Intensive farmland recession multi-stage ecological purification system

Abstract

The invention relates to an intensive farmland recession multistage ecological purification system, and belongs to the technical field of water treatment, the system comprises a precipitation slow flow unit, an aerobic reaction tank, an anaerobic reaction tank and an ecological treatment unit, the precipitation slow flow unit can carry out regulation, storage and slow flow on incoming water, and precipitate suspended solids and particulate pollutants; an aeration device and a plurality of three-dimensional floating wetlands are arranged in the aerobic reaction tank, and the three-dimensional floating wetlands are used for providing an adhesion growth carrier and a rhizosphere microenvironment; a plurality of bio-membrane reactors are arranged in the anaerobic reaction tank, and the bio-membrane reactors are used for providing anaerobic adhesion growth interfaces to enrich denitrifying microorganisms; the ecological treatment unit is used for ecologically and stably purifying the effluent to inhibit the fluctuation of water quality parameters. The device has the advantages that various pollutants such as suspended solids, nitrogen and phosphorus can be efficiently removed, and meanwhile the occupied area can be effectively reduced.

Description

Technical Field

[0001] This application relates to the field of water treatment technology, and in particular to an intensive multi-stage ecological purification system for farmland runoff. Background Technology

[0002] Agricultural runoff is characterized by highly concentrated discharge periods, large instantaneous flow rates, and drastic fluctuations in pollution load and water quality. Its main pollutants are total nitrogen (TN) and total phosphorus (TP), with generally high concentrations, making it a significant source of eutrophication in downstream water bodies. Existing ecological treatment projects for agricultural runoff mostly employ ecological interception ditch systems such as vertical and horizontal subsurface flow wetlands, combined with stabilization ponds / ecological ponds to construct purification systems.

[0003] However, ecological interception ditch systems such as vertical subsurface flow wetlands, horizontal subsurface flow wetlands, and reed gully wetlands mostly rely on seepage through the bed pores or rapid surface flow. Under peak inflow conditions, short-circuiting, deviated flow, and bypassing are prone to occur, resulting in insufficient effective contact time between pollutants and filler / rhizosphere microorganisms. The overall reaction intensity is limited, making it difficult to stably achieve reduction of TN and TP.

[0004] Furthermore, the instantaneous flow rate of farmland runoff is large and the concentration fluctuates significantly. During peak impacts, wetland systems are prone to local overload of the bed, making it difficult to maintain a stable reaction environment (dissolved oxygen, redox conditions). This in turn disturbs key processes such as nitrification and denitrification, resulting in significant fluctuations in effluent quality.

[0005] Meanwhile, due to the high content of suspended solids (SS) and fine particulate matter in the incoming water, it is easy to deposit and accumulate on the surface of the wetland or in the pore channels, causing pore blockage, a decrease in the permeability coefficient, and further inducing flow deviation, short flow and reducing the effective treatment volume; once blocked, it is often necessary to overhaul the bed or replace the packing, which makes operation and maintenance difficult and costly.

[0006] Limited by factors such as effective retention time, bed blockage, and shock loads, traditional subsurface flow wetlands have limited reduction capacity per unit area for total nitrogen (TN) and total phosphorus (TP). To achieve a considerable reduction effect, it is usually necessary to significantly increase the wetland area and reservoir capacity, which leads to an increase in land area. However, even with an expanded scale, the purification effect may still be unstable due to hydraulic short-circuiting and microbial community disturbance caused by peak inflow. Summary of the Invention

[0007] In order to achieve efficient removal of various pollutants such as suspended solids, nitrogen, and phosphorus while effectively reducing the land area occupied, this application provides an intensive multi-stage ecological purification system for farmland runoff.

[0008] The intensive multi-stage ecological purification system for farmland drainage provided in this application adopts the following technical solution: An intensive, multi-stage ecological purification system for farmland runoff includes a sedimentation and slow-flow unit, an aerobic reaction tank, an anaerobic reaction tank, and an ecological treatment unit. The sedimentation and slow-flow unit can receive farmland runoff and regulate and slow the flow of incoming water, settling suspended solids and particulate pollutants. The aerobic reaction tank can receive the discharge water from the sedimentation and slow flow unit. The aerobic reaction tank is equipped with an aeration device and several three-dimensional floating wetlands. The three-dimensional floating wetlands are used to provide attached growth carriers and rhizosphere microenvironment. The anaerobic reactor can receive the effluent from the aerobic reactor. The anaerobic reactor is equipped with several biofilm reactors, which are used to provide an anaerobic attachment and growth interface to enrich denitrifying microorganisms. The ecological treatment unit can receive the effluent from the anaerobic reactor and is used to perform ecological stabilization purification on the effluent to suppress fluctuations in water quality parameters.

[0009] By adopting the above technical solution, this system incorporates a sedimentation and slow-flow unit at the front end to regulate and dissipate farmland runoff, reducing instantaneous flow impacts and prioritizing the removal of suspended solids and particulate pollutants, thereby minimizing hydraulic disturbance and particulate load in subsequent reaction units. Furthermore, both the aerobic and anaerobic reaction tanks utilize open water bodies, providing sufficient effective volume even at greater water depths. This allows for more stable retention and distribution of water within the reaction tanks, reducing the risk of short-circuiting and flow deviation, and increasing the probability of effective contact between pollutants and the biofilm and rhizosphere microenvironment.

[0010] The aeration device provides adjustable dissolved oxygen to the pool and creates localized circulating mixing, ensuring uniform water distribution and improving residence time distribution. The three-dimensional floating wetland provides a three-dimensional attachment carrier and rhizosphere microenvironment for microorganisms, promoting the formation of stable biofilms by aerobic microorganisms and enhancing aerobic reaction processes such as nitrification. Unlike traditional vertical / horizontal subsurface flow wetlands that rely on seepage through the pores of the bed, this invention does not require filling the entire reaction space with packing material, avoiding pore blockage and flow deviation problems caused by high suspended solids (SS) or fine particle deposition. Furthermore, the three-dimensional floating wetland can be modularly assembled and disassembled, facilitating inspection, replacement, and operation and maintenance management. The anaerobic reactor provides ample volume at greater water depths and further extends the effective reaction time of the water body; simultaneously, the biofilm reactor provides an anaerobic attachment and growth interface for denitrifying microorganisms. Because the upstream sedimentation and slow-flow unit and the aerobic reactor have significantly reduced SS content and hydraulic disturbance, the water flow within the anaerobic reactor is smoother and more evenly distributed, which is conducive to the full utilization of denitrification by each biofilm reactor and reduces the problems of clogging, flow deviation, and microbial erosion common in traditional seepage bed structures. Furthermore, the biofilm reactor can be periodically removed for maintenance and replacement, and it is convenient to replenish microbial agents according to the receding water period, improving long-term operational stability. After undergoing multi-stage treatment involving sedimentation and slow flow, aerobic enhancement, and anaerobic enhancement, fluctuations in effluent quality have been effectively suppressed and stabilized. Upon entering the ecological treatment unit, the effluent primarily serves as an ecological buffer and provides further stabilization and purification. Because the aforementioned enhancement units increase the reaction intensity and pollution reduction capacity per unit volume, the ecological treatment unit can be appropriately reduced in size while still meeting water quality stability requirements. This allows the system to achieve more efficient reduction and more stable purification of TN / TP in farmland runoff within a smaller footprint, demonstrating significant advantages in intensive management.

[0011] Optionally, a filtration unit is also included, which is used to receive the effluent from the anaerobic reactor and discharge the effluent into the biological pond, and the filtration unit is used to further remove total phosphorus and ammonia nitrogen.

[0012] By adopting the above technical solution, a filtration unit is installed between the anaerobic reactor and the ecological treatment unit. This allows the effluent from the anaerobic reactor to undergo a further filtration enhancement process before entering the ecological treatment unit, reducing its load on the unit. Consequently, the ecological treatment unit primarily undertakes ecological buffering and final stabilization purification functions, resulting in more stable overall effluent quality. Furthermore, the scale of the final ecological treatment unit can be appropriately optimized while meeting purification and stabilization requirements, further improving the system's integration level.

[0013] Optionally, the sedimentation and slow-flow unit includes a sedimentation pond, in which several guide dams are provided, and several collection troughs are provided in the sedimentation pond. The collection troughs correspond one-to-one with the guide dams and are located on the water-facing side of the guide dams.

[0014] By adopting the above technical solutions, the guide dams installed in the sedimentation pond are used to dissipate energy and distribute the incoming water jet, changing the flow pattern and creating a relatively stable slow-flow zone in front of each guide dam. This reduces short-circuiting and turbulent disturbances, improves hydraulic efficiency, and increases the effective settling opportunities for particulate matter. The guide dams, while guiding the water flow path, reduce the impact of instantaneous flow velocity, promote the settling of suspended solids and fine particulate matter in farmland runoff, and simultaneously enhance the interception and removal of suspended / particulate phosphorus. Furthermore, corresponding sludge collection troughs are installed on the upstream side of each guide dam, allowing the settled sludge to be concentrated and stored at predetermined locations. This facilitates subsequent centralized dredging, reduces the risk of secondary mudslides, and thus improves the long-term operational stability and maintenance convenience of the sedimentation pond.

[0015] Optionally, the aeration device is a solar-powered aerator, and the three-dimensional floating wetland includes a wetland planting carrier on which emergent aquatic plants are planted, and fiber packing is suspended at the bottom of the wetland planting carrier.

[0016] By adopting the above technical solutions, plant roots can form a rhizosphere microenvironment and provide an attachment interface for microorganisms; fiber packing is suspended at the bottom of the planting carrier. As a high specific surface area biofilm carrier, the fiber packing can immobilize and enrich aerobic microorganisms such as nitrifying bacteria, so that microorganisms form a composite biofilm on the surface of the fiber packing and plant roots, thereby improving the biomass retention capacity and enhancing the shock resistance stability against instantaneous large flow and water quality fluctuations.

[0017] Optionally, the solar-powered aerator has an oxygenation capacity of 0.6-0.78 kgO2 / h, with 1-2 units deployed per acre. The wetland planting carrier is composed of a composite of polyester fiber and plant fiber, with a mass ratio of polyester fiber to plant fiber of (2-3):(1-2). The buoyancy of the wetland planting carrier is 50-60 kg / m³. 2 The plant planting holes are 25-30 holes / m², and the emergent aquatic plants include water celery, aquatic canna, evergreen iris, and sweet flag, with a planting ratio of (1-2):(1-2):(2-3):(1-2). The aerobic reaction tank has a water depth of 1.5-2m, a hydraulic retention time of ≥2.5 days, and a fiber packing density of 9 strands / m². 2 Length is 1-1.5m, specific surface area ≥300m² 2 / m 3 Fiber packing material should cover at least 30% of the pond area, and the dosage of nitrifying bacteria should be 20-30 mL / m². 3 .

[0018] By adopting the above technical solution, the solar aerator continuously supplies oxygen to the aerobic zone according to the oxygenation capacity and arrangement density, forming a circulating mixture. Combined with a water depth of 1.5 to 2 m and a residence time of ≥2.5 days, the dissolved oxygen and flow pattern in the pool are more uniform and stable, reducing short-circuiting and impact disturbances. Polyester fiber and plant fiber form a continuous rhizosphere zone under specified buoyancy and pore density conditions. The high specific surface area fiber packing suspended at the bottom further provides a three-dimensional attachment interface, enabling the added nitrifying bacteria to quickly attach to the biofilm and be immobilized and enriched over a long period of time. Thus, the ammonia nitrogen nitrification conversion efficiency and shock resistance stability are significantly improved under conditions of smaller footprint.

[0019] Optionally, the water depth in the anaerobic reaction zone is 2.5-3m, the biofilm reactor includes a frame cage, each frame cage containing suspended polyurethane suspended packing balls, and the frame cages occupy at least 60% of the pond area, with the polyurethane suspended packing balls having a specific surface area of ​​at least 580m². 2 / m 3 The initial dosage of denitrifying bacteria is 50-60 g / m³. 3 Subsequent periodic supplementation dosage is 25-30g / m³. 3 .

[0020] By adopting the above technical solution, the anaerobic reaction zone uses a water depth of 3-3.5 m to provide sufficient effective volume and enhance hydraulic buffering. The polyurethane suspended packing balls suspended in the frame cage provide a high specific surface area immobilization attachment interface for denitrifying microorganisms, enabling the added denitrifying bacteria to quickly attach to the biofilm and accumulate for a long time, improving biomass retention and shock resistance stability, thereby enhancing the denitrification removal effect of nitrate nitrogen. At the same time, since the carrier is an open suspended structure, it does not rely on seepage pores, reducing the risk of clogging and flow deviation, and facilitating removal, maintenance, and replenishment of bacteria.

[0021] Optionally, the filtration section includes several permeable dams, and a packing bed is provided between adjacent permeable dams. The packing bed is provided with a floating plant bed, and the plant roots of the floating plant bed extend into the packing bed.

[0022] By adopting the above technical solution, the packing bed is used to adsorb / fix total phosphorus and further intercept and remove ammonia nitrogen. The floating plant bed allows plant roots to extend into the packing bed, forming a rhizosphere-packing-microorganism complex reaction interface, which promotes biofilm attachment and nutrient absorption, further stabilizes and reduces the nitrogen and phosphorus load entering the ecological treatment unit and suppresses water quality fluctuations.

[0023] Optionally, the permeable dam includes gabion mesh, and the gabion mesh is filled with crushed stone with a particle size of 30-50mm; The number of permeable dams is four. The filter media of the packing bed between the two permeable dams closest to the upstream water level includes calcium-aluminum-based phosphorus removal packing with a particle size of 50-80mm. The filter media of the packing bed between the two middle permeable dams includes volcanic rock with a particle size of 30-50mm. The filter media of the packing bed between the two permeable dams closest to the downstream water level includes natural zeolite with a particle size of 20-30mm.

[0024] By adopting the above technical solutions, the permeable dam uses gabion mesh and is filled with crushed stone, which can play a role in staged energy dissipation and rectification while ensuring water permeability and flow. This allows water to flow evenly into each section of the packing bed and reduces the risk of scouring and clogging. The upstream section uses calcium-aluminum-based phosphorus removal packing to preferentially adsorb and fix total phosphorus and reduce phosphorus load. The middle section uses volcanic rock to provide high porosity and attachment interface to facilitate biofilm growth and further stabilize water quality. The downstream section uses natural zeolite to further reduce ammonia nitrogen through ion exchange / adsorption, thereby achieving a staged and enhanced synergistic purification effect, reducing the nitrogen and phosphorus impact entering the ecological treatment unit and improving the stability of the effluent.

[0025] Optionally, the ecological treatment unit includes an ecological pond with a slope ratio of 1:2-1:4. Turf is laid above the water level on the slope of the ecological pond. Emergent plants are planted at the water-land interface of the ecological pond. Floating-leaved plants and submerged plants are planted in the ecological pond. Filter-feeding shellfish, benthic scraping snails, and freshwater fish are also introduced into the ecological pond. A sluice gate is installed at the drainage point of the ecological pond, and a circulating pump station is installed on the drainage side of the sluice gate to pump the outflow to the farmland irrigation canal.

[0026] By adopting the above technical solutions, the ecological pond forms a stable water-land transition zone through the inner slope. The turf can stabilize the slope to prevent erosion and intercept sediment carried by non-point sources. Emergent plants are planted in the water-land transition zone, and floating-leaved plants and submerged plants are planted in the pond to construct a three-dimensional aquatic vegetation community, providing a multi-layered habitat for microbial attachment and nutrient absorption, and synergistically improving the reduction of nitrogen and phosphorus and the water quality buffering capacity. Simultaneously, filter-feeding shellfish, benthic scraping snails, and freshwater fish are introduced. Filter-feeding shellfish can filter-feed on plankton and organic detritus, while benthic scraping snails can scrape organic detritus from plant leaf surfaces and humus from the bottom sediment. Freshwater fish can feed on phytoplankton and zooplankton, and reproduce with shellfish to form a symbiotic relationship, thereby maintaining the stability of the aquatic ecosystem. The sluice gate facilitates the control of water level and residence time, and the circulating pump station lifts the treated effluent back to the farmland irrigation canals, realizing reuse and circulation, reducing the external discharge load and improving water resource utilization efficiency.

[0027] Optionally, the emergent plants include reeds, cattails, arrowhead, wild rice, and water celery, with a planting ratio of (1-2):(1-2):(2-3):(2-3):(2-3), and a planting density of not less than 16 plants / m2. The floating-leaved plants include lotus, water lilies, water chestnuts, and water lettuce, with a planting ratio of (1-2):(5-6):(1-2):(2-3), and a planting density of not less than 1 clump / m2. The submerged plants include hydrangea, foxtail grass, pondweed, and pickerelweed, with a planting ratio of (2-3):(2-3):(2-3):(1-2):(2-3). -2), the planting density is not less than 100 plants / m2, the filter-feeding shellfish include Triangular sail mussel and pleated crown mussel, the stocking density of Triangular sail mussel and pleated crown mussel is not less than 10kg / mu, and the ratio is (1-2):(1-2), the benthic scraping snails include square ring snail, pear-shaped ring snail, copper-rust ring snail and field snail, the stocking density of square ring snail, pear-shaped ring snail, copper-rust ring snail and field snail is not less than 1kg / mu, and the ratio is (1-2):(1-2):(1-2):(1-2), the freshwater fish include silver carp, bighead carp and bitterling, the stocking density of silver carp, bighead carp and bitterling is not less than 5kg / mu, and the ratio is (1-2):(1-2):(1-2).

[0028] By adopting the above technical solution, and by configuring emergent plants, floating-leaved plants, and submerged plants in the ecological pond according to the aforementioned proportions and minimum densities to construct a three-dimensional aquatic vegetation community, a continuous absorption, fixation, and rhizosphere attachment interface can be formed at different water depths and habitat levels. This promotes the plant absorption and microbial transformation of nitrogen and phosphorus nutrients, while enhancing the water body's shading, flow stabilization, and sedimentation conditions, inhibiting abnormal algal reproduction, and reducing water quality fluctuations. Furthermore, the introduction of filter-feeding shellfish to filter-feed on planktonic plants and organic debris, benthic scraping snails to scrape and clean plant leaf attachments and bottom sediment surface humus, and freshwater fish to feed on plankton and form an ecological synergy with shellfish, can further improve water transparency, reduce the risk of organic suspended matter and endogenous release, thereby enhancing the ecological pond's ability to stably reduce total nitrogen and total phosphorus and maintain the long-term stable operation of the aquatic ecosystem.

[0029] In summary, this application includes at least one of the following beneficial technical effects: 1. This system incorporates a sedimentation and slow-flow unit at the front end to regulate and slow the flow of farmland runoff, reducing instantaneous flow impacts and prioritizing the removal of suspended solids and particulate pollutants, thereby minimizing hydraulic disturbance and particulate load in subsequent reaction units. Furthermore, both the aerobic and anaerobic reaction tanks utilize open water bodies, providing ample effective volume even at greater water depths. This allows for more stable retention and distribution of water within the reaction tanks, reducing the risk of short-circuiting and flow deviation, and increasing the probability of effective contact between pollutants and the biofilm and rhizosphere microenvironment. 2. The aeration device provides adjustable dissolved oxygen in the pool and forms localized circulating mixing, ensuring uniform water distribution and improving residence time distribution. The three-dimensional floating wetland provides a three-dimensional attachment carrier and rhizosphere microenvironment for microorganisms, promoting the formation of stable biofilms by aerobic microorganisms and enhancing aerobic reaction processes such as nitrification. Unlike traditional vertical / horizontal subsurface flow wetlands that rely on seepage through the pores of the bed, this invention does not require filling the entire reaction space with packing material, avoiding pore blockage and flow deviation problems caused by high suspended solids (SS) or fine particle deposition. Furthermore, the three-dimensional floating wetland can be modularly disassembled, facilitating inspection, replacement, and operation and maintenance management. 3. The anaerobic reactor provides ample volume at greater water depths and further extends the effective reaction time of the water body; simultaneously, the biofilm reactor provides an anaerobic attachment and growth interface for denitrifying microorganisms. Since the upstream sedimentation and slow-flow unit and the aerobic reactor have significantly reduced SS content and hydraulic disturbance, the water flow in the anaerobic reactor is smoother and more evenly distributed, which is conducive to the full utilization of denitrification by each biofilm reactor and reduces the problems of clogging, flow deviation, and microbial erosion and disturbance commonly found in traditional seepage bed structures. Furthermore, the biofilm reactor can be periodically removed for maintenance and replacement, and it is convenient to replenish the microbial agent according to the receding water period, improving long-term operational stability. 4. After multi-stage treatment involving sedimentation and slow flow, aerobic enhancement, and anaerobic enhancement, fluctuations in effluent quality have been effectively suppressed and stabilized. Upon entering the ecological treatment unit, it primarily serves as an ecological buffer and further stabilizes and purifies the water. Because the aforementioned enhancement units increase the reaction intensity and pollution reduction capacity per unit volume, the ecological pond can be appropriately reduced in size while still meeting water quality stability requirements. This allows the system to achieve more efficient reduction and more stable purification of TN / TP in farmland runoff with a smaller footprint, demonstrating significant advantages in intensive management. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of an embodiment of this application.

[0031] Figure 2 This is a schematic diagram illustrating the structure of the aerobic and anaerobic reactors in the embodiments of this application.

[0032] Figure 3 yes Figure 2 An enlarged schematic diagram of part A in the middle.

[0033] Figure 4 yes Figure 2 Enlarged diagram of part B.

[0034] Figure 5 This is a schematic diagram illustrating the structure of the polyurethane suspended filler ball in the embodiments of this application.

[0035] Figure 6 This is a schematic diagram illustrating the structure of the permeable dam and the filler bed in the embodiments of this application.

[0036] Figure 7 This is a schematic diagram illustrating the structure of the ecological treatment unit in an embodiment of this application.

[0037] Explanation of reference numerals in the attached diagrams: 1. Sedimentation and slow-flow unit; 11. Sedimentation pond; 12. Diversion dam; 13. Collection trough; 2. Aerobic reaction tank; 21. Aeration device; 211. Solar aerator; 22. Three-dimensional floating wetland; 221. Wetland planting carrier; 222. Emergent aquatic plants; 223. Fiber packing material; 3. Anaerobic reaction tank; 31. Biofilm reactor; 311. Frame cage; 312. Polyurethane suspended packing balls; 4. Filtration unit; 41. Permeable dam; 411. Gabion mesh; 42. Packing bed; 43. Floating plant bed; 5. Ecological treatment unit; 51. Ecological pond; 52. Turf; 53. Emergent plants; 54. Floating-leaved plants; 55. Submerged plants; 56. Outlet gate; 57. Circulation pump station. Detailed Implementation

[0038] The following is in conjunction with the appendix Figure 1-7 This application will be described in further detail.

[0039] This application discloses an intensive multi-stage ecological purification system for farmland drainage.

[0040] like Figure 1 The intensive multi-stage ecological purification system for farmland runoff includes a sedimentation and slow-flow unit 1, an aerobic reaction tank 2, an anaerobic reaction tank 3, a filtration unit 4, and an ecological treatment unit 5. The sedimentation and slow-flow unit 1 can receive farmland runoff and regulate and slow the flow of incoming water, settling suspended solids and particulate pollutants; In this embodiment of the application, the sedimentation and slow-flow unit 1 includes a sedimentation pond 11, a plurality of guide dams 12 are provided in the sedimentation pond 11, and a plurality of collection tanks 13 are provided in the sedimentation pond 11. The collection tanks 13 correspond one-to-one with the guide dams 12 and are located on the water-facing side of the guide dams 12. Specifically, the sedimentation pond 11 is designed with a water depth of 2.0-2.5m. The guide dam 12 is an arc-shaped dam, with the arcuate indentation of the guide dam 12 oriented in the same direction as the water flow. The guide dams 12 are arranged in three rows, with one, two, and one dam in each row. The two guide dams 12 at the upstream and downstream ends are of the same length, while the two guide dams 12 in the middle of the sedimentation pond 11 are shorter than the upstream and downstream guide dams 12. The upstream guide dams 12 are arranged in the front middle of the sedimentation pond 11, the downstream guide dams 12 are arranged in the rear middle of the sedimentation pond 11, and the two middle guide dams 12 are arranged in the middle of the sedimentation pond 11 and located on both sides of the sedimentation pond 11. The two middle guide dams 12 have space for water to pass through, and the front and rear guide dams 12 are parallel along the water flow direction. The ends of the two middle guide dams 12 that are close to each other overlap with the projections of the front and rear guide dams 12 in the water flow direction. Each collection trough 13 and its corresponding diversion dam 12 form an arc-shaped line segment from a top-down perspective. The diversion dam 12 adopts a masonry retaining wall structure, with a width of 0.5m and a height of 2.0m. The length of the two front and rear diversion dams 12 is 1 / 2 the width of the pond bottom, with a height of 2.5m and an arc of 30°-40°. The length of the two middle diversion dams 12 is 1 / 4 the width of the pond bottom, with a height of 2.5m. The collection trough 13 is 5m wide and 1m deep, adopting a trapezoidal reinforced concrete structure with a slope of 1:1. The collection trough 13 is used to store settled sludge, which is periodically pumped out using a sludge pump. The diversion dam 12 guides the water flow while effectively slowing down the flow velocity, with a hydraulic retention time of 12 hours. This prolongs the hydraulic retention time of the water in front of the dam, promotes the sedimentation of suspended particulate matter in farmland runoff, and enhances the removal of suspended or particulate phosphorus.

[0041] In other embodiments, the sedimentation and slow-flow unit 1 also includes a pond body, within which multiple straight baffle walls (which can be placed obliquely) are arranged. Adjacent baffle walls are staggered to form an "S-shaped flow path," which can also extend the flow path, weaken the inlet jet, and reduce short-circuiting. Alternatively, gabions or grid-type permeable structures can be installed in the pond body to dissipate energy and rectify the water flow, while avoiding complete water blockage that could cause local scouring; a mud collection trough is still arranged on the water-facing side to achieve directional sedimentation.

[0042] like Figure 2 and Figure 3 The aerobic reaction tank 2 can receive the discharge water from the sedimentation and slow flow unit 1. The aerobic reaction tank 2 is equipped with an aeration device 21 and several three-dimensional floating wetlands 22. The three-dimensional floating wetlands 22 are used to provide attached growth carriers and rhizosphere microenvironment. Specifically, aerobic reaction tank 2 is a seepage-proof structure. From bottom to top, the tank bottom consists of a compacted soil layer and a seepage-proof layer. The soil layer is approximately 500 mm thick and compacted. The seepage-proof layer uses a seepage-proof blanket to reduce the risk of leakage and ensure effective water depth. The designed water depth of aerobic reaction tank 2 is 1.5 m. Aeration device 21 is a solar-powered aerator 211, with an oxygenation capacity of 0.6–0.78 kgO2 / h. One aerator is deployed per acre to maintain a dissolved oxygen concentration in the aerobic zone of no less than 5 mg / L. Aeration also promotes water circulation and mixing, improves the flow distribution within the tank, and increases the contact opportunities between the water and the biofilm.

[0043] The three-dimensional floating wetland 22 includes a wetland planting carrier 221, which is floated on the water surface. The carrier is a composite of polyester fiber and plant fiber, with a polyester fiber to plant fiber mass ratio of 2:1. The carrier buoyancy is 50 kg / m², and the plant planting hole density is 25 holes / m². Emergent aquatic plants 222, including water celery, aquatic canna, evergreen iris, and sweet flag, are planted on the wetland planting carrier 221 in a planting ratio of 1:1:2:1 to construct a continuous rhizosphere and provide a rhizosphere attachment interface.

[0044] High-density flexible fiber packing material 223 is suspended at the bottom of the wetland planting carrier 221. The fiber packing material 223 is made of PP material, with a density of 9 pieces / m², a single piece length of 1.5 m, and a specific surface area of ​​300 m² / m³. It is arranged to cover 30% of the area of ​​the aerobic reaction tank 2 to form a high specific surface area three-dimensional attachment carrier. During the start-up phase, nitrifying bacteria are added to the aerobic reaction tank 2 at a dosage of 20 mL / m³, which allows nitrifying bacteria to quickly attach to the fiber packing material 223 and the surface of plant roots and form a composite biofilm, thereby enhancing the conversion of ammonia nitrogen to nitrate nitrogen and improving the system's shock resistance stability.

[0045] like Figure 1 and Figure 3Several wetland planting carriers 221 can be installed, arranged sequentially along the water flow direction in the aerobic reaction tank 2, with solar aerators 211 arranged on both sides of each wetland planting carrier 221. A diffusion distribution structure can also be installed at the inlet end of the aerobic reaction tank 2 to ensure uniform water distribution and weaken the inlet jet, while an overflow weir is installed at the outlet end to achieve uniform outflow. The solar aerators 211 can operate in continuous or intermittent aeration modes, and their operating time can be adjusted according to the instantaneous flow rate and dissolved oxygen monitoring results during the receding water period. The wetland planting carriers 221 and fiber packing 223 adopt a modular and detachable structure, allowing for partial lifting, maintenance, or replacement without emptying the tank.

[0046] In other embodiments, the aeration device 21 may also be a solar-powered waterwheel aerator or an impeller-driven aerator, and the bottom of the wetland planting carrier 221 may be covered with a film curtain or film rope to form a high specific surface area attachment surface similar to a curtain, which is convenient for lifting and cleaning.

[0047] like Figure 1 , Figure 2 and Figure 4 Anaerobic reactor 3 can receive the effluent from aerobic reactor 2. Anaerobic reactor 3 is equipped with several biofilm reactors 31, which are used to provide an anaerobic attachment and growth interface to enrich denitrifying microorganisms. Specifically, partition walls are installed at the effluent ends of both the aerobic reactor 2 and the anaerobic reactor 3. These partition walls create relatively independent effluent zones to stabilize water levels and flow patterns. Outlets are located at the bottom of the partition walls, allowing water to be evenly discharged from the bottom of the reactor body, thus reducing surface short-flow and entrainment of floating matter. A layer of crushed stone with a particle size of 50–150 mm is laid between the effluent ends of the aerobic reactor 2 and the influent ends of the anaerobic reactor 3. This crushed stone layer serves to dissipate energy, rectify the flow, and trap residual suspended solids, while also preventing erosion and stabilizing the substrate.

[0048] like Figure 1 and Figure 5 The anaerobic reactor 3 is designed with a water depth of approximately 2.5m. Several biofilm reactors 31 are installed at the bottom of the anaerobic reactor 3. Each biofilm reactor 31 includes a frame cage 311. Each frame cage 311 adopts a galvanized frame structure, with a single unit size of 6m × 6m × 1m. Polyurethane suspended packing balls 312 are suspended inside the frame cage 311 as attachment carriers for denitrifying bacteria. The specific surface area of ​​the polyurethane suspended packing balls 312 is not less than 580 m² / m³. Several frame cages 311 are arranged equidistantly along the water flow direction to form multiple rows and columns. The frame cages 311 are arranged to cover approximately 60% of the area of ​​the anaerobic reactor 3, and the spacing between adjacent frame cages 311 is approximately 3m to ensure that the water flow can pass evenly between the frame arrays and fully contact the biofilm.

[0049] The polyurethane suspended packing balls 312 are suspended with a horizontal spacing of approximately 20cm, a vertical spacing of approximately 10cm, and a suspension length of approximately 1m, thus forming a stable three-dimensional attachment interface and preventing water flow bypass caused by excessive carrier density. During the start-up phase of the anaerobic reactor 3, denitrifying bacteria are added at a dosage of 50g / m³. In subsequent operation, a supplementary addition of 25g / m³ is made annually during the drainage period, allowing denitrifying bacteria to continuously accumulate on the carrier surface and form a stable biofilm, thereby enhancing the denitrification removal of nitrate nitrogen and improving the system's shock resistance stability. The frame cage 311 has a modular structure, allowing for section lifting and maintenance, carrier replacement, or bacterial replenishment under conditions of no water interruption or partial venting, reducing the difficulty of long-term operation and maintenance.

[0050] In other embodiments, the biofilm reactor 31 in the anaerobic reactor 3, in addition to using suspended polyurethane suspended packing balls 312, can also use combined packing, attached membrane curtains, attached membrane ropes, or honeycomb carrier modules as attachment carriers for denitrifying microorganisms; the frame cage 311 can be arranged in a staggered, zoned series arrangement, or in conjunction with permeable flow guiding components to improve hydraulic distribution and reduce short-circuiting; the gravel layer at the connection between the aerobic reactor 2 and the anaerobic reactor 3 can be replaced with a gabion mattress, a pebble layer, or a multi-stage particle size transition layer to achieve energy dissipation, rectification, and scour prevention. These alternative structures can also achieve the effects of immobilizing and enriching denitrifying bacteria, improving shock resistance, and reducing the difficulty of clogging and maintenance.

[0051] The biological enhancement pond formed by combining the above-mentioned aerobic reaction tank 2 and anaerobic reaction tank 3 has a hydraulic retention time of 2.5 days, a total nitrogen reduction load of 3.5 g / (m2·d), and a removal rate of over 30%.

[0052] like Figure 1 and Figure 6 The filtration unit 4 is used to receive the effluent from the anaerobic reactor 3 and discharge the water to the ecological treatment unit 5. The filtration unit 4 is used to further remove total phosphorus and ammonia nitrogen. Specifically, the filtration unit 4 is located between the anaerobic reaction tank 3 and the ecological treatment unit 5, and the filtration unit 4 is designed with a water depth of approximately 0.5m. The filtration unit 4 includes several permeable dams 41 and a packing bed 42 located between adjacent permeable dams 41, and a floating plant bed 43 is provided on each packing bed 42. The plant roots of the floating plant bed 43 extend into the packing bed 42 to form a synergistic purification structure of packing adsorption—rhizosphere microorganisms—plant absorption.

[0053] In this embodiment, there are four permeable dams 41, arranged sequentially along the water flow direction, with adjacent permeable dams 41 spaced approximately 5m apart. The height of the two outer permeable dams 41 near the upstream and downstream water levels is higher than that of the two middle permeable dams 41, so as to form segmented water level differences within the filtration unit 4 and achieve graded energy dissipation and uniform water distribution, thereby reducing the risk of short-circuiting and scouring and increasing the effective contact time between the water and each section of the packing bed 42. The permeable dams 41 adopt a gabion mesh 411 structure, and the gabion mesh 411 is filled with crushed stone with a particle size of 30-50 mm; the two outer permeable dams 41 have a height of 0.7m and a width of 0.5m, while the two middle permeable dams 41 have a height of 0.6m and a width of 0.5m.

[0054] Four permeable dams 41 divide the filter unit 4 into three sections of packing bed 42, and the filter media in each section of packing bed 42 is set according to function: The packing bed 42 between the outer permeable dam 41 near the upstream water level and the adjacent permeable dam 41 is made of calcium-aluminum-based phosphorus removal packing with a particle size of 50-80 mm, a porosity of about 60%, and an adsorption capacity of about 2 mg / g for phosphorus in the water. It is used to preferentially reduce the total phosphorus load in the incoming water and reduce the subsequent migration of phosphorus. The filling bed 42 between the two permeable dams 41 is made of volcanic rock with a particle size of 30-50 mm, a porosity of about 50%, and a phosphorus adsorption capacity of about 1 mg / g. It is used to provide high porosity and attachment interface, promote the growth of rhizosphere biofilm, and further buffer and stabilize water quality. The filling bed 42 between the outer permeable dam 41 near the downstream water level and the adjacent permeable dam 41 is made of natural zeolite with a particle size of 20-30 mm, a porosity of about 40%, and an ammonia nitrogen adsorption capacity of about 1 mg / g. It is used to further reduce residual ammonia nitrogen through ion exchange / adsorption.

[0055] The floating plant bed 43 may specifically include a floating bed on which aquatic plants are planted, with their roots extending into the interior of the packing bed 42 to form a rhizosphere microenvironment on the packing surface and promote microbial attachment and metabolism. The floating bed also provides shade to the water surface to inhibit algae growth, and further enhances effluent stability through the interception of fine particles and colloids by the roots. Through the water distribution and energy dissipation of the graded permeable dam 41, the adsorption and fixation of the segmented differential packing, and the enhancement effect of rhizosphere microorganisms, further removal of total phosphorus and ammonia nitrogen is achieved, reducing the nitrogen and phosphorus shock load entering the ecological treatment unit 5.

[0056] like Figure 1 and Figure 7 The ecological treatment unit 5 is used to receive the effluent from the filtration unit 4 and to perform ecological stabilization purification on the effluent to suppress fluctuations in water quality parameters.

[0057] Ecological treatment unit 5 includes an ecological pond 51, with a designed water depth of 2.0m, a maximum water depth of 2.6m, and a hydraulic retention time of 6 days. The slope ratio of the ecological pond 51 is 1:2 to 1:4, and turf 52 is laid above the water level to stabilize the slope, prevent erosion, and intercept runoff carrying sediment. Emergent plants 53, including reeds, cattails, arrowhead, wild rice, and water celery, are planted on the water-land interface slope (waterfront zone) of the ecological pond 51. The planting ratio of emergent plants 53 is 1:1:2:2:2, and the planting density is not less than 16 plants / m², to construct a rhizosphere and enhance the absorption and fixation of nitrogen and phosphorus and the interception and sedimentation of suspended solids. Floating-leaved plants 54 and submerged plants 55 are planted in the water area of ​​ecological pond 51. The floating-leaved plants 54 include lotus, water lily, water chestnut and duckweed, with a planting ratio of 1:5:1:2 and a planting density of not less than 1 clump / m². The submerged plants 55 include hydrangea, myriophyllum, pondweed and pickled mustard, with a planting ratio of 2:2:2:1 and a planting density of not less than 100 plants / m², in order to enhance the absorption of nutrients such as nitrate nitrogen and stabilize the water transparency and dissolved oxygen conditions.

[0058] Filter-feeding shellfish (not shown in the figure), benthic scraping snails (not shown in the figure), and freshwater fish (not shown in the figure) were introduced into ecological pond 51 to establish a stable biological community structure: Filter-feeding shellfish, including the triangular sail mussel and the pleated crown mussel, were introduced at a density of 10 kg / mu in a 1:1 ratio to filter planktonic plants and animals and organic detritus in the water; Benthic scraping snails, including the square-shaped ring snail, the pear-shaped ring snail, the copper-rust ring snail, and the field snail, were introduced at a density of 1 kg / mu in a 1:1:1:1 ratio to scrape the surface of plant leaves and the surface humus of the bottom mud; Freshwater fish, including silver carp, bighead carp, and bitterling, were introduced at a density of 5 kg / mu in a 1:1:1 ratio. Among them, silver carp and bighead carp feed on phytoplankton and zooplankton to inhibit algae growth, while bitterling reproduce with shellfish to form an ecological synergy to maintain community stability. Through the combined effects of plant absorption, natural sedimentation, rhizosphere / sludge microbial processes, and biological filter feeding and scraping, Ecological Pond 51 achieves further reduction of total nitrogen and total phosphorus and stable buffering of effluent water quality.

[0059] A sluice gate 56 is installed at the drainage point of ecological pond 51. A circulating pump station 57 is installed on the drainage side of sluice gate 56 to pump the effluent to agricultural irrigation canals for reuse. Sluice gate 56 has a gate length of 10m and a width of 2m, and consists of five 600×600mm stainless steel square gates. In terms of operation and control, the gates are opened during non-drainage periods to maintain the water level of each process unit at the design depth; during drainage periods, the gates are closed to raise the water level of each process unit to the maximum design depth, thereby increasing the storage depth (storage capacity) by approximately 0.6m to cope with the impact of the instantaneous increase in flow rate during drainage periods. The system effluent is pumped by circulating pump station 57 into agricultural irrigation canals for storage and secondary irrigation, achieving non-direct discharge of agricultural drainage and resource reuse, thereby reducing the nitrogen and phosphorus load discharged and protecting the environmental quality of downstream water bodies.

[0060] In this embodiment, the sedimentation pond 11 and the aerobic reaction tank 2 have the same width. The length of the anaerobic reaction tank 3 is the same as the sum of the lengths of the sedimentation pond 11 and the aerobic reaction tank 2. The sedimentation pond 11 and the aerobic reaction tank 2 are arranged side by side on one side of the anaerobic reaction tank 3. The length of the filtration unit 4 is the same as the length of the anaerobic reaction tank 3. The filtration unit 4 is located on the side of the anaerobic reaction tank 3 away from the aerobic reaction tank 2. The width of the filtration unit 4 is 1 / 3 of the width of the anaerobic reaction tank 3. The width of the biological pond is the same as the sum of the widths of the aerobic reaction tank 2, the filtration unit 4, and the anaerobic reaction tank 3. This allows all the ponds to be combined into a square pond system, which is compact and further reduces the land area occupied. In other embodiments, if the quality of the farmland drainage water is good, the filtration unit 4 may not be installed, and the water discharged from the anaerobic reaction tank 3 may be directly discharged into the ecological pond 51.

[0061] The implementation principle of this application embodiment is as follows: Sedimentation pond 11, aerobic reaction tank 2, anaerobic reaction tank 3, filtration unit 4, and ecological treatment unit 5 are scientifically connected in series, forming a complete path for the step-by-step reduction of pollutants. Sedimentation pond 11 performs physical interception and preliminary purification; aerobic reaction tank 2 and anaerobic reaction tank 3 serve as core biological enhancement zones; filtration unit 4 performs deep filtration and adsorption; and ecological treatment unit 5 serves as the final ecological stabilization and natural purification, ensuring the system's synergistic and efficient removal of multiple pollutants such as suspended solids, nitrogen, and phosphorus, and enhancing the system's resilience to fluctuations in water quality and quantity.

[0062] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An intensive, multi-stage ecological purification system for farmland runoff, characterized in that: It includes a sedimentation and slow-flow unit (1), an aerobic reaction tank (2), an anaerobic reaction tank (3), and an ecological treatment unit (5). The sedimentation and slow-flow unit (1) can receive farmland runoff and regulate and slow the flow of incoming water, and precipitate suspended solids and particulate pollutants; The aerobic reaction tank (2) can receive the discharge water from the sedimentation and slow flow unit (1). The aerobic reaction tank (2) is equipped with an aeration device (21) and several three-dimensional floating wetlands (22). The three-dimensional floating wetlands (22) are used to provide attached growth carriers and rhizosphere microenvironment. The anaerobic reactor (3) can receive the effluent from the aerobic reactor (2). The anaerobic reactor (3) is equipped with several biofilm reactors (31). The biofilm reactors (31) are used to provide an anaerobic attachment growth interface to enrich denitrifying microorganisms. The ecological treatment unit (5) can receive the effluent from the anaerobic reactor (3) and is used to perform ecological stabilization purification on the effluent to suppress fluctuations in water quality parameters.

2. The intensive multi-stage ecological purification system for farmland runoff as described in claim 1, characterized in that: It also includes a filtration unit (4), which is used to receive the effluent from the anaerobic reaction tank (3) and discharge the effluent to the ecological treatment unit (5). The filtration unit (4) is used to further remove total phosphorus and ammonia nitrogen.

3. The intensive multi-stage ecological purification system for farmland runoff as described in claim 1, characterized in that: The sedimentation and slow-flow unit (1) includes a sedimentation pond (11), a number of guide dams (12) are provided in the sedimentation pond (11), and a number of collection troughs (13) are provided in the sedimentation pond (11). The collection troughs (13) correspond one-to-one with the guide dams (12) and are located on the water-facing side of the guide dams (12).

4. The intensive multi-stage ecological purification system for farmland runoff as described in claim 1, characterized in that: The aeration device (21) is a solar aerator (211), the three-dimensional floating wetland (22) includes a wetland planting carrier (221), emergent aquatic plants (222) are planted on the wetland planting carrier (221), and fiber filler (223) is suspended at the bottom of the wetland planting carrier (221).

5. The intensive multi-stage ecological purification system for farmland runoff as described in claim 4, characterized in that: The solar-powered aerator (211) has an oxygenation capacity of 0.6-0.78 kgO2 / h, with 1-2 units deployed per acre. The wetland planting carrier (221) is composed of polyester fiber and plant fiber composite, with a mass ratio of polyester fiber to plant fiber of (2-3):(1-2). The buoyancy of the wetland planting carrier (221) is 50-60 kg / m³. 2 The plant planting holes are 25-30 holes / m², and the emergent aquatic plants (222) include water celery, aquatic canna, evergreen iris and sweet flag, and the planting ratio of water celery, aquatic canna, evergreen iris and sweet flag is (1-2):(1-2):(2-3):(1-2). The water depth of the aerobic reaction tank (2) is 1.5-2m, and the fiber packing material (223) is arranged at a density of 9 strands / m². 2 Length is 1-1.5m, specific surface area ≥300m² 2 / m 3 The fiber packing material (223) occupies no less than 30% of the pond area, and the amount of nitrifying bacteria added to the aerobic reaction tank (2) is 20-30 mL / m². 3 .

6. The intensive multi-stage ecological purification system for farmland runoff as described in claim 1, characterized in that: The anaerobic reactor (3) has a water depth of 2.5-3m. The biofilm reactor (31) includes a frame cage (311), with polyurethane suspended packing balls (312) suspended inside each frame cage (311). The frame cages (311) occupy no less than 60% of the pond area, and the polyurethane suspended packing balls (312) have a specific surface area of ​​no less than 580m². 2 / m 3 The initial dosage of denitrifying bacteria in the anaerobic reactor (3) is 50-60 g / m³. 3 Subsequent periodic supplementation dosage is 25-30g / m³. 3 .

7. The intensive farmland drainage multi-stage ecological purification system according to claim 2, characterized in that: The filtration unit (4) includes several permeable dams (41), and a packing bed (42) is provided between adjacent permeable dams (41). A floating plant bed (43) is provided on the packing bed (42), and the plant roots of the floating plant bed (43) extend into the packing bed (42).

8. The intensive farmland drainage multi-stage ecological purification system according to claim 7, characterized in that: The permeable dam (41) includes a gabion mesh (411), which is filled with crushed stone with a particle size of 30-50mm. There are four permeable dams (41). The filter media of the packing bed (42) between the two permeable dams (41) near the upstream water level includes calcium-aluminum-based phosphorus removal packing with a particle size of 50-80 mm. The filter media of the packing bed (42) between the two permeable dams (41) in the middle includes volcanic rock with a particle size of 30-50 mm. The filter media of the packing bed (42) between the two permeable dams (41) near the downstream water level includes natural zeolite with a particle size of 20-30 mm.

9. The intensive multi-stage ecological purification system for farmland runoff as described in claim 1, characterized in that: The ecological treatment unit (5) includes an ecological pond (51), the slope ratio of the ecological pond (51) is 1:2-1:4, the ecological pond (51) is covered with turf (52) above the water level line, emergent plants (53) are planted at the water-land junction of the ecological pond (51), floating-leaved plants (54) and submerged plants (55) are planted in the ecological pond (51), filter-feeding shellfish, benthic scraping snails and freshwater fish are also placed in the ecological pond (51), a sluice gate (56) is set at the drainage point of the ecological pond (51), a circulating pump station (57) is set on the drainage side of the sluice gate (56), and the circulating pump station (57) lifts the water to the farmland irrigation canal.

10. The intensive farmland drainage multi-stage ecological purification system according to claim 9, characterized in that: The emergent plants (53) include reeds, cattails, arrowhead, wild rice, and water celery. The planting ratio of reeds, cattails, arrowhead, wild rice, and water celery is (1-2):(1-2):(2-3):(2-3):(2-3), and the planting density is not less than 16 plants / m2. The floating-leaved plants (54) include lotus, water lilies, gorgon fruit, and water lily. The planting ratio of lotus, water lilies, gorgon fruit, and water lily is (1-2):(5-6):(1-2):(2-3), and the planting density is not less than 1 clump / m2. 2 The submerged plants (55) include *Hydrilla verticillata*, *Myriophyllum spicatum*, *Potamogeton crispus*, and *Potamogeton crispus*, with a planting ratio of (2-3):(2-3):(2-3):(1-2), and a planting density of not less than 100 plants / m². 2 The filter-feeding shellfish include the triangular sail mussel and the pleated crown mussel, with a stocking density of no less than 10 kg / mu and a ratio of (1-2):(1-2). The benthic scraping snails include the square-shaped ring snail, the pear-shaped ring snail, the copper-rust ring snail, and the field snail, with a stocking density of no less than 1 kg / mu and a ratio of (1-2):(1-2):(1-2):(1-2). The freshwater fish include silver carp, bighead carp, and bitterling, with a stocking density of no less than 5 kg / mu and a ratio of (1-2):(1-2):(1-2).

Images