Periodic self-reoxygenation weak current intervention type constructed wetland system and operation method thereof

Abstract

The invention relates to the technical field of water pollution control and ecological restoration, in particular to a periodic self-reoxygenation weak current intervention type constructed wetland system and an operation method thereof. The system is based on a vertical flow constructed wetland, water enters from the upper end, a cathode and an anode of a bioelectrochemical system are sequentially connected in the water flow direction, and meanwhile, periodic water storage and drainage are realized by adopting a siphon water outlet system. In the water storage period, the sewage flows through the cathode area, and nitrate nitrogen is subjected to electrochemical-biological synergistic reduction at the cathode; in the drainage period, along with water level drop and flow state change, the anode area environment is converted into a proper condition, and nitrate nitrogen is continuously subjected to biological denitrification reduction at the anode; through the relay action of the cathode-anode in time and space, the multi-stage reinforced removal of nitrate nitrogen is realized. The system is especially suitable for high nitrogen load sewage treatment, and has the characteristics of high self-reoxygenation efficiency, strong denitrification performance, stable operation and energy conservation.

Description

Technical Field

[0001] This invention relates to the field of water pollution control and ecological restoration technology, specifically to a periodic self-oxygenating weak electrical intervention type constructed wetland system and its operation method. Background Technology

[0002] Vertical flow constructed wetlands, as a common ecological treatment technology, involve water flowing vertically through a packing layer, relying on natural methods such as atmospheric diffusion and oxygen transport by plant roots for reoxygenation. However, this reoxygenation method is inefficient and unstable, leading to a chronically hypoxic state within the system. The severe deficiency of dissolved oxygen directly hinders the crucial step of converting ammonia nitrogen to nitrate nitrogen through nitrification, resulting in incomplete ammonia nitrogen removal and limiting the substrate supply for subsequent denitrification. This is the fundamental bottleneck preventing further improvements in the denitrification efficiency of traditional vertical flow constructed wetlands.

[0003] To enhance nitrogen removal, existing technologies attempt to introduce bioelectrochemical systems into vertical flow constructed wetlands. This involves placing electrodes within the packing material and applying a weak voltage to promote nitrate reduction (denitrification) through the directional transfer of electrons. However, simple electrochemical intervention often exacerbates the system's existing anoxic conditions. Specifically, the oxygen reduction reaction at the cathode or the cathodic respiration of microorganisms actively consumes dissolved oxygen in the water and environment; simultaneously, the anodic oxidation of organic matter does not produce oxygen. This "oxygen-consuming, non-oxygen-generating" electrochemical reaction, combined with the already insufficient reoxygenation capacity of vertical flow wetlands, further worsens the overall oxidation environment of the system, further inhibiting the aerobic process of ammonia nitrification. This creates a vicious cycle of "anoxic inhibition of nitrification → insufficient nitrate production → lack of substrate for electrochemical denitrification," preventing the expected nitrogen removal effect of the technology integration from being achieved.

[0004] Therefore, the key to overcoming the aforementioned technical bottleneck lies in how to effectively address or compensate for the oxygen consumption caused by the introduction of a bioelectrochemical system to enhance denitrification, while simultaneously creating stable and efficient aerobic conditions for ammonia nitrification. This invention addresses this problem by proposing a hydraulic operation mode that combines a vertical flow constructed wetland with a bioelectrochemical system and siphon-based periodic reoxygenation, fundamentally breaking through the bottleneck of the difficulty in further improving the nitrogen removal efficiency of traditional vertical flow constructed wetlands. Summary of the Invention

[0005] The purpose of this invention is to provide a periodic self-oxygenating weak electrical intervention constructed wetland system and its operation method, so as to solve the problems of poor ammonia nitrogen nitrification efficiency and nitrate nitrogen removal efficiency caused by hypoxia in existing vertical flow constructed wetlands.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a periodic self-oxygenating weak electrical intervention type constructed wetland system, based on a vertical flow constructed wetland system. The vertical flow constructed wetland system is water-intaken from the top, and the cathode and anode of the bioelectrochemical system are sequentially connected along the water flow direction of the vertical flow constructed wetland system. A siphon water discharge system is used to periodically store and drain water from the vertical flow constructed wetland system to achieve self-oxygenation of the vertical flow constructed wetland system. During the water storage period of the vertical flow constructed wetland system, nitrate nitrogen undergoes electrochemical-biological synergistic denitrification reduction at the negative electrode. During the drainage period of the vertical flow constructed wetland system, nitrate nitrogen undergoes biological denitrification reduction at the positive electrode, achieving multi-stage enhanced removal of nitrate nitrogen in time and space.

[0007] Furthermore, the vertical flow constructed wetland system is provided with a volcanic rock filter layer and a zeolite filter layer laid from bottom to top. A water distribution pipe is installed above the vertical flow constructed wetland system, and wetland plants are planted on the surface of the vertical flow constructed wetland system. The water in the vertical flow constructed wetland system flows from top to bottom and is collected into the water outlet trough through the outlet on one side of the bottom. A water outlet pipe is installed on one side of the water outlet trough.

[0008] Furthermore, the water outlet pipe is located at two-fifths to two-thirds of the height of the zeolite filter media layer from bottom to top.

[0009] Furthermore, the distance between the cathode and anode of the electrochemical system is set such that the cathode of the electrochemical system is not higher than the height of the water outlet pipe.

[0010] Furthermore, the outlet pipe is connected to the siphon pipe, which is inverted U-shaped, and the highest position of the siphon pipe coincides with the highest liquid level during operation of the vertical flow constructed wetland system.

[0011] Furthermore, the siphon is a variable diameter pipe, with a narrower diameter at the highest point and a wider diameter on both sides of the highest point. A damper is installed at the outlet of the siphon.

[0012] Furthermore, both the cathode and anode of the bioelectrochemical system comprise an electrode body consisting of carbon fiber felt sandwiched between two stainless steel meshes.

[0013] The operation method of a periodic self-oxygenating, low-electricity-intervention-type constructed wetland system includes the following steps:

[0014] S1. Inoculate the constructed wetland system with activated sludge from the anoxic section of the wastewater treatment plant, start the system and run it stably. S2. After the system is running stably, water enters the water storage stage through the water distribution pipe. When the liquid level in the system rises to the highest position of the siphon pipe, the siphon effect is triggered and the system enters the drainage stage. S3. When the liquid level in the system is lower than the height of the outlet pipe, drainage stops and the system enters a new round of water storage. S4, and S2~S3, realize the alternating cycle of water storage and drainage in the system, and remove pollutants during the cycle.

[0015] Furthermore, the applied voltage during startup is 0.1±0.02V, and the applied voltage during steady-state operation is 0.3±0.05V.

[0016] Furthermore, the drainage stage is controlled to last for 1 to 3 hours.

[0017] The beneficial effects of this invention are: 1. The core of this invention lies in the introduction of a siphon water discharge system, which enables the wetland to switch between "water storage-drainage" cycles. During the drainage period, the system quickly empties the water, and a large amount of air is naturally drawn into the pores of the packing material, achieving forced and efficient reoxygenation of the packing bed. This process is completed automatically by hydraulic power without the need for additional aeration energy consumption, which completely reverses the shortcomings of traditional vertical flow wetlands and simple electrochemical wetlands in terms of reoxygenation capacity, and provides the necessary and stable dissolved oxygen environment for the full nitrification of ammonia nitrogen. 2. This invention breaks the original vicious cycle by coupling "periodic reoxygenation" with "weak electrical intervention." During the drainage reoxygenation period, an aerobic zone is formed in the upper part of the system, efficiently completing the conversion of ammonia nitrogen to nitrate nitrogen (nitrification). In the subsequent water storage period and the initial stage of drainage, these newly generated nitrate nitrogens are significantly reduced by electrochemical processes (denitrification) as they flow through specific electrode areas. In particular, the precise sequential design of "water flow direction from cathode to anode" ensures that the cathode preferentially removes some nitrate nitrogen during the water storage period, while the anoxic anode area formed during the drainage period can then take over to remove newly generated nitrate nitrogen, achieving spatiotemporal connection and maximizing efficiency of the denitrification process. 3. The stable periodic reoxygenation of this invention ensures the continuous progress of the nitrification process, thus providing a foundation for deep denitrification; the coupled electrochemical system not only directly accelerates the reduction of nitrate nitrogen, but its micro-electrocatalytic effect at the anode also helps to break down some recalcitrant organic matter, improving the overall COD removal; the system operation relies on natural siphon and extremely low voltage (0.1~0.3V), requires no complex electromechanical equipment, has extremely low energy consumption, and is easy to manage. It is particularly suitable for rural areas or decentralized wastewater treatment scenarios where power supply is inconvenient and maintenance requirements are low, and has good technical and economic efficiency and applicability. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the constructed wetland system of the present invention; Figure 2 This is a comparison chart of the pollutant removal effects of Embodiment 1 and Embodiment 2 of the present invention; Figure 3 This is a comparison chart of the pollutant removal effects of Embodiment 2 of the present invention and a traditional vertical flow constructed wetland.

[0019] The names corresponding to each mark in the diagram: 1. Water distribution pipe; 2. Zeolite filter media layer; 3. Cathode electrode plate; 4. DC power supply; 5. Resistor; 6. Anode electrode plate; 7. Volcanic rock filter media; 8. High-level water outlet pipe; 9. Low-level water outlet pipe; 10. Multi-diameter combined siphon pipe; 11. Damper; 12. Iron frame. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0021] The periodic self-oxygenating weak electrical intervention type constructed wetland system of this invention is an integrated coupling device of vertical flow constructed wetland, bioelectrochemical system and siphon water discharge system. The core achieves efficient sewage treatment through the synergistic effect of "weak electrical enhancement reaction + periodic self-oxygenation".

[0022] like Figure 1 As shown, in terms of its structure, the vertical flow constructed wetland is laid with zeolite filter media (adsorbing pollutants such as ammonia nitrogen) and volcanic rock filter media (providing support, forming large pores and ensuring permeability) from top to bottom. The upper part of the wetland is equipped with water distribution pipes with uniform water distribution holes to distribute water evenly and avoid short circuits. Yellow iris and other plants are planted on the surface (yellow iris is highly adaptable and has a well-developed root system, which can not only absorb nutrients such as nitrogen and phosphorus in the water, but its roots also provide a carrier for the growth of microbial films).

[0023] The bioelectrochemical system contains a combined electrode consisting of a stainless steel mesh sandwiched with carbon felt (the carbon felt (carbon fiber felt) is sandwiched between two stainless steel meshes as the main electrode body, where the stainless steel meshes mainly serve as the framework and current collector, and the activated carbon block serves as the main body of the bioelectrode, playing the role of enriching electroactive microorganisms, denitrification, and phosphorus removal). Two combined electrodes of the same shape are used as the anode and cathode, respectively, and are placed in parallel in the bioelectrochemical system tank, with the upper one being the cathode and the lower one being the anode, providing a potential difference between the cathode and anode of the bioelectrochemical system. The external circuit connects the electrodes to form a closed loop.

[0024] The siphon water outlet system adopts a multi-stage variable diameter siphon pipe. The inner diameter of the top section is smaller than the inner diameter of the left and right sections on both sides of the top section. This combined structure can effectively control the flow rate and flow rate changes during the drainage process. The multi-stage variable diameter design is conducive to forming a smooth siphon start-up and shutdown process. The highest position of the siphon pipe (top section) is fixed by an iron frame to match the highest water level of the device. A damper is installed at the outlet to regulate the flow rate. The siphon pipe is combined with the low-level outlet pipe or the high-level outlet pipe to form a drainage path.

[0025] During operation, activated sludge from the anoxic section of the wastewater treatment plant is first inoculated onto the electrodes and filter media to complete biofilm formation. After the wastewater is evenly distributed through the distribution pipes, it first flows through the upper cathode. Electroactive microorganisms (such as Arthrobacter) on the cathode surface receive electrons from the external circuit, reducing nitrate nitrogen to nitrogen gas. At the same time, the microorganisms catalyze proton reduction to produce hydrogen, driving hydrogen autotrophic denitrification to further enhance denitrification. Subsequently, the wastewater flows through the lower anode. Electroactive microorganisms (such as Denitrosoma) in the anode area decompose organic matter and transfer electrons to the external circuit. They can also convert recalcitrant organic matter into smaller molecules to improve bioavailability.

[0026] When the wastewater level rises to the set height of the siphon pipe, the siphon effect is triggered, and under the action of atmospheric pressure difference, a drainage stage lasting about 1 to 3 hours is entered. During the water level drop, air is drawn into the pores of the packing material, making the upper and middle zeolite filter media area an oxygen-rich zone (ammonia nitrogen is converted into nitrate nitrogen through nitrification), while the lower and middle volcanic rock filter media area forms an anoxic-anaerobic zone due to limited oxygen replenishment (the previously generated nitrate nitrogen is reduced to nitrogen gas through denitrification). When the water level drops to the height of the siphon pipe inlet, the siphon effect stops, and the water distribution pipe continues to replenish water to enter the next cycle. Finally, the treated wastewater is discharged through the low-level effluent pipe, achieving the synergistic removal of nitrogen, phosphorus, and organic matter.

[0027] Example 1 In this embodiment, the periodic self-oxygenating weak electrical intervention type constructed wetland system of the present invention is constructed, wherein the height of the volcanic rock filter media layer is 17cm, and the particle size of the volcanic rock filter media is 1~3cm; the height of the zeolite filter media layer is 17cm, and the particle size is 4~8mm; the surface planting density of Iris tectorum is 100 plants / m². 2 .

[0028] The cathode and anode of the bioelectrochemical system of this invention are set in the volcanic rock filter media layer. Both the cathode and anode are combined electrodes made of stainless steel mesh and carbon felt. The stainless steel mesh has a pore size of 6 mm and a wire diameter of 0.8 mm. The distance between the cathode and anode is 12 cm. The control unit is composed of a 1000Ω cement resistor and a DC regulated power supply with an output accuracy of 0.01V.

[0029] In this embodiment, a low-level water outlet pipe is adopted, and the height of the low-level water outlet pipe is level with the bottom height of the zeolite filter media layer. The low-level water outlet pipe is connected to the siphon pipe, which is a multi-stage variable diameter siphon pipe with an inner diameter of 8mm at the top and 16mm at the left and right sides.

[0030] Under room temperature conditions, the influent was a high-concentration complex carbon source; the water quality was COD = 180 mg / L, total nitrogen (TN) = 60 mg / L, and ammonia nitrogen (NH4) = 180 mg / L. + -N) = 48 mg / L, total phosphorus (TP) = 5 mg / L.

[0031] During the system startup phase, activated sludge (5.6 g / L) from the anoxic treatment section of the wastewater treatment plant was inoculated onto the bioelectrodes and biofilter packing to accelerate system startup. Stable operation for 20 days was then implemented to ensure successful biofilm formation on the electrodes and filter packing and the enrichment of functional microorganisms.

[0032] The bioelectrochemical system uses an applied voltage of 0.1V during the start-up phase and 0.3V during the stabilization phase after 20 days. The low-level outlet pipe of the low-voltage artificial wetland is connected to the siphon pipe to form a 3-hour circulating operation mode.

[0033] Wastewater flows vertically through the zeolite filter media layer, cathode electrode plate, volcanic filter media layer, anode electrode plate, and bottom volcanic rock filter media layer from the water inlet of the distribution pipe, and exits through the outlet at the bottom of the baffle. When the water level reaches the siphon activation level, the low-level outlet drains water quickly through the siphon. After the drainage is completed, as the water level drops, air is naturally drawn into the pores of the wetland matrix, achieving periodic reoxygenation.

[0034] Example 2 In this embodiment, the periodic self-oxygenating weak electrical intervention type constructed wetland system of the present invention is constructed. The difference between the constructed wetland system in this embodiment and that in embodiment 1 is that a high-level water outlet pipe is used in this embodiment. The high-level water outlet pipe is located at half the height of the zeolite filter media layer. Otherwise, it is the same as in embodiment 1.

[0035] Under room temperature conditions, the influent was a high-concentration complex carbon source; the water quality was COD = 180 mg / L, total nitrogen (TN) = 60 mg / L, and ammonia nitrogen (NH4) = 180 mg / L. + -N) = 48 mg / L, total phosphorus (TP) = 5 mg / L.

[0036] During the system startup phase, activated sludge (5.6 g / L) from the anoxic treatment section of the wastewater treatment plant was inoculated onto the bioelectrodes and biofilter packing to accelerate system startup. Stable operation for 20 days was then implemented to ensure successful biofilm formation on the electrodes and filter packing and the enrichment of functional microorganisms.

[0037] The bioelectrochemical system was started with an applied voltage of 0.1V, and stabilized with a voltage of 0.3V after 20 days. The high-level effluent pipe of the low-voltage intervention constructed wetland was connected to the siphon pipe to form a 1-hour circulating operation mode, which aimed to explore the influence of different reoxygenation zone sizes on pollutant removal performance.

[0038] The operation mode is similar to that of Example 1. Wastewater flows vertically from the water inlet pipe through the zeolite filter media layer, cathode electrode plate, volcanic rock filter media layer, anode electrode plate and bottom volcanic rock filter media layer, and exits through the outlet at the bottom of the baffle. When the water level reaches the siphon start-up water level, the high-level outlet pipe drains water quickly through the siphon pipe. After the drainage is completed, as the water level drops, air is naturally drawn into the pores of the wetland matrix to achieve periodic reoxygenation.

[0039] Compared with Example 1, this example reduces the volume of the periodic reoxygenation zone by changing the position of the outlet pipe, thereby optimizing the spatial ratio of the reoxygenation zone and the anoxic zone inside the wetland.

[0040] The investigation revealed that the advantages of the bioelectrochemical process in this embodiment are more obvious than those in Example 1, such as... Figure 2 As shown, the system is particularly effective at removing nitrate nitrogen. Continuous weak electrical intervention and a large anoxic zone volume enhance the bioelectrochemical-driven denitrification process, achieving efficient removal of nitrate nitrogen. At the same time, by regulating the reoxygenation zone, the system allows carbon sources to be used more for denitrification rather than aerobic decomposition, improving carbon source utilization efficiency. In this embodiment, by regulating the reoxygenation wetland area, a more efficient weak electrical intervention constructed wetland system is constructed.

[0041] Comparative Example 1 To verify the wastewater treatment advantages of the system of the present invention, a traditional vertical flow constructed wetland was set up as a parallel control with Example 2. Except for the absence of a bioelectrochemical system and a siphon effluent system, the structure, filter media ratio, plant planting, influent water quality (COD=180mg / L, TN=60mg / L, etc.), and operating environment of this control example were identical to Example 2. The operation relied solely on atmospheric diffusion and natural reoxygenation through plant root secretion, using a conventional high-level gravity effluent method. The dissolved oxygen data during operation are shown in the table below: Table 1 Comparison of dissolved oxygen content during operation between this comparative example and Example 2

[0042] The experiment continuously monitored the dissolved oxygen content and pollutant removal efficiency in the upper and lower parts of the system for 6–36 days. The results showed that the dissolved oxygen in the upper part of the traditional vertical flow constructed wetland fluctuated between 0.73 and 1.01 mg / L, and in the lower part between 0.47 and 0.66 mg / L. The overall dissolved oxygen level was significantly lower than that of the self-oxygenating, weakly electrically intervened constructed wetland of this invention, and the reoxygenation effect was unstable. Furthermore, its removal efficiency for ammonia nitrogen, nitrate nitrogen, TP, and COD was far lower than that of Example 2. This fully demonstrates that the present invention, through the coupled design of siphon-based periodic self-oxygenation and weakly electrically intervened technology, effectively solves the problem of insufficient reoxygenation capacity in traditional vertical flow constructed wetlands, and significantly improves pollutant removal performance (e.g., ...). Figure 3 (as shown in the figure). In contrast, the technical solution of the present invention has more advantages in the process of sewage treatment.

[0043] Comparative Example 2 To verify the rationality of the electrode arrangement of the bioelectrochemical system of the present invention, with the cathode on top and the anode on the bottom, a control experiment with reversed electrode arrangement was set up as Comparative Example 2, which was conducted in parallel with Example 2. This comparative example differed from Example 2 only in that the electrode arrangement of the bioelectrochemical system was changed to anode on top and cathode on the bottom; all other aspects of the device structure, filter media ratio, plant cultivation, and influent water quality (COD=180mg / L, TN=60mg / L, NH4+) remained the same. + The parameters (such as -N=48mg / L) and operating parameters (0.1V during startup, 0.3V during stabilization, and siphon storage-drainage mode with a 1h drainage cycle) are completely consistent with those in Example 2, ensuring the single variable principle of the control experiment.

[0044] The experimental results show that Example 2 achieved efficient removal of nitrate nitrogen by relying on the arrangement of cathode on top and anode on the bottom, with a removal rate of more than 85%. In contrast, the nitrate nitrogen removal rate of Comparative Example 2, with the anode on top and cathode on the bottom in a reverse arrangement, was only about 40%, and the denitrification effect was significantly worse than that of Example 2.

[0045] The reason for this is that the water flow in this invention is from top to bottom, and the arrangement of the cathode on top and the anode on the bottom is adapted to the hydraulic cycle of water storage and drainage: during the water storage period, the sewage flows through the cathode first, and nitrate nitrogen can be rapidly reduced by electrochemical-biological synergistic denitrification at the cathode. During the drainage period, the anoxic environment created by the drop in water level matches the lower anode area, realizing the relay denitrification of nitrate nitrogen and forming a multi-stage denitrification system in time and space. However, the reverse arrangement of the anode on top and the cathode on the bottom causes the sewage to flow through the anode first during the water storage period, which cannot give full play to the electrochemical-biological synergistic denitrification advantage of the cathode. During the drainage period, the oxygen reduction reaction in the lower cathode area consumes dissolved oxygen and is misaligned with the flow pattern and dissolved oxygen environment during the drainage period, which disrupts the time and space connection of the denitrification process. At the same time, electroactive denitrifying microorganisms cannot be effectively enriched in the suitable electrode area, ultimately resulting in a significantly poor nitrate nitrogen removal effect.

[0046] The results fully demonstrate that the electrode arrangement design with the cathode on top and the anode on the bottom in this invention is the key to achieving efficient removal of nitrate nitrogen. The reverse arrangement cannot achieve the synergistic matching between the hydraulic cycle and electrochemical-biological denitrification, and cannot achieve the expected nitrogen removal effect.

[0047] This invention is not limited to the preferred embodiments described above. Anyone can derive other forms of products under the guidance of this invention. However, regardless of any changes made in their shape or structure, any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A cyclically self-reoxygenating, low dielectric permittivity constructed wetland system, based on a vertical flow constructed wetland system, characterized in that: The vertical flow constructed wetland system is connected with the cathode and the anode of the bioelectrochemical system in sequence from the top to the bottom along the water flow direction of the vertical flow constructed wetland system, and the vertical flow constructed wetland system is periodically filled with water and drained by using a siphon water outlet system to realize self-reoxygenation of the vertical flow constructed wetland system; during the water storage period of the vertical flow constructed wetland system, nitrate is electrochemically-biologically synergistically denitrified at the negative electrode, and during the water drainage period of the vertical flow constructed wetland system, nitrate is biologically denitrified at the positive electrode, so that the nitrate is removed in multiple stages in time and space.

2. The periodic, self-reoxygenating, low dielectric, constructed wetland system of claim 1, wherein: The vertical flow constructed wetland system is connected with the cathode and the anode of the bioelectrochemical system in sequence from the top to the bottom along the water flow direction of the vertical flow constructed wetland system, and the vertical flow constructed wetland system is periodically filled with water and drained by using a siphon water outlet system to realize self-reoxygenation of the vertical flow constructed wetland system; during the water storage period of the vertical flow constructed wetland system, nitrate is electrochemically-biologically synergistically denitrified at the negative electrode, and during the water drainage period of the vertical flow constructed wetland system, nitrate is biologically denitrified at the positive electrode, so that the nitrate is removed in multiple stages in time and space.

3. The periodic, self-reoxygenating, low dielectric, constructed wetland system of claim 2, wherein: The water outlet pipe is located at a position of two-fifths to two-thirds of the height of the zeolite filter layer from the bottom to the top.

4. The periodic, self-reoxygenating, low dielectric, constructed wetland system of claim 3, wherein: The distance between the cathode and the anode of the electrochemical system is set, and the height of the cathode of the electrochemical system is not higher than that of the water outlet pipe.

5. The periodic, self-reoxygenating, low-energy, dielectric, constructed wetland system of claim 2, wherein: The water outlet pipe is connected with the siphon pipe, the siphon pipe is in an inverted U shape, the highest position of the siphon pipe is consistent with the highest liquid level of the vertical flow constructed wetland system during operation.

6. The periodic, self-reoxygenating, low dielectric, constructed wetland system of claim 5, wherein: The siphon pipe is a variable-diameter pipe, the diameter of the siphon pipe is relatively narrow at the highest position, the diameters of the siphon pipe on both sides of the highest position are relatively wide, and a damper is arranged at the water outlet of the siphon pipe.

7. The periodic, self-reoxygenating, low-energy, dielectric, constructed wetland system of claim 1, wherein: The cathode and the anode of the bioelectrochemical system each include an electrode main body composed of two stainless steel meshes clamping a carbon fiber felt therebetween.

8. The method of operating a cyclically oxic anoxic constructed wetland system according to any one of claims 1 to 7, characterized in that The method comprises the following steps: S1, inoculating activated sludge in an anoxic section of a sewage treatment plant into the constructed wetland system, starting the system and stably operating; S2, after the system is stably operated, water is introduced into the system through the water distribution pipe to enter a water storage stage, when the liquid level in the system rises to the highest position of the siphon pipe, the siphon effect is triggered and the system enters a water drainage stage; S3, when the liquid level in the system is lower than the height of the water outlet pipe, the water drainage stops, and the system enters a new water storage stage; S4, the steps S2 to S3 are repeated to realize the alternating circulation of water storage and water drainage of the system, and the removal of pollutants in the circulation process.

9. The method of operating a cyclically self-reoxygenating constructed wetland system of the weakly dielectric type according to claim 8, characterized in that: The external voltage during the starting period is 0.1±0.02 V, and the external voltage during the stable period is 0.3±0.05 V.

10. The method of operating a cyclically self-reoxygenating constructed wetland system of the weakly dielectric type according to claim 8, characterized in that: The time control of the water drainage stage is 1-3 h.

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