A system and method for treating combined sewer overflows

Abstract

The present application relates to a kind of system and method for treating overflow sewage of combined flow system pipeline, the system includes magnetic flocculation device, the separation device connected with the magnetic flocculation device and the magnetic sludge separator and denitrification device matched with the separation device, wherein the micro-nano bubbles generated by bubble generator can provide upward buoyancy for magnetic flocculation body, and the magnetic field generated by the power supply of magnetic barrel can overcome the gravity of magnetic flocculation body to produce suction force on magnetic flocculation body, which can effectively reduce the amount of magnetic flocculation body deposited at the bottom of separation device, micro-nano aeration rod is arranged around composite ecological filler column, and the micro-nano bubbles generated by micro-nano aeration rod can scour composite ecological filler column, which can effectively alleviate the problem of suspended solids in overflow sewage blocking filler pores, and improve its working exchange capacity, compared with traditional composite ecological filler adsorption method, the use time of composite ecological filler column can be extended by 35-40%.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a system and method for treating overflow sewage from combined sewer systems. Background Technology

[0002] With the acceleration of urbanization in my country and the continuous expansion of urban areas, municipal drainage networks have entered a period of rapid construction. However, due to the influence of different natural and economic conditions in different regions, the traditional combined sewer system is still widely used in major cities. Although many cities are currently promoting the construction of separate sewer systems, many cities still retain the combined sewer system.

[0003] However, during periods of heavy rain or snowmelt, when a large amount of rainwater flows into the drainage system, and the flow rate within the combined sewer system exceeds the interception capacity, the excess mixed sewage will be directly discharged into the receiving water body. This sewage is known as combined sewer overflow. Since combined sewers contain not only rainwater but also domestic sewage and industrial wastewater, the overflow sewage contains not only pathogenic microorganisms, nutrients such as nitrogen and phosphorus, and pathogens, but also toxic and harmful substances. These substances pose a serious threat to urban water bodies, making combined sewer overflow pollution one of the main sources of rainwater pollution in my country's natural water bodies. With my country's increasing emphasis on the ecological environment, effectively controlling and managing combined sewer overflow pollution has become a major challenge in my country's urbanization process.

[0004] Currently, research on the treatment of combined sewer overflow pollution focuses on front-end, mid-end, and end-of-pipe treatment. Front-end treatment addresses the pollution at its source, mainly including rainwater and sewage separation projects and sponge city construction. However, these technologies require large land areas, significant investment, and are time-consuming. Mid-end treatment refers to regular flushing and maintenance of the pipes, which requires substantial manpower and resources. Therefore, end-of-pipe treatment is currently the primary treatment method and measure, involving centralized treatment at the discharge outlet. End-of-pipe treatment typically employs integrated devices (filtration, coagulation, flocculation, and chemical agents). When existing devices remove small particulate suspended solids from overflow sewage through flocculation, the resulting flocs tend to accumulate at the bottom of the device and are difficult to clean. Furthermore, when existing devices remove ammonia nitrogen from overflow sewage using packed columns, residual suspended solids in the overflow sewage easily clog the pores of the packed columns, increasing water flow resistance and reducing the working exchange capacity, thus shortening the service life of the packed columns. This not only reduces removal efficiency but also increases operating costs. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, this invention provides a system and method for treating overflow sewage from combined sewer systems. This system can effectively reduce the amount of magnetic flocculants deposited at the bottom of the separation device, effectively alleviate the problem of suspended solids in overflow sewage clogging the pores of the packing material, and extend the service life of the composite ecological packing column.

[0006] The technical solution of the present invention is as follows: a system for treating overflow sewage from combined sewer systems, the system comprising a magnetic flocculation device, a separation device connected to the magnetic flocculation device, and a magnetic mud separator and a denitrification device that cooperate with the separation device;

[0007] The magnetic flocculation device can aggregate small-diameter suspended matter in the overflow sewage into magnetic flocs by adding coagulant, magnetic seeds and flocculant to the overflow sewage.

[0008] The separation device includes a bubble generating device, a magnetic adsorption device that cooperates with the bubble generating device, and a magnetic mud cleaning device that cooperates with the magnetic adsorption device. The bubble generating device can output micro-nano bubbles with a diameter of 50nm to 50μm into the separation device. The magnetic adsorption device includes a magnetic bucket for adsorbing magnetic flocs. The magnetic mud cleaning device includes a magnetic mud scraper for scraping off the magnetic flocs on the magnetic bucket and a brush that cooperates with the magnetic mud scraper.

[0009] The magnetic mud separator can separate the magnetic seeds and flocs in the magnetic flocs;

[0010] The denitrification device includes several composite ecological packing columns and micro-nano aeration rods that cooperate with the composite ecological packing columns. The packing material in the composite ecological packing columns is mainly composed of modified green zeolite, rice husk charcoal, vermiculite and pyrite mixed in a mass ratio of (70-85):(90-110):(100-120):(10-25). The air source for the micro-nano aeration rods is either air or pure oxygen.

[0011] Furthermore, the bubble generating device includes a micro / nano bubble generator, an aeration rod that cooperates with the micro / nano bubble generator, and a bubble delivery pipe that connects the micro / nano bubble generator and the aeration rod.

[0012] Furthermore, the side of the magnetic barrel is evenly divided into three regions along the axial direction, each of which can generate a magnetic field when energized individually.

[0013] Furthermore, the outer layer of the filler in the composite ecological filler column is wrapped with a 150-200 mesh nylon mesh.

[0014] Furthermore, the modified green zeolite has a particle size of 1-3 mm, the rice husk charcoal has a particle size of 0.2-0.25 mm, the vermiculite has a particle size of 1-3 mm, and the pyrite has a particle size of 4-8 mm.

[0015] Furthermore, the modified green zeolite is prepared by pyrolyzing natural green zeolite at a high temperature of 250°C for 3 hours, followed by shaking in a 0.03%–0.05% sodium citrate solution at a shaking speed of 200–300 r / min for 6 hours.

[0016] Furthermore, the magnetic flocculation device includes a coagulation zone and a flocculation zone, and the flocculation zone is also equipped with a flocculation enhancement tank.

[0017] Furthermore, the magnetic mud cleaning device includes a rotating belt for driving the brush.

[0018] A method for treating combined sewer overflow wastewater, comprising the above-described system for treating combined sewer overflow wastewater, the method comprising the following steps:

[0019] (1) Retaining large particulate impurities in overflow sewage: Overflow sewage from combined sewer systems first passes through a screen and grit chamber, where larger suspended solids, floating objects, and gravel in the overflow sewage are all retained;

[0020] (2) Flocculation of small particulate impurities in overflow wastewater: The intercepted overflow wastewater first enters the coagulation zone of the magnetic flocculation device. In the coagulation zone, coagulant and magnetic seeds are added and quickly stirred together with the overflow wastewater. Under the action of the coagulant, the suspended particulate matter and magnetic seeds in the overflow wastewater will aggregate together to form magnetic coagulants. Then the coagulants enter the flocculation zone along with the overflow wastewater. After adding flocculant, the coagulants are slowly stirred in the flocculation enhancement tank to form magnetic coagulants.

[0021] (3) Separation of small particulate impurities in overflow sewage: Small particulate impurities that form magnetic flocs enter the separation device along with the overflow sewage. A large number of micro-nano bubbles generated by the bubble generator will adhere to the magnetic flocs. The magnetic barrel in the magnetic adsorption device is energized and forms a strong magnetic field. The magnetic flocs suspended in the overflow sewage are quickly attracted to the magnetic barrel under the combined action of magnetic force and buoyancy generated by micro-nano bubbles. The magnetic flocs adsorbed on the magnetic barrel are cleaned by the magnetic mud cleaning device to the magnetic mud separator. The overflow sewage will enter the denitrification device.

[0022] (4) Removal of ammonia nitrogen from overflow sewage: After the overflow sewage enters the denitrification device, the composite ecological packing column immersed in micro-nano bubble water will adsorb the ammonia nitrogen in the overflow sewage, and then the nano bubbles will be discharged into the ecosystem along with the overflow sewage.

[0023] The beneficial technical effects of this invention are as follows:

[0024] The present invention discloses a system for treating overflow sewage, wherein the micro-nano bubbles generated by the bubble generator provide upward buoyancy to the magnetic flocculants, and the magnetic field generated by the energized magnetic barrel on the magnetic flocculants can overcome the downward gravity of the magnetic flocculants, effectively reducing the amount of magnetic flocculants deposited at the bottom of the separation device. Furthermore, by adjusting the current intensity of the magnetic barrel and the aeration rate of the micro-nano bubbles, the magnetic force and buoyancy can be enhanced to cope with changes in the volume and quality of the overflow sewage, thereby significantly improving the removal efficiency of magnetic flocculants in overflow sewage. Compared with traditional magnetic coagulation technology, the removal efficiency can be improved by 25-30%.

[0025] The present invention discloses a system for treating overflow sewage, in which micro-nano aeration rods are arranged around a composite ecological packing column. The micro-nano bubbles generated by the micro-nano aeration rods can flush the composite ecological packing column, effectively alleviating the problem of suspended solids in the overflow sewage clogging the pores of the packing and improving its working exchange capacity. Compared with the traditional composite ecological packing adsorption method, it can extend the service life of the composite ecological packing column by 35-40%.

[0026] This invention discloses a system for treating overflow sewage. When the concentration of pollutants in the overflow sewage is high, micro-nano aeration rods inject pure oxygen nanobubbles into the water by switching the air source of the nanobubbles. The pure oxygen nanobubbles react with pyrite in the composite ecological packing column. This reaction generates hydroxyl radicals (·OH) with extremely strong oxidizing properties, thereby promoting the cleaning and regeneration of the surface of the remaining packing material in the composite ecological packing column, extending the service life of the composite ecological packing column, and reducing the replacement frequency and usage cost of the composite ecological packing column. In addition, the pure oxygen nanobubbles also provide stable and continuous dissolved oxygen for the discharged overflow sewage. The high dissolved oxygen content helps the remaining ammonia nitrogen in the overflow sewage to be oxidized into nitrate by microorganisms. At the same time, it can also stimulate and enhance the metabolic activity of aquatic organisms in the overflow sewage, thereby improving the self-purification capacity of the discharged overflow sewage.

[0027] The present invention provides a method for treating overflow sewage that can effectively remove sand and suspended solids (SS) from overflow sewage in combined sewer systems, and reduce pollutants such as chemical oxygen demand (COD), total phosphorus (TP), and ammonia nitrogen (NH3). Compared with traditional coagulation technology, the present invention increases the removal rates of suspended solids (SS), chemical oxygen demand (COD), total phosphorus (TP), and ammonia nitrogen (NH3) by 25-30%, 12-15%, 15-20%, and 70-80%, respectively, and reduces the hydraulic retention time by 25-30%. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of a system for treating overflow sewage according to the present invention;

[0029] Figure 2 yes Figure 1 Schematic diagram of the separation device;

[0030] Figure 3 This is a flowchart of a method for treating overflow sewage according to the present invention.

[0031] In the picture

[0032] Magnetic flocculation device 1, coagulation zone 11, water inlet 111, agitator 112, flocculation zone 12, flocculation enhancement tank 121;

[0033] Separation device 2, bubble generating device 21, micro-nano bubble generator 211, aeration rod 212, conveying pipe 213, magnetic adsorption device 22, magnetic bucket 221, drive pump 222, magnetic mud cleaning device 23, rotating belt 231, brush 232, magnetic mud scraper 233.

[0034] Magnetic mud separator 3, denitrification device 4, working zone 1 41, working zone 2 42, composite ecological packing column 43, micro-nano aeration rod 44. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0036] Example 1:

[0037] like Figure 1 As shown, this embodiment provides a system for treating overflow sewage from combined sewer systems. The system includes a magnetic flocculation device 1, a separation device 2 connected to the magnetic flocculation device 1, and a magnetic mud separator 3 and a denitrification device 4 that cooperate with the separation device 2.

[0038] like Figure 1 As shown, the magnetic flocculation device 1 is provided with a coagulation zone 11 and a flocculation zone 12. The coagulation zone 11 is provided with an inlet 111 for overflow sewage to pass through and an agitator 112 for mixing coagulant, impurities in overflow sewage and magnetic seeds into magnetic coagulants. The flocculation zone 12 is provided with a flocculation enhancement tank 121 for mixing flocculant and coagulants into magnetic coagulants. The coagulant is polyferric chloride, the magnetic seed is iron(III) oxide, and the flocculant is anionic polyacrylamide.

[0039] like Figures 1-3As shown, the separation device 2 includes a bubble generating device 21, a magnetic adsorption device 22 that cooperates with the bubble generating device 21, and a magnetic mud cleaning device 23 that cooperates with the magnetic adsorption device 22. The bubble generating device 21 includes a micro-nano bubble generator 211, an aeration rod 212 that cooperates with the micro-nano bubble generator 211, and a bubble delivery pipe 213 that connects the micro-nano bubble generator 211 and the aeration rod 212. The bubble generating device 21 adjusts the aeration rate of the micro-nano bubbles in a timely manner according to the overflow sewage volume and water quality changes. The air source of the micro-nano bubble generator 211 is air. The micro-nano bubble generator 211 generates micro-nano bubbles, which are input into the aeration rod 212 through the bubble delivery pipe 213 and then introduced into the separation device 2 for air flotation. The diameter of the micro-nano bubbles output by the aeration rod 212 is 50nm to 50μm, preferably 10μm, and then adheres to the magnetic flocs from the magnetic flocculation device 1.

[0040] like Figures 1-3 As shown, the magnetic adsorption device 22 includes a magnetic barrel 221 and a drive pump 222 for driving the magnetic barrel 221. The side of the cylindrical magnetic barrel 221 is evenly divided into three regions along the axial direction. Each region can generate a magnetic field when energized individually. Among them, two regions located below the liquid surface are the main working areas, which are energized and generate a magnetic field when working. The remaining region located above the liquid surface is not energized during operation to facilitate the operation of the magnetic sludge cleaning device 23. The drive pump 222 is a variable frequency pump, which can adjust the rotation speed of the magnetic barrel 221 in a timely manner according to the overflow sewage volume and water quality changes. The two regions below the liquid surface are energized during operation. A strong magnetic field will be generated. Due to the surface tension of the water, the magnetic bucket 221 will cause the water to flow laterally when it rotates, which will cause the magnetic flocs on the water surface to approach the magnetic bucket 221. At that time, the magnetic flocs suspended in the water will be quickly attracted to the magnetic bucket 221 under the combined action of magnetic force and buoyancy generated by micro-nano bubbles. As the magnetic bucket 221 rotates, when an area located below the liquid surface rotates to the liquid surface, the power in this area will be cut off and the magnetic field will disappear. The magnetic mud cleaning device 23 will clean the magnetic flocs adsorbed in this area into the magnetic mud separator 3. The overflow wastewater after adsorption will flow further to the denitrification device 4.

[0041] like Figures 1-3As shown, the magnetic mud cleaning device 23 is located directly above the magnetic bucket 221, including a rotating belt 231, a brush 232 mounted on the rotating belt 231, and a magnetic mud scraper 233 that cooperates with the brush 232. The ends of the brush 232 and the magnetic mud scraper 233 can both come into contact with the area of ​​the magnetic bucket 221 above the liquid surface. When the magnetic mud cleaning device 23 is working, the magnetic mud scraper 233 will first scrape the magnetic flocs adsorbed on the side of the magnetic bucket 221 from the side of the rotating magnetic bucket 221. Then, the brush 232, driven by the rotating belt 231, will collect the scraped magnetic flocs to one end of the magnetic bucket 221 and finally brush the magnetic flocs into the magnetic mud separator 3.

[0042] like Figures 1-3 As shown, the magnetic mud separator 3 is connected to the separation device 2 and the magnetic flocculation device 1 respectively. The magnetic mud separator 3 will separate the magnetic seeds and flocs from the magnetic flocs from the separation device 2, and then recover the magnetic seeds and return them to the magnetic flocculation device 1.

[0043] like Figure 1 , Figure 3 As shown, the denitrification device 4 is equipped with a working zone 41 and a working zone 42. Both working zones 41 and 42 are equipped with multiple sets of composite ecological packing columns 43 for adsorbing ammonia nitrogen in overflow sewage, and micro-nano aeration rods 44 are installed below the composite ecological packing columns 43. Working zones 41 and 42 can be used alternately. When one zone needs to be regenerated or the composite ecological packing column 43 needs to be replaced, the other zone is operated.

[0044] like Figure 1 , Figure 3 As shown, the composite ecological filler column 43 uses stainless steel as a frame, and the frame is filled with a variety of mixed fillers. The outer layer of the filler is wrapped with 150-200 mesh, preferably 160 mesh nylon mesh. The filler inside the composite ecological filler column 43 is mainly composed of modified green zeolite, rice husk charcoal, vermiculite and pyrite in a mass ratio of (70-85):(90-110):(100-120):(10-25), preferably 80:100:110:15; and the particle size of the modified green zeolite is 1-3 mm. The particle size of rice husk charcoal is 0.2-0.25 mm, preferably 0.22 mm; the particle size of vermiculite is 1-3 mm, preferably 2 mm; and the particle size of pyrite is 4-8 mm, preferably 6 mm. The modified green zeolite is prepared by pyrolyzing natural green zeolite at 250°C for 3 hours, followed by shaking in a 0.03%-0.05%, preferably 0.04% sodium citrate solution at a shaking speed of 200-300 r / min, preferably 250 r / min, for 6 hours.

[0045] like Figure 1 , Figure 3As shown, the micro-nano aeration rod 44 introduces a large number of micro-nano bubbles into the denitrification device 4. The micro-nano bubbles will flush the composite ecological packing column 43 from bottom to top, which alleviates the problem of suspended matter clogging the pores of the packing column and avoids the problem of reducing the working exchange capacity of the composite ecological packing column 43 due to clogging.

[0046] like Figure 1 , Figure 3 As shown, the air source for the micro-nano aeration rod 44 is either air or pure oxygen. When the composite ecological packing is working normally, the air source for the micro-nano aeration rod 44 is air. When the pollutant concentration in the overflow sewage is high, the air source for the micro-nano aeration rod 44 will be adjusted from air to pure oxygen. The pure oxygen nanobubbles will react with the pyrite in the composite ecological packing. This reaction can generate a small amount of highly oxidizing hydroxyl radicals (·OH), thereby promoting the cleaning and regeneration of the surface of the remaining packing in the composite ecological packing column 43, which will extend the service life of the packing column and reduce the number of replacements and the cost of use. In addition, the pure oxygen nanobubbles are stable air chambers with long-term stability, which can continuously provide oxygen to the effluent, thereby ensuring that the treated overflow sewage still has a continuous and high dissolved oxygen content after entering the aquatic ecosystem. The high dissolved oxygen content helps the remaining ammonia nitrogen in the overflow sewage to be oxidized into nitrate by microorganisms, and can also stimulate and enhance the metabolic activities of aquatic organisms, thereby improving the self-purification capacity of the receiving water body.

[0047] Example 2:

[0048] This embodiment provides a method for treating overflow sewage from combined sewer systems, including the system for treating overflow sewage from combined sewer systems described in Embodiment 1. The method includes the following steps:

[0049] (1) Retaining large particulate impurities in overflow sewage: Overflow sewage from combined sewer systems first passes through a screen and grit chamber, where larger suspended solids, floating objects, and gravel in the overflow sewage are all retained;

[0050] (2) Flocculation of small particulate impurities in overflow sewage: The intercepted overflow sewage first enters the coagulation zone 11 in the magnetic flocculation device 1. In the coagulation zone 11, coagulant and magnetic seeds are added and quickly stirred together with the overflow sewage. Under the action of coagulant, the suspended particulate matter and magnetic seeds in the overflow sewage will aggregate together to form magnetic coagulants. Then the coagulants enter the flocculation zone 12 along with the overflow sewage. After adding flocculant, after being slowly stirred by the flocculation enhancement tank 121, magnetic coagulants are formed.

[0051] (3) Separation of small particulate impurities in overflow sewage: Small particulate impurities that form magnetic flocs enter the separation device 2 with the overflow sewage. A large number of micro-nano bubbles generated by the bubble generator 21 will adhere to the magnetic flocs. The magnetic barrel 221 in the magnetic adsorption device 22 is powered on and forms a strong magnetic field. The magnetic flocs suspended in the overflow sewage are quickly attracted to the magnetic barrel 221 under the combined action of magnetic force and buoyancy generated by micro-nano bubbles. The magnetic flocs adsorbed on the magnetic barrel 221 are cleaned to the magnetic mud separator 3 by the magnetic mud cleaning device 23. The overflow sewage will enter the denitrification device 4.

[0052] (4) Removal of ammonia nitrogen from overflow sewage: After the overflow sewage enters the denitrification device 4, the composite ecological packing column 43 immersed in the micro-nano bubble water will adsorb the ammonia nitrogen in the overflow sewage, and then the nano bubbles will be discharged into the ecosystem along with the overflow sewage.

[0053] The present invention provides a method for treating overflow sewage that can effectively remove sand and suspended solids (SS) from overflow sewage in combined sewer systems, and reduce pollutants such as chemical oxygen demand (COD), total phosphorus (TP), and ammonia nitrogen (NH3). Compared with traditional coagulation technology, the present invention increases the removal rates of suspended solids (SS), chemical oxygen demand (COD), total phosphorus (TP), and ammonia nitrogen (NH3) by 25-30%, 12-15%, 15-20%, and 70-80%, respectively, and reduces the hydraulic retention time by 25-30%.

Claims

1. A system for treating combined sewer overflow wastewater, comprising: The system comprises a magnetic flocculation device, a separation device connected with the magnetic flocculation device, and a magnetic sludge separator and a denitrification device matched with the separation device; The magnetic flocculation device can make small-particle suspended matters in the overflow sewage into magnetic flocculation by adding coagulants, magnetic seeds and flocculants into the overflow sewage; The separation device comprises a bubble generating device, a magnetic adsorption device matched with the bubble generating device, and a magnetic sludge cleaning device matched with the magnetic adsorption device, the bubble generating device can output micro-nano bubbles with a diameter of 50 nm-50 μm into the separation device, the magnetic adsorption device comprises a magnetic barrel for adsorbing magnetic flocculation, the magnetic sludge cleaning device comprises a magnetic sludge scraper for scraping off the magnetic flocculation on the magnetic barrel, and a brush matched with the magnetic sludge scraper; The magnetic sludge separator can separate magnetic seeds and flocculation in the magnetic flocculation; The denitrification device comprises a plurality of composite ecological filler columns and micro-nano aeration rods matched with the composite ecological filler columns, the filler in the composite ecological filler column is composed of modified green zeolite, rice husk carbon, vermiculite and pyrite at a mass ratio of (70-85):(90-110):(100-120):(10-25), and the air source of the micro-nano aeration rod is one of air or pure oxygen; The bubble generating device comprises a micro-nano bubble generator, an aeration rod matched with the micro-nano bubble generator, and a bubble conveying pipe connecting the micro-nano bubble generator and the aeration rod; The side of the magnetic barrel is evenly divided into three regions along the axial direction, and a magnetic field can be obtained after individual power supply; The particle size of the modified green zeolite is 1-3 mm, the particle size of the rice husk carbon is 0.2-0.25 mm, the particle size of the vermiculite is 1-3 mm, and the particle size of the pyrite is 4-8 mm; The modified green zeolite is prepared by pyrolyzing natural green zeolite at a high temperature of 250°C for 3 h, and then oscillating in a 0.03%-0.05% sodium citrate solution at an oscillation speed of 200-300 r / min for 6 h.

2. The system for treating combined sewer overflow wastewater of claim 1, wherein, The outer layer of the filler in the composite ecological filler column is wrapped with a 150-200 mesh nylon net.

3. The system for treating combined sewer overflow wastewater of claim 1, wherein, The magnetic flocculation device comprises a coagulation zone and a flocculation zone, and the flocculation zone is further provided with a flocculation strengthening barrel.

4. The system for treating combined sewer overflow wastewater of claim 1, wherein, The magnetic sludge cleaning device comprises a rotating belt for driving the brush.

5. A method for treating overflow sewage of a combined sewer, comprising the system for treating overflow sewage of a combined sewer according to any one of claims 1-4, the method comprising the following steps: (1) trapping large-particle impurities in the overflow sewage: the overflow sewage of the combined sewer is first passed through a grid and a grit chamber, and larger suspended matters, floating matters and sand in the overflow sewage are all trapped; (2) flocculation of small particles in the overflow sewage: the intercepted overflow sewage first enters the coagulation zone of the magnetic flocculation device, a coagulant and magnetic seeds are added in the coagulation zone and are rapidly stirred with the overflow sewage, under the action of the coagulant, the suspended particles in the overflow sewage and the magnetic seeds are gathered together to form magnetic coagulation; then the coagulation is mixed with the overflow sewage into the flocculation zone, after adding flocculant, and then slowly stirring through the flocculation strengthening barrel, magnetic flocculation is formed; (3) separation of small particles in the overflow sewage: the small particles forming the magnetic flocculation are mixed with the overflow sewage into the separation device, a large number of micro-nano bubbles generated by the bubble generating device are adhered to the magnetic flocculation, the magnetic barrel in the magnetic adsorption device is electrified and forms a strong magnetic field, the suspended magnetic flocculation in the overflow sewage is quickly attracted to the magnetic barrel under the joint action of the magnetic force and the buoyancy generated by the micro-nano bubbles, the magnetic flocculation adsorbed on the magnetic barrel is cleaned by the magnetic sludge cleaning device to the magnetic sludge separator, and the overflow sewage enters the denitrification device; (4) removal of ammonia nitrogen in the overflow sewage: after the overflow sewage enters the denitrification device, the composite ecological filler column immersed in the micro-nano bubble water will adsorb the ammonia nitrogen in the overflow sewage, and then the nano bubbles will be discharged with the overflow sewage into the ecological system.

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