Natural-ecology-imitating treatment structure for coal mine wastewater and multi-stage purification method

Abstract

The invention discloses a coal mine wastewater natural ecology imitating treatment structure and a multi-stage purification method. The coal mine wastewater natural ecology imitating treatment structure and the multi-stage purification method are suitable for wastewater ecological restoration and resource utilization of historical waste coal mines and high-sulfur coal mining areas. A purification mechanism of a natural ecological system is fully utilized, and deep purification of the coal mine wastewater is realized through a synergistic effect of physical, chemical and biological effects. Compared with a common water quality purification structure, the device has the remarkable advantages of being high in pertinence, high in treatment efficiency, environmentally friendly in ecological environment and the like. Meanwhile, through reasonable size design and plant configuration, the stability and reliability of the treatment system are ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental protection engineering, and particularly relates to a coal mine wastewater natural-ecological treatment structure and a multi-stage purification method. BACKGROUND

[0002] Coal mine wastewater (especially acidic coal mine wastewater) is a highly polluted water body formed by the oxidation of sulfides (such as pyrite FeS2) during coal mining, and is mainly characterized by strong acidity (pH = 1-3), high heavy metals (Fe2+ / Fe3+, Pb2+, Cd2+, Mn, etc.), and high sulfate (SO42-). Because abandoned coal mines have not been effectively repaired, a large amount of leaching wastewater is easily generated during heavy rain, which will cause serious ecological pollution (such as water acidification, heavy metal enrichment, and biological death) if directly discharged into rivers and lakes.

[0003] The prior art has the following disadvantages: first, the traditional treatment process (such as neutralizing agents + membrane separation) has high construction and operation costs; second, it has poor treatment effect on rain and sewage mixed flow (large water fluctuation and complex pollutant composition), and is difficult to adapt to the disordered discharge scene of abandoned coal mines; third, the industrial process destroys the natural landscape and is disconnected with the ecological restoration goal of the mining area; and fourth, it is single-functioned, only focusing on water purification, and not taking into account ecological restoration (such as biodiversity restoration and habitat construction).

[0004] Patent No. CN116161801A discloses a coal mine acidic wastewater treatment device, system and method, which can effectively remove (metal) ions in coal mine acidic wastewater, and can effectively reduce water acidity and improve water pH, thereby improving water quality, but has large sludge production and poor ecological friendliness. Patent No. CN112079444B discloses a natural-ecological wetland system and purification method, which includes an artificial ecological channel, an artificial plant ecological pond, and an artificial substrate ecological pond. Although it utilizes plant-microbial synergistic purification, it is only applicable to rural domestic sewage or farmland non-point source pollution (low pollutant concentration and stable water quantity), and cannot handle the high acid and high heavy metal characteristics of coal mine wastewater, which is prone to plant death. SUMMARY

[0005] The purpose of the present application is to solve the problems of large amount of chemical reagent used, low heavy metal removal efficiency, high energy consumption, poor water quantity adaptability, and insufficient ecological environmental friendliness in the existing coal mine wastewater treatment technology.

[0006] The technical solution of the present application is a coal mine wastewater natural-ecological treatment structure, which comprises five ecological purification units connected in sequence by pipelines, including 1st ecological sedimentation pond: the water flow in the pond is in a horizontal S-shaped flow pattern, and an interception and adsorption net membrane is arranged in the middle of the pond. 2nd stage: the 2nd stage is a forced oxidation pond with an ecological filter dam at the inlet end, and a micro-porous aerator and a microbial attachment base alternately arranged at the bottom of the pond, and an ecological floating bed arranged on the surface of the pond; 3rd stage: the 3rd stage is an acid adjusting pond with a vertical S-shaped flow pattern, and the pond is filled with lime and natural manganese sand filter material, and the area filled with the natural manganese sand filter material is planted with emergent plants; 4th stage: the 4th stage is a deep purification pond with a horizontal S-shaped flow pattern, and the bottom of the pond is filled with hydroxyapatite and zeolite mixed fillers from bottom to top, and the emergent plants are planted above the zeolite mixed fillers; 5th stage: the 5th stage is an aquatic plant pond with a variety of plants, and fish and shellfish are proliferated and released, and the variety of plants includes submerged plants, floating leaf plants and emergent plants.

[0007] Further, the 1st stage ecological sedimentation pond and the 4th stage deep purification pond are provided with a plurality of partition walls perpendicular to the direction of incoming water, one side of the partition wall is fixedly connected with the bank slope, the other side is provided with a vertical gap, and the gap positions of adjacent partition walls are staggered to guide the water flow in the pond to form a horizontal S-shaped flow.

[0008] Further, the adsorption net film is hung between the partition walls of the 1st stage ecological sedimentation pond, and the submerged plants and the floating leaf plants are planted on the bottom layer and the surface layer of the pond, respectively. The adsorption net film includes a polyethylene interception adsorption net film with a mesh size of 2 mm, and a plurality of floating balls are arranged at equal intervals on the upper part of the interception adsorption net film, and a gabion counterweight is arranged on the lower part, and the gabion counterweight is filled with gravel.

[0009] Further, the ecological filter dam is composed of two rows of pine piles driven into the bottom of the pond to form a skeleton, and the space between the pine piles is filled with medium-coarse sand with a particle size of 2-4 mm and pebbles with a particle size of 5-10 mm from inside to outside; the periphery of the pine pile is reinforced with gabion, the gap between the pine pile and the gabion is filled with geotextile, and the top of the ecological filter dam is planted with emergent plants; The microbial attachment base includes a fiber center rope, and a three-dimensional elastic filler is fixed around the fiber center rope, and a floating ball and a counterweight stone block are connected to the upper end and the lower end of the fiber center rope, respectively.

[0010] Further, in the 3rd stage acid adjusting pond, three partition walls are arranged perpendicular to the direction of incoming water; wherein, the bottom of the first partition wall and the third partition wall leaves a water flow channel between the bottom of the partition wall and the bottom of the pond, and the second partition wall is embedded in the bottom of the pond, and the top of the second partition wall is lower than the first partition wall, so as to guide the water flow to form a vertical S-shaped flow; The space in the first partition wall is filled with natural manganese sand filter material at the lower layer and lime at the upper layer, and the natural manganese sand filter material with a particle size of 0.8-1.5 mm is laid in the 3rd stage acid adjusting pond (C) except the area of the first partition wall.

[0011] Furthermore, the first-stage ecological sedimentation pond draws water through a concrete-cast No. 1 water collection channel; the effluent from the first-stage ecological sedimentation pond enters the second-stage forced oxidation pond via the ecological filter dam; the effluent from the second-stage forced oxidation pond enters the third-stage acid regulation pond via the No. 2 water collection channel and the No. 3 water distribution channel; the effluent from the third-stage acid regulation pond enters the fourth-stage deep purification pond via the No. 3 water collection channel and the No. 4 water distribution channel; and the effluent from the fourth-stage deep purification pond enters the fifth-stage aquatic plant pond via the No. 4 water collection channel.

[0012] Furthermore, the coal mine wastewater simulated natural ecological treatment structure is a wide and shallow structure, and the bottom of all its purification units is treated with HDPE geomembrane combined with a 30mm thick clay layer for seepage prevention.

[0013] A multi-stage purification method for coal mine wastewater based on a simulated natural ecological treatment structure includes the following steps: Step 1: Wastewater enters the primary ecological sedimentation pond, where large suspended solids are removed by gravity sedimentation, the biodegradability of the wastewater is improved by hydrolysis and acidification, and some organic matter is removed by adsorption. Step 2: Wastewater enters the secondary forced oxidation pond, where microporous aerators aerate and oxidize Fe²⁺ to... Fe³⁺, and removes part of the chemical oxygen demand (COD) and ammonia nitrogen (NH3-N); Step 3: The wastewater enters the three-stage acidic conditioning pond, where the pH is adjusted to the medium-alkaline range through lime neutralization. The residual Fe²⁺ and Mn²⁺ are catalytically oxidized by natural manganese sand filter media, promoting the precipitation of heavy metal hydroxides and removing some sulfates. Step 4: Wastewater enters a four-stage deep purification pond, where heavy metal ions and residual nitrogen and phosphorus pollutants are deeply removed through the ion exchange of hydroxyapatite and the adsorption of zeolite mixed packing material, combined with the synergistic effect of plants and microorganisms. Step 5: Wastewater enters a 5-stage aquatic plant pond, which enhances nitrogen and phosphorus removal and provides habitat for aquatic organisms by creating a diverse aquatic plant and animal ecosystem.

[0014] Furthermore, the primary ecological sedimentation pond (A) undergoes a hydrolysis and acidification reaction, specifically, The Fe²⁺ oxidation reaction occurs in the second-stage forced oxidation pond (B), specifically, The third-level acidic conditioning pond (C) undergoes neutralization and heavy metal precipitation reactions, specifically as follows: The fourth-stage deep purification pond (D) undergoes an ion exchange reaction, specifically, The 5-stage aquatic plant pond (E) occurs ammonium ion nitrification reaction, in the aquatic plant pond, ammonia nitrogen (NH3-N) is converted into nitrate (NO3-) under the action of nitrifying bacteria, and the total nitrogen removal is realized by combining the denitrification process (anaerobic condition), specifically, .

[0015] Further, the effluent water quality after the 5-stage aquatic plant pond treatment reaches the following indexes: pH = 6.8-7.2, SS≤18 mg / L, Fe²⁺<0.5 mg / L, Pb²⁺<0.05 mg / L, COD≤32 mg / L, NH3-N<3 mg / L, which is superior to the limit requirement of the Coal Industry Pollutant Discharge Standard (GB 20426-2006) The beneficial effects of the present application 1. The natural multi-stage S-shaped flow design is arranged alternately through the gap of the partition wall, the water flow is guided to flow horizontally in the ecological sedimentation pond and the deep purification pond in the form of S, the flow rate is reduced, the hydraulic retention time (HRT=24-48h) is prolonged, and the gravity sedimentation and plant-filter adsorption efficiency are strengthened; the acid adjusting pond adopts a vertical S-shaped flow state, the bottom of the partition wall is left empty / inserted, vertical mixing is promoted, and short flow is avoided. Compared with the traditional straight-line flow process, the SS removal rate is increased by 30%, and the heavy metal (Pb²⁺, Cd²⁺) removal rate is increased by 25%.

[0016] 2. Natural materials and functional fillers are used for synergistic purification, the ecological sedimentation pond uses PE net film (mesh 2mm) to intercept fine particles, replacing the traditional grid (to avoid blockage); the acid adjusting pond is paved with natural manganese sand filter material (particle size 0.8-1.5mm), which converts Fe²⁺ into Fe³⁺ by using the catalytic oxidation effect of MnO2 (without additional addition of oxidizing agent); the deep purification pond is filled with hydroxyapatite and zeolite mixed fillers (volume ratio 1:1), which fix heavy metals (Pb²⁺, Cd²⁺) and sulfate (SO4²⁻) through ion exchange. Compared with the chemical agent method, the dosage of the agent is reduced by 80%, and the sludge yield is reduced by 60%.

[0017] 3. Rainwater and sewage mixed flow adaptive design, the whole system is designed as "wide and shallow type" (pond body width 10-20m, water depth 1.0-3.0m), and is matched with No. 1, No. 2, No. 3 and No. 4 water collecting pools, which can accommodate large flow of wastewater in the rainy season, and slowly release the treatment in the dry season through the ecological filter dam. Compared with the traditional sewage treatment plant, only stable flow can be treated, and the treatment capacity of rainwater and sewage mixed flow is greatly improved, and the effluent water quality is stable and up to standard.

[0018] 4. Ecological landscape and biodiversity construction, full system matching planting emergent, floating leaf, submerged plants, proliferation of fish (silver carp, bighead carp) and shellfish (mussel, snail), forming a complex food chain of "plant-microorganism-animal" (such as "algae->rotifer->silver carp" "residual branches->bacteria->benthic animals"), taking into account water purification and ecological restoration. System biodiversity index > 2.5, providing habitat for birds and fish, and landscape effect close to natural wetlands. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0020] Figure 1 is a cross-sectional schematic diagram of the coal mine wastewater natural ecological treatment structure and method in the present application; Figure 2 is a plan schematic diagram of the coal mine wastewater natural ecological treatment structure and method in the present application; Figure 3 is a schematic diagram of the interception and adsorption net membrane structure in the present application; Figure 4 is a schematic diagram of the ecological filter dam structure in the present application; Figure 5 is a schematic diagram of the microbial attachment base structure in the present application; The drawings are as follows: 1-coal mine wastewater and runoff surface source, 2-pipeline, 3-1st water collection channel, 4-water surface, 5-plain soil ramming, 6-HDPE impermeable membrane, 7-separation wall, 8-interception and adsorption net membrane, 9-submerged plant, 10-floating leaf plant, 11-emergent plant, 12-ecological filter dam, 13-micro-porous aerator, 14-microbial attachment base, 15-ecological floating bed, 16-2nd water collection channel, 17-3rd water collection channel, 18-lime, 19-natural manganese sand filter material, 20-3rd water collection tank, 21-4th water distribution tank, 22-hydroxyapatite, 23-zeolite filler, 24-4th water collection channel, 26-float ball, 27-polyethylene interception and adsorption net membrane, 28-weighted stone cage, 29-weighted stone block, 30-fiber center rope, 31-three-dimensional elastic filler, 32-Gabion stone cage, 33-geotextile, 34-pine pile, 35-medium coarse sand, 36-pebble, A-1st ecological sedimentation pond, B-2nd forced oxidation pond, C-2nd forced oxidation pond, D-4th deep purification pond, E-5th aquatic plant pond. DETAILED DESCRIPTION

[0021] The present application will be further described below in connection with the accompanying drawings and specific embodiments, but should not be understood as limiting the scope of the subject matter described herein to the following examples, and any modifications, replacements and changes made according to ordinary technical knowledge and common practices in the art without departing from the above technical ideas of the present application are included in the scope of the present application.

[0022] The present application aims to maximize the use of natural physical, chemical and biological processes to remove pollutants by constructing a multi-stage natural purification system, and to reduce or avoid the overuse of chemical reagents. The acid adjustment pond and the deep purification pond are specially designed to effectively remove heavy metals in wastewater by utilizing the packing characteristics of natural manganese sand, hydroxyapatite and zeolite. The entire treatment system relies on natural forces (such as gravity flow, microbial action) to operate, reducing external forces, and the microporous aeration mainly uses solar panels for power supply, reducing energy consumption and operation and maintenance costs. Through the structure of ecological sedimentation pond (ecological filter dam) → forced oxidation pond → acid adjustment pond → deep purification pond → aquatic plant pond, a diversified ecological system is constructed to improve the adaptability of the system to water fluctuations, promote biodiversity, and enhance the ecological environment friendliness of the treatment system.

[0023] Reference Figures 1-5 A coal mine wastewater natural-ecological treatment structure and a multi-stage purification method, the treatment structure is a series of 5-stage ecological purification units, including: ecological sedimentation pond A → forced oxidation pond B → acid adjustment pond C → deep purification pond D → aquatic plant pond E, with a matching water collection channel and water distribution pool, the water collection channel includes No. 1 water collection channel 3, No. 2 water collection channel 16, No. 3 water collection channel 17, No. 3 water collection pool 20, No. 4 water distribution pool 21, No. 4 water collection channel 24, and also has an ecological filter dam 12, etc. auxiliary, the upstream of the ecological sedimentation pond A is connected with a coal mine wastewater and runoff source 1, the coal mine wastewater and runoff source 1 enters the No. 1 water collection channel 3 through the pipeline 2, and the water surface 4 of the No. 1 water collection channel 3 has a soil ramming 5, the whole system pond bottom adopts HDPF impermeable membrane 6 combined with 30mm thick clay impermeable. The purification method realizes wastewater purification and ecological restoration through multi-stage flow state control, filler adsorption, and plant-microorganism synergistic effect.

[0024] Purification process flow: coal mine wastewater (runoff source) → No. 1 water collection channel (concrete pouring) → 1-stage ecological sedimentation pond (S-type flow state + net film interception) → ecological filter dam (pine pile + sand gravel) → 2-stage forced oxidation pond (solar aeration + submerged plant) → No. 2 water collection channel → No. 3 water distribution channel → 3-stage acid adjustment pond (lime adjustment + natural manganese sand) → No. 3 water collection channel → No. 4 water distribution channel → 4-stage deep purification pond (hydroxyapatite + zeolite filler + plant purification) → No. 4 water collection channel → 5-stage aquatic plant pond (various plants + fish and shellfish) → clear water reuse (irrigation, landscape water) or discharge.

[0025] The 1st level system ecological sedimentation pond has the function of removing large particle SS by gravity settling, improving biodegradability by hydrolytic acidification, and removing part of organic matter by adsorption. The structure design: the pond body is poured by concrete No. 1 water collecting channel 3 (width 0.8-1.2m, depth 1.2m) is introduced into the pond body, which is divided into 5 sections by 4 partition walls 7 (height 3.0m, thickness 0.5m) vertically to the water direction. The partition wall is close to the bank slope on one side, and the other side leaves a vertical gap of 0.5-1m (the gap position is in turn exchange), which guides the water flow to flow horizontally in S shape; 2# and 3# partition wall hangs interception adsorption net film 8 (material PE, mesh 2mm, float ball is arranged on the net film with 1m interval, and the bottom is weighted with stone cage (filled with gravel)), the net film is 0.5m away from the water surface and 1.0m away from the bottom of the pool; the bottom is planted with submerged plants 9 (vallisneria, black algae), the surface is planted with floating leaf plants 10 (nymphaea, trapa) and emergent plants 11 (reed, cattail), and the plant coverage is 10%-15%; the water depth of the ecological sedimentation pond is controlled at 2.5-3.0m, and the water depth of the submerged plant planting area is controlled at 1.0-1.5m.

[0026] The 2nd stage system is a forced oxidation pond, which functions to oxidize Fe2+ to Fe3+ (promote precipitation) by aeration, and remove part of COD and NH3-N. The structure design: an ecological filter dam 12 is arranged at the water inlet end to prevent suspended solids and plant residues from entering the 2nd stage system, the filter dam 12 is fixed by two rows of pine piles (spacing 1.0 m, penetrating into the pool bottom 1.5 m), filled with medium-coarse sand (particle size 2-4 mm) and surface pebbles (particle size 5-10 mm) in the middle, and reinforced with steel reinforcement cages (size 1.0 m x 1.0 m x 1.5 m) on the periphery, aquatic plants are planted on the top of the ecological filter dam, the ecological filter dam 12 receives the water treated by the sedimentation tank, and delivers the treated water to the next stage treatment unit. The ecological filter dam 12 provides a good water flow channel and allows aquatic plants and microorganisms to attach and grow. The ecological filter dam 12 is composed of two rows of pine piles 34 driven into the bottom of the pond, and the space between the pine piles 34 is filled with medium-coarse sand 35 with a particle size of 2-4 mm and pebbles 36 with a particle size of 5-10 mm from inside to outside; the periphery of the pine piles 34 is reinforced with gabion 32, and the gap between the pine piles 34 and the gabion 32 is filled with geotextile 33; aquatic plants 11 are planted on the top of the ecological filter dam 12, and the aquatic plants and microorganisms further remove suspended solids and part of organic matter by absorption, adsorption and degradation. The application of the ecological filter dam increases the diversity of the ecological system, improves the treatment efficiency, and the planting of aquatic plants also enhances the aesthetics of the treatment system; the forced oxidation pond has a water depth of 1.0-2.0 m, and submerged plant combinations (Myriophyllum spicatum, Potamogeton crispus) are arranged at the bottom of the pond, ecological floating beds 15 are arranged in the pond body, and microbial attachment bases 14 are arranged below the ecological floating beds, the microbial attachment base 14 includes a fiber center rope 30, a three-dimensional elastic filler 31 is fixed around the fiber center rope 30, and a floating ball 26 and a counterweight stone 29 are connected to the upper end and the lower end of the fiber center rope 30 respectively. Microorganisms attach to the substrate to form a biofilm, which removes organic matter and part of heavy metals in wastewater through degradation, and a solar micro-porous aerator 13 (power 1.5 KW, aerator head spacing 2.0 m, bottom aeration) is arranged; the effluent enters the 3rd water distribution tank through the No. 2 water collection tank 16 (PVC pipe connection, pipe diameter 500 mm).

[0027] The third-stage system acidic adjusting pond has the function of adjusting pH to neutral and slightly alkaline, removing heavy metals and part of sulfates by natural manganese sand catalytic oxidation of Fe2+ / Mn2+. The structural design is that three partition walls are arranged in the vertical water inflow direction of the pond body, 50 cm gap is left at the bottom of the first and third partition walls, the second partition wall is embedded in the pool bottom and is 30 cm higher than the first partition wall, so as to guide the water flow to flow vertically in S shape; the first partition wall is filled with natural manganese sand filter material 19 in the lower layer and lime 18 (CaO) in the upper layer, and the other areas are paved with natural manganese sand filter material 19 (particle size 0.8-1.5 mm, filling thickness 1.0-1.5 m); the surface is planted with emergent plants (Acorus calamus, water onion), the plant roots form an aerobic zone (nitrification reaction), and the bottom layer forms an anaerobic zone (denitrification reaction); the periphery of the pond body is naturally sloped (slope 1:5), and the slope surface is planted with herbaceous plants (goat grass) to fix soil.

[0028] The fourth-stage system deep purification pond has the function of deeply removing heavy metals and residual nitrogen and phosphorus through ion exchange and plant-microorganism synergistic effect. The pond body is divided into five sections by three partition walls vertically to the water inflow direction, one side of the partition wall is close to the shore slope, and the other side leaves a vertical gap of 0.5-1 m (the gap positions are exchange in turn), so as to guide the water flow to flow horizontally in S shape, the pond bottom is filled with hydroxyapatite 22 and zeolite mixed filler 23 (volume ratio 1:1, filling thickness 1.0-1.2 m), and the filler layer is planted with emergent plants (reed, wild rice); the effluent enters the fifth-stage aquatic plant pond through the No. 4 water collecting pool 24 (PVC pipe connection).

[0029] The fifth-stage system aquatic plant pond has the function of constructing a diversified water ecological system, strengthening nitrogen and phosphorus removal, and providing a biological habitat. The structural design is that the pond body is designed according to the terrain elevation, the water depth is 1.5-2.5 m, emergent plants (reed, cattail), floating leaf plants (water lily, water shield), and submerged plants (duckweed, pondweed) are planted, and the plant density is ≥16 plants / m2; filter-feeding fish (silver carp, bighead carp, density 50 tails / mu) and benthic shellfish (river mussels, snails, density 200 kg / mu) are proliferated and released, forming a "plant-microorganism-animal" synergistic purification system; the periphery is provided with ecological revetment (block stone + planted grass).

[0030] The chemical reactions of each unit pond are as follows: ① Hydrolysis and acidification reaction (ecological precipitation pond) ② Fe2+ oxidation reaction (forced oxidation pond) ③ Neutralization and heavy metal precipitation reaction (acidic adjusting pond) Neutralizing acidic wastewater (pH promotion), generating difficultly soluble CaSO4 precipitate, reducing the concentration of sulfate radical.

[0031] MnO2) to catalyze the oxidation of Fe2+ to Fe3+, promoting the precipitation of metal hydroxides. Fe3+ further hydrolyzes to form Fe(OH)3 colloids, which adsorb suspended solids and heavy metal ions. Mn2+ can be subsequently adsorbed and fixed by hydroxyapatite.

[0032] ④ Ion exchange reaction (advanced purification pond) In the advanced purification pond, hydroxyapatite (Ca 10 (PO4)6(OH)2) adsorbs heavy metal ions (such as Pb2+, Cd2+) through ion exchange, releasing Ca2+, fixing heavy metals, and reducing their biological toxicity. Zeolites assist in heavy metal removal through adsorption-desorption.

[0033] ⑤ Ammonium ion nitrification reaction (aquatic plant pond) In the aquatic plant pond, ammonia nitrogen (NH3-N) is converted to nitrate (NO3-) under the action of nitrifying bacteria, and total nitrogen removal is achieved through the denitrification process (anaerobic conditions).

[0034] Plant growth feasibility in coal mine wastewater treatment ponds. According to research literature, emergent plants such as reed, cattail, and water onion show strong adaptability in coal mine wastewater treatment. The net photosynthetic rate and transpiration rate of water oat, water onion, and alocasia in coal mine wastewater are significantly higher than that of the control, indicating that they can adapt to high-pollutant environments through photosynthesis. The root systems of reed and cattail can adsorb and fix heavy metals such as Pb2+ and Cd2+, reducing their toxicity to plant growth. By adding lime to adjust the pH to neutral to slightly alkaline (pH 6-9), the stress of acidity on plant roots can be alleviated. Ecological sedimentation ponds (2.5-3.0 m) and forced oxidation ponds (1.0-2.0 m) are planted in different layers (emergent + floating leaf plants) to adapt to different water depths and avoid root hypoxia. The aquatic plant pond (1.5-2.5 m) uses a multi-level design to provide habitat for fish and benthic organisms, indirectly promoting plant community stability. Natural manganese sand (acidic adjustment pond) releases Mn2+ as an essential trace element for plant growth. Hydroxyapatite and zeolite (advanced purification pond) adsorb heavy metals, reducing the risk of plants absorbing pollutants. Submerged plants (vallisneria and ranunculus) release organic acids through their roots, activating nutrients in the sediment and providing nitrogen and phosphorus supplements for other plants. According to the structure of this patent (such as pH regulation, filler optimization) and plant selection (reed, cattail, water onion, etc.), plants in coal mine wastewater treatment ponds can grow healthily, and work together with microorganisms and substrates to achieve efficient removal of pollutants.

[0035] Example: A historical abandoned coal mine in Guizhou Province is located in a karst topography area. Due to long-term disordered mining, the mine acid wastewater (containing rain runoff) is seriously polluted. The annual rainfall is 1200 mm, and the wastewater flow rate is as high as 800 m³ / h in the rainy season. The water quality is strongly acidic (pH=2.8), rich in Fe²⁺ (1200 mg / L), Pb²⁺ (0.8 mg / L) and suspended solids (SS=2500 mg / L), with COD of 350 mg / L and NH3-N of 25 mg / L, causing serious damage to the surrounding water body and ecology. In view of this problem, the project adopts a 5-stage natural ecological treatment system for treatment. The bottom of the engineering area is rammed and then laid with HDPE impermeable membrane 6 covered with 0.3 m clay 5 layers, which plays a role in impermeability. The coal mine wastewater 1 flows from east to west through the PVC pipe 2 with a diameter of about 300 mm into the No. 1 water collection ditch 1, flows into the ecological sedimentation pond (60 m×25 m×2.5 m) through the north-south partition wall 7, the partition wall leaves a gap of 0.5-1 m in the south and north, the water flow forms a horizontal S-shaped flow pattern, and the polyethylene interception and adsorption net film 8 (mesh 1.5-2 mm) is used to remove more than 80% of the suspended solids, and a small amount of submerged plants 9 (bitter grass, fox tail) and floating leaf plants 10 (water turtle, big weed) are planted to strengthen the sedimentation and hydrolysis acidification effect; the water flow further passes through the ecological filter dam 12 (10 m×25 m×3 m) into the forced oxidation pond (40 m×25 m×2.0 m), the forced oxidation pond is equipped with solar energy micro-porous aerator 13 (power 300 W×4 sets), and the microorganism attachment base 14 and ecological floating bed 15 are used to oxidize Fe²⁺ to Fe³⁺, and the dissolved oxygen (DO) is increased to more than 3 mg / L. The water flow enters the No. 2 water collection tank 16 through the PVC pipe 2 with a diameter of about 300 mm into the No. 3 water distribution ditch 17 into the acid adjusting pond (50 m×30 m×2.5 m), through the north-south partition wall 7, the partition wall leaves a gap of 0.5-1 m in the upper and lower parts, the water flow forms a vertical S-shaped flow pattern, the first partition wall is filled with lime 18 in the upper layer and natural manganese sand 19 (particle size 0.8-1.5 mm) in the lower layer, and the rest of the area is filled with natural manganese sand 19, which adjusts the pH from 2.8 to 7.0-7.5, catalyzes the precipitation of heavy metal hydroxides.The water flow into No. 3 collecting pool 20 enters No. 4 water distribution channel 21 through a PVC pipe 2 with a diameter of about 300 mm, and enters a deep purification pond (40 m x 30 m x 2.0 m), the deep purification pond uses a mixed filler 23 (volume ratio 1:1) of hydroxyapatite 22 and zeolite to adsorb heavy metals such as Pb²⁺ and Cd²⁺ through ion exchange, and further purifies nutrients in combination with emergent plants 11 (reed, cattail, and water onion); the water flow into No. 4 collecting pool 24 enters an aquatic plant pond (60 m x 30 m x 2.5 m) through a PVC pipe 2 with a diameter of about 300 mm, the aquatic plant pond constructs a "emergent-flooding-submerged" complex community (reed, water chestnut, and duckweed), releases Hypophthalmichthys nobilis (30 tails / mu), Aristichthys nobilis (90 tails / mu), and shellfish (200 kg / mu), arranges (25) ecological islands, creates bird habitats, and forms a complete food chain to strengthen ecological restoration. After the system is operated, the effluent water quality is stable and up to standard, pH = 6.8-7.2, SS is reduced to 18 mg / L, Fe²⁺ < 0.5 mg / L, Pb²⁺ < 0.05 mg / L, COD is reduced to 32 mg / L, NH3-N < 3 mg / L, which is much better than the "Coal Industry Pollutant Discharge Standard" (GB 20426-2006).

[0036] The application creates a high-efficiency and environmentally-friendly coal mine wastewater natural-ecological treatment system. The system fully utilizes the purification mechanism of natural ecological system, and realizes deep purification of coal mine wastewater through the synergistic effect of physical, chemical and biological actions. Compared with general water quality purification structures, the application has the advantages of strong pertinence, high treatment efficiency, and friendly ecological environment. Meanwhile, through reasonable size design and plant configuration, the stability and reliability of the treatment system are ensured.

[0037] The coal mine wastewater natural-ecological treatment structure and the multi-stage purification method provided by the application are described in detail above, and specific examples are applied to describe the structure and working principle of the application. The above examples are only used to help understand the method and core idea of the application. It should be pointed out that the ordinary skilled in the art can make some improvements and modifications to the application without departing from the principles of the application, and these improvements and modifications also fall within the scope of protection of the claims of the application.

Claims

1. A natural ecological treatment structure for coal mine wastewater, characterized in that: Includes five levels of ecological purification units connected sequentially via pipe (2), including Level 1 ecological sedimentation pond (A): The water flow in the pond is in a horizontal S-shaped state, and an intercepting and adsorption mesh (8) is set in the middle of the pond. Level 2 forced oxidation pond (B): An ecological filter dam (12) is installed at the water inlet. Microporous aerators (13) and microbial attachment substrates (14) are alternately arranged at the bottom of the pond. An ecological floating bed (15) is laid on the surface of the pond. Level 3 acidic conditioning pond (C): The water flow in the pond is vertical S-shaped. The pond is filled with lime (18) and natural manganese sand filter media (19). Emergent plants (11) are planted in the area filled with natural manganese sand filter media (19). Level 4 deep purification pond (D): The water flow in the pond is in a horizontal S-shaped state. The bottom of the pond is filled with hydroxyapatite (22) and zeolite mixed filler (23) from bottom to top. Emergent plants (11) are planted above the zeolite mixed filler (23). Level 5 Aquatic Plant Pond (E): Plants a variety of plants and releases fish and shellfish. The plants include submerged plants (9), floating-leaved plants (10) and emergent plants (11).

2. The coal mine wastewater simulated natural ecological treatment structure according to claim 1, characterized in that: The Level 1 ecological sedimentation pond (A) and the Level 4 deep purification pond (D) are equipped with several partition walls (7) perpendicular to the direction of water inflow. One side of the partition wall (7) is fixedly connected to the bank slope, and the other side has a vertical gap. The gaps of adjacent partition walls (7) are staggered to guide the water flow in the pond to form a horizontal S-shaped flow.

3. The coal mine wastewater simulated natural ecological treatment structure according to claim 2, characterized in that: An adsorption mesh (8) is installed between the partition walls (7) of the Level 1 ecological sedimentation pond (A), and submerged plants (9) and floating-leaved plants (10) are planted in the bottom and surface layers of the pond, respectively. The adsorption mesh (8) includes a polyethylene interception and adsorption mesh (27) with a mesh size of 2 mm. Floats (26) are evenly spaced on the upper part of the interception and adsorption mesh (27), and a gabion counterweight (28) is provided on the lower part. The gabion counterweight (28) is filled with crushed stones.

4. The coal mine wastewater simulated natural ecological treatment structure according to claim 1, characterized in that: The ecological filter dam (12) is framed by two rows of pine piles (34) driven into the bottom of the pond. The space between the pine piles (34) is filled from the inside out with medium-coarse sand (35) with a particle size of 2-4 mm and pebbles (36) with a particle size of 5-10 mm. The outer perimeter of the pine piles (34) is reinforced with gabion cages (32). The gap between the pine piles (34) and the gabion cages (32) is filled with geotextile (33). Emergent plants (11) are planted on the top of the ecological filter dam (12). The microbial attachment substrate (14) includes a fiber central rope (30), and three-dimensional elastic filler (31) is fixed around the fiber central rope (30). The upper and lower ends of the fiber central rope (30) are respectively connected to a float (26) and a counterweight stone (29).

5. The coal mine wastewater simulated natural ecological treatment structure according to claim 1, characterized in that: In the three-stage acidic conditioning pond (C), three partition walls (7) are set perpendicular to the direction of incoming water; among them, the bottom of the first and third partition walls are left with water flow channels between them and the bottom of the pond, and the second partition wall is embedded in the bottom of the pond, with its top elevation lower than that of the first partition wall, so as to guide the water flow to form a vertical S-shaped flow. The lower layer of the space inside the first partition wall is filled with natural manganese sand filter material (19), and the upper layer is filled with lime (18). In the third-level acidic conditioning pond (C), except for the area of ​​the first partition wall, natural manganese sand filter material (19) with a particle size of 0.8 to 1.5 mm is laid.

6. The coal mine wastewater simulated natural ecological treatment structure according to claim 1, characterized in that: The first-level ecological sedimentation pond (A) draws water through the No. 1 water collection channel (1) made of concrete; the effluent from the first-level ecological sedimentation pond (A) enters the second-level forced oxidation pond (B) through the ecological filter dam (12); the effluent from the second-level forced oxidation pond (B) enters the third-level acid regulation pond (C) through the No. 2 water collection channel (16) and the No. 3 water distribution channel (17); the effluent from the third-level acid regulation pond (C) enters the fourth-level deep purification pond (D) through the No. 3 water collection channel (20) and the No. 4 water distribution channel (21); the effluent from the fourth-level deep purification pond (D) enters the fifth-level aquatic plant pond (E) through the No. 4 water collection channel (24).

7. The coal mine wastewater simulated natural ecological treatment structure according to claim 1, characterized in that: The coal mine wastewater treatment structure is a shallow and wide structure, and the bottom of all purification units is treated with HDPE geomembrane combined with a 30mm thick clay layer for seepage prevention.

8. The multi-stage purification method based on a simulated natural ecological treatment structure for coal mine wastewater according to any one of claims 1-7, characterized in that: Includes the following steps: Step 1: Wastewater enters the primary ecological sedimentation pond (A), where large suspended solids (SS) are removed by gravity sedimentation, the biodegradability of the wastewater is improved by hydrolysis and acidification, and some organic matter is removed by adsorption. Step 2: Wastewater enters the secondary forced oxidation pond (B), where it is oxygenated by a microporous aerator (13) to oxidize Fe²⁺ into Fe. Fe³⁺, and removes part of the chemical oxygen demand (COD) and ammonia nitrogen (NH3-N). Step 3: Wastewater enters the third-stage acidic conditioning pond (C), where the pH is adjusted to the medium-alkaline range by the neutralization effect of lime (18), and the residual Fe²⁺ and Mn²⁺ are catalytically oxidized by natural manganese sand filter media (19), which promotes the precipitation of heavy metal hydroxides and removes some sulfates; Step 4: Wastewater enters the 4-stage deep purification pond (D), where heavy metal ions and residual nitrogen and phosphorus pollutants are deeply removed through the ion exchange of hydroxyapatite (22) and the adsorption of zeolite mixed packing material (23), combined with the synergistic effect of plants and microorganisms. Step 5: Wastewater enters the Level 5 aquatic plant pond (E), which enhances nitrogen and phosphorus removal and provides habitat for aquatic organisms by creating a diverse aquatic plant and animal ecosystem.

9. The multi-stage purification method based on a simulated natural ecological treatment structure for coal mine wastewater according to claim 8, characterized in that: The first-level ecological sedimentation pond (A) undergoes a hydrolysis and acidification reaction, specifically, The Fe²⁺ oxidation reaction occurs in the second-stage forced oxidation pond (B), specifically, The third-level acidic conditioning pond (C) undergoes neutralization and heavy metal precipitation reactions, specifically as follows: The fourth-stage deep purification pond (D) undergoes an ion exchange reaction, specifically, The fifth-level aquatic plant pond (E) undergoes ammonium ion nitrification. In the aquatic plant pond, ammonia nitrogen (NH3-N) is converted into nitrate (NO3⁻) by nitrifying bacteria. Combined with denitrification (under anoxic conditions), total nitrogen removal is achieved. Specifically, 。 10. The multi-stage purification method based on a simulated natural ecological treatment structure for coal mine wastewater according to claim 8, characterized in that: The effluent from the Level 5 aquatic plant pond (E) meets the following criteria: pH = 6.8–7.2, SS ≤ 18 mg / L, Fe²⁺ < 0.5 mg / L, Pb²⁺ < 0.05 mg / L, COD ≤ 32 mg / L, and NH₃-N < 3 mg / L. These criteria are superior to the limits set by the "Emission Standard of Pollutants for Coal Industry" (GB20426-2006).

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