Device and method for solving hydrogen sulfide generation in sulfur autotrophic denitrification nitrogen removal system

Abstract

The present invention relates to a device and method for solving the problem of hydrogen sulfide generation in a sulfur autotrophic denitrification nitrogen removal system, belonging to the technical field of sewage treatment. The device of the present invention includes a reactor, a water inlet pipe, a water inlet pump, a PLC control cabinet, a nitrate probe, a dissolved oxygen probe, a blower, a solenoid valve, an air pipe, and a water outlet pipe; on the one hand, when there is a small amount of oxygen, hydrogen sulfide reacts with oxygen to generate elemental sulfur, and on the other hand, the elemental sulfur is used as the electron donor required for sulfur autotrophic denitrification nitrogen removal, realizing resource recovery while removing hydrogen sulfide; on the other hand, the environment of the sulfur autotrophic denitrification nitrogen removal system is changed from an anoxic environment to an aerobic environment, which has a certain inhibitory effect on the sulfur autotrophic denitrification nitrogen removal effect, making it impossible to completely remove the nitrate carried in the sewage, leaving a certain amount of nitrate in the sulfur autotrophic denitrification nitrogen removal system. Furthermore, the remaining nitrate will react with hydrogen sulfide to generate N2, thus fundamentally solving the problem of hydrogen sulfide generation.

Description

Technical Field

[0001] The present invention relates to a device and method for solving the generation of hydrogen sulfide in a sulfur autotrophic denitrification nitrogen removal system, belonging to the technical field of sewage treatment. Background Art

[0002] Currently, most scientific research and engineering applications utilize the sulfur autotrophic denitrification nitrogen removal technology for advanced sewage denitrification. The sulfur autotrophic denitrification nitrogen removal technology uses reduced sulfur sources such as sodium sulfide (Na2S), sodium thiosulfate (Na2S2O3), and elemental sulfur (S) as electron donors, and CO3 2- , HCO3 - , CO2 as inorganic carbon sources, and reduces NO3 - -N to N2 in an anoxic environment, which is a new type of autotrophic denitrification technology. During operation, no carbon source needs to be added, and it has the characteristics of high denitrification efficiency, avoiding secondary pollution of COD, and low operating cost. However, there are still the following problems:

[0003] During the sulfur autotrophic denitrification nitrogen removal process, by-products such as sulfides and sulfates will be generated. Among them, sulfides include hydrogen sulfide, bisulfide ions, sulfide ions, etc. If the sewage contains NO3 - -N, then NO3 - -N will further react with sulfides such as hydrogen sulfide, bisulfide ions, and sulfide ions to generate N2, thereby inhibiting the generation of hydrogen sulfide. However, when the NO3 - -N concentration is as low as 0 mg / L, sulfides such as hydrogen sulfide, bisulfide ions, and sulfide ions will combine with H + to form H2S, and H2S will escape from the water into the air, forming a malodorous pollution.

[0004] Hydrogen sulfide (H2S) has a strong rotten egg odor, which not only directly endangers human health but also corrodes equipment, pipelines, and instruments in sewage. Therefore, related research on solving the generation of hydrogen sulfide in the sulfur autotrophic denitrification nitrogen removal system has attracted much attention. However, the existing methods mainly collect the generated hydrogen sulfide gas and remove it through methods such as adsorption, neutralization, and oxidation in a deodorization device, which have problems such as large investment, high cost, and secondary pollution. More importantly, there is no device and method for inhibiting the generation of hydrogen sulfide in the sulfur autotrophic denitrification nitrogen removal system from the source. Summary of the Invention

[0005] To solve the above problems, the present invention first provides a device for solving the generation of hydrogen sulfide in a sulfur autotrophic denitrification nitrogen removal system, including a reactor, a water inlet pipe, a water inlet pump, a PLC control cabinet, a nitrate probe, a dissolved oxygen probe, a blower, a solenoid valve, an air pipeline, and a water outlet pipe;

[0006] The reactor is a columnar container. Preferably, it can be a cylindrical container or a quadrangular prism container. The blower is connected to the PLC control cabinet. The PLC control cabinet is connected to a nitrate probe and a dissolved oxygen probe by signal lines. Both the nitrate probe and the dissolved oxygen probe extend into the reactor from the top of the reactor.

[0007] It should be understood that both the blower and the PLC control cabinet are located outside the reactor. Preferably, the nitrate probe and the dissolved oxygen probe can be suspended inside the reactor through signal lines. The nitrate probe and the dissolved oxygen probe are probes for measuring the nitrate concentration and the dissolved oxygen concentration inside the reactor respectively.

[0008] One end of the air pipeline is connected to the blower, and the other end passes through the inner wall of the reactor and extends into the reactor. A plurality of air distribution pipes are symmetrically arranged on both sides of the air pipeline. Each air distribution pipe is provided with one or more air distribution nozzles facing the bottom of the reactor. The solenoid valve is arranged on the air pipeline and is located outside the reactor. The solenoid valve is connected to the PLC control cabinet. The reason for selecting the solenoid valve is to realize the automatic control of the solenoid valve by the PLC. The water inlet pipe is provided with a water inlet pump, a sulfur dosing pump, and an alkalinity dosing pump.

[0009] In the present invention, the bottom of the reactor is the part with the minimum height of the reactor from the ground, and the top of the reactor is the part with the maximum height of the reactor from the ground.

[0010] It should be understood that the air pipeline can be any common pipeline for passing air. The two sides of the air pipeline refer to the two sides perpendicular to the air inlet direction. The air distribution pipes are symmetrically arranged on both sides of the air pipeline with the air pipeline as the axis of symmetry. Both the air distribution pipes and the air distribution nozzles are pipe fittings with lengths less than that of the air pipeline and are both connected to the air pipeline. The solenoid valve is used to isolate the inside of the reactor from the outside when the blower is in the closed state, preventing the sewage inside the reactor from leaking through the air pipeline.

[0011] Inside the reactor, the air pipeline, the air distribution pipes, and the air distribution nozzles are all located in the height space of 1 / 20 - 1 / 15 of the reactor height, and the nitrate probe and the dissolved oxygen probe are both located in the height space greater than 1 / 2 of the reactor height.

[0012] In the present invention, the height of the reactor refers to the vertical distance from the top of the reactor to the bottom of the reactor. The height space refers to the vertical cylindrical space formed within a specific proportion of the height range inside the reactor. Preferably, the air pipeline, the air distribution pipes, and the air distribution nozzles are located in the height space of 1 / 20 - 1 / 15 of the reactor height. Preferably, the nitrate probe and the dissolved oxygen probe are both located at the position of 3 / 4 of the reactor height.

[0013] The height space between the air duct and the bottom of the reactor is communicated with the water inlet pipe, and a solenoid valve is arranged on the air duct; the height space between the nitrate probe, the dissolved oxygen probe and the top is communicated with the water outlet pipe.

[0014] The present invention also provides a method for using a device based on solving the generation of hydrogen sulfide in a sulfur autotrophic denitrification nitrogen removal system, including the following steps:

[0015] Step 1: The sewage containing nitrate, sulfur and sodium bicarbonate alkalinity substances are respectively introduced into the reactor by a water inlet pump, a sulfur dosing pump and an alkalinity dosing pump to carry out sulfur autotrophic denitrification nitrogen removal reaction;

[0016] Theoretically, during the sulfur autotrophic denitrification nitrogen removal reaction process, microorganisms in the reactor use elemental sulfur as an electron donor and sodium bicarbonate alkalinity substances as an inorganic carbon source to reduce NO3 - -N to N2 in an anoxic environment, and nitrate will be gradually removed. In this process, by-products such as sulfide and sulfate will be generated. Among them, sulfide includes hydrogen sulfide, bisulfide ion, sulfide ion, etc. The nitrate contained in the sewage will further react with sulfide to generate N2, thereby inhibiting the generation of hydrogen sulfide.

[0017] The nitrate concentration in the sewage in the reactor is monitored in real time through a nitrate probe. When it is monitored that the nitrate concentration drops to 0 mg / L, the sewage will not contain nitrate and cannot further react with sulfide to generate N2. At this time, the sulfide in the sewage in the reactor will combine with H + in the sewage to form hydrogen sulfide; to solve the generation of hydrogen sulfide in the sewage in the reactor, the solenoid valve and the blower are sequentially opened through the PLC control cabinet, and air is introduced into the reactor through the air duct, so that the hydrogen sulfide in the reactor reacts with the oxygen in the air to generate elemental sulfur and water, thereby the hydrogen sulfide is initially removed; such a practice not only solves the problem of hydrogen sulfide already generated in the sewage, but also generates elemental sulfur, which can be used as an electron donor required for sulfur autotrophic denitrification nitrogen removal, realizing resource recovery and reuse;

[0018] At the same time, with the introduction of air, the anoxic environment (i.e., the dissolved oxygen concentration is 0) in the reactor becomes a facultative anoxic environment (i.e., the dissolved oxygen concentration ranges from 0 to 0.5 mg / L and is not 0). The facultative anoxic environment has a certain inhibitory effect on the anoxic denitrification effect of sulfur autotrophic denitrification, making the nitrate in the sewage unable to be completely removed and the nitrate concentration gradually rising. The gradually rising nitrate reacts with hydrogen sulfide to generate N2, realizing the further removal of hydrogen sulfide.

[0019] Considering not to damage the anoxic denitrification effect of sulfur autotrophic denitrification during the process of solving the problem of hydrogen sulfide generation in the sulfur autotrophic denitrification nitrogen removal system, the following steps are further designed. On the one hand, monitor that the dissolved oxygen concentration is not higher than 0.5 mg / L to ensure that the inside of the reactor will not become an aerobic environment (i.e., the dissolved oxygen concentration is greater than 0.5 mg / L), which is convenient for the rapid recovery of the anoxic environment and the sulfur autotrophic denitrification nitrogen removal effect in the reactor after the blower and solenoid valve are closed; on the other hand, monitor that the nitrate concentration is not higher than 4 mg / L to ensure that the nitrate concentration in the reactor effluent is at a low level and achieve deep sewage denitrification.

[0020] Step 2: As air continues to be introduced, when the PLC control cabinet monitors that the dissolved oxygen concentration is higher than 0.5 mg / L or the nitrate concentration is higher than 4 mg / L, the blower and solenoid valve are closed. Then, the dissolved oxygen concentration in the sewage in the reactor begins to decrease. When the PLC control cabinet monitors that the dissolved oxygen concentration reaches 0 mg / L, the environment in the reactor changes from a facultative anaerobic environment to an anoxic environment, and the sulfur autotrophic denitrification nitrogen removal reaction begins. The nitrate continues to be consumed and thus the concentration decreases. The microorganisms in the reactor use elemental sulfur as the electron donor and alkalinity as the inorganic carbon source to reduce NO3 - -N in the sewage to N2 under an anoxic environment;

[0021] Step 3: As the sulfur autotrophic denitrification nitrogen removal reaction in the reactor proceeds, the PLC control cabinet monitors the nitrate concentration in real time. When it monitors that the nitrate concentration in the sewage in the reactor is lower than 2 mg / L, the solenoid valve and blower are reopened;

[0022] Step 4: As air is introduced, due to the certain inhibitory effect on the sulfur autotrophic anoxic denitrification effect and the continuous entry of sewage into the reactor through the feed pump, the nitrate concentration in the sewage in the reactor will gradually increase; when the PLC control cabinet monitors again that the dissolved oxygen concentration is higher than 0.5 mg / L or the nitrate concentration is higher than 4 mg / L, the solenoid valve and blower are closed in sequence, and Steps 2 to 3 are repeated, so as to always maintain the nitrate concentration above 2 mg / L and ensure that there is always NO3 - -N in the reactor, which will further react with sulfides such as hydrogen sulfide, bisulfide ions, and sulfide ions to generate N2, thus solving and avoiding the generation of hydrogen sulfide.

[0023] The beneficial effects of the present invention:

[0024] 1. The present invention utilizes the principle that when there is a small amount of oxygen, hydrogen sulfide reacts with oxygen to generate elemental sulfur and water, which not only solves the problem of hydrogen sulfide already generated in the sewage, but also generates elemental sulfur, which can be used as the electron donor required for sulfur autotrophic denitrification nitrogen removal and realizes resource recovery.

[0025] 2. The present invention utilizes the principle that when a small amount of oxygen is present, the environment of the sulfur autotrophic denitrification system can be changed from an anoxic environment to an aerobic environment, thereby inhibiting the sulfur autotrophic denitrification effect, preventing the complete removal of nitrates carried in the sewage, leaving a certain amount of nitrates in the sulfur autotrophic denitrification system. Subsequently, the remaining nitrates react further with hydrogen sulfide to generate N2, thus fundamentally solving the problem of hydrogen sulfide generation. At the same time, the effect of deep denitrification is also ensured.

[0026] 3. The device of the present invention is equipped with nitrate, dissolved oxygen monitoring instruments and a PLC control cabinet. According to the nitrate concentration and dissolved oxygen concentration, the PLC starts and stops the blower and solenoid valve in real time, with the advantages of real-time monitoring and automatic control, ensuring that there will be no problem of hydrogen sulfide generation.

[0027] 4. The device of the present invention and its usage method fundamentally solve the problem of hydrogen sulfide generation in the sulfur autotrophic denitrification system, eliminating the need to add a deodorization device as in traditional methods. It not only realizes resource recycling and reuse but also does not cause malodorous pollution to the air. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the front view of the overall structure in an embodiment of the present invention.

[0029] Figure 2 It is the top view of the air distribution pipe structure in a reactor in an embodiment of the present invention.

[0030] Figure 3 It is the top view of the air distribution pipe structure in another reactor in an embodiment of the present invention.

[0031] In the figure, 1. Reactor, 2. Inlet pipe, 3. Inlet water pump, 4. Blower, 5. Air pipe, 6. Solenoid valve, 7. Air distribution pipe, 8. Air diffuser pipe, 9. Nitrate probe, 10. Dissolved oxygen probe, 11. Signal line, 12. PLC control cabinet, 13. Outlet pipe, 14. Sulfur dosing pump, 15. Alkalinity dosing pump. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Example 1

[0033] As Figure 1 shown, the present invention first provides a device for solving the problem of hydrogen sulfide generation in the sulfur autotrophic denitrification system, including a reactor 1, an inlet pipe 2, an inlet water pump 3, a blower 4, an air pipe 5, a solenoid valve 6, an air distribution pipe 7, an air diffuser pipe 8, a nitrate probe 9, a dissolved oxygen probe 10, a signal line 11, a PLC control cabinet 12, an outlet pipe 13, a sulfur dosing pump 14, and an alkalinity dosing pump 15.

[0034] The blower 4 is connected to the PLC control cabinet 12. The PLC control cabinet 12 is connected to the nitrate probe 9 and the dissolved oxygen probe 10 by two signal lines 11. Both the nitrate probe 9 and the dissolved oxygen probe 10 extend into the reactor 1 from the top of the reactor 1.

[0035] As Figure 2 , Figure 3 shown, the reactor 1 can be a cylindrical container or a quadrangular prism container; one end of the air duct 5 is connected to the blower 4, and the other end passes through the inner wall of the reactor 1 and extends into the reactor 1. A plurality of air distribution pipes 7 are symmetrically arranged on both sides of the air duct 5, and each air distribution pipe 7 is provided with a plurality of air distribution pipes 8 facing the bottom of the reactor; the solenoid valve 6 is arranged on the air duct 5 and is located outside the reactor 1, and the solenoid valve 6 is connected to the PLC control cabinet 12.

[0036] Inside the reactor 1, the air duct 5 and the air distribution pipe 7 are both located at the position of 1 / 10 of the reactor height, and the air distribution pipe 8 is located in the height space of 1 / 20 - 1 / 15 of the reactor height; the nitrate probe 9 and the dissolved oxygen probe 10 are both located at the position of 3 / 4 of the reactor height.

[0037] The height space between the air duct 5 and the bottom of the reactor 1 is communicated with the water inlet pipe 2, and a water inlet pump 3 is arranged on the air duct 5; the height space between the nitrate probe 9, the dissolved oxygen probe 10 and the top opening is communicated with the water outlet pipe 13.

[0038] The water inlet pipe 2 is provided with a water inlet pump 3, a sulfur dosing pump 14, and an alkalinity dosing pump 15.

[0039] Example 2

[0040] The present invention also provides a method for using a device based on solving hydrogen sulfide generation in a sulfur autotrophic denitrification nitrogen removal system, including the following steps:

[0041] Step 1: The water inlet pump 3, the sulfur dosing pump 14, and the alkalinity dosing pump 15 respectively introduce sewage containing nitrate, sulfur, and sodium bicarbonate alkalinity substances into the reactor 1 to carry out sulfur autotrophic denitrification nitrogen removal reaction;

[0042] Theoretically, during the sulfur autotrophic denitrification nitrogen removal reaction, the microorganisms in the reactor 1 use elemental sulfur as an electron donor and sodium bicarbonate alkalinity substances as an inorganic carbon source to reduce NO3 - -N to N2 in an anoxic environment, and the nitrate will be gradually removed. In this process, by-products such as sulfide and sulfate will be generated. The sulfide includes hydrogen sulfide, bisulfide ion, sulfide ion, etc. The nitrate in the sewage further reacts with the sulfide to generate N2.

[0043] The nitrate concentration in the sewage in the reactor 1 is monitored in real time by the nitrate probe 9. When the monitored nitrate concentration drops to 0 mg / L, the sulfide in the sewage in the reactor 1 combines with H + to form hydrogen sulfide; to solve the generation of hydrogen sulfide in the sewage in the reactor 1, the solenoid valve 6 and the blower 4 are sequentially opened under the control of the PLC control cabinet 12, and air is introduced into the reactor 1 through the air pipeline 5, so that the hydrogen sulfide in the reactor 1 reacts with the oxygen in the air to generate elemental sulfur and water, thereby the hydrogen sulfide is preliminarily removed; such a practice not only solves the problem of the generated hydrogen sulfide in the sewage, but also generates elemental sulfur, which can be used as an electron donor required for sulfur autotrophic denitrification and nitrogen removal, realizing resource recovery and reuse;

[0044] At the same time, with the introduction of air, the environment in the reactor 1 changes from an anoxic environment (i.e., the dissolved oxygen concentration is 0) to a facultative anoxic environment (i.e., the dissolved oxygen concentration is within the range of 0 - 0.5 mg / L and non-zero). The facultative anoxic environment has a certain inhibitory effect on the sulfur autotrophic denitrification and anoxic nitrogen removal effect, making the nitrate in the sewage unable to be completely removed and the nitrate concentration gradually rise. The residual nitrate reacts with hydrogen sulfide to generate N2, realizing the further removal of hydrogen sulfide.

[0045] Considering not to damage the sulfur autotrophic denitrification and anoxic nitrogen removal effect during the process of solving the problem of hydrogen sulfide generation in the sulfur autotrophic denitrification and nitrogen removal system, the following steps are further designed. On the one hand, monitor the dissolved oxygen concentration not higher than 0.5 mg / L to ensure that the inside of the reactor 1 becomes an aerobic environment, which is convenient for the rapid recovery of the anoxic environment and the sulfur autotrophic denitrification and nitrogen removal effect in the reactor 1 after the blower 4 and the solenoid valve 6 are closed; on the other hand, monitor the nitrate concentration not higher than 4 mg / L to ensure that the nitrate concentration in the effluent of the reactor 1 is at a low level, realizing the deep denitrification of the sewage.

[0046] Step 2: With the continuous introduction of air, when the PLC control cabinet 12 monitors that the dissolved oxygen concentration is higher than 0.5 mg / L or the nitrate concentration is higher than 4 mg / L, the blower 4 and the solenoid valve 6 are closed. Then, the dissolved oxygen concentration in the sewage in the reactor 1 begins to decrease. When the PLC control cabinet 12 monitors that the dissolved oxygen concentration reaches 0 mg / L, the environment in the reactor 1 changes from a facultative anoxic environment to an anoxic environment, and the sulfur autotrophic denitrification and nitrogen removal reaction starts. The nitrate continues to be consumed and thus the concentration decreases. The microorganisms in the reactor 1 use elemental sulfur as an electron donor and alkalinity as an inorganic carbon source to reduce NO3--N in the sewage to N2 under an anoxic environment;

[0047] Step 3: With the progress of the sulfur autotrophic denitrification and nitrogen removal reaction in the reactor 1, the PLC control cabinet 12 monitors the nitrate concentration in real time. When it is monitored that the nitrate concentration in the sewage in the reactor 1 is lower than 2 mg / L, the solenoid valve 6 and the blower 4 are reopened;

[0048] Step 4: With the introduction of air, since the anoxic denitrification effect of sulfur autotrophic denitrification is inhibited to a certain extent and sewage continuously enters the reactor 1 through the feed water pump, the nitrate concentration in the sewage in the reactor 1 will gradually increase; when the PLC control cabinet 12 monitors again that the dissolved oxygen concentration is higher than 0.5 mg / L or the nitrate concentration is higher than 4 mg / L, the solenoid valve 6 and the blower 4 are closed in sequence, and steps two to three are repeated, so as to always maintain the nitrate concentration above 2 mg / L, ensure that there is always NO3--N in the reactor 1, and will further react with sulfides such as hydrogen sulfide, bisulfide ions, and sulfide ions to generate N2, thereby solving and avoiding the generation of hydrogen sulfide.

[0049] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A method for solving the problem of hydrogen sulfide generation in a sulfur autotrophic denitrification nitrogen removal system, characterized in that the device used in the method includes a reactor, a water inlet pipe, a water inlet pump, a PLC control cabinet, a nitrate probe, a dissolved oxygen probe, a blower, a solenoid valve, an air pipe and a water outlet pipe; the reactor is a cylindrical container; the blower is connected to the PLC control cabinet, the PLC control cabinet is connected to the nitrate probe and the dissolved oxygen probe by signal lines, and both the nitrate probe and the dissolved oxygen probe extend into the reactor from the top of the reactor; one end of the air pipe is connected to the blower, and the other end passes through the inner wall of the reactor and extends into the reactor. A plurality of air distribution pipes are symmetrically arranged on both sides of the air pipe, and each air distribution pipe is provided with one or more air distribution pipes facing the bottom of the reactor; the solenoid valve is arranged on the air pipe and is located outside the reactor, and the solenoid valve is connected to the PLC control cabinet by a signal line; inside the reactor, the air pipe, the air distribution pipe and the air distribution pipe are all located in the height space of 1 / 20 - 1 / 15 of the reactor height, and both the nitrate probe and the dissolved oxygen probe are located in the height space greater than 1 / 2 of the reactor height; the height space between the air pipe and the bottom of the reactor is communicated with the water inlet pipe, and a solenoid valve is arranged on the air pipe; the height space between the nitrate probe, the dissolved oxygen probe and the top is communicated with the water outlet pipe; a water inlet pump, a sulfur dosing pump and an alkalinity dosing pump are arranged on the water inlet pipe; the method includes the following steps: Step 1: The water inlet pump, the sulfur dosing pump, and the alkalinity dosing pump respectively introduce sewage containing nitrate, sulfur, and sodium bicarbonate alkalinity substances into the reactor for sulfur autotrophic denitrification nitrogen removal reaction; the nitrate concentration in the sewage in the reactor is monitored in real time through the nitrate probe. When the monitored nitrate concentration drops to 0 mg / L, the sulfide in the sewage in the reactor combines with H+ to form hydrogen sulfide; the solenoid valve and the blower are controlled to be opened in sequence through the PLC control cabinet, and air is introduced into the reactor through the air pipe, so that the hydrogen sulfide in the reactor reacts with the oxygen in the air to generate elemental sulfur and water, thereby the hydrogen sulfide is initially removed; Step 2: With the continuous introduction of air, when the PLC control cabinet monitors that the dissolved oxygen concentration is higher than 0.5 mg / L or the nitrate concentration is higher than 4 mg / L, the blower and solenoid valve are closed; when the PLC control cabinet monitors that the dissolved oxygen concentration reaches 0 mg / L, the environment in the reactor changes from an anoxic-aerobic environment to an anoxic environment, and the sulfur autotrophic denitrification nitrogen removal reaction begins. The nitrate continues to be consumed and thus the concentration decreases. The microorganisms in the reactor use elemental sulfur as the electron donor and alkalinity as the inorganic carbon source to reduce NO3 - -N in the sewage to N2 under an anoxic environment; Step 3: As the sulfur autotrophic denitrification nitrogen removal reaction in the reactor proceeds, the PLC control cabinet monitors the nitrate concentration in real time. When the monitored nitrate concentration in the sewage in the reactor is lower than 2 mg / L, the solenoid valve and the blower are reopened; Step 4: When the PLC control cabinet monitors again that the dissolved oxygen concentration is higher than 0.5 mg / L or the nitrate concentration is higher than 4 mg / L, the solenoid valve and the blower are closed in sequence, and Steps 2 to 3 are repeated.

2. The method according to claim 1, wherein The reactor is a cylindrical container.

3. The method according to claim 1, characterized in that, The reactor is a quadrangular prism container.

4. The method according to claim 1, wherein Both the nitrate probe and the dissolved oxygen probe are located at the position of 3 / 4 of the reactor height.

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