A composite constructed wetland system based on dissolved oxygen regulation and a method for operating the same

Abstract

The present application belongs to the technical field of sewage treatment, and particularly relates to a composite constructed wetland system based on dissolved oxygen regulation and a running method thereof. The composite constructed wetland system of 'no-vegetation horizontal subsurface flow + vegetation composite vertical flow + vegetation horizontal subsurface flow' constructed by the present application can realize segmented water inflow from the water inflow pipe of the no-vegetation horizontal subsurface flow constructed wetland and the water distribution inflow pipe of the downflow pool B, and can optimize water flow and redox environment, so that the problem of carbon source shortage can be solved without supplement of additional carbon source, nitrogen and phosphorus removal efficiency is improved, and the system is suitable for treatment of low carbon-nitrogen ratio wastewater.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a composite constructed wetland system based on dissolved oxygen regulation and its operation method. Background Technology

[0002] Constructed wetlands, as a wastewater treatment technology, have been widely used in the field of wastewater treatment in recent years due to their advantages such as low construction and operating costs, simple operation, low energy efficiency, and good effluent quality. The working principle of constructed wetlands is based on the ecosystem of natural wetlands, utilizing the synergistic effect of plant roots and microbial communities to remove pollutants from water through physical, chemical, and biodegradation methods. Subsurface flow constructed wetlands (SSFCWs) are one of the most common and widely used types of constructed wetlands. They can be divided into horizontal subsurface flow (HSSFCWs) and vertical subsurface flow (VSSFCWs) according to the water flow pattern. The former is usually in a water-saturated state, with its aerobic zone likely located around the roots and rhizomes, while the latter, due to the intermittent water supply, is often unsaturated and has a larger proportion of aerobic zone.

[0003] Composite vertical flow constructed wetlands (IVCWs) connect HSSFCWs and VSSFCWs through a difference in substrate height to achieve natural reoxygenation. Although this configuration combines the nitrification capacity of vertical subsurface flow constructed wetlands with the denitrification effect of horizontal subsurface flow constructed wetlands, it may be limited by a limited carbon source when treating wastewater with a low C / N ratio, making it difficult to maintain a sufficient denitrification reaction, resulting in reduced nitrogen removal efficiency. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a composite constructed wetland system based on dissolved oxygen regulation and its operation method. This composite constructed wetland system can effectively purify wastewater with a low carbon-to-nitrogen ratio without the need to supplement an additional carbon source.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a composite constructed wetland system based on dissolved oxygen regulation, comprising: a horizontal subsurface flow constructed wetland A without vegetation, a composite vertical flow constructed wetland with vegetation, and a horizontal subsurface flow constructed wetland D with vegetation connected in series;

[0007] The constructed wetland with vegetation and vertical flow includes a downflow pool B and an upflow pool C connected in series.

[0008] The unvegetated horizontal subsurface flow constructed wetland A is equipped with an inlet pipe 1;

[0009] A water inlet pipe 2 is installed at the upper end of the downstream pool B.

[0010] Preferably, the length ratio of the vegetation-free horizontal subsurface flow constructed wetland A, the vegetated hybrid vertical flow constructed wetland, and the vegetated horizontal subsurface flow constructed wetland D is 2:3 to 4:2 to 3.

[0011] Preferably, a first upper water pipe 3 and a first lower water pipe 4 are arranged in the downstream tank B, and a second upper water pipe 5 and a second lower water pipe 6 are arranged in the upstream tank C; the first upper water pipe 3, the first lower water pipe 4, the second upper water pipe 5, and the second lower water pipe 6 are all "rich"-shaped pipes; a collecting water pipe 7 is arranged in the vegetation-free horizontal subsurface flow constructed wetland A; a water distribution pipe 8 and a water outlet pipe 9 are arranged in the vegetated horizontal subsurface flow constructed wetland D;

[0012] The collecting water pipe 7 in the vegetation-free horizontal subsurface flow constructed wetland A is connected to the upper water pipe 3 of the downstream tank B; the first lower water pipe 4 of the downstream tank B is connected to the second lower water pipe 6 of the upstream tank C; the second upper water pipe 5 of the upstream tank C is connected to the water distribution pipe 8 of the vegetated horizontal subsurface flow constructed wetland D;

[0013] The water diversion inlet pipe 2 of the downstream tank B is communicated with the first upper water pipe 3 of the downstream tank B.

[0014] Preferably, the height of the filler in the vegetation-free horizontal subsurface flow constructed wetland A is 60 to 100 cm; the height of the filler in the downstream tank B is 70 to 120 cm and > the height of the filler in the vegetation-free horizontal subsurface flow constructed wetland A; the height of the filler in the upstream tank C is 50 to 105 cm and < the height of the filler in the downstream tank B; the height of the filler in the vegetated horizontal subsurface flow constructed wetland D is 50 to 105 cm and = the height of the filler in the upstream tank C.

[0015] Preferably, the filler of the vegetation-free horizontal subsurface flow constructed wetland A includes a coarse gravel layer, a medium gravel layer, and a zeolite layer arranged in sequence from bottom to top; the thickness of the coarse gravel layer in the vegetation-free horizontal subsurface flow constructed wetland A is 10 to 30 cm, the thickness of the medium gravel layer is 30 to 80 cm, and the thickness of the zeolite layer is 10 to 30 cm;

[0016] The filler of the downstream tank B includes a coarse gravel layer, a medium gravel layer, a zeolite layer, and a soil layer arranged in sequence from bottom to top; the thickness of the coarse gravel layer in the downstream tank B is 10 to 30 cm, the thickness of the medium gravel layer is 30 to 80 cm, the thickness of the zeolite layer is 10 to 30 cm, and the thickness of the soil layer is 10 to 20 cm;

[0017] The filler of the upstream tank C includes a coarse gravel layer, a medium gravel layer, a zeolite layer, and a soil layer arranged in sequence from bottom to top; the thickness of the coarse gravel layer in the upstream tank C is 10 to 30 cm, the thickness of the medium gravel layer is 20 to 65 cm, the thickness of the zeolite layer is 10 to 30 cm, and the thickness of the soil layer is 10 to 30 cm;

[0018] The filler material of the vegetated horizontal subsurface flow constructed wetland D includes a coarse gravel layer, a medium gravel layer, a zeolite layer, and a loam layer arranged sequentially from bottom to top; the thickness of the coarse gravel layer in the vegetated horizontal subsurface flow constructed wetland D is 10~30cm, the thickness of the medium gravel layer is 20~65cm, the thickness of the zeolite layer is 10~30cm, and the thickness of the loam layer is 10~30cm.

[0019] The coarse gravel layer has a coarse gravel particle size of 40-60 mm; the medium gravel layer has a medium gravel particle size of 20-30 mm; and the zeolite layer has a zeolite particle size of 0.5-10 mm.

[0020] Preferably, the plants in the vegetated composite vertical flow constructed wetland and the vegetated horizontal subsurface flow constructed wetland D are wetland emergent plants; the wetland emergent plants include one or more of reeds, cattails, water plantains, reed shoots and sedges.

[0021] Preferably, the plant density in both the vegetated vertical flow constructed wetland and the vegetated horizontal subsurface flow constructed wetland D is 45-50 plants / m². 2 .

[0022] The present invention also provides an operation method for a composite constructed wetland system based on dissolved oxygen regulation. Water is introduced into the composite constructed wetland system described above in a segmented two-stage water inlet manner. The first stage of water inlet is in the water inlet pipe 1 of the unvegetated horizontal subsurface flow constructed wetland A, and the second stage of water inlet is in the water distribution inlet pipe 2 of the downstream pool B of the vegetated composite vertical flow constructed wetland.

[0023] The nitrogen-to-phosphorus ratio of the influent to the composite constructed wetland system based on dissolved oxygen regulation is 10-25:1.

[0024] Preferably, the flow rate of the first inlet is 3~5m³ / h. 3 / h; the flow rate of the second stage inlet is 1.5~2.5m³ / h. 3 / h.

[0025] Preferably, the time for the first stage of water intake and the second stage of water intake are independently 8~24h, and the hydraulic retention time is independently 8~24h.

[0026] This invention provides a composite constructed wetland system based on dissolved oxygen regulation, comprising: a horizontal subsurface flow constructed wetland A without vegetation, a composite vertical flow constructed wetland with vegetation, and a horizontal subsurface flow constructed wetland D with vegetation connected in series; the composite vertical flow constructed wetland with vegetation includes a downstream pool B and an upstream pool C connected in series; the horizontal subsurface flow constructed wetland A without vegetation is provided with an inlet pipe 1; and a water distribution inlet pipe 2 is provided at the upper end of the downstream pool B.

[0027] This invention constructs a composite artificial wetland system consisting of "a horizontal subsurface flow without vegetation + a combined vertical flow with vegetation + another horizontal subsurface flow with vegetation." The initial section, a horizontal subsurface flow without vegetation, provides a relatively stable anaerobic environment, allowing organic matter to be stored as an internal carbon source in the form of polyhydroxyalkanoates (PHAs) by polyphosphate-accumulating bacteria (PAOs) and polysaccharide-accumulating bacteria (GAOs). This carbon source is primarily used for phosphorus absorption and release, while simultaneously removing organic matter and reducing carbon source waste during the aerobic phase. Subsequently, the combined vertical flow... The floating pool provides the primary aerobic environment, allowing ammonia nitrogen to be converted into nitrate nitrogen or nitrite nitrogen through nitrification (or short-cut nitrification), and PHAs to be converted into glycogen (Gly). Simultaneously, PAOs undergo aerobic superphosphate uptake. Finally, the primary anoxic environment at the bottom and lower middle layers of the composite vertical flow floating pool, and in the middle to end areas of the vegetated horizontal subsurface flow constructed wetland, promotes microbial utilization of the internal carbon source stored in the aerobic section to complete denitrification (and short-cut denitrification) and anaerobic ammonia oxidation for nitrogen removal and denitrification for phosphorus removal. Based on this, the present invention uses segmented water intake from the inlet pipe of the unvegetated horizontal subsurface flow constructed wetland A and the branch inlet pipe of the floating pool B. The purpose of this secondary water intake for the composite vertical flow constructed wetland is to provide additional substrate (NH4+) for nitrifying bacteria in the aerobic section and denitrifying bacteria in the anoxic section. + NO3 - and NO2 - This invention optimizes the water flow and redox environment at each stage, supplementing the carbon source through secondary influent without requiring additional carbon source replenishment. This solves the carbon source shortage problem, improves nitrogen and phosphorus removal efficiency, and is suitable for treating wastewater with low carbon-to-nitrogen ratios. The system utilizes the synergistic effect of plant roots and microorganisms, reducing reliance on aeration equipment, thereby lowering energy consumption and operating costs, while enhancing system stability and sustainability. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the composite constructed wetland system based on dissolved oxygen regulation provided by the present invention. From top to bottom, these are a front view, an upper top view, and a lower top view. A represents a horizontal subsurface flow constructed wetland without vegetation; B represents a downstream pool in a composite vertical flow constructed wetland with vegetation; C represents an upstream pool in a composite vertical flow constructed wetland with vegetation; D represents a horizontal subsurface flow constructed wetland with vegetation; 1-inlet pipe of the horizontal subsurface flow constructed wetland without vegetation; 2-water distribution inlet pipe of the downstream pool; 3-first upper layer... 4-First lower water pipe, 5-Second upper water pipe, 6-Second lower water pipe, 7-Collection pipe of horizontal subsurface flow artificial wetland A without vegetation, 8-Distribution pipe, 9-Outlet pipe, 10-Water tank, 11-Water pump, 12-First valve, 13-Second valve, 14-Third valve, 15-Fourth valve, 16-Inlet flow meter, 17-Distribution inlet flow meter, 18-Detection outlet pipe, 19-First detection valve, 20-Second detection valve. Detailed Implementation

[0029] like Figure 1 As shown, the present invention provides a composite constructed wetland system based on dissolved oxygen regulation, comprising: a horizontal subsurface flow constructed wetland A without vegetation, a composite vertical flow constructed wetland with vegetation, and a horizontal subsurface flow constructed wetland D with vegetation connected in series.

[0030] The constructed wetland with vegetation and vertical flow includes a downflow pool B and an upflow pool C connected in series.

[0031] The unvegetated horizontal subsurface flow constructed wetland A is equipped with an inlet pipe 1;

[0032] A water inlet pipe 2 is installed at the upper end of the downstream pool B.

[0033] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0034] In one implementation, the length ratio of the unvegetated horizontal subsurface flow constructed wetland A, the vegetated composite vertical flow constructed wetland, and the vegetated horizontal subsurface flow constructed wetland D is 2:3~4:2~3, with a specific ratio of 2:3:3 in this embodiment; the dimensions of the unvegetated horizontal subsurface flow constructed wetland A are 3m×2m×1.1m; the dimensions of the vegetated composite vertical flow constructed wetland are 4.5m×2m×1.1m; the dimensions of the vegetated horizontal subsurface flow constructed wetland D are 4.5m×2m×1.1m; and the length ratio of the downstream pool B to the upstream pool C is 1~2:1, with a specific ratio of 1:1 in this embodiment.

[0035] By limiting the length ratio of unvegetated horizontal subsurface flow constructed wetland A, vegetated composite vertical flow constructed wetland, and vegetated horizontal subsurface flow constructed wetland D to the above range, this invention can more rationally allocate the proportions of anaerobic, aerobic, and anoxic environments, ensuring sufficient time for nitrification and denitrification reactions, thereby improving nitrogen removal efficiency.

[0036] In one implementation, a first valve 12 and an inlet flow meter 16 are installed on the inlet pipe of the vegetation-free horizontal subsurface flow constructed wetland A; a second valve 13 and a flow meter 17 are installed on the water distribution inlet pipe of the downstream pool B.

[0037] As an implementation manner, a first upper water pipe 3 and a first lower water pipe 4 are arranged in the downstream pool B, and a second upper water pipe 5 and a second lower water pipe 6 are arranged in the upstream pool C; the first upper water pipe 3, the first lower water pipe 4, the second upper water pipe 5 and the second lower water pipe 6 are all "rich" - shaped pipes; the first upper water pipe 3 and the second lower water pipe 6 are water - distributing "rich" - shaped pipes; the first lower water pipe 4 and the second upper water pipe 5 are water - collecting "rich" - shaped pipes; a collecting pipe 7 is arranged in the vegetation - free horizontal subsurface flow constructed wetland A; a water - distributing pipe 8 and a water outlet pipe 9 are arranged in the vegetation - covered horizontal subsurface flow constructed wetland D.

[0038] As an implementation manner, the "rich" - shaped pipes, the collecting pipe 7 in the vegetation - free horizontal subsurface flow constructed wetland A and the water - distributing pipe 8 in the vegetation - covered horizontal subsurface flow constructed wetland D are all polyvinyl chloride (PVC) pipes; the nominal outer diameter of the polyvinyl chloride (PVC) pipe is 32 mm; the water outlet pipe 9 in the vegetation - covered horizontal subsurface flow constructed wetland D, the water inlet pipe 1 of the vegetation - free horizontal subsurface flow constructed wetland A and the water - dividing inlet pipe 2 of the downstream pool B are all flexible hoses.

[0039] As an implementation manner, the composite constructed wetland system based on dissolved oxygen regulation further includes: a water pool 10 and a water pump 11 placed in the water pool; the water pump 11 is a reflux pump; the water pool 10 is connected to the vegetation - free horizontal subsurface flow constructed wetland A through the water inlet pipe 1 of the vegetation - free horizontal subsurface flow constructed wetland A, and the water pool 10 is also connected to the first upper water pipe 3 of the downstream pool B through the water - dividing inlet pipe 2 of the downstream pool B.

[0040] As an implementation manner, the collecting pipe 7 in the vegetation - free horizontal subsurface flow constructed wetland A is connected to the first upper water pipe 3 of the downstream pool B; the lower water pipe 3 of the downstream pool B is connected to the first lower water pipe 4 of the upstream pool C; the second upper water pipe 5 of the upstream pool C is connected to the water - distributing pipe 8 of the vegetation - covered horizontal subsurface flow constructed wetland D.

[0041] As an implementation manner, a third valve 14 is arranged in front of the upper water pipe of the downstream pool B; a fourth valve 15 is arranged in front of the water inlet pipe of the vegetation - covered horizontal subsurface flow constructed wetland D; a detection water outlet pipe 18 is arranged at the end of the vegetation - free horizontal subsurface flow constructed wetland A and the upstream pool C, a first detection valve 19 is arranged at the end of the detection water outlet pipe 18 near the vegetation - free horizontal subsurface flow constructed wetland A, and a second detection valve 20 is arranged at the end of the detection water outlet pipe 18 near the upstream pool C, which is convenient for sampling.

[0042] As an implementation manner, the first valve 12, the second valve 13, the third valve 14, the fourth valve 15, the first detection valve 19 and the second detection valve are ball valves.

[0043] In the present invention, a part of the water in the pool directly enters the vegetation-free horizontal subsurface flow constructed wetland A through the water inlet pipe, and then flows out and enters the upper "丰"-shaped pipeline of the downstream pool B. Another part of the water in the pool bypasses the vegetation-free horizontal subsurface flow constructed wetland A and enters the upper "丰"-shaped pipeline of the downstream pool B through the water distribution pipe. The water in the upper "丰"-shaped pipeline of the downstream pool B vertically flows to the bottom "丰"-shaped pipeline and enters the bottom "丰"-shaped pipeline of the upstream pool C connected thereto. As the water level rises, it enters the upper "丰"-shaped pipeline of the upstream pool C. When the liquid level passes the holes of the "丰"-shaped pipeline, it will be collected and enter the last vegetated horizontal subsurface flow constructed wetland D, and finally flows out from the lower end of the horizontal flow.

[0044] In the present invention, water is fed in segments from the water inlet pipe of the vegetation-free horizontal subsurface flow constructed wetland A and the water distribution inlet pipe of the downstream pool B. The purpose of the secondary water inlet for the composite vertical flow constructed wetland is to provide additional substrates for nitrifying bacteria in the aerobic section and denitrifying bacteria in the anoxic section, so as to avoid excessive consumption of the front-end substrates and limit the full progress of anaerobic ammonium oxidation in the last section. The specific mechanism of the secondary water inlet is as follows: ① Nitrifying bacteria in the aerobic section are supplemented to provide NH4-N to ensure its transformation into NO3-N and NO2-N (NH4 + -N → NO2 - -N → NO3 - -N; NH4 + -N → NO2 - -N); and then ② provide substrates for the reaction of anaerobic ammonium oxidizing bacteria at the end (NO3 - -N → NO2 - -N → N2; NO3 - -N → NO2 - -N); in addition, ③ the secondary water inlet can also provide a small amount of NO2-N and NO3-N as substrates for the above reactions; at the same time, ④ the secondary water inlet provides substrates for denitrifying bacteria at the end. Among them, the NO2-N produced by endogenous short-term denitrification will also be used as a reaction substrate for anaerobic ammonium oxidizing bacteria.

[0045] As an implementation manner, the height of the filler in the vegetation-free horizontal subsurface flow constructed wetland A is 60-100 cm, and in a specific embodiment, it is 80 cm; the height of the filler in the downstream pool B is 70-120 cm and > the height of the filler in the vegetation-free horizontal subsurface flow constructed wetland A, and in a specific embodiment, it is 90 cm; the height of the filler in the upstream pool C is 50-105 cm and < the height of the filler in the downstream pool B, and in a specific embodiment, it is 75 cm; the height of the filler in the vegetated horizontal subsurface flow constructed wetland D is 50-105 cm and = the height of the filler in the upstream pool C, and in a specific embodiment, it is 75 cm.

[0046] The present invention designs the height of the packing material in the downflow pool B to be greater than the height of the packing material in the unvegetated horizontal subsurface flow constructed wetland A, so that the unvegetated horizontal subsurface flow constructed wetland A has a liquid seal, and the height of the packing material in the upflow pool C to be less than the height of the packing material in the downflow pool B, so that a height difference is formed between the downflow pool B and the upflow pool C.

[0047] The vegetation-free horizontal subsurface flow constructed wetland A of the present invention is a vegetation-free oxygen-secreting horizontal subsurface flow wetland that can provide a relatively stable anaerobic environment, allowing organic matter to be stored by polyphosphate-accumulating bacteria (PAOs) and polysaccharide-accumulating bacteria (GAOs) as an internal carbon source in the form of polyhydroxyalkanoates (PHAs), while simultaneously removing organic matter and reducing the waste of carbon sources in the aerobic stage.

[0048] Oxygen content control primarily depends on the wetland type. In wetlands with combined vertical flow, the packing material can naturally reoxygenate through the height difference with the packing material in the upstream pool, achieving an aerobic state in the upper and middle sections of the downstream pool to the entire downstream pool. However, in the subsequent upstream pool, as the flow velocity decreases and dissolved oxygen is consumed, it gradually returns to a mixed state of (aerobic / ) anoxic and anaerobic. That is, the downstream pool is in an aerobic + partially anoxic state, while the upstream pool is in a mixed state.

[0049] In a vegetated, vertically flowing constructed wetland, the downstream pool provides the primary aerobic environment, allowing ammonia nitrogen to be converted into nitrate nitrogen or nitrite nitrogen through nitrification (or short-cut nitrification), and PHAs to be converted into glycogen (Gly). At the same time, PAOs aerobically absorb excess phosphorus. Finally, the primary anoxic environment in the upstream section of the vertically flowing constructed wetland and the horizontally flowing constructed wetland D with vegetation promotes the use of internal carbon sources stored in the aerobic section to complete denitrification (and short-cut denitrification), anaerobic ammonia oxidation for nitrogen removal, and denitrification for phosphorus removal.

[0050] In one embodiment, the filler material of the vegetation-free horizontal subsurface flow constructed wetland A includes a coarse gravel layer, a medium gravel layer, and a zeolite layer arranged sequentially from bottom to top; the thickness of the coarse gravel layer in the vegetation-free horizontal subsurface flow constructed wetland A is 10~30cm, specifically 15cm in this embodiment; the thickness of the medium gravel layer is 30~80cm, specifically 35cm in this embodiment; and the thickness of the zeolite layer is 10~30cm, specifically 30cm in this embodiment.

[0051] In one embodiment, the packing material of the downstream pool B includes a coarse gravel layer, a medium gravel layer, a zeolite layer, and a loam layer arranged sequentially from bottom to top; the thickness of the coarse gravel layer in the downstream pool B is 10~30cm, specifically 15cm in this embodiment; the thickness of the medium gravel layer is 30~80cm, specifically 35cm in this embodiment; the thickness of the zeolite layer is 10~30cm, specifically 20cm in this embodiment; and the thickness of the loam layer is 10~20cm, specifically 20cm in this embodiment.

[0052] In one embodiment, the packing material of the ascending pool C includes, from bottom to top, a coarse gravel layer, a medium gravel layer, a zeolite layer, and a loam layer; the thickness of the coarse gravel layer in the ascending pool C is 10~30cm, specifically 15cm in this embodiment; the thickness of the medium gravel layer is 20~65cm, specifically 20cm in this embodiment; the thickness of the zeolite layer is 10~30cm, specifically 20cm in this embodiment; and the thickness of the loam layer is 10~30cm, specifically 20cm in this embodiment.

[0053] In one embodiment, the filler material of the vegetated horizontal subsurface flow constructed wetland D includes, from bottom to top, a coarse gravel layer, a medium gravel layer, a zeolite layer, and a loam layer; the thickness of the coarse gravel layer in the vegetated horizontal subsurface flow constructed wetland D is 10~30cm, specifically 15cm in this embodiment; the thickness of the medium gravel layer is 20~65cm, specifically 20cm in this embodiment; the thickness of the zeolite layer is 10~30cm, specifically 20cm in this embodiment; and the thickness of the loam layer is 10~30cm, specifically 20cm in this embodiment.

[0054] In this invention, the type and thickness of the packing material in each layer affect pollution removal mainly because porosity affects flow rate, plant growth, microbial colonization, and dissolved oxygen (DO). The height difference of the packing material in each section of the constructed wetland is the most important factor. The non-vegetated horizontal subsurface flow constructed wetland A (80cm) is lower than the downstream pool B (90cm), which allows the non-vegetated horizontal subsurface flow constructed wetland A to form a 10cm liquid seal, reducing contact with air and thus lowering DO. The height difference between the downstream pool B (90cm) and the upstream pool C (75cm) satisfies the conditions for natural reoxygenation. Finally, the vegetated horizontal subsurface flow constructed wetland D (75cm) does not need to form a height difference with the previous section.

[0055] In one embodiment, the coarse gravel layer has a particle size of 40-60 mm, specifically 45-55 mm in this embodiment; the medium gravel layer has a particle size of 20-30 mm, specifically 20-25 mm in this embodiment; and the zeolite layer has a particle size of 0.5-10 mm, specifically 10 mm in this embodiment. This invention does not specifically limit the composition of the loam in the loam layer; any loam well-known in the art can be used. In a specific embodiment of this invention, the loam in the loam layer consists of 40 wt% sand, 40 wt% silt, and 20 wt% clay.

[0056] The soil used in this invention has good air permeability and drainage, making it neither easy to accumulate water nor easy to dry out. Furthermore, the organic matter and clay components can adsorb nitrogen and phosphorus pollutants in the water, and can also provide a rich growth environment for microorganisms and plants, promoting the removal of pollutants.

[0057] To reduce the possibility of clogging, the bottom layer of the filler used in this invention is coarse gravel, and the size gradually decreases from bottom to top. This also provides support for the plants and is beneficial to their growth.

[0058] Among the fillers used in this invention, gravel is the cheapest, so it was used in the largest proportion to reduce costs. Zeolite is the most expensive and has the most significant adsorption capacity for nitrogen and phosphorus, but its pollutant removal mechanism is ion exchange, and its ion exchange capacity is limited. Excessive filling may also require periodic replacement or regeneration. Therefore, this invention uses as little zeolite as possible.

[0059] As one implementation method, the plants in the constructed wetland with vegetation and the constructed wetland with vegetation and horizontal subsurface flow (D) are emergent wetland plants; the emergent wetland plants include reeds (… Phragmites australis ),cat-tail( Sparganium erectum ), Alisma ( Alisma aquatica ), reed vegetable ( Aquatic eel ) and sedge ( Papyrus One or more of the following, specifically reeds in this embodiment. The main function of plants is to increase oxygen secretion (DO) through root system secretion and to provide a more suitable environment for microbial colonization.

[0060] In one implementation, the plant density in both the vegetated vertical flow constructed wetland and the vegetated horizontal subsurface flow constructed wetland D is 45-50 plants / m². 2 In the specific embodiment, it is 48 plants / m². 2 .

[0061] Reeds have well-developed root systems and strong oxygen secretion capabilities, which can promote the activity of microorganisms in the water and thus accelerate the degradation of organic matter. Through intermittent water intake, plants and microorganisms jointly create an environment in which aerobic and hypoxic conditions coexist within the system, giving full play to their synergistic effects.

[0062] High-density planting, with its greater total root volume and surface area, facilitates the absorption of dissolved nitrogen and adsorption of phosphorus in water; however, it can also impede water flow, potentially hindering pollutant removal. Therefore, this invention adheres to the principle of planting neither too dense nor too sparse. The reeds used in this invention have deep taproots and lateral roots that extend radially outwards, forming a broad root network without excessively dense interroot pores. The planting density used in this invention meets these conditions. For other wetland plants with finer root systems, a lower planting density may be necessary to avoid obstructing water flow.

[0063] Furthermore, another advantage of the constructed wetland system provided by this invention, which combines "non-vegetated horizontal subsurface flow + vegetated composite vertical flow + vegetated horizontal subsurface flow," is its ability to reduce emissions of the important greenhouse gas nitrous oxide through short-cut denitrification. This is because the short-cut denitrification occurring in the anaerobic section bypasses the traditional denitrification process of "NO → N2O (nitrous oxide) → N2," instead producing NO3... - Converted to NO2 - It was then used directly as a substrate for anaerobic ammonium oxidation.

[0064] The present invention also provides an operation method for a composite constructed wetland system based on dissolved oxygen regulation. Water is introduced into the composite constructed wetland system described above in a segmented two-stage water inlet manner. The first stage of water inlet is in the water inlet pipe 1 of the unvegetated horizontal subsurface flow constructed wetland A, and the second stage of water inlet is in the water distribution inlet pipe 2 of the downstream pool B of the vegetated composite vertical flow constructed wetland.

[0065] The nitrogen-to-phosphorus ratio of the influent to the composite constructed wetland system based on dissolved oxygen regulation is 10-25:1.

[0066] In one implementation, both the first and second influent stages are rural domestic sewage; the ammonia nitrogen concentration of the rural domestic sewage is 10~40 mg / L, specifically 20~30 mg / L in this embodiment; the nitrate nitrogen concentration is 1~10 mg / L, specifically 5~8 mg / L in this embodiment; the nitrite concentration is 0~1 mg / L, specifically 0.1~0.5 mg / L in this embodiment; the phosphate concentration is 1~4 mg / L, specifically 1~2 mg / L in this embodiment; the COD concentration is 100~300 mg / L, specifically 130~200 mg / L in this embodiment; the pH value is 6~8, specifically 7 in this embodiment; and the nitrogen-phosphorus ratio is 10~25:1, specifically 15~23:1 in this embodiment.

[0067] In one implementation method, the flow rate of the first inlet water is 3~5m³ / h. 3 / h, in a specific embodiment it is 3m 3 / h; the flow rate of the second stage inlet is 1.5~2.5m³ / h. 3 / h, in a specific embodiment it is 2m 3 / h; the time for the first and second water intake stages is 8~24h independently, with 12h in the specific embodiment; the hydraulic residence time is 8~24h independently, with 12h in the specific embodiment.

[0068] This invention divides the influent into two sections by front-end diversion. The first section flows into the frontmost unvegetated horizontal subsurface flow constructed wetland A, while the other section bypasses unvegetated horizontal subsurface flow constructed wetland A and directly enters the downstream pool of the vegetated composite vertical flow constructed wetland. The purpose of the secondary influent for the composite vertical flow is to provide additional substrate for nitrifying bacteria in the aerobic section and denitrifying bacteria in the anoxic section, so as to avoid excessive consumption of substrate at the front end, which would limit the full progress of anaerobic ammonia oxidation at the end.

[0069] This invention limits the flow rates of the first and second influent stages within the aforementioned range to ensure that dissolved oxygen (DO) reaches ideal values ​​in each stage. The influence of flow rate is reflected in: 1. Water flow velocity affects DO; the faster the flow velocity, the higher the DO, and the easier it is for the organism to aerobic; 2. The ratio of the two influent stages is such that the second influent stage (i.e., the wastewater directly entering the composite vertical flow) is less than the first influent stage (i.e., the wastewater entering the non-vegetated horizontal subsurface flow constructed wetland A from the very beginning). This avoids excessive secondary entry of pollutants, which would reduce removal efficiency, because the purpose of the secondary influent is to provide NH4 for the reaction in the anoxic stage. + NO3 - and NO2 - Substrate.

[0070] In one implementation, the dissolved oxygen (DO) in the unvegetated horizontal subsurface flow constructed wetland A is ≤0.2 mg / L, specifically 0.1~0.2 mg / L in this embodiment; the dissolved oxygen (DO) in the downstream pool B is 0.5~14 mg / L, specifically 0.8~6.8 mg / L in this embodiment; the dissolved oxygen (DO) in the upstream pool C is 0.2~6 mg / L, specifically 0.3~3.6 mg / L in this embodiment; and the dissolved oxygen (DO) in the vegetated horizontal subsurface flow constructed wetland D is 0.2~2 mg / L, specifically 0.9~1.9 mg / L in this embodiment.

[0071] The dissolved oxygen range mentioned above refers to the dissolved oxygen value that can be monitored in any section of the constructed wetland. Small fluctuations in the influent, effluent, or atmospheric contact area that exceed the range are considered to be within a reasonable range and acceptable, as long as the conditions are generally met: anaerobic in pond A, aerobic in pond B, anoxic to aerobic mixed state in pond C, and anoxic in pond D.

[0072] The artificial wetland combination and water inlet method of the present invention can regulate the redox conditions in the wetland, provide better oxygen conditions for functional microorganisms, facilitate the survival and reproduction of the corresponding functional microorganisms, drive the benign coupling and competition of key functional microorganisms involved in the nitrogen and phosphorus cycle, and thus achieve effective removal of nitrogen and phosphorus pollutants.

[0073] This invention addresses the challenges of low nitrogen removal capacity and high energy consumption and cost of wastewater treatment processes in traditional constructed wetlands by constructing a composite constructed wetland system consisting of "non-vegetated horizontal subsurface flow + vegetated composite vertical flow + vegetated horizontal subsurface flow". The composite constructed wetland system provided by this invention has the advantages of low influent carbon-to-nitrogen ratio requirements, low operating costs, and no secondary pollution in the effluent, thus promoting the reduction of nitrous oxide emissions.

[0074] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0075] Example 1

[0076] like Figure 1 As shown, the composite constructed wetland system based on dissolved oxygen regulation consists of a horizontal subsurface flow constructed wetland A without vegetation, a vertical flow constructed wetland with vegetation (composed of a downflow pool B and an upflow pool C connected in series), and a horizontal subsurface flow constructed wetland D with vegetation connected in series. The width and depth of each pool are 2m and 1.1m, respectively, and the lengths are 3m, 4.5m, and 4.5m, respectively. The length ratio of pools B and C is 1:1. The filling materials of each pool from bottom to top are as follows: Pool A contains a 15cm thick coarse gravel layer, a 35cm thick medium gravel layer, and a 30cm thick zeolite layer; Pool B contains a 15cm thick coarse gravel layer and a 35cm thick medium gravel layer. Pond B consists of a 15cm thick coarse gravel layer, a 20cm thick medium gravel layer, a 20cm thick zeolite layer, and a 20cm thick loam layer; Pond C consists of a 15cm thick coarse gravel layer, a 20cm thick medium gravel layer, a 20cm thick zeolite layer, and a 20cm thick loam layer; Pond D consists of a 15cm thick coarse gravel layer, a 20cm thick medium gravel layer, a 20cm thick zeolite layer, and a 20cm thick loam layer. The coarse gravel has a particle size of 40-60mm, the medium gravel has a particle size of 20-30mm, the zeolite has a particle size of 10mm, and the loam consists of 40wt% sand, 40wt% silt, and 20wt% clay. The reed planting density in ponds B, C, and D is 48 plants / m². 2 ;

[0077] The inlet pipe of the unvegetated horizontal subsurface flow constructed wetland A is equipped with a first valve 12 (ball valve) and an inlet pipe flow meter 16; the inlet pipe of the downstream pool B is equipped with a second valve 13 (ball valve) and an inlet pipe flow meter 17.

[0078] The downstream pool B is equipped with a first upper water pipe 3 and a first lower water pipe 4, and the upstream pool C is equipped with a second upper water pipe 5 and a second lower water pipe 6; the first upper water pipe 3, the first lower water pipe 4, the second upper water pipe 5, and the second lower water pipe 6 are all "abundant" type pipes, the first upper water pipe 3 and the second lower water pipe 6 are "abundant" type water distribution pipes, and the first lower water pipe 4 and the second upper water pipe 5 are "abundant" type water collection pipes; the non-vegetated horizontal subsurface flow constructed wetland A is equipped with a water collection pipe 7; the... A water distribution pipe 8 and an outlet pipe 9 are installed in the vegetated horizontal subsurface flow constructed wetland D; the “Feng”-shaped pipe, the water collection pipe 7 in the non-vegetated horizontal subsurface flow constructed wetland A, and the water distribution pipe 8 in the vegetated horizontal subsurface flow constructed wetland D are all polyvinyl chloride (PVC) pipes; the nominal outer diameter of the polyvinyl chloride (PVC) pipe is 32mm; the outlet pipe 9 in the vegetated horizontal subsurface flow constructed wetland D, the inlet pipe 1 of the non-vegetated horizontal subsurface flow constructed wetland A, and the water distribution inlet pipe 2 of the downstream pool B are all flexible hoses.

[0079] The composite constructed wetland system based on dissolved oxygen regulation further includes: a water tank 10 and a water pump placed in the water tank; the water pump is a return pump 11; the water tank 10 is connected to the unvegetated horizontal subsurface flow constructed wetland A through the water inlet pipe 1 of the unvegetated horizontal subsurface flow constructed wetland A, and the water tank 10 is also connected to the first upper water pipe 3 of the downstream pool B through the water distribution inlet pipe 2 of the downstream pool B;

[0080] The water collection pipe 7 in the unvegetated horizontal subsurface flow constructed wetland A is connected to the first upper water pipe 3 of the downstream pool B; the lower water pipe 3 of the downstream pool B is connected to the first lower water pipe 4 of the upstream pool C; and the second upper water pipe 5 of the upstream pool C is connected to the water distribution pipe 8 of the vegetated horizontal subsurface flow constructed wetland D.

[0081] A third valve 14 (ball valve) is installed before the upper water pipe of the downstream pool B; a fourth valve 15 (ball valve) is installed before the inlet pipe of the vegetated horizontal subsurface flow constructed wetland D; a detection outlet pipe 18 is installed at the tail end of the non-vegetated horizontal subsurface flow constructed wetland A and the upstream pool C, a first detection valve 19 (ball valve) is installed near the end of the non-vegetated horizontal subsurface flow constructed wetland A, and a second detection valve 20 (ball valve) is installed near the end of the detection outlet pipe 18 near the upstream pool C, for easy sampling;

[0082] The influent was simulated rural domestic sewage: COD 130 mg / L, NH4+ + -N 25mg / L, NO3 - -N 6mg / L, NO2 - -N 0.2 mg / L, PO4 3--P 1.4mg / L, pH=7; the water inlet method is a segmented two-stage inlet, with the first stage of inlet water entering the inlet pipe 1 of the unvegetated horizontal subsurface flow constructed wetland A, and the second stage of inlet water entering the branch inlet pipe 2 of the downstream pool B of the vegetated composite vertical flow constructed wetland; the effluent from the unvegetated horizontal subsurface flow constructed wetland A is re-inleted into the downstream pool B; the flow rate of the first stage inlet water is 3m³ / L. 3 / h; the flow rate of the second stage inlet is 2m³ / h. 3 / h; the influent time for the first and second stages is 12 hours, and the hydraulic retention time is 12 hours, achieving one complete wastewater purification cycle per day. The DO concentrations in tanks A, B, C, and D are 0.1~0.2 mg / L, 0.8~6.8 mg / L, 0.3~3.6 mg / L, and 0.9~1.9 mg / L, respectively. Effluent samples are analyzed for COD and NH4+ using a fully automated chemical analyzer within 24 hours. + -N, NO3 - -N, NO2 - -N and PO4 3- -P, the pH value of the water was measured using a portable pH meter, and greenhouse gases were measured using the static chamber method.

[0083] After three months of operation, the overall COD removal rate of the constructed wetland system was 92.31%, and the NH4 removal rate was [not specified]. + -N removal rate was 98.62%, NO3 removal rate was 98.62%. - -N removal rate was 66.46%, NO2 - -N removal rate was 73.94%, PO4 3- -P removal rate was 42.21%, effluent pH was 6.9–7.4, and the seven-day cumulative emission flux of greenhouse gas N2O was 3.47 mg·m³ for the downstream pool B. -2 ·h -1 Ascending pool C 14.49 mg·m -2 ·h -1 Constructed wetlands with vegetated horizontal subsurface flow (D 4.70 mg·m³) -2 ·h -1 .

[0084] Comparative Example 1

[0085] The difference from Example 1 is that the unvegetated horizontal subsurface flow constructed wetland A is removed, while the rest is the same as in Example 1.

[0086] After three months of operation, the constructed wetland system has reduced overall NH4 levels. + -N removal rate was 41.73%, NO3 - -N removal rate was 54.90%, NO2 - -N removal rate was -6.85%, PO4 3--P removal rate was -106.5%, and effluent pH was 6.9~7.4.

[0087] Comparative Example 2

[0088] The difference from Example 1 is that the constructed wetland D with vegetation horizontal subsurface flow is removed, while the rest is the same as in Example 1.

[0089] After three months of operation, the constructed wetland system has reduced overall NH4 levels. + -N removal rate was 93.30%, NO3 - -N removal rate was 1.81%, NO2 - -N removal rate was 61.70%, PO4 3- -P removal rate was 56.33%, and effluent pH was 6.9~7.4.

[0090] Comparative Example 3

[0091] The difference from Example 1 is that the unvegetated horizontal subsurface flow constructed wetland A and the vegetated horizontal subsurface flow constructed wetland D are removed, while the rest is the same as in Example 1.

[0092] After three months of operation, the constructed wetland system has reduced overall NH4 levels. + -N removal rate was -15.69%, NO3 - -N removal rate was 39.71%, NO2 - -N removal rate was -57.01%, PO4 3- -P removal rate was -56.05%, and effluent pH was 6.9~7.4.

[0093] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A composite constructed wetland system based on dissolved oxygen regulation, characterized in that, Comprising: A vegetation-free horizontal subsurface flow constructed wetland (A), a vegetated composite vertical flow constructed wetland, and a vegetated horizontal subsurface flow constructed wetland (D) connected in series; The vegetated composite vertical flow constructed wetland comprises a downward flow pool (B) and an upward flow pool (C) connected in series; The vegetation-free horizontal subsurface flow constructed wetland (A) is provided with an influent pipe (1); The upper end of the downward flow pool (B) is provided with a water distribution influent pipe (2); The height of the filler in the vegetation-free horizontal subsurface flow constructed wetland (A) is 60 - 100 cm; the height of the filler in the downward flow pool (B) is 70 - 120 cm and > the height of the filler in the vegetation-free horizontal subsurface flow constructed wetland (A); the height of the filler in the upward flow pool (C) is 50 - 105 cm and < the height of the filler in the downward flow pool (B); the height of the filler in the vegetated horizontal subsurface flow constructed wetland (D) is 50 - 105 cm and = the height of the filler in the upward flow pool (C).

2. The composite constructed wetland system according to claim 1, characterized in that, The length ratio of the vegetation-free horizontal subsurface flow constructed wetland (A), the vegetated composite vertical flow constructed wetland, and the vegetated horizontal subsurface flow constructed wetland (D) is 2:3 - 4:2 - 3.

3. The composite constructed wetland system according to claim 1, characterized in that, The downward flow pool (B) is provided with a first upper layer water pipe (3) and a first lower layer water pipe (4), and the upward flow pool (C) is provided with a second upper layer water pipe (5) and a second lower layer water pipe (6); the first upper layer water pipe (3), the first lower layer water pipe (4), the second upper layer water pipe (5), and the second lower layer water pipe (6) are all "Feng"-type pipes; the vegetation-free horizontal subsurface flow constructed wetland (A) is provided with a collecting pipe (7); the vegetated horizontal subsurface flow constructed wetland (D) is provided with a water distribution pipe (8) and an effluent pipe (9); The collecting pipe (7) in the vegetation-free horizontal subsurface flow constructed wetland (A) is connected to the upper layer water pipe (3) of the downward flow pool (B); the first lower layer water pipe (4) of the downward flow pool (B) is connected to the second lower layer water pipe (6) of the upward flow pool (C); the second upper layer water pipe (5) of the upward flow pool (C) is connected to the water distribution pipe (8) of the vegetated horizontal subsurface flow constructed wetland (D); The water distribution influent pipe (2) of the downward flow pool (B) is communicated with the first upper layer water pipe (3) of the downward flow pool (B).

4. The composite constructed wetland system according to claim 1, characterized in that, The filler of the vegetation-free horizontal subsurface flow constructed wetland (A) comprises a coarse gravel layer, a medium gravel layer, and a zeolite layer arranged in sequence from bottom to top; the thickness of the coarse gravel layer in the vegetation-free horizontal subsurface flow constructed wetland (A) is 10 - 30 cm, the thickness of the medium gravel layer is 30 - 80 cm, and the thickness of the zeolite layer is 10 - 30 cm; The filler of the downward flow pool (B) comprises a coarse gravel layer, a medium gravel layer, a zeolite layer, and a soil layer arranged in sequence from bottom to top; the thickness of the coarse gravel layer in the downward flow pool (B) is 10 - 30 cm, the thickness of the medium gravel layer is 30 - 80 cm, the thickness of the zeolite layer is 10 - 30 cm, and the thickness of the soil layer is 10 - 20 cm; The filler material of the ascending pool (C) includes a coarse gravel layer, a medium gravel layer, a zeolite layer and a loam layer arranged from bottom to top; the thickness of the coarse gravel layer in the ascending pool (C) is 10~30cm, the thickness of the medium gravel layer is 20~65cm, the thickness of the zeolite layer is 10~30cm, and the thickness of the loam layer is 10~30cm. The fill material of the vegetated horizontal subsurface flow constructed wetland (D) includes a coarse gravel layer, a medium gravel layer, a zeolite layer and a loam layer arranged sequentially from bottom to top; the thickness of the coarse gravel layer in the vegetated horizontal subsurface flow constructed wetland (D) is 10~30cm, the thickness of the medium gravel layer is 20~65cm, the thickness of the zeolite layer is 10~30cm, and the thickness of the loam layer is 10~30cm. The coarse gravel layer has a coarse gravel particle size of 40-60 mm; the medium gravel layer has a medium gravel particle size of 20-30 mm; and the zeolite layer has a zeolite particle size of 0.5-10 mm.

5. The composite constructed wetland system according to claim 1, characterized in that, The plants in the constructed wetland with vegetation and the constructed wetland with vegetation and horizontal subsurface flow (D) are emergent wetland plants; the emergent wetland plants include one or more of reeds, cattails, water plantains, reed shoots and sedges.

6. The composite constructed wetland system according to claim 1 or 5, characterized in that, The plant density in the vegetated vertical flow constructed wetland and the vegetated horizontal subsurface flow constructed wetland (D) is independently 45-50 plants / m². 2 .

7. A method for operating a composite constructed wetland system based on dissolved oxygen regulation, characterized in that, Water is introduced into the composite artificial wetland system according to any one of claims 1 to 6 in a segmented two-stage water inlet manner. The first stage of water inlet is in the water inlet pipe (1) of the unvegetated horizontal subsurface flow artificial wetland (A), and the second stage of water inlet is in the water distribution inlet pipe (2) of the downstream pool (B) of the vegetated composite vertical flow artificial wetland. The nitrogen-to-phosphorus ratio of the influent to the composite constructed wetland system based on dissolved oxygen regulation is 10-25:

1.

8. The operating method according to claim 7, characterized in that, The flow rate of the first stage of water intake is 3~5m³. 3 / h; the flow rate of the second stage inlet is 1.5~2.5m³ / h. 3 / h.

9. The operating method according to claim 7 or 8, characterized in that, The time for the first and second stages of water intake is 8 to 24 hours, and the hydraulic retention time is also 8 to 24 hours.

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