Multistage composite ecological wetland tail water purification system

Abstract

The invention relates to a multistage composite ecological wetland tail water purification system, which belongs to the technical field of sewage treatment, and comprises an adjusting tank, a water quality monitoring device, a medicament adding device, a vertical subsurface flow wetland, a reed ditch wetland and an ecological pond, the adjusting tank can buffer the inflow water, the water quality monitoring device can obtain inflow water quality parameters, and the agent adding device can add agents based on the water quality parameters; the vertical subsurface flow wetland is used for carrying out nitration reaction on ammonia nitrogen under the action of attached microorganisms in an aerobic environment; the reed ditch wetland is used for carrying out denitrification reaction on nitrate nitrogen under the action of attached microorganisms in an anoxic environment; the ecological pond is used for further reducing the content of suspended solids, organic pollutants and nutritive salt in the water body. The method has the effects that the adaptive capacity of the constructed wetland system to the tail water of the sewage treatment plant is improved, and the deep purification effect on residual pollutants in the tail water is enhanced.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, and in particular to a multi-stage composite ecological wetland effluent purification system. Background Technology

[0002] Constructed wetlands, as a water treatment technology based on ecological engineering principles, often exhibit fluctuations in effluent quality and quantity due to the influence of upstream process operation and external conditions during deep purification of wastewater treatment plants. Existing wetland treatment systems still face several technical challenges in actual operation: Firstly, some systems lack effective water volume buffering and water quality regulation units at the front end. When influent conditions change abnormally, it can easily affect the hydraulic conditions and biological reaction environment of subsequent wetland treatment units, thus impacting the stability of effluent quality. Secondly, conventional wetland systems have relatively limited removal pathways for residual recalcitrant organic matter and low-concentration complex pollutants in the effluent, lacking dedicated, ecologically-based deep purification pathways. Summary of the Invention

[0003] In order to improve the adaptability of constructed wetland systems to wastewater treatment plant effluent and enhance the deep purification effect on residual pollutants in the effluent, this application provides a multi-stage composite ecological wetland effluent purification system.

[0004] The multi-stage composite ecological wetland tailwater purification system provided in this application adopts the following technical solution: A multi-stage composite ecological wetland tailwater purification system includes an equalization pond, a water quality monitoring device, a chemical dosing device, a vertical subsurface flow wetland, a reed ditch wetland, and an ecological pond; The regulating tank can buffer the influent flow, the water quality monitoring device can acquire influent water quality parameters, and the chemical dosing device can dosing chemicals based on the water quality parameters. The vertical subsurface flow wetland is used to receive water discharged from the regulating pond and to nitrify ammonia nitrogen in an aerobic environment through the action of attached microorganisms. At the same time, it reduces the content of suspended solids, organic pollutants and nutrients in the water through filtration and biodegradation. The reed gully wetland is used to receive water discharged from the vertical subsurface flow wetland, and in an oxygen-deficient environment, it carries out denitrification of nitrate nitrogen through the action of attached microorganisms, further reducing the content of suspended solids, organic pollutants and nutrients in the water. The ecological pond is used to receive water discharged from the reed gully wetland, further reducing the content of suspended solids, organic pollutants and nutrients in the water.

[0005] By adopting the above technical solution and setting up an equalization tank at the front end of the system, the influent flow and pollution load are buffered and equalized, reducing the impact of instantaneous hydraulic shock and pollution load fluctuations on the operation of the vertical subsurface flow wetland, which is conducive to maintaining the stability of the biological reaction environment inside the packing medium. Vertical subsurface flow wetlands remove and transform organic pollutants and ammonia nitrogen under aerobic conditions, reducing the organic load and suspended solids content entering the reed gully wetland, reducing the risk of anaerobic deterioration caused by the accumulation of organic matter in subsequent units, thereby inhibiting the occurrence of water odor and ecological imbalance. Under anaerobic conditions, the reed-filled wetland denitrifies nitrate nitrogen, further reducing pollutants and enhancing the system's ability to deeply purify nitrogen-containing wastewater. Meanwhile, the ecological pond, as a final-stage ecological regulation unit, buffers and stabilizes the system's effluent under slow-flow conditions through the synergistic effect of aquatic biological communities and attached biofilms, reducing water quality fluctuations during multi-stage treatment processes.

[0006] Through multi-level functional zoning and a synergistic purification process chain, the pre-treatment regulating pond not only regulates water quantity and quality but also actively reduces the load on subsequent biological treatment by adding chemicals for "enhanced pretreatment." The vertical subsurface flow wetland serves as the core purification unit, achieving efficient nitrogen and phosphorus removal and organic matter degradation. The reed-lined wetland creates a vast biofilm attachment area and complex microhabitats, specifically targeting the deep biodegradation and ecological filtration of recalcitrant organic matter. The final ecological pond functions as an "ecological stabilizer" and "biodiversity enhancement zone," achieving the final ecologicalization and activation of the effluent through the construction of a complete aquatic food chain, forming an organic whole where pollutants are transformed step by step and ecological functions are enhanced at each stage.

[0007] Optionally, the reed-lined wetland includes a distribution ditch, a collection ditch, porous field ridges, and a regulating weir. The porous field ridges are located between the collection ditch and the distribution ditch. The distribution ditch is used to receive water discharged from the vertical subsurface flow wetland. The regulating weir is used to raise the water level of the distribution ditch, so that the water in the distribution ditch is discharged into the collection ditch after passing through the porous field ridges. The water in the collection ditch is discharged into the ecological pond.

[0008] By adopting the above technical solution, and by setting up porous field ridges between the distribution ditch and the collection ditch, and using regulating weirs to control the water level in the distribution ditch, the water body can penetrate the porous field ridge structure under the drive of the water level difference. This can effectively extend the hydraulic path of the water body in the wetland unit, reduce short-circuiting, and improve the contact efficiency between the water body and the filler medium and the microbial reaction interface. This is conducive to further reduction of pollutants. Moreover, since the water body is forced to flow through the reaction zone under the action of the water level difference, the effective utilization rate of the wetland per unit area is improved, thereby reducing the system's land area under the same treatment scale.

[0009] Optionally, the porous field ridge includes a wetland ridge layer, a corn stalk layer on the wetland ridge layer, a first soil layer on the corn stalk layer, a rapeseed stalk layer on the first soil layer, a second soil layer on the rapeseed stalk layer, a silt layer on the second soil layer, and a cover soil on the silt layer. The porous field ridge also includes reeds.

[0010] By adopting the above technical solution, the field ridge is composed of natural root holes formed by the growth of reeds and artificial root holes formed by the decay of straw. This effectively changes the pore structure of the subsurface soil in the early stage of wetland construction, accelerates the wetland soil development process, provides a large area of ​​biofilm attachment for microorganisms, and at the same time, the straw acts as an endogenous carbon source during the decay process, providing electron donors for denitrifying bacteria inside the field ridge, forming a small biofilm reactor, which enables the degradation of organic pollutants in the tailwater. During the process of the tailwater penetrating the root hole system of the wetland bed, the interception, filtration and purification of recalcitrant organic matter and trace amounts of toxic and harmful substances are achieved. Furthermore, the biodegradable organic materials gradually form interconnected pore structures during operation, which helps maintain the permeability inside the field ridges, reduces the risk of media densification, and thus improves the hydraulic stability of the wetland unit in the long term. At the same time, while removing pollutants, the complex structure of the porous field ridge-ditch system provides habitats for microorganisms and small benthic animals, restoring the ecological activity of the water body.

[0011] Optionally, the water distribution ditch is arranged in a winding manner, the porous field ridge has a slope structure, and a wire mesh is installed at the slope of the porous field ridge.

[0012] By adopting the above technical solutions, the porous field ridges with slope structures are beneficial to improving the overall structural stability of the field ridges and mitigating the scouring effect of water flow. At the same time, the slope structure can increase the contact interface between the water body and the field ridge medium. The installation of a wire mesh structure at the slope helps to enhance the slope's scouring resistance and prevent the loss of the medium, thereby maintaining the long-term stability of the field ridge's porous structure. The meandering design of the water distribution ditches helps to extend the water flow path and reduce short-circuiting.

[0013] Optionally, the drainage end of the regulating tank is connected to a main water distribution pipe, the main water distribution pipe is connected to several secondary water distribution pipes, the several secondary water distribution pipes are evenly distributed in the vertical subsurface flow wetland, the secondary water distribution pipes are connected to perforated water distribution pipes, and the perforated water distribution pipes are located in the upper layer of the packing material of the vertical subsurface flow wetland.

[0014] By adopting the above technical solution, a graded water distribution structure consisting of main water distribution pipes, secondary water distribution pipes and perforated water distribution pipes is used to achieve uniform distribution of water in the vertical subsurface flow wetland, reduce local concentrated water inflow and water flow short-circuiting, and improve the effective utilization rate of wetland units.

[0015] Optionally, the vertical subsurface flow wetland includes a bottom support layer, a middle transition layer on the bottom support layer, and an upper planting layer on the middle transition layer. The particle size of the upper planting layer, the middle transition layer, and the bottom support layer increases progressively, and the thickness of the middle transition layer and the upper planting layer are both greater than the thickness of the bottom support layer.

[0016] By adopting the above technical solution, the upper planting layer and the middle transition layer form the main pollutant reaction zone, while the bottom support layer forms the main drainage zone. The upper planting layer and the middle transition layer can increase the pollutant interception capacity and delay the development of blockage, while the smaller thickness and larger particle size of the bottom layer are conducive to reducing sediment accumulation, ensuring the smooth drainage of the bottom support layer, reducing the risk of overall blockage of the wetland unit, and improving the long-term stability of the system.

[0017] Optionally, the upper planting layer includes crushed stone and zeolite, the particle size of the crushed stone and zeolite is 8-15mm, the volume ratio of crushed stone to zeolite is 1:2, and the upper planting layer also includes reeds, canna lilies, cattails and canna lilies. The intermediate transition layer includes crushed stone and ceramsite, with a particle size of 15-35mm and a volume ratio of crushed stone to ceramsite of 1:3. The underlying support layer comprises crushed stone with a particle size of 35-60mm.

[0018] By adopting the above technical solution, the zeolite in the upper planting layer has a high cation exchange capacity and adsorption effect on ammonia nitrogen. In the early stage of water entering the vertical subsurface flow wetland, it forms an adsorption buffer effect on ammonia nitrogen, reduces the instantaneous load of ammonia nitrogen, slows down the speed at which ammonia nitrogen enters the deep reaction zone, reduces the impact on the lower microbial system, provides a porous attachment interface for nitrifying bacteria, and enhances the attachment ability of microorganisms. The crushed stone in the upper planting layer mainly provides structural support and stabilizes the pore structure, which helps maintain the overall porosity of the upper filler, improves the permeability of the filler layer, and avoids excessive hydraulic resistance due to a high proportion of zeolite. The ceramsite in the intermediate transition layer provides a high specific surface area, enhances microbial attachment, forms a stable biofilm reaction zone, improves the biodegradation capacity of organic pollutants, and reduces the overall density of the packing. Meanwhile, the crushed stone in the intermediate transition layer provides structural stability, prevents the ceramsite from being concentrated and compacted, and maintains the smooth flow of the overall hydraulic channels. The gravel in the bottom support layer forms a drainage layer, ensuring smooth drainage at the bottom, reducing hydraulic resistance, providing support, reducing the impact of blockage on the overall system, facilitating air replenishment, and improving oxygen supply conditions. Mixed planting of various plants creates a multi-layered root zone structure due to the different root depths of each plant. Different growth cycles complement each other, reducing the risk of seasonal decline and improving the overall ecological stability of the system.

[0019] Optionally, the reagent dosing device includes an integrated PAC dosing device and a microbial agent dosing device, and the water quality monitoring device is used to detect the water quality at the inlet of the regulating tank.

[0020] Optionally, the ecological pond includes a pond body, the bottom of which is provided with multiple topographic units of different elevations, the two ends of which are respectively designated as inlet and outlet, the side walls of the pond body are slope structures, emergent plants are planted at the waterway junction slopes of the pond body, submerged plants and floating-leaved plants are planted in the central water area of ​​the pond body, and aquatic fish and benthic animals are stocked in the pond body.

[0021] By adopting the above-mentioned technical solution, multiple topographic units at different elevations form a micro-topographic structure with undulating elevations. This facilitates the creation of different water depth zones within the pond, constructing multi-layered aquatic habitats including shallow, medium, and relatively deep water areas, providing suitable growth conditions for submerged and floating-leaved plants. Simultaneously, the micro-topographic structure alters water flow paths, enhancing contact between the water body and bottom sediment, plant roots, and attached biofilms, thereby improving the efficiency of pollutant physical adsorption and biodegradation.

[0022] The pond has an inlet and an outlet at its two ends, creating a directional flow path for the water. With the help of the micro-topographical structure, the water moves forward in an approximate plug flow pattern within the pond. During this flow, the water comes into contact with the bottom sediment, plant roots, and attached microorganisms in sequence. Through physical interception, chemical adsorption, and biological reactions, nutrients such as nitrogen and phosphorus are further removed from the water, improving the stability of the effluent quality.

[0023] Emergent plants' root systems can stabilize slope soil and enhance bank stability. They also participate in water purification by absorbing nutrients and providing an interface for microbial attachment. The establishment of slope zones creates a transitional area between water and land, which is beneficial for improving the habitat diversity of ecological ponds.

[0024] Submerged plants release oxygen through photosynthesis, improving the dissolved oxygen environment in the water and absorbing nitrogen and phosphorus nutrients. Floating-leaved plants inhibit excessive algae growth by providing shade through their leaves, while also absorbing nutrients from the water. Submerged, floating-leaved, and emergent plants together construct a multi-layered aquatic plant community structure, enhancing the system's overall capacity for nutrient absorption.

[0025] Aquatic fish and benthic animals are stocked in the ecological pond. Fish can regulate the structure of the plankton community and inhibit abnormal algal proliferation; benthic animals can improve the structure of the bottom sediment and promote the decomposition of sedimentary organic matter. By constructing a complete ecosystem that includes plant and aquatic animal communities, it is beneficial to form a stable aquatic food chain structure and improve the ecological buffering capacity of the ecological pond.

[0026] Optionally, the underwater slope ratio of the pond is 1:3, the above-water slope ratio is 1:3-1:5, the emergent plants include yellow iris, umbrella grass, canna lily, and Siberian iris, the submerged plants include pondweed, goldfish algae, foxtail algae, eelgrass, hydrangea, and pondweed, the floating-leaved plants include water lily and water caltrop, the aquatic fish include silver carp, bighead carp, snakehead, and black carp, and the benthic animals include snails and freshwater mussels.

[0027] By adopting the above technical solutions, an underwater slope ratio of 1:3 helps to ensure slope stability, prevent water erosion from causing collapse, and provide a suitable water depth transition area for submerged and floating-leaved plants; an above-water slope ratio of 1:3–1:5 forms a relatively gentle bank slope structure, which is conducive to the root growth of emergent plants, while enhancing bank slope stability and reducing the risk of rainwater erosion. Different emergent plants have roots of varying depths, which helps to form a multi-layered root structure and stabilize the slope soil. Different submerged plants adapt to different water depths, which improves community stability. Silver carp and bighead carp mainly filter-feed on plankton, which helps to control the amount of phytoplankton. Snakehead and grass carp participate in food chain regulation, which helps to maintain ecological balance and reduce the risk of algal blooms.

[0028] By combining emergent plants, submerged plants, floating-leaved plants, aquatic fish, and benthic animals, a multi-layered aquatic community structure is formed, and a relatively complete aquatic food chain system is constructed. This is conducive to improving the ecological pond's comprehensive absorption capacity of nutrients, enhancing the system's adaptability to seasonal changes, and improving the ecological stability before tailwater discharge.

[0029] In summary, this application includes at least one of the following beneficial technical effects: 1. Based on the pollutant removal mechanism, a four-stage unit with clearly defined functions and interconnected steps was designed. The equalization tank not only regulates water quantity and quality but also enhances pretreatment by adding chemicals, reducing the load on subsequent biological treatment. The vertical subsurface flow wetland, as the core purification unit, achieves efficient nitrogen and phosphorus removal and organic matter degradation through optimized plant configuration and water distribution system. The reed-lined gully wetland utilizes straw and reed root hole systems to create a huge biofilm attachment area and complex microenvironment, specifically for deep biodegradation and ecological filtration of recalcitrant organic matter. The final ecological pond serves as an ecological stabilizer and biodiversity enhancement zone, achieving the final ecologicalization and activation of the effluent by constructing a complete aquatic food chain, forming an organic whole where pollutants are transformed step by step and ecological functions are enhanced step by step. 2. Combining the root holes naturally formed by the growth of reeds and the artificial root holes formed by the decay of straw, a highly efficient three-dimensional biofilm attachment and mass transfer system is constructed. This system not only greatly increases the habitat space for microorganisms, but its complex pore structure also enables efficient interception and adsorption of colloidal particles and recalcitrant organic matter, prolonging the hydraulic retention time and providing a suitable living environment for slow-growing, specialized degradative bacteria, ensuring that the effluent COD and other indicators meet the standards. 3. The regulating pond, through the integration of coagulant and microbial agent dosing devices, can quickly transform into a highly efficient emergency pretreatment pond in the event of abnormal influent, ensuring the resilience of the entire system. Simultaneously, in the ecological pond unit, diverse habitats (deep water areas, shallow water areas, mudflats, islands, etc.) are created through system design, and aquatic animals are scientifically introduced, and submerged, emergent, and floating-leaved plants are planted to establish an aquatic ecosystem with high biodiversity and ecological balance. This construction of ecological resilience ensures that the system not only outputs clean water but also a healthy, self-regulating local ecosystem. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of an embodiment of this application.

[0031] Figure 2 This is a schematic diagram illustrating the structure of the main water distribution pipe, the secondary water distribution pipe, and the perforated water distribution pipe in the embodiments of this application.

[0032] Figure 3 This is a schematic diagram illustrating the structure of a vertical subsurface flow wetland, as described in an embodiment of this application.

[0033] Figure 4 This is a schematic diagram illustrating the structure of the Weigou Wetland in an embodiment of this application.

[0034] Figure 5 This is a schematic diagram illustrating the structure of the ecological pond in an embodiment of this application.

[0035] Explanation of reference numerals in the attached diagrams: 1. Regulating pond; 2. Water quality monitoring device; 3. Chemical dosing device; 4. Vertical subsurface flow wetland; 41. Bottom support layer; 42. Middle transition layer; 43. Upper planting layer; 5. Reed ditch wetland; 51. Distribution ditch; 52. Collection ditch; 53. Porous field ridge; 531. Wetland ridge layer; 532. Corn stalk layer; 533. First soil layer; 534. Rapeseed stalk layer; 535. Second soil layer; 536. Silt layer; 537. Covering soil; 538. Net cage; 6. Ecological pond; 61. Pond body; 62. Topographic unit; 63. Emergent plants; 64. Submerged plants; 65. Floating-leaved plants; 71. Main water distribution pipe; 72. Secondary water distribution pipe; 73. Perforated water distribution pipe. Detailed Implementation

[0036] The following is in conjunction with the appendix Figure 1-5 This application will be described in further detail.

[0037] This application discloses a multi-stage composite ecological wetland tailwater purification system.

[0038] like Figure 1 The multi-stage composite ecological wetland tailwater purification system includes a regulating pond 1, a water quality monitoring device 2, a chemical dosing device 3, a vertical subsurface flow wetland 4, a reed gully wetland 5, and an ecological pond 6. The water flows sequentially through the regulating pond 1, the vertical subsurface flow wetland 4, the reed gully wetland 5, and the ecological pond 6.

[0039] The equalization tank 1 can buffer the influent flow, the water quality monitoring device 2 can acquire the influent water quality parameters, and the chemical dosing device 3 can dosing chemicals based on the water quality parameters.

[0040] In this embodiment, the regulating tank 1 is a rectangular reinforced concrete structure with an inlet and an outlet. The tank has a preset volume to temporarily store the wastewater entering the system, reducing instantaneous fluctuations in the influent flow rate and creating relatively stable flow conditions before the water enters the subsequent vertical subsurface flow wetland 4. The volume of the regulating tank 1 allows for a certain hydraulic retention time within the tank, thus buffering against water flow shocks. In other embodiments, the regulating tank 1 can be an underground tank, an earthen pond structure, or an integrated pretreatment module. A labyrinth baffle can also be installed within the tank to adjust the hydraulic retention time. In this embodiment, the designed hydraulic retention time is 6.0 hours, and the water depth of the regulating tank 1 is 1.6 meters.

[0041] A water quality monitoring device 2 is installed at the inlet of the equalization tank 1 to perform real-time water quality monitoring before the effluent enters the equalization tank 1. In this embodiment, the water quality monitoring device 2 includes a combination of online COD analyzers, online ammonia nitrogen analyzers, and online total phosphorus analyzers; other embodiments may further include pH sensors and dissolved oxygen sensors. The water quality monitoring device 2 acquires water samples through a sampling system. The reagent dosing device 3 is electrically connected to the water quality monitoring device 2. In this embodiment, the reagent dosing device 3 includes an integrated PAC dosing device, a microbial agent dosing device, a control module, a signal receiving module, and a metering pump. The signal receiving module is used to receive the detection data transmitted by the water quality monitoring device 2. The control module determines whether the water quality is abnormal according to a preset threshold and controls the metering pump to start or stop. The integrated PAC dosing device includes a reagent storage tank, a reagent dissolving unit, and an automatic metering unit, used for enhanced removal of suspended solids and total phosphorus in the effluent. The microbial agent dosing device is used to supplement functional bacteria when water quality fluctuates or the load increases, thereby improving the system's biological treatment capacity. In other embodiments, the reagent dosing device 3 may also include other flocculant dosing units or carbon source dosing units. In this embodiment, the preset threshold for water quality parameters is set according to the Class A standard of the "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants" (GB18918-2002).

[0042] When the water quality monitoring device 2 detects that the concentrations of COD, ammonia nitrogen, or total phosphorus in the influent exceed the set threshold, the control module adjusts the dosage of PAC or microbial agent according to the degree of exceedance, and adds the agent to the inlet or body of the equalization tank 1 through the delivery pipeline, so that the effluent is enhanced before entering the vertical subsurface flow wetland 4. When the detected value returns to the normal range, the control module reduces or stops the agent addition. Through the above automatic control process, real-time monitoring and dynamic adjustment of the influent water quality are achieved, reducing the impact of influent volume and water quality fluctuations on subsequent wetland units and improving the overall operational stability of the system.

[0043] like Figure 2 and Figure 3 The vertical subsurface flow wetland 4 is used to receive water discharged from the regulating pond 1, and nitrifies ammonia nitrogen through the action of attached microorganisms in an aerobic environment. At the same time, it reduces the content of suspended solids, organic pollutants and nutrients in the water through filtration and biodegradation.

[0044] In this embodiment of the application, the water flow pattern of the vertical subsurface flow wetland 4 is from top to bottom. The drainage end of the regulating tank 1 is connected to a main water distribution pipe 71. The main water distribution pipe 71 is connected to several secondary water distribution pipes 72. The several secondary water distribution pipes 72 are evenly distributed in the vertical subsurface flow wetland 4. The secondary water distribution pipes 72 are connected to perforated water distribution pipes 73. The perforated water distribution pipes 73 are located in the upper layer of the filling material of the vertical subsurface flow wetland 4. Specifically, the main water distribution pipe 71 is a De200PE pipe, the secondary water distribution pipes 72 are De150PE pipes, and the perforated water distribution pipes 73 are De80PE pipes.

[0045] In other embodiments, the effluent from the regulating tank 1 can first enter a distribution channel or distribution trough located on the wetland inlet side. The distribution channel is provided with multiple equally spaced overflow outlets or toothed overflow weirs, so that the water enters the wetland surface or below the surface from each overflow outlet with approximately the same head, thereby achieving uniform water distribution under gravity conditions.

[0046] In this embodiment, the vertical subsurface flow wetland 4 includes a bottom support layer 41, a middle transition layer 42 disposed on the bottom support layer 41, and an upper planting layer 43 disposed on the middle transition layer 42. The particle size of the upper planting layer 43, the middle transition layer 42, and the bottom support layer 41 increases progressively. The thickness of the middle transition layer 42 and the upper planting layer 43 are both greater than the thickness of the bottom support layer 41. A perforated water distribution pipe 73 extends into the upper planting layer 43. The vertical subsurface flow wetland 4 is set with a surface hydraulic load of 0.8m. 3 / m 2 •d, residence time 20h, COD reduction load 12g / m 2 ·d, ammonia nitrogen reduction load 2.4g / m 2 ·d, TP load reduction 0.08g / m 2 ·d, unit area 1250m² 2 The wetland bed is 1.4m thick and the filler has an average porosity of 45%.

[0047] Specifically, the upper planting layer (43) has a thickness of 0.5m and a particle size of 8-15mm, with crushed stone and zeolite mixed at a volume ratio of 1:2. The middle transition layer (42) has a thickness of 0.6m and a particle size of 15-35mm, with crushed stone and expanded clay mixed at a volume ratio of 1:3. The bottom support layer (41) has a thickness of 0.3m and uses widely available crushed stone with a particle size of 35-60mm. Reeds and Thalia dealbata are planted at 16 clumps / m². 2 25 clumps / m² of cattails and canna lilies 2 .

[0048] In other embodiments, the vertical subsurface flow wetland 4 still employs a top-down water distribution method, with perforated water pipes 73 extending into the upper planting layer 43, allowing water to seep downwards from the upper filler material to the bottom collection system for discharge. The wetland bed thickness is 1.2m, and the average porosity of the filler material is 40%~50%. The upper planting layer 43 has a filler thickness of 0.45m and comprises gravel and volcanic rock with a particle size of 6-12mm, and a volume ratio of gravel to volcanic rock of 1:2; the middle transition layer 42 has a filler thickness of 0.5m and comprises gravel and slag with a particle size of 15-30mm, and a volume ratio of gravel to slag of 1:4; the bottom support layer 41 has a filler thickness of 0.25m and uses pebbles with a particle size of 30~50mm. One or more combinations of reeds, cattails, canna lilies, or tamarisk are selected, with a planting density of 15~30 clumps / m².

[0049] like Figure 4Weigou Wetland 5 is used to receive water discharged from Vertical Subsurface Flow Wetland 4, and in an oxygen-deficient environment, it carries out denitrification of nitrate nitrogen through the action of attached microorganisms, further reducing the content of suspended solids, organic pollutants and nutrients in the water. In this embodiment, the reed gully wetland 5 includes a distribution ditch 51, a collection ditch 52, porous field ridges 53, and a regulating weir (not shown in the figure). The porous field ridges 53 are located between the collection ditch 52 and the distribution ditch 51. Specifically, the porous field ridges 53 can be arranged in two rows, with the distribution ditch 51 meandering between the two rows of porous field ridges 53. Each of the two rows of porous field ridges 53 has a collection ditch 52 on its side away from the distribution ditch 51. The distribution ditch 51 is used to receive water discharged from the bottom support layer 41. The regulating weir is located at the end of the distribution ditch 51 away from its inlet to raise the water level of the distribution ditch 51, so that the water in the distribution ditch 51 is discharged into the collection ditch 52 after passing through the porous field ridges 53. The water in the collection ditch 52 is discharged into the ecological pond 6.

[0050] In other embodiments, the porous field ridges 53 can be configured with a multi-row staggered arrangement, with the distribution ditches 51 and collection ditches 52 alternating, so that the water body forms a multi-level penetration path within the reed marsh wetland 5, thereby improving the pollutant removal efficiency. The collection ditches 52 can also be set in the middle of the reed marsh wetland 5, with the distribution ditches 51 respectively set on both sides, so that the water body penetrates the porous field ridges 53 from the outside to the inside and collects into the collection ditches 52.

[0051] The porous field ridge 53 includes a wetland ridge layer 531, a corn stalk layer 532 on top of the wetland ridge layer 531, a first soil layer 533 on top of the corn stalk layer 532, a rapeseed stalk layer 534 on top of the first soil layer 533, a second soil layer 535 on top of the rapeseed stalk layer 534, a silt layer 536 on top of the second soil layer 535, and a covering soil layer 537 on top of the silt layer 536. The porous field ridge 53 also includes reeds, with the reed roots at least embedded in the second soil layer 535. Specifically, the wetland ridge layer 531 is 600 mm thick, the corn stalk layer 532, rapeseed stalk layer 534, first soil layer 533, second soil layer 535, and covering soil layer 537 are all 150 mm thick, the silt layer 536 is 50 mm thick, and the corn stalk layer 532 is planted at a rate of 2.7 kg / m². 2 The application rate of rapeseed straw in the planting layer was 3.6 kg / m². 2The wetland ridge layer 531 has a width of 9500mm, and the soil cover layer 537 has a width of 3000mm. The wetland ridge layer 531, corn stalk layer 532, soil layer, rapeseed stalk layer 534, soil layer, silt layer 536, and soil cover layer 537 combine to form a platform-shaped structure in longitudinal section. The designed water depth for the distribution ditch 51 is 1.4m, and the designed water depth for the collection ditch 52 is 1.2m, with a head loss of 0.2m. Net cages 538 are installed on the slopes of the porous field embankments 53. The surface hydraulic load of the reed-lined wetland 5 is 1.1m. 3 / m 2 •d, residence time 20h, COD reduction load 5g / m 2 ·d, Ammonia nitrogen reduction load 1g / m 2 ·d, TP load reduction 0.1g / m 2 •d, the slope of the embankment is 1:2.5. Compared with traditional surface flow wetlands, the reed-lined gully wetland 5 reduces the land area by 35%. The porous embankment 53 removes pollutants, and its complex structure provides habitats for microorganisms and small benthic animals, restoring the ecological activity of the aquatic body.

[0052] In other embodiments, the porous field ridge 53 includes a wetland ridge layer 531, on which a first straw layer, a soil layer, a second straw layer, and a covering soil 537 are sequentially arranged. The first straw layer and / or the second straw layer may be one or more of corn straw, rapeseed straw, rice straw, wheat straw, or mixtures thereof. The soil layer may be undisturbed soil, imported soil, or mixed soil. In some embodiments, a silt layer 536 or a humus layer may be provided between the soil layer and the covering soil 537 to improve the field ridge's adsorption capacity for pollutants and enhance the microbial attachment and growth environment. The reed roots are at least embedded in the soil layer and extend to the silt layer 536 or the humus layer, allowing the reed roots to form a natural root hole structure, which, together with the pores formed by the decomposition of straw, constitutes the seepage channels inside the field ridge.

[0053] like Figure 5 Ecological pond 6 is used to receive water discharged from reed gully wetland 5, further reducing the content of suspended solids, organic pollutants and nutrients in the water.

[0054] Specifically, the ecological pond 6 includes a pond body 61, which is an open water structure with an inlet and an outlet. The inlet of the pond body 61 is connected to the outlet of the collection ditch 52, and the outlet of the pond body 61 is connected to the system's outlet pipeline, allowing water to flow directionally from the inlet to the outlet. In this embodiment, the bottom of the pond body 61 is provided with multiple topographic units 62 at different elevations to form a micro-topographic structure with varying elevations. The topographic units 62 can be locally raised areas, shallow areas, gentle slope transition areas, and relatively deep water areas, creating different water depth zones within the pond body 61 to accommodate the growth needs of different types of aquatic plants and improve the habitat diversity of the ecological pond 6. The sidewalls of the pond body 61 are designed as slope structures to form a water-land transition zone and improve the stability of the bank slope.

[0055] Emergent plants 63 are planted on the slope at the water-land interface of pond 61. The roots of emergent plants 63 stabilize the slope soil and participate in nutrient absorption, while also providing an interface for microbial attachment and growth. Submerged plants 64 and floating-leaved plants 65 are planted in the central water area of ​​pond 61. Submerged plants 64 absorb nutrients such as nitrogen and phosphorus from the water and improve the aquatic ecological conditions, while floating-leaved plants 65 inhibit abnormal algal growth and further stabilize water quality through shading and absorption. By placing emergent plants 63 on the slope and submerged plants 64 and floating-leaved plants 65 in the central water area, a zonal configuration of the plant community is achieved, thereby improving the stability and purification capacity of the plant system within the ecological pond 6.

[0056] In addition, in this embodiment, aquatic fish and benthic animals are stocked in the pond 61. The aquatic fish are used to regulate the structure of the aquatic biological community, and the benthic animals are used to promote the decomposition of organic matter in the bottom sediment and improve the bottom sediment environment. By introducing aquatic fish and benthic animals, a relatively complete aquatic food chain structure is constructed, which improves the stability and self-regulation capacity of the ecosystem in the ecological pond 6.

[0057] Specifically, the water depth in the pond is 0.5-1.5m, the hydraulic retention time is 1 day, the water slope ratio of the pond body 61 is 1:3, and the water slope ratio of the pond body 61 is 1:3-1:5. The emergent plants 63 include yellow iris, umbrella sedge, canna lily, and Siberian iris, with a unit density of 18 clumps / m². 2 The 64 submerged plants included *Potamogeton crispus*, *Ceratophyllum demersum*, *Myriophyllum spicatum*, *Vallisneria natans*, *Hydrilla verticillata*, and *Potamogeton pectinii*, with *Potamogeton crispus*, *Ceratophyllum demersum*, and *Myriophyllum spicatum* as the main plants, and *Vallisneria natans*, *Hydrilla verticillata*, and *Potamogeton pectinii* as secondary plants. The mixed planting density was 60 plants / m². 2 Floating-leaved plants 65 include water lilies and water chestnuts, with a unit density of 2 clumps / m². 2 Aquatic fish include silver carp, bighead carp, snakehead, and grass carp, while benthic animals include snails and freshwater mussels.

[0058] The implementation principle of this application embodiment is as follows: by setting up an equalization tank 1 at the front end of the system, the influent water volume and pollution load are buffered and equalized, reducing the impact of instantaneous hydraulic shock and pollution load fluctuations on the operating state of the vertical subsurface flow wetland 4, thereby helping to maintain the stability of the biological reaction environment inside the packing medium. Vertical subsurface flow wetland 4 removes and transforms organic pollutants and ammonia nitrogen under aerobic conditions, reducing the organic load and suspended solids content entering reed gully wetland 5, reducing the risk of anaerobic deterioration caused by the accumulation of organic matter in subsequent units, thereby inhibiting the occurrence of water odor and ecological imbalance. Under anoxic conditions, Weigou Wetland 5 performs denitrification of nitrate nitrogen, further reducing pollutants and thus improving the system's deep purification capacity for nitrogen-containing effluent. Meanwhile, Ecological Pond 6, as the final ecological regulation unit, buffers and stabilizes the system's effluent under slow-flow conditions through the synergistic effect of aquatic biological communities and attached biofilms, reducing water quality fluctuations during multi-stage treatment.

[0059] Through multi-level functional zoning and a collaborative purification process chain, the pre-treatment regulating pond not only regulates water quantity and quality but also actively reduces the load on subsequent biological treatment by adding chemicals for "enhanced pretreatment." Vertical subsurface flow wetland 4 serves as the core purification unit, achieving efficient nitrogen and phosphorus removal and organic matter degradation. Reed-lined gully wetland 5 creates a vast biofilm attachment area and complex microhabitats, specifically targeting the deep biodegradation and ecological filtration of recalcitrant organic matter. Finally, ecological pond 6 functions as an "ecological stabilizer" and "biodiversity enhancement zone," constructing a complete aquatic food chain to achieve the final ecological transformation and activation of the effluent, forming an organic whole where pollutants are transformed step by step and ecological functions are enhanced at each stage.

[0060] The above are all preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A multi-stage composite ecological wetland tailwater purification system, characterized in that: It includes a regulating pond (1), a water quality monitoring device (2), a chemical dosing device (3), a vertical subsurface flow wetland (4), a reed gully wetland (5), and an ecological pond (6); The regulating tank (1) can buffer the influent flow, the water quality monitoring device (2) can acquire the influent water quality parameters, and the chemical dosing device (3) can dosing chemicals based on the water quality parameters. The vertical subsurface flow wetland (4) is used to receive water discharged from the regulating pond (1) and nitrify ammonia nitrogen through the action of attached microorganisms in an aerobic environment. At the same time, it reduces the content of suspended solids, organic pollutants and nutrients in the water through filtration and biodegradation. The reed gully wetland (5) is used to receive the water discharged from the vertical subsurface flow wetland (4), and in an oxygen-deficient environment, it carries out denitrification of nitrate nitrogen through the action of attached microorganisms, further reducing the content of suspended solids, organic pollutants and nutrients in the water. The ecological pond (6) is used to receive water discharged from the reed gully wetland (5) to further reduce the content of suspended solids, organic pollutants and nutrients in the water.

2. The multi-stage composite ecological wetland tailwater purification system according to claim 1, characterized in that: The reed gully wetland (5) includes a water distribution ditch (51), a water collection ditch (52), a porous field ridge (53), and a regulating weir. The porous field ridge (53) is located between the water collection ditch (52) and the water distribution ditch (51). The water distribution ditch (51) is used to receive water discharged from the vertical subsurface flow wetland (4). The regulating weir is used to raise the water level of the water distribution ditch (51) so that the water in the water distribution ditch (51) is discharged into the water collection ditch (52) after passing through the porous field ridge (53). The water in the water collection ditch (52) is discharged into the ecological pond (6).

3. The multi-stage composite ecological wetland tailwater purification system according to claim 2, characterized in that: The porous field ridge (53) includes a wetland ridge layer (531), a corn stalk layer (532) on the wetland ridge layer (531), a first soil layer (533) on the corn stalk layer (532), a rapeseed stalk layer (534) on the first soil layer (533), a second soil layer (535) on the rapeseed stalk layer (534), a silt layer (536) on the second soil layer (535), and a cover soil (537) on the silt layer (536). The porous field ridge (53) also includes reeds.

4. The multi-stage composite ecological wetland tailwater purification system according to claim 2, characterized in that: The water distribution ditch (51) is arranged in a meandering manner, the porous field ridge (53) has a slope structure, and a net cage (538) is installed at the slope of the porous field ridge (53).

5. The multi-stage composite ecological wetland tailwater purification system according to claim 1, characterized in that: The drainage end of the regulating tank (1) is connected to a main water distribution pipe (71), the main water distribution pipe (71) is connected to several secondary water distribution pipes (72), the several secondary water distribution pipes (72) are evenly distributed in the vertical subsurface flow wetland (4), the secondary water distribution pipes (72) are connected to perforated water distribution pipes (73), and the perforated water distribution pipes (73) are located in the upper layer of filler material of the vertical subsurface flow wetland (4).

6. The multi-stage composite ecological wetland tailwater purification system according to claim 1, characterized in that: The vertical subsurface flow wetland (4) includes a bottom support layer (41), a middle transition layer (42) is provided on the bottom support layer (41), and an upper planting layer (43) is provided on the middle transition layer (42). The particle size of the upper planting layer (43), the middle transition layer (42) and the bottom support layer (41) increases progressively. The thickness of the middle transition layer (42) and the thickness of the upper planting layer (43) are both greater than the thickness of the bottom support layer (41).

7. The multi-stage composite ecological wetland tailwater purification system according to claim 6, characterized in that: The upper planting layer (43) includes crushed stone and zeolite, the particle size of crushed stone and zeolite is 8-15mm, the volume ratio of crushed stone to zeolite is 1:2, and the upper planting layer (43) also includes reeds, canna lilies, cattails and canna lilies. The intermediate transition layer (42) includes crushed stone and ceramsite, with a particle size of 15-35 mm and a volume ratio of crushed stone to ceramsite of 1:

3. The underlying support layer (41) includes crushed stone with a particle size of 35-60 mm.

8. The multi-stage composite ecological wetland tailwater purification system according to claim 1, characterized in that: The dosing device (3) includes an integrated PAC dosing device and a microbial agent dosing device, and the water quality monitoring device (2) is used to detect the water quality at the inlet of the regulating tank (1).

9. The multi-stage composite ecological wetland tailwater purification system according to claim 1, characterized in that: The ecological pond (6) includes a pond body (61), the bottom of which is provided with multiple terrain units (62) of different elevations. The two ends of the pond body (61) are respectively set as the inlet and outlet. The side walls of the pond body (61) are slope structures. Emergent plants (63) are planted at the waterway junction slope of the pond body (61). Submerged plants (64) and floating-leaved plants (65) are planted in the central water area of ​​the pond body (61). Aquatic fish and benthic animals are raised in the pond body (61).

10. The multi-stage composite ecological wetland tailwater purification system according to claim 9, characterized in that: The underwater slope ratio of the pond body (61) is 1:3, and the above-water slope ratio of the pond body (61) is 1:3-1:

5. The emergent plants (63) include yellow iris, umbrella grass, canna lily and Siberian iris. The submerged plants (64) include pondweed, goldfish algae, foxtail algae, eelgrass, hydrangea and pondweed. The floating-leaved plants (65) include water lily and water lily. The aquatic fish include silver carp, bighead carp, snakehead and black carp. The benthic animals include snails and freshwater mussels.

Images