A municipal sewage low-temperature high-efficiency denitrification treatment method

Abstract

The application discloses a kind of municipal sewage low-temperature high-efficiency nitrogen removal treatment methods, it is related to wastewater treatment technical field, including obtaining dissolved oxygen data and first flow data in the internal reflux liquid from the end of aerobic tank to anoxic tank, and obtaining second flow data of carbon source adding system;Determine the dissolved oxygen mass loading data of internal reflux liquid into anoxic tank;Determine the theoretical reduction equivalent data of carbon source;Determine the ratio data based on dissolved oxygen mass loading data and theoretical reduction equivalent data of carbon source;In the case where ratio data is greater than first threshold data, suspend execution of carbon source feedforward calculation logic based on nitrate load, and execute hierarchical control instructions containing first frequency reduction instruction, second frequency reduction instruction and incremental instruction in order until ratio data is less than or equal to second threshold data;The application improves the treatment effect of water pollution, and guarantees that effluent quality is stable and meets the standard and the economy of carbon source addition.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a low-temperature, high-efficiency denitrification method for municipal wastewater. Background Technology

[0002] In water pollution treatment—especially in the low-temperature winter operation scenario of municipal wastewater A / O processes—existing systems typically employ a conventional treatment method to ensure denitrification efficiency, which involves setting a fixed internal recirculation ratio and issuing carbon source addition instructions based on empirical ratios at ambient temperature. However, when water temperatures continue to drop in winter, the metabolic rate of denitrifying bacteria decreases significantly, and the fixed recirculation ratio continuously carries dissolved oxygen from the aerobic tank into the anoxic tank.

[0003] Because traditional control logic lacks quantitative judgment on the consumption of carbon sources by dissolved oxygen during reflux, the system lacks accurate knowledge of the current carbon-nitrogen balance. This forces maintenance personnel to increase the amount of carbon source added based on experience when the total nitrogen in the effluent increases. However, excessive carbon source cannot be consumed in time due to the slow metabolism of microorganisms, resulting in excessive COD in the effluent. At the same time, dissolved oxygen preferentially consumes carbon source, resulting in insufficient carbon source for denitrification, and the total nitrogen in the effluent also exceeds the standard. Ultimately, this leads to both total nitrogen and COD exceeding the standard, accompanied by waste of carbon source reagents and power consumption, resulting in poor water pollution treatment effect. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a low-temperature, high-efficiency denitrification treatment method for municipal wastewater.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a method for low-temperature, high-efficiency nitrogen removal treatment of municipal wastewater, comprising: Acquire dissolved oxygen data and first flow rate data in the internal reflux liquid from the end of the aerobic tank to the anoxic tank, and acquire second flow rate data of the carbon source dosing system; Based on the dissolved oxygen data and the first flow rate data, the dissolved oxygen mass load data brought into the anoxic tank by the internal reflux liquid is determined; Based on the second flow rate data and the theoretical oxygen equivalent coefficient of the currently added carbon source, the theoretical reduction equivalent data of the carbon source is determined; Based on the dissolved oxygen mass load data and the theoretical reduction equivalent data of the carbon source, the ratio data is determined; If the ratio data is greater than the first threshold data, the execution of the carbon source feedforward calculation logic based on nitrate load is paused, and a hierarchical control instruction including a first frequency reduction instruction, a second frequency reduction instruction, and an incremental instruction is executed sequentially until the ratio data is less than or equal to the second threshold data; wherein, the first threshold data is greater than the second threshold data; The first frequency reduction command is used to control the aeration equipment in the aerobic tank to reduce its frequency, the second frequency reduction command is used to control the internal circulation return pump to reduce its frequency, and the incremental command is used to control the carbon source addition system to increase the amount of carbon source added.

[0006] As a preferred embodiment of the present invention, the sequential execution of the hierarchical control instructions comprising a first frequency reduction instruction, a second frequency reduction instruction, and an incremental instruction includes: The first frequency reduction command is sent to the aeration device, and the ratio data is reacquired after waiting for a first set time. If the reacquired ratio data is greater than the second threshold data, then the second frequency reduction command is sent to the internal circulation return pump, and the ratio data is reacquired again after waiting for the second set time, as well as the oxidation-reduction potential data at the head of the anoxic pool. If the ratio data obtained again is less than or equal to the second threshold data, and the redox potential data is greater than the third threshold data, then the incremental command is issued to the carbon source dosing system.

[0007] As a preferred embodiment of the present invention, after issuing the incremental command to the carbon source dosing system, the method further includes: Continuously acquire the redox potential data that is updated in real time; If the real-time updated redox potential data is less than or equal to the fourth threshold data, the release action is executed sequentially in the reverse order of the hierarchical control command. The release actions sequentially include: issuing a reduction command to the carbon source addition system, issuing a first recovery command to the internal circulation return pump, and issuing a second recovery command to the aeration equipment; After the release action is completed, the carbon source feedforward calculation logic based on nitrate load is resumed.

[0008] As a preferred embodiment of the present invention, the method further includes: If the ratio data is less than or equal to the second threshold data, the carbon and nitrogen calculation model is maintained to output the dosing command; If the ratio data is greater than the second threshold data and less than or equal to the first threshold data, then the acquisition frequency of the dissolved oxygen data, the first flow data, and the second flow data is increased, and the time-series change rate of the ratio data is acquired. If the time-series change rate indicates that the ratio data continues to rise within a continuously set number of control cycles, then the hierarchical control command is executed.

[0009] As a preferred embodiment of the present invention, the step of maintaining the execution of the carbon and nitrogen calculation model to output the dosing command includes: Acquire influent flow rate data, influent nitrate nitrogen data, and effluent nitrate nitrogen data; Based on the influent flow rate data and the difference between the influent nitrate nitrogen data and the effluent nitrate nitrogen data, the basic dosage data is determined; The dosing instruction is generated based on the basic dosing data and then sent to the carbon source dosing system.

[0010] As a preferred embodiment of the present invention, before determining the theoretical reduction equivalent data of the carbon source based on the second flow rate data and the theoretical oxygen equivalent coefficient of the currently added carbon source, the method further includes: Obtain carbon source type identification data, and based on the carbon source type identification data, match and obtain the corresponding theoretical oxygen equivalent coefficient from the storage database; If a change in the carbon source type identification data is detected, the fluctuation range of the ratio data is obtained within the set calibration period after the change. The first threshold data and the second threshold data are updated based on the fluctuation range.

[0011] As a preferred embodiment of the present invention, the following limitations apply when executing the first down-frequency instruction, the second down-frequency instruction, and the incremental instruction: The cumulative reduction of the first frequency reduction instruction does not exceed the first limit ratio of the current frequency of the aeration device. If the first limit ratio is reached and the ratio data obtained again is still greater than the second threshold data, then the second frequency reduction instruction is executed. The cumulative reduction of the second frequency reduction instruction does not exceed the second limit ratio of the current frequency of the internal circulation reflux pump. If the second limit ratio is reached and the redox potential data is still greater than the third threshold data, then the incremental instruction is executed. The cumulative increase of the incremental instruction shall not exceed the third limit ratio of the current addition amount of the carbon source addition system.

[0012] As a preferred embodiment of the present invention, the method further includes: If a malfunction is detected in the first acquisition device used to acquire the dissolved oxygen data, or in the second acquisition device used to acquire the first flow rate data, the ratio data is configured to a first alternative value that is greater than the first threshold data. Skip the execution of the first down-frequency instruction and directly execute the second down-frequency instruction and the incremental instruction.

[0013] As a preferred embodiment of the present invention, the method further includes: After the hierarchical control command is issued, if no feedback signal is received from the corresponding execution device within the set response time, or if the deviation between the actual frequency data indicated by the feedback signal and the target frequency data is greater than the fifth threshold data, the same command is issued again. If the feedback signal is not received after the set number of times the signal is sent again, the corresponding execution device will be marked as in a failed state, and the execution devices that are not in the failed state will be controlled to run according to the set second alternative value.

[0014] As a preferred embodiment of the present invention, the method further includes: After executing multiple complete cycles containing the first frequency reduction instruction, the second frequency reduction instruction, and the incremental instruction, if the ratio data is greater than the second threshold data and the redox potential data is greater than the third threshold data, the control strategy is switched to the target control state. The target control state includes: configuring the operating frequency of the internal circulation reflux pump to a set conversion ratio, and configuring the second flow rate data of the carbon source dosing system to the minimum dose data.

[0015] The beneficial effects of this invention are: This application establishes a multi-level intervention mechanism in low-temperature denitrification control by setting a ratio based on dissolved oxygen mass load data and carbon source theoretical reduction equivalent data. When this ratio exceeds a first threshold, the conventional carbon source feedforward calculation logic is suspended, and instead, a hierarchical control command including a first frequency reduction command, a second frequency reduction command, and an incremental command is executed sequentially. This mechanism uses the degree of carbon source consumption by refluxed dissolved oxygen as the criterion for judgment. When the ratio exceeds the limit, the original calculation model's transmission path is cut off, and intervention is carried out step by step in the order of first reducing the dissolved oxygen source, then cutting off the dissolved oxygen transport, and finally replenishing the carbon source loss. This allows each execution device to respond hierarchically according to actual needs, avoiding over-adjustment or blind dosing in a single dimension. It solves the problem of double exceedance of total nitrogen and COD in effluent caused by a fixed reflux ratio at low temperatures in existing technologies, ensuring stable compliance of effluent water quality and the economic efficiency of carbon source addition, and also improving the treatment effect of water pollution. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the workflow of the low-temperature and high-efficiency nitrogen removal treatment method for municipal wastewater according to the present invention; Figure 2 This is a structural block diagram of the low-temperature, high-efficiency nitrogen removal system for municipal wastewater according to the present invention. Detailed Implementation

[0017] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. The components of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0018] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0019] like Figures 1-2 As shown, this invention provides a low-temperature, high-efficiency nitrogen removal method for municipal wastewater treatment, applicable to A / O process biological nitrogen removal systems that include aerobic and anoxic tanks, and also suitable for A... 2 A / O deformation processes such as / O and modified UCT.

[0020] In a specific implementation of this embodiment, a dissolved oxygen sensor and an electromagnetic flow meter are deployed at the end of the internal circulation return pipe.

[0021] The dissolved oxygen sensor is used to collect the dissolved oxygen concentration in the internal reflux liquid from the end of the aerobic tank to the anoxic tank in real time, and the electromagnetic flow meter is used to collect the instantaneous flow rate of the internal reflux liquid as the first flow rate data.

[0022] Setting the monitoring points at the end of the return pipe, adjacent to the inlet of the anoxic tank, is problematic. If dissolved oxygen concentration is only collected at the end of the aerobic tank, the concentration may decrease during transmission through the return pipe due to aerobic metabolic activity of the biofilm attached to the pipe wall, failing to accurately reflect the actual amount of dissolved oxygen entering the anoxic tank. Dissolved oxygen concentration collected at the end of the internal circulation return pipe provides a more accurate representation of the dissolved oxygen level entering the anoxic tank.

[0023] Simultaneously, the system acquires the current mass flow rate of the carbon source being added at the outlet of the dosing pump in the carbon source dosing system, as the second flow rate data. The system also stores the theoretical oxygen equivalent coefficient corresponding to the currently added carbon source, which represents the mass of oxygen that can be consumed per unit mass of carbon source under complete oxidation conditions, and its value depends on the chemical composition of the carbon source.

[0024] The system calculates two core indicators based on the data collected above.

[0025] The first is the dissolved oxygen mass load data, which is equal to the product of the dissolved oxygen concentration at the end of the return pipe and the first flow rate data, representing the total mass of dissolved oxygen carried from the aerobic tank to the anoxic tank through internal circulation return per unit time.

[0026] The second is the theoretical reduction equivalent data of the carbon source, which is equal to the product of the second flow rate data of the carbon source addition system and the theoretical oxygen equivalent coefficient of the currently added carbon source. It represents the total mass of dissolved oxygen that the currently added carbon source can theoretically consume under complete oxidation conditions per unit time.

[0027] The system then calculates the ratio between the two. This ratio directly reflects the relative relationship between the total dissolved oxygen brought into the anoxic tank by the current recirculation and the theoretical reduction capacity of the current carbon source dosage.

[0028] In anoxic tanks, dissolved oxygen and nitrate nitrogen compete for carbon sources. Dissolved oxygen, as a superior electron acceptor, preferentially consumes the carbon source added to the system. When the ratio is low, it indicates that the reducing capacity of the carbon source is sufficient to consume the dissolved oxygen brought in by the recirculation and there is still a surplus to supply the denitrification reaction. When the ratio rises to near or above the safety threshold, it means that the dissolved oxygen brought in by the recirculation is consuming a large amount of the carbon source that should be used for denitrification, and the denitrification reaction faces the risk of carbon starvation.

[0029] Based on this, this embodiment sets two threshold data with numerical differences, wherein the first threshold data is greater than the second threshold data.

[0030] The first threshold data serves as the critical value for triggering the hierarchical control command, and the second threshold data serves as the critical value for the system to stop the hierarchical control command and resume normal operation. There is a difference between the two thresholds to prevent the system from frequently switching due to signal fluctuations near the critical value.

[0031] The system calculates the ratio data in real time during each control cycle and compares it with the first threshold data.

[0032] When the ratio data is lower than or equal to the second threshold data, the system maintains normal operation and outputs carbon source addition instructions according to the conventional carbon source feedforward calculation logic based on nitrate load.

[0033] When the ratio exceeds the first threshold, it means that the dissolved oxygen brought in by the recirculation has approached the danger threshold in terms of carbon source consumption. At this point, the system suspends the execution of the conventional carbon source feedforward calculation logic based on nitrate load and executes the three-level control instructions in sequence: First, a first frequency reduction command is issued to the aeration equipment at the end of the aerobic tank to reduce the source of dissolved oxygen production. Then, a second frequency reduction command is issued to the internal circulation return pump to physically cut off the dissolved oxygen transport path. Finally, an incremental command is issued to the carbon source addition system to compensate for the carbon source that has been consumed by dissolved oxygen.

[0034] The rationale behind this sequential execution logic is that it first addresses the source of dissolved oxygen generation, then the dissolved oxygen transport channels, and finally performs passive compensation of the carbon source, thus avoiding the inefficient cycle of "replenishing the carbon source while continuing to input large amounts of dissolved oxygen."

[0035] The above three levels of control commands are executed in a set order, and the system re-evaluates the ratio data after each level is executed.

[0036] If the ratio data falls back to a safe range of less than or equal to the second threshold data after executing a certain level, subsequent levels will not be executed. The system maintains the current state and continues to monitor, thereby avoiding excessive intervention and realizing control that intervenes step by step as needed. When the ratio data falls back below the second threshold data, the system resumes executing the regular carbon source feedforward calculation logic, completing a complete closed loop from emergency control to normal operation.

[0037] It should be noted that the specific values ​​of the first threshold data and the second threshold data mentioned above can be configured by those skilled in the art based on factors such as the hydraulic retention time of the anoxic tank, sludge concentration, and influent water quality characteristics. This embodiment does not impose an absolute limitation on this.

[0038] The module functions involved in the above processing include, but are not limited to: a data acquisition module for acquiring the above-mentioned monitoring data, a load calculation module for calculating dissolved oxygen mass load data and carbon source theoretical reduction equivalent data, a gating judgment module for comparing the above two and generating a gating judgment signal, and a linkage execution module for performing the above-mentioned three-level physical linkage decoupling actions.

[0039] Furthermore, the aforementioned hierarchical control instructions comprise three levels: a first frequency reduction instruction, a second frequency reduction instruction, and an incremental instruction. Their execution order has a clear progressive relationship; the prerequisite for executing the next level is that the system state has not yet returned to the safety boundary after the execution of the previous level. This sequential design avoids over-adjustment caused by simultaneously executing multiple levels of intervention actions.

[0040] Specifically, the system first sends a first frequency reduction command to the aeration equipment at the end of the aerobic tank, instructing the aeration equipment to reduce its operating frequency.

[0041] The reason for making reducing aeration the first action is that the dissolved oxygen concentration at the end of the aerobic tank is the direct source of dissolved oxygen in the return liquid. If the dissolved oxygen concentration can be reduced at the source, the total amount of dissolved oxygen in the subsequent return transport process will naturally decrease.

[0042] After the first frequency reduction command is issued, the system does not immediately proceed to the next stage, but waits for the first set time. There is a physical response delay from the time the frequency reduction command from the aeration equipment is issued to the actual change in dissolved oxygen concentration at the end of the aerobic tank. This is because changes in fan speed, oxygen transfer efficiency, and the uniform mixing within the tank all require time.

[0043] Data collected without sufficient response time cannot accurately reflect the actual effect of frequency reduction.

[0044] As an example of engineering implementation, the first set duration can be set to 1 to 5 minutes, for example, a larger value can be used when the pool volume is large or the influent flow rate is large, and a smaller value can be used otherwise. The above values ​​are only examples to illustrate the feasibility of the scheme and do not constitute an absolute limitation.

[0045] After waiting for the first set time, the system reacquires dissolved oxygen and first flow rate data and recalculates the ratio data. The reacquired ratio data is then compared with the second threshold data. If the ratio is less than or equal to the second threshold data, it indicates that the first-stage frequency reduction action has brought the ratio of dissolved oxygen brought in by the recirculation to the carbon source reduction capacity back to a safe range. The system does not need to execute subsequent stages; it can maintain its current operating state and continue monitoring.

[0046] Conversely, if the reacquired ratio data is still greater than the second threshold data, it indicates that source reduction alone is insufficient to reduce the oxygen in the recirculation to a safe level. At this time, the system issues a second frequency reduction command to the internal circulation recirculation pump.

[0047] The goal of this frequency reduction command is to reduce the instantaneous flow rate of the internal circulation return, thereby directly reducing the total amount of dissolved oxygen transported to the anoxic pool along the transport path.

[0048] The step size of the second frequency reduction command is larger than that of the first frequency reduction command. The reason is that the effect of the return flow rate on the absolute dissolved oxygen load is approximately linear. When the flow rate decreases by a certain percentage, the dissolved oxygen load decreases by the same percentage, and the response relationship is relatively direct. However, the effect of the aeration frequency on the dissolved oxygen concentration at the end of the aerobic tank is limited by oxygen transfer kinetics. The change in dissolved oxygen concentration caused by the same percentage frequency adjustment is relatively gradual.

[0049] Therefore, taking larger frequency reduction steps when further intervention is needed can achieve the load reduction target more quickly. After the second frequency reduction command is issued, the system also waits for the second set time. The setting logic of this second set time is consistent with that of the first set time. After the internal circulation return pump reduces its frequency, the change in return flow rate needs time to be transmitted to the inlet of the anoxic tank, and the mixing state in the anoxic tank also needs time to reach a new equilibrium.

[0050] The second set duration can also be selected within the range of 1 to 5 minutes, preferably consistent with the first set duration.

[0051] After waiting for the second set time, the system re-acquires the ratio data and simultaneously acquires the redox potential data at the head of the anoxic pool. The redox potential data is introduced here as an independent verification indicator. Its purpose is twofold: the ratio data reflects the macroscopic quantitative relationship between total dissolved oxygen and carbon source reduction capacity, while the redox potential directly reflects the actual redox environment of the water at the head of the anoxic pool. The two data corroborate each other, allowing for a more accurate determination of whether the anoxic environment has truly been restored.

[0052] At this point, the third-level trigger judgment is initiated. If the ratio data obtained again is less than or equal to the second threshold data, it indicates that the macroscopic dissolved oxygen load has returned to a safe range after the first two levels of intervention.

[0053] Based on this, the system further determines whether the redox potential data is greater than the third threshold data. If the redox potential at the beginning of the anoxic pool is still high (e.g., above -50mV), it indicates that there is still residual dissolved oxygen in the water, and the anoxic environment has not been fully restored. Under these dual conditions, the system issues an incremental command to the carbon source addition system. While maintaining the effects of the first two stages of intervention, it accelerates the consumption of residual dissolved oxygen by supplementing additional carbon sources, so that the redox environment in the anoxic pool can be completely restored to a normal anaerobic state.

[0054] The third threshold data can be set to -50mV. When the ORP value at the head of the anoxic pool is higher than -50mV, it indicates that there is still free dissolved oxygen or extremely high nitrate concentration in the water, and the metabolism of denitrifying bacteria is significantly inhibited.

[0055] Furthermore, after issuing incremental commands to the carbon source dosing system, the system continuously acquires real-time updated redox potential data. This data comes from the ORP electrode deployed at the head of the anoxic tank, which is located in the mixing area after the return liquid falls into the anoxic tank, and can reflect the actual redox state of the water at the inlet of the anoxic tank.

[0056] Because there is a certain time lag between changes in redox potential and changes in dissolved oxygen concentration, dissolved oxygen needs to undergo a consumption process by microorganisms after entering the anoxic tank before it is reflected in the ORP value. Therefore, after issuing an incremental command, the system does not immediately determine the recovery conditions, but continuously monitors the evolution trend of the ORP value until the value stabilizes at a certain level.

[0057] When the system detects that the real-time updated redox potential data is less than or equal to the fourth threshold data (e.g., -100mV), it indicates that the anoxic environment at the head of the anoxic pool has been effectively restored.

[0058] During anoxic denitrification, the optimal redox environment for the growth of denitrifying bacteria is typically maintained between -100mV and -200mV. When the ORP value falls below -100mV, it indicates that dissolved oxygen in the water has been largely depleted, and the carbon source supply is relatively sufficient, allowing the denitrification reaction to proceed normally. Denitrifying bacteria can metabolize normally in environments below -50mV, so setting the recovery threshold at -100mV provides a safety margin.

[0059] At this point, the system triggers a release action. The execution order of this release action is the reverse of the execution order of the graded control commands. During graded control, aeration is reduced first, then reflux is reduced, and finally the carbon source is increased; during release, the carbon source is reduced first, then reflux is restored, and finally aeration is restored.

[0060] During the emergency control phase, adding carbon sources is the last intervention measure, aimed at compensating for the carbon sources that have been consumed by dissolved oxygen in order to quickly restore the hypoxic environment. However, during the recovery phase, since the hypoxic environment has been restored, continuing to maintain the amount of additional carbon sources may lead to a carbon surplus. Therefore, reducing the amount of additional carbon sources is the most urgent task.

[0061] After the carbon source dosage is restored to normal levels, the reflux ratio is gradually restored, and finally the aeration frequency is restored. Following the principle of "removing the last intervention applied before removing the first intervention applied", the system can smoothly transition from emergency control to normal operation.

[0062] Specifically, the aforementioned deactivation actions sequentially include: issuing a reduction command to the carbon source addition system to reduce the amount of carbon source added due to the previous increment command; issuing a first recovery command to the internal circulation return pump to restore the operating frequency of the return pump to the level before the tiered control; and issuing a second recovery command to the aeration equipment at the end of the aerobic tank to restore the operating frequency of the aeration equipment to the level before the tiered control. Each deactivation action is separated by a physical response cycle to observe the actual impact of the previous deactivation action on the system state and to avoid new fluctuations caused by the superposition of multiple deactivation actions.

[0063] After completing the aforementioned deactivation steps, the system resumes executing the carbon source feedforward calculation logic based on nitrate load. This means the system returns from the "pause-intervention-recovery" state of emergency control to the "monitoring-calculation-execution" state of normal operation, restarting a new round of real-time monitoring and judgment cycle with a gating signal composed of the first and second threshold data. This ensures a complete closed loop of the control process, starting from normal operation, through abnormal triggering, graded intervention, and state recovery, and finally returning to normal operation, with each cycle accompanied by a reassessment of the actual physical state of the system.

[0064] Furthermore, when the ratio is less than or equal to the second threshold, it indicates that the total amount of dissolved oxygen brought in by the current recirculation is within a safe range, and the theoretical reduction capacity of the carbon source is sufficient to consume the recirculated dissolved oxygen while still having a relatively sufficient surplus to supply the denitrification reaction. Under this condition, the system continues to execute the carbon and nitrogen calculation model to output the dosing command.

[0065] The carbon and nitrogen calculation model is a conventional feedforward model based on the influent nitrate load to calculate the carbon source dosage. Its output results are within a safe range and can meet the process requirements. Therefore, the system maintains normal operation without the need to activate the staged control command. Since this model itself is well-known in the field, it will not be described in detail here.

[0066] When the ratio is greater than the second threshold and less than or equal to the first threshold, the system enters the warning zone.

[0067] Within this range, the dissolved oxygen brought in by the recirculation has already occupied a significant proportion of the theoretical reduction capacity of the carbon source. The safety margin is narrowing but has not yet reached the danger boundary. At this time, the system does not immediately execute the graded control command, but will actively increase the frequency of acquiring dissolved oxygen data, first flow rate data, and second flow rate data. For example, the sampling period will be shortened from the usual 60 seconds to 30 seconds.

[0068] The purpose of increasing the acquisition frequency is to capture the subtle changing trends of ratio data with more intensive data sampling when the system state approaches the danger boundary, thus providing a more accurate basis for subsequent decision-making. Simultaneously, the system acquires the time-series rate of change of ratio data.

[0069] The time-series rate of change reflects the direction and magnitude of change in ratio data between adjacent control cycles. It is introduced into the judgment logic because the instantaneous value of the ratio data only reflects the state at the current moment, while the time-series rate of change reflects the trend of the state—whether it is stabilizing, slowly rising, or rapidly deteriorating. Relying solely on instantaneous values ​​for judgment is prone to misjudgment due to signal fluctuations; introducing the time-series rate of change adds a trend dimension to the judgment.

[0070] When the ratio of the time sequence change rate indicator continues to rise within a set number of control cycles, the system executes a hierarchical control command.

[0071] The value of this continuous setting is typically between 2 and 5 cycles, for example, it can be set to 3 cycles. The requirement for continuity is to prevent false triggering caused by a single signal fluctuation. Only when the ratio data shows a continuous upward trend is it determined that the system is indeed approaching the danger zone. At this time, activating the graded control command can advance the intervention time to before the danger zone is triggered, avoiding processing after the system has actually entered the danger zone.

[0072] In actual operation, if graded control is triggered by occasional fluctuations in a single sample value, it will cause frequent operation of the aeration blower, return pump, and dosing pump, which will not only affect the lifespan of the equipment but may also cause unnecessary disturbances to the stability of the process. The above values ​​are only examples to illustrate the feasibility of the solution and do not constitute absolute limitations.

[0073] Furthermore, the system acquires influent flow rate data, influent nitrate nitrogen data, and effluent nitrate nitrogen data. Influent flow rate data comes from an electromagnetic or ultrasonic flow meter installed on the main influent pipe, representing the volume of wastewater entering the biological treatment system per unit time. Influent nitrate nitrogen data comes from an online nitrate nitrogen analyzer installed on the influent pipe, representing the nitrate nitrogen concentration entering the anoxic tank. Effluent nitrate nitrogen data comes from an online nitrate nitrogen analyzer installed at the effluent end of the anoxic tank, representing the residual nitrate nitrogen concentration after the denitrification reaction.

[0074] The system determines the basic dosage data based on the influent flow rate data and the difference between the influent nitrate nitrogen data and the effluent nitrate nitrogen data.

[0075] Its calculation principle is based on the stoichiometric relationship of the denitrification reaction. A certain amount of carbon source needs to be consumed for each unit mass of nitrate nitrogen reduced. This amount of consumption is determined by the type of carbon source and the metabolic efficiency of denitrifying bacteria.

[0076] The difference between the influent nitrate nitrogen data and the effluent nitrate nitrogen data reflects the total amount of nitrate nitrogen reduced by denitrifying bacteria in the anoxic tank. Multiplying this by the influent flow rate data yields the total mass of nitrate nitrogen reduced per unit time. Combining this with the stoichiometric coefficient of the carbon source allows us to calculate the theoretical carbon source requirement.

[0077] The system generates dosing instructions based on basic dosing data and sends these instructions to the carbon source dosing system. The dosing instructions are typically sent to the frequency converter or regulating valve of the carbon source dosing pump in the form of frequency signals or valve opening signals, controlling the pump speed or valve opening to physically execute the carbon source dosing.

[0078] The calculation method for the above basic addition data is a well-known method for calculating the addition of denitrification carbon sources in this field, and will not be elaborated here.

[0079] The improvement of this invention lies in the fact that, after calculating the basic dosing data, it is not directly issued as a final command unconditionally. Instead, the ratio of dissolved oxygen mass load data to the theoretical reduction equivalent data of carbon source, as described in the aforementioned embodiments, is used to determine whether the ratio is within a safe range before converting it into a dosing command. This "calculate first, verify later, then execute" logic ensures the rationality of the carbon source dosing command at the physicochemical level. Only when the dissolved oxygen brought in by the reflux does not significantly consume the carbon source is the result of the conventional calculation model allowed to be executed.

[0080] Furthermore, in the actual operation of wastewater treatment plants, the type of carbon source may change due to seasonal variations or fluctuations in procurement costs. For example, glucose, which is cheaper, may be used in summer, while sodium acetate, which has a faster denitrification rate, may be used in winter. Different carbon sources have significantly different molecular structures and oxidation states, resulting in drastically different theoretical oxygen equivalent coefficients γ.

[0081] When the carbon source type is switched, even if the second flow rate data remains unchanged, the theoretical reduction equivalent data of the carbon source will change abruptly, resulting in a physical shift in the overall distribution range of the ratio data ρ. If the original threshold is used, the system may experience false triggering or slow response.

[0082] To adapt to this abrupt change in physicochemical properties, the system first acquires carbon source type identification data. This identification data serves as the retrieval basis for querying the corresponding relational database stored in memory, thereby matching and obtaining the corresponding theoretical oxygen equivalent coefficient γ.

[0083] If a change in carbon source type identification data is detected, the system will continuously record the changes in the ratio data ρ at a higher sampling frequency (e.g., once every 30 seconds, while the normal sampling period is 1 to 2 minutes) within the set calibration period after the change, and obtain the maximum value ρ of its fluctuation range. max With minimum value ρ min .

[0084] As an example of engineering implementation, ρ max With ρ min The arithmetic extreme value of all sampled values ​​within the calibration period can be used, or the statistical quantile value can be used to avoid interference from extreme outliers. For example, the 95th quantile value can be used as ρ. max The 5th percentile value is used as ρ min .

[0085] Take the average value ρ of the ratio data during the last stable operating cycle before the carbon source switch. ref As a benchmark, the definition of the "stable operating cycle" is: the standard deviation of the ratio data within this cycle does not exceed 15% of its average value, and no hierarchical control command is triggered.

[0086] To prevent the updated threshold from being scaled incorrectly in the opposite direction (e.g., incorrectly lowering the upper limit of danger threshold, leading to frequent false alarms) and to avoid excessive adjustment causing system oscillations, this embodiment adopts a threshold reconstruction model with unidirectional constraints and saturation truncation.

[0087] The physical design logic of the reconstructed model is as follows: the upper limit of the actual fluctuation of the ratio data ρ after the carbon source is switched. max Higher than historical benchmark ρ refThis means that the system faces a higher risk of dissolved oxygen suppression under the same operating conditions. Therefore, the upper limit threshold α1 of danger should be relaxed accordingly so that the graded control command can be triggered under more relaxed conditions. Conversely, when ρ max Not higher than ρ ref At that time, α1 should not be tightened downwards, otherwise it will cause the system to frequently trigger false triggers under normal fluctuations.

[0088] Similarly, when the lower limit of the actual fluctuation of the ratio data ρ min Below historical benchmark ρ ref When this is the case, it means that the system has a wider safety margin under the same operating conditions. Therefore, the lower safety limit threshold α2 should be tightened accordingly so that the system exits the hierarchical control command only when the risk level is higher. Conversely, when ρ min Not lower than ρ ref At this time, α2 should not be relaxed upwards, otherwise it will cause the system to exit the hierarchical control instructions too early and the timing of resuming normal operation will be inappropriate.

[0089] Based on the above design logic, the updated first threshold data α1' and the updated second threshold data α2' are determined as follows: ; ; Where α1 and α2 are the first and second threshold data before the switch, respectively; ε is the minimum anti-zero bias constant (e.g., 10). -6 ).

[0090] The max(1,...) and min(1,...) in the formula constitute a unidirectional constraint, ensuring that α1' will only widen upwards and not tighten downwards, and α2' will only tighten downwards and not widen upwards; the outer min(1.2α1,...) and max(0.8α2,...) constitute a saturation cutoff method, limiting the maximum adjustment range of the threshold to within ±20% of the original baseline, ensuring a smooth transition of the biochemical system in the initial stage of carbon source switching.

[0091] After the above update process is completed, the system uses the updated first threshold data and second threshold data to overwrite the original trigger boundary in the gating judgment, thus completing the physical reconstruction of the control baseline. The values ​​of the calibration period and cutoff ratio mentioned above are merely engineering examples to illustrate the feasibility of the scheme and do not constitute an absolute limitation on the scope of protection of this application.

[0092] To facilitate understanding, Table 1 provides typical theoretical values ​​for several commonly used carbon sources for the theoretical oxygen equivalent coefficient γ mentioned above. This table is intended to help those skilled in the art understand the differences in γ values ​​corresponding to different types of carbon sources.

[0093]

[0094] Table 1. Theoretical oxygen equivalent coefficients and typical application scenarios of commonly used carbon sources As can be seen from Table 1: Sodium acetate has a low to medium γ value (0.78), but due to its simple molecular structure, it can be directly utilized by denitrifying bacteria. Therefore, it is widely used in low-temperature rapid denitrification scenarios in winter.

[0095] Methanol has a higher γ value (1.50) than sodium acetate, and its reducing power per unit mass of carbon source is stronger. However, its molecular weight is smaller, and it requires an acclimatization period of about 2 to 4 weeks for the denitrifying bacteria to adapt, resulting in a long engineering start-up period.

[0096] Glucose has a moderate γ value (1.07) and a low price, but its molecular weight is large and its microbial metabolic pathway is long. Its denitrification rate is significantly lower than that of sodium acetate under low temperature conditions, so it is usually only used in summer normal temperature conditions.

[0097] Ethanol has the highest γ value (2.09) among the carbon sources listed in the table, and has the strongest theoretical reduction capacity per unit mass of carbon source. However, it is highly volatile and has high storage requirements, and is usually only used in the co-treatment of specific industrial wastewater.

[0098] The γ value of the composite carbon source is 1.00 when converted to COD equivalent, but its actual value depends on the ratio of each component.

[0099] The above differences in γ values ​​indicate that when a wastewater treatment plant switches carbon source types under different seasons or operating conditions, even if the same carbon source mass flow rate is maintained, the theoretical reduction equivalent data of the carbon source will change significantly due to the change in γ values.

[0100] This change will cause a physical shift in the overall distribution range of the ratio data ρ. If the original threshold data is used, the system may experience false triggering or slow response. Therefore, when the carbon source type changes, the first and second threshold data need to be adaptively updated to match the physicochemical properties of the new carbon source.

[0101] Furthermore, during the execution of hierarchical control instructions, the cumulative decrease or increase of each level is constrained by a limit ratio.

[0102] The cumulative reduction of the first frequency reduction command shall not exceed the first limit ratio of the current frequency of the aeration equipment.

[0103] The basis for determining the first limit ratio is that excessive reduction in aeration will cause the dissolved oxygen concentration in the aerobic tank to drop below the critical level where the activity of nitrifying bacteria is inhibited, thereby affecting the oxidation effect of ammonia nitrogen, i.e., the nitrification function is impaired.

[0104] Optionally, the first limit ratio can be set to 20%, because when the aeration rate is reduced by more than 20%, the dissolved oxygen concentration in the aerobic tank may drop to below 1.0 mg / L, and the activity of nitrifying bacteria will be significantly inhibited when the dissolved oxygen concentration is below 1.0 mg / L.

[0105] If the first limit ratio is reached and the reacquired ratio data is still greater than the second threshold data, it means that simply reducing aeration is not enough to reduce the oxygen in the return flow to a safe level, and continuing to reduce aeration will endanger the nitrification function. At this time, the system enters the second stage and issues a second frequency reduction command to the internal circulation return pump.

[0106] The cumulative reduction of the second frequency reduction command shall not exceed the second limit ratio of the current frequency of the internal circulation reflux pump.

[0107] The basis for this second limit ratio is that an excessive reduction in the reflux ratio will reduce the total amount of nitrate carried into the anoxic tank by the reflux liquid. When the nitrate supply is lower than the minimum requirement for the denitrification reaction, the total nitrogen in the effluent will increase.

[0108] Optionally, the second limit ratio can be set to 30%, because when the recirculation ratio is reduced by more than 30%, the total amount of nitrate brought into the anoxic tank by the recirculation may be lower than the minimum requirement for the denitrification reaction, resulting in a relative excess of carbon source in the anoxic tank, a limited denitrification rate, and an upward trend in the total nitrogen in the effluent.

[0109] If the second limit ratio is reached and the redox potential data is still greater than the third threshold data, it indicates that the hypoxic environment has not yet been restored, and continued reflux will endanger the nitrate supply. At this time, the system executes the third stage and issues an incremental command to the carbon source addition system.

[0110] The cumulative increase of incremental instructions shall not exceed the third limit ratio of the current carbon source addition amount of the carbon source addition system.

[0111] The basis for determining the third limit ratio is that excessive increases in carbon source addition may exceed the metabolic capacity of denitrifying bacteria at low temperatures, resulting in unconsumed carbon being discharged with the effluent and causing the risk of COD exceeding the standard.

[0112] Optionally, the third limit ratio can be set to 25%, because when the carbon source addition increases by more than 25%, the carbon source that exceeds the metabolic capacity of the denitrifying bacteria at low temperatures will not be consumed in time, leading to a significant increase in the risk of COD exceeding the standard in the effluent.

[0113] The specific values ​​of the first, second, and third limiting ratios mentioned above are not fixed and can be adjusted by those skilled in the art according to specific process conditions (such as the volume of the aerobic tank, the type of aeration equipment, the characteristics of the return pump, and the type of carbon source). The above values ​​are only examples to illustrate the feasibility of the scheme and do not constitute absolute limitations.

[0114] Furthermore, when the first acquisition device used to obtain dissolved oxygen data malfunctions, the system cannot obtain the dissolved oxygen concentration at the end of the return pipe, and therefore cannot calculate the dissolved oxygen mass load data and ratio data.

[0115] Similarly, when the second acquisition device used to obtain the first flow rate data malfunctions, the system cannot obtain the instantaneous flow rate of the internal circulation return, nor can it calculate the aforementioned indicators. In such cases, the system neither knows whether the ratio data is already in the danger zone nor whether the hypoxic environment is still being maintained normally.

[0116] Due to a lack of judgment criteria, if the system continues to operate normally, it may face the risk that the dissolved oxygen brought in by the backflow will continue to consume the carbon source without timely intervention.

[0117] Therefore, the system adopts a conservative strategy: the ratio data is configured to a first alternative value that is greater than the first threshold data, thereby forcibly triggering the execution logic of the hierarchical control instruction.

[0118] The selection of this first alternative value must ensure that the judgment of the danger zone can be triggered under any circumstances. Optionally, the first alternative value can be set to 0.9, because the typical value of the first threshold data is 0.8, and setting the alternative value to 0.9 can numerically ensure that the triggering condition is met. This value is only an example to illustrate the feasibility of the scheme and does not constitute an absolute limitation.

[0119] After the hierarchical control command is triggered, the system skips the execution of the first frequency reduction command and directly executes the second frequency reduction command and the incremental command.

[0120] The purpose of skipping the first frequency reduction command is that the goal of the first-level frequency reduction command is to reduce the dissolved oxygen concentration at the end of the aerobic tank, and the effect of this action needs to be verified by the data collected by the dissolved oxygen sensor at the end of the return pipe.

[0121] When the sensor itself is faulty, the system cannot confirm whether the aeration reduction action is effective. Continuing to execute the aeration reduction command may lead to a situation where "the action has been executed, but the effect cannot be verified".

[0122] More importantly, in the absence of ratio data, the system's primary objective is to ensure that the anoxic environment of the anoxic tank is not disrupted by dissolved oxygen, rather than precisely controlling the carbon-nitrogen ratio. Therefore, directly executing the second-level frequency reduction command—that is, physically reducing the flow rate of the internal circulation return—can directly reduce the total amount of dissolved oxygen transported to the anoxic tank, making it the most direct and reliable intervention method. Based on this, combining it with incremental carbon source replenishment commands can further accelerate the recovery of the anoxic environment.

[0123] The above strategy reflects the system's operational logic of switching from "accurate control" to "safety first" under sensor failure conditions, prioritizing the physical environmental safety of the anoxic pool rather than pursuing accurate carbon-nitrogen ratio matching.

[0124] It should be noted that if the ORP electrode also fails, the system will stop using redox potential data as a basis for judgment and instead control the system based solely on the first alternative value, and will issue an alarm signal to prompt maintenance personnel to perform repairs.

[0125] The specific values ​​for each threshold and the detection methods for sensor faults (such as signals exceeding the range or signals remaining unchanged for more than a set duration) have been described in detail and will not be repeated here.

[0126] Furthermore, after the hierarchical control command is issued, the system needs to ensure that the executing equipment actually responds to the command. In practice, the correspondence between command issuance and equipment response is not always perfect. Communication lines may be affected by on-site electrical interference, causing signal loss; the frequency converter may fail to correctly parse the frequency command due to internal parameter setting deviations; or the equipment itself may have mechanical jamming, preventing the actual speed from reaching the target value. Therefore, the system is equipped with a feedback confirmation method.

[0127] When the system issues a graded control command to the aeration equipment, internal circulation return pump, or carbon source dosing system, the system starts timing and waits for the corresponding actuator to return a feedback signal. This feedback signal usually comes from the frequency converter or intelligent actuator associated with the actuator, and its content includes at least the current real-time operating frequency of the equipment.

[0128] If the system does not receive a feedback signal within the set response time (which can be set to 10 to 30 seconds (e.g., preferably 15 seconds)), or if the deviation between the actual frequency data indicated by the feedback signal and the target frequency data issued in the command is greater than the fifth threshold data, it indicates that the execution device has failed to respond normally to this control command.

[0129] The value of the fifth threshold data should allow for a certain amount of engineering error. A small deviation between the actual frequency and the target frequency is usually permissible, but when the deviation exceeds a certain range, it means that there is a substantial deviation between the instruction and the execution.

[0130] For example, the fifth threshold data can be set to 5%, that is, when the deviation between the actual frequency and the target frequency is within ±5%, it is considered to be executed in place; when the deviation exceeds ±5%, it is judged as not responding normally.

[0131] The basis for this value is that the control accuracy of commonly used variable frequency equipment (such as ABB, Siemens and other brands) in sewage treatment plants is usually between ±0.5% and ±2%. Setting the deviation tolerance to 5% has covered the conventional measurement and control errors. Exceeding this range indicates that there is a substantial deviation between the command and the execution.

[0132] In this situation, the system will not immediately determine that the device has permanently failed, but will instead perform a retry and issue the same command again.

[0133] The reason for retrying is that problems such as communication interruption, temporary inverter overload, or brief mechanical malfunction may be resolved with a single retry. If no valid feedback signal is received after a set number of retryes, the corresponding actuator is marked as faulty. This faulty status signifies that the system will no longer issue subsequent hierarchical control commands to the device, because multiple failed retries indicate that the problem is not a momentary communication interference, but rather a persistent fault in the device itself or related links.

[0134] After a certain execution device is marked as faulty, the system controls the execution devices that are not in a faulty state to operate according to the set second alternative value.

[0135] For example, if the aeration equipment fails, the current frequency is maintained and all interventions to the equipment are suspended, and the only response is to adjust the return pump and the dosing pump; if the return pump fails, 80% of the current frequency is used as a replacement value and further frequency reduction interventions to the return pump are suspended, and the only response is to adjust the aeration and carbon source.

[0136] In extreme cases of equipment failure, rather than blindly implementing the full pre-set plan, it is better to allow still-usable equipment to continue operating within safety boundaries, thereby maintaining a minimum level of system stability. Once maintenance personnel have completed equipment repairs and manually cleared the failure status, the system resumes its normal hierarchical control command issuance process.

[0137] Furthermore, when the system continuously executes multiple complete cycles containing the first frequency reduction command, the second frequency reduction command, and the incremental command, and the ratio data is still greater than the second threshold data and the redox potential data is still greater than the third threshold data, it means that the system's conventional intervention methods, including source reduction (reducing aeration), path interruption (reducing reflux), and carbon source compensation (increasing carbon source), have failed to effectively relieve the dissolved oxygen inhibition state in the anoxic pond.

[0138] At this point, continuing to repeat the same three-level linkage action is no longer meaningful, because previous rounds of execution have proven that these intervention measures cannot reverse the system's runaway trend under the current conditions.

[0139] In this situation, the system switches its control strategy to a target control state. This target control state is not the normal operating state of the system, but rather an engineering fallback measure under conditions of deep loss of control.

[0140] The core logic is that since the anoxic environment cannot be restored through conventional means, the system's primary goal should shift from "pursuing denitrification efficiency" to "maintaining the basic survival of the biological system," that is, preventing the large-scale death of the microbial community in the activated sludge due to prolonged anoxic conditions or insufficient carbon sources. If the activated sludge system completely collapses, the wastewater treatment plant will face a re-cultivation cycle lasting several weeks or even longer, during which the effluent quality cannot be guaranteed at all, with consequences far exceeding short-term effluent exceedances.

[0141] Specifically, the target control status includes two aspects.

[0142] Firstly, the operating frequency of the internal circulation reflux pump is configured to a set conversion ratio, which is usually 70% of the current operating frequency. The purpose is to maintain a minimum level of nitrate supply while avoiding excessive reflux oxygen load.

[0143] Secondly, the second flow rate data of the carbon source addition system is configured as the minimum dosage data. The minimum dosage is set based on the minimum carbon source supply required to maintain the basic metabolism of activated sludge in the anoxic tank, rather than the conventional demand calculated based on the influent nitrate load.

[0144] The minimum dosage data can be preset by maintenance personnel based on actual operating conditions such as sludge concentration and water temperature in the anoxic tank, or it can be automatically estimated by the system based on historical operating data. For example, the estimated value can be obtained by multiplying the average carbon source dosage during the most recent 7 days of normal operation by a coefficient of 0.3 to 0.5. The above values ​​are only examples to illustrate the feasibility of the scheme and do not constitute absolute limitations.

[0145] Under target control mode, the system continuously monitors ratio and redox potential data. If both gradually return to the normal range during subsequent operation (i.e., the ratio falls below the second threshold and the redox potential falls below the fourth threshold), the system automatically exits target control mode and switches back to normal control mode. If both remain abnormal, the system maintains target control mode and continuously sends alarm signals to maintenance personnel until manual intervention is required to troubleshoot the fault.

[0146] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for low-temperature, high-efficiency nitrogen removal treatment of municipal wastewater, characterized in that, include: Acquire dissolved oxygen data and first flow rate data in the internal reflux liquid from the end of the aerobic tank to the anoxic tank, and acquire second flow rate data of the carbon source dosing system; Based on the dissolved oxygen data and the first flow rate data, the dissolved oxygen mass load data brought into the anoxic tank by the internal reflux liquid is determined; Based on the second flow rate data and the theoretical oxygen equivalent coefficient of the currently added carbon source, the theoretical reduction equivalent data of the carbon source is determined; Based on the dissolved oxygen mass load data and the theoretical reduction equivalent data of the carbon source, the ratio data is determined; If the ratio data is greater than the first threshold data, the execution of the carbon source feedforward calculation logic based on nitrate load is paused, and a hierarchical control instruction including a first frequency reduction instruction, a second frequency reduction instruction, and an incremental instruction is executed sequentially until the ratio data is less than or equal to the second threshold data; wherein, the first threshold data is greater than the second threshold data; The first frequency reduction command is used to control the aeration equipment in the aerobic tank to reduce its frequency, the second frequency reduction command is used to control the internal circulation return pump to reduce its frequency, and the incremental command is used to control the carbon source addition system to increase the amount of carbon source added.

2. The method for low-temperature, high-efficiency nitrogen removal treatment of municipal wastewater according to claim 1, characterized in that, The sequential execution of hierarchical control instructions, including a first down-frequency instruction, a second down-frequency instruction, and an incremental instruction, includes: The first frequency reduction command is sent to the aeration device, and the ratio data is reacquired after waiting for a first set time. If the reacquired ratio data is greater than the second threshold data, then the second frequency reduction command is sent to the internal circulation return pump, and the ratio data is reacquired again after waiting for the second set time, as well as the oxidation-reduction potential data at the head of the anoxic pool. If the ratio data obtained again is less than or equal to the second threshold data, and the redox potential data is greater than the third threshold data, then the incremental command is issued to the carbon source dosing system.

3. The method for low-temperature, high-efficiency nitrogen removal treatment of municipal wastewater according to claim 2, characterized in that, After issuing the incremental command to the carbon source dosing system, the method further includes: Continuously acquire the redox potential data that is updated in real time; If the real-time updated redox potential data is less than or equal to the fourth threshold data, the release action is executed sequentially in the reverse order of the hierarchical control command. The release actions sequentially include: issuing a reduction command to the carbon source addition system, issuing a first recovery command to the internal circulation return pump, and issuing a second recovery command to the aeration equipment; After the release action is completed, the carbon source feedforward calculation logic based on nitrate load is resumed.

4. The method for low-temperature, high-efficiency nitrogen removal treatment of municipal wastewater according to claim 1, characterized in that, The method further includes: If the ratio data is less than or equal to the second threshold data, the carbon and nitrogen calculation model is maintained to output the dosing command; If the ratio data is greater than the second threshold data and less than or equal to the first threshold data, then the acquisition frequency of the dissolved oxygen data, the first flow data, and the second flow data is increased, and the time-series change rate of the ratio data is acquired. If the time-series change rate indicates that the ratio data continues to rise within a continuously set number of control cycles, then the hierarchical control command is executed.

5. The method for low-temperature, high-efficiency nitrogen removal treatment of municipal wastewater according to claim 4, characterized in that, The maintenance of the carbon and nitrogen calculation model to output dosing instructions includes: Acquire influent flow rate data, influent nitrate nitrogen data, and effluent nitrate nitrogen data; Based on the influent flow rate data and the difference between the influent nitrate nitrogen data and the effluent nitrate nitrogen data, the basic dosage data is determined; The dosing instruction is generated based on the basic dosing data and then sent to the carbon source dosing system.

6. The method for low-temperature, high-efficiency nitrogen removal treatment of municipal wastewater according to claim 1, characterized in that, Before determining the theoretical reduction equivalent data of the carbon source based on the second flow rate data and the theoretical oxygen equivalent coefficient of the currently added carbon source, the method further includes: Obtain carbon source type identification data, and based on the carbon source type identification data, match and obtain the corresponding theoretical oxygen equivalent coefficient from the storage database; If a change in the carbon source type identification data is detected, the fluctuation range of the ratio data is obtained within the set calibration period after the change. The first threshold data and the second threshold data are updated based on the fluctuation range.

7. The method for low-temperature, high-efficiency nitrogen removal treatment of municipal wastewater according to claim 2, characterized in that, When executing the first down-frequency instruction, the second down-frequency instruction, and the incremental instruction, the following restrictions apply: The cumulative reduction of the first frequency reduction instruction does not exceed the first limit ratio of the current frequency of the aeration device. If the first limit ratio is reached and the ratio data obtained again is still greater than the second threshold data, then the second frequency reduction instruction is executed. The cumulative reduction of the second frequency reduction instruction does not exceed the second limit ratio of the current frequency of the internal circulation reflux pump. If the second limit ratio is reached and the redox potential data is still greater than the third threshold data, then the incremental instruction is executed. The cumulative increase of the incremental instruction shall not exceed the third limit ratio of the current addition amount of the carbon source addition system.

8. A method for low-temperature, high-efficiency nitrogen removal treatment of municipal wastewater according to claim 2, characterized in that, The method further includes: If a malfunction is detected in the first acquisition device used to acquire the dissolved oxygen data, or in the second acquisition device used to acquire the first flow rate data, the ratio data is configured to a first alternative value that is greater than the first threshold data. Skip the execution of the first down-frequency instruction and directly execute the second down-frequency instruction and the incremental instruction.

9. A method for low-temperature, high-efficiency nitrogen removal treatment of municipal wastewater according to claim 1, characterized in that, The method further includes: After the hierarchical control command is issued, if no feedback signal is received from the corresponding execution device within the set response time, or if the deviation between the actual frequency data indicated by the feedback signal and the target frequency data is greater than the fifth threshold data, the same command is issued again. If the feedback signal is not received after the set number of times the signal is sent again, the corresponding execution device will be marked as in a failed state, and the execution devices that are not in the failed state will be controlled to run according to the set second alternative value.

10. A method for low-temperature, high-efficiency denitrification treatment of municipal wastewater according to claim 2, characterized in that, The method further includes: After executing multiple complete cycles containing the first frequency reduction instruction, the second frequency reduction instruction, and the incremental instruction, if the ratio data is greater than the second threshold data and the redox potential data is greater than the third threshold data, the control strategy is switched to the target control state. The target control state includes: configuring the operating frequency of the internal circulation reflux pump to a set conversion ratio, and configuring the second flow rate data of the carbon source dosing system to the minimum dose data.

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