A method for in-situ remediation of urban river water body by using a composite ecological floating bed

Abstract

The present application relates to water environment remediation technical field, disclose a kind of in-situ remediation of urban river water using composite ecological floating bed method, method includes: constructing composite ecological floating bed unit, in planting basket planting emergent plants, in rhizosphere region burying the rhizosphere regulation matrix that iron modified biochar particle and calcium peroxide particle are mixed to constitute;Laying strip-shaped bottom improvement layer by zeolite, biological ceramsite and slow-release carbon source particle in river bottom;Plant fiber guide medium formed by reed stem fragment filled in polyamide mesh tube is hung below floating bed unit, constructs organic carbon vertical transport channel;Put composite microbial inoculum;Multiple floating bed units are arranged into floating bed array;Operation maintenance management is carried out.The present application constructs organic carbon vertical transport channel and directs the transport of plant litter to bottom improvement layer as denitrification carbon source, solves the problem that natural carbon source directly soaks water in prior art and causes release rate difficult to control.

Description

Technical Field

[0001] This invention relates to the field of water environment restoration technology, specifically a method for in-situ restoration of urban river water bodies using composite ecological floating beds. Background Technology

[0002] Ecological floating bed technology has been widely used in the treatment of eutrophic water bodies such as urban rivers due to its advantages such as in-situ remediation, no land occupation, and no need for external power. This technology mainly uses floating bed plants to absorb nutrients such as nitrogen and phosphorus from the water body, and uses the microbial community attached to the surface of the plant roots to adsorb and degrade organic and inorganic pollutants. However, due to the limitations of the structure of the ecological floating bed itself, the purification capacity of floating bed plants for deep water bodies is limited, and the amount of pollutants absorbed and assimilated by the plant roots and degraded by the microorganisms on the root surface is difficult to meet the remediation needs of heavily polluted water bodies.

[0003] In existing technologies, to improve the denitrification effect of floating beds, natural cellulose materials such as corn stalks, rice straw, and reeds are usually added to the floating bed system as external carbon sources to improve the carbon-nitrogen ratio imbalance of the system. For example, some studies have added reed straw to floating bed constructed wetlands. The results show that the carbon source released by the decomposition of reed residues can increase the carbon-nitrogen ratio of the system and promote the increase of denitrification functional gene abundance. However, this type of external carbon source has significant technical drawbacks: when plant residues decompose in large quantities in the water at one time, it will cause a sharp increase in the chemical oxygen demand of the water, and the system will be in a state of hypoxia for a long time. At the same time, the natural carbon sources such as straw added in the existing technology are directly immersed in the water, and their decomposition rate is difficult to control, which can easily lead to the release of carbon sources too fast or too slow, affecting the stability and persistence of the denitrification process. In addition, if the litter and root debris produced by the floating bed plants are not cleaned up in time, they will also cause secondary pollution after rotting. Summary of the Invention

[0004] The purpose of this invention is to provide a method for in-situ restoration of urban river water bodies using composite ecological floating beds, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for in-situ restoration of urban river water bodies using composite ecological floating beds, comprising the following steps:

[0006] S1. Constructing a composite ecological floating bed unit: Combining the floating bed frame, buoyancy carrier, and plant planting basket to form a modular floating bed substrate, planting emergent plants in the planting basket, and burying the rhizosphere regulation substrate in the rhizosphere area of ​​the emergent plants. The rhizosphere regulation substrate is composed of iron-modified biochar particles and calcium peroxide particles in a volume ratio of 3:1-5:1. The particle size of the iron-modified biochar particles is 2-5mm, the particle size of the calcium peroxide particles is 1-3mm, and the calcium peroxide particles are coated with a sodium alginate film with a thickness of 0.1-0.3mm.

[0007] S2. Laying a bottom sediment improvement layer: Laying a bottom sediment improvement substrate in the area to be repaired at the bottom of the river. The bottom sediment improvement substrate is composed of a mixture of zeolite, bio-ceramic particles and slow-release carbon source particles, forming a strip-shaped bottom sediment improvement zone extending along the direction of water flow.

[0008] S3. Constructing a vertical transport channel for plant-derived organic carbon: A plant fiber guiding medium is suspended below the floating bed unit. The upper end of the plant fiber guiding medium connects to the bottom of the planting basket, and the lower end extends 5-15 cm above the substrate amendment layer. The plant fiber guiding medium is formed by filling polyamide mesh tubes with reed stem fragments that have been crushed, soaked in alkali solution, and washed. The length of the reed stem fragments is 2-5 cm, the mesh size of the polyamide mesh tube is 3-8 mm, and the filling density of the reed stem fragments in the polyamide mesh tube is 0.15-0.30 g / cm³. 3 ;

[0009] S4. Add compound microbial agents: Pre-implant the compound microbial agents containing aerobic denitrifying bacteria and polyphosphate-accumulating bacteria into the internal pores of the plant fiber carrier, and add the compound microbial agents to the surface of the substrate improvement layer.

[0010] S5. Combined floating bed units form a restoration array: Multiple composite ecological floating bed units are arranged and connected in sequence along the direction of river flow to form a floating bed array covering the water surface to be restored, with water flow channels maintained between each floating bed unit;

[0011] S6. Operation and maintenance management: Harvest the above-ground parts of emergent plants regularly, clean the biofilm that falls off the surface of the plant fiber guiding medium regularly, and replenish the microbial agent on the surface of the substrate improvement layer.

[0012] As a preferred embodiment of the present invention, the method for coating the calcium peroxide particles with a sodium alginate film in step S1 is as follows:

[0013] Immerse calcium peroxide particles in a sodium alginate solution with a mass concentration of 1%-3% and stir continuously for 10-30 minutes. Then remove them and place them in a calcium chloride solution with a mass concentration of 2%-5% for cross-linking and curing for 5-15 minutes. After removing them, rinse the surface with deionized water and dry them at 40-60℃ for 2-4 hours to form calcium peroxide particles coated with a sodium alginate film.

[0014] After calcium peroxide particles are coated with a sodium alginate film, a polylactic acid (PLA) inner layer and a PLA outer layer are sequentially coated on the outer layer of the sodium alginate film. The thickness of the PLA inner layer is 0.2-0.5 mm, and the thickness of the PLA outer layer is 0.5-1.0 mm. 5%-10% starch particles by mass are added to the PLA inner layer, while no starch particles are added to the PLA outer layer.

[0015] As a preferred embodiment of the present invention, the method for preparing the iron-modified biochar particles in step S1 is as follows:

[0016] After crushing the corn stalks to a particle size of 1-3 mm, they are placed in a tube furnace and heated to 450-550 °C at a heating rate of 5-10 °C / min under a nitrogen atmosphere for primary pyrolysis and carbonization. After holding at this temperature for 2-4 hours, the temperature is naturally cooled to room temperature to obtain the primary pyrolysis product of biochar.

[0017] The biochar primary pyrolysis product is immersed in a mixed solution of ferrous chloride and ferric chloride with a mass concentration of 0.3-0.8 mol / L for 4-8 hours. The molar ratio of ferrous chloride to ferric chloride in the mixed solution is 1:1-2:1. After immersion, the product is filtered out and dried at 60-80℃ for 4-8 hours to obtain the iron-loaded biochar intermediate.

[0018] The iron-loaded biochar intermediate was placed in a tube furnace and heated to 300-400℃ at a heating rate of 8-12℃ / min under a nitrogen atmosphere for a second low-temperature heat treatment. After holding at this temperature for 1-2 hours, it was naturally cooled to room temperature to obtain iron-modified biochar particles.

[0019] As a preferred technical solution of the present invention, the slow-release carbon source particles in step S2 are core-shell structured particles. The core of the core-shell structured particles is composed of a cross-linked mixture of polyvinyl alcohol and starch in a mass ratio of 3:1-5:1. Nano zero-valent iron particles are incorporated into the cross-linked mixture, and the mass fraction of the nano zero-valent iron particles is 5%-15%.

[0020] The outer shell of the core-shell structured particles is formed by melting and coating the core surface with a mixture of polycaprolactone and activated carbon powder at a mass ratio of 7:1-9:1. The thickness of the outer shell is 0.3-0.8 mm, and release pores with a diameter of 0.5-1.5 mm are formed on the outer shell. The distribution density of the release pores on the outer shell surface is 2-4 pores / cm². 2 ;

[0021] Before laying the substrate improvement matrix, mix zeolite, bio-ceramic particles, and core-shell structured slow-release carbon source particles evenly in a volume ratio of 2:2:1, then soak them in an enrichment culture solution containing denitrifying bacteria for 24-48 hours. After soaking, drain the surface water before laying.

[0022] As a preferred technical solution of the present invention, when laying the bottom sediment improvement layer in step S2, multiple strip-shaped bottom sediment improvement strips are arranged at intervals along the cross section of the river channel. A gravel layer is laid in the interval area between two adjacent bottom sediment improvement strips. The gravel layer has a particle size of 3-6cm. The upper surface of the gravel layer is 5-15cm higher than the upper surface of the bottom sediment improvement strip. An impermeable geotextile is laid under the gravel layer.

[0023] An inclined guide surface is provided on the water-facing end face of each strip of bottom sediment improvement zone. The angle between the inclined guide surface and the upper surface of the bottom sediment improvement zone is 30-60°. A layer of coarse sand with a particle size of 1-2cm is laid on the surface of the inclined guide surface. The thickness of the coarse sand layer is 2-5cm.

[0024] A vertical cut-off surface is set at the downstream end of each strip of substrate improvement zone. A row of wooden or bamboo stakes is buried at the vertical cut-off surface and inserted vertically into the substrate improvement layer. The diameter of the wooden or bamboo stakes is 5-10cm, the spacing between adjacent wooden or bamboo stakes is 2-5cm, and the height of the wooden or bamboo stakes protruding from the upper surface of the substrate improvement layer is 5-15cm.

[0025] As a preferred embodiment of the present invention, the alkaline soaking conditions for the reed stem fragments in step S3 are as follows:

[0026] After crushing the reed stems to a length of 2-5cm, soak them in a 2%-5% sodium hydroxide solution for 12-24 hours. After filtering, rinse with deionized water until the pH of the washing solution is 7.0-8.0, and then dry at 60-80℃ until the moisture content is less than 10%.

[0027] Reed stem fragments are divided into high carbon-nitrogen ratio fragments and low carbon-nitrogen ratio fragments according to the carbon-nitrogen ratio. The carbon-nitrogen ratio of the high carbon-nitrogen ratio fragments is 40:1-60:1, and the carbon-nitrogen ratio of the low carbon-nitrogen ratio fragments is 15:1-25:1. The high carbon-nitrogen ratio fragments and the low carbon-nitrogen ratio fragments are mixed at a mass ratio of 2:1-3:1 and then filled into polyamide mesh tubes.

[0028] Before filling, soak the high carbon-to-nitrogen ratio fragments in a hydrogen peroxide solution with a mass concentration of 0.5%-1.5% for 2-4 hours. After soaking, remove and drain the surface water before mixing with the low carbon-to-nitrogen ratio fragments.

[0029] As a preferred technical solution of the present invention, in step S3, the upper end of the polyamide mesh tube is fixed to the bottom of the planting basket by nylon cable ties, and the lower end of the polyamide mesh tube is suspended by a lead weight with a mass of 50-200g. 3-5 polyamide mesh tubes are evenly spaced along the width direction of the floating bed unit, and the distance between two adjacent polyamide mesh tubes is 15-30cm.

[0030] The polyamide mesh tube is provided with annular support rings spaced along the axial direction. The annular support rings are made of polypropylene and the spacing between the annular support rings is 10-20cm.

[0031] The outer wall of the polyamide mesh tube is wrapped with polyhydroxyalkanoate braided tape, the width of which is 1-2cm and the winding spacing is 5-10cm.

[0032] As a preferred technical solution of the present invention, in step S4, the composite microbial agent is a mixture of aerobic denitrifying bacteria, polyphosphate bacteria and Bacillus subtilis in a live bacteria ratio of 2:1:1. When pre-implanting the plant fiber carrier into the internal pores, the carrier is immersed in the mixed bacterial solution for oscillation loading. After the loading is completed, the carrier is drained and directly installed on the floating bed unit.

[0033] The composite microbial agent added to the surface of the substrate improvement layer is sodium alginate-encapsulated immobilized microspheres. The immobilized microspheres have a diameter of 3-5 mm and contain zero-valent iron particles with a particle size of 50-100 μm. The mass of the zero-valent iron particles accounts for 2%-8% of the total mass of the immobilized microspheres.

[0034] During the preparation of immobilized microspheres, 0.5%-1.5% by mass of hydroxyethyl cellulose is added to the mixture of sodium alginate and bacterial solution.

[0035] As a preferred technical solution of the present invention, when arranging the floating bed units in step S5, the floating bed array is divided into a front adsorption zone, a middle biodegradation zone and a terminal deep purification zone along the water flow direction. Zeolite adsorption baskets are added to the floating bed frames of each floating bed unit in the front adsorption zone, and the zeolite adsorption baskets are filled with natural zeolite. The spacing between adjacent floating bed units in the middle biodegradation zone is 10-20cm. An interception net is added to the bottom of each floating bed unit. Plant fiber carriers with a length greater than 2m are suspended below the floating bed units in the terminal deep purification zone.

[0036] The emergent plants planted in the floating bed units in the front-end adsorption zone, the middle biodegradation zone and the terminal deep purification zone are different. Canna lilies are planted in the front-end adsorption zone, Thalia dealbata is planted in the middle biodegradation zone and Acorus calamus is planted in the terminal deep purification zone.

[0037] The planting density of canna lilies in the front-end adsorption zone is 12-16 plants / m². 2The planting density of Thalia dealbata in the middle biodegradation zone is 8-12 plants / m². 2 The planting density of calamus in the terminal deep purification zone is 16-20 plants / m². 2 .

[0038] As a preferred technical solution of the present invention, the cycle of periodically harvesting the above-ground parts of emergent plants in step S6 is 30-60 days, and the plant height is retained at 15-25cm after harvesting.

[0039] The frequency of cleaning the biofilm that has fallen off the surface of the plant fiber guiding medium is once every 7-15 days. When cleaning, the upstream water flow channel of the floating bed array should be closed for 10-20 minutes.

[0040] The replenishment cycle for the surface microbial agent of the substrate amendment layer is 20-40 days, and the replenishment amount is 30%-50% of the initial amount;

[0041] Check the consumption of reed stem fragments inside the polyamide mesh every 30-60 days. When the consumption of reed stem fragments exceeds 50% of the initial filling amount, replenish the reed stem fragments to the initial filling density.

[0042] In step S6, when harvesting the above-ground parts of emergent plants, the plants in the front adsorption zone, the middle biodegradation zone, and the terminal deep purification zone are harvested independently. The above-ground parts of canna lilies harvested in the front adsorption zone are crushed and backfilled to the upstream end of the substrate improvement layer. The above-ground parts of canna lilies harvested in the middle biodegradation zone are crushed and backfilled to the middle section of the substrate improvement layer. The above-ground parts of calamus harvested in the terminal deep purification zone are crushed and backfilled to the downstream end of the substrate improvement layer.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] 1. This invention constructs a vertical transport channel for plant-derived organic carbon, which directionally transports litter and root secretions produced by floating bed plants to the substrate improvement layer along the plant fiber guide medium. This allows the organic carbon released from the decomposition of plant residues to be utilized by denitrifying bacteria in the substrate improvement layer. This solves the secondary pollution problem caused by the direct decomposition of plant residues in water bodies, which leads to an increase in chemical oxygen demand, and provides a continuous and stable carbon source supply for the substrate denitrification process.

[0045] 2. In this invention, reed stem fragments are soaked in alkaline solution and washed with water before being filled into polyamide mesh tubes. The physical wrapping and guiding effect of the mesh tubes concentrates the carbon source release area above the substrate improvement layer, avoiding the problem of natural carbon sources being directly soaked in water and the release rate being difficult to control in the prior art.

[0046] 3. In this invention, the outer layer of calcium peroxide particles is sequentially coated with a sodium alginate film, a polylactic acid inner layer, and a polylactic acid outer layer. Through the multi-layer coating structure, the time-sequential release of calcium peroxide is achieved, which delays the oxygen release time and allows the rhizosphere to still receive dissolved oxygen replenishment in the later stages of floating bed operation. Combined with the electron transfer promoting effect of iron-modified biochar particles, the aerobic microbial purification function of plant rhizosphere is effectively enhanced.

[0047] 4. In this invention, the bottom sediment improvement layer is laid in a strip-like manner, and a gravel layer is set between adjacent bottom sediment improvement strips to form an alternating aerobic and anoxic microenvironment. Combined with the inclined flow guide surface at the water-facing end of the bottom sediment improvement strip and the vertical interception surface at the downstream end, the orderly guidance and full contact of water flow on the surface of the bottom sediment improvement layer are realized, thereby improving the purification efficiency of the bottom sediment improvement layer.

[0048] 5. This invention divides the floating bed array into a front-end adsorption zone, a middle-section biodegradation zone, and a terminal deep purification zone, and configures different functional plants and differentiated planting densities in each zone, thereby achieving a stepped purification function configuration along the water flow direction, so that the purification advantages of different plants complement each other in the water flow direction. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the overall process of a method for in-situ restoration of urban river water bodies using a composite ecological floating bed, according to the present invention. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] Example 1

[0052] like Figure 1 As shown, this invention provides a method for in-situ restoration of urban river water bodies using composite ecological floating beds, comprising the following steps:

[0053] S1. Constructing a composite ecological floating bed unit: Combining the floating bed frame, buoyancy carrier, and plant planting basket to form a modular floating bed substrate, planting emergent plants in the planting basket, and burying the rhizosphere regulation substrate in the rhizosphere area of ​​the emergent plants. The rhizosphere regulation substrate is composed of iron-modified biochar particles and calcium peroxide particles in a volume ratio of 3:1-5:1. The particle size of the iron-modified biochar particles is 2-5mm, the particle size of the calcium peroxide particles is 1-3mm, and the calcium peroxide particles are coated with a sodium alginate film with a thickness of 0.1-0.3mm.

[0054] S2. Laying a bottom sediment improvement layer: Laying a bottom sediment improvement substrate in the area to be repaired at the bottom of the river. The bottom sediment improvement substrate is composed of a mixture of zeolite, bio-ceramic particles and slow-release carbon source particles, forming a strip-shaped bottom sediment improvement zone extending along the direction of water flow.

[0055] S3. Constructing a vertical transport channel for plant-derived organic carbon: A plant fiber guiding medium is suspended below the floating bed unit. The upper end of the plant fiber guiding medium connects to the bottom of the planting basket, and the lower end extends 5-15 cm above the substrate amendment layer. The plant fiber guiding medium is formed by filling polyamide mesh tubes with reed stem fragments that have been crushed, soaked in alkali solution, and washed. The length of the reed stem fragments is 2-5 cm, the mesh size of the polyamide mesh tube is 3-8 mm, and the filling density of the reed stem fragments in the polyamide mesh tube is 0.15-0.30 g / cm³. 3 ;

[0056] S4. Add compound microbial agents: Pre-implant the compound microbial agents containing aerobic denitrifying bacteria and polyphosphate-accumulating bacteria into the internal pores of the plant fiber carrier, and add the compound microbial agents to the surface of the substrate improvement layer.

[0057] S5. Combined floating bed units form a restoration array: Multiple composite ecological floating bed units are arranged and connected in sequence along the direction of river flow to form a floating bed array covering the water surface to be restored, with water flow channels maintained between each floating bed unit;

[0058] S6. Operation and maintenance management: Harvest the above-ground parts of emergent plants regularly, clean the biofilm that falls off the surface of the plant fiber guiding medium regularly, and replenish the microbial agent on the surface of the substrate improvement layer.

[0059] Furthermore, the method for coating the calcium peroxide particles with a sodium alginate film in step S1 is as follows:

[0060] Immerse calcium peroxide particles in a sodium alginate solution with a mass concentration of 1%-3% and stir continuously for 10-30 minutes. Then remove them and place them in a calcium chloride solution with a mass concentration of 2%-5% for cross-linking and curing for 5-15 minutes. After removing them, rinse the surface with deionized water and dry them at 40-60℃ for 2-4 hours to form calcium peroxide particles coated with a sodium alginate film.

[0061] After calcium peroxide particles are coated with a sodium alginate film, a polylactic acid (PLA) inner layer and a PLA outer layer are sequentially coated on the outer layer of the sodium alginate film. The thickness of the PLA inner layer is 0.2-0.5 mm, and the thickness of the PLA outer layer is 0.5-1.0 mm. 5%-10% starch particles by mass are added to the PLA inner layer, while no starch particles are added to the PLA outer layer.

[0062] Furthermore, the preparation method of the iron-modified biochar particles in step S1 is as follows:

[0063] After crushing the corn stalks to a particle size of 1-3 mm, they are placed in a tube furnace and heated to 450-550 °C at a heating rate of 5-10 °C / min under a nitrogen atmosphere for primary pyrolysis and carbonization. After holding at this temperature for 2-4 hours, the temperature is naturally cooled to room temperature to obtain the primary pyrolysis product of biochar.

[0064] The biochar primary pyrolysis product is immersed in a mixed solution of ferrous chloride and ferric chloride with a mass concentration of 0.3-0.8 mol / L for 4-8 hours. The molar ratio of ferrous chloride to ferric chloride in the mixed solution is 1:1-2:1. After immersion, the product is filtered out and dried at 60-80℃ for 4-8 hours to obtain the iron-loaded biochar intermediate.

[0065] The iron-loaded biochar intermediate was placed in a tube furnace and heated to 300-400℃ at a heating rate of 8-12℃ / min under a nitrogen atmosphere for a second low-temperature heat treatment. After holding at this temperature for 1-2 hours, it was naturally cooled to room temperature to obtain iron-modified biochar particles.

[0066] Furthermore, in step S2, the slow-release carbon source particles are core-shell structured particles. The core of the core-shell structured particles is composed of a cross-linked mixture of polyvinyl alcohol and starch in a mass ratio of 3:1 to 5:1. Nano-zero valent iron particles are incorporated into the cross-linked mixture, and the mass fraction of the nano-zero valent iron particles is 5% to 15%.

[0067] The outer shell of the core-shell structured particles is formed by melting and coating the core surface with a mixture of polycaprolactone and activated carbon powder at a mass ratio of 7:1-9:1. The thickness of the outer shell is 0.3-0.8 mm, and release pores with a diameter of 0.5-1.5 mm are formed on the outer shell. The distribution density of the release pores on the outer shell surface is 2-4 pores / cm². 2 ;

[0068] Before laying the substrate improvement matrix, mix zeolite, bio-ceramic particles, and core-shell structured slow-release carbon source particles evenly in a volume ratio of 2:2:1, then soak them in an enrichment culture solution containing denitrifying bacteria for 24-48 hours. After soaking, drain the surface water before laying.

[0069] Furthermore, in step S2, when laying the bottom sediment improvement layer, multiple strip-shaped bottom sediment improvement strips are set along the cross-sectional direction of the river channel. A gravel layer is laid in the interval area between two adjacent bottom sediment improvement strips. The gravel layer has a particle size of 3-6cm. The upper surface of the gravel layer is 5-15cm higher than the upper surface of the bottom sediment improvement strip. An impermeable geotextile is laid under the gravel layer.

[0070] An inclined guide surface is provided on the water-facing end face of each strip of bottom sediment improvement zone. The angle between the inclined guide surface and the upper surface of the bottom sediment improvement zone is 30-60°. A layer of coarse sand with a particle size of 1-2cm is laid on the surface of the inclined guide surface. The thickness of the coarse sand layer is 2-5cm.

[0071] A vertical cut-off surface is set at the downstream end of each strip of substrate improvement zone. A row of wooden or bamboo stakes is buried at the vertical cut-off surface and inserted vertically into the substrate improvement layer. The diameter of the wooden or bamboo stakes is 5-10cm, the spacing between adjacent wooden or bamboo stakes is 2-5cm, and the height of the wooden or bamboo stakes protruding from the upper surface of the substrate improvement layer is 5-15cm.

[0072] Furthermore, the alkaline soaking conditions for the reed stem fragments in step S3 are as follows:

[0073] After crushing the reed stems to a length of 2-5cm, soak them in a 2%-5% sodium hydroxide solution for 12-24 hours. After filtering, rinse with deionized water until the pH of the washing solution is 7.0-8.0, and then dry at 60-80℃ until the moisture content is less than 10%.

[0074] Reed stem fragments are divided into high carbon-nitrogen ratio fragments and low carbon-nitrogen ratio fragments according to the carbon-nitrogen ratio. The carbon-nitrogen ratio of the high carbon-nitrogen ratio fragments is 40:1-60:1, and the carbon-nitrogen ratio of the low carbon-nitrogen ratio fragments is 15:1-25:1. The high carbon-nitrogen ratio fragments and the low carbon-nitrogen ratio fragments are mixed at a mass ratio of 2:1-3:1 and then filled into polyamide mesh tubes.

[0075] Before filling, soak the high carbon-to-nitrogen ratio fragments in a hydrogen peroxide solution with a mass concentration of 0.5%-1.5% for 2-4 hours. After soaking, remove and drain the surface water before mixing with the low carbon-to-nitrogen ratio fragments.

[0076] Furthermore, in step S3, the upper end of the polyamide mesh tube is fixed to the bottom of the planting basket with nylon cable ties, and a lead weight is suspended from the lower end of the polyamide mesh tube. The weight has a mass of 50-200g. 3-5 polyamide mesh tubes are evenly spaced along the width of the floating bed unit, and the distance between two adjacent polyamide mesh tubes is 15-30cm.

[0077] The polyamide mesh tube is provided with annular support rings spaced along the axial direction. The annular support rings are made of polypropylene and the spacing between the annular support rings is 10-20cm.

[0078] The outer wall of the polyamide mesh tube is wrapped with polyhydroxyalkanoate braided tape, the width of which is 1-2cm and the winding spacing is 5-10cm.

[0079] Furthermore, in step S4, the composite microbial agent is a mixture of aerobic denitrifying bacteria, polyphosphate-accumulating bacteria and Bacillus subtilis in a live bacteria ratio of 2:1:1. When pre-implanting it into the internal pores of the plant fiber carrier, the carrier is immersed in the mixed bacterial solution for oscillation loading. After loading is completed, the carrier is drained and directly installed on the floating bed unit.

[0080] The composite microbial agent added to the surface of the substrate improvement layer is sodium alginate-encapsulated immobilized microspheres. The immobilized microspheres have a diameter of 3-5 mm and contain zero-valent iron particles with a particle size of 50-100 μm. The mass of the zero-valent iron particles accounts for 2%-8% of the total mass of the immobilized microspheres.

[0081] During the preparation of immobilized microspheres, 0.5%-1.5% by mass of hydroxyethyl cellulose is added to the mixture of sodium alginate and bacterial solution.

[0082] Furthermore, in step S5, when arranging the floating bed units, the floating bed array is divided into a front-end adsorption zone, a middle-section biodegradation zone, and a final deep purification zone along the water flow direction. Zeolite adsorption baskets are added to the floating bed frames of each floating bed unit in the front-end adsorption zone, and the zeolite adsorption baskets are filled with natural zeolite. The spacing between adjacent floating bed units in the middle-section biodegradation zone is 10-20cm, and an interception net is added to the bottom of each floating bed unit. Plant fiber carriers with a length greater than 2m are suspended below the floating bed units in the final deep purification zone.

[0083] The emergent plants planted in the floating bed units in the front-end adsorption zone, the middle biodegradation zone and the terminal deep purification zone are different. Canna lilies are planted in the front-end adsorption zone, Thalia dealbata is planted in the middle biodegradation zone and Acorus calamus is planted in the terminal deep purification zone.

[0084] The planting density of canna lilies in the front-end adsorption zone is 12-16 plants / m². 2 The planting density of Thalia dealbata in the middle biodegradation zone is 8-12 plants / m². 2 The planting density of calamus in the terminal deep purification zone is 16-20 plants / m². 2 .

[0085] Furthermore, in step S6, the above-ground parts of emergent plants are harvested periodically every 30-60 days, and the plant height is retained at 15-25cm after harvesting.

[0086] The frequency of cleaning the biofilm that has fallen off the surface of the plant fiber guiding medium is once every 7-15 days. When cleaning, the upstream water flow channel of the floating bed array should be closed for 10-20 minutes.

[0087] The replenishment cycle for the surface microbial agent of the substrate amendment layer is 20-40 days, and the replenishment amount is 30%-50% of the initial amount;

[0088] Check the consumption of reed stem fragments inside the polyamide mesh every 30-60 days. When the consumption of reed stem fragments exceeds 50% of the initial filling amount, replenish the reed stem fragments to the initial filling density.

[0089] In step S6, when harvesting the above-ground parts of emergent plants, the plants in the front adsorption zone, the middle biodegradation zone, and the terminal deep purification zone are harvested independently. The above-ground parts of canna lilies harvested in the front adsorption zone are crushed and backfilled to the upstream end of the substrate improvement layer. The above-ground parts of canna lilies harvested in the middle biodegradation zone are crushed and backfilled to the middle section of the substrate improvement layer. The above-ground parts of calamus harvested in the terminal deep purification zone are crushed and backfilled to the downstream end of the substrate improvement layer.

[0090] Example 2

[0091] Taking a city river in the Yangtze River Delta region as an example, the river is 3.2 km long, with an average width of 18 m and an average depth of 1.5 m. The water body has long been in a state worse than Class V, with the main indicators exceeding the standards being ammonia nitrogen and total phosphorus. The method of this invention was used for in-situ remediation, and the river section was 500 m long.

[0092] In step S1, iron-modified biochar particles are prepared according to the following specific parameters: corn stalks are crushed to a particle size of 2 mm and placed in a tube furnace under a nitrogen atmosphere at a heating rate of 8 °C / min to 500 °C for primary pyrolysis carbonization. After holding at this temperature for 3 h, the mixture is naturally cooled to room temperature to obtain the primary pyrolysis product of biochar. The primary pyrolysis product of biochar is then immersed in a 0.5 mol / L mixed solution of ferrous chloride and ferric chloride for 6 h, with a molar ratio of ferrous chloride to ferric chloride of 1.5:1. After immersion, the product is filtered out and dried at 70 °C for 6 h to obtain the final product. Iron-loaded biochar intermediates were obtained. The iron-loaded biochar intermediates were placed in a tube furnace and heated to 350°C at a heating rate of 10°C / min under a nitrogen atmosphere for a second low-temperature heat treatment. After holding at this temperature for 1.5 hours, the temperature was naturally cooled to room temperature to obtain iron-modified biochar particles. The first pyrolysis carbonization caused the corn stalks to form a carbonized skeleton with a porous structure. The second low-temperature heat treatment caused the ferric ions loaded on the surface of the biochar to be partially reduced to ferrous ions by the carbonaceous components in the biochar, forming a mixed valence state iron oxide layer containing ferric and ferrous iron on the surface of the biochar particles.

[0093] The coating method for the sodium alginate film on the outer layer of calcium peroxide particles is as follows: Calcium peroxide particles are immersed in a 2% sodium alginate solution and stirred continuously for 20 minutes. After stirring, they are removed and placed in a 3% calcium chloride solution for cross-linking and curing for 10 minutes. The particles are then rinsed with deionized water and dried at 50°C for 3 hours to form calcium peroxide particles coated with a sodium alginate film. After coating the calcium peroxide particles with the sodium alginate film, a polylactic acid inner layer and a polylactic acid outer layer are sequentially coated onto the outer layer of the sodium alginate film. The inner layer of polylactic acid (PLA) is 0.3 mm thick, and the outer layer of PLA is 0.8 mm thick. 8% starch granules by mass are incorporated into the inner layer of PLA, while no starch granules are incorporated into the outer layer. The starch granules incorporated into the inner layer of PLA preferentially hydrolyze to form pores upon contact with water, causing the inner layer of PLA to degrade before the outer layer. Iron-modified biochar granules and coated calcium peroxide granules are mixed at a volume ratio of 4:1 and then buried in the rhizosphere area of ​​emergent plants at a depth of 5 cm below the bottom of the planting basket.

[0094] In step S2, the slow-release carbon source particles adopt a core-shell structure. The core is composed of a cross-linked blend of polyvinyl alcohol and starch in a mass ratio of 4:1, with nano-zero-valent iron particles incorporated into the cross-linked blend, the mass fraction of which is 10%. The outer shell is formed by melting and coating the core surface with a mixture of polycaprolactone and activated carbon powder in a mass ratio of 8:1, with a shell thickness of 0.5 mm. Release pores with a diameter of 1.0 mm are formed on the shell, and the distribution density of the release pores on the shell surface is 3 pores / cm². 2 The carbon source material in the core diffuses outward through the release pores. Before laying the substrate improvement matrix, zeolite, bio-ceramic particles and core-shell structure slow-release carbon source particles are mixed evenly in a volume ratio of 2:2:1, and then soaked in an enrichment culture solution containing denitrifying bacteria for 36 hours. After soaking, the surface water is drained before laying.

[0095] In step S3, the alkaline soaking conditions for the reed stem fragments are as follows: After the reed stems are broken into 3cm lengths, they are soaked in a 3% sodium hydroxide solution for 18 hours. After filtration, they are rinsed with deionized water until the pH of the washing solution reaches 7.5, and then dried at 70℃ until the moisture content is below 10%. The reed stem fragments are divided into high carbon-to-nitrogen ratio fragments and low carbon-to-nitrogen ratio fragments according to their carbon-to-nitrogen ratio. The carbon-to-nitrogen ratio of the high carbon-to-nitrogen ratio fragments is 50:1, and the carbon-to-nitrogen ratio of the low carbon-to-nitrogen ratio fragments is 20:1. The high carbon-to-nitrogen ratio fragments and low carbon-to-nitrogen ratio fragments are mixed at a mass ratio of 2.5:1 and then filled into polyamide mesh tubes. Before filling, the high carbon-to-nitrogen ratio fragments are placed in a 1.0% sodium hydroxide solution. The fiber was soaked in hydrogen peroxide solution for 3 hours. After soaking, it was removed, the surface water was drained, and then it was mixed with low carbon-nitrogen ratio fragments. Hydrogen peroxide treatment caused the lignin on the surface of high carbon-nitrogen ratio fragments to be oxidized and degraded, increasing the number of hydrophilic oxygen-containing functional groups on the fiber surface. The upper end of the polyamide mesh tube was fixed to the bottom of the planting basket with nylon cable ties, and a lead weight with a mass of 100g was suspended from the lower end of the polyamide mesh tube. Four polyamide mesh tubes were evenly spaced along the width of the floating bed unit, and the distance between two adjacent polyamide mesh tubes was 20cm. Annular support rings were set at intervals along the axial direction inside the polyamide mesh tube. The annular support rings were made of polypropylene and the distance between the annular support rings was 15cm.

[0096] In step S4, the composite microbial agent is a mixture of aerobic denitrifying bacteria, polyphosphate-accumulating bacteria, and Bacillus subtilis in a live bacteria ratio of 2:1:1. When pre-implanting the plant fiber carrier into its internal pores, the carrier is immersed in the mixed bacterial solution for oscillation loading. After loading, the carrier is drained and installed on the floating bed unit. The composite microbial agent added to the surface of the substrate improvement layer is sodium alginate-embedded immobilized microspheres with a diameter of 4 mm. The immobilized microspheres contain 80 μm zero-valent iron particles, and the mass of the zero-valent iron particles accounts for 5% of the total mass of the immobilized microspheres. During the preparation of the immobilized microspheres, 1.0% by mass of hydroxyethyl cellulose is added to the mixture of sodium alginate and bacterial solution.

[0097] In step S5, when arranging the floating bed units, the floating bed array is divided into a front-end adsorption zone, a middle-section biodegradation zone, and a final deep purification zone along the water flow direction. Canna lilies are planted in the front-end adsorption zone at a density of 14 plants / m². 2 Thalia dealbata is planted in the middle biodegradation zone at a density of 10 plants / m². 2 Sweet flag (Acorus calamus) is planted in the terminal deep purification zone at a density of 18 plants / m². 2 .

[0098] In step S6, the above-ground parts of emergent plants are harvested periodically every 45 days, with a plant height of 20cm retained after harvesting. The surface of the plant fiber guiding medium is cleaned regularly every 10 days, with the upstream water flow channel of the floating bed array closed for 15 minutes during cleaning. The surface microbial agent for the bottom sediment improvement layer is replenished every 30 days, with a replenishment amount of 40% of the initial amount. Every 45 days, the consumption of reed stem fragments in the polyamide mesh is checked. When the consumption of reed stem fragments exceeds 50% of the initial filling amount, reed stem fragments are replenished to the initial filling density. After 90 days of operation, monitoring data shows that the ammonia nitrogen concentration in the river section decreased from the initial 8.2 mg / L to 1.5 mg / L, the total phosphorus concentration decreased from 1.2 mg / L to 0.3 mg / L, and the dissolved oxygen concentration increased from 1.8 mg / L to 4.5 mg / L.

[0099] Example 3

[0100] Taking a city river in the Pearl River Delta region as an example, the river is 1.8km long, 12m wide, and 1.2m deep. The water has been black and smelly for a long time, and the main pollutants exceeding the standards are ammonia nitrogen, total phosphorus and COD. The method of this invention was used for in-situ remediation, and the river section was 300m long.

[0101] In step S2, when laying the bottom sediment improvement layer, multiple strip-shaped bottom sediment improvement zones are set up at intervals along the cross-sectional direction of the river channel. A gravel layer with a particle size of 4 cm is laid in the interval area between adjacent bottom sediment improvement zones. The upper surface of the gravel layer is 10 cm higher than the upper surface of the bottom sediment improvement zone. A geotextile with a two-layer fabric and one-membrane structure is laid below the gravel layer. The upper and lower layers are polypropylene non-woven geotextile, and the middle layer is a polyethylene geomembrane with a thickness of 0.3 mm. Each strip-shaped bottom sediment improvement layer... An inclined guide surface is set on the water-facing end face of the belt, with an angle of 45° between the inclined guide surface and the upper surface of the bottom sediment improvement belt. A layer of coarse sand with a particle size of 1.5cm and a thickness of 3cm is laid on the surface of the inclined guide surface. A vertical interception surface is set on the downstream end face of each strip bottom sediment improvement belt. A row of bamboo stakes with a diameter of 8cm is buried at the vertical interception surface and inserted vertically into the bottom sediment improvement layer. The spacing between adjacent bamboo stakes is 3cm, and the height of the bamboo stakes protruding from the upper surface of the bottom sediment improvement layer is 10cm.

[0102] In step S3, a polyhydroxyalkanoate braided tape is wrapped around the outer wall of the polyamide mesh tube. The width of the polyhydroxyalkanoate braided tape is 1.5 cm and the winding spacing is 8 cm. The polyhydroxyalkanoate gradually hydrolyzes into low molecular weight organic acids in the river water, and the hydrolysis products diffuse downward along the outer wall of the polyamide mesh tube.

[0103] In step S4, the hydroxyethyl cellulose added during the preparation of immobilized microspheres of the composite microbial agent has a mass fraction of 1.2%, and the mass of zero-valent iron particles accounts for 6% of the total mass of the immobilized microspheres.

[0104] In step S5, after the floating bed array is divided into a front-end adsorption zone, a middle-section biodegradation zone, and a final deep purification zone, a zeolite adsorption basket is added to the floating bed frame of each floating bed unit in the front-end adsorption zone. The zeolite adsorption basket is filled with natural zeolite with a particle size of 2cm. The spacing between adjacent floating bed units in the middle-section biodegradation zone is 15cm. An interception net is added to the bottom of each floating bed unit. The interception net is located between the artificial aquatic plants and the bottom sediment improvement layer. In the final deep purification zone, a plant fiber carrier with a length of 2.5m is suspended below the floating bed unit.

[0105] In step S6, when harvesting the aboveground parts of emergent plants, the plants in the front-end adsorption zone, the middle biodegradation zone, and the terminal deep purification zone were harvested independently. The aboveground parts of canna lilies harvested in the front-end adsorption zone were crushed and backfilled into the upstream end of the bottom sediment improvement layer. The aboveground parts of canna lilies harvested in the middle biodegradation zone were crushed and backfilled into the middle section of the bottom sediment improvement layer. The aboveground parts of calamus harvested in the terminal deep purification zone were crushed and backfilled into the downstream end of the bottom sediment improvement layer. After 120 days of operation, monitoring data showed that the ammonia nitrogen concentration in the river section decreased from the initial 12.5 mg / L to 2.1 mg / L, the total phosphorus concentration decreased from 1.8 mg / L to 0.4 mg / L, the COD concentration decreased from 65 mg / L to 22 mg / L, and the dissolved oxygen concentration increased from 0.9 mg / L to 3.8 mg / L.

[0106] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for in-situ restoration of urban river water bodies using composite ecological floating beds, characterized in that, Includes the following steps: S1. Constructing a composite ecological floating bed unit: Combining the floating bed frame, buoyancy carrier, and plant planting basket to form a modular floating bed substrate, planting emergent plants in the planting basket, and burying the rhizosphere regulation substrate in the rhizosphere area of ​​the emergent plants. The rhizosphere regulation substrate is composed of iron-modified biochar particles and calcium peroxide particles in a volume ratio of 3:1-5:

1. The particle size of the iron-modified biochar particles is 2-5mm, the particle size of the calcium peroxide particles is 1-3mm, and the calcium peroxide particles are coated with a sodium alginate film with a thickness of 0.1-0.3mm. S2. Laying a bottom sediment improvement layer: Laying a bottom sediment improvement substrate in the area to be repaired at the bottom of the river. The bottom sediment improvement substrate is composed of a mixture of zeolite, bio-ceramic particles and slow-release carbon source particles, forming a strip-shaped bottom sediment improvement zone extending along the direction of water flow. S3. Constructing a vertical transport channel for plant-derived organic carbon: A plant fiber guiding medium is suspended below the floating bed unit. The upper end of the plant fiber guiding medium connects to the bottom of the planting basket, and the lower end extends 5-15 cm above the substrate amendment layer. The plant fiber guiding medium is formed by filling polyamide mesh tubes with reed stem fragments that have been crushed, soaked in alkali solution, and washed. The length of the reed stem fragments is 2-5 cm, the mesh size of the polyamide mesh tube is 3-8 mm, and the filling density of the reed stem fragments in the polyamide mesh tube is 0.15-0.30 g / cm³. 3 ; S4. Add compound microbial agents: Pre-implant the compound microbial agents containing aerobic denitrifying bacteria and polyphosphate-accumulating bacteria into the internal pores of the plant fiber carrier, and add the compound microbial agents to the surface of the substrate improvement layer. S5. Combined floating bed units form a restoration array: Multiple composite ecological floating bed units are arranged and connected in sequence along the direction of river flow to form a floating bed array covering the water surface to be restored, with water flow channels maintained between each floating bed unit; S6. Operation, maintenance and management: Harvest the above-ground parts of emergent plants regularly, clean the biofilm that falls off the surface of the plant fiber guiding medium regularly, and replenish the microbial agent on the surface of the substrate improvement layer.

2. The method according to claim 1, characterized in that, The method for coating the calcium peroxide particles with a sodium alginate film in step S1 is as follows: Immerse calcium peroxide particles in a sodium alginate solution with a mass concentration of 1%-3% and stir continuously for 10-30 minutes. Then remove them and place them in a calcium chloride solution with a mass concentration of 2%-5% for cross-linking and curing for 5-15 minutes. After removing them, rinse the surface with deionized water and dry them at 40-60℃ for 2-4 hours to form calcium peroxide particles coated with a sodium alginate film. After calcium peroxide particles are coated with a sodium alginate film, a polylactic acid (PLA) inner layer and a PLA outer layer are sequentially coated on the outer layer of the sodium alginate film. The thickness of the PLA inner layer is 0.2-0.5 mm, and the thickness of the PLA outer layer is 0.5-1.0 mm. 5%-10% starch particles by mass are added to the PLA inner layer, while no starch particles are added to the PLA outer layer.

3. The method according to claim 1, characterized in that, The method for preparing the iron-modified biochar particles in step S1 is as follows: After crushing the corn stalks to a particle size of 1-3 mm, they are placed in a tube furnace and heated to 450-550 °C at a heating rate of 5-10 °C / min under a nitrogen atmosphere for primary pyrolysis and carbonization. After holding at this temperature for 2-4 hours, the temperature is naturally cooled to room temperature to obtain the primary pyrolysis product of biochar. The biochar primary pyrolysis product is immersed in a mixed solution of ferrous chloride and ferric chloride with a mass concentration of 0.3-0.8 mol / L for 4-8 hours. The molar ratio of ferrous chloride to ferric chloride in the mixed solution is 1:1-2:

1. After immersion, the product is filtered out and dried at 60-80℃ for 4-8 hours to obtain the iron-loaded biochar intermediate. The iron-loaded biochar intermediate was placed in a tube furnace and heated to 300-400℃ at a heating rate of 8-12℃ / min under a nitrogen atmosphere for a second low-temperature heat treatment. After holding at this temperature for 1-2 hours, it was naturally cooled to room temperature to obtain iron-modified biochar particles.

4. The method according to claim 1, characterized in that, In step S2, the slow-release carbon source particles are core-shell structured particles. The core of the core-shell structured particles is composed of a cross-linked mixture of polyvinyl alcohol and starch in a mass ratio of 3:1 to 5:

1. Nano zero-valent iron particles are incorporated into the cross-linked mixture, and the mass fraction of the nano zero-valent iron particles is 5% to 15%. The outer shell of the core-shell structured particles is formed by melting and coating the core surface with a mixture of polycaprolactone and activated carbon powder at a mass ratio of 7:1-9:

1. The thickness of the outer shell is 0.3-0.8 mm, and release pores with a diameter of 0.5-1.5 mm are formed on the outer shell. The distribution density of the release pores on the outer shell surface is 2-4 pores / cm². 2 ; Before laying the substrate improvement matrix, mix zeolite, bio-ceramic particles, and core-shell structured slow-release carbon source particles evenly in a volume ratio of 2:2:1, then soak them in an enrichment culture solution containing denitrifying bacteria for 24-48 hours. After soaking, drain the surface water before laying.

5. The method according to claim 1, characterized in that, In step S2, when laying the bottom sediment improvement layer, multiple strip-shaped bottom sediment improvement strips are set along the cross-sectional direction of the river channel. A gravel layer is laid in the interval area between two adjacent bottom sediment improvement strips. The gravel layer has a particle size of 3-6cm. The upper surface of the gravel layer is 5-15cm higher than the upper surface of the bottom sediment improvement strip. An impermeable geotextile is laid under the gravel layer. An inclined guide surface is provided on the water-facing end face of each strip of bottom sediment improvement zone. The angle between the inclined guide surface and the upper surface of the bottom sediment improvement zone is 30-60°. A layer of coarse sand with a particle size of 1-2cm is laid on the surface of the inclined guide surface. The thickness of the coarse sand layer is 2-5cm. A vertical cut-off surface is set at the downstream end of each strip of substrate improvement zone. A row of wooden or bamboo stakes is buried at the vertical cut-off surface and inserted vertically into the substrate improvement layer. The diameter of the wooden or bamboo stakes is 5-10cm, the spacing between adjacent wooden or bamboo stakes is 2-5cm, and the height of the wooden or bamboo stakes protruding from the upper surface of the substrate improvement layer is 5-15cm.

6. The method according to claim 1, characterized in that, The alkaline soaking conditions for the reed stem fragments in step S3 are as follows: After crushing the reed stems to a length of 2-5cm, soak them in a 2%-5% sodium hydroxide solution for 12-24 hours. After filtering, rinse with deionized water until the pH of the washing solution is 7.0-8.0, and then dry at 60-80℃ until the moisture content is less than 10%. Reed stem fragments are divided into high carbon-nitrogen ratio fragments and low carbon-nitrogen ratio fragments according to the carbon-nitrogen ratio. The carbon-nitrogen ratio of the high carbon-nitrogen ratio fragments is 40:1-60:1, and the carbon-nitrogen ratio of the low carbon-nitrogen ratio fragments is 15:1-25:

1. The high carbon-nitrogen ratio fragments and the low carbon-nitrogen ratio fragments are mixed at a mass ratio of 2:1-3:1 and then filled into polyamide mesh tubes. Before filling, soak the high carbon-to-nitrogen ratio fragments in a hydrogen peroxide solution with a mass concentration of 0.5%-1.5% for 2-4 hours. After soaking, remove and drain the surface water before mixing with the low carbon-to-nitrogen ratio fragments.

7. The method according to claim 1, characterized in that, In step S3, the upper end of the polyamide mesh tube is fixed to the bottom of the planting basket with nylon cable ties, and a lead weight is suspended from the lower end of the polyamide mesh tube. The weight has a mass of 50-200g. 3-5 polyamide mesh tubes are evenly spaced along the width of the floating bed unit, and the distance between two adjacent polyamide mesh tubes is 15-30cm. The polyamide mesh tube is provided with annular support rings spaced along the axial direction. The annular support rings are made of polypropylene and the spacing between the annular support rings is 10-20cm. The outer wall of the polyamide mesh tube is wrapped with polyhydroxyalkanoate braided tape, the width of which is 1-2cm and the winding spacing is 5-10cm.

8. The method according to claim 1, characterized in that, In step S4, the composite microbial agent is a mixture of aerobic denitrifying bacteria, polyphosphate-accumulating bacteria and Bacillus subtilis in a live bacteria ratio of 2:1:

1. When pre-implanting it into the internal pores of the plant fiber carrier, the carrier is immersed in the mixed bacterial solution for oscillation loading. After loading is completed, the carrier is drained and directly installed on the floating bed unit. The composite microbial agent added to the surface of the substrate improvement layer is sodium alginate-encapsulated immobilized microspheres. The immobilized microspheres have a diameter of 3-5 mm and contain zero-valent iron particles with a particle size of 50-100 μm. The mass of the zero-valent iron particles accounts for 2%-8% of the total mass of the immobilized microspheres. During the preparation of immobilized microspheres, 0.5%-1.5% by mass of hydroxyethyl cellulose is added to the mixture of sodium alginate and bacterial solution.

9. The method according to claim 1, characterized in that, In step S5, when arranging the floating bed units, the floating bed array is divided into a front adsorption zone, a middle biodegradation zone, and a final deep purification zone along the water flow direction. Zeolite adsorption baskets are added to the floating bed frames of each floating bed unit in the front adsorption zone, and the zeolite adsorption baskets are filled with natural zeolite. The spacing between adjacent floating bed units in the middle biodegradation zone is 10-20cm. An interception net is added to the bottom of each floating bed unit. Plant fiber carriers with a length greater than 2m are suspended below the floating bed units in the final deep purification zone. The emergent plants planted in the floating bed units in the front-end adsorption zone, the middle biodegradation zone and the terminal deep purification zone are different. Canna lilies are planted in the front-end adsorption zone, Thalia dealbata is planted in the middle biodegradation zone and Acorus calamus is planted in the terminal deep purification zone. The planting density of canna lilies in the front-end adsorption zone is 12-16 plants / m². 2 The planting density of Thalia dealbata in the middle biodegradation zone is 8-12 plants / m². 2 The planting density of calamus in the terminal deep purification zone is 16-20 plants / m². 2 .

10. The method according to claim 1, characterized in that, In step S6, the periodic harvesting of the above-ground parts of emergent plants is 30-60 days, and the plant height is retained at 15-25cm after harvesting. The frequency of cleaning the biofilm that has fallen off the surface of the plant fiber guiding medium is once every 7-15 days. When cleaning, the upstream water flow channel of the floating bed array should be closed for 10-20 minutes. The replenishment cycle for the surface microbial agent of the substrate amendment layer is 20-40 days, and the replenishment amount is 30%-50% of the initial amount; Check the consumption of reed stem fragments inside the polyamide mesh every 30-60 days. When the consumption of reed stem fragments exceeds 50% of the initial filling amount, replenish the reed stem fragments to the initial filling density. In step S6, when harvesting the above-ground parts of emergent plants, the plants in the front adsorption zone, the middle biodegradation zone, and the terminal deep purification zone are harvested independently. The above-ground parts of canna lilies harvested in the front adsorption zone are crushed and backfilled to the upstream end of the substrate improvement layer. The above-ground parts of canna lilies harvested in the middle biodegradation zone are crushed and backfilled to the middle section of the substrate improvement layer. The above-ground parts of calamus harvested in the terminal deep purification zone are crushed and backfilled to the downstream end of the substrate improvement layer.

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