Wastewater treatment system and wastewater treatment method

Abstract

To provide a wastewater treatment system and a wastewater treatment method capable of improving treatment efficiency of wastewater.SOLUTION: A wastewater treatment system is assembled with a wastewater treatment tank, a plurality of blowers, a plurality of diffusers, an aeration pipe that has a first aeration pipe end part connected to a blower and a second aeration pipe end part connected to a diffuser, a plurality of aeration pipe valves, a sensor that detects a state of wastewater in the wastewater treatment tank, and a control part, wherein the second aeration pipe end part has a second aeration pipe branching part connected to each diffuser, each aeration pipe valve is provided in each second aeration pipe branching part, the control part is constituted so as to conduct a blower control treatment that determines the number of operating blowers based on a detection result by the sensor and an aeration pipe valve control treatment that determines an aeration pipe valve opening number based on a number of operating blower and controls so that only the aeration pipe valves of the determined aeration pipe valve opening number are in the open state, and in the aeration pipe valve control treatment, the control part determines the aeration pipe valve opening number in a manner that the aeration pipe valve opening number becomes smaller as the number of operating blowers becomes smaller.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] BACKGROUND ART Conventionally, there have been wastewater treatment systems equipped with a blower that sends air into a wastewater treatment tank (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7386472 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional wastewater treatment systems, there is room for improvement in the wastewater treatment efficiency.

[0005] The present invention has been made to solve the above-mentioned problems, and has an object to provide a wastewater treatment system and a wastewater treatment method that can improve the wastewater treatment efficiency. [Means for solving the problem]

[0006] [1] A wastewater treatment system, a wastewater treatment tank configured to treat wastewater; a plurality of blowers disposed outside the wastewater treatment tank and configured to blow air; a plurality of diffusers disposed within the wastewater treatment tank; an air diffuser having a first air diffuser end connected to the plurality of blowers and a second air diffuser end connected to the plurality of diffusers; A plurality of air diffusion pipe valves each configured to be openable and closable; a sensor configured to detect the state of wastewater in the wastewater treatment tank; A control unit; Equipped with the second diffuser end portion has a plurality of second diffuser branch portions connected to the plurality of diffusers, respectively; Each of the plurality of air diffusion pipe valves is provided in each of the plurality of second air diffusion pipe branch portions, The control unit a blower control process for determining the number of operating blowers based on the detection result by the sensor and controlling the plurality of blowers so that only the blowers of the number of operating blowers are operated; An air diffusion valve control process that determines the number of open air diffusion valves based on the number of operating blowers and controls the plurality of air diffusion valves so that only the air diffusion valves of the number of open air diffusion valves are in an open state; and In the air diffuser valve control process, the control unit determines the air diffuser valve opening number so that the air diffuser valve opening number becomes smaller as the number of operating blowers becomes smaller.

[0007] [2] The wastewater treatment system comprises: a chimney pipe that connects the air inside the wastewater treatment tank with the air outside the wastewater treatment tank; an odor fan configured to send air inside the wastewater treatment tank to the outside of the wastewater treatment tank through the odor pipe; a return pipe having a first return pipe end connected to a portion of the flue pipe on the discharge side of the odor fan and a second return pipe end; Furthermore, The wastewater treatment system described in [1], wherein the second return pipe end has a plurality of return pipe branches arranged in the vicinity of each of the plurality of second aeration pipe branches within the wastewater in the wastewater treatment tank.

[0008] [3] The wastewater treatment system comprises: A plurality of return pipe valves each configured to be openable and closable Furthermore, a plurality of return pipe valves are provided in each of the plurality of return pipe branches; The control unit a return pipe valve control process that determines an open number of return pipe valves based on the number of operating blowers, and controls the plurality of return pipe valves so that only the return pipe valves of the open number of return pipe valves are in an open state. The wastewater treatment system according to [2], further configured to perform the following.

[0009] [4] In the return pipe valve control process, the control unit determines the return pipe valve opening number so that the smaller the number of operating blowers, the larger the return pipe valve opening number.

[0010] [5] In the return pipe valve control process, the control unit opens the return pipe valve provided in the return pipe branch section that is located near the second aeration pipe branch section in which the aeration pipe valve that is closed in the aeration pipe valve control process is provided, among the multiple return pipe valves. This is a wastewater treatment system described in [3] or [4].

[0011] [6] A wastewater treatment system described in any one of [1] to [5], wherein in the air diffuser valve control process, the control unit changes the combination of the air diffuser valves to be opened at every predetermined timer time while the number of open air diffuser valves is equal to or greater than 1 and less than the maximum number.

[0012] [7] The wastewater treatment system comprises: a plurality of bypass pipes provided corresponding to the plurality of second aeration pipe branch portions, respectively; a plurality of bypass pipe valves provided in the plurality of bypass pipes, each of which is configured to be openable and closable; Furthermore, each of the plurality of bypass pipes has a first bypass pipe end connected to an upstream end of the second aeration pipe branch portion corresponding to that bypass pipe, and a second bypass pipe end located in the vicinity of the second aeration pipe branch portion corresponding to that bypass pipe within the wastewater in the wastewater treatment tank; each of the plurality of bypass pipes is configured to have a lower piping resistance than each of the plurality of second aeration pipe branch sections; The control unit a bypass valve control process for determining an open number of bypass pipe valves based on the number of operating blowers, and controlling the plurality of bypass pipe valves so that only the bypass pipe valves of the determined open number of bypass pipe valves are in an open state; The wastewater treatment system according to any one of [1] to [6], which is configured to carry out the following.

[0013] [8] In the bypass pipe valve control process, the control unit opens the bypass pipe valve provided in the bypass pipe corresponding to the second aeration pipe branch section in which the aeration pipe valve that is closed in the aeration pipe valve control process is provided, among the plurality of bypass pipe valves. The wastewater treatment system described in [7].

[0014] [9] A wastewater treatment method used in the wastewater treatment system according to any one of [1] to [8], a blower control step in which the control unit determines the number of operating blowers based on the detection result by the sensor and controls the plurality of blowers so that only the blowers corresponding to the number of operating blowers are operated among the plurality of blowers; The control unit determines the number of open air diffuser valves based on the number of operating blowers, and controls the plurality of open air diffuser valves so that only the open air diffuser valves corresponding to the number of open air diffuser valves are in an open state. Including, In the air diffuser valve control step, the control unit determines the air diffuser valve opening number so that the smaller the number of operating blowers, the smaller the air diffuser valve opening number. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a wastewater treatment system and a wastewater treatment method that can improve the wastewater treatment efficiency. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of a wastewater treatment system according to a first embodiment of the present invention. [Figure 2] 2A and 2B are diagrams for explaining a wastewater treatment method according to a first embodiment of the present invention, in which FIG. 2(a) is a graph showing an example of temporal changes in dissolved oxygen (DO) concentration detected by a sensor in a wastewater treatment system, and FIG. 2(b) is a timing chart showing an example of the operation of various devices in the wastewater treatment system. [Figure 3] 3 is a flowchart for explaining the wastewater treatment method of FIG. 2. [Figure 4] FIG. 4 is a schematic diagram of a wastewater treatment system according to a second embodiment of the present invention. [Figure 5] 5A and 5B are diagrams for explaining a wastewater treatment method according to a third embodiment of the present invention, in which FIG. 5(a) is a graph showing an example of the temporal change in dissolved oxygen (DO) concentration detected by a sensor in the wastewater treatment system, and FIG. 5(b) is a timing chart showing an example of the operation of various devices in the wastewater treatment system. [Figure 6] 6 is a flowchart for explaining the wastewater treatment method of FIG. 5. [Figure 7] FIG. 10 is a schematic diagram of a wastewater treatment system according to a fourth embodiment of the present invention. [Figure 8] 8A and 8B are diagrams for explaining a wastewater treatment method according to a fourth embodiment of the present invention, in which FIG. 8(a) is a graph showing an example of the change over time in the dissolved oxygen (DO) concentration detected by a sensor in the wastewater treatment system, and FIG. 8(b) is a timing chart showing an example of the operation of various devices in the wastewater treatment system. [Figure 9] 9 is a flowchart for explaining the wastewater treatment method of FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0017] The wastewater treatment system of the present invention is suitable for installation on the premises of, for example, an apartment complex or other multi-family home, or a single-family home, where food waste (hereinafter simply referred to as food waste) pulverized in a garbage disposal installed in the kitchen of each dwelling unit is flowed down a dedicated pipe together with wastewater and treated in the wastewater treatment tank of the wastewater treatment system. In the wastewater treatment tank, the food waste is treated by aerobic microorganisms. For this purpose, a blower supplies air (and thus oxygen) to the food waste and wastewater in the wastewater treatment tank, aerating and agitating the food waste and wastewater in the tank. The treated water from the wastewater treatment tank is discharged, for example, into a public sewer system or an advanced treatment combined septic tank installed in the apartment complex. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a wastewater treatment system and a wastewater treatment method according to the present invention will be described with reference to the drawings.

[0018] First, a schematic configuration of a wastewater treatment system 1 according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of the wastewater treatment system 1 according to the first embodiment of the present invention. The wastewater treatment system 1 according to the first embodiment includes a wastewater treatment tank K, a plurality of blowers B (B1 to B3), a plurality of diffusers D, an air diffusion pipe L, a plurality of air diffusion pipe valves LV (LV1 to LV3), a sensor S, a control unit CT, a flue pipe E, an odor fan F, a return pipe R, and a plurality of return pipe valves RV (RV1 to RV3).

[0019] The wastewater treatment tank K is configured to treat wastewater W. Wastewater W (raw water) containing food waste flows into the wastewater treatment tank K, the flowing-in wastewater W (raw water) is treated within the wastewater treatment tank K, and the treated wastewater W (treated water) is discharged to the outside (for example, to a public sewer system or an advanced treatment combined septic tank installed in an apartment building). The wastewater treatment tank K is buried underground within the premises of, for example, an apartment building or other apartment complex, or a detached house. The wastewater treatment tank K may be divided into a plurality of partition tanks KD by one or more partition walls KW, as shown in Fig. 1. In the example of Fig. 1, the wastewater treatment tank K is divided into three partition tanks KD (KD1 to KD3) by two partition walls KW, and wastewater W flows into the partition tank KD1, KD2, and KD3 in that order, where it is treated and then discharged to the outside. In the wastewater treatment tank K (more specifically, in the example of FIG. 1, the partitioning tank KD2), the food waste in the wastewater W is decomposed (treated) by aerobic microorganisms. In this example, the wastewater treatment tank K (more specifically, in the example of FIG. 1, the partitioning tank KD2) uses a carrier flow system in which the wastewater W and carriers are flowed while the wastewater W is treated by aerobic microorganisms attached to the carriers. Improving the fluidity of the wastewater W in the wastewater treatment tank K (more specifically, in the example of FIG. 1, the partitioning tank KD2) leads to an improvement in the contact efficiency between the carriers and the wastewater W, which in turn leads to an improvement in the treatment efficiency of the wastewater W and also leads to suppression of anaerobic reaction and the generation of foul odors caused by the retention of carriers. In the example of Figure 1, as described above, the partition tank KD2 is configured to treat the wastewater W by aerobic microorganisms, but when the wastewater treatment tank K has multiple partition tanks KD as in this example, any one or more partition tanks KD in the wastewater treatment tank K may be configured to treat the wastewater W by aerobic microorganisms.

[0020] The plurality of blowers B (air blowers) are each arranged outside the wastewater treatment tank K and configured to blow out air. In the example of FIG. 1, three blowers B (B1 to B3) are provided, but the number of blowers B may be any number as long as it is two or more. The plurality of blowers B may be installed, for example, in a machine room formed underground near where the wastewater treatment tank K is buried.

[0021] The multiple diffusers D are each disposed in the wastewater W in the wastewater treatment tank K. The multiple diffusers D are disposed at intervals from one another in the wastewater treatment tank K. The diffusers D are configured to atomize air sent from the blower B through the air diffusion pipe L and diffuse the air into the wastewater W in the wastewater treatment tank K. By providing the diffusers D, air (particularly oxygen) becomes more easily dissolved in the wastewater W. In the example of FIG. 1, the number of diffusers D is the same as the number of blowers B (three), but the number of diffusers D may be different from the number of blowers B. When the wastewater treatment tank K has multiple partition tanks KD as in the example of Figure 1, it is preferable that multiple diffusers D be placed in the wastewater W in one or more partition tanks KD (in the example of Figure 1, partition tank KD2) configured to treat the wastewater W with aerobic microorganisms in the wastewater treatment tank K. As in the example of FIG. 1, it is preferable to arrange a plurality of diffusers D in one divided vessel KD (divided vessel KD2 in the example of FIG. 1). As shown in the example of Figure 1, multiple diffusers D may be arranged near the bottom wall of the wastewater treatment tank K (i.e., closer to the bottom wall of the wastewater treatment tank K in the vertical direction than the water surface of the wastewater W). The diffuser D is configured to diffuse air, for example, upward.

[0022] The air diffusion pipe L extends between the plurality of blowers B and the plurality of diffusers D, and connects the plurality of blowers B to the plurality of diffusers D. The air diffusion pipe L has a first air diffusion pipe end L1 connected to the plurality of blowers B and a second air diffusion pipe end L2 connected to the plurality of diffusers D. The first diffuser pipe end L1 branches into a plurality of first diffuser pipe branch portions L1B (i.e., it has a plurality of first diffuser pipe branch portions L1B). The number of first diffuser pipe branch portions L1B is the same as the number of blowers B. Each of the plurality of first diffuser pipe branch portions L1B is connected to each of the plurality of blowers B. The second diffuser pipe end L2 is branched into a plurality of second diffuser pipe branch portions L2B (L2B1 to L2B3) (i.e., it has a plurality of second diffuser pipe branch portions L2B). The number of second diffuser pipe branch portions L2B is the same as the number of diffusers D. Each of the plurality of second diffuser pipe branch portions L2B is connected to a respective one of the plurality of diffusers D. In the example of FIG. 1, each of the plurality of second diffuser pipe branch portions L2B extends substantially in the vertical direction, and a corresponding diffuser D is connected to each of the lower ends (downstream ends) of the second diffuser pipes. The air diffusion pipe L is unified in a portion between the first air diffusion pipe end portion L1 and the second air diffusion pipe end portion L2.

[0023] The plurality of air diffusion pipe valves LV (LV1 to LV3) are each configured to be able to open and close. The air diffusion pipe valves LV are configured as, for example, on-off valves. The air diffusion pipe valves LV are configured as, for example, automatic valves such as electromagnetic, electric, or air-operated valves. The number of diffuser pipe valves LV is the same as the number of second diffuser pipe branch portions L2B. Each of the multiple diffuser pipe valves LV (LV1 to LV3) is provided at each of the multiple second diffuser pipe branch portions L2B (L2B1 to L2B3). When the diffuser pipe valve LV opens and closes, the flow path of the second diffuser pipe branch portion L2B to which the diffuser pipe valve LV is provided opens and closes, and as a result, the diffusion operation of the diffuser D connected to the end (downstream end) of the second diffuser pipe branch portion L2B starts and stops. The opening and closing of the air diffuser valve LV is controlled by the control unit CT.

[0024] The sensor S is configured to detect the state of the wastewater W in the wastewater treatment tank K. The sensor S can be disposed in the wastewater W in the wastewater treatment tank K. When the wastewater treatment tank K has multiple partitioned tanks KD, it is preferable that the sensor S is disposed in the wastewater W in the partitioned tank KD configured to treat the wastewater W with aerobic microorganisms in the wastewater treatment tank K. In the example of Fig. 1, the sensor S is disposed in the wastewater W of the partitioned tank KD2. In this example, the sensor S is configured to detect the concentration (mg / L) of dissolved oxygen (DO) of the wastewater W in the wastewater treatment tank K (separate tank KD2 in the example of FIG. 1) as the state of the wastewater W in the wastewater treatment tank K. In this case, the sensor S may be configured, for example, by a known fluorescent dissolved oxygen sensor (DO sensor). However, the sensor S may be configured to detect the pH, temperature, etc. of the wastewater W in the wastewater treatment tank K as the state of the wastewater W in the wastewater treatment tank K. The detection result of the state of the wastewater W in the wastewater treatment tank K by the sensor S is output to the control unit CT continuously or periodically.

[0025] The chimney pipe E connects the air inside the wastewater treatment tank K with the air outside the wastewater treatment tank K. The chimney pipe E has a first chimney pipe end E1 located inside the wastewater treatment tank K and above the wastewater W, and a second chimney pipe end E2 located outside the wastewater treatment tank K. The air from the second chimney pipe end E2 is, for example, open to the atmosphere. As shown in the example of FIG. 1, the chimney pipe E (more specifically, for example, the second chimney pipe end E2) may be provided with an adjustment valve CV1 whose opening degree can be adjusted. The adjustment valve CV1 may be configured to be manually operated, or may be configured to be controlled by the control unit CT. The adjustment valve CV1 does not necessarily have to be provided.

[0026] The odor fan F is provided in the flue pipe E. The odor fan F is configured to send air inside the wastewater treatment tank K to the outside of the wastewater treatment tank K via the flue pipe E. The odor fan F may be disposed outside the wastewater treatment tank K, as in the example of FIG. 1. The odor vent pipe E and the odor fan F allow odors in the wastewater treatment tank K to escape to the outside of the wastewater treatment tank K (for example, to the atmosphere). The odor fan F is, for example, operated at all times.

[0027] The return pipe R is configured to return a portion of the air sucked from the wastewater treatment tank K by the chimney pipe E and the odor fan F to the wastewater W of the wastewater treatment tank K (in the example of FIG. 1, the partition tank KD2). The return pipe R has a first return pipe end R1 connected to a portion of the chimney pipe E on the discharge side of the odor fan F (for example, the second chimney pipe end E2), and a second return pipe end R2. The second return pipe end portion R2 is branched into a plurality of return pipe branch portions R2B (R2B1 to R2B3) (i.e., the second return pipe end portion R2 has a plurality of return pipe branch portions R2B). At least the distal end (downstream) portion of each of the plurality of return pipe branch portions R2B is located within the wastewater W in the wastewater treatment tank K. When the wastewater treatment tank K has multiple partition tanks KD as in the example of Figure 1, it is preferable that at least the terminal (downstream) portion of each of the multiple return pipe branch sections R2B is arranged in the wastewater W in one or more partition tanks KD (in the example of Figure 1, partition tank KD2) configured to treat the wastewater W by aerobic microorganisms in the wastewater treatment tank K. In this way, a portion of the air within the wastewater treatment tank K drawn in through the chimney pipe E by the odor fan F is released to the outside of the wastewater treatment tank K (e.g., the atmosphere) from the second chimney pipe end E2 of the chimney pipe E, while another portion of the air drawn in through the chimney pipe E by the odor fan F passes through the return pipe R and is discharged from the terminal ends (downstream ends R2Be) of the multiple return pipe branches R2B into the wastewater W within the wastewater treatment tank K. Therefore, discharging air into the wastewater W within the wastewater treatment tank K through the return pipe R improves the fluidity within the wastewater treatment tank K, thereby increasing the contact efficiency between the carriers within the wastewater treatment tank K and the wastewater W. This improves the treatment efficiency of the wastewater W and also suppresses the generation of anaerobic odors due to carrier retention. Since these advantages can be achieved by improving the fluidity within the wastewater treatment tank K, the fact that the air discharged through the return pipe R may not be oxygen-rich is not a problem. The discharge of air from the return pipe R utilizes the blowing function of the odor fan F, so when installing the odor fan F as in this example, there is no need to add a separate dedicated facility, which saves space and reduces power consumption.

[0028] In the example of FIG. 1, the number of return pipe branches R2B (R2B1-R2B3) is the same as the number of second diffuser pipe branches L2B (L2B1-L2B3), and each return pipe branch R2B is provided corresponding to a separate second diffuser pipe branch L2B. In this example, the return pipe branches R2B1-R2B3 are provided corresponding to the second diffuser pipe branches L2B1-L2B3, respectively. The multiple return pipe branches R2B are arranged near each of the multiple second diffuser pipe branches L2B (i.e., the corresponding second diffuser pipe branch L2B) in the wastewater W in the wastewater treatment tank K. This allows the air discharged from the multiple return pipe branches R2B to act to supplement the air diffusion of the diffusers D connected to the corresponding second diffuser pipe branches L2B. Here, the fact that the return pipe branch R2B is located "near" the second diffuser pipe branch L2B corresponding to the return pipe branch R2B means that the distance between the return pipe branch R2B and the corresponding second diffuser pipe branch L2B is shorter than each of the distances between the return pipe branch R2B and each of the other second diffuser pipe branches L2B.

[0029] In the example of FIG. 1, each of the plurality of return pipe branch portions R2B extends substantially in the vertical direction, and the lower end portion of each faces downward and forms a downstream end portion R2Be. 1, it is preferable that the downstream end R2Be of each of the multiple return pipe branches R2B be located near the diffuser D connected to the corresponding second diffuser pipe branch L2B in the wastewater W in the wastewater treatment tank K. Here, "the downstream end R2Be of a return pipe branch R2B being located "near" the diffuser D connected to the second diffuser pipe branch L2B corresponding to that return pipe branch R2B means that the distance between the downstream end R2Be of that return pipe branch R2B and the diffuser D connected to the corresponding second diffuser pipe branch L2B is shorter than each of the distances between the downstream end R2Be of that return pipe branch R2B and the diffusers D connected to the other second diffuser pipe branches L2B.

[0030] The return pipe branch R2B may be made of, for example, a single pipe, and in that case, the downstream end R2Be of the return pipe branch R2B may be formed by cutting out the single pipe (and thus the cut surface of the single pipe). In this case, the resistance of the return pipe branch R2B can be reduced.

[0031] As shown in the example of FIG. 1, the return pipe R (more specifically, for example, the first return pipe end R1) may be provided with an adjustment valve CV2 whose opening degree is adjustable. The adjustment valve CV2 may be configured to be manually operated, or may be configured to be controlled by the control unit CT. The adjustment valve CV2 does not necessarily have to be provided.

[0032] As in the example of FIG. 1, the first return pipe end R1 may be connected to a portion of the flue pipe E between the odor fan F and the downstream regulating valve CV1.

[0033] The plurality of return pipe valves RV (RV1 to RV3) are each configured to be openable and closable. The return pipe valves RV are configured, for example, as on-off valves. The return pipe valves RV are configured, for example, as automatic valves such as electromagnetic, electric, or air-operated valves. The number of return pipe valves RV is the same as the number of return pipe branches R2B. Each of the multiple return pipe valves RV (RV1 to RV3) is provided at each of the multiple return pipe branches R2B (R2B1 to R2B3). By opening and closing the return pipe valve RV, the flow path of the return pipe branch R2B at which the return pipe valve RV is provided opens and closes, and thus the discharge of air from the downstream end R2Be of the return pipe branch R2B is started or stopped. The opening and closing of the return pipe valve RV is controlled by the control unit CT.

[0034] The control unit CT is composed of a processor device such as a PLC (Programmable Logic Controller) or a CPU (Central Processing Unit), and executes a program stored in a memory unit (not shown) to control various other devices in the wastewater treatment system 1 (sensor S, blower B, air diffuser valve LV, return pipe valve RV, memory unit, etc.) while performing various processes described below. Details of the processes performed by the control unit CT will be described later. Communication between the control unit CT and the various other devices in the wastewater treatment system 1 may be achieved by any method such as wireless communication and / or wired communication. The storage unit (not shown) is composed of, for example, a ROM and / or a RAM, and stores various information such as programs to be executed by the control unit CT and detection results from the sensor S. The storage unit may be located outside the control unit CT or inside the control unit CT.

[0035] Next, a wastewater treatment method according to a first embodiment of the present invention will be illustrated with reference to Figures 2 and 3. Figure 2(a) is a graph showing an example of temporal changes in the dissolved oxygen (DO) concentration in the wastewater treatment tank K detected by the sensor S of the wastewater treatment system 1, and Figure 2(b) is a timing chart showing an example of operations of various devices in the wastewater treatment system 1 according to the wastewater treatment method according to the first embodiment of the present invention when the value of the amount of dissolved oxygen in the wastewater treatment tank K changes as shown in the graph of Figure 2(a). Figure 3 is a flowchart for explaining the wastewater treatment method of Figure 2. The wastewater treatment method in the example of Figures 2 to 3 is carried out using the wastewater treatment system 1 of the first embodiment described above with reference to Figure 1, but the wastewater treatment method of the first embodiment may also be carried out using a wastewater treatment system 1 having a configuration different from that of Figure 1. The control unit CT receives as needed (continuously or periodically) the detection results from the sensor S (in this example, the concentration (mg / L) of dissolved oxygen (DO) in the wastewater W in the wastewater treatment tank K (specifically, the partitioned tank KD2)). In the first embodiment, the control unit CT is configured to perform a blower control process (blower control step) SB, an air diffuser valve control process (air diffuser valve control step) SL, and a return pipe valve control process (return pipe valve control step) SR in parallel, based on the detection results from the sensor S. In this embodiment, the control unit CT may be configured to store an accumulated operating time obtained by accumulating the operating time (time during which the blowers B are in an operating state (ON)) of each blower B, and / or an accumulated open time obtained by accumulating the open time (time during which the blowers are in an open state (ON)) of each air diffuser valve LV and / or each return pipe valve RV.

[0036] In the blower control process (blower control step) SB, the control unit CT controls the plurality of blowers B (B1 to B3) based on the detection results of the sensor S. More specifically, the control unit CT determines the number of operating blowers based on the detection results of the sensor S, and controls the plurality of blowers B so that only the blowers B corresponding to the number of operating blowers are operated (ON) (and consequently the remaining blowers B are stopped (OFF)). 2 and 3, the control unit CT determines the number of operating blowers so that the higher the dissolved oxygen (DO) concentration (mg / L) of the wastewater W in the wastewater treatment tank K (specifically, the partitioned tank KD2) detected by the sensor S, the fewer the number of operating blowers. This makes it possible to keep the dissolved oxygen concentration of the wastewater W in the wastewater treatment tank K (specifically, the partitioned tank KD2) within an appropriate range, and also reduces the number of operating blowers B while there is little need for aeration and agitation of the food waste and wastewater W in the wastewater treatment tank K. This makes it possible to avoid excessive aeration and agitation, thereby preventing deterioration of the water quality of the treated water and reducing unnecessary power consumption. 2 and 3, when the dissolved oxygen concentration is less than a predetermined reference value + 1 (first threshold) (mg / L), the control unit CT determines the number of operating blowers to be "3" (FIG. 3: step GA; YES in step SGI → step GE), when the dissolved oxygen concentration is equal to or greater than the reference value + 1 (first threshold) (mg / L) and less than the reference value + 2 (second threshold) (mg / L), the control unit CT determines the number of operating blowers to be "2" (FIG. 3: YES in step SGF → step GB; YES in step SGH → step GD), and when the dissolved oxygen concentration is equal to or greater than the reference value + 2 (second threshold) (mg / L), the control unit CT determines the number of operating blowers to be "1" (FIG. 3: YES in step SGG → step GC). Note that the values ​​of the first threshold and the second threshold may be set to any values ​​different from those in this example. In the examples of Figures 2 and 3, the control unit CT always sets the number of operating blowers to one or more, thereby ensuring that one or more blowers B are always operating. This makes it easier to maintain good activity of aerobic microorganisms in the wastewater treatment tank K. However, the control unit CT may also set the number of operating blowers to zero (and ultimately have none of the blowers B operate). In the blower control process (blower control step) SB, when the number of operating blowers is less than the maximum number (three in this example), any conditions may be used to select the blower B to be operated. For example, from the viewpoint of improving the lifespan of the blowers B, it is preferable that the blowers B are operated in rotation as appropriate, and for example, as shown in the examples of Figures 2 and 3, the blower B with the shortest cumulative operating time may be preferentially selected and operated (conversely, the blower B with the longest cumulative operating time may be preferentially stopped).

[0037] In the air diffusion valve control process (air diffusion valve control step) SL, the control unit CT controls the multiple air diffusion valves LV (LV1 to LV3) based on the number of operating blowers determined in the blower control process (blower control step) SB. More specifically, the control unit CT determines the number of open air diffusion valves based on the number of operating blowers, and controls the multiple air diffusion valves LV so that only the air diffusion valves LV corresponding to the number of open air diffusion valves among the multiple air diffusion valves LV are open (ON) (and consequently the remaining air diffusion valves LV are closed (OFF)). In other words, the multiple air diffusion valves LV are individually controlled following the control of the multiple blowers B. By controlling the multiple air diffusion valves LV, the air diffusion operation from the diffusers D corresponding to the multiple air diffusion valves LV (i.e., connected via the same second air diffusion pipe branch portion L2B) is controlled. In the air diffuser valve control process (air diffuser valve control step) SL, the control unit CT determines the number of air diffuser valves to be opened so that the fewer the number of operating blowers, the smaller the number of air diffuser valves to be opened. For example, in the example of FIGS. 2 to 3, when the number of operating blowers is "3," the control unit CT determines the number of air diffuser valves to be opened as "3" (FIGS. 2 to 3: steps GA and GE), when the number of operating blowers is "2," the control unit CT determines the number of air diffuser valves to be opened as "2" (FIGS. 2 to 3: steps GB and GD), and when the number of operating blowers is "1," the control unit CT determines the number of air diffuser valves to be opened as "1" (FIGS. 2 to 3: step GC). In this way, by setting the number of air diffuser valves to be opened as the number of operating blowers B is smaller, the number of operating diffusers D is reduced as the number of operating blowers B is smaller, and the amount of air diffused per operating diffuser D can be increased accordingly. This improves the air atomization efficiency (and thus the oxygen dissolution efficiency) of each operating diffuser D, and also improves the fluidity within the wastewater treatment tank K. This in turn improves the treatment efficiency of the wastewater W, and also prevents anaerobic conditions and the generation of foul odors due to retention of carriers. Note that if all diffusers D are always operated regardless of the number of operating blowers, the amount of air diffused per diffuser D will decrease when the number of operating blowers decreases, which could result in a decrease in the fluidity within the wastewater treatment tank K. In addition, when determining the number of open air diffuser valves, the number of open air diffuser valves does not have to be the same as the number of operating blowers, and may be different numbers, so that the smaller the number of operating blowers, the smaller the number of open air diffuser valves. In the air diffuser valve control process (air diffuser valve control step) SL, when the number of open air diffuser valves is less than the maximum number (three in this example), the air diffuser valves LV to be opened may be selected under any conditions. For example, from the viewpoint of more uniform flow within the wastewater treatment tank K, it is preferable that the multiple air diffuser valves LV are opened (ON) in an appropriate rotation, and for example, as in the example of Figures 2 to 3, the air diffuser valves LV with the shorter cumulative open time may be preferentially selected and opened (ON) (conversely, the air diffuser valves LV with the longer cumulative open time may be preferentially closed (OFF)).

[0038] In the return pipe valve control process (return pipe valve control step) SR, the control unit CT controls the plurality of return pipe valves RV (RV1 to RV3) based on the number of operating blowers determined in the blower control process (blower control step) SB. More specifically, the control unit CT determines the number of open return pipe valves based on the number of operating blowers, and controls the plurality of return pipe valves RV so that only the return pipe valves RV corresponding to the open number of return pipe valves are open (ON) (and consequently the remaining return pipe valves RV are closed (OFF)). In other words, the plurality of return pipe valves RV are individually controlled in accordance with the control of the plurality of blowers B. By controlling the plurality of return pipe valves RV, the discharge operation of air from the downstream ends R2Be of the plurality of return pipe branch sections R2B to which the plurality of return pipe valves RV are respectively provided is controlled. In this way, by setting the number of return pipe valves RV to be opened according to the number of operating blowers B, air can be discharged more efficiently through the return pipe R, and ultimately the fluidity within the wastewater treatment tank K can be further improved.

[0039] 2 to 3, in the return pipe valve control process (return pipe valve control step) SR, the control unit CT determines the number of return pipe valves to be opened so that the smaller the number of operating blowers, the larger the number of open return pipe valves. For example, in the example of Figures 2 to 3, the control unit CT determines the number of open return pipe valves to be "0" when the number of operating blowers is "3" (Figures 2 to 3: step GA; step GE), determines the number of open return pipe valves to be "1" when the number of operating blowers is "2" (Figures 2 to 3: step GB; step GD), and determines the number of open return pipe valves to be "2" when the number of operating blowers is "1" (Figures 2 to 3: step GC). In this way, by setting the return pipe valve opening number to a larger number as the number of operating blowers decreases, the fewer the number of operating blowers B (and therefore the fewer the number of operating diffusers D), the more air is discharged from the downstream ends R2Be of the return pipe branches R2B, and therefore the fluidity of the stopped diffusers D can be more efficiently compensated for by the discharge of air through the return pipe R. If all return pipe branches R2B were always open, there is a risk that the discharge rate from the downstream ends R2Be of the return pipe branches R2B would always be small. However, by reducing the return pipe valve opening number (and therefore the number of open return pipe branches R2B) as needed, the discharge rate from the downstream ends R2Be of the open return pipe branches R2B can be increased accordingly, and thus the fluidity can be improved more efficiently. However, it is not essential that the number of open return pipe valves be increased as the number of operating blowers decreases, and the number of open return pipe valves may be determined based on the number of operating blowers under any conditions.

[0040] 2-3, in the return pipe valve control process (return pipe valve control step) SR, the control unit CT opens the return pipe valve RV provided in the return pipe branch R2B located near the second diffuser pipe branch L2B provided with the diffuser pipe valve LV that is closed in the diffuser pipe valve control process (diffuser pipe valve control step) SL. For example, in the example of FIGS. 2-3, when the control unit CT closes the diffuser pipe valve LV1, it opens the return pipe valve RV1 (FIGS. 2-3: step GB; step GC), when the control unit CT closes the diffuser pipe valve LV2, it opens the return pipe valve RV2 (FIGS. 2-3: step GC; step GD), and when the control unit CT closes the diffuser pipe valve LV3, it opens the return pipe valve RV3 (FIG. 2: step GB; step GC). In this way, by opening the return pipe valve RV provided in the return pipe branch R2B located near the second diffuser pipe branch L2B where the diffuser pipe valve LV to be closed is provided, the fluidity near the diffuser D that is stopped by the diffuser pipe valve LV can be efficiently compensated for by the nearby return pipe branch R2B. However, in the return pipe valve control process (return pipe valve control step) SR, when the number of open return pipe valves is less than the maximum number (in this example, three), the return pipe valve RV to be opened may be selected under any conditions, not limited to the above example.

[0041] The present invention is not limited to the above-described embodiment, but also includes various other embodiments and modifications.

[0042] For example, in each example described in this specification, the return pipe valve RV may not be provided, and therefore the return pipe valve control process (return pipe valve control step) SR may not be performed. In that case, for example, the multiple return pipe branches R2B may be kept open at all times, allowing air to be discharged from the downstream end R2Be.

[0043] Alternatively, in each example described in this specification, the return pipe R and the return pipe valve RV may not be provided, as in the second embodiment shown in Fig. 4. In that case, the return pipe valve control process (return pipe valve control step) SR is not performed. Even in such a case, the treatment efficiency of the wastewater W can be improved by the air diffusion pipe valve control process (air diffusion pipe valve control step) SL.

[0044] In addition, in each example described in this specification, the odor flue pipe E and the odor fan F do not necessarily have to be provided.

[0045] Next, a wastewater treatment method according to a third embodiment of the present invention will be illustrated with reference to Figures 5 and 6. Figures 5 and 6 correspond to Figures 2 and 3, respectively, and are drawings according to the third embodiment. In describing the wastewater treatment method according to the third embodiment shown in Figures 5 and 6, the return pipe R and return pipe valve RV (and thus the return pipe valve control process (return pipe valve control step) SR) described above in relation to the first embodiment will not be mentioned, but these may be provided (and thus the return pipe valve control process (return pipe valve control step) SR may be performed), or may not be provided as in the embodiment of Figure 4 (and thus the return pipe valve control process (return pipe valve control step) SR may not be performed). In other respects, the third embodiment may employ the configuration and method described above in relation to the first embodiment. In the example shown in Figures 2 and 3, in the air diffusion valve control process (air diffusion valve control step) SL, the control unit CT does not change the combination of air diffusion valves LV to be opened until the number of air diffusion valves open that has been determined is changed (i.e., while the number of air diffusion valves open remains constant). On the other hand, in the third embodiment (Figures 5 to 6), in the air diffusion valve control process (air diffusion valve control step) SL, the control unit CT changes the combination of air diffusion valves LV to be opened every predetermined timer time T1 while the number of open air diffusion valves is equal to or greater than 1 and less than the maximum number (Figures 5 to 6: step NB; step NC; step ND). Here, for convenience, the term "combination of air diffuser valves LV to be opened" is intended to encompass the case where there is only one air diffuser valve LV to be opened, and in the case where there is only one air diffuser valve LV to be opened, it refers to the air diffuser valve LV itself to be opened. As for the method of selecting the combination of air diffuser pipe valves LV to be opened for each predetermined timer time T1, it may be selected under any conditions, as described above. For example, it is preferable that the plurality of air diffuser pipe valves LV are opened (ON) by rotating them as appropriate. For example, as in the example of Figures 5 to 6, the air diffuser pipe valve LV with the shorter cumulative open time may be preferentially selected and opened (ON) (conversely, the air diffuser pipe valve LV with the longer cumulative open time may be preferentially closed (OFF)). As in the third embodiment, in the air diffuser valve control process (air diffuser valve control step) SL, while the number of open air diffuser valves is equal to or greater than 1 and less than the maximum number, the combination of air diffuser valves LV to be opened is changed every predetermined timer time T1, thereby effectively avoiding the risk of the same air diffuser valve LV being closed for a long period of time, and thus the diffuser D corresponding to that air diffuser valve LV being stopped for a long period of time, which would cause flow to stagnate in the vicinity, and ultimately making the fluidity in the wastewater treatment tank K uniform and improved. This improves the contact efficiency between the carriers and the wastewater W, thereby improving the treatment efficiency of the wastewater W and suppressing anaerobic effluent caused by carrier stagnation, which would result in foul odors.

[0046] Next, a wastewater treatment system 1 and a wastewater treatment method according to a fourth embodiment of the present invention will be illustrated with reference to Figures 7 to 9. Figures 7 to 9 correspond to Figures 1 to 3, respectively, and are drawings according to the fourth embodiment. In describing the wastewater treatment system 1 and wastewater treatment method according to the fourth embodiment shown in FIGS. 7 to 9, the return pipe R and return pipe valve RV (and thus the return pipe valve control process (return pipe valve control step) SR) described above in relation to the first embodiment will not be mentioned, but these may be provided (and thus the return pipe valve control process (return pipe valve control step) SR may be performed), or, as in the embodiment of FIG. 4, they may not be provided (and thus the return pipe valve control process (return pipe valve control step) SR may not be performed). Furthermore, in the example shown in FIGS. 8 to 9, the timer control described above in relation to the third embodiment is not performed in the air diffusion pipe valve control process (air diffusion pipe valve control step) SL, but the timer control described above in relation to the third embodiment may be performed in the fourth embodiment. In other respects, the fourth embodiment may employ the configuration and method described above in relation to the first embodiment. In the fourth embodiment (FIGS. 7 to 9), the wastewater treatment system 1 further includes a plurality of bypass pipes P (P1 to P3) and a plurality of bypass pipe valves PV (PV1 to PV3) (FIG. 7).

[0047] The number of bypass pipes P is the same as the number of second diffuser pipe branch portions L2B, and each bypass pipe P is provided corresponding to a separate second diffuser pipe branch portion L2B. In other words, the multiple bypass pipes P are provided corresponding to the multiple second diffuser pipe branch portions L2B, respectively. In this example, the bypass pipes P1 to P3 are provided corresponding to the second diffuser pipe branch portions L2B1 to L2B3, respectively. Each of the multiple bypass pipes P has a first bypass pipe end portion Pe1 connected to the upstream end portion L2Be of the second aeration pipe branch portion L2B corresponding to that bypass pipe P, and a second bypass pipe end portion Pe2 located in the wastewater W in the wastewater treatment tank K near the second aeration pipe branch portion L2B corresponding to that bypass pipe P. Because the second bypass pipe end portion Pe2 of each of the multiple bypass pipes P is located near the corresponding second aeration pipe branch portion L2B, the air discharged from the multiple bypass pipes P can act to supplement the air diffusion of the diffusers D connected to the corresponding second aeration pipe branch portion L2B. Here, the second bypass pipe end portion Pe2 of the bypass pipe P being located "near" the second aeration pipe branch portion L2B corresponding to the bypass pipe P means that the distance between the second bypass pipe end portion Pe2 of the bypass pipe P and the corresponding second aeration pipe branch portion L2B is shorter than each of the distances between the second bypass pipe end portion Pe2 of the bypass pipe P and each of the other second aeration pipe branch portions L2B.

[0048] In the example of FIG. 7, each of the multiple bypass pipes P extends substantially in the vertical direction, and the lower end of each of them faces downward and forms a second bypass pipe end Pe2. 7, it is preferable that the second bypass pipe end portion Pe2 of each of the multiple bypass pipes P is disposed near the diffuser D connected to the corresponding second aeration pipe branch portion L2B in the wastewater W in the wastewater treatment tank K. Here, "near" the second bypass pipe end portion Pe2 of the bypass pipe P to the diffuser D connected to the corresponding second aeration pipe branch portion L2B of the bypass pipe P means that the distance between the second bypass pipe end portion Pe2 of the bypass pipe P and the diffuser D connected to the corresponding second aeration pipe branch portion L2B is shorter than each of the distances between the second bypass pipe end portion Pe2 of the bypass pipe P and the diffusers D connected to the other second aeration pipe branches L2B.

[0049] Each of the multiple bypass pipes P is configured to have less piping resistance than each of the multiple second diffuser pipe branches L2B. This makes it easier to increase the amount of air discharged through the bypass pipe P, and ultimately makes it possible to more efficiently compensate for the fluidity loss caused by the stopped diffuser D by discharging air through the bypass pipe P. One method for configuring the bypass pipe P so that it has less piping resistance than the second diffuser pipe branch portion L2B is to configure the bypass pipe P from a single pipe and form the second bypass pipe end portion Pe2 of the bypass pipe P by cutting out the single pipe (and thus the cut surface of the single pipe). This makes the resistance of the second bypass pipe end portion Pe2 less than that of the diffuser D connected to the end portion of the second diffuser pipe branch portion L2B, and therefore the piping resistance of the bypass pipe P can be less than that of the second diffuser pipe branch portion L2B.

[0050] The plurality of bypass valves PV (PV1 to PV3) are each configured to be openable and closable. The bypass valves PV are configured, for example, as on-off valves. The bypass valves PV are configured, for example, as automatic valves such as electromagnetic, electric, or air-operated valves. The number of bypass pipe valves PV is the same as the number of bypass pipes P. Each of the multiple bypass pipe valves PV is provided for each of the multiple bypass pipes P. By opening and closing the bypass pipe valve PV, the flow path of the bypass pipe P to which the bypass pipe valve PV is provided opens and closes, and thus the discharge of air from the second bypass pipe end Pe2 of the bypass pipe P is started or stopped. The opening and closing of the bypass pipe valve PV is controlled by the control unit CT.

[0051] As illustrated in Figures 8 and 9, in the wastewater treatment method according to the fourth embodiment, the control unit CT is configured to perform a blower control process (blower control step) SB, an aeration pipe valve control process (aeration pipe valve control step) SL, and a bypass pipe valve control process (bypass pipe valve control step) SP in parallel based on the detection results from the sensor S. In this embodiment, the control unit CT may be configured to store an accumulated operating time obtained by accumulating the operating time (time during which the blowers B are in an operating state (ON)) of each blower B, and / or an accumulated open time obtained by accumulating the open time (time during which the blowers are in an open state (ON)) of each air diffuser valve LV and / or each bypass valve PV.

[0052] In the bypass valve control process (bypass valve control step) SP, the control unit CT controls the multiple bypass valves PV (PV1 to PV3) based on the number of operating blowers determined in the blower control process (blower control step) SB. More specifically, the control unit CT determines the number of open bypass valves based on the number of operating blowers, and controls the multiple bypass valves PV so that only the bypass valves PV corresponding to the number of open bypass valves are open (ON) (and ultimately the remaining bypass valves PV are closed (OFF)). In other words, the multiple bypass valves PV are individually controlled in accordance with the control of the multiple blowers B. The control of the multiple bypass valves PV controls the discharge operation of air from second bypass pipe ends Pe2 of the multiple bypass pipes P to which the multiple bypass valves PV are respectively provided. In this way, by setting the number of bypass pipe valves PV to be opened according to the number of operating blowers B, air can be discharged more efficiently through the bypass pipe P, thereby further improving the fluidity within the wastewater treatment tank K.

[0053] 8 to 9, in the bypass pipe valve control process (bypass pipe valve control step) SP, the control unit CT opens the bypass pipe valve PV provided in the bypass pipe P corresponding to the second air diffuser pipe branch portion L2B provided with the air diffuser pipe valve LV that is closed in the air diffuser pipe valve control process, among the multiple bypass pipe valves PV. For example, in the example of FIGS. 8 to 9, when the control unit CT closes the air diffuser pipe valve LV1, it opens the bypass pipe valve PV1 (FIGS. 8 to 9: step QB; step QC), when the control unit CT closes the air diffuser pipe valve LV2, it opens the bypass pipe valve PV2 (FIGS. 8 to 9: step QC; step QD), and when the control unit CT closes the air diffuser pipe valve LV3, it opens the bypass pipe valve PV3 (FIG. 8: step QB; step QC). In this way, by opening the bypass pipe valve PV provided in the bypass pipe P located near the second diffuser pipe branch L2B where the diffuser pipe valve LV to be closed is provided, the fluidity near the diffuser D that is stopped by the diffuser pipe valve LV can be efficiently compensated for by the nearby bypass pipe P. However, in the bypass pipe valve control process (bypass pipe valve control step) SP, when the number of open bypass pipe valves is less than the maximum number (in this example, three), the selection of the bypass pipe valves PV to be opened may be made under any conditions, not limited to the above example. [Industrial Applicability]

[0054] The wastewater treatment system of the present invention can be suitably used, for example, to be installed on the premises of an apartment complex or other collective housing unit, or a detached house, and to allow food waste that has been crushed in a disposer installed in the kitchen of each dwelling unit to flow down a dedicated pipe together with wastewater and be treated in the wastewater treatment tank of the wastewater treatment system. [Explanation of symbols]

[0055] 1. Wastewater treatment system K Wastewater treatment tank KW Partition Wall KD, KD1, KD2, KD3 sectional tanks CT control section B, B1, B2, B3 blowers D Diffuser L Diffuser pipe L1 1st diffuser pipe end L1B First air diffuser branch L2 2nd diffuser pipe end L2B, L2B1, L2B2, L2B3 Second diffuser branch L2Be upstream end LV, LV1, LV2, LV3 air diffuser valve S sensor E odor tube E1 1st stink tube end E2 2nd stink pipe end F Odor Fan CV1, CV2 regulating valves R Return pipe R1 End of first return pipe R2 End of second return pipe R2B, R2B1, R2B2, R2B3 return pipe branch R2Be downstream end RV, RV1, RV2, RV3 return valves W Drainage P, P1, P2, P3 bypass pipes Pe1 First bypass pipe end Pe2 End of second bypass pipe PV, PV1, PV2, PV3 bypass valves

Claims

1. A wastewater treatment system comprising: a wastewater treatment tank configured to treat wastewater; a plurality of blowers disposed outside the wastewater treatment tank and configured to blow air; a plurality of diffusers disposed within the wastewater treatment tank; an air diffuser having a first air diffuser end connected to the plurality of blowers and a second air diffuser end connected to the plurality of diffusers; A plurality of air diffusion pipe valves each configured to be openable and closable; a sensor configured to detect the state of wastewater in the wastewater treatment tank; A control unit; Equipped with the second diffuser end portion has a plurality of second diffuser branch portions connected to the plurality of diffusers, respectively; the plurality of air diffuser valves are provided at the plurality of second air diffuser branch portions, respectively; The control unit a blower control process for determining the number of operating blowers based on the detection result by the sensor and controlling the plurality of blowers so that only the blowers of the number of operating blowers are operated; An air diffusion valve control process that determines the number of open air diffusion valves based on the number of operating blowers and controls the plurality of air diffusion valves so that only the air diffusion valves of the number of open air diffusion valves are in an open state; and In the air diffuser valve control process, the control unit determines the air diffuser valve opening number so that the air diffuser valve opening number becomes smaller as the number of operating blowers becomes smaller.

2. The wastewater treatment system comprises: a chimney pipe that connects the air inside the wastewater treatment tank with the air outside the wastewater treatment tank; an odor fan configured to send air inside the wastewater treatment tank to the outside of the wastewater treatment tank through the odor pipe; a return pipe having a first return pipe end connected to a portion of the flue pipe on the discharge side of the odor fan and a second return pipe end; Furthermore, 2. The wastewater treatment system according to claim 1, wherein the second return pipe end portion has a plurality of return pipe branches arranged in the wastewater in the wastewater treatment tank near each of the plurality of second aeration pipe branches.

3. The wastewater treatment system comprises: A plurality of return pipe valves each configured to be openable and closable Furthermore, a plurality of return pipe valves are provided in each of the plurality of return pipe branches; The control unit a return pipe valve control process that determines an open number of return pipe valves based on the number of operating blowers, and controls the plurality of return pipe valves so that only the return pipe valves of the open number of return pipe valves are in an open state. The wastewater treatment system of claim 2 , further configured to:

4. The wastewater treatment system according to claim 3 , wherein in the return pipe valve control process, the control unit determines the return pipe valve opening number so that the smaller the number of operating blowers, the larger the return pipe valve opening number.

5. 4. The wastewater treatment system according to claim 3, wherein in the return pipe valve control process, the control unit opens the return pipe valve provided in the return pipe branch section that is arranged near the second aeration pipe branch section in which the aeration pipe valve that is closed in the aeration pipe valve control process is provided, among the plurality of return pipe valves.

6. 2. The wastewater treatment system according to claim 1, wherein in the air diffuser valve control process, the control unit changes the combination of the air diffuser valves to be opened for each predetermined timer time while the number of open air diffuser valves is equal to or greater than one and less than a maximum number.

7. The wastewater treatment system comprises: a plurality of bypass pipes provided corresponding to the plurality of second aeration pipe branch portions, respectively; a plurality of bypass pipe valves provided in the plurality of bypass pipes, each of which is configured to be openable and closable; Furthermore, each of the plurality of bypass pipes has a first bypass pipe end connected to an upstream end of the second aeration pipe branch portion corresponding to that bypass pipe, and a second bypass pipe end located in the vicinity of the second aeration pipe branch portion corresponding to that bypass pipe within the wastewater in the wastewater treatment tank; each of the plurality of bypass pipes is configured to have a lower piping resistance than each of the plurality of second aeration pipe branch sections; The control unit a bypass valve control process for determining an open number of bypass pipe valves based on the number of operating blowers, and controlling the plurality of bypass pipe valves so that only the bypass pipe valves of the determined open number of bypass pipe valves are in an open state; The wastewater treatment system of claim 1 , configured to:

8. 8. The wastewater treatment system according to claim 7, wherein in the bypass pipe valve control process, the control unit opens the bypass pipe valve provided in the bypass pipe corresponding to the second aeration pipe branch section in which the aeration pipe valve that is to be closed in the aeration pipe valve control process is provided, among the plurality of bypass pipe valves.

9. A wastewater treatment method used in the wastewater treatment system according to any one of claims 1 to 8, a blower control step in which the control unit determines the number of operating blowers based on the detection result by the sensor and controls the plurality of blowers so that only the blowers corresponding to the number of operating blowers are operated among the plurality of blowers; The control unit determines the number of open air diffuser valves based on the number of operating blowers, and controls the plurality of open air diffuser valves so that only the open air diffuser valves corresponding to the number of open air diffuser valves are in an open state. Including, In the air diffuser valve control step, the control unit determines the air diffuser valve opening number so that the smaller the number of operating blowers, the smaller the air diffuser valve opening number.

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