Multistage composite constructed wetland coupled ecological floating bed system

Abstract

The utility model discloses a multi-stage composite constructed wetland coupled ecological floating bed system, which belongs to the technical field of water pollution control and ecological restoration, and comprises a pretreatment unit, a multi-stage constructed wetland module and an ecological floating bed module, the multi-stage constructed wetland module respectively adopts zeolite, charcoal and oyster shell filler, and combines with reed, acorus calamus and other plants, and the ecological floating bed module is connected with the pretreatment unit. Suspended matters, COD (Chemical Oxygen Demand), ammonia nitrogen and total phosphorus are removed in a grading manner; the ecological floating bed module is arranged in a final-stage wetland water outlet area, cress and thalia dealbata are planted by adopting a modified polyethylene frame, and a load biological rope is suspended below the ecological floating bed module. Oyster shell filler chemical phosphorus removal, three-stage wetland-floating bed feedback coupling nitrogen removal and anti-blocking grading design are innovatively introduced, the effluent standard that COD is smaller than or equal to 30 mg / L, ammonia nitrogen is smaller than or equal to 2 mg / L and total phosphorus is smaller than or equal to 0.5 mg / L is achieved, and meanwhile the operation and maintenance cost is reduced through economic crop planting. The system has high efficiency, long-term effect and resource benefit, and is suitable for treatment of domestic sewage, agricultural non-point source and river eutrophication water.

Description

TECHNICAL FIELD

[0001] The utility model relates to water pollution control and ecological restoration technical field especially, relates to a kind of multistage composite constructed wetland coupling ecological floating bed system. BACKGROUND

[0002] With the acceleration of urbanization and the intensification of industrial and agricultural activities, water pollution problems are increasingly prominent, traditional wastewater treatment technology (such as chemical method, activated sludge method) can effectively remove pollutants, but there are problems such as high operation cost, high energy consumption, easy to produce secondary pollution, etc. Under this background, ecological management technology gradually becomes a research hotspot in the field of water environment restoration due to its environmental friendliness, low cost and sustainability. As two typical ecological treatment technologies, constructed wetland and ecological floating bed have been widely applied in practice, but their respective technical limitations limit the further improvement of treatment effect.

[0003] Traditional constructed wetland has the following problems, single structure design is mostly used, single pollutant removal approach, low efficiency, it is difficult to realize the synergistic and efficient removal of nitrogen, phosphorus, organic matter, heavy metal and other pollutants. For example, the removal of ammonia nitrogen in traditional subsurface flow wetland depends on microbial nitrification, but under low temperature or high load conditions, insufficient dissolved oxygen can easily lead to a sharp drop in denitrification efficiency; at the same time, the problems of high risk of substrate blockage, long hydraulic retention time, large land occupation area also restrict its popularization and application. In addition, the single wetland unit has weak impact load capacity, is easily affected by seasonal changes or water quality fluctuations, resulting in insufficient effluent stability, low microbial activity, easy to block, lack of adaptability to low temperature environment. UTILITY MODEL CONTENT

[0004] To solve the problems of low treatment efficiency, low microbial activity, easy to block and lack of adaptability to low temperature environment, the utility model provides a kind of multistage composite constructed wetland coupling ecological floating bed system, and the technical scheme is as follows:

[0005] A kind of multistage composite constructed wetland coupling ecological floating bed system, including pretreatment unit, multistage constructed wetland module and ecological floating bed module;

[0006] The pretreatment unit includes grid well and adjusting sedimentation tank, artificial grid is installed in the grid well, and the grid bar gap of the artificial grid is 5mm;

[0007] The multistage constructed wetland module includes first vertical flow wetland, second horizontal flow wetland and third tidal flow wetland, the main filter material layer of the first vertical flow wetland is zeolite layer, the filler layer of the second horizontal flow wetland is biochar and volcanic rock from left to right, and the main filter material layer of the third tidal flow wetland is oyster shell layer, and the lower drainage layer of the first vertical flow wetland and the third tidal flow wetland is gravel;

[0008] The ecological floating bed module comprises a floating bed carrier and a polyester biological rope, is arranged in an effluent area of a final-stage wetland, plants of the ecological floating bed module are configured as reevesia japonica and water celery, the floating bed carrier adopts a modified polyethylene frame, and the polyester biological rope is arranged at the bottom of the floating bed carrier.

[0009] The modular design can be flexibly matched with different treatment scales, is suitable for comprehensive treatment of domestic sewage, agricultural non-point source pollution and eutrophication river, has a large-scale application potential, and realizes "oxygenation-anoxia-oxygenation" environment through three-stage wetlands in series, breaks through the denitrification and phosphorus removal bottleneck of traditional processes by combining oyster shell fillers (chemical phosphorus removal) and biochar / volcanic rock (enhanced denitrification).

[0010] Preferably, the hydraulic retention time of the adjusting sedimentation tank is 2h, and the surface load is 1.2m 3 / (m 2 ·h).

[0011] Preferably, the particle size of the zeolite layer is 10-20mm, and the thickness is 600mm, and the particle size of the gravel is 30-50mm, and the thickness is 300mm.

[0012] Preferably, the plants of the first-stage vertical flow wetland are reeds, the planting density of the reeds is 6-8 / m 2 , and the root depth is 60-80cm.

[0013] Preferably, the particle size of the biochar is 5-10mm, the specific surface area is greater than or equal to 800m 2 / g, the volume accounts for 40% of the total volume, the particle size of the volcanic rock is 15-25mm, and the volume accounts for 60% of the total volume.

[0014] Preferably, the plants of the second-stage horizontal flow wetland are acorus calamus, and the planting density of the acorus calamus is 4-6 / m 2 .

[0015] Preferably, the particle size of the oyster shell layer is 20-30mm, and the thickness is 600mm, and the third-stage tidal flow wetland is emptied once a week.

[0016] Preferably, the modified polyethylene frame is added with 2% nano-TiO2 ultraviolet resistance agent, and the porosity is greater than or equal to 80%.

[0017] Preferably, the proportion of the water celery is 70%, the planting density is 25 / m 2 , the proportion of the reevesia japonica is 30%, the planting density is 8 / m 2 , and the root depth is greater than or equal to 1.2m.

[0018] Preferably, the length of the polyester biological rope is 1.5m, and the specific surface area is greater than or equal to 500m2 / m 3 The suspension interval is 20cm, and the biofilm thickness is 1-2mm.

[0019] The tidal flow wetland is subjected to hydraulic flushing every week, so that the permeability coefficient is restored to 95% of the initial value, and the permeability coefficient of the filler is maintained at 87% after the system is operated for 1 year, thereby significantly prolonging the maintenance period, greatly improving the anti-clogging performance, prolonging the service life of the modified polyethylene floating bed (anti-ultraviolet + anti-erosion) to more than 10 years, and reducing the replacement frequency of the biofilm assembly (polyester biological rope), so that the system can be stably and long-efectively operated.

[0020] Beneficial effects:

[0021] The beneficial effects of the technical scheme of the utility model are as follows:

[0022] 1. The multi-stage composite constructed wetland coupled ecological floating bed system adopts modular design, can be flexibly matched with different treatment scales, is suitable for comprehensive treatment of domestic sewage, agricultural non-point source pollution and eutrophication river, has potential for large-scale application, realizes "oxygenation-anoxia-oxygenation" environment through three-stage wetlands in series, and breaks through the bottleneck of traditional process denitrification and phosphorus removal in combination with oyster shell filler (chemical phosphorus removal) and biochar / volcanic rock (intensified denitrification).

[0023] 2. The multi-stage composite constructed wetland coupled ecological floating bed system, the permeability coefficient of the tidal flow wetland is restored to 95% of the initial value through hydraulic flushing every week, and the permeability coefficient of the filler is maintained at 87% after the system is operated for 1 year, thereby significantly prolonging the maintenance period, greatly improving the anti-clogging performance, prolonging the service life of the modified polyethylene floating bed (anti-ultraviolet + anti-erosion) to more than 10 years, reducing the replacement frequency of the biofilm assembly (polyester biological rope), and enabling the system to be stably and long-efectively operated.

[0024] 3. The multi-stage composite constructed wetland coupled ecological floating bed system, water celery and reed orchid are combined to be planted, realizes "pollution treatment-income" virtuous cycle, has lower operation and maintenance cost than traditional process, is suitable for low-cost demand of decentralized sewage treatment, and the plant root systems of reed, aconite and the like promote microbial proliferation and improve water self-purification capacity; the ecological floating bed enhances landscape effect, is suitable for river and landscape water body repair, filler gradation and plant selection optimization ensure stable operation of the system under complex conditions such as low temperature and high load. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical scheme of the embodiments of the utility model, the following will briefly introduce the drawings needed to be used in the embodiments, and it should be understood that the following drawings only show some embodiments of the utility model, and therefore should not be regarded as a limitation to the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0026] Figure 1 This is a schematic diagram of the overall structure of a multi-level composite artificial wetland coupled ecological floating bed system according to this utility model.

[0027] In the diagram: 1. Grille well; 2. Equalizing sedimentation tank; 3. Primary vertical flow wetland; 4. Gravel; 5. Zeolite layer; 6. Reed; 7. Biochar; 8. Volcanic rock; 9. Sweet flag; 10. Secondary horizontal flow wetland; 11. Oyster shell layer; 12. Tertiary tidal flow wetland; 13. Thalia dealbata; 14. Water celery; 15. Floating bed carrier; 16. Polyester bio-rope. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this utility model, not all of them. Therefore, the following detailed description of the embodiments of this utility model provided in the accompanying drawings is not intended to limit the scope of the claimed utility model, but merely to represent selected embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model.

[0029] like Figure 1 As shown, a multi-level composite artificial wetland coupled with an ecological floating bed system includes a pretreatment unit, a multi-level artificial wetland module, and an ecological floating bed module;

[0030] The pretreatment unit includes a bar screen well 1 and an equalization sedimentation tank 2. The pretreatment unit can be integrated with a multi-stage constructed wetland module or it can be separated. The bar screen well 1 is equipped with an artificial bar screen with a bar spacing of 5mm.

[0031] In this embodiment, the hydraulic retention time of sedimentation tank 2 is adjusted to 2 hours, and the surface loading is 1.2 m³. 3 / (m 2 •h) Removes suspended solids from wastewater and regulates water quality and quantity to prevent blockage of subsequent wetland units and fluctuations in water quantity and quality load that could affect the normal operation of multi-stage constructed wetland modules.

[0032] like Figure 1 As shown, the multi-level constructed wetland module includes a primary vertical flow wetland 3, a secondary horizontal flow wetland 10, and a tertiary tidal flow wetland 12;

[0033] The main filter layer of the primary vertical flow wetland 3 is zeolite layer 5, with a particle size of 10-20 mm and a thickness of 600 mm. The plant selected for the primary vertical flow wetland 3 is reed 6, with a planting density of 6-8 plants / m².2 , the root depth is 60-80 cm, the pollution resistance is strong, the root exudates promote the proliferation of nitrifying bacteria, the first vertical flow wetland 3 can provide an aerobic environment, and adsorbs and degrades COD, ammonia nitrogen and SS;

[0034] The filler layer of the second horizontal flow wetland 10 is composed of biochar 7 and volcanic rock 8 from left to right, the particle size of the biochar 7 is 5-10 mm, the specific surface area is greater than or equal to 800 m 2 / g, the volume accounts for 40% of the total volume, the particle size of the volcanic rock 8 is 15-25 mm, the volume accounts for 60% of the total volume, the plants of the second horizontal flow wetland 10 are selected from Acorus calamus 9, and the planting density of the Acorus calamus 9 is 4-6 plants per square meter 2 , the root exudates of organic acids strengthen denitrification, the second horizontal flow wetland 10 can provide an anoxic environment, denitrify the reaction product nitrate nitrogen of ammonia nitrogen into nitrogen, and realize the strengthened denitrification;

[0035] The main filter layer of the third tidal flow wetland 12 is an oyster shell layer 11, the particle size of the oyster shell layer 11 is 20-30 mm, and the thickness is 600 mm, Ca3(PO4)2precipitates are formed by the release of calcium ions, the third tidal flow wetland 12 is emptied once a week, the lower drainage layer of the first vertical flow wetland 3 and the third tidal flow wetland 12 is gravel 4, the particle size of the gravel 4 is 30-50 mm, and the thickness is 300 mm, so as to enhance the permeability, the third tidal flow wetland 12 is emptied once a week, the permeability coefficient is restored to 95% of the initial value by hydraulic flushing, the wetland can be effectively prevented from being blocked, and the third tidal flow wetland 12 can strengthen the removal of phosphorus.

[0036] In the embodiment, multi-stage treatment is adopted, and an aerobic-anoxic-aerobic multi-stage treatment is formed, the aerobic section degrades COD and ammonia nitrogen, the anoxic section removes total nitrogen, effectively preventing water eutrophication, the subsequent aerobic section realizes the dual functions of biological and chemical phosphorus removal, further removes residual COD and ammonia nitrogen in the water, and greatly improves the treatment efficiency of the system.

[0037] As shown in Figure 1 , the ecological floating bed module includes a floating bed carrier 15 and a polyester bio-rope 16, the ecological floating bed module is arranged in the effluent area of the last-stage wetland, the plants of the ecological floating bed module are configured as Acorus calamus 13 and Oenanthe javanica 14, the floating bed carrier 15 adopts a modified polyethylene frame, the modified polyethylene frame is added with 2% nano-TiO2 ultraviolet resistance agent, the porosity is greater than or equal to 80%, the polyester bio-rope 16 is arranged at the bottom of the floating bed carrier 15, the length of the polyester bio-rope 16 is 1.5 m, the specific surface area is greater than or equal to 500 m 2 / m 3 ; the hanging interval is 20 cm, and the biofilm thickness is 1-2 mm.

[0038] In the embodiment, the proportion of the Oenanthe javanica 14 is 70%, and the planting density is 25 plants per square meter.2 The proportion of Rehmannia glutinosa Libosch 13 is 30%, and the planting density is 8 plants / m 2 , and the root depth is ≥1.2 m.

[0039] Example 1:

[0040] Referring to Figure 1 , the sewage first passes through the grid well 1, the grid well 1 has a grid strip gap of 5 mm, and the suspended solids with a particle size ≥5 mm are intercepted; then enters the adjusting sedimentation tank 2, the hydraulic retention time is 2 h, the surface load is 1.2 m 3 / (m 2 ·h), further removes the suspended solids in the sewage, and performs the adjusting function of water quality and quantity. After passing through the adjusting sedimentation tank 2, the sewage enters the first vertical flow wetland 3, the filler layer in the first vertical flow wetland 3 has an upper layer of zeolite layer 5 with a particle size of 10-20 mm and a thickness of 60 cm, and a lower layer of gravel 4 with a particle size of 30-50 mm and a thickness of 30 cm to enhance the permeability. The plant is selected to be reed 6, the planting density is 6-8 plants / m 2 , and the root depth is 60-80 cm; the strong pollution resistance and root exudates promote the proliferation of nitrifying bacteria; the first vertical flow wetland 3 provides an aerobic environment, degrades COD, and adsorbs ammonia nitrogen and SS.

[0041] After the sewage is treated by the first vertical flow wetland 3, it enters the second horizontal flow wetland 10.

[0042] The filler layer from left to right is biochar 7 and volcanic rock 8. The biochar 7 has a particle size of 5-10 mm, a specific surface area ≥800 m 2 / g, and a volume of 40% of the total volume. The volcanic rock 8 has a particle size of 15-25 mm and a volume of 60% of the total volume. The plant is acaleph 9, the planting density is 4-6 plants / m 2 , and the root exudates organic acid strengthens denitrification; the second horizontal flow wetland 10 provides an anoxic environment, further decomposes refractory COD, and strengthens denitrification.

[0043] After the sewage is treated by the second horizontal flow wetland 10, it enters the third tidal flow wetland 12. The filler layer has an upper layer of oyster shell layer 11 with a particle size of 20-30 mm, a CaCO3 content ≥90%, and a thickness of 60 cm to form Ca3(PO4)2 precipitation by releasing calcium ions; and a lower layer of gravel 4 with a particle size of 30-50 mm and a thickness of 30 cm to enhance the permeability; the tidal flow wetland is emptied once a week, and the permeability coefficient is restored to 95% of the initial value by hydraulic flushing, which can effectively prevent the wetland from being blocked. The main function of the third tidal flow wetland 12 is to strengthen phosphorus removal by biological and chemical double action.

[0044] The sewage is treated by the three-stage tidal flow wetland 12 and then enters the ecological floating bed module 17. The ecological floating bed module 17 is arranged at the water outlet area of the last-stage wetland. The floating bed carrier 15 adopts a modified polyethylene frame (2% nano-TiO2 anti-ultraviolet agent is added, the porosity is greater than or equal to 80%, and the service life is greater than or equal to 10 years); the plant configuration adopts economic crops water celery 14, the proportion is 70%, and the planting density is 25 plants per square meter 2 . Landscape plants Aizoon 13, the proportion is 30%, the planting density is 8 plants per square meter 2 , and the root depth is greater than or equal to 1.2 m; the polyester biological rope 16 is hung below the floating bed carrier 15, the length is 1.5 m, the specific surface area is greater than or equal to 500 m 2 / m 3 ; the hanging interval is 20 cm; the ecological floating bed module further degrades organic matter, adds landscape ornamental effect and economic value, and reduces system operation and maintenance cost

[0045] Example 2

[0046] This example is used for rural domestic sewage treatment, and the treatment scale is 50 m 3 / d. The pretreatment unit is a grid well and a regulating sedimentation tank. The grid well: the manual grid gap is 5 mm, the debris is intercepted once a day, and the regulating sedimentation tank: the hydraulic retention time is 2 h, the surface load is 1.2 m 3 / (m 2 ·h), and the specific size of the regulating sedimentation tank is 2 m x 1 m x 2 m.

[0047] Multi-stage artificial wetland module

[0048] The specific size of the first-stage vertical flow wetland is 10 m x 5 m x 1.5 m. The upper layer of the filler is a cover layer, which adopts gravel with a particle size of 5-10 mm and a thickness of 300 mm. The main filter layer is a zeolite layer with a particle size of 10-20 mm and a thickness of 600 mm. The drainage layer adopts gravel with a particle size of 30-50 mm and a thickness of 300 mm. The reed has a planting density of 7 plants per square meter 2 . The perforated pipe is used to uniformly distribute water, the bottom is provided with a water collecting layer, the pH value of the zeolite layer is detected regularly, and is maintained at 6.5-7.5.

[0049] The specific size of the second-stage horizontal flow wetland is 20 m x 5 m x 1.5 m. The upper layer of the filler is a cover layer, which adopts gravel with a particle size of 5-10 mm and a thickness of 300 mm. The left side is filled with biochar with a particle size of 5-10 mm, a filling height of 900 mm, and a volume ratio of 40%, and the right side is filled with volcanic rock with a particle size of 15-25 mm, a filling height of 900 mm, and a volume ratio of 60%. Acorus calamus has a planting density of 5 plants per square meter 2 ;

[0050] The specific size of the tertiary tidal flow wetland is 10 m x 5 m x 1.5 m. The upper layer of the filler is a cover layer, which uses gravel with a particle size of 5-10 mm, and the thickness is 300 mm. The main filter layer is an oyster shell layer with a particle size of 20-30 mm and a thickness of 600 mm. The drainage layer uses gravel with a particle size of 30-50 mm and a thickness of 300 mm. It is emptied once a week, and the permeability coefficient is restored by hydraulic flushing to ensure the effect of chemical phosphorus removal.

[0051] The ecological floating bed module area is 40 square meters, and the specific size is 10 m x 4 m. The ecological floating bed: water celery (70% area, planting density 25 plants / m 2 ), and reforce flower (30% area, planting density 8 plants / m 2 ). The floating bed carrier: modified polyethylene frame (porosity 85%), check the integrity of the ultraviolet-resistant coating every half year; biological rope maintenance: clean once a quarter, and the biological membrane thickness is controlled at 1-2 mm;

[0052] Plant harvesting: water celery is harvested once a quarter, and reforce flower is pruned twice a year, and the harvested material is used for feed or landscape sales.

[0053] The following table is the treatment effect and data comparison of the embodiment and the traditional process:

[0054] COD ammonia nitrogen TP average influent water quality of the system 380 mg / L 45 mg / L 7 mg / L average effluent water quality of the system 30 1.5 0.4 removal rate of the system 92.11％ 96.67％ 94.29％ average effluent water quality of the traditional process 80 15 4 removal rate of the traditional process 78.95％ 66.67％ 42.86％

[0055] Long-term performance:

[0056] Filler permeability coefficient: 87% of the initial value after 1 year;

[0057] Operation and maintenance cost: 0.58 yuan / m 3 , the average of traditional system is 1.2 yuan / m 3 , reduced by 52%;

[0058] Economic benefits: water celery annual output value is 6720 yuan, reforce flower landscape value-added is 3840 yuan / year, total income is 10560 yuan, offsetting the operation and maintenance cost.

[0059] The embodiment is aimed at the characteristics of rural domestic sewage, and realizes efficient removal and resource utilization of pollutants through the coupling design of pretreatment-multistage constructed wetland module-floating bed. The effluent of the system is higher than the first level A standard of "Urban Sewage Treatment Plant Pollutant Discharge Standard" (GB 18918-2002), and the operation and maintenance cost is significantly reduced by planting economic crops. The case verifies the applicability and long-term effectiveness of the utility model in decentralized sewage treatment, and provides an innovative solution for rural water environment governance. The above embodiment data is based on the actual operation monitoring results for 1 year, and there is no clogging problem during the system operation, the plant growth is good, the filler performance is stable, and it has the value of large-scale popularization.

[0060] The above merely describes preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A multi-stage composite artificial wetland coupled ecological floating bed system, characterized in that, It includes a pretreatment unit, a multi-stage constructed wetland module, and an ecological floating bed module; The pretreatment unit includes a bar screen well (1) and a settling tank (2). The bar screen well (1) is equipped with an artificial bar screen with a bar spacing of 5 mm. The multi-level constructed wetland module includes a primary vertical flow wetland (3), a secondary horizontal flow wetland (10), and a tertiary tidal flow wetland (12). The main filter layer of the primary vertical flow wetland (3) is a zeolite layer (5). The filler layers of the secondary horizontal flow wetland (10) are biochar (7) and volcanic rock (8) from left to right. The main filter layer of the tertiary tidal flow wetland (12) is an oyster shell layer (11). The lower drainage layers of both the primary vertical flow wetland (3) and the tertiary tidal flow wetland (12) are made of gravel (4). The ecological floating bed module includes a floating bed carrier (15) and a polyester bio-rope (16). The ecological floating bed module is set in the outlet area of ​​the final wetland. The plant configuration of the ecological floating bed module is Thalia dealbata (13) and water celery (14). The floating bed carrier (15) adopts a modified polyethylene frame. The polyester bio-rope (16) is set at the bottom of the floating bed carrier (15).

2. The multi-stage composite artificial wetland coupled ecological floating bed system according to claim 1, characterized in that, The hydraulic retention time of the regulating sedimentation tank (2) is 2 hours, and the surface loading is 1.2 m³. 3 / (m 2 ·h).

3. The multi-stage composite artificial wetland coupled ecological floating bed system according to claim 1, characterized in that, The zeolite layer (5) has a particle size of 10-20 mm and a thickness of 600 mm, and the gravel (4) has a particle size of 30-50 mm and a thickness of 300 mm.

4. The multi-stage composite artificial wetland coupled ecological floating bed system according to claim 1, characterized in that, The plants selected for the primary vertical flow wetland (3) are reeds (6), and the planting density of the reeds (6) is 6-8 plants / m². 2 The root system is 60-80cm deep.

5. A multi-stage composite artificial wetland coupled ecological floating bed system according to claim 1, characterized in that, The biochar (7) has a particle size of 5-10 mm and a specific surface area of ​​≥800 m². 2 / g, accounting for 40% of the total volume, and the volcanic rock (8) has a particle size of 15-25mm and accounts for 60% of the total volume.

6. The multi-stage composite artificial wetland coupled ecological floating bed system according to claim 1, characterized in that, The plant selected for the secondary horizontal flow wetland (10) is sweet flag (9), and the planting density of sweet flag (9) is 4-6 plants / m². 2 .

7. A multi-stage composite artificial wetland coupled ecological floating bed system according to claim 1, characterized in that, The oyster shells (11) have a particle size of 20-30 mm and a thickness of 600 mm. The three-level tidal wetland (12) is emptied once a week.

8. A multi-stage composite artificial wetland coupled ecological floating bed system according to claim 1, characterized in that, The modified polyethylene framework is supplemented with 2% nano-TiO2 UV stabilizer, and has a porosity ≥80%.

9. A multi-stage composite artificial wetland coupled ecological floating bed system according to claim 1, characterized in that, The water celery (14) accounted for 70% of the total plant, with a planting density of 25 plants / m². 2 The proportion of Thalia dealbata (13) is 30%, and the planting density is 8 plants / m². 2 Root depth ≥ 1.2m.

10. A multi-level composite artificial wetland coupled ecological floating bed system according to claim 1, characterized in that, The polyester bio-rope (16) has a length of 1.5m and a specific surface area ≥500m². 2 / m 3 The suspension spacing is 20cm, and the biofilm thickness is 1-2mm.

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