A process and device for nitrogen and phosphorus removal by combining a stepped power supply with a series of stabilization ponds

Abstract

The invention discloses a device and a process for denitrification and phosphorus removal by combining a stepped power supply with a series of stabilization ponds, belonging to the field of sewage biological treatment. The device mainly comprises an electrolytic cell (1), an aerobic pond (2), and a facultative pond (4). The specific technological process is as follows: Sewage first enters the electrolytic cell (1) for electrolysis of sodium chloride, and then enters the ecological floating bed of the aerobic pond (2) through the diversion device between the electrolytic cell (1) and the aerobic pond (2) to remove organic matters and carry out nitrification reaction; Then, the sewage enters the facultative pond (4) from the bottom of the aerobic pond (2), where denitrification and phosphorus removal are carried out. After that, the clear water is filtered through biochar (16) and then discharged, and 15-20% of the clear water is refluxed to the electrolytic cell (1), and the remaining clear water is directly reused for coastal buildings; The sludge is discharged to the digestion pit (19) at the bottom of the facultative pond (4). The invention can remove coastal urban sewage with high C / N and high salt content, and no external carbon source is required, thus reducing costs.

Description

Technical Field

[0001] The present invention relates to a process and device for denitrification and phosphorus removal by combining a stepped power supply with a series of stabilization ponds, belonging to the field of sewage biological treatment.

[0002] Background Art

[0003] At present, the sewage in our country still faces the problem of eutrophication. For the sewage and initial rainwater discharged from offshore buildings, there are also problems of high C / N ratio and high salinity.

[0004] Since the concept of treating sewage with microalgae was proposed in the 1950s of the last century, this process has received more and more attention. Microalgae play an important role in purifying natural water bodies in the natural environment, using nitrogen, phosphorus and organic matter in water as nutrients, light energy as energy, and water as an electron acceptor. Under photosynthesis, microalgae grow themselves, and at the same time, nitrogen, phosphorus and organic pollutants in water are removed. Moreover, the cost is low and no secondary pollution is generated.

[0005] The electro-biological coupling technology is a biofilm technology under electrochemical action. By combining the advantages of biological methods and electrochemical methods, the pollutants in domestic sewage can be effectively degraded, and the cost is also saved.

[0006] At present, the vast majority of environmental protection achievements related to the symbiosis of bacteria and algae are concentrated in the treatment of fresh water. There are relatively few reports on the in-situ ecological restoration of organically polluted water bodies in high-salt application scenarios such as offshore areas. CN111252889A discloses a high-salt wastewater treatment device and method combining the symbiosis method of bacteria and algae and a membrane biofilm reactor. For the treatment of high-salt wastewater, the microorganisms are domesticated and cultured, and salt-tolerant strains are screened for denitrification and phosphorus removal, and the excessive Cl ions in the water are not utilized to promote denitrification and phosphorus removal.

[0007] CN112209540A discloses a zero-discharge coupling process for high-salt and high-COD wastewater, in which the salt and organic pollutants in the wastewater are separated by an electrodialysis system, and the organic pollutants are removed by an electro-oxidation system. CN113830956A discloses a deep treatment process for shale gas fracturing flowback fluid and produced water, and its main purpose is to target the produced water in shale gas fields. For the problems of high salt and high C / N ratio, the current technology generally uses salt-tolerant algae and bacteria for denitrification and phosphorus removal, electrolysis or advanced oxidation of high-salt sewage. The process is relatively complex, and the effects of denitrification, phosphorus removal and COD removal are relatively average. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a process and device for nitrogen and phosphorus removal by combining a stepped power supply with a series of stabilization ponds in view of the deficiencies of the above-mentioned existing technologies. By combining an electrolytic cell with bacteria and algae, while electrolyzing high-salt water, not only can the Cl - content be reduced to generate ClO with oxidation and disinfection capabilities - , but also the current can be used to stimulate bacteria and algae, activate their activity, and thereby improve their nitrogen and phosphorus removal capabilities.

[0009] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0010] A process for nitrogen and phosphorus removal by combining a stepped power supply with a series of stabilization ponds includes the following steps:

[0011] (1) Feed the sewage to be treated into the electrolytic cell for electrolysis of sodium chloride, which can reduce the Cl - content and generate ClO with oxidation and disinfection capabilities - ;

[0012] (2) When the sewage in step (1) is electrolyzed until the chloride ion content is reduced to less than 200 mg / L, it is fed into the aerobic pond through a diversion device, and the removal of organic matter and nitrification reaction are carried out in the aerobic pond;

[0013] (3) The bottom effluent of the aerobic pond enters the facultative pond, where denitrification and phosphorus removal reactions are carried out using bacteria, algae and suspended fillers, and it is divided into two parts: clear water and sludge. Among them, the clear water is further filtered through kapok biochar to obtain purified water, and 15-20% of the purified water is recycled to the electrolytic cell, and the remaining purified water is directly reused for coastal buildings; the sludge is collected in the digestion pit at the bottom of the facultative pond and can be anaerobically digested by itself.

[0014] According to the above scheme, the external power supply of the electrolytic cell is a stepped power supply. When the chloride ion concentration in the electrolytic cell is ≥200 mg / L, the current density adopts the first step (80-120 mA / cm 2 ) for electrolysis of sodium chloride; when the chloride ion concentration <200 mg / L, the current density adopts the second step (0.4-0.6 mA / cm 2 ) to activate the activity of algae and bacteria and improve their nitrogen and phosphorus removal capabilities.

[0015] According to the above scheme, the stabilization ponds include an aerobic pond and a facultative pond.

[0016] According to the above scheme, the sewage is a mixed water body of the water body polluted by organic matter in the offshore area and the sewage discharged from coastal buildings, which is characterized by a high C / N (molar ratio), about 10-15, an influent salt content of 12,000 mg / L-20,000 mg / L, and most of the salt is mainly NaCl (NaCl is not less than 80% of the total salt).

[0017] According to the above scheme, an ecological floating bed is set in the aerobic pond to adsorb nitrifying bacteria and star algae; the bottom effluent of the aerobic pond meets the requirements of COD≤30mg / L, NH4 + -N≤5mg / L, TP≤0.5mg / L.

[0018] According to the above scheme, the bacteria and algae used in the facultative pond are denitrifying phosphate-accumulating bacteria and oil-producing microalgae Asteraceae 11B7; the effluent of the facultative pond meets the requirements of COD≤30mg / L, NH4 + -N≤1.5mg / L, TN≤1.5mg / L, TP≤0.3mg / L.

[0019] The present invention also provides a device for denitrification and dephosphorization using a stepped power supply in combination with a series of stabilization ponds, compatible with the above process. The device comprises an electrolytic cell, an aerobic pond, and a facultative pond. The electrolytic cell is connected to the inlet of the aerobic pond via a flow guide, and the outlet of the aerobic pond is connected to the inlet below the facultative pond. The electrolytic cell is provided with an inlet for inputting sewage and an inlet for returning purified water from the facultative pond. The facultative pond is provided with an outlet for returning purified water to the electrolytic cell and an outlet for directly discharging purified water to the outside above the electrolytic cell.

[0020] The electrolytic cell is provided with a rapid chloride ion analyzer, an anode, and a cathode; the anode and cathode are respectively connected to the positive and negative electrodes of a stepped power supply provided outside the electrolytic cell; the rapid chloride ion analyzer is provided with a sensor for transmitting the chloride ion content to a controller to adjust the stepped power supply;

[0021] The aerobic pond is provided with an ecological floating bed, which comprises a three-dimensional filler layer and a ceramsite layer from bottom to top, and an aquatic plant Acorus calamus is arranged on the ceramsite layer; and the three-dimensional filler layer of the ecological floating bed is used to absorb nitrifying bacteria and asteraceae;

[0022] A digestion pit is provided at the bottom of the facultative pond, and a water outlet connected to the outside and a reflux port connected to the electrolytic cell are provided above the facultative pond; a suspended filler and kapok activated carbon fixed above the suspended filler are provided inside the facultative pond, and a stirring device is provided for internal stirring; and the suspended filler is used to adsorb denitrifying polyphosphate bacteria and oil-producing microalgae.

[0023] According to the above solution, the facultative pond is also equipped with a stirring device.

[0024] According to the above solution, the anode is a conductive carbon nanotube, and the cathode is a stainless steel cathode plate.

[0025] According to the above scheme, the suspended filler and the three-dimensional filler are made of polyurethane and acetate fiber synthetic polymer materials respectively.

[0026] According to the above scheme, the external power supply device of the electrolytic cell is a stepped power supply, and the current density can be switched in real time according to the concentration of chloride ions. When the chloride ion concentration inside the device is less than 200 mg / L, the chemical sensor on the chloride ion rapid detector transmits information to the controller, and the controller then regulates the power supply device to automatically switch the current density, and the current density is adjusted from about 100 mA / cm 2 to about 0.5 mA / cm 2 When the current density is about 100 mA / cm 2 at this time, the electrolytic cell electrolyzes the sodium chloride solution, and it will generate ClO - ; when the current density is about 0.5 mA / cm 2 at this time, the electrolysis stops, and the weak current existing in the device will stimulate the algae and bacteria.

[0027] According to the above scheme, the opening and closing of the diversion device between the electrolytic cell and the aerobic pond are jointly regulated by the sensor on the chloride ion detector and the controller. When the chloride ion concentration in the electrolytic cell is less than 200 mg / L and the current density is about 0.5 mA / cm 2 at this time, the diversion device starts, making the electrolytic cell and the aerobic pond communicate with each other, and the electrolyzed sewage will flow from the electrolytic cell to the aerobic pond.

[0028] According to the above scheme, the material of the diversion device is corrosion-resistant PVC (polyvinyl chloride).

[0029] According to the above scheme, the aerobic pond requires sufficient light for the algae to carry out photosynthesis to produce oxygen, and all the pond water is in an aerobic state, and aerobic microorganisms carry out the degradation of organic matter and nitrification.

[0030] According to the above scheme, the suspended fillers in the facultative pond can flow freely therein, and the algae and bacteria can fully contact the pollutants in the water to achieve the purpose of removing pollutants. In addition, a stirring device is also provided in the facultative pond to make the nitrogen generated by the reaction better escape from the facultative pond and promote the shedding of the aged biofilm in the suspended fillers.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1) The present invention adopts a stepped power supply, which can be adjusted according to the chloride ion concentration in the electrolytic cell, so that the sewage can be electrolyzed at a high current density to reduce the salt content, which is beneficial to reducing the inhibitory effect of high salt on the metabolic activities of the algae-bacteria symbiotic system, and the electrolysis generates oxidizing ClO - to remove part of the COD in the water; at a low current density, the activity of the algae and bacteria can be improved, and their ability to remove ammonia nitrogen and organic matter can be improved;

[0033] 2) In the aerobic pond of the present invention, the form of an ecological floating bed is adopted, and the functions of plants and microorganisms can be utilized to remove N and P and oxidize organic matter. Moreover, without adding an external carbon source, the oleaginous microalgae in the facultative pond itself can provide a carbon source for denitrification and oxygen for the facultative pond, which can reduce the treatment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The figure is a schematic structural diagram of the step - type power supply combined with a series of stabilization ponds for nitrogen and phosphorus removal according to the present invention. Among them: the electrolytic cell (1) includes a power supply device (6), a controller (7), a chloride ion detector (8), an anode (9), a cathode (10), and a diversion device (11); the aerobic pond (2) includes calamus (12), ceramsite (13), three - dimensional packing (14), and an ecological floating bed frame (15); the facultative pond (4) includes kapok activated carbon (16), a stirring device (17), suspended packing (18), and a digestion pit (19); as well as a lift pump (3), a reflux pump (5), and illumination (20). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the present invention is not limited to the following embodiments.

[0036] As Figure 1 shown, the device for nitrogen and phosphorus removal by the step - type power supply combined with a series of stabilization ponds adopted in the following embodiments includes an electrolytic cell (1), an aerobic pond (2), and a facultative pond (4);

[0037] An inlet for inputting domestic sewage and an inlet for the clarified water refluxed from the facultative pond (4) are provided on the electrolytic cell (1); a diversion device is provided between the electrolytic cell (1) and the aerobic pond (2); an inlet for the effluent from the aerobic pond (2) is provided at one - third of the height of the facultative pond (4), and an outlet for the purified water after being treated by the facultative pond is provided above, including an outlet for the purified water refluxed to the electrolytic cell and an outlet for directly discharging the purified water to the outside.

[0038] Furthermore, in the power supply device (6) of the electrolytic cell (1), the anode (9) material is carbon nanotubes with a large specific surface area and good electrical conductivity, and the cathode (10) material is a stainless - steel cathode (10) plate, which has the characteristics of stainlessness and corrosion resistance.

[0039] Furthermore, the power supply device of the electrolytic cell (1) is a step - type power supply device (6), and the current density can be switched in real - time according to the concentration of chloride ions. When the chloride ion concentration inside the device is less than 200 mg / L, the chemical sensor on the chloride ion detector (8) transmits information to the controller (7), and the controller (7) then regulates the power supply device (6) to automatically switch the current density. The current density changes from 100 mA / cm2 Adjust to 0.5 mA / cm 2 。

[0040] Furthermore, a chloride ion detector (8) is provided in the electrolytic cell (1). The opening and closing of the diversion device between the electrolytic cell (1) and the aerobic pond (2) are jointly regulated by the chemical sensor on the chloride ion detector (8) and the controller (7). When the chloride ion concentration ≤ 200 mg / L and the current density is 0.5 mA / dm 2 , the diversion device starts to work and rotates 45° to the right along the rotation center at the bottom to connect the electrolytic cell (1) and the aerobic pond (2) to each other. When the chloride ion concentration > 200 mg / L and the current density is 100 mA / cm 2 , at this time, the electrolytic cell (1) electrolyzes the sodium chloride solution, and it will generate CIO - ; when the current density is 0.5 mA / cm 2 , the electrolysis stops, and the weak current existing in the device will stimulate the bacteria and algae.

[0041] Furthermore, an ecological floating bed is provided in the aerobic pond (2), which is composed of the upper-layer plant calamus (12), the middle-layer ceramsite floating body (13) and the lower-layer three-dimensional filler acetate fiber (14); the three-dimensional filler (14) is used for adsorbing nitrifying bacteria and Pediastrum to grow and reproduce; the filling rate of the three-dimensional filler layer in the biological floating bed is 70% - 80%, the upper surface of the ceramsite layer is basically flush with the normal water level, and the coverage area of the aquatic plants growing above the ceramsite layer accounts for 60% - 70% of the aerobic pond. The aerobic pond (2) uses sufficient light to enable the algae to carry out photosynthesis to produce oxygen, and all the pond water is in an aerobic state, and the aerobic microorganisms carry out the degradation of organic matter and nitrification.

[0042] Furthermore, polyurethane suspended fillers (18) and a kapok activated carbon filter layer fixed above the suspended fillers are provided in the facultative pond (4). The suspended fillers are used for adsorbing denitrifying phosphorus-accumulating bacteria and the oil-producing microalgae Coelastrum sp. 11B7; the filling rate of the suspended fillers in the facultative pond is 40%, and the suspended fillers can flow freely in the water, and the algae and bacteria can fully contact the pollutants in the water to achieve the purpose of removing pollutants; the facultative pond (4) is also provided with a stirring device (17) to better discharge nitrogen from the facultative pond (4) and promote the shedding of the aged biofilm in the suspended fillers (18); the bottom slope of the facultative pond (4) is set to 0.005, and a digestion pit (19) is provided inside to facilitate the concentration of phosphorus-rich sludge, which can be spontaneously digested.

[0043] In the following embodiments, during the start-up stage of the aerobic pond and the facultative pond:

[0044] First, place the ecological floating bed in the aerobic pond; place the suspended fillers in the facultative pond;

[0045] Secondly, fill the aerobic pond and facultative pond with sewage, and add two pre-prepared mixed solutions of bacteria and algae (add the mixed solution of nitrifying bacteria and Pediastrum to the aerobic pond, and add the mixed solution of denitrifying phosphorus-accumulating bacteria and oleaginous microalgae Coelastrum 11B7 to the facultative pond). Then, keep the aerobic pond aerated for 24 hours and let it settle for 1.5 hours to achieve the adsorption and film formation of bacteria and algae on the three-dimensional fillers in the aerobic pond and the suspended fillers in the facultative pond, as well as the cultivation.

[0046] Then, the whole system adopts the method of increasing the influent flow rate in stages. The influent flow rate gradually increases from 40 L / d. By controlling the influent flow rate, adjusting the addition amount of the mixed solution of bacteria and algae and the cultivation degree, the effluent indexes of the aerobic pond and the facultative pond are monitored and adjusted. Take samples from the outlet of the system every other day to analyze the concentration changes of COD, ammonia nitrogen, TP, etc. When the operation conditions of each pond are good and the COD removal rate of the whole system reaches 75%, the influent flow rate can be increased by 10 - 15%. If the effluent COD basically does not decrease, the influent volume should be reduced or the influent should be stopped temporarily to further cultivate the mixed solution of bacteria and algae in the pond. When the bottom effluent of the aerobic pond meets COD < 30 mg / L, NH4 + -N < 5 mg / L, TP < 0.5 mg / L, and the effluent of the facultative pond meets COD < 30 mg / L, NH4 + -N < 1.5 mg / L, TN < 1.5 mg / L, TP < 0.3 mg / L, and the biological phase is relatively stable, indicating that the cultivation of bacteria and algae is mature, and the aerobic pond and the facultative pond are successfully started.

[0047] Among them, the involved bacteria and algae are enriched and cultured by conventional methods and then centrifuged; the centrifuged algal liquid and bacterial liquid are respectively placed in conical flasks, diluted with water by the same volume, and then the algal liquid and bacterial liquid are mixed at a volume ratio of 10:1 to obtain the mixed solution of bacteria and algae, with a total concentration of about 3 - 4 g / L.

[0048] Example 1

[0049] A process for nitrogen and phosphorus removal by combining a stepped power supply with a series of stabilization ponds based on the above device specifically includes the following steps:

[0050] (1) Use actual domestic sewage as the raw water, and the specific water quality is as follows: COD = 350 - 750 mg / L, NH4 + -N = 30 - 60 mg / L, TN = 30 - 65 mg / L, TP = 4 - 6 mg / L, C / N is about 12, and the salt content is about 20000 mg / L;

[0051] Introduce the raw water into the electrolytic cell (1), and at the same time turn on the power supply (current density is 100 mA / cm 2 , the first echelon current) for electrolysis; when the chloride ion content in the sewage is reduced to less than 200 mg / L, the power supply is switched to a low current density of 0.5 mA / cm2 (Second echelon current), the diversion device is opened, and the sewage enters the aerobic pond (2);

[0052] (2) After the organic matter in the sewage is degraded and nitrification reaction occurs in the ecological floating bed in the aerobic pond (2) (the hydraulic retention time of the sewage in the aerobic pond (2) is 4 d, and the temperature is controlled at 25-28 °C), it then flows out from the bottom of the aerobic pond (2) and flows to the facultative pond (4); among them, the sign of the successful start of the aerobic pond (2) is that the COD of the system effluent < 30 mg / L, NH4 + -N < 5 mg / L, TP < 0.5 mg / L;

[0053] (3) The hydraulic retention time of the sewage in the facultative pond (4) is 7 d, and the temperature is controlled at 25-28 °C; the bottom effluent of the aerobic pond undergoes denitrification and phosphorus removal under the action of the suspended packing (18), and the effluent reaches the water quality discharge standard. Finally, it is filtered through the kapok biochar (16) and discharged from the discharge port, and 15-20% of the effluent is continuously recycled to the electrolytic cell (1). The final effluent COD < 30 mg / L, NH 4+ -N < 1.5 mg / L, TN < 1.5 mg / L, TP < 0.3 mg / L, and the effluent meets the Class IV water body standard.

[0054] Example 2

[0055] This example is basically the same as Example 1, the difference is that the specific water quality of the raw water is as follows: COD = 800-1000 mg / L, NH4 + -N = 50-70 mg / L, TP = 6-8 mg / L, TN = 50-75 mg / L, C / N is about 15, and the salt content is about 16000 mg / L; the hydraulic retention time of the aerobic pond is 5 d, and the hydraulic retention time of the facultative pond is 8 d, and the temperature is controlled at 28-30 °C.

[0056] The final effluent COD of Example 2 is 25-30 mg / L, TP ≤ 0.3 mg / L, NH4 + -N ≤ 1.5 mg / L, TN ≤ 1.5 mg / L, and the effluent meets the Class IV water body standard.

[0057] Example 3

[0058] This example is basically the same as Example 1, the difference is that the specific water quality of the raw water is as follows: COD = 150-400 mg / L, NH4 + -N = 15-40 mg / L, TP = 3-4 mg / L, TN = 15-45 mg / L, C / N is about 10, and the salt content is about 12000 mg / L; the hydraulic retention time of the aerobic pond is 3 d, and the hydraulic retention time of the facultative pond is 6 d, and the temperature is controlled at 23-26 °C.

[0059] In Example 3, the final effluent COD is 20 - 25 mg / L, TP ≤ 0.3 mg / L, NH4 + -N ≤ 1.5 mg / L, TN ≤ 1.5 mg / L, and the effluent meets the Class-IV water body standard.

[0060] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several improvements and modifications can be made, and these all belong to the protection scope of the present invention.

Claims

1. A process for nitrogen and phosphorus removal by combining a stepped power supply with a series of stabilization ponds, characterized in that It includes the following steps: (1) Feed the sewage to be treated into the electrolytic cell for electrolysis of sodium chloride. The external power supply of the electrolytic cell is a stepped power supply. Among them, when the chloride ion concentration in the electrolytic cell ≥ 200 mg / L, the current density adopts the first step of 80 - 120 mA / cm 2 for electrolysis of sodium chloride. When the chloride ion concentration < 200 mg / L, the current density adopts the second step of 0.4 - 0.6 mA / cm 2 ; The C / N molar ratio of the sewage to be treated is 10 - 15, the influent salt content is 12000mg / L - 20000mg / L, and the salt is mainly NaCl. (2) After the sewage in step (1) is electrolyzed until the chloride ion content is reduced to less than 200 mg / L, it is sent to the aerobic pond through a diversion device. An ecological floating bed is provided in the aerobic pond, and nitrifying bacteria and Pediastrum are added. After the degradation of organic matter and nitrification reaction are carried out in the aerobic pond, the bottom effluent of the aerobic pond meets the requirements of COD ≤ 30 mg / L, NH4 + -N ≤ 5 mg / L, and TP ≤ 0.5 mg / L; (3) The bottom effluent of the aerobic pond enters the facultative pond, where denitrification reaction for nitrogen removal and phosphorus removal is carried out using bacteria, algae and suspended fillers, and it is divided into two parts: clear water and sludge. (4) The clear water is further filtered through biochar to obtain purified water. Part of the purified water is refluxed to the electrolytic cell, and the remaining purified water is directly discharged. (5) The sludge is concentrated in the digestion pit at the bottom of the facultative pond. The bacteria and algae used in the facultative pond are denitrifying polyphosphate-accumulating organisms and oil-producing microalgae. The effluent of the facultative pond meets the standards of COD ≤ 30 mg / L, NH4 + -N ≤ 1.5 mg / L, TN ≤ 1.5 mg / L, and TP ≤ 0.3 mg / L.

2. The process for nitrogen and phosphorus removal by combining a stepped power supply with a series of stabilization ponds according to claim 1, characterized in that The sewage to be treated is domestic sewage, and its water quality is as follows: COD = 100 - 1500 mg / L, NH4 + -N concentration is 10 - 100 mg / L, TP = 1 - 10 mg / L, TN = 10 - 100 mg / L.

3. The process for nitrogen and phosphorus removal by combining a stepped power supply with a series of stabilization ponds according to claim 1, characterized in that The hydraulic retention time of the aerobic pond is 3 - 5 days, and the hydraulic retention time of the facultative pond is 6 - 8 days.

4. The device for nitrogen and phosphorus removal by using a stepped power supply combined with a series of stabilization ponds in the process described in claim 1, comprising an electrolytic cell, an aerobic pond and a facultative pond, characterized in that The electrolytic cell is connected to the inlet of the aerobic pond through a diversion device, and the outlet of the aerobic pond is connected to the inlet below the facultative pond through a pump. A chlorine ion detector, an anode and a cathode are arranged in the electrolytic cell; the anode and the cathode are respectively connected to the positive electrode and the negative electrode of a stepped power supply arranged outside the electrolytic cell; the chlorine ion detector is equipped with a sensor for transmitting the chlorine ion content to the controller to realize the adjustment of the stepped power supply. An ecological floating bed is arranged in the aerobic pond. The ecological floating bed includes a three-dimensional packing layer and a ceramsite layer from bottom to top, and aquatic plants grow on the ceramsite layer; moreover, the three-dimensional packing layer of the ecological floating bed is used to adsorb nitrifying bacteria and Pediastrum. A digestion pit is arranged at the bottom of the facultative pond, and an outlet communicating with the outside and a reflux port communicating with the electrolytic cell are arranged above; a suspended filler and an activated carbon filter layer fixed on the upper part of the facultative pond are arranged inside the facultative pond, and a stirring device is arranged for internal stirring; moreover, the suspended filler is used to adsorb denitrifying phosphorus-accumulating bacteria and oleaginous microalgae.

5. The device for denitrification and phosphorus removal by combining a stepped power supply with a series of stabilization ponds according to claim 4, characterized in that The anode is a conductive carbon nanotube, and the cathode is a stainless steel cathode plate; the external power supply device of the electrolytic cell is a stepped power supply, and the current density is switched in real time according to the concentration of chlorine ions in the electrolytic cell.

6. The device for denitrification and phosphorus removal by combining a stepped power supply with a series of stabilization ponds according to claim 4, wherein The three-dimensional packing layer of the biological floating bed uses acetate fiber, and the filling rate of the three-dimensional packing layer in the biological floating bed is 70% - 80%. The coverage area of the aquatic plants growing above the ceramsite layer accounts for 60% - 70% of the aerobic pond; the suspended filler of the facultative pond uses polyurethane, and the filling rate is 30 - 50%.

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