally air-dried, ground through a 2 mm sieve, and continuously stirred with 50 L of tap water for 12 hours. After natural settling, the supernatant is extracted to obtain the soil leachate. Furthermore, the crosslinking agent can be a conventional crosslinking agent in the art; in this invention, the preferred crosslinking agent is a 10 g / L CaCl2 solution.

[0021] The aforementioned multi-stage nitrogen and phosphorus treatment and recovery system for surface runoff in tea garden slopes can be prepared using conventional methods in the field. In this invention, a balanced adsorption method is employed to adsorb the microbial agent onto the biochar surface. Phosphate-solubilizing bacteria are used to construct a microbial composite agent at a ratio of 1:5 to 2:1 (biomass ratio). LB medium is used, and the agent is loaded onto the biochar surface at a liquid-to-solid ratio of 20 ml: 1 g. After constant temperature shaking at 25°C for 24 hours, high-speed centrifugation is performed to separate the solid and liquid components, thus separating the biochar loaded with the microbial agent.

[0022] In the aforementioned multi-stage nitrogen and phosphorus treatment and recovery system for surface runoff on tea plantation slopes, the spacing between adjacent permeable reactive walls is no greater than 10cm, the wall thickness is no more than 20cm, and the bulk density of the wall above the soil is no less than 1.8g / cm³. 3The bulk density of the wall below the soil should not exceed 2g / cm³. 3 .

[0023] In the aforementioned multi-stage nitrogen and phosphorus treatment and recycling system for surface runoff on tea garden slopes, the soil bricks laid in the water collection ditch are at least two layers deep, with adjacent layers of soil bricks staggered.

[0024] In the aforementioned multi-stage nitrogen and phosphorus treatment and recycling system for surface runoff on tea garden slopes, the soil bricks are no more than 6cm high, no more than 12cm wide, with a tooth height of no more than 4cm and a tooth width of no less than 2cm.

[0025] In the above-mentioned multi-stage treatment and recycling system for nitrogen and phosphorus in surface runoff on tea garden slopes, the pebbles are filled between the teeth of the soil bricks and in the remaining spaces in the trenches. The median particle size of the pebbles filled between the teeth is no greater than 2 mm, while the pebbles in the remaining parts are larger than 2 mm.

[0026] This invention also provides a method for multi-stage treatment and recovery of nitrogen and phosphorus from surface runoff on tea plantation slopes, comprising the following steps:

[0027] S1. During the winter season from December to February of the following year, the above-mentioned multi-stage treatment and recovery system for nitrogen and phosphorus in surface runoff of tea garden slopes shall be set up on the tea garden slopes.

[0028] S2. During the spring, summer and autumn seasons from March to November of the following year, no maintenance is generally required. After heavy rainfall, remove the silt intercepted by the vegetation strip on the multi-level soil seepage ditches to keep the runoff water seepage smooth.

[0029] S3. In the winter of December to February of the following year, the M-shaped soil bricks in the multi-level soil seepage trenches 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 trenches are reconstructed.

[0030] S4. Reconstruct the multi-stage permeable reactive barrier every three years, and reuse the barrier soil in the tea garden.

[0031] In step S3 above, the soil will clump together. After sieving, it can be dispersed into small particles, which helps to release nutrients.

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

[0033] 1. This invention achieves nitrogen and phosphorus pollution control and recycling through a coupled design of permeable reactive walls and multi-stage soil seepage ditches, and by regulating slope runoff, biochar adsorption, wall-ditch composite slope hydrological processes, and microbial inoculant nutrient conversion. The permeable reactive walls and soil bricks reused in tea garden soil replenish soil nutrients, improve soil physicochemical properties, and promote sustainable ecological development.

[0034] 2. This invention improves the biochar filler by loading microbial agents onto the surface of the biochar, effectively enhancing its efficiency in recovering nitrogen and phosphorus from runoff. Lithium slag is used as aggregate to fill the pores of the biochar, increasing the overall rigidity of the material and neutralizing its alkalinity. This forms insoluble iron phosphate and aluminum phosphate compounds on the surface, which is beneficial for the biological nitrogen fixation and stability of ammonium nitrogen by the microbial agents. The combination of these two materials solves the problem of poor physical performance of pure biochar, increases the density of the mixture, and reduces the upward movement of biochar in the soil due to long-term soil particle settling. Secondly, it improves the strength and mechanical properties of the mixture and delays its aggregation with the soil structure. Furthermore, in the short term, the lithium slag adjusts the surface pH of the biochar, improving the fixation of nitrogen and phosphorus on its surface; in the long term, the lithium slag can be released with water and interact with soil organic matter, regulating the soil's physical structure. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the multi-stage treatment and recovery system for nitrogen and phosphorus in surface runoff on tea plantation slopes, as per the present invention.

[0036] Figure 2 This is a schematic diagram of the soil brick arrangement in the multi-stage soil seepage trench of the present invention;

[0037] Figure 3 This refers to the average recovery rates of TN and TP in the experimental examples;

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

[0039] Explanation of the attached diagram labels: 1. Tea garden slope; 2. Drainage ditch; 3. Multi-stage permeable reactive barrier; 4. Multi-stage soil seepage ditch. Detailed Implementation

[0040] The technical solutions of various embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are part of the present invention.

[0041] Example 1

[0042] This embodiment provides a multi-stage nitrogen and phosphorus treatment and recovery system for surface runoff on tea plantation slopes, such as... Figure 1 As shown, the site includes a tea garden slope 1, a drainage ditch 2 located on the tea garden slope 1, and a multi-stage permeable reactive barrier 3 and a multi-stage soil seepage ditch 4 located on the tea garden slope 1. The drainage ditch 2 located on the tea garden slope 1 is the original soil drainage ditch of the tea garden. Surface runoff passing through the multi-stage permeable reactive barrier 3 enters the multi-stage soil seepage ditch 4, and the water overflows from the multi-stage soil seepage ditch 4 back to the original soil drainage ditch.

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

[0044]

[0045] In the formula: H n The height of the wall above the soil, with a maximum value not exceeding 5cm, H n-1 =0.6H n ;

[0046] C is the slope runoff coefficient, which ranges from 0 to 1 and is dimensionless.

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

[0048] θ represents the slope, measured in degrees (°).

[0049] The spacing between adjacent permeable reactive walls shall not exceed 10cm, the wall thickness shall not exceed 20cm, and the bulk density of the wall above the soil shall not be less than 1.8g / cm³. 3 The bulk density of the wall below the soil should not exceed 2g / cm³. 3 .

[0050] The multi-stage soil seepage trench 4 is installed adjacent to the final stage permeable reactive wall, including a collection ditch perpendicular to the slope. The bottom and sides of the trench are compacted. M-shaped soil bricks are placed inside the collection ditch and filled with pebbles to facilitate water passage. The upper part of the collection ditch is filled with vegetation. Figure 2 As shown, the soil bricks laid in the drainage ditch are arranged in two layers, with adjacent layers of soil bricks staggered. The soil bricks are no more than 6cm high, no more than 12cm wide, with a tooth height of no more than 4cm and a tooth width of no less than 2cm. Pebbles are filled between the teeth of the soil bricks and in the remaining space of the ditch. The median particle size of the pebbles filling the teeth is no greater than 2mm, while the pebbles filling the remaining part are greater than 2mm.

[0051] A permeable reactive barrier consists of a permeable reactive barrier body and biochar filler within the body. Soil bricks consist of a soil brick body and biochar filler within the body. The proportion of biochar filler in a permeable reactive barrier is 5%–10%, while the proportion in soil bricks is 15%–20%. Both the permeable reactive barrier and the biochar filler in soil bricks can adsorb nitrogen and phosphorus from surface runoff.

[0052] Biochar filler is prepared from biochar, lithium slag, sodium alginate-cassava starch, and a crosslinking agent through a low-temperature crosslinking reaction. The biochar must meet the requirements of the "Biochar" standard (NY / T 3672-2020), with a median particle size of not less than 18 mesh, preferably 30-40 mesh, and a specific surface area of ​​not less than 100 m². 2 / g, biochar can be produced by pyrolysis of biochar produced from tea garden pruning at high temperature (>650℃), and the lignin content of the raw material is not less than 20%.

[0053] To improve the recovery efficiency of nitrogen and phosphorus from runoff by biochar, microbial inoculants were loaded onto its surface. Therefore, the biochar was microbial inoculant-loaded biochar, and the microbial inoculants were adsorbed onto the surface of the biochar using a balanced adsorption method. Phosphate-solubilizing bacteria were used to construct a microbial composite inoculant at a ratio of 1:5 to 2:1 (biomass ratio). LB medium was used, and the inoculants were loaded onto the surface of the biochar at a liquid-to-solid ratio of 20 ml: 1 g. After constant temperature shaking at 25°C for 24 h, the solid and liquid components were separated by high-speed centrifugation to separate the microbial inoculant-loaded biochar.

[0054] Biochar packing specifically includes the following steps:

[0055] S1. After mixing biochar loaded with microbial inoculant and 100-mesh lithium slag in a ratio of 1:1.5, a preliminary mixture is obtained.

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

[0057] S3. Add the prepared mixture to the prepared mixture at a solid-liquid ratio of 1g:20mL, stir and mix evenly until it becomes viscous to obtain the mixed liquid;

[0058] S4. Inject the mixed liquid into a mold equipped with a hemp mesh. Add 10 g / L CaCl2 solution to the mold as a crosslinking agent. Crosslink at 3-5℃ for 8-12 h to prepare a colloidal plate. After cleaning, the biochar filler is obtained.

[0059] Hemp netting is a net woven from natural hemp fibers, with each mesh size measuring 1cm x 1cm.

[0060] Soil leachate is prepared by the following steps: 5 kg of topsoil from the application site is selected, air-dried naturally, ground and passed through a 2 mm sieve, and stirred continuously with 50 L of tap water for 12 hours. After natural sedimentation, the supernatant is extracted and passed through a 0.45 μm membrane to obtain soil leachate.

[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 multi-stage treatment and recovery system for nitrogen and phosphorus in surface runoff on the slopes of tea gardens should be carried out during the winter months of December to February of the following year.

[0062] Example 2

[0063] This embodiment provides a multi-stage treatment and recovery method for nitrogen and phosphorus from surface runoff on tea plantation slopes, including the following steps:

[0064] S1. During the winter season from December to February of the following year, the above-mentioned multi-stage treatment and recovery system for nitrogen and phosphorus of surface runoff on the tea garden slope 1 shall be set up.

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

[0066] S3. In the winter of December to February of the following year, the M-type soil bricks in the multi-level soil seepage trench 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 trench 4 is reconstructed.

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

[0068] Experimental Example

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

[0070] A percolation device with dimensions of 25cm x 10cm x 85cm was constructed to simulate the recovery efficiency of nitrogen and phosphorus in water. The efficiency was compared between simple soil, soil with added biochar (5% by mass), and biochar soil with added microbial inoculant (5% by mass). The influent flow rate was 10 cm / d, with TP at 5–6 mg / L and TN at 40–45 mg / L. The start-up period was 10 days, followed by continuous operation for 30 days. The average recovery rates of TN and TP after 30 days were as follows: Figure 3 As shown.

[0071] For simple soil samples, the recovery rates of total nitrogen and total phosphorus in the effluent increased to 68.19% and 92.70% respectively after adding biochar, indicating that biochar can effectively improve the recovery of total nitrogen and total phosphorus in water. Furthermore, after using microbial inoculants to load biochar, the recovery rates of total nitrogen and total phosphorus in the effluent further increased to 76.07% and 96.30%, demonstrating that the composite material of microbial inoculants and biochar can enhance the effect of biochar, and that biochar, as a carrier, can also improve biological activity.

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

[0073] By constructing a slope with a 5° angle, a length of 25cm, and a width of 10cm, and a runoff rate of 10mm / d, traditional permeable reactive barriers, reactive barriers + seepage trenches, and multi-stage reactive barriers + multi-stage seepage trenches (multi-stage recovery technology) were constructed. The nitrogen and phosphorus recovery effects in surface runoff were compared, and the results are as follows: Figure 4 As shown.

[0074] The results showed that traditional permeable reactive walls have a certain recovery effect on nitrogen and phosphorus in runoff. Since total phosphorus in runoff exists mostly in particulate form, the recovery rate of total nitrogen is slightly lower than that of total phosphorus. However, the recovery rate of total nitrogen was significantly improved after the multi-stage combined process. Furthermore, after adopting the multi-stage combined process, the recovery rate of total nitrogen increased from 72.50% to 92.51%, and the recovery rate of total phosphorus also increased to 99.45%, indicating that the multi-stage combined recovery process has a better enhancement effect than the traditional permeable reactive wall.

[0075] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for multi-stage treatment and recovery of nitrogen and phosphorus from surface runoff on tea garden slopes, comprising a tea garden slope (1) and a drainage ditch (2) set on the tea garden slope (1), characterized in that: It also includes a multi-level permeable reactive wall (3) and a multi-level soil seepage ditch (4) set on the tea garden slope (1). The multi-level permeable reactive wall (3) includes at least three levels of permeable reactive walls set in parallel at intervals. The multi-level soil seepage ditch (4) is set up adjacent to the last level of permeable reactive wall and includes a water collection ditch perpendicular to the slope direction. M-shaped soil bricks are set up in the water collection ditch and filled with pebbles. The upper part of the water collection ditch is filled with vegetation. The surface runoff through the multi-level permeable reactive wall (3) enters the multi-level soil seepage ditch (4) and then overflows through the multi-level soil seepage ditch (4) to the drainage ditch (2) of the tea garden slope (1). The permeable reactive wall comprises a permeable reactive wall body and biochar filler material filled within the permeable reactive wall body, wherein the proportion of biochar filler material in the permeable reactive wall body is 5% to 10%; the soil bricks comprise soil brick bodies and biochar filler material filled within the soil brick bodies, wherein the proportion of biochar filler material in the soil bricks is 15% to 20%. The biochar filler is prepared by a low-temperature cross-linking reaction using biochar, lithium slag, sodium alginate-cassava starch, and cross-linking agent as raw materials. The biochar is biochar loaded with microbial agents. The preparation method of the biochar packing includes the following steps: S1. After mixing biochar loaded with microbial inoculant and lithium slag in a ratio of 1:1.5 to 2, a preliminary mixture is obtained; S2. Sodium alginate and cassava starch are added to the soil leachate to obtain a preparative mixture, wherein the mass fraction of sodium alginate in the preparative mixture is 2-5% and the mass fraction of cassava starch is 20-30%. S3. Add the prepared mixture to the prepared mixture at a solid-liquid ratio of 1g:10-20mL, stir and mix evenly until it becomes viscous to obtain a mixed liquid; S4. Inject the mixed liquid into the mold, add a crosslinking agent to the mold, and crosslink at 3-5℃ for 8-12 hours to prepare a colloidal plate. After cleaning, the biochar filler is obtained.

2. The method for multi-stage treatment and recovery of nitrogen and phosphorus from surface runoff in tea garden slopes according to claim 1, characterized in that: In step S3, a hemp net is also added to the mold. The hemp net is a net woven from hemp fibers.

3. The method for multi-stage treatment and recovery of nitrogen and phosphorus from surface runoff in tea garden slopes according to claim 1, characterized in that: The distance between adjacent permeable reactive walls shall not exceed 10cm, the wall thickness shall not exceed 20cm, and the bulk density of the wall above the soil shall not be less than 1.8g / cm³. 3 The bulk density of the wall below the soil should not exceed 2 g / cm³. 3 .

4. The multi-stage treatment and recovery method for nitrogen and phosphorus in surface runoff from tea garden slopes according to any one of claims 1-3, characterized in that: The soil bricks laid in the water collection ditch shall be in at least two layers, with adjacent layers of soil bricks staggered; the soil bricks shall not exceed 6cm in height, 12cm in width, 4cm in tooth height, and 2cm in tooth width.

5. The method for multi-stage treatment and recovery of nitrogen and phosphorus from surface runoff in tea garden slopes according to any one of claims 1-3, characterized in that: The pebbles fill the spaces between the teeth of the soil bricks and the remaining spaces in the trenches. The median particle size of the pebbles filling the spaces between the teeth is no greater than 2 mm, while the pebbles filling the remaining spaces are greater than 2 mm.

6. The method for multi-stage treatment and recovery of nitrogen and phosphorus from surface runoff in tea garden slopes according to any one of claims 1-3, characterized in that: Includes the following steps: S1. During the winter season from December to February of the following year, the multi-stage treatment and recovery method for nitrogen and phosphorus of surface runoff on the tea garden slope (1) shall be deployed. S2. During the spring, summer and autumn seasons from March to November of the following year, maintenance is generally not required. After heavy rainfall, remove the silt intercepted by the vegetation belt on the multi-level soil seepage ditch (4) to keep the runoff water seepage smooth. S3. In the winter of December to February of the following year, the M-type soil bricks in the multi-level soil seepage trench (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 trench (4) is reconstructed. S4. Reconstruct the multi-level permeable reactive wall (3) every three years and reuse the wall material for the tea garden soil.

Images