Sludge treatment control system and sludge treatment control method

Abstract

To realize a sludge treatment control system that can easily stabilize a liquid level in a mixed sludge storage tank.SOLUTION: A sludge treatment control system includes: a calculation unit (52) for calculating an estimated liquid level based on a current liquid level of a mixed sludge storage tank (28), a planned input amounts of primary settling sludge and excess sludge, and a planned transfer amount of mixed sludge; and a correction unit (53) that corrects the estimated liquid level by increasing the planned transfer amount when the estimated liquid level exceeds an allowable upper limit value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a sludge treatment control system and a sludge treatment control method. [Background technology]

[0002] Sewage treatment is broadly divided into water treatment and sludge treatment. In water treatment, wastewater introduced into a sewage treatment facility is separated into water and sludge. Specifically, primary sludge is separated by settling in a primary settling tank, and excess sludge (excess activated sludge) is separated by settling in a final settling tank. In sludge treatment, the water content of the sludge (primary sludge and excess sludge) separated by water treatment is reduced to reduce the volume of sludge. Patent Documents 1 and 2 disclose inventions related to such sludge quantity control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6621659 [Patent Document 2] Japanese Patent Application Publication No. 61-242700 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the inventions disclosed in the cited documents 1 and 2 do not take into consideration unexpected fluctuations in the amount of sludge input from the water treatment facility. Therefore, such fluctuations in the amount of sludge input cause fluctuations in the liquid level in the mixed sludge storage tank, which stores the primary sludge and excess sludge. This makes it necessary to stop the input of sludge from the water treatment facility or change the set value of the sludge input amount. This requires a lot of maintenance work.

[0005] One aspect of the present invention has been made in consideration of the above-mentioned problems, and its purpose is to realize a sludge treatment control system that can easily stabilize the liquid level in a mixed sludge storage tank. [Means for solving the problem]

[0006] In order to solve the above problems, the sludge treatment control system of aspect 1 of the present invention comprises a calculation unit that calculates an estimated liquid level in the mixed sludge storage tank after a predetermined time based on the current liquid level in the mixed sludge storage tank, the planned amount of primary settling sludge and excess sludge to be charged into the mixed sludge storage tank from upstream, and the planned amount of mixed sludge to be transferred downstream from the mixed sludge storage tank, and a correction unit that makes a correction to increase the planned transfer amount if the estimated liquid level exceeds the allowable upper limit value of the liquid level of the mixed sludge storage tank.

[0007] In the sludge treatment control system according to a second aspect of the present invention, in the first aspect, the correction unit may correct the planned transfer amount so that the estimated liquid level falls below the allowable upper limit value.

[0008] In the sludge treatment control system according to aspect 3 of the present invention, in aspect 1 or 2 above, the correction unit may increase the planned transfer amount by increasing the amount of mixed sludge transferred downstream from the mixed sludge storage tank per transfer.

[0009] In order to solve the above problems, the sludge treatment control method of aspect 4 of the present invention includes a calculation step of calculating an estimated liquid level in the mixed sludge storage tank after a predetermined time based on the current liquid level in the mixed sludge storage tank, the planned amount of primary settling sludge and excess sludge to be charged into the mixed sludge storage tank from upstream, and the planned amount of mixed sludge to be transferred downstream from the mixed sludge storage tank, and a correction step of making a correction to increase the planned transfer amount if the estimated liquid level exceeds the allowable upper limit value of the liquid level of the mixed sludge storage tank. [Effects of the Invention]

[0010] According to one aspect of the present invention, the liquid level in the mixed sludge storage tank can be easily stabilized. [Brief explanation of the drawings]

[0011] [Figure 1]1 is a schematic diagram showing a general configuration of a sewage treatment system according to a reference embodiment. [Figure 2] 10 is a graph showing an example of the transition of the liquid level in a mixed sludge storage tank according to a reference embodiment. [Figure 3] 10 is a graph showing another example of the transition of the liquid level in the mixed sludge storage tank according to the reference embodiment. [Figure 4] 1 is a schematic diagram showing a schematic configuration of a sewage treatment system according to a first embodiment. [Figure 5] 4 is a graph showing a change in the liquid level in the mixed sludge storage tank accompanying correction of the planned transfer amount by the sludge treatment control system according to the first embodiment. [Figure 6] 4 is a graph showing an example of the transition of the liquid level in the mixed sludge storage tank according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Reference form] Prior to describing the sewage treatment system 100A of the first embodiment, a sewage treatment system 100 as a reference embodiment will be described. For ease of explanation, components having the same functions as those described in the reference embodiment will be denoted by the same reference numerals in the following embodiments, and their descriptions will not be repeated. Also, for the sake of brevity, descriptions of matters similar to those in the publicly known art will be omitted as appropriate.

[0013] <Configuration example of sewage treatment system 100> Fig. 1 is a schematic diagram showing the general configuration of a sewage treatment system 100 according to a reference embodiment. As shown in Fig. 1, the sewage treatment system 100 includes a water treatment facility 10 and a sludge treatment facility 20. The water treatment facility 10 separates wastewater introduced into the sewage treatment facility into water and sludge. The sludge treatment facility 20 reduces the volume of the sludge separated in the water treatment facility 10.

[0014] The water treatment facility 10 includes a primary sedimentation tank 11, a primary sludge extraction pump 12, a primary sludge extraction amount sensor 13, a final sedimentation tank 14, an excess sludge extraction pump 15, and an excess sludge extraction amount sensor 16.

[0015] The primary sedimentation tank 11 receives wastewater introduced into the sewage treatment facility and separates primary sludge from the wastewater by settling. The primary sludge extraction pump 12 extracts the primary sludge produced in the primary sedimentation tank 11 and sends it to the gravity thickening tank 21 of the sludge treatment facility 20. The primary sludge extraction amount sensor 13 detects the amount of primary sludge extracted by the primary sludge extraction pump 12.

[0016] The final settling tank 14 receives the wastewater sent from the primary settling tank 11 and subjected to microbial decomposition treatment in a reaction tank (not shown), and settles and separates excess sludge from the wastewater. An excess sludge extraction pump 15 extracts the excess sludge produced in the final settling tank 14 and sends it to an excess sludge storage tank 24 in the sludge treatment facility 20. An excess sludge extraction amount sensor 16 detects the amount of excess sludge extracted by the excess sludge extraction pump 15.

[0017] The sludge treatment facility 20 includes a gravity thickening tank 21, a first-settled sludge injection pump 22, a first-settled sludge injection amount sensor 23, an excess sludge storage tank 24, an excess sludge injection pump 25, an excess sludge injection amount sensor 26, a mechanical thickener 27, a mixed sludge storage tank 28, and a liquid level sensor 29.

[0018] The gravity thickening tank 21 stores and thickens the primary sludge sent from the primary sedimentation tank 11. The volume of the gravity thickening tank 21 is, for example, 268.8 m 3 The primary sludge input pump 22 sends the primary sludge that has been gravity thickened in the gravity thickening tank 21 to the mixed sludge storage tank 28. The primary sludge input amount sensor 23 detects the amount of primary sludge input into the mixed sludge storage tank 28.

[0019] The excess sludge storage tank 24 stores the excess sludge sent from the final settling tank 14. The volume of the excess sludge storage tank 24 is, for example, 44 m 3The excess sludge input pump 25 sends the excess sludge stored in the excess sludge storage tank 24 to the mixed sludge storage tank 28 via the mechanical thickener 27. The excess sludge input amount sensor 26 detects the amount of excess sludge input into the mixed sludge storage tank 28 via the mechanical thickener 27. The mechanical thickener 27 reduces the moisture content of the excess sludge by flotation thickening. As a result, the volume of the excess sludge is reduced by the thickening rate due to flotation thickening. The thickening rate due to flotation thickening is, for example, approximately 14%. In other words, the amount actually input into the mixed sludge storage tank 28 is the volume of excess sludge detected by the excess sludge input amount sensor 26 multiplied by the thickening rate due to flotation thickening (approximately 14%).

[0020] The mixed sludge storage tank 28 mixes the primary sludge sent from the gravity thickener 21 (upstream) with the excess sludge sent from the mechanical thickener 27 (upstream) to produce mixed sludge. The mixed sludge storage tank 28 stores the mixed sludge. The volume of the mixed sludge storage tank 28 is, for example, 15 m 3 The liquid level sensor 29 detects the liquid level of the mixed sludge stored in the mixed sludge storage tank 28.

[0021] The sludge treatment facility 20 further includes a mixed sludge transfer amount sensor 31, a mixed sludge transfer pump 32, a digestion tank 33 (downstream), a digested sludge pump 34, a digested sludge storage tank 35, and a dehydrator 36.

[0022] The mixed sludge transfer pump 32 extracts the mixed sludge stored in the mixed sludge storage tank 28 and sends it to the digestion tank 33. The mixed sludge transfer amount sensor 31 detects the amount of mixed sludge transferred from the mixed sludge storage tank 28 to the digestion tank 33 by the mixed sludge transfer pump 32.

[0023] The digestion tank 33 reduces the moisture content of the mixed sludge by decomposing the organic matter in the mixed sludge, thereby producing digested sludge (i.e., reducing the volume of sludge). For example, in the digestion tank 33, in order to decompose the organic matter in the mixed sludge, the mixed sludge is retained at a temperature of about 35°C in a heated mesophilic digestion zone for a sludge retention period of about 20 to 30 days. To ensure the sludge retention period, the amount of mixed sludge transferred to the digestion tank 33 per day is limited so as not to exceed a predetermined limit value. The total volume of the digestion tank 33 is, for example, 2206 m 3 That's about it.

[0024] The digested sludge pump 34 sends the digested sludge produced in the digestion tank 33 to the dehydrator 36 via the digested sludge storage tank 35. The dehydrator 36 further dehydrates the digested sludge to produce dehydrated cake. The dehydrated cake is transported to a biogas power plant. The amount of dehydrated cake transported is limited so as not to exceed a predetermined limit value (planned transport value).

[0025] <Pump management device 40> The sewage treatment system 100 further includes pump management devices 40a to 40e that manage the operation of the primary sludge extraction pump 12, excess sludge extraction pump 15, primary sludge injection pump 22, mixed sludge transfer pump 32, and digested sludge pump 34, respectively. The pump management devices 40a to 40e have the same configuration. For convenience, only the detailed configuration of pump management device 40d is shown in FIG. 1. Hereinafter, when there is no need to particularly distinguish between the pump management devices 40a to 40e, they will be simply referred to as pump management device 40.

[0026] The pump management device 40 includes a setting unit 41, an operation command unit 42, and a stop command unit 43. The pump management device 40 switches the pump on and off using an ATS (automatic time schedule) and a PC (preset counter).

[0027] The setting unit 41 sets a start time setting value for starting pump operation and a transfer amount setting value for the amount of water transferred by the pump for each operation. The setting unit 41 sets the start time setting value and the transfer amount setting value based on an input signal input to the pump management device 40 by, for example, a user. The setting unit 41 outputs the start time setting value to the operation command unit 42 and outputs the transfer amount setting value to the stop command unit 43.

[0028] The operation command unit 42 starts the pump at a predetermined time in accordance with the start time setting value. The stop command unit 43 stops the pump when the pump has transferred sludge by the transfer amount setting value since starting operation. Specifically, the stop command unit 43 obtains the pump transfer amount per unit time from a sensor that detects the pump transfer amount. The stop command unit 43 accumulates the pump transfer amount per unit time, and when the accumulated value of the transfer amount from the predetermined time reaches the transfer amount setting value obtained from the setting unit 41, the stop command unit 43 stops the pump operation.

[0029] Each pump is operated according to a preset time schedule under the control of pump management devices 40a to 40e. The excess sludge injection pump 25 is not controlled by the pump management device 40 because it operates constantly.

[0030] <Changes in liquid level in mixed sludge storage tank 28> Fig. 2 is a graph showing an example of the transition of the liquid level in the mixed sludge storage tank 28. In the example shown in Fig. 2, the introduction of primary sludge into the mixed sludge storage tank 28 is carried out by the ATS at a predetermined cycle every hour. The amount of primary sludge introduced per hour is 0.9 to 1.1 m 3 In addition, excess sludge is constantly being added to the mixed sludge storage tank 28. The amount of excess sludge added per hour is approximately 1.1 m 3 The mixed sludge is transferred from the mixed sludge storage tank 28 by the ATS, with two hours of operation and one hour of rest being repeated. The amount of mixed sludge transferred per hour during transfer is 3.1 to 3.3 m 3 is.

[0031] At this time, the amount of primary sludge input per day was approximately 23.9 m 3 The amount of excess sludge input per day is approximately 26.7 m 3 The amount of mixed sludge transported per day is approximately 50.1 m 3 2, the input amount and the transfer amount in one day are balanced, and therefore the liquid level in the mixed sludge storage tank 28 does not fluctuate throughout the day.

[0032] Figure 3 is a graph showing another example of the transition of the liquid level in the mixed sludge storage tank 28. In the example shown in Figure 3, the amount of primary sludge input into the mixed sludge storage tank 28 has increased compared to the example shown in Figure 2 due to an unexpected fluctuation. In the example shown in Figure 3, the amount of primary sludge input per hour is about 1.1 m 3 The amount of excess sludge input per hour is the same as the example shown in Figure 2, at approximately 1.1 m 3 The amount of mixed sludge transferred per hour during transfer is approximately 3.1 m 3 is.

[0033] At this time, the amount of primary sludge input per day is approximately 26.4 m 3 The amount of excess sludge input per day is approximately 26.7 m 3 The amount of mixed sludge transported per day is approximately 49.6 m 3 3, the amount of sludge input and the amount of sludge transferred in one day are not balanced, and therefore the liquid level in the mixed sludge storage tank 28 gradually rises.

[0034] Unexpected fluctuations in the amount of sludge input, as shown in Figure 3, occur when the concentration of the sludge extracted from the water treatment facility 10 fluctuates, affecting the concentration rate in the thickening equipment (gravity thickener 21, mechanical thickener 27, etc.). Factors that cause fluctuations in sludge concentration include an increase in the amount of sewage inflow due to rain, etc., in a combined sewer system, or increased microbial activity due to rising temperatures, resulting in an increase in excess sludge.

[0035] When the liquid level in the mixed sludge storage tank 28 exceeds the allowable upper limit, the excess sludge is returned to the water treatment facility 10, which may adversely affect the water treatment in the water treatment facility 10. Therefore, when an unexpected change occurs in the amount of sludge input, some measure must be taken to prevent the liquid level in the mixed sludge storage tank 28 from exceeding the allowable upper limit.

[0036] In the reference embodiment, to deal with such unexpected fluctuations in the amount of sludge input, the amount of initial sludge input by the initial sludge input pump 22 and / or the amount of excess sludge input by the excess sludge input pump 25 are reduced. Such a reduction in the amount of sludge input is performed by the user changing the time schedule or the setting value of the preset counter set in the pump management device 40. Alternatively, the reduction is performed by the user stopping the operation of the pump to stop the input of sludge.

[0037] However, it would require a great deal of effort for the user to take the above measures every time an unexpected fluctuation in the amount of sludge input occurs. Therefore, the present inventors have discovered that the configuration of the sewage treatment system 100A shown in the following embodiment 1 makes it possible to easily stabilize the liquid level in the mixed sludge storage tank 28.

[0038] [Embodiment 1] Fig. 4 is a schematic diagram showing the overall configuration of a sewage treatment system 100A according to Embodiment 1. As shown in Fig. 4, the sewage treatment system 100A differs from the sewage treatment system 100 according to Reference Embodiment 1 in that it includes a sludge treatment control system 50 in addition to a water treatment facility 10, a sludge treatment facility 20, and a pump management device 40. The configuration of the sludge treatment control system 50 for stabilizing the liquid level in the mixed sludge storage tank 28 will be described below with reference to Fig. 4. For convenience, the water treatment facility 10 is not shown in Fig. 4.

[0039] <Sludge treatment control system 50> The sludge treatment control system 50 includes an acquisition unit 51, a calculation unit 52, a correction unit 53, and an output unit 54. The sludge treatment control system 50 corrects the mixed sludge transfer amount setting value set in the setting unit 41 of the pump management device 40d in response to unexpected fluctuations in the amount of sludge input.

[0040] The acquisition unit 51 acquires information from the sludge treatment facility 20 and the pump management device 40 for determining whether or not the set value for the amount of mixed sludge to be transferred needs to be corrected. Specifically, the acquisition unit 51 acquires the liquid level (current liquid level) of the mixed sludge stored in the mixed sludge storage tank 28 at the current time t0 from the liquid level sensor 29. The acquisition unit 51 also acquires the set value for the amount of initial settling sludge to be transferred from the setting unit 41 of the pump management device 40c. The acquisition unit 51 also acquires the amount of excess sludge input per hour from the excess sludge input amount sensor 26. The acquisition unit 51 also acquires the set value for the amount of mixed sludge to be transferred from the setting unit 41 of the pump management device 40d. The acquisition unit 51 may acquire the above-mentioned information at a predetermined time in a day, for example, or may acquire the above-mentioned information using an input signal input by the user as a trigger.

[0041] Based on the information acquired by the acquisition unit 51, the calculation unit 52 calculates the liquid level (estimated liquid level) of the mixed sludge storage tank 28 at a target time t1, which is a predetermined time after the current time t0. The target time t1 is, for example, the end of a one-day cycle. Specifically, first, the calculation unit 52 calculates the input amount (planned input amount) of initial settling sludge that is scheduled to be input by the target time t1 from the set value of the transfer amount of initial settling sludge. The calculation unit 52 also calculates the input amount (planned input amount) of excess sludge that is scheduled to be input by the target time t1 from the input amount of excess sludge per hour. The calculation unit 52 also calculates the transfer amount (planned transfer amount) of mixed sludge that is scheduled to be transferred by the target time t1 from the set value of the transfer amount of mixed sludge. Next, the calculation unit 52 calculates the estimated liquid level of the mixed sludge storage tank 28 based on the planned input amounts of initial settling sludge and excess sludge and the planned transfer amount of mixed sludge. The method of calculating the estimated liquid level by the calculation unit 52 will be described in detail below with reference to FIG.

[0042] The correction unit 53 makes a correction to increase the planned transfer amount of mixed sludge when the estimated liquid level in the mixed sludge storage tank 28 exceeds the allowable upper limit value of the liquid level in the mixed sludge storage tank 28. The correction unit 53 corrects the planned transfer amount of mixed sludge so that the estimated liquid level in the mixed sludge storage tank 28 falls below the allowable upper limit value.

[0043] In detail, the correction unit 53 increases the planned transfer amount by increasing the transfer amount of mixed sludge transferred per time from the mixed sludge storage tank 28 to the digestion tank 33 (i.e., the transfer amount set value of the mixed sludge transfer pump 32). In other words, the correction unit 53 corrects the transfer amount set value of the mixed sludge transfer pump 32 to a value (corrected transfer amount set value) that causes the estimated liquid level of the mixed sludge storage tank 28 to fall below the allowable upper limit value.

[0044] The output unit 54 outputs the corrected transfer rate setting value calculated by the correction unit 53 to the setting unit 41 of the pump management device 40d. As a result, the transfer rate setting value of the mixed sludge transfer pump 32 is updated to the corrected transfer rate setting value.

[0045] <Adjustment of planned transfer volume> 5 is a graph showing the change in the liquid level in the mixed sludge storage tank 28 accompanying the correction of the planned transfer amount by the sludge treatment control system 50. A sludge treatment control method by the sludge treatment control system 50 will now be described with reference to FIG.

[0046] First, the acquisition unit 51 acquires the current liquid level of the mixed sludge storage tank 28 at the current time t0 (see point A1 in FIG. 5).

[0047] Next, the calculation unit 52 calculates the liquid level (liquid level after addition) at target time t1, which reflects only the rise in liquid level due to the addition of initial sludge and excess sludge from the current time t0 to the target time t1 (see point A2 in Figure 5). Here, (liquid level after addition) = (current liquid level) + (planned amount of initial sludge and excess sludge to be added) ÷ (bottom area of ​​mixed sludge storage tank 28). Note that (planned amount of initial sludge to be added) = (set value of transfer amount of initial sludge) × (number of times planned to add initial sludge from the current time t0 to the target time t1), and (planned amount of excess sludge to be added) = (amount of excess sludge to be added per hour) × (predetermined time t1 - t0).

[0048] Next, the calculation unit 52 calculates the liquid level (post-transfer liquid level) at the target time t1 that reflects only the decrease in the liquid level due to the transfer of mixed sludge from the current time t0 to the target time t1 (see point A3 in Figure 5). Here, (post-transfer liquid level) = (current liquid level) - (planned amount of mixed sludge to be transferred) ÷ (bottom area of ​​mixed sludge storage tank 28). Also, (planned amount of mixed sludge to be transferred) = (set value of mixed sludge transfer amount) × (number of mixed sludge transfers planned from the current time t0 to the target time t1).

[0049] Next, the calculation unit 52 calculates the estimated liquid level (see point A4 in Figure 5) (calculation step), where (estimated liquid level) = (current liquid level) + (rise in liquid level due to the addition of initial settling sludge and excess sludge) - (decrease in liquid level due to the transfer of mixed sludge).

[0050] Next, the correction unit 53 determines whether the liquid level in the mixed sludge storage tank 28 will exceed the allowable upper limit between the current time t0 and the target time t1. In the example shown in Figure 5, on the line connecting point A1 indicating the current liquid level and point A4 indicating the estimated liquid level, the liquid level in the mixed sludge storage tank 28 exceeds the allowable upper limit at point A5. In other words, it is predicted that the liquid level in the mixed sludge storage tank 28 will exceed the allowable upper limit after time t2, which corresponds to point A5.

[0051] Next, when it is predicted that the liquid level in the mixed sludge storage tank 28 will exceed the allowable upper limit, the correction unit 53 makes a correction to increase the planned transfer amount of mixed sludge (correction step). In detail, the correction unit 53 calculates an increase in the planned transfer amount of mixed sludge so that the estimated liquid level in the mixed sludge storage tank 28 becomes a value (corrected liquid level) smaller than the allowable upper limit. Here, (increase in planned transfer amount of mixed sludge) = ((estimated liquid level) - (corrected liquid level)) × (bottom area of ​​mixed sludge storage tank 28). Then, the correction unit 53 calculates an increase in the transfer amount set value of mixed sludge from the increase in the planned transfer amount of mixed sludge, and calculates the corrected transfer amount set value. Here, (increase in the set value of the transfer amount of mixed sludge) = (increase in the planned transfer amount of mixed sludge) ÷ (number of mixed sludge transfers planned from the current time t0 to the target time t1), and (corrected transfer amount set value) = (set value of the transfer amount of mixed sludge) + (increase in the set value of the transfer amount of mixed sludge).

[0052] 5, the correction unit 53 makes a correction to increase the planned transfer amount of mixed sludge, and as a result, point A4 indicating the estimated liquid level changes to point A6, which is below the allowable upper limit. In other words, the liquid level in the mixed sludge storage tank 28 falls within the allowable range.

[0053] <Changes in liquid level in mixed sludge storage tank 28> Fig. 6 is a graph showing an example of the transition of the liquid level in the mixed sludge storage tank 28 according to the first embodiment. In the example shown in Fig. 6, similar to the example shown in Fig. 3, the amount of initial sludge introduced into the mixed sludge storage tank 28 is higher than usual due to an unexpected fluctuation. As a result, the liquid level in the mixed sludge storage tank 28 is gradually rising and may exceed the allowable upper limit. Therefore, at a predetermined time (2:00 PM), the sludge treatment control system 50 sets midnight as the target time t1 and makes a correction to increase the planned amount of mixed sludge to be transferred as described above.

[0054] In the example shown in Figure 6, in order to stabilize the liquid level in the mixed sludge storage tank 28, the sludge treatment control system 50 lowers the estimated liquid level by 75 cm. That is, the bottom area of ​​the mixed sludge storage tank 28 (approximately 4.52 m) 2 ), the sludge treatment control system 50 calculates the planned amount of mixed sludge to be transported as 3.4 m3 Since the number of times that mixed sludge is to be transferred between the current time t0 and the target time t1 is seven, the sludge treatment control system 50 increases the set value of the amount of mixed sludge to be transferred by 3.4÷7 to 0.49 m. 3 As a result, the liquid level in the mixed sludge storage tank 28 stops rising after 2:00 PM.

[0055] The increase in the planned amount of mixed sludge to be transported (3.4 m in the example shown in Figure 6) 3 ) is the volume of the digestion tank 33 (e.g., 2206 m 3 ), which is sufficiently small. Therefore, the amount of change in the amount of sludge in the digestion tank 33 due to an increase in the planned amount of mixed sludge to be transferred is a fully tolerable amount.

[0056] 6, the set value for the amount of mixed sludge to be transferred may be corrected so that the liquid level in the mixed sludge storage tank 28 at the end of the daily cycle is approximately equal to the liquid level in the mixed sludge storage tank 28 at the start of the daily cycle. This makes it possible to balance the amount of sludge input and the amount of transfer in a day even if there is an unexpected fluctuation in the amount of sludge input from the water treatment facility.

[0057] <Action and effect> With the above configuration, the liquid level in the mixed sludge storage tank 28 can be automatically kept within an allowable range in response to unexpected fluctuations in the amount of sludge input from the water treatment facility. Therefore, the user does not need to change the pump transfer rate setting, and the liquid level in the mixed sludge storage tank 28 can be easily stabilized. Furthermore, sludge in excess of the allowable upper limit of the mixed sludge storage tank 28 is not returned to the water treatment facility 10, so there is no adverse effect on water treatment in the water treatment facility 10.

[0058] Furthermore, there is no need to reduce or stop the amount of sludge being fed from the gravity thickening tank 21 and the mechanical thickener 27 to the mixed sludge storage tank 28. This allows sludge to be fed into the mixed sludge storage tank 28 in a planned manner, enabling stable operation of the facilities related to the sewage treatment system 100A.

[0059] Furthermore, the increase in the planned amount of mixed sludge to be transferred is sufficiently small compared to the capacity of the digesting tank 33. Therefore, the digesting tank 33 functions as a buffer against unexpected fluctuations in the amount of sludge input, making it possible to appropriately respond to unexpected fluctuations in the amount of sludge input.

[0060] Furthermore, in this embodiment, the planned transfer amount is increased by increasing the transfer amount setting value of the mixed sludge transfer pump 32. This does not change the number of times the mixed sludge transfer pump 32 is switched on and off, thereby reducing deterioration of the mixed sludge transfer pump 32 due to repeated on / off switching.

[0061] [Modification] The correction unit 53 may increase the planned transfer amount by increasing the number of times that mixed sludge is transferred from the mixed sludge storage tank 28 to the digestion tank 33 by the target time t1. That is, the correction unit 53 may increase the planned transfer amount by changing the start time setting value of the mixed sludge transfer pump 32 so as to increase the number of transfers. This eliminates the need to change the transfer amount setting value of the mixed sludge transfer pump 32.

[0062] Furthermore, when the target time t1 is the end of a one-day cycle, the correction unit 53 may correct the planned transfer amount of mixed sludge so that the estimated liquid level becomes the normal liquid level. Here, the normal liquid level is the liquid level in the mixed sludge storage tank 28 at the start of the one-day cycle. This makes it possible to balance the input amount and transfer amount in one day.

[0063] Furthermore, the acquisition unit 51 may acquire an integrated value of the amount of mixed sludge transferred in a one-day cycle from the mixed sludge transfer amount sensor 31. Then, the output unit 54 may stop the extraction of mixed sludge by the mixed sludge transfer pump 32 when the integrated value exceeds a specified transfer amount value. This makes it possible to ensure a sufficient number of sludge retention days for the mixed sludge in the digestion tank 33. Furthermore, the operation of the dehydrator 36 can be planned so that the amount of dehydrated cake discharged from the dehydrator 36 does not exceed a predetermined limit value.

[0064] [Software implementation example] The functions of the sludge treatment control system 50 (hereinafter referred to as the "device") can be realized by a program that causes a computer to function as the device, and a program that causes a computer to function as each control block of the device (particularly the calculation unit 52 and the correction unit 53).

[0065] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The control device and storage device execute the program, thereby realizing the functions described in each of the above embodiments.

[0066] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0067] Furthermore, some or all of the functions of the control blocks can be realized by logic circuits. For example, integrated circuits in which logic circuits functioning as the control blocks are formed are also included in the scope of the present invention. In addition, the functions of the control blocks can also be realized by, for example, a quantum computer.

[0068] Furthermore, each process described in each of the above embodiments may be executed by AI (Artificial Intelligence). In this case, the AI ​​may run on the control device or on another device (for example, an edge computer or a cloud server).

[0069] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0070] 21 Gravity concentration tank (upstream) 27 Mechanical concentrator (upstream) 28 Mixed sludge storage tank 33 Digestion tank (downstream) 50 Sludge treatment control system 52 Calculation section 53 Correction section

Claims

1. a calculation unit that calculates an estimated liquid level of the mixed sludge storage tank after a predetermined time based on the current liquid level of the mixed sludge storage tank, the planned amount of primary settling sludge and excess sludge to be charged into the mixed sludge storage tank from upstream, and the planned amount of mixed sludge to be transferred downstream from the mixed sludge storage tank; a correction unit that performs a correction to increase the planned transfer amount when the estimated liquid level exceeds the allowable upper limit of the liquid level of the mixed sludge storage tank.

2. The sludge treatment control system according to claim 1 , wherein the correction unit corrects the planned transfer amount so that the estimated liquid level falls below the allowable upper limit value.

3. The sludge treatment control system according to claim 1 , wherein the correction unit increases the planned transfer amount by increasing the amount of the mixed sludge transferred downstream from the mixed sludge storage tank per transfer.

4. a calculation step of calculating an estimated liquid level of the mixed sludge storage tank after a predetermined time based on the current liquid level of the mixed sludge storage tank, the planned amount of primary settling sludge and excess sludge to be charged into the mixed sludge storage tank from upstream, and the planned amount of mixed sludge to be transferred downstream from the mixed sludge storage tank; a correction step of increasing the planned transfer amount when the estimated liquid level exceeds an allowable upper limit of the liquid level in the mixed sludge storage tank.

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