Optimized dissolved oxygen and dosing control method for A2O+MBR process

Abstract

The present application relates to sewage treatment technical field, aims at solving the problem that due to the limited range of dissolved oxygen detector, the dissolved oxygen index cannot guide the action of air inlet fan and air inlet valve in low dissolved oxygen area, the high efficient denitrification state cannot be maintained, and the dosing point of phosphorus removal agent is the end of aerobic II area, the feedback time is long, the control efficiency is low, and the effluent total phosphorus is unstable, a kind of optimization dissolved oxygen, dosing control method suitable for A2O+MBR process is provided;The method comprises data acquisition, reagent dosing control and dissolved oxygen control;The present application controls the combined action of fan opening degree and each to be controlled area valve through oxidation-reduction potential, completes the linkage automatic control of oxidation-reduction potential of biochemical pool, low dissolved oxygen area and dissolved oxygen in aerobic area, effectively guides the action of aeration system fan and valve, and can maintain high efficient denitrification state;The orthophosphate value at the end of aerobic area is used as the dosing basis of phosphorus removal agent, which is more accurate and efficient.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to a method suitable for A 2 Optimized dissolved oxygen and chemical dosing control methods for O+MBR process. Background Technology

[0002] In traditional municipal wastewater treatment plant control models, to ensure sufficient oxidation and decomposition of organic matter while balancing the inhibitory effect of dissolved oxygen in the returned sludge on denitrification, the oxygen content in the aerobic zone of the biological treatment tank is typically controlled at 2.0 mg / L or higher. With the increasing national standards for nitrogen discharge from wastewater treatment plants, enhanced denitrification during the biological treatment process has become increasingly important. Many wastewater treatment plants are upgrading to meet new environmental requirements, adding membrane technology to their existing processes. Therefore, the number of municipal wastewater treatment plants using the MBR (Mechanical Bioreactor) process is constantly increasing.

[0003] like Figure 1 As shown, in A 2 In the O+MBR process, wastewater and sludge are discharged from the membrane zone after three stages of recirculation. The first stage recirculation returns from the end of the membrane zone to the beginning of the aerobic zone I, replenishing the sludge concentration in the biological treatment tank. The second stage recirculation returns from the end of aerobic zone I to the beginning of the anoxic zone for denitrification. The third stage recirculation returns from the anoxic zone to the anaerobic zone, replenishing the sludge concentration in the anaerobic zone while promoting phosphorus release by polyphosphate-accumulating organisms. The dissolved oxygen target in the aerobic zone is 2.0 mg / L or higher. Simultaneously, chemical phosphorus removal is implemented to ensure stable compliance with total phosphorus standards in the effluent.

[0004] Compared to traditional A 2 O process, A 2 The O+MBR process connects a membrane tank to the end of the conventional biological treatment tank. The membrane tank maintains a certain aeration rate, which is equivalent to adding an aeration zone at the end of the traditional biological treatment tank. The nitrification reaction mainly occurs in the aerobic zone and the membrane tank area.

[0005] Therefore, in A 2 In the O+MBR process, the aerobic zone I can be adjusted to a low dissolved oxygen zone, with dissolved oxygen controlled at around 0.5 mg / L. This not only ensures the aerobic reaction but also maintains a facultative anaerobic environment, which is beneficial for improving the simultaneous nitrification and denitrification rate, reducing power consumption, minimizing the adverse effects of oxygen in the returned sludge on the denitrification process, improving denitrification efficiency, and comprehensively enhancing nitrogen removal.

[0006] Since the lower limit of dissolved oxygen online detector is 0.5 mg / L, in actual process control, there are often situations where the dissolved oxygen level in the low dissolved oxygen zone is lower than the lower limit of the detector. At this time, the dissolved oxygen index cannot guide the operation of the air intake fan and air intake valve in the aerobic zone, and the state of efficient denitrification cannot be maintained.

[0007] Traditional chemical phosphorus removal agents are mainly added based on the total phosphorus in the effluent. However, the dosing point for phosphorus removal agents is at the end of the aerobic zone II, which results in long feedback time, low control efficiency, and instability in the total phosphorus in the effluent. Summary of the Invention

[0008] This invention aims to provide a solution suitable for A 2 Optimized dissolved oxygen and chemical dosing control methods for O+MBR process to solve the problems in A 2 In the O+MBR process, after adjusting the aerobic zone I to a low dissolved oxygen zone, the limited range of the dissolved oxygen online detector makes it impossible to guide the operation of the air intake fan and air intake valve in the low dissolved oxygen zone based on the dissolved oxygen index. This results in the inability to maintain a high-efficiency denitrification state. Furthermore, the dosing of phosphorus removal agents is mainly based on the total phosphorus in the effluent, but the phosphorus removal agent dosing point is at the end of the aerobic zone II. This leads to long feedback time, low control efficiency, and instability in the total phosphorus in the effluent.

[0009] This invention is achieved using the following technical solution:

[0010] This invention provides a method suitable for A 2 Optimized dissolved oxygen and chemical dosing control methods for O+MBR process, among which A 2 The biological treatment tank of the O+MBR process includes an anaerobic zone, an anoxic zone, a low dissolved oxygen zone, an aerobic zone, and a membrane zone connected in sequence. The end of the membrane zone is connected in reverse to the front of the low dissolved oxygen zone, the end of the low dissolved oxygen zone is connected in reverse to the front of the anoxic zone, and the anoxic zone is connected in reverse to the anaerobic zone. A phosphorus removal agent dosing port is provided at the end of the aerobic zone.

[0011] The method includes data acquisition, reagent dosing control, and dissolved oxygen control;

[0012] Data acquisition includes collecting redox potential data at the end of the anoxic zone, orthophosphate values ​​at the end of the aerobic zone, effluent ammonia nitrogen data, influent flow rate data, influent water quality data, actual dissolved oxygen values ​​in the low dissolved oxygen zone, and actual dissolved oxygen values ​​in the middle and later sections of the aerobic zone.

[0013] The chemical dosing control includes: using the orthophosphate value at the end of the aerobic zone as the basis for phosphorus removal chemical dosing; and performing PID control calculations based on the target value and actual value of orthophosphate at the effluent point at the end of the aerobic zone to dynamically control the phosphorus removal chemical dosing.

[0014] Dissolved oxygen control includes: using the oxidation-reduction potential at the end of the anoxic zone as the control index, and using effluent ammonia nitrogen data, influent flow rate data, influent water quality data, actual dissolved oxygen value in the low dissolved oxygen zone, and actual dissolved oxygen value in the middle and later stages of the aerobic zone as auxiliary control parameters to adjust the air volume of the aeration system.

[0015] As a preferred technical solution:

[0016] The specific steps for controlling the addition of chemicals are as follows:

[0017] S101: Set the target value of orthophosphate at the end effluent point of the aerobic zone;

[0018] S102: PID control calculation is performed based on the target value of orthophosphate and the actual value of orthophosphate at the end of the aerobic zone effluent obtained from data acquisition. The PID control calculation is based on the target value of orthophosphate and the actual value of orthophosphate to form the control deviation. The proportional, integral and derivative of the deviation are linearly combined to form the control quantity. The concentration of phosphorus removal agent is obtained based on the control quantity.

[0019] S103: Calculate the required dosage of phosphorus removal agent based on the concentration of the phosphorus removal agent and the actual effluent volume;

[0020] S104: The phosphorus removal agent dosage calculated in step S103 is the target value of the phosphorus removal agent dosage. PI control calculation is performed based on the target value and the actual value of the phosphorus removal agent dosage. The PI control calculation uses the target value and the actual value of the phosphorus removal agent dosage to form the control deviation. The proportion and integral of the deviation are linearly combined to form the control quantity. The operating frequency of the diaphragm pump for pesticide dosing is controlled based on the control quantity.

[0021] As a preferred technical solution:

[0022] The method further includes step S105: performing intermittent dosing of the agent by the diaphragm pump according to the orthophosphate compensation calculation to obtain the dosage and dosing time;

[0023] The orthophosphate compensation calculation is as follows: when the automatic dosing control system for phosphorus removal agents switches from manual to automatic dosing, stable control is performed, that is, the dosage of phosphorus removal agents is gradually adjusted so that it smoothly transitions from the dosage in manual mode to the target dosage in automatic mode, so that the switch from manual to automatic phosphorus removal agent dosing control can be stable.

[0024] As a preferred technical solution:

[0025] The phosphorus removal agent used is PAC (phosphorus compound), and the dosage of PAC is calculated according to the following formula:

[0026]

[0027] The liquid volume refers to the actual outflow of water.

[0028] As a preferred technical solution:

[0029] Dissolved oxygen control specifically includes the following steps:

[0030] S201: Set the target value for the redox potential in the anoxic zone;

[0031] S202: Perform peak filtering and arithmetic average filtering on the collected data;

[0032] S203: Perform fuzzy PID control calculations based on the target value and actual value of the redox potential to obtain fuzzy control correction quantities ΔKp, ΔTi, and ΔTd. Based on the initial values ​​of Kp(t-1), Ti(t-1), and Td(t-1) of the fuzzy PID controller and the fuzzy control correction quantities ΔKp, ΔTi, and ΔTd, obtain the values ​​of Kp(t), Ti(t), and Td(t) of the fuzzy PID controller, respectively.

[0033] S204: PID control calculation is performed based on the target value of oxidation-reduction potential, the actual value of oxidation-reduction potential, and the values ​​of Kp(t), Ti(t), and Td(t). The PID control calculation uses the target value of oxidation-reduction potential and the actual value of oxidation-reduction potential to form the control deviation. The deviation e(t) is linearly combined with the proportional Kp, integral Ti, and derivative Td to form the control quantity, which controls the fan.

[0034] As a preferred technical solution:

[0035] Step S202 specifically includes:

[0036] Peak filtering and arithmetic average filtering are applied to the real-time operating data collected, including ORP data at the end of the anoxic zone, effluent ammonia nitrogen data, influent flow rate data, influent water quality data, and dissolved oxygen data in the middle and later stages of the low dissolved oxygen zone and the aerobic zone.

[0037] As a preferred technical solution:

[0038] The method further includes S205: combining actual control requirements, and based on inlet flow compensation, ammonia nitrogen over-limit compensation, start-stop fan air volume connection compensation, pipe pressure over-limit compensation, and fan current compensation, to realize the operation control correction and deviation of the fan and valve, so as to obtain the air supply volume suitable for the low dissolved oxygen zone and the aerobic zone.

[0039] As a preferred technical solution:

[0040] Step S205 specifically involves: combining process experience with the results of fuzzy PID control algorithm calculations to determine 5 control decision trees and the priority of compensation control actions. The priorities from high to low are: fan protection action, fan unit start-up and shutdown action, ORP, ammonia nitrogen, DO anomalies, influent water quality fluctuations, and PID control module output. The fuzzy PID control results are then used to determine and output the final control command through the decision tree.

[0041] As a preferred technical solution:

[0042] The method further includes S206: each control zone has a valve that controls its aeration volume, and the aeration volume of the control zone is determined by the opening degree of the valve; each valve controls the redistribution of the air supply provided by the fan according to the different air demand of each control zone, so as to meet the air demand of each control zone.

[0043] S207: Based on the target and actual values ​​of the oxidation-reduction potential in the low dissolved oxygen zone and the target and actual values ​​of the dissolved oxygen in the aerobic zone, PID control calculations are performed to solve the air demand of each zone to be controlled.

[0044] S208: Obtain the target air volume of each control zone, and control the valve opening through PI control calculation. The PI control calculation is based on the control deviation between the target air volume and the actual air volume. The ratio and integral of the deviation are linearly combined to form the control quantity, which controls the valve.

[0045] S209: The results of PI control calculations are used as the basis for adjusting the opening of each valve; by adjusting the valve opening to match the air demand of the controlled area, linear control of the air demand of the controlled area is achieved.

[0046] The controlled areas include low dissolved oxygen areas and aerobic areas.

[0047] As a preferred technical solution:

[0048] Step S203 specifically includes:

[0049] Fuzzification is performed by defining the fuzzy condition set for the inputs e(t) and ec(t) of the fuzzy PID controller and the outputs ΔKp, ΔTi, and ΔTd, and defining the fuzzy control rule table for the inputs e(t) and ec(t) and the outputs ΔKp, ΔTi, and ΔTd. Defuzzification is then performed, during which the fuzzy control corrections ΔKp, ΔTi, and ΔTd are obtained from the fuzzy control rule table. Based on the initial values ​​of Kp(t-1), Ti(t-1), and Td(t-1) of the fuzzy PID controller and the fuzzy control corrections ΔKp, ΔTi, and ΔTd, the values ​​of Kp(t), Ti(t), and Td(t) of the fuzzy PID controller are obtained respectively.

[0050] As a preferred technical solution:

[0051] Step S207 specifically includes: PID control calculation based on the target and actual values ​​of oxidation-reduction potential in the low dissolved oxygen zone and the target and actual values ​​of dissolved oxygen in the aerobic zone to form control deviations respectively. The deviations are then linearly combined using proportional Kp, integral Ti, and derivative Td to form control quantities. The required air volume for each zone to be controlled is then calculated based on the control quantities.

[0052] As a preferred technical solution:

[0053] In step S102, the PID control algorithm is loaded into the PID controller for PID calculation. The dosage control amount of the added agent is obtained by applying automation technology. The required concentration of the phosphorus removal agent is determined based on the dosage control amount.

[0054] In step S104, the PI control algorithm is loaded into the PI controller for PI calculation to obtain the control quantity, and the operating frequency of the drug dosing diaphragm pump is controlled by the PI controller.

[0055] In step S204, the PID control algorithm is loaded into the PID controller, and the PID controller controls the operating air volume of the fan.

[0056] In step S208, the PI control algorithm is loaded into the PI controller, and the opening degree of the valve is controlled by the PI controller.

[0057] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0058] 1. This invention adjusts the aerobic zone I from a conventional aerobic zone to a low dissolved oxygen zone, saving electricity costs in terms of aeration. The low dissolved oxygen zone creates a facultative anaerobic environment, allowing nitrifying and denitrifying bacteria to coexist in the same space and simultaneously undergo nitrification and denitrification reactions, thus enhancing biological nitrogen removal and reducing the need for denitrification chemicals. The low dissolved oxygen content of the nitrified liquid returned from the low dissolved oxygen zone to the anoxic zone minimizes the impact on the anoxic environment, better maintaining it and enhancing denitrification efficiency. The chemical phosphorus removal agent dosage is changed from the effluent total phosphorus meter value to the orthophosphate value at the end of the aerobic zone in the biological treatment tank, optimizing the original feedforward reaction into a forward reaction. Real-time monitoring of orthophosphate trends and timely and accurate dosage of phosphorus removal agents based on orthophosphate values ​​result in greater accuracy and efficiency, shorter feedback time, higher control efficiency, and ensured stable effluent total phosphorus.

[0059] 2. This invention uses the oxidation-reduction potential at the end of the anoxic zone of the biological treatment tank as the control target, and uses effluent ammonia nitrogen data, influent flow rate data, influent water quality data, dissolved oxygen in the middle and later stages of the aerobic zone, and dissolved oxygen in the aerobic zone of the membrane tank as auxiliary control parameters to ensure that the effluent meets the discharge standards while enhancing biological denitrification.

[0060] 3. This invention employs a control method based on oxidation-reduction potential (ORP) as the core indicator, ensuring stable dissolved oxygen control within the target value in the low dissolved oxygen zone. By controlling the fan opening based on ORP and coordinating the operation of dissolved oxygen control valves in each controlled zone, it achieves automatic linkage control of the ORP in the biological treatment tank with dissolved oxygen in both the low and aerobic zones. This effectively guides the operation of the aeration system's fans and valves, solving the challenge of controlling low dissolved oxygen. The ORP in the anoxic zone of the biological treatment tank is controlled between -200 and -80 mV, the dissolved oxygen concentration in the low dissolved oxygen zone is controlled between 0.1 and 0.5 mg / L, and the dissolved oxygen concentration in the aerobic zone is controlled between 1 and 2 mg / L. This stabilizes the nitrogen and phosphorus removal efficiency in the low dissolved oxygen zone of the biological treatment tank. Simultaneously, the low dissolved oxygen nitrification liquid is returned to the upstream anoxic zone, providing more favorable conditions for denitrification and helping to maintain a high-efficiency denitrification state.

[0061] 4. This invention can be quickly implemented through an automatic control program and integrates fuzzy PID control to achieve automatic tuning of PID parameters. It is simple and easy to use, and no longer relies on manual adjustment in practice, resulting in a high degree of automation. Attached Figure Description

[0062] Figure 1 A in the prior art 2 O+MBR process flow diagram.

[0063] Figure 2 The improved version A of this invention 2 O+MBR process flow diagram.

[0064] Figure 3 This is a schematic diagram of the fuzzy PID control algorithm.

[0065] Figure 4 This is a flowchart for influent flow rate compensation.

[0066] Figure 5 This is a flowchart for ammonia nitrogen exceeding the limit compensation.

[0067] Figure 6 This is a flowchart for ORP over-limit compensation.

[0068] Figure 7 This is a flowchart for DO over-limit compensation in the low dissolved oxygen zone.

[0069] Figure 8 This is a flowchart for pipe pressure over-limit compensation.

[0070] Figure 9 This is a flowchart for wind turbine current compensation.

[0071] Figure 10 This is a flowchart for the air volume compensation during start-up and shutdown of the fan.

[0072] Figure 11 This is a flowchart for DO over-limit compensation in the aerobic zone. Detailed Implementation

[0073] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0074] Example 1

[0075] This embodiment proposes a method applicable to A 2 Optimized dissolved oxygen and chemical dosing control methods for O+MBR processes, including, for example Figure 2 As shown, A 2 The O+MBR process's biological treatment tank includes an anaerobic zone, an anoxic zone, a low-dissolved oxygen zone, an aerobic zone, and a membrane zone. These zones are sequentially connected. The end of the membrane zone is connected in reverse to the beginning of the low-dissolved oxygen zone. Wastewater and sludge from the end of the membrane zone are returned to the low-dissolved oxygen zone. Similarly, the end of the low-dissolved oxygen zone is connected in reverse to the beginning of the anoxic zone, and wastewater and sludge from the low-dissolved oxygen zone are returned to the anoxic zone. The anoxic zone is also connected in reverse to the anaerobic zone, and wastewater and sludge from the anoxic zone are returned to the anaerobic zone. The dissolved oxygen level in the low-dissolved oxygen zone is 0.1–0.5 mg / L, while the dissolved oxygen level in the aerobic zone is approximately 2.0 mg / L under normal aeration. A chemical dosing port is located at the end of the aerobic zone, through which PAC (phosphorus chloride) is added based on the orthophosphate level at the end of the aerobic zone.

[0076] Compared to the existing A 2 In the O+MBR process, this invention adjusts the aerobic zone I from a conventional aerobic zone to a low dissolved oxygen zone, saving electricity costs in terms of aeration. The low dissolved oxygen zone creates a facultative anaerobic environment, allowing nitrifying and denitrifying bacteria to coexist in the same space and simultaneously undergo nitrification and denitrification reactions, enhancing biological nitrogen removal and reducing the need for denitrification chemicals. The low dissolved oxygen content of the nitrified liquid returned from the low dissolved oxygen zone to the anoxic zone minimizes the impact on the anoxic environment, better maintaining it and enhancing denitrification efficiency. The dosage of chemical phosphorus removal agents is changed from the total phosphorus meter reading in the effluent to the orthophosphate value at the end of the aerobic zone in the biological treatment tank, optimizing the original feedforward reaction into a forward reaction. Real-time monitoring of orthophosphate trends allows for timely and accurate dosing of phosphorus removal agents based on orthophosphate values, resulting in greater accuracy and efficiency.

[0077] Since the lower limit of dissolved oxygen measurement of the online dissolved oxygen detector is 0.5 mg / L, but in actual process control, there are often situations where the dissolved oxygen level is lower than the lower limit of measurement. At this time, it is impossible to guide the operation of the air intake fan and air intake valve in the low dissolved oxygen zone based on the dissolved oxygen index, and the state of efficient denitrification cannot be maintained.

[0078] The above applies to A2 Optimization of dissolved oxygen, chemical dosing control methods, data acquisition, chemical dosing control, and dissolved oxygen control in O+MBR process;

[0079] Data acquisition includes collecting redox potential data at the end of the anoxic zone, orthophosphate values ​​at the end of the aerobic zone, effluent ammonia nitrogen data, influent flow rate data, influent water quality data, actual dissolved oxygen values ​​in the low dissolved oxygen zone, and actual dissolved oxygen values ​​in the middle and later sections of the aerobic zone.

[0080] In practical applications, an online ORP (oxidation-reduction potential) instrument is installed at the end of the anoxic zone, and an online DO (dissolved oxygen) instrument is installed in the low dissolved oxygen zone and the later part of the aerobic zone. The actual ORP value at the end of the anoxic zone is obtained through the online ORP instrument, and the actual dissolved oxygen value in the low dissolved oxygen zone and the later part of the aerobic zone is obtained through the online DO instrument.

[0081] The chemical dosing control includes: using the orthophosphate value at the end of the aerobic zone as the basis for PAC chemical dosing; performing PID control calculations based on the target value and actual value of orthophosphate at the outlet of the aerobic zone to dynamically control the phosphorus removal chemical dosing; and saving power consumption of the chemical dosing diaphragm pump and PAC chemical consumption by reasonably controlling the amount of PAC chemical added.

[0082] Dissolved oxygen control includes: using the oxidation-reduction potential at the end of the anoxic zone as the control index, and using effluent ammonia nitrogen data, influent flow rate data, influent water quality data, actual dissolved oxygen value in the low dissolved oxygen zone, and actual dissolved oxygen value in the middle and later stages of the aerobic zone as auxiliary control parameters to adjust the air volume of the aeration system.

[0083] The specific steps for controlling the addition of chemicals are as follows:

[0084] S101: Set the target value of orthophosphate at the end of the aerobic zone effluent point.

[0085] S102: PID control calculations are performed based on the target orthophosphate value and the actual orthophosphate value at the aerobic zone's end effluent point obtained from data acquisition. The PID control calculations use the target and actual orthophosphate values ​​to form the control deviation. The proportional, integral, and derivative of the deviation are linearly combined to form the control quantity. The PAC dosage concentration is then obtained from the control quantity. In practical applications, the PID control algorithm is loaded into a PID controller for PID calculations to obtain the control quantity. The required PAC dosage concentration is then determined based on the control quantity.

[0086] S103: Calculate the required dosage of PAC based on the PAC dosage concentration and actual effluent flow rate. The PAC dosage is calculated using the following formula:

[0087]

[0088] This formula relates the dosage of PAC, the concentration of PAC, and the volume of liquid (i.e., the actual effluent volume). The required dosage of PAC can be calculated using this formula, which solves the problem of the PAC dosing control system relying on historical data and reduces the complexity of the system.

[0089] S104: Based on the PAC dosage (i.e., the target value of PAC dosage) and the actual value of PAC dosage calculated in step S103, PI control calculation is performed. The PI control calculation uses the target value of PAC dosage and the actual value of PAC dosage to form the control deviation. The ratio and integral of the deviation are linearly combined to form the control quantity. The PI control algorithm is loaded into the PI controller for PI calculation to obtain the control quantity. The operating frequency of the diaphragm pump for drug dosing is controlled by the PI controller.

[0090] The operating frequency of the diaphragm pump corresponding to PAC dosing is controlled by PI control calculation, so as to dynamically control the diaphragm pump corresponding to PAC dosing. This solves the problem of relying on a fixed frequency for PAC dosing. This method can achieve dynamic control of the dosing.

[0091] S105: Based on orthophosphate compensation calculation, the diaphragm pump is used for intermittent dosing of the reagent to obtain the appropriate dosage and dosing time.

[0092] The orthophosphate compensation calculation is as follows: When the PAC automatic dosing control system switches from manual to automatic dosing, the actual orthophosphate value may fluctuate. Therefore, PAC dosing stabilization control is required. During the adjustment transition time, the PAC dosing amount is gradually adjusted to smoothly transition from the dosing amount in manual mode to the target dosing amount in automatic mode. This ensures a stable transition when switching from manual to automatic PAC dosing control, without frequent start-stop cycles or sudden spikes in total phosphorus control.

[0093] In summary, by determining the PAC dosage based on the calculation method for PAC concentration, dynamic addition of PAC dosage combined with liquid volume is achieved, thus realizing automatic control of PAC dosing. Furthermore, the basis for chemical phosphorus removal agent addition has been changed from the total phosphorus meter value of the effluent to the orthophosphate value at the end of the aerobic zone of the biological treatment tank. The original feedback reaction has been optimized into a positive feedback reaction, with real-time detection of orthophosphate trends and timely and accurate addition of phosphorus removal agents based on orthophosphate values, resulting in greater accuracy and efficiency.

[0094] Dissolved oxygen control specifically includes the following steps:

[0095] S201: Set the target value of ORP (oxidation-reduction potential) for the anoxic zone.

[0096] S202: Perform peak filtering and arithmetic average filtering on the collected real-time operating data, including ORP data at the end of the anoxic zone, effluent ammonia nitrogen data, influent flow rate data, influent water quality data, and dissolved oxygen data in the middle and later stages of the low dissolved oxygen zone and aerobic zone.

[0097] S203: Perform fuzzy PID control calculations based on the ORP target value and the actual ORP value;

[0098] First, fuzzification is performed. The inputs of the fuzzy PID controller are the deviation e(t) and the corresponding deviation change rate ec(t). e(t) is the deviation between the target value and the actual value, e(t) = r(t) - c(t). Here, ec(t) is the difference between the ORP target value and the ORP actual value, ec(t) is the deviation change rate, and ec(t) is the deviation between the current deviation and the previous deviation, ec(t) = e(t) - e(t-1). Here, ec(t) is the difference between the current ORP difference and the previous ORP difference.

[0099] Define the fuzzy condition set of inputs e(t), ec(t) and outputs ΔKp, ΔTi, ΔTd as a level 7 fuzzy subset {NB, NM, NS, ZO, PS, PM, PB}, where N represents negative, P represents positive, B represents large, M represents medium, S represents small, and ZO represents 0. The membership function of the fuzzy subset is as follows:

[0100]

[0101] Based on actual operating experience, the parameter values ​​a, b, c, d, e, and f are set. In this embodiment, the deviation of the initial value X by ±5% is used as the limit value for c and d, the deviation of the initial value X by ±30% is used as the limit value for b and e, and the deviation of the initial value X by ±60% is used as the limit value for a and f.

[0102] Define a fuzzy control rule table for the inputs e(t), ec(t) and the outputs ΔKp, ΔTi, and ΔTd. The fuzzy control rule table is in the form of IF input THEN output (standard Mamdani form).

[0103] Defuzzification is performed, during which the fuzzy control correction quantities ΔKp, ΔTi, and ΔTd are obtained according to the fuzzy control rule table. The values ​​of Kp(t), Ti(t), and Td(t) of the fuzzy PID controller are obtained by adding their initial values ​​Kp(t-1), Ti(t-1), and Td(t-1) to the fuzzy control correction quantities ΔKp, ΔTi, and ΔTd. The calculation formula is as follows:

[0104]

[0105] S204: PID control calculation is performed based on the target value of ORP, the actual value of ORP, and the values ​​of Kp(t), Ti(t), and Td(t). The PID control calculation forms the control deviation e(t) based on the target value of ORP and the actual value of ORP. The deviation e(t) is linearly combined with the proportional (Kp), integral (Ti), and derivative (Td) values ​​to form the control quantity u(t), which controls the fan. By loading the PID control algorithm into the PID controller, the operation of the fan is controlled by the PID controller.

[0106] Specifically, the fan guide vane control or fan frequency control is performed based on the calculation results of PID control. That is, the PID controller generates control commands for the fan guide vane opening or fan frequency, and the control commands are used to control the fan guide vane or fan frequency.

[0107] S205: Based on actual control needs, the operation control correction and deviation of fans and valves are achieved by compensating for inlet flow rate, ammonia nitrogen over-limit, fan start-stop air volume connection, pipe pressure over-limit, and fan current, thereby obtaining the appropriate air supply volume for low dissolved oxygen and aerobic zones.

[0108] Specifically, the process involves combining process experience with the results of fuzzy PID control algorithm calculations to determine 5 control decision trees and the priority of compensation control actions. The priorities, from high to low, are: fan protection actions, fan unit start-up and shutdown actions, ORP, ammonia nitrogen, and DO anomalies, influent water quality fluctuations, and PID control module outputs. The fuzzy PID control results are then used to determine and output the final control command through the decision tree.

[0109] S206: Each control zone (low dissolved oxygen zone and aerobic zone) has a valve to control its aeration volume. The aeration volume of the control zone is determined by the opening degree of the valve. Each valve controls the redistribution of the air supply provided by the blower according to the different air demand of each control zone to meet the air demand of each control zone.

[0110] S207: Based on the target and actual values ​​of the oxidation-reduction potential in the low dissolved oxygen zone and the target and actual values ​​of the dissolved oxygen in the aerobic zone, PID control calculations are performed to determine the required air volume for each controlled zone. The PID control calculations use the target and actual dissolved oxygen values ​​for each controlled zone to form the control deviation. The deviation is then linearly combined using proportional (Kp), integral (Ti), and derivative (Td) values ​​to form the control quantity. The required air volume for each controlled zone is then determined based on the control quantity.

[0111] S208: Obtain the target air volume for each control zone and control the valve opening through PI control calculation. The PI control calculation forms a control deviation based on the target air volume and the actual air volume. The proportional (Kp) and integral (Ti) of the deviation are linearly combined to form the control quantity to control the valve. By loading the PI control algorithm into the PI controller, the valve opening is controlled by the PI controller.

[0112] S209: The results of PI control calculations are used as the basis for adjusting the opening of each valve; by adjusting the valve opening to match the air demand of the controlled area, linear control of the air demand of the controlled area is achieved.

[0113] The combined action of the ORP (oxidation-reduction potential) control fan opening and the DO (dissolved oxygen) control valves in each controlled zone achieves automatic linkage control of the ORP in the biological treatment tank with the dissolved oxygen in the low-dissolved oxygen zone and the aerobic zone. This solves the problem of controlling low dissolved oxygen, and the valve control method is universally applicable, such as butterfly valves, plunger valves, diamond valves, and elliptical valves. Ultimately, the ORP in the anoxic zone of the biological treatment tank is controlled at -200 to -80 mV, the dissolved oxygen concentration in the low-dissolved oxygen zone is controlled at 0.1 to 0.5 mg / L, and the dissolved oxygen concentration in the aerobic zone is controlled at 1 to 2 mg / L. This stabilizes the nitrogen and phosphorus removal effect in the low-dissolved oxygen biological treatment tank, while the low-dissolved oxygen nitrification liquid is returned to the upstream anoxic zone, providing more favorable denitrification conditions.

[0114] The compensation for influent flow rate, ammonia nitrogen exceeding limits, ORP exceeding limits, DO exceeding limits, blower start / stop airflow connection, membrane system DO exceeding limits, pipe pressure exceeding limits, and blower current protection are explained below:

[0115] Influent flow compensation: After processing abnormal flow values ​​through the "data processing system," the influent flow value is dynamically assessed. When the influent flow fluctuation is significantly large or small, the guide vanes or frequency of the blower are adjusted in advance to compensate for the untimely control of dissolved oxygen in the biological treatment tank caused by the fluctuation in influent flow. This reduces the impact of influent flow fluctuations on the dissolved oxygen control of the biological treatment tank, thereby affecting the control effect. The flowchart is as follows: Figure 4 As shown.

[0116] Ammonia nitrogen exceedance compensation: After processing abnormal ammonia nitrogen values ​​through the "data processing system," the effluent ammonia nitrogen is judged to exceed the limit. When the effluent ammonia nitrogen value exceeds the preset value, the air volume needs to be increased, thereby adjusting the guide vanes or frequency of the blower to supplement the oxygen lacking due to incomplete ammonia nitrogen reaction in the aerobic zone, thus meeting the ammonia nitrogen effluent compliance requirements. The flowchart is as follows: Figure 5 As shown.

[0117] ORP Over-Limit Compensation: After processing abnormal ORP values ​​through the "Data Processing System," the ORP in the anoxic zone of the biological treatment tank is judged to be exceeding the limit. When the ORP in the anoxic zone exceeds the preset value, the air volume needs to be reduced, thereby adjusting the guide vanes or frequency of the blower. When the ORP in the anoxic zone is lower than the preset value, the air volume needs to be increased, thereby adjusting the guide vanes or frequency of the blower. The flowchart is as follows: Figure 6 As shown, exceeding the ORP limit will cause insufficient redox reaction conditions in the biological treatment tank. In order to compensate for the lack of timely control and meet the requirements of ORP control, emergency control adjustments are made.

[0118] Low dissolved oxygen (DO) over-limit compensation: After processing abnormal dissolved oxygen values ​​through the "data processing system," the dissolved oxygen in the low dissolved oxygen zone is judged to be exceeding the limit. When the dissolved oxygen in the low dissolved oxygen zone exceeds the preset value, the air volume needs to be reduced, thereby adjusting the fan guide vanes or frequency. The flowchart is as follows. Figure 7 As shown. Excessive dissolved oxygen can cause over-aeration or under-aeration. To compensate for any delays in control and meet dissolved oxygen control requirements, emergency control adjustments are necessary.

[0119] Pipe pressure over-limit compensation: After processing abnormal fan supply pipe pressure values ​​through the "data processing system," the system determines if the fan supply pipe pressure exceeds the preset value. When the fan supply pipe pressure exceeds the preset value, the air volume needs to be reduced, thereby adjusting the fan's guide vanes or frequency. The flowchart is as follows: Figure 8 As shown. To ensure stable operation of the fan, exceeding the limit in the duct pressure not only poses a safety hazard but can also cause surge in other fans with lower outlet pressures. In this case, reducing the fan guide vane opening or frequency is necessary to ensure the safety of the fan duct system.

[0120] Fan current compensation: After processing abnormal fan current values ​​through the "data processing system," a fan current over-limit judgment will be performed. When the fan current value exceeds the preset value, the air volume needs to be reduced, thereby adjusting the fan guide vanes or frequency. The flowchart is as follows. Figure 9 As shown. The stable operation of the fan must not exceed its rated power. In order to protect the normal use of the fan, the protection action should be activated in time when the fan current exceeds the limit.

[0121] Start-up and shutdown fan airflow compensation: When fans start or stop, the airflow changes, causing fluctuations in dissolved oxygen in the biological treatment tank. This is detrimental to the automatic control of dissolved oxygen in the tank. To address this issue, a start-up and shutdown fan airflow compensation system is implemented. This system reduces the impact of airflow fluctuations on the dissolved oxygen in the biological treatment tank when fans start or stop, ensuring a smooth transition in airflow before and after changes in the number of fans. The flowchart is as follows: Figure 10 As shown.

[0122] Aerobic Zone DO Exceedance Compensation: After processing abnormal dissolved oxygen values ​​through the "data processing system," the dissolved oxygen in the aerobic zone is assessed for exceeding limits. When the dissolved oxygen in the aerobic zone exceeds the preset value, the airflow needs to be reduced, thereby adjusting the blower guide vanes or frequency. When the dissolved oxygen in the aerobic zone is below the preset value, the airflow needs to be increased, thereby adjusting the blower guide vanes or frequency. Exceeding dissolved oxygen limits can cause over-aeration or under-aeration in the membrane system. To meet the dissolved oxygen control requirements of the aerobic zone, adjustments are made to the membrane system blower control and the biological treatment tank blower control. The flowchart is as follows: Figure 11 As shown.

[0123] The control algorithm used in this embodiment:

[0124] Fuzzy PID control algorithm: The fuzzy PID controller used has a two-input, three-output structure. The inputs to the fuzzy controller are the deviation e(t) and the corresponding rate of change of deviation ec(t), and the output is the PID controller parameter correction ΔK. p ΔT i ΔT d During the operation of the control system, the input quantities e(t) and ec(t) undergo fuzzification, fuzzy inference, and defuzzification to obtain the online correction quantity ΔK. p ΔT i ΔT d , perform K p T i T d Real-time adjustment, control logic schematic diagram as follows Figure 3 As shown.

[0125] The control deviation is determined by the given value and the actual output value, and the K value is used for fuzzy PID control. p T i T d The real-time adjusted value is used to construct the control quantity by linearly combining the proportional, integral, and derivative values ​​of the deviation, and then controlling the controlled object. The formula is as follows:

[0126]

[0127] Where u(t) is the output signal of the fuzzy PID controller; p is the proportional operator; Kp is the proportional coefficient; Ti is the integral coefficient; Td is the derivative coefficient; Kd is the differential gain of the derivative coefficient: Kd(t) = Td(t) - Td(t-1); e(t) is the deviation signal of the control system, also known as the input signal of the controller. The deviation between the given target value r(t) and the actual output value c(t) is: e(t) = r(t) - c(t).

[0128] PID control algorithm: Based on the given value and the actual output value, the control deviation is formed. The deviation is then linearly combined using proportional, integral, and derivative terms to form the control quantity, which controls the controlled object. The formula is as follows:

[0129]

[0130] Where u(t) is the output signal of the PID controller; p is the proportional operator; Kp is the proportional coefficient; Ti is the integral coefficient; Td is the derivative coefficient; Kd is the differential gain of the derivative coefficient: Kd(t) = Td(t) - Td(t-1); e(t) is the deviation signal of the control system, also known as the input signal of the controller. The deviation between the given target value r(t) and the actual output value c(t) is: e(t) = r(t) - c(t).

[0131] PI control algorithm: Based on the control deviation between the given value and the actual output value, the proportional and integral components of the deviation are linearly combined to form the control quantity, which controls the controlled object. The formula is as follows:

[0132]

[0133] In the above formula, u(t) is the output signal of the PI controller; p is the proportional operator; Kp is the proportional coefficient, which proportionally reflects the deviation signal e(t) of the control system; Ti is the integral coefficient; e(t) is the deviation signal of the control system, also known as the input signal of the controller. The deviation between the given target value r(t) and the actual output value c(t) is: e(t) = r(t) - c(t).

[0134] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An optimized dissolved oxygen and chemical dosing control method suitable for A²O+MBR process. Its features are: in, The biological treatment tank of the A²O+MBR process includes an anaerobic zone, an anoxic zone, a low dissolved oxygen zone, an aerobic zone, and a membrane zone connected in sequence. The end of the membrane zone is connected in reverse to the front of the low dissolved oxygen zone, the end of the low dissolved oxygen zone is connected in reverse to the front of the anoxic zone, and the anoxic zone is connected in reverse to the anaerobic zone. A phosphorus removal agent dosing port is provided at the end of the aerobic zone. The method includes data acquisition, reagent dosing control, and dissolved oxygen control; Data acquisition includes collecting redox potential data at the end of the anoxic zone, orthophosphate values ​​at the end of the aerobic zone, effluent ammonia nitrogen data, influent flow rate data, influent water quality data, actual dissolved oxygen values ​​in the low dissolved oxygen zone, and actual dissolved oxygen values ​​in the middle and later sections of the aerobic zone. The chemical dosing control includes: using the orthophosphate value at the end of the aerobic zone as the basis for phosphorus removal chemical dosing; and performing PID control calculations based on the target value and actual value of orthophosphate at the effluent point at the end of the aerobic zone to dynamically control the phosphorus removal chemical dosing. Dissolved oxygen control includes: using the oxidation-reduction potential at the end of the anoxic zone as the control index, and using effluent ammonia nitrogen data, influent flow rate data, influent water quality data, actual dissolved oxygen value in the low dissolved oxygen zone, and actual dissolved oxygen value in the middle and later stages of the aerobic zone as auxiliary control parameters to adjust the air volume of the aeration system. Dissolved oxygen control specifically includes the following steps: S201: Set the target value for the redox potential in the anoxic zone; S202: Peak filtering and arithmetic average filtering are performed on the collected oxidation-reduction potential data at the end of the anoxic zone, effluent ammonia nitrogen data, influent flow rate data, influent water quality data, and dissolved oxygen data in the middle and later stages of the low dissolved oxygen zone and aerobic zone. S203: Perform fuzzy PID control calculations based on the target value and actual value of the redox potential to obtain fuzzy control correction quantities ΔKp, ΔTi, and ΔTd. Based on the initial values ​​of Kp(t-1), Ti(t-1), and Td(t-1) of the fuzzy PID controller and the fuzzy control correction quantities ΔKp, ΔTi, and ΔTd, obtain the values ​​of Kp(t), Ti(t), and Td(t) of the fuzzy PID controller, respectively. S204: PID control calculations are performed based on the target and actual redox potential values, as well as the values ​​of Kp(t), Ti(t), and Td(t). The PID control calculations use the target and actual redox potential values ​​to form the control deviation, and proportionally convert the deviation e(t). ,integral and differential The fan is controlled by forming control variables through linear combinations; S205: Based on actual control needs, the operation control correction and deviation of the fan and valve are achieved by compensating for inlet flow rate, ammonia nitrogen over-limit, start-stop fan volume connection compensation, pipe pressure over-limit compensation and fan current compensation, so as to obtain the air supply volume suitable for low dissolved oxygen zone and aerobic zone. S206: Each control zone has a corresponding valve that controls its aeration volume. The aeration volume of the control zone is determined by the opening degree of the valve. Each valve controls the redistribution of the air supply provided by the blower according to the different air demand of each control zone to meet the air demand of each control zone. S207: Based on the target and actual values ​​of the oxidation-reduction potential in the low dissolved oxygen zone and the target and actual values ​​of the dissolved oxygen in the aerobic zone, PID control calculations are performed to solve the air demand of each zone to be controlled. S208: Obtain the target air volume of each control zone, and control the valve opening through PI control calculation. The PI control calculation is based on the control deviation between the target air volume and the actual air volume. The ratio and integral of the deviation are linearly combined to form the control quantity, which controls the valve. S209: The results of PI control calculations are used as the basis for adjusting the opening of each valve; by adjusting the valve opening to match the air demand of the controlled area, linear control of the air demand of the controlled area is achieved. By controlling the fan opening based on the oxidation-reduction potential and coordinating the operation of the dissolved oxygen control valves in each controlled zone, the automatic linkage control of the ORP in the biological treatment tank and the dissolved oxygen in the low-oxygen and aerobic zones is achieved.

2. The optimized dissolved oxygen and chemical dosing control method for A²O+MBR process according to claim 1, characterized in that: The specific steps for controlling the addition of chemicals are as follows: S101: Set the target value of orthophosphate at the end effluent point of the aerobic zone; S102: PID control calculation is performed based on the target value of orthophosphate and the actual value of orthophosphate at the end of the aerobic zone effluent obtained from data acquisition. The PID control calculation is based on the target value of orthophosphate and the actual value of orthophosphate to form the control deviation. The proportional, integral and derivative of the deviation are linearly combined to form the control quantity. The concentration of phosphorus removal agent is obtained based on the control quantity. S103: Calculate the required dosage of phosphorus removal agent based on the concentration of the phosphorus removal agent and the actual effluent volume; S104: The phosphorus removal agent dosage calculated in step S103 is the target value of the phosphorus removal agent dosage. PI control calculation is performed based on the target value and the actual value of the phosphorus removal agent dosage. The PI control calculation uses the target value and the actual value of the phosphorus removal agent dosage to form the control deviation. The proportion and integral of the deviation are linearly combined to form the control quantity. The operating frequency of the diaphragm pump for pesticide dosing is controlled based on the control quantity.

3. The optimized dissolved oxygen and chemical dosing control method for A²O+MBR process according to claim 2, characterized in that: It also includes step S105: performing intermittent dosing of the agent by the diaphragm pump according to the orthophosphate compensation calculation, and obtaining the dosage and dosing time; The orthophosphate compensation calculation is as follows: when the automatic dosing control system for phosphorus removal agents switches from manual to automatic dosing, stable control is performed, that is, the dosage of phosphorus removal agents is gradually adjusted so that it smoothly transitions from the dosage in manual mode to the target dosage in automatic mode, so that the switch from manual to automatic phosphorus removal agent dosing control can be stable.

4. The optimized dissolved oxygen and chemical dosing control method for A²O+MBR process according to claim 2, characterized in that: The phosphorus removal agent used is PAC (phosphorus compound), and the dosage of PAC is calculated according to the following formula: ； The liquid volume refers to the actual outflow of water.

5. The optimized dissolved oxygen and chemical dosing control method applicable to A²O+MBR process according to claim 1, characterized in that: Step S205 specifically involves: combining process experience with the results of fuzzy PID control algorithm calculations to determine 5 control decision trees and the priority of compensation control actions. The priorities from high to low are: fan protection action, fan unit start-up and shutdown action, ORP, ammonia nitrogen, DO anomalies, influent water quality fluctuations, and PID control module output. The fuzzy PID control results are then used to determine and output the final control command through the decision tree.

6. The optimized dissolved oxygen and chemical dosing control method for A²O+MBR process according to claim 1, characterized in that: Step S203 specifically includes: Fuzzification is performed by defining the fuzzy condition set for the inputs e(t), ec(t) and outputs ΔKp, ΔTi, and ΔTd of the fuzzy PID controller, and defining the fuzzy control rule table for the inputs e(t), ec(t) and outputs ΔKp, ΔTi, and ΔTd. Defuzzification is then performed, during which the fuzzy control corrections ΔKp, ΔTi, and ΔTd are obtained based on the fuzzy control rule table. The values ​​of Kp(t), Ti(t), and Td(t) of the fuzzy PID controller are obtained based on the initial values ​​of Kp(t-1), Ti(t-1), and Td(t-1) of the fuzzy PID controller and the fuzzy control corrections ΔKp, ΔTi, and ΔTd, respectively.

7. The optimized dissolved oxygen and chemical dosing control method for A²O+MBR process according to claim 1, characterized in that: Step S207 specifically includes: PID control calculation based on the target value and actual value of dissolved oxygen in each controlled area to form the control deviation, and proportionally... ,integral and differential The control quantity is constructed by linear combination, and the air demand of each control zone is solved based on the control quantity.

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