Double-backflow wetland combined purification system

Abstract

The utility model discloses a double-backflow wetland combined purification system, which comprises a regulation and storage unit, a subsurface flow wetland and a surface flow wetland which are sequentially arranged and communicated along the water flow direction, an outer backflow pipeline which flows back to the regulation and storage unit is connected between the surface flow wetland and the regulation and storage unit, an inner backflow pipeline is connected onto the subsurface flow wetland, and the inner backflow pipeline is connected onto the surface flow wetland. The water inlet end of the internal reflux pipeline is connected to the rear part of the underflow unit, and the water outlet end of the internal reflux pipeline is connected to the front part of the underflow unit. According to the utility model, through a double-reflux water distribution mode and a process flow of stage treatment according to water quality and water quantity, the impact of the quality of incoming water exceeding the standard on the wetland system is prevented, the operation stability of the wetland system under the low-temperature condition in winter is improved, the blockage of the wetland filler is delayed through a multistage structure, the service life of the wetland is prolonged, and the water quality of the wetland is improved. The long-term stable and efficient operation of the wetland is ensured.

Description

Technical Field

[0001] The utility model belongs to the technical field of sewage treatment and relates to a double-return wetland combined purification system. Background Art

[0002] Artificial wetland combination technology is usually used for deep treatment of tailwater from sewage treatment plants and purification of surface water to reduce the content of pollutants in water and to supplement environmental water such as rivers and lakes, water for green space irrigation, and water for environmental sanitation and cleaning. However, the temperature in the upper reaches of the Yellow River is low in winter, and there are problems such as easy freezing of water bodies, unstable water quality and quantity, difficulty in improving standards, and high difficulty in operation and maintenance. Therefore, in view of the climate and hydrological characteristics of the upper reaches of the Yellow River, improvements to the wetland process are proposed to enable deep treatment of related sewage. Utility Model Content

[0003] The utility model aims to provide a double-return wetland combined purification system, which is suitable for use in low temperature and water-scarce environment in winter, for example, suitable for use in the upper reaches of the Yellow River, to achieve deep treatment of sewage.

[0004] The purpose of the utility model can be achieved through the following technical solutions:

[0005] A double-return wetland combined purification system comprises a regulating and storing unit, a subsurface flow wetland and a surface flow wetland which are sequentially arranged and connected along the water flow direction; an external return flow pipe which returns to the regulating and storing unit is connected between the surface flow wetland and the regulating and storing unit; an internal return flow pipe is connected to the subsurface flow wetland; a water inlet end of the internal return flow pipe is connected to the rear of the subsurface flow unit, and a water outlet end is connected to the front of the subsurface flow unit.

[0006] Optionally, the regulating and storing unit includes a communicating regulating and storing tank and an emergency tank, and a gate is provided on a water flow channel communicating the regulating and storing tank and the emergency tank.

[0007] Optionally, the storage unit is buried underground with a depth of ≥3.5m, a length-to-width ratio of ≥2, and a hydraulic retention time of ≥8h.

[0008] Optionally, it includes an incoming water channel, the ends of which are connected to a first branch and a second branch, the first branch is connected to the emergency pool, and the second branch is connected to the submerged flow wetland; gate valves are respectively provided on the first branch and the second branch; the emergency pool is connected to the submerged flow unit.

[0009] Optionally, the submerged flow wetland unit includes an inlet channel, an outlet channel and at least two levels of horizontal wetland units arranged in sequence; the inlet end of the internal return pipe is connected to the outlet channel, and the outlet end thereof is connected to the inlet channel.

[0010] Optionally, the horizontal wetland unit comprises a wetland pool, a filler layer is arranged in the middle of the wetland pool, and aquatic plants are planted in the filler layer to form a first aquatic plant layer; a first impermeable layer is arranged at the bottom of the wetland pool.

[0011] Optionally, the subsurface flow wetland has a depth of 1.5-1.8 m, an effective water depth of 1.2 m, an extra height of ≥ 0.5 m, and a hydraulic retention time of 2 days.

[0012] Optionally, the first anti-seepage layer includes a 300 mm thick clay layer and a HDPE two-cloth-one-film composite geotextile covering the clay layer.

[0013] Optionally, the compaction degree of the clay layer is ≥ 94%.

[0014] Optionally, the specification of the HDPE two-cloth-one-film composite geotextile is 1400g / m2.

[0015] Optionally, the filler of the packing layer is one or more of crushed stone, pebble, zeolite, and volcanic rock, and the particle size of the filler is 20 mm-60 mm.

[0016] Optionally, the filler particle size of the filler layer of the horizontal wetland unit at any level is smaller than the filler particle size of the filler layer of the horizontal submerged flow wetland unit at the previous level adjacent thereto.

[0017] Optionally, the surface flow wetland includes a purification pool, a second impermeable layer is provided at the bottom of the purification pool, and the second impermeable layer includes a 300 mm thick clay layer and a HDPE two-cloth-one-film composite geotextile covering the clay layer.

[0018] Optionally, emergent plants, submerged plants and floating-leaf plants are also planted in the surface flow wetland.

[0019] Optionally, the water depth of the surface flow wetland is 1.5m and the hydraulic retention time is 12h.

[0020] Optionally, the inner reflux pipe is connected to a reflux water pump; the outer reflux pipe is connected to a return water pump.

[0021] Optionally, the reflux flow rate of the internal reflux pipeline is 30% of the design flow rate.

[0022] Optionally, the reflux flow rate of the external reflux pipeline is 20%-50% of the design flow rate.

[0023] Optionally, it includes a control computer and a server communicatively connected to the control computer, and also includes a first water quality sensor, a second water quality sensor and a first water level sensor communicatively connected to the control computer respectively, the first water quality sensor is arranged at the water outlet position of the surface flow wetland, the second water quality sensor is arranged at the outlet channel, and the first water level sensor is arranged in the subsurface flow wetland.

[0024] Optionally, the control computer is communicatively connected to the reflux water pump and the return water pump respectively, and is also communicatively connected to the gate valves of the first branch and the second branch respectively.

[0025] The beneficial effects of the utility model include:

[0026] The utility model provides a double-return wetland combined purification system. The multi-level subsurface wetland structure delays the clogging of the wetland filler, prolongs the operating life of the wetland, and ensures the long-term stable and efficient operation of the wetland. The beneficial effects obtained by this utility model patent include:

[0027] 1. In seasons with more rain, such as short-term rainstorms in summer, mud is easy to run under the sewage treatment plant under such weather conditions, and the surface water is also prone to high turbidity. The regulating and storage unit has both emergency and regulating functions. On the one hand, as a front unit, it can play the role of pre-sedimentation and homogenization to prevent the high concentration of particulate matter in the upstream water from clogging the wetland matrix filler. On the other hand, the adjustable storage tank can store the water that meets the water quality requirements after wetland purification for regulation and reuse, which can play a certain auxiliary role in regional municipal water use, reduce municipal water pressure, and improve regional water resource utilization.

[0028] 2. Subsurface flow wetlands can effectively share the pollution load and improve the efficiency of sewage purification by grading and connecting multiple levels of horizontal wetland units with gradually decreasing filler particle sizes.

[0029] 3. In the upper reaches of the Yellow River, the amount and quality of water vary greatly in different seasons. The establishment of an internal return pipe can, on the one hand, achieve multiple treatments and purifications of the water body and extend the hydraulic retention time. On the other hand, due to the good circulating water dynamic conditions, especially in the winter season, the water inside the wetland will not freeze, thus ensuring the wetland purification efficiency and significantly increasing the wetland's ability to resist shock loads.

[0030] 4. For areas with concentrated rainstorms but water shortage and drought most of the time, such as the upper reaches of the Yellow River, the double-return wetland combined purification system disclosed in the utility model can ensure the vitality of the wetland system through the return system when the incoming water volume is small, maintain the growth requirements of plants, and avoid long-term water shortages that lead to deterioration of the wetland system; on the other hand, when the incoming water quality is poor, it can be circulated and purified to ensure that the effluent is stable and meets the standards by setting an external return system.

[0031] 5. The double-return wetland combined purification system disclosed in the utility model is equipped with a variety of operating conditions. It can automatically adjust according to water quality and quantity in conjunction with the real-time monitoring system, provide timely feedback in emergency situations, and realize intelligent operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a cross-sectional schematic diagram of the double-return wetland combined purification system disclosed in the utility model.

[0033] In the figure: 1. regulating and storage unit; 11. emergency pool; 12. regulating and storage pool; 13. gate; 2. subsurface flow wetland; 21. inlet channel; 22. first aquatic plant layer; 23. filler layer; 24. first anti-seepage layer; 25. outlet channel; 3. surface flow wetland; 31. second aquatic plant layer; 32. second anti-seepage layer; 4. internal return flow pipe; 5. external return flow pipe. DETAILED DESCRIPTION

[0034] The utility model provides a double-return wetland combined purification system, which is suitable for high-altitude and water-deficient areas in the upper reaches of rivers, such as the high-altitude and water-deficient areas in the upper reaches of the Yellow River. Through the combination of regulation and storage units and multi-stage combined wetland forms, combined with a double-return circulation system, the wetland's ability to resist shock loads is enhanced, the system's operating stability, overall purification efficiency and regional water resource utilization rate are improved, and it is not easy to freeze in winter, delaying blockage and facilitating operation and maintenance, thereby extending the operating life of the wetland and ensuring the long-term stable and efficient operation of the wetland.

[0035] The utility model is further described below in conjunction with the accompanying drawings and embodiments.

[0036] like Figure 1 The figure shows an exemplary embodiment of the double-return wetland combined purification system disclosed in the present utility model.

[0037] The utility model provides a double-return wetland combined purification system, comprising a regulating and storing unit 1, a subsurface wetland 2 and a surface wetland 3 which are sequentially arranged and connected along the water flow direction.

[0038] The storage unit 1 includes an emergency pool 11, and the sewage to be treated flows into the emergency pool 11 through an inlet pipe or a channel. The sewage entering the emergency pool 11 will be stagnant and precipitated in the emergency pool 11 for a certain period of time, and the particulate matter in the sewage will settle at the bottom of the emergency pool 11. The precipitated sewage will flow into the subsurface wetland 2.

[0039] The subsurface wetland 2 includes at least two levels of horizontal wetland units, which are arranged in an upstream and downstream order and are interconnected. The sewage precipitated in the emergency pool 11 flows through the two levels of horizontal wetland units in sequence.

[0040] The horizontal wetland unit includes a wetland pool. A first impermeable layer 24 is provided at the bottom of the wetland pool to reduce leakage and avoid pollution problems caused by sewage leakage as much as possible. A packing layer 23 is also arranged in the wetland pool. The packing layer 23 is mainly composed of porous fillers, so the packing layer 23 has a large number of pores. When sewage flows through the packing layer 23, pollutants such as fine particles will be intercepted by the packing layer 23, thereby further purifying the sewage. On the other hand, the gaps in the packing layer 23 can also provide a good growth environment for microorganisms that decompose organic pollutants such as nitrogen and phosphorus, and these microorganisms help to further improve the purification effect of sewage.

[0041] Many aquatic plants are also planted in the wetland pool, forming a first aquatic plant layer 22 on the upper layer of the water in the wetland pool. The first aquatic plant layer 22 can utilize the physiological characteristics and root system of aquatic plants to further purify sewage by absorbing, degrading and transforming pollutants.

[0042] Furthermore, the filler particle size of the filler layer 23 of any one level of the multi-level horizontal wetland units is smaller than the filler particle size of the filler layer 23 of the previous level of the wetland unit, but larger than the filler particle size of the filler layer 23 of the next level of the wetland unit.

[0043] In an exemplary embodiment, the subsurface wetland 2 includes three levels of horizontal wetland units arranged in sequence, wherein the particle size of the packing layer 23 of the first level horizontal wetland unit is larger than the particle size of the packing layer 23 of the second and third level horizontal wetland units, and the packing particle size of the packing layer 23 of the second level horizontal wetland unit is also larger than the packing particle size of the packing layer 23 of the third level horizontal wetland unit, thereby the three levels of horizontal wetland units can respectively intercept particulate pollutants of different diameters or sediment in the water, and can give full play to the interception effect of the packing layer 23 of the two levels of horizontal wetland units to achieve better purification effect. The multi-level structure delays the clogging of the wetland filler, prolongs the operating life of the wetland, and ensures the long-term stable and efficient operation of the wetland.

[0044] The submerged wetland 2 also includes an inlet channel 21 arranged at the front and an outlet channel 25 arranged at the rear, wherein the inlet channel 21 is arranged upstream of the first-level horizontal wetland unit and is connected to the first-level horizontal wetland unit, that is, the water flowing out of the emergency pool 11 first enters the inlet channel 21, and then flows into the first-level horizontal wetland unit through the inlet channel 21. The outlet channel 25 is arranged downstream of the last-level horizontal wetland unit and is connected to the outlet of the last-level horizontal wetland unit, and the water flowing out of the horizontal wetland unit flows out of the submerged wetland 2 through the outlet channel 25.

[0045] The water inlet channel 21 and the water outlet channel 25 can both play the role of uniform water flow and control the water level, so that the water flowing into the submerged flow wetland 2 and the water flowing out of the submerged flow wetland 2 can flow uniformly.

[0046] Furthermore, the water passage connecting the water inlet channel 21 and the first-level horizontal wetland unit is connected to the lower middle part of the wall of the wetland pool of the first-level horizontal wetland unit, so that the water flowing out of the water inlet channel 21 can directly flow into the packing layer 23, so that the water can flow through the packing layer 23, thereby avoiding untreated water flowing directly downstream.

[0047] Similarly, the water flow communication channels of the two adjacent horizontal wetland units are also arranged at the lower part of the wall of the wetland pool of the downstream horizontal wetland unit to ensure that the water flow can flow through the filler layer 23 of the horizontal wetland unit.

[0048] Furthermore, an internal return pipe 4 is provided between the outlet channel 25 and the inlet channel 21, that is, the inlet channel 21 and the outlet channel 25 are directly connected through the internal return pipe 4. Specifically, the water inlet end of the internal return pipe 4 is connected to the outlet channel 25, and the water outlet end is connected to the inlet channel 21. The internal return pipe 4 is also connected to a return water pump, so the water flow in the outlet channel 25 can flow back to the inlet channel 21 through the internal return pipe 4, and then flow into the horizontal wetland unit through the inlet channel 21 to achieve secondary treatment and purification. By providing the internal return pipe 4, the recycling treatment of sewage can be achieved, effectively avoiding the problem that the pollutant content of the water flowing out of the submerged wetland 2 is still high, and ensuring that the water flowing out of the submerged wetland 2 meets the treatment requirements.

[0049] On the one hand, the internal recirculation pipe 4 can realize multiple treatment and purification of the water body and extend the hydraulic retention time. On the other hand, due to the good circulating water dynamic conditions, the water body inside the wetland will not freeze, especially in the winter season, thus ensuring the wetland purification efficiency and significantly increasing the wetland's ability to resist impact loads.

[0050] Specifically, in order to ensure the sewage treatment effect, the return flow rate of the internal return pipe 4 is 30% of the flow rate of the submerged flow wetland 2.

[0051] Furthermore, the buried depth of the internal return pipe 4 is ≥1.5m. On the one hand, it can avoid human damage, rust, aging and other problems caused by the internal return pipe 4 being exposed to the ground. On the other hand, placing the pipe underground can also reduce the negative impact of the pipe on the natural landscape and improve the ecology of the horizontal subsurface flow wetland 2.

[0052] The filler layer 23 is made of crushed stone, pebbles, zeolite, volcanic rock, etc., and the particle size is 20mm-60mm.

[0053] The anti-seepage layer includes a clay layer and a geotextile layer covering the surface of the clay layer. The geotextile layer can reduce the scouring of the clay layer by water flow on one hand, and can also improve the anti-seepage effect of the anti-seepage layer on the other hand.

[0054] In order to ensure the anti-seepage effect of the anti-seepage layer, the compaction degree of the clay layer is ≥94%.

[0055] In an exemplary embodiment, the geotextile is a HDPE two-cloth-one-film composite geotextile, and the specification of the HDPE two-cloth-one-film composite geotextile is 1400g / m2.

[0056] The aquatic plants planted in the subsurface wetland 2 are emergent plants. Common emergent plants such as reeds, cattails, calamus, loosestrife and other cold-resistant emergent plants can be planted to ensure that the water purification effect can be achieved in winter.

[0057] External water enters the dual-return wetland combined purification system disclosed in the utility model through the water channel. The ends of the water channel are connected to a first pipeline and a second pipeline that are independent of each other, wherein the first pipeline is connected to the emergency pool 11, and the second pipeline is connected to the subsurface wetland 2. Gate valves are provided on the first branch and the second branch. When the gate valve of the second branch is closed, the water can only enter the emergency pool 11 through the first branch; when the gate valve of the first branch is closed and the gate valve of the second branch is kept open, the water can directly enter the subsurface wetland 2. If the amount of water is small, such as in winter, the water can be set to flow directly into the subsurface wetland 2, which can reduce the impact on the surface river runoff, thereby reducing the impact on the production and living water on both sides of the river.

[0058] The surface flow wetland 3 is arranged downstream of the subsurface flow wetland 2, and the water flowing out of the outlet channel 25 will enter the surface flow wetland 3. The surface flow wetland 3 includes a purification pool, and a second anti-seepage layer 32 is arranged at the bottom of the purification pool. The second anti-seepage layer 32 includes a clay layer covering the bottom of the purification pool and a geotextile layer laid on the surface of the clay layer. The geotextile layer can reduce the scouring of the clay layer by water flow on the one hand, and can also improve the anti-seepage effect of the clay layer on the other hand.

[0059] In order to ensure the anti-seepage effect of the second anti-seepage layer 32, the compaction degree of the clay layer is ≥ 94%.

[0060] Preferably, the geotextile is a HDPE two-cloth-one-film composite geotextile, and the specification of the HDPE two-cloth-one-film composite geotextile is 1400g / m2

[0061] In order to further purify the sewage, aquatic plants are also planted in the surface flow wetland 3 to form a second aquatic plant layer 31, and the aquatic plants include emergent plants, submerged plants and floating leaf plants.

[0062] Specifically, the emergent plants planted in the surface flow wetland 3 can be selected from reeds, cattails, calamus, loosestrife, etc., the submerged plants can be selected from dwarf cold-resistant Vallisneria, Potamogeton, Ceratophyllum, etc., and the floating leaf plants can be selected from varieties such as cold-resistant water lilies.

[0063] The water depth of the surface flow wetland 3 is 1.50 m, and the hydraulic retention time is 12 h, so as to ensure the retention time of sewage in the surface flow wetland 33 to further purify the sewage.

[0064] The regulating and storing unit 1 further comprises a regulating and storing tank 12 connected to the emergency tank 11. The regulating and storing tank 12 can be used to store regulating and storing water to replenish water flow to the subsurface wetland 2 and the surface wetland 3 in the dry season to maintain the water level of the wetland.

[0065] An openable gate 13 is provided in the water flow channel connecting the regulating reservoir 12 and the emergency pool 11. When the gate 13 is opened, the water in the regulating reservoir 12 can enter the emergency pool 11. If the water quality of the water entering the regulating reservoir 12 does not meet the standard, the water in the regulating reservoir 12 is discharged into the emergency pool 11 to re-purify the water that does not meet the standard.

[0066] The surface flow wetland 3 is also connected to an external return pipe 5. The inlet end of the external return pipe 5 is connected to the surface flow wetland 3, and the outlet end is connected to the regulating reservoir 12, which is also connected to a return water pump. The treated water discharged from the surface flow wetland 3 can enter the regulating reservoir 12 through the external return pipe 5 for storage and standby, and can be used for greening, irrigation or regulating the water level of the wetland.

[0067] An external reflow system is set up. On the one hand, when the incoming water volume is small, the reflow system can be used to ensure the vitality of the wetland system, maintain the growth needs of plants, and avoid long-term water shortages that may lead to deterioration of the wetland system. On the other hand, when the incoming water quality is poor, it is circulated and purified to ensure that the output water is stable and meets the standards.

[0068] The substandard water discharged from the surface flow wetland 3 will enter the regulating reservoir 12 through the external return pipe 5, and then enter the emergency pool 11 for sedimentation before flowing into the subsurface flow wetland 2 to enter the secondary treatment process. It should be understood that if the sewage after the secondary treatment still does not meet the standards, it can still enter the purification process again through the external return pipe 5 to ensure that the water discharged into the natural water body meets the standards.

[0069] If the water returned from the surface flow wetland 3 meets the treatment requirements, it is temporarily stored in the regulating reservoir 12 for standby use. At this time, the gate 13 is closed to ensure that the regulating reservoir 12 and the emergency reservoir 11 are independent of each other.

[0070] When the upstream water flow is large, the gate 13 can also be opened to use the regulating reservoir 12 to temporarily expand the emergency pool 11, so that the regulating reservoir unit 1 can accommodate more sewage and improve the sewage treatment capacity of the entire system.

[0071] Specifically, the external return flow pipe 5 is 20%-50% of the design flow rate.

[0072] Preferably, the burial depth of the external return pipe 5 and its accessories is ≥1.5m. On the one hand, it can avoid the problems of human damage, rust, aging, etc. caused by the external return pipe 5 being exposed to the ground. On the other hand, placing the external return pipe 5 underground can also reduce the negative impact of the pipe on the landscape and improve the ecology of the subsurface wetland 2.

[0073] The storage unit 1 is a semi-buried structure with an effective water depth of 3.5m, an extra height of 0.5m, and a hydraulic retention time of 8h. The wetland pool of the horizontal wetland unit in the subsurface wetland 2 is a reinforced concrete structure with an effective water depth of 1.2m, an extra height of 0.3m, and a hydraulic retention time of 2d. The surface wetland 3 is an impermeable pond with an effective water depth of 1.5m and a water retention time of 12h.

[0074] In an exemplary embodiment, the regulating and storage unit 1 is a concrete tank body that is mostly buried underground, and a partition wall arranged in the middle of the tank body divides the inside of the tank body into a regulating and storage tank 12 and an emergency tank 11. A water flow channel is formed on the partition wall for water flow, and a gate 13 is arranged on the water flow channel. The tank body has a top cover to prevent external foreign matter from entering and causing further pollution of the water body in the tank body.

[0075] The double-return wetland combined purification system also includes a water body monitoring system, which includes a control computer, a server, a first water quality sensor for monitoring the water quality of water discharged from the surface flow wetland 3, and a second water quality sensor for monitoring the water quality of water flowing out of the subsurface flow wetland 2. The first water quality sensor and the second water quality sensor are communicatively connected to the control computer, and the control computer receives and records the monitoring data of the first water quality sensor and the second water quality sensor, and transmits the monitoring data to the server for storage.

[0076] The control computer is also communicated with the return water pump and the return water pump. If the first water quality sensor detects that the water quality of the water flowing out of the surface flow wetland 3 does not meet the discharge requirements, the return water pump will work to make the water flow of the surface flow wetland 3 flow back to the regulating reservoir 12 through the external return pipe 5, and then the gate 13 will open, and the water to be treated in the regulating reservoir 12 will enter the emergency pool 11 and enter the water flow treatment process.

[0077] The gate 13 is also in communication connection with the control computer, and the control computer can control the opening and closing of the gate 13 to achieve water flow control of the regulating reservoir 12 and the emergency pool 11.

[0078] The second water quality sensor is arranged in the outlet channel 25. If the water quality flowing into the outlet channel 25 does not meet the standard, the control computer will control the return water pump to start, and the substandard water in the outlet channel 25 will be transported to the inlet channel 21 through the internal return pipe 4 and flow into the subsurface wetland 2 again for secondary purification.

[0079] The subsurface wetland 2 is provided with a first water level sensor for monitoring the water level, and the surface wetland 3 is also provided with a second water level sensor for monitoring the water level, and the first water level sensor and the second water level sensor are respectively connected to the control computer for communication. When the water level in the subsurface wetland 2 or the surface wetland 3 is too low to affect the wetland landscape or has a negative impact on plant growth, the control computer will send a control instruction to the gate 13, so that the water in the storage tank 12 can flow into the subsurface wetland 2 and the surface wetland 3.

[0080] The double-return wetland combined purification system disclosed in the utility model is divided into three working conditions according to whether the incoming water quality meets the standard, whether the incoming water volume meets the design requirements, and whether it is a winter low temperature period.

[0081] Working condition 1: When the incoming water quality exceeds the standard or the incoming water is less, the incoming water enters the emergency pool 11, the subsurface wetland 2, and the surface wetland 3 of the regulating and storage unit 1 in sequence, and the internal return pipe 4 and the external return pipe 5 are kept open. At the same time, the gate 13 of the regulating and storage unit 1 is also in an open state to ensure multiple circulation and purification of the water body.

[0082] Working condition 2: The incoming water quality meets the discharge requirements and the amount of water is large. The incoming water enters the emergency pool 11, subsurface wetland 2 and surface wetland 3 of the regulating and storage unit 1 in turn. The internal return pipe 4 and the closed gate station of the regulating and storage unit 1 are both closed. The external return pipe 5 is opened and closed intermittently to ensure that the regulating and storage unit 112 is full of water, and the remaining tail water is discharged.

[0083] Working condition 3: In winter, under low temperature conditions, the incoming water enters the emergency pool 11, subsurface wetland 2, and surface wetland 3 of the storage unit 1 in turn, the internal return pipe 4 is opened, the external return pipe is closed, and the tail water is directly discharged. The water purification effect of the combined process reaches a COD removal rate of 40%-60%, an ammonia nitrogen removal rate of 40%-70%, and a TP removal rate of 40%-60%. It does not freeze in winter and can achieve stable operation.

[0084] The above-mentioned related explanations and descriptions of the embodiments are for the purpose of facilitating the understanding and application of the present invention by ordinary technicians in the technical field. It is obvious that those familiar with the technical field can easily make various modifications to these contents and apply the general principles described herein to other embodiments without creative work. The present invention is not limited to the above-mentioned related explanations and descriptions of the embodiments. Improvements and modifications made by technicians in the field based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A double-return wetland combined purification system, characterized in that: The invention comprises a regulating and storing unit, a submerged flow wetland unit and a surface flow wetland which are sequentially arranged and connected along the water flow direction; an external return flow pipe returning to the regulating and storing unit is connected between the surface flow wetland and the regulating and storing unit; an internal return flow pipe is connected to the submerged flow wetland unit; an inlet end of the internal return flow pipe is connected to the rear of the submerged flow wetland unit, and an outlet end is connected to the front of the submerged flow wetland unit.

2. The double-return wetland combined purification system according to claim 1 is characterized in that: The regulating and storing unit comprises a connected regulating and storing pool and an emergency pool, and a gate is arranged on the water flow channel connecting the regulating and storing pool and the emergency pool; the regulating and storing unit is buried underground, with a depth of ≥3.5m, an aspect ratio of ≥2, and a hydraulic retention time of ≥8h.

3. The double-return wetland combined purification system according to claim 2 is characterized in that: It comprises an incoming water channel, the ends of which are connected with a first branch and a second branch, the first branch is connected with the emergency pool, and the second branch is connected with the submerged wetland unit; gate valves are respectively arranged on the first branch and the second branch; the emergency pool is connected with the submerged wetland unit.

4. The double-return wetland combined purification system according to claim 1 is characterized in that: The subsurface wetland unit includes an inlet channel, an outlet channel and at least two levels of horizontal wetland units arranged in sequence; the inlet end of the internal return pipe is connected to the outlet channel, and the outlet end thereof is connected to the inlet channel; the horizontal wetland unit includes a wetland pool, a filler layer is arranged in the middle of the wetland pool, and aquatic plants are planted in the filler layer to form a first aquatic plant layer; a first impermeable layer is arranged at the bottom of the wetland pool; the depth of the wetland pool is 1.5-1.8m, the effective water depth is 1.2m, the superelevation is ≥0.5m, and the hydraulic retention time is 2d; the first impermeable layer includes a 300mm thick clay layer and a HDPE two-cloth-one-film composite geotextile covering the clay layer.

5. The double-return wetland combined purification system according to claim 4 is characterized in that: The compaction degree of the clay layer is ≥94%; the specification of the HDPE two-cloth-one-film composite geotextile is 1400g / m 2 .

6. The double-return wetland combined purification system according to claim 4 is characterized in that: The filler of the packing layer is one of crushed stone, pebbles, zeolite and volcanic rock, and the particle size of the filler is 20mm-60mm; the filler particle size of the packing layer of the horizontal wetland unit at any level is smaller than the filler particle size of the packing layer of the adjacent previous level of horizontal wetland unit.

7. The double-return wetland combined purification system according to claim 1 is characterized in that: The surface flow wetland includes a purification pool, a second impermeable layer is arranged at the bottom of the purification pool, and the second impermeable layer includes a 300 mm thick clay layer and a HDPE two-cloth-one-film composite geotextile covering the clay layer; emergent plants, submerged plants and floating leaf plants are also planted in the surface flow wetland; the water depth of the surface flow wetland is 1.5 m, and the hydraulic retention time is 12 h.

8. The double-return wetland combined purification system according to claim 1 is characterized in that: The inner return pipe is connected with a return water pump; the outer return pipe is connected with a return water pump; the return flow rate of the inner return pipe is 30% of the design flow rate; the return flow rate of the outer return pipe is 20%-50% of the design flow rate.

9. The double-return wetland combined purification system according to claim 1 is characterized in that: It includes a control computer and a server connected to the control computer for communication, and also includes a first water quality sensor, a second water quality sensor and a first water level sensor connected to the control computer for communication, respectively. The first water quality sensor is arranged at the water outlet position of the surface flow wetland, the second water quality sensor is arranged at the outlet channel, and the first water level sensor is arranged in the submerged flow wetland unit.

10. The double-return wetland combined purification system according to claim 9, characterized in that: The control computer is respectively connected to the gate plate, the reflux water pump and the return water pump in communication, and is also respectively connected to the gate valves of the first branch and the second branch in communication.

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