A distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland

Abstract

The present invention relates to the field of farmland water pollution treatment, and specifically to a distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland, comprising a water inlet and outlet purification device for farmland drainage outlets arranged in sequence, a specialized adsorption catalytic reactor at a key node of a ditch, and a sunken long-term interception module arranged at the estuary of the ditch. The present invention can intercept and purify high-concentration carbon, nitrogen and phosphorus in farmland drainage produced by heavy rainfall during the rice growth period, especially during the field flooding period and after fertilization. The materials used have high adsorption capacity, high catalytic activity, easy recycling, and environmental friendliness. The technical modules involved are simple to prepare, have strong adaptability, high flexibility, and long-lasting effects. The system does not occupy additional land, is low in cost, and is plug-and-play, does not require engineering construction costs, and is simple to operate and maintain. It can achieve stable "standard" emissions of carbon, nitrogen and phosphorus in farmland drainage and improve biodiversity.

Description

Technical Field

[0001] The present invention relates to the field of farmland water pollution treatment, and in particular to a distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland. Background Art

[0002] The extensive application of chemical fertilizers in farmland is a source of agricultural non-point source pollution. Farmland runoff is large in volume and often high in nutrients. Direct discharge into receiving water bodies can pollute the surrounding aquatic environment. In recent years, the construction of high-standard farmland has been widely implemented nationwide. However, early high-standard farmland development focused on increasing productivity while paying insufficient attention to improving the quality of the farmland's ecological environment. The accompanying drainage ditches were often simple hardened cement ditches, which effectively failed to fully utilize the ditches' ecosystem services.

[0003] Ecological ditches regulate excess runoff and facilitate material recycling, while also incorporating characteristics of both streams and wetlands. They are crucial for managing farmland non-point source pollution. Utilizing existing farmland drainage ditches through limited ecological renovation of farmland outfalls, key ditch nodes, and river / beach inlets, to maximize their ecological services, thereby improving drainage during flooding periods and intercepting high-concentration carbon, nitrogen, and phosphorus in the drained water caused by heavy rainfall following fertilization, is of great practical significance.

[0004] The development of new, inexpensive, and efficient environmental materials is a breakthrough in solving the problem of nitrogen and phosphorus emissions at the end of farmland. Environmental nanomaterials have demonstrated good results in industrial and domestic sewage treatment, river management, and drinking water purification. However, there is little research and application on the reduction of nitrogen and phosphorus in farmland runoff, and the purification effect of different environmental materials and aquatic plants on carbon, nitrogen, and phosphorus in farmland runoff is still unclear. Summary of the Invention

[0005] The purpose of the present invention is to provide a distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland.

[0006] The present invention constructs a distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland by deploying enhanced purification devices loaded with high-efficiency denitrification and phosphorus removal environmental nanomaterials at key nodes of farmland drainage outlets and ecological ditches, and combining them with aquatic plant interception wetlands with high-efficiency nitrogen and phosphorus absorption performance and landscape features deployed at the ditch estuary. Through "environmental material adsorption catalysis - surrounding biological efficient absorption - long-term absorption by aquatic plants", stable "up-to-standard" emissions of carbon, nitrogen and phosphorus in rice field drainage are achieved, as well as enhanced biodiversity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland, characterized by comprising a water inlet and outlet purification device arranged in sequence at the farmland drainage outlet, a specific adsorption catalytic reactor at the key node of the ditch, and a sunken long-term interception module arranged at the ditch estuary;

[0008] The inlet and outlet water purification device is placed at the drainage outlet of the rice field, and includes a box body and an adsorption filler located inside the box body. It is used to filter and settle suspended particulate matter (SS), particulate nitrogen, and particulate phosphorus in the drainage water of the farmland (such as the drainage water of the rice field) in situ, and to perform preliminary interception and adsorption of dissolved nitrogen, phosphorus, and COD. During irrigation, the nitrogen and phosphorus adsorbed by the adsorption filler are flushed back to the farmland through reverse water inflow.

[0009] The specific adsorption catalytic reactor at the key nodes of the ditch is set up close to the farmland drainage ditch. The key nodes of the ditch include the ecological ditch water confluence and the front end of the ecological ditch into the river. The specific adsorption catalytic reactor includes a reactor with a photocatalyst evenly coated on the surface and cover, and a specific adsorption material located inside the reactor. The specific adsorption material is used to enhance the removal of ammonia nitrogen, phosphorus, and COD in the drainage of rice fields.

[0010] The sunken long-term interception module at the ditch estuary is composed of a reinforced interception weir and a sunken ditch wetland; the sunken ditch wetland includes a bottom matrix, aquatic plants arranged at the bottom of the ditch, and surrounding organisms with high nitrogen and phosphorus absorption performance and landscape aquatic plant roots and surface growth, so as to further intercept and remove nitrogen, phosphorus and COD from farmland drainage (such as rice field drainage); the reinforced interception weir is composed of a stainless steel frame, internal adsorption filler, surface iron-carbon microspheres and planted plants, and is installed at the front end or both sides of the sunken ditch wetland.

[0011] In a preferred embodiment, the inlet and outlet water purification device comprises a tank housing with a mixture of zeolite (5-20mm particle size) and volcanic rock (5-20mm particle size) at a mass ratio of 1:0.5-2 (forming the zeolite and volcanic rock filling layer). The middle layer of the tank is filled with an adsorbent filler consisting of 65-80% zeolite (1-5mm particle size), 15-30% ceramsite (3-8mm particle size), and 1-5% biochar. The larger zeolite and volcanic rock filling on the sides of the tank primarily serves to settle sediment carried in farmland drainage and to filter and settle suspended particulate matter (SS), particulate nitrogen, and particulate phosphorus in situ. The smaller adsorbent filler in the middle layer primarily serves to initially intercept dissolved nitrogen, phosphorus, and COD.

[0012] Furthermore, the inlet and outlet water purification device has a housing including several evenly distributed front water inlets and at least one terminal drain outlet. When irrigating farmland, water is poured into the terminal drain outlet at a limited and controllable speed (0.1 to 2 m / s), and the nitrogen and phosphorus adsorbed by the adsorption filler are slowly flushed back into the farmland, while simultaneously achieving the function of backwashing the adsorption filler in the inlet and outlet water purification device. In addition, the irrigation also causes the zeolite and volcanic rock filling layers to slowly release nitrogen and phosphorus. The nitrogen and phosphorus slowly released by the zeolite and volcanic rock filling layers are mainly in a particulate state, while the nitrogen and phosphorus slowly released by the adsorption filler are mainly in a dissolved state.

[0013] Specifically, the inlet and outlet water purification device for the farmland drainage outlet is installed on one side of the rice paddy drainage outlet. It is constructed as a rectangular box of appropriate size based on the geographical location and shape of the farmland drainage outlet. The box is 0.5-1.2m long, 0.4-1.0m wide, and 0.3-0.8m deep (the top of the box is 2-4cm lower than the field ridge). An overflow outlet is set at the front of the box (the opening depth is 2-4cm below the top of the box); 2-3 rows of seepage holes (front water inlet) are evenly distributed on its lower side, with a diameter of 0.5-1.5cm. The lower layer of seepage holes (i.e., the lowest row of seepage holes) is 8-10cm above the field surface. The drainage outlet is located at the end of the box, with a wire mesh installed on the surface (to prevent the filler in the last compartment of the box from falling out). Its height is no lower than the lower layer of seepage holes on the front side, and the diameter is 5-25cm. The interior of the chamber is divided into three to four compartments by evenly spaced drainage flaps along the direction of farmland drainage. The sides are filled with a mixture of 5-20mm zeolite and 5-20mm volcanic rock at a mass ratio of 1:0.5-2. The middle layer is filled with high-performance adsorption filler (referred to as adsorption filler) to filter and settle suspended particulate matter (SS), particulate nitrogen, and particulate phosphorus in the paddy field drainage, while also providing a preliminary interception of dissolved nitrogen, phosphorus, and COD. A 3-6cm gap is left on the left or right side of each drainage flap to allow drainage water to flow in a serpentine pattern. For high-standard farmland, dual-purpose irrigation and drainage ditches are configured. During irrigation, water flows in reverse, flushing nitrogen and phosphorus adsorbed by the high-performance adsorption filler back into the fields, recycling nutrients and extending the life of the adsorption filler. During rainfall, water enters the inlet and outlet water purification system through seepage holes or overflow outlets, where it is filtered and settled before entering the ditch through the drainage outlet.

[0014] In a preferred embodiment, the specific adsorption catalytic reactor at the key node of the ditch includes a water-flowing folding plate for limiting the movement path of the farmland drainage water. The water-flowing folding plate divides the reactor into several partitions, and the several partitions include an adsorption matrix layer and different specific adsorption material layers; the photocatalyst evenly coated on the surface and cover of the reactor is used to remove COD in the farmland drainage water.

[0015] Furthermore, in the specific adsorption catalytic reactor at the key node of the ditch, the adsorption matrix or specific adsorption material is first placed in a nylon mesh, then placed in a stainless steel basket and then placed in the reactor.

[0016] Specifically, the specific adsorption catalytic reactor at the key node of the ditch is placed at the key node of the ecological ditch (such as the confluence of the ecological ditch, the front end of the ecological ditch into the river / river), and is placed close to the farmland drainage ditch. The specific adsorption catalytic reactor at the key node of the ditch is 0.8 to 2.0 meters long, the width is the same as or slightly narrower than the ditch width, and the depth is 0.4 to 1.0 meters (not exceeding 2 / 3 of the ditch depth). The overflow port is located at the front end of the reactor, and the depth of the overflow port opening is 1 / 5 to 1 / 3 of the reactor depth; the drain port is located in the middle of the end of the reactor and consists of multiple small holes with an aperture of 0.5 to 5.0 cm. A 3 to 6 cm gap is left on the left or right side of each water diversion plate in the reactor, so that the water from the farmland flows in a serpentine shape (the structure of the water diversion plate in the reactor refers to the water diversion plate in the inlet and outlet water purification device). The reactor is divided into multiple layers along the discharge direction of farmland water by the overflow port and the water folding plate. The first layer is filled with adsorption matrix such as zeolite / volcanic stone with a particle size of 3-10mm, ceramsite with a particle size of 5-10mm, biochar, etc.; the other layers are filled with special adsorption materials, which are used to absorb NH4 + , TP, COD and other pollutants are simultaneously enhanced and removed. The adsorption matrix or specialized adsorption material is first placed in a nylon mesh of appropriate size, then placed in a stainless steel basket and placed in the reactor for easy cleaning and replacement. The reactor box is made of materials such as 5-10mm plexiglass, PVC board or stainless steel plate, and a layer of photocatalyst is evenly coated on the surface. At the same time, during the paddy season, a cover plate loaded with photocatalyst is placed on the upper surface of the reactor to enhance the removal of COD in the rice field runoff. At other times, a stainless steel mesh is placed on the upper surface of the reactor to intercept debris such as dead branches and fallen leaves.

[0017] The drainage water from farmland first passes through the adsorption matrix layer, which filters and settles the suspended particulate matter SS, particulate nitrogen, and particulate phosphorus, and then passes through three different specific adsorption material layers to carry out targeted and efficient interception of dissolved nitrogen, dissolved phosphorus, and COD.

[0018] After rainfall, the water from the paddy field enters the reactor through the overflow port (the overflow port is located at the front end of the reactor), and flows to the left or right side in an alternating manner under the obstruction of multiple water-flowing folding plates in the middle of the reactor. + , TN, TP, COD and other pollutants are removed through adsorption catalysis of specific adsorption materials and finally flow out from the drain outlet at the end.

[0019] In a preferred embodiment, the sunken ditch wetland is set at the estuary of the ditch, with a length of 10 to 20 meters, and is dug 10 to 30 cm deep to fill the bottom matrix; the bottom matrix is composed of zeolite or volcanic rock and specific adsorption material in a mass ratio of 1:0.5 to 2, and is laid with a thickness of 8 to 20 cm.

[0020] Furthermore, in the sunken ditch wetland, the roots of aquatic plants are first wrapped with planting bags filled with bottom matrix and carbon source materials before being planted.

[0021] Specifically, at the end of the ditch, a sunken ditch wetland is constructed at the estuary. The length and configuration are determined according to the pollution intensity of the runoff water body and the on-site conditions. It is generally 10 to 20 meters, and the bottom matrix is filled 10 to 30 cm below. The bottom matrix is composed of zeolite or volcanic stone and specific adsorption material in a mass ratio of 1:0.5 to 2. The zeolite or volcanic stone is laid on the bottom layer, and the specific adsorption material is laid on the upper layer with a thickness of 8 to 20 cm. Emergent plants such as pickerel grass, calamus (summer), water celery, and iris (winter) are planted on it. The roots of the plants are first wrapped with a non-woven planting bag filled with the bottom matrix and a small amount of straw, sawdust and other carbon sources, and then planted in the bottom of the ditch. By planting aquatic plants, the hydraulic retention time of runoff drainage can be increased, and a certain physical interception effect can be produced on suspended particulate matter SS and particulate nitrogen and phosphorus; at the same time, the bottom matrix can have a certain effect on NH4 + , TP and other pollutants; not only that, the surrounding organisms at the roots and surface of plants can remove nitrogen through nitrification and denitrification, thereby achieving further interception and removal of nitrogen and phosphorus.

[0022] In a preferred embodiment, the height of the reinforced interception weir does not exceed 2 / 3 of the ditch depth, and the front inclination angle is 20-45°, wherein the front inclination angle of the reinforced interception weir is the angle between the inclined surface of the weir and the extended surface of the bottom.

[0023] Furthermore, the reinforced interception weir has an adsorption filler filled inside the stainless steel frame, and then 5-10 cm iron-carbon microspheres are filled on its surface; a row of emergent plants is planted 20-30 cm in front of the reinforced interception weir (referring to the distance from the front end of the reinforced interception weir to the emergent plants along the direction of water flow from farmland), and two rows of herbaceous plants are planted in the middle and upper parts; the reinforced interception weir is used to intercept farmland drainage, and the iron-carbon microspheres in the weir body remove nitrogen, phosphorus and COD through micro-electrolysis and nitrification and denitrification of plant roots or surrounding organisms attached to the surface.

[0024] Specifically, the stainless steel frame is composed of a stainless steel pipe rack, the height of the weir is about 30 to 50 cm (not exceeding 2 / 3 of the ditch depth), and the front inclination angle is 20 to 45 degrees. The interior of the reinforced intercepting weir is filled with high-performance adsorption filler, and the filling height is 5 to 10 cm below the stainless steel pipe rack (that is, starting from the bottom of the stainless steel pipe rack and filling evenly upward until the top surface of the adsorption filler is 5 to 10 cm lower than the top of the stainless steel pipe rack), and then the upper surface of the adsorption filler is filled (covered) with a 5 to 10 cm thick layer of iron-carbon microspheres, and the top surface of the iron-carbon microsphere layer is basically flush with the top of the stainless steel pipe rack. Along the direction of water flow back from the farmland, the front 20 to 30 cm of the reinforced intercepting weir is planted with emergent plants such as pickerel grass, calamus or iris (planting density: 9 to 25 bushes / m 2 ), and plant ryegrass, moss and other herbaceous plants that are drought-resistant and flood-resistant and have the ability to purify nitrogen and phosphorus in the middle and upper parts (ryegrass seed sowing density: 2-5g / m 2 , Carex planting density: 16-25 clumps / m 2 ).

[0025] The setting of the reinforced interception weir can intercept the runoff water (agricultural drainage) and reduce its impact load. The design of the weir slope can increase the contact area between the internal material and the runoff water, thereby improving the reaction efficiency. After rainfall, the runoff water flows from the top of the weir into the sunken ditch wetland, the dissolved oxygen increases, and the COD removal rate in the runoff water is improved; the ditch runoff water gradually infiltrates from bottom to top and from front to back in the weir, effectively reducing the water flow rate and increasing the contact area between the runoff water and the iron-carbon microspheres and adsorption fillers; the iron-carbon material uses micro-electrolysis, with iron and activated carbon as the anode and cathode, to form countless small primary batteries, which produce oxidation-reduction, flocculation and precipitation, etc.; the presence of ditch plants forms an aerobic-anoxic-anaerobic environment from near to far near the plant roots, and the growth of epiphytes on its surface promotes the nitrification and denitrification process, and the Fe produced by iron-carbon micro-electrolysis 2+ The organic matter in the water and sediment can act as electron donors to promote denitrification and improve nitrogen removal.

[0026] In a preferred embodiment, the preparation steps of the adsorption filler are as follows: the mass ratio is 65-80% of zeolite with a particle size of 1-5 mm, 15-30% of ceramsite with a particle size of 3-8 mm, and 1-5% of biochar;

[0027] The specific adsorption material is used for efficient adsorption of nitrogen and phosphorus. The preparation steps are as follows: using the impregnation and roasting method, biomass raw materials such as straw, zeolite or volcanic rock are immersed in 0.5-2 mol / LMgCl2, LaCl3 or TiO2 solution at a mass ratio of 1:0.5-1:0.5-1 for 10-12 hours, and roasted at 450-550℃ for 3-5 hours to prepare the NH4 removal agent. +, TP, COD specific adsorption material; biomass raw materials or zeolite or volcanic rock, and MgCl2, LaCl3 or TiO2 solution mass ratio is 0.5 to 1:2;

[0028] The method for loading a photocatalyst onto a reactor surface or cover plate is as follows: sodium silicate is first dissolved in water to obtain a 0.5% sodium silicate solution. 10.00g of TiO2 and ZnO are then added to the 0.5% sodium silicate solution at a mass ratio of 1:0.5-2 to form a suspension. After mixing thoroughly, the suspension is ultrasonicated for 30-60 minutes and magnetically stirred for 10-30 minutes. The suspension is then evenly coated onto a glass plate and then air-dried at room temperature or dried in a 55°C oven. By adjusting the concentration of the sodium silicate solution, the ratio of the solution to the photocatalyst, and optimizing the mixing process, the photocatalytic material can be coated onto the support surface at room temperature. This results in mild reaction conditions, low energy consumption, and excellent catalytic efficacy.

[0029] The preparation process of iron-carbon microspheres loaded in the reinforced interception weir is as follows: iron filings and activated carbon are mixed in a mass ratio of 1.5-2.5:8, 4-6% sodium carboxymethyl cellulose solution is added, and calcined at 400-600°C for 0.5-1h to prepare iron-carbon microspheres with a particle size of 5-8mm.

[0030] The benefits of the present invention lie in: providing a distributed nitrogen, phosphorus and COD multi-pollutant interception and purification system suitable for high-standard farmland, which can intercept and purify high-concentration carbon, nitrogen and phosphorus in farmland drainage generated by heavy rainfall during the rice growth period, especially the flooding period and after fertilization. The materials used have high adsorption capacity, high catalytic activity, easy recycling and environmental friendliness. The technical modules involved are simple to prepare, have strong adaptability, high flexibility and long-lasting effects. The system does not occupy additional land, is low in cost, and is plug-and-play, does not require engineering construction costs, and is simple to operate and maintain. It can achieve stable "standard" emissions of carbon, nitrogen and phosphorus in farmland drainage and improve biodiversity. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 .Structural diagram of a distributed nitrogen, phosphorus, and COD multi-pollutant control and purification system suitable for high-standard farmland;

[0032] Figure 2 . Schematic diagram of the water purification device at the inlet and outlet of the farmland drainage outlet;

[0033] Figure 3 Schematic diagram of the specialized adsorption catalytic reactor at the key node of the ditch;

[0034] Figure 4 .Schematic diagram of the reinforced interception weir;

[0035] Figure 5 .Schematic diagram of sunken ditch wetland;

[0036] Figure 6 The removal performance of the inlet and outlet water purification devices for suspended solids, particulate nitrogen, particulate phosphorus, TN and TP;

[0037] Figure 7 Specific adsorption catalytic reactor for (a) COD and (b) NH4 + , TP removal performance;

[0038] Figure 8 TP and TN removal performance of the sunken ditch wetland during (a) the static incubation period and (b) the flow experiment period;

[0039] Figure 9 Effects of the iron-carbon microsphere-plant coupling system on (a) TN and (b) NO3 - removal performance;

[0040] In the attached figure, 1 is the inlet and outlet water purification device box, 2 is the partition, 3 is the high-performance adsorption material, 4 is the end drain port, 5 is the front water inlet, 6 is the specific adsorption catalytic reactor box, 7 is the water flow folding plate, 8 is the specific adsorption material, 9 is the stainless steel basket, 10 is the overflow port, 11 is the cover plate, 12 is the reinforced intercepting weir, 13 is the stainless steel frame, 14 is the aquatic plant, 15 is the bottom matrix, 16 is the surrounding organisms, 17 is the reinforced intercepting weir slope, 18 is the reinforced intercepting weir bottom, 19 is the front inclination angle, and 20 is the iron-carbon microspheres. DETAILED DESCRIPTION

[0041] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] In the following examples, the following steps are used to construct a distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland.

[0043] like Figure 1-5 As shown, a distributed nitrogen, phosphorus, and COD multi-pollutant control and purification system suitable for high-standard farmland consists of a water purification device at the farmland drainage outlet, a specialized adsorption catalytic reactor at key ditch nodes, and a sunken long-term interception module deployed at the ditch estuary. Farmland runoff flows sequentially through the water purification device at the farmland drainage outlet, the specialized adsorption catalytic reactor at key ditch nodes, and the sunken long-term interception module deployed at the ditch estuary.

[0044] The inlet and outlet water purification device for the farmland drainage outlet is placed on one side of the rice field drainage outlet. It is constructed as a rectangular box based on the geographical location and the shape of the farmland drainage outlet. The inlet and outlet water purification device box 1 is 0.8m long, 0.6m wide, and 0.6m deep (the top of the box is 3cm lower than the ridge). An overflow port is set at the front of the box (the opening depth is 3cm downward from the top of the box); two rows of seepage holes (front water inlet) are evenly distributed on its lower side, with a diameter of 1cm. The lower seepage holes (i.e., the seepage holes in the bottom row) are 8cm high from the field surface. The drainage outlet is located at the end of the box (i.e., the rear end), and a wire mesh is installed on the surface. Its height is not lower than the lower seepage holes, and the diameter is 15cm. The interior of the box consists of four compartments 2 separated by several drainage flaps evenly spaced along the direction of drainage. Each flap has a 5cm gap on the left or right side, allowing drainage water to flow in a serpentine pattern. The two side compartments are filled with a 1:1 mass ratio of 10mm zeolite and 10mm volcanic rock. The two middle compartments are filled with high-performance adsorbent filler 3 (referred to as adsorbent filler) to filter and settle suspended particulate matter (SS), particulate nitrogen, and particulate phosphorus in the paddy drainage water, and to provide preliminary interception of dissolved nitrogen, phosphorus, and COD. The width and depth of each of the four compartments are 0.6m, and the length of each compartment along the drainage flow direction is equal (0.17m, referring to the filler length, not including the thickness of the drainage flaps). Dual-purpose irrigation and drainage ditches designed for high-standard farmland allow reverse flow during irrigation, flushing nitrogen and phosphorus adsorbed by the high-performance adsorbent filler back into the fields, recycling nutrients and extending the life of the adsorbent filler. When irrigating farmland, water is poured into the terminal drain outlet 4 at a limited and controllable speed, and the nitrogen and phosphorus adsorbed by the adsorption filler are slowly flushed back to the farmland, realizing the function of backwashing the filler in the device. Under rainfall, the water enters the inlet and outlet water purification device through the seepage hole (i.e. the front water inlet 5) or the overflow port 10, and enters the ditch after filtration and sedimentation. The preparation steps of the high-performance adsorption filler are as follows: the mass ratio is 75% of zeolite with a particle size of 3mm, 22% of ceramsite with a particle size of 5mm, and 3% of biochar, and the biochar is straw biochar (obtained by roasting straw at 550℃ for 3h).

[0045] Specific adsorption catalytic reactor at the key node of the ditch: It is placed at the key node of the ecological ditch (such as the confluence of the ecological ditch, the front end of the ecological ditch into the bay / river), and is placed close to the farmland drainage ditch. The specific adsorption catalytic reactor at the key node of the ditch is 1.5m long, the width is the same as or slightly narrower than the ditch width, and the depth is 0.6m. It is divided into multiple layers by the overflow port 10 and the water diversion plate 7 along the discharge direction of the farmland drainage. The overflow port 10 is located at the front end of the reactor, and the depth of the overflow port opening is 1 / 4 of the depth of the reactor; the drainage port is located in the middle of the end (i.e., the rear end) of the reactor and consists of multiple small holes with an aperture of 3.0cm. A 5cm gap is left on the left or right side of each water diversion plate in the reactor, so that the farmland drainage water flows in a serpentine shape. Along the discharge direction of farmland drainage, the first interlayer is filled with 5mm zeolite / volcanic stone, 8mm ceramsite, and biochar powder as adsorption matrix (the mass ratio of 5mm zeolite, 5mm volcanic stone, ceramsite, and biochar is 1:0.5:0.5:0.5, and the biochar is the aforementioned straw biochar); the other three interlayers are filled with specific adsorption materials 8, which are used to absorb NH4 + , TP, and COD pollutants are removed synchronously and enhanced (ammonium ions are removed by modifying zeolite with MgCl2 solution, TP is removed by modifying volcanic rock with LaCl3, and COD is removed by modifying straw biochar with TiO2). The adsorption matrix or specific adsorption material is first placed in a nylon mesh of appropriate size, and then placed in a stainless steel basket 9 and placed in the reactor for easy cleaning and replacement. The specific adsorption catalytic reactor housing 6 is made of 8mm thick organic glass, and a 3mm thick layer of photocatalyst is evenly coated on the surface. At the same time, a cover plate 11 loaded with a 3mm thick photocatalyst is placed on the upper surface of the reactor during the rice paddy season to enhance the removal of COD from the rice field; at other times, a stainless steel mesh is placed on the upper surface of the reactor to intercept debris such as dead branches and leaves. The method for loading the photocatalyst on the surface or cover of the reactor is as follows: first, dissolve sodium silicate in water to obtain a 0.5% (mass fraction) sodium silicate solution, then add 10.00g TiO2 and 10.00g ZnO to 200mL of 0.5% sodium silicate aqueous solution to form a suspension, mix evenly, ultrasonicate for 30 minutes, magnetically stir for 20 minutes, and then evenly apply it to a glass plate, and then place it in a 55°C oven for drying; the final photocatalyst is loaded on the surface or cover of the reactor with a thickness of 3mm. The preparation process of the specific adsorption material is: immerse the zeolite in a 1mol / L MgCl2 solution for 12 hours (the mass ratio of zeolite to MgCl2 solution is: 1:4), calcine at 500°C for 3 hours, and prepare a NH4 removal agent. +A specific adsorption material for removing TP was prepared by soaking volcanic rock in 1mol / LLaCl3 solution for 12h (the mass ratio of volcanic rock to LaCl3 solution was 1:4) and calcining at 500℃ for 3h to obtain a specific adsorption material for removing COD; straw was immersed in 1mol / LTiO2 solution for 12h (the mass ratio of straw to TiO2 solution was 1:4) and calcined at 500℃ for 3h to obtain a specific adsorption material for removing COD.

[0046] Reinforced interception weir 12: Reinforced interception weir 12 is installed at the front end of the sunken ditch wetland. Reinforced interception weir 12 consists of a stainless steel frame 13, internal high-performance adsorption filler (the adsorption filler is the same as the adsorption filler in the inlet and outlet water purification device), surface iron-carbon microspheres and plants planted on it. The stainless steel frame is composed of a stainless steel pipe frame. The weir body is 40 cm high and the width is consistent with the ditch width. The front inclination angle 19 (that is, the angle between the inclined surface 17 of the reinforced interception weir and the extended surface of the bottom 18 of the reinforced interception weir) is 100 mm. Figure 4 The dotted line in the middle is an extension of the front inclination angle, and the dotted line does not belong to the structure of the reinforced interception weir) is 25°. The interior of the stainless steel frame is filled with high-performance adsorption filler, and the filling height is 10 cm below the stainless steel pipe frame (that is, starting from the bottom of the stainless steel pipe frame and filling evenly upward until the top surface of the adsorption filler is 10 cm below the top of the stainless steel pipe frame), and then 20 layers of 8 cm thick iron-carbon microspheres are filled on the upper surface of the adsorption filler (that is, the surface layer), and the top surface of the iron-carbon microsphere layer is basically flush with the top of the stainless steel pipe frame. A row of irises is planted 30 cm in front of the reinforced interception weir (planting density: 15 clusters / m 2 ), two rows of moss were planted in the middle and upper part (planting density: 20 clumps / m 2 The iron-carbon microspheres 20 loaded in the reinforced interception weir 12 are prepared as follows: 2 parts by weight of iron filings and 8 parts by weight of activated carbon are mixed, 100 parts by weight of a 5% sodium carboxymethyl cellulose solution is added, and the mixture is calcined at 500° C. for 0.5 h in a muffle furnace to produce iron-carbon microspheres 20 with a particle size of 6 mm.

[0047] At the end of the ditch, at the river mouth, a sunken ditch wetland was constructed with a length of 15m. The bottom substrate 15 was filled 20cm below the surface. The bottom substrate 15 was composed of a 10mm zeolite or 10mm volcanic rock (zeolite or volcanic rock) mixed with a specific adsorption material composite in a mass ratio of 1:1 to obtain modified zeolite or modified volcanic rock. The bottom substrate was laid with a thickness of 15cm. The specific adsorption material was prepared by soaking the zeolite in a 1mol / LMgCl2 solution for 12h (the mass ratio of zeolite to MgCl2 solution was 1:4) and calcining it at 500℃ for 3h to obtain a NH4 removal agent. +A specific adsorption material for TP removal was prepared by immersing volcanic rock in a 1 mol / L LaCl₃ solution for 12 hours (mass ratio of volcanic rock to LaCl₃ solution: 1:4) and then calcining at 500°C for 3 hours. A specific adsorption material for COD removal was prepared by immersing straw in a 1 mol / L TiO₂ solution for 12 hours (mass ratio of straw to TiO₂ solution: 1:4) and then calcining at 500°C for 3 hours. The three specific adsorption materials formed a specific adsorption material composite, with a mass ratio of 1:1:1. Emergent aquatic plants such as sedge grass and calamus (summer) and water celery and iris (winter) were planted on the bottom substrate. The plant roots were first wrapped in a non-woven planting bag filled with the bottom substrate and a small amount of straw and sawdust (the mass ratio of bottom substrate: straw: sawdust was 1:0.1:0.1, the bottom substrate here being the same as the above-mentioned bottom substrate) before being planted in the trench bottom. By planting aquatic plants 14, the hydraulic retention time of runoff drainage can be increased, and a certain physical interception effect can be produced on suspended particulate matter SS and particulate nitrogen and phosphorus; at the same time, the bottom matrix can + , TP and other pollutants; not only that, the surrounding organisms 16 on the roots and surface of plants can remove nitrogen through nitrification and denitrification, thereby further intercepting and removing nitrogen and phosphorus.

[0048] Example 1: Overall technical introduction and base demonstration effect

[0049] Figure 1 This is a specific embodiment of the present invention. A distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland is composed of an inlet and outlet water purification device at the farmland drainage outlet, a specific adsorption catalytic reactor at the key node of the ditch, and a sunken long-term interception module arranged at the ditch estuary.

[0050] The inlet and outlet water purification device of the farmland drainage outlet is built according to the geographical location and shape of the farmland drainage outlet. The matrix and high-performance adsorption filler inside the box can filter and settle SS and particulate nitrogen and phosphorus in the runoff drainage in situ, and preliminarily intercept dissolved nitrogen and phosphorus and COD. The specialized adsorption catalytic reactor at the key node of the ditch consists of a reactor box, a water flow folding plate, a specialized adsorption material, a stainless steel basket, a plexiglass cover and a drainage outlet. The matrix such as zeolite, volcanic stone, ceramsite and biochar filled in the internal interlayer plays the role of filtering and settling SS and NH4 + and PO4 3+ It has an interception effect. The other interlayers are filled with zeolite / volcanic rock / biochar. Through the impregnation and roasting method, MgCl2, LaCl3, and TiO2 are loaded to prepare specific adsorption materials for the NH4 +, TP, COD and other pollutants. A layer of photocatalyst is coated on the surface of the box and the organic glass cover to enhance the removal of COD in the rice field. The bottom matrix of the sunken ditch wetland arranged at the estuary of the ditch is + and PO4 3+ It has a certain adsorption and interception effect. Through the growth of aquatic plants with high nitrogen and phosphorus absorption properties and landscape value (primarily pickerel grass and calamus in summer, and water celery and iris in winter), as well as the absorption of ditch bottom plants and the surrounding biomass, it achieves long-term interception of nitrogen and phosphorus from rice field runoff. The reinforced interception weir installed at the front end of the sunken ditch wetland can intercept runoff water and reduce its impact load. The iron-carbon microspheres in the weir body enhance the removal of nitrogen, phosphorus, organic matter and other pollutants through micro-electrolysis and nitrification and denitrification by the organisms attached to the plant root surface.

[0051] The actual operation results of the system show that the system can effectively reduce the TN and NH4 + The removal rates of TN and NH4 in the riverbanks were 12.2% to 38.9% and 66.9% to 95.3% respectively, and the removal rate of TP was 46.0% to 66.7%, effectively achieving long-term interception and purification of farmland runoff. + and TP concentrations were 1.47 mg / L, 0.07 mg / L and 0.01 mg / L, respectively, which were lower than those in the control river (TN, NH4 + and TP concentrations were 3.18 mg / L, 0.30 mg / L and 0.05 mg / L, respectively; the control river was not equipped with any control and purification system); the phytoplankton species composition of the catchment river in the technical implementation area was rich, the dominant phytoplankton in the water body were mainly diatoms, cryptophytes, and euglena, and the dominant zooplankton in the water body were mainly protozoa, with rich species composition and good community diversity; while in the control river, cyanobacteria species accounted for a large proportion of the dominant algae groups, and water bloom algae such as Microcystis and Anabaena curledensis had become dominant, and the degree of eutrophication of the water body was high.

[0052] Example 2: Module-based operation results

[0053] Inlet and outlet water purification device:

[0054] Field trials have shown that the inlet and outlet water purification device filled with adsorbent fillers and zeolite / volcanic rock matrix has a good effect on removing suspended solids, particulate nitrogen, and particulate phosphorus in rice paddy runoff, with removal rates reaching 19.5%, 58.1%, and 82.8%, respectively. Its removal rates for dissolved nitrogen and phosphorus can reach 48.4% and 56.2%, respectively, and for TN and TP, the removal rates can reach 54.9% and 73.0%, respectively. Figure 6 ).

[0055] Specific adsorption catalytic reactor:

[0056] The actual ditch monitoring results show that the specialized adsorption catalytic reactors at key nodes of the ditch from July to October can achieve simultaneous removal of carbon, nitrogen and phosphorus from rice field runoff: at high influent concentrations (COD concentrations of 100-150 mg / L), the average daily removal rate can reach 16.78%; at low influent concentrations (COD concentrations of 50-75 mg / L), the average daily removal rate can reach 55.51%. + The average daily removal rate is between 20.92% and 51.45%, and the average daily removal rate of TP is between 19.21% and 64.73% ( Figure 7 ).

[0057] Sunken ditch wetlands where ditches flow into rivers:

[0058] The simulation test results show that under static conditions, the combination of modified zeolite / volcanic rock bottom matrix and Siberian iris has a better removal effect on N and P in the early stage of the experiment. On the 4th day, the removal rates of TN and TP reached 34.67% and 64.19%, respectively. On the 7th day, the removal rates of TN and TP reached 77.60% and 76.32%, respectively, which are higher than those of the combination of ordinary zeolite / volcanic rock bottom matrix and Siberian iris. Under flowing water conditions (flow rate range of 2.5-3.5L / h), the average removal rates of modified zeolite and Siberian iris for TP and TN reached 58.82% and 39.72%, respectively, which are higher than those of other treatments ( Figure 8 ).

[0059] Iron-carbon microspheres and plant coupling system:

[0060] The simulation test results show that the surface layer of the enhanced interception weir - the iron-carbon microsphere-plant coupling system showed a good nitrogen removal effect on the first day of the test, and the NO 3- The pollution load reduction rate reached 50.55%, which was significantly higher than that of the pure plant or pure iron-carbon microsphere system (P<0.05). The pure plant system refers to the system without iron-carbon microspheres and only the effect of plants; the pure iron-carbon microsphere system refers to the system without plants and only iron-carbon microspheres. After 13 days of the experiment, the iron-carbon microsphere-plant coupling system had a TN pollution load reduction rate of 78.30%, which was significantly higher than that of the pure plant or pure iron-carbon microsphere system (P<0.05). Figure 9 shown.

[0061] The above embodiments are only used to illustrate the technical solutions of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form, and any technical solutions obtained by equivalent replacement or equivalent transformation fall within the scope of protection of the present invention.

Claims

1. A distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland, characterized by: It includes the water purification devices at the inlet and outlet of farmland drainage outlets, the specialized adsorption catalytic reactors at the key nodes of the ditch, and the sunken long-term interception modules at the estuary of the ditch; The inlet and outlet water purification device is placed at the drainage outlet of the rice field, and includes a box body and an adsorption filler located inside the box body. It is used to filter and settle suspended particulate matter, particulate nitrogen, and particulate phosphorus in the drainage water from the farmland in situ, and to perform preliminary interception and adsorption of dissolved nitrogen, phosphorus, and COD. During irrigation, the nitrogen and phosphorus adsorbed by the adsorption filler are flushed back to the farmland through reverse water inflow. The specific adsorption catalytic reactor at the key nodes of the ditch is set up close to the farmland drainage ditch. The key nodes of the ditch include the ecological ditch water confluence and the front end of the ecological ditch into the river. The specific adsorption catalytic reactor includes a reactor with a photocatalyst evenly coated on the surface and cover, and a specific adsorption material located inside the reactor. The specific adsorption material is used to enhance the removal of ammonia nitrogen, phosphorus, and COD in the drainage of rice fields. The sunken long-term interception module at the ditch estuary is composed of a reinforced interception weir and a sunken ditch wetland; the sunken ditch wetland includes a bottom matrix, aquatic plants arranged at the bottom of the ditch, the roots of aquatic plants and surrounding organisms growing on the surface; the reinforced interception weir is composed of a stainless steel frame, internal adsorption filler, surface iron-carbon microspheres and planted plants, and is installed at the front end or both sides of the sunken ditch wetland; the reinforced interception weir has an adsorption filler filled inside the stainless steel frame and 5-10 cm iron-carbon microspheres filled on its surface; emergent plants are planted 20-30 cm in front of the reinforced interception weir, and herbaceous plants are planted in the middle and upper parts; the reinforced interception weir is used to intercept the drainage of farmland, and the iron-carbon microspheres in the weir body remove nitrogen, phosphorus and COD through micro-electrolysis and nitrification and denitrification of plant roots or surrounding organisms attached to the surface.

2. A distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland according to claim 1, characterized in that: The described inlet and outlet water purification device is filled with zeolite with a particle size of 5-20 mm and volcanic rock with a particle size of 5-20 mm at a mass ratio of 1:0.5-2 on both sides of the interior of the box, and the middle layer inside the box is filled with adsorption filler, which is composed of 65-80% zeolite with a particle size of 1-5 mm, 15-30% ceramsite with a particle size of 3-8 mm, and 1-5% biochar in a mass ratio.

3. The distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland according to claim 1 is characterized in that: The inlet and outlet water purification device has a box body including several evenly distributed front water inlets and at least one terminal drainage outlet; when watering the farmland, water is poured into the terminal drainage outlet at a limited and controllable speed, and the nitrogen and phosphorus adsorbed by the adsorption filler are slowly washed back to the farmland, while backwashing the adsorption filler in the inlet and outlet water purification device is achieved.

4. The distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland according to claim 1, characterized in that: The specific adsorption catalytic reactor at the key node of the ditch includes a water-flowing folding plate for limiting the movement path of farmland drainage water. The water-flowing folding plate divides the reactor into several layers, and the several layers include an adsorption matrix layer and different specific adsorption material layers; the photocatalyst evenly coated on the surface and cover of the reactor is used to remove COD in the farmland drainage water.

5. A distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland according to claim 4, characterized in that: In the specific adsorption catalytic reactor at the key node of the ditch, the adsorption matrix or specific adsorption material is first placed in a nylon net, then placed in a stainless steel basket and then placed in the reactor.

6. The distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland according to claim 1, characterized in that: The sunken ditch wetland is set at the estuary of the ditch, with a length of 10 to 20 meters. The bottom matrix is filled 10 to 30 cm below the ditch; the bottom matrix is composed of zeolite or volcanic rock and specific adsorption material in a mass ratio of 1:0.5 to 2, and the laying thickness is 8 to 20 cm.

7. The distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland according to claim 1, characterized in that: In the sunken ditch wetland, before the aquatic plants are planted, their roots are first wrapped with planting bags filled with bottom matrix and carbon source material.

8. The distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland according to claim 1, characterized in that: The height of the reinforced intercepting weir shall not exceed 2 / 3 of the ditch depth, and the front inclination angle shall be 20~45°.

9. A distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland according to any one of claims 1 to 8, characterized in that: The preparation steps of the adsorption filler are as follows: the mass ratio is 65-80% of zeolite with a particle size of 1-5 mm, 15-30% of ceramsite with a particle size of 3-8 mm, and 1-5% of biochar; The specific adsorption material is used for efficient adsorption of nitrogen and phosphorus. The preparation steps are as follows: using the impregnation and roasting method, the zeolite is immersed in a 0.5-2 mol / L MgCl2 solution for 10-12 hours, and roasted at 450-550℃ for 3-5 hours to prepare the NH4 removal + Special adsorption materials; Volcanic rock was immersed in 0.5-2 mol / L LaCl3 solution for 10-12 hours and then calcined at 450-550℃ for 3-5 hours to prepare a specific adsorption material for removing TP. Biomass raw materials were immersed in 0.5-2 mol / L TiO2 solution for 10-12 hours and then calcined at 450-550℃ for 3-5 hours to prepare a specific adsorption material for removing COD. The mass ratio of zeolite to MgCl2 solution was 0.5-1:2; the mass ratio of volcanic rock to LaCl3 solution was 0.5-1:2; and the mass ratio of biomass raw materials to TiO2 solution was 0.5-1:

2. The method for loading the photocatalyst on the reactor surface or cover is as follows: first, sodium silicate is dissolved in water to obtain a 0.5% sodium silicate solution, and then 10.00 g of TiO2 and ZnO are added to the 0.5% sodium silicate aqueous solution at a mass ratio of 1:0.5-2 to form a suspension. After uniform mixing, the suspension is ultrasonicated for 30-60 minutes and magnetically stirred for 10-30 minutes. The suspension is then evenly coated on a glass plate and then air-dried or oven-dried at room temperature. The preparation process of iron-carbon microspheres loaded in the reinforced interception weir is as follows: iron filings and activated carbon are mixed in a mass ratio of 1.5-2.5:8, 4-6% sodium carboxymethyl cellulose solution is added, and calcined at 400-600°C for 0.5-1h to produce iron-carbon microspheres with a particle size of 5-8 mm.

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