A bypass multi-stage composite constructed wetland treatment system and method

Abstract

This invention discloses a bypass multi-stage composite constructed wetland treatment system and method. The system includes a facultative pond, a composite vertical subsurface flow constructed wetland, a surface flow constructed wetland, and a storage tank, all connected by sequential waterways. In the facultative pond, a floating plant platform is provided at the upper layer; the bottom layer contains an ecological substrate for microbial growth and reproduction. The composite vertical subsurface flow constructed wetland includes a downstream pool and an upstream pool connected by sequential waterways. Both the downstream and upstream pools have, from top to bottom, an insulation layer, a purification layer, and a support layer. In the downstream pool, a water distribution pipe is installed within the insulation layer, and a drainage channel A is installed within the support layer. In the upstream pool, a water collection pipe is installed within the insulation layer, and a drainage channel B is installed within the support layer. Drainage channels A and B are connected. The filling substrate of the surface flow constructed wetland consists of three layers: a lower layer of larger-diameter ceramsite, a middle layer of smaller-diameter ceramsite, and an upper layer of planting soil, where plants with well-developed root systems and hollow stems are planted. This invention enables complementary performance of water treatment processes.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and more particularly to a bypass multi-stage composite constructed wetland treatment system and method. Background Technology

[0002] Currently, many large and medium-sized factories in my country are located on the outskirts of towns and cities. Over the long term, production and processing have led to water pollution in these areas. This, coupled with the increasing hardening of urban surfaces and the runoff problems caused by intensive agricultural planting, has severely damaged the urban water environment. Water environment protection is closely related to human health and is crucial to the development of urban ecological civilization. Water ecological restoration is a necessary measure to improve water quality, enhance the aquatic ecosystem, and remove black and odorous conditions from urban rivers; it is also an important component of ecosystem protection.

[0003] Constructed wetlands are a nature-based solution that has been successfully used to retain and purify stormwater runoff. While larger constructed wetlands can remove more pollution, urban space, infrastructure, and social and economic constraints often preclude the construction of large-scale constructed wetlands. Constructed wetlands mainly come in two forms: subsurface flow and surface flow. Although surface flow constructed wetlands are effective at treating chemical oxygen demand (COD) and biochemical oxygen demand (BOD), their removal rates for ammonia nitrogen and total phosphorus are limited and highly variable. Furthermore, because wetland systems are open to the atmosphere, odor and fly problems are difficult to manage. While subsurface flow constructed wetlands offer higher pollutant removal efficiency compared to surface flow systems, they also face common operational challenges, such as complex control systems and clogging. Clogging can lead to bypassing or even short-circuiting of the wastewater, affecting its retention time and resulting in substandard effluent quality. Moreover, constructed wetlands are not highly adaptable to seasonal changes, especially in cold northern regions where their operating cycles are short, and they may even be unable to operate during winter. Summary of the Invention

[0004] To fully utilize urban space, this invention provides a bypass multi-stage composite constructed wetland treatment system and method. Through material selection and process design, it aims to ensure water treatment effectiveness while minimizing scale, and addresses the problem of low purification efficiency or even inoperability of conventional wetland treatment systems in winter.

[0005] The technical solution adopted by this invention to solve the technical problems existing in the prior art is as follows:

[0006] A bypass multi-stage composite constructed wetland treatment system, characterized in that it includes a facultative pond, a composite vertical subsurface flow constructed wetland, a surface flow constructed wetland, and a water storage tank that are connected in sequence by waterways;

[0007] Within the facultative pond, a floating plant platform is provided at the upper level; and an ecological substrate for the growth and reproduction of microorganisms is provided at the bottom level.

[0008] The composite vertical subsurface flow constructed wetland includes a downstream pool and an upstream pool connected by sequential water channels; a retaining wall is provided between the downstream pool and the upstream pool; both the downstream pool and the upstream pool are equipped with an insulated composite packing bed system; the insulated composite packing bed system consists of an insulation layer, a purification layer, and a support layer from top to bottom; in the downstream pool, a water distribution pipe is installed in the insulation layer, and a drainage channel A is installed in the support layer; in the upstream pool, a water collection pipe is installed in the insulation layer, and a drainage channel B is installed in the support layer; drainage channel A and drainage channel B are connected.

[0009] The surface flow constructed wetland has a three-layer filling substrate: a lower layer of larger diameter ceramsite, a middle layer of smaller diameter ceramsite, and an upper layer of planting soil. Plants with well-developed root systems and hollow stems are planted in the planting soil layer. Multiple water flow retaining walls are set up perpendicular to the water flow direction in the surface flow constructed wetland.

[0010] The water to be treated enters the facultative pond, and the water in the facultative pond enters the downstream pool of the composite vertical flow constructed wetland through the water distribution pipe; in the downstream pool, the water flows out from the water distribution pipe, and then flows sequentially through the purification layer and the support layer to the drainage ditch A; the water flows from the drainage ditch A into the drainage ditch B; in the upstream pool, the water in the drainage ditch B flows sequentially through the support layer and the purification layer and then into the water collection pipe in the insulation layer; the water collected by the water collection pipe flows into the surface flow constructed wetland; a first outlet end baffle is provided between the surface flow constructed wetland and the water storage tank, and the water in the surface flow constructed wetland overflows from the first outlet end baffle to the water storage tank and is collected by the water storage tank.

[0011] Furthermore, it also includes a winter bypass pipe directly connected to the reservoir. The water collection pipe includes multiple water collection branch pipes and a water collection main pipe connected to each water collection branch pipe. The water collection branch pipes are located in the insulation layer of the upstream reservoir. The water collection main pipe has two outlets and two outlet valves: a first outlet and a first outlet valve connected to the first outlet; a second outlet and a second outlet valve connected to the second outlet; the first outlet is connected to the surface flow constructed wetland; the second outlet is connected to the winter bypass pipe; when the surface temperature is greater than zero degrees, the second outlet valve is closed; when the surface temperature is less than or equal to zero degrees, the first outlet valve is closed.

[0012] Furthermore, a slow-flowing area formed by concrete columns and retaining walls is also provided within the facultative pond.

[0013] Furthermore, a water distribution channel and a valve well are sequentially arranged between the facultative pond and the composite vertical subsurface flow constructed wetland, with a water distribution valve installed in the valve well; the inlet of the water distribution valve is connected to the water distribution channel, and the outlet of the water distribution valve is connected to the water distribution pipe; water in the facultative pond flows into the water distribution channel through a water pump.

[0014] Furthermore, a second outlet baffle wall is provided around the reservoir, and an inlet pipe connected to the reservoir is provided inside the second outlet baffle wall. When the water level in the reservoir reaches the inlet of the inlet pipe, the water in the reservoir flows into the inlet pipe and into the river.

[0015] Furthermore, both drainage ditch A and drainage ditch B are 11-13cm deep, and their bottom surfaces are on the same plane; the angle between their bottom surfaces and the horizontal plane is 8°-12°, and they slope downwards from drainage ditch A to drainage ditch B.

[0016] Furthermore, the diameter of the water collection pipe in the upstream pool is 10-12cm, and a water collection port with a diameter of 18-20cm is set every 1.4-1.6m.

[0017] Furthermore, in the thermal insulation composite filler bed system, the support layer is made of limestone crushed stone with a particle size of 16-64mm and a thickness of 350-450mm; the purification layer is made of a mixed material composed of limestone, volcanic rock and zeolite with a particle size of 8-32mm and a thickness of 650-750mm; and the thermal insulation layer is made of a mixed material composed of perlite and volcanic rock with a particle size of 8-32mm and a thickness of 90-110mm.

[0018] Furthermore, the surface flow constructed wetland is 2m deep; its three-layer filling substrate has the following layers: the lower layer is 55-65cm high with a particle size of 7-8mm; the middle layer is 25-35cm high with a particle size of 2.5-3.5mm; the upper planting soil layer is 9-11cm high; and the planting density of the wetland is 40-60 plants / m². 2 .

[0019] The present invention also provides a bypass multi-stage composite constructed wetland treatment method utilizing the above-mentioned bypass multi-stage composite constructed wetland treatment system, the method being:

[0020] The water to be treated enters the facultative pond, where plants on the floating plant platform purify the water; the ecological substrate at the bottom of the facultative pond allows anaerobic microorganisms to reproduce and ferment, taking oxygen from nitrate or carbonate ions under anaerobic conditions.

[0021] Water from the facultative pond enters the downstream pool of the composite vertical flow constructed wetland through the water distribution pipe; in the downstream pool, after the water flows out from the water distribution pipe, it flows downstream to the drainage ditch A, where the water is purified by the substrate in the purification layer of the downstream pool; in the upstream pool, the water in the drainage ditch B flows upstream into the water collection pipe in the insulation layer, where the water is purified again by the substrate in the purification layer of the upstream pool.

[0022] Water collected by the collection pipe flows into the surface flow constructed wetland; the middle and lower layers of the surface flow constructed wetland are filled with ceramsite material, which adsorbs microorganisms and purifies the water; the planting soil layer of the surface flow constructed wetland is planted with plants with well-developed root systems and hollow stems to increase the dissolved oxygen content in the water.

[0023] The water flow retaining walls and the first outlet retaining wall in the surface flow constructed wetland are used to increase the length of the water flow path and increase the contact time between the water and the biofilm formed on the roots and stems of the plants in the surface flow constructed wetland; the water storage tank is used to collect and store the purified water.

[0024] The advantages and positive effects of this invention are: it is a physical-biological-ecological combined treatment system that can achieve the complementary advantages and disadvantages of each individual water treatment process, overcome the problems of large area and low efficiency in winter of traditional constructed wetland technology, has high efficiency in removing organic matter and nitrogen and phosphorus, occupies a small area, can adapt to the space constraints of urban areas, is noiseless and odorless, and is conducive to landscape improvement.

[0025] The slow-flow zone formed by the concrete columns and retaining walls in the facultative pond can reduce the energy of the water flow and enhance the settling effect.

[0026] The facultative pond is designed to be relatively deep, comprising a surface aerobic zone, a bottom anaerobic zone, and a central facultative zone. The surface water is rich in dissolved oxygen, which is beneficial for plant growth; the facultative layer contains facultative microorganisms; the bottom water is anaerobic, and its biodegradability can be increased through hydrolysis and acidification. An ecological substrate is placed at the bottom of the facultative pond to provide conditions for the attachment and growth of anaerobic microorganisms, further improving the microbial treatment effect.

[0027] Vertical upflow and vertical downflow are the two most common forms of vertical flow constructed wetlands. However, single-stage constructed wetlands cannot provide both aerobic and anaerobic environments at the same time, making it difficult to achieve high levels of nitrogen and phosphorus removal. Composite vertical flow subsurface flow constructed wetlands can complement the advantages of single-stage constructed wetlands, thereby enhancing the wastewater purification effect.

[0028] The composite vertical subsurface flow constructed wetland selects perlite and volcanic rock as the surface insulation layer, which have excellent thermal insulation properties, to reduce the temperature loss in the filling bed during winter. It also selects low-temperature reeds, cattails, and water onions as the dominant species in the subsurface flow wetland to form a low-temperature resistant plant community, which effectively ensures the stable operation of the wetland system under low-temperature conditions in winter.

[0029] In cold winters, surface flow constructed wetlands suffer from low efficiency or even cannot operate. Water in the upflow pool of a composite vertical subsurface flow constructed wetland can be collected through a water collection pipe and directly cross the surface flow constructed wetland through a winter bypass pipe into a water storage tank.

[0030] In surface flow constructed wetlands, multiple flow barriers are evenly installed perpendicular to the water flow direction. This increases the length of the water flow path. Simultaneously, the interception effect of plant roots and stems allows water to come into more thorough contact with the biofilm formed on the roots and stems, leading to degradation and purification of wastewater. Plants with well-developed root systems and hollow stems, such as reeds and cattails, can increase the dissolved oxygen content in the water. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a bypass multi-stage composite constructed wetland treatment system according to the present invention;

[0032] Figure 2 This is a cross-sectional view of a bypass multi-stage composite constructed wetland treatment system according to the present invention.

[0033] In the diagram: 1. Concrete column, 2. Concrete retaining wall, 3. Facultative pond, 4. Wetland inlet lift pump, 5. Water distribution channel, 6. Valve well, 7. Water distribution pipe, 8. Downstream pool, 9. Inter-pool retaining wall, 10. Upstream pool, 11. Water collection pipe, 12. First outlet valve, 13. Surface flow artificial wetland, 14. Water flow retaining wall, 15. First outlet end retaining wall, 16. Water storage tank, 17. Second outlet end retaining wall, 18. Low-temperature resistant plants, 19. Insulation layer, 20. Purification layer, 21. Supporting layer, 22-1. Drainage channel A, 22-2. Drainage channel B, 23. Impermeable layer, 24. Winter bypass pipe, 25. Planting soil layer, 26. Smaller particle size ceramsite layer, 27. Larger particle size ceramsite layer, 28. River inlet pipe. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0035] In the description of this invention, the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. The terms "connected" and "linked" used in this invention should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through intermediate components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0036] Please see Figures 1 to 2 A bypass multi-stage composite constructed wetland treatment system includes a facultative pond 3, a composite vertical subsurface flow constructed wetland, a surface flow constructed wetland 13, and a water storage tank 16 connected in sequence by waterways.

[0037] Within the facultative pond 3, a floating plant platform is provided in the upper layer; and an ecological substrate for the growth and reproduction of microorganisms is provided in the lower layer.

[0038] The composite vertical subsurface flow constructed wetland includes a downstream pool 8 and an upstream pool 10 connected sequentially by waterways; a retaining wall 9 is provided between the downstream pool 8 and the upstream pool 10; both the downstream pool 8 and the upstream pool 10 are equipped with an insulated composite packing bed system; the insulated composite packing bed system consists of an insulation layer 19, a purification layer 20, and a support layer 21 arranged sequentially from top to bottom; in the downstream pool 8, a water distribution pipe 7 is installed within the insulation layer, and a drainage channel A22-1 is installed within the support layer; in the upstream pool 10, a water collection pipe 11 is installed within the insulation layer, and a drainage channel B22-2 is installed within the support layer; drainage channels A22-1 and B22-2 are connected; low-temperature resistant plants 18 are planted on the surface of the downstream pool 8 and the upstream pool 10. An impermeable layer 23 is provided at the bottom of the composite vertical subsurface flow constructed wetland.

[0039] The surface flow constructed wetland 13 has a three-layer filling substrate: a lower layer of larger-diameter expanded clay aggregate 27, a middle layer of smaller-diameter expanded clay aggregate 26, and an upper layer of planting soil 25, which is planted with plants with well-developed root systems and hollow stems. Multiple water flow barriers 14 are installed within the surface flow constructed wetland 13 perpendicular to the water flow direction. These barriers 14 are used to change the direction of water flow, allowing the water to meander around them and flow towards the reservoir 16.

[0040] The water to be treated enters the facultative pond 3, and the water in the facultative pond 3 enters the downstream pool 8 of the composite vertical flow constructed wetland through the water distribution pipe 7. In the downstream pool 8, the water flows out from the water distribution pipe 7, and then flows sequentially through the purification layer and the support layer to the drainage ditch A22-1, forming a downstream flow. The water flows from the drainage ditch A22-1 into the drainage ditch B22-2. In the upstream pool 10, the water in the drainage ditch B22-2 flows sequentially through the support layer and the purification layer and then flows into the water collection pipe 11 in the insulation layer, forming an upstream flow. The water collected by the water collection pipe 11 flows into the surface flow constructed wetland 13. A first outlet end baffle 15 is provided between the surface flow constructed wetland 13 and the water storage tank 16. The water in the surface flow constructed wetland 13 overflows from the first outlet end baffle 15 into the water storage tank 16 and is collected by the water storage tank 16.

[0041] An impermeable layer 23 is provided at the bottom of both the composite vertical subsurface flow constructed wetland and the surface flow constructed wetland 13.

[0042] Preferably, a slow-flow area formed by concrete columns 1 and concrete retaining walls 2 may also be provided in the facultative pond 3.

[0043] The water awaiting treatment in the river channel is introduced into the ditch via a bypass lifting device and then into the facultative pond 3. The pond also receives rainwater runoff from roads, farmland, etc. After entering the facultative pond 3, the water first enters the slow-flow area formed by the concrete column 1 and the retaining wall, which reduces the energy of the water flow and enhances the settling effect. This effectively settles suspended solids in the river inflow or rainwater runoff, reducing the sediment content of the water. The facultative pond 3 can be up to 3 meters deep. Sunlight can only penetrate the upper layer of water in the facultative pond 3. With the help of atmospheric reoxygenation, the upper water has a high oxygen concentration and is an aerobic layer. Plants on the floating plant platform can grow well, thus playing a role in water purification. The lower part of the facultative pond 3 is an anaerobic layer, composed of settled sludge and dead algae and bacteria. The bottom of the facultative pond 3 has an ecological substrate for the growth and reproduction of microorganisms, allowing anaerobic microorganisms to play a dominant role in anaerobic fermentation. Between the aerobic and anaerobic layers is the facultative layer, where dissolved oxygen is very low. Generally, dissolved oxygen is present during the day, but it is in an anaerobic state at night. Facultative microorganisms exist in this layer. These microorganisms can utilize free molecular oxygen and also take oxygen from nitrate or carbonate ions under anaerobic conditions.

[0044] Preferably, a water distribution channel 5 and a valve well 6 can be sequentially provided between the facultative pond 3 and the composite vertical subsurface flow constructed wetland. A water distribution valve can be installed in the valve well 6. The inlet of the water distribution valve is connected to the water distribution channel 5, and the outlet of the water distribution valve is connected to the water distribution pipe 7. Water in the facultative pond 3 can flow into the water distribution channel 5 through a water pump.

[0045] Preferably, the cross-sectional width of the water distribution channel 5 can be 1m and the depth can be 2m; the inlet diameter of the water distribution valve can be 25-30cm.

[0046] Preferably, drainage ditch A22-1 and drainage ditch B22-2 can both be 11-13cm deep, and their bottom surfaces can be on the same plane; and the angle between their bottom surfaces and the horizontal plane can be 8°-12°, sloping downward from drainage ditch A22-1 to drainage ditch B22-2.

[0047] Preferably, the diameter of the water distribution pipe 7 in the downstream pool 8 can be 10-12cm, and a water distribution port can be provided every 1.4-1.6m. The diameter of the water collection pipe 11 in the upstream pool 10 can be 10-12cm, and a water collection port can be provided every 1.4-1.6m, with a diameter of 18-20cm.

[0048] Preferably, in the thermal insulation composite filler bed system, the support layer can be made of limestone crushed stone with a particle size of 16-64mm and a thickness of 350-450mm; the purification layer can be made of a mixture of limestone, volcanic rock, and zeolite with a particle size of 8-32mm and a thickness of 650-750mm; the thermal insulation layer can be made of a mixture of perlite and volcanic rock with a particle size of 8-32mm and a thickness of 90-110mm; the planting density of plants on the composite vertical subsurface flow constructed wetland can be 40-60 plants / m². 2 .

[0049] Water from the facultative pond 3 is pumped into the distribution channel 5 of the composite vertical flow subsurface flow constructed wetland via pumps such as the wetland inlet lift pump 4. The water is then introduced into the downstream pool 8 via the distribution pipe 7 connected to the distribution channel 5. In the downstream pool 8, the substrate consists of a support layer (limestone gravel), a purification layer (limestone, volcanic rock, and zeolite composite functional filler), and an insulation layer (perlite and volcanic rock) – a composite filler bed structure that facilitates the normal functioning of the filler in each zone. Simultaneously, it forms a heat-insulating layer on the surface of the filler bed, blocking the impact of low atmospheric temperatures on the wetland interior and effectively preventing water temperature dissipation within the wetland bed. Furthermore, the upper layer plants preferentially include low-temperature tolerant plants such as reeds, cattails, and water onions, forming a low-temperature tolerant plant community, thereby reducing the impact of winter freezing in northern constructed wetlands. The distribution pipe 7 is located within the insulation layer and flows downwards, being purified sequentially by plant roots and the substrate within the purification layer. After the water flows downward into the drainage ditch in the support layer, it enters the upward pool 10 through the drainage ditch, forming an upward flow. The water is purified again after entering the upward pool 10, and finally collected by the water collection pipes 11 laid in the insulation layer and flows into the surface flow artificial wetland 13.

[0050] Preferably, a second outlet baffle wall 17 can be provided around the water storage tank 16, and an inlet pipe 28 connected to the water storage tank 16 can be provided inside the second outlet baffle wall 17. When the water level in the water storage tank 16 reaches the inlet of the inlet pipe 28, the water in the water storage tank 16 flows into the inlet pipe 28 and can flow into the river through the inlet pipe 28.

[0051] Preferably, the surface flow constructed wetland 13 can be 2m deep; in its three-layer filling matrix layer, the lower layer can be 55-65cm high and the particle size can be 7-8mm; the middle layer can be 25-35cm high and the particle size can be 2.5-3.5mm; the upper planting soil layer can be 9-11cm high; the planting density of the wetland can be 40-60 plants / m². 2 .

[0052] Water enters the surface flow constructed wetland 13, where lightweight expanded clay granules replace traditional soil or gravel as the substrate. The bottom layer consists of large-diameter expanded clay granules, the middle layer of small-diameter expanded clay granules, and the top layer is covered with topsoil planted with plants with well-developed root systems and hollow stems, such as reeds and cattails. Using expanded clay granules as the substrate avoids surface short-circuiting in the soil system. The porous nature of the expanded clay granules significantly increases the surface area, which is more conducive to microbial metabolic activity than gravel, thus improving water purification. Plants with well-developed root systems and hollow stems, such as reeds and cattails, can increase the dissolved oxygen content in the water. After treatment, the water reaches the outlet retaining wall and, as the water level gradually rises, flows along the wall into the storage tank 16 after reaching a certain limit.

[0053] Preferably, it may also include a winter bypass pipe 24 directly connected to the reservoir. The water collection pipe 11 may include multiple branch pipes 11 and a main pipe 11 connected to each branch pipe 11. The branch pipes 11 are located in the insulation layer of the upstream pool 10. The main pipe 11 has two outlets and two outlet valves: a first outlet and a first outlet valve 12 connected to the first outlet; a second outlet and a second outlet valve connected to the second outlet. The first outlet is connected to the surface flow constructed wetland 13. The second outlet is connected to the winter bypass pipe 24. When the surface temperature is greater than zero degrees Celsius, the second outlet valve is closed. Water treated by the composite vertical flow subsurface flow constructed wetland enters the surface flow constructed wetland 13 through the first outlet. When the surface temperature is less than or equal to zero degrees Celsius, the first outlet valve 12 is closed. Water treated by the composite vertical flow subsurface flow constructed wetland flows directly into the reservoir 16 through the winter bypass pipe 24, bypassing the surface flow constructed wetland 13.

[0054] In the cold winters of northern regions, the surface flow constructed wetland 13 is greatly affected by temperature, leading to low efficiency and even freezing of the water surface, rendering it unable to operate normally. Therefore, the water in the upstream pool of the composite vertical subsurface flow constructed wetland can be collected through the collection pipe 11 and then flow directly into the storage tank 16 through the winter bypass pipe 24, bypassing the surface flow constructed wetland 13. Finally, once the water in the storage tank 16 reaches a certain volume, it enters the original river channel through the river inlet pipe 28.

[0055] The present invention also provides an embodiment of a bypass multi-stage composite constructed wetland treatment method utilizing the above-described bypass multi-stage composite constructed wetland treatment system, the method being as follows:

[0056] The water to be treated enters facultative pond 3, where plants on the floating plant platform purify the water; the bottom ecological substrate of facultative pond 3 allows anaerobic microorganisms to reproduce and ferment, taking oxygen from nitrate or carbonate ions under anaerobic conditions.

[0057] Water in the facultative pond 3 enters the downstream pool 8 of the composite vertical flow constructed wetland through the water distribution pipe 7; in the downstream pool 8, after the water flows out from the water distribution pipe 7, it flows downstream to the drainage ditch A22-1, where the water is purified by the substrate in the purification layer of the downstream pool 8; in the upstream pool 10, the water in the drainage ditch B22-2 flows upstream into the water collection pipe 11 in the insulation layer, where the water is purified again by the substrate in the purification layer of the upstream pool 10.

[0058] Water collected by the collection pipe 11 flows into the surface flow constructed wetland 13; the middle and lower layers of the surface flow constructed wetland 13 are filled with ceramsite material to adsorb microorganisms and purify the water; the planting soil layer 25 of the surface flow constructed wetland 13 is planted with plants with well-developed root systems and hollow stems to increase the dissolved oxygen content in the water.

[0059] The surface flow constructed wetland 13 is equipped with multiple water flow baffles 14; the water flow baffles 14 and the first outlet baffle 15 in the surface flow constructed wetland 13 are used to increase the length of the water flow path and increase the contact time between the water and the biofilm generated on the roots and stems of the plants in the surface flow constructed wetland 13; the water storage tank 16 is used to collect and store the purified water.

[0060] The structure and working principle of the present invention will be further illustrated below with reference to a preferred embodiment:

[0061] Figure 1This is a schematic diagram of a bypass multi-stage composite constructed wetland treatment system according to the present invention. The facultative pond 3 has a length, width, and depth of 16m, 16m, and 3m, respectively. A wetland inlet pump 4 is installed at the bottom of the pond. The pipe connected to the inlet pump has a diameter of approximately 25-30cm. Water from the facultative pond 3 enters directly into a distribution channel 5 with a length, width, and depth of 16m, 1m, and 2m, respectively. The valve well 6 has the same specifications as the distribution channel 5. Water from the distribution channel 5 enters the downstream pool 8 of the composite vertical subsurface flow constructed wetland through distribution pipes 7. The distribution pipes 7 have a diameter of approximately 10-12cm and are laid in the middle of the insulation layer. A water inlet is set approximately every 1.5m. The water then flows downstream to drainage channel A22-1, which is 12cm high and is used to receive water from above. The channel has an inclination angle of approximately 10°, tilting downwards towards the upstream pool 10 to facilitate water delivery to the upstream pool 10. The upper water collection pipe 11 of the upper pool 10 is laid below the insulation layer to collect incoming water. The diameter of the water collection pipe 11 is approximately 10-12 cm, and a water collection inlet with a diameter of approximately 20 cm is installed approximately every 1.5 m. The overall length, width, and depth of the composite vertical subsurface flow constructed wetland are 29 m, 16 m, and 2 m respectively. The overall filling substrate, from bottom to top, consists of: a support layer of limestone crushed stone, 400 mm thick with a particle size of 16-64 mm; a purification layer of a mixture of limestone, volcanic rock, and zeolite, 700 mm thick with a particle size of 8-32 mm; and an insulation layer of a mixture of perlite and volcanic rock, 100 mm thick with a particle size of 8-32 mm. The planting density of the wetland is 50 plants / m². 2 The surface flow constructed wetland 13 has a length, width, and depth of 16m, 16m, and 2m respectively. The filling substrate consists of three layers: the bottom layer is filled with large-diameter expanded clay aggregate (7-8mm) to a height of 60cm; the middle layer is filled with small-diameter expanded clay aggregate (2.5-3.5mm) to a height of 30cm; and the top layer is a topsoil layer approximately 10cm high. The planting density on the wetland is 50 plants / m². 2 .

[0062] A first outlet retaining wall 15 is installed between the surface flow constructed wetland 13 and the reservoir 16. The first outlet retaining wall 15 is relatively low, with a height of approximately 1.2m. When the water depth in the surface flow wetland exceeds the soil layer by 20cm, it overflows from the first outlet retaining wall 15 and is collected by the reservoir 16. A second outlet retaining wall 17 is also installed around the reservoir 16, enclosing the reservoir 16 together with the first outlet retaining wall 15. The water depth in the reservoir 16 is 60cm. When the water level is too high, the water enters the river inlet pipe 28 installed inside the second outlet retaining wall 17 and flows into the original river channel.

[0063] The water treatment process of a bypass multi-stage composite constructed wetland treatment system is as follows:

[0064] (1) Untreated water in the river channel first enters the bypass branch canal through the bypass lifting device. The water in the bypass branch canal contains a large amount of kinetic energy and has a fast flow velocity. After the water flows out of the bypass branch canal, it first enters the slow-flow area formed by the concrete column 1 and the retaining wall in the facultative pond 3. The slow-flow area can significantly reduce the kinetic energy of the water and enhance the settling effect, effectively removing total suspended particulate matter in the river water. The hydraulic retention time of the facultative pond 3 is relatively long. The deep pond divides the water body into an aerobic layer, a facultative layer and an anaerobic layer. The aerobic layer can be planted with aquatic plants, mainly floating-leaved and emergent plants. The facultative layer contains facultative microorganisms, which can utilize free molecular oxygen and also absorb oxygen from nitrate or carbonate ions under anaerobic conditions. The water at the bottom of the pond is in an anaerobic state, and the biodegradability of the water can be increased through hydrolysis and acidification. An ecological substrate is set at the bottom of the end of the facultative pond 3 to provide conditions for the attachment and growth of anaerobic microorganisms, further improving the microbial treatment effect. However, due to the limited volume of the facultative pond 3 and insufficient water flow within it, the volume of water that can be treated is limited, and some of the water enters the subsequent treatment system. Since the facultative pond 3 is relatively deep, the system cannot provide a sufficient hydraulic gradient for the water flow. Therefore, a wetland inlet lift pump 4 is installed inside the facultative pond 3 to allow water to enter the distribution channel 5.

[0065] (2) After entering the distribution channel 5, the water flows through the distribution pipe 7 into the downstream pool 8 of the composite vertical subsurface flow constructed wetland. Then, it flows sequentially through drainage channels A22-1 and B22-2 to the upstream pool 10. The water passes through two purification layers. The volcanic rock in the purification layers has a good removal effect on nitrogen and phosphorus. In addition, the mixed use of zeolite and limestone can play a synergistic role, improving the removal effect on TN (total nitrogen) and TP (total phosphorus). Furthermore, the water distribution method of the composite vertical subsurface flow constructed wetland provides better reoxygenation, resulting in higher dissolved oxygen in the effluent. However, after the wetland has been operating for a period of time, the higher dissolved oxygen value leads to the accumulation of more microorganisms in the composite vertical subsurface flow constructed wetland, such as nitrifying bacteria and polyphosphate-accumulating bacteria. These microorganisms can further remove nitrogen and phosphorus through biochemical reactions. However, because the growth and reproduction of microorganisms exacerbate the consumption of dissolved oxygen in the vertical subsurface flow constructed wetland, the dissolved oxygen content of the effluent after treatment by the vertical subsurface flow constructed wetland is relatively low. Water treated by the upstream pool 10 is collected by the water collection pipe 11 and sent into the surface flow constructed wetland 13.

[0066] (3) The water flowing into the surface flow constructed wetland 13 comes into more full contact with the biofilm formed on the plant roots and stems due to the interception effect of the plant roots and stems. Organic matter can be removed through adsorption, absorption and biodegradation by the plant root biofilm, thus purifying the wastewater. The water flows around the first outlet end retaining wall 15, which increases the length of the water flow path and thus increases the degradation time of pollutants in the water. As for the problem of low dissolved oxygen content in the water, plants with well-developed root systems and hollow stems have a better oxygen transport capacity and can increase the dissolved oxygen content in the water. The water level in the surface flow constructed wetland 13 overflows after exceeding the top surface of the first outlet end retaining wall 15 and is collected by the water storage tank 16. A river inlet pipe 28 connected to the water storage tank 16 is set at a certain height on the second outlet end retaining wall 17. When the water storage tank 16 stores a certain amount of water, the liquid level reaches the inlet of the river inlet pipe 28, and the water in the water storage tank 16 flows into the river pipe 28 and flows into the original river channel.

[0067] (4) In cold winters, the surface flow constructed wetland 13 is greatly affected by temperature. The water in the upstream pool 10 of the composite vertical subsurface flow constructed wetland can be collected through the collection pipe 11 and then flow directly into the storage pool 16 through the winter bypass pipe 24. Since the storage pool 16 is designed to be shallow, the water can be enriched with oxygen in the atmosphere within the storage pool 16 to increase the dissolved oxygen content. Finally, after the water in the storage pool 16 reaches a certain volume, it enters the original river channel through the river inlet pipe 28.

[0068] This invention patent discloses a bypass multi-stage composite constructed wetland treatment system for purifying small urban rivers. It combines a facultative pond 3, a composite vertical subsurface flow constructed wetland 13, a surface flow constructed wetland 13, and a storage tank 16 according to their respective water treatment performance, achieving a complementary effect. This combination increases the water retention time in the early stages, ensuring sufficient time for degradation reactions in each treatment process. Ultimately, through multiple physical, chemical, and biological reactions, the raw water in the river is fully treated, resulting in a significant reduction in organic matter and eutrophic substances such as nitrogen and phosphorus. Furthermore, the system has a small overall footprint, lower pipeline maintenance and construction costs, less impact on the external environment, and is adaptable to seasonal changes and the limited treatment space in small urban rivers.

[0069] The embodiments described above are only used to illustrate the technical ideas and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The patent scope of the present invention should not be limited by these embodiments. That is, any equivalent changes or modifications made in accordance with the spirit disclosed in the present invention still fall within the patent scope of the present invention.

Claims

1. A bypass multi-stage composite constructed wetland treatment system, characterized in that, It includes facultative ponds, composite vertical subsurface flow constructed wetlands, surface flow constructed wetlands, and water storage ponds that are connected by sequential waterways; Within the facultative pond, a floating plant platform is provided at the upper level; and an ecological substrate for the growth and reproduction of microorganisms is provided at the bottom level. The composite vertical subsurface flow constructed wetland includes a downstream pool and an upstream pool connected by sequential water channels; a retaining wall is provided between the downstream pool and the upstream pool; both the downstream pool and the upstream pool are equipped with an insulated composite packing bed system; the insulated composite packing bed system consists of an insulation layer, a purification layer, and a support layer from top to bottom; in the downstream pool, a water distribution pipe is installed in the insulation layer, and a drainage channel A is installed in the support layer; in the upstream pool, a water collection pipe is installed in the insulation layer, and a drainage channel B is installed in the support layer; drainage channel A and drainage channel B are connected. The surface flow constructed wetland has a three-layer filling substrate: a lower layer of larger diameter ceramsite, a middle layer of smaller diameter ceramsite, and an upper layer of planting soil. Plants with well-developed root systems and hollow stems are planted in the planting soil layer. Multiple water flow retaining walls are set up perpendicular to the water flow direction in the surface flow constructed wetland. The water to be treated enters the facultative pond, and the water in the facultative pond enters the downstream pool of the composite vertical subsurface flow constructed wetland through the water distribution pipe; in the downstream pool, the water flows out from the water distribution pipe, and then flows sequentially through the purification layer and the support layer to the drainage ditch A; the water flows from the drainage ditch A into the drainage ditch B; in the upstream pool, the water in the drainage ditch B flows sequentially through the support layer and the purification layer and then into the water collection pipe in the insulation layer; the water collected by the water collection pipe flows into the surface flow constructed wetland; a first outlet end baffle is set between the surface flow constructed wetland and the water storage tank, and the water in the surface flow constructed wetland overflows from the first outlet end baffle to the water storage tank and is collected by the water storage tank; It also includes a winter bypass pipe directly connected to the reservoir. The water collection pipe includes multiple water collection branch pipes and a water collection main pipe connected to each water collection branch pipe. The water collection branch pipes are located in the insulation layer of the upstream reservoir. The water collection main pipe has two outlets and two outlet valves: a first outlet and a first outlet valve connected to the first outlet; a second outlet and a second outlet valve connected to the second outlet; the first outlet is connected to the surface flow constructed wetland; the second outlet is connected to the winter bypass pipe; when the surface temperature is greater than zero degrees, the second outlet valve is closed; when the surface temperature is less than or equal to zero degrees, the first outlet valve is closed.

2. The bypass multi-stage composite constructed wetland treatment system according to claim 1, characterized in that, The facultative pond also features a slow-flowing area formed by concrete columns and retaining walls.

3. The bypass multi-stage composite constructed wetland treatment system according to claim 1, characterized in that, Between the facultative pond and the composite vertical subsurface flow constructed wetland, a water distribution channel and a valve well are arranged in sequence, with a water distribution valve installed in the valve well; the inlet of the water distribution valve is connected to the water distribution channel, and the outlet of the water distribution valve is connected to the water distribution pipe; water in the facultative pond flows into the water distribution channel through a water pump.

4. The bypass multi-stage composite constructed wetland treatment system according to claim 1, characterized in that, A second outlet retaining wall is installed around the reservoir. Inside the second outlet retaining wall, there is an inlet pipe that connects to the reservoir. When the water level in the reservoir reaches the inlet of the inlet pipe, the water in the reservoir flows into the inlet pipe and into the river.

5. The bypass multi-stage composite constructed wetland treatment system according to claim 1, characterized in that, Drainage ditch A and drainage ditch B are both 11-13cm deep, and their bottom surfaces are on the same plane; the angle between their bottom surfaces and the horizontal plane is 8°-12°, and they slope downwards from drainage ditch A to drainage ditch B.

6. The bypass multi-stage composite constructed wetland treatment system according to claim 1, characterized in that, The diameter of the water collection pipe in the upstream pool is 10-12cm, and a water collection port with a diameter of 18-20cm is set every 1.4-1.6m.

7. The bypass multi-stage composite constructed wetland treatment system according to claim 1, characterized in that, In the thermal insulation composite filler bed system, the support layer is made of limestone crushed stone with a particle size of 16-64 mm and a thickness of 350-450 mm; the purification layer is made of a mixed material composed of limestone, volcanic rock and zeolite with a particle size of 8-32 mm and a thickness of 650-750 mm; and the thermal insulation layer is made of a mixed material composed of perlite and volcanic rock with a particle size of 8-32 mm and a thickness of 90-110 mm.

8. The bypass multi-stage composite constructed wetland treatment system according to claim 1, characterized in that, The surface flow constructed wetland is 2m deep; its three-layer filling substrate has the following layers: the lower layer is 55-65 cm high with a particle size of 7-8 mm; the middle layer is 25-35 cm high with a particle size of 2.5-3.5 mm; the upper layer of planting soil is 9-11 cm high; and the planting density on the wetland is 40-60 plants / m². 2 .

9. A method for bypassing multi-stage composite constructed wetland treatment using the bypass multi-stage composite constructed wetland treatment system according to any one of claims 1 to 8, the method comprising: The water to be treated enters the facultative pond, where plants on the floating plant platform purify the water; the ecological substrate at the bottom of the facultative pond allows anaerobic microorganisms to reproduce and ferment, taking oxygen from nitrate or carbonate ions under anaerobic conditions. Water from the facultative pond enters the downstream pool of the composite vertical subsurface flow constructed wetland through the water distribution pipe; in the downstream pool, after the water flows out from the water distribution pipe, it flows downstream to drainage ditch A, where the water is purified by the substrate in the purification layer of the downstream pool; in the upstream pool, the water in drainage ditch B flows upstream into the water collection pipe in the insulation layer, where the water is purified again by the substrate in the purification layer of the upstream pool. Water collected by the collection pipe flows into the surface flow constructed wetland; the middle and lower layers of the surface flow constructed wetland are filled with ceramsite material, which adsorbs microorganisms and purifies the water; the planting soil layer of the surface flow constructed wetland is planted with plants with well-developed root systems and hollow stems to increase the dissolved oxygen content in the water. The water flow retaining walls and the first outlet retaining wall in the surface flow constructed wetland are used to increase the length of the water flow path and increase the contact time between the water and the biofilm formed on the roots and stems of the plants in the surface flow constructed wetland; the water storage tank is used to collect and store the purified water.

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