Farmland leaching system

Abstract

The invention discloses a farmland leaching system, and belongs to the technical field of farmland remediation, the farmland leaching system comprises a leaching pipe, a collecting pipe and a leaching pool formed by digging a farmland, an impermeable membrane is arranged on the inner wall of the leaching pool, a permeable layer, a filtering membrane layer and a polluted soil layer are sequentially laid in the leaching pool from bottom to top, the permeable rate of the permeable layer is larger than that of the polluted soil layer, and the filtering membrane layer is arranged in the leaching pool. The leaching pipe is provided with a spraying head used for spraying leacheate to the polluted soil layer, the collecting pipe is communicated with the permeable layer, and the polluted soil layer is formed by backfilling farmland polluted soil. A leaching pool is dug in a farmland, polluted soil of the farmland is filled into the leaching pool, and pollutants (heavy metals and / or harmful organic matters) in the polluted soil can be taken away through infiltration of leaching liquid and are discharged and collected through a collecting pipe of a permeable layer, so that the pollutants in the polluted soil are really removed, the in-situ remediation of the polluted soil is realized, and under the protection of an impermeable membrane, the pollution of the polluted soil is reduced. The leaching liquid does not need to be leaked to the deep layer or the side, the leaching tail liquid is effectively recycled, and secondary pollution is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of farmland restoration, and in particular to a farmland leaching system. Background Art

[0002] At present, farmland restoration mainly adopts safety control measures, but does not really remove pollution. For example, passivation conditioning can change the chemical form of pollutants through conditioning agents, reduce the mobility and bioavailability of pollutants, but does not reduce the total amount of pollutants. In addition, the conditioning agent is only effective for 2 to 3 years, and is expensive. The restoration cost is high, and the income from farming cannot offset the cost of pollution control. Non-accumulative plants need to be subdivided into genotypes, which farmers cannot identify and master. Therefore, even after the heavy pollution area is repaired, it is still impossible to cultivate. There is an urgent need for a farmland restoration technology that can truly remove pollution. Summary of the invention

[0003] The purpose of the present invention is to solve the above-mentioned technical problems and provide a farmland elution system that can truly remove pollutants (such as heavy metals) in contaminated soil, achieve in-situ restoration of farmland through elution, and in the presence of an impermeable membrane and a permeable layer, the elution tail liquid can be effectively recovered without worrying about the elution liquid leaking into the deep layer or to the side and causing secondary pollution. It can be used for the treatment and restoration of farmland heavy metal pollution, organic-inorganic composite pollution, saline-alkali land, etc.

[0004] To achieve the above-mentioned purpose, the present invention provides the following scheme: The present invention discloses a farmland elution system, comprising a elution pipe, a collecting pipe and a elution pool excavated in a farmland, the inner wall of the elution pool is provided with an impermeable membrane, and a permeable layer, a filter membrane layer and a contaminated soil layer are sequentially laid in the elution pool from bottom to top, the water permeability of the permeable layer is greater than that of the contaminated soil layer, the elution pipe is provided with a spray head for spraying elution liquid onto the contaminated soil layer, the collecting pipe is connected to the permeable layer, and the contaminated soil layer is formed by backfilling contaminated soil from farmland.

[0005] Preferably, a drainage slope is left below the impermeable membrane at the bottom of the leaching pool, the collecting pipe is connected to one end of the permeable layer close to the bottom of the drainage slope, and the top surface of the permeable layer is arranged horizontally.

[0006] Preferably, the slope of the drainage slope is not higher than 60°.

[0007] Preferably, the contaminated soil layer is farmland contaminated soil that has been granulated.

[0008] Preferably, the permeable layer is formed by the accumulation of agricultural waste, the filtration membrane layer is made of biodegradable filter cloth, and the anti-seepage membrane is made of geomembrane.

[0009] Preferably, the agricultural waste and the biodegradable filter cloth are used for incineration or biocomposting to replenish the organic matter loss after leaching of the contaminated soil layer.

[0010] Preferably, it also comprises agricultural wastes for enzymatic hydrolysis to form enzymatic hydrolysate, and the enzymatic hydrolysate is used for granulation treatment of the contaminated soil layer.

[0011] Preferably, it also includes a collecting and processing device, which includes a sedimentation tank, a liquid inlet pipe, a liquid outlet pipe, an adsorption column, a first water pump and a clear liquid tank. The sedimentation tank and the clear liquid tank are both excavated from farmland. The inner walls of the sedimentation tank and the inner walls of the clear liquid tank are both provided with anti-seepage membranes. A sedimentation baffle is provided in the sedimentation tank, and the sedimentation baffle divides the sedimentation tank into a sedimentation area and an overflow area. The sedimentation area is connected to the permeable layer through the collecting pipe. The liquid inlet of the adsorption column is connected to the liquid outlet end of the liquid inlet pipe through the first water pump, and the liquid inlet end of the liquid inlet pipe extends into the overflow area. The liquid outlet of the adsorption column is connected to the liquid inlet end of the liquid outlet pipe, and the liquid outlet end of the liquid outlet pipe is located above the clear liquid tank. The adsorption column is filled with pollutant adsorption filler.

[0012] Preferably, it further comprises a leaching liquid supply device, the leaching liquid supply device comprises a medicine barrel, a drain port is provided at the bottom of the medicine barrel, and the drain port is connected to the leaching pipe through a second water pump.

[0013] Preferably, it also includes a liquid extraction pipe, a liquid inlet is provided on the top of the medicine barrel, the liquid inlet is connected to the liquid inlet end of the liquid extraction pipe, the liquid outlet end of the liquid extraction pipe extends into the clear liquid pool, and a third water pump is provided on the liquid extraction pipe.

[0014] Compared with the prior art, the present invention has achieved the following technical effects:

[0015] In the present invention, a leaching pool is dug in the farmland, the farmland contaminated soil is filled into the leaching pool, and the leaching liquid is sprayed through the spray head. The leaching liquid can infiltrate and take away the pollutants (heavy metals and / or harmful organic matter) in the contaminated soil, and then penetrate into the permeable layer after filtration by the filter membrane layer, and then be discharged and collected by the collection pipe of the permeable layer, so that the heavy metals and other pollution in the contaminated soil are truly removed. Due to the design of the soil granulation and the higher permeability permeable layer, the collection problem of the leaching tail liquid of the farmland soil is effectively realized, the problem of high water content of the soil and the retention of the leaching tail liquid in the field is solved, and the contaminated soil is repaired in situ, and in the presence of the impermeable membrane, there is no need to worry about the leaching liquid leaking to the deep layer or the side, causing secondary pollution. The agricultural waste in the permeable layer can be incinerated or composted on site, which greatly reduces the cost of farmland pollution control. The technical implementation does not require very specialized equipment, making the promotion and application of in-situ leaching possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the analysis of these drawings without paying creative work.

[0017] Figure 1 Schematic diagram of the structure of the farmland washing system in an embodiment of the present invention;

[0018] Figure 2 is a schematic cross-sectional structural diagram of a leaching pool in an embodiment of the present invention;

[0019] Figure 3 It is a schematic diagram of the cross-sectional three-dimensional structure of the elution tank in the embodiment of the present invention;

[0020] Figure 4 Schematic diagram of the cross-sectional three-dimensional structure of the elution pool (permeable layer) in the embodiment of the present invention;

[0021] Figure 5 It is a schematic diagram of the cross-sectional three-dimensional structure of the elution pool (drainage soil slope) in an embodiment of the present invention.

[0022] Explanation of the reference numerals: 1. elution tank; 2. sedimentation tank; 3. clear liquid tank; 4. reagent barrel; 5. anti-seepage membrane; 6. drainage slope; 7. permeable layer; 8. filter membrane layer; 9. polluted soil layer; 10. elution pipe; 11. sprinkler head; 12. collection pipe; 13. liquid inlet pipe; 14. liquid outlet pipe; 15. liquid extraction pipe; 16. adsorption column; 17. first water pump; 18. second water pump; 19. third water pump; 20. valve; 21. support frame; 22. sedimentation baffle. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 analyzed and obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] The purpose of the present invention is to provide a farmland elution system to solve the problems existing in the prior art. A elution pool is dug in the farmland, contaminated soil from the farmland is filled into the elution pool, and elution liquid is sprayed through a sprinkler head. The elution liquid can infiltrate and carry away pollutants (heavy metals and / or harmful organic matter) in the contaminated soil, and then penetrate into the permeable layer after being filtered through the filter membrane layer, and then be discharged and collected by the collection pipe of the permeable layer, thereby truly removing pollutants such as heavy metals in the contaminated soil and achieving the purpose of in-situ repair of the contaminated soil. In addition, in the presence of an impermeable membrane, there is no need to worry about the elution liquid leaking to the deep layer or the side to cause secondary pollution.

[0025] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figures 1 to 5 As shown, this embodiment provides a farmland elution system, including a elution tank 1, a elution pipe 10 and a collection pipe 12. The elution tank 1 is excavated in the farmland, such as directly excavating the elution tank 1 in the area to be repaired in the farmland, or excavating the elution tank 1 beside the area to be repaired in the farmland. An impermeable membrane 5 is provided on the inner wall of the elution tank 1, and the inner wall refers to the bottom wall and side wall inside the elution tank 1. A permeable layer 7, a filter membrane layer 8 and a contaminated soil layer 9 are laid in the elution tank 1 from bottom to top. The contaminated soil layer 9 is the contaminated soil in the area to be repaired in the farmland. The water permeability rate of the permeable layer 7 is greater than that of the contaminated soil layer 9. A spray head 11 is provided on the elution pipe 10, and the spray head 11 is used to spray elution liquid onto the top surface of the contaminated soil layer 9. The number and position of the spray heads 11 are set according to needs, and the spray range needs to be able to cover the entire top surface of the contaminated soil layer 9. The collecting pipe 12 passes through the impermeable membrane 5 of the side wall, and then extends into the permeable layer 7 to achieve communication with the permeable layer 7. The contaminated soil layer 9 is formed by backfilling contaminated soil from farmland.

[0027] Working principle:

[0028] The eluent is supplied to the spray head 11 through the eluent pipe 10, and then the eluent is sprayed to the top surface of the contaminated soil layer 9 through the spray head 11. The eluent infiltrates along the contaminated soil layer 9, and the pollutants in the contaminated soil layer 9 infiltrate together with the eluent ( Figure 2The direction indicated by the middle arrow is the approximate flow direction of the eluent. Usually, the pollutants are heavy metals and / or harmful organic matter. Then, after being filtered by the filter membrane layer 8, impurities such as soil particles and stone particles will be intercepted and retained above the filter membrane layer 8. The pollutants will continue to infiltrate into the permeable layer 7 with the eluent. Because the permeability of the permeable layer 7 is greater than that of the contaminated soil layer 9, the eluent infiltrates more easily. Then, it is discharged and collected by the collection pipe 12 for subsequent treatment. The heavy metals and / or harmful organic matter in the contaminated soil are truly removed. And because of the presence of the impermeable membrane 5, there is no need to worry that the eluent will infiltrate into the deeper soil with the pollutants. The contaminated soil after the pollutants are removed can be returned to the farmland for use.

[0029] In one embodiment, the depth of the leaching pool 1 is set according to the volume of contaminated soil to be treated, but needs to be dug to the plow bottom layer or below the plow bottom layer but not yet exposed to groundwater.

[0030] In one embodiment, a drainage slope 6 is left below the impermeable membrane 5 at the bottom of the elution tank 1. The drainage slope 6 can be directly reserved during excavation, or it can be accumulated at the bottom of the elution tank 1 at a later stage. The collecting pipe 12 is connected to one end of the permeable layer 7 near the bottom of the drainage slope 6. The slope surface of the drainage slope 6 can be used to guide the eluent in the permeable layer 7 to move to the location of the collecting pipe 12, thereby improving the eluent collection rate. Compared with the flat bottom of the elution tank 1, the residual eluent in the elution tank 1 can be effectively reduced. The top surface of the permeable layer 7 is arranged horizontally, so that from the top to the bottom of the drainage slope 6, the thickness of the permeable layer 7 will gradually increase to form a reverse slope, which is conducive to the concentration of the eluent at the bottom of the drainage slope 6, and is conducive to smooth entry into the collecting pipe 12 for external discharge collection.

[0031] In one embodiment, the slope of the drainage slope 6 is not higher than 60°.

[0032] In one embodiment, the elution tank 1 is a rectangular tank body, but other shapes of tank bodies, such as a circular tank body, are not excluded, but the rectangular tank body is preferred.

[0033] In one embodiment, the contaminated soil layer 9 is a granulated contaminated soil of a farmland. After the granulation treatment, the clay in the contaminated soil will be reduced, and the granular soil will increase, so that the infiltration rate will be effectively improved. Granulation is more suitable for soils with poor permeability such as clay or high organic matter content. Granulation can be granulated using a dedicated granulator, but the cost is relatively high and is not suitable for on-site use. Therefore, an enzymolysis solution can be used, sprayed onto the soil surface, and simply mixed, and solidified for a certain period of time to achieve granulation. The enzymolysis solution is obtained by enzymolysis of agricultural waste, such as straw, corn cobs or branches.

[0034] Taking the cultivated soil of a certain place as an example, the content of original soil less than 0.074mm accounts for 42%: first, water containing cellulase is mixed with agricultural waste in a liquid-solid ratio of 5:1, where the amount of cellulase is 0.1%, and the enzymatic hydrolyzate is obtained after 3 hours of enzymatic hydrolysis. Then the enzymatic hydrolyzate is sprayed on the soil surface, mixed briefly, and solidified for more than 12 hours to complete the granulation treatment. The amount of enzymatic hydrolyzate greater than 1% can meet the requirements. After granulation treatment, the proportion of particles with a particle size less than 0.074mm in the cultivated soil increased by about 9%; the number of particles with a particle size less than 0.1mm increased by about 6%, and the number of particles with a particle size less than 1mm increased by about 3%. The effective infiltration rate is higher than 20L·m -2 ·h -1 , meeting the requirements of heap leaching. After leaching, the total amount of Pb and Cd in the soil sample dropped to 306.1 and 0.26 mg kg respectively -1 , the effective Pb and Cd contents were reduced to 16.64 and 0.03 mg·kg -1 After a single chemical leaching for one day, the removal rates of Pb and Cd reached 78.50% and 97.30% respectively.

[0035] In one embodiment, the permeable layer 7 is an agricultural waste layer, such as straw, corn cobs and / or dead branches and leaves. When the agricultural waste layer is piled up, the density of each area is similar as much as possible, that is, the size of the gaps generated in each area is similar, so that the infiltration rate of each area is similar, and the stability of the pile is guaranteed. The filter membrane layer 8 adopts a biodegradable filter cloth. The use of agricultural waste layers and biodegradable filter cloths can be returned to the field after on-site biological fermentation or incineration after the heap leaching is completed, replenishing the organic matter lost due to leaching, etc., killing two birds with one stone. Of course, before fermentation or incineration, try to clean it with clean water to avoid heavy metals or harmful organic matter residues. The anti-seepage membrane 5 adopts a geomembrane, which is a geotechnical anti-seepage material composited with a plastic film as an anti-seepage substrate and a non-woven fabric.

[0036] In one embodiment, agricultural waste (permeable layer 7) and biodegradable filter cloth (filtration membrane layer 8) are used for incineration or biocomposting and are recycled into the washed soil to replenish the organic matter loss after the contaminated soil layer is washed.

[0037] In one embodiment, agricultural waste is also included for enzymatic hydrolysis to form enzymatic hydrolysis solution, and the enzymatic hydrolysis solution is used for granulation treatment of the contaminated soil layer 9. Specifically, the agricultural waste can be divided into two parts: a first part of agricultural waste and a second part of agricultural waste, wherein the first part of agricultural waste is used to pave the permeable layer 7, and the second part of agricultural waste is subjected to an appropriate degree of enzymatic hydrolysis to obtain an enzymatic hydrolysis solution (mainly sugar compounds and / or nitrogen-containing compounds), and the enzymatic hydrolysis solution is mixed with the contaminated soil layer 9 for granulation treatment.

[0038] In one embodiment, the thickest area of ​​the water-permeable layer 7 is less than 1 m, that is, the thickness of the thickest area where agricultural waste such as dead branches and fallen leaves are deposited is less than 1 m.

[0039] In one embodiment, the filtration pore size of the filtration membrane layer 8 is less than 2 mm.

[0040] In one embodiment, a collection and treatment device is also included. The collection and treatment device includes a sedimentation tank 2, a clear liquid tank 3, a liquid inlet pipe 13, a liquid outlet pipe 14, an adsorption column 16 and a first water pump 17. The sedimentation tank 2 and the clear liquid tank 3 are both excavated from farmland. The inner wall of the sedimentation tank 2 and the inner wall of the clear liquid tank 3 are both provided with an impermeable membrane 5, and the impermeable membrane 5 can also be a geomembrane. A vertically arranged sedimentation baffle 22 is provided in the sedimentation tank 2, and the sedimentation baffle 22 divides the sedimentation tank 2 into a sedimentation area and an overflow area. The sedimentation area is connected to the permeable layer 7 through the collection pipe 12, and the specific liquid inlet end of the collection pipe 12 extends into the permeable layer 7, and the liquid outlet end of the collection pipe 12 is located above the sedimentation area. The liquid inlet of the adsorption column 16 is connected to the liquid outlet end of the liquid inlet pipe 13 through the first water pump 17, and the liquid inlet end of the liquid inlet pipe 13 extends into the overflow area. The liquid outlet of the adsorption column 16 is connected to the liquid inlet end of the liquid outlet pipe 14, and the liquid outlet end of the liquid outlet pipe 14 is located above the clear liquid pool 3. The adsorption column is filled with pollutant adsorption filler for adsorbing pollutants.

[0041] Working principle:

[0042] The eluent flows from the collecting pipe 12 into the sedimentation area of ​​the sedimentation tank 2. Impurities and particles will remain in the sedimentation area under the obstruction of the sedimentation baffle 22, while the liquid level of the eluent rises until it exceeds the sedimentation baffle 22, and then overflows into the overflow area. Then the first water pump 17 is turned on, and the liquid inlet pipe 13 draws the liquid in the overflow area into the adsorption column 16. The heavy metals or harmful organic matter in the liquid are adsorbed by the pollutant adsorption filler. The adsorbed liquid flows into the clear liquid tank 3. After manual detection, whether the heavy metal content is about to reach the qualified content, if it is about to reach the qualified content or below, it can be used as clean water.

[0043] In one embodiment, the type of pollutant adsorption filler is determined by the type of pollutant. If you want to remove heavy metals, you can choose fillers that can adsorb heavy metals. If you want to remove harmful organic matter, you can choose fillers that can adsorb harmful organic matter. And the type of heavy metals is different, and the selected filler also needs to be adjusted. For example: for heavy metal pollution such as Pb, Cd, Cu, Cr, the adsorption filler can be one or more of biochar, oyster, and zeolite as fillers; for As and Hg, additional coordination and complexation in metal organic frameworks (MOFs in English, Metal organic Framework in English) can be added; if it is a heavy metal complex organic pollutant, the filler is modified biochar; if it is a heavy metal complex hydrophobic organic matter (such as phenol, pesticides, drugs), resin adsorption is used; if there is adsorption of volatile organic compounds (VOCs) and some dyes, zeolite is used.

[0044] In one embodiment, a valve 20 is provided on the liquid outlet pipe 14 to control the opening and closing of the liquid outlet end of the liquid outlet pipe 14 .

[0045] In one embodiment, the number of adsorption columns 16 is set according to actual conditions. For example, when multiple adsorption columns 16 are used, the multiple adsorption columns 16 need to be used in series.

[0046] In one embodiment, a rinsing liquid supply device is further included. The rinsing liquid supply device includes a medicine barrel 4, in which the rinsing liquid is contained, and a drain port is provided at the bottom of the medicine barrel 4, which is connected to the rinsing pipe 10 through a second water pump 18. When the second water pump 18 is turned on, the rinsing liquid can be pumped from the medicine barrel 4 into the rinsing pipe 10, and the rinsing liquid is sprayed to the rinsing pool 1 by the spray head 11.

[0047] In one embodiment, the medicine barrel 4 is installed on the support frame 21 .

[0048] In one embodiment, a liquid extraction tube 15 is included. A liquid inlet is provided on the top of the medicine barrel 4, and the liquid inlet is connected to the liquid inlet end of the liquid extraction tube 15. The liquid outlet end of the liquid extraction tube 15 extends into the clear liquid pool 3. A third water pump 19 is provided on the liquid extraction tube 15. When the third water pump 19 is started, the liquid extraction tube 15 can extract the liquid that meets the standards in the clear liquid pool 3 into the medicine barrel 4 to replenish the clean water. A medicine port is started on the medicine barrel 4, and the corresponding medicine is added to prepare and replenish the consumption of the eluent. It should be noted that before starting the third water pump 19, it is necessary to use a test kit or a detection device to detect whether the clean water in the clear liquid pool 3 meets the standards. If it does not meet the standards, it will not be sent to the medicine barrel 4, but the external clean water will be filled into the medicine barrel 4 from the medicine port, and the medicine will be added for preparation. Liquid that does not meet the standards in the clear liquid tank 3 can be pumped out and sent elsewhere for subsequent treatment, or pumped back to the sedimentation tank 2 for additional treatment using an on-site treatment device. Adsorption columns 16 can also be added based on the compliance status to ensure that the liquid in the clear liquid tank 3 meets the standards without the need for additional treatment.

[0049] In one embodiment, the eluent is purchased and formulated according to the type of heavy metal or harmful organic matter. Heavy metal pollution: chelating agent (citric acid, GLDA) or weak acid (to avoid soil acidification) is preferred. Organic pollution: surfactant (Tween 80) or solvent (ethanol) solubilization and elution. Complex pollution: step-by-step elution or complex formula (surfactant + chelating agent). Radioactive pollution: strong acid or highly selective complexing agent (DTPA).

[0050] For example:

[0051] When the pollutants are heavy metals (Pb, Cd), the recommended eluent is 0.1-0.5M citric acid + 0.05M FeCl3; the concentration range is 5:1-10:1 liquid-solid ratio, and the spraying time is 2-6 hours.

[0052] When the pollutant is: petroleum hydrocarbon; recommended eluent: 2% to 5% rhamnolipid solution; concentration range: liquid-to-solid ratio is 3:1 to 5:1; spray treatment time: 4 to 12 hours;

[0053] When the pollutant is hexavalent chromium; recommended eluent: 0.1M FeSO4 + 0.05M H2SO4; concentration range: liquid-solid ratio 5:1; spray treatment time: 1 to 3 hours;

[0054] When the pollutant is: polychlorinated biphenyls; recommended eluent: 5% to 10% ethanol + 0.1% Tween 80; concentration range: liquid-solid ratio 5:1 to 8:1; spray treatment time: 6 to 24 hours.

[0055] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A farmland washing system, characterized in that: It includes a leaching pipe, a collecting pipe and a leaching pool excavated in a farmland, wherein an impermeable membrane is arranged on the inner wall of the leaching pool, and a permeable layer, a filtration membrane layer and a contaminated soil layer are laid in sequence from bottom to top in the leaching pool, the permeability rate of the permeable layer is greater than that of the contaminated soil layer, the leaching pipe is provided with a spray head for spraying leaching liquid to the contaminated soil layer, the collecting pipe is connected with the permeable layer, and the contaminated soil layer is formed by backfilling contaminated soil from farmland.

2. The farmland washing system according to claim 1, characterized in that: A drainage soil slope is left below the anti-seepage membrane at the bottom of the leaching pool, the collecting pipe is connected with one end of the permeable layer close to the bottom of the drainage soil slope, and the top surface of the permeable layer is arranged horizontally.

3. The farmland washing system according to claim 2, characterized in that: The slope of the drainage soil slope is not higher than 60°.

4. The farmland washing system according to claim 1, characterized in that: The contaminated soil layer is farmland contaminated soil that has been granulated.

5. The farmland washing system according to claim 4, characterized in that: The permeable layer is formed by the accumulation of agricultural wastes, the filter membrane layer adopts biodegradable filter cloth, and the anti-seepage membrane adopts geomembrane.

6. The farmland washing system according to claim 5, characterized in that: The agricultural waste and the biodegradable filter cloth are used for incineration or biocomposting to supplement the organic matter loss after leaching of the contaminated soil layer.

7. The farmland washing system according to claim 5, characterized in that: It also includes agricultural wastes used for enzymolysis to form enzymolysis solution, and the enzymolysis solution is used for granulation treatment of the contaminated soil layer.

8. The farmland washing system according to any one of claims 1 to 7, characterized in that: It also includes a collecting and processing device, which includes a sedimentation tank, a liquid inlet pipe, a liquid outlet pipe, an adsorption column, a first water pump and a clear liquid tank. The sedimentation tank and the clear liquid tank are both excavated from farmland. The inner walls of the sedimentation tank and the inner walls of the clear liquid tank are both provided with anti-seepage membranes. A sedimentation baffle is provided in the sedimentation tank, and the sedimentation baffle divides the sedimentation tank into a sedimentation area and an overflow area. The sedimentation area is connected to the permeable layer through the collecting pipe. The liquid inlet of the adsorption column is connected to the liquid outlet end of the liquid inlet pipe through the first water pump, and the liquid inlet end of the liquid inlet pipe extends into the overflow area. The liquid outlet of the adsorption column is connected to the liquid inlet end of the liquid outlet pipe, and the liquid outlet end of the liquid outlet pipe is located above the clear liquid tank. The adsorption column is filled with pollutant adsorption filler.

9. The farmland washing system according to claim 8, characterized in that: It also includes a leaching liquid supply device, which includes a medicine barrel. A drainage port is provided at the bottom of the medicine barrel, and the drainage port is connected to the leaching pipe through a second water pump.

10. The farmland washing system according to claim 9, characterized in that: It also includes a liquid extraction pipe. The top of the medicine barrel is provided with a liquid inlet, the liquid inlet is connected to the liquid inlet end of the liquid extraction pipe, the liquid outlet end of the liquid extraction pipe extends into the clear liquid pool, and a third water pump is provided on the liquid extraction pipe.

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