A system and process for deep denitrification of sewage by anaerobic ammonium oxidation coupled with endogenous denitrification

Abstract

The present invention provides an anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification system and process. The system mainly includes a front anaerobic ammonia oxidation unit and a rear endogenous denitrification unit. The effluent from the water quality regulating tank first enters the anaerobic tank to absorb the internal carbon source; then the effluent enters the anaerobic ammonia oxidation unit to perform anaerobic ammonia oxidation to achieve preliminary denitrification. Then the sewage enters the rear endogenous denitrification unit, and in the dynamic aerobic tank, with the cooperation of detection instruments and control equipment, dynamic and precise nitrification is performed, and then the rear endogenous denitrification is performed in the anoxic tank, so as to achieve deep denitrification. The system and process solve the problem of poor denitrification effect or low denitrification efficiency of the traditional single anaerobic ammonia oxidation process or AOA process, and realizes the simultaneous improvement of denitrification efficiency and effect.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to an anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification system and process. Background Art

[0002] At present, in addition to the mainstream denitrification process, the newer biological denitrification processes mainly include anaerobic ammonium oxidation process and endogenous denitrification process. The anaerobic ammonium oxidation process is an autotrophic denitrification process. The biggest advantage is that it does not require a carbon source and only requires half of the nitrification, saving aeration time, but the disadvantage is that anaerobic ammonium oxidizing bacteria have strict requirements on the environment, including dissolved oxygen concentration, organic matter concentration and the ratio of ammonia nitrogen and nitrite nitrogen. These factors lead to a low total nitrogen removal rate in the anaerobic ammonium oxidation process, and the effluent needs further treatment. The endogenous denitrification process uses the characteristic that denitrifying bacteria can store internal carbon sources. By setting up special functional areas, this characteristic is strengthened to achieve deep denitrification of sewage. The biggest advantage of this process is that the denitrification effect is good, which can reach more than 98%, but the disadvantage is that the denitrification rate is relatively low, so the residence time required by the system is also relatively long.

[0003] Therefore, it is necessary to develop a deep denitrification system and process for wastewater that can not only deeply denitrify, but also achieve high-efficiency denitrification anaerobic ammonia oxidation coupled with endogenous denitrification. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides an anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification system and process, which can improve the total nitrogen and ammonia nitrogen removal rates and ensure that the total nitrogen and ammonia nitrogen in the effluent are stable and meet the standards; at the same time, it can solve the problem of low denitrification efficiency of a single endogenous denitrification system and process, and also reduce the denitrification treatment cost as a whole. The specific technical scheme is as follows:

[0005] The present invention first provides an anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification system, comprising a water quality regulating tank, an anaerobic tank, an anaerobic ammonia oxidation tank, a plurality of dynamic aerobic tanks, a plurality of anoxic tanks, a secondary sedimentation tank and a sludge concentration tank;

[0006] The water quality regulating tank, the anaerobic tank, the anaerobic ammonia oxidation tank, the plurality of dynamic aerobic tanks, the plurality of anoxic tanks, the secondary sedimentation tank and the sludge concentration tank are sequentially connected through pipelines, a sludge return pipe is connected between the front end of the secondary sedimentation tank and the anaerobic tank, and a sludge pump is arranged on the sludge return pipe;

[0007] The anaerobic tank and the anoxic tank are both equipped with agitators, and the anaerobic ammonia oxidation tank and the dynamic aerobic tank are both equipped with aeration devices and agitators.

[0008] In some specific embodiments of the present invention, the anaerobic ammonium oxidation tank is provided with a filler to which anaerobic ammonium oxidizing bacteria are attached.

[0009] In some specific embodiments of the present invention, the anaerobic ammonia oxidation tank is provided with a DO detector, and the dynamic aerobic tank is provided with a PH detector and a DO detector.

[0010] In some specific embodiments of the present invention, a PLC controller is further included, and the PLC controller is communicatively connected with the pH detector, the DO detector, the aeration equipment and the agitator respectively.

[0011] The present invention also provides a process for deep denitrification of sewage by anaerobic ammonium oxidation coupled with endogenous denitrification, comprising the following process steps:

[0012] (1) After being treated in the water quality regulating tank, the sewage enters the anaerobic tank and only needs to be stirred. The retention time is T1 hours;

[0013] (2) The effluent from the anaerobic tank enters the anaerobic ammonia oxidation tank, aerated and stirred, and the dissolved oxygen is controlled at 0.7 mg / L-1.3 mg / L. The residence time is T2 hours, and then the effluent from the anaerobic tank enters the dynamic aerobic tank;

[0014] (4) After the effluent from the anaerobic tank enters several dynamic aerobic tanks, the retention time of each dynamic aerobic tank is T3 hours. Nitrification is carried out under the action of stirring and aeration to degrade ammonia nitrogen and remaining organic matter in the sewage. When it is detected that the dissolved oxygen in one of the dynamic aerobic tanks is still higher than 4 mg / L when the aeration volume is lower than 30% of the normal aeration volume, and the pH value rises at this time, the aeration of this dynamic aerobic tank and the subsequent dynamic aerobic tanks are automatically turned off and become anoxic tanks. Only the agitator of the anoxic tank is turned on;

[0015] (5) Sewage entering the anoxic tank, the total residence time in the anoxic tank is T4 hours, and denitrification is achieved through endogenous denitrification by denitrifying bacteria;

[0016] (6) After the sewage in the anoxic tank is discharged, it enters the secondary sedimentation tank to achieve mud and water separation. The sludge is pumped to the front end of the anaerobic tank through the sludge pump, the supernatant is discharged, and the biological sludge is discharged into the sludge thickening tank.

[0017] In some specific embodiments of the present invention, T1=total nitrogen concentration in sewage (mg / L)×0.02; T2=total nitrogen concentration in sewage (mg / L)×0.04.

[0018] In some specific embodiments of the present invention, T2=total nitrogen concentration in sewage (mg / L)×a, where a=0.03-0.06; T3=total nitrogen concentration in sewage (mg / L)×b, where b=0.03-0.06.

[0019] In some specific embodiments of the present invention, T2+T3=total nitrogen concentration in sewage (mg / L)×0.09.

[0020] In some specific embodiments of the present invention, the dissolved oxygen concentration during aeration of the dynamic aerobic tank is controlled at 2 mg / L-4 mg / L.

[0021] In some specific embodiments of the present invention, the carbon-nitrogen ratio is adjusted in the water quality regulating tank so that the carbon-nitrogen ratio of the anaerobic tank influent is 4-5.

[0022] In some specific embodiments of the present invention, the sludge return ratio of the secondary sedimentation tank is 100%-120%.

[0023] The beneficial effects of the present invention are:

[0024] ① Short water retention time, high denitrification efficiency, low denitrification cost, beneficial to commercial operation;

[0025] ② The system operates in an anaerobic-anaerobic ammonium oxidation-dynamic aerobic anoxic mode to improve the system's total nitrogen removal rate and effluent stability, reduce aeration energy consumption, and support the dual carbon policy; when the system has a sewage carbon-nitrogen ratio of 4-5, the total nitrogen in the effluent is stably up to standard and no external carbon source is required.

[0026] ③Equipped with pH and DO detectors, combined with PLC and aeration equipment that can automatically adjust the aeration volume, it can realize automatic switching and variable frequency operation of equipment, further reduce labor costs, save energy consumption, and support the dual carbon policy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 A schematic diagram of the anaerobic ammonium oxidation coupled endogenous denitrification sewage deep denitrification system provided by the present invention;

[0029] Figure 2 This is a schematic diagram of the process flow of the control group in Example 3 of the present invention;

[0030] Figure 3 The data of the removal effect of COD in sewage by two processes in Example 3 of the present invention are as follows;

[0031] Figure 4 The data of the removal effect of two processes on ammonia nitrogen and total nitrogen in sewage in Example 3 of the present invention are as follows;

[0032] Figure 5 The denitrification performance under different HRT conditions of the two processes in Example 4 of the present invention;

[0033] Figure 6 The data are as follows: the removal of COD and nitrogen from sewage in each process stage of the process of the present invention in Example 4 of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention and should not be used to limit the protection scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0035] Example 1: A system for deep denitrification of sewage by anaerobic ammonium oxidation coupled with endogenous denitrification

[0036] like Figure 1 As shown, an anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification system includes a water quality regulating tank, an anaerobic tank, an anaerobic ammonia oxidation tank, a plurality of dynamic aerobic tanks, a plurality of anoxic tanks, a secondary sedimentation tank and a sludge concentration tank; the water quality regulating tank, the anaerobic tank, the anaerobic ammonia oxidation tank, a plurality of dynamic aerobic tanks, a plurality of anoxic tanks, a secondary sedimentation tank and a sludge concentration tank are connected in sequence through pipelines; a sludge return pipe is connected between the front ends of the secondary sedimentation tank and the anaerobic tank, and a sludge pump is arranged on the sludge return pipe; the anaerobic ammonia oxidation tank is provided with a filler attached with anaerobic ammonia oxidizing bacteria; the anaerobic ammonia oxidation tank and the dynamic aerobic tank are both equipped with an aeration device and a stirrer; the anaerobic tank and the anoxic tank are both equipped with a stirrer, the anaerobic ammonia oxidation tank is provided with a DO detector, and the dynamic aerobic tank is provided with a PH detector and a DO detector; the PLC controller is respectively connected to the PH detector, the DO detector, the aeration equipment and the stirrer for communication.

[0037] The anaerobic ammonium oxidation coupled endogenous denitrification sewage deep denitrification system of the present invention mainly comprises two main parts: an anaerobic ammonium oxidation part and an endogenous denitrification part. The specific sewage treatment process is as follows:

[0038] ① Water quality regulation, denitrifying bacteria absorb internal carbon source

[0039] The water quality regulating tank regulates the incoming water so that the carbon-nitrogen ratio of the anaerobic tank inlet water is between 4-5; after the water enters the anaerobic tank, it is stirred. The hydraulic retention time of this stage is the total nitrogen concentration of the sewage × 0.02 hours. The denitrifying bacteria absorb the internal carbon source, which on the one hand lays the foundation for the subsequent endogenous denitrification, and on the other hand can reduce the carbon-nitrogen ratio, creating conditions for anaerobic ammonia oxidation denitrification in the aerobic zone.

[0040] ②Anaerobic ammonium oxidation

[0041] The effluent from the anaerobic tank enters the anaerobic ammonium oxidation tank, which is equipped with a large amount of fillers with anaerobic ammonium oxidizing bacteria attached, which is conducive to the growth of anaerobic ammonium oxidizing bacteria on the fillers and achieves the maximum enrichment of anaerobic ammonium oxidizing bacteria. At the same time, the hydraulic retention time of this stage is the total nitrogen concentration of the sewage × 0.04 hours. The dissolved oxygen at this stage needs to be controlled at about 1mg / L±0.3mg / L. If the dissolved oxygen is too low, it is not conducive to nitrification in the system. If the dissolved oxygen is too high, it is not conducive to anaerobic ammonium oxidation in the system.

[0042] ③ Endogenous denitrification

[0043] Entering the dynamic aerobic pool, the dissolved oxygen concentration during aeration is controlled at 2mg / L-4mg / L. At the same time, in order to shorten the nitrification time as much as possible, the over-aeration time needs to be reduced. In order to achieve accurate aeration of sewage, several relatively independent dynamic aerobic pools are set up (each dynamic aerobic pool is connected by a pipe and is almost completely mixed). DO detectors and pH detectors are set in the dynamic aerobic pools. The changes in pH and DO in the dynamic aerobic pools can be observed to determine whether the system has completed nitrification (at the end of nitrification, the dissolved oxygen (DO) of the sewage will increase relatively due to the decrease in the activity of nitrifying bacteria and the reduction in oxygen consumption; and since nitrification consumes the alkalinity in the sewage, the pH value of the dynamic aerobic pool will gradually decrease. After the nitrification is completed, the pH value will gradually increase). When it is detected that the dissolved oxygen in one of the dynamic aerobic pools is still higher than 4 mg / L when the aeration volume is lower than 30% of the normal aeration volume, and the pH value rises at this time, it can be determined that the system has completed nitrification, and this dynamic aerobic pool and subsequent dynamic aerobic pools can stop aeration, which saves energy and ensures complete nitrification in the shortest possible time.

[0044] Entering the anoxic pool, deep denitrification is achieved through endogenous denitrification by denitrifying bacteria.

[0045] The hydraulic retention time of the dynamic aerobic tank in this stage is the total nitrogen concentration of the sewage × (0.03~0.06) hours, the hydraulic retention time of the anoxic tank is the total nitrogen concentration of the sewage × (0.03~0.06) hours, and the total retention time of the dynamic aerobic tank and the anoxic tank is the total nitrogen concentration of the sewage × 0.09 hours).

[0046] Through the treatment in the anaerobic section, the organic matter in the sewage is greatly reduced, and the carbon-nitrogen ratio of the sewage is reduced from the original 4-5 to 1-2; through the treatment in the anaerobic ammonia oxidation section, the removal rates of ammonia nitrogen and total nitrogen in the effluent are 70%-90% and 40%-60% respectively; through the treatment in the dynamic aerobic section, the removal rates of ammonia nitrogen and total nitrogen in the effluent are 95%-98% and 60%-80% respectively; through the treatment in the anoxic section, the removal rates of ammonia nitrogen and total nitrogen in the effluent are 98%-99% and 95%-98% respectively.

[0047] Example 2: A deep denitrification process for anaerobic ammonium oxidation coupled with endogenous denitrification of wastewater

[0048] The process in this embodiment is based on the system in Example 1, and is mainly used for the treatment of high ammonia nitrogen industrial wastewater, with the main influent indicators being COD 2400mg / L to 2600mg / L and ammonia nitrogen 500mg / L to 640mg / L. After being pretreated in the primary sedimentation tank, the sewage enters the water quality regulating tank, where the water quality is regulated to ensure that the carbon-nitrogen ratio of the anaerobic tank inlet is between 4 and 5. After the sewage enters the anaerobic tank, it only needs to be stirred for 12 hours, and the denitrifying bacteria absorb the internal carbon source; the effluent from the anaerobic tank enters the anaerobic ammonia oxidation tank, aerated and stirred, and the dissolved oxygen is controlled at about 1mg / L, and the residence time is 24 hours. Then the effluent from the anaerobic tank enters the dynamic aerobic tank. The retention time of the dynamic aerobic pool is 24 hours. Nitrification is carried out under the action of stirring and aeration. The dissolved oxygen is controlled at 2mg / L-4mg / L to degrade the ammonia nitrogen and remaining organic matter in the sewage. When it is detected that the dissolved oxygen in one of the dynamic aerobic pools is still higher than 4mg / L when the aeration volume is lower than 30% of the normal aeration volume, and the pH value rises at this time, the aeration of this dynamic aerobic pool and the subsequent dynamic aerobic pools will automatically shut down and become anoxic pools. The anoxic pool only turns on the agitator. After the sewage enters the anoxic pool, it only needs to be stirred. The hydraulic retention time of the anoxic pool is 30 hours to complete the endogenous denitrification deep denitrification.

[0049] The sewage finally enters the secondary sedimentation tank for mud and water separation, the supernatant is discharged, and the sludge is pumped back to the front end of the anaerobic tank through the sludge pump. The sludge return ratio is 100%-120%, and the remaining sludge is discharged into the sludge thickening tank.

[0050] Example 3: Comparison of denitrification effects of high ammonia nitrogen industrial wastewater treatment based on the traditional AOA process and the anaerobic ammonium oxidation coupled endogenous denitrification wastewater deep denitrification process of the present invention

[0051] A control group was set up, and the control group used the traditional AOA process. The process flow chart is as follows Figure 2 shown.

[0052] The conventional AOA process and the anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification process of the present invention were respectively used to treat a certain industrial sewage, and the influent indexes were: COD was 2500mg / L±100mg / L, and the total nitrogen concentration was 570mg / L±70mg / .

[0053] Figure 3 The data show that the COD removal of sewage by the process of the present invention is about 400 mg / L, and the removal rate is about 85%. The data show that the COD removal of sewage by the process of the present invention is basically the same as that of the traditional activated sludge process.

[0054] Figure 4 The removal of ammonia nitrogen and total nitrogen in sewage by the anaerobic ammonium oxidation coupled endogenous denitrification sewage deep denitrification process is shown. Through the treatment of this process, the effluent concentrations of ammonia nitrogen and total nitrogen in sewage are lower than 1mg / L and 30mg / L respectively, and the removal rates are greater than 99% and 95% respectively. The main reason for the high removal rate of total nitrogen is that the system's anaerobic ammonium oxidation denitrification and endogenous denitrification effects are obvious, ensuring that the system has a continuous and efficient denitrification efficiency.

[0055] Example 4: Comparison of denitrification efficiency of high ammonia nitrogen industrial wastewater treatment based on the traditional AOA process and the anaerobic ammonium oxidation coupled endogenous denitrification wastewater deep denitrification process of the present invention

[0056] In order to compare the difference in denitrification efficiency between the control group process and the anaerobic ammonium oxidation coupled endogenous denitrification sewage deep denitrification process of the present invention, the denitrification effects of the two systems were compared by adopting the same influent and continuously shortening the HRT strategy. The influent of the two systems was the same, and the initial HRT was set to 120 hours, and then the HRT of the system influent was gradually reduced to observe the effluent conditions of the two systems. Figure 5 It shows the changes of system denitrification under different HRT conditions of the two systems. Figure 5 It can be seen that the total nitrogen removal of the two processes is basically the same at the beginning, but because the anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification process of the present invention is coupled with anaerobic ammonia oxidation denitrification, the total nitrogen in the effluent at the aerobic end is lower. The total nitrogen concentration at the end of the aerobic tank of the anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification process of the present invention is about 100 mg / L, while the control group process only has simultaneous nitrification and denitrification in the aerobic tank, and the total nitrogen concentration is about 200 mg / L, which is about twice the difference between the two. As the residence time continues to shorten, the total nitrogen in the effluent of the aerobic tank of the control group process continues to rise, causing the final effluent total nitrogen to continue to rise. The total nitrogen concentration in the effluent of the aerobic tank of the anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification process of the present invention benefits from the rapid denitrification ability of anaerobic ammonia oxidation, and is relatively stable. When the HRT is finally maintained at 90 hours, the total nitrogen effluent concentration of the anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification process of the present invention has been within 30 mg / L, while the total nitrogen effluent of the endogenous denitrification denitrification process of the control group process has reached more than 50 mg / L. It can be seen that the anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification process of the present invention has the advantages of high denitrification efficiency and shorter HRT compared with the traditional AOA process.

[0057] The removal of sewage pollutants in each process section of the anaerobic ammonium oxidation coupled endogenous denitrification sewage deep denitrification process of the present invention is as follows Figure 6 As shown. Figure 6It can be seen that after the sewage enters the anaerobic tank of the system, the removal of organic matter and ammonia nitrogen is very obvious. Because there is no denitrification and nitrification in the anaerobic tank, and there is no dissolved oxygen, the only possible reason is that COD and ammonia nitrogen are absorbed into the body by the sludge. After adsorption and absorption in the anaerobic tank, the COD and total nitrogen concentrations of the sewage have dropped to 445mg / L and 228mg / L before entering the anaerobic ammonia oxidation reaction tank. The treatment of the anaerobic tank has laid a good foundation for the subsequent anaerobic ammonia oxidation denitrification. Through the treatment of the anaerobic tank, the carbon-nitrogen ratio of the sewage has dropped from 4.47 of the raw water to 1.95, creating good conditions for anaerobic ammonia oxidation. Subsequently, the sewage enters the anaerobic ammonia oxidation denitrification tank. At this stage, the COD of the sewage decreases slightly, but the removal rate is limited. In this process section, the removal effect of ammonia nitrogen and total nitrogen in the sewage is obvious. The effluent ammonia nitrogen and total nitrogen in this stage are reduced to 87 and 125 respectively. Compared with the anaerobic tank influent, the removal rates of ammonia nitrogen and total nitrogen are 57.5% and 43% respectively. Unlike the anaerobic tank, which "removes" pollutants by adsorption, this stage mainly achieves the real removal of ammonia nitrogen and total nitrogen in sewage through the action of anaerobic ammonium oxidation, nitrification and SND. The sewage then enters the dynamic aerobic tank for final nitrification and SND. After treatment in the aerobic tank, the effluent ammonia nitrogen concentration is 2mg / L, and the effluent total nitrogen concentration is 92mg / L. Compared with the anaerobic ammonium oxidation influent, the removal rates of ammonia nitrogen and total nitrogen are 97% and 26%, respectively. The total nitrogen removal in the aerobic tank mainly relies on SND, so the removal effect of total nitrogen is relatively weak. After treatment in this section, the COD of the sewage and the final effluent COD concentration are basically the same, which is 386mg / L, indicating that after passing through the aerobic tank, the biodegradable organic matter in the sewage has been completely removed. The sewage then enters the anoxic tank. Endogenous denitrification occurs in the anoxic tank. In the anoxic tank, most of the remaining total nitrogen in the sewage is effectively removed, and the total nitrogen in the effluent reaches 26mg / L, which is 71% of the removal rate compared with the aerobic tank influent.

[0058] In summary, the anaerobic ammonia oxidation coupled endogenous denitrification sewage deep denitrification process of the present invention is used to treat a certain industrial sewage with a COD of 2500 mg / L and a total nitrogen concentration of 550 mg / L. The effluent COD, total nitrogen and ammonia nitrogen are respectively lower than 390 mg / L, 30 mg / L and 3 mg / L, and the effluent total nitrogen and ammonia nitrogen concentrations are far lower than the national Class A emission standard. It can be seen that the sewage deep denitrification system and process of the present invention have strong impact resistance and can obtain stable and efficient COD removal and denitrification effects under the conditions of high load rate and short hydraulic retention time.

[0059] The above-mentioned specific implementations are only specific cases of the present invention. The patent protection scope of the present invention includes but is not limited to the product form and style of the above-mentioned specific implementations. Any appropriate changes or modifications made to them by ordinary technicians in the technical field that conform to the claims of the present invention shall fall within the patent protection scope of the present invention.

Claims

1. A deep denitrification process for anaerobic ammonium oxidation coupled with endogenous denitrification of sewage, characterized by: (1) After being treated in the water quality regulating tank, the sewage enters the anaerobic tank and only needs to be stirred. The retention time is T1 hours; (2) The effluent from the anaerobic tank enters the anaerobic ammonia oxidation tank, where it is aerated and stirred, and the dissolved oxygen is controlled at 0.7 mg / L-1.3 mg / L. The retention time is T2 hours, and then the effluent from the anaerobic tank enters the dynamic aerobic tank; (3) After the effluent from the anaerobic tank enters several dynamic aerobic tanks, the retention time of each dynamic aerobic tank is T3 hours. Nitrification is carried out under the action of stirring and aeration to degrade the ammonia nitrogen and remaining organic matter in the sewage. When it is detected that the dissolved oxygen in one of the dynamic aerobic tanks is still higher than 4 mg / L when the aeration volume is lower than 30% of the normal aeration volume, and the pH value rises at this time, the aeration of this dynamic aerobic tank and the subsequent dynamic aerobic tanks will automatically shut down and become anoxic tanks. Only the agitator in the anoxic tank will be turned on. (4) Sewage entering the anoxic tank, the total residence time of the anoxic tank is T4 hours, and denitrification is achieved through endogenous denitrification by denitrifying bacteria; (5) After the sewage in the anoxic tank is discharged, it enters the secondary sedimentation tank to achieve mud and water separation. The sludge is pumped to the front end of the anaerobic tank through the sludge pump, the supernatant is discharged, and the remaining sludge is discharged into the sludge thickening tank; T1 = total nitrogen concentration in sewage (mg / L) × 0.02; T2 = total nitrogen concentration in sewage (mg / L) × 0.04; T3 = total nitrogen concentration in sewage (mg / L) × a, where a = 0.03-0.06; T4 = total nitrogen concentration in sewage (mg / L) × b, where b = 0.03-0.06; T3+T4=total nitrogen concentration of sewage (mg / L)×0.09; The dissolved oxygen concentration during aeration of the dynamic aerobic tank is controlled at 2 mg / L-4 mg / L; The sludge return ratio of the secondary sedimentation tank is 100%-120%; The water quality regulating tank adjusts the carbon-nitrogen ratio so that the carbon-nitrogen ratio of the anaerobic tank influent is 4-5.

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