A smart continuous flow deep treatment system and method for nitrogen and phosphorus with low activated sludge concentration in wastewater effluent

Abstract

This invention relates to an intelligent continuous flow system and method for deep nitrogen and phosphorus removal from wastewater treatment plant effluent with low-activity sludge concentration. Belonging to the technical field of wastewater treatment system purification, the system is designed based on the denitrification phosphorus removal principle. It consists of a nitrification tank, three anaerobic tanks, three anoxic tanks, one aerobic tank, and a sedimentation tank. By measuring the nitrate nitrogen concentration in the effluent and precisely adding an organic carbon source, the system controls the endpoints of nitrification and denitrification reactions online. Due to its short hydraulic retention time, the system can operate at high speed and efficiency, produces no byproducts, and avoids secondary pollution. The purified water meets or exceeds Class III standards of my country's surface water quality standards. This invention provides a better technical solution for addressing the secondary eutrophication pollution caused by surface discharge of effluent from existing wastewater treatment plants and the challenges of upgrading existing wastewater treatment plants. It also has significant implications for the restoration of water quality in water source protection areas and eutrophic water bodies.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment system technology, and in particular to an intelligent continuous flow deep treatment system and method for nitrogen and phosphorus concentration of low-active sludge in wastewater effluent. Background Technology

[0002] In recent years, with the continuous development of cities and the improvement of people's living standards, the amount of urban sewage generated has been increasing. The eutrophication trend of surface lakes and rivers, which serve as receiving sites for sewage treatment plant effluent, remains severe. Water bodies that are already slightly and moderately eutrophic have always been difficult to treat and restore, while the risk of eutrophication remains for oligotrophic and mesotrophic water bodies. In my country, most sewage treatment plants discharge their effluent directly into nearby rivers, lakes, and reservoirs via surface runoff. Although most urban sewage treatment plant effluent meets the Class A or Class B discharge standards of the "GB18918-2002 Discharge Standard of Pollutants for Urban Sewage Treatment Plants," the total nitrogen and total phosphorus concentrations in these standards are still far higher than the minimum Class V water quality standard of my country's surface water quality standard GB3838-2002. Therefore, with the increasing demands for quality of life and environment, there is an urgent need for advanced and even ultra-advanced treatment of wastewater treatment plant effluent, that is, to treat wastewater effluent to meet the Class III or Class IV standards of the "Surface Water Environmental Quality Standard" (GB3838-2002). Currently, wastewater treatment plants in my country are undergoing upgrading and renovation; however, existing advanced effluent treatment (i.e., tertiary treatment) technologies such as adsorption, flocculation sedimentation, ion exchange, and membrane separation are still insufficient to meet surface water environmental quality standards due to their low cost and purification efficiency. Therefore, the advanced purification of nitrogen, phosphorus, and eutrophic substances in wastewater effluent has become an urgent and crucial challenge in water environment management.

[0003] Denitrification for phosphorus removal is an advanced process that utilizes both nitrogen and phosphorus, achieving simultaneous removal with relatively low sludge production. Its principles have been widely applied in wastewater treatment processes such as A2O, making it particularly suitable for municipal wastewater treatment. However, there are relatively few patents and research papers on deep purification processes using activated sludge for wastewater effluent with low nitrogen and phosphorus concentrations. Some researchers have modified biological filters into denitrifying biological filters, achieving significant nitrogen removal, but some nitrogen remains. Furthermore, the lack of specific phosphorus purification measures results in low phosphorus purification efficiency. This is because in normal wastewater treatment processes, the activated sludge from denitrification releases high concentrations of phosphorus after anaerobic treatment. Due to the extremely low nitrogen concentration in the effluent, conventional denitrification processes cannot absorb phosphorus through denitrification, leading to a large discharge of phosphorus. This disrupts the normal living environment for denitrifying bacteria, causing system collapse. Summary of the Invention

[0004] This invention addresses the issue of significant phosphorus release from activated sludge during anaerobic denitrification and phosphorus removal processes, coupled with the low nitrogen concentration in wastewater effluent. When the anaerobic activated sludge is mixed with the wastewater effluent in the anoxic tank, the nitrogen-to-phosphorus ratio is far lower than that of normal denitrification processes, resulting in a large amount of phosphorus remaining unremoved at the end of denitrification. Therefore, this invention improves the denitrification and phosphorus removal process by employing intelligent automatic control technology. By controlling the ORP (Operating Rate of Return) in the anoxic tank, the amount of activated sludge entering the anoxic tank is strictly controlled. The activated sludge concentration is matched with the nitrogen concentration in the effluent to a level that is compatible with the concentration of activated sludge and phosphorus in the anaerobic treatment. At the same time, by strictly controlling the anoxic and anaerobic environments in the anaerobic and anoxic tanks, oxygen is prevented from entering and consuming organic carbon sources, thus affecting the anoxic and anaerobic environments. This allows for rapid denitrification in the anoxic zone even at a relatively low activated sludge concentration, and excessive enrichment and absorption of phosphorus, thereby achieving stable phosphorus removal. In addition, online control is used to control the endpoint of continuous flow denitrification, so that nitrogen can be almost completely removed by denitrification.

[0005] This invention provides an intelligent continuous flow deep treatment system for nitrogen and phosphorus of low-active sludge concentration in wastewater treatment plant effluent, comprising: a nitrification tank, a first flow tank, a primary anoxic tank, a secondary anoxic tank, a tertiary anoxic tank, an aerobic tank, a sedimentation tank, a sludge return pump, a primary anaerobic tank, a secondary anaerobic tank, a tertiary anaerobic tank, an external carbon source storage tank, an external carbon source addition pump, a submersible mixer, and a controller.

[0006] The outlets and inlets of the nitrification tank, the first flow tank, the first-stage anoxic tank, the second-stage anoxic tank, the third-stage anoxic tank, the aerobic tank, the sedimentation tank, the sludge return pump, the first-stage anaerobic tank, the second-stage anaerobic tank, and the third-stage anaerobic tank are connected sequentially by a connecting pipe, and the outlet of the third-stage anaerobic tank is connected to the first-stage anoxic tank and the second-stage anoxic tank respectively.

[0007] The submersible mixers are multiple and rotate respectively inside the primary anoxic tank, the secondary anoxic tank, the tertiary anoxic tank, the aerobic pool, the primary anaerobic tank, the secondary anaerobic tank, and the tertiary anaerobic tank;

[0008] The controller is electrically connected to the sludge return pump, the external carbon source addition pump, and the multiple submersible mixers.

[0009] The beneficial effects of this invention are as follows: Addressing the characteristics of wastewater treatment plant effluent with low CODcr content, ammonia nitrogen and nitrate nitrogen being the main nitrogen forms, and phosphorus primarily in the form of orthophosphate, this invention utilizes the principle that denitrifying phosphorus-removing bacteria can simultaneously remove nitrogen and phosphorus. The wastewater effluent first enters a nitrification tank, where aeration thoroughly oxidizes and nitrifies the ammonia nitrogen. The nitrate nitrogen concentration in the effluent is then measured, and the required external carbon source for denitrification is accurately estimated. The activated sludge settled in the sedimentation tank is returned to the anaerobic tank, where an external carbon source is added according to the estimated amount for anaerobic treatment. This process is repeated through primary, secondary, and tertiary anaerobic tanks before being returned to the effluent. The primary anoxic tank mixes with the nitrified effluent. Through denitrification and phosphorus removal by denitrifying and phosphorus-removing bacteria, the ORP values ​​of the primary and tertiary anoxic tanks are controlled to achieve the denitrification endpoint, thus realizing deep nitrogen removal and denitrification absorption of phosphorus. Afterward, the effluent passes through an aerobic tank for aerobic aeration, which strips the nitrogen produced by denitrification, improves the settling performance of activated sludge, and enhances aerobic phosphorus absorption. Finally, the effluent enters the settling tank, where solid-liquid separation yields purified water, ultimately achieving deep nitrogen and phosphorus removal. Most of the activated sludge is returned to the anaerobic tank for anaerobic treatment, and the cycle repeats continuously. This process is based on the principle of dual sludge denitrification technology and adopts intelligent online control technology to remove nitrogen and phosphorus from the effluent of sewage treatment plants at an ultra-deep level. It solves the problem of upgrading existing sewage treatment plants and completely solves the problem of secondary eutrophication pollution caused by the surface discharge of effluent from existing sewage treatment plants. The purified surface water can reach the Class III or above quality standard. Its discharge is of great significance for the protection of water source water quality protection areas, the protection of oligotrophic and mesotrophic lakes and rivers from eutrophication, and the restoration of water quality in already eutrophic water bodies.

[0010] Based on the above technical solution, the present invention can be further improved as follows.

[0011] Furthermore, it also includes a nitrification frequency converter, a nitrification aeration pump, nitrification aeration heads, a nitrification gas flow meter, a first valve, a second valve, a nitrification DO online detector, and a sludge discharge valve; the bottom of the nitrification tank is conical with a sludge discharge hole at the conical bottom, and a sludge discharge valve is installed on the sludge discharge hole; there are multiple nitrification aeration heads divided into two groups, which are respectively fixed in the lower part of the packing layer and the lower part of the packing layer in the nitrification tank, spaced apart vertically, dividing the interior of the packing layer of the nitrification tank into an aeration zone in the upper middle part and a de-aeration zone in the lower part; the nitrification frequency converter is electrically connected to the nitrification aeration pump; the nitrification aeration pump is located outside the nitrification tank, and the nitrification aeration pump is connected to the nitrification gas flow meter through a gas pipeline. The nitrification gas flow meter branches into two sets of branches via a gas pipeline. A first valve and a second valve are installed on these two sets of branches, respectively. The two sets of branches extend into the lower part and bottom of the packing layer inside the nitrification tank and connect to the upper and lower sets of multiple nitrification aeration heads. The online nitrification DO detector is installed inside the first flow tank. The inlet of the sampling pump is connected to the connecting pipe between the outlet of the nitrification tank and the first flow tank. The inlet of the online nitrate nitrogen detector is connected to the outlet of the sampling pump. The controller is electrically connected to the nitrification frequency converter, the nitrification gas flow meter, the first valve, the second valve, the online nitrification DO detector, and the sludge discharge valve.

[0012] The further beneficial effects of the above-mentioned method are as follows: The controller opens the first valve and closes the second valve. The effluent from the wastewater treatment plant is injected from above the nitrification tank by the influent pump, passes down through the upper packing zone (aeration zone), and then enters the lower packing layer (aeration zone) where there is no aeration. The controller controls the aeration intensity of the nitrification aeration pump by controlling the frequency of the nitrification inverter. When a small amount of ammonia nitrogen or nitrite nitrogen remains in the effluent entering the aeration zone, it will consume DO in the aeration zone. At this time, the controller detects the DO concentration of the effluent from the nitrification tank through the nitrification DO online detector and controls the aeration intensity within a suitable range to achieve complete nitrification and oxidation of ammonia nitrogen in the effluent from the nitrification tank, while keeping the DO concentration at a relatively low level. This achieves complete nitrification and reduces the consumption of external carbon sources in the entire system, thus lowering the carbon-to-nitrogen ratio. The packing layer of the nitrification tank needs to be cleaned regularly. The cleaning method is to close the first valve, open the second valve, and the controller adjusts the aeration intensity of the nitrification aeration pump to the maximum by controlling the frequency of the nitrification frequency converter. The gas from the nitrification aeration pump enters through the second valve and the pipeline into multiple aeration heads at the bottom of the packing layer, blowing off the sludge deposited in the deaeration zone and settling it at the bottom of the nitrification tank. After aeration, let it stand for a period of time, and then discharge the detached activated sludge by draining water downwards.

[0013] Furthermore, it also includes a sampling pump, an online nitrate nitrogen detector, an external carbon source addition pump, and a liquid level gauge; the inlet of the sampling pump is connected to the connecting pipe between the outlet of the nitrification tank and the first flow tank; the inlet of the online nitrate nitrogen detector is connected to the outlet of the sampling pump; the inlet and outlet of the external carbon source addition pump are connected to the pipe between the outlet of the external carbon source storage tank and the inlet of the primary anaerobic tank; the liquid level gauge is fixed at the top inside the tertiary anaerobic tank; the controller is electrically connected to the sampling pump, the online nitrate nitrogen detector, the external carbon source addition pump, and the liquid level gauge.

[0014] The further beneficial effects of the above are as follows: the sampling pump collects water samples from the nitrification tank and sends them to the online nitrate nitrogen detector to determine the nitrate nitrogen concentration. The controller estimates the flow rate of the external carbon source based on the measured nitrate nitrogen concentration or the known total nitrogen concentration, combined with the carbon-nitrogen ratio. The external carbon source addition pump adds the external carbon source from the external carbon source storage tank to the primary anaerobic tank at the estimated flow rate, completing the quantitative addition of the external carbon source. The controller sets a control water level line in the tertiary anaerobic tank. The controller reads the liquid level height through the liquid level gauge and adjusts the carbon-nitrogen ratio coefficient according to the liquid level, so that the system can automatically and dynamically adjust when the effluent quality of the wastewater treatment plant changes.

[0015] Furthermore, it also includes a first metering pump and an online ORP detector for hypoxia. The first metering pump is installed on the connecting pipe between the tertiary anaerobic tank and the primary hypoxia tank; the online ORP detector for hypoxia is installed inside the primary hypoxia tank; and the controller is electrically connected to the first metering pump and the online ORP detector for hypoxia, respectively.

[0016] The further beneficial effects of the above are: the controller controls the flow rate of the anaerobic activated sludge delivered to the primary anoxic tank by controlling the first metering pump, and controls the ORP of the primary anoxic tank to be near the set range, thereby realizing the process control of denitrification. By controlling the ORP of the primary anoxic tank, denitrification is allowed to proceed step by step, which is beneficial for the absorption of phosphorus during denitrification.

[0017] Furthermore, it also includes a second flow tank, a first sludge pump, a second sludge pump, an online denitrification pH meter, an online denitrification ORP meter, an online denitrification conductivity meter, and a second metering pump; the submersible mixer is installed inside the second flow tank, and its inlet is connected to the outlet of the first-stage anoxic tank and the outlet of the third-stage anoxic tank respectively through a connecting pipe, and its outlet is connected to the inlet of the third-stage anoxic tank; the first sludge pump is installed on the connecting pipe between the inlet of the second flow tank and the outlet of the first-stage anoxic tank; the second sludge pump is installed on the second flow tank... The inlet of the flow tank is connected to the outlet of the third-stage anoxic tank via a connecting pipe; the online denitrification pH meter, the online denitrification ORP meter, and the online denitrification conductivity meter are all installed in the second flow tank; the second metering pump is installed on the connecting pipe between the third-stage anaerobic tank and the second-stage anoxic tank; the controller is electrically connected to the first sludge pump, the second sludge pump, the submersible mixer, the online denitrification pH meter, the online denitrification ORP meter, the online denitrification conductivity meter, and the second metering pump, respectively.

[0018] The further beneficial effects of adopting the above are:

[0019] 1. Controller controls the denitrification endpoint: During normal operation of the second flow tank, the second sludge pump continuously and rapidly transports the sludge mixture from the tertiary anoxic tank to the second flow tank, and then returns it from the top of the second flow tank to the tertiary anoxic tank. The controller reads the ORP value of the online ORP detector in the second flow tank (which is equivalent to detecting the ORP value of the tertiary anoxic tank), and controls the flow rate of the activated sludge after anaerobic treatment delivered by the second metering pump to keep the ORP value of the tertiary anoxic tank within a set range. This set ORP range corresponds to the ORP value near the denitrification endpoint, so that the denitrification endpoint can be controlled, achieving deep nitrogen removal, while avoiding problems such as the secondary release of phosphorus caused by the conversion of the anoxic state to the anaerobic state when the denitrification endpoint is delayed, or poor nitrogen purification efficiency caused by the denitrification not reaching the endpoint.

[0020] 2. The controller determines the ORP control range when the denitrification endpoint of the third anoxic tank is reached: The second sludge pump is turned off, the first sludge pump is turned on, and the activated sludge mixture from the first anoxic tank is transferred to the second flow tank through the first sludge pump. Then the first sludge pump is stopped. The controller observes the changes in pH, ORP, and conductivity values ​​of the sludge mixture in the second flow tank to determine the denitrification endpoint. That is, when the pH rises and then falls, and at the same time the conductivity is stable or fluctuates slightly, or begins to rise, it indicates that denitrification has reached the denitrification endpoint. The ORP value at this time is used as the control range of the ORP value of the new second anoxic tank.

[0021] Furthermore, it also includes an aerobic aeration pump, an aerobic frequency converter, an aerobic gas flow meter, an aerobic DO online detector, and an aerobic ORP online detector. The aerobic aeration pump is located outside the aerobic tank; the aerobic aeration head is fixed inside the aerobic tank and extends out of the aerobic tank, communicating with the aerobic aeration pump; the aerobic gas flow meter is installed on the connecting pipe between the outlet of the aerobic aeration pump and the aerobic aeration head; the aerobic DO online detector and the aerobic ORP online detector are both fixed inside the aerobic tank; the aerobic frequency converter is electrically connected to the aerobic aeration pump; and the controller is electrically connected to the aerobic frequency converter, the aerobic gas flow meter, the aerobic DO online detector, and the aerobic ORP online detector, respectively.

[0022] The further beneficial effects of the above-mentioned method are as follows: The controller reads the ORP and DO values ​​from the online aerobic ORP and DO detectors in the aerobic tank, and controls the aeration frequency of the aerobic aeration pump through the aerobic frequency converter, thereby controlling the aeration intensity of the aerobic tank. Ultimately, this achieves DO control or ORP control of the aerobic tank. Through the aerobic aeration effect of the aerobic tank, on the one hand, the nitrogen gas produced by denitrification is blown off, which is conducive to the static settling and separation of activated sludge, preventing the activated sludge from floating. On the other hand, aerobic aeration enhances the aerobic absorption of phosphorus by microorganisms. At the same time, the aerobic environment is conducive to the activated sludge not releasing phosphorus again due to lack of oxygen during settling, thus ensuring phosphorus removal.

[0023] Furthermore, it also includes a stirring motor, a scraper, and a sludge pump. The stirring motor is fixed at the top of the settling tank and its output shaft extends into the settling tank. The scraper is located inside the settling tank and contacts the tank wall. The scraper is fixed on the output shaft of the stirring motor. The sludge pump is connected to the outlet of the settling tank through a connecting pipe. The controller is electrically connected to the stirring motor and the sludge pump respectively.

[0024] The further beneficial effects of the above-mentioned method are as follows: the sludge mixture from the aerobic tank eventually flows into the settling tank. The scraper plate at the bottom of the settling tank, through the slow rotation of the stirring motor, scrapes the sludge deposited on the conical tank wall into the bottom of the cone. Finally, the supernatant from the overflow weir of the settling tank flows out as the purified water of the system. Some of the remaining sludge is discharged quantitatively by the sludge discharge pump, while most of the activated sludge is returned to the primary anaerobic tank by the sludge return pump. The action of the scraper can compress the activated sludge, promote sludge circulation, and reduce the flow rate of the sludge return pump.

[0025] Furthermore, it also includes multiple exhaust pipes, which are respectively installed at the top of the primary anoxic tank, the secondary anoxic tank, the tertiary anoxic tank, the primary anaerobic tank, the secondary anaerobic tank, and the tertiary anaerobic tank; the liquid level of the aerobic tank is higher than the tops of the primary anoxic tank, the secondary anoxic tank, and the tertiary anoxic tank, and lower than the exhaust ports of the exhaust pipes on the primary anoxic tank, the secondary anoxic tank, and the tertiary anoxic tank; the tops of the primary anoxic tank, the secondary anoxic tank, and the tertiary anoxic tank are all conical apexes;

[0026] The further beneficial effect of adopting the above is that the liquid level in the aerobic tank is higher than the top of the primary anoxic tank, the secondary anoxic tank, and the tertiary anoxic tank, but lower than the exhaust pipes on the three tanks. This prevents air from entering the three anoxic tanks and ensures that the low-concentration activated sludge can still achieve the anoxic denitrification endpoint.

[0027] In addition, two intelligent continuous flow methods for deep treatment of nitrogen and phosphorus in low-concentration sludge of wastewater effluent are provided:

[0028] The first method involves the following steps:

[0029] When the ammonia nitrogen concentration in the effluent of a wastewater treatment plant is low or the requirements for total nitrogen purification are not high, the effluent of the wastewater treatment plant is not nitrified and a nitrification tank is not used. This is the operating procedure.

[0030] System influent, external carbon source addition rate adjustment, external carbon source addition, and carbon-nitrogen ratio adjustment: S1, the influent pump directly delivers the wastewater treatment plant effluent to the primary anoxic tank. The sampling pump collects influent water samples and sends them to the online nitrate nitrogen analyzer to determine the nitrate nitrogen concentration. The controller estimates the flow rate of the external carbon source based on the measured nitrate nitrogen concentration or the known total nitrogen concentration, combined with the carbon-nitrogen ratio. The external carbon source addition pump adds the external carbon source from the external carbon source storage tank to the primary anaerobic tank at the estimated flow rate. The controller sets a control water level line in the tertiary anaerobic tank. The controller reads the liquid level height through the liquid level gauge and adjusts the carbon-nitrogen ratio coefficient by comparing the liquid level height with the control water level line.

[0031] Activated sludge anaerobic treatment process: S2, the settling tank transports the returned activated sludge to the primary anaerobic tank via a sludge return pump, where it is anaerobically mixed with an external carbon source supplied by an external carbon source addition pump at a set flow rate. The mixture then flows into the secondary anaerobic tank, and finally into the tertiary anaerobic tank. In the primary, secondary, and tertiary anaerobic tanks, the activated sludge anaerobically releases phosphorus and absorbs organic matter to synthesize internal carbon sources.

[0032] Denitrification process control: S3, the controller adds the activated sludge that has been anaerobically treated in the three-stage anaerobic tank to the first-stage anoxic tank through the first metering pump. The sludge is then mixed with the wastewater effluent transferred from the influent pump in anoxic conditions. The controller controls the ORP value of the first-stage anoxic tank by controlling the flow rate of the first metering pump, so that it reaches the set control range.

[0033] Operating mode of the second flow tank: S5. When the second flow tank is in normal denitrification control: the second sludge pump continuously and rapidly transports the sludge mixture from the tertiary anoxic tank to the second flow tank, and then returns it from the top of the second flow tank to the tertiary anoxic tank. The submersible agitator of the second flow tank is always in the stirring state. When it is necessary to determine the denitrification endpoint: the second sludge pump is turned off, the first sludge pump is turned on, the activated sludge mixture from the primary anoxic tank is transferred to the second flow tank, and then the first sludge pump is stopped. The sludge mixture in the second flow tank stops flowing in and out, and the submersible agitator of the second flow tank is always in the stirring state.

[0034] Determination of the ORP control range at the end of denitrification reaction: S6, switch the second flow tank to the state when the denitrification end point is determined. The controller observes the changes in pH, ORP and conductivity values ​​of the online denitrification pH detector, online denitrification ORP detector and online denitrification conductivity detector in the second flow tank. That is, when the pH rises and then falls, and at the same time the conductivity is stable or fluctuates slightly, or begins to rise, it indicates that denitrification has reached the end point. The ORP value at this time is taken as the new ORP value control range of the secondary anoxic tank.

[0035] Denitrification endpoint control: S4, the sludge mixed liquor flows out of the primary anoxic tank and then into the secondary and tertiary anoxic tanks in sequence, switching the second flow tank to normal operation. The controller controls the ORP value of the second flow tank (i.e., the ORP value of the tertiary anoxic tank) by controlling the flow rate of the anaerobic activated sludge added to the secondary anoxic tank by the second metering pump, so that it reaches the vicinity of the set denitrification endpoint ORP control range.

[0036] Aerobic reaction: S7, the sludge mixed liquor flows out from the tertiary anoxic tank and into the aerobic tank. The controller reads the ORP and DO values ​​from the aerobic ORP and DO online detectors in the aerobic tank, and controls the aeration frequency of the aerobic aeration pump through the aerobic frequency converter, thereby controlling the aeration intensity of the aerobic tank. Ultimately, this achieves DO or ORP control in the aerobic tank. Through the aerobic aeration in the aerobic tank, on the one hand, the nitrogen gas produced by denitrification is blown off, which is conducive to the static settling and separation of activated sludge and prevents the activated sludge from floating. On the other hand, aerobic aeration enhances the aerobic absorption of phosphorus by microorganisms. At the same time, the aerobic environment is conducive to the activated sludge not releasing phosphorus again due to anoxic conditions during settling, thus ensuring phosphorus removal. The ORP control range of the aerobic tank is 0 to +120mv, and the DO control range is 1.5-3mg / L. One parameter can be selected for control, and the control range is determined by actual operation.

[0037] Sludge settling: The sludge mixture from S8 and the aerobic tank eventually flows into the settling tank. The scraper at the bottom of the settling tank is slowly rotated by the stirring motor to scrape the sludge deposited on the conical tank wall into the bottom of the cone. Finally, the supernatant from the overflow weir of the settling tank flows out as the system's purified water. Some of the remaining sludge is discharged quantitatively by the sludge discharge pump, while most of the activated sludge is returned to the primary anaerobic tank by the sludge return pump.

[0038] Adjustment of the ratio of sludge return pump velocity to wastewater treatment plant effluent influent velocity: S9. Control the ratio of sludge return pump velocity to wastewater treatment plant effluent influent velocity between 1 / 40 and 1 / 5, and adopt a low activated sludge concentration strategy to adapt to changes in the nitrogen concentration and water quality characteristics of wastewater treatment plant effluent. The higher the nitrogen concentration of wastewater treatment plant effluent, the larger this ratio will be, and vice versa.

[0039] The second method involves the following steps:

[0040] When the ammonia nitrogen concentration in the effluent of a wastewater treatment plant is high or the requirements for total nitrogen purification are high, the effluent must first enter the nitrification tank for aerobic aeration nitrification treatment.

[0041] System influent and aerobic nitrification: S1, wastewater effluent from the wastewater treatment plant is pumped to the nitrification tank, passes through the aeration and deaeration zones of the packing layer, flows out from the bottom of the nitrification tank, flows through the first flow tank into the first-stage anoxic tank, and the controller controls the aeration intensity of the nitrification aeration pump through the nitrification frequency converter to control the DO concentration within a certain range, so that the ammonia nitrogen in the wastewater effluent can be completely nitrified aerobically while maintaining a low DO concentration; Cleaning method of the nitrification tank: The biofilm on the packing is cleaned regularly according to the ammonia nitrogen concentration and CODcr concentration of the influent to avoid clogging. The cleaning method is to close the first valve, open the second valve, and then the controller controls the nitrification frequency converter to increase the aeration rate to flush the packing with air bubbles. After that, the sludge discharge valve of the nitrification tank is opened to drain water downwards to wash away the biofilm and water;

[0042] External carbon source addition rate adjustment, external carbon source addition, and carbon-nitrogen ratio adjustment: S1. When the wastewater treatment plant effluent needs to undergo nitrification, the sampling pump collects the effluent from the nitrification tank and sends it to the online nitrate nitrogen detector to measure the nitrate nitrogen concentration. The controller estimates the flow rate of the external carbon source based on the measured nitrate nitrogen concentration or the known total nitrogen concentration, combined with the carbon-nitrogen ratio. The external carbon source addition pump adds the external carbon source from the external carbon source storage tank to the primary anaerobic tank at the estimated flow rate. The controller sets a control water level line in the tertiary anaerobic tank. The controller reads the liquid level height through the liquid level gauge and adjusts the carbon-nitrogen ratio coefficient by comparing the liquid level height with the control water level line.

[0043] Activated sludge anaerobic treatment process: S3, the settling tank transports the returned activated sludge to the primary anaerobic tank through the sludge return pump, and mixes it with the external carbon source delivered by the external carbon source addition pump at a set flow rate for anaerobic mixing, then flows into the secondary anaerobic tank, and finally into the tertiary anaerobic tank.

[0044] Denitrification process control: S4, the controller adds the anaerobic activated sludge to the primary anoxic tank through the first metering pump and mixes it with the nitrified liquid transferred from the nitrification tank in anoxic conditions. The controller controls the ORP value of the primary anoxic tank by controlling the flow rate of the first metering pump to make it reach the set control range.

[0045] Operating mode of the second flow tank: S5. When the second flow tank is in normal denitrification control: the second sludge pump continuously and rapidly transports the sludge mixture from the tertiary anoxic tank to the second flow tank, and then returns it from the top of the second flow tank to the tertiary anoxic tank. The submersible agitator of the second flow tank is always in the stirring state. When it is necessary to determine the denitrification endpoint: the second sludge pump is turned off, the first sludge pump is turned on, the activated sludge mixture from the primary anoxic tank is transferred to the second flow tank, and then the first sludge pump is stopped. The sludge mixture in the flow tank stops flowing in and out, and the submersible agitator of the second flow tank is always in the stirring state.

[0046] To determine the ORP control range at the end of the denitrification reaction, S7 and the controller observe the changes in pH, ORP and conductivity values ​​of the sludge mixture in the second flow tank. That is, when the pH rises and then falls, and at the same time the conductivity is stable or fluctuates slightly, or begins to rise, it indicates that denitrification has reached the end of denitrification. The ORP value at this time is taken as the new ORP control range for the secondary anoxic tank.

[0047] Denitrification endpoint control: S4, the sludge mixed liquor flows out of the primary anoxic tank and then into the secondary and tertiary anoxic tanks in sequence, switching the second flow tank to normal operation. The controller controls the ORP value of the second flow tank (i.e., the ORP value of the tertiary anoxic tank) by controlling the flow rate of the anaerobic activated sludge added to the secondary anoxic tank by the second metering pump, so that it reaches the vicinity of the set denitrification endpoint ORP control range.

[0048] Aerobic reaction: S8 and sludge mixed liquor flow through the primary anoxic tank, secondary anoxic tank, and tertiary anoxic tank before flowing into the aerobic tank. The controller reads the ORP and DO values ​​from the aerobic ORP and DO online detectors in the aerobic tank and controls the aeration frequency of the aerobic aeration pump through the aerobic frequency converter, thereby controlling the aeration intensity of the aerobic tank and ultimately achieving DO or ORP control in the aerobic tank. Through the aerobic aeration in the aerobic tank, on the one hand, the nitrogen gas produced by denitrification is blown off, which is conducive to the static settling and separation of activated sludge and prevents the activated sludge from floating. On the other hand, aerobic aeration enhances the aerobic absorption of phosphorus by microorganisms. At the same time, the aerobic environment is conducive to the activated sludge not releasing phosphorus again due to anoxic conditions during settling, thus ensuring phosphorus removal. The ORP control range of the aerobic tank is 0 to +120mv, and the DO control range is 1.5-3mg / L. One parameter can be selected for control, and the control range is determined by actual operation.

[0049] Sludge settling: The sludge mixture from S9 and the aerobic tank eventually flows into the settling tank. The scraper at the bottom of the settling tank is slowly rotated by the stirring motor to scrape the sludge deposited on the conical tank wall into the bottom of the cone. Finally, the supernatant from the overflow weir of the settling tank flows out as the system's purified water. Some of the remaining sludge is discharged quantitatively by the sludge discharge pump, while most of the activated sludge is returned to the primary anaerobic tank by the sludge return pump.

[0050] Adjustment of the ratio of sludge return pump flow rate to wastewater treatment plant effluent influent flow rate: S9. Control the ratio of sludge return pump flow rate to wastewater treatment plant effluent influent flow rate between 1 / 40 and 1 / 5. Adopt a low activated sludge concentration strategy to adapt to changes in the nitrogen concentration and water quality characteristics of wastewater treatment plant effluent. The higher the nitrogen concentration of wastewater treatment plant effluent, the larger this ratio will be, and vice versa.

[0051] Hydraulic retention time: 1.5-2 hours for primary and secondary anaerobic tanks, 0.75-2 hours for tertiary anaerobic tanks, 20-60 minutes for the total hydraulic retention time of the three anoxic tanks, 5-20 minutes for the aerobic tank, and 15-60 minutes for the nitrification tank. Suitable for wastewater treatment plant effluent with influent total nitrogen concentration of 4-40 mg / L and total phosphorus concentration of 0.3-3 mg / L. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the structure of an intelligent continuous flow deep treatment system for nitrogen and phosphorus of low-active sludge concentration in wastewater treatment plant effluent according to the present invention.

[0053] The attached diagram lists the components represented by each number as follows:

[0054] 1. Nitrification tank; 2. First flow tank; 3. Primary anoxic tank; 4. Secondary anoxic tank; 5. Tertiary anoxic tank; 6. Aerobic tank; 7. Settling tank; 8. Sludge return pump; 9. Primary anaerobic tank; 10. Secondary anaerobic tank; 11. Tertiary anaerobic tank; 12. Nitrification aeration pump; 13. Nitrification aeration head; 14. Aerobic aeration pump; 15. Aerobic aeration head; 16. External carbon source storage tank; 17. External carbon source addition pump; 18. Submersible mixer; 19. Controller; 20. Nitrification frequency converter; 21. Nitrification gas flow meter; 22. First valve; 23. Second valve; 24. Nitrification DO online detector; 25. Sampling pump; 26. 27. Nitrate nitrogen online detector; 28. First metering pump; 29. ​​Second metering pump; 30. Anoxic ORP online detector; 31. Aerobic frequency converter; 32. Aerobic gas flow meter; 33. Aerobic DO online detector; 34. Aerobic ORP online detector; 35. Stirring motor; 36. Sludge scraper; 37. Sludge pump; 38. Second flow tank; 39. First sludge pump; 40. Second sludge pump; 41. Denitrification pH online detector; 42. Denitrification ORP online detector; 43. Denitrification conductivity online detector; 44. Exhaust pipe; 45. Sludge valve; 46. Inlet pump; 47. Liquid level gauge. Detailed Implementation

[0055] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0056] like Figure 1As shown, an intelligent continuous flow deep treatment system for nitrogen and phosphorus of low-active sludge concentration in wastewater treatment plant effluent includes: a nitrification tank 1, a first flow tank 2, a primary anoxic tank 3, a secondary anoxic tank 4, a tertiary anoxic tank 5, an aerobic tank 6, a settling tank 7, a sludge return pump 8, a primary anaerobic tank 9, a secondary anaerobic tank 10, a tertiary anaerobic tank 11, an external carbon source storage tank 16, an external carbon source addition pump 17, a submersible mixer 18, and a controller 19.

[0057] The outlets and inlets of the nitrification tank 1, the first flow tank 2, the primary anoxic tank 3, the secondary anoxic tank 4, the tertiary anoxic tank 5, the aerobic tank 6, the settling tank 7, the sludge return pump 8, the primary anaerobic tank 9, the secondary anaerobic tank 10, and the tertiary anaerobic tank 11 are connected in sequence through connecting pipes, and the outlet of the tertiary anaerobic tank 11 is connected to the primary anoxic tank 3 and the secondary anoxic tank 4 respectively.

[0058] There are multiple submersible mixers 18, which rotate separately in the primary anoxic tank 3, the secondary anoxic tank 4, the tertiary anoxic tank 5, the aerobic tank 6, the primary anaerobic tank 9, the secondary anaerobic tank 10, and the tertiary anaerobic tank 11.

[0059] The controller 19 is electrically connected to the sludge return pump 8, the external carbon source addition pump 17, and multiple submersible mixers 18.

[0060] In some specific embodiments, the system also includes a nitrification frequency converter 20, a nitrification aeration pump 12, a nitrification aeration head 13, a nitrification gas flow meter 21, a first valve 22, a second valve 23, a sludge discharge valve 44, and a nitrification DO online detector 24; the bottom of the nitrification tank 1 is conical, and a sludge discharge hole is provided at the conical bottom, on which a sludge discharge valve 44 is installed; there are multiple nitrification aeration heads 13 divided into two groups, which are respectively fixed in the lower part of the packing layer and the lower part of the packing layer in the nitrification tank 1, spaced apart vertically, dividing the interior of the packing layer of the nitrification tank 1 into an aeration zone in the upper middle part and a de-aeration zone in the lower part; the nitrification frequency converter 20 is electrically connected to the nitrification aeration pump 12; the nitrification aeration pump 12... Located outside the nitrification tank 1, the nitrification aeration pump 12 is connected to the nitrification gas flow meter 21 via a gas pipeline; the nitrification gas flow meter 21 branches into two sets of upper and lower branches via the gas pipeline, and the first valve 22 and the second valve 23 are installed on the two sets of upper and lower branches respectively. The two sets of branches extend into the lower part and bottom of the packing layer inside the nitrification tank 1 and are connected to the upper and lower sets of multiple nitrification aeration heads 13; the nitrification DO online detector 24 is installed in the first flow tank 2; the controller 19 is electrically connected to the nitrification frequency converter 20, the nitrification gas flow meter 21, the first valve 22, the second valve 23, the sludge discharge valve 44 and the nitrification DO online detector 24 respectively.

[0061] In some specific embodiments, the system also includes a sampling pump 25, an online nitrate nitrogen detector 26, an external carbon source addition pump 17, and a liquid level gauge 46; the inlet of the sampling pump 25 is connected to the connecting pipe between the outlet of the nitrification tank 1 and the first flow tank 2; the inlet of the online nitrate nitrogen detector 26 is connected to the outlet of the sampling pump 25; the inlet and outlet of the external carbon source addition pump 17 are connected to the pipe between the outlet of the external carbon source storage tank 16 and the inlet of the primary anaerobic tank 9; the liquid level gauge 46 is fixed to the top of the interior of the tertiary anaerobic tank 11; and the controller 17 is electrically connected to the sampling pump 25, the online nitrate nitrogen detector 26, the external carbon source addition pump 17, and the liquid level gauge 46.

[0062] In some specific embodiments, a first metering pump 27 and an online ORP detector 29 are also included. The first metering pump 27 is installed on the connecting pipe between the tertiary anaerobic tank 11 and the primary anoxic tank 3; the online ORP detector 29 is installed inside the primary anoxic tank 3; and the controller 19 is electrically connected to the first metering pump 27 and the online ORP detector 29.

[0063] In some specific embodiments, the system also includes a second flow tank 37, a first sludge pump 38, a second sludge pump 39, an online denitrification pH meter 40, an online denitrification ORP meter 41, an online denitrification conductivity meter 42, a submersible mixer 18, and a second metering pump 28. The second flow tank 37 is equipped with a submersible mixer 18, whose inlet is connected to the outlet of the primary anoxic tank 3 and the outlet of the tertiary anoxic tank 5 via a connecting pipe, and whose outlet is connected to the inlet of the tertiary anoxic tank 5. The first sludge pump 38 is installed on the connecting pipe between the inlet of the second flow tank 37 and the outlet of the primary anoxic tank 3. The sludge pump 39 is installed on the connecting pipe between the inlet of the second flow tank 37 and the outlet of the third-stage anoxic tank 5; the online denitrification pH meter 40, the online denitrification ORP meter 41, and the online denitrification conductivity meter 42 are all installed in the second flow tank 37; the second metering pump 28 is installed on the connecting pipe between the third-stage anaerobic tank 11 and the second-stage anoxic tank; the controller 19 is electrically connected to the first sludge pump 38, the second sludge pump 39, the submersible mixer 18, the online denitrification pH meter 40, the online denitrification ORP meter 41, the online denitrification conductivity meter 42, and the second metering pump 28.

[0064] In some specific embodiments, the system also includes an aerobic aeration pump 14, an aerobic frequency converter 30, an aerobic gas flow meter 31, an aerobic DO online detector 32, and an aerobic ORP online detector 33. The aerobic aeration pump 14 is located outside the aerobic tank 6; the aerobic aeration head 15 is fixed inside the aerobic tank 6 and extends out of the aerobic tank 6 and communicates with the aerobic aeration pump 14; the aerobic gas flow meter 31 is installed on the connecting pipe between the outlet of the aerobic aeration pump 14 and the aerobic aeration head 15; the aerobic DO online detector 32 and the aerobic ORP online detector 33 are both fixed inside the aerobic tank 6; the aerobic frequency converter 30 is electrically connected to the aerobic aeration pump 14; and the controller 19 is electrically connected to the aerobic frequency converter 30, the aerobic gas flow meter 31, the aerobic DO online detector 32, and the aerobic ORP online detector 33, respectively.

[0065] In some specific embodiments, the system also includes a stirring motor 34, a scraper 35, and a sludge pump 36. The stirring motor 34 is fixed at the top of the settling tank 7 and its output shaft extends into the settling tank 7. The scraper 35 is located inside the settling tank 7 and contacts the tank wall of the settling tank 7. The scraper 35 is fixed on the output shaft of the stirring motor 34. The sludge pump 36 is connected to the outlet of the settling tank 7 through a connecting pipe. The controller 19 is electrically connected to the stirring motor 34 and the sludge pump 36 respectively.

[0066] In some specific embodiments, multiple exhaust pipes 43 may also be included, which are respectively installed at the top of the primary anoxic tank 3, the secondary anoxic tank 4, the tertiary anoxic tank 5, the primary anaerobic tank 9, the secondary anaerobic tank 10, and the tertiary anaerobic tank 11; the liquid level of the aerobic tank 6 is higher than the top of the primary anoxic tank 3, the secondary anoxic tank 4, and the tertiary anoxic tank 5, and lower than the exhaust ports of the exhaust pipes 43 on the primary anoxic tank 3, the secondary anoxic tank 4, and the tertiary anoxic tank 5; the tops of the primary anoxic tank 3, the secondary anoxic tank 4, and the tertiary anoxic tank 5 are all conical apexes.

[0067] In addition, two intelligent continuous flow methods for deep treatment of nitrogen and phosphorus in low-concentration sludge of wastewater effluent are provided:

[0068] The first method involves the following steps:

[0069] When the ammonia nitrogen concentration in the effluent of a wastewater treatment plant is low or the requirements for total nitrogen purification are not high, the effluent of the wastewater treatment plant may not be nitrified, and nitrification tank 1 may not be used. The following operating steps can be adopted.

[0070] System influent, external carbon source addition rate adjustment, external carbon source addition, and carbon-nitrogen ratio adjustment: S1, the influent pump 45 directly delivers the wastewater treatment plant effluent to the primary anoxic tank 3, the sampling pump 25 collects influent water samples and sends them to the online nitrate nitrogen detector 26 to determine the nitrate nitrogen concentration; the controller 19 estimates the flow rate of the added carbon source based on the measured nitrate nitrogen concentration or the known total nitrogen concentration, combined with the carbon-nitrogen ratio; the external carbon source addition pump 17 adds the external carbon source from the external carbon source storage tank 16 to the primary anaerobic tank 9 at the estimated flow rate; the controller 19 sets a control water level line in the tertiary anaerobic tank 11, and the controller 19 reads the liquid level height through the liquid level gauge 46, and adjusts the carbon-nitrogen ratio coefficient by comparing the liquid level height with the control water level line;

[0071] Activated sludge anaerobic treatment process: S2 and settling tank 7 transport the returned activated sludge to the primary anaerobic tank 9 via sludge return pump 8, and anaerobically mix it with the external carbon source delivered by external carbon source addition pump 17 at a set flow rate. Then it flows into the secondary anaerobic tank 10, and finally into the tertiary anaerobic tank 11. In the primary anaerobic tank 9, secondary anaerobic tank 10 and tertiary anaerobic tank 11, the activated sludge anaerobically releases phosphorus and absorbs organic matter to synthesize internal carbon sources.

[0072] Denitrification process control: S3, the controller 19 adds the activated sludge that has been anaerobically treated in the tertiary anaerobic tank 11 to the primary anoxic tank 3 through the first metering pump 27 and mixes it with the wastewater effluent transferred from the influent pump 45 in anoxic mixing. The controller 19 controls the ORP value of the primary anoxic tank 3 by controlling the flow rate of the first metering pump 27, so that it reaches the set control range.

[0073] Operating mode of the second flow tank 37: S5. When the second flow tank 37 is in normal operation of denitrification control: the second sludge pump 39 continuously and rapidly transports the sludge mixture from the tertiary anoxic tank 5 to the second flow tank 37, and then returns it from the top of the second flow tank 37 to the tertiary anoxic tank 5. The submersible agitator 18 of the second flow tank 37 is always in the stirring state. When it is necessary to determine the denitrification endpoint: the second sludge pump 39 is turned off, the first sludge pump 38 is turned on, the activated sludge mixture from the primary anoxic tank 3 is transferred to the second flow tank 37, and then the first sludge pump 38 is stopped. The sludge mixture in the second flow tank 37 stops flowing in and out, and the submersible agitator 18 of the second flow tank 37 is always in the stirring state.

[0074] To determine the ORP control range at the end of the denitrification reaction, S7 and controller 19 observe the changes in pH, ORP, and conductivity values ​​in the second flow tank 37 using the online denitrification pH detector 40, online denitrification ORP detector 41, and online denitrification conductivity detector 42. When pH rises and then falls, while conductivity remains stable or fluctuates slightly, or begins to rise, it indicates that denitrification has reached the end of the denitrification process. The ORP value at this point is then used as the new ORP control range for the secondary anoxic tank 4.

[0075] Denitrification endpoint control: S4, the sludge mixed liquor flows out of the primary anoxic tank 3 and flows into the secondary anoxic tank 4 and the tertiary anoxic tank 5 in sequence, switching the second flow tank 37 to normal operation. The controller 19 controls the flow rate of the anaerobic activated sludge added to the secondary anoxic tank 4 by the second metering pump 28 to control the ORP value of the second flow tank 37, i.e. the ORP value of the tertiary anoxic tank 5, so that it reaches the vicinity of the set denitrification endpoint ORP control range.

[0076] Aerobic reaction: S7, the sludge mixture flows out from the tertiary anoxic tank 5 and into the aerobic tank 6. The controller 19 reads the ORP and DO values ​​of the aerobic ORP online detector 33 and the aerobic DO online detector 32 in the aerobic tank 6, and controls the aeration frequency of the aerobic aeration pump 14 through the aerobic frequency converter 30, thereby controlling the aeration intensity of the aerobic tank 6, and finally achieving DO control or ORP control of the aerobic tank 6. Through the aerobic aeration of the aerobic tank 6, on the one hand, the nitrogen gas produced by denitrification is blown off, which is conducive to the static settling and separation of activated sludge and prevents the activated sludge from floating. On the other hand, aerobic aeration enhances the aerobic absorption of phosphorus by microorganisms. At the same time, the aerobic environment is conducive to the activated sludge not releasing phosphorus again due to hypoxia during the settling period, thus ensuring phosphorus removal. The ORP control range of the aerobic tank 6 is 0 to +120mv, and the DO control is between 1.5-3mg / L. One parameter can be selected for control, and the control range is determined by actual operation.

[0077] Sludge settling: The sludge mixture from S8 and aerobic tank 6 eventually flows into settling tank 7. The scraper 35 at the bottom of settling tank 7 is slowly rotated by stirring motor 34 to scrape the sludge deposited on the conical tank wall into the bottom of the cone. Finally, the supernatant from the overflow weir of settling tank 7 flows out as the system purified water. Some of the remaining sludge is discharged quantitatively by sludge discharge pump 36, while most of the activated sludge is returned to the primary anaerobic tank 9 by sludge return pump 8.

[0078] Adjustment of the ratio of sludge return pump velocity to wastewater treatment plant effluent influent velocity: S9. Control the ratio of sludge return pump velocity to wastewater treatment plant effluent influent velocity between 1 / 40 and 1 / 5, and adopt a low activated sludge concentration strategy to adapt to changes in the nitrogen concentration and water quality characteristics of wastewater treatment plant effluent. The higher the nitrogen concentration of wastewater treatment plant effluent, the larger this ratio will be, and vice versa.

[0079] The second method involves the following steps:

[0080] When the ammonia nitrogen concentration in the effluent of a wastewater treatment plant is high or the requirements for total nitrogen purification are high, the effluent must first enter the nitrification tank and undergo aerobic aeration nitrification treatment. The following operation steps are adopted.

[0081] System influent and aerobic nitrification: S1, the wastewater effluent from the wastewater treatment plant is pumped to the nitrification tank 1 by the influent pump 45, passes through the aeration zone and the deaeration zone of the packing layer, flows out from the bottom of the nitrification tank 1, passes through the first flow tank 2 and flows into the first-stage anoxic tank 3. The controller 19 controls the aeration intensity of the nitrification aeration pump 12 by controlling the nitrification frequency converter 20, and controls the DO concentration within a certain range, so that the ammonia nitrogen in the wastewater treatment plant effluent can be completely nitrified aerobically, while maintaining a low DO concentration.

[0082] External carbon source addition rate adjustment, external carbon source addition, and carbon-nitrogen ratio adjustment: S1, sampling pump 25 collects effluent from nitrification tank 1 and sends it to nitrate nitrogen online detector 26 to measure nitrate nitrogen concentration. Controller 19 estimates the flow rate of the external carbon source based on the measured nitrate nitrogen concentration or known total nitrogen concentration, combined with the carbon-nitrogen ratio. External carbon source addition pump 17 adds the external carbon source from external carbon source storage tank 16 to primary anaerobic tank 9 at the estimated flow rate. Controller 19 sets a control water level line in tertiary anaerobic tank 11. Controller 19 reads the liquid level height through liquid level gauge 46 and adjusts the carbon-nitrogen ratio coefficient by comparing the liquid level height with the control water level line.

[0083] Activated sludge anaerobic treatment process: S3, controller 19 returns the activated sludge settled in the settling tank 7 to the primary anaerobic tank 9 through the sludge return pump 8, and anaerobically mixes it with the external carbon source delivered by the external carbon source addition pump 17 at a set flow rate. Then it flows into the secondary anaerobic tank 10, and finally into the tertiary anaerobic tank 11. The activated sludge releases phosphorus anaerobically in the primary anaerobic tank 9, the secondary anaerobic tank 10 and the tertiary anaerobic tank 11, and absorbs organic matter to synthesize internal carbon sources.

[0084] Denitrification process control: S4, the controller 19 adds the anaerobic activated sludge to the primary anoxic tank 3 through the first metering pump 27 and mixes it with the nitrification liquid transferred from the nitrification tank 1 in anoxic stirring. The controller 19 controls the ORP value of the primary anoxic tank 3 by controlling the flow rate of the first metering pump 27, so that it reaches the set control range.

[0085] Operating mode of the second flow tank 37: S5. When the second flow tank 37 is in normal operation of denitrification control: the second sludge pump 39 continuously and rapidly transports the sludge mixture from the tertiary anoxic tank 5 to the second flow tank 37, and then returns it from the top of the second flow tank 37 to the tertiary anoxic tank 5. The submersible agitator 18 of the second flow tank 37 is always in the stirring state. When it is necessary to determine the denitrification endpoint: the second sludge pump 39 is turned off, the first sludge pump 38 is turned on, the activated sludge mixture from the primary anoxic tank 3 is transferred to the second flow tank 37, and then the first sludge pump 38 is stopped. The sludge mixture in the second flow tank 37 stops flowing in and out, and the submersible agitator 18 of the second flow tank 37 is always in the stirring state.

[0086] To determine the ORP control range at the end of the denitrification reaction, S7 and controller 19 observe the changes in pH, ORP, and conductivity values ​​in the second flow tank 37 using the online denitrification pH detector 40, online denitrification ORP detector 41, and online denitrification conductivity detector 42. When pH rises and then falls, while conductivity remains stable or fluctuates slightly, or begins to rise, it indicates that denitrification has reached the end of the denitrification process. The ORP value at this point is then used as the new ORP control range for the secondary anoxic tank 4.

[0087] Denitrification endpoint control: S4, the sludge mixed liquor comes out from the primary anoxic tank 3 and flows into the secondary anoxic tank 4 and the tertiary anoxic tank 5 in sequence, switching the second flow tank 37 to normal operation. The controller 19 controls the flow rate of the anaerobic activated sludge added to the secondary anoxic tank 4 by controlling the second metering pump 28 to control the ORP value of the second flow tank 37, i.e. the ORP value of the tertiary anoxic tank 5, so that it reaches the vicinity of the set denitrification endpoint ORP control range.

[0088] Aerobic reaction: S8 and sludge mixed liquor flow successively through primary anoxic tank 3, secondary anoxic tank 4, and tertiary anoxic tank 5 before flowing into aerobic tank 6. Controller 19 reads the ORP and DO values ​​from the aerobic ORP online detector 33 and aerobic DO online detector 32 in aerobic tank 6, and controls the aeration frequency of aerobic aeration pump 14 via aerobic frequency converter 30, thereby controlling the aeration intensity of aerobic tank 6. Ultimately, this achieves DO or ORP control in aerobic tank 6, through the aerobic aeration action of aerobic tank 6. On the one hand, the nitrogen gas produced by denitrification is stripped off, which is conducive to the static settling and separation of activated sludge, and the activated sludge will not float. On the other hand, aerobic aeration enhances the aerobic absorption of phosphorus by microorganisms. At the same time, the aerobic environment is conducive to the activated sludge not releasing phosphorus again due to lack of oxygen during the settling period, thus ensuring phosphorus removal. The ORP control range of aerobic tank 6 is 0 to +120mv, and the DO is controlled between 1.5-3mg / L. One parameter can be selected for control, and the control range is determined by the actual operation.

[0089] Sludge settling: The sludge mixture from S9 and aerobic tank 6 eventually flows into settling tank 7. The scraper 35 at the bottom of settling tank 7 is slowly rotated by stirring motor 34 to scrape the sludge deposited on the conical tank wall into the bottom of the cone. Finally, the supernatant from the overflow weir of settling tank 7 flows out as the system purified water. Some of the remaining sludge is discharged quantitatively by sludge discharge pump 36, while most of the activated sludge is returned to the primary anaerobic tank 9 by sludge return pump 8.

[0090] Adjustment of the ratio of sludge return pump velocity to wastewater treatment plant effluent influent velocity: S9. Control the ratio of sludge return pump velocity to wastewater treatment plant effluent influent velocity between 1 / 40 and 1 / 5, and adopt a low activated sludge concentration strategy to adapt to changes in the nitrogen concentration and water quality characteristics of wastewater treatment plant effluent. The higher the nitrogen concentration of wastewater treatment plant effluent, the larger this ratio will be, and vice versa.

[0091] Example 1: When the influent CODcr concentration of the wastewater treatment plant effluent was 13 mg / L, the total nitrogen concentration was 15 mg / L, and the total phosphorus concentration was 1 mg / L, with sodium acetate as the added organic carbon source, the ratio of sludge return flow rate to the influent flow rate was 1 / 20, the carbon-to-nitrogen ratio of the added carbon source was 5.4, the ORP control range of the secondary anoxic tank was -60 mV, and the ORP control range of the tertiary anoxic tank was -160 mV, the effluent CODcr concentration was 12 mg / L, the total nitrogen concentration was 0.5 mg / L, and the total phosphorus concentration was 0.23 mg / L, achieving deep purification of nitrogen and phosphorus. The total nitrogen and total phosphorus indicators of the effluent met the Class III-IV standards for surface water quality in lakes and reservoirs. The total hydraulic retention time of the primary, secondary, and tertiary anoxic tanks was 45 minutes, the hydraulic retention time of the aerobic tank was 10 minutes, the DO concentration of the aerobic tank was controlled at 2.1 mg / L, and the sludge retention time was 14 days.

[0092] Example 2: When the influent CODcr concentration of the wastewater treatment plant effluent was 18 mg / L, the total nitrogen concentration was 7.4 mg / L, and the total phosphorus concentration was 0.95 mg / L, with sodium acetate as the added organic carbon source, the ratio of sludge return flow rate to wastewater treatment plant effluent influent flow rate was 0.8 / 20, the carbon-nitrogen ratio of the added carbon source was 6.1, the ORP control range of the secondary anoxic tank was -55 mv, the ORP control range of the tertiary anoxic tank was -154 mv, the effluent CODcr concentration was 11 mg / L, the total nitrogen concentration was 0.8 mg / L, and the total phosphorus concentration was 0.2 mg / L, achieving deep purification of nitrogen and phosphorus. The total nitrogen and total phosphorus indicators of the effluent met the Class III-IV standards for surface water quality in lakes and reservoirs. The total hydraulic retention time for the primary, secondary, and tertiary anoxic tanks is 40 minutes, the hydraulic retention time for the aerobic tank is 10 minutes, the DO concentration in the aerobic tank is controlled at 2.2 mg / L, and the sludge retention time is 12 days.

[0093] Compared with iron-based autotrophic denitrification, sulfur-based autotrophic denitrification, pyrite autotrophic denitrification, microalgae biological treatment systems, and solid organic carbon source denitrification processes (see Table 1), this intelligent continuous flow low-active sludge concentration nitrogen and phosphorus deep treatment system for wastewater treatment plant effluent has a shorter hydraulic retention time, higher reactor operating efficiency, no by-products, and can simultaneously achieve deep removal of nitrogen and phosphorus. It is more suitable for water remediation, deep reuse of wastewater, and water resource recycling. While the pyrite autotrophic denitrification process has high nitrogen and phosphorus purification efficiency and does not require the addition of an external carbon source, it produces high levels of sulfate and iron ion by-products, which significantly impact water quality and limit deep water reuse, making large-scale application difficult.

[0094] Table 1. Comparison of this intelligent continuous flow low-activated sludge concentration nitrogen and phosphorus deep treatment system for wastewater effluent with various advanced processes.

[0095]

Claims

1. An intelligent continuous-flow low-activated sludge concentration nitrogen and phosphorus deep treatment system for tail water of a sewage plant, characterized in that, The utility model relates to a kind of wastewater treatment systems, including: Nitrification tank (1), first flow tank (2), first stage anoxic tank (3), second stage anoxic tank (4), third stage anoxic tank (5), aerobic tank (6), sedimentation tank (7), sludge return pump (8), first stage anaerobic tank (9), second stage anaerobic tank (10), third stage anaerobic tank (11), external carbon source storage tank (16), external carbon source adding pump (17), submersible mixer (18) and controller (19); It also includes second flow tank (37), first sludge pump (38), second sludge pump (39), denitrification pH online detector (40), denitrification ORP online detector (41), denitrification conductivity online detector (42), submersible mixer (18) and second metering pump (28);The inside of the second flow tank (37) is provided with the submersible mixer (18), and the inlet hole is communicated with the outlet hole of the first stage anoxic tank (3) and the outlet hole of the third stage anoxic tank (5) through the communication pipe, and the outlet hole is communicated with the inlet hole of the third stage anoxic tank (5);The first sludge pump (38) is installed on the communication pipe between the inlet hole of the second flow tank (37) and the outlet hole of the first stage anoxic tank (3);The second sludge pump (39) is installed on the communication pipe between the inlet hole of the second flow tank (37) and the outlet hole of the third stage anoxic tank (5);The denitrification pH online detector (40), the denitrification ORP online detector (41) and the denitrification conductivity online detector (42) are all installed in the second flow tank (37);The second metering pump (28) is installed on the communication pipe between the third stage anaerobic tank (11) and the second stage anoxic tank;The controller (19) is electrically connected with the first sludge pump (38), the second sludge pump (39), the submersible mixer (18), the denitrification pH online detector (40), the denitrification ORP online detector (41), the denitrification conductivity online detector (42) and the second metering pump (28), respectively; The operation mode of the second flow tank (37) is as follows: when the second flow tank (37) is in normal operation under denitrification control, the second sludge pump (39) continuously and quickly transports the sludge mixture in the third stage anoxic tank (5) to the second flow tank (37), and then returns to the third stage anoxic tank (5) from the top of the second flow tank (37), and the submersible mixer (18) of the second flow tank (37) is always in stirring state;When it is necessary to determine the denitrification end point, the second sludge pump (39) is closed, the first sludge pump (38) is opened, the activated sludge mixture in the first stage anoxic tank (3) is transferred to the second flow tank (37), then the first sludge pump (38) is stopped, the sludge mixture in the second flow tank (37) stops flowing in and out, and the submersible mixer (18) of the second flow tank (37) is always in stirring state. The determination of the ORP control range of the denitrification reaction end point, the controller (19) observes the changes of the pH, ORP and conductivity values of the denitrification pH on-line detector (40), the denitrification ORP on-line detector (41) and the denitrification conductivity on-line detector (42) in the second flow tank (37), when the pH appears to rise and then to drop, while the conductivity is steadily fluctuating or starts to rise, it indicates that the denitrification reaches the denitrification end point, and the ORP value at this time is taken as the ORP value control range of the secondary anoxic tank (4); The denitrification end point control: the sludge mixed liquor flows into the secondary anoxic tank (4) and the tertiary anoxic tank (5) in turn from the primary anoxic tank (3), the second flow tank (37) is switched to the normal operation state, the controller (19) controls the ORP value of the second flow tank (37) by controlling the flow rate of the anaerobic treated activated sludge added to the secondary anoxic tank (4) by the second metering pump (28), so that it reaches the vicinity of the set denitrification end point ORP control range.

2. The intelligent continuous-flow low-activated-sludge-concentration nitrogen and phosphorus advanced treatment system for tail water of a sewage plant according to claim 1, characterized in that, The outlet and inlet of the nitrification tank (1), the first flow tank (2), the primary anoxic tank (3), the secondary anoxic tank (4), the tertiary anoxic tank (5), the aerobic tank (6), the sedimentation tank (7), the sludge return pump (8), the primary anaerobic tank (9), the secondary anaerobic tank (10) and the tertiary anaerobic tank (11) are connected in turn by communication pipes, and the outlet of the tertiary anaerobic tank (11) is connected with the primary anoxic tank (3) and the secondary anoxic tank (4) respectively; The submersible mixers (18) are multiple and rotate in the primary anoxic tank (3), the secondary anoxic tank (4), the tertiary anoxic tank (5), the aerobic tank (6), the primary anaerobic tank (9), the secondary anaerobic tank (10) and the tertiary anaerobic tank (11) respectively; The controller (19) is electrically connected with the sludge return pump (8), the external carbon source adding pump (17) and multiple submersible mixers (18) respectively.

3. The intelligent continuous-flow low-activated-sludge-concentration nitrogen and phosphorus advanced treatment system for tail water of a sewage plant according to claim 1, characterized in that, It also includes nitrification frequency converter (20), nitrification aeration pump (12), nitrification aeration head (13), nitrification gas flow meter (21), first valve (22), second valve (23), sludge discharge valve (44) and nitrification DO online detector (24); the bottom end of the nitrification tank (1) is a conical body, and the conical bottom end is provided with a sludge discharge hole, and the sludge discharge valve (44) is installed on the sludge discharge hole; the nitrification aeration head (13) is multiple and divided into two groups, respectively fixed in the middle and lower part of the filler layer in the nitrification tank (1) and the lower part of the filler layer, spaced apart, and the filler layer inside the nitrification tank (1) is divided into the upper aeration zone and the lower gas zone; the nitrification frequency converter (20) is electrically connected with the nitrification aeration pump (12); the nitrification aeration pump (12) is located outside the nitrification tank (1), and the nitrification aeration pump (12) is connected with the nitrification gas flow meter (21) through a gas pipeline; the nitrification gas flow meter (21) is divided into two groups of branch pipes through a gas pipeline, and the first valve (22) and the second valve (23) are respectively installed on the two groups of branch pipes, and the two groups of branch pipes are respectively extended into the middle and lower part of the filler layer in the nitrification tank (1) and the bottom and connected with the upper and lower groups of multiple nitrification aeration heads (13); the nitrification DO online detector (24) is installed in the first flow tank (2); the controller (19) is electrically connected with the nitrification frequency converter (20), the nitrification gas flow meter (21), the first valve (22), the second valve (23), the sludge discharge valve (44) and the nitrification DO online detector (24).

4. The intelligent continuous-flow low-activated-sludge-concentration nitrogen and phosphorus advanced treatment system for tail water of a sewage plant according to claim 1, characterized in that, It also includes sampling pump (25), nitrate nitrogen online detector (26), external carbon source adding pump (17) and liquid level gauge (46); the inlet hole of the sampling pump (25) is communicated on the communication pipe between the outlet hole of the nitrification tank (1) and the first flow tank (2); the inlet hole of the nitrate nitrogen online detector (26) is communicated with the outlet hole of the sampling pump (25); the inlet and outlet of the external carbon source adding pump (17) are communicated on the pipeline between the outlet hole of the external carbon source storage tank (16) and the inlet hole of the primary anaerobic tank (9); the liquid level gauge (46) is fixed at the top end inside the tertiary anaerobic tank (11); the controller (19) is electrically connected with the sampling pump (25), the nitrate nitrogen online detector (26), the external carbon source adding pump (17) and the liquid level gauge (46).

5. The intelligent continuous-flow low-activated-sludge-concentration nitrogen and phosphorus advanced treatment system for tail water of a sewage plant according to claim 1, characterized in that, It also includes first metering pump (27) and anoxic ORP online detector (29), the first metering pump (27) is installed on the communication pipe between the tertiary anaerobic tank (11) and the primary anoxic tank (3); the anoxic ORP online detector (29) is installed in the primary anoxic tank (3); the controller (19) is electrically connected with the first metering pump (27) and the anoxic ORP online detector (29).

6. The intelligent continuous-flow low-activated-sludge-concentration nitrogen and phosphorus advanced treatment system for tail water of a sewage plant according to claim 1, characterized in that, The aerobic aeration pump (14) is located outside the aerobic tank (6); the aerobic aeration head (15) is fixed in the aerobic tank (6) and extends out of the aerobic tank (6) and communicates with the aerobic aeration pump (14); the aerobic gas flow detector (31) is installed on the communication pipe between the outlet hole of the aerobic aeration pump (14) and the aerobic aeration head (15); the aerobic DO online detector (32) and the aerobic ORP online detector (33) are both fixed in the aerobic tank (6); the aerobic frequency converter (30) is electrically connected with the aerobic aeration pump (14); and the controller (19) is electrically connected with the aerobic frequency converter (30), the aerobic gas flow detector (31), the aerobic DO online detector (32) and the aerobic ORP online detector (33) respectively.

7. The intelligent continuous-flow low-activated-sludge-concentration nitrogen and phosphorus advanced treatment system for tail water of a sewage plant according to claim 1, characterized in that, The stirring motor (34) is fixed at the top end of the sedimentation tank (7) and its output shaft extends into the sedimentation tank (7); the mud scraping plate (35) is located in the sedimentation tank (7) and in contact with the tank wall of the sedimentation tank (7), and the mud scraping plate (35) is fixed on the output shaft of the stirring motor (34); the sludge pump (36) communicates with the outlet hole of the sedimentation tank (7) through a communication pipe; and the controller (19) is electrically connected with the stirring motor (34) and the sludge pump (36) respectively.

8. The intelligent continuous-flow low-activated-sludge-concentration nitrogen and phosphorus advanced treatment system for tail water of a sewage plant according to claim 1, characterized in that, The aerobic tank (6) has a liquid level higher than the top ends of the first-stage anoxic tank (3), the second-stage anoxic tank (4) and the third-stage anoxic tank (5) and lower than the exhaust ports of the exhaust pipes (43) on the first-stage anoxic tank (3), the second-stage anoxic tank (4) and the third-stage anoxic tank (5); and the top ends of the first-stage anoxic tank (3), the second-stage anoxic tank (4) and the third-stage anoxic tank (5) are all conical.

9. An intelligent continuous-flow low-activated-sludge-concentration nitrogen and phosphorus deep treatment method for tail water of a sewage plant, characterized in that, The sewage plant tail water intelligent continuous flow low-activity sludge concentration nitrogen and phosphorus deep treatment system comprises the sewage plant tail water intelligent continuous flow low-activity sludge concentration nitrogen and phosphorus deep treatment system according to any one of claims 1-8, and the specific steps are as follows: When the ammonia nitrogen concentration of the sewage plant tail water is low or the total nitrogen purification requirement is not high, the sewage plant tail water can not be nitrified, the nitrification tank (1) is not used, and the following operation steps are adopted. System water, external carbon source addition rate adjustment, external carbon source addition and carbon nitrogen ratio adjustment: S1, the water pump (45) directly transports the tail water of the sewage plant to the first stage anoxic tank (3), and the sampling pump (25) collects the influent water sample to the nitrate nitrogen online detector (26) to measure the nitrate nitrogen concentration; the controller (19) estimates the flow rate of the added carbon source according to the measured nitrate nitrogen concentration or the known total nitrogen concentration, combined with the carbon nitrogen ratio; the external carbon source addition pump (17) adds the external carbon source in the external carbon source storage tank (16) to the first stage anaerobic tank (9) according to the estimated flow rate; the controller (19) sets the control water level line in the third stage anaerobic tank (11), and the controller (19) reads the liquid level height through the liquid level gauge (46), and adjusts the carbon nitrogen ratio coefficient by comparing the height of the liquid level height and the control water level line; Active sludge anaerobic treatment process: S2, the return sludge pump (8) transports the returned active sludge to the first stage anaerobic tank (9) through the settling tank (7), and the external carbon source addition pump (17) transports the external carbon source with a set flow rate to carry out anaerobic mixing and stirring, and then flows into the second stage anaerobic tank (10), and finally flows into the third stage anaerobic tank (11); the active sludge releases phosphorus in the first stage anaerobic tank (9), the second stage anaerobic tank (10) and the third stage anaerobic tank (11) in an anaerobic state, absorbs organic matter to synthesize internal carbon source; Denitrification reaction process control: S3, the controller (19) adds the active sludge treated by the third stage anaerobic tank (11) to the first stage anoxic tank (3) through the first metering pump (27) to carry out anoxic stirring and mixing with the tail water of the sewage plant transferred by the water pump (45), and the controller (19) controls the flow rate of the first metering pump (27) to control the ORP value of the first stage anoxic tank (3) to reach the set control range; The operation mode of the second flow tank (37): S4, when the second flow tank (37) is in the normal operation of denitrification control: the second sludge pump (39) continuously and quickly transports the sludge mixture of the third stage anoxic tank (5) to the second flow tank (37), and then returns to the third stage anoxic tank (5) from the top of the second flow tank (37), and the submersible agitator (18) of the second flow tank (37) is always in the stirring state; when the denitrification endpoint needs to be determined: close the second sludge pump (39), open the first sludge pump (38), transfer the active sludge mixture of the first stage anoxic tank (3) to the second flow tank (37), then stop the first sludge pump (38), the sludge mixture in the second flow tank (37) stops flowing in and out, and the submersible agitator (18) of the second flow tank (37) is always in the stirring state; Determination of the denitrification end-point ORP control range, S5, the controller (19) observes the changes of pH, ORP and conductivity values of the denitrification pH on-line detector (40), the denitrification ORP on-line detector (41) and the denitrification conductivity on-line detector (42) in the second flow tank (37), when the pH appears to rise and then to fall, while the conductivity fluctuates steadily, or begins to rise, it indicates that the denitrification reaches the denitrification end-point, and the ORP value at this time is taken as the ORP value control range of the secondary anoxic tank (4); Denitrification end-point control: S6, the sludge mixed liquor flows from the primary anoxic tank (3) into the secondary anoxic tank (4) and the tertiary anoxic tank (5) in turn, the second flow tank (37) is switched to the normal running state, the controller (19) controls the ORP value of the second flow tank (37) by controlling the flow rate of the anaerobic treated activated sludge added to the secondary anoxic tank (4) through the second metering pump (28), so that it reaches the vicinity of the set denitrification end-point ORP control range; Aerobic reaction: S7, the sludge mixed liquor flows out of the tertiary anoxic tank (5) and flows into the aerobic tank (6), the controller (19) reads the ORP and DO values of the aerobic ORP on-line detector (33) and the aerobic DO on-line detector (32) in the aerobic tank (6), controls the aeration frequency of the aerobic aeration pump (14) through the aerobic frequency converter (30), and then controls the aeration intensity of the aerobic tank (6), finally realizes the DO control or ORP control of the aerobic tank (6), through the aerobic aeration of the aerobic tank (6), on the one hand, the nitrogen produced by denitrification is stripped, which is beneficial to the standing and settling separation of the activated sludge, and the activated sludge will not float, on the other hand, the aerobic aeration strengthens the aerobic absorption of phosphorus by microorganisms, and the aerobic environment is conducive to the activated sludge not to release phosphorus again during the settling period, thereby ensuring the removal of phosphorus; the ORP control range of the aerobic tank (6) is 0 to +120mv, and the DO is controlled between 1.5-3mg / L, and one of the parameters can be selected to control; Sludge settling: S8, the sludge mixed liquor in the aerobic tank (6) finally flows into the settling tank (7), the mud scraper (35) arranged at the bottom of the settling tank (7) slowly rotates through the stirring motor (34) to scrape the sludge deposited on the conical tank wall into the conical bottom, finally, the supernatant flows out of the system as purified water through the overflow weir of the settling tank (7), part of the remaining sludge is quantitatively discharged through the sludge discharge pump (36), and most of the activated sludge is returned to the primary anaerobic tank (9) through the sludge return pump (8); Adjustment of the ratio of the sludge return pump flow rate to the sewage plant tail water inflow rate: S9, the ratio of the sludge return pump flow rate to the sewage plant tail water inflow rate is controlled between 1 / 40-1 / 5, a low activated sludge concentration strategy is adopted to adapt to the changes of the nitrogen concentration of the sewage plant tail water, the higher the nitrogen concentration of the sewage plant tail water, the larger the ratio, and vice versa.

10. An intelligent continuous-flow low-activity-sludge-concentration nitrogen and phosphorus deep treatment method for tail water of a sewage plant, characterized in that, The intelligent continuous-flow low-activated-sludge-concentration nitrogen and phosphorus advanced treatment system for sewage plant tail water according to any one of claims 1-8, the specific steps are as follows: When the ammonia nitrogen concentration of the tail water of the sewage plant is high or the total nitrogen purification requirement is high, the tail water of the sewage plant first needs to be subjected to aerobic aeration and nitrification treatment, and the following operation steps are adopted; System water inlet and aerobic nitrification: S1, the tail water of the sewage plant is transported to the nitrification tank (1) through the water inlet pump (45), passes through the aeration zone and the air shortage zone of the filler layer, flows out from the bottom of the nitrification tank (1), passes through the first flow tank (2) and flows into the first-stage anoxic tank (3), the controller (19) controls the aeration intensity of the nitrification aeration pump (12) by controlling the nitrification frequency converter (20), so that the DO concentration is controlled within a certain range, so that the ammonia nitrogen in the tail water of the sewage plant can be completely subjected to aerobic nitrification, and at the same time, a relatively low DO concentration can be maintained; External carbon source addition rate adjustment, external carbon source addition and carbon-nitrogen ratio adjustment: S2, the sampling pump (25) collects the effluent of the nitrification tank (1) and sends it to the nitrate nitrogen online detector (26) to measure the nitrate nitrogen concentration, the controller (19) estimates the flow rate of the added carbon source according to the measured nitrate nitrogen concentration or the known total nitrogen concentration, and adjusts the carbon-nitrogen ratio; the external carbon source addition pump (17) adds the external carbon source in the external carbon source storage tank (16) to the first-stage anaerobic tank (9) at the estimated flow rate; the controller (19) sets a control water level line in the third-stage anaerobic tank (11), and the controller (19) reads the liquid level height through the liquid level gauge (46) and adjusts the carbon-nitrogen ratio coefficient by comparing the height of the liquid level height with the control water level line; Active sludge anaerobic treatment process: S3, the controller (19) returns the active sludge settled in the sedimentation tank (7) to the first-stage anaerobic tank (9) through the sludge return pump (8), and mixes and stirs the active sludge with the external carbon source added by the external carbon source addition pump (17) at a set flow rate, and then flows into the second-stage anaerobic tank (10) and finally flows into the third-stage anaerobic tank (11); the active sludge releases phosphorus in the first-stage anaerobic tank (9), the second-stage anaerobic tank (10) and the third-stage anaerobic tank (11) in an anaerobic manner, absorbs organic matter and synthesizes internal carbon source; Denitrification reaction process control: S4, the controller (19) adds the anaerobically treated active sludge into the first-stage anoxic tank (3) through the first metering pump (27) and mixes and stirs it with the nitrified liquid transferred from the nitrification tank (1); the controller (19) controls the ORP value of the first-stage anoxic tank (3) by controlling the flow rate of the first metering pump (27), so that the ORP value reaches the set control range. The operation mode of the second flow tank (37) is as follows: S5, when the second flow tank (37) is in normal operation under denitrification control: the second sludge pump (39) continuously and quickly transports the sludge mixed liquid in the third anoxic tank (5) to the second flow tank (37), and then returns to the third anoxic tank (5) from the top of the second flow tank (37), and the submersible agitator (18) of the second flow tank (37) is always in the stirring state; when it is necessary to determine the denitrification end point: the second sludge pump (39) is closed, and the first sludge pump (38) is opened, the activated sludge mixed liquid in the first anoxic tank (3) is transferred to the second flow tank (37), then the first sludge pump (38) is stopped, the sludge mixed liquid in the second flow tank (37) stops flowing in and out, and the submersible agitator (18) of the second flow tank (37) is always in the stirring state; Determination of the ORP control range of the denitrification reaction end point, S6, the controller (19) observes the changes of the pH, ORP and conductivity values of the denitrification pH online detector (40), the denitrification ORP online detector (41) and the denitrification conductivity online detector (42) in the second flow tank (37), when the pH appears to rise and then to fall, and at the same time the conductivity stably fluctuates up and down or begins to rise, it indicates that the denitrification reaches the denitrification end point, and the ORP value at this time is taken as the ORP value control range of the second anoxic tank (4); Denitrification end point control: S7, the sludge mixed liquid flows out from the first anoxic tank (3), flows into the second anoxic tank (4) and the third anoxic tank (5) in turn, and the second flow tank (37) is switched to the normal operation state, the controller (19) controls the flow rate of the activated sludge after anaerobic treatment added to the second anoxic tank (4) by controlling the second metering pump (28) to control the ORP value of the second flow tank (37), so that it reaches the vicinity of the set denitrification end point ORP control range; Aerobic reaction: S8, after the sludge mixed liquid flows through the first anoxic tank (3), the second anoxic tank (4) and the third anoxic tank (5) in turn, it flows into the aerobic tank (6), the controller (19) reads the ORP and DO values of the aerobic ORP online detector (33) and the aerobic DO online detector (32) in the aerobic tank (6), controls the aeration frequency of the aerobic aeration pump (14) through the aerobic frequency converter (30), and then controls the aeration intensity of the aerobic tank (6), finally realizes the DO control or ORP control of the aerobic tank (6), through the aerobic aeration of the aerobic tank (6), on the one hand, the nitrogen produced in the denitrification is stripped, which is beneficial to the static setting and separation of the activated sludge, and the activated sludge will not float, on the other hand, the aerobic aeration strengthens the aerobic absorption of phosphorus by microorganisms, and at the same time, the aerobic environment is beneficial to the activated sludge during the setting period, and the activated sludge will not release phosphorus again due to anoxic, so as to ensure the removal of phosphorus, the ORP control range of the aerobic tank (6) is 0 to +120mv, and the DO is controlled between 1.5-3mg / L, and one parameter is selected to control. Sludge sedimentation: S9, the sludge mixed liquor of the aerobic tank (6) finally flows into the sedimentation tank (7), the mud scraper (35) arranged at the bottom of the sedimentation tank (7) slowly rotates through the stirring motor (34) to scrape the sludge deposited on the conical wall into the conical bottom, finally, the supernatant of the overflow weir of the sedimentation tank (7) flows out as the purified water of the system, part of the residual sludge is quantitatively discharged through the sludge discharge pump (36), and most of the activated sludge is returned to the primary anaerobic tank (9) through the sludge return pump (8); Adjustment of the ratio of the sludge return pump flow rate to the sewage plant tail water inflow rate: S10, the ratio of the sludge return pump flow rate to the sewage plant tail water inflow rate is controlled to be between 1 / 40-1 / 5, a low activated sludge concentration strategy is adopted to adapt to the change of the water quality characteristics of the nitrogen concentration of the sewage plant tail water, the higher the nitrogen concentration of the sewage plant tail water, the larger the ratio, and vice versa.

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