An optimized control method and system for sludge return control

Abstract

The present invention discloses a sludge return control optimization control method and system, which relates to the technical field of sewage treatment. The method includes: first calculating the external return flow rate; correcting the calculation result according to the influencing factors pH and hydraulic retention time and generating a correction result, and adjusting the sludge retention time; making a judgment based on the predicted result of the water inlet trend; comparing the correction result with the current external return flow rate, judging whether the comparison result is consistent with the water flow trend, and adjusting the return pump; comparing the total nitrogen of the effluent at a specific time node in the future with the set value, judging whether the external return flow control meets the standard, and making correction adjustments if it does not meet the standard; adjusting the internal return flow rate by monitoring the ORP of the denitrification tank. Predicting the water flow trend through real-time data, and controlling the external return ratio in combination with the current sludge concentration, sludge retention time, pH, and hydraulic retention time, monitoring the future changes in the total nitrogen of the effluent for correction and adjustment; and synchronously calculating the internal return ratio to control the operating parameters of the return pump.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a sludge return control optimization control method and system. Background Art

[0002] The activated sludge method is currently a mainstream sewage treatment method. It relies on activated sludge (phosphate-accumulating bacteria, nitrifying bacteria, denitrifying bacteria, etc.) to carry out different microbial reactions in different dissolved oxygen zones to decompose organic matter and harmful components in sewage. The biological pool is divided into anaerobic pools, anoxic pools and aerobic pools, which respectively carry out phosphate accumulation, PHB synthesis - denitrification - phosphorus release, and nitrification reactions. The sludge flows with the water body and converges to the secondary sedimentation tank. If there is no aging and inactivation, the sludge at the bottom of the secondary sedimentation tank needs to be returned to the beginning of the biological pool. This process is called external return flow. The purpose is to achieve microbial circulation. The ratio of the sludge return flow to the biological pool inlet is called the external return flow ratio. The scientific name of internal return flow is nitrification liquid return flow, which is to return the nitrate nitrogen produced by the nitrification reaction in the aeration tank to the anoxic pool to provide combined oxygen for denitrification and carry out denitrification reaction. The ratio of the nitrification liquid return flow to the biological pool inlet flow is called the internal return flow ratio.

[0003] Increasing the external recirculation ratio is beneficial for increasing the activated sludge's ability to resist shock loads within a certain period of time, inhibiting the occurrence of activated sludge aging under low-load conditions, and reducing the impact of pH on biochemical reactions. However, the time required for activated sludge to degrade excess organic matter is shortened, the degradation effect is insufficient, the activated sludge is not easy to enter the exhaustion stage, and the sedimentation is poor. Lowering the external recirculation ratio is beneficial for extending the static time of the activated sludge settled at the bottom of the secondary sedimentation tank and increasing the sludge activity, but the shock resistance effect is poor and it may also cause insufficient microbial counts and insufficient reactions. Increasing the internal recirculation ratio is beneficial for the denitrification reaction, but it will cause excessive DO from the aerobic section to flow into the anoxic section, increasing the burden on the aeration system. Lowering the ratio will not guarantee the nutrients necessary for the denitrifying bacteria to carry out biochemical reactions. Existing technologies are unable to jointly control the internal and external recirculation of the biological pool, resulting in low sewage treatment efficiency.

[0004] The "five-factor adjustable sewage treatment device" disclosed in Chinese patent literature, with authorization announcement number CN100457652C, is a five-factor adjustable sewage treatment device, which is an improved device for the A / A / O sewage treatment process. It mainly includes a primary sedimentation tank, an anaerobic tank, an anoxic tank, an aerobic tank and a secondary sedimentation tank; however, the sewage treatment effect is still not high if it is only improved from a structural perspective. Summary of the Invention

[0005] The present invention solves the problem that the existing sewage treatment methods cannot take into account multiple factors, resulting in low sewage treatment efficiency. It proposes an optimized control method and system for sludge reflux control, which predicts the water volume trend through real-time data, and combines the current sludge concentration, sludge retention time, pH, and hydraulic retention time to control the external reflux ratio, monitors the change of total nitrogen in the future effluent for correction and adjustment; synchronously calculates the internal reflux ratio to control the operating parameters of the reflux pump.

[0006] To achieve the above object, the present invention adopts the following technical solutions: An optimized control method for sludge reflux control includes the following steps:

[0007] S1, Obtain the external reflux volume according to the external reflux ratio and the influent flow rate of the biological tank, and generate a calculation result;

[0008] S2, Correct the calculation result according to the influencing factors pH and hydraulic retention time, and generate a correction result, and adjust the sludge retention time;

[0009] S3, Judge according to the prediction result of the influent volume trend; Compare the correction result with the current external reflux volume, judge whether the comparison result conforms to the water volume trend, and adjust the reflux pump;

[0010] S4, Compare the total nitrogen in the effluent at a specific future time node with the set value, judge whether the external reflux control meets the standard, if not, perform correction and adjustment;

[0011] S5, Adjust the internal reflux volume according to the monitored ORP of the denitrification tank.

[0012] In the present invention, first calculate the external reflux volume as the calculation result, then correct the calculation result in the form of weights with pH and hydraulic retention time, and adjust the sludge retention time in the form of conditional triggering; then predict the trend of the influent volume to obtain the prediction result of the influent volume trend, compare the correction result obtained in step S2 with the current external reflux volume, if the obtained comparison result conforms to the water volume trend, directly adjust the reflux pump, if it does not conform to the water volume trend, perform manual judgment; after adjusting the reflux pump, perform control compliance verification, judge whether the external reflux control meets the standard according to the comparison of the total nitrogen in the effluent at a certain future time node and the set value, if not, perform correction and adjustment, and specifically adjust the correction weight to obtain a more accurate result; finally, the calculated internal flow can also be adjusted according to the monitored ORP of the denitrification tank.

[0013] Preferably, the step S2 includes the following steps:

[0014] S21, Perform weighted calculation on the calculation result, pH, and hydraulic retention time, and generate a correction result according to each correction weight;

[0015] S22 adjusts the sludge retention time in a conditional trigger form. If the sludge retention time is within the normal range, no adjustment is made; if the sludge retention time is not within the normal range, the correction result is adjusted.

[0016] In the present invention, since the calculation result does not consider the pH value and the retention time of the sewage to be treated in the biological tank, the result is not very accurate. Therefore, pH and hydraulic retention time are introduced in the form of weights, where the hydraulic retention time is the average retention time of the sewage to be treated in the biological tank. In addition, for the sludge retention time, a conditional trigger form is adopted to determine whether to make an adjustment. If the sludge retention time is too long or too short, the correction result is adjusted accordingly. Generally, the adjustment range is 2%-5%.

[0017] Preferably, the step of judging whether the comparison result conforms to the water volume trend and adjusting the reflux pump specifically includes the following steps:

[0018] If the comparison result conforms to the water volume trend, the result is output and the operating frequency of the reflux pump is adjusted using the PID algorithm;

[0019] If the comparison result does not conform to the water volume trend, an alarm message is generated, and it is determined manually whether to adjust the external reflux volume.

[0020] In the present invention, the external reflux volume is positively correlated with the influent water volume. When the influent water volume increases, the external reflux volume also increases; conversely, it decreases. If the comparison result conforms to the water volume trend, the operating frequency of the reflux pump is directly adjusted to control the reflux pump; if it does not conform to the water volume trend, it is determined manually whether to adjust the correction result. At the same time, an alarm message is generated on the man-machine interface, and relevant data is displayed for reference.

[0021] Preferably, the prediction result of the influent water volume trend is predicted through big data analysis or a function of flow rate and time is generated by collecting the influent flow rate, and the first derivative and the second derivative are solved for prediction.

[0022] In the present invention, for a PLC control system equipped with an edge computing gateway, the influent flow rate can be predicted through big data analysis. For a general PLC control system whose computing power does not support big data, a flow rate-time function is made by collecting the influent flow rate, the first derivative is solved to analyze the change trend, the second derivative is solved to analyze the change rate, and the reflux ratio control strategy is adjusted according to the positive or negative of the derivative.

[0023] Preferably, step S4 specifically includes:

[0024] The total nitrogen in the effluent after n hours of collection is compared with the set value of the total nitrogen in the effluent. If the error between the total nitrogen in the effluent and the set value of the total nitrogen in the effluent is within 2%, the external reflux control meets the standard. If the error between the total nitrogen in the effluent and the set value of the total nitrogen in the effluent is outside 2%, the external reflux control does not meet the standard, and step S2 does not need to be executed. At the same time, traceability is carried out to find problems to adjust the correction weight, and then step S2 is re-executed according to the adjusted correction weight.

[0025] In the present invention, n is greater than 0. After collecting the total nitrogen in the effluent after n hours, the data is compared with the pre-set set value of the total nitrogen in the effluent. If the error between the two is within 2%, the control effect meets the standard. If not, the correction link of the above step S2 is cancelled and directly controlled by the calculation result in step S1. At the same time, problems are traced back in the background to adjust the correction weight. After the total nitrogen in the effluent directly controlled by step S1 meets the standard, the correction link of step S2 is restored with the newly calculated weight coefficient, and the normal control process is switched back.

[0026] Preferably, the step of adjusting the correction weight specifically includes:

[0027] S41, go back n hours from the moment when it is judged that the external reflux control does not meet the standard, and extract the historical calculated values of the calculation result, pH, and hydraulic retention time with a time span of x minutes;

[0028] S42, compare the calculated value at each time point with the calculated value at the previous time point. If the value increases, it is recorded as "+", and if the value decreases, it is recorded as "-" to obtain the historical increase and decrease trends of the three factors;

[0029] S43, judge whether the deviation state of the non-compliant total nitrogen in the effluent is larger or smaller than the set value, and record them as "+" and "-" respectively; S44, count the number of times the three factors have different signs from the deviation state of the total nitrogen in the effluent, and determine the adjusted correction weight according to the number of times.

[0030] In the present invention, the historical calculated values based on the three factors are obtained, and the calculated value at a certain time point is compared with the calculated value at the previous time point. If the calculated value at a certain time point increases relative to the calculated value at the previous time point, it is recorded as "+", and if it decreases, it is recorded as "-", and the historical increase and decrease trends of the three factors based on time are obtained; at the same time, it is determined whether the deviation state of the non-compliant total nitrogen in the effluent is larger or smaller than the set value, which is also represented by "+" and "-". Finally, the number of times the three factors have different signs from the deviation state of the total nitrogen in the effluent is counted, and the correction weight is newly adjusted.

[0031] Preferably, the weight of the factor with the largest number of times having a sign different from the deviation state of the total nitrogen in the effluent is reduced by k, the weight of the factor with the smallest number of times having a sign different from the deviation state of the total nitrogen in the effluent is increased by 0.8k, and the weight of the factor with the second largest number of times having a sign different from the deviation state of the total nitrogen in the effluent is increased by 0.2k, where the range of k is 0 - 1.

[0032] Among the three factors of the present invention, the weight with the largest number of times having a sign different is reduced by k, and the other two factors are increased by 0.8k and 0.2k respectively, and finally the adjusted correction weight is obtained.

[0033] Preferably, step S5 specifically includes: calculating the internal reflux flow rate according to the external reflux ratio, the influent flow rate, and the total nitrogen in the influent, and then adjusting the internal reflux flow rate according to the monitored ORP of the denitrification tank. If the monitoring result is higher than the set range, the internal reflux flow rate is reduced according to the proportional coefficient; if the detection result is normal, the reflux pump is directly controlled according to the internal reflux flow rate.

[0034] In the present invention, first, the internal reflux flow rate is calculated according to the calculation formula, and then the ORP in the denitrification tank is monitored in real time. If the monitoring result is normal, no adjustment is required; if the monitoring result is higher than the set range, the internal reflux flow rate is reduced according to the set proportional system.

[0035] Preferably, the calculation formula for the external reflux flow rate in step S1 is:

[0036]

[0037] where R is the external reflux ratio, Q is the influent flow rate of the biological tank, MLSS is the sludge concentration in the aerobic section, and RSS is the concentration of the returned sludge.

[0038] In the present invention, the external reflux flow rate calculated in step S1 is the calculation result.

[0039] A sludge reflux control optimization control system applicable to the above-mentioned sludge reflux control optimization control method includes an acquisition module, which includes several measuring instruments. The measuring instruments send the collected data to the CPU module through the AI / DI module or the switch;

[0040] The CPU module calculates the external reflux flow rate, predicts the trend of the influent volume, corrects the reflux flow rate, judges the trend of the water volume, and performs control compliance verification; at the same time, it calculates the internal reflux flow rate;

[0041] The control module includes several reflux pumps and corresponding frequency converters, and adjusts the working frequency of the reflux pumps according to the CPU module.

[0042] The system of the present invention mainly includes a collection module, a CPU module, and a control module. The collection module is connected to the CPU module, and the CPU module is connected to the control module. The collection module can collect corresponding data through measuring instruments and send it to the CPU module through a switch or an AI / DI module. The CPU module can perform functions such as processing calculations, corrections, and trend judgments, generate a final result instruction, and send the final result instruction to the control module to achieve the control of the reflux pump.

[0043] The present invention has the following beneficial effects:

[0044] A sludge reflux control optimization method and system of the present invention predict the water volume trend through real-time data, and control the external reflux ratio in combination with the current sludge concentration, sludge retention time, pH, and hydraulic retention time, monitor the future change of the total nitrogen in the effluent for correction and adjustment; synchronously calculate the internal reflux ratio to control the operating parameters of the reflux pump; improve the effect of sewage treatment. Description of the Drawings

[0045] Figure 1 is a flowchart of a part of a sludge reflux control optimization method of the present invention;

[0046] Figure 2 is a flowchart of another part of a sludge reflux control optimization method of the present invention;

[0047] Figure 3 is a schematic structural diagram of a sludge reflux control optimization system of the present invention. Detailed Embodiments

[0048] To make the purpose, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described here are only the best embodiments of the present invention, only used to explain the present invention, and do not limit the protection scope of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0049] Embodiment 1:

[0050] This embodiment proposes a sludge reflux control optimization method, referring to Figure 1 , and mainly includes the following steps.

[0051] Step S1, obtain the external reflux volume and generate a calculation result according to the external reflux ratio and the influent flow rate of the biological tank; more specifically, in this step, first, the external reflux ratio R is mainly calculated according to the sludge concentration MLSS in the aerobic section and the reflux sludge concentration RSS, and the calculation formula is:

[0052]

[0053] Among them, Q R is the external reflux flow rate, and Q is the influent flow rate of the biological pool. Therefore, the external reflux flow rate is:

[0054]

[0055] The initial control value is calculated from the above formula, and then corrected according to other influencing factors.

[0056] Step S2: Correct the calculation result according to the influencing factors of pH and hydraulic retention time to generate a correction result, and adjust the sludge retention time; specifically, it mainly includes the following sub-steps.

[0057] Step S21: Perform a weighted calculation on the calculation result, pH, and hydraulic retention time, and generate a correction result according to each correction weight; in this embodiment, the weight factors of the calculation result, pH, and hydraulic retention time are 0.5, 0.3, and 0.2 respectively. For details, please refer to Figure 1 and then a correction result is generated.

[0058] S22: Adjust the sludge retention time in a conditional trigger form. If the sludge retention time is within the normal range, no adjustment is made; if the sludge retention time is not within the normal range, the correction result is adjusted; in this implementation, if the sludge retention time is within the normal range, and this normal range is a pre-set threshold range, it does not participate in the entire control process. If it is detected that the sludge retention time is too long, the correction result is increased by 2%-5% in a timely manner. If it is detected that the sludge retention time is too short, the correction result is decreased by 2%-5%.

[0059] Step S3: Make a judgment based on the predicted result of the influent volume trend; compare the correction result with the current external reflux flow rate, determine whether the comparison result conforms to the water volume trend, and adjust the reflux pump; more specifically, determining whether the comparison result conforms to the water volume trend and adjusting the reflux pump specifically includes the following steps:

[0060] If the comparison result conforms to the water volume trend, output the result and use the PID algorithm to adjust the operating frequency of the reflux pump;

[0061] If the comparison result does not conform to the water volume trend, generate an alarm message, and it is determined manually whether to adjust the external reflux flow rate.

[0062] In this embodiment, the external reflux flow rate is positively correlated with the influent flow rate. When the influent flow rate increases, the external reflux flow rate also increases; conversely, it decreases. If the comparison result conforms to the water volume trend, the operating frequency of the reflux pump is directly adjusted to control the reflux pump; if it does not conform to the water volume trend, it is decided by the operator whether to adjust the correction result. At the same time, an alarm message is generated on the man-machine interface, and relevant data is displayed for reference.

[0063] The prediction result of the influent flow rate trend is predicted through big data analysis or a function of flow rate and time is generated by collecting the influent flow rate, and the first derivative and the second derivative are solved for prediction.

[0064] More specifically, the biochemical reaction stage of sewage treatment takes a long time, generally about 8 hours, and the time occupied by the anaerobic, anoxic, and aerobic sections is approximately 1:1:(3 - 4). Therefore, it takes a long time to see the control effect after adjusting the reflux ratio. The entire system has a large time lag and a poor response ability to sudden changes in flow rate. Therefore, the reflux ratio is controlled in advance by predicting the flow rate trend to improve the adaptability to flow rate changes.

[0065] In this embodiment, for the PLC control system equipped with an edge computing gateway, the influent flow rate can be predicted through big data analysis. For a general PLC control system whose computing power does not support big data, a flow rate-time function is made by collecting the influent flow rate, the first derivative is solved to analyze the change trend, the second derivative is solved to analyze the change rate, and the reflux ratio control strategy is adjusted according to the positive and negative of the derivative. The specific control parameters can be referred to in Table 1:

[0066] Table 1 Specific control parameters for predicting the influent flow rate trend

[0067]

[0068] Step S4: Compare the total nitrogen in the effluent at a specific future time node with the set value to determine whether the external reflux control is up to standard. If it is not up to standard, perform a correction adjustment. Specifically, step S4 includes:

[0069] Collect the total nitrogen in the effluent after n hours and compare it with the set value of the total nitrogen in the effluent. If the error between the total nitrogen in the effluent and the set value of the total nitrogen in the effluent is within 2%, the external reflux control is up to standard. If the error between the total nitrogen in the effluent and the set value of the total nitrogen in the effluent is outside 2%, the external reflux control is not up to standard. Then, step S2 does not need to be executed, and at the same time, traceability is carried out to find the problem to adjust the correction weight, and then step S2 is re-executed according to the adjusted correction weight.

[0070] In this embodiment, the external reflux control effect is reflected by the total nitrogen in the effluent. Therefore, the total nitrogen in the effluent is used as the verification basis. By comparing the total nitrogen in the effluent at a specific future time node with the set value, it is determined whether the control target is achieved. Taking the hydraulic retention time of 8 hours as an example, the total nitrogen in the effluent after 8 hours is collected and compared with the set value of the total nitrogen in the effluent. If the error is less than 2%, it is considered qualified. If not, the CPU module cuts off the correction link in step S2, and the control adjustment is directly performed based on the calculation result obtained by the formula in step S1. At the same time, the corresponding data results are traced back in the background to find problems to adjust the correction weight. After the total nitrogen in the effluent directly controlled by the calculation result obtained in step S1 reaches the standard, the newly calculated weight factor is used to resume the execution of step S2.

[0071] The steps of adjusting the correction weight specifically include:

[0072] Step S41, go back n hours from the moment when the external reflux control is judged to be unqualified, and extract the historical calculated values of the calculation result, pH, and hydraulic retention time with a time span of x minutes; in this embodiment, n is 8 and x is 5, and the historical calculated values of the calculation result, pH, and hydraulic retention time are extracted with a time span of 5 minutes.

[0073] Step S42, compare the calculated value at each time point with the calculated value at the previous time point. If the value increases, it is recorded as "+", and if the value decreases, it is recorded as "-" to obtain the historical increase and decrease trends of the three factors.

[0074] Step S43, judge whether the deviation state of the unqualified total nitrogen in the effluent is larger or smaller than the set value, and record them as "+" and "-" respectively.

[0075] Step S44, count the number of times the three factors have different signs from the deviation state of the total nitrogen in the effluent, and determine the adjusted correction weight according to the number of times.

[0076] In this embodiment, the example of adjusting the correction weight refers to Table 2:

[0077] Table 2 Statistical table of adjusting the correction weight

[0078]

[0079] Among them, HRT is the hydraulic retention time.

[0080] The weight of the factor with the most times of different signs from the deviation state of the total nitrogen in the effluent is reduced by k, the weight of the factor with the least times of different signs from the deviation state of the total nitrogen in the effluent is increased by 0.8k, and the weight of the factor with the second most times of different signs from the deviation state of the total nitrogen in the effluent is increased by 0.2k. The range of k is 0-1.

[0081] In this embodiment, k is 0.1. As can be seen from Table 2, the weight of the calculation result increases by 0.08, the weight of pH correction increases by 0.02, and the weight of HRT correction decreases by 0.1.

[0082] Reference Figure 2 , step S5, adjusting the internal reflux flow rate according to the ORP of the denitrification tank obtained by monitoring; specifically including: calculating the internal reflux flow rate according to the external reflux ratio, influent flow rate, and total nitrogen in the influent, and then adjusting the internal reflux flow rate according to the ORP of the denitrification tank obtained by monitoring. If the monitoring result is higher than the set range, the internal reflux flow rate is reduced according to the proportional coefficient; if the detection result is normal, the reflux pump is directly controlled according to the internal reflux flow rate.

[0083] Specifically, the internal reflux is controlled depending on the denitrification efficiency. The formula for calculating the denitrification efficiency is:

[0084]

[0085]

[0086] where η is the denitrification efficiency, r is the internal reflux ratio, and T N进 、T N出 are the total nitrogen in the influent and effluent. Therefore, the formula for calculating the internal reflux ratio r is:

[0087]

[0088] The internal reflux flow rate Q r is then:

[0089]

[0090] where the set value of the total nitrogen in the effluent is set according to the local wastewater discharge standard.

[0091] In this embodiment, the nitrification liquid reflux will cause the DO in the aerobic zone to flow into the anaerobic zone together. The more DO it carries, the greater the impact on denitrification. Excessive DO will destroy the denitrification environment, making heterotrophic bacteria dominant, and ultimately leading to nitrification collapse. Generally, the ORP of the denitrification tank is controlled at -100 to -150 mv. When it is higher than this range, an alarm message is generated, and the control system reduces the internal reflux flow rate calculated according to the original proportion until the ORP returns to the normal range. The proportional coefficient is set according to the on-site process and is set to 90% in this embodiment.

[0092] Reference Figure 3 , this embodiment also proposes an optimized control system for sludge reflux control, which is applicable to the above-mentioned optimized control method for sludge reflux control, including:

[0093] The acquisition module includes several measuring instruments, and the measuring instruments send the collected data to the CPU module through the AI / DI module or switch;

[0094] The CPU module calculates the external reflux flow rate, predicts the trend of the influent water volume, corrects the reflux flow rate, judges the water volume trend, and performs control compliance verification; at the same time, it calculates the internal reflux flow rate; in this module, the above functions can refer to steps S1 to S5 of the method of this embodiment.

[0095] The control module includes several reflux pumps and corresponding frequency converters, and adjusts the working frequency of the reflux pumps according to the CPU module.

[0096] Among them, the above system mainly includes a collection module, a CPU module, and a control module. The collection module is connected to the CPU module, and the CPU module is connected to the control module. The collection module can collect corresponding data through measuring instruments and send it to the CPU module through a switch or an AI / DI module. The CPU module can process functions such as calculation, correction, and trend judgment, generate a final result instruction, and send the final result instruction to the control module to achieve the control of the reflux pump.

[0097] In this embodiment, taking the most widely used PLC control system as an example, a series of control processes of the present invention are completed.

[0098] In this embodiment, first, the external reflux flow rate is calculated as the calculation result, and then the pH value and the hydraulic retention time are used to correct the calculation result in the form of weights, and the sludge retention time is adjusted in the form of conditional triggering; then, the trend of the influent water volume is predicted to obtain the prediction result of the influent water volume trend. The correction result obtained in step S2 is compared with the current external reflux flow rate. If the comparison result conforms to the water volume trend, the reflux pump is directly adjusted. If it does not conform to the water volume trend, manual judgment is performed; after the reflux pump is adjusted, control compliance verification is carried out. According to the comparison between the total nitrogen in the effluent at a certain future time node and the set value, it is judged whether the external reflux control is up to standard. If it is not up to standard, correction adjustment is carried out, specifically adjusting the correction weight to obtain a more accurate result; finally, the calculated internal flow rate can also be adjusted according to the monitored ORP of the denitrification tank.

[0099] In this embodiment, since the calculation result does not consider the acidity and alkalinity and the retention time of the sewage to be treated in the biological tank, the result is not very accurate. Therefore, pH and hydraulic retention time are introduced in the form of weights, where the hydraulic retention time is the average retention time of the sewage to be treated in the biological tank; in addition, for the sludge retention time, a conditional triggering form is adopted to determine whether to adjust. If the sludge retention time is too long or too short, the correction result is adjusted accordingly. Generally, the adjustment range is 2%-5%.

[0100] The hydraulic retention time, namely HRT, refers to the average retention time of the wastewater to be treated in the biological tank. For biological treatment, the HRT should meet the corresponding process requirements. Otherwise, if the hydraulic retention time is insufficient, the biochemical reaction will be incomplete and the treatment degree will be weak; if the hydraulic retention time is too long, it will lead to sludge aging in the system.

[0101] In this embodiment, after collecting the total nitrogen in the effluent after n hours, the data is compared with the preset set value of the total nitrogen in the effluent. If the error between the two is within 2%, it means that the control effect meets the standard. If it does not meet the standard, the correction link in step S2 above is cancelled and directly controlled by the calculation result in step S1. At the same time, the problem is traced back in the background to adjust the correction weight. After the total nitrogen in the effluent directly controlled by step S1 meets the standard, the correction link in step S2 is restored with the newly calculated weight coefficient, and the normal control process is switched back.

[0102] In this embodiment, the historical calculated values based on three factors are obtained. The calculated value at a certain time point is compared with the calculated value at the previous time point. If the calculated value at a certain time point increases relative to the calculated value at the previous time point, it is recorded as "+", if it decreases, it is recorded as "-", and the historical increase and decrease trends of the three factors based on time are obtained; at the same time, it is determined whether the deviation state of the unqualified total nitrogen in the effluent is larger or smaller than the set value, which is also represented by "+" and "-". Finally, the number of times of different signs between the three factors and the deviation state of the total nitrogen in the effluent is counted, and the correction weight is newly adjusted.

[0103] In this embodiment, first, the internal reflux flow rate is calculated according to the calculation formula, and then the ORP in the denitrification tank is monitored in real time. If the monitoring result is normal, no adjustment is required; if the monitoring result is higher than the set range, the internal reflux flow rate is reduced according to the set proportional system.

[0104] Embodiment 2

[0105] On the basis of Embodiment 1, in the process of external reflux control, in order to ensure the safe and stable operation of the biochemical reaction, some high and low limits are set in the control method. If the calculation result exceeds the highest limit, the highest limit value is directly used for control; if it is lower than the lowest limit, the lowest limit value is directly used for control, and an alarm message is generated at the same time; specifically, reference can be made to Table 3:

[0106] Table 3 High and low limit values in the process of external reflux control

[0107] Limit value External reflux ratio 30％～70％ Change in external reflux ratio Not exceeding 5% Change in external reflux flow rate Not exceeding 10% 。

Claims

1. An optimized control method for sludge return control, characterized in that, Including: S1. Obtain the external return flow rate according to the external reflux ratio and the influent flow rate of the biological pool, and generate a calculation result; S2. Correct the calculation result according to the influencing factors of pH and hydraulic retention time to generate a correction result, and adjust the sludge retention time; including: performing a weighted calculation on the calculation result, pH, and hydraulic retention time, and generating a correction result according to each correction weight; the weight factors of the calculation result, pH, and hydraulic retention time are 0.5, 0.3, and 0.2 respectively; Adjust the sludge retention time in the form of conditional triggering. If the sludge retention time is within the normal range, no adjustment is made; if the sludge retention time is not within the normal range, adjust the correction result; S3. Judge according to the prediction result of the influent flow rate trend; compare the correction result with the current external return flow rate, judge whether the comparison result conforms to the water volume trend, and adjust the reflux pump; S4. Compare the total nitrogen of the effluent at a specific future time node with the set value to judge whether the external reflux control meets the standard. If it does not meet the standard, perform a correction adjustment; including: collecting the total nitrogen of the effluent after n hours, comparing it with the set value of the total nitrogen of the effluent. If the error between the total nitrogen of the effluent and the set value of the total nitrogen of the effluent is within 2%, the external reflux control meets the standard, otherwise the external reflux control does not meet the standard. Then, do not execute S2, and at the same time trace back to find the problem to adjust the correction weight, and then re-execute S2 according to the adjusted correction weight; S5. Adjust the internal return flow rate through the ORP of the denitrification tank obtained by monitoring.

2. The optimized control method for sludge return control according to claim 1, wherein The step of judging whether the comparison result conforms to the water volume trend and adjusting the reflux pump specifically includes the following steps: If the comparison result conforms to the water volume trend, output the result and use the PID algorithm to adjust the operating frequency of the reflux pump; If the comparison result does not conform to the water volume trend, generate an alarm message, and manually determine whether to adjust the external return flow rate.

3. The optimized control method for sludge reflux control according to claim 2, characterized in that, The prediction result of the influent flow rate trend is predicted through big data analysis or generates a function of flow rate and time by collecting the influent flow rate, and solves the first derivative and the second derivative for prediction.

4. The optimized control method for sludge reflux control according to claim 1, wherein, The steps of adjusting the correction weight specifically include: S41. Go back n hours from the moment when it is judged that the external reflux control does not meet the standard, and extract the historical calculated values of the calculation result, pH, and hydraulic retention time with a time span of x minutes; S42. Compare the calculated value at each time point with the calculated value at the previous time point. If the value increases, record it as "+", if the value decreases, record it as "-", and obtain the historical increase and decrease trends of the three factors; S43. Judge whether the deviation state of the non-compliant total nitrogen of the effluent is larger or smaller than the set value, and record them as "+" and "-" respectively; S44. Count the number of times when the three factors have different signs from the deviation state of the total nitrogen of the effluent, and determine the adjusted correction weight according to the number of times.

5. The optimized control method for sludge reflux control according to claim 4, characterized in that, The weight of the factor with the most number of times of different signs from the deviation state of the total nitrogen of the effluent is reduced by k, the weight of the factor with the least number of times of different signs from the deviation state of the total nitrogen of the effluent is increased by 0.8k, and the weight of the factor with the second most number of times of different signs from the deviation state of the total nitrogen of the effluent is increased by 0.2k, and the range of k is 0-1.

6. A method for optimizing the control of sludge reflux according to claim 1 or 3 or 4 or 5, characterized in that, The specific steps of step S5 include: calculating the internal reflux flow rate according to the external reflux ratio, influent flow rate, and total influent nitrogen, and then adjusting the internal reflux flow rate according to the monitored ORP of the denitrification tank. If the monitoring result is higher than the set range, the internal reflux flow rate is reduced according to the proportional coefficient; if the detection result is normal, the reflux pump is directly controlled according to the internal reflux flow rate.

7. The optimized control method for sludge reflux control according to claim 1, characterized in that The calculation formula for the external reflux flow rate in step S1 is: ， where R is the external reflux ratio, Q is the influent flow rate of the biological tank, MLSS is the sludge concentration in the aerobic section, and RSS is the concentration of the returned sludge.

8. A sludge return control optimization control system, applicable to a sludge return control optimization control method according to any one of claims 1-7, characterized in that, including a collection module, including a number of measuring instruments, and the measuring instruments send the collected data to the CPU module through the AI / DI module or switch; a CPU module, which calculates the external reflux flow rate, predicts the trend of the influent flow rate, corrects the reflux flow rate, judges the trend of the water volume, and performs control compliance verification; at the same time, it calculates the internal reflux flow rate; a control module, including a number of reflux pumps and corresponding frequency converters, which adjusts the operating frequency of the reflux pumps according to the CPU module.

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