Low-grade cultivated land quality improving system and method based on stabilization pond

Abstract

The invention relates to a low-grade cultivated land quality improving system and method based on a stabilization pond. The low-grade cultivated land quality improvement system based on the stabilization pond comprises the following units: 1) low-grade cultivated land; 2) a stabilization pond; (3) ditch network construction; and 4) a clear water backflow unit and a sludge backflow unit. The invention further provides a low-grade cultivated land quality improvement method based on the system. The system and the method provided by the invention realize cyclic utilization of soil-water-bottom mud resources and nutrients in agricultural production, can reduce the use amount of chemical fertilizers in farmland, reduce the agricultural production cost, reduce environmental pollution caused in the production and use processes of the chemical fertilizers, and conform to the concept of sustainable development.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cultivated land ecological environment protection, and in particular to a system and method for effectively improving low-quality cultivated land by using a stabilization pond to improve the ecological quality and sustainable production capacity of farmland. BACKGROUND

[0002] With the acceleration of urban construction and the continuous expansion of construction land, the precious cultivated land resources are becoming increasingly scarce. At the same time, the excessive use of fertilizers and pesticides in agricultural production and the improper disposal of livestock and poultry breeding waste have caused serious pollution of the ecological environment of farmland.

[0003] The current traditional cultivated land pollution control technology has significant limitations. Some measures only collect farmland runoff water simply, and cannot achieve the fundamental removal of pollutants and efficient use of resources. Physical repair technology is costly, and chemical repair can easily cause secondary pollution, and both are difficult to be combined with routine production activities in farmland. In the practice of cultivated land governance, the construction of runoff ecological interception systems is lagging, fine treatment technology is insufficient, and the factor guarantee mechanism is imperfect, which still outstandingly restricts the improvement of the effectiveness of farmland pollution control. Therefore, it is urgent to develop a simple, cost-effective, environmentally friendly and resource recycling technical solution to systematically solve the problems of soil fertility cultivation and pollution control of low-quality cultivated land. SUMMARY

[0004] TECHNICAL OBJECTIVE The technical objective of the present application is to solve the problems of soil fertility cultivation and pollution control of low-quality cultivated land by providing a system and / or method based on a stabilization pond.

[0005] TECHNICAL SCHEME In one aspect, the present application provides a low-grade cultivated land quality improvement system based on a stabilization pond, which comprises the following units: 1) Low-grade cultivated land, wherein the low-grade cultivated land is cultivated land below grade 7 evaluated based on the method described in "Cultivated Land Quality Grade" (GB T33469-2016), and the cultivated land type is mainly paddy field; 2) Stabilization pond: located 20-1000m downstream of the low-grade cultivated land and more low-lying than the low-grade cultivated land, provided with a bottom impermeable layer and a dike, the impermeable layer uses high-density polyethylene (HDPE) impermeable film with a thickness of 1.5-2.0mm, and the dike uses a simple earth-rock structure and is divided into an anaerobic zone, a facultative zone and an aerobic zone inside according to the direction of water flow, the anaerobic zone, the facultative zone and the aerobic zone are connected by flow guide facilities, The stabilization pond is used for purification treatment of farmland runoff water from the low-grade cultivated land, 3) the ditch network: which is composed of ditches, is arranged at the periphery of the low-grade farmland and is in communication with the stabilization pond and the low-grade farmland, is constructed according to the farmland topography and the water flow direction, the bottom and the slope are paved with ecological bricks, and a grid and a sedimentation tank are further arranged in the interior, The ditch network is used for collecting and pretreating the farmland backflow water; and 4) the clean water and sludge backflow unit: which is in communication with the stabilization pond and the low-grade farmland, is composed of a pump and a pipeline, and is used for returning the treated clean water of the stabilization pond and the sludge at the bottom of the pond to the low-grade farmland.

[0006] In the specific embodiment, in the stabilization pond, In the anaerobic zone, aquatic plants are planted and screened and domesticated anaerobic microbial flora are introduced, so as to decompose macromolecular organic matters into small molecular organic matters and to convert part of the nutrients such as nitrogen and phosphorus into ammonia nitrogen and phosphate form.

[0007] In the facultative zone, water plants with pollution tolerance are planted, and facultative microorganisms are introduced to further degrade organic matters and to preliminarily absorb nutrients such as nitrogen and phosphorus; In the aerobic zone, aquatic plants are planted and plankton and filter-feeding fish are introduced to completely decompose the remaining organic matters into carbon dioxide and water and to further remove nitrogen, phosphorus and algae in the water, so as to deeply purify the water quality.

[0008] In the specific embodiment, in the stabilization pond, In the anaerobic zone, the aquatic plants are selected from cattail and Vallisneria; the anaerobic microbial flora are selected from one or more of methanogens and hydrolytic acidification bacteria; In the facultative zone, the aquatic plants are selected from one or more of Acorus calamus, Schoenoplectus juncoides, Hydrilla verticillata and Ceratophyllum demersum, and the facultative microorganisms are selected from the bacterial species of Bacillus; In the aerobic zone, the aquatic plants are selected from one or more of Nymphaea, Ceratophyllum demersum, Elodea canadensis, Canna indica and Ranunculus sinensis, the plankton is selected from one or more of rotifer and cladocera, and the filter-feeding fish is selected from one or more of Hypophthalmichthys molitrix and Aristichthys nobilis. In the aerobic zone, the plankton can prey on algae and bacteria to maintain the ecological balance of the water body, and the filter-feeding fish feeds on plankton and organic detritus to further purify the water quality.

[0009] In the specific embodiment, the volume ratio of the anaerobic zone, the facultative zone and the aerobic zone of the stabilization pond is 1:(1.2-3.0):(0.6-2.0) In the specific embodiment, when the stabilization pond is constructed, the topsoil with a thickness of 30-60 cm from the ground surface is collected by digging and is paved on the farmland.

[0010] In the specific embodiment, in the ditch network, A grating is installed at the inlet of the ditch, and a sedimentation tank is installed at the connection between the ditch and the stabilization pond, and / or The aquatic plants in the ditch network are selected from one or more of the following: sweet flag, iris, and / or The drainage network is also equipped with flow regulation devices.

[0011] The flow regulation device in the ditch network of this application automatically adjusts the amount of water entering the stabilization pond based on the flow rate of farmland runoff and the real-time processing capacity of the stabilization pond, ensuring the stable operation of the stabilization pond. Preferably, the flow regulation device is an electric regulating valve.

[0012] In the system of this application, the bar screens in the ditch network filter and intercept large particulate impurities such as straw and plastic film in the farmland runoff; the sedimentation tank allows suspended solids such as silt in the water to settle down, reducing the load on the subsequent stabilization pond treatment.

[0013] On the other hand, the present invention provides a method for improving the quality of low-grade arable land using the above-described system, the method comprising the following steps: 1) Drainage from low-grade farmland is diverted into stabilization ponds through a network of ditches; 2) Water purification treatment is carried out in the stabilization pond; 3) The purified water from the stabilization pond is reused for farmland irrigation using the clean water return unit and the sludge return unit, and the nutrient-rich sludge from the bottom of the stabilization pond generated during the purification process is applied to farmland.

[0014] In a specific implementation, in step 2, the hydraulic retention time of each area of ​​the anaerobic zone, facultative zone, and aerobic zone of the stabilization pond is controlled to be 1-7 days, 5-10 days, and 3-5 days, respectively.

[0015] In a specific implementation, in step 2, during the operation of the stabilization pond, the water quality, microbial quantity and activity indicators of each area are monitored regularly, and the amount of microbial feed and the maintenance and management of aquatic plants are adjusted in a timely manner according to the monitoring results to ensure the efficient operation of the stabilization pond.

[0016] In a specific implementation, in step 3, before reusing the purified water and pond bottom sludge, it is ensured that the quality of the reused water meets the "Standards for Irrigation Water Quality" (GB5084-2021), and that the organic matter content of the pond bottom sludge is not less than 25-30 g / kg, and the heavy metal index does not exceed the minimum value of the standard limit for each heavy metal factor in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control" (GB15618-2018).

[0017] In a specific implementation, step 3 includes disinfection treatment of the sludge before reuse. The control indicators and key hygiene indicators of the treated sludge meet the Class A standard of the "Standard for Pollutant Control of Agricultural Sludge" (GB4284-2018).

[0018] In a specific implementation, the method also includes regularly monitoring the soil of the cultivated land during the process of improving the quality of low-grade cultivated land. The monitoring standards are in accordance with the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control" (GB15618-2018) and the "Evaluation Standard for Environmental Quality of Edible Agricultural Products Production Area" (HJ 332-2006).

[0019] Beneficial effects: (1) This application is the first to couple three major modules: ditch pretreatment, stabilization pond graded purification, and water / sludge resource reuse, forming a closed-loop technology for the whole process, solving the core pain point of existing technologies that "emphasize treatment and neglect recycling"; it is the first to clearly define that the purified water from the stabilization pond (irrigated after meeting the standards) and the silt at the bottom of the pond (returned to the field after disinfection and testing to meet the standards) are simultaneously reused for cultivated land, realizing the cycle of "return water resource utilization - soil fertility improvement - reduction of chemical fertilizer dependence", which is different from the existing technology model of "purified water is directly discharged and bottom silt is disposed of as waste".

[0020] (2) This application addresses the problems of "simple structure, low purification efficiency and weak shock resistance" of traditional stabilization pond systems by making a breakthrough design in terms of structural zoning and ecological community configuration: for the first time, the volume ratio and hydraulic retention time of the "anaerobic zone-facultative zone-aerobic zone" of the stabilization pond are clearly defined, solving the problem of unstable purification effect caused by the experience-based setting of traditional stabilization ponds.

[0021] (3) This application innovatively adopts the "topsoil excavation-backfilling farmland" pond construction method: during construction, topsoil with a thickness of 30-60cm from the ground surface is collected and reused in farmland, which not only avoids the waste of precious topsoil resources, but also solves the problem of traditional stabilization pond construction damaging the top fertile soil and causing a temporary decline in farmland fertility.

[0022] (4) This application is the first to deeply bind the farmland quality grading standard with the governance technology to achieve “precise targeted restoration”, which is different from the existing problem of “high cost and inapplicability and mismatch of effect” caused by not distinguishing farmland grades and uniformly adopting “physical / chemical restoration”.

[0023] (5) This application introduces an electric flow regulation device into the ditch network, which can automatically adjust the inflow of water according to the farmland drainage flow (such as the difference between the rainy season and the irrigation period) and the real-time treatment capacity of the stabilization pond, and establish a three-in-one monitoring system of "water quality-microorganism-soil" (refer to GB15618-2018, HJ332-2006). The amount of microorganisms added and the plant maintenance strategy can be dynamically adjusted according to the monitoring results to achieve precise management "according to time and place".

[0024] (6) This application takes into account both “low cost” and “easy implementation”, adapts to farmland scenarios, and breaks through the limitations of traditional technologies that either treat pollution or improve fertility, making it difficult to achieve both simultaneously. It achieves the synergy of the two core objectives through technical design.

[0025] In summary, this application achieves the following beneficial effects by constructing a network of stabilizing ponds and ditches around farmland: Simple and effective pollutant removal: Through the synergistic effect of the ecosystem composed of anaerobic, facultative, and aerobic microorganisms, as well as aquatic plants, zooplankton, and fish within the stabilization pond, it has a highly efficient removal capacity for pollutants such as organic matter, nitrogen, phosphorus, and pesticide residues in agricultural runoff. Actual testing has shown that, under reasonable operating conditions, the stabilization pond can achieve a removal rate of over 60% for chemical oxygen demand (COD), over 65% for ammonia nitrogen, and over 85% for total phosphorus, thus reducing agricultural non-point source pollution to a certain extent and protecting the surrounding water and soil environment.

[0026] Improving soil structure and fertility: Reusing purified water for farmland irrigation avoids the problem of aggravated soil pollution caused by using contaminated water for irrigation. At the same time, pond bottom silt is treated and applied to farmland as organic fertilizer, increasing the organic matter content in the soil, improving soil aggregate structure, and enhancing soil aeration, permeability, and fertilizer retention, thereby improving soil fertility and contributing to the improvement of agricultural product quality.

[0027] Resource recycling: This invention achieves the recycling of soil, water, and sediment resources and nutrients. Farmland runoff is purified in stabilization ponds and then reused for irrigation, conserving water resources. Topsoil is fully collected during pond construction and reused on farmland surfaces; silt meeting safe utilization requirements is returned to the fields as fertilizer, reducing fertilizer use, lowering agricultural production costs, and minimizing environmental pollution caused by fertilizer production and use, thus aligning with the concept of sustainable development. Attached Figure Description

[0028] Figure 1 The flowchart of the method for improving the quality of low-grade farmland based on stabilization ponds according to this application is illustrated schematically.

[0029] Figure 2The diagram schematically illustrates the components of the low-grade farmland quality improvement system based on stabilization ponds of this application.

[0030] Figure 3 The structure of the stabilization pond of this application is illustrated schematically.

[0031] exist Figure 2 and Figure 3 In the diagram, dashed arrows indicate the direction of water flow, while solid arrows indicate the direction of sludge flow.

[0032] Figure Labels 1 - Cultivated land 2—Ditch 3 - Stabilizing Pond 31 - Anaerobic Zone 32—Familiarity Zone 33 - Aerobic Zone 4 - Sludge Return Unit 5 - Clean Water Recirculation Unit 6 - Sedimentation tank 7 - Pump Detailed Implementation The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0033] Example 1: The illustrative method for improving the quality of low-grade arable land in this application is as follows: Figure 1 As shown in the diagram: First, the quality of arable land is evaluated, and low-grade arable land is screened. Based on the screening results, the site selection and construction of stabilization ponds are determined, while topsoil resources are reused. Then, the stabilization pond ecosystem is constructed. Agricultural runoff is collected and pre-treated using an agricultural runoff treatment chain. Next, the collected agricultural runoff is purified using the constructed stabilization ponds. After that, the purified water is reused for arable land, while the bottom sediment is treated. Finally, recycling and monitoring are carried out. The treated bottom sediment can be reused in the arable land ecosystem, while the arable land soil is monitored for a long time, forming a closed loop of "arable land → stabilization pond → arable land".

[0034] This application illustrates a low-grade farmland quality improvement system based on stabilization ponds, such as... Figure 2 As shown: The system consists of farmland 1, ditches 2, sedimentation tanks 6, and stabilization ponds 3. Each unit is linked through water flow and material circulation. Farmland 1: As the source area of ​​runoff, farmland runoff that carries agricultural production and generates pollutants such as nitrogen and phosphorus; Ditch 2: It is responsible for collecting and transporting runoff, and centralizing the scattered runoff from farmland into the treatment system; Sedimentation tank 6: for preliminary sedimentation of incoming runoff; Stabilization pond 3: comprises three treatment units: anaerobic zone 31, facultative zone 32, and aerobic zone 33. Simultaneously, it is equipped with sludge return unit 4 and clean water return unit 5 to realize the resource-based reuse of bottom sludge and clean water.

[0035] Environmental conditions for implementation: A reclaimed farmland in the lower reaches of the Yangtze River was selected as arable land 1. The average annual temperature of this plot is 18.5℃, and the annual precipitation is about 1000 mm. To the south of the farmland is a low-lying, idle land of about 15 mu (approximately 1 hectare), historically muddy, near a natural river, and with no residential areas or other sensitive locations nearby. The average concentrations of major pollutants in the farmland runoff were as follows: COD concentration 50.12 mg / L, ammonia nitrogen concentration 3.05 mg / L, and total phosphorus concentration 0.34 mg / L.

[0036] The assessment of arable land quality is based on Section 4.1.4 of the "Arable Land Quality Grading" standard (GB T33469-2016), which classifies arable land quality into 10 grades. A higher comprehensive arable land quality index indicates a higher level of arable land quality. Grade 1 arable land has the highest quality, while Grade 10 arable land has the lowest quality. Arable land quality monitoring and evaluation: Through on-site surveys, data collection, and investigations by five personnel from the land management department, the ownership unit, the historical enterprise, and surrounding residents, it was found that the land was historically used as a small machine processing enterprise and agricultural implement warehouse. The land has now been reclaimed as farmland, mainly used for rice cultivation. Irrigation and drainage conditions are average, lacking a systematic irrigation canal network. The entire plot is relatively uniform. As an assessment unit, 10 samples of the topsoil layer (within 50cm below the ground surface) and profile samples (maximum profile depth 1.2m) were collected using a grid sampling method. The monitoring results showed that the plot had an average effective soil layer of 60cm, an organic matter content of 7.9g / kg, a light soil bulk density, low soil nutrients, and a pH of 9.0. The weights and membership degrees of each indicator were determined by the analytic hierarchy process and the Delphi method. Finally, the comprehensive arable land index was calculated to determine the assessment grade, and the plot was classified as Grade 7, which is considered poor-quality arable land.

[0037] The illustrative stable pond of this application Figure 3 As shown, it includes a three-stage treatment unit consisting of an anaerobic zone 31, a facultative zone 32, and an aerobic zone 33. Different aquatic plants (e.g., emergent and submerged plants) are planted in each of the three zones to meet different organic matter treatment needs. The sludge return unit 4 and the clear water return unit 5 use pump 7 to reuse the treated clear water and sludge from the stabilization pond 3 for resource recovery.

[0038] Construction of Stabilization Pond 3: The site of Stabilization Pond 3 is located downstream of the farmland, approximately 85m from the south side of the farmland. During construction, topsoil with an average thickness of approximately 35cm was stripped and collected. No garbage or other contaminants were found in the soil. Sampling tests showed that the topsoil contained no obvious foreign impurities, rapid heavy metal testing showed no pollutant exceedances, and the organic matter content was high, averaging 31.5g / kg. The average pH was 8.5, the average soil bulk density was 1.41, and the average soil moisture content was 38.0%, making it suitable for preliminary improvement of the aforementioned farmland, increasing the effective topsoil thickness. Stabilization Pond 3 was constructed with an anaerobic zone 31, a facultative zone 32, and an aerobic zone 33 in a volume ratio of 1:2:2. The water depth in anaerobic zone 31 was 2.5m, in facultative zone 32 it was 1.5m, and in aerobic zone 33 it was 1m. The pond bottom was laid with an HDPE geomembrane, and the embankment was a 1m high earth-stone structure. Deflector walls and pipes are installed between different areas to ensure smooth water flow (see...) Figure 3 ).

[0039] Ecosystem Construction: In anaerobic zone 31, anaerobic microbial communities are introduced at an inoculation rate of 45 grams per cubic meter of wastewater, along with commonly found emergent and submerged plants: 5 clumps of cattail per square meter and 100 plants of Vallisneria natans per square meter. In facultative zone 32, emergent plants such as Acorus calamus are planted at a density of 8-12 clumps per square meter, and submerged plants such as Ceratophyllum demersum are planted at a density of 60-80 plants per square meter. If the content of pollutants such as organic matter in the wastewater increases due to fluctuations in water volume, Bacillus subtilis inoculant is added at a dosage of 300 grams per cubic meter, and adjusted according to the actual situation. In aerobic zone 33, emergent plants such as Canna indica are planted at a density of 10-15 clumps per square meter, and submerged plants such as Myriophyllum spicatum are planted at a density of 40-60 plants per square meter.

[0040] Farmland runoff collection and pretreatment: An ecological ditch network 2, with a total length of 1200m, is constructed around the farmland. The bottom and slopes are paved with ecological bricks and planted with aquatic plants such as calamus and iris. A grating with a bar spacing of 20mm is installed at the ditch entrance. The sedimentation tank 6 has dimensions of 10m in length, 5m in width, and 2m in depth.

[0041] Operation and Management: Farmland runoff, after pretreatment, enters Stabilization Pond 3. Water quality in all areas of Stabilization Pond 3 is monitored regularly, with COD, ammonia nitrogen, and total phosphorus monitored weekly, and microbial quantity and activity tested monthly. Based on monitoring results, microbial communities are replenished as needed, and aquatic plants are pruned and maintained. The bottom sludge of the stabilization pond is cleaned every two weeks. After disinfection and treatment, heavy metal and key hygienic indicators are significantly lower than the Class A standard in the "Standard for Pollutant Control of Agricultural Sludge" (GB4284-2018) before being applied to farmland.

[0042] Implementation Results: After one quarter of operation, testing revealed that the COD concentration of the purified water treated in Stabilization Pond 3 decreased to below 15.5 mg / L, ammonia nitrogen concentration decreased to below 0.92 mg / L, and total phosphorus concentration decreased to below 0.05 mg / L, demonstrating a significant water purification effect. Simultaneously, a subsequent assessment of farmland quality after reusing topsoil and bottom sediment showed that soil organic matter content increased to 14.6 g / kg, soil pH improved to 8.4, and soil bulk density at various locations stabilized at 1.25-1.40 g / cm³. 3 The thickness of the topsoil layer has been significantly increased to 75cm, and the overall quality of the cultivated land has been improved to grade 5. This has saved about 20% of the costs of irrigation water and fertilizers used to improve soil quality, resulting in significant quality improvement and economic benefits.

[0043] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of this invention should still fall within the scope of this patent.

Claims

1. A system for improving the quality of low-grade arable land based on stabilization ponds, characterized in that, The system includes the following units: 1) Low-grade cultivated land, wherein the low-grade cultivated land refers to cultivated land of grade 7 or below as evaluated based on the method of "Cultivated Land Quality Grade" (GB T33469-2016), and the cultivated land type is mainly paddy field; 2) Stabilization pond: Located 20-1000m downstream of the low-grade farmland, in a lower-lying area, it is equipped with a bottom impermeable layer and a dike. The impermeable layer uses a high-density polyethylene geomembrane with a thickness of 1.5-2.0mm. The dike uses a simple earth and stone structure and is internally divided into anaerobic, facultative, and aerobic zones according to the water flow direction. These zones are connected by a flow diversion facility. The stabilization pond is used for the purification of farmland runoff from low-grade arable land. 3) Ditch network: This network consists of ditches that are set up around the low-grade farmland and connected to stabilization ponds and the low-grade farmland. It is constructed according to the topography of the farmland and the direction of water flow, with ecological bricks paved at the bottom and on the slopes. It also includes internal gratings and sedimentation tanks. The drainage network is used for the collection and pretreatment of farmland runoff; and 4) Clean water return unit and sludge return unit: It is connected to the stabilization pond and low-grade farmland, and consists of pumps and pipelines. It is used to return the purified water and sludge from the bottom of the stabilization pond to the low-grade farmland.

2. The system according to claim 1, characterized in that, In the stabilization pond, Aquatic plants such as cattail and Vallisneria are planted in the anaerobic zone, and anaerobic microbial communities that have been screened and domesticated are introduced to decompose large organic molecules into small organic molecules and convert some nitrogen and phosphorus nutrients into ammonia nitrogen and phosphate. In the facultative zone, pollution-tolerant aquatic plants are planted, and facultative microorganisms are introduced to further degrade organic matter and to initially absorb nitrogen and phosphorus nutrients. Aquatic plants are planted in the aerobic zone, and zooplankton and filter-feeding fish are introduced to completely decompose the remaining organic matter into carbon dioxide and water, and further remove nitrogen, phosphorus and algae from the water, thereby achieving deep purification of the water quality.

3. The system according to claim 2, characterized in that, In the stabilization pond, In the anaerobic zone, the aquatic plants are selected from cattail and Vallisneria natans, and the anaerobic microbial community is selected from one or more of methanogenic bacteria and hydrolytic acidifying bacteria. In the facultative zone, the aquatic plants are selected from one or more of the following: sweet flag, water onion, hydrangea and goldfish algae; and the facultative microorganisms are selected from species of the genus Bacillus. In the aerobic zone, the aquatic plants are selected from one or more of water lilies, goldfish algae, euglena, canna lilies and foxtail algae; the zooplankton are selected from one or more of rotifers and cladocerans; and the filter-feeding fish are selected from one or more of silver carp and bighead carp.

4. The system according to claim 1, characterized in that, The volume ratio of the anaerobic zone, facultative zone, and aerobic zone in the stabilization pond is 1:(1.2-3.0):(0.6-2.0).

5. The system according to claim 1, characterized in that, When constructing stabilization ponds, the topsoil 30-60cm below the surface is excavated, collected, and then spread back onto the farmland.

6. The system according to claim 1, characterized in that, In the ditch network, A grating is installed at the inlet of the ditch, and a sedimentation tank is installed at the connection between the ditch and the stabilization pond, and / or The aquatic plants in the ditch network are selected from one or more of the following: sweet flag, iris, and / or The drainage network is also equipped with flow regulation devices.

7. A method for improving the quality of low-grade arable land using the system as described in any one of claims 1-6, characterized in that, The method includes the following steps: 1) Drainage from low-grade farmland is diverted into stabilization ponds through a network of ditches; 2) Water purification treatment is carried out in the stabilization pond; 3) The purified water from the stabilization pond is reused for farmland irrigation using the clean water return unit and the sludge return unit, and the nutrient-rich sludge from the bottom of the stabilization pond generated during the purification process is applied to farmland.

8. The method according to claim 7, characterized in that, In step 2, the hydraulic retention time of each zone in the anaerobic zone, facultative zone, and aerobic zone of the stabilization pond is controlled to be 1-7 days, 5-10 days, and 3-5 days, respectively.

9. The method according to claim 7, characterized in that, In step 3, before reusing the purified water and pond bottom sludge, ensure that the quality of the reused water meets the GB5084-2021 "Standards for Irrigation Water Quality", and ensure that the organic matter content of the pond bottom sludge reaches 25-30 g / kg, and that the heavy metal index does not exceed the minimum value of the standard limit for each heavy metal factor in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control" (GB15618-2018).

10. The method according to claim 7, characterized in that, The method also includes regularly monitoring the soil of cultivated land during the process of improving the quality of low-grade cultivated land. The monitoring standards are in accordance with the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control" (GB15618-2018) and the "Evaluation Standard for Environmental Quality of Edible Agricultural Products Production Area" (HJ 332-2006).

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