Composite artificial wetland system based on dissolved oxygen regulation and operation method thereof

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to a composite artificial wetland system based on dissolved oxygen regulation and an operation method thereof. According to the constructed'vegetation-free horizontal subsurface flow + vegetation composite vertical flow + vegetation horizontal subsurface flow 'composite constructed wetland system, water can be fed from the water inlet pipe of the vegetation-free horizontal subsurface flow constructed wetland and the water diversion inlet pipe of the downstream pool B in a segmented manner, the water flow and the oxidation-reduction environment of each segment are optimized, additional carbon sources do not need to be supplemented, and the cost is reduced. The problem of carbon source shortage can be solved, the nitrogen and phosphorus removal efficiency is improved, and the method is suitable for treating low-carbon-nitrogen-ratio wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and particularly relates to a composite constructed wetland system based on dissolved oxygen regulation and an operation method thereof. Background Art

[0002] As a sewage treatment technology, constructed wetlands have been widely used in the field of sewage treatment in recent years due to their low construction and operation costs, simple operation, low energy efficiency, and good effluent quality. The working principle of constructed wetlands is based on the ecological system of natural wetlands, using the synergistic effect of plant roots and microbial communities to remove pollutants in water through physical, chemical, and biological degradation. Subsurface flow constructed wetlands (SSFCWs) are one of the most common and widely used types of constructed wetlands. According to the water flow pattern, they can be divided into horizontal subsurface flow (HSSFCWs) and vertical subsurface flow (VSSFCWs). The former is usually in a water-saturated state, and the aerobic zone may occur around the roots and rhizomes, while the latter is often unsaturated and has a larger proportion of the aerobic zone due to the intermittent supply of water.

[0003] Integrated vertical flow constructed wetlands (IVCWs) connect HSSFCWs and VSSFCWs through the height difference of the substrate to achieve natural reoxygenation. Although this configuration can combine the nitrification ability of vertical subsurface flow constructed wetlands with the denitrification of horizontal subsurface flow constructed wetlands, it may be limited by the limited carbon source when treating low carbon-nitrogen ratio wastewater, making it difficult to maintain the full progress of the denitrification reaction and resulting in a decrease in 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 an operation method thereof, which can effectively purify low carbon-nitrogen ratio wastewater without adding additional carbon sources.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a composite constructed wetland system based on dissolved oxygen regulation, comprising: a vegetation-free horizontal subsurface flow constructed wetland A, a vegetated integrated vertical flow constructed wetland, and a vegetated horizontal subsurface flow constructed wetland D connected in series;

[0007] The vegetated integrated vertical flow constructed wetland comprises a downstream tank B and an upstream tank C connected in series;

[0008] The vegetation-free horizontal subsurface flow constructed wetland A is provided with an inlet pipe 1;

[0009] The upper end of the downstream tank B is provided with a water distribution inlet pipe 2.

[0010] Preferably, 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 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 Fengzi 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 distribution 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 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 in sequence from bottom to top; the thickness of the coarse gravel layer in the vegetated horizontal subsurface flow constructed wetland D is 10 - 30 cm, the thickness of the medium gravel layer is 20 - 65 cm, the thickness of the zeolite layer is 10 - 30 cm, and the thickness of the loam layer is 10 - 30 cm;

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

[0020] Preferably, the plants in the vegetated hybrid 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 reed, cattail, alisma, bulrush, and sedge.

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

[0022] The present invention also provides an operation method of a composite constructed wetland system based on dissolved oxygen regulation. Water is fed into the composite constructed wetland system according to the segmented secondary water inlet mode. The first - stage water inlet is in the water inlet pipe 1 of the non - vegetated horizontal subsurface flow constructed wetland A, and the second - stage water inlet is in the water distribution inlet pipe 2 of the downward - flow pool B in the vegetated hybrid vertical flow constructed wetland;

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

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

[0025] Preferably, the time of the first - stage water inlet and the second - stage water inlet is independently 8 - 24 h, and the hydraulic retention time is independently 8 - 24 h.

[0026] The present invention provides a composite constructed wetland system based on dissolved oxygen regulation, including: a non - vegetated horizontal subsurface flow constructed wetland A, a vegetated hybrid vertical flow constructed wetland, and a vegetated horizontal subsurface flow constructed wetland D connected in series; the vegetated hybrid vertical flow constructed wetland includes a downward - flow pool B and an upward - flow pool C connected in series; the non - vegetated horizontal subsurface flow constructed wetland A is provided with a water inlet pipe 1; the upper end of the downward - flow pool B is provided with a water distribution inlet pipe 2.

[0027] The present invention constructs a composite constructed wetland system of "vegetation-free horizontal subsurface flow + vegetation composite vertical flow + vegetation horizontal subsurface flow". The first-stage vegetation-free horizontal subsurface flow for oxygen secretion can provide a relatively stable anaerobic environment, enabling organic matter to be stored as an internal carbon source in the form of polyhydroxyalkanoates (PHAs) by polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs). This part of the carbon source is mainly used for phosphorus absorption and release, while achieving the removal of organic matter and reducing the waste of carbon source in the aerobic stage. Subsequently, the downward flow pool of the composite vertical flow will provide the main aerobic environment, enabling ammonia nitrogen to be converted into nitrate nitrogen or nitrite nitrogen through nitrification (or shortcut nitrification), converting PHAs into glycogen (Gly), and simultaneously PAOs aerobically over-absorbing phosphorus. Finally, the main anoxic environments at the bottom, middle and lower layers of the upward flow pool of the composite vertical flow and in the middle to end regions of the vegetation horizontal subsurface flow constructed wetland can promote microorganisms to utilize the internal carbon source stored in the aerobic stage to complete denitrification (and shortcut denitrification), anaerobic ammonium oxidation for nitrogen removal and denitrifying phosphorus removal. On this basis, the present invention divides the water inlet pipe of the vegetation-free horizontal subsurface flow constructed wetland A and the water distribution inlet pipe of the downward flow pool B for segmented water inlet. The purpose of the secondary water inlet of the composite vertical flow constructed wetland is to provide additional substrates (NH4 + 、NO3 - and NO2 - substrates) for nitrifying bacteria in the aerobic stage and denitrifying bacteria in the anoxic stage, so as to avoid excessive consumption of the front-end substrates and limit the full progress of anaerobic ammonium oxidation in the last stage. The present invention optimizes the water flow and redox environment in each section, supplements the carbon source by means of secondary water inlet, and does not require additional carbon source supplementation, solves the problem of carbon source shortage, improves the nitrogen and phosphorus removal efficiency, and is applicable to the treatment of low-carbon-nitrogen ratio wastewater. This system utilizes the synergistic effect of plant roots and microorganisms, reduces the dependence on oxygenation equipment, thereby reducing energy consumption and operating costs, and simultaneously enhancing the stability and sustainability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 FIG. 1 is a schematic diagram of the composite constructed wetland system based on dissolved oxygen regulation provided by the present invention, which are respectively a front view, a top view of the upper layer and a top view of the lower layer from top to bottom. Among them, A is a vegetation-free horizontal subsurface flow constructed wetland, B is the downward flow pool in the vegetation composite vertical flow constructed wetland, C is the upward flow pool in the vegetation composite vertical flow constructed wetland, D is a vegetation horizontal subsurface flow constructed wetland, 1 is the water inlet pipe of the vegetation-free horizontal subsurface flow constructed wetland, 2 is the water distribution inlet pipe of the downward flow pool, 3 is the first upper layer water pipe, 4 is the first lower layer water pipe, 5 is the second upper layer water pipe, 6 is the second lower layer water pipe, 7 is the collecting pipe of the vegetation-free horizontal subsurface flow constructed wetland A, 8 is the water distribution pipe, 9 is the outlet pipe, 10 is the water pool, 11 is the water pump, 12 is the first valve, 13 is the second valve, 14 is the third valve, 15 is the fourth valve, 16 is the water inlet pipe flowmeter, 17 is the water distribution inlet pipe flowmeter, 18 is the detected outlet pipe, 19 is the first detection valve, and 20 is the second detection valve. Detailed implementation manners

[0029] As shown Figure 1 in the figure, the present invention provides a composite constructed wetland system based on dissolved oxygen regulation, including: 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;

[0030] The vegetated composite vertical flow constructed wetland includes a downstream tank B and an upstream tank C connected in series;

[0031] The vegetation-free horizontal subsurface flow constructed wetland A is provided with an inlet pipe 1;

[0032] The upper end of the downstream tank B is provided with a water distribution inlet pipe 2.

[0033] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used, and commercially available products well-known to those skilled in the art can be used.

[0034] As an implementation manner, 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, specifically 2:3:3 in specific embodiments; the size of the vegetation-free horizontal subsurface flow constructed wetland A is 3m×2m×1.1m; the size of the vegetated composite vertical flow constructed wetland is 4.5m×2m×1.1m; the size of the vegetated horizontal subsurface flow constructed wetland D is 4.5m×2m×1.1m; the length ratio of the downstream tank B and the upstream tank C is 1-2:1, specifically 1:1 in specific embodiments.

[0035] By limiting 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 within the above range, the present invention can more reasonably allocate the proportions of anaerobic, aerobic, and anoxic conditions, ensure sufficient time for nitrification and denitrification reactions, and thus improve the denitrification effect.

[0036] As an implementation manner, a first valve 12 and an inlet pipe flowmeter 16 are arranged on the inlet pipe of the vegetation-free horizontal subsurface flow constructed wetland A; a second valve 13 and a water distribution inlet pipe flowmeter 17 are arranged on the water distribution inlet pipe of the downstream tank 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 Fengzi pipes; the first upper water pipe 3 and the second lower water pipe 6 are water distribution Fengzi pipes; the first lower water pipe 4 and the second upper water pipe 5 are water collection Fengzi pipes; a water collection 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 vegetation horizontal subsurface flow constructed wetland D.

[0038] As an implementation manner, the Fengzi pipes, the water collection pipe 7 in the vegetation-free horizontal subsurface flow constructed wetland A and the water distribution pipe 8 in the vegetation 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 horizontal subsurface flow constructed wetland D, the water inlet pipe 1 of the vegetation-free horizontal subsurface flow constructed wetland A and the water distribution inlet pipe 2 of the downstream pool B are all 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 communicated with 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 communicated with the first upper water pipe 3 of the downstream pool B through the water distribution inlet pipe 2 of the downstream pool B.

[0040] As an implementation manner, the water collection 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 distribution pipe 8 of the vegetation 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 horizontal subsurface flow constructed wetland D; a detection water outlet pipe 18 is arranged at the tail ends 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 20 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 Fengzi pipe of the downward pool B. Another part of the water in the pool bypasses the vegetation-free horizontal subsurface flow constructed wetland A and enters the upper Fengzi pipe of the downward pool B through the water distribution pipe. The water in the upper Fengzi pipe of the downward pool B flows vertically to the bottom Fengzi pipe and enters the bottom Fengzi pipe of the upward pool C connected thereto. As the water level rises, it enters the upper Fengzi pipe of the upward pool C. When the liquid level passes over the hole of the Fengzi pipe, it will be collected and enter the last section of the vegetation 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 downward pool B. The purpose of the secondary water inlet of 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 substrate 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 The nitrifying bacteria in the aerobic section are supplemented with 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 mode, 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 downward 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 upward pool C is 50-105 cm and < the height of the filler in the downward pool B, and in a specific embodiment, it is 75 cm; the height of the filler in the vegetation horizontal subsurface flow constructed wetland D is 50-105 cm and = the height of the filler in the upward pool C, and in a specific embodiment, it is 75 cm.

[0046] In the present invention, the height of the packing in the downstream pond B > the height of the packing in the vegetation-free horizontal subsurface flow constructed wetland A, so that the vegetation-free horizontal subsurface flow constructed wetland A has a liquid seal. The height of the packing in the upstream pond C < the height of the packing in the downstream pond B, so as to form a height difference between the downstream pond B and the upstream pond 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, which can provide a relatively stable anaerobic environment, enabling organic matter to be stored as an internal carbon source in the form of polyhydroxyalkanoates (PHAs) by polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs). At the same time, the removal of organic matter is achieved and the waste of carbon source in the aerobic stage is reduced.

[0048] The control of oxygen content mainly depends on the type of wetland. In the composite vertical flow wetland, the packing can form natural reoxygenation through the height difference with the packing in the upstream pond, reaching an aerobic state in the upper to full section of the downstream pond, and then gradually returning to a mixed state of (aerobic / ) anoxic and anaerobic with the decrease in flow rate and consumption of dissolved oxygen in the subsequent upstream pond. That is, the downstream pond is in an aerobic + partially anoxic state, while the upstream pond is in a mixed state.

[0049] The downstream pond in the vegetated composite vertical flow constructed wetland will provide a mainly aerobic environment, enabling ammonia nitrogen to be converted into nitrate nitrogen or nitrite nitrogen through nitrification (or shortcut nitrification), converting PHAs into glycogen (Gly), and at the same time, PAOs aerobically over-accumulate phosphorus. Finally, the mainly anoxic environment in the upper part of the composite vertical flow upstream section and the vegetated horizontal subsurface flow constructed wetland D can promote microorganisms to utilize the internal carbon source stored in the aerobic section to complete denitrification (and shortcut denitrification), anaerobic ammonia oxidation for nitrogen removal, and denitrifying phosphorus removal.

[0050] As an implementation mode, the packing 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 - 30 cm, specifically 15 cm in a specific embodiment; the thickness of the medium gravel layer is 30 - 80 cm, specifically 35 cm in a specific embodiment; the thickness of the zeolite layer is 10 - 30 cm, specifically 30 cm in a specific embodiment.

[0051] As an implementation mode, the packing of the downstream pond 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 pond B is 10 - 30 cm, specifically 15 cm in a specific embodiment; the thickness of the medium gravel layer is 30 - 80 cm, specifically 35 cm in a specific embodiment; the thickness of the zeolite layer is 10 - 30 cm, specifically 20 cm in a specific embodiment; the thickness of the soil layer is 10 - 20 cm, specifically 20 cm in a specific embodiment.

[0052] As an implementation manner, the fillers of the upper flow pond C include a coarse gravel layer, a medium gravel layer, a zeolite layer and a loam layer arranged in sequence from bottom to top; the thickness of the coarse gravel layer in the upper flow pond C is 10 - 30 cm, specifically 15 cm in a specific embodiment, the thickness of the medium gravel layer is 20 - 65 cm, specifically 20 cm in a specific embodiment, the thickness of the zeolite layer is 10 - 30 cm, specifically 20 cm in a specific embodiment, and the thickness of the loam layer is 10 - 30 cm, specifically 20 cm in a specific embodiment.

[0053] As an implementation manner, the fillers of the vegetated horizontal subsurface flow constructed wetland D include a coarse gravel layer, a medium gravel layer, a zeolite layer and a loam layer arranged in sequence from bottom to top; the thickness of the coarse gravel layer in the vegetated horizontal subsurface flow constructed wetland D is 10 - 30 cm, specifically 15 cm in a specific embodiment, the thickness of the medium gravel layer is 20 - 65 cm, specifically 20 cm in a specific embodiment, the thickness of the zeolite layer is 10 - 30 cm, specifically 20 cm in a specific embodiment, and the thickness of the loam layer is 10 - 30 cm, specifically 20 cm in a specific embodiment.

[0054] In the present invention, the influence of the type and thickness of the fillers set in each layer on pollution removal mainly lies in that the porosity will affect the flow velocity, plant growth, microbial colonization and DO. The height difference of the fillers in each section of the constructed wetland in the present invention is the most important factor. The non-vegetated horizontal subsurface flow constructed wetland A (80 cm) being lower than the down-flow pond B (90 cm) can form a 10-cm liquid seal in the non-vegetated horizontal subsurface flow constructed wetland A to reduce the contact with air and lower DO; while the height difference between the down-flow pond B (90 cm) and the upper flow pond C (75 cm) enables it to meet the conditions for natural reoxygenation. Finally, the vegetated horizontal subsurface flow constructed wetland D (75 cm) does not need to form a height difference with the previous section.

[0055] As an implementation manner, the particle size of the coarse gravels in the coarse gravel layer is 40 - 60 mm, specifically 45 - 55 mm in a specific embodiment; the particle size of the medium gravels in the medium gravel layer is 20 - 30 mm, specifically 20 - 25 mm in a specific embodiment; the particle size of the zeolites in the zeolite layer is 0.5 - 10 mm, specifically 10 mm in a specific embodiment. The present invention has no special limitation on the composition of the loam in the loam layer, and the well-known loam in the art can be used. In a specific embodiment of the present invention, the loam in the loam layer is composed of 40 wt% sand grains, 40 wt% silt and 20 wt% clay particles.

[0056] The loam used in the present invention has good air permeability and drainage property, is neither prone to waterlogging nor drought, and the organic matter and clay components can adsorb nitrogen and phosphorus pollutants in water, and can also provide a rich growth environment for microorganisms and plants to promote the removal of pollutants.

[0057] To reduce the possibility of clogging, the bottom layer of the filler used in the present invention is coarse gravel, and the size gradually decreases from bottom to top, which can also provide support for plants and facilitate the growth of plants.

[0058] Among the fillers used in the present invention, gravel has the lowest price, so the largest proportion of filling is carried out to reduce costs. Zeolite has the highest cost and the most significant adsorption capacity for nitrogen and phosphorus. However, its pollutant removal mechanism is ion exchange, and its ion exchange capacity is limited. Excessive filling may also involve the need for regular replacement or regeneration. Therefore, the present invention uses as little zeolite as possible.

[0059] As an implementation mode, 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 several of Phragmites australis, Sparganium erectum, Alisma plantago-aquatica, Rorippa aquatica, and Cyperus papyrus, and in a specific embodiment, it is Phragmites australis. The main function of the plants is to enhance DO by root oxygen secretion and provide a more suitable environment for the colonization of microorganisms.

[0060] As an implementation mode, the plant density in the vegetated composite vertical flow constructed wetland and the vegetated horizontal subsurface flow constructed wetland D is independently 45 - 50 plants / m 2 , and in a specific embodiment, it is 48 plants / m 2 .

[0061] The roots of Phragmites australis are well-developed and have strong oxygen secretion ability, which can promote the activity of microorganisms in the water body, thereby accelerating the degradation of organic matter. Through the intermittent water inlet mode, plants and microorganisms jointly create an environment with both aerobic and anoxic conditions in the system, giving full play to their synergistic effect.

[0062] High-density plant planting means more total root mass and surface area, which is beneficial to the absorption of dissolved nitrogen and the adsorption of phosphorus in water; however, this will also hinder the water flow velocity and may instead affect pollutant removal. Therefore, the present invention adheres to the planting principle of "not too dense nor too sparse". The Phragmites australis used in the present invention has a main root deeply rooted in the ground and lateral roots spreading radially around, forming a wide root network while the inter-root pores are not too dense. The planting density used in the present invention meets the above conditions. If other wetland plants with finer roots are used, the planting density may need to be reduced to avoid hindering water flow.

[0063] In addition, another advantage of the "vegetation-free horizontal subsurface flow + vegetated composite vertical flow + vegetated horizontal subsurface flow" constructed wetland system provided by the present invention is that it can reduce the emission of nitrous oxide, an important greenhouse gas, through shortcut denitrification. Since the shortcut denitrification occurring in the anaerobic section bypasses the "NO→N2O (nitrous oxide)→N2" process in traditional denitrification, and directly uses NO3 - converted to NO2 - as the reaction substrate for anaerobic ammonium oxidation directly after that.

[0064] The present invention also provides an operation method for a composite constructed wetland system based on dissolved oxygen regulation. Water is fed into the composite constructed wetland system described in the above technical solution in a segmented secondary water inlet mode. The first-stage water inlet is in the water inlet pipe 1 of the vegetation-free horizontal subsurface flow constructed wetland A, and the second-stage water inlet is in the water distribution inlet pipe 2 of the downward-flow pool B in the vegetated composite vertical flow constructed wetland;

[0065] The dissolved oxygen in the vegetation-free horizontal subsurface flow constructed wetland A is ≤0.2 mg / L; the dissolved oxygen in the downward-flow pool B is 0.2 - 0.6 mg / L; the dissolved oxygen in the upward-flow pool C is 0.08 - 0.6 mg / L; the dissolved oxygen in the vegetated horizontal subsurface flow constructed wetland D is 0.2 - 0.5 mg / L;

[0066] The nitrogen-phosphorus ratio of the influent water of the composite constructed wetland system based on dissolved oxygen regulation is 10 - 25:1.

[0067] As an implementation mode, both the first-stage water inlet and the second-stage water inlet are rural domestic sewage; the ammonia nitrogen concentration of the rural domestic sewage is 10 - 40 mg / L, specifically 20 - 30 mg / L in specific embodiments, the nitrate nitrogen concentration is 1 - 10 mg / L, specifically 5 - 8 mg / L in specific embodiments, the nitrite concentration is 0 - 1 mg / L, specifically 0.1 - 0.5 mg / L in specific embodiments, the phosphate concentration is 1 - 4 mg / L, specifically 1 - 2 mg / L in specific embodiments, the COD concentration is 100 - 300 mg / L, specifically 130 - 200 mg / L in specific embodiments, the pH value is 6 - 8, specifically 7 in specific embodiments, and the nitrogen-phosphorus ratio is 10 - 25:1, specifically 15 - 23:1 in specific embodiments.

[0068] As an implementation mode, the flow rate of the first-stage water inlet is 3 - 5 m 3 / h, specifically 3 m 3 / h in specific embodiments; the flow rate of the second-stage water inlet is 1.5 - 2.5 m 3 / h, specifically 2 m 3 / h in specific embodiments; the time of the first-stage water inlet and the second-stage water inlet is independently 8 - 24 h, specifically 12 h in specific embodiments, and the hydraulic retention time is independently 8 - 24 h, specifically 12 h in specific embodiments.

[0069] In the present invention, through front-end shunt, the influent water is divided into two segments. The first segment flows into the vegetation-free horizontal subsurface flow constructed wetland A at the very front end, and the other segment bypasses the vegetation-free horizontal subsurface flow constructed wetland A and directly enters the down-flow pond of the vegetated composite vertical flow constructed wetland. The purpose of the secondary influent to the composite vertical flow 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.

[0070] The present invention limits the flow rates of the first segment influent water and the second segment influent water within the above ranges to make the dissolved oxygen in each segment reach the ideal value. The influence of the flow rate is reflected in: 1. The water flow velocity affects DO. The faster the flow velocity, the greater the DO, and the easier it is for aerobic conditions to occur; 2. The ratio of the two segments of influent water. The second segment influent water (i.e., the sewage directly entering the composite vertical flow) is less than the first segment influent water (i.e., the sewage entering the vegetation-free horizontal subsurface flow constructed wetland A from the very front end), which can avoid excessive pollutants entering the second time and reducing the removal efficiency, because the purpose of the secondary influent is to provide NH4 + , NO3 - and NO2 - substrates.

[0071] As an implementation manner, the dissolved oxygen (DO) in the vegetation-free horizontal subsurface flow constructed wetland A is ≤ 0.2 mg / L, and in a specific embodiment, it is 0.1 - 0.2 mg / L; the dissolved oxygen (DO) in the down-flow pond B is 0.5 - 14 mg / L, and in a specific embodiment, it is 0.8 - 6.8 mg / L; the dissolved oxygen (DO) in the up-flow pond C is 0.2 - 6 mg / L, and in a specific embodiment, it is 0.3 - 3.6 mg / L; the dissolved oxygen (DO) in the vegetated horizontal subsurface flow constructed wetland D is 0.2 - 2 mg / L, and in a specific embodiment, it is 0.9 - 1.9 mg / L.

[0072] The above-mentioned dissolved oxygen range refers to the dissolved oxygen values that can be monitored in any segment of the constructed wetland. Small fluctuations in the influent and effluent or the small part of the air contact surface that exceed the range values are considered within a reasonable range and acceptable, as long as it is ensured that generally, the anaerobic condition in pond A, the aerobic condition in pond B, the anoxic-aerobic mixed state in pond C, and the anoxic condition in pond D are satisfied.

[0073] The constructed wetland combination and the influent water mode 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 corresponding functional microorganisms, drive the positive coupling and competition of key functional microorganisms participating in the nitrogen and phosphorus cycles, and thus effectively remove nitrogen and phosphorus pollutants.

[0074] The present invention constructs a composite constructed wetland system of "vegetation-free horizontal subsurface flow + vegetation composite vertical flow + vegetation horizontal subsurface flow" to improve the problems of low denitrification ability caused by insufficient carbon sources in traditional constructed wetlands, high energy consumption and high cost in the implementation of sewage treatment processes. The composite constructed wetland system provided by the present invention has the advantages of low influent carbon-nitrogen ratio requirement, low operating cost, and no secondary pollution in the effluent, and can promote the emission reduction of the greenhouse gas nitrous oxide.

[0075] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention, but they cannot be understood as limiting the protection scope of the present invention.

[0076] Example 1

[0077] As Figure 1 shown, the composite constructed wetland system based on dissolved oxygen regulation is composed of a vegetation-free horizontal subsurface flow constructed wetland A, a vegetation composite vertical flow constructed wetland (composed of a downstream pond B and an upstream pond C connected in series), and a vegetation horizontal subsurface flow constructed wetland D connected in series. The width and depth of each pond are 2 m and 1.1 m respectively, and the lengths are 3 m, 4.5 m, and 4.5 m in sequence. The length ratio of ponds B and C is 1:1. The fillers in each pond from bottom to top are as follows: in pond A, there is a 15-cm-thick layer of coarse gravel, a 35-cm-thick layer of medium gravel, and a 30-cm-thick layer of zeolite; in pond B, there is a 15-cm-thick layer of coarse gravel, a 35-cm-thick layer of medium gravel, a 20-cm-thick layer of zeolite, and a 20-cm-thick layer of loam; in pond C, there is a 15-cm-thick layer of coarse gravel, a 20-cm-thick layer of medium gravel, a 20-cm-thick layer of zeolite, and a 20-cm-thick layer of loam; in pond D, there is a 15-cm-thick layer of coarse gravel, a 20-cm-thick layer of medium gravel, a 20-cm-thick layer of zeolite, and a 20-cm-thick layer of loam. The particle size of the coarse gravel is 40 - 60 mm, the particle size of the medium gravel is 20 - 30 mm, the particle size of the zeolite is 10 mm, and the loam is composed of 40 wt% sand particles, 40 wt% silt, and 20 wt% clay particles. Among them, the reed planting density in ponds B, C, and D is 48 plants / m 2 ;

[0078] A first valve 12 (ball valve) and an influent pipe flowmeter 16 are provided on the influent pipe of the vegetation-free horizontal subsurface flow constructed wetland A; a second valve 13 (ball valve) and a branch influent pipe flowmeter 17 are provided on the branch influent pipe of the downstream pond B;

[0079] In the downstream pool B, a first upper water pipe 3 and a first lower water pipe 4 are arranged, and in the upstream pool C, a second upper water pipe 5 and a second lower water pipe 6 are arranged; 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 Fengzi pipes, the first upper water pipe 3 and the second lower water pipe 6 are water-distributing Fengzi pipes, and the first lower water pipe 4 and the second upper water pipe 5 are water-collecting Fengzi pipes; a water-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 vegetated horizontal subsurface flow constructed wetland D; the Fengzi pipes, the water-collecting pipe 7 in the vegetation-free horizontal subsurface flow constructed wetland A and the water-distributing 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 32 mm; the water outlet pipe 9 in the vegetated horizontal subsurface flow constructed wetland D, the water inlet pipe 1 of the vegetation-free horizontal subsurface flow constructed wetland A and the water-distributing inlet pipe 2 of the downstream pool B are all flexible pipes.

[0080] The composite constructed wetland system based on dissolved oxygen regulation further includes: a pool 10 and a water pump placed in the pool; the water pump is a reflux pump 11; the 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 pool 10 is also connected to the first upper water pipe 3 of the downstream pool B through the water-distributing inlet pipe 2 of the downstream pool B;

[0081] The water-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 vegetated horizontal subsurface flow constructed wetland D;

[0082] A third valve 14 (ball valve) is arranged in front of the upper water pipe of the downstream pool B; a fourth valve 15 (ball valve) is arranged in front of the water inlet pipe of the vegetated horizontal subsurface flow constructed wetland D; a detection water outlet pipe 18 is arranged at the tail ends of the vegetation-free horizontal subsurface flow constructed wetland A and the upstream pool C, a first detection valve 19 (ball valve) 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 (ball valve) is arranged at the end of the detection water outlet pipe 18 near the upstream pool C, which is convenient for sampling;

[0083] The influent is simulated rural domestic sewage: COD 130 mg / L, NH4 + -N 25 mg / L, NO3 - -N 6 mg / L, NO2 - -N 0.2 mg / L, PO4 3--P 1.4 mg / L, pH = 7; The influent mode is segmented secondary influent. The first-stage influent enters through the influent pipe 1 of the vegetation-free horizontal subsurface flow constructed wetland A, and the second-stage influent enters through the water distribution influent pipe 2 of the down-flow pond B in the vegetated composite vertical flow constructed wetland; The effluent of the vegetation-free horizontal subsurface flow constructed wetland A is re-influent into the down-flow pond B; The flow rate of the first-stage influent is 3 m 3 / h; The flow rate of the second-stage influent is 2 m 3 / h; The time of the first-stage influent and the second-stage influent is 12 h, the hydraulic retention time is 12 h, and a complete sewage purification cycle is achieved daily. The DO in ponds A, B, C, and D is 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. The effluent samples are used to detect COD, NH4 + -N, NO3 - -N, NO2 - -N, and PO4 3- -P within 24 h, the effluent pH value is measured with a portable pH meter, and greenhouse gases are measured by the static chamber method.

[0084] The composite constructed wetland system operates for three months. The overall COD removal rate is 92.31%, the NH4 + -N removal rate is 98.62%, the NO3 - -N removal rate is 66.46%, the NO2 - -N removal rate is 73.94%, the PO4 3- -P removal rate is 42.21%, the effluent pH is 6.9 - 7.4, and the seven-day cumulative emission flux of the greenhouse gas N2O is 3.47 mg·m -2 ·h -1 for the down-flow pond B, 14.49 mg·m -2 ·h -1 for the up-flow pond C, and 4.70 mg·m -2 ·h -1 .

[0085] Comparative Example 1

[0086] The difference from Example 1 is that the vegetation-free horizontal subsurface flow constructed wetland A is removed, and the rest is the same as Example 1.

[0087] The constructed wetland system operates for three months. The overall NH4 + -N removal rate is 41.73%, the NO3 - -N removal rate is 54.90%, the NO2 - -N removal rate is -6.85%, the PO4 3-The -P removal rate is -106.5%, and the pH of the effluent is 6.9 - 7.4.

[0088] Comparative Example 2

[0089] The difference from Example 1 is that the vegetated horizontal subsurface flow constructed wetland D is removed, and the rest is the same as Example 1.

[0090] The constructed wetland system operates for three months, and the overall NH4 + -N removal rate is 93.30%, NO3 - -N removal rate is 1.81%, NO2 - -N removal rate is 61.70%, PO4 3- -P removal rate is 56.33%, and the pH of the effluent is 6.9 - 7.4.

[0091] Comparative Example 3

[0092] The difference from Example 1 is that the non-vegetated horizontal subsurface flow constructed wetland A and the vegetated horizontal subsurface flow constructed wetland D are removed, and the rest is the same as Example 1.

[0093] The constructed wetland system operates for three months, and the overall NH4 + -N removal rate is -15.69%, NO3 - -N removal rate is 39.71%, NO2 - -N removal rate is -57.01%, PO4 3- -P removal rate is -56.05%, and the pH of the effluent is 6.9 - 7.4.

[0094] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention rather than all embodiments. People can also obtain other embodiments based on these embodiments without creative efforts, 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 hybrid vertical flow constructed wetland, and a vegetated horizontal subsurface flow constructed wetland (D) connected in series; The vegetated hybrid vertical flow constructed wetland includes a down-flow pond (B) and an up-flow pond (C) connected in series; The vegetation-free horizontal subsurface flow constructed wetland (A) is provided with an inlet pipe (1); The upper end of the down-flow pond (B) is provided with a water distribution inlet pipe (2).

2. The composite constructed wetland system according to claim 1, wherein 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 - 4:2 - 3.

3. The composite constructed wetland system according to claim 1, characterized in that, A first upper layer water pipe (3) and a first lower layer water pipe (4) are arranged in the down-flow pond (B), and a second upper layer water pipe (5) and a second lower layer water pipe (6) are arranged in the up-flow pond (C); 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 Fengzi pipes; the vegetation-free horizontal subsurface flow constructed wetland (A) is provided with a water collecting pipe (7); a water distribution pipe (8) and an outlet pipe (9) are arranged in the vegetated horizontal subsurface flow constructed wetland (D); The water collecting pipe (7) in the vegetation-free horizontal subsurface flow constructed wetland (A) is connected to the upper layer water pipe (3) of the down-flow pond (B); the first lower layer water pipe (4) of the down-flow pond (B) is connected to the second lower layer water pipe (6) of the up-flow pond (C); the second upper layer water pipe (5) of the up-flow pond (C) is connected to the water distribution pipe (8) of the vegetated horizontal subsurface flow constructed wetland (D); The water distribution inlet pipe (2) of the down-flow pond (B) is communicated with the first upper layer water pipe (3) of the down-flow pond (B).

4. The composite constructed wetland system according to claim 1, characterized in that 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 down-flow pond (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 up-flow pond (C) is 50 - 105 cm and < the height of the filler in the down-flow pond (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 up-flow pond (C).

5. The composite constructed wetland system according to claim 4, characterized in that, 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 - 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 down-flow pond (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 down-flow pond (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 packing materials of the up-flow pond (C) include a coarse gravel layer, a medium gravel layer, a zeolite layer, and a loam layer arranged in sequence from bottom to top; the thickness of the coarse gravel layer in the up-flow pond (C) is 10 - 30 cm, the thickness of the medium gravel layer is 20 - 65 cm, the thickness of the zeolite layer is 10 - 30 cm, and the thickness of the loam layer is 10 - 30 cm; The packing materials of the vegetated horizontal subsurface flow constructed wetland (D) include a coarse gravel layer, a medium gravel layer, a zeolite layer, and a loam layer arranged in sequence from bottom to top; the thickness of the coarse gravel layer in the vegetated horizontal subsurface flow constructed wetland (D) is 10 - 30 cm, the thickness of the medium gravel layer is 20 - 65 cm, the thickness of the zeolite layer is 10 - 30 cm, and the thickness of the loam layer is 10 - 30 cm; The particle size of the coarse gravel in the coarse gravel layer is 40 - 60 mm; the particle size of the medium gravel in the medium gravel layer is 20 - 30 mm; the particle size of the zeolite in the zeolite layer is 0.5 - 10 mm.

6. The composite constructed wetland system according to claim 1, characterized in that The plants in the vegetated compound vertical flow constructed wetland and the vegetated horizontal subsurface flow constructed wetland (D) are wetland emergent plants; the wetland emergent plants include one or several of reed, cattail, alisma, bulrush, and sedge.

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

8. An operation method of a composite constructed wetland system based on dissolved oxygen regulation, characterized in that, Water is fed into the compound constructed wetland system according to the segmented secondary water inlet mode described in any one of claims 1 - 7. The first-stage water inlet is in the water inlet pipe (1) of the non-vegetated horizontal subsurface flow constructed wetland (A), and the second-stage water inlet is in the water distribution inlet pipe (2) of the down-flow pond (B) of the vegetated compound vertical flow constructed wetland; The nitrogen-phosphorus ratio of the influent water of the compound constructed wetland system based on dissolved oxygen regulation is 10 - 25:

1.

9. The operating method according to claim 8, characterized in that The flow rate of the first-stage influent is 3 to 5 m 3 / h; the flow rate of the second-stage influent is 1.5 to 2.5 m 3 / h.

10. The operating method according to claim 8 or 9, characterized in that, The time of the first-stage water inlet and the second-stage water inlet is independently 8 - 24 h, and the hydraulic retention time is independently 8 - 24 h.

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