Ecological ditch and farmland small ecological purification pond collaborative purification system and method

Abstract

The invention relates to the technical field of farmland drainage and purification, and particularly discloses an ecological ditch and farmland small ecological purification pond collaborative purification system and method.The system comprises a water inlet unit, an ecological ditch unit, a farmland small ecological purification pond unit and a water outlet unit which are communicated in sequence; the water inlet unit comprises a water inlet and a water inlet adjusting tank, the water inlet is communicated with a farmland drainage source, the water inlet adjusting tank is used for temporarily storing farmland drainage and adjusting drainage flow and water quality, and a water outlet of the water inlet adjusting tank is communicated with the water inlet end of the ecological ditch unit; the ecological ditch unit comprises a ditch body, and a front interception area, a microorganism purification area and a plant purification area are sequentially arranged in the ditch body in the water flow direction. According to the synergistic purification system and method for the ecological ditch and the small ecological purification pond for the farmland, the settling speed of large-particle solid impurities is greatly increased, and meanwhile the removal rate of suspended solids in water is high.

Description

Technical Field

[0001] This invention relates to the field of farmland drainage purification technology, specifically to a collaborative purification system and method of ecological ditches and small-scale ecological purification ponds in farmland. Background Technology

[0002] With the development of large-scale and intensive agriculture, farmland drainage has become one of the main sources of agricultural non-point source pollution. Farmland drainage not only contains a large number of large particulate solid impurities (such as soil silt, crop residues, undecomposed organic fertilizer particles, etc.), but also carries nitrogen, phosphorus nutrients and pesticide residues. If it is directly discharged into natural water bodies or enters subsequent ecological purification systems, it can easily cause problems such as eutrophication of water bodies, blockage of purification facilities, and reduced purification efficiency. Therefore, it is crucial to pre-treat farmland drainage to remove large particulate solid impurities.

[0003] As the first treatment unit in an ecological purification system for farmland drainage (such as a synergistic purification system of ecological ditches and small ecological purification ponds in farmland), the core function of the influent regulating pond is to remove large particulate solid impurities from the drainage through sedimentation, so as to provide a stable influent water quality for subsequent purification units (such as the microbial purification zone and plant purification zone of the ecological ditch). However, traditional influent equalization tanks rely on natural sedimentation, which has significant technical shortcomings: On the one hand, the particle size of solid impurities in farmland drainage varies greatly (from a few micrometers to millimeters). Fine particles (particle size <50μm) have a negative surface charge and strong dispersibility, resulting in extremely slow natural settling speed (only 0.8-1.2mm / s), requiring a sedimentation time of 40-60 minutes. This not only increases the footprint of the equalization tank but also makes it difficult to meet the requirements of "instant treatment and rapid discharge" of farmland drainage. On the other hand, natural sedimentation only removes 60%-70% of suspended solids (SS). The unremoved solid impurities will quickly clog the filter screen in the pre-interception zone (cleaning cycle is only 3 days) after entering the subsequent ecological ditch. At the same time, they will adhere and accumulate on the surface of the packing material in the microbial purification zone, hindering the contact between functional microorganisms and pollutants, and significantly reducing the overall treatment efficiency of the ecological purification system.

[0004] To address the shortcomings of traditional natural sedimentation, existing technologies often employ the addition of flocculants to enhance the sedimentation effect. Commonly used flocculants are mainly divided into two categories: inorganic flocculants and organic flocculants. Inorganic flocculants (such as polyaluminum chloride PAC and aluminum sulfate) neutralize the surface charge of impurities by generating metal hydroxyl ions through hydrolysis, promoting particle aggregation. However, when used alone, the resulting flocs are small in size and low in density, easily leading to floating or dispersion. Furthermore, excessive addition of some inorganic flocculants (such as high-aluminum PAC) can result in excessive aluminum ion residues in the water, inhibiting the root growth of emergent plants in subsequent ecological ditches and the activity of benthic microorganisms in purification ponds, thus violating the environmental protection concept of ecological purification. Organic flocculants (such as polyacrylamide PAM and chitosan) can form large-sized flocs through the entanglement of polymer chains, but pure organic flocculants are expensive, and synthetic organic flocculants (such as PAM) are difficult to degrade and easily produce environmental residues, making them unsuitable for the long-term operation of farmland ecosystems.

[0005] Furthermore, in existing farmland drainage pretreatment technologies, some attempts are made to combine inorganic and organic flocculants. However, these technologies have not been specifically optimized for the characteristics of farmland drainage water quality (such as pH values ​​mostly between 6.5 and 8.0 and solid impurities containing a large amount of clay). This often leads to problems such as pH imbalance in the compound system and poor compatibility between the flocculant and impurities, resulting in unstable sedimentation effects. At the same time, most existing compound flocculants are in powder form, which easily generates dust during addition and makes it difficult to accurately control the dosage, easily causing local concentrations to be too high or too low, further affecting sedimentation efficiency. Summary of the Invention

[0006] To solve the above technical problems, the present invention is achieved through the following technical solution: a collaborative purification system and method of ecological ditch and small ecological purification pond in farmland, comprising an inlet unit, an ecological ditch unit, a small ecological purification pond in farmland and an outlet unit connected in sequence. The water intake unit includes an inlet and an inlet regulating pool. The inlet is connected to the farmland drainage source. The inlet regulating pool is used to temporarily store farmland drainage and regulate the drainage flow and water quality. The outlet of the inlet regulating pool is connected to the inlet end of the ecological ditch unit. The ecological ditch unit includes a ditch body, in which a pre-interception zone, a microbial purification zone, and a plant purification zone are arranged sequentially along the water flow direction. The pre-interception zone is equipped with a detachable filter assembly for intercepting solid impurities in farmland drainage. The microbial purification zone is filled with microbial carrier filler, and the surface of the microbial carrier filler is covered with functional microbial flora that degrade pollutants. The plant purification zone is planted with emergent plants. The farmland small-scale ecological purification pond unit includes a purification pond body. The inlet end of the purification pond body is connected to the outlet end of the ecological ditch unit. At least one flow guide baffle is provided in the purification pond body. The flow guide baffle divides the internal space of the purification pond body into at least two serial purification sub-areas. Each purification sub-area is planted with submerged plants and floating-leaved plants. The bottom of the purification pond body is covered with a bottom mud layer, and the bottom mud layer is inoculated with benthic microorganisms. The water outlet unit includes a water outlet and a water quality monitoring device. The water outlet is connected to the water outlet end of the purification pond body. The water quality monitoring device is installed at the water outlet and is used to monitor the water quality parameters of the purified water in real time.

[0007] Preferably, the filter assembly includes at least two layers of filter screens, and the mesh size of adjacent layers of filter screens gradually decreases along the water flow direction. The edge of the filter assembly is detachably connected to the inner wall of the ditch body. The side wall of the ditch body is provided with an inspection port corresponding to the position of the pre-interception area for removing the filter assembly for cleaning or replacement.

[0008] Preferably, the microbial carrier filler is at least one of porous ceramsite, polyurethane sponge, or biochar, the filling height of the microbial carrier filler is 1 / 2 of the depth of the ditch body, and the microbial carrier filler is fixed inside the ditch body by a grid support.

[0009] Preferably, the emergent plant is at least one of reed, cattail, or calamus, and the planting density of the emergent plant is 7 plants / m²; the submerged plant is at least one of Vallisneria natans, Hydrilla verticillata, or Ceratophyllum demersum, and the floating-leaved plant is at least one of water lily or water caltrop, and the planting area ratio of the submerged plant to the floating-leaved plant is 4:1.

[0010] Preferably, the height of the flow guide baffle is lower than the height of the pool wall of the purification pond body, the bottom of the flow guide baffle is sealed to the bottom of the purification pond body, and water flow is connected between two adjacent purification sub-zones through the overflow port at the top of the flow guide baffle, and an interception net is provided at the overflow port.

[0011] Preferably, it also includes an aeration unit, which includes an aeration pump and an aeration pipe. The aeration pipe is laid at the bottom of the microbial purification zone and the purification pond body. Multiple aeration heads are provided on the aeration pipe. The aeration pump provides oxygen to the microbial purification zone and the purification pond body through the aeration pipe.

[0012] Preferably, the water quality monitoring device includes a pH sensor, a dissolved oxygen sensor, a chemical oxygen demand sensor, and a total nitrogen and total phosphorus sensor. The water quality monitoring device is also connected to a data transmission module for transmitting the monitored water quality parameters to a remote monitoring platform in real time.

[0013] A purification method for a synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland includes the following steps: S1: Farmland drainage enters the inlet regulating tank through the inlet, and a sedimentation-promoting additive is added to the regulating tank. Flow rate adjustment and preliminary sedimentation are carried out in the inlet regulating tank to remove some large-particle solid impurities. S2: The wastewater treated in step S1 enters the pre-interception zone of the ecological ditch unit, where the remaining solid impurities are intercepted by the filter assembly. Then the water flows into the microbial purification zone, where the organic pollutants and nitrogen and phosphorus compounds in the wastewater are degraded by the functional microbial community on the surface of the microbial carrier packing. S3: The drainage after step S2 enters the plant purification zone of the ecological ditch unit, where nitrogen and phosphorus nutrients are further removed through the absorption of the emergent plants. At the same time, the roots of the emergent plants provide an attachment carrier for microorganisms, enhancing the purification effect of microorganisms. S4: The wastewater treated in step S3 enters the small ecological purification pond unit in the farmland. Under the guidance of the flow guide baffle, it flows through each purification sub-zone in sequence. Through the absorption of the submerged plants and floating-leaved plants and the degradation of the benthic microorganisms in the bottom mud layer, the pollutants in the wastewater are deeply removed. S5: The wastewater after deep purification in step S4 flows to the outlet. The water quality parameters of the effluent are monitored by the water quality monitoring device. If the water quality meets the standards, it is discharged or reused through the outlet. If the water quality does not meet the standards, the wastewater is returned to the inlet regulating tank for re-purification.

[0014] Preferably, during the purification process in steps S2 and S4, the aeration unit aerates the microbial purification zone and the interior of the purification pond, controlling the dissolved oxygen concentration in the microbial purification zone to be 3 mg / L and the dissolved oxygen concentration inside the purification pond to be 2 mg / L.

[0015] Preferably, the method for preparing the precipitation-promoting additive includes: Raw material pretreatment: Modified bentonite and modified chitosan were prepared, and PAC was pretreated. Raw material mixing: The pretreated modified bentonite, PAC, modified chitosan, sodium bicarbonate and starch were mixed evenly. Granulation: Add deionized water to the well-mixed powder, stir, and then feed it into a rotary granulator to make cylindrical granules with a particle size of 2 mm. Drying and sieving: The granulated particles are fed into a belt dryer, dried, and then sent to a vibrating screen to screen out particles of 2mm, thus obtaining the finished sedimentation additive.

[0016] It has the following beneficial effects: This synergistic purification system and method combining ecological ditches and small-scale ecological purification ponds in farmland addresses the pain points of existing farmland drainage pretreatment, such as low natural sedimentation efficiency, high ecological risks of traditional flocculants, and poor compatibility of compound systems. Through a composite design and supporting preparation and application processes of "natural matrix + inorganic flocculation + organic coagulation aid," it achieves multi-dimensional technological breakthroughs. Regarding sedimentation efficiency, the adsorption and weight-increasing effects of modified bentonite, the charge neutralization effect of PAC, and the floc entanglement effect of modified chitosan significantly improve the settling speed of large solid particles, while also achieving a high removal rate of suspended solids in the water. This substantially reduces the footprint of the influent regulating pond and decreases the impurity load on subsequent purification units. In terms of ecological safety, all selected components are eco-friendly materials; the modified bentonite can be utilized by benthic organisms, and the PAC aluminum... The residual ion content is far below the national standard limit. Modified chitosan and starch can be completely degraded within a period of time, and experiments have verified that it has minimal impact on the growth of emergent plants and the activity of microorganisms, which is in line with the concept of ecological purification. In terms of system adaptation and cost control, the pH of the additive is adjusted to 7.0 by using sodium bicarbonate to adapt to the drainage characteristics of farmland. The 2mm granular formulation, combined with the pipeline mixing and dosing device, allows for precise dosage control, avoiding dust and concentration fluctuations. At the same time, due to the high impurity removal rate, the cleaning cycle of the ecological ditch filter screen is extended, reducing the maintenance cost of the filler. In terms of large-scale application, the five-step process of "pretreatment-mixing-granulation-drying" is mature and controllable, with a high finished product qualification rate and high raw material utilization rate. The granular formulation has a shelf life of 6 months and is convenient to store and use. It can be promoted in ecological purification systems of different scales of farmland without complex equipment modifications. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 within the scope of protection of the present invention.

[0018] This invention provides a technical solution: a collaborative purification system of ecological ditch and small ecological purification pond in farmland, comprising an inlet unit, an ecological ditch unit, a small ecological purification pond in farmland, and an outlet unit connected in sequence. The water intake unit includes an inlet and an inlet regulating pool. The inlet is connected to the farmland drainage source. The inlet regulating pool is used to temporarily store farmland drainage and regulate the drainage flow and water quality. The outlet of the inlet regulating pool is connected to the inlet end of the ecological ditch unit. The ecological ditch unit includes a ditch body. Within the ditch body, a pre-interception zone, a microbial purification zone, and a plant purification zone are sequentially arranged along the water flow direction. The pre-interception zone contains a detachable filter assembly for intercepting solid impurities in farmland drainage. The filter assembly includes at least two layers of filter screens, with the mesh size of adjacent layers gradually decreasing along the water flow direction. The edge of the filter assembly is detachably connected to the inner wall of the ditch body. An inspection port is provided on the side wall of the ditch body corresponding to the pre-interception zone for removing the filter assembly for cleaning or replacement. The microbial purification zone is filled with microbial carrier packing material. The surface is covered with functional microbial flora that degrade pollutants. The microbial carrier filler is at least one of porous ceramsite, polyurethane sponge, or biochar. The filling height of the microbial carrier filler is 1 / 2 of the depth of the ditch body, and the microbial carrier filler is fixed inside the ditch body by a grid support. The plant purification area is planted with emergent plants, which are at least one of reed, cattail, or calamus, and the planting density of the emergent plants is 7 plants / m². The submerged plants are at least one of Vallisneria natans, Hydrilla verticillata, or Ceratophyllum demersum. The floating-leaved plants are at least one of water lily or water chestnut, and the planting area ratio of the submerged plants to the floating-leaved plants is 4:1. The farmland small-scale ecological purification pond unit includes a purification pond body. The inlet end of the purification pond body is connected to the outlet end of the ecological ditch unit. At least one flow guide baffle is provided in the purification pond body. The flow guide baffle divides the internal space of the purification pond body into at least two serially connected purification sub-areas. Each purification sub-area is planted with submerged plants and floating-leaved plants. The bottom of the purification pond body is covered with a bottom mud layer inoculated with benthic microorganisms. The height of the flow guide baffle is lower than the height of the pond wall of the purification pond body. The bottom of the flow guide baffle is sealed to the bottom of the purification pond body. The water flow between two adjacent purification sub-areas is achieved through the overflow port at the top of the flow guide baffle, and an interception net is provided at the overflow port. The water outlet unit includes a water outlet and a water quality monitoring device. The water outlet is connected to the water outlet end of the purification pond body. The water quality monitoring device is installed at the water outlet and is used to monitor the water quality parameters of the purified water in real time. The water quality monitoring device includes a pH sensor, a dissolved oxygen sensor, a chemical oxygen demand sensor, and a total nitrogen and total phosphorus sensor. The water quality monitoring device is also connected to a data transmission module for transmitting the monitored water quality parameters to a remote monitoring platform in real time. It also includes an aeration unit, which includes an aeration pump and an aeration pipe. The aeration pipe is laid at the bottom of the microbial purification zone and the purification pond body. Multiple aeration heads are installed on the aeration pipe. The aeration pump provides oxygen to the microbial purification zone and the purification pond body through the aeration pipe.

[0019] A purification method for a synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland includes the following steps: S1: Farmland drainage enters the inlet regulating tank through the inlet, and a sedimentation-promoting additive is added to the regulating tank. Flow rate adjustment and preliminary sedimentation are carried out in the inlet regulating tank to remove some large-particle solid impurities. S2: The wastewater treated in step S1 enters the pre-interception zone of the ecological ditch unit, where the remaining solid impurities are intercepted by the filter assembly. Then the water flows into the microbial purification zone, where the organic pollutants and nitrogen and phosphorus compounds in the wastewater are degraded by the functional microbial community on the surface of the microbial carrier packing. S3: The drainage after step S2 enters the plant purification zone of the ecological ditch unit, where nitrogen and phosphorus nutrients are further removed through the absorption of the emergent plants. At the same time, the roots of the emergent plants provide an attachment carrier for microorganisms, enhancing the purification effect of microorganisms. S4: The wastewater treated in step S3 enters the small ecological purification pond unit in the farmland. Under the guidance of the flow guide baffle, it flows through each purification sub-zone in sequence. Through the absorption of the submerged plants and floating-leaved plants and the degradation of the benthic microorganisms in the bottom mud layer, the pollutants in the wastewater are deeply removed. S5: The wastewater after deep purification in step S4 flows to the outlet. The water quality parameters of the effluent are monitored by the water quality monitoring device. If the water quality meets the standards, it is discharged or reused through the outlet. If the water quality does not meet the standards, the wastewater is returned to the inlet regulating tank for re-purification.

[0020] The method for preparing the precipitation-promoting additive includes: Step 1: Raw material pretreatment; Preparation of modified bentonite: Take natural bentonite with a particle size of less than 200 mesh, add 12% of its mass of deionized water, stir into a paste, add 5% of its mass of hydrochloric acid solution, stir and react in a constant temperature water bath at 65℃ for 2 hours to achieve the expansion of the pore structure of bentonite. After the reaction is completed, wash with deionized water until pH=7.0, put it in an oven at 105℃ to dry for 4 hours, pulverize and pass through a 300-mesh sieve to obtain modified bentonite powder for later use; Preparation of modified chitosan: Chitosan with a particle size of 100 mesh was added to a 2% (w / w) acetic acid solution and stirred until completely dissolved. Then, 3% (w / w) propylene oxide was added to the chitosan and stirred at 50°C for 1.5 h to improve the water solubility and adsorption of chitosan. After the reaction, a 5% (w / w) sodium hydroxide solution was added to neutralize to pH=7.0, and modified chitosan was precipitated. After filtration, it was washed three times with deionized water, vacuum dried at 80°C for 3 h, pulverized and passed through a 200-mesh sieve for later use. PAC pretreatment: Take powdered industrial-grade PAC and dry it in an 80℃ oven for 2 hours to remove surface adsorbed water and prevent clumping during subsequent mixing. Step 2: Mixing and dispersing; Add 65% of the pretreated modified bentonite, 18% of PAC, 8% of the modified chitosan, 5% of the sodium bicarbonate, and 4% of the starch into a double helix conical mixer according to the mass ratio. Control the mixer speed at 300 r / min and mix at room temperature for 30 min. During this period, stop the machine every 10 min, open the observation port, and use a sampling spoon to check the mixing uniformity. Step 3: Granulation (to prevent dust and control dosage); Add 14% of the mass of deionized water to the uniformly mixed powder and stir to form a moist powder. Then feed it into a rotary granulator and control the granulator drum speed at 60 r / min and the temperature at 50℃ to produce cylindrical granules with a particle size of 2 mm. During the granulation process, a small amount of dust generated is removed by a fan. The dust is collected by a bag filter and returned to the mixer to improve the utilization rate of raw materials. Step 4: Drying and sieving; The granulated particles are fed into a belt dryer and a three-stage drying process is adopted: the first stage is at 80℃ for 1 hour to remove surface moisture; the second stage is at 100℃ for 1.5 hours to remove internal moisture; and the third stage is at 70℃ for 0.5 hours to cool and set. After drying, the particles are sent to a vibrating screen to screen out particles with a diameter of 2mm. Fine powder with a diameter of <1mm is returned to the granulator for regranulation, and coarse particles with a diameter of >2mm are crushed and returned to the mixer.

[0021] Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art and related fields based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described and explained in the present invention, unless otherwise specified or limited, shall be implemented according to conventional means in the art.

Claims

1. A synergistic purification system combining ecological ditches and small-scale ecological purification ponds in farmland, characterized in that, It includes an inlet unit, an ecological ditch unit, a small ecological purification pond unit for farmland, and an outlet unit that are connected in sequence. The water intake unit includes an inlet and an inlet regulating pool. The inlet is connected to the farmland drainage source. The inlet regulating pool is used to temporarily store farmland drainage and regulate the drainage flow and water quality. The outlet of the inlet regulating pool is connected to the inlet end of the ecological ditch unit. The ecological ditch unit includes a ditch body, in which a pre-interception zone, a microbial purification zone, and a plant purification zone are arranged sequentially along the water flow direction. The pre-interception zone is equipped with a detachable filter assembly for intercepting solid impurities in farmland drainage. The microbial purification zone is filled with microbial carrier filler, and the surface of the microbial carrier filler is covered with functional microbial flora that degrade pollutants. The plant purification zone is planted with emergent plants. The farmland small-scale ecological purification pond unit includes a purification pond body. The inlet end of the purification pond body is connected to the outlet end of the ecological ditch unit. At least one flow guide baffle is provided in the purification pond body. The flow guide baffle divides the internal space of the purification pond body into at least two serial purification sub-areas. Each purification sub-area is planted with submerged plants and floating-leaved plants. The bottom of the purification pond body is covered with a bottom mud layer, and the bottom mud layer is inoculated with benthic microorganisms. The water outlet unit includes a water outlet and a water quality monitoring device. The water outlet is connected to the water outlet end of the purification pond body. The water quality monitoring device is installed at the water outlet and is used to monitor the water quality parameters of the purified water in real time.

2. The synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland according to claim 1, characterized in that, The filter assembly includes at least two layers of filter screens, and the mesh size of adjacent layers of filter screens gradually decreases along the water flow direction. The edge of the filter assembly is detachably connected to the inner wall of the ditch body. The side wall of the ditch body is provided with an inspection port corresponding to the position of the pre-interception area for removing the filter assembly for cleaning or replacement.

3. The synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland according to claim 1, characterized in that, The microbial carrier filler is at least one of porous ceramsite, polyurethane sponge, or biochar. The filling height of the microbial carrier filler is 1 / 2 of the depth of the ditch body, and the microbial carrier filler is fixed inside the ditch body by a grid support.

4. The synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland according to claim 1, characterized in that, The emergent plants are at least one of reeds, cattails, or sweet flag, and the planting density of the emergent plants is 7 plants / m². The submerged plants are at least one of Vallisneria natans, Hydrilla verticillata, or Ceratophyllum demersum. The floating-leaved plants are at least one of water lilies or water lilies. The planting area ratio of the submerged plants to the floating-leaved plants is 4:

1.

5. The synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland according to claim 1, characterized in that, The height of the flow guide baffle is lower than the height of the pool wall of the purification pond body. The bottom of the flow guide baffle is sealed to the bottom of the purification pond body. Water flow is connected between two adjacent purification sub-zones through the overflow port at the top of the flow guide baffle, and an interception net is provided at the overflow port.

6. The synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland according to claim 1, characterized in that, It also includes an aeration unit, which includes an aeration pump and an aeration pipe. The aeration pipe is laid at the bottom of the microbial purification zone and the purification pond body. Multiple aeration heads are installed on the aeration pipe. The aeration pump provides oxygen to the microbial purification zone and the purification pond body through the aeration pipe.

7. The synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland according to claim 6, characterized in that, The water quality monitoring device includes a pH sensor, a dissolved oxygen sensor, a chemical oxygen demand sensor, and a total nitrogen and total phosphorus sensor. The water quality monitoring device is also connected to a data transmission module for transmitting the monitored water quality parameters to a remote monitoring platform in real time.

8. A purification method based on the synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland as described in claim 7, characterized in that, Includes the following steps: S1: Farmland drainage enters the inlet regulating tank through the inlet, and a sedimentation-promoting additive is added to the regulating tank. Flow rate adjustment and preliminary sedimentation are carried out in the inlet regulating tank to remove some large-particle solid impurities. S2: The wastewater treated in step S1 enters the pre-interception zone of the ecological ditch unit, where the remaining solid impurities are intercepted by the filter assembly. Then the water flows into the microbial purification zone, where the organic pollutants and nitrogen and phosphorus compounds in the wastewater are degraded by the functional microbial community on the surface of the microbial carrier packing. S3: The drainage after step S2 enters the plant purification zone of the ecological ditch unit, where nitrogen and phosphorus nutrients are further removed through the absorption of the emergent plants. At the same time, the roots of the emergent plants provide an attachment carrier for microorganisms, enhancing the purification effect of microorganisms. S4: The wastewater treated in step S3 enters the small ecological purification pond unit in the farmland. Under the guidance of the flow guide baffle, it flows through each purification sub-zone in sequence. Through the absorption of the submerged plants and floating-leaved plants and the degradation of the benthic microorganisms in the bottom mud layer, the pollutants in the wastewater are deeply removed. S5: The wastewater after deep purification in step S4 flows to the outlet. The water quality parameters of the effluent are monitored by the water quality monitoring device. If the water quality meets the standards, it is discharged or reused through the outlet. If the water quality does not meet the standards, the wastewater is returned to the inlet regulating tank for re-purification.

9. The purification method of the synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland according to claim 8, characterized in that, During the purification process in steps S2 and S4, the aeration unit aerates the microbial purification zone and the interior of the purification pond, controlling the dissolved oxygen concentration in the microbial purification zone to 3 mg / L and the dissolved oxygen concentration inside the purification pond to 2 mg / L.

10. The purification method of the synergistic purification system of ecological ditches and small-scale ecological purification ponds in farmland according to claim 8, characterized in that, The method for preparing the precipitation-promoting additive includes: Raw material pretreatment: Modified bentonite and modified chitosan were prepared, and PAC was pretreated. Raw material mixing: The pretreated modified bentonite, PAC, modified chitosan, sodium bicarbonate and starch were mixed evenly. Granulation: Add deionized water to the well-mixed powder, stir, and then feed it into a rotary granulator to make cylindrical granules with a particle size of 2 mm. Drying and sieving: The granulated particles are fed into a belt dryer, dried, and then sent to a vibrating screen to screen out particles of 2mm, thus obtaining the finished sedimentation additive.