Ecological system for deeply purifying tail water of sewage plant

Abstract

The utility model discloses an ecological system for deep purification of tail water of a sewage plant, which comprises a wetland purification unit, a vegetable purification unit and a symbiotic ecological unit, the wetland purification unit is arranged on the upstream of the vegetable purification unit, and the symbiotic ecological unit is arranged in the vegetable purification unit. According to the characteristics of water area, water environment conditions and the like, the wetland purification unit, the vegetable purification unit and the symbiotic ecological unit are constructed, the three units promote each other in the water treatment process, ecological treatment, tail water resource utilization and system stability improvement are achieved, and the purification efficiency of the system is kept for a long time; the planting range, the planting density and the planting mode of the aquatic vegetables are comprehensively planned, meanwhile, according to hydrodynamic conditions, combined with the impact resistance of the system, emergent aquatic plants are increased for water body slow flow in a large water body flow rate or large area, the survival rate and growth vigor of the aquatic vegetables can be effectively increased, and the space utilization rate is increased by reasonably arranging the vegetables and the plants, so that the ecological environment is improved. The purification capability of the system is enhanced.

Description

Technical Field

[0001] The utility model belongs to the technical field of environmental protection, and in particular relates to an ecological system for deep purification of tail water from a sewage plant. Background Art

[0002] Wastewater treatment plant tailwater is typically treated extensively before being used as a supplemental water source for natural water bodies and reused in cities. Currently, deep purification of wastewater plant tailwater in my country primarily relies on ecological restoration. This is primarily because ecological restoration not only purifies water bodies through the synergistic purification effects of plants, microorganisms, animals, and fillers within the ecosystem, but also significantly enhances the system's landscape and improves its ecological benefits.

[0003] Ecological restoration has been widely used due to its unique advantages, but there are also the following problems in the application process: (1) Due to the lack of systematicity and integrity, plant restoration is often the main method in ecological restoration construction, and important components of the ecosystem such as benthic animals, microorganisms, and animals are lacking. The proportions of various parts of the system are not coordinated, resulting in the lack of ecosystem structure and low ecological stability; (2) Tailwater resource utilization is to recycle and utilize useful substances in sewage. The most commonly used method is to rely on plants to absorb nutrients in tailwater and improve water quality through plant harvesting. However, plant harvesting and disposal require certain processing costs. Using vegetables as a way to utilize tailwater resources can effectively solve the problem of pollution purification. At the same time, vegetables generate economic value after harvesting, which is the most economical and effective way to utilize tailwater resources. In rural areas, a large number of plots are used for vegetable cultivation. If these plots are transformed and used for hydroponic vegetable cultivation, vegetables can be provided in all seasons through vegetable rotation. This will not only promote the further improvement of tailwater without changing the planting nature of the plots, but also provide economic benefits for local farmers through hydroponic vegetable cultivation. It is a resource utilization method suitable for rural areas; (3) The purification capacity and stability of the ecosystem are related to the dynamic factors of the water body, such as water flow velocity, water area and other environmental factors. It is also related to the system's utilization rate of water space. During the design and construction process, the environmental factors of the system and the method of system configuration are often ignored, and the spatial utilization rate of plants is low, which reduces the stability and processing efficiency of the entire system. Utility Model Content

[0004] In order to solve the technical problems existing in the prior art, the purpose of the utility model is to provide an ecosystem for deep purification of tail water from a sewage plant.

[0005] In order to achieve the above purpose and the above technical effects, the technical solution adopted by the present invention is:

[0006] An ecosystem for deep purification of tail water from a sewage treatment plant comprises a wetland purification unit, a vegetable purification unit and a symbiotic ecological unit. The wetland purification unit is arranged upstream of the vegetable purification unit, and the symbiotic ecological unit is arranged within the vegetable purification unit.

[0007] Furthermore, the wetland purification unit includes a water distribution area, a filling area and a water collection area which are sequentially arranged and connected along the water flow direction. The water distribution area is provided with an inlet pipe I, and the filling area is provided with fillers. The tail water of the sewage treatment plant enters the water distribution area from the inlet pipe I, and the outlet water of the water distribution area flows into the filling area and the water collection area in turn and then enters the vegetable purification unit.

[0008] Furthermore, the water distribution area and the filling area are connected through a water distribution pipe, the filling area and the water collection area are connected through an outlet pipe I, and the water collection area and the vegetable purification unit are connected through an outlet pipe II. The tail water of the sewage treatment plant enters the water distribution area from the inlet pipe I, then enters the filling area through the water distribution pipe, then enters the water collection area through the outlet pipe I, and finally enters the vegetable purification unit through the outlet pipe II.

[0009] Furthermore, the filling area includes gravel filling, zeolite filling and pebble filling arranged in sequence along the water flow direction, the gravel filling and zeolite filling as well as the zeolite filling and pebble filling are separated by permeable baffles respectively, and emergent plants are planted above the gravel filling, zeolite filling and pebble filling.

[0010] Furthermore, the particle size of the crushed stone filler is 2-4 cm, the particle size of the zeolite filler is 3-10 mm, and the particle size of the pebble filler is 3-10 mm.

[0011] Furthermore, planting soil of the same thickness is provided above the crushed stone filler, the zeolite filler and the pebble filler, and emergent plants are planted on the planting soil.

[0012] Furthermore, aquatic vegetables are planted in the vegetable purification unit through hydroponic vegetable floating boards, there is a height difference between the water outlet pipe II and the hydroponic vegetable floating boards, and the placement direction of the hydroponic vegetable floating boards is parallel to the water flow direction.

[0013] Furthermore, when the water flow rate is 0-0.01 m / s, the outlet pipe II is arranged above the hydroponic vegetable floating plate.

[0014] Furthermore, when the water flow rate is 0.01-0.7m / s, the outlet pipe II is arranged below the hydroponic vegetable floating board, and an emergent plant planting area is arranged inside the vegetable purification unit, downstream of the outlet pipe II and upstream of the symbiotic ecological unit. The designed water depth of the emergent plant planting area is 0.2-0.5m, and emergent plants are planted in the emergent plant planting area.

[0015] Furthermore, the symbiotic ecological unit includes benthic animals or submerged plants and benthic animals, and the submerged plants are planted in water areas without aquatic vegetable coverage.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] The utility model discloses an ecosystem for deep purification of tail water from a sewage treatment plant. According to the characteristics of water area, water environment conditions and the like, a wetland purification unit, a vegetable purification unit and a symbiotic ecological unit are constructed, which are suitable for different flow rates and different water areas. During the water treatment process, the three units promote each other to achieve ecological management, resource utilization of tail water and improvement of system stability, maintain the purification efficiency of the system for a long time, and maximize the ecological and economic benefits of the system. According to the root size, plant coverage, water flow rate and other aspects of the vegetables, the planting range, planting density and planting method of aquatic vegetables are comprehensively planned. At the same time, according to the hydrodynamic conditions and the impact resistance of the system, emergent plants are added in areas with large or larger water flow rates to slow the water flow, which can effectively improve the survival rate and growth of aquatic vegetables. By rationally arranging vegetables and plants, the space utilization rate is improved, and the interaction between plants, vegetables and microorganisms is utilized to enhance the purification capacity of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the structure of the utility model when the water flow rate is relatively low;

[0019] Figure 2 for Figure 1 A partial enlarged view of the middle part;

[0020] Figure 3 This is a schematic diagram of the structure of the utility model when the water flow rate is large or relatively large;

[0021] Figure 4 for Figure 3 A partial enlarged view of point B in the middle;

[0022] Figure 5 for Figure 3 A partial enlarged view of point C in the middle;

[0023] Among them, 1. Wetland purification unit; 2. Water inlet pipe I; 3. Water distribution area; 4. Filling area; 5. Water collection area; 6. Permeable baffle; 7. Gravel; 8. Zeolite; 9. Pebbles; 10. Outlet pipe II; 11. Aquatic vegetables; 12. Hydroponic vegetable floating board; 13. Submerged plants; 14. Benthic animals; 15. Emergent plants; 16. Drain pipe; 17. Vegetable purification unit; 18. Symbiotic ecological unit; 19. Emergent plant planting area; 20. Outlet pipe I; 21. Planting soil; 22. Water distribution pipe; 23. Outlet hole. DETAILED DESCRIPTION

[0024] The present invention is described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0025] The following is a brief summary of one or more aspects to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all conceivable aspects and is neither intended to identify key or critical elements of all aspects nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that will be provided later.

[0026] like Figure 1-5 As shown, an ecosystem for deep purification of sewage treatment plant tail water includes a wetland purification unit 1, a vegetable purification unit 17 and a symbiotic ecological unit 18, wherein the wetland purification unit 1 is arranged upstream of the vegetable purification unit 17, and the symbiotic ecological unit 18 is arranged inside the vegetable purification unit 17.

[0027] Wetland purification unit 1 uses an artificial wetland to purify tailwater and reduce pollution loads. The artificial wetland is a horizontal flow wetland, divided into a water distribution area 3, a filling area 4, and a water collection area 5 along the direction of water flow. A drain pipe 16 is installed within the water collection area 5, 0.1-0.15m near the bottom, to drain the water from the wetland purification unit 1. The fillers in the filler area 4 are divided into three types along the horizontal direction: crushed stone filler 7, zeolite filler 8, and pebble filler 9. The crushed stone filler 7 has a particle size of 2-4 cm and a height of 0.6-0.8 m, the zeolite filler 8 has a particle size of 3-10 mm and a height of 0.6-0.8 m, and the pebble filler 9 has a particle size of 3-10 mm and a height of 0.6-0.8 m. The crushed stone filler 7 and the zeolite filler 8, and the zeolite filler 8 and the pebble filler 9 are separated by a permeable baffle 6. A planting soil 21 with a thickness of 20-25 cm is set above the above three types of fillers. Emergent plants 15, such as calamus, canna, iris, etc., are planted above the planting soil 21. The planting density of the emergent plants 15 is 10-25 plants / m 2 The tail water of the sewage treatment plant enters the wetland purification unit 1 from the water inlet pipe Ⅰ2 set in the water distribution area 3. After the water flow is evenly distributed through the water distribution area 3, the tail water enters the filling area 4 from the water distribution pipe 22 set between the water distribution area 3 and the filling area 4. A number of water outlet holes 23 are opened on the water distribution pipe 22. The tail water passes through the crushed stone filling 7, zeolite filling 8 and pebble filling 9 in turn for purification, and then enters the water collection area 5 through the outlet pipe Ⅰ20 set between the filling area 4 and the water collection area 5. The water collection area 5 is connected to the vegetable purification unit 17 through the outlet pipe Ⅱ10. The outlet water of the water collection area 5 enters the vegetable purification unit 17 through the outlet pipe Ⅱ10.

[0028] The average depth of the vegetable purification unit 17 is 0.8-1.5m. The vegetable purification unit 17 is mainly composed of aquatic vegetables 11. The types of aquatic vegetables 11 are mainly aquatic vegetable varieties that can be grown all season, such as horse ear head, dragon tooth king, green leafy cabbage, meat vegetable, chicken feather vegetable, etc. The aquatic vegetables 11 are arranged at the rear of the wetland purification unit 1. The total coverage of vegetables and plants in the vegetable purification unit 17 does not exceed 60% of the water area. An emptying pipe 16 is also provided inside the vegetable purification unit 17 near the bottom at a distance of 0.1-0.15m to drain the water in the vegetable purification unit 17. Hydroponic vegetable floating boards 12 are used to grow aquatic vegetables 11 inside the vegetable purification unit 17. The size and placement of the hydroponic vegetable floating boards 12 are determined by factors such as the size of the water surface, the dissolved oxygen level in the water body, and the water flow rate. There is a height difference between the outlet pipe II 10 and the hydroponic vegetable floating board 12. The outlet pipe II 10 is set above the hydroponic vegetable floating board 12 or below the hydroponic vegetable floating board 12 according to the water flow rate. The selection principle is:

[0029] like Figure 1-2 As shown, for water areas with low water velocity (0-0.01 m / s), the type of aquatic vegetables 11 is not restricted, and the outlet pipe II 10 is set above the hydroponic vegetable floating board 12;

[0030] like Figure 3-5 As shown, for water areas with a high water flow rate (0.2-0.7 m / s), the outlet pipe II 10 is set below the hydroponic vegetable floating board 12, and an emergent plant planting area 19 is set inside the vegetable purification unit 17 and located downstream of the outlet pipe II 10 and upstream of the symbiotic ecological unit 18. The emergent plant planting area is kept at a distance greater than 0.5 m in radius from the outlet pipe II 10, within a range of 0.5-1 m, and the designed water depth of the emergent plant planting area is 0.2-0.5 m. Emergent plants 15, such as canna, loosestrife, rush, calamus, etc., are planted in the emergent plant planting area, with a planting density of 10-25 plants / m 2 The outflow from the water collection area 5 first enters the emergent plant planting area through the outlet pipe II 10. The emergent plants 15 block the water flow and reduce the water flow rate. Aquatic vegetables 11 are planted above and downstream of the emergent plant planting area and in the vegetable purification unit 17, that is, aquatic vegetables 11 are planted within the vegetable purification unit 17 within a radius of 1m from the outlet pipe II 10. The aquatic vegetables 11 are selected from vegetable varieties with large plants and well-developed root systems, and horse ear vegetables are preferred. The placement direction of the hydroponic vegetable floating board 12 is parallel to the water flow direction to reduce the adverse effect of the water flow on the growth of vegetables.

[0031] like Figure 3-5As shown, for water areas with a relatively high water flow rate (0.01-0.2 m / s), the outlet pipe II 10 is arranged below the hydroponic vegetable floating plate 12, and an emergent plant planting area 19 is arranged inside the vegetable purification unit 17 and downstream of the outlet pipe II 10 and upstream of the symbiotic ecological unit 18. The emergent plant planting area is kept at a distance greater than 0.3 m in radius from the outlet pipe II 10, within a range of 0.3-0.7 m. The designed water depth of the emergent plant planting area is 0.2-0.5 m, and emergent plants 15, such as canna, loosestrife, rush, calamus, etc., are planted in the emergent plant planting area, with a planting density of 10-25 plants / m 2 The outflow from the water collection area 5 first enters the emergent plant planting area through the outlet pipe Ⅱ10, and the water flow is blocked by the emergent plants 15 to reduce the water flow rate. Aquatic vegetables 11 are planted above the downstream of the emergent plant planting area and in the vegetable purification unit 17, that is, aquatic vegetables 11 are planted inside the vegetable purification unit 17 outside the radius of 0.7m from the outlet pipe Ⅱ10. Aquatic vegetables 11 are preferably selected from vegetable varieties with relatively developed root systems and strong plant tolerance, such as Longyahuang and green-leafed cabbage. The placement direction of the hydroponic vegetable floating board 12 is parallel to the water flow direction to slow down the adverse effects of the water flow on the growth of vegetables. The vegetable purification unit 17 is kept outside the radius of 0.7m from the water inlet.

[0032] The number of planting holes and the spacing between the planting holes on the hydroponic vegetable floating board 12 are determined by the coverage of the planted vegetables. The planting hole spacing is 10-25cm and the hole diameter is 25-40mm. For vegetables with small plant coverage (such as broccoli), a hydroponic vegetable floating board 12 with a planting hole spacing of 10cm and a hole spacing of 25-35mm is used.

[0033] The steps for growing vegetables on the hydroponic vegetable floating plate 12 are as follows:

[0034] First, remove the seedlings of aquatic vegetables 11 from the soil-cultured seedling tray. For vegetables with few or short roots, carefully use your fingers to break the vegetables into separate vegetable plants, and then plant them in the planting holes. For vegetables with many or entangled roots, first soak the vegetable roots in a small amount of water for 3-8 seconds and gently shake the vegetable roots. After rinsing, gently separate the vegetable roots with your hands, and then plant the vegetables. Use planting cotton to clamp the end of the vegetable stem close to the root system, and then place the plant roots in the planting hole. Fix the plant by plugging the planting cotton into the planting hole.

[0035] The symbiotic ecological unit 18 includes benthic animals 14 or submerged plants 13 and benthic animals 14. According to the area of ​​the water area, appropriate numbers of submerged plants 13 and benthic animals 14 are added to the bottom of the vegetable purification unit 17. The submerged plants 13 are planted in the water area without aquatic vegetables 11 covering the submerged plants 13. The planting density of the submerged plants 13 is preferably 30-50 plants / m 2After planting submerged plants13, depending on the completeness of ecological elements, snails, clams, fish, etc. are appropriately released as benthic animals14, and low-temperature-resistant microorganisms are added to the bottom mud to form a stable water ecosystem and improve the purification efficiency of the system.

[0036] The submerged plants 13 are selected and arranged according to the water depth and water flow velocity. The specific arrangement method is as follows:

[0037] For waters with a depth of 0.5-1.2m, a very slow water velocity (0-0.01m / s), and low water transparency, submerged plants 13 include Vallisneria serrata and Hydrilla verticillata.

[0038] For waters with a water depth of 0.5-1.2m, a very low water velocity (0-0.01m / s), and high water transparency, submerged plants 13 are selected such as hornwort, foxtail algae, and comb-toothed pondweed.

[0039] For waters with a depth of 1.2-1.5m, a very slow water velocity (0-0.01m / s), and low water transparency, submerged plants 13 should be selected, such as Vallisneria;

[0040] For waters with a water depth of 1.2-1.5m, a very low water flow rate (0-0.01m / s) and high water transparency, submerged plants 13 are planted together with plants such as duckweed and foxtail algae. In waters with a higher water flow rate (0.01-0.7m / s), submerged plants 13 are uniformly selected as Elodea. In waters with an even higher water flow rate (greater than 0.7m / s), submerged plants 13 are not planted.

[0041] Example 1

[0042] The experimental site was the Hengtong Hehai Project Base. The water used in the experiment consisted of tailwater from the sewage treatment plant, which passed through wetland purification unit 1, vegetable purification unit 17, and symbiotic ecological unit 18 before being discharged. Wetland purification unit 1 measures 1.5 m long, 1.1 m wide, and 1.1 m high. The horizontal flow wetland is divided into a water distribution area 3, a filling area 4, and a catchment area 5 along the water flow direction. Water distribution area 3, serving as the tailwater inlet, measures 0.3 m long, 1.1 m wide, and 1.1 m high. Filling area 4 measures 1 m long, 1.1 m wide, and 1.1 m high. The fillers in filling area 4 are divided horizontally into three types: crushed stone 7, zeolite 8, and pebble 9. These three types of fillers are separated by permeable baffles 6 and topped with a 20 cm thick layer of planting soil 21. After being purified by the fillers, tailwater from water distribution area 3 enters catchment area 5, which measures 0.2 m long, 1.1 m wide, and 1.1 m high. The tailwater from wetland purification unit 1 enters vegetable purification unit 17, with an outlet velocity of 0.005 m / s. Vegetable purification unit 17 measures 1.1 m long, 1.1 m wide, and 1.1 m high. Hydroponic vegetable floating plates 12 are used to grow aquatic vegetables 11 within vegetable purification unit 17. These vegetables include safflower, dragon tooth king, and green-leafed cabbage. Appropriate quantities of submerged plants 13 and benthic animals 14 are introduced into vegetable purification unit 17 based on the water area. Submerged plants 13 include Vallisneria and Myriophyllum, while benthic animals 14 include benthic snails.

[0043] Initial tail water quality: COD Mn 7.199 mg / L, ammonia nitrogen NH4 + -N is 1.069 mg / L, total phosphorus TP is 0.914 mg / L, total nitrogen TN is 10.59 mg / L, tail water quality is level B, tail water volume is 1t, system operation cycle is 15 days, system daily cycle is 4 hours, and the COD, ammonia nitrogen, total nitrogen and total phosphorus water quality data after treatment of the ecosystem of the sewage plant tail water deep purification in this embodiment are measured 1, 4, 7, 11, 13 and 15 days after operation, and the survival rate and nutritional indicators of the aquatic vegetables 11 are measured at the end of the experiment. The results are recorded in the following Tables 1-2, Table 1 shows the water quality before and after treatment, and Table 2 shows the survival rate of the aquatic vegetables 11.

[0044] Table 1

[0045] Time (d) <![CDATA[COD Mn (mg / L)]]> <![CDATA[NH4 + -N(mg / L)]]> Total phosphorus (mg / L) Total nitrogen (mg / L) 0 7.199 1.069 0.914 10.59 1 7.147 0.536 0.339 9.264 4 7.096 0.249 0.294 9.072 7 6.679 0.083 0.206 7.957 11 5.863 0.053 0.119 7.767 13 5.537 0.044 0.111 7.413 15 5.424 0.031 0.029 6.146 15-day removal rate 24.7％ 97.1％ 96.8％ 42.0％

[0046] As can be seen from Table 1, the deep purification ecosystem of the sewage plant tail water in this embodiment can effectively reduce the COD in the tail water. Mn 、Ammonia nitrogen NH4 + -N, total phosphorus TP, total nitrogen TN pollutant content. COD MnAfter 7 days, the pollutant purification capacity gradually increased and reached a relatively stable state on the 13th day. On the 15th day, COD Mn The removal rate of NH4 reaches 24.6%. + -N purification effect is better within 1-7 days, and the purification effect slows down after 7 days. This is mainly because the system relies on the filler to purify NH4 + -N adsorption, after 7 days, microbial biofilm is enhanced, resulting in NH4 + -N removal rate increased to more than 97%. The system's ability to remove TN was poor in the first 4 days. After 4 days, as the vegetables and plants grew adaptively and the microbial activity increased, the system's denitrification function was enhanced, resulting in improved TN removal. On the 15th day, the TN removal rate had reached 42%. TP had the strongest adsorption effect within 1 day, which was closely related to the strong adsorption performance of the filler. After 1 day, the TP removal effect remained at a high level. The main reason was the increase in the biomass of plants and microorganisms, and the increase in the biological uptake of nutrients, resulting in a better TP removal effect of the system. Within 15 days, the TP removal effect had reached 96.8%. Analyzing the water quality data of the system from day 1 to day 15, the treatment effect of the entire system had reached a relatively stable state on the 13th day. Analyzing the water quality data on the 15th day, the effluent COD Mn is 5.424 mg / L, TP is 0.029 mg / L, NH4 + -N is 0.031mg / L and TN is 6.146mg / L, and the effluent NH4 + -N and TP water quality can reach Class I surface water standard, and TN can reach Class A urban sewage standard.

[0047] Table 2

[0048] variety Quantity (stock) Survival rate (%) Cultivation cycle (days) Dragon Bud King 17 100 15 Green leafy cabbage 39 100 15 Horse ears 32 100 15

[0049] As shown in Table 2, the survival rate of Longyahuang, Green Leaf Bordered Cabbage and Horse Ear Head Plant is 100%, indicating that these aquatic vegetables can adapt well to the current water quality and can be better used in Class B water quality.

[0050] Parts or structures not specifically described in the present invention may adopt existing technologies or existing products and will not be described in detail here.

[0051] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. An ecosystem for deep purification of sewage plant tail water, characterized in that: It comprises a wetland purification unit, a vegetable purification unit and a symbiotic ecological unit. The wetland purification unit is arranged upstream of the vegetable purification unit, and the symbiotic ecological unit is arranged inside the vegetable purification unit.

2. The ecosystem for deep purification of tail water from a sewage treatment plant according to claim 1, characterized in that: The wetland purification unit includes a water distribution area, a filling area and a water collection area which are sequentially arranged and connected along the water flow direction. The water distribution area is provided with an inlet pipe I, and the filling area is provided with fillers. The tail water of the sewage treatment plant enters the water distribution area from the inlet pipe I, and the outlet water of the water distribution area flows into the filling area and the water collection area in turn and then enters the vegetable purification unit.

3. The ecosystem for deep purification of tail water from a sewage treatment plant according to claim 2, characterized in that: The water distribution area and the filling area are connected through a water distribution pipe, the filling area and the water collection area are connected through an outlet pipe I, and the water collection area and the vegetable purification unit are connected through an outlet pipe II. The tail water of the sewage treatment plant enters the water distribution area from the inlet pipe I, then enters the filling area through the water distribution pipe, then enters the water collection area through the outlet pipe I, and finally enters the vegetable purification unit through the outlet pipe II.

4. The ecosystem for deep purification of tail water from a sewage treatment plant according to claim 2, characterized in that: The filling area includes crushed stone filling, zeolite filling and pebble filling arranged in sequence along the water flow direction. The crushed stone filling and the zeolite filling, as well as the zeolite filling and the pebble filling are separated by permeable baffles respectively. Emergent plants are planted above the crushed stone filling, zeolite filling and pebble filling.

5. The ecosystem for deep purification of tail water from a sewage treatment plant according to claim 4, characterized in that: The particle size of the crushed stone filler is 2-4 cm, the particle size of the zeolite filler is 3-10 mm, and the particle size of the pebble filler is 3-10 mm.

6. The ecosystem for deep purification of tail water from a sewage treatment plant according to claim 4, characterized in that: Planting soil of the same thickness is arranged above the crushed stone filler, the zeolite filler and the pebble filler, and emergent plants are planted on the planting soil.

7. The ecosystem for deep purification of tail water from a sewage treatment plant according to claim 3, characterized in that: Aquatic vegetables are planted in the vegetable purification unit through hydroponic vegetable floating boards. There is a height difference between the water outlet pipe II and the hydroponic vegetable floating boards, and the placement direction of the hydroponic vegetable floating boards is parallel to the water flow direction.

8. The ecosystem for deep purification of tail water from a sewage treatment plant according to claim 7, characterized in that: When the water flow rate is 0-0.01 m / s, the outlet pipe II is arranged above the hydroponic vegetable floating plate.

9. The ecosystem for deep purification of tail water from a sewage treatment plant according to claim 7, characterized in that: When the water flow rate is 0.01-0.7m / s, the outlet pipe II is arranged below the hydroponic vegetable floating board, and an emergent plant planting area is arranged inside the vegetable purification unit, downstream of the outlet pipe II and upstream of the symbiotic ecological unit. The designed water depth of the emergent plant planting area is 0.2-0.5m, and emergent plants are planted in the emergent plant planting area.

10. The ecosystem for deep purification of tail water from a sewage treatment plant according to claim 1 or 9, characterized in that: The symbiotic ecological unit includes benthic animals or submerged plants and benthic animals, and the submerged plants are planted in water areas without aquatic vegetable cover above.

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