Method and device for improving concentration of sludge fed into dehydrator

Abstract

The invention discloses a method and a device for improving the concentration of sludge fed into a dehydrator, relates to the field of sewage treatment, utilizes the existing sludge return pipeline as a residual sludge taking point, does not need to add an additional sludge concentration facility, simplifies the process flow, and saves the land occupation and capital construction investment. Meanwhile, the sludge concentration control and the sludge inlet requirement of a dewatering system are unified, the sludge return ratio is accurately regulated and controlled, the return sludge concentration is stabilized in a proper range required by efficient operation of the dewatering machine, the sludge inlet concentration is improved and stabilized, the dewatering performance of the sludge is improved, and a dual regulation strategy of coarse regulation of the number of machines and fine regulation of the frequency is adopted; the large-amplitude change can be quickly responded, fluctuation can be reduced, fine adjustment can be carried out in a steady state, frequent starting and stopping of the pump and severe fluctuation of reflux quantity are avoided, and impact on equipment is small.

Description

A method and apparatus for increasing the sludge concentration at the feed of a dewatering machine Technical Field

[0001] This invention relates to the field of wastewater treatment, and in particular to a method and apparatus for increasing the sludge concentration at the feed of a dewatering machine. Background Technology

[0002] The activated sludge process is a widely used wastewater treatment method. During the wastewater treatment process, it is necessary to maintain the sludge concentration in the biological treatment tank within a certain range. Therefore, a certain amount of activated sludge needs to be discharged from the biological treatment system every day to maintain the sludge balance of the biological treatment system. This discharged activated sludge is called excess sludge. The moisture content of excess sludge is generally above 99%, and it needs to be concentrated and dewatered to reduce the moisture content to below 80% before disposal.

[0003] Normally, the excess sludge is discharged from the secondary sedimentation tank. First, it needs to pass through a sludge thickening device to reduce the moisture content of the excess sludge from 99% to 95%–97%, and increase the concentration of the excess sludge to a certain value before it can enter the dewatering machine for dewatering, reducing the moisture content of the excess sludge to below 80%, and finally undergoing harmless, volume-reducing and resource-based treatment.

[0004] Therefore, increasing the concentration of residual sludge before it enters the dewatering machine is the key to the efficient operation of the dewatering machine. The commonly used sludge thickening methods are gravity thickening and mechanical thickening. Both of these require the construction of dedicated sludge thickening facilities, and have high construction and operating costs, as well as being relatively complicated to manage.

[0005] Therefore, we propose a method and device to increase the sludge concentration at the feed of a dewatering machine in order to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a method and apparatus for increasing the sludge concentration at the feed of a dewatering machine, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for increasing the sludge concentration entering a dewatering machine, comprising the following steps: S1: setting a target return sludge concentration in the biological treatment tank; S2: real-time monitoring of the sludge concentration in the biological treatment tank, the return sludge flow rate, and the total influent flow rate of the system; S3: calculating the current sludge return ratio based on the sludge concentration, the return sludge flow rate, and the total influent flow rate; S4: calculating the target sludge return ratio based on the set target return sludge concentration and the sludge concentration in the biological treatment tank; S5: comparing the current sludge return ratio with the target sludge return ratio to obtain the difference, and comparing the difference with a preset threshold; S6: adjusting the operating frequency or number of return sludge pumps according to the comparison result to change the sludge return flow rate, adjusting the sludge return ratio to approach the target sludge return ratio.

[0008] Preferably, based on steps S2 and S3, all monitored data are uploaded to the central processor to calculate the current sludge return ratio and the target sludge return ratio, compare the difference between the two, and upload the comparison data to the central controller.

[0009] Preferably, based on step S5, when performing difference comparison, it is determined whether the difference exceeds the set difference threshold. If it exceeds the set threshold, there are two cases: if the current sludge return ratio is less than the calculated target sludge return ratio, the amount of returned sludge needs to be increased, the instruction is output, and the corresponding operation is executed; if the current sludge return ratio is greater than the calculated target sludge return ratio, the amount of returned sludge needs to be decreased, the instruction is output, and the corresponding operation is executed; if it does not exceed the set threshold, the current state remains unchanged, the instruction is output, and the corresponding operation is executed.

[0010] Preferably, step S6 specifically includes: when the deviation value is greater than a preset threshold and the current sludge return ratio is less than the target sludge return ratio, increasing the number of operating sludge return pumps or increasing their operating frequency to increase the sludge return flow rate; when the deviation value is greater than a preset threshold and the current sludge return ratio is greater than the target sludge return ratio, decreasing the number of operating sludge return pumps or decreasing their operating frequency to reduce the sludge return flow rate; when the deviation value is less than or equal to a preset threshold, maintaining the current state.

[0011] Preferably, when the deviation value is greater than a preset threshold, the adjustment selected by the instruction control includes: comparing the difference between the calculated current sludge return ratio and the calculated target sludge return ratio; when the deviation is not within the normal range, a large adjustment is adopted, which is a coarse adjustment by increasing or stopping the number of running return sludge pumps to make the current sludge return ratio quickly approach the target sludge return ratio; after the deviation value returns to the normal range, a fine adjustment is made by adjusting the operating frequency of the return sludge pumps; when the deviation is within the normal range, a variable frequency fine adjustment is adopted, which is a fine adjustment by adjusting the operating frequency of the return sludge pumps to make the current sludge return ratio smoothly approach the target sludge return ratio.

[0012] A device for increasing the sludge concentration at the inlet of a dewatering machine includes: a biological treatment tank, which has an anaerobic zone, an anoxic zone, and an aerobic zone arranged sequentially inside; a secondary sedimentation tank connected to the outlet of the biological treatment tank; a sludge return pipe connecting the sludge zone of the secondary sedimentation tank and the anaerobic zone of the biological treatment tank; at least two sludge return pumps installed on the sludge return pipe for transporting the sludge return from the secondary sedimentation tank to the biological treatment tank; a residual sludge discharge pipe with its inlet end connected to the sludge return pipe; and a dewatering machine that receives residual sludge through the residual sludge discharge pipe for dewatering.

[0013] Preferably, the reflux sludge pump is electrically connected to a reflux pump frequency converter.

[0014] Preferably, the return sludge pipe is equipped with a sludge flow meter and a sludge control valve, which are used to monitor the amount of return sludge and the amount of dewatered sludge, respectively.

[0015] Preferably, the residual sludge discharge pipe is sequentially equipped with a residual sludge pump, a sludge homogenization tank, a sludge screw pump, and a dewatering machine connected to the outlet of the sludge screw pump.

[0016] Preferably, it also includes a PAM dosing device and a vortex sludge mixer, wherein the outlet of the PAM dosing device is connected to the waste sludge discharge pipe, and the vortex sludge mixer is located on the waste sludge discharge pipe downstream of the dosing point of the PAM dosing device.

[0017] The technical effects and advantages of this invention are as follows:

[0018] By precisely controlling the sludge return ratio, the concentration of returned sludge is stabilized within the appropriate range required for the efficient operation of the dewatering machine. The increase and stabilization of the sludge inlet concentration improves the sludge dewatering performance.

[0019] The dual adjustment strategy of coarse adjustment of the number of pumps and fine adjustment of frequency can quickly respond to large changes and reduce fluctuations, while also making fine adjustments in steady state to avoid frequent pump start-stop and drastic fluctuations in return flow, thus minimizing the impact on the equipment.

[0020] Based on closed-loop control using real-time monitoring data and target values, reliance on human experience is reduced, and automated control of sludge return concentration and dewatering machine feed concentration is achieved.

[0021] By using the existing sludge return pipeline as the sludge collection point, there is no need to add additional sludge thickening facilities, which simplifies the process, saves land and infrastructure investment, and unifies sludge concentration control with the sludge inlet requirements of the dewatering system. Attached Figure Description

[0022] Figure 1 is an overall flowchart of the present invention;

[0023] Figure 2 is a flowchart of the monitoring process of the present invention;

[0024] Figure 3 is a flowchart of the calculation and decision-making process of the present invention;

[0025] Figure 4 is a flowchart of the execution process of the present invention;

[0026] Figure 5 is a flowchart of the cyclic monitoring process of the present invention;

[0027] Figure 6 is a schematic diagram of the overall structure of the device of the present invention.

[0028] In the diagram: 1. Biological treatment tank; 2. Secondary sedimentation tank; 3. Return sludge pump station; 4. Return sludge pump; 5. Return pump frequency converter; 6. Sludge flow meter; 7. Return sludge pipe; 8. Sludge control valve; 9. Waste sludge pump station; 10. Waste sludge pump; 11. Dewatering machine; 12. Waste sludge pipe; 13. Sludge screw pump; 14. Sludge homogenizing tank; 15. PAM dosing device; 16. Swirl sludge mixer; 17. Agitator. Detailed Implementation

[0029] 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, and 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.

[0030] This invention provides a method and apparatus for increasing the sludge concentration at the inlet of a dewatering machine, as shown in Figures 1-6, comprising the following steps: S1: setting a target return sludge concentration in the biological treatment tank; S2: real-time monitoring of the sludge concentration in the biological treatment tank, the return sludge flow rate, and the total influent flow rate of the system; S3: calculating the current sludge return ratio based on the sludge concentration, the return sludge flow rate, and the total influent flow rate; S4: calculating the target sludge return ratio based on the set target return sludge concentration and the sludge concentration in the biological treatment tank; S5: comparing the current sludge return ratio with the target sludge return ratio to obtain the difference, and comparing the difference with a preset threshold; S6: adjusting the operating frequency or number of return sludge pumps 4 according to the comparison result to change the sludge return flow rate, adjusting the sludge return ratio to approach the target sludge return ratio.

[0031] Based on steps S2 and S3, all monitored data are uploaded to the central processor to calculate the current sludge return ratio and the target sludge return ratio, compare the difference between the two, and upload the comparison data to the central controller.

[0032] Based on step S5, when performing difference comparison, it is determined whether the difference exceeds the set difference threshold. If it exceeds the set threshold, there are two cases: if the current sludge return ratio is less than the calculated target sludge return ratio, the amount of returned sludge needs to be increased, the instruction is output, and the corresponding operation is executed; if the current sludge return ratio is greater than the calculated target sludge return ratio, the amount of returned sludge needs to be decreased, the instruction is output, and the corresponding operation is executed; if it does not exceed the set threshold, the current state remains unchanged, the instruction is output, and the corresponding operation is executed.

[0033] Step S6 specifically includes: when the deviation value is greater than the preset threshold and the current sludge return ratio is less than the target sludge return ratio, the sludge return flow rate is increased by increasing the number of operating sludge return pumps 4 or increasing their operating frequency; when the deviation value is greater than the preset threshold and the current sludge return ratio is greater than the target sludge return ratio, the sludge return flow rate is reduced by decreasing the number of operating sludge return pumps 4 or decreasing their operating frequency; when the deviation value is less than or equal to the preset threshold, the current state is maintained.

[0034] A device for increasing the sludge concentration at the inlet of a dewatering machine includes a biological treatment tank 1, a secondary sedimentation tank 2, a return sludge pipe 7, at least two return sludge pumps 4, a residual sludge discharge pipe 12, and a dewatering machine 11. The secondary sedimentation tank 2 is connected to the outlet of the biological treatment tank 1. The return sludge pipe 7 connects the sludge zone of the secondary sedimentation tank 2 with the anaerobic zone of the biological treatment tank 1. At least two return sludge pumps 4 are installed on the return sludge pipe 7 for transporting the return sludge from the secondary sedimentation tank 2 to the biological treatment tank 1. The residual sludge discharge pipe 12... The outlet is connected to the return sludge pipe 7; the dewatering machine 11 receives the remaining sludge through the remaining sludge discharge pipe 12 for dewatering; the activated sludge after biochemical reaction in the biological treatment tank 1 enters the secondary sedimentation tank 2, where sedimentation achieves sludge-water separation, and the settled activated sludge flows by static pressure to the return sludge pump station 3, where the sludge return pump 4 returns the activated sludge to the anaerobic zone in the biological treatment tank 1. The return sludge pump 4 is frequency-controlled, and the sludge return flow rate can be changed by adjusting the frequency.

[0035] The biological treatment tank 1 is divided into an anaerobic zone, an anoxic zone, and an aerobic zone in sequence. The activated sludge undergoes biochemical reactions in the anaerobic zone, anoxic zone, and aerobic zone.

[0036] The waste sludge discharge pipe 12 is sequentially equipped with a waste sludge pump 10, a sludge homogenizing tank 14, a sludge screw pump 13, and a dewatering machine 11 connected to the outlet of the sludge screw pump 13.

[0037] The outlet of the PAM dosing device 15 is connected to the waste sludge discharge pipe 12, and the vortex sludge mixer 16 is located on the waste sludge discharge pipe 12 downstream of the dosing point of the PAM dosing device 15.

[0038] The return sludge pump 4 is electrically connected to a return pump frequency converter 5, which is used to control the number and frequency of the return sludge pump 4. By increasing or decreasing the number of sludge return pumps 4 and adjusting the frequency of the return sludge pump 4, the sludge return flow rate is changed, thereby changing the sludge return ratio.

[0039] The dewatered sludge is taken from the return sludge pipe 7. The return sludge pipe 7 is equipped with an electromagnetic sludge flow meter 6 and a sludge control valve 8, which can monitor the amount of return sludge and dewatered sludge, and can be controlled and adjusted through the sludge control valve 8. The sludge enters the sludge pump room 9 through the return sludge pipe 7. The sludge is pumped to the sludge homogenization tank 14 by the sludge pump 10 in the sludge pump room 9 for stirring and mixing, and is transported to the dewatering machine 11 by the sludge screw pump 13 with cutting function.

[0040] A stirrer 17 is installed in the sludge homogenization tank 14 to stir and mix the remaining sludge in the sludge homogenization tank 14.

[0041] The sludge screw pump 13 and the dewatering machine 11 are connected by the residual sludge pipe 12. Under the action of the sludge screw pump 13, the residual sludge is transported to the dewatering machine 11 through the residual sludge pipe 12.

[0042] A PAM dosing device 15 is connected to the residual sludge pipe 12. The prepared chemical solution from the PAM dosing device 15 is injected into the residual sludge pipe 12. After being mixed and flocculated with the residual sludge by the cyclone sludge mixer 16 connected to the sludge pipe 12, it enters the dewatering machine 11 for dewatering, producing sludge cake with a moisture content of less than 80%.

[0043] Since the residual sludge dewatered by the dewatering machine 11 is taken from the return sludge pipe 7, its sludge concentration is equal to that of the return sludge concentration. The sludge return flow rate can be changed by increasing or decreasing the number of sludge return pumps 4 in operation and adjusting the frequency of the return sludge pumps 4, thereby changing the sludge return ratio.

[0044] The formula for calculating the concentration of sludge returned from the biological treatment tank is as follows:

[0045] in The concentration of sludge returned from the biological treatment tank is mg / L; The concentration of sludge in the biological treatment tank is mg / L; This refers to the sludge return ratio; the formula for calculating the sludge return ratio is: in This refers to the amount of sludge returned; This represents the total influent volume; according to the formula for calculating the concentration of returned sludge in the biological treatment tank, the concentration of sludge in the biological treatment tank can be adjusted... Sludge return ratio Can change the concentration of return sludge .

[0046] The system employs a combination of variable frequency return pumps and adjustments based on the number of pumps, enabling continuous adjustment of the sludge return ratio. This allows for precise control of the concentration of returned sludge and the concentration of residual sludge after dewatering, creating favorable conditions for efficient dewatering of the sludge dewatering machine 11 and significantly improving the efficiency of sludge dewatering.

[0047] For specific adjustments, please refer to the following examples: When the sludge concentration in the biological treatment tank is... =4000mg / L, in order to meet the sludge concentration requirement at the inlet of dewatering machine 11 To meet the requirement of 12000 mg / L, the sludge return ratio can be adjusted by changing the frequency or the number of operating return sludge pumps. =0.5, which can be calculated using the formula for the concentration of sludge returned from the biological treatment tank: It can be seen that in order to obtain the required sludge concentration for the dewatering machine 11, it can be easily obtained by changing the sludge return ratio or controlling the sludge concentration in the biological treatment tank. Furthermore, the return sludge concentration and the residual sludge concentration can be continuously and accurately adjusted by frequency conversion adjustment of the return sludge pump 4 or by increasing or decreasing the number of operating pumps, so as to meet the sludge concentration required by the dewatering machine 11, improve the dewatering efficiency of the dewatering machine 11, save operating costs, and simplify the process.

[0048] The specific control method is as follows: When sewage treatment needs to be started, the operator first sets the concentration of the returned sludge in the biological treatment tank 1, and at the same time monitors the sludge concentration in the biological treatment tank 1 in real time through the online sludge flow meter 6, monitors the amount of returned sludge through the sludge control valve 8, and monitors the total influent flow through the influent flow meter; all the monitored data are uploaded to the central processor, the current sludge return ratio is calculated and compared with the calculated target sludge return ratio, the difference between the two is compared, and the comparison data is uploaded to the central controller.

[0049] When performing difference comparison, it is determined whether the difference exceeds the set difference threshold, which can be manually set according to actual production needs. When the set threshold is exceeded, there are two situations: if the current sludge return ratio is less than the calculated target sludge return ratio, the amount of returned sludge needs to be increased, the command is output, and the corresponding operation is executed; if the current sludge return ratio is greater than the calculated target sludge return ratio, the amount of returned sludge needs to be decreased, the command is output, and the corresponding operation is executed; if the set threshold is not exceeded, the current state remains unchanged, the command is output, and the corresponding operation is executed.

[0050] When the output command is to increase the amount of returned sludge, control selection is performed. The difference between the calculated current sludge return ratio and the calculated target sludge return ratio is compared and judged. The comparison data is uploaded to the central controller for evaluation. When the deviation is within the normal range, variable frequency fine adjustment is used to minimize impact. This increases the amount of returned sludge by increasing the operating frequency of the return pump. When the amount of returned sludge increases, the current returned sludge flow rate changes. When the deviation value exceeds a preset threshold, the control selection adjustment includes: comparing the current sludge return ratio with the calculated target... The difference in sludge return ratio is compared and judged: when the deviation is not within the normal range, the deviation is large, and a large adjustment is adopted. This is done by increasing or stopping the number of running return sludge pumps 4 to make the current sludge return ratio quickly approach the target sludge return ratio. After the deviation value returns to the normal range, fine adjustment is performed by adjusting the operating frequency of return sludge pumps 4. When the deviation is within the normal range, variable frequency fine adjustment is adopted. This is done by adjusting the operating frequency of return sludge pumps 4 to make the current sludge return ratio steadily approach the target sludge return ratio.

[0051] Specifically: when the deviation is outside the normal range, indicating a large deviation, a significant increase in adjustment is used for rapid correction. This is achieved by coarse adjustment through increasing the number of return pumps, which increases the amount of returned sludge by adding one more pump. As the amount of returned sludge increases, the current return sludge flow rate changes. After coarse adjustment, it is necessary to determine whether the deviation has returned to the normal range. Once it has returned to the normal range, frequency conversion fine adjustment is used to achieve dual adjustment: rapid adjustment of the return sludge flow rate, and protection of the device through fine adjustment when fluctuations are small.

[0052] When the output command is to reduce the amount of returned sludge, the control selection is performed. The difference between the calculated current sludge return ratio and the calculated target sludge return ratio is compared and judged. When the deviation is within the normal range, frequency conversion fine adjustment is adopted to achieve the effect of minimizing impact. This is achieved by reducing the operating frequency of the return pump to reduce the amount of returned sludge. When the amount of returned sludge decreases, the current return sludge flow rate changes.

[0053] When the deviation is outside the normal range, the deviation is large. A significant reduction in adjustment is adopted to quickly correct it. Coarse adjustment is made by stopping the number of return pumps. The amount of return sludge is reduced by stopping one return pump. When the amount of return sludge is reduced, the current return sludge flow rate changes.

[0054] After coarse adjustment, it is necessary to determine whether the deviation has returned to the normal range. When it has returned to the normal range, frequency conversion fine adjustment is then used to achieve dual adjustment, namely, rapid adjustment of the return sludge flow rate, and fine adjustment to protect the device when the fluctuation is small.

[0055] When the output command is to maintain the current state, the number of pumps in operation and the frequency remain unchanged, and the amount of sludge returned is stable.

[0056] When executing the output command, the current amount of returned sludge changes. The difference between the calculated current sludge return ratio and the calculated target sludge return ratio is compared to determine whether the return ratio is close to the target value. If it is close to the target value, the state is maintained, and the return sludge flow rate, total influent flow rate, and biological sludge concentration are monitored in real time. The current sludge return ratio and the template sludge return ratio are calculated periodically, the difference is compared, and the command is re-output.

[0057] If the reflux ratio does not approach the target value, continue to output the same command;

[0058] If the current instruction is to increase the return flow rate, the output quality will increase the return flow rate, and the control selection will be re-selected. By comparing the difference between the calculated current sludge return ratio and the calculated target sludge return ratio, the corresponding fine adjustment control and large increase control will be selected, and the corresponding operation will be executed. That is, the corresponding operation of increasing the operating frequency of the return pump or adding another return pump will be executed to increase the amount of returned sludge and change the current return sludge flow rate. The difference between the calculated current sludge return ratio and the calculated target sludge return ratio will be compared again to determine whether the return ratio is close to the target value. This cycle will be repeated until it is close to the target value and then maintained.

[0059] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for increasing the sludge concentration at the feed of a dewatering machine, characterized in that, Includes the following steps: S1: Set the target concentration of returned sludge in the biological treatment tank; S2: Real-time monitoring of sludge concentration, return sludge flow rate, and total system influent flow rate in the biological treatment tank; S3: Calculate the current sludge return ratio based on sludge concentration, return sludge flow rate, and total influent flow rate; S4: Calculate the target sludge return ratio based on the set target return sludge concentration and the sludge concentration in the biological treatment tank; S5: Compare the current sludge return ratio with the target sludge return ratio to obtain the difference, and compare the difference with the preset threshold. S6: Based on the comparison results, adjust the operating frequency or number of operating return sludge pumps (4) to change the sludge return flow rate and adjust the sludge return ratio to be close to the target sludge return ratio.

2. The method for increasing the sludge concentration at the feed of a dewatering machine according to claim 1, characterized in that, Based on steps S2 and S3, all monitored data are uploaded to the central processor to calculate the current sludge return ratio and the target sludge return ratio, compare the difference between the two, and upload the comparison data to the central controller.

3. The method for increasing the sludge concentration at the feed of a dewatering machine according to claim 1, characterized in that, Based on step S5, when performing difference comparison, it is determined whether the difference exceeds the set difference threshold. When the set threshold is exceeded, there are two situations: if the current sludge return ratio is less than the calculated target sludge return ratio, the amount of sludge to be returned needs to be increased, the instruction is output, and the corresponding operation is executed. The current sludge return ratio is greater than the calculated target sludge return ratio. At this time, it is necessary to reduce the amount of sludge returned. Output this instruction and execute the corresponding operation. If the threshold is not exceeded, the current state remains unchanged, the instruction is output, and the corresponding operation is executed.

4. The method for increasing the sludge concentration at the feed of a dewatering machine according to claim 1, characterized in that, Step S6 specifically includes: when the deviation value is greater than the preset threshold and the current sludge return ratio is less than the target sludge return ratio, the sludge return flow is increased by increasing the number of running sludge return pumps (4) or increasing their operating frequency; when the deviation value is greater than the preset threshold and the current sludge return ratio is greater than the target sludge return ratio, the sludge return flow is reduced by decreasing the number of running sludge return pumps (4) or decreasing their operating frequency; when the deviation value is less than or equal to the preset threshold, the current state is maintained.

5. The method for increasing the sludge concentration at the feed of a dewatering machine according to claim 4, characterized in that, When the deviation value is greater than the preset threshold, the adjustment selected by the instruction control includes: comparing the difference between the current sludge return ratio and the calculated target sludge return ratio; when the deviation is not within the normal range, the deviation is large, and large adjustment is adopted. The coarse adjustment is carried out by increasing or stopping the number of running return sludge pumps (4) so ​​that the current sludge return ratio quickly approaches the target sludge return ratio. After the deviation value returns to the normal range, fine adjustment is carried out by adjusting the operating frequency of the return sludge pumps (4); when the deviation is within the normal range, frequency conversion fine adjustment is adopted. Fine adjustment is carried out by adjusting the operating frequency of the return sludge pumps (4) so ​​that the current sludge return ratio smoothly approaches the target sludge return ratio.

6. A device for increasing the sludge concentration at the inlet of a dewatering machine, based on a method for increasing the sludge concentration at the inlet of a dewatering machine according to any one of claims 1-5, characterized in that, include: The biological treatment tank (1) is divided into an anaerobic zone, an anoxic zone and an aerobic zone in sequence. Secondary sedimentation tank (2) is connected to the outlet of the biological treatment tank (1); return sludge pipe (7) connects the sludge zone of the secondary sedimentation tank (2) with the anaerobic zone of the biological treatment tank (1); at least two return sludge pumps (4) are installed on the return sludge pipe (7) to transport the return sludge from the secondary sedimentation tank (2) to the biological treatment tank (1); The inlet end of the residual sludge discharge pipe (12) is connected to the return sludge pipe (7); the dewatering machine (11) receives the residual sludge through the residual sludge discharge pipe (12) for dewatering.

7. The device for increasing the sludge concentration at the feed of a dewatering machine according to claim 6, characterized in that, The reflux sludge pump (4) is electrically connected to a reflux pump frequency converter (5).

8. The device for increasing the sludge concentration at the feed of a dewatering machine according to claim 6, characterized in that, The return sludge pipe (7) is equipped with a sludge flow meter (6) and a sludge control valve (8), which are used to monitor the amount of return sludge and the amount of dewatered sludge, respectively.

9. The device for increasing the sludge concentration at the feed of a dewatering machine according to claim 6, characterized in that, The residual sludge discharge pipe (12) is sequentially equipped with a residual sludge pump (10), a sludge homogenizing tank (14), a sludge screw pump (13), and a dewatering machine (11) connected to the outlet of the sludge screw pump (13).

10. The device for increasing the sludge concentration at the feed of a dewatering machine according to claim 6, characterized in that, It also includes a PAM dosing device (15) and a vortex sludge mixer (16), the outlet of which is connected to the residual sludge discharge pipe (12), and the vortex sludge mixer (16) is located on the residual sludge discharge pipe (12) downstream of the dosing point of the PAM dosing device (15).

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