Water treatment system, control device, and water treatment method

Abstract

To provide a water treatment system, a control device, and a water treatment method capable of suppressing nitrification of nitrogen components in liquid while removing organic matter contained in the liquid.SOLUTION: A water treatment system comprises a tank for treating liquid, a supply device for supplying oxygen into the tank through a plurality of diffusion parts located in the lower part of the tank, a control device for controlling the supply of oxygen from each of the plurality of diffusion parts, a measurement device for measuring water quality of the liquid, and a measurement device for measuring the nitrification state of nitrogen contained in the liquid. The control device controls the supply of oxygen from each of the plurality of air diffusion parts so that the water quality measured by the measurement device satisfies the first condition and the nitrification state measured by the measurement device satisfies the second condition.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a water treatment system, a control device, and a water treatment method.

Background Art

[0002] In a treatment system (hereinafter also referred to as a water treatment system) for treating a liquid such as sewage (hereinafter simply referred to as a liquid), as a method for removing organic substances contained in the liquid, for example, an activated sludge method in which organic substances are decomposed by microorganisms (hereinafter also referred to as activated sludge) propagated in a reaction tank is used (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the water treatment system as described above, a method that enables suppression of nitrification of nitrogen components contained in the liquid while removing organic substances contained in the liquid is desired.

Means for Solving the Problems

[0005] The water treatment system in the present disclosure includes a tank for treating a liquid, a supply device for supplying oxygen into the tank via a plurality of air diffusing parts arranged at a lower part of the tank, a control device for controlling the supply of the oxygen from the plurality of air diffusing parts, a measuring device for measuring the water quality of the liquid, and a measuring device for measuring the nitrification state of nitrogen contained in the liquid. The control device controls the supply of the oxygen from the plurality of air diffusing parts so that the water quality measured by the measuring device satisfies a first condition and the nitrification state measured by the measuring device satisfies a second condition.

Effects of the Invention

[0006] The water treatment system described herein makes it possible to remove organic matter contained in the liquid while suppressing the nitrification of nitrogen components contained in the liquid. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a diagram illustrating the configuration of the water treatment system 1000 in the first embodiment. [Figure 2] Figure 2 is a diagram illustrating the configuration of the water treatment system 1000 in the first embodiment. [Figure 3] Figure 3 is a diagram illustrating the configuration of the water treatment system 1000 in the first embodiment. [Figure 4] Figure 4 is a diagram illustrating the functions of the control device 100. [Figure 5] Figure 5 is a diagram illustrating the hardware configuration of the control device 100. [Figure 6] Figure 6 is a flowchart illustrating the aeration control process in the first embodiment. [Figure 7] Figure 7 is a flowchart illustrating the aeration control process in the first modified example. [Figure 8] Figure 8 is a flowchart illustrating the aeration control process in the second modified example. [Modes for carrying out the invention]

[0008] Embodiments of this disclosure will be described below with reference to the drawings. However, this description should not be interpreted as limiting, and will not limit the subject matter described in the claims. Furthermore, various changes, substitutions, and modifications can be made without departing from the spirit and scope of this disclosure. Different embodiments can also be combined as appropriate.

[0009] [Water treatment system 1000 in the first embodiment] First, the configuration of the water treatment system 1000 in the first embodiment will be described. Figures 1 to 3 are diagrams illustrating the configuration of the water treatment system 1000 in the first embodiment.

[0010] The water treatment system 1000 is, for example, a sludge treatment system using the activated sludge method. Specifically, as shown in Figure 1, the water treatment system 1000 includes, for example, a primary sedimentation tank 10, a reaction tank 20 (hereinafter also simply referred to as tank 20), a final sedimentation tank 30, and a supply device 40.

[0011] The primary sedimentation tank 10 separates pollutants such as organic matter (for example, solid organic matter) contained in the liquid (hereinafter also referred to as the water to be treated) by sedimentation. The primary sedimentation tank 10 then discharges the separated pollutants as primary sedimentation sludge to a concentrator (not shown) and discharges the water to be treated after the separation of pollutants to the reaction tank 20.

[0012] The reaction tank 20 has, for example, a tank body 21 from which the water to be treated is discharged from the primary sedimentation tank 10. The reaction tank 20 also has, for example, one or more aeration units 22 and one or more aeration units 23 that supply a gas containing at least oxygen A (hereinafter also simply referred to as oxygen A) from the lower part (bottom) of the tank body 21 to the activated sludge (aerobic microorganisms) present in the tank body 21. The water to be treated in the reaction tank 20 is then treated, for example, by biological treatment.

[0013] Specifically, in the reaction tank 20, for example, aeration treatment is performed to supply oxygen A to the activated sludge present in the tank body 21. Then, in the reaction tank 20, for example, as the water to be treated flows (moves) through the reaction tank 20 from the primary sedimentation tank 10 to the final sedimentation tank 30, the activated sludge decomposes (consumes) organic matter (for example, soluble organic matter) contained in the water to be treated. Hereinafter, the direction in which the water to be treated flows through the reaction tank 20 (the direction from the primary sedimentation tank 10 to the final sedimentation tank 30) will also be simply referred to as the flow direction. After the organic matter has been decomposed by the activated sludge, the water to be treated is then discharged from the reaction tank 20 to the final sedimentation tank 30.

[0014] Here, in the region within the reaction tank 20, for example, there are included a region 20a under anaerobic conditions where oxygen A is not sufficiently supplied (hereinafter also referred to as the anaerobic region 20a), and a region 20b under aerobic conditions where oxygen A is sufficiently supplied (hereinafter also referred to as the aerobic region 20b).

[0015] Specifically, in the example shown in FIG. 1, in the anaerobic region 20a, for example, a small amount of oxygen A for stirring the activated sludge is supplied from the diffuser 22. Also, in the example shown in FIG. 1, in the aerobic region 20b, for example, oxygen A necessary for activating the activated sludge is supplied from each of a plurality of diffusers 23 (diffuser 23a, diffuser 23b, diffuser 23c, diffuser 23d, diffuser 23e, and diffuser 23f).

[0016] And in the anaerobic region 20a, for example, phosphorus contained in the activated sludge is released into the treated water by anaerobic microorganisms contained in the activated sludge. Thereafter, the phosphorus released into the treated water is taken up by aerobic microorganisms contained in the activated sludge, for example, in the aerobic region 20b.

[0017] Also, in the aerobic region 20b, for example, the organic matter contained in the treated water discharged from the primary sedimentation tank 10 is oxidized and decomposed by BOD (Biochemical Oxygen Demand) oxidizing bacteria, which are aerobic microorganisms contained in the activated sludge. That is, in the aerobic region 20b, for example, the organic matter contained in the treated water discharged from the primary sedimentation tank 10 is removed.

[0018] Furthermore, in the aerobic region 20b, for example, ammonia nitrogen in the treated water is nitrified to nitrite nitrogen by nitrifying bacteria, which are aerobic microorganisms in the activated sludge, and the nitrified nitrite nitrogen is nitrified to nitrate nitrogen.

[0019] The final sedimentation tank 30 separates and discharges the activated sludge contained in the treated water discharged from the reaction tank 20, for example. Then, the final sedimentation tank 30 supplies a part of the activated sludge to a thickener (not shown) as excess sludge, and returns the activated sludge other than the excess sludge to the reaction tank 20 as return sludge. Further, the final sedimentation tank 30 discharges the treated water (supernatant) after separating the activated sludge to a subsequent sterilization treatment device (not shown), for example. Thereafter, the sterilization treatment device sterilizes the treated water discharged from the final sedimentation tank 30, for example, and discharges the sterilized treated water into a river or the like.

[0020] The supply device 40 is, for example, a blower and supplies oxygen A to the reaction tank 20. Specifically, the supply device 40 supplies oxygen A into the reaction tank 20 through a plurality of air diffusing parts 23 provided in the reaction tank 20, for example.

[0021] In the example shown in FIG. 1, six air diffusing parts 23 (air diffusing part 23a, air diffusing part 23b, air diffusing part 23c, air diffusing part 23d, air diffusing part 23e, and air diffusing part 23f) are installed in the reaction tank 20 along the flow direction. And in the example shown in FIG. 1, oxygen A from the supply device 40 is supplied to the air diffusing part 23a through a pipe L (hereinafter also referred to as pipe L1), oxygen A from the supply device 40 is supplied to the air diffusing part 23b through a pipe L (hereinafter also referred to as pipe L2), oxygen A from the supply device 40 is supplied to the air diffusing part 23c through a pipe L (hereinafter also referred to as pipe L3), oxygen A from the supply device 40 is supplied to the air diffusing part 23d through a pipe L (hereinafter also referred to as pipe L4), oxygen A from the supply device 40 is supplied to the air diffusing part 23e through a pipe L (hereinafter also referred to as pipe L5), and oxygen A from the supply device 40 is supplied to the air diffusing part 23f through a pipe L (hereinafter also referred to as pipe L6). Hereinafter, the case where six air diffusing parts 23 are provided in the reaction tank 20 will be described, but the reaction tank 20 may be provided with, for example, a number of air diffusing parts 23 other than six. Further, hereinafter, the case where a plurality of air diffusing parts 23 are arranged in a straight line along the flow direction in the reaction tank 20 will be described, but the reaction tank 20 may be installed so as to spread in a planar shape at the bottom of the reaction tank 20, for example.

[0022] Furthermore, in the example shown in Figure 1, oxygen A from the supply device 40 is supplied to the aeration unit 22, for example, via pipe L (hereinafter also referred to as pipe L7). Pipe L7 may be a pipe with a smaller capacity than each of pipes L1, L2, L3, L4, L5, and L6.

[0023] In the water treatment system 1000, for example, in the reaction tank 20, in addition to operations that remove organic matter contained in the water to be treated and nitrify ammonia nitrogen contained in the water to be treated (hereinafter also referred to as nitrification acceleration operation), operations that remove organic matter contained in the water to be treated while suppressing the nitrification of ammonia nitrogen contained in the water to be treated (hereinafter also referred to as nitrification suppression operation) may be performed. Specifically, in the water treatment system 1000, for example, during periods when the need to remove ammonia nitrogen contained in the water to be treated is low (for example, in winter when microbial activity decreases), nitrification suppression operation is performed instead of nitrification acceleration operation.

[0024] As a result, the water treatment system 1000 can reduce the amount of oxygen A that needs to be supplied from the supply device 40 to the reaction tank 20, for example, compared to when nitrification acceleration operation is performed. In addition, the water treatment system 1000 can shorten the ASRT (Aerobic Solids Retention Time) in the reaction tank 20 because, for example, it is no longer necessary to cultivate nitrifying bacteria in the reaction tank 20. Therefore, the water treatment system 1000 can reduce the energy required for supplying oxygen A to the reaction tank 20 and the energy required for transporting the returned sludge, for example.

[0025] However, if nitrification of ammonia nitrogen proceeds only partially during nitrification-suppressed operation, nitrogen generated from the reduction of nitrates, for example, may hinder the settling of activated sludge in the final sedimentation tank 30. In addition, nitrifying bacteria that proliferate in the reaction tank 20 may contribute to increasing the BOD concentration of the treated water.

[0026] Therefore, in the water treatment system 1000, when performing nitrification suppression operation, it is necessary to adjust the amount of oxygen A supplied to the reaction tank 20 to an amount that is necessary for BOD oxidizing bacteria to remove organic matter, and that can suppress the growth of nitrifying bacteria. In other words, in the water treatment system 1000, in this case, it is necessary to simultaneously control BOD oxidizing bacteria, which are preferable with a large amount of oxygen A, and nitrifying bacteria, which are preferable with a small amount of oxygen A. Consequently, if the control of nitrification suppression operation is performed manually by the operator, the workload of the operator will increase compared to when the control of nitrification acceleration operation is performed.

[0027] Therefore, in this embodiment, the water treatment system 1000 is provided with, for example, a plurality of valves V for adjusting the amount of oxygen A supplied to each of the plurality of pipes L that supply oxygen A to the reaction tank 20, as shown in Figure 1, etc. Furthermore, the water treatment system 1000 is provided with, for example, a measuring device 24 (hereinafter also referred to as the first measuring device 24) for measuring the water quality of the water to be treated and a measuring device 25 (hereinafter also referred to as the second measuring device 25) for measuring the nitrification state of nitrogen contained in the water to be treated.

[0028] Furthermore, the water treatment system 1000 in this embodiment performs a process (hereinafter also called aeration control process) that controls the region in which oxygen A is supplied (hereinafter also called the aeration region) and the region in which oxygen A is not supplied (hereinafter also called the aeration restriction region) by, for example, controlling the opening and closing of each of the multiple valves V based on the measurement results from the first measuring device 24 and the second measuring device 25 (hereinafter collectively referred to as opening and closing control). Open control is, for example, a control that opens the valve V to allow oxygen A to be supplied to the aeration unit 23 (i.e., a control that sets the opening degree of valve V to a state that is not 0). Close control is, for example, a control that closes the valve V to prevent the supply of oxygen A to the aeration unit 23 (i.e., a control that sets the opening degree of valve V to 0), or a control that supplies a small amount of oxygen A to the aeration unit 23 so that the activated sludge in the reaction tank 20 does not settle (i.e., a control that sets the opening degree of valve V to a state that is close to 0).

[0029] Specifically, in the example shown in Figures 1 to 3, the water treatment system 1000 is provided with, for example, valves V (hereinafter also called valve V1) for adjusting the amount of oxygen A supplied from the aeration unit 23b to the reaction tank 20, valve V (hereinafter also called valve V2) for adjusting the amount of oxygen A supplied from the aeration unit 23c to the reaction tank 20, valve V (hereinafter also called valve V3) for adjusting the amount of oxygen A supplied from the aeration unit 23d to the reaction tank 20, and valve V (hereinafter also called valve V4) for adjusting the amount of oxygen A supplied from the aeration unit 23e to the reaction tank 20, in each of the pipes L2, L3, L4, and L5 that supply oxygen A to the reaction tank 20. The water treatment system 1000 controls the supply of oxygen A from the aeration units 23b, 23c, 23d, and 23e by controlling the opening and closing of valves V1, V2, V3, and V4, respectively, so that the water quality measured by the first measuring device 24 satisfies the conditions (hereinafter also referred to as the first condition) and the nitrogen nitrification state measured by the second measuring device 25 satisfies the conditions (hereinafter also referred to as the second condition), thereby dividing the aerobic region 20b into an aeration region and an aeration-restricted region. More specifically, as shown in Figure 3, the water treatment system 1000 controls the water so that regions 20b1 and 20b3 become aeration regions and region 20b2 becomes an aeration-restricted region, for example, by controlling the opening of valves V1 and V4 and the closing of valves V2 and V3.

[0030] In other words, in this embodiment, the water treatment system 1000 determines, for example, that if the water quality measured by the first measuring device 24 satisfies the first condition and that sufficient removal of organic matter has been performed from the water quality measured by the first measuring device 24, it is highly likely that the removal of organic matter will continue even if the amount of oxygen A supplied to the reaction tank 20 is reduced. Therefore, in this case, the water treatment system 1000, for example, reduces the amount of oxygen A supplied to the reaction tank 20 to expand the aeration restriction area and starts control to suppress the growth of nitrifying bacteria while continuing sufficient removal of organic matter. Specifically, the water treatment system 1000, for example, by referring to the water quality measured by the first measuring device 24 and the nitrification state measured by the second measuring device 25, expands the aeration restriction area by controlling the closing of valve V, thereby achieving both sufficient removal of organic matter and suppression of the growth of nitrifying bacteria.

[0031] On the other hand, in this embodiment, if the water treatment system 1000 determines, for example, that the water quality measured by the first measuring device 24 does not meet the first condition and that sufficient removal of organic matter has not been performed from the water quality measured by the first measuring device 24, it determines that it is necessary to prioritize securing the amount of organic matter removed over suppressing the growth of nitrifying bacteria. Therefore, in this case, the water treatment system 1000 controls the system to reduce the aeration restriction area by increasing the amount of oxygen A supplied to the reaction tank 20, for example, so that sufficient removal of organic matter is performed. Specifically, the water treatment system 1000 controls the system to reduce the aeration restriction area by controlling the opening of valve V while referring to the water quality measured by the first measuring device 24, for example, so that sufficient removal of organic matter is performed.

[0032] As a result, in the water treatment system 1000 of this embodiment, for example, nitrification suppression operation in the reaction tank 20 can be performed automatically. Therefore, in the water treatment system 1000, for example, the burden on the operator associated with nitrification suppression operation can be reduced.

[0033] As shown in Figure 1, for example, a valve V (hereinafter also called valve V5) may be provided in a pipe L (hereinafter also called pipe L8) that connects pipes L1, L2, L3, L4, L5, L6, and L7 (hereinafter also simply called pipe L1, etc.) to the supply device 40, to adjust the amount (total amount) of oxygen A supplied from the supply device 40 to pipes L1, etc.

[0034] Furthermore, in the water treatment system 1000, for example, as a preliminary process to the aeration control process, the amount of oxygen A supplied from the supply device 40 and the opening and closing of the valve V5 are controlled to control the amount of oxygen A supplied to each aeration unit 23 (the total amount of oxygen A supplied).

[0035] Specifically, in the water treatment system 1000, for example, the amount of oxygen A supplied from the supply device 40 and the opening and closing of the valve V5 may be controlled so that the water quality measured by the first measuring device 24 satisfies the first condition, and the nitrogen nitrification state measured by the second measuring device 25 satisfies the second condition.

[0036] As a result, if, for example, adjusting the amount of oxygen A supplied from the supply device 40 and controlling the opening and closing of valve V5 does not result in the water quality measured by the first measuring device 24 satisfying the first condition and the nitrogen nitrification state measured by the second measuring device 25 satisfying the second condition (i.e., it is not possible to achieve both sufficient removal of organic matter in the reaction tank 20 and suppression of the growth of nitrifying bacteria), the water treatment system 1000 may start aeration control treatment. Specifically, the water treatment system 1000 may, for example, start aeration control treatment when the amount of oxygen A supplied from the supply device 40 reaches a predetermined upper limit.

[0037] In other words, adjusting the amount of oxygen A supplied from the supply device 40 and controlling the opening and closing of valve V5 may be less burdensome for the operator than, for example, control by aeration control. Therefore, the water treatment system 1000 may attempt to achieve both sufficient removal of organic matter in the reaction tank 20 and suppression of nitrifying bacteria growth by adjusting the amount of oxygen A supplied from the supply device 40 and controlling the opening and closing of valve V5 before performing aeration control. This makes it possible to further reduce the burden on the operator in the water treatment system 1000.

[0038] Furthermore, the following description will focus on the case where the first measuring device 24 and the second measuring device 25 are each installed on the final sedimentation tank 30 side within the reaction vessel 20. However, the first measuring device 24 and the second measuring device 25 may, for example, be installed in the piping connecting the reaction vessel 20 and the final sedimentation tank 30, or in the final sedimentation tank 30 itself. Furthermore, the following description will focus on the case where five valves V (valves V1, V2, V3, V4, and V5) are installed in each of the multiple pipes L. However, in the reaction vessel 20, for example, a number of valves V other than five may be installed in each of the multiple pipes L.

[0039] Furthermore, the water treatment system 1000 may also be provided with a valve (not shown) in the piping L7 that supplies oxygen A to the reaction tank 20, for example, to adjust the amount of oxygen A supplied from the aeration unit 22 to the reaction tank 20.

[0040] [Control device 100 in the first embodiment] Next, the configuration of the control device 100 in the first embodiment will be described. Figure 4 is a diagram illustrating the hardware configuration of the control device 100. Figure 5 is a diagram illustrating the functions of the control device 100.

[0041] As shown in Figures 4 and 5, the water treatment system 1000 has a control device 100 that performs aeration control processing.

[0042] As shown in Figure 4, the control device 100 is a computer device having, for example, a CPU 101 which is a processor, memory 102, a communication device 103, and a storage medium 104. Each part is connected to the others, for example, via a bus 105.

[0043] The storage medium 104 has, for example, a program storage area (not shown) for storing a program (not shown) for performing aeration control processing. The storage medium 104 also has, for example, a storage unit 130 (hereinafter also referred to as the information storage area 130) for storing information used when performing aeration control processing. The storage medium 104 may be, for example, an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0044] The CPU 101 performs aeration control processing, for example, by executing a program loaded from the storage medium 104 into the memory 102.

[0045] The communication device 103 accesses, for example, an operating terminal (not shown) where an operator inputs necessary information via a network (not shown), such as the Internet.

[0046] Then, as shown in Figure 5, the control device 100 controls the opening and closing of each of the multiple valves V in the aeration control process. The control device 100 may also, for example, adjust the amount of oxygen A supplied from the supply device 40 and control the opening and closing of valves V5 before the aeration control process. A specific example of the aeration control process will be described below.

[0047] [Aeration control process in the first embodiment] Next, the aeration control process in the first embodiment will be described. Figure 6 is a flowchart illustrating the aeration control process in the first embodiment.

[0048] The control device 100 acquires, for example, a value indicating water quality measured by the first measuring device 24 (hereinafter also referred to as the water quality value) (step S1 in Figure 6).

[0049] Specifically, the control device 100 acquires, for example, the water quality values ​​measured by the first measuring device 24 at regular intervals such as every tens of seconds to every few minutes.

[0050] The first measuring device 24 may be, for example, a COD meter that measures the COD (Chemical Oxygen Demand) value in the reaction vessel 20. In this case, the control device 100 may, for example, acquire the COD value measured by the first measuring device 24 as a water quality value. The first measuring device 24 may also measure, for example, other water quality values ​​that have a correlation with the BOD value in the reaction vessel 20.

[0051] Then, the control device 100 determines, for example, whether the water quality value acquired in step S1 satisfies the first condition (step S2 in Figure 6). Specifically, the control device 100 determines, for example, whether the COD value acquired in step S1 is below a threshold (hereinafter also referred to as the first threshold).

[0052] As a result, for example, if the water quality value obtained in step S1 is determined not to satisfy the first condition (NO in step S2), the control device 100 increases the number of aeration units 23 that supply oxygen A to the reaction tank 20 by, for example, controlling the opening of at least one of the multiple valves V, thereby increasing the aeration area (decreasing the aeration restriction area) (step S3 in Figure 6). Then, the control device 100 returns to step S1, for example.

[0053] In other words, for example, if the water quality value obtained from the first measuring device 24 does not meet the first condition, the control device 100 determines that the removal of organic matter by BOD oxidizing bacteria in the reaction tank 20 is not sufficient. Therefore, in this case, the control device 100 controls the system to activate the BOD oxidizing bacteria by increasing the amount of oxygen A (aeration rate) supplied to the reaction tank 20, for example, so that the amount of organic matter removed in the reaction tank 20 increases.

[0054] This makes it possible for the control device 100 to control, for example, the removal of organic matter in the reaction vessel 20 in a stable manner.

[0055] On the other hand, for example, if it is determined that the water quality value obtained in step S1 satisfies the first condition (YES in step S2), the control device 100 obtains a value indicating the nitrification state measured by the second measuring device 25 (hereinafter also referred to as the nitrification state value) (step S4 in Figure 6).

[0056] Specifically, the control device 100 acquires, for example, the nitrification state value measured by the second measuring device 25 at periodic intervals such as every tens of seconds to a few minutes.

[0057] The second measuring device 25 may be, for example, a NOx meter that measures the NOx value inside the reaction vessel 20. In this case, the control device 100 may, for example, acquire the NOx value measured by the second measuring device 25 as the nitrification state value.

[0058] In other words, for example, if the water quality value obtained from the first measuring device 24 satisfies the first condition, the control device 100 determines that organic matter has been sufficiently removed by BOD-oxidizing bacteria in the reaction tank 20. Therefore, in this case, the control device 100 determines that there is room to reduce the amount of oxygen A supplied to the reaction tank 20, and starts controlling the nitrification state of the water to be treated in the reaction tank 20.

[0059] Then, the control device 100 determines, for example, whether the nitrification state value acquired in step S4 satisfies the second condition (step S5 in Figure 6). Specifically, the control device 100 determines, for example, whether the NOx value acquired in step S4 is below a threshold (hereinafter also referred to as the second threshold).

[0060] Furthermore, the control device 100 may perform step S5 at a frequency of, for example, once every few days. That is, the control device 100 may perform step S5 at a lower frequency than step S4, rather than performing step S5 each time a nitrification state value is acquired in step S4. Also, if the control device 100 performs step S5 at a frequency of, for example, once every few days, it may perform step S4 at a similar frequency (for example, once every few days).

[0061] As a result, for example, if the control device 100 determines that the nitrification state value obtained in step S4 does not satisfy the second condition (NO in step S5), the control device 100 reduces the number of aeration units 23 that supply oxygen A to the reaction vessel 20 by closing at least one of the multiple valves V, thereby increasing the aeration restriction area (reducing the aeration area) (step S6 in Figure 6). Then, the control device 100 returns to step S1, for example.

[0062] In other words, for example, if the nitrification status value obtained from the second measuring device 25 does not satisfy the second condition, the control device 100 determines that nitrifying bacteria are proliferating in the reaction tank 20. Therefore, in this case, the control device 100 suppresses the growth of nitrifying bacteria by, for example, reducing the amount of oxygen A (aeration rate) supplied to the reaction tank 20, and controls the system so that nitrification of ammonia nitrogen in the reaction tank 20 is suppressed.

[0063] Furthermore, if closing valve V in step S6 results in insufficient removal of organic matter in the reaction tank 20, the water quality value measured in step S1 of the subsequent aeration control treatment will no longer meet the first condition, and valve V3 will be opened in step S3 of the subsequent aeration control treatment. Therefore, the control device 100 can automatically control the process so that the amount of organic matter removed increases again, even if, for example, the amount of organic matter removed temporarily decreases due to opening valve V in step S6.

[0064] On the other hand, if, for example, the control device 100 determines that the nitrification status value obtained in step S4 satisfies the second condition (YES in step S5), the control device 100 returns to step S1, for example.

[0065] In other words, for example, if the water quality value obtained from the first measuring device 24 satisfies the first condition, and the nitrification state value obtained from the second measuring device 25 satisfies the second condition, the control device 100 determines that organic matter has been sufficiently removed in the reaction tank 20, and that the nitrification of ammonia nitrogen is also suppressed. Therefore, in this case, the control device 100 does not perform opening and closing control of the multiple valves V.

[0066] Thus, the water treatment system 1000 in this embodiment includes, for example, a tank 20 for treating liquid, a supply device 40 for supplying oxygen A into the tank 20 via a plurality of aeration units 23 located at the bottom of the tank 20, a control device 100 for controlling the supply of oxygen A from the plurality of aeration units 23, a first measuring device 24 for measuring the water quality of the liquid, and a second measuring device 25 for measuring the nitrification state of nitrogen contained in the liquid. The control device 100 controls the supply of oxygen A from the plurality of aeration units 23, for example, so that the water quality measured by the first measuring device 24 satisfies a first condition and the nitrification state measured by the second measuring device 25 satisfies a second condition.

[0067] Specifically, in this embodiment, the first measuring device 24 measures, for example, the concentration of organic matter contained in the liquid, and the control device 100 determines, for example, that the water quality of the liquid satisfies the first condition if the concentration measured by the first measuring device 24 is below a first threshold.

[0068] Furthermore, in this embodiment, the second measuring device 25 measures, for example, the concentration of nitrogen compounds contained in the liquid, and the control device 100 determines, for example, that the nitrification state of nitrogen contained in the liquid satisfies the second condition if the concentration measured by the second measuring device 25 is below the second threshold.

[0069] Furthermore, the control device 100 in this embodiment controls, for example, the number of oxygen A-supplying diffusers 23 among the plurality of diffusers 23 so that the water quality of the liquid satisfies the first condition and the nitrification state of nitrogen contained in the liquid satisfies the second condition.

[0070] More specifically, in this embodiment, the control device 100 reduces the number of oxygen A-supplying diffusers 23 among the plurality of diffusers 23 if, for example, the water quality of the liquid satisfies the first condition and the nitrification state of nitrogen contained in the liquid does not satisfy the second condition.

[0071] Furthermore, in this embodiment, if the water quality of the liquid does not meet the first condition, the control device 100 increases the number of aeration units 23 that supply oxygen A among the multiple aeration units 23.

[0072] As a result, the control device 100 in this embodiment can, for example, sufficiently remove organic matter in the reaction vessel 20 while suppressing the growth of nitrifying bacteria (nitrification of ammonia nitrogen).

[0073] The control device 100 may, for example, pre-store in the information storage area 130 correspondence information (not shown) that shows the correspondence between the minimum ASRT required to maintain nitrifying bacteria in the reaction tank 20 and the water temperature of the water to be treated in the reaction tank 20.

[0074] Furthermore, in step S6, the control device 100 may, for example, refer to the corresponding information stored in the information storage area 130 to identify the ASRT (hereinafter also referred to as a specific ASRT) corresponding to the water temperature measured by a water thermometer (not shown) installed in the reaction vessel 20. In addition, the control device 100 may, for example, control the closing of at least one of the multiple valves V so that the ASRT in the reaction vessel 20 becomes less than or equal to the specific ASRT, thereby reducing the number of diffusers 23 that supply oxygen A to the reaction vessel 20.

[0075] Furthermore, in step S6, if, for example, closing at least one of the multiple valves V would prevent the fluidity of the activated sludge (the fluidity necessary for removing organic matter in the reaction tank 20) ​​from being maintained, the control device 100 may, instead of closing at least one of the multiple valves V, reduce the amount of return sludge supplied from the final sedimentation tank 30 to the reaction tank 20, thereby reducing the amount of activated sludge in the reaction tank 20 and suppressing the growth of nitrifying bacteria. In other words, in this case, the control device 100 may, for example, suppress the growth of nitrifying bacteria in the reaction tank 20 by controlling the MLSS (Mixed liquor suspended solids) in the reaction tank 20 to decrease.

[0076] [Aeration control process in the first modified example of the first embodiment] Next, the aeration control process in the first modified example of the first embodiment (hereinafter also simply referred to as the first modified example) will be described. Figure 7 is a flowchart illustrating the aeration control process in the first modified example.

[0077] In this modified example, the aeration control process involves, for example, controlling the opening and closing of each of the multiple valves V, as well as controlling the degree of opening of each of the multiple valves V, thereby sufficiently removing organic matter in the reaction vessel 20 while suppressing the nitrification of ammonia nitrogen.

[0078] The control device 100 acquires the water quality values ​​measured by the first measuring device 24, for example, as described in Figure 6 (step S1 in Figure 7).

[0079] Then, the control device 100 determines, for example, whether the water quality value obtained in step S1 satisfies the first condition, as described in Figure 6 (step S2 in Figure 7).

[0080] As a result, for example, if it is determined that the water quality value obtained in step S1 does not satisfy the first condition (NO in step S2), the control device 100 determines whether or not the water quality value obtained in step S1 satisfies the third condition (step S31 in Figure 7). The third condition is, for example, a condition for determining whether or not a treatment to improve the water quality in the reaction tank 20 was performed in the previous aeration control treatment.

[0081] Specifically, the control device 100 determines that the water quality value obtained in step S1 satisfies the third condition if, for example, step S32 was performed in the previous aeration control process (i.e., it was determined that the water quality value did not satisfy the first condition in step S2 of the previous aeration control process). Alternatively, the control device 100 may determine that the water quality value obtained in step S1 satisfies the third condition if, for example, step S32 was performed consecutively a predetermined number of times in the aeration control processes performed up to the previous time.

[0082] Then, if the control device 100 determines that the water quality value obtained in step S1 does not satisfy the third condition (NO in S31), it increases the opening degree of at least one of the multiple valves V (step S32 in Figure 7). After that, the control device 100 returns to step S1, for example.

[0083] Specifically, in this case, the control device 100 increases the opening degree of one of the multiple valves V that supplies oxygen A (the valve V whose opening degree is not 0).

[0084] In other words, the case in which the water quality value obtained in step S1 does not satisfy the third condition is, for example, when the water quality value of the water to be treated in the reaction tank 20 no longer satisfies the first condition, but control to improve the water quality value has not yet been performed. In this case, the control device 100 increases the amount of oxygen A supplied to the reaction tank 20 by, for example, increasing the opening degree of at least one of the multiple valves V.

[0085] In the first modified example, for example, the opening control of a predetermined number of valves V among the multiple valves V may be performed in advance at a timing before the aeration control process is carried out. In other words, in the first modified example, for example, the supply of oxygen A from a predetermined number of diffusers 23 may be adjusted in advance at a timing before the aeration control process is carried out. Also, in the first modified example, for example, the opening degree of each of the predetermined number of valves V may be adjusted in advance to a predetermined opening degree.

[0086] On the other hand, if the water quality value obtained in step S1 is determined to satisfy the third condition (YES in S31), the control device 100 increases the number of aeration units 23 that supply oxygen A to the reaction tank 20 by, for example, controlling the opening of at least one of the multiple valves V, thereby increasing the aeration area (decreasing the aeration restriction area) (step S33 in Figure 7).

[0087] Specifically, in this case, the control device 100 controls the opening of, for example, the valve V among the multiple valves V that is not supplying oxygen A (the valve V with an opening degree of 0).

[0088] In other words, the condition that the water quality value obtained in step S1 satisfies the third condition is, for example, when, despite control to improve the water quality value of the water to be treated in the reaction tank 20 (control to increase the opening of valve V) being performed in the previous aeration control treatment, the improvement in water quality value is still insufficient. Therefore, in this case, the control device 100 performs further control to improve the water quality value of the water to be treated in the reaction tank 20. Specifically, in this case, the control device 100 increases the amount of oxygen A supplied to the reaction tank 20 by controlling the opening of valve V, thereby increasing ASRT.

[0089] In other words, if the control device 100 detects, for example, that the water quality value of the water to be treated in the reaction tank 20 no longer meets the first condition, it will perform a stepwise control of increasing the opening of valve V and then opening valve V to ensure that the water quality value of the water to be treated in the reaction tank 20 meets the first condition.

[0090] Returning to Figure 7, for example, if it is determined that the water quality value obtained in step S1 satisfies the first condition (YES in step S2), the control device 100 obtains the nitrification status value measured by the second measuring device 25, for example, as described in Figure 6 (step S4 in Figure 7).

[0091] Then, the control device 100 determines, for example, whether the nitrification state value obtained in step S4 satisfies the second condition, as described in Figure 6 (step S5 in Figure 7).

[0092] As a result, for example, if it is determined that the nitrification state value obtained in step S4 does not satisfy the second condition (NO in step S5), the control device 100 determines whether or not the nitrification state value obtained in step S4 satisfies the fourth condition (step S61 in Figure 7). The fourth condition is, for example, a condition for determining whether or not a process to improve the nitrogen nitrification state in the reaction vessel 20 was performed in the previous aeration control process.

[0093] Specifically, the control device 100 determines that the nitrification state value obtained in step S4 satisfies the fourth condition if, for example, step S62 was performed in the previous aeration control process (and it was determined in step S5 of the previous aeration control process that the nitrification state value did not satisfy the second condition). Alternatively, the control device 100 may determine that the nitrification state value obtained in step S4 satisfies the fourth condition if, for example, step S62 was performed consecutively a predetermined number of times in the aeration control processes performed up to the previous time.

[0094] Then, if the control device 100 determines that the nitrification status value obtained in step S4 does not satisfy the fourth condition (NO in S61), the control device 100 reduces the opening degree of at least one of the multiple valves V (step S62 in Figure 7). After that, the control device 100 returns to step S1, for example.

[0095] Specifically, in this case, the control device 100 reduces the opening degree of one of the multiple valves V that supplies oxygen A (the valve V whose opening degree is not 0).

[0096] In other words, the case in which the nitrification state value obtained in step S4 does not satisfy the fourth condition is, for example, when the nitrification state value of nitrogen contained in the water to be treated in the reaction vessel 20 no longer satisfies the second condition, and no control has yet been performed to improve that nitrification state value. In this case, the control device 100 reduces the amount of oxygen A supplied to the reaction vessel 20 by, for example, reducing the opening degree of at least one of the multiple valves V.

[0097] On the other hand, if the control device 100 determines that the nitrification state value obtained in step S4 satisfies the fourth condition (YES in S61), the control device 100 reduces the number of aeration units 23 that supply oxygen A to the reaction vessel 20 by, for example, closing at least one of the multiple valves V, thereby increasing the aeration restriction area (decreasing the aeration area) (step S63 in Figure 7).

[0098] Specifically, in this case, the control device 100 performs closing control on the valve V (valve V with an opening degree other than 0) that supplies oxygen A among the multiple valves V.

[0099] In other words, the fourth condition is met when, for example, the nitrification state value obtained in step S4 satisfies the fourth condition when, despite control to improve the nitrogen nitrification state value in the reaction vessel 20 (control to reduce the opening of valve V) being performed in the previous aeration control process, the improvement in the nitrification state value is still insufficient. Therefore, in this case, the control device 100 performs further control to improve the nitrogen nitrification state value in the reaction vessel 20. Specifically, in this case, the control device 100 shortens the ASRT by reducing the amount of oxygen A supplied to the reaction vessel 20, for example, by closing valve V.

[0100] In other words, if the control device 100 detects, for example, that the nitrogen nitrification state value in the reaction vessel 20 no longer satisfies the second condition, it will perform a stepwise control of reducing the opening of valve V and then closing valve V to ensure that the nitrogen nitrification state value in the reaction vessel 20 satisfies the second condition.

[0101] Thus, the control device 100 in this embodiment determines, for example, the number of oxygen A-supplying diffusers 23 among the plurality of diffusers 23 such that the liquid water quality satisfies the first condition and the nitrification state of nitrogen contained in the liquid satisfies the second condition, and controls the amount of oxygen A supplied from the diffusers 23 corresponding to the determined number among the plurality of diffusers 23.

[0102] Specifically, for example, in the stage before step S3 or step S6 (hereinafter collectively referred to as step S3, etc.), the number of aeration units 23 whose valve V has been controlled to open in advance (i.e., the number indicated by the initial value) is determined as the number of aeration units 23 that supply oxygen A. Also, for example, in the stage after step S3, etc. has been performed, the number of aeration units 23 that supply oxygen A is determined as the number of aeration units 23 whose valve V has been controlled to open in the stage after step S3, etc. has been performed (the number of aeration units 23 whose valve V has been controlled to open in the stage after step S3, etc. has been performed).

[0103] As a result, the control device 100 in this modified example can, for example, control the liquid water quality in the reaction vessel 20 so that it stably satisfies the first condition, while also controlling the nitrogen nitrification state in the reaction vessel 20 so that it satisfies the second condition, similar to the case described in Figure 6, etc.

[0104] Furthermore, the control device 100 can reduce the frequency of valve V opening and closing control by, for example, controlling the opening of valve V only when water quality cannot be controlled by adjusting the opening degree of valve V. Therefore, the control device 100 can reduce the burden on the operator associated with controlling the water quality of the liquid.

[0105] Furthermore, the control device 100 can reduce the frequency of valve V opening and closing control by, for example, controlling the opening of valve V only when it is not possible to control the nitrification state of nitrogen by adjusting the opening degree of valve V. Therefore, the control device 100 can reduce the burden on the operator associated with controlling the nitrification state of nitrogen contained in the liquid.

[0106] [Aeration control process in a second modified example of the first embodiment] Next, the aeration control process in the second modified example of the first embodiment (hereinafter also simply referred to as the second modified example) will be described. Figure 8 is a flowchart illustrating the aeration control process in the modified example.

[0107] In this modified example, the aeration control process involves, for example, controlling the opening and closing of each of the multiple valves V, as well as controlling the amount of sludge returned to the reaction tank 20 (controlling the amount of activated sludge used to remove organic matter in the reaction tank 20). This allows for sufficient removal of organic matter in the reaction tank 20 while suppressing the nitrification of ammonia nitrogen.

[0108] The control device 100 acquires the water quality values ​​measured by the first measuring device 24, for example, as described in Figure 6 (step S1 in Figure 8).

[0109] Then, the control device 100 determines, for example, whether the water quality value obtained in step S1 satisfies the first condition, as described in Figure 6 (step S2 in Figure 8).

[0110] As a result, for example, if it is determined that the water quality value obtained in step S1 does not satisfy the first condition (NO in step S2), the control device 100 determines whether or not the water quality value obtained in step S1 satisfies the third condition, as explained in Figure 7 (step S31 in Figure 8).

[0111] Then, if the water quality value obtained in step S1 is determined not to satisfy the third condition (NO in S31), the control device 100 increases the number of aeration units 23 that supply oxygen A to the reaction tank 20 by, for example, controlling the opening of at least one of the multiple valves V, thereby increasing the aeration area (decreasing the aeration restriction area) (step S34 in Figure 8). After that, the control device 100 returns to step S1, for example.

[0112] Specifically, in this case, the control device 100 controls the opening of, for example, the valve V among the multiple valves V that is not supplying oxygen A (the valve V with an opening degree of 0).

[0113] In other words, if the water quality value obtained in step S1 does not satisfy the third condition, it means, for example, that after the water quality value of the treated water in the reaction tank 20 no longer satisfies the first condition, no control has yet been performed to improve that water quality value. Therefore, in this case, the control device 100 increases the amount of oxygen A supplied to the reaction tank 20 and increases ASRT by, for example, opening at least one of the multiple valves V.

[0114] On the other hand, if the water quality values ​​obtained in step S1 are determined to satisfy the third condition (YES in S31), the control device 100 increases, for example, the amount of return sludge (the amount of activated sludge in the reaction tank 20) ​​(step S35 in Figure 8).

[0115] In other words, the condition that the water quality value obtained in step S1 satisfies the third condition is, for example, when, despite control (opening valve V) to improve the water quality value of the water to be treated in the reaction tank 20 being performed in the previous aeration control treatment, the improvement in water quality value is still insufficient. Therefore, in this case, the control device 100 performs further control to improve the water quality value of the water to be treated in the reaction tank 20. Specifically, the control device 100 increases the ASRT by, for example, increasing the amount of sludge returned to the reaction tank 20.

[0116] In other words, if the control device 100 detects, for example, that the water quality value of the water to be treated in the reaction tank 20 no longer meets the first condition, it will perform a stepwise control of opening the valve V and increasing the amount of returned sludge to ensure that the water quality value of the water to be treated in the reaction tank 20 meets the first condition.

[0117] Returning to Figure 8, for example, if it is determined that the water quality value obtained in step S1 satisfies the first condition (YES in step S2), the control device 100 obtains the nitrification status value measured by the second measuring device 25, for example, as described in Figure 6 (step S4 in Figure 8).

[0118] Then, the control device 100 determines, for example, whether the nitrification state value obtained in step S4 satisfies the second condition, as described in Figure 6 (step S5 in Figure 8).

[0119] As a result, for example, if it is determined that the nitrification status value obtained in step S4 does not satisfy the second condition (NO in step S5), the control device 100 determines whether or not the nitrification status value obtained in step S4 satisfies the fourth condition, as explained in Figure 7 (step S61 in Figure 8).

[0120] Then, if the control device 100 determines that the nitrification state value obtained in step S4 does not satisfy the fourth condition (NO in S61), the control device 100 reduces the number of aeration units 23 that supply oxygen A to the reaction vessel 20 by, for example, controlling the closing of at least one of the multiple valves V (one or more valves V), thereby increasing the aeration restriction area (reducing the aeration area) (step S64 in Figure 8). After that, the control device 100 returns to step S1, for example.

[0121] Specifically, in this case, the control device 100 performs closing control on the valve V (valve V with an opening degree other than 0) that supplies oxygen A among the multiple valves V.

[0122] In other words, if the nitrification state value obtained in step S4 does not satisfy the fourth condition, for example, it means that after the nitrification state value of nitrogen contained in the water to be treated in the reaction vessel 20 no longer satisfies the second condition, control to improve that nitrification state value has not yet been performed. Therefore, in this case, the control device 100 reduces the amount of oxygen A supplied to the reaction vessel 20 by closing at least one of the multiple valves V, thereby shortening the ASRT.

[0123] On the other hand, if the nitrification state value obtained in step S4 is determined to satisfy the fourth condition (YES in S61), the control device 100 reduces, for example, the amount of returned sludge (the amount of activated sludge in the reaction tank 20) ​​(step S65 in Figure 8).

[0124] In other words, the fourth condition is met when, for example, the nitrification state value obtained in step S4 satisfies the fourth condition when, despite control (closing control of valve V) to improve the nitrogen nitrification state value in the reaction tank 20 being performed in the previous aeration control treatment, the improvement in the nitrification state value is still insufficient. Therefore, in this case, the control device 100 performs further control to improve the nitrogen nitrification state value in the reaction tank 20. Specifically, in this case, the control device 100 shortens the ASRT by performing control to reduce the amount of sludge returned to the reaction tank 20.

[0125] In other words, if the control device 100 detects, for example, that the nitrogen nitrification state value in the reaction tank 20 no longer satisfies the second condition, it will perform a stepwise control of closing the valve V and reducing the amount of returned sludge so that the nitrogen nitrification state value in the reaction tank 20 satisfies the second condition.

[0126] Thus, in this embodiment, the control device 100 controls the amount of activated sludge used to treat the liquid in the tank 20, for example, so that the liquid water quality satisfies the first condition and the nitrification state of the nitrogen contained in the liquid satisfies the second condition.

[0127] As a result, the control device 100 in this modified example can, for example, control the liquid water quality in the reaction vessel 20 so that it stably satisfies the first condition, while also controlling the nitrogen nitrification state in the reaction vessel 20 so that it satisfies the second condition, similar to the case described in Figure 6, etc.

[0128] [Aeration control process in a third modified example of the first embodiment] Next, the aeration control process in the third modified example of the first embodiment (hereinafter also simply referred to as the third modified example) will be described.

[0129] In this modified example, the aeration control treatment further controls the amount of sludge returned to the reaction tank 20, as in the aeration control treatment in the first modified example.

[0130] Specifically, for example, in step S31 of Figure 7, if it is determined that step S33 of Figure 7 was performed in the previous aeration control process, the control device 100 performs control to increase the amount of returned sludge, similar to step S35 of Figure 8.

[0131] In other words, if the control device 100 detects, for example, that the water quality value of the water to be treated in the reaction tank 20 no longer meets the first condition, it performs a series of steps, including increasing the opening of valve V, opening valve V, and increasing the amount of returned sludge, to control the water quality value of the water to be treated in the reaction tank 20 to meet the first condition.

[0132] Furthermore, for example, if step S61 in Figure 7 determines that step S63 in Figure 7 was performed in the previous aeration control process, the control device 100 performs control to reduce the amount of returned sludge, similar to step S65 in Figure 8.

[0133] In other words, if the control device 100 detects, for example, that the nitrogen nitrification state value in the reaction tank 20 no longer satisfies the second condition, it performs a series of actions, including reducing the opening of valve V, closing valve V, and reducing the amount of returned sludge, to control the system so that the nitrogen nitrification state value in the reaction tank 20 satisfies the second condition.

[0134] As a result, the control device 100 in this modified example can, for example, control the liquid water quality in the reaction vessel 20 so that it stably satisfies the first condition, while also controlling the nitrogen nitrification state in the reaction vessel 20 so that it satisfies the second condition, similar to the case described in Figure 6, etc. [Explanation of Symbols]

[0135] 10: Primary sedimentation tank 20: Reaction tank 20a: Anaerobic region 20b: Aerobic region 20b1: Aeration area 20b2: Aeration restriction area 20b3: Aeration area 21: Tank body 22: Aeration unit 23: Aeration unit 23a: Air diffuser 23b: Air diffuser 23c: Diffusion part 23d: Diffusion part 23e: Diffusion section 23f: Diffusion section 24: Measuring device 25: Measuring device 30: Final sedimentation tank 40: Supply device 100: Control device 101: CPU 102: Memory 103: Communication device 104: Storage medium 105: Bus 130: Information storage area 1000: Water treatment system A: Oxygen L: Piping L1: Piping L2: Piping L3: Piping L4: Piping L5: Piping L6: Piping L7: Piping L8: Piping V: valve V1: valve V2: Valve V3: Valve V4: Valve V5: Valve

Claims

1. A tank for processing liquids, A supply device that supplies oxygen into the tank via a plurality of air diffusers located at the bottom of the tank, A control device that controls the supply of oxygen from each of the plurality of aeration units, A first measuring device for measuring the water quality of the aforementioned liquid, The system includes a second measuring device for measuring the nitrification state of nitrogen contained in the liquid, A water treatment system in which the control device controls the supply of oxygen from the plurality of aeration units such that the water quality measured by the first measuring device satisfies a first condition and the nitrification state measured by the second measuring device satisfies a second condition.

2. The first measuring device measures the concentration of organic matter contained in the liquid as the water quality, The water treatment system according to claim 1, wherein the control device determines that the water quality satisfies the first condition when the concentration measured by the first measuring device is less than or equal to a first threshold.

3. The second measuring device measures the concentration of nitrogen compounds contained in the liquid as the nitrification state, The water treatment system according to claim 1, wherein the control device determines that the nitrification state satisfies the second condition when the concentration measured by the second measuring device is less than or equal to a second threshold.

4. The water treatment system according to claim 1, wherein the control device determines the number of oxygen-supplying aeration units among the plurality of aeration units such that the water quality satisfies a first condition and the nitrification state satisfies a second condition, and controls the amount of oxygen supplied from the aeration units corresponding to the number among the plurality of aeration units.

5. The water treatment system according to claim 1, wherein the control device controls the number of oxygen-supplying aeration units among the plurality of aeration units such that the water quality satisfies a first condition and the nitrification state satisfies a second condition.

6. The water treatment system according to claim 1, wherein the control device controls the amount of activated sludge used to treat the liquid in the tank such that the water quality satisfies a first condition and the nitrification state satisfies a second condition.

7. A control device for a water treatment system comprising: a tank for processing a liquid; a supply device for supplying oxygen into the tank via a plurality of aeration units located at the bottom of the tank; a first measuring device for measuring the water quality of the liquid; and a second measuring device for measuring the nitrification state of nitrogen contained in the liquid, A control device that controls the supply of oxygen from the plurality of aeration units such that the water quality measured by the first measuring device satisfies a first condition, and the nitrification state measured by the second measuring device satisfies a second condition.

8. A water treatment method for a water treatment system comprising: a tank for processing a liquid; a supply device for supplying oxygen into the tank via a plurality of aeration units located at the bottom of the tank; a first measuring device for measuring the water quality of the liquid; and a second measuring device for measuring the nitrification state of nitrogen contained in the liquid, A water treatment method that controls the supply of oxygen from a plurality of aeration units such that the water quality measured by the first measuring device satisfies a first condition, and the nitrification state measured by the second measuring device satisfies a second condition.

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