Distributed nitrogen-phosphorus and COD (Chemical Oxygen Demand) multi-pollutant blocking, controlling and purifying system suitable for high-standard farmland

Abstract

The invention relates to the field of farmland water pollution treatment, in particular to a distributed nitrogen-phosphorus and COD (chemical oxygen demand) multi-pollutant blocking, controlling and purifying system suitable for high-standard farmland, which comprises an inlet and outlet water purifying device of a farmland water outlet, an obligate adsorption catalytic reactor of a ditch key node and a sunken long-acting intercepting module arranged at a ditch river entrance which are arranged in sequence. The method can intercept and purify carbon, nitrogen and phosphorus in high-concentration farmland recession generated by heavy rainfall in the rice growing period, especially in the field steeping period and after fertilization, and the used materials have the properties of high adsorption capacity, high catalytic activity, easiness in recycling, environment friendliness and the like; related technical modules are simple to prepare, the system has the characteristics of strong adaptability, high flexibility and lasting effect, the system does not occupy extra land, is low in cost, is plug-and-play, does not need engineering construction cost, is simple to operate and maintain, and can realize stable up-to-standard emission of carbon, nitrogen and phosphorus in farmland drainage and biodiversity improvement.

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 large-scale application of chemical fertilizers in farmland is one of the sources of agricultural non-point source pollution. The amount of water discharged from farmland is large, and the nutrient content is usually high. Direct discharge into the receiving water body will pollute the surrounding water environment. In recent years, the construction of high-standard farmland has been widely carried out across the country. However, the early construction of high-standard farmland focused on improving production capacity and paid insufficient attention to improving the ecological environment quality of farmland. The supporting drainage ditches were usually built as simple hardened cement ditches, resulting in the ineffective performance of the ecosystem service function of the ditches.

[0003] Ecological ditches have the functions of regulating excessive runoff discharge and realizing material circulation. They also have the characteristics of streams and wetlands, and are a key link in the control of farmland non-point source pollution. How to utilize the existing farmland drainage ditches and perform limited ecological transformation of farmland drainage outlets, key ditch nodes, and river / beach inlets to give full play to their ecological service functions, thereby improving the drainage of farmland during the flooding period and the interception of high-concentration carbon, nitrogen, and phosphorus in the drainage caused by heavy rainfall after fertilization, has important practical significance.

[0004] The development of new, cheap and efficient environmental materials is a breakthrough in solving the 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 - efficient absorption by surrounding organisms - long-term absorption by aquatic plants", stable "up-to-standard" emissions of carbon, nitrogen and phosphorus in rice field drainage water and enhanced biodiversity are achieved.

[0007] In order to achieve the above objectives, the technical solution adopted by the present invention is as follows: 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 of 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 water inlet and outlet purification device is placed at the drainage outlet of the paddy field, and comprises a box body and an adsorption filler located inside the box body, and is used for in-situ filtering and settling of suspended particulate matter (SS), particulate nitrogen and particulate phosphorus in the farmland drainage (e.g., paddy field drainage), and preliminary interception and adsorption of dissolved nitrogen, phosphorus and COD; during irrigation, the nitrogen and phosphorus adsorbed by the adsorption filler are washed back to the farmland through reverse water inflow;

[0009] The specific adsorption catalytic reactor at the key node of the ditch is set close to the farmland drainage ditch. The key node of the ditch includes 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 plate, 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 fillers, 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 water purification device for the inlet and outlet is filled with zeolite with a particle size of 5 to 20 mm and volcanic rock with a particle size of 5 to 20 mm at a mass ratio of 1:0.5 to 2 on both sides of the box (as a zeolite and volcanic rock filling layer), and the middle layer inside the box is filled with adsorption filler, which is composed of 65 to 80% zeolite with a particle size of 1 to 5 mm, 15 to 30% ceramsite with a particle size of 3 to 8 mm, and 1 to 5% biochar in a mass ratio. Zeolite and volcanic rock with larger particle sizes are filled on both sides of the box, mainly to settle the silt carried in the farmland drainage, and to filter and settle the suspended particles ss, particulate nitrogen, and particulate phosphorus in situ; the middle layer is filled with adsorption filler with smaller particles, mainly to preliminarily intercept dissolved nitrogen, phosphorus, and COD.

[0012] Furthermore, the inlet and outlet water purification device has a casing including a plurality of evenly distributed front water inlets and at least one terminal drainage outlet; when water is irrigated into the farmland, water is irrigated into the terminal drainage outlet at a limited and controllable speed (0.1-2 m / s), and the nitrogen and phosphorus adsorbed by the adsorption filler are slowly flushed back to the farmland, while the function of backwashing the adsorption filler in the inlet and outlet water purification device is realized; in addition, watering also causes the zeolite and volcanic rock filling layers to slowly release nitrogen and phosphorus, and the nitrogen and phosphorus slowly released by the zeolite and volcanic rock filling layers are mainly in a particle state, and the nitrogen and phosphorus slowly released by the adsorption filler are mainly in a dissolved state.

[0013] Specifically, the water purification device for the inlet and outlet of the farmland drainage outlet is placed on one side of the rice field drainage outlet, and is constructed as a rectangular box of appropriate size according to the geographical location and the 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 ridge). An overflow port is set at the front of the box (the opening depth is 2-4cm down from the top of the box); 2-3 rows of seepage holes (front water inlet) are evenly distributed on its lower side, with a seepage hole diameter of 0.5-1.5cm, and the lower layer of seepage holes (i.e., the lowest row of seepage holes) are 8-10cm high from the field surface. The drainage outlet is located at the end of the box, and a wire mesh is installed on the surface (to prevent the filler in the last compartment of the box from falling out). Its height is not lower than the lower seepage hole on the front side, and the diameter is 5-25cm. The inside of the box is divided into 3 to 4 compartments by water-flowing folding plates evenly distributed along the direction of farmland drainage. The two sides are filled with zeolite with a particle size of 5 to 20 mm and volcanic rock with a particle size of 5 to 20 mm at a mass ratio of 1:0.5 to 2. The middle layer is filled with high-performance adsorption fillers (abbreviated as adsorption fillers) to filter and settle suspended particles SS, particulate nitrogen, and particulate phosphorus in the drainage of rice fields in situ, and to preliminarily intercept dissolved nitrogen, phosphorus, and COD. A 3 to 6 cm gap is left on the left or right side of each water-flowing folding plate, so that the drainage of farmland flows in a serpentine shape. For the irrigation and drainage dual-purpose ditch configured for high-standard farmland, the nitrogen and phosphorus adsorbed by the high-performance adsorption filler are flushed back to the farmland through reverse water inflow during irrigation, so that the nutrients are recycled and the service life of the adsorption filler is increased. Under rainfall, it enters the inlet and outlet water purification device through the seepage hole or overflow port, and enters the ditch through the drainage port after filtration and sedimentation.

[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 farmland drainage water. The water-flowing folding plate divides the reactor into a number of 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 drainage water from farmland.

[0015] Furthermore, in the specific adsorption catalytic reactor at the key node of the ditch, the adsorption matrix or the specific adsorption material is first loaded into a nylon net, 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 entering 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 m long, the width is the same as or slightly narrower than the ditch width, and the depth is 0.4 to 1.0 m (not exceeding 2 / 3 of the ditch depth). The overflow port is located at the front end of the reactor, and the overflow port opening depth 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-flowing fold in the reactor, so that the farmland drain water flows in a serpentine shape (the structure of the water-flowing fold in the reactor refers to the water-flowing fold in the inlet and outlet water purification device). The reactor is divided into multiple layers by overflow ports and water-flowing folding plates along the discharge direction of farmland drainage. The first layer is filled with adsorption matrices such as zeolite / volcanic stone with a particle size of 3 to 10 mm, ceramsite with a particle size of 5 to 10 mm, and biochar; the other layers are filled with specific adsorption materials, which are used to absorb NH4 + , TP, COD and other pollutants are removed synchronously and enhanced. The adsorption matrix or specific adsorption material is first placed in a nylon net 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 5-10mm organic glass, PVC board or stainless steel board, and a layer of photocatalyst is evenly coated on the surface. At the same time, a cover plate loaded with photocatalyst is placed on the upper surface of the reactor during the paddy field flooding period to enhance the removal of COD from the rice field; at other times, a stainless steel net is placed on the upper surface of the reactor to intercept debris such as dead branches and leaves.

[0017] The water discharged from farmland first passes through the adsorption matrix layer, and then filters and settles the suspended particulate matter SS, particulate nitrogen and particulate phosphorus through the adsorption matrix. It 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 through the overflow port of the reactor (the overflow port is located at the front end of the reactor), and flows alternately to the left or right side under the obstruction of multiple water-flowing folding plates in the middle of the reactor. + Pollutants such as TN, TP, COD, etc. 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 ditch estuary, with a length of 10 to 20 meters, and is dug 10 to 30 cm 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 ground. 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 carbon source materials such as straw and sawdust, and then planted in the bottom of the ditch. Through the planting of 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 be used for NH4 + , TP and other pollutants can be adsorbed; not only that, the surrounding organisms at the roots and surface of plants can remove nitrogen through nitrification and denitrification, 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 20-45°, which refers to the angle between the inclined surface of the weir and the bottom extension surface.

[0023] Furthermore, the reinforced intercepting 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 intercepting weir (referring to the distance from the front end of the reinforced intercepting 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 intercepting 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°. 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 a 5 to 10 cm thick iron-carbon microsphere layer is filled (covered) on the upper surface of the adsorption filler, 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 withdrawal from 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 drought-resistant and flood-resistant herbs that 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 slope of the weir can increase the contact area between the internal material and the runoff water and improve 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; 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, and the preparation steps are as follows: using the impregnation and roasting method, the biomass raw materials such as straw, zeolite or volcanic rock are immersed in 0.5-2mol / LMgCl2, LaCl3 or TiO2 solution at a mass ratio of 1:0.5-1:0.5-1 for 10-12h, and roasted at 450-550℃ for 3-5h to prepare the NH4 removal agent. +, TP, COD specific adsorption materials; biomass raw materials or zeolite or volcanic rock, and MgCl2, LaCl3 or TiO2 solution mass ratio of 0.5 ~ 1:2;

[0028] The method of loading the photocatalyst on the surface or cover of the reactor is as follows: firstly, sodium silicate is dissolved in water to obtain a 0.5% sodium silicate solution, and then 10.00g 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, and after being evenly mixed, ultrasonicated for 30-60 minutes, magnetically stirred for 10-30 minutes, and then evenly coated on a glass plate, and then air-dried at room temperature or placed in a 55°C oven for drying. 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 on the surface of the carrier at room temperature, with mild reaction conditions, low energy consumption, and good catalytic effect.

[0029] The preparation process of the 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 that it provides 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 produced by heavy rainfall during the rice growing period, especially the flooding period and after fertilization. The materials used have high adsorption capacity, high catalytic activity, easy recycling, environmental friendliness and other properties. The technical modules involved are simple to prepare, have strong adaptability, high flexibility and 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 the 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 specific adsorption catalytic reactor at the key node of the ditch;

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

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

[0036] Figure 6 .Removal performance of the inlet and outlet water purification device 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 .Removal performance of TP and TN by sunken ditch wetland in (a) static cultivation period and (b) flowing water experimental period;

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

[0040] In the attached drawings, 1 is the inlet and outlet water purification device box, 2 is the partition, 3 is the high-performance adsorption material, 4 is the terminal 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 interception 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 slope of the reinforced interception weir, 18 is the bottom of the reinforced interception weir, 19 is the front inclination angle, and 20 is the iron-carbon microspheres. DETAILED DESCRIPTION

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

[0042] In the following embodiments, 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 in the figure, a distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland consists of a water inlet and outlet purification device at the farmland drainage outlet, a specific adsorption catalytic reactor at the key node of the ditch, and a sinking long-term interception module arranged at the ditch estuary. The farmland drainage flows through the water inlet and outlet purification device at the farmland drainage outlet, the specific adsorption catalytic reactor at the key node of the ditch, and the sinking long-term interception module arranged at the ditch estuary.

[0044] The inlet and outlet water purification device of the farmland drainage outlet is placed on one side of the rice field drainage outlet. It is built into a rectangular box according to 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 down from the top of the box); 2 rows of seepage holes (front water inlet) are evenly distributed on its lower side, with a diameter of 1cm, and the lower seepage holes (i.e. the seepage holes in the lowest 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 is composed of four compartments 2 separated by several water-flowing folding plates evenly distributed along the direction of farmland drainage. A 5cm gap is left on the left or right side of each water-flowing folding plate, so that the farmland drainage water flows in a serpentine shape; the two compartments on both sides are filled with zeolite with a particle size of 10mm and volcanic rock with a particle size of 10mm in a mass ratio of 1:1, and the two middle compartments are filled with high-performance adsorption fillers 3 (referred to as adsorption fillers for short) to filter and settle suspended particles SS, particulate nitrogen, and particulate phosphorus in the rice field drainage water in situ, and to preliminarily intercept dissolved nitrogen, phosphorus, and COD. The width and depth of the four compartments are both 0.6m, and the length of the four compartments along the direction of farmland drainage water is equal (all 0.17m, referring to the length of the filler, and the thickness of the water-flowing folding plate is not included). For the irrigation and drainage dual-purpose ditches configured for high-standard farmland, the nitrogen and phosphorus adsorbed by the high-performance adsorption fillers are flushed back to the farmland through reverse water inflow during irrigation, so that the nutrients are recycled and the service life of the adsorption fillers is increased. When the farmland is irrigated, the end drain port 4 is irrigated at a limited and controllable speed, and the nitrogen and phosphorus adsorbed by the adsorption filler are slowly washed back to the farmland, realizing the function of backwashing the filler in the device. Under rainfall, it 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 high-performance adsorption filler are as follows: the mass ratio is 75% zeolite with a particle size of 3mm, 22% ceramsite with a particle size of 5mm, and 3% 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 entering 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 compartments by the overflow port 10 and the water diversion fold 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 is composed 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 fold 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 adsorb NH4 + , TP, and COD pollutants are removed synchronously and enhanced (among which, the material obtained by modifying zeolite with MgCl2 solution is used for the removal of ammonium ions, the material obtained by modifying volcanic rock with LaCl3 is used for the removal of TP, and the material obtained by modifying straw biochar with TiO2 is used for the removal of COD). The adsorption matrix or the specific adsorption material is first placed in a nylon net of suitable 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 box 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, during the rice season, a cover plate 11 loaded with a 3mm thick photocatalyst is placed on the upper surface of the reactor to enhance the removal of COD from the rice field; at other times, a stainless steel net is placed on the upper surface of the reactor to intercept debris such as dead branches and leaves. The method of 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 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 on a glass plate, and then put it in a 55°C oven for drying; the final photocatalyst is loaded on the reactor surface or cover with a thickness of 3mm. The preparation process of the specific adsorption material is: immerse the zeolite in a 1mol / L MgCl2 solution for 12h (the mass ratio of zeolite to MgCl2 solution is: 1:4), and calcine at 500°C for 3h to 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] Strengthened interception weir 12: Strengthened interception weir 12 is installed at the front end of the sunken ditch wetland. Strengthened interception weir 12 consists of a stainless steel frame 13, high-performance adsorption filler inside (the adsorption filler is the same as the adsorption filler in the inlet and outlet water purification device), iron-carbon microspheres on the surface, and plants planted on it. The stainless steel frame is composed of a stainless steel pipe frame, the height of the weir is 40cm, the width is consistent with the width of the ditch, and the front inclination angle 19 (that is, the angle between the inclined surface 17 of the strengthened interception weir and the extended surface of the bottom 18 of the strengthened interception weir, Figure 4 The dotted line in the middle is an extension of the front inclination angle (the dotted line does not belong to the structure of the enhanced interception dam) which is 25°. The stainless steel frame is filled with high-performance adsorption filler, and the filling height is 10 cm below the stainless steel pipe frame (i.e., starting from the bottom of the stainless steel pipe frame and filling evenly upward until the top of the adsorption filler is 10 cm below the top of the stainless steel pipe frame). Then, 20 layers of 8 cm thick iron-carbon microspheres are filled on the upper surface of the adsorption filler (i.e., the surface layer). 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 enhanced interception dam (planting density: 15 clumps / m 2 ), two rows of moss were planted in the middle and upper part (planting density: 20 clumps / m 2 The preparation process of the iron-carbon microspheres 20 loaded in the reinforced interception weir 12 is as follows: 2 parts by weight of iron filings and 8 parts by weight of activated carbon are mixed, 100 parts by weight of 5% sodium carboxymethyl cellulose solution is added, and the mixture is calcined at 500° C. for 0.5 h in a muffle furnace to prepare iron-carbon microspheres 20 with a particle size of 6 mm.

[0047] At the end of the ditch, at the estuary, a sunken ditch wetland was constructed with a length of 15m, and the bottom matrix 15 was filled 20cm below the surface. The bottom matrix 15 was made of a mixture of zeolite with a particle size of 10mm or volcanic rock with a particle size of 10mm (zeolite or volcanic rock was selected) and a specific adsorption material composite in a mass ratio of 1:1 to obtain modified zeolite or modified volcanic rock, and the bottom matrix was laid with a thickness of 15cm; the specific adsorption material preparation process was as follows: the zeolite was immersed in a 1mol / LMgCl2 solution for 12h (the mass ratio of zeolite to MgCl2 solution was 1:4), and calcined at 500℃ for 3h to obtain a NH4 removal agent. +The 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 roasting at 500℃ for 3h to obtain the specific adsorption material for removing TP; the straw was soaked in 1mol / LTiO2 solution for 12h (the mass ratio of straw to TiO2 solution was 1:4) and roasted at 500℃ for 3h to obtain the specific adsorption material for removing COD. The three specific adsorption materials constituted a specific adsorption material composite, and the mass ratio of the three was 1:1:1. The bottom substrate was planted with water plants such as pickerel grass, calamus (summer), water celery, and iris (winter). The roots of the plants were first wrapped with a non-woven planting bag filled with bottom substrate and a small amount of straw and sawdust (the mass ratio of bottom substrate: straw: sawdust was 1:0.1:0.1, and the bottom substrate here was the same as the aforementioned bottom substrate), and then planted in the bottom of the ditch. By planting aquatic plants 14, the hydraulic retention time of runoff drainage can be increased, and a certain physical interception effect can be exerted 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 at 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 water purification device for the inlet and outlet 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 is composed of a reactor box, a water 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, biochar, etc. filled in the internal interlayer plays a role in filtering and settling SS and NH4 + and PO4 3+ The zeolite / volcanic rock / biochar filled in other interlayers are loaded with MgCl2, LaCl3, and TiO2 through impregnation and roasting to prepare specific adsorption materials for NH4 +, TP, COD and other pollutants. A layer of photocatalyst is coated on the surface of the box and the plexiglass cover to enhance the removal of COD from the rice field. The bottom matrix of the sunken ditch wetland arranged at the estuary of the ditch + and PO4 3+ It has a certain adsorption and interception effect. Through the growth of aquatic plants that have high nitrogen and phosphorus absorption performance and are both landscape-oriented (mainly pickerel grass and calamus in summer, and mainly water celery and iris in winter), as well as the absorption of ditch bottom plants and plant surface surrounding organisms, it can achieve 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 can enhance the removal of nitrogen, phosphorus, organic matter and other pollutants through micro-electrolysis and nitrification and denitrification of epiphytes on the surface of plant roots.

[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 river reached 12.2% to 38.9% and 66.9% to 95.3% respectively, and the removal rate of TP reached 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, all lower than the control river (TN, NH4 + and TP concentrations were 3.18 mg / L, 0.30 mg / L and 0.05 mg / L, respectively, and the control river was not equipped with any barrier 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, euglena, etc., the dominant zooplankton in the water body were mainly protozoa, the species composition was rich, and the diversity of the biological community was good; while in the control river, cyanobacteria species accounted for a large proportion of the algae groups that formed the dominant species, and water bloom algae such as Microcystis and curled fish algae had become dominant, and the degree of eutrophication of the water body was relatively high.

[0052] Example 2: Module-based operation results

[0053] Inlet and outlet water purification device:

[0054] Field tests have shown that the water inlet and outlet purification device filled with adsorption fillers and zeolite / volcanic stone matrix has a good removal effect on suspended solids, particulate nitrogen and particulate phosphorus in rice field 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 specific adsorption catalytic reactor at the key nodes of the ditch from July to October can achieve simultaneous removal of carbon, nitrogen and phosphorus from the rice field drainage: at high influent concentration (COD concentration of 100-150 mg / L), the average daily removal rate can reach 16.78%; at low influent concentration (COD concentration 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 at the mouth of a ditch:

[0058] The simulation test results show that under static conditions, the combination of modified zeolite / volcanic rock and Siberian iris had 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, and on the 7th day, the removal rates of TN and TP reached 77.60% and 76.32%, respectively, which were higher than those of the combination of ordinary zeolite / volcanic rock and Siberian iris. Under flowing water conditions (flow rate range of 2.5-3.5L / h), the average removal rates of TP and TN by the combination of modified zeolite and Siberian iris reached 58.82% and 39.72%, respectively, which were 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 pure plant or pure iron-carbon microsphere system (P<0.05). The pure plant system refers to the system without iron-carbon microspheres, but only the effect of plants; the pure iron-carbon microsphere system refers to the system without plants, but 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 pure plant or pure iron-carbon microsphere system (P<0.05). Fig. 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 shall fall within the protection scope of the present invention.

Claims

1. A distributed nitrogen, phosphorus and COD multi-pollutant control and purification system suitable for high-standard farmland, characterized in that: It includes the water purification device of the farmland drainage outlet, the specialized adsorption catalytic reactor at the key node of the ditch and the sunken long-term interception module arranged at the ditch estuary; The water inlet and outlet 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, which is used to filter and settle suspended particulate matter, particulate nitrogen and particulate phosphorus in the farmland drainage water in situ, and to preliminarily intercept and adsorb dissolved nitrogen, phosphorus and COD; when irrigating, the nitrogen and phosphorus adsorbed by the adsorption filler are washed back to the farmland through reverse water inflow; The specific adsorption catalytic reactor at the key node of the ditch is set close to the farmland drainage ditch. The key node of the ditch includes 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 plate, 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, roots of aquatic plants and surrounding organisms growing on the surface; the reinforced interception weir is composed of a stainless steel frame, internal adsorption fillers, surface iron-carbon microspheres and planted plants, and is installed at the front end or both sides of the sunken ditch wetland.

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 inlet and outlet water purification device described herein has two sides of the interior of the box filled with zeolite with a particle size of 5 to 20 mm and volcanic rock with a particle size of 5 to 20 mm in a mass ratio of 1:0.5 to 2, and the middle layer inside the box is filled with adsorption filler, which is composed of 65 to 80% zeolite with a particle size of 1 to 5 mm, 15 to 30% ceramsite with a particle size of 3 to 8 mm, and 1 to 5% biochar in a mass ratio.

3. 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 inlet and outlet water purification device has a box body including a plurality of evenly distributed front water inlets and at least one terminal drainage outlet; when water is irrigated into the farmland, water is irrigated 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. 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 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 a number of 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.

5. A 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 specific adsorption catalytic reactor at the key node of the ditch, the adsorption matrix or the specific adsorption material is firstly placed in a nylon net, and then placed in a stainless steel basket and then placed in the reactor.

6. 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 sunken ditch wetland is set at the ditch estuary, with a length of 10 to 20 meters, and is dug 10 to 30 cm to fill the bottom matrix; the bottom matrix is ​​composed of zeolite or volcanic stone 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.

7. A 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 materials.

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 to 45°.

9. 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 reinforced interception weir has an adsorption filler filled inside the stainless steel frame, and then iron-carbon microspheres are filled in the surface 5 to 10 cm; emergent plants are planted in the front 20 to 30 cm 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.

10. 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 9, 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, and the preparation steps are as follows: using the impregnation and roasting method, the biomass raw material or zeolite or volcanic rock is immersed in 0.5-2mol / LMgCl2, LaCl3 or TiO2 solution for 10-12h, and roasted at 450-550℃ for 3-5h to prepare the NH4 removal + , TP, COD specific adsorption materials; The mass ratio of biomass raw material or zeolite or volcanic rock to MgCl2, LaCl3 or TiO2 solution is 0.5 to 1:2; The method for loading the photocatalyst on the surface or cover of the reactor is as follows: first, sodium silicate is dissolved in water to obtain a 0.5% sodium silicate solution, and then 10.00g of TiO2 and ZnO are added to the 0.5% sodium silicate aqueous solution in a mass ratio of 1:0.5-2 to form a suspension. After mixing evenly, ultrasonicate for 30-60 minutes, magnetically stir for 10-30 minutes, and then evenly apply it on a glass plate, and then air-dry or bake it at room temperature. The preparation process of the 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.

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