Surface runoff cascade treatment system and ecological purification method

Abstract

The application relates to a surface runoff cascade treatment system and an ecological purification method. The surface runoff cascade treatment system comprises a primary filtration unit, two or more deep purification units and a phosphorus removal unit which are connected in cascade along a natural terrain; the water outlet end and the water inlet end of two adjacent units are connected through a cascade baffling drop structure; the cascade baffling drop structure comprises one or more drainage openings of different heights arranged at the water outlet end, and each drainage opening can be opened and closed as required. The system is coupled with three systems of structured cascade reoxygenation, adjustable lag storage purification operation mode and ecological-engineering coupling of plant root systems and fillers, and the three systems are coupled with each other to solve the core defects of the prior art from the structure.

Description

Technical Field

[0001] This article relates to runoff ecological purification technology, particularly a surface runoff cascade treatment system and ecological purification method. Background Technology

[0002] River and lake buffer zones, as key ecological engineering measures for intercepting surface runoff and reducing non-point source pollution, have been widely used in the field of water environment management. Their traditional form mainly relies on vegetation strips of a certain width, purifying runoff pollutants through soil infiltration, plant absorption, and microbial degradation. However, traditional vegetation buffer zones suffer from bottlenecks in practical applications, including limited purification efficiency, large land area requirements, and unstable removal of dissolved pollutants (especially ammonia nitrogen), making it difficult to meet increasingly stringent water quality requirements for receiving water bodies.

[0003] To improve purification efficiency, existing technologies have developed various enhanced buffer zones or constructed wetland structures, such as filler-enhanced subsurface flow buffer zones and modular constructed wetlands. These technologies enhance pollutant retention capacity by filling ditches or pools with absorbent fillers such as zeolite and ceramsite, and design subsurface flow or baffled flow patterns to extend hydraulic retention time. Chinese patent CN119569170B also discloses a surface runoff purification system that uses valve-controlled venting and reoxygenation via vent pipes. This system vents through a water-contaminated switch linked to a valve, addressing the problem of insufficient effective volume in "perpetually flooded areas," and introduces air through vent pipes to promote pollutant degradation. However, this technical solution still relies on the coordination of manual control components and the ventilation structure, resulting in a relatively complex structure, and it lacks a flexible operating mode switching mechanism designed for the instantaneous impact characteristics of surface runoff. Meanwhile, in practical engineering applications and long-term operation, existing technologies still have a series of inherent and interrelated defects, which restrict their full effectiveness and widespread application, and make them difficult to adapt to the core characteristics of intermittent surface runoff and the instantaneous impact of water quality and quantity: 1. Insufficient internal dissolved oxygen replenishment leads to limited and unstable nitrogen removal efficiency. Existing reinforced buffer zones or subsurface flow constructed wetlands mostly employ advection or deflection flow patterns, with oxygen replenishment primarily relying on natural diffusion from the water surface or limited transport by plant roots. While some technologies incorporate reoxygenation structures such as aeration pipes, they still depend on negative pressure or wind power, making reoxygenation efficiency highly susceptible to environmental conditions. Anoxic zones easily form within the system, especially in the middle and later stages, severely limiting the oxygen-consuming nitrification process and resulting in low ammonia nitrogen removal efficiency from runoff, with significant fluctuations under low temperature or high load conditions. Public research indicates that the average ammonia nitrogen removal rate of traditional subsurface flow wetlands can be as low as approximately 35% in winter. The fundamental reason is that existing structures lack a highly efficient, stable, and energy-free forced reoxygenation mechanism, failing to guarantee the continuous dissolved oxygen demand of the nitrification reaction along the process. 2. The existing facilities have a single functional structure and operating mode, making them unable to adapt to the instantaneous impact and hydrological fluctuations of runoff. The structural parameters of existing facilities (such as inundation depth and flow path length) are typically fixed. Even if some technologies can achieve drainage, a dynamic switching logic of "purification-storage" has not been established. Faced with rainfall events of varying intensities, durations, and intervals, existing technologies cannot flexibly adjust between the two core functions of "pursuing high purification efficiency" and "handling flood peak regulation." For example, the runoff at the beginning of a rainstorm experiences significant instantaneous impacts in water quality and quantity. The system needs maximum storage capacity to intercept high concentrations of initial rainwater pollution, but a fixed structure may overflow pollution due to premature full flow. Under normal rainfall conditions, insufficient hydraulic retention time may result in incomplete pollutant purification. The root cause of these deficiencies lies in the lack of a physical basis and operating strategy for continuous and flexible control of key operating parameters (such as inundation ratio), making it difficult to cope with the instantaneous impact characteristics of runoff. 3. Insufficient synergy between ecological elements and engineering structures leads to extremely poor long-term sustainability, particularly during extreme periods of inactivity in the dry season. While existing technologies may introduce wetland plants or specialized fillers, these often represent simple functional additions, failing to achieve deep coupling between ecological processes and engineering structures. On one hand, once the filler's adsorption capacity is saturated, the system's purification efficiency rapidly declines with prolonged operation without an effective in-situ biological regeneration mechanism. On the other hand, the "idleness" of the system during rainfall intervals leads to the drying of the filler layer and a decrease in microbial activity, requiring a long recovery period to regain a stable purification state upon re-injection. More critically, during long periods of inactivity in the dry season with no rainfall runoff, the filler layer easily dries out completely, plants wither, and a large number of microorganisms die, causing the system to almost completely lose its purification activity and become unable to maintain the oxygen supply from plant roots. Even when rainfall arrives, a long recovery period is required, making it unable to cope with the instantaneous impact of initial rainfall or to degrade pollution loads during the dry season. Furthermore, packing blockage is a common problem during long-term operation. Existing technologies have failed to systematically design ecological elements such as plants as core functional components to maintain the long-term permeability and biological activity of the system, and the synergistic effect of ecology and engineering has not been effectively realized.

[0004] In summary, existing technologies suffer from inherent defects such as weak reoxygenation capacity, single operation mode, and disconnect from ecological engineering. As a result, when treating micro-polluted runoff around rivers and lakes, they generally face a series of unresolved technical problems, including difficulty in continuously improving denitrification efficiency, inability to adapt to the intermittent and instantaneous impact characteristics of runoff, insufficient long-term operational stability, easy loss of system activity during extreme intermittent periods in the dry season, interruption of oxygen supply from plant roots, and inability to degrade pollution loads. Summary of the Invention

[0005] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of this application.

[0006] This application addresses the shortcomings of existing surface runoff purification technologies, such as weak reoxygenation capacity, single operation mode, and insufficient ecological and engineering synergy. It addresses the intermittent nature of surface runoff, the instantaneous impact of water quality and quantity, and the long-term intermittent nature of dry seasons with no runoff. The application provides a cascaded surface runoff treatment system and method. Through the deep coupling of three core designs—structured cascaded reoxygenation, adjustable operation mode, and plant root microenvironment regulation—and integrating the function of maintaining the activity of photovoltaic water replenishment during dry seasons, the system achieves rapid interception and efficient degradation of runoff pollutants, as well as long-term stable operation. Simultaneously, it incorporates flood peak regulation functions, ensuring the activity of system microorganisms and plants during dry seasons with no runoff, maintaining oxygen supply from plant roots to the microorganisms inside the packing material, and promoting the degradation of pollutant loads during dry seasons.

[0007] The first aspect of this application provides a surface runoff cascade treatment system, including a primary filtration unit, two or more deep purification units, and a phosphorus removal unit connected in a stepped manner along the natural terrain.

[0008] In an exemplary embodiment, in the surface runoff cascade treatment system, the outlet and inlet of two adjacent units are connected by a cascade deflector structure; the cascade deflector structure includes one or more drainage outlets at different heights disposed at the outlet, each of the drainage outlets being able to open and close as needed; Optionally, the primary filtration unit may be provided with one drain outlet, while the deep purification unit and phosphorus removal unit may be provided with multiple drain outlets at different heights.

[0009] In one exemplary embodiment, the primary filtration unit, the deep purification unit, and the phosphorus removal unit each include, from top to bottom, suitable plants and a packing layer; the suitable plants are planted on the packing layer and their roots penetrate deep into the packing layer.

[0010] In one exemplary embodiment, the drain outlet is located above the packing layer.

[0011] In one exemplary embodiment, the primary filtration unit includes two layers: an upper layer filled with gravel with a particle size of 8-10 mm and a lower layer filled with gravel with a particle size of 3-5 mm. Optionally, the mass ratio of the upper packing layer to the lower packing layer is 1:1.

[0012] In one exemplary embodiment, the deep purification unit is wherein the packing layer is filled with adsorption packing.

[0013] In one exemplary embodiment, the adsorption packing material includes one or more of the following: ceramsite, zeolite, iron-manganese (Fe / Mn) ore, etc. Optionally, the particle size of the adsorption filler is 5-15 mm and the porosity is >50%.

[0014] In one exemplary embodiment, the deep purification unit further includes a water collection area filler located below the adsorption filler. Optionally, the filler material in the catchment area is gravel with a particle size of 5-15 mm and a porosity of >50%.

[0015] In one exemplary embodiment, the phosphorus removal unit is wherein the packing layer is filled with a phosphorus removal adsorbent; Optionally, the phosphorus removal adsorbent has a particle size of 5-10 mm and a porosity of >50%.

[0016] In one exemplary embodiment, the phosphorus removal adsorbent is selected from one or more of bentonite, modified zeolite, bauxite, etc.

[0017] In one exemplary embodiment, the suitable plant is a pollution-tolerant, well-developed root system functional aquatic plant, selected from one or two regionally adapted plants such as arrowhead and water hyacinth.

[0018] In one exemplary embodiment, the tiered deflector structure further includes a deflector pipe that is matched with the drain outlet.

[0019] In one exemplary embodiment, the surface runoff cascade treatment system further includes a subsystem for maintaining the activity of photovoltaic water replenishment during the dry season.

[0020] In an exemplary embodiment, the dry season photovoltaic water replenishment activity maintenance subsystem includes a solar panel, a water pump, and water pipes connected to both ends of the water pump. The solar panel and the water pump are electrically connected. One end of the water pipe of the water pump extends into the river or lake water, and the other end of the water pipe is connected to one or more of the primary filtration unit, the deep purification unit, and the phosphorus removal unit. Optionally, one end of the water pump extends into the river or lake water, and the other end of the water pump is connected to the primary filtration unit.

[0021] The second aspect of this application provides a method for cascade ecological purification of surface runoff, using the aforementioned cascade treatment system for surface runoff, comprising the following steps: 1) After the surface runoff flows into the surface runoff cascade treatment system, it enters the primary filtration unit along the natural terrain. Under the action of gravity, it flows from top to bottom through the filler layer and plant root zone in the primary filtration unit to complete the primary filtration. 2) The surface runoff after primary filtration falls through the stepped baffle structure at the outlet of the primary filtration unit and enters the first deep purification unit; under the action of gravity, it flows from top to bottom through the packing layer and plant root zone in the first deep purification unit, removing reducing pollutants and completing the first deep purification. 3) After the first deep purification, the surface runoff flows through the remaining deep purification units and phosphorus removal units in sequence, and the "purification-cascade reoxygenation" process is repeated in each unit. 4) Surface runoff falls and is discharged through the stepped baffle structure at the outlet of the phosphorus removal unit, completing the purification treatment.

[0022] In one exemplary embodiment, the method further includes: adjusting the drop height of two adjacent units by opening / closing the drain outlets at different heights in the tiered deflector structure.

[0023] In one exemplary embodiment, the drop height between two adjacent units is 0.3-0.7m.

[0024] In an exemplary embodiment, the method further includes an operation mode switching step, comprising: adjusting the inundation ratio of each unit in the surface runoff cascade treatment system through the cascade deflector structure according to rainfall intensity, runoff pollution load, and flood peak storage requirements, thereby switching the operation mode between a storage-purification mode; specifically: The inundation ratio of each unit in the surface runoff cascade treatment system is adjusted by opening / closing different drainage outlets in the cascade deflector structure.

[0025] In one exemplary embodiment, the inundation ratio of each unit in the surface runoff cascade treatment system is gradient-adjusted within the range of 40%-100%.

[0026] In an exemplary embodiment, when the runoff pollution load is high at the beginning of rainfall, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 60%-80%, and the surface runoff cascade treatment system activates a high-efficiency purification mode. Under moderate rainfall intensity, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 80%-100%. When the flood peak arrives during the rainy season, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 100%, and the surface runoff cascade treatment system is activated in maximum storage mode. During periods of inactivity in rainfall, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 40%-60%.

[0027] In one exemplary embodiment, the method further includes: when there is no rainfall runoff, replenishing water through a dry season photovoltaic water replenishment activity maintenance subsystem; specifically: The solar panels in the dry season photovoltaic water replenishment activity maintenance subsystem generate photovoltaic power, and water pumps are used to draw water from rivers and lakes to replenish the surface runoff cascade treatment system.

[0028] Compared with existing related technologies, this application has the following technical effects: This application system achieves synergistic effects through the coupling and interaction of three major systems: structured tiered reoxygenation, adjustable operation mode retention and purification, and ecological-engineering coupling of plant root-driven and packing materials. This structurally addresses the core deficiencies of existing technologies. Specifically: 1) Structured cascade reoxygenation: The cascaded baffle structure ensures that runoff always enters the next unit from top to bottom, guaranteeing that the runoff in each unit flows from top to bottom. This avoids the problems of short-circuiting water flow and packing scouring caused by the alternating flow direction of traditional vertical baffles. By opening / closing the drain outlets at different heights, different cascade aeration effects are achieved, making each cascade a mandatory reoxygenation event for the corresponding unit. This achieves "on-demand supply" and "gradual refresh" of dissolved oxygen to match the needs of the denitrification process. The height of the cascade is strictly determined according to the peak range of reoxygenation energy utilization efficiency, eliminating the need for additional energy-consuming equipment such as pumps and fans. This significantly increases the dissolved oxygen concentration in the runoff, providing sufficient dissolved oxygen for aerobic biodegradation in the next purification unit. This ensures that the aerobic nitrification reaction proceeds efficiently and continuously, fundamentally solving the problem of limited denitrification efficiency caused by oxygen deficiency in the later stages of traditional purification facilities. 2) Adjustable operation mode: Based on rainfall intensity, runoff pollution load and flood peak storage requirements, each unit can flexibly adjust the inundation ratio by opening / closing different drainage outlets, and complete the switching between purification and storage functions. This gives the static ecological purification facility the ability to dynamically respond to complex hydrological conditions, and solves the problem that the existing technology has fixed structural parameters and rigid operation mode, which cannot take into account both purification efficiency and flood peak storage. 3) Eco-engineering coupling of plant root system and packing material: The microenvironment regulation driven by plant roots enables the all-weather, three-dimensional synergistic purification of the system in this application. Through the precise vertical spatial coupling of specific functional plants and packing material layers, plant roots are used as the core component of ecological regulation to maintain microbial activity during rainfall intervals and construct a three-dimensional microenvironment within the purification unit. While performing structured tiered reoxygenation, the "aerobic at the top and anoxic at the bottom" microenvironment constructed by plant roots simultaneously achieves nitrification and denitrification reactions within the unit, significantly improving the system's nitrogen removal efficiency and solving the problems of low and unstable nitrogen removal efficiency in traditional systems. The coupling of functional plants and packing material layers achieves deep synergy between ecological elements and engineering structures. Plant roots not only provide continuous oxygen supply for microorganisms but also absorb nutrients such as nitrogen and phosphorus from runoff, further enhancing pollutant removal. At the same time, the root penetration enhances the permeability of the packing material layer, effectively alleviating the problem of packing material blockage. The accumulation of plant biomass provides more attachment sites for microorganisms, forming a "plant-packing material-microorganism" synergistic purification system, ensuring the long-term stability and sustainability of the system. 4) Targeting the intermittent nature of runoff purification and the extreme intervals during the dry season, the root systems of specific functional plants (such as arrowhead and water hyacinth) are precisely coupled with the filler layer in vertical space. This is combined with a subsystem for maintaining the activity of photovoltaic water replenishment during the dry season, forming an integrated ecological regulation system. This system not only utilizes the "biological pump" effect of plant roots to continuously supply oxygen during regular rainfall intervals to maintain microbial activity, but also naturally constructs a stable microenvironment of "aerobic at the top and anoxic at the bottom" within a single treatment unit, enhancing the multi-pathway transformation of pollutants. Furthermore, photovoltaic water replenishment maintains the moisture of the filler layer and the activity of plants and microorganisms during the dry season, ensuring continuous oxygen supply from plant roots and promoting the degradation of pollution load during the dry season. This enables the system to operate stably year-round and around the clock, solving the core defects of traditional technologies such as loss of activity during the dry season, inability to degrade pollution, and long recovery periods after rainfall. This represents a performance upgrade from "physical structure oxygen supply" to "ecosystem self-sustaining throughout the entire cycle."

[0029] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application can be realized and obtained by means of the embodiments described in the description and the accompanying drawings. Attached Figure Description

[0030] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0031] Figure 1 This is a schematic diagram of the surface runoff cascade treatment system of this application; Figure 2 This is a schematic diagram illustrating the regulation of the retention-purification function of the surface runoff cascade treatment system in this application; Figure 3 This is a schematic diagram of the structure of the solar photovoltaic water replenishment activity maintenance subsystem of the surface runoff cascade treatment system in this application during the dry season; Figure 4 The curve showing the variation of energy utilization rate of natural cascade aeration and reoxygenation in the cascade deflector structure of this application with the elevation difference is shown.

[0032] Explanation of reference numerals in the attached figures: 1. Primary filtration unit; 2. Deep purification unit; 3. Phosphorus removal unit; 4. Drain outlet; 5. Solar panel; 6. Water pump; 7. Water pipe. Detailed Implementation

[0033] This application describes several embodiments, but these descriptions are exemplary and not limiting, and it will be apparent to those skilled in the art that many more embodiments and implementations are possible within the scope of the embodiments described herein. Although many possible combinations of features are shown in the drawings and discussed in the detailed description, many other combinations of the disclosed features are also possible. Unless specifically limited, any feature or element of any embodiment may be used in combination with, or may replace, any feature or element of any other embodiment.

[0034] This application includes and contemplates combinations of features and elements known to those skilled in the art. The embodiments, features, and elements disclosed in this application can also be combined with any conventional features or elements to form unique inventive solutions. Any feature or element of any embodiment can also be combined with features or elements from other inventive solutions to form another unique inventive solution. Therefore, it should be understood that any feature shown and / or discussed in this application can be implemented individually or in any suitable combination. Therefore, the embodiments are not limited except by the limitations imposed by the appended claims and their equivalents. Furthermore, various modifications and changes can be made within the scope of the appended claims.

[0035] Furthermore, in describing representative embodiments, the specification may have presented methods and / or processes as a specific sequence of steps. However, the method or process should not be limited to the specific order of steps described herein, to the extent that it does not depend on such a specific order. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps set forth in the specification should not be construed as a limitation of the claims. Moreover, the claims concerning the method and / or process should not be limited to the steps performed in the written order, and those skilled in the art will readily understand that these orders can be varied and still remain within the spirit and scope of the embodiments of this application.

[0036] This application provides a surface runoff cascade treatment system, including a primary filtration unit, two or more deep purification units, and a phosphorus removal unit connected in a stepped manner along the natural terrain.

[0037] In this embodiment of the application, in the surface runoff cascade treatment system, the outlet and inlet of two adjacent units are connected by a cascade deflector structure; the cascade deflector structure includes one or more drainage outlets at different heights at the outlet, and each drainage outlet can be opened and closed as needed; Optionally, the primary filtration unit may be provided with one drain outlet, while the deep purification unit and phosphorus removal unit may be provided with multiple drain outlets at different heights.

[0038] In this embodiment, the primary filtration unit, the deep purification unit, and the phosphorus removal unit each include, from top to bottom, suitable plants and a packing layer; the suitable plants are planted on the packing layer and their roots penetrate deep into the packing layer.

[0039] In this embodiment, the drain outlet is located above the packing layer.

[0040] In this embodiment of the application, the primary filtration unit includes two layers: the upper layer is filled with gravel with a particle size of 8-10 mm, and the lower layer is filled with gravel with a particle size of 3-5 mm, forming a gradient filtration system with "coarse at the top and fine at the bottom" to efficiently intercept suspended particulate matter in runoff and prevent clogging of the packing material in subsequent units from the source. Optionally, the mass ratio of the upper packing layer to the lower packing layer is 1:1.

[0041] In this embodiment of the application, the deep purification unit is filled with adsorption packing material in the packing layer to adsorb and remove reducing pollutants (ammonia nitrogen, COD) and attach a biofilm with pollutant degradation function.

[0042] In the embodiments of this application, the adsorption packing includes one or more of the following: ceramsite, zeolite, and iron-manganese (Fe / Mn) ore; Optionally, the particle size of the adsorption filler is 5-15 mm and the porosity is >50%.

[0043] In this embodiment of the application, the deep purification unit further includes a water collection area filler located below the adsorption filler to ensure hydraulic permeability; Optionally, the filler material in the catchment area is gravel with a particle size of 5-15 mm and a porosity of >50%.

[0044] In this embodiment of the application, the phosphorus removal unit is filled with a phosphorus removal adsorbent in the packing layer to achieve step-by-step targeted purification of pollutants; Optionally, the phosphorus removal adsorbent has a particle size of 5-10 mm and a porosity of >50%.

[0045] In the embodiments of this application, the phosphorus removal adsorbent is selected from one or more of bentonite, modified zeolite, bauxite, etc.

[0046] In this embodiment of the application, the suitable plant is a functional aquatic plant that is pollution-tolerant and has a well-developed root system, selected from one or two regionally adaptable plants such as arrowhead and water hyacinth.

[0047] In this embodiment, the tiered deflector structure further includes a deflector pipe that is matched with the drain outlet.

[0048] In this embodiment of the application, the surface runoff cascade treatment system further includes a subsystem for maintaining the activity of photovoltaic water replenishment during the dry season.

[0049] In this embodiment of the application, the solar water replenishment activity maintenance subsystem for dry season includes a solar panel, a water pump, and water pipes connected to both ends of the water pump. The solar panel and the water pump are electrically connected. One end of the water pipe of the water pump extends into the river or lake water, and the other end of the water pipe is connected to one or more of the primary filtration unit, the deep purification unit, and the phosphorus removal unit, so as to draw river or lake water through photovoltaic power generation to replenish the surface runoff cascade treatment system. Optionally, one end of the water pump extends into the river or lake water, and the other end of the water pump is connected to the primary filtration unit.

[0050] In this embodiment, the surface runoff cascade treatment system can be directly applied to surface runoff scenarios with a slope of 20% or more. The number of units in the surface runoff cascade treatment system can be flexibly adjusted according to the adsorption capacity of the filler and the average load of the rainfall runoff field.

[0051] This application also provides a method for cascade ecological purification of surface runoff, using the above-mentioned cascade treatment system for surface runoff, including the following steps: 1) After the surface runoff flows into the surface runoff cascade treatment system, it enters the primary filtration unit along the natural terrain. Under the action of gravity, it flows from top to bottom through the filler layer and plant root zone in the primary filtration unit, intercepting suspended particulate matter in the surface runoff and completing the primary filtration. 2) The surface runoff after primary filtration falls through the stepped baffle structure at the outlet of the primary filtration unit, making full contact with the air to achieve natural aeration and reoxygenation. After the dissolved oxygen concentration increases, it enters the first deep purification unit. Under the action of gravity, it flows from top to bottom through the packing layer and plant root zone in the first deep purification unit to remove reducing pollutants and complete the first deep purification. 3) After the first deep purification, the surface runoff flows through the remaining deep purification units and phosphorus removal units in sequence, and the "purification-cascade reoxygenation" process is repeated in each unit to achieve the gradual refresh of dissolved oxygen and the stepwise degradation of pollutants. 4) Surface runoff falls and is discharged through the stepped baffle structure at the outlet of the phosphorus removal unit, completing the purification treatment.

[0052] In this embodiment of the application, the method further includes: adjusting the drop height of two adjacent units by opening / closing the drainage outlets at different heights in the tiered deflector structure.

[0053] In this embodiment of the application, the drop height between two adjacent units is 0.3-0.7m.

[0054] In this embodiment of the application, the method further includes an operation mode switching step, comprising: adjusting the inundation ratio of each unit in the surface runoff cascade treatment system through the cascade deflector structure according to rainfall intensity, runoff pollution load, and flood peak storage requirements, thereby switching the operation mode between storage and purification modes; specifically: The inundation ratio of each unit in the surface runoff cascade treatment system is adjusted by opening / closing different drainage outlets in the cascade deflector structure.

[0055] In this embodiment of the application, the inundation ratio of each unit in the surface runoff cascade treatment system is gradually adjusted within the range of 40%-100%.

[0056] In this embodiment of the application, when the runoff pollution load is high at the beginning of rainfall, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 60%-80%, and the surface runoff cascade treatment system starts a high-efficiency purification mode to achieve the adsorption and biodegradation of pollutants. The adsorption performance of the packing layer is used to quickly intercept pollutants, and the high dissolved oxygen environment is combined to achieve rapid degradation of pollutants. Under moderate rainfall intensity, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 80%-100% to balance purification and retention and avoid runoff overflow. When the flood peak arrives during the rainy season, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 100%, and the surface runoff cascade treatment system is put into maximum storage mode to realize the regulation and interception of flood peak runoff, so as to make full use of the system volume to intercept flood peak runoff and reduce the flood control pressure on the receiving water body. During periods of inactivity in rainfall, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 40-60% to allow the retained runoff to be slowly purified, maintain the moisture of the packing layer, continuously supply oxygen through the "biological pump" action of plant roots, maintain microbial activity, and slowly degrade the pollutants intercepted in the early stage, thereby achieving in-situ biological regeneration of the packing material and avoiding adsorption saturation and overflow pollution of the packing material.

[0057] In this embodiment of the application, the method further includes: when there is no rainfall runoff, replenishing water through a dry season photovoltaic water replenishment activity maintenance subsystem; specifically: The solar panels in the dry season photovoltaic water replenishment activity maintenance subsystem generate photovoltaic power, and water pumps are used to draw water from rivers and lakes to replenish the surface runoff cascade treatment system.

[0058] The present application will be further described in detail below with reference to specific embodiments, but these embodiments should not be construed as limiting the present application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this invention.

[0059] Example 1 like Figures 1 to 3 As shown, this embodiment provides a surface runoff cascade treatment system, including a primary filtration unit 1, two or more deep purification units 2, and a phosphorus removal unit 3 connected in a stepped manner along the natural terrain.

[0060] The primary filtration unit 1, the deep purification unit 2, and the phosphorus removal unit 3 each include a suitable plant and a filler layer from top to bottom; the suitable plant is planted on the filler layer and the roots of the suitable plant penetrate deep into the filler layer.

[0061] In the primary filtration unit 1, the packing layer includes upper and lower layers. The upper layer is filled with gravel with a particle size of 8-10 mm, and the lower layer is filled with gravel with a particle size of 3-5 mm, forming a gradient filtration system that efficiently intercepts suspended particulate matter in runoff and prevents clogging of the packing in subsequent units from the source. In the deep purification unit, the packing layer comprises two layers: the upper layer is filled with adsorption packing to deeply remove reducing pollutants (ammonia nitrogen, COD); the lower layer is filled with water catchment packing to ensure hydraulic permeability. The adsorption packing includes one or more of the following: ceramsite, zeolite, Fe / Mn ore, etc., with a particle size of 5-15 mm and a porosity > 50%. The water catchment packing is gravel, with a particle size of 5-15 mm and a porosity > 50%. In the phosphorus removal unit, the packing layer is filled with a phosphorus removal adsorbent to achieve step-by-step targeted purification of pollutants; the particle size of the phosphorus removal adsorbent is 5-10 mm, and the porosity is >50%; the phosphorus removal adsorbent is selected from one or more of bentonite, modified zeolite, bauxite, etc.

[0062] The suitable plants are pollution-tolerant, well-developed root systems, and functional aquatic plants selected from one or two regionally adaptable plants such as arrowhead and water hyacinth.

[0063] In the said stepped surface runoff treatment system, the water outlet end and water inlet end of two adjacent units are connected through a stepped baffling drop structure. The stepped baffling drop structure comprises one or more drainage outlets 4 with different heights arranged at the water outlet end and baffling pipes (not shown) matched with the drainage outlets 4, and each of the drainage outlets 4 can be opened and closed as required. In this embodiment, one drainage outlet 4 is arranged at the highest position of the water outlet end of the primary filtration unit 1, and a plurality of drainage outlets 4 are arranged at different heights of the water outlet ends of the deep purification unit 2 and the phosphorus removal unit 3. The stepped baffling drop structure can also control the submergence ratio of each unit in the said stepped surface runoff treatment system to be adjusted in a gradient within the range of 40%-100%.

[0064] As Figure 3 shown, the said stepped surface runoff treatment system further comprises a dry-season photovoltaic water-replenishment activity maintenance subsystem; the said dry-season photovoltaic water-replenishment activity maintenance subsystem comprises a solar panel 5, a water pump 6 and water pipes 7 connected to both ends of the water pump, wherein the solar panel 5 is electrically connected to the water pump 6, the water pipe 7 at one end of the water pump 6 extends into river and lake water, and the water pipe 7 at the other end is connected to one or more of the primary filtration unit 1, the deep purification unit 2 and the phosphorus removal unit 3 to replenish water for each unit of the said stepped surface runoff treatment system. In this embodiment, the water pump 6 pumps river and lake water into the primary filtration unit 1 for replenishment.

[0065] In this embodiment, the said stepped surface runoff treatment system can be directly applied to large-slope surface runoff scenarios with a slope of 20% or above, and the number of units of the said stepped surface runoff treatment system can be flexibly adjusted according to the adsorption capacity of the filler and the average load of rainfall runoff field.

[0066] Example 2 This embodiment provides a stepped ecological purification method for surface runoff, which uses the stepped surface runoff treatment system described in Example 1, and comprises the following steps: 1) After surface runoff converges into the said stepped surface runoff treatment system, it enters the primary filtration unit 1 along the natural terrain, flows through the filler layer and plant root zone in the primary filtration unit 1 from top to bottom under the action of gravity, intercepts suspended particulate matters in the surface runoff, and completes primary filtration; 2) The surface runoff after primary filtration drops through the stepped baffling drop structure at the water outlet end of the primary filtration unit 1, fully contacts with air to realize natural aeration and reoxygenation, and after the dissolved oxygen concentration is increased, it enters the first deep purification unit; under the action of gravity, it flows through the filler layer and plant root zone in the said first deep purification unit from top to bottom, removes reductive pollutants, and completes the first deep purification; 3) After the first deep purification, the surface runoff flows through the remaining deep purification unit and phosphorus removal unit 3 in sequence. The "purification-cascade reoxygenation" process is repeated in each unit to achieve the gradual refresh of dissolved oxygen and the stepwise degradation of pollutants. 4) The deeply purified surface runoff falls and is discharged through the stepped baffle structure at the outlet of the phosphorus removal unit 3, completing the purification treatment.

[0067] In the method described, the drop height of two adjacent units is adjusted by opening / closing the drain outlets 4 at different heights in the tiered baffle structure. The relationship between the drop height difference between two adjacent units and the aeration effect is as follows: Figure 4 As shown, in this method, the drop height between two adjacent units is controlled to be 0.3-0.7m.

[0068] The method further includes a storage-purification mode switching step, comprising: according to rainfall intensity, runoff pollution load, and flood peak storage requirements, changing the inundation ratio within each unit by opening / closing different drainage outlets in the cascade deflector structure, thereby switching the operating mode between storage-purification modes; specifically: When the runoff pollution load is high at the beginning of rainfall, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 60%-80%, and the surface runoff cascade treatment system starts the high-efficiency purification mode to achieve the adsorption and biodegradation of pollutants. The adsorption performance of the packing layer is used to quickly intercept pollutants, and the high dissolved oxygen environment is combined to achieve rapid degradation of pollutants. Under moderate rainfall intensity, the inundation ratio in each unit of the surface runoff cascade treatment system is gradually increased to 80%-100% to balance purification and storage and avoid runoff overflow. When the flood peak arrives during the rainy season, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 100%, and the surface runoff cascade treatment system is put into maximum storage mode to realize the regulation and interception of flood peak runoff, so as to make full use of the system volume to intercept flood peak runoff and reduce the flood control pressure on the receiving water body. During periods of inactivity in rainfall, the inundation ratio in each unit of the surface runoff cascade treatment system is adjusted to 40%-60% to allow the retained runoff to be slowly purified, maintain the moisture of the packing layer, continuously supply oxygen through the "biological pump" action of plant roots, maintain microbial activity, and slowly degrade the pollutants intercepted in the early stage, thereby achieving in-situ biological regeneration of the packing material and avoiding adsorption saturation and overflow pollution of the packing material.

[0069] like Figure 3 As shown, the method further includes: when there is no rainfall runoff, water is replenished through the dry season photovoltaic water replenishment activity maintenance subsystem; specifically: the solar panels 5 in the dry season photovoltaic water replenishment activity maintenance subsystem generate photovoltaic power, and the water pump 6 is used to pump river and lake water to replenish the surface runoff cascade treatment system.

[0070] The surface runoff cascade treatment system and purification method described in the embodiments of this application can achieve the following technical effects: 1) Purification efficiency is significantly improved Compared with traditional systems that rely on soil infiltration and limited-width natural vegetation buffer zones (NH3-N removal rate of about 70%), the ammonia nitrogen removal rate in this application system is consistently 83%-95%, and the TP removal rate (>95%) is significantly higher than that of common bioretention ponds (average about 50%). The ammonia nitrogen in the effluent from this application system is <0.2mg / L, which is comprehensively better than the Class III surface water standard, and the pollution load reduction capacity per unit area is outstanding. 2) The hydraulic load and operational flexibility are significantly better than those of traditional constructed wetlands and fixed facilities. In terms of hydraulic load, the average value of the system in this application is 1.17m. 3 / (m 2 The recommended hydraulic loading for a composite vertical flow constructed wetland to achieve similar effluent standards is only about 0.2 m (h), while the recommended hydraulic loading for a composite vertical flow constructed wetland is only about 0.2 m. 3 / (m 2 ·h), and requires a hydraulic residence time of up to 72 hours.

[0071] In terms of adaptability, the flooding ratio of this application system is continuously adjustable from 40% to 100%, and can be flexibly switched between "high-efficiency purification mode" (removal rate priority) and "maximum retention mode" (flood peak control priority), while traditional bioretention ponds and vegetated swales have single functions and are not adjustable. This gives the system of this application higher space utilization efficiency and strategic ability to cope with uncertain rainfall.

[0072] 3) The deep integration of ecology and engineering has overcome the engineering challenges of performance degradation during low temperatures, regular intermittent periods, and extreme intermittent periods during the dry season, achieving stable operation throughout the year. Compared to subsurface flow constructed wetlands, which are also constrained by internal dissolved oxygen (where ammonia nitrogen removal rates can drop to ~35% in winter), this application utilizes the "all-weather biological oxygenation pump" effect of plant roots to maintain microbial activity during regular rainfall intervals, resulting in a significantly higher ammonia nitrogen degradation rate (0.88 mg / (L·h)) compared to systems without plants. For long-term intermittent periods without runoff during the dry season, photovoltaic water replenishment maintains the moisture of the packing layer, ensuring plant survival and microbial activity. More importantly, it maintains the continuous oxygen supply capacity of the plant roots, not only preventing the system from losing its purification capacity due to prolonged lack of runoff but also promoting the slow degradation of pollutant loads during the dry season, achieving continuous year-round pollutant removal. Simultaneously, the clean energy-driven water replenishment design requires no additional energy consumption, and the system requires no recovery period when rainfall arrives, directly and efficiently responding to the instantaneous impact of initial rainfall. This completely solves the pain points of traditional engineering facilities, such as functional stagnation during non-operational periods, loss of activity during the dry season, and inability to degrade pollutants, achieving an upgrade from "effective per event" to "stable throughout the year, around the clock."

[0073] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0074] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include at least one of those features.

[0075] In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise expressly and specifically limited.

[0076] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," "fixing," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0077] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0078] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0079] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A surface runoff cascade treatment system, comprising a primary filtration unit, two or more deep purification units, and a phosphorus removal unit connected in a stepped manner along the natural terrain; the outlet and inlet of two adjacent units are connected by a cascade baffle structure; the cascade baffle structure includes one or more drainage outlets at different heights at the outlet, each of the drainage outlets being able to be opened and closed as needed.

2. The surface runoff cascade treatment system according to claim 1, wherein, The primary filtration unit, the deep purification unit, and the phosphorus removal unit each include, from top to bottom, suitable plants and a packing layer; the suitable plants are planted on the packing layer and their roots penetrate deep into the packing layer.

3. The surface runoff cascade treatment system according to claim 2, wherein, In the primary filtration unit, the packing layer comprises two layers: the upper layer is filled with gravel with a particle size of 8-10 mm, and the lower layer is filled with gravel with a particle size of 3-5 mm; and / or In the deep purification unit, the packing layer is filled with adsorption packing; and / or In the phosphorus removal unit, the packing layer is filled with phosphorus adsorbent.

4. The surface runoff cascade treatment system according to claim 3, wherein, The adsorption packing material includes one or more of the following: ceramsite, zeolite, and iron-manganese ore; and / or The adsorption filler has a particle size of 5-15 mm and a porosity > 50%; and / or The phosphorus removal adsorbent is selected from one or more of bentonite, modified zeolite, and bauxite; and / or The phosphorus removal adsorbent has a particle size of 5-10 mm and a porosity of >50%.

5. The surface runoff cascade treatment system according to claim 4, wherein, In the deep purification unit, the packing layer also includes a water collection area packing located below the adsorption packing; Optionally, the filler material in the catchment area is gravel with a particle size of 5-15 mm and a porosity of >50%.

6. The surface runoff cascade treatment system according to any one of claims 2 to 5, wherein, The suitable plants are pollution-tolerant, functional aquatic plants with well-developed root systems. Optionally, the suitable plant is selected from one or both of arrowhead and water hyacinth.

7. The surface runoff cascade treatment system according to any one of claims 1 to 5, wherein, The surface runoff cascade treatment system also includes a subsystem for maintaining the activity of photovoltaic water replenishment during the dry season; Optionally, the dry season photovoltaic water replenishment activity maintenance subsystem includes a solar panel, a water pump, and water pipes connected to both ends of the water pump. The solar panel and the water pump are electrically connected. One end of the water pump extends into the river or lake water, and the other end of the water pipe is connected to one or more of the primary filtration unit, the deep purification unit, and the phosphorus removal unit.

8. A method for cascade ecological purification of surface runoff, using a surface runoff cascade treatment system according to any one of claims 1 to 7, comprising the following steps: 1) After surface runoff flows into the surface runoff cascade treatment system, it enters the primary filtration unit along the natural terrain. Under the action of gravity, it flows from top to bottom through the filler layer and plant root zone in the primary filtration unit to complete the primary filtration. 2) The surface runoff after primary filtration falls through the stepped baffle structure at the outlet of the primary filtration unit and enters the first deep purification unit; under the action of gravity, it flows from top to bottom through the packing layer and plant root zone in the first deep purification unit, completing the first deep purification. 3) After the first deep purification, the surface runoff flows through the remaining deep purification units and phosphorus removal units in sequence, and the "purification-cascade reoxygenation" process is repeated in each unit. 4) Surface runoff falls and is discharged through the stepped baffle structure at the outlet of the phosphorus removal unit, completing the purification treatment.

9. The method according to claim 8, wherein, The method further includes: adjusting the drop height of two adjacent units by opening / closing the drainage outlets at different heights in the tiered deflector structure; Optionally, the drop height between two adjacent units is 0.3-0.7m.

10. The method according to claim 8 or 9, wherein, The method also includes an operation mode switching step, which includes: adjusting the inundation ratio of each unit in the surface runoff cascade treatment system through the cascade deflector structure according to the rainfall intensity, runoff pollution load and flood peak storage requirements, and switching the operation mode between storage and purification modes. Optionally, the inundation ratio of each unit in the surface runoff cascade treatment system is gradient-adjusted within the range of 40%-100%.

11. The method according to claim 8 or 9, wherein, The method further includes replenishing the surface runoff cascade treatment system with water through a solar photovoltaic water replenishment activity maintenance subsystem during the dry season.

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