Simultaneous denitrification and phosphorus removal rainwater biological retention facility capable of coping with heavy rainfall

Abstract

The application discloses a synchronous denitrification and dephosphorization rainwater biological retention facility capable of simultaneously coping with heavy rainfall, relates to the technical field of sponge city construction, and comprises a pool body, wherein an overflow layer, a covering layer, a filter layer, an upper drainage layer, a biochar layer, a submerged layer and a lower drainage layer are sequentially arranged in the pool body from top to bottom; the upper drainage layer and the lower drainage layer are each provided with a drainage pipe; the water outlet of the lower drainage pipe is lifted to be flush with the top of the submerged layer; the submerged layer comprises iron shavings and quartz sand materials; an overflow well is arranged in the pool body; the water outlets of the upper drainage pipe and the lower drainage pipe are both connected into the overflow well; a water level control valve is arranged in the pool body and used for controlling the opening and closing of the water outlet of the upper drainage pipe. The application can automatically adjust the water outlet path according to the rainwater flow, overcomes the problem that dissolved oxygen in rainwater runoff breaks through the submerged layer and reduces the denitrification and dephosphorization performance of the facility under the condition of heavy rainfall, improves the removal capacity of the facility for dissolved pollutants, and has a longer service life.

Description

Technical Field

[0001] This invention relates to the field of sponge city construction technology, and in particular to a rainwater biological retention facility that can simultaneously denitrify and remove phosphorus from rainwater and cope with heavy rainfall. Background Technology

[0002] Eutrophication has become a global problem, potentially leading to algal blooms, algal expansion, and water quality deterioration. A key contributing factor is the increased transport of nutrients in stormwater runoff against the backdrop of rising urbanization and accelerating climate change.

[0003] Low-impact development (LID) infrastructure such as bioretention ponds has been widely applied in watersheds to control runoff pollution. Traditional sand-based bioretention ponds achieve stable removal of particulate pollutants through physical processes such as filtration and sedimentation. However, due to their unreasonable structure and limited functionality of the packing material, they are still unable to effectively reduce dissolved pollutants such as organic matter, ammonia nitrogen, nitrate nitrogen, and phosphate in stormwater runoff. Existing research mainly improves the removal efficiency of dissolved pollutants in bioretention ponds through two methods: structural modification and substrate modification.

[0004] Structural improvements typically involve raising the height of the effluent pipe to functionally separate aerobic and anoxic zones within the facility, providing a suitable growth environment for nitrifying and denitrifying bacteria and extending the hydraulic retention time, thereby optimizing the removal of dissolved pollutants. However, structural improvements also have limitations. Bioretention facilities are usually designed to handle rainfall with a 0-1 year return period. When rainfall is heavy, insufficient drainage capacity can easily lead to flooding of the facility and surrounding areas, damaging vegetation and causing waterlogging risks. More importantly, rainwater runoff carries large amounts of dissolved oxygen into the flooded area, disrupting the original anoxic environment and affecting the microbial community structure, resulting in a significant reduction in the facility's denitrification performance.

[0005] Biochar is a porous material produced by the pyrolysis of biomass. Rich in various active groups, its surface possesses a slight polarity, enabling it to adsorb nonpolar molecules such as O2 and CO2. Furthermore, phenolic groups and other functional groups on the biochar surface can react with O2, reducing the dissolved oxygen content in rainwater runoff. The abundant pore structure of biochar not only provides numerous active sites for adsorption and reaction but also, by extending the mass transfer path of gas molecules within the bioretention facility and increasing mass transfer resistance, hinders O2 from entering the flooded area during the dry season, thus effectively protecting the oxygen-deficient environment of the flooded area.

[0006] Matrix improvement refers to the addition of functional fillers to facilities. Some studies achieve rapid adsorption of organic matter and ammonia nitrogen by adding highly adsorbent media such as biochar and vermiculite, or promote heterotrophic or autotrophic denitrification processes to remove nitrate nitrogen by adding organic or inorganic electron donors such as wood chips and sulfur. Other studies promote the flocculation and precipitation of dissolved phosphorus by adding aluminum-based or iron-based water treatment residues. However, most fillers can only remove single pollutants. In addition, adding solid carbon sources poses risks of organic matter leakage and facility blockage, which can easily lead to secondary water pollution and increased facility operation and maintenance costs. Adding sulfur can cause a rapid decrease in the system pH and severe sulfate leaching, affecting microbial growth and metabolism and the system's redox potential, resulting in poor water treatment performance.

[0007] Iron shavings are a type of zero-valent iron (ZVFe). As a common industrial byproduct, they were previously often discarded or landfilled as waste, leading to resource waste and environmental pollution. ZVFe possesses a certain electron-donating capacity, allowing it to participate in the nitrogen cycle under microbial drive. Furthermore, the autotrophic denitrification process of iron produces low-product byproducts and poses no risk of clogging, making it suitable for rainwater denitrification. In addition, the Fe produced from the dissolution of ZVFe... 2+ It can be further oxidized to Fe 3+ This facilitates the flocculation and precipitation of dissolved phosphorus in rainwater runoff. Compared to traditional methods, zero-valent iron provides a simpler and more efficient solution. However, when dealing with large amounts of rainfall, O2 in the rainwater, acting as an effective oxidant, reacts with zero-valent iron, causing Fe... 3+ Excessive release, excessive Fe 3+ Subsequently, under neutral conditions in the rainwater ring, rapid hydrolysis and precipitation occur, resulting in passivation of the zero-valent iron surface and excessive turbidity and color in the water, which is detrimental to the denitrification process and the effectiveness of rainwater treatment. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a simultaneous nitrogen and phosphorus removal rainwater biological retention facility that can simultaneously cope with heavy rainfall. This facility solves the problem of dissolved oxygen in rainwater runoff disrupting the originally oxygen-deficient environment under conditions of heavy rain, torrential rain, and extreme rainfall, and effectively removes organic pollutants, dissolved nitrogen, and dissolved phosphorus from rainwater runoff.

[0009] In order to achieve the objective of this invention, the following solution is proposed:

[0010] A rainwater bioretention facility capable of simultaneously denitrifying and removing phosphorus from rainwater and coping with heavy rainfall, comprising a pool body.

[0011] The pool contains, from top to bottom, an overflow layer, a covering layer, a filter layer, an upper drainage layer, a biochar layer, a submerged layer, and a lower drainage layer. The upper drainage layer contains an upper drainage pipe, and the lower drainage layer contains a lower drainage pipe. Both the upper and lower drainage pipes have multiple inlet holes on their side walls. The outlet of the lower drainage pipe is raised to be level with the top of the submerged layer. The submerged layer contains iron shavings and quartz sand.

[0012] The pool is equipped with an overflow well with a cover; the outlets of the upper and lower drainage pipes are connected to the overflow well, and the water from the overflow well flows into the municipal stormwater network.

[0013] The pool is equipped with a water level control valve to control the opening and closing of the upper drainage pipe outlet.

[0014] Furthermore, a 5cm to 10cm clearance is provided between the overflow well opening and the top of the pool; the well cover is either a grid or a vertical structure.

[0015] Furthermore, the water level control valve includes a pilot valve and a main valve. The main valve is located at the outlet of the upper drainage pipe, and the pilot valve is located in the overflow layer. The pilot valve is used to control the opening and closing of the main valve.

[0016] Furthermore, the water level H controlled by the upper drainage pipe is determined according to the following formula:

[0017]

[0018] In the formula: The overall permeability of the cover layer and filter layer; Design water accumulation time; For the hydraulic load of the facility, ,in A For the area of ​​facility penetration, For design runoff, , The comprehensive runoff coefficient of the catchment area. For the area served by the facilities, To design the intensity of the rainstorm, , The design return period is defined as a value ranging from 5 to 30 years. For rainfall duration, A1, c, b, and n are local parameters;

[0019] The overflow discharge capacity is verified according to the following formula:

[0020]

[0021] In the formula: The actual water-passing area of ​​the manhole cover (12) , The number of holes in the width direction. The length of the grate hole. Where C is the width of the grate opening and C is the orifice coefficient. It is the acceleration due to gravity. The water depth above the wellhead is [missing information]. The blocking coefficient is used for calculation. hour, The maximum return period is defined as 30 to 100 years. This refers to the overall penetration rate of the facility.

[0022] Furthermore, the filter layer contains biochar and quartz sand materials, which are uniformly mixed and filled in a volume ratio of (15~25):(75~85). The biochar particle size range is 0mm~2mm, the filter layer height is 30cm~50cm, and the permeability is not less than 200mm / h.

[0023] Furthermore, the biochar layer contains biochar material with a particle size range of 0mm to 1mm, a biochar layer height of 5cm to 10cm, and a permeability of not less than 200mm / h.

[0024] Furthermore, the raw material for biochar preparation is agricultural waste, including hardwood branches and nut shells. The raw material is prepared by slow pyrolysis at a temperature of 300℃~600℃ under limited oxygen conditions, with a heating rate of 0.01℃~2℃ / s.

[0025] Furthermore, the iron shavings and quartz sand materials in the flooding layer are uniformly mixed and filled in a volume ratio of (15~25):(75~85). The height of the flooding layer is 30cm~40cm, the permeability is not less than 200mm / h, and the overall permeability of the facility is 200mm / h~600mm / h.

[0026] Furthermore, the thickness of the iron shavings ranges from 0mm to 2mm, and the width ranges from 1cm to 4cm.

[0027] Furthermore, the quartz sand includes four particle size ranges: 10-16 mesh, 26-40 mesh, 40-170 mesh, and 80-120 mesh. When used as a filter layer, the volume ratio is (20-30):(20-30):(20-30):(20-30), and when used as a flooding layer, the volume ratio is (0-30):(15-20):(15-20):(20-50).

[0028] The working principle of this invention is as follows: When dealing with rainfall with a return period of 1 to 5 years, the upper drainage pipe does not operate, and the rainwater runoff flows sequentially through the facility cover layer, filter layer, upper drainage layer, biochar layer, and submerged layer, and then flows into the overflow well through the lower drainage pipe; when dealing with rainfall with a return period of 5 to 30 years, the higher rainwater inflow causes water to accumulate in the facility overflow layer during the middle and later stages of rainfall. When the water level reaches the control level, it will trigger the pilot valve installed in the overflow layer and control the main valve installed at the outlet of the upper drainage pipe to open. At this time, under the effect of water flow short-circuiting, the rainwater runoff passes through the facility filter layer and directly enters the overflow well through the upper drainage pipe, no longer flowing through the submerged layer; when dealing with extreme rainfall conditions with a return period of more than 30 years, the water depth in the facility quickly reaches the top elevation of the overflow well, and the rainwater runoff enters the overflow well directly without passing through the interior of the facility.

[0029] The beneficial effects of this invention are as follows: This invention provides three water discharge methods: upper drainage pipe discharge, lower drainage pipe discharge, and overflow discharge, which can automatically adjust the water discharge path of the bioretention facility according to changes in rainwater flow. When dealing with light to moderate rain, rainwater runoff carries a large amount of pollutants to the facility's filter layer. After being intercepted and precipitated by the filter layer and adsorbed by biochar, particulate pollutants, dissolved organic matter, and ammonia nitrogen are effectively removed. Subsequently, the rainwater enters the facility's flooding layer, where iron shavings dissolve to produce Fe. 2+ Electron-supported autotrophic denitrification nitrogen removal, while Fe 2+ Fe formed by oxidation 3+ Phosphorus is effectively removed through adsorption and complexation. Clean rainwater flows into the overflow well through the lower drainage pipe. After the rainfall ends, some residual nitrate nitrogen and dissolved phosphorus will continue to react with iron shavings in the flooded layer. When dealing with heavy rain, the rainwater flow path is the same as during light and moderate rain. At this time, the biochar layer in the facility can reduce dissolved oxygen in the rainwater runoff through O2 adsorption and chemical reaction processes. After the rainfall ends, the O2 desorbed by the biochar will diffuse back into the atmosphere, thus effectively protecting the oxygen-deficient environment of the flooded layer in the long term. When dealing with torrential rain, the effect of the facility matrix on reducing dissolved oxygen in the rainwater runoff is very limited. At this time, the concentration of pollutants in the rainwater runoff is relatively low. After the rainwater is treated by the filter layer to remove particulate pollutants, dissolved organic matter and ammonia nitrogen, it flows into the overflow well. When dealing with extreme rainfall conditions, the rainwater runoff flows directly into the overflow well after simple screening of large particulate pollutants by the manhole cover grating. By adjusting the opening of the upper drainage pipe to control the water level and the height of the overflow well, the facility can adapt to different rainfall conditions, thereby effectively protecting the flooded layer of the facility, enabling the facility to effectively remove nitrogen and phosphorus, and having a longer service life. Attached Figure Description

[0030] Figure 1 A schematic diagram of the internal structure of the bioretention facility is shown. Detailed Implementation

[0031] like Figure 1As shown, the present invention provides a rainwater biological retention facility that can simultaneously cope with heavy rainfall and remove nitrogen and phosphorus, including a pool body 13.

[0032] The pool body 13 is arranged from top to bottom as follows: overflow layer 1, covering layer 2, filter layer 3, upper drainage layer 4, biochar layer 5, submerged layer 6, and lower drainage layer 7. The upper drainage layer 4 is equipped with an upper drainage pipe 8, and the lower drainage layer 7 is equipped with a lower drainage pipe 10. The side walls of the upper drainage pipe 8 and the lower drainage pipe 10 are equipped with multiple water inlets. The outlet of the lower drainage pipe 10 is raised to be flush with the top of the submerged layer 6.

[0033] Figure 1 In the middle, the pool body 13 is equipped with an overflow well 11, which is constructed at the lowest elevation of the cover layer 2 according to the actual situation. The elevation of the overflow well 11 opening should be set according to the local rainfall conditions, and the difference between the elevation of the overflow well 11 and the cover layer 2 is the height of the overflow layer 1. A 5cm to 10cm clearance is reserved between the well opening and the top of the pool body 13. The well opening is equipped with a manhole cover 12, which is either a grid design or a vertical design, to prevent leaves, floating garbage and other foreign objects from accumulating at the well opening during heavy rain, thus preventing the overflow well 11 from being obstructed. The outlets of the upper drainage pipe 8 and the lower drainage pipe 10 are both connected to the overflow well 11, and the water from the overflow well 11 flows into the municipal stormwater pipe network.

[0034] Figure 1 In the middle, the pool body 13 is equipped with a water level control valve 9, which includes a pilot valve 91 and a main valve 92. The main valve 92 is located at the outlet of the upper drain pipe 8, and the pilot valve 91 is located in the overflow layer 1. The pilot valve 91 is used to control the opening and closing of the main valve 92.

[0035] Figure 1 In the design, a grass and stone buffer zone 14 is provided around the pool body 13. Its purpose is to reduce the flow velocity of rainwater runoff, disperse the flow rate of rainwater runoff, and intercept large foreign objects, thereby reducing the erosion and damage of the pool body 13 caused by rainwater runoff and preventing blockage of the pool body 13 due to the accumulation of large foreign objects, thus extending the service life of the facility. To ensure stability, the slope of the grass and stone buffer zone 14 is less than 1:3, and it is naturally connected with the facility and the surrounding greenery.

[0036] The water level H controlled by the upper drainage pipe 8 is determined according to the following formula:

[0037] First, determine the design runoff based on local rainfall conditions. The calculation formula is: ,in, The comprehensive runoff coefficient of the catchment area. For the area served by the facilities, To design the intensity of the rainstorm, , For the design recurrence period, For rainfall duration, A1, c, b, and n are local parameters.

[0038] Then, based on the design runoff... Determine the control water level H of the upper drainage pipe 8 and the height of the overflow layer 1. When calculating H, It should be the minimum runoff generated by the catchment area when rainwater flows out of the upper drainage pipe 8. The timeframe is selected from 5 to 30 years; when calculating the height of overflow layer 1, It should be the maximum runoff generated when the entire catchment area of ​​the watershed participates in the runoff. The maximum recurrence period is selected from 30 to 100 years.

[0039] Hydraulic load of facilities at different design runoff rates According to the formula The calculation is performed, where A is the area of ​​the facility's penetration.

[0040] Control water level H according to formula Calculations are performed, in which, The overall permeability of the facility's cover layer 2 and filter layer 3 can be obtained after selecting the type and ratio of the facility's filler material in the early stages. The design water accumulation time is calculated. Taking a 10-year return period 1-hour rainfall event in Chongqing as an example, assuming the catchment area is 20 times the facility area, the comprehensive runoff coefficient of the catchment area is selected as 0.7, the overall permeability of the facility's covering layer 2 and filter layer 3 is 300 mm / h, and the water accumulation time is 10 minutes, the calculated hydraulic load of the facility is 628.03 mm. 3 / mm 2 •h, the controlled water level is 117.47mm, take 120mm. Overflow layer 1 height According to the formula Perform calculations. The value should be in the range of 10cm to 30cm.

[0041] In this embodiment, the overflow well 11 is constructed of brick, and the wellhead is a vertical single-grate rainwater inlet. For specific implementation, the overflow well 11 and wellhead can be selected according to the national standard drawing 16S518 "Rainwater Inlets," and the formula should be followed. Verify the wellhead dimensions, among which, This refers to the actual water-passing area of ​​the manhole cover (12). , The number of holes in the width direction. The length of the grate hole. Where is the width of the grate opening, and C is the opening coefficient. When the grate opening has rounded corners, C is 0.6; when the grate opening has square corners, C is 0.8. For gravitational acceleration, take 9.8m. 2 / s, The water depth above the wellhead is [missing information]. The blocking coefficient is... This refers to the overall penetration rate of the facility.

[0042] In this embodiment, the substrate of the covering layer 2 is gravel with a particle size of 1cm to 3cm, and the height of the covering layer 2 is 5cm to 10cm. Its main purpose is to protect the structure of the facility and prevent low-density substrates such as biochar and quartz sand from being washed away by the water flow. At the same time, it can intercept large particulate pollutants in rainwater runoff and reduce the risk of facility blockage. In specific implementation, materials such as pebbles, gravel, and wood chips with a particle size of 1cm to 3cm can also be used.

[0043] Filter layer 3 comprises biochar and quartz sand, uniformly mixed and packed in a volume ratio of (15~25):(75~85). The biochar particle size ranges from 0mm to 2mm, and the quartz sand includes four particle size ranges: 10 mesh~16 mesh, 26 mesh~40 mesh, 40 mesh~170 mesh, and 80 mesh~120 mesh, uniformly mixed in a volume ratio of (20~30):(20~30):(20~30):(20~30). The height of filter layer 3 is 30cm~50cm, and the permeability should not be less than 200mm / h.

[0044] The filter layer 3 is planted with drought-resistant, flood-resistant plants with well-developed root systems to increase the removal of pollutants and meet landscape requirements. Native plants are given priority, and the planting density can be appropriately increased compared with the conventional planting density to increase the green area and enhance the ornamental value.

[0045] Biochar layer 5 contains biochar material with a particle size range of 0mm to 1mm, a height of 5cm to 10cm, and a permeability of not less than 200mm / h.

[0046] The raw materials used for biochar preparation are agricultural waste such as hardwood branches and nut shells. The preparation conditions are slow pyrolysis at 300℃~600℃ in a nitrogen atmosphere (heating rate 0.01℃ / s~2℃ / s).

[0047] The flooding layer 6 comprises iron shavings and silica sand, uniformly mixed and filled in a volume ratio of (15~25):(75~85). The iron shavings have a thickness ranging from 0mm to 2mm and a width ranging from 1cm to 4cm. The silica sand comprises four particle size ranges: 10 mesh to 16 mesh, 26 mesh to 40 mesh, 40 mesh to 170 mesh, and 80 mesh to 120 mesh, uniformly mixed in a volume ratio of (0~30):(15~20):(15~20):(20~50). The flooding layer 6 has a height of 30cm to 40cm and a permeability not less than 200mm / h.

[0048] The upper drainage layer 4 and the lower drainage layer 7 are made of gravel with a particle size of 1cm to 2cm to prevent the collapse of biochar, quartz sand and other substrates from causing damage to the facility structure and blockage of drainage pipes. The height of the upper drainage layer 4 and the lower drainage layer 7 is 5cm to 15cm.

[0049] The overall permeability range of the facility should be 200mm / h to 600mm / h. This permeability range ensures the water conveyance capacity of the facility while achieving a good effect on the removal of pollutants from rainwater runoff.

[0050] Working principle of the invention:

[0051] When dealing with light to moderate rain, rainwater runoff washes over the surface and carries a large amount of pollutants into the facility. At this time, the hydraulic load of the facility is less than the overall permeability of the facility, and water will not accumulate in the overflow layer 1. The rainwater runoff entering the facility first flows through the cover layer 2, where the gravel, pebbles and other fillers can effectively trap large particulate pollutants.

[0052] During light to moderate rain, rainwater flows into filter layer 3 after passing through cover layer 2. The small-diameter quartz sand and biochar filler in filter layer 3 filter out small particulate pollutants. Simultaneously, the cationic adsorption capacity of biochar allows it to rapidly adsorb dissolved organic pollutants and ammonia nitrogen carried by the rainwater. Biochar also releases appropriate nutrients to support plant growth and rapid microbial development, and its porous structure is conducive to microbial colonization. Through the synergistic effects of biochar adsorption, plant transformation, and microbial transformation, organic pollutants and ammonia nitrogen in rainwater runoff can be effectively removed by the filter layer.

[0053] During light to moderate rain, rainwater flows through the cover layer 2, filter layer 3, upper drainage layer 4, and biochar layer 5 into the flooded layer 6. Because the outlet of the lower drainage pipe 10 is raised to the top height of the flooded layer 6, the flooded layer 6 remains submerged, providing a favorable environment for denitrification. At this time, iron shavings continuously supply electrons and remove nitrate nitrogen through an iron autotrophic denitrification process mediated by microorganisms. Simultaneously, Fe produced from the dissolution of iron shavings... 3+ It can also effectively remove phosphorus through adsorption and complexation. Finally, the treated clean rainwater flows into the overflow well 11 through the lower drainage pipe 10.

[0054] During heavy rain, the hydraulic load of the facility remains less than the overall permeability of the facility, and the rainwater flow path within the facility is consistent with that during light and moderate rain. Before entering the inundation layer 6, the rainwater runoff enters the biochar layer 5. At this time, the biochar layer 5 can reduce the dissolved oxygen in the rainwater runoff through O2 adsorption and chemical reaction processes. After the rainfall ends, the O2 desorbed by the biochar is redispersed into the atmosphere, thus effectively protecting the oxygen-deficient environment of the inundation layer 6 in the long term.

[0055] During heavy rain, the hydraulic load of the facility exceeded its overall permeability, causing flooding to begin in overflow layer 1. The designed water accumulation time was t... pSubsequently, the pollutant concentration of the incoming rainwater runoff is relatively low. At this point, the water depth of overflow layer 1 reaches the control level, triggering the pilot valve 91 installed in overflow layer 1. This controls the opening of the main valve 92 installed in the upper drainage pipe 8. After the rainwater runoff passes through the filter layer 3 to remove particulate pollutants, dissolved organic matter, and ammonia nitrogen, the outflow flows directly into the overflow well 11 through the upper drainage pipe 8 under the effect of water flow short-circuiting. Since the effect of the facility matrix on reducing dissolved oxygen in rainwater runoff is very limited during heavy rain, rainwater runoff no longer passes through the flood layer 6 to protect the oxygen-deficient environment of the flood layer 6.

[0056] Under extreme rainfall conditions, the hydraulic load of the facility far exceeds its overall permeability, causing the water depth in overflow layer 1 to increase rapidly. The facility needs to drain water quickly to prevent root rot caused by rainwater accumulation and road flooding. At this time, water in overflow layer 1 above the overflow well 11 flows directly into the overflow well 11 after large particulate pollutants are removed by the well cover 12. Water below the well opening is treated by the filter layer 3 and then flows into the overflow well 11 through the upper drainage pipe 8.

[0057] When the water depth in the overflow layer 1 is lower than the control water level, the pilot valve 91 drives the main valve 92 of the upper drainage pipe 9 to close, and the facility resumes water discharge from the lower drainage pipe 10.

[0058] The above embodiments are only used to illustrate the technical concept and features of the present invention, and are not intended to be unique or to limit the present invention. Those skilled in the art should understand that various changes or equivalent substitutions made to the present invention without departing from its scope are all within the protection scope of the present invention.

Claims

1. A simultaneous nitrogen and phosphorus removal rainwater biological retention facility capable of coping with heavy rainfall, characterized in that, Including the pool body (13); The pool body (13) is arranged from top to bottom as follows: overflow layer (1), covering layer (2), filter layer (3), upper drainage layer (4), biochar layer (5), submerged layer (6) and lower drainage layer (7). The upper drainage layer (4) is provided with an upper drainage pipe (8), and the lower drainage layer (7) is provided with a lower drainage pipe (10). The side walls of the upper drainage pipe (8) and the lower drainage pipe (10) are provided with multiple water inlets. The outlet of the lower drainage pipe (10) is raised to be flush with the top of the submerged layer (6). The submerged layer (6) contains iron shavings and quartz sand materials. An overflow well (11) is provided inside the pool body (13), and a well cover (12) is installed at the well opening; the outlets of the upper drainage pipe (8) and the lower drainage pipe (10) are connected to the overflow well (11), and the water outlet of the overflow well (11) flows into the municipal rainwater pipe network; The pool body (13) is equipped with a water level control valve (9) to control the opening and closing of the outlet of the upper drainage pipe (8); The water level control valve (9) includes a pilot valve (91) and a main valve (92). The main valve (92) is located at the outlet of the upper drainage pipe (8), and the pilot valve (91) is located in the overflow layer (1). The pilot valve (91) is used to control the opening and closing of the main valve (92). The water level H controlled by the upper drainage pipe (8) is determined according to the following formula: In the formula: The overall permeability of the cover layer (2) and the filter layer (3); Design water accumulation time; For the hydraulic load of the facility, ,in A For the area of ​​facility penetration, For design runoff, , The comprehensive runoff coefficient of the catchment area. For the area served by the facilities, To design the intensity of the rainstorm, , The design return period is defined as a value ranging from 5 to 30 years. For rainfall duration, A1, c, b, and n are local parameters; The overflow discharge capacity of the overflow well (11) is verified according to the following formula: In the formula: The actual water-passing area of ​​the manhole cover (12) , The number of holes in the width direction. The length of the grate hole. Where C is the width of the grate opening and C is the orifice coefficient. It is the acceleration due to gravity. The water depth above the wellhead is [missing information]. The blocking coefficient is used for calculation. hour, The maximum return period is defined as 30 to 100 years. For the overall penetration rate of facilities; The filter layer (3) contains biochar and quartz sand materials, which are uniformly mixed and filled in a volume ratio of (15~25):(75~85). The biochar particle size range is 0mm~2mm, the filter layer (3) height is 30cm~50cm, and the permeability is not less than 200mm / h. The biochar layer (5) contains biochar material with a biochar particle size range of 0 mm to 1 mm, a biochar layer (5) height of 5 cm to 10 cm, and a permeability of not less than 200 mm / h; The iron shavings and quartz sand materials of the flooding layer (6) are uniformly mixed and filled in a volume ratio of (15~25):(75~85). The height of the flooding layer (6) is 30cm~40cm, the permeability is not less than 200mm / h, and the overall permeability range of the facility is 200mm / h~600mm / h. Quartz sand includes four particle size ranges: 10 mesh to 16 mesh, 26 mesh to 40 mesh, 40 mesh to 170 mesh and 80 mesh to 120 mesh. When used in filter layer (3), the volume ratio is (20 to 30): (20 to 30): (20 to 30): (20 to 30): (20 to 30). When used in flooding layer (6), the volume ratio is (0 to 30): (15 to 20): (15 to 20): (20 to 50). When dealing with rainfall with a return period of 1 to 5 years, the upper drainage pipe (8) is not in operation. Rainwater runoff flows sequentially through the facility cover layer (2), filter layer (3), upper drainage layer (4), biochar layer (5) and flooding layer (6), and then flows into the overflow well (11) through the lower drainage pipe (10). When dealing with rainfall with a return period of 5 to 30 years, the pilot valve (91) will be triggered when the water level reaches the control level, and then the main valve (92) will be opened. The rainwater runoff will pass through the facility filter layer (3) and then directly enter the overflow well (11) through the upper drainage pipe (8). When dealing with extreme rainfall conditions with a return period of more than 30 years, rainwater runoff enters the overflow well directly without passing through the interior of the facility (11).

2. The rainwater bioretention facility for simultaneous nitrogen and phosphorus removal, capable of coping with heavy rainfall, as described in claim 1, is characterized in that... The overflow well (11) has a 5cm~10cm extra height reserved from the wellhead to the top of the pool body (13); the well cover (12) is a grid or a vertical structure.

3. The rainwater bioretention facility for simultaneous nitrogen and phosphorus removal, capable of coping with heavy rainfall, as described in claim 1, is characterized in that... The raw material for biochar preparation is agricultural waste, including hardwood branches and nut shells. The raw material is prepared by slow pyrolysis at a temperature of 300℃~600℃ under limited oxygen conditions, with a heating rate of 0.01℃~2℃ / s.

4. The rainwater bioretention facility for simultaneous nitrogen and phosphorus removal, capable of coping with heavy rainfall, as described in claim 1, is characterized in that... The thickness of the shavings ranges from 0mm to 2mm, and the width ranges from 1cm to 4cm.

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