A combined constructed wetland system and method for treating pond culture wastewater

Abstract

The application discloses a combined overflow wetland system and method for treating pond aquaculture wastewater, and belongs to the field of water treatment technology. The combined overflow wetland system comprises a support structure fixed at the bottom of a pond slope, a purification unit stacked on the upper surface of the pond slope and blocked by the support structure, and a capillary water distribution structure arranged above the purification unit. Water flows through the purification unit in a combined manner of local vertical flow and overall overflow, and the pond aquaculture wastewater is treated by combining physical treatment, biological treatment and ecological treatment. The combined overflow wetland system integrates physical treatment, biological treatment and ecological treatment, and aims to solve the problem that concentrated discharge of aquaculture tail water is difficult to be treated deeply.

Description

Technical Field

[0001] This invention belongs to the field of pond aquaculture wastewater treatment, and relates to a combined overflow wetland system and method for treating pond aquaculture wastewater. Background Technology

[0002] The discharge of aquaculture wastewater and pollution from aquaculture continues to increase, and direct discharge will pollute the surrounding waterways.

[0003] Aquaculture wastewater is characterized by large discharge volumes, low pollutant concentrations, but complex pollutant types. Traditional physical treatment methods, such as mechanical filtration, adsorption, and foam separation, can only effectively remove suspended pollutants and cannot address dissolved pollutants. Traditional chemical treatment methods, such as flocculation, neutralization, complexation, and oxidation-reduction, provide rapid water quality regulation, but require large dosages, significantly increasing aquaculture costs and causing side effects, including secondary pollution. Both of these methods have significant drawbacks when applied alone to aquaculture wastewater treatment. Therefore, cost-effective and comprehensive biological or integrated treatment methods are the key future development directions for pond aquaculture wastewater treatment technology. Among these, ecological ditch technology transforms drainage ditches into ecological ditches with water purification functions; constructed wetland technology utilizes the synergistic effects of substrates, plants, and microorganisms to achieve compliant discharge of aquaculture wastewater; and the "three ponds and two dams" or "four ponds and three dams" technologies recommended in relevant technical guidelines comprehensively purify water using physical and biological ecological methods. These technologies are effective at removing various pollutants, but they also generally suffer from long purification cycles, low treatment efficiency, and large land area requirements.

[0004] The invention patent with publication number CN115124203A provides a multi-cycle tailwater treatment system, which improves the "three ponds and two dams" purification pond technology by adding a pond and a channel tailwater treatment system and a pond bottom sewage tailwater treatment system. The three systems cooperate or alternately to treat the tailwater and reuse it. This technology improves the treatment efficiency of aquaculture tailwater, but it also greatly increases the land area of ​​the purification system, increases land use costs and daily operation and maintenance costs, resulting in poor economic benefits and difficulty in market promotion.

[0005] The invention patent with publication number CN115557626A provides a method for the ex-situ ecological treatment of aquaculture pond wastewater. It constructs a treatment unit based on three ponds, purifying the wastewater through intermittent addition of microbial inoculants, construction of ecological floating island restoration areas, artificial aquatic plant filler restoration areas, ecological floating frame restoration areas, and composite matrix filter dams. Almost all purification processes take place within the purification area of ​​the second pond. This invention's treatment method requires a small footprint and enables the recycling of pond wastewater. However, due to the relatively small volume of the three ponds, this method is practically only suitable for small-scale pond aquaculture, and the filter media in the composite matrix filter dam also faces the challenge of inconvenient replacement.

[0006] In summary, existing aquaculture wastewater treatment technologies all have drawbacks to varying degrees, such as high cost and poor effectiveness, necessitating the exploration of more efficient, economical, and environmentally friendly methods for treating aquaculture wastewater. Summary of the Invention

[0007] In response to the characteristics of large volume and low pollutant concentration in aquaculture wastewater, this invention discloses a combined overflow wetland system and method for treating pond aquaculture wastewater. It constructs a combined aquaculture wastewater treatment technology that integrates "jet circulating biological filter - assembled vertical flow wetland - combined overflow wetland". This technology integrates physical treatment, biological treatment and ecological treatment, and aims to solve the problem of difficult treatment of centralized aquaculture wastewater discharge.

[0008] This invention provides a vertically and horizontally combined overflow constructed wetland technology, the specific technical solution of which is as follows:

[0009] A combined overflow wetland system for treating pond aquaculture wastewater includes:

[0010] A support structure fixed to the bottom of the pond slope;

[0011] The purification units are stacked on the pond slope using a supporting structure to block the flow of water.

[0012] The capillary water distribution structure located above the purification unit allows water to flow through the purification unit via a combination of vertical infiltration and overall diffused flow. The purification unit treats pond aquaculture wastewater through a combination of physical, biological, and ecological methods.

[0013] Furthermore, the purification unit uses perforated mesh bags filled with sludge biochar ceramic granule packing material (publication number CN115477527A) and granular humus biological packing material wrapped with water-purifying plant seeds (publication number CN111533243A).

[0014] Furthermore, in a single purification unit, the weight percentage of granular humic biological packing containing water-purifying plant seeds is 0-20%, with the remainder being sludge biochar ceramic granular packing; the granular humic biological packing and sludge biochar ceramic granular packing in the purification unit are replaced every 1-2 years.

[0015] Furthermore, with the support structure as support, the filled purification units are laid horizontally upwards along the pond slope, with the bottom of the upper purification unit connected to the top of the lower purification unit, and no gaps left between the purification units; the number of layers of the stacked purification units is set to 1 to 3.

[0016] Furthermore, the mesh size of the perforated mesh bag is smaller than the particle size of the granular humic biological filler and the sludge biochar ceramsite granular filler. The particle size of the granular humic biological filler is 8mm to 12mm; the particle size of the sludge biochar ceramsite granular filler is 15mm to 20mm.

[0017] Furthermore, the water-purifying plant seeds include one or more of the following: alfalfa, Bermuda grass, crested wheatgrass, Kentucky bluegrass, ryegrass, alkali grass, tall fescue, ice grass, and barnyard grass; the seed density in the granular humic biological filler is 2 to 5 seeds per filler; and each purification unit contains 400 to 800 water-purifying plant seeds.

[0018] Furthermore, the capillary water distribution structure includes a water distribution main pipe, water distribution branch pipes, fiber fabric capillary water distribution pipes (publication number CN111468518A), and water pipe supports; the water distribution main pipe is laid out on the surface of the pond slope along the slope extension direction, collects the upper-level effluent, and completes the primary water distribution of the combined overflow wetland system; water distribution branch pipes are uniformly arranged on the water distribution main pipe and on the side closer to the inside of the pond, parallel to the slope inclination of the pond; fiber fabric capillary water distribution pipes are symmetrically arranged on both sides of each water distribution branch pipe to achieve uniform water distribution without dead corners.

[0019] Furthermore, the diameter of the main water distribution pipe is 100mm to 300mm; the length of the fiber fabric capillary water distribution pipe is set to 1m to 2m; and the spacing of the branch water distribution pipes is twice the length of the fiber fabric capillary water distribution pipe.

[0020] Furthermore, the support structure includes a waste plastic shell and a steel conical rod. The waste plastic shell is a cone formed by extruding waste plastic, and the steel conical rod is wrapped inside.

[0021] Furthermore, the height of the support structure is 0.4m to 0.7m; the support structure is vertically inserted into the pond slope, and the length of the inserted part is 0.15m to 0.25m.

[0022] The above-mentioned method for treating pond aquaculture wastewater using a combined overflow wetland system includes:

[0023] Clean the pond slope;

[0024] Anchoring support structures on the pond slope;

[0025] The purification units are stacked on the pond slope using a supporting structure to block the flow of water.

[0026] A capillary water distribution structure is installed above the purification unit. The capillary water distribution is evenly distributed to the surface of the purification unit by gravity. The water flows through the packing material of the purification unit, where local vertical flow and overall diffuse flow occur. By combining the packing material with plant roots through physical, chemical and biological processes, organic matter and nutrients such as nitrogen and phosphorus are removed, thus achieving deep treatment of aquaculture wastewater.

[0027] The specific method is as follows:

[0028] 1. Clean the slope: Remove debris from the slope of the purification pond to make the slope smooth;

[0029] 2. Anchoring support piles: Lay out the lines to determine the vertical positioning of the horizontally laid purification unit perpendicular to the extension direction of the slope (purification unit axis positioning). Determine the position of the support pile at the point 200mm from the bottom side of the positioning axis closest to the water surface, and drive the support pile vertically into the slope soil to ensure stability.

[0030] 3. Laying purification units: Using support piles as support, lay the filled purification units horizontally upward along the slope. The bottom of the upper purification unit is connected to the top of the lower purification unit, and there are no gaps between the purification units. After the first layer of purification units fills the slope, continue to lay the second layer of purification units. The number of layers of purification units is designed to be 1 to 3.

[0031] 4. Install capillary water distribution structure: The capillary water inlet enters the water distribution branch pipe from the water distribution main pipe by gravity flow, and then is evenly distributed to the surface of the purification unit through the fiber fabric capillary water distribution pipes on both sides of the water distribution branch pipe with capillary water distribution function; the water flow undergoes local vertical flow and overall diffuse flow process in the packing of the purification unit, and the packing and plant roots combine physical, chemical and biological processes to remove organic matter and nutrients such as nitrogen and phosphorus, so as to achieve deep treatment of aquaculture effluent.

[0032] 5. Packing replacement: Replace the packing in the purification unit every 1-2 years.

[0033] The beneficial effects of this invention are as follows:

[0034] (1) The combined overflow wetland system of the present invention uses waste plastic to make support piles, sewage sludge to make biochar ceramsite granules filler, and existing garbage screened humus soil to make granular humus biological filler, successfully realizing "waste treatment", and also reducing the operation and maintenance cost of the combined overflow wetland system, which is economical, environmentally friendly and more adaptable to the market.

[0035] (2) The combined overflow wetland system of the present invention organically combines two wetland modes: local vertical flow and overall overflow, solving the problem of treating low-concentration, high-volume aquaculture wastewater and achieving deep treatment of aquaculture wastewater. Specifically, the water flows through the packing material and plant roots through a combination of vertical infiltration and overall overflow. Solid suspended matter is intercepted and filtered by the packing material, organic pollutants and total nitrogen are degraded and absorbed by the microorganisms and plant system growing on the surface of the granular humic biological packing material, and phosphorus and its derivatives are adsorbed by the sludge biochar ceramic granular packing material and simultaneously absorbed by the plant roots as nutrients, thus giving full play to the good purification functions of the combined overflow wetland system in filtering suspended matter, removing nitrogen and phosphorus.

[0036] (3) The combined overflow wetland system of the present invention uses perforated mesh bags filled with biochar ceramic particles and granular humic biological filler wrapped with plant seeds to construct a purification unit, which solves the problem of difficult replacement of filler. Attached Figure Description

[0037] Figure 1 A cross-sectional view of a combined overflow wetland system;

[0038] Figure 2 This is a plan view of the capillary water distribution structure of a combined overflow wetland system.

[0039] Among them, 1-support pile, 101-waste plastic shell, 102-steel cone rod; 2-purification unit, 201-sludge biochar ceramsite granular filler, 202-granular humus biological filler, 203-water purification plant seeds; 3-capillary water distribution structure, 301-water distribution main pipe, 302-water distribution branch pipe, 303-fiber fabric capillary water distribution pipe, 304-water pipe support; 4-purification pond slope. Detailed Implementation

[0040] To make the technical means, creative features, achieved objectives, and effects of this invention readily understandable, the technical solutions in the embodiments of this invention are clearly and completely described below with reference to the accompanying drawings. It should be understood that the described embodiments are only a part of the embodiments of this invention, and not all of them.

[0041] like Figure 1 , Figure 2 As shown, the combined overflow wetland system for treating pond aquaculture wastewater in this embodiment includes a support pile 1 anchored at the bottom of the purification pond slope 4, a purification unit 2 stacked on the purification pond slope 4 using the support pile 1 to block the flow, and a capillary water distribution structure 3 set directly above the purification unit 2.

[0042] Among them, the support pile 1 includes a waste plastic shell 101 and a steel cone rod 102. The waste plastic shell 101 is a cone formed by extruding waste plastic, and the inside is wrapped with a steel cone rod 102 with a diameter of 12mm to 20mm.

[0043] The bottom of the support pile 1 is conical, and the upper and middle parts of the support pile 1 are cylindrical. The height of the support pile 1 is set to 0.4m to 0.7m, the length of the conical part is set to 0.1m to 0.2m, and the outer diameter of the support pile 1 is set to 30mm to 50mm.

[0044] The support pile 1 is vertically inserted into the bottom of the slope 4 of the purification pond, and the length of the inserted part is set to 0.15m to 0.25m.

[0045] The purification unit 2 includes a perforated mesh bag made of polypropylene (PP). The perforated mesh bag is filled with two types of fillers: sludge biochar ceramic granule filler 201 (the specific preparation method is detailed in Chinese Patent No. CN115477527A, entitled "A Method for Producing Biochar Ceramic Granule Filler", which will not be described in detail here) and granular humic biological filler 202 (the specific preparation method is detailed in Chinese Patent No. CN111533243A, entitled "A Granular Humic Biological Filler, Production Method and Application", which will not be described in detail here).

[0046] The perforated mesh bag has a length of 600mm to 900mm, a width of 300mm to 500mm, and a thickness of 150mm to 200mm after filling. The mesh diameter is designed to be 5mm to 10mm. The perforated mesh bag in purification unit 2 can be sealed with plastic tie-down straps to prevent filler leakage.

[0047] Furthermore, the purification unit 2 also includes water-purifying plant seeds 203, specifically one or more of alfalfa, Bermuda grass, crested wheatgrass, Kentucky bluegrass, ryegrass, alkali grass, tall fescue, ice grass, and barnyard grass, coated with granular humus filler 202, with a density of 2 to 5 seeds per filler, and each purification unit 2 contains 400 to 800 seeds.

[0048] Furthermore, the weight percentage of granular humic biological filler 202 (including the aforementioned water purification plant seeds 203) in purification unit 2 is designed to be 0-20%, and the particle size of granular humic biological filler 202 should be larger than the mesh diameter of the perforated mesh bag of purification unit 2, set to 8mm-12mm; the remaining part is sludge biochar ceramic granular filler 201, and the particle size of sludge biochar ceramic granular filler 201 should be larger than the mesh diameter of the perforated mesh bag of purification unit 2, set to 15mm-20mm.

[0049] The capillary water distribution structure 3 includes a water distribution main pipe 301, a water distribution branch pipe 302, a fiber fabric capillary water distribution pipe 303 (for details, please refer to Chinese Patent No. CN111468518A, the patent name is a fiber capillary water distribution pipe, water distribution system and water distribution method, which will not be described in detail here) and a water pipe support 304.

[0050] like Figure 2 As shown, the main water distribution pipe 301 is also a prefabricated vertical flow wetland outlet pipe, laid along the slope extension direction on the slope surface. Its function is to collect the upper-level effluent and complete the primary water distribution of the combined overflow wetland system. On the main water distribution pipe 301, located near the purification pond, a 40mm circular hole is opened every 2m to 4m in the slope inclination direction. The opening is connected to the branch water distribution pipe 302 parallel to the slope inclination using an additional connector pipe fitting. Then, DN15 (nominal diameter 15mm) fiber fabric capillary water distribution pipes 303 are symmetrically arranged on both sides of each branch water distribution pipe 302 via reducing four-way connectors. The spacing between the fiber fabric capillary water distribution pipes 303 is designed to be 0.3m to 0.5m, utilizing fiber capillary uniform water distribution technology to achieve uniform water distribution over long distances with low head. The water pipe support 304 is installed at the lower part of the above-mentioned water pipes (water distribution main pipe 301, water distribution branch pipe 302, and fiber fabric capillary water distribution pipe 303) to support the above-mentioned water pipes suspended in the air.

[0051] Furthermore, the diameter of the water distribution main pipe 301 should preferably be set to 100mm to 300mm.

[0052] Furthermore, the bottom of the water distribution branch pipe 302 is sealed, and the length of the water distribution branch pipe 302 should be consistent with the distance from the water distribution main pipe 301 of the combined overflow wetland to the support pile 1 (the length of the purification unit 2 laid in the slope inclination direction).

[0053] Furthermore, the length of the fiber fabric capillary water distribution pipe 303 is set to 1m to 2m, and the water distribution area should cover the entire combined overflow constructed wetland system, with no dead corners in water distribution, so as to achieve uniform water distribution across the entire surface of the wetland.

[0054] The specific method for assembling the combined overflow wetland system for treating pond aquaculture wastewater and treating the effluent in this embodiment is as follows:

[0055] 1. Clean the slope: Remove debris from slope 4 of the purification pond to make the slope smooth;

[0056] 2. Anchoring support pile 1: Lay out the line to determine the vertical positioning of the horizontally laid purification unit 2 perpendicular to the extension direction of the slope (positioning of the axis of purification unit 2). Determine the position of support pile 1 at the point 200mm from the bottom side of the positioning axis near the water surface. Drive support pile 1 vertically into the soil of the purification pond slope 4 to ensure stability.

[0057] 3. Laying purification unit 2: With support pile 1 as support, lay the filled purification unit 2 horizontally upward along the slope. The bottom of the upper purification unit 2 is connected to the top of the lower purification unit 2, and there are no gaps between the purification units 2. After the first layer of purification unit 2 has covered the slope, continue to lay the second layer of purification unit 2. The number of layers of purification unit 2 is designed to be 1 to 3.

[0058] 4. Install capillary water distribution structure 3: The capillary water inlet enters the water distribution branch pipe 302 from the water distribution main pipe 301 by gravity flow, and then is evenly distributed to the surface of the purification unit 2 through the fiber fabric capillary water distribution pipes 303 on both sides of the water distribution branch pipe 302 with capillary water distribution function; the water flow undergoes local vertical flow and overall diffuse flow process in the packing of the purification unit 2, and the packing and plant roots combine physical, chemical and biological processes to remove organic matter and nutrients such as nitrogen and phosphorus, so as to achieve deep treatment of aquaculture wastewater.

[0059] 5. Replacement of packing material: The packing material in purification unit 2 (sludge biochar ceramic granular packing material 201 and granular humic biological packing material 202) should be replaced every 1-2 years.

[0060] Example 1:

[0061] A combined overflow wetland system was applied to a 400-square-meter aquaculture pond as part of a purification pond. The pond's dimensions were 3m x 8m. The influent COD was 50±10mg / L, total nitrogen was 2.0±0.5mg / L, total phosphorus was 0.6±0.2mg / L, and suspended solids concentration was 120±20mg / L.

[0062] The combined overflow wetland system has a support pile 1 installed at the bottom of the purification pond slope 4. The support pile 1 is internally encased with a steel cone rod 102 with a diameter of 15mm. The support pile 1 has a height of 0.6m and an outer diameter of 40mm. The support pile 1 is vertically inserted into the purification pond slope 4, with an insertion length of 0.2m.

[0063] The perforated mesh bag of purification unit 2 is 600mm long and 400mm wide, with a mesh diameter of 6mm±1mm. It is made of non-woven fabric using polypropylene as the raw material. Purification unit 2 is filled with two types of fillers: sludge biochar ceramsite granular filler 201 and granular humic biological filler 202. The granular humic biological filler 202 has a weight percentage of 10%, a particle size of 8mm, and each granule contains 2-5 seeds of Kentucky bluegrass and Imperata cylindrica. The sludge biochar ceramsite granular filler 201 has a weight percentage of 90%, and a particle size of 20mm. The perforated mesh bag of purification unit 2 is 150mm thick after filling.

[0064] The capillary water distribution structure 3 includes a main water distribution pipe 301, branch water distribution pipes 302, fiber fabric capillary water distribution pipes 303, and pipe supports 304. The main water distribution pipe 301 is also a prefabricated vertical flow wetland outlet pipe, laid along the slope extension direction on the slope surface. The main water distribution pipe 301 has a diameter of 100mm and its function is to collect the upstream effluent and complete the primary water distribution of the combined overflow constructed wetland. On the side of the main water distribution pipe 301 closest to the purification pond, a 40mm circular hole is opened every 3m in the slope inclination direction. The openings are connected to the branch water distribution pipes 302 parallel to the slope inclination using additional connector pipe fittings. Then, DN15 fiber fabric capillary water distribution pipes 303 are symmetrically arranged on both sides of the branch water distribution pipes 302 via reducing four-way connectors, with a pipe spacing of 0.3m and a pipe length of 1.5m. This utilizes fiber capillary uniform water distribution technology to achieve uniform water distribution over long distances with low head. Water pipe support 304 is installed at the bottom of each level of water pipe to support the suspended water distribution pipe.

[0065] Furthermore, the bottom of the water distribution branch pipe 302 and the fiber fabric capillary water distribution pipe 303 are sealed, and the length of the water distribution branch pipe 302 is 3m.

[0066] The specific method for assembling and treating the tailwater of the combined overflow wetland system for treating pond aquaculture wastewater in this embodiment is as follows:

[0067] Clean the slope: Clean the debris on the slope 4 of the purification pond to make the slope smooth. For any uneven areas, add purification unit 2 later to make it smooth.

[0068] Anchoring support pile 1: Lay out the line to determine the position of support pile 1, and insert support pile 1 vertically into the slope soil to a certain depth;

[0069] Laying purification unit 2: Using support pile 1 as support, lay the completed purification unit 2 horizontally upwards. The bottom of the upper purification unit 2 should be placed on the top of the lower purification unit 2, and there should be no gaps between the purification units 2. After the first layer of purification unit 2 has covered the slope, continue to lay the second layer of purification unit 2.

[0070] Install capillary water distribution structure 3: Set up capillary water distribution structure 3 according to the above technical solution requirements. The inlet water enters the water distribution branch pipe 302 from the water distribution main pipe 301 by gravity flow, and seeps out from the fiber capillary water distribution pipe 303 at a uniform speed through capillary action to achieve the effect of uniform water distribution. The water flows through the packing and plant roots in a combination of vertical infiltration and overall overflow. Solid suspended matter is intercepted and filtered by the packing. Organic pollutants and total nitrogen are degraded and absorbed by the microorganisms and plant system growing on the surface of the granular humic biological packing 202. Phosphorus and its derivatives are adsorbed by the sludge biochar ceramic granular packing 201 and are also absorbed by the plant roots as nutrients. This gives full play to the good purification function of the combined overflow wetland system in filtering suspended matter, removing nitrogen and phosphorus.

[0071] Packing replacement: The packing in purification unit 2 should be replaced once a year.

[0072] The combined overflow wetland system operated stably for 12 months. During this period, the dissolved oxygen concentration in the wetland system remained between 0.8 and 1.5 mg / L, and the pH remained between 7.5 and 8. After stabilization, the COD of the wetland effluent remained below 10 mg / L, total nitrogen below 2.0 mg / L, total phosphorus below 0.4 mg / L, and suspended solids below 35 mg / L. During operation, purification unit 2 did not experience any breakage or disintegration.

[0073] Example 2:

[0074] A combined overflow wetland was applied to a 20-mu (approximately 3.3 hectares) aquaculture pond as part of a purification pond. The wetland occupies an area of ​​600 square meters and measures 10m x 60m. The influent COD of the pond is 75±15mg / L, total nitrogen is 2.5±0.5mg / L, total phosphorus is 0.8±0.2mg / L, and suspended solids concentration is 120±20mg / L.

[0075] The combined overflow wetland system has a support pile 1 installed at the bottom of the purification pond slope 4. The support pile 1 is internally encased with a steel cone rod 102 with a diameter of 20mm. The support pile 1 has a height of 0.6m and an outer diameter of 30mm. The support pile 1 is vertically inserted into the purification pond slope 4, with an insertion length of 0.15m.

[0076] The perforated mesh bag of purification unit 2 is 900mm long and 500mm wide, with a mesh diameter of 9mm±1mm. It is made of non-woven fabric using polypropylene as the raw material. Purification unit 2 is filled with two types of fillers: sludge biochar ceramsite granular filler 201 and granular humic biological filler 202. In the first stage, the weight percentage of granular humic biological filler 202 is 15%, and the weight percentage of sludge biochar ceramsite granular filler 201 is 85%. In the second stage (after filler replacement), the weight percentage of granular humic biological filler 202 is 5%, and the weight percentage of sludge biochar ceramsite granular filler 201 is 95%. The particle size of granular humic biological filler 202 is 12mm, and the particle size of sludge biochar ceramsite granular filler 201 is 20mm. Each granular humic biological filler 202 contains 3-5 water-purifying plant seeds 203, mainly alfalfa, crested wheatgrass, ryegrass, and alkali grass. The thickness of the perforated mesh bag in the filled purification unit 2 is 150mm.

[0077] The capillary water distribution structure 3 includes a main water distribution pipe 301, branch water distribution pipes 302, fiber fabric capillary water distribution pipes 303, and pipe supports 304. The main water distribution pipe 301 is also a prefabricated vertical flow wetland outlet pipe, laid along the slope extension direction on the slope surface. The main water distribution pipe 301 has a diameter of 200mm and its function is to collect the upstream effluent and complete the primary water distribution of the combined overflow constructed wetland. On the side of the main water distribution pipe 301 closest to the purification pond, a 40mm circular hole is opened every 4m in the slope inclination direction. The openings are connected to the branch water distribution pipes 302 parallel to the slope inclination using additional connector pipe fittings. Then, DN15 fiber fabric capillary water distribution pipes 303 are symmetrically arranged on both sides of the branch water distribution pipes 302 via reducing four-way connectors, with a pipe spacing of 0.5m and a pipe length of 2m. This utilizes fiber capillary uniform water distribution technology to achieve uniform water distribution over long distances with low head. Water pipe support 304 is installed at the bottom of each level of water pipe to support the suspended water distribution pipe.

[0078] Furthermore, the bottom of the water distribution branch pipe 302 and the fiber fabric capillary water distribution pipe 303 are sealed, and the length of the water distribution branch pipe 302 is 6m.

[0079] The specific method for assembling and treating the tailwater of the combined overflow wetland system for treating pond aquaculture wastewater in this embodiment is as follows:

[0080] Clean the slope: Remove debris from the slope 4 of the purification pond to make the slope smooth;

[0081] Anchoring support pile 1: Lay out the line to determine the position of support pile 1, and insert support pile 1 vertically into the soil of the slope 4 of the purification pond by 0.15m;

[0082] Laying purification unit 2: Using support pile 1 as support, lay the completed purification unit 2 horizontally upwards. The bottom of the upper purification unit 2 should be placed on the top of the lower purification unit 2, and there should be no gaps between the purification units 2. After the first layer of purification unit 2 has covered the slope, continue to lay the second layer of purification unit 2... The number of layers of purification unit 2 stacked is 3.

[0083] Install capillary water distribution structure 3: Set up capillary water distribution structure 3 as required above. The inlet water enters the water distribution branch pipe 302 from the water distribution main pipe 301 by gravity flow and seeps out from the fiber capillary water distribution pipe 303 at a uniform speed through capillary action to achieve the effect of uniform water distribution. The water flows through the packing and plant roots in a combination of vertical infiltration and overall flow. Solid suspended matter is intercepted and filtered by the packing. Organic pollutants and total nitrogen are degraded and absorbed by the microorganisms and plant system growing on the surface of the granular humic biological packing 202. Phosphorus and its derivatives are adsorbed by the sludge biochar ceramic granular packing 201 and are absorbed by the plant roots as nutrients. This combination of flow wetland has a good purification function of filtering suspended matter, removing nitrogen and phosphorus.

[0084] Packing Replacement: The packing materials (201, 202) in purification unit 2 should be replaced every 18 months.

[0085] The combined overflow wetland system operated stably for 36 months. During this period, the dissolved oxygen concentration in the wetland system remained at 1-1.8 mg / L, and the pH remained at 7.5-8.

[0086] During the first 18 months, the COD concentration in the wetland effluent remained below 15 mg / L, the total nitrogen below 2.8 mg / L, the total phosphorus below 0.5 mg / L, and the suspended solids concentration below 37 mg / L. During operation, purification unit 2 did not experience any cracking or falling.

[0087] During the 19th to 36th month, the COD concentration of the wetland effluent remained stable at around 12 mg / L, the total nitrogen remained below 2.2 mg / L, the total phosphorus remained below 0.3 mg / L, and the suspended solids concentration remained below 30 mg / L. During the operation, the purification unit 2 did not experience any cracking or falling.

[0088] The above description is merely a preferred embodiment of the present invention and does not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A combined overflow wetland for treating pond aquaculture wastewater, characterized in that, include: A support structure fixed to the bottom of the pond slope, wherein the support structure is a pile; The purification units are stacked on the pond slope using a support structure to block the flow of water. Each purification unit is an independent module that can be quickly replaced. The purification unit uses perforated mesh bags filled with sludge biochar ceramic granules and granular humic biological fillers that encapsulate water-purifying plant seeds. The mesh size of the perforated mesh bags is smaller than the particle size of the granular humic biological fillers and the sludge biochar ceramic granules. In a single purification unit, the weight percentage of granular humic biological filler containing water-purifying plant seeds is 0-20%, with the remainder being sludge biochar ceramic granular filler; the particle size of the granular humic biological filler is 8 mm-12 mm; the particle size of the sludge biochar ceramic granular filler is 15 mm-20 mm; the water-purifying plant seeds include one or more of the following: alfalfa, Bermuda grass, crested wheatgrass, Kentucky bluegrass, ryegrass, alkali grass, tall fescue, ice grass, and barnyard grass. A capillary water distribution structure is installed above the purification unit. Water flows through the purification unit through a combination of vertical infiltration and overall overflow. The purification unit treats pond aquaculture wastewater through a combination of physical, biological, and ecological methods. The capillary water distribution structure includes a water distribution main pipe, water distribution branch pipes, fiber fabric capillary water distribution pipes, and water pipe supports. The water distribution main pipe is laid out along the slope extension direction on the surface of the pond slope to collect the upper-level effluent and complete the primary water distribution of the combined overflow wetland system. The water distribution branch pipes are evenly arranged on the water distribution main pipe and on the side closer to the inside of the pond, parallel to the slope inclination of the pond. Fiber fabric capillary water distribution pipes are symmetrically arranged on both sides of each water distribution branch pipe to achieve uniform water distribution without dead corners.

2. The combined overflow wetland for treating pond aquaculture wastewater as described in claim 1, characterized in that, The granular humic biological packing material and sludge biochar ceramic granular packing material in the purification unit are replaced every 1-2 years.

3. The combined overflow wetland for treating pond aquaculture wastewater as described in claim 1, characterized in that, Supported by a supporting structure, the completed purification units are laid horizontally upwards along the pond slope, with the bottom of the upper purification unit connected to the top of the lower purification unit, and no gaps left between the purification units; the number of layers of the stacked purification units is set to 1 to 3.

4. The combined overflow wetland for treating pond aquaculture wastewater as described in claim 1, characterized in that, The seed density in the granular humic biological filler is 2-5 seeds per filler; each purification unit contains 400-800 water-purifying plant seeds.

5. A combined overflow wetland for treating pond aquaculture wastewater as described in claim 1, characterized in that, The diameter of the main water distribution pipe is 100mm~300mm; the length of the fiber fabric capillary water distribution pipe is set to 1m~2m; the spacing of the water distribution branch pipes is twice the length of the fiber fabric capillary water distribution pipe.

6. A combined overflow wetland for treating pond aquaculture wastewater as described in any one of claims 1-4, characterized in that, The support structure includes a waste plastic shell and a steel conical rod. The waste plastic shell is a cone formed by extruding waste plastic, and the steel conical rod is wrapped inside. The height of the support structure is 0.4 m to 0.7 m. The support structure is vertically inserted into the pond slope, and the length of the inserted part is 0.15 m to 0.25 m.

7. A treatment method for pond aquaculture wastewater using a combined overflow wetland according to any one of claims 1-6, characterized in that, The method includes: Clean the pond slope; Anchoring support structures on the pond slope; The purification units are stacked on the pond slope using a supporting structure to block the flow of water. A capillary water distribution structure is installed above the purification unit. The capillary water distribution is evenly distributed to the surface of the purification unit by gravity. The water flows through the packing material of the purification unit, where local vertical flow and overall diffuse flow occur. By using the packing material and plant roots to combine physical, chemical and biological processes, organic matter and nitrogen and phosphorus nutrients are removed, thus achieving deep treatment of aquaculture wastewater.

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